Mshs
email: catherine.esnard@univ-poitiers.fr

Confirmatory Information Processing in Legal Decision: Effect of Intimate Conviction

Keywords: Cognitive distortions, Juror decision making, Mock-juries, Processing strategy, Social cognition CONFIRMATORY

A large body of research has focused on legal decision-making in mixed courts of lay and professional judges. However, few studies have been conducted to test the impact on evidence processing of the intimate conviction instruction (ICI), a decision rule based on impression formation used in civil law systems. The influence of the two facets of the ICI (the decision rule and the motivation requirement) on confirmatory information processing (CIP) was studied in a harm-to-person case. Using a methodology combining the simulated juror and CIP paradigms, the decision rule (based on impression vs. rationality) and the motivation requirement (required vs. not required) were manipulated to observe their impact on assimilation and selective exposure biases. Results showed significant interactions of the two facets of the ICI but only on the assimilation bias. These results are discussed in the light of the evidence processes in the context of legal decision-making in criminal courts.

INTRODUCTION

Over the past few years, there has been an on going debate among European lawyers about the intimate conviction instruction (ICI) that governs the decision-making process in most Continental judicial systems (e.g., France, Germany and Belgium). In the French criminal system, the ICI has two facets. First, there is the decision rule, which prompts jurors to ask "what impression has been made on their reason by the evidence brought against the accused and the arguments of his defense" to decide their verdict. Second, the ICI specifies that "the law does not ask the judges to account for the means by which they convinced themselves" (Article 353 of the French Code of Criminal Procedure -Appendix A). In other words, professional and lay judges are told that 1) they should use their impression to make their decision, and 2) they do not have to motivate this decision, i.e. they do not have to justify this decision. Since 2010, the European Court of Human Rights has penalized several European countries for violating the right to a fair trial by failing to satisfy the right of the defendant (and the people) to understand the verdict by receiving a motivated decision (Art. 6, ECHR).

These countries reacted in a variety of ways. In France, a slight alteration to the ICI concerning the motivation was introduced in 2011, while in Belgium, the term IC was removed and replaced by reasonable doubt. Above and beyond these modifications, each legal decision now is systematically associated with a motivation. To our knowledge, there has been only one study of the impact of the ICI on legal decision-making and information processing [START_REF] Esnard | Effects of the instruction of "intime conviction" on judicial information processing[END_REF] in social psychology research. The objective of the present study was thus to extend its results by testing the effects of the two facets of the ICI (i.e. decision rule and judgment motivation) on jurors' evidence processing. As suggested in [START_REF] Esnard | Effects of the instruction of "intime conviction" on judicial information processing[END_REF] conclusions, evidence processing was investigated within the framework of confirmatory information processing (CIP; [START_REF] Fischer | A new look at selective-exposure effects: An integrative model[END_REF] in a CONFIRMATORY PROCESSING IN LEGAL DECISION similar legal contexts (i.e., harm to a person).

Judicial Decisions Based on Intimate Conviction

Esnard et al. 's results (2013) showed that the ICI used in French criminal courts, as opposed to one that does not espouse IC principles, generates different types of information processing and judicial decisions. These authors showed that the ICI also encouraged information processing that was experiential (i.e., based on subjectivity, affect and emotion) rather than rational (i.e., based on logical analysis; Epstein, 1994). Moreover, this study showed that the different instructions resulted in different legal decisions. The ICI resulted in more proprosecution decisions than the opposite one. Because this study used an appeal case (the defendant had originally been sentenced to 10 years' imprisonment), the authors suggested that the ICI encourages a confirmatory bias. No significant difference was observed between the ICI group and the control group, suggesting that the IC-induced mode is close to a spontaneous mode. However, this study had two limitations. First, it failed to disentangle the two facets of the ICI (i.e., decision rule and motivation requirement). It was therefore not clear whether the results were due to the decision rule (based on impression vs. rationality), the motivation requirement (required vs. not required), or the interaction between the two.

The first objective of this study was thus to test the separate effects of these two facets and their interaction on judicial information processing. Second, the information processing indicators did not significantly mediate the impact of the instructions on the legal decision.

Furthermore, the participants performed the measures of information processing after they had made their decision. Thus, in line with [START_REF] Esnard | Effects of the instruction of "intime conviction" on judicial information processing[END_REF]'s conclusions, we suggest that participants were in a CIP situation. The second objective of our study was thus to confirm that the two facets of the ICI trigger a CIP bias.

CONFIRMATORY PROCESSING IN LEGAL DECISION

Confirmatory Information Processing

CIP refers to the tendency to favor decision-consistent information over decision-inconsistent information during information evaluation and searching. This results in both an assimilation bias and a selective exposure bias [START_REF] Fischer | A new look at selective-exposure effects: An integrative model[END_REF][START_REF] Frey | Recent research on selective exposure[END_REF][START_REF] Hart | Feeling validated versus being correct: A meta-analysis of selective exposure to information[END_REF]. Assimilation bias refers to individuals' tendency to assess decision-consistent information as more credible and important than decision-inconsistent information [START_REF] Greitemeyer | Preference-consistent evaluation of information in the hidden profile paradigm: Beyond group-level explanations for the dominance of shared information in group decisions[END_REF]. Selective exposure bias refers to individuals' tendency to actively seek and select decision-consistent information in the environment (Fischer et al., 2008). In the CIP experimental paradigm, participants begin by making a preliminary decision. They are then offered access to decision-consistent and decision-inconsistent items of information, and asked to assess the importance and credibility of these items (i.e., measure of the assimilation bias). Then, they select the items they want to read in full (i.e., measure of selective exposure). At the end, they make their final decision. CIP depends on individuals' goals in terms of motivational and cognitive processes [START_REF] Fischer | A new look at selective-exposure effects: An integrative model[END_REF][START_REF] Hart | Feeling validated versus being correct: A meta-analysis of selective exposure to information[END_REF]. On a motivational process level, individuals are motivated to expose themselves to decision-consistent information and/or avoid decision-inconsistent information, in order to reduce the discomfort of dissonance arousal. With a cognitive process, individuals are rational and seek the most accurate decision and the best quality of information. However, because their evaluation of the information is dependent on their decision, individuals' perception of information quality is biased, and they systematically favor decision-consistent information. CIP has been observed in a range of decision-making contexts, including politics, management and economics (e.g., Fischer et al., 2008;Fischer, Fischer et al., 2010). Two studies used the legal decision context to investigate the effect of information characteristics on CIP: [START_REF] Sears | Effects of expected familiarity with arguments upon opinion change and selective exposure[END_REF]' study explored information familiarity; Fischer et al.

(2008 -Study 1)'one explored information quality. However, these authors did not investigate CONFIRMATORY PROCESSING IN LEGAL DECISION the construction of legal decisions. For instance, in the field of legal decision research, several studies have highlighted the relevance of investigating the anchoring effect in first impressions in the context of legal decision-making (e.g., [START_REF] Englich | Sentencing under uncertainty: Anchoring effects in the courtroom[END_REF][START_REF] Englich | The last word in court: A hidden disadvantage of the defense[END_REF][START_REF] Farina | Anchoring in judicial decision making[END_REF]. However, theses studies did not focused on legal procedures. In the present study, we precisely questioned the contribution of legal procedure to individual's cognitive biases and suggested that the two facets of the ICI contribute to CIP bias. Fischer et al., (2010) investigated the impact of decision-making mode on CIP, contrasting a deliberate mode (i.e., participants were instructed to think about the pros and cons for 5 minutes before their preliminary decision), an intuitive mode (i.e., participants were instructed to make their preliminary decision as spontaneously and intuitively as possible), and a distracted mode (i.e., participants performed a distraction task before making their preliminary decision; control group). Results showed that both the deliberate and intuitive groups exhibited a CIP bias, compared with the control group. In a second study, the authors showed that these two modes gave participants a reason for their decision that strengthened their confidence in their decision which, in turn, resulted in CIP. These results suggest that an instruction requiring the legal decision to be based on impression or on objectivity results in CIP in both cases. The meta-analysis conducted by [START_REF] Steblay | The impact on juror verdicts of judicial instruction to disregard inadmissible evidence: A meta-analysis[END_REF] attest that judicial instructions have been found to be ineffective in preventing jurors from, for example, using inadmissible evidence. However, mock-jurors are likely to be driven by an accuracy motivation for reaching the best decision [START_REF] Bornstein | The ecological validity of jury simulations: Is the jury still out?[END_REF]. Accordingly, if an instruction tells them how to reach the best decision, we suggest that they will follow that instruction's guidance. The decision rule of the IC instruction suggests that partiality is acceptable, CONFIRMATORY PROCESSING IN LEGAL DECISION whereas a decision rule that requires the legal decision to be based on rationality suggests that partiality is not acceptable. Thus, if both decision rules result in a CIP bias, an impression decision rule will result in a stronger bias than a rational decision rule.

CIP and the Decision Rule

CIP and the Motivations Behind Decisions

To our knowledge, the effect of the motivation requirement on CIP has never been studied.

However, we can refer to other studies in the field of selective exposure (for a review, see [START_REF] Hart | Feeling validated versus being correct: A meta-analysis of selective exposure to information[END_REF][START_REF] Perrissol | L'exposition sélective: Bilan et perspectives[END_REF]. For example, if participants know that they are going to take part in a debate, they are more likely to expose themselves to dissonant information [START_REF] Canon | Self-confidence and selective exposure to information[END_REF]Chaffe and McLeod, 1973;[START_REF] Freedman | Preference for dissonant information[END_REF]. [START_REF] Freedman | Preference for dissonant information[END_REF] compared three experimental conditions: defending the preferred position, taking part in a debate, and assessing others' preferences (control group). Participants chose to expose themselves to the information that was most useful for their goal: decision-inconsistent information in the debate group, and decision-consistent information in the preferred position group. The decisive criterion appears to be the usefulness of the information [START_REF] Frey | Recent research on selective exposure[END_REF][START_REF] Hart | Feeling validated versus being correct: A meta-analysis of selective exposure to information[END_REF]. Other authors have suggested that a desirability bias can also affect participants [START_REF] Hart | Feeling validated versus being correct: A meta-analysis of selective exposure to information[END_REF][START_REF] Lavoie | Selective exposure in a field setting[END_REF]Olson et al., 2009). When they show that they are ready to expose themselves to decision-inconsistent information, participants also show that they are receptive to contrary information, open to debate, impartial and openminded. In a legal decision situation, we would expect an explicit decision motivation requirement to ensure that the decision rule is actually followed by the jurors. When the motivation is required, the participants will want to present a good picture of themselves by showing that they follow the decision rule and base their decision on information that is useful for reaching their decision, as defined by the instruction. In a situation where the decision rule is based on impression, participants are more likely to use their impression, CONFIRMATORY PROCESSING IN LEGAL DECISION whereas in the opposite situation (e.g., decision rule based on objectivity), they are more likely to consider both prosecution and defense arguments, regardless of their preliminary decision. When the motivation is not required, individuals are under less of a social desirability constraint, and are therefore freer to follow their own decision rule. We would expect both the impression and the rational decision rules to result in CIP. The influences of the two facets of the ICI on information processing should therefore be interdependent.

Overview and hypotheses

The objective of the present study was to test the effects of the two facets of the ICI on CIP, based on the experimental material developed by [START_REF] Esnard | Effects of the instruction of "intime conviction" on judicial information processing[END_REF], using a case of harm to a person. This study featured a novel combination of two experimental paradigms: the mockjuror paradigm [START_REF] Bornstein | The ecological validity of jury simulations: Is the jury still out?[END_REF] and the CIP paradigm [START_REF] Fischer | Selective exposure to information: The impact of information limits[END_REF]Fischer et al., 2008). It followed a 2 (decision rule: impression vs. rational) x 2 (motivation: required vs. not required) between-participants factorial design. The dependent variables were assimilation bias and selective exposure scores (Fischer et al., 2008;Fischer et al., 2010). Because we assumed that the influences of the two facets of the ICI are interdependent, we expected to observe an interaction effect of the two independent variables on CIP scores: we predicted that when the motivation was required, the impression decision rule would result in a stronger CIP bias than a rational decision rule would do. By contrast, when the motivation was not required, we expected no difference between the CIP bias resulting from the two decision rules. In addition, when the decision rule was based on impression, no different CIP bias were expected in the required and not required motivation conditions. When the decision rule was based on rationality, however, we expected to observe a stronger CIP bias when the motivation was not required than when it was.

CONFIRMATORY PROCESSING IN LEGAL DECISION

METHOD

Participants and Design

Ninety

Procedure and trial stimuli

The study featured a combination of the mock-juror paradigm [START_REF] Bornstein | The ecological validity of jury simulations: Is the jury still out?[END_REF] and the CIP paradigm [START_REF] Fischer | Selective exposure to information: The impact of information limits[END_REF]Fischer et al., 2008). After signing the consent form, participants were asked to take on the role of jurors in a criminal court, which implied that they would have to render a legal judgment. Regarding the manipulation of the decision rule, participants were instructed to process the case's evidence by striving either to listen to their personal impression (impression group) or to be as objective and rigorous as possible (rational group). The motivation manipulation consisted in explicitly informing participants that they would either have to argue and justify their decision (motivation required group) or would not have to argue or justify their decision (motivation not required group). Participants then read a vignette describing the case's judicial context (i.e., first judgment, appeal, charges) and the main pieces of evidence. This vignette was built on the criminal appeal hearing used in [START_REF] Esnard | Effects of the instruction of "intime conviction" on judicial information processing[END_REF]. In the original trial, the defendant had been sentenced to 10 years' imprisonment for attempting to murder his best friend when he found out that he was having an affair with his wife. For his appeal, the defendant appeared before a new court and a new CONFIRMATORY PROCESSING IN LEGAL DECISION jury. He did not deny the facts. The judgment therefore concerned the attribution of mitigating circumstances to the defendant and the potential revision of the initial custodial sentence. The vignette was 14 lines (i.e., 190 words) long (the full experimental material is available in Appendix B). After reading the vignette, participants completed the legal decision measures and assimilation bias measures, followed by the selective exposure measures. They provided their legal decisions one more time at the end of the study. After providing their demographic data (i.e., sex and age), the participants were thanked and debriefed.

Measures

Legal decisions

Participants were asked to indicate whether the defendant should benefit or not from mitigating circumstances, and to indicate the level of their confidence in their decision on a 10-point scale ranging from 1 (Not at all) to 10 (Totally). The preliminary decision measure was a 4-point scale (ranging from None and a few to a lot of and all mitigating circumstances) in order to be included in factorial design to test CIP biases. However, this plan had to be dropped out because none of the participants indicated that the defendant should benefit from all the mitigating circumstances, and very few of them stated that he should benefit from a lot of mitigating circumstances (n = 9, 9.67%). Thus, it has been decided to split participants in two groups, one pro-prosecution group, who decided that the defendant should not benefit from any mitigating circumstances; and one pro-defense group who decided that the defendant should benefit from mitigating circumstances. The CIP biases scores were computed following the method of Fischer et al. (2010).

Assimilation bias

After participants had made a preliminary legal decision, they were informed that additional information from the police file was available and that they would have the opportunity to CONFIRMATORY PROCESSING IN LEGAL DECISION change their decision if they felt the need to do so. This additional information consisted of eight single-sentence statements. Four statements were in favor of the prosecution and four statements were in favor of the defense. These statements were based on the actual case's pieces of evidence. For example, one of the statements in favor of the prosecution was "[The defendant] loaded longer bullets in his weapon before going to [the victim's] house".

Participants were asked to rate the importance and credibility of the eight statements on 10point scales ranging from 1 (Not at all) to 10 (Totally). Four versions of the questionnaire displaying the statements in four different orders were randomly distributed across participants. Credibility and importance ratings were collapsed into a single evidence evaluation score for the defense (Pearson r = .47, p = .0001) and a single evidence evaluation score for the prosecution (Pearson r = .49, p = .0001). An assimilation bias score was computed by subtracting the mean evaluation score for the decision-inconsistent statements from the mean evaluation score for the decision-consistent statements (Fischer et al., 2008;Fischer et al., 2010).

Selective exposure

Participants were then told that they could have access to one-page testimonies from the police file corresponding to each of the eight statements. They were asked to choose which ones they would like to read. They were informed that they could choose as many testimonies as they wished, from 0 to 8. Answers were dichotomous ("Yes, I would like to read this document" vs. "No, I do not want to read this document"). Four versions of the questionnaire were constructed, based on the statement order for the assimilation bias measures. Scores of exposure for the defense and for the prosecution were computed by adding the number of selected statements. A selective exposure bias score was computed by subtracting the exposure score for the decision-inconsistent statements from the exposure score for the decision-consistent statements.

CONFIRMATORY PROCESSING IN LEGAL DECISION

RESULTS

Analyses were conducted according to a 2 (decision rule: impression vs. rational) x 2 (motivation: required vs. not required) between-participants factorial design. A binary logistic regression was conducted to test the effect of the independent variables on the preliminary decision, and linear regressions were conducted for the other dependent variables. Means and standard deviations for confidence ratings, assimilation bias scores and selective exposure scores are displayed in Table 1.

[Insert Table 1 here]

Preliminary decision

Sixty-one (65.59%) participants indicated that the defendant should benefit from mitigating circumstances and 32 participants (34.40%) thought that he had no mitigating circumstances.

Logistic regression analysis showed no significant impact of the manipulated variables on the preliminary decision.

[Insert Table 2 here]

Confidence

Participants were generally very confident in their preliminary decision (M = 7.38, SD = 1.57). The regression analysis showed no significant effect of motivation and decision rule conditions on the confidence ratings (ts < 1).

Legal decisions and CIP

CONFIRMATORY PROCESSING IN LEGAL DECISION

The preliminary decision significantly affected both assimilation bias (β = -1.10, SE = .198, t = -5.60, p = .0001, 95% CI [-1.50, -0.71]) and selective exposure bias (β = -.305, SE = .144, t = -2.17, p = .043, 95% CI [-0.59, -0.01]) scores. Pro-prosecution participants (i.e., those who decided that the defendant should not benefit from any mitigating circumstances) were more biased in their evidence evaluations (Mpro-prosecution = 1.68, SD = 2.09 vs. Mpro-defense = -0.53, SD = 1.64) and evidence exposure (Mpro-prosecution = 0.59, SD = 1.41 vs. Mpro-defense = -0.01, SD = 1.27) than pro-defense participants (i.e., those who decided that the defendant should benefit from mitigating circumstances). Simple t tests against zero indicated that pro-prosecution participants exhibited significant assimilation, t(31) = 4.55, p = .0001, and selective exposure, t(31) = 2.38, p = .024, biases toward decision-consistent information. Pro-defendant participants exhibited a significant reversed assimilation bias toward decision-inconsistent information, t(60) = -2.52, p = .014, and a nonsignificant selective exposure bias, t(60) < 1.

Confidence ratings were not significantly associated with the bias scores (assimilation bias: r = .18, p = .072; selective exposure: r = .11, p = .27).

[Insert Table 2 here]

Assimilation bias

Regression analysis revealed nonsignificant main effects of decision rule and motivation (β = -.008, SE = .211, t < 1 and β = -.22, SE = .221, t = -1.06, p = .290, 95% CI [-0.64, 0.19]) and a significant interaction (β = .56, SE = .211, t = 2.67, p = .009, 95% CI [0.14, 0.98] on the assimilation bias score; Figure 1 1 ). Simple effects on the assimilation bias score were analyzed with Bonferroni post hoc tests. The two decision rule groups comparisons were nonsignificant when the motivation was required (p = .061) and not required (p = .062). The rational groups comparison confirmed that the motivation not required group differed 1 The same pattern of results is observed with the preliminary decision entered in the analyses.

CONFIRMATORY PROCESSING IN LEGAL DECISION

significantly from the motivation required group (p = .009). When the motivation was not required, participants exhibited an assimilation bias, whereas when the motivation was required, participants favored decision-inconsistent information. The comparison of the impression groups indicated that the motivation manipulation had no significant impact on the assimilation bias score (p = .260). Simple t tests against zero revealed a significant assimilation bias for the rational/ motivation not required group, t(21) = 2.16, p = .042, but not for the other three experimental groups (rational/motivation required: t(24) = -1.70, p = .101; impression/ motivation not required: t( 22) < 1; impression/ motivation required: t(23) = 1.17, p = .252).

[Insert Figure 1 here]

Selective exposure

The main effects of decision rule and motivation, and the interaction between the two inductions on the selective exposure bias score were not significant (ts < 1). Simple t tests against zero showed no significant selective exposure bias (rational/ motivation not required: t(21) < 1; rational/ motivation required: t(24) = 1.12, p = .273; impression/ motivation not required: t(22) < 1; impression/ motivation required: t(22) <1).

DISCUSSION

This study tested the effects of the two facets of the ICI on CIP, namely the tendency to favor decision-consistent information over decision-inconsistent information during information evaluation and searching. It was conducted in a legal context of harm to a person, in line with [START_REF] Esnard | Effects of the instruction of "intime conviction" on judicial information processing[END_REF]. We expected to observe an interactional effect of the two independent CONFIRMATORY PROCESSING IN LEGAL DECISION variables (decision rule: impression vs. rational; motivation: required vs. not required) on assimilation bias and selective exposure scores.

A significant interaction between decision rule and motivation was observed for assimilation bias. As expected, when participants received the rational decision rule, they exhibited stronger assimilation bias when the motivation was not required than when it was. These results suggest that when participants were instructed to be objective, they showed themselves to be open-minded and assessed favorably inconsistent information when the reasons for their decision are going to be public. In contrast, when participants thought they can keep the reasons underlying their decision for themselves, the rational group displayed an assimilation bias, as though the absence of required motivation removed the control that participants needed to maintain objectivity. This difference between motivation groups was not significant for participants who received the impression decision rule suggesting that participants are less under social desirability constraints regardless the motivation requirement. In the context of this study, the social desirability pressure could have come from the experimenter or the peers participating in the study. We could expect this pressure to be stronger in the actual context of legal judgment with a real case to judge next to professional judges.

Unlike results obtained in the line of research on the CIP [START_REF] Fischer | A new look at selective-exposure effects: An integrative model[END_REF][START_REF] Hart | Feeling validated versus being correct: A meta-analysis of selective exposure to information[END_REF], we noticed a lack of convergence between assimilation bias and selective exposure results. More specifically, the independent variables had a significant impact on assimilation biases but not on selective exposure. The mock-juror paradigm may have placed participants in a different situation than the participants in the studies using CIP paradigm only. We can assume that the present study reports one of the specificities of judicial decision. Whatever, if these results did not support Fischer et al. (2010)'s results, further studies are needed to clarify this point. We can also underline that the quite small cell sizes could explain some nonsignificant effects.

CONFIRMATORY PROCESSING IN LEGAL DECISION

We also observed that the preliminary decision impacted the biases. Pro-prosecution participants exhibited significant decision-consistent biases whereas pro-defense participants exhibited significant reversed bias (or decision-inconsistent biases). Mock-jurors probably focused on their decision and were strongly aware of the issues surrounding that decision. The contribution of the preliminary decision in the CIP should deserve more attention in further research.

LIMITATIONS AND FURTHER STUDIES

In a context of harm to a person, participants are probably challenged on affective dimensions (e.g., love, anger) and the emotional mobilization can vary in both nature and intensity.

Further studies need to take into account the emotional arousal elicited by the legal context either to control for its potential impact or to have a deeper understanding in the contribution of emotions in the confirmatory information processing.

Besides, the ecological validity of this study could be improved at different levels. First, participants read a vignette about the case to judge as suggested by the classical CIP paradigm (e.g. Fisher et al, 2010Fisher et al, , 2011)). However, an actual trial includes more information than a vignette and, as a consequence, requires a more important cognitive load. Second, the present study focused on the initial individual processing. The ICI is given to jurors at the beginning of the trial and repeated before they retire to deliberate. Thus, the decision rule and the motivation requirement can impact jurors' decisions and information processing both at the start of a trial and when they retire to deliberate. If individual pre-deliberation verdicts are good predictors of the jury's final verdict (Sandys and Dillehay, 1995), it would be useful to consider the link between ICI and CIP after jury deliberations, as collective decision-making involves specific processes of social influence that could impact jurors' judgment and information processing.

CONFIRMATORY PROCESSING IN LEGAL DECISION

CONCLUSION

This experimental study provided several insights into implicit sociocognitive processes that are not recognizable at a declaratory level, but which may subtend jurors' construction of judicial decisions. Was it relevant to modify the ICI following the ECHR condemnations? We could certainly recommend more clearly registering the need to consider contradictory evidence for the prosecution and defense, to reduce the possible confirmation bias generated by the legal instruction. Furthermore, we found that, in some circumstances, the two facets of the ICI (decision rule and motivation requirement) were interdependent. The European debate on the motivation requirement should therefore include a discussion about the decision rule, too. Our results highlight the need for more interest and deeper investigation of the processes involved in the effect of the ICI on the construction of judicial decisions and, at the end, to be able to clearly inform judicial systems.

  -three first-year psychology undergraduates from the University de Poitiers, France (75 women, 18 men; Mage = 19.23 years, SD = 1.84, range: 17-29) took part in the study in exchange for a course credit. The study was based on a 2 (decision rule: impression vs. rational) x 2 (motivation: required vs. not required) between-participants factorial design (nimpression/motivation required = 23, nimpression/motivation not-required = 23; nrational/motivation required = 25, nrational/motivation not-required = 22).

Table 1

 1 Mean (Standard Deviation) Confidence Ratings and Assimilation and Selective ExposureBias Scores as a Function of the Motivation and Decision Rule Manipulations.Binary Logistic Regressions Predicting Mitigating Circumstances Decisions.

		Decision rule
	Motivation	Rational	Impression	Total
		Confidence
	Required	7.20 (1.55)	7.35 (1.55)	7.27 (1.54)
	Not required	7.59 (1.70)	7.39 (1.27)	7.49 (1.48)
	Total	7.38 (1.62)	7.37 (1.40)
		Assimilation bias
	Required	-0.52 (1.53)	0.58 (2.39)	0.46 (2.12)
	Not required	1.05 (2.28)	-0.09 (1.84)	-0.007 (2.05)
	Total	0.21 (2.05)	0.24 (2.14)
		Selective exposure
	Required	0.36 (1.60)	0.08 (1.08)	0.22 (1.37)
	Not required	0.18 (1.46)	0.13 (1.21)	0.15 (1.33)
	Total	0.27 (1.52)	0.10 (1.13)

Acknowledgements. This research was supported by a grant from La Mission de Recherche Droit et Justice (France).

APPENDIX A: ARTICLE 353 OF THE FRENCH CODE OF CRIMINAL PROCEDURE

The law does not ask the judges to account for the means by which they convinced themselves; it does not charge them with any rule from which they shall specifically derive the fullness and adequacy of evidence. It requires them to question themselves in silence and reflection and to seek in the sincerity of their conscience what impression has been made on their reason by the evidence brought against the accused and the arguments of his defense.

The law asks them but this single question, which encloses the full scope of their duties: 'Are you inwardly convinced?' (Transl. Legifrance).

APPENDIX B: EXPERIMENTAL MATERIAL

Case vignette

The Loire criminal court sentenced Xavier B. to 10 years' imprisonment for attempting to murder of his best friend Guy G. In detention, he appealed this decision and has been summoned to appear before an appeal court with 12 jurors. Xavier B. has always worked, he is an ordinary citizen. He married Patricia M. with whom he is deeply in love. The couple quickly ran into difficulties because Patricia M. often flirted at parties, according to Xavier B. Xavier B. admits that he was often jealous. Xavier B. states that he was always faithful to his wife.

His friend Guy G. is also married. The two couples used to meet frequently, they often gave each other a helping hand, and liked each other a lot.

One evening, Xavier B. came back from work later than usual, and found Guy G.'s car parked in front of his house. All the lights were on. Xavier B. discovered his friend Guy G. and his wife kissing and fondling each other.

A few months later, Xavier B. went to Guy G.'s house with a rifle and attempted to kill him.

CONFIRMATORY PROCESSING IN LEGAL DECISION

Evidence statements

Pro-defense

Pro-prosecution

• Xavier B. had never been in trouble with the law and used to lead a normal life before these events.

• Xavier B. caught Guy G. in the arms of his wife.

• Xavier B. expresses considerable remorse, and has apologized to Guy G. and his family.

• Patricia M. had planned the adulterous scene beforehand.

• Guy G. was saved thanks to a false tooth that stopped the bullet reaching his brain.

• Xavier B. loaded longer bullets in his weapon before going to Guy G.'s house.

• Guy G. still feels threatened by Xavier B.

• Xavier B. shot Guy G. several times.


Ara Kim

Damien P Debecker
email: damien.debecker@uclouvain.be

François Devred

Vincent Dubois

Clément Sanchez

Capucine Sassoye
email: capucine.sassoye@upmc.fr

CO 2 methanation on Ru/TiO 2 catalysts: On the effect of mixing anatase and rutile TiO 2 supports

teaching and research institutions in France or abroad, or from public or private research centers.

Introduction

In recent years, there has been increasing pressure in the society to curb CO 2 emissions and develop efficient CO 2 capture, storage and utilization technologies [1][2][3][4]. The reduction of CO 2 emissions is recognized as a long term task as it requires efficient use of energy and switching from fossil fuels towards less carbon intensive energy sources such as hydrogen and renewable energy [4,5]. In regard to the reduction of CO 2 in the atmosphere, two major strategies have been proposed: CO 2 capture and storage, or usage of CO 2 [4,[6][7][8][9][10][11][12]. The usage of CO 2 is particularly promising as increasing amounts of low-cost and relatively pure CO 2 from current and scheduled plants for carbon capture and storage will be available at nearly zero cost [13].

Among different catalytic conversion processes of CO 2 , the hydrogenation of CO 2 to methane, so-called CO 2 methanation, is attractive: the reaction can be carried out under atmospheric pressure, the produced CH 4 can be directly injected into already existing natural gas pipelines, and it can be used as a fuel or raw material for production of other chemicals [10]. Thus, CO 2 methanation can serve as a tool for H 2 produced from renewable resources to be efficiently utilized as an energy vector since transportation of H 2 is limited due to its low volumetric energy density [14].

CO 2 methanation via heterogeneous catalysts has received considerable attention in recent years [3,10,15]. Numerous supported metals, such as Ni, Ru, Rh, Pd, Co, and Mg on various oxide supports, including TiO 2 , SiO 2 , Al 2 O 3 , CeO 2 , MgO and ZrO 2 , have been investigated [16][17][18][19][20][21][22][23]. The main research objective has been to obtain the best catalytic performance in terms of stability, selectivity, CO 2 conversion, and CH 4 production, especially aimed at mild reaction conditions (i.e. low reaction temperature). Ru/TiO 2 catalyst is widely recognized as one of the most attractive formulation [15,[24][25][26][27][28][29], allowing to obtain ∼100% selectivity to methane when operating under mild reaction conditions (e.g. at atmospheric pressure and ∼200 °C or lower). Yet, the structure-performance relationship appears to be a key for the development of high performance catalysts.

The crystal structure of TiO 2 support was shown to play an important role that dictates the morphology of Ru species, thereby affecting the catalytic performance in CO 2 methanation. In a recent contribution, we showed that Ru/TiO 2 catalyst supported on the commercial TiO 2 -P25 from Degussa, which is composed of 20% rutile and 80% anatase phases, presents the highest catalytic performance compared to Ru/TiO 2 catalysts supported on pure anatase TiO 2 or rutile TiO 2 [24]. Our observations were in accordance with the previously reported studies in which highly dispersed and stable RuO 2 species were formed on rutile TiO 2 owing to the lattice matching with rutile TiO 2 support in HCl oxidation [30][31][32] and CO 2 methanation [28].

The high catalytic performance was found to be correlated to the high Ru dispersion, which itself was dictated by three phenomena [24]. First, thin layers of RuO 2 were formed on the rutile TiO 2 particles during annealing, owing to the lattice matching between rutile TiO 2 and rutile RuO 2 phases. These species generate highly dispersed Ru nanoparticles upon reduction [33]. This behavior is the opposite to the case of the anatase TiO 2 support onto which RuO 2 sinters heavily, leading to extremely low Ru dispersion in the final catalyst. Second, on the mixed support, we evidenced the migration of RuO 2 nanoparticles from anatase particles to rutile particles, where they maintained a good dispersion. Third, the homemade supports suffered from heavy sintering upon annealing which resulted in a significant loss of specific surface area andmore importantlyin the trapping of RuO 2 layers by sandwiching between rutile TiO 2 rods. Thus the mixed support allowed reaching higher performance because (i) it contained rutile TiO 2 particles which favor the dispersion of the Ru phase and (ii) it contains anatase TiO 2 particles from which Ru migrates, but which impede the sintering of rutile TiO 2 particles.

In this contribution, we present experimental data to elucidate the origin of such beneficial effect of mixing anatase and rutile. Ru/ TiO 2 catalysts are prepared by deposition of pre-synthesized RuO 2 nanoparticles on mixtures of rutile and anatase TiO 2 with various mixing ratios while keeping other parameters constant (Ru loading and annealing condition). Rutile and anatase phases are mixed at three different stages of catalyst preparation, i.e. before RuO 2 deposition, before annealing, or after annealing. For those catalysts based on mixed supports at various ratio of rutile to anatase, we define "synergy" as the result of greater methane production rate as compared to the weighted average methane production rate of the pure rutile TiO 2 and pure anatase TiO 2 supported catalysts. We verify whether higher activity can be explained by the formation of more active Ru species or whether it is simply governed by dispersion. Both homemade and commercial rutile and anatase TiO 2 are exploited in an attempt to separate the crystalline structural effect from the effect of thermal stability (vs. sintering).

Experimental

Catalyst preparation

Homemade rutile and anatase TiO 2 supports were prepared as previously described [24]. The commercial TiO 2 nanopowder was obtained from Sigma-Aldrich; anatase nanopowder (99.7% trace metal basis, particle size < 25 nm) and rutile nanopowder (99.5% trace metal basis, particle size < 100 nm). A highly stable colloidal suspension of monodispersed RuO 2 nanoparticles [34,35] was obtained by a dropwise

addition of 15%v/v H 2 O 2 diluted in H 2 O into 0.011 M RuCl 3 •xH 2 O (x = 3-5) dissolved in H 2 O
so that the final concentration of Ru ≈ 0.007 M. The solution was heated at 95 °C for 2 h. Once cooled to room temperature, an appropriate amount of TiO 2 powder was added to the colloidal suspension of RuO 2 nanoparticles to yield 2.2 wt.% of Ru in the final catalyst. The mixture was put in an oven at 50 °C overnight and the excess water was removed by rotary evaporation. The resulting powder was then calcined at 450 °C for 16 h in static air (this step is called "annealing" in the following).

To prepare catalysts based on the mixing of two pure supports, the mixing was done at different stages of the preparation. The schematics of catalyst preparation involving the mixing of anatase and rutile TiO 2 phases are shown in Fig. 1.

First, pure rutile and anatase supports were mechanically mixed in various mass ratios (rutile to anatase = 5:5, 3:7, 2:8, 1:9 for homemade TiO 2 supports and rutile to anatase = 5:5, 2:8 for commercial TiO 2 supports) followed by the deposition of RuO 2 NPs, drying and annealing. This procedure is referred to as "mixing 1". The catalysts are denoted as (R + A)55, (R + A)37, (R + A)28, and (R + A)19 for homemade TiO 2 supports and C(R + A)55 and C(R + A)28 for commercial TiO 2 supports respectively, where the numbers indicate the anatase-to-rutile mass ratio and "C" indicates the commercial origin of the supports.

Second, RuO 2 NPs were deposited and dried on rutile and anatase supports separately then mixed in various ratios right before annealing. This procedure is referred to as "mixing 2". The catalysts are noted (R + A)55-BA, (R + A)37-BA, (R + A)28-BA, and (R + A)19-BA for homemade TiO 2 supports and C(R + A)55-BA and C(R + A)28-BA for commercial TiO 2 supports, where "BA" stands for "before annealing".

Third, RuO 2 NPs were deposited and dried on rutile and anatase supports separately, annealed separately (i.e. the complete catalyst preparation procedure), and then mixed in various ratios. This procedure is referred to as "mixing 3". The catalysts are noted (R + A)55-AA, (R + A)37-AA, (R + A)28-AA, and (R + A)19-AA for homemade TiO 2 supports and C(R + A)55-AA and C(R + A)28-AA for commercial TiO 2 supports, where "AA" stands for "after annealing".

For comparison, pure anatase supported catalysts and pure rutile supported catalysts were prepared and denoted as A100 and R100 for homemade anatase and rutile supported catalysts respectively and CA100 and CR100 for commercial anatase and rutile supported catalysts respectively. Table 1 summarizes the studied catalysts.

Catalyst characterization

ICP-AES elemental analysis of the catalysts resulted in Ru contents of 2.35-2.60 wt.%, indicating no Ru loss during the entire synthesis process (small variation comes from the variation in the water content in the RuCl3.xH2O (x = 3-5) precursor).

The specific surface area of the catalysts was obtained by nitrogen adsorption-desorption isotherm collected at -196 °C on a BELSORBmini II (BEL Japan, Inc.). The samples were outgassed for overnight at 140 °C prior to the analysis. SBET was calculated applying the Brunauer, Emmet and Teller (BET) method for N 2 relative pressure in range of 0.05 < P/P 0 < 0.30.

H 2 chemisorption at 100 °C was used to measure the exposed Ru atoms using ASAP 2010C apparatus from Micrometrics. Catalyst weight between 150 and 200 mg was loaded into a Pyrex tube, and subsequently degassed in He at 150 °C for 30 min. After evacuation, the sample was reduced in pure H 2 at 200 °C for 2 h (same as in situ reduction for methanation, see Section 2.3) followed by purging with He at 100 °C for 1 h and adsorption of H 2 . Two isotherms were measured in the range of 0.08-95 kPa. The first accounts for reversible and irreversible chemisorption. The sample was evacuated to desorb reversibly adsorbed H 2 . The second isotherm was then measured which accounts only for the reversibly adsorbed H 2 . The subtraction of the linear part of the two isotherms gave the total amount of irreversibly adsorbed (chemisorbed) H 2 . The amount of surface Ru atoms was calculated from the amount of chemisorbed H 2 assuming that the chemisorption stoichiometry is H:Ru = 1 [36]. It should be noted that the amount of surface Ru is possibly overestimated due to H 2 spillover on the titania support [37]. Reported values of dispersiondefined as surface Ru atoms divided by total Ru atoms in the catalystcan be used to compare catalysts among each other but should not be taken as absolute numbers.

Transmission electron microscopy (TEM) images were obtained with a FEI Tecnai 120 Twin microscope, operating at 120 kV and equipped with a GatanOrius CCD numeric camera. The samples were prepared by ultrasonic dispersion of the powders in water and a droplet of the dispersion was then placed onto a carbon-coated copper grid.

High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images were obtained using a Jeol 2200FS microscope equipped with a spherical aberration corrector on the probe and an EDX system from Jeol.The convergence semi-angle of the probe was 30 mrad and the current was 150 pA. The inner and the outer semiangles for the dark-field detector (upper DF detector) were 100 and 170 mrad, respectively. The sample preparation was the same as described in TEM sample preparation.

X-ray diffraction (XRD) measurements were performed using Cu Kα radiation in a Bruker D8 Advance diffractometer equipped with a Lynx eye detector. The 2θ diffractograms were recorded between 24 and 50°w ith a step size of 0.04°and a steep time of 20 s/step. The ICDD-PDF2

database was used to identify the crystalline phases. Deconvolution of TiO 2 and RuO 2 XRD peaks was performed using WinPLOTR 2014 software [START_REF] Roisnel | WinPLOTR, a Graphic Tool for Powder Diffraction[END_REF]. The Scherrer equation [START_REF] Patterson | [END_REF] was used to calculate the crystallite size of TiO 2 particles. From TEM analysis, commercial particles and homemade pure anatase shows roughly isotropic shapes whereas homemade pure rutile TiO 2 particle crystalize as c-axis oriented needles. Thus, both commercial and homemade pure anatase TiO 2 particle sizes were evaluated taking into account all XRD peaks width. The (001) rutile diffraction peak being forbidden, no easy estimation of the homemade rutile TiO 2 needle length could be made. Rutile needle width was estimated from the (110) diffraction peaks.

Methanation reaction

200 mg of catalyst with particle size between 100 and 315 μm was loaded in a continuous flow fixed bed reactor and reduced in situ at 200 °C for 2 h under 30 ml/min of H 2 prior to the catalytic reaction. The reaction was carried out at 1 atm between 50 °C and 200 °C under a reaction mixture of 20 ml/min (CO 2 (10 vol.%), H 2 (40 vol.%) diluted in He). Considering the dilution and the low level of conversion, variations in flow rate due to the methanation reaction are neglected. Each temperature was maintained for 52 min (3 GC injections). The exit gases were quantified using a gas chromatograph (Varian CP3800), equipped with Hayesep Q, Molsieve 5A, and CP-Sil-5CB columns. The separated gases were detected with a flame ionization detector (CH 4 ) and a thermal conductivity detector (CO and CO 2 ). Analysis parameters were set as to allow an analysis each 19 min and to obtain measurements accurate within about 1% (relative) for the methane production rate (mole of methane produced per gram of catalyst per second). All transfer lines were maintained at 110 °C to avoid water condensation.

Results and discussion

3.1. Mixture of homemade anatase and rutile TiO 2

Activity of the catalysts obtained by mixing after annealing (Mixing 3)

In the chosen reaction conditions, the selectivity to methane for all catalysts was 100%. CO 2 conversion values are provided in the electronic supplementary information (ESI), in Table S1 andS2. Here, catalytic activities are discussed in terms of methane production rates, based on the mass of catalyst (μmol CH4 •g cat -1 s -1 ). The activity of the catalysts obtained at different ratios of rutile: anatase mixing are shown as a function of anatase content in the catalysts (Fig. 2). The dotted lines represent the calculated weighted average activity of pure rutile TiO 2 supported catalyst and pure anatase TiO 2 supported catalyst.

For the catalysts mixed after being prepared and annealed separately on rutile and anatase TiO 2 supports (mixing 3), the catalytic activity of each mixing ratio corresponded closely to the weighted average of the activity of the pure rutile supported and anatase supported catalysts. This shows that there is no impact of the co-presence of rutile and anatase TiO 2 particles during reaction.

(R + A)19 (R + A)19-BA (R + A)19-AA 20% 80% (R + A)28 (R + A)28-BA (R + A)28-AA C(R + A)28 C(R + A)28-AA 30% 70% (R + A)37 (R + A)37-BA (R + A)37-AA 50% 50% (R + A)55 (R + A)55-BA (R + A)55-AA C(R + A)55 C(R + A)55-AA 100% 0% R100 (no mixing) CR100 (no mixing)
Table 1 Catalysts nomenclature, nominal support composition and preparation procedure.

Activity of the catalysts obtained by mixing before annealing (Mixing 2)

The RuO 2 nanoparticles were deposited separately on rutile and anatase TiO 2 supports and then the resulting materials were mixed before annealing. The catalytic activities were found to be significantly above the calculated weighted average activity line, as shown in Fig. 2 (center). In other words, the observed catalytic activity with the mixed catalysts was higher than the weighted average activity of the respective pure catalysts; there is a beneficial cooperation between the two mixed parts. Such beneficial effect is commonly called "synergy".

The synergistic effect was not obvious for (R + A)55-BA and (R + A) 37-BA, but was evident for (R + A)28-BA and (R + A)19-BA.

Activity of the catalysts obtained by mixing before RuO 2 deposition (Mixing 1)

The catalysts were prepared by mixing rutile and anatase TiO 2 supports prior to RuO 2 nanoparticles deposition (Fig. 2, left). The synergy was observed in a similar manner as in the case of catalysts in mixing 2 series. Again, the synergy was especially significant with the catalