Dr Sourav Ghosh
email: ghosh@insa-toulouse.fr

Dr Thibault Ourlin

Pier-Francesco Fazzini

Lise-Marie Lacroix

Simon Tricard

Jerome Esvan

Prof Simon Cayez

Dr Bruno Chaudret
email: chaudret@insa-toulouse.fr

Dr P.-F Fazzini

Dr L.-M Lacroix

Magnetically induced CO 2 methanation in continuous flow over supported nickel catalysts with improved energy efficiency

Keywords: energy efficiency, heterogeneous catalysis, magnetically induced catalysis, power-to-gas, supported catalysts. 10

Here we report a new selective and efficient catalytic system for magnetically induced catalytic CO2 methanation composed of an abundant iron-based heating agent, namely a commercial iron wool, combined with supported Nickel nanoparticles (Ni NPs) as catalysts. The effect of metal oxide support was evaluated by preparing different 10wt% Ni catalyst (TiO2, ZrO2, CeO2, and CeZrO2) via organometallic decomposition route. As prepared catalysts were thoroughly characterized using powder X-ray diffraction, electron microscopy, elemental analysis, vibrating sample magnetometer, and X-ray photoelectron spectroscopy techniques. High conversion and selectivity toward methane were observed at mid-temperature range, hence, improving energy efficiency of the process with respect to the previous results under magnetic heating conditions. To gain further insight into the catalytic system, the effects of the synthesis method and of 0.5wt% Ru doping were evaluated. Finally, the dynamic nature of magnetically induced heating was demonstrated through fast stop-and-go experiments, proving the suitability of this technology for the storage of intermittent renewable energy through P2G process.

Introduction

The constantly increasing CO2 emissions and the imminent depletion of fossil resources has led the world organizations to agree on new strategies to supply the global energy demand in a greener and more sustainable way. [1] Since cutting CO2 emissions to zero seems today impossible, it appears necessary that the chemical industry would have to play a key role in the CO2 valorization. [2] In that prospect, the integration of the century-old Sabatier reaction in power-togas (P2G) processes has recently ascended as a possible outcome. In such a process, water electrolysis-generated H2 produced with renewable electricity excess would be used to hydrogenate CO2 into methane, the storage and transportation of which has been established for a long time. [3][4][5] Herein, the process has been schematically shown in scheme 1.

Scheme 1. Pictorial depiction of power-to-gas (P2G) process.

One of the main challenges constraining the conventional P2G process is the intrinsic intermittency of renewable energies. [6] It implies that any technology that would be used to hydrogenate CO2 must display high dynamicity and efficiency to fully convert the hydrogen while it's available. However, in heterogeneous catalysis, the typical joule-heating mediated processes need high heating time (slow temperature ramp) to reach the desired reaction temperature. To address this issue, we have dedicated many efforts in the past years in our group to develop magnetic heating as an alternative way to heat catalytic systems in much more efficient and faster way.

This technology relies on the fact that ferromagnetic and electrical conductor materials will release heat through hysteresis losses and eddy currents generation whenever immersed in an 10.1002/cssc.202201724

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ChemSusChem alternating magnetic field. [START_REF] Rudnev | Handbook of induction heating[END_REF] Such magnetic heating is both a well-established mode of heating, for instance in the contact-less pre-heating of steel billet in the iron industry, [START_REF] Lucia | [END_REF] and also a promising field of research, typically in the case of magnetic nanoparticles (MNPs) hyperthermia for the cancer treatment field. [9] In heterogeneous catalysis, it was previously shown that this in-situ generated heat could be successfully used to trigger catalytic reactions such as Fischer-Tropsch, [10] CO2 methanation, [11,12] methane dry reforming, [13][14][15] propane dehydrogenation, [13] as well as reactions in solution such as C-O cleavage of ethers and ketones. [16,17] The main advantage exploited for the P2G scenario is the dynamic nature of magnetically induced catalysis. Few hundreds of degrees can be reached in few seconds at the very core of the reactor, which avoids unnecessary heating of the whole reactor and furnace, saving both time and energy and therefore being an appropriate response to intermittency. [18] From a catalytic point of view, additional advantages arise from magnetic heating, such as suppression of heat-transfer limitations as a result of localized heating [18] or ease of heat management and reactor design in the case of exothermic reactions. [19] Finally, previous work from our group underlined the high energy efficiency of this mean of heating, as it was proven that magnetic heating required 5 times less power than oven joule-heating to trigger the Sabatier reaction in same conditions and yields of reaction. [20] Previous experiments have used MNPs as either dual heating-catalytic agent or heating agent only, and it was found that the sintering or agglomeration can lead to a change in the heating power over time, [21] making them in some cases unsuitable for extended use in industrial catalytic systems. Moreover, the chemical synthesis of the aforementioned is complex which translates into significant time and money consumption. Therefore, it appeared necessary to simplify the heating agent involved. A first attempt by Faure et

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ChemSusChem (SiC) particles as a spacer. [20] However, despite its low heating power, this Fe powder, like magnetic nanoparticles, was shown to sinter in the presence of magnetic induction. [20] One of the main goals of magnetically induced catalysis for Sabatier reaction, if implementation at the industrial scale is considered, is energy efficiency. Furthermore, the process needs to be scalable, cheap and commercially viable. Consequently, the search for new Fe materials was continued in order to find out the suitable heating agent, which would be combined with an optimized Ni based methanation catalyst. In the present study, an iron wool (Fe wool), composed of multiple ~50-100 µm iron microwires, and traditionally used for the abrasive cleaning of surfaces, was used as a heating agent. In spite of its comparatively lower heating power (with respect to MNPs), it is a convenient (air stable and abundant) as well as cheap heating agent. Furthermore, its spongy morphology allows an easy separation from the catalytic powder, and also acts as a spacer, avoiding pressure overload in the reactor.

For the catalytic function, Ni was chosen as an active metal as it is long-time established that it is a reasonable tradeoff between price, activity and methane selectivity for the Sabatier reaction. [22,23] Morphology [24] and dispersion [25,26] of Ni particles is of great interest in the literature, as it is believed that such properties strongly influence catalytic activity, methane selectivity, and stability. In this study, we have synthesized Ni NPs through an organometallic decomposition route, leading to monodisperse in size and homogeneously dispersed NPs. As a point of comparison, typical Ni impregnation method was carried out. It is also well known that metal oxide supports play a key role in the overall activity displayed by the catalyst. [27,28] Amount and strength of acidic/basic sites, reducibility or amount of oxygen vacancies are typical intrinsic properties of metal oxide supports that can be used advantageously to tailor catalyst activity. Therefore, and in order to assess support effects, Ni NPs were synthesized on four different metal oxide supports,

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ChemSusChem namely TiO2 (P25), ZrO2, CeO2, and CeZrO2, and used as catalysts. Eventually, the effect of Ru doping was assessed, since Ru is known as a more active metal for CO2 activation. [23,29] The physical mixture of the Fe wool and the supported Ni NPs powder was used as the catalytic bed.

Herein, we describe the use of a catalytic system based on commercial Fe wool and Ni catalysts for the selective hydrogenation of CO2 into methane in the presence of magnetic heating. Energy efficiency of the process, effect of support and synthesis method are assessed.

Results and Discussion

Synthesis and characterization of as prepared catalysts

The supported nickel catalysts (10 wt.%) were prepared by thermal decomposition of the organometallic precursor, Ni(COD)2 at 150°C in mesitylene under argon atmosphere, in the presence of an oxide support (see experimental section for details). The synthetic method is robust and scalable up to gram scale. As prepared supported nickel catalysts were characterized using powder XRD, BET, SEM and SEM-EDS mapping, ICP-AES, BF TEM, STEM-EDS elemental mapping, and VSM techniques. Figure 1 shows the stack plot of the powder XRD patterns of different catalysts. The powder XRD pattern of supported nickel catalysts confirm the respective crystallographic phases of the supports whereas the patterns are devoid of diffraction peaks corresponding to the fcc (face-centered cubic) phase of metallic nickel (the black vertical drop lines in figure 1). The absence of nickel diffraction peaks results from the amorphous nature of the nickel which was further supported by the high-resolution transmission electron microscopy (HRTEM) study and magnetic measurements (further discussed in the following section). Table 1 tabulates the surface area and elemental analysis data of the as prepared supported catalysts. The nickel concentration within the samples were measured by elemental analysis. The ICP-AES measurements confirm the ~10 wt% nickel content for all the catalysts. The surface area of the as prepared catalysts was determined from the nitrogen adsorption-desorption isotherms via applying the BET method. The N2 adsorption-desorption isotherms are shown on figure S5 (ESI).

The BET surface area of the as prepared supported nickel samples is measured to be 20, 15, 71, and 77 m 2 .g -1 for CeO2, ZrO2, CeZrO2 and TiO2 supports, respectively. The shape of the isotherms is corresponding to the type II, which is typical for macroporous or non-porous solids. The surface area values resemble the macroscopic geometric dimensions of the supports; the relatively large 3). Magnetic properties of the as prepared catalysts were measured using vibrating sample magnetometry (VSM) and presented in ESI. The saturation magnetization values normalized with respect to the nickel and the coercive fields at 300 and 5 K were tabulated in table S1 and figure S11 (ESI). All the samples except 10%Ni/CeZrO2, showed superparamagnetic behavior at 300 K, whereas at 5 K the NPs exhibit a ferromagnetic behavior. In case of 10%Ni/CeZrO2, the NPs behave like superparamagnetic at both 300 and 5 K. Moreover at 300 K and 5 K, for few of these samples, the magnetization curve at high field of 3 T does not saturate which corresponds to the possible contribution of paramagnetic species present within the system. Herein, the paramagnetic contribution was deduced and the saturation magnetization values were calculated for the 10.1002/cssc.202201724

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ChemSusChem respective samples. The saturation magnetization at 5 K for all the samples were found to be higher than at 300 K. The saturation magnetization (at 5 K) of all the as prepared samples follows the trend, (24.4 emu gNi -1 ) 10%Ni/CeO2 ~ (20.8 emu gNi -1 ) 10%Ni/ZrO2 > (16.4 emu gNi -1 )

10%Ni/TiO2 > (3.5 emu gNi -1 ) 10%Ni/CeZrO2, which is in line with the particles size of the nickel; the larger nickel particles showing higher saturation magnetization than the smaller particles. The saturation magnetization values of all the samples (<25 emu gNi -1 ) are significantly lower than the bulk magnetization of nickel (55 emu gNi -1 ). This could be probably due to the poor crystallinity of Ni NPs. After cooling down at 5 K and under the applied magnetic field of 3 T, no exchange bias was observed, in agreement with the absence of oxidation (ESI). The coercive field was found to be 30-45 mT for all the samples at 5 K and comparatively higher than 300 K. In the ZFC curve, the presence of a blocking temperature (TB) indicative of a ferro to paramagnetic transition, was observed respectively at 66 K, 47 K, and 20 K for 10%Ni/CeO2, 10%Ni/ZrO2, and 10%Ni/TiO2 respectively (figure S12, table S1). For 10%Ni/CeZrO2, TB was found to be below 5 K in agreement with its smallest particle size distribution among all other samples. Further details were given in the ESI. Overall, the magnetic measurement data confirm the other characterization data and demonstrate the presence of metallic nickel nanoparticles presence within the as prepared supported nickel catalysts.

Catalytic performances

The as prepared catalysts were loaded in a glass reactor equipped with a frit and located inside an air-cooled coil delivering an AMF with a frequency of 100 kHz. The composite (catalyst and Fe wool mixture) bed showed good heating efficiency once immersed in the alternating magnetic field (AMF). The temperature ramp rate was high for all catalyst composites (70-100 ˚C min -1 )

and led to a mean temperature of the composite found between 70 and 350°C according to the coil 10.1002/cssc.202201724

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ChemSusChem power. The temperature response for 10%Ni/TiO2 catalyst (along with Fe wool) is discussed as a model system (details in the section -"Stability and the effect of dynamic magnetic heating on catalytic activity"). Earlier work from our group (Faure et. al.) using Fe powder has emphasized the beneficial role of eddy current generation within the composite bed for producing heat. [20] Herein, the eddy currents flowing through the macroscopic and anisotropic Fe wool under the AMF induces the heating of the catalyst composites. On the other hand, probable very minor contribution of heating of Ni NPs of supported nickel catalysts due to hysteresis loss under the AMF cannot be completely ruled out (Curie temperature of bulk Ni, Tc= 355˚C). [START_REF] Coey | Magnetism and Magnetic Materials[END_REF] The CO2 conversion (𝑋 𝐶𝑂 2 ) and CH4 selectivity (𝑆 𝐶𝐻 4 ) were measured for all the catalysts in the 75 -350°C temperature range by modulating the applied magnetic field from 1 to 10 mT RMS, at two different GHSV (1500 and 7500 mL gcat -1 h -1 ). Catalytic performances (𝑋 𝐶𝑂 2 and 𝑆 𝐶𝐻 4 ) for all four catalysts with respect to the temperature are outlined on figure 4

and figure S13 (ESI). At low

GHSV for all the catalysts, 𝑋 𝐶𝑂 2 increases progressively with increasing temperature and reaches ~95-97% at different reaction temperatures depending on the catalysts with very high 𝑆 𝐶𝐻 4 (>99%).

The highest 𝑋 𝐶𝑂 2 values obtained for four different catalysts in terms of reactor temperature (~200˚C) follows the order, 10%Ni/CeZrO2 ~ 10%Ni/TiO2 > 10%Ni/CeO2 ~ 10%Ni/ZrO2. The 𝑆 𝐶𝐻 4 remained >99% at lower temperature (<300˚C), but at >300°C, CO2 conversion and selectivity towards CH4 decreased in favor of the reverse water gas shift (RWGS) reaction due to the thermodynamic equilibrium. [3] In the case of 10%Ni/CeZrO2 and 10%Ni/TiO2, the highest catalytic activity was observed at lower temperature as compared to the other catalysts and these two-catalysts showed up to 60% 𝑋 𝐶𝑂 2 at 150°C, which is a fairly low temperature for CO2 activation. The temperature measured is the average temperature of the composite bed consisting of Fe wool and supported Ni NPs. It must be pointed out that, in our current set up, and for 10.1002/cssc.202201724

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ChemSusChem comparison purposes, the temperature was measured at the top of the catalyst bed and assumed to be homogeneous throughout the reactor, although this assumption cannot be correct. Thus, it is very challenging to measure the actual surface temperature of catalytically active ferromagnetic metals nanostructures under AMF, [10,[30][31][32] and furthermore, in the heterogeneous catalyst composite we cannot use a simple thermo-couple to measure the mean temperature of the catalytic system. However, considering the previous literature it can be assumed that the actual temperature of the surface of the Ni NPs is probably only slightly underestimated.

At higher GHSV, 𝑋 𝐶𝑂 2 of different catalysts were found to be comparatively lower than at lower GHSV, due to the relative lower residence time of the reactant (figure S13, SI). In the case of 10%Ni/TiO2, 10%Ni/ZrO2, and 10%Ni/CeO2, ~80% 𝑋 𝐶𝑂 2 was observed at 200, 250, and 265˚C, respectively, whereas ~93% of 𝑋 𝐶𝑂 2 was observed for 10%Ni/CeZrO2 at 200˚C. Furthermore, the thermodynamic equilibrium of CO2 conversion and the corresponding CH4 selectivity at 1 bar pressure are shown as a comparison scale on figure 4 and figure S13 (ESI). [START_REF] Gao | [END_REF] The CO2 conversion and CH4 selectivity at different GHSV were found to be close to the thermodynamic limit. ) at 7500 mL gcat -1 h -1 GHSV. [31] We believe that the current process and the methane production rate could be further improved with the newly designed reactor in our lab which can operate at higher flow rates (or GHSV). Although considering the low temperature catalytic activity of these supported catalysts, it can be stated that methanation under AMF clearly outperforms conventional heating mediated processes reported for similar supported catalysts, because of a better heat management of AMF induced processes (kinetically limited process rather than the heat transfers limited process). [18,31] (𝑆 𝐶𝐻 4 ) vs. temperature plots. The thermodynamic equilibrium CO2 conversion and CH4 selectivity at 1 bar pressure is shown as a green line in both graphs. [START_REF] Gao | [END_REF] The higher catalytic activity for 10%Ni/TiO2 and 10%Ni/CeZrO2 as compared to the 10%Ni/CeO2 and 10%Ni/ZrO2 at lower reaction temperature could be rationalized in terms of the respectively. Table 1 shows the Ni NPs size before and after catalysis. Qualitatively, the size and shape of the support crystals in case of spent catalysts remain unchanged after the catalysis with respect to the as prepared catalysts. The calculated Ni NPs size for the CeO2, ZrO2, CeZrO2, and TiO2 supported samples are 12.4 ± 3.3, 14.9 ± 4.2 nm, 5.9 ± 1. Overall, these experiments show that the system does not undergo any critical evolution during the magnetically heated catalysis.

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ChemSusChem important to the improved crystallinity of Ni NPs, the saturation magnetization of the Ni improved largely as compared to their parent analogues and approaches the bulk saturation magnetization of nickel (55 emu gNi -1 ). Slightly higher saturation magnetization of the spent catalysts than the bulk nickel could be rationalized to the presence of small Fe wool impurities in the samples, which was further supported by the powder XRD data. In case of the spent catalysts, no exchange bias was observed at 5 K under 3 T applied magnetic field, further confirming the absence of oxidation.

Magnetic properties measurement data analyses are discussed in the ESI.

In order to evaluate the electronic effects of the supports on nickel and the possible origin of the differences in catalytic activity, Ni 2p core level XPS spectra were measured for 10%Ni/CeO2, 10%Ni/ZrO2, 10%Ni/CeZrO2, and 10%Ni/TiO2, before and after catalysis. The stacked plot of Ni 2p3/2 core level spectra of as prepared and spent catalysts for each supported nickel sample is given in figure S21 and S31 (ESI). The qualitative analysis of XPS spectra from peak maxima demonstrate the presence of Ni 0 and oxidized Ni 2+ species at the surfaces of all fresh and spent catalysts. Partial oxidation of the catalysts could not be prevented due to air exposure of all samples during the transfer to the instrument. The qualitative analysis of binding energies of the 2p3/2 metallic Ni peak for different as prepared catalysts are in the range of 852.4-852.5 eV. The binding energies corresponding to metallic Ni in the spent catalysts were found to be slightly lower (852.2-852.1 eV) than in the as prepared catalysts. Very slight variations of binding energies of Ni 0 were indeed observed by changing the substrate before catalysis, and almost no variation was observed after catalysis. As such differences of ~0.1-0.2 eV was in the margin of error of the measurements, it was difficult to deduce any significant information from this study. In any case, effects of metalsupport interaction on the electronic density of Ni 0 , if they exist, are extremely weak, and less important than the reductive treatment effect associated to the catalytic conditions. All these results

10.1002/cssc.202201724

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ChemSusChem and characterizations of post catalysis samples indicate that, the different reducible supports used in this work have a strong influence on the deposited nickel particles size, and dispersion, which probably dictate the catalytic activity and the methane selectivity at different extents. Moreover, these results are quite encouraging for further investigating in detail the performances of these catalysts and for evaluating their performances for other catalytic transformations.

Energy efficiency of the process

An important criterion to be considered when considering the possibility to develop catalysis using magnetic induction is the overall energy efficiency of the process. High energy costs would definitively prevent this technology to be implemented in P2G process, and therefore efforts have been made to evaluate and improve the energy efficiency of the process reported herein. [33] There are very few reports to the best our knowledge which have discussed the energy efficiency of a catalytic process under magnetic induction mediated heating. [20,34] Recently, Almind et al. has discussed the optimization of the coil geometries and its influence on the energy efficiency of the induction-heated methane steam reforming reaction. [34] The ability of our process to store energy was assessed using a typical efficiency ratio, considering the output power, carried by the CH4 flow, divided by the input power, carried by H2 flow and the power required for the coil (equation 1). [33] 𝜂 = 𝑃 (𝐶𝐻 4 ) 𝑃(𝐻 2 ) + 𝑃 𝐶𝑜𝑖𝑙 × 100 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 (1) In this definition, the power carried by gases is the power that would be generated by the combustion of that gas flow (equation 2), or:

𝑃(𝑋) = ṁ(𝑋) × 𝐻𝐻𝑉(𝑋) 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 (2)
10.1002/cssc.202201724

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ChemSusChem where, ṁ(X) is the mass flow rate of the gas (mg s -1 ) and HHV(X) is the highest heating value (J mg -1 ) of the gas. Because of the high intrinsic heating values of CH4 and H2, and in the ideal case where PCoil is 0 W, the energy efficiency ratio is capped at 83% as seen on figure 6. Also, the figure 6 clearly shows that getting close to that top can be achieved by 1) decreasing PCoil, especially at low flow rates, and 2) overall increasing the CH4 out flow rate. In this study, the magnetic field needed for CO2 methanation was < 12 mT RMS which requires for the coil a minimum working power PCoil = 70 W. In the ideal case scenario, at 125 mL min -1 flow (GHSV=7500 mL gcat -1 h -1 ) and 𝑌 𝐶𝐻 4 = 100%, and considering the necessary PCoil value, the energy efficiency (ƞ) cannot exceed 17.4%. Therefore, we will consider that this is the maximum value reachable for our present set-up. Figure 7 depicts the energy efficiency obtained for 10%Ni/CeO2, 10%Ni/ZrO2, 10%Ni/CeZrO2, and 10%Ni/TiO2 catalyst, at both high and low 10.1002/cssc.202201724

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ChemSusChem GHSV, as a function of the magnetic field applied. Because all the catalysts are operative in the same range of magnetic field, the energy efficiency is mainly dominated by the CH4 yield, and therefore, the most active catalysts also appear to be the most energy efficient. For all the catalysts, the energy efficiency at low GHSV (1500 mL gcat -1 h -1 ) reaches the laboratory set up limit (~4%).

On the other hand, 10%Ni/CeZrO2 was the most efficient catalyst at high GHSV (7500 mL gcat -1 h -1 ), reaching η = 16.2% for the process (shown as red working point on figure 6). Moreover, the experimental values illustrate well that a higher flow will yield a higher energy efficiency ratio if

PCoil can be kept in the same of order of magnitude, since at low GHSV (1500 mL gcat -1 h -1 ), η was ≤ 4% (shown as blue working point on figure 6). Overall, the reported catalysts work quite efficiently at low to mid temperature (200-300°C) range with high energy efficiency at two different GHSV.

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ChemSusChem efficiency at 7500 mL gcat -1 h -1 GHSV and the dashed lines correspond to the values obtained at 1500 mL gcat -1 h -1 GHSV.

In a previous report by Faure et.al., the maximum energy efficiency of ~4% at low flow (25 mL.min -1 ) had been reached. [20] In the present study, the 17% energy efficiency at 125 mL min -1 flow that was predicted was nearly reached. In that previous study, the catalytic bed was made of 10%Ni/CeO2 as a catalyst, commercial iron powder as a heating agent and SiC particles as a spacer.

The improvement herein observed is mainly due to, 1) the use Fe wool, a better heating agent SAR-wise, allowing the use of a lower magnetic field and low operational power for the coil, 2) the use of a more active catalyst, namely 10%Ni/CeZrO2, enabling high conversion rate at higher GHSV. The maximum energy efficiency calculated for the other catalysts at high GHSV, namely 10%Ni/CeO2, 10%Ni/ZrO2, and 10%Ni/TiO2 was slightly less (~ 14% as compared to the 16.2% for 10%Ni/CeZrO2). However, considering the cost, catalytic activity, and the availability of the supports, TiO2 supported catalyst (10%Ni/TiO2) was chosen as a model system and modifications of the catalysts were carried out to achieve a higher energy efficiency at high flow/GHSV (125 mL min -1 /7500 mL gcat -1 h -1 ).

Modification of 10%Ni/TiO2 and its catalytic performance

With the aim of exploring the effect of the synthetic method on the catalytic activity, 10 wt% nickel supported on TiO2 was synthesized by the conventional impregnation method. The onset of the reduction of calcined 10%Ni/TiO2_CI was investigated using in-situ XRD technique and found that 300 ˚C is enough to initiate the reduction of nickel oxide to nickel (details in ESI). The as prepared calcined sample was characterized using XRD, SEM and SEM-EDS elemental mapping, It has been reported that both Ru and Ni supported on TiO2 are the efficient catalysts for Sabatier reaction [22][23][24][25][26][27][28][29] and that a small amount of Ru doping could alter the CO2 methanation activity and the CO/CH4 selectivity of Ni/TiO2. In order to investigate the effect of Ru doping on Ni/TiO2 in catalytic activity and overall energy efficiency of the process, 10%RuNi/TiO2 was synthesized via sequential decomposition of Ni and Ru precursors and was tested for Sabatier reaction. The elemental composition was measured to be ~9.5% Ni and 0.5% Ru, via ICP-AES and SEM-EDS methods (table 2). The as prepared 10%RuNi/TiO2 was characterized using XRD, SEM and SEM-EDS elemental mapping, BF TEM, STEM EDS elemental mapping, and XPS techniques (details structural characterization data discussed in the ESI). The structural and morphological characterization of 10%RuNi/TiO2 showed that both Ni and Ru are homogeneously distributed over TiO2 and the overall structure matches well with the pure nickel analogue 10%Ni/TiO2. The catalytic activity of the 10%RuNi/TiO2 and 10%Ni/TiO2_CI for Sabatier reaction was investigated at two different gas flow (25 and 125 mL min -1 ) and compared with the 10%Ni/TiO2 for a same amount of catalyst mass loading (figure 8a, figure S30 in the ESI). The characterizations of the spent 10%RuNi/TiO2 and 10%Ni/TiO2_CI catalysts are discussed in the ESI. It was found that at 25 mL min -1 gas flow (GHSV=1500 mL gcat -1 h -1 ), both 10%Ni/TiO2 and 10%Ni/TiO2_CI exhibit similar temperature vs 𝑋 𝐶𝑂 2 profiles, whereas 10%RuNi/TiO2 needed a slightly higher temperature (~255˚C) to achieve the yields and selectivity's of 10%Ni/TiO2 (~96% 𝑋 𝐶𝑂 2 and >99%

𝑆 𝐶𝐻 4 achieved at ~200˚C) (figure S30a, ESI). Interestingly at 125 mL min -1 gas flow (GHSV=7500 mL gcat -1 h -1 ), the 10%Ni/TiO2 and 10%Ni/TiO2_CI samples showed similar temperature vs 𝑋 𝐶𝑂 2 profile with maximum conversion of ~81% (~99% 𝑆 𝐶𝐻 4 at 210˚C), however 10%RuNi/TiO2 needed slightly higher temperature (250˚C) to achieve even higher conversion ~92% (𝑋 𝐶𝑂 2 ) with >99% 𝑆 𝐶𝐻 4 . Although at high GHSV with increasing temperature, the 𝑆 𝐶𝐻 4 dropped for all the samples and follow the order, 10%Ni/TiO2 <10%Ni/TiO2_CI <10%RuNi/TiO2 (at 350°C). The Ru The normalized methane production rate at high GHSV and at 200˚C follows the order, 10%Ni/TiO2 >10%Ni/TiO2_CI ~10%RuNi/TiO2, whereas upon increasing the temperature to 250˚C, the 𝑋 𝐶𝑂 2 and 𝑆 𝐶𝐻 4 for 10%RuNi/TiO2 increases and the normalized methane production rate (0.64 𝑚𝑜𝑙 𝐶𝐻 4 𝑔 𝑁𝑖 -1 ℎ -1 ) becomes comparable with the 10%Ni/TiO2 (0.68 𝑚𝑜𝑙 𝐶𝐻 4 𝑔 𝑁𝑖 -1 ℎ -1 ). At this point, it is worth mentioning that, the 𝑆 𝐶𝐻 4 was >99% for 10%RuNi/TiO2 as compared to the ~97% for 10%Ni/TiO2 at 250˚C. The 𝑋 𝐶𝑂 2 and temperature of the system with respect to the applied magnetic field is shown in figure S30b (ESI). At low GHSV, the energy efficiency for all the three samples is close to the theoretical limit (~4%). At high GHSV, 10%RuNi/TiO2 at is the most energy efficient catalyst (figure 8b). In order to further improve the process, we are currently investigating the semi-industrial upgrade of our apparatus to be able to work at much higher reactant flow rates.

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ChemSusChem (grey), 10%RuNi/TiO2 (red), and 10%Ni/TiO2_CI (blue) catalyst at two different GHSV (1500 and 7500 mL gcat -1 h -1 ) plotted with respect to the applied magnetic field. The solid and dashed line correspond to the energy efficiency values obtained at 7500 and 1500 mL gcat -1 h -1 GHSV, respectively.

Stability and the effect of dynamic magnetic heating on catalytic activity

The key perk of magnetic heating being its dynamic behavior, and in order to model intermittency, a catalytic test was performed with the coil alternating between on and off power during a 7 h run. The catalytic test was performed at 7500 mL gcat -1 h -1 GHSV using 10%Ni/TiO2 as the catalyst. Figure 9 shows the catalytic behavior of 10%Ni/TiO2 and the reactor temperature profile under random coil power on/off condition. As soon as the coil turned on, the temperature reached approx. 200°C in 2 min and within 15-20 min of reaction, 𝑋 𝐶𝑂 2 reached its usual value of approx. 80%. Similarly, when the coil was turned off, the reactor returned to room temperature (~30˚C) in the course of approx. 2-3 min and the resulting 𝑋 𝐶𝑂 2 value dropped below 10%.

Although, the selectivity towards CH4 remained at >99%. Over 8 random on/off cycles, the ~80% 𝑋 𝐶𝑂 2 value could always be reached repeatedly. This particular experiment further demonstrates the applicability of the Sabatier process under magnetic induction mediated heating towards intermittency. The catalytic stability test was performed for 10%Ni/TiO2 catalyst at ~220˚C and 7500 mL gcat -1 h -1 GHSV (1:4 CO2 to H2 v/v ratio) for 45 h on stream. Figure 10 shows the stability test result for 10%Ni/TiO2 catalyst. It was found that the 𝑋 𝐶𝑂 2 and 𝑆 𝐶𝐻 4 values remain stable over the 45 hours' time period. The catalytic stability test for the 10Ni/TiO2 along with iron wool also demonstrates the robustness of the concept towards large scale implementation of Sabatier process under magnetic heating condition.

Conclusions

In this work, we describe the design of a catalytic system for CO2 methanation adapted to magnetic heating. The heating agent used is a cheap commercial iron wool heated by Eddy currents. The catalyst consists of 10% Ni prepared by an organometallic approach and deposited on four different oxides (TiO2, CeO2, ZrO2, CeZrO2). In the case of the TiO2 support, the performances of the Ni catalyst were compared with those of an analogous 10% Ni catalyst prepared by a classical impregnation/reduction method and with those of a Ru0.5Ni9.5 catalyst. All catalysts were thoroughly characterized before and after catalysis by state-of-the-art methods. In all cases, the system proved to be very selective for methane production at low working temperatures and reached excellent CO2 conversion values (up to ~90% at 7500 mL gcat -1 h -1 GSHV). Furthermore,

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stop and go experiments demonstrated the adaptation of this system to intermittency. Finally, the energy efficiency of the catalyst could approach the theoretical limit of our lab-scale set-up. We are now transposing this system to a pilot scale where the theoretical limit of energy efficiency is much higher and which should allow evaluating the interest in this process at the industrial scale.

Experimental section

Accepted Manuscript

Synthesis of supported Ni NPs

Synthesis of supported Ni NPs via Organometallic decomposition route

The supported Ni NPs (10 wt%) were prepared by thermal decomposition of Ni(COD)2

precursor in presence of the support and inspired by the previous literature report. [20] All the organometallic decomposition manipulation step was carried out in a Fisher-Porter (FP) bottle. In a typical procedure, support (2.5 g) was added to a yellow-solution of Ni(COD)2 (1.301 g, containing 0.278 g Ni) in mesitylene (30 mL) in the glove box. The reaction mixture was vigorously stirred for 1 h at room temperature, and then introduced in a 150°C pre-heated oil bath for 1 h, with vigorous stirring under Ar atmosphere. The black powder obtained was collected by decantation, and washed with 4×10 mL of toluene. Finally, the powder was dried under vacuum for 6 h and stored inside the glove box.

Synthesis of Titania supported Ni NPs via impregnation method

The catalysts have been first prepared from organometallic precursors which, in turn, were prepared and handled using mesitylene, toluene and THF as solvents. However, after having identified the best catalyst, we turned to an alternative classical synthesis which uses water as a solvent. Also, TiO2 supported Ni NPs with 10 wt% metal loading was prepared by conventional impregnation method. Typically, 5 g of TiO2 was added to an aqueous solution of nickel nitrate (2.572 g, 8 mL) and the solution was stirred for 3 h. After that, the resultant slurry was dried at 110˚C for 12 h, followed by calcination under air at 300˚C for 3 h. The sample is named as 10%Ni/TiO2_CI. Finally, the sample was reduced in-situ in the reactor under magnetic induction mediated heating. Typically, 0.8 g of Fe wool and 1 g of 10%Ni/TiO2_CI was loaded together in a glass reactor (detailed information about the catalytic reactor and catalytic reaction setup was 10.1002/cssc.202201724

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ChemSusChem given in the catalytic test section) and the temperature was raised to 300˚C and hold for 2 h under 30 mL min -1 of pure H2 flow. It has been observed that during the reduction process, the reactor temperature increased from 300 to 314˚C. The increase of temperature could be due to the contribution of additional heat generated by exothermic reduction process of nickel oxide to nickel.

Followed by the reduction of nickel oxide, the reactor temperature decreased to 80˚C and the gas flow was changed from pure H2 to a mixture of H2 and CO2 and subsequently, the catalytic reaction was started.

Synthesis of Titania supported RuNi NPs via Organometallic decomposition route

TiO2 supported Ni@Ru NPs (10 wt% total metal content) were prepared by decomposition of Ni(COD)2 followed by the decomposition of Ru(COD)(COT) in presence of TiO2 support. In a typical procedure, TiO2 (1.34 g) was added to a yellow-solution of Ni(COD)2 (0.694 g, 9.5 wt% Ni) in mesitylene (25 mL) in the glove box. The obtained solution was vigorously stirred for 1 h at 30˚C, and then introduced in a 150°C pre-heated oil bath for 1 h, with stirring under Ar atmosphere. The black powder obtained was separated by decantation, and washed 3 times with 5 mL of THF. After the last washing, 10 mL of THF was added and the FP bottle was charged with 3 bars of H2 and stirred for 2 h at 30˚C. 1 bar of pressure drop was noted during this period.

Subsequently, the residual H2 was vented inside the glove box, and the solution is stirred for additional 5 min to remove the dissolved H2. Subsequently, Ru(COD)(COT) (0.027 g, 0.5 wt% Ru) was introduced in the reaction mixture and the resulting solution was stirred for 2 h at 30˚C.

Finally, the solution was exposed to 3 bars of H2 for 4 h. The black powder obtained was separated by decantation, and washed with 3×5 mL of THF. After washing, the powder was dried under vacuum for 6 h. The sample is abbreviated as 10%RuNi/TiO2.

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ChemSusChem Chimie de Coordination (LCC) in Toulouse. The photoelectron emission spectra were recorded using a monochromatized Al-Kα (hν = 1486.6 eV) source on a ThermoScientific K-Alpha system.

The X-ray Spot size was about 400 µm. The Pass energy was fixed at 30 eV with a step of 0.1 eV for core levels and 160 eV for surveys (step 1eV). The spectrometer energy calibration was done using the Au 4f7/2 (83.9 ± 0.1 eV) and Cu 2p3/2 (932.8 ± 0.1 eV) photoelectron lines. XPS spectra were recorded in direct mode N (Ec) and the background signal was removed using the Shirley method. The flood Gun was used to neutralize charge effects on the top surface. Each spectrum was calibrated using the C1s (284.6 ± 0.1 eV) peak position. The error in the measurements are ±0.1 eV. The magnetic properties of the samples were measured using a vibrating scanning magnetometer (VSM, in the physical property measurement system (PPMS Evercool II) from Quantum Design). The magnetization versus magnetic field measurements (hysteresis loop) at 300 and 5 K were carried out up to ±3T external field. The temperature dependent magnetic susceptibility at zero-field-cooled (ZFC) and field-cooled (FC) conditions were measured at 5 mT field in the 5 -300 K range. For the magnetic measurements dry powder samples were loaded in a capsule inside the glovebox.

Catalytic tests

The catalytic tests were carried out in a borosilicate glass reactor (dint = 1 cm, L = 18 cm) with porous silica bed fused at the middle. The reactor was placed in an air-cooled coil delivering an alternating magnetic field (AMF) oscillating at a frequency of 100 kHz with an amplitude between 0 and 42 mT RMS provided by Induction Partners. For this study, the applied magnetic field was kept < 12 mT RMS, and the coil's power required was Pcoil = 70W. The reactor was equipped with a glass capillary at the top, allowing to measure the temperature at the surface of the catalytic bed with K-type temperature probe. The gas configuration was down-flow, and a round bottom flask For a catalytic test, 1 g of catalyst and 0.8 g of Fe wool (heating-agent) were loaded together in the reactor. Experiments were carried out at two different gas flow namely, 25 and 125 mL min -1 (H2/CO2 ratio of 4/1, v/v), corresponding respectively to GHSVs of 1500 and 7500 mL gcat -1 h -1 .

The Fe wool mass was not considered in GHSV, since Fe wool catalytic activity was tested as negligible. Temperature (75 to 360°C) was adjusted through modulating the applied magnetic field from 1 to 12 mT RMS. Steady state was considered to be reached within 30 minutes at each temperature tested.

10.1002/cssc.202201724

Accepted Manuscript

Table of contents entry:

Highly energy efficient and dynamic CO2 methanation was achieved using supported nickel catalysts and commercial iron wool under induction heating conditions and in continuous flow Accepted Manuscript

Figure 1 .

 1 Figure 1. Stack plot of powder XRD patterns of as prepared catalysts; 10%Ni/CeO2 (ICDD: 00-

Figure 2 .Figure 3 .

 23 Figure 2. BF TEM images of as prepared, a) 10%Ni/CeO2, b) 10%Ni/ZrO2, c) 10%Ni/CeZrO2,

Figure 4 .

 4 Figure 4. Catalytic activity of 10%Ni/CeO2, 10%Ni/ZrO2, 10%Ni/CeZrO2, and 10%Ni/TiO2 at

  10.1002/cssc.202201724Accepted ManuscriptChemSusChem better dispersion of the nickel NPs, lower NPs size, and high surface area for 10%Ni/TiO2 and 10%Ni/CeZrO2 catalysts. Each catalyst was further characterized using powder XRD, BF TEM, VSM, and XPS techniques after 14 hours of catalytic test under different temperatures and flow rates. Powder XRD patterns were compared for both as-prepared and spent catalysts for each supported nickel catalysts and are given in figures S15 (ESI). In case of the as-prepared catalysts, due to the small crystallite size of the Ni NPs, Ni(0) diffraction peaks were absent. However, in case of the spent catalysts, additional diffraction peaks for fcc Ni(0) were observed, because of the nanoparticles sintering and crystallization of the Ni NPs during catalysis experiments. Also, in the same pattern and at a similar 2-theta value, bcc (body-centered cubic) Fe(0) could be identified and attributed to the leaching of Fe wool particles while recovering the post-catalytic sample. The presence of both Ni(0) and Fe(0) were confirmed for spent 10%Ni/TiO2 catalysts as a model system through Rietveld refinement (figure S16, ESI). Hence, the crystallite size calculation from the XRD patterns could not be carried out for the spent catalysts.In order to further evaluate the extent of sintering of Ni NPs during the catalytic test, BF TEM analysis was performed for all the spent catalysts. BF TEM images and the respective histograms of the Ni NPs size distribution for the spent catalyst are presented on figure5and figure S17 (ESI),

  3 and 6.2 ± 1.4, respectively. The relative extent of sintering of Ni NPs in the spent catalysts for CeZrO2 and TiO2 supported samples was found to be lower as compared to the ZrO2 and CeO2. Despite the presence of a relatively smaller size of Ni NPs in the case of the TiO2 and CeZrO2 supports, moderate increase in the Ni 10.1002/cssc.202201724 Accepted Manuscript ChemSusChem NPs size in the case of the TiO2 and CeZrO2 supports, as compared to the CeO2 and ZrO2 supports, further indicates the reduced surface mobility of the Ni NPs and their higher degree of dispersion on CeZrO2 and TiO2 supports. The STEM-EDS elemental mapping further shows that in spite of the sintering of Ni NPs, the distribution of the NPs is still uniform and less aggregated. The STEM-EDS elemental mapping of 10%Ni/CeZrO2, and 10%Ni/TiO2 are shown in figure S18 (ESI).

Figure 5 .

 5 Figure 5. BF TEM images of spent catalyst, a) 10%Ni/CeO2, b) 10%Ni/ZrO2, c) 10%Ni/CeZrO2,

Figure 6 .

 6 Figure 6. Energy efficiency of the process plotted against methane outflow rate at different

Figure 7 .

 7 Figure 7. Energy efficiency of the Sabatier reaction for 10%Ni/CeO2 (red), 10%Ni/ZrO2 (grey),

Figure 8 .

 8 Figure 8. a) Catalytic conversion of CO2 vs. temperature plot for 10%Ni/TiO2, 10%Ni/TiO2_CI,

Figure 9 .

 9 Figure 9. 𝑋 𝐶𝑂 2 and 𝑆 𝐶𝐻 4 (left hand Y-axis) and temperature (right hand Y-axis) as a function of

Figure 10 .

 10 Figure 10. Catalytic stability test of 10%Ni/TiO2 at GHSV = 7500 mL gcat -1 h -1 (H2 flow = 100ml

mode 10 .

 10 1002/cssc.202201724

  al. used microscopic Fe powder and silicon carbide 10.1002/cssc.202201724

Table 1 .

 1 Surface area and elemental analysis of the as prepared catalyst, and comparison of Ni particles size before and after

	10.1002/cssc.202201724

catalysis Catalyst Elemental analysis (Ni) of as prepared catalyst [wt%] SBET [m 2 g -1 ] Particles size [nm] from TEM ICP SEM EDS As prepared After catalysis

	ChemSusChem	10.1002/cssc.202201724
	7.6 ± 1.9 and 7.4 ± 1.6 nm) compared to CeZrO2 and TiO2 (respectively 3.2 ± 0.7 and 4.6 ± 1.0
	nm). The Ni NPs size distribution was largely correlated with the surface area of the materials;
	supports having higher surface area led to the better dispersion of Ni NPs with relatively small
	sizes. In order to obtain the structural information of the Ni NPs, HRTEM images were recorded
	10%Ni/CeO2 10%Ni/ZrO2 10%Ni/CeZrO2 10.7 9.3 10.1 10%Ni/TiO2 7.6 The SEM image and SEM-EDS elemental mapping of the as prepared catalysts were given in 10.8 20 7.6±1.9 12.4±3.3 9 15 7.4±1.6 14.9±4.2 8.5 71 3.2±0.7 5.9±1.3 6.9 77 4.6±1 6.2±1.4 figure S6,7 (ESI). The SEM-EDS elemental mapping of different region confirms the homogeneous distribution of the nickel all over supports for all the as prepared catalysts. Furthermore, the EDS elemental quantification of the nickel agrees with the elemental analysis data obtained using ICP-AES technique. The BF TEM images of the as prepared supported nickel samples are shown on figure 2. The size and shape of the respective supports remained almost the same after the Ni NPs deposition. The nickel NPs particles size obtained from bright field TEM and presented on figure S9 (ESI). The images showed that the nickel crystallinity is poor (amorphous structure) and the corresponding FFT patterns are inconclusive for nickel nanocrystals. The results agree with the powder XRD data which was devoid of any diffraction peaks corresponds to the metallic Ni. Nevertheless, the nickel nanoparticles were found to be uniformly distributed throughout the supports at nanoscale using STEM-EDS elemental mapping (figure S10 and figure	Accepted Manuscript
	images are 7.6 ± 1.9, 7.4±1.6, 3.2 ± 0.7, and 4.6 ± 1.0 nm for CeO2, ZrO2, CeZrO2 and TiO2
	supports, respectively (table 1). The nickel NPs size distribution histograms were given in figure
	S8 (ESI). On CeO2 and ZrO2, larger NPs and a broader size dispersion were observed (respectively

  BF TEM, XPS, and ICP-AES techniques, and the spent catalyst (after reduction followed by catalysis) was characterized by XRD, BF TEM, STEM EDS elemental mapping, and XPS techniques. The characterization details and discussion are given in the ESI. The as prepared samples morphology and structural characterization refers to the structure consist of TiO2 supported homogeneously dispersed NiO NPs.

	10.1002/cssc.202201724
	Accepted Manuscript

Table 2 .

 2 Elemental and particles size analysis data of 10%Ni/TiO2, 10%RuNi/TiO2 and

	10.1002/cssc.202201724

  TiO2, not only increases the catalytic activity (𝑋 𝐶𝑂 2 ), but also increases the 𝑆 𝐶𝐻 4 and the 10%RuNi/TiO2 sample exhibit 88% 𝑋 𝐶𝑂 2 with >99% 𝑆 𝐶𝐻 4 at 350˚C.

	ChemSusChem	10.1002/cssc.202201724
	doping to Ni/
		Accepted Manuscript

  ChemSusChemat the bottom of the reactor was placed to collect the water (a side product of the reaction). A typical catalytic testing setup figure was given in the figureS4 (ESI).The outlet gases were analyzed by gas chromatography (PerkinElmer 580) equipped with both a Thermal Conductivity Detector (TCD) and a Mass Spectrometer (PerkinElmer Clarus SQ8T).CO2 conversion (𝑋 𝐶𝑂 2 ), selectivity towards CH4 (𝑆 𝐶𝐻 4 ), and CH4 yield (𝑌 𝐶𝐻 4 ) were calculated using a relative ratio of chromatogram areas of the carbon-based reactants and products, as described in equations 3-5. The response factors (RFgas) of each gas for the thermal conductivity detector were assessed by injecting a known concentration of these gases in the TCD. 𝑋 𝐶𝑂 2 = ( 𝐴 𝐶𝐻 4 × 𝑅𝐹 𝐶𝐻 4 + 𝐴 𝐶𝑂 × 𝑅𝐹 𝐶𝑂 𝐴 𝐶𝑂 2 × 𝑅𝐹 𝐶𝑂 2 + 𝐴 𝐶𝐻 4 × 𝑅𝐹 𝐶𝐻 4 + 𝐴 𝐶𝑂 × 𝑅𝐹 𝐶𝑂

	10.1002/cssc.202201724
	) × 100 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 (4) 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 (3) 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 (5) ) × 100 𝑌 𝐶𝐻 4 = (𝑆 𝐶𝐻 4 × 𝑋 𝐶𝑂 2 ) × 100 𝐴 𝐶𝐻 4 × 𝑅𝐹 𝐶𝐻 4 𝐴 𝐶𝐻 4 × 𝑅𝐹 𝐶𝐻 4 + 𝐴 𝐶𝑂 × 𝑅𝐹 𝐶𝑂 𝑆 𝐶𝐻 4 = (	Accepted Manuscript

Acknowledgments 10.1002/cssc.202201724

Characterization of the catalysts

Powder X-ray diffraction (XRD) patterns were recorded using a PANalytical Empyrean diffractometer (Co source, Kα -1.79 Ǻ). In-situ XRD experiment was performed for 10%Ni/TiO2_CI sample and the experimental details were given in the ESI. Scanning electron microscopy (SEM) imaging was carried out using a JEOL JSM-7800F microscope with field emission gun (FEG) source. SEM-EDS elemental mapping was carried out with an EDS Bruker XFlash detector attached to the microscope. Bright field transmission electron microscopy (BF TEM) imaging was carried out for obtaining the histogram of nickel NPs dispersed in different supports using a JEOL JEM 1400 TEM microscope equipped with a tungsten filament and the operating voltage was 120 kV. For each sample, 150 particles were measured on the ImageJ software for plotting the histogram. High resolution transmission electron microscopy (HRTEM) images were acquired using a probe Cs corrector and cold FEG gun equipped JEM-ARM200F microscope. The resolution of the microscope is: TEM imaging resolution = 1.9 Å point, and 1.0 Å line, and STEM imaging resolution = 0.78 Å (STEM HAADF 200kV). The camera used for the imaging was GATAN ULTRASCAN 2k × 2k Model 994. STEM-EDS elemental mapping was carried out using a high angle SDD CENTURIO-X (resolution 129 eV) detector attached to the TEM. The operating voltage of the microscope was 200 kV. The equipment is installed in the R.

Castaing micro-characterization platform in Toulouse. Nitrogen physisorption isotherms were obtained using an Autosorb iQ (Model 6) instrument from Quantachrome. Specific surface area was calculated using Brunauer-Emmett-Teller (BET) method. The samples were degassed at 200˚C for 4 h prior to the measurement. Elemental analysis of nickel was performed via Inductively Coupled Plasma -Atomic Emission Spectroscopy (ICP-AES) method using an iCAP 6300 ICP Duo Spectrometer. ICP-AES measurements were carried out at the Laboratoire de 10.1002/cssc.202201724

Accepted Manuscript

ChemSusChem

For the catalytic stability test, 1 g of 10Ni/TiO2 and 0.8 of iron wool were loaded together in the reactor. The reactor was placed in the 100 kHz coil and the power was adjusted to reach the temperature ~220°C. For security reasons, the reactive gas mixture (H2/CO2 -1:4 v/v ratio, H2 flow = 100ml min -1 , and CO2 flow = 25 mL min -1 , GHSV = 7500 mL gcat -1 h -1 ) was passed through the reactor during day time (~9 h each day). At night the reactive gas mixture (H2 and CO2) switched to argon and the coil remains turned on at a constant power throughout the manipulation.

ASSOCIATED CONTENT

Supporting Information

Additional characterization data for commercial supports and as prepared catalyst, additional experimental procedures, additional catalytic tests data and analysis, magnetic property analysis data for as prepared and spent catalyst, and spent catalyst characterization data.

Author Contributions ‡These authors contributed equally.

Conflicts of interest

The authors declare no conflict of interest.

Accepted Manuscript

ChemSusChem

Authors gratefully acknowledge the funding from the ERC Advance grant (MONACAT 2015-694159). Authors thank Dr. Jaime Mazario (LPCNO, INSA Toulouse) for his valuable suggestions.


Yoann Tatarenko

Philippe Pouletaut

Malayannan Subramaniam

Alexandra Josse

Théophile Cocquerez

John Hawse

Simon Chatelin

Sabine F Bensamoun

Impact of Klf10 deletion in muscle fibers elasticity as a function of ageing

Keywords: aging, elastic properties, Klf10, skeletal muscle fiber, knockout mice

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Klf10, a Krüppel-like transcription factor, was originally discovered in human osteoblasts as a TGFβ inducible early gene [1]. Since 2004, our group has characterized the role of Klf10 in the musculo-skeletal system, including bone, tendon and muscle tissues. The role of Klf10 in relationship to age has only been investigated in tendon tissue at both the tendon fiber [2] and the tenocyte level [3]. An important role of Klf10 in the aging process of tendon has been demonstrated. Based on recent discoveries about the influence of Klf10 in the transversal and longitudinal elasticities of muscle fiber, it was of interest to further elucidate the impact of Klf10 in the aging process of muscle fiber.

Methods

62 Klf10 KO (knockout) slow and fast twitch fibers were extracted from soleus (slow muscle) and EDL (fast muscle) of 3 month (Nsoleus = 16, NEDL = 14) and 21 month (Nsoleus = 18, NEDL = 14) old female Klf10 knockout mice. The fibers were immersed in a bath which was filled with a relaxing solution. Preconditioning tests and two passive mechanical tests (ramp stretch and relaxation) were performed on single fibers attached at both extremities to a force transducer (5 mN) and to a motor. Both mechanical tests applied a stretch of 50% of the original fiber length, corresponding to an elongation of about 1 mm. The ramp stretch and the relaxation tests were performed with a velocity of 2.10 -4 m.s -1 and 2.10 -2 m.s -1 , respectively. The dynamic (σd) and static (σs) stresses were estimated by dividing the force by the crosssectional area [4].

Results

The normalized hysteresis area values showed that all aged fibers decrease less rapidly, demonstrating the differences of preconditioning between young and aged fibers. The elastic properties of the slow fiber showed a significant decrease as a function of age while the fast fiber revealed a stabilization of the elastic properties from 3 months to 21 months (Fig1).

Discussion

Analyzing the effects of aging on tissues is difficult due to the risk of the mortality of the mice before the age point and due to the expensive cost of longitudinal studies. Another limitation to our study is the lack of data for aged wild-type mice. However, this preliminary project has demonstrated age-dependent changes in the elasticity of slow twitch muscle fibers which may relate to loss of Klf10 expression for which additional studies are required to support this possibility. Regardless, our finding provides the first insights into the potential roles of Klf10 during the aging process in muscle tissue.

Fig. 1 :

 1 Fig.1: Elastic properties of slow and fast twitch fibers as a function of age. *** P < 0.001 (Mann-Whitney test)

Acknowledgements

This study was funded by the Research Department of UTC within the framework of AMI International.


Nicolas Prevost
email: nicolas.prevost@paris-lavillette.archi.fr

Marc Leyral

Marc Hymans

Albin Breugnot

Quentin Chef

Sylvain Ebode

Wided Cherif

Building crossings in wicker: flexible construction of a postformed footbridge in active bending stiffened during service phase

Keywords: Footbridge, wicker, dynamic relaxation, form finding, elastic bending, earth mortar

The first traces of basketry date back to the Sumerian's period (4000 years BC). From now on, these braiding techniques have been used to craft vernacular shelters, clothes, furniture and tools. However, they are uncommonly used in architecture and are generally limited to non-structural filling elements. To our knowledge, the Baya project developed in 2020-2021 at ENSA-Paris-la Villette and CentraleSupélec schools was one of the first examples of a braided wicker structural shell in architecture. Based on the braiding optimization algorithm developed during this previous project, our research intends to question one step beyond: crossings. This innovative research is demonstrated by the realization of a 12.8-meter-long footbridge for the Utopies Constructives festival in Richelieu's Park. The footbridge, which echoes the reed boats of the Uros, a Peruvian tribe, will be braided flat before being moistened and shaped by buckling; then it will be stiffened post-buckling by braiding the railings together. Building in a flexible way, then stiffening during the service phase is both the constructive process of elastic gridshells and the one used by basket weavers who braid the green wicker, which then stiffens once the object is formed.

Introduction

Wicker is a natural fiber, collected once a year during winter. Its height can reach 3.5 meters. It is produced by young willow cuttings. It grows in the climates encountered in Metropolitan France. It resists low temperatures and even frost.

It's a very minimal cultivation, requiring limited inputs and maintenance, which makes it possible to diversify the forest cover. Its water consumption and its CO2 emissions are low (wicker is also capable of storing carbon, but the quantified evaluation of this benefit depends directly on the life span of the object that is made with). The wicker production also reduces floods, silting of rivers and streams, and slow soil erosion. At the dawn of the climate crisis, the ecological qualities of wicker are leading a growing number of designers to question its possible use in architecture.

Nevertheless, in France, the amount of willow plantations has drastically decreased throughout the last century, from 25 000 in 1890 to only 400 during the 1990s. The plastic revolution has led to a change

Proceedings of the IASS 2022 Symposium affiliated with APCS 2022 conference

Innovation•Sustainability•Legacy 2 in the French consumption habits and a decline in the demand for basketry products. The department of Indre-et-Loire, where our project is realized, undertakes actions for the conservation of this craft.

Basketry is a craft that has emerged very early in human history. The first traces of wicker objects date back to the Sumerian civilization (4 000 BC) and the first traces of basketry were found in Fayum in Upper Egypt, around 10 000 BC. Everywhere on the planet, people began to weave natural fibers for the design of objects, clothes, or shelters, thanks to local raw material and local know-how.

Architecture and construction have slightly opened their doors to the art of wickerwork, but it is mostly limited to non-structural filling. Porky Hoeffer, particularly, with the construction of woven huts, conceptualizes the designs of crossing, somewhere between timber skeleton and wicker. To continue this path, a team of students and teachers from ENSA Paris-la Villette and CentraleSupélec has been developing the BAYA project since 2021: an algorithm created to optimize the braiding of structural shells for architecture.

As a demonstration, a suspended nest has been created with this algorithm [4]. Our research is a continuation of this project: indeed, we will use the BAYA algorithm to cross long spans with wicker, and we will try to improve this tool thanks to this new feedback. Laura Ellen Bacon produces largescale artistic objects, including relatively long-span crossings, but these are not intended to support any external load such as the weight of users. Finally, one of the best examples of braided wicker crossings is found among the Uros people in Peru, with their boats made of totora, the local rush (in case of rough sea, the boat is not supported by the water in its entire length and must therefore be able to resist bending). These observations naturally lead us to question the feasibility of a crossing for architecture, using a construction method derived from wickerwork. In our methodology, which we will detail later, proof will be the answer to that question, since we propose the construction of a wicker footbridge with a span of almost 13 meters. 2. Crossings with a wicker footbridge 2.1. Qualitative approach: obstacles to the design of a crossing made of braids Thanks to our interviews with designers and basket makers, to the available literature and to the Baya nest project's feedback, we managed to identify the following obstacles to our crossing project:

• Durability: like timber, wicker is sensitive to UV, moisture, fungal and wood-eating insect attack. Moreover, the small cross-section of the stems maximizes the exposed surface in relation to the volume of needed material, which makes the plant fibers even more sensitive to their environment. Solutions do exist -essentially the same as for timber: heat and/or autoclave treatments -but to date we do not have enough feedback on the durability of these fibers when used in architecture, and even less if they are left outdoor and unprotected.

• Evolvability of the material: like timber, wicker and plant fibers creep. However, there is few information about it. For Baya, for example, we extrapolated the creep of timber onto wicker without really knowing the impact of this hypothesis. Furthermore, wicker is soft when green (or soaked) and becomes stiff when dried: an advantage for basketry since braiding requires handling a soft material and the object designed often needs to have sufficient stiffness for its use. However, as it dries, the wicker also becomes more "brittle". We do not yet know the impact of this characteristic to evolve on a structure bearing short and long-term loads.

• Node slipping: This is the main feedback from the Baya project. Despite the numerical experiments that allowed us to create this design tool, the nodes of the full-scale project were slipping at each use, causing deformation of the structure under load/unload cycles. This reaction could be described by the term "fatigue creep", although it is obviously due to different reasons from those that cause these two phenomena: creep is the deformation of a structural element subjected to a long-term loading. In our case, we deal with load/unload cycles (hence the parallel with "fatigue") caused by a short-term variable load. A "hysteresis cycle of deformation by slipping" is certainly a more accurate term to define the phenomena.

• Lightness: here again, a characteristic that may at first appear to be an advantage. However, when crossing with an arch, for example, one wishes to limit the deformation of the funicular under variable loads. In fact, if the funicular comes out of the arch, the section decompresses and the masonry arch collapses. For this purpose, the arch is usually designed in such a way that its self-weight (and any additional dead loads) is significantly dominant over the live loads. Then the lightness of wicker would be a handicap for this type of design. However, the capacity of wicker to resist traction makes a significative difference between masonry arches and ours, when subjected to live loads located in specific positions. This important issue will be developed later in the article.

Development of a braided wicker footbridge project

Project background

To contextualize our research, we designed a footbridge for the 1 st edition of the Utopies Constructives festival which will take place in spring 2023 in the city of Richelieu (Indre-et-Loire, France Utopies Constructives [START_REF] Bouhaya | Thesis -Optimisation structurelle des gridshells[END_REF] with students from ENSAPLV [START_REF] Douthe | Thesis -Étude des structures élancées précontraintes en matériaux composites : application à la conception des gridshells[END_REF] , CentraleSupélec [START_REF] Galassi | Failure modes prediction of masonry voussoir arches on moving supports[END_REF] , Ecole Duperré [START_REF] Leyral | The Baya Nest pavilion project: braided pattern optimization for hanging shell structures by dynamic relaxation[END_REF] , Ecole Boulle [START_REF] Méry | Mémoire sur l'équilibre des voûtes en berceau[END_REF] Supervisors : Marc Leyral

Marc Leyral Quentin Chef Marc Hymans Nicolas Prévost, Marc Hymans Marc Leyral, Carine Terrasson

Osier de Gué-Droit (6) (1)

Utopies Constructives : Marc HYMANS, Geoffrey CLAMOUR, Camille SINEAU, Camille DE BROISSIA, Anna DANIELSSON, Benjamin MAROLLEAU (La Teinturerie) ; [START_REF] Douthe | Thesis -Étude des structures élancées précontraintes en matériaux composites : application à la conception des gridshells[END_REF] ENSAPLV : Nicolas PREVOST, Albin BREUGNOT, Victor BARDY, Mélanie BENTO, Salomé CHANTOB ; [START_REF] Galassi | Failure modes prediction of masonry voussoir arches on moving supports[END_REF] CentraleSupelec : Emmanuel BERREBI, Maggy ZHOU, Ethan AZERAD, Théodore TARRIDE ; [START_REF] Leyral | The Baya Nest pavilion project: braided pattern optimization for hanging shell structures by dynamic relaxation[END_REF] Ecole Duperré : Léa ROUSSEL, Ines TOUAMI, Emma BULANT, Garance BASSEPORTE, Emma ANGE, Flavie THIBAUD, Marion LEANDRE, Manon POUJOULY, Sharleen SIVAC ; [START_REF] Méry | Mémoire sur l'équilibre des voûtes en berceau[END_REF] Ecole Boulle : Anouchka BURON, Svetlana GOLUNSKI, Anouk JOURDAN-DORSTER, Ines MACIA, Arnaud BOURGANEL, Jeanne FAUST-DEKEUWER, Enzo AUDION, Renan LHONOREY, Celia BANYIK, Charlotte TIRARD, Coline JOUSSET ; (6) Osier de Gué-droit : Matthieu BOYER, Séverine BOYER, Patrick BOYER Recreating an architectural walk path around the old site of the castle, the project is set in an exceptional site. In the park of more than 475 hectares, which was an integral part of the Cardinal de Richelieu's castle (dismantled during the 19th century), the project takes place over a moat. In this site, which combines nature and tranquility, old moats cut the park into geometric shapes. They banks cannot bear horizontal load, which constrains the choice of the structural typology of the footbridge. In this context, and to respect our site, the keywords of the project are frugality and low-tech.

General construction method

The execution of the footbridge is based on the construction of post-formed elastic gridshells:

1. The object is first made (by braiding the wicker) flat and flexible ► In our case, the footbridge is braided flat from wicker and the railings are regularly split in order to drastically reduce the bending stiffness of the deck.

It is then shaped by buckling

► The ropes connecting the legs are put under tension, compressing the footbridge deck, which begins to buckle.

3. Once in its final shape, it is stiffened for the service phase ► The interruptions in the railings are stitched together, forming a structural U shape one meter high by one meter wide.

In its service phase, the bridge works like a bowstring bridge (unless one walks directly on the arch). The arch is compressed by its self-weight and the loads of the users. The horizontal reaction generated at the supports is balanced by the traction in the ropes that were used to shape the arch in its assembly phase. This allows the footbridge to be raised onto land before being pushed over the moat. To limit the knots slipping observed on Baya, horizontal bamboos are inserted between the strings to increase tension, hence applying pre-compression to the bow.

Ultimately, anti-lateral buckling elements are added between the ropes and the deck as explained below. We will discuss later whether the deck should be weighted with clay soil. From a logistical point of view, instead of cutting the railings, we chose to prefabricate the bridge offsite in six sections, which are easier to transport. Then we assembled the flat pieces together by sewing the center part (the deck), leaving the future railings open in the first place. Now the overall shape of the project, its static diagram and its construction method have been defined, the braiding of the arch forming the deck must be designed. To do this, we used the BAYA algorithm, which is able to draw the optimal braiding of any shell for a given load.

Initial conception using numerical models

BAYA: structural shells design and optimization algorithm for the architecture

This chapter is quoted and adapted from [4] with the permission of the authors.

BAYA algorithm is applicable to any loaded surface, such as shells, as well as simpler elements like beams. These elements constitute the entire structure of the project. The loads circulate through the entire width of the structural surface of the shell and put it under tensile and compressive stress.

After observing the behavior of the stems, on a 30*30 cm specimen, we defined the relation between the geometrical characteristics of the braid and its mechanical behavior when it is subjected to a given loads field. This output fed the algorithm BAYA, capable to calculate the principal stresses of any shell under various loading cases and to give its optimal braiding.

The laws of optimal braiding

Methodology: our numerical simulation is conducted by dynamic relaxation, a method that allows us to solve static equilibrium problems by a fictitious dynamic calculation. Bouhaya [1] explains that the objective is to find the equilibrium position of a structure subjected to a set of loads by a pseudodynamic calculation : "it is an iterative method that describes the movement of the structure from the moment of loading to its equilibrium […]" and, "according to [Barnes], "the basis of the method is to trace step-by-step for small time increments, Δt, the motion of each node of a structure [from an initial disturbed instant] until, due to artificial damping, the structure comes to rest in static equilibrium."

In a braid constrained in the plane, we have three types of forces: the forces due to the bending of the strands that one must bend to pass above and then below the strands of the other layer, the spring forces related to the axial deformation of the strands (Hooke's law) and the friction forces at the knots.

We decided to study the reaction of a braided specimen subjected to a field of principal stresses in compression and tension. The material, round wicker stems, is a fixed setting of the test (E, A, fyt). The objective is to understand the influence of the different braiding parameters listed below: The study of the specimen shows us the following principles (cf. [4] for more detail):

• As expected, the yield ratio Tmax / (A * fyt) is a linear function of the tensile strength Fσ1

• Local buckling (Cmax compared to Euler's force) is not an issue with regular n1 and n2 densities • Global buckling (out-of-plane instability) depends mainly on compressive strength Fσ2

• Friction forces raise with Fσ1 and fall with Fσ2 ; which explains why instability failure appears with lower compression values when tension is not high enough • High values of Fσ2 lead to knots translation or rotation, even negative friction (decompression) • Positive friction force possesses a physical limit (depends on the diameter of strands) • Changing the braiding angle θ has little effect if the input forces are almost parallel to the strands (α close to zero); which validates the idea of braiding along the principal stresses.

BAYA algorithm for optimal braiding of architectural shells

The BAYA algorithm determines the principal stresses for any shell under a given load. Thanks to the above optimal braiding laws, it is able to give the ideal braiding for the shell. The algorithm can be applied to any loaded surface, including basketry items such as baskets, we have chosen to illustrate its presentation on an isostatic beam on two supports loaded by a uniformly distributed force.

1. Geometry of the studied shell: The shell surface, the position of the support points and the loads are the input data of BAYA algorithm. 2. Finite element mesh of the shell: The surface is discretized into small rectangular isosceles triangles, each representing a finite element of it. 3. Obtaining efforts: in the finite element edges by dynamic relaxation. 4. Obtaining the principal stresses: deduced from the forces by rotation of stresses' coordinate system on the largest support reaction of the right-angled isosceles triangle. 5. Braiding of the shell: by using the laws defined above. Figure 11: Meshing, strains and principal stresses, and optimal braiding by BAYA for the given example.

Application to the wicker footbridge

During the construction phase, the deck functions as a gridshell and thus has an elastica shape. During the service phase, it functions as an arch under a quasi-distributed load, so the ideal shape is rather the inverted catenary one. The shape of a hanging chain (hyperbolic cosine) only depend on its axial stiffness and the elastica shape of flexible rod depend both on its axial stiffness and on its bending stiffness. Nevertheless, bending stiffness is negligible compared to the axial stiffness. This is what Douthe [2] argues : "the stiffness of the shell comes from its shape and that this shape has been specially studied to take up the dead weight loads by membrane stress, i.e. only by axial forces in the gridshell elements. However, (...) the material resists well to axial forces (much better at least than to bending forces), the dimensions of the gridshell elements can therefore be reduced (…). This reduction in cross-sections is accompanied by a decrease in inertia so that the bending stiffness of the elements is low, which legitimizes retrospectively the initial hypothesis and the form finding using a net model."

Based on his work, we know that the elastica shape almost functions as a funicular if the angle of attack α is less than 65° (optimum at 57.5°), corresponding to a pL 3 /EI ratio below 65. We retained this value for the design of the footbridge. The overall shape of the arch resolved, we had now to use BAYA algorithm to predict an optimal braiding pattern for the deck (for the service phase).

The load is bore by the U-shaped deck; the whole structural thickness is thus put under stress. To calculate complex rounded shapes, the algorithm simplifies the surface into a mesh of simple geometric shapes. BAYA gives the braiding of these finite elements, the density and orientation of the strands according to the value of the stress and its orientation in these finite elements. Let us note that, density can be reached in plane or in thickness, which could change the structure's rigidity.

Figure 13: Optimal braiding of the bridge according to BAYA (the real diameter and number of strands have been reduced for a better reading) and corresponding 3D insertion (with the anti-buckling bamboos).

Confronting experiment with construction

Once we managed to demonstrate the constructive feasibility on small-scale models, we compared our structural design to the results of our experiment: this step is necessary because BAYA does not take into account a certain number of parameters such as node slipping, buckling and overturning, and the calculation of the deflections. Therefore, we built a 1:5 scale model. The tests that followed brought us two very significant benefits:

1. A real checking of the structural feasibility of the footbridge project, its resistance and the improvements that could be done. 2. Tangible feedback of the BAYA algorithm and a collect of some data in order to make corrections and improvements, for instance data on the previously mentioned parameters that are not taken into account yet.

Structural failure modes

In order to develop a methodology for experimental analysis, we have to anticipate the structural failure modes that could ruin the footbridge. We have selected five of them in the first instance: M1, M2 and M3 failure modes are normally taken into account by BAYA. We have calculated them with a maximum load equivalent to the weight of four people on the real scale footbridge. It is important to point out that these failure modes are very sensitive to the variations of the position of the funicular in relation to the neutral fiber of the section. Indeed, if the line of thrust, representing the normal force N in the arch, is offset comparing to the neutral fiber of the arch sections, a bending moment M appears in relation to it. Depending on its position, it can considerably increase the compression of the arch, but it can also locally cause traction. Considering the low flexural stiffness of the deckdue to the material and the braidingthe M4 failure mode appears critical. However, BAYA, in the design of the ideal braid, only takes in consideration local stresses and not the global instabilities. This failure mode was not numerically anticipated and the results of the model tests will therefore be of considerable help in this respect.

A quick calculation shows that the M5 failure method is far from the conditions of use. However, to be conservative, we will add redundancy by doubling the ropes.

Research methodology

In this static scheme, Q is the punctual load of the users on the footbridge placed in the middle of the arch (less favorable than in the numerical analysis) and g is the distributed load of the footbridge's own weight, including any dead weight from the clay soil we may add on the deck. In a masonry arch, the maximum risk of failure generally comes from a variable heavy and punctual load, as stated by Édouard Méry [5], a Ponts et Chaussées engineer, in the first half of the 19th century: "When a heavy load is made to pass over a vault, the line of thrust successively takes on various forms, as would a suspension chain, and while it undergoes these oscillations, it must always remain enclosed between the intrados and extrados of the vault so that the latter does not fall." Once again, comparing a wicker bridge to a masonry arch has obvious limits but is a good place to start.

Consequently, in order to minimize this risk, the variable load must not exceed a certain proportion of the distributed load, that we initially set at 50%. This means that for a permissible load Q, an equal dead weight must be distributed on the footbridge. If L = 12.80m is the span and La = 14.80m is the total length of the arch of the footbridge (length of the spring line), we then have: Q = g*La where 𝑀 is the bending moment. Thus, the stress of a 1:1 scale footbridge under a given load is the same as that of a 1:5 scale bridge under a load 5 times smaller because 5*5 2 *5/(5 4 ) = 1 2) Scaling of the deflection.

The maximum deflection in an equivalent beam is 𝑑 ≈

.2. Principle of loading and evaluation of the model

We want to know how many people weighing 80 kg maximum could stand on the 1:1 project. Let us recall that, for each person, the same amount of dead weight shall be added to the footbridge. The physical model will be loaded in approximatively 4kg increments of Q. The deflection at the center of the bridge is measured at each increment. At 12kg the bridge will be fully unloaded, and the deflection measured (residual amount of deflection is then evaluated). The loading will continue in the same way until failure. A second test is carried out without distributed additional loads.

Results and analysis

The results of the first two loading tests are given in the table below. We note that:

• As designed, the 1:1 footbridge should support only 1 person's weight of 5*18,8 = 94 kg • The typology of failure is the M4 mode of overall arch buckling, the only one that we could not precisely forecast by calculation. • The hypothesis of classical arch failure mode is challenged by the fact that wicker is capable of resisting to tension, unlike a masonry arch. In this context, the experience shows that the ballasting of the footbridge is not an asset.

In order to increase the load capacity of the structure, we decided to add anti-buckling elements (bamboo tubes) between the deck and the ropes, the latter being self-tensioned with spacers in order to limit their deformation (it is important that the support of the tubes are completely blocked). We note that:

• Once modified, the footbridge should be able to support the weight of 2 to 3 people (5*44=220 kg). The main difference with the numerical prediction (400 kg) is that, in the numerical prediction, the load was divided into 4 loads of 100 kg each positioned at 1/8, 3/8, 5/8 and 7/8 of the length of the footbridge. Therefore, the physical model confirms, rather correctly, the BAYA numerical model. • The failure occurred on the extrados at a stitch between module 1 and module 2 (we have 6 modules in total). The buckling started in the center of the footbridge: increased attention must be paid to the execution of the stitch, the handrails and to the tension of the ropes supporting the feet of the anti-buckling elements. Correctly doing that should increase significantly this result. • The failure mode is M1. The local traction is maximum close to the base of the arch as it is expected in a classic masonry arch, because the position naturally taken by the funicular in an arch is that of passive thrust (the funicular is close to the intrados close to the feet of the arch, and on the extrados at its center). A rounded, braiding wicker handrail will be added to scale 1:1, to take up this traction on the extrados more efficiently.

Conclusion

• Our footbridge uses 500kg of material and is made of 90,1% wicker (around 1 m 3 ) plus 8.5% bamboo and 1.4% rope. In order to make a 100% footbridge, we should explore a tubular shape, more rigid, and therefore more stable regarding buckling. We could also avoid the ropes if the abutments could withstand a horizontal reaction.

• The data will be analyzed in order to develop a new version of BAYA. The objective is to integrate a first approach to the calculation of the deflection and to take into account the slip of the braided nodes. Another necessary improvement would be to evaluate global buckling failure loads numerically. After that, the contributions of the study of the wicker crossing will be transposable to other structural shell projects for architectural use.

Figure 1 :

 1 Figure 1: Porky Hoeffer's project, Baya nest [4], Uros' boats [Vittorio Carlucci], Laura Ellen Bacon's project.

Figure 2 .

 2 Figure 2. Construction phasing of the footbridge (a) and optimal wicker braiding designed by BAYA (b)

Figure 3 :

 3 Figure 3: Timeline of the project's design and construction; participation of the different contributors.

Figure 4 :

 4 Figure 4: Project site.

Figure 5 :

 5 Figure 5: Construction phasing of the footbridge (before adding anti-buckling elements).

•Figure 7 :

 7 Figure 7: Input parameters on the geometry of a braided specimen.

  Figure 6: Diagram of a braided specimen subjected to a given stress field.

Figure 9 :Figure 10 :

 910 Figure 9: Principal stresses on a finite element.

Figure 12 :

 12 Figure 12: Diagram of the problem studied by Douthe, and evolution of the distance to the hanging chain form with the angle α.

Figure 14 :

 14 Figure 14: Additional force N + M in the arch coming from the eccentricity of the pressure curve with respect to the neutral fiber position and stress diagram in the U-shaped section.

Figure 15 :

 15 Figure 15: Static scheme of the footbridge in service.

5 *h

 5 𝑔 * 𝐿 𝑎 * 𝐿 3 384 𝐸𝐼 + 𝑄 * 𝐿 3 48 𝐸𝐼 . Thus, the deflection/span or deflection/rise ratio of the 1:1 scale footbridge under a given load are the same ratio of the 1:5 scale model under a load 5 times smaller because 5*5*5 3 /(5 4 ) = 5 Proceedings of the IASS 2022 Symposium affiliated with APCS 2022 conference Innovation•Sustainability•Legacy 10 4.2

Figure 16 :

 16 Figure 16: Braiding and loading tests on the 1:5 model.

Figure 17 :

 17 Figure 17: Braiding and loading tests on the 1:5 model.

Figure 18 :

 18 Figure 18: Failure of the wicker bridge and analysis of the zones of maximum traction, and analogy with the classical failure of a masonry arch (illustration from Galassi et al.[3]).

4. 4 . Construction to scale 1 Figure 19 :

 4119 Figure 19: Construction of the footbridge during workcamp I (june-22). The bridge will be finished in august-22.

  Architecture have designed one of the two footbridges that will be exhibited. Built in wicker and with a span of 12.80 meters, this construction was carried out with the participation of the Duperré, Boulle and Oliver de Serres art schools during a workcamp supervised by the BETA and la Teinturerie, helped by wickerworkers from the oseraie de Gué-Droit.

	). It is organized by the BETA and la Teinturerie, in partnership with la Chancellerie des Universités de Paris and le Campus des Métiers d'Art et du Design. For this occasion, our team of students from ENSA Paris-la Villette and CentraleSupélec with teachers Date: September 2022 ►Static principles Scale: 1/15 Date: December 2022 ►Construction method Scale: 1/5 Date: May 2022 ►Loading tests Scale: 1 Date: June 2022 ►Footbridge construction Spring 2023 from Construire l'Scale: 1/100 Marc Leyral Nicolas Prévost Albin Breugnot Nicolas Prévost

Table 2 :

 2 The footbridge expected failure typologies.

	M1 Failure	M2 Failure	M3 Failure	M4 Failure	M5 Failure
	Wicker failure by	Wicker stress failure by	Local wicker failure by	Failure by global	Ropes failure by
	traction	compression.	buckling	buckling.	traction.

Table 3 :

 3 Planned loading tests and equivalence for extrapolation of results to scale 1.

	Number of people	1	2	3	4	5	6
	Footbridge loading	Q (kg)	80	160	240	320	400	480
	Scale 1:1	g (kg/m)	5.4	10.8	16.2	21.6	27	32.4
	Footbridge loading	Q (kg)	16	32	48	64	80	96
	Scale 1:5	g (kg/m)	5.4	10.8	16.2	21.6	27	32.4

Table 4 :

 4 Results

of the first loading tests (without anti-buckling).

Table 5 :

 5 Results of load tests on the modified model (with anti-buckling).

Proceedings of the IASS 2022 Symposium affiliated with APCS 2022 conference Innovation•Sustainability•Legacy

Acknowledgements

Benjamin Marolleau, from La Teinturerie, Christophe Kerrero, rector at Chancellerie des Universités de Paris, Florianne Le Thiez-Carotenuto from Chancellerie des Universités de Paris, Superior school of applied arts Boulle, Superior school of applied arts Dupperré, Campus métiers d'art, Séverine & Patrick Boyer (Osier de Gué-droit). Anna Danielsson. Geoffrey Clamour and Camille Sineau (BETA).

All the students, tutors and wickerworkers who took part in the workcamp.

Valéry Schollaert, ornithologist, Roger Hérisset, basketry expert and doctor in ethnology at the UBO, and Prof. Ph.D. François Guéna, Scientific Director of the MAP-MAACC laboratory (ENSAPLV). Pierre Jehel and Arnaud Lafont from the CentraleSupélec school. Joshua Guiffrey for proofreading.

The ENSA of Paris-la-Villette, Caroline Lecourtois, director, Vincentella De Comarmond, deputy director, Frédéric Sallet general secretary, Anne d'Orazio, President of the Board, Jérôme Candevan, accounting officer, Anaïs Campanaud, jurist, Philippe Agricole (maintenance shop), Philippe Bourdier, in charge of student life and Marc Fayolle De Mans, Jacques Bergna and Alain Raynaud (model workshop). Yann Nussaume, Rosa de Marco and Olivier Jeudy from AMP research unit. Suzel Balez, Nazila Belkadi and Dalil Hamani from the teaching team. Salomé Chantob, Victor Bardy, Mélanie Bento students at ENSAPLV, Ethan Azerad, Emmanuel Berrebi, Théodore Tarride, Maggy Zhou, students at Central-Supélec. The students who participated to elaborate the BAYA algorithm and the Baya project in 2021. And those who has worked to improve the algorithm: Alexis Meyer, Bastien Frobert, Marc Pouyanne, Louise Delhaye, Jérôme Garcia.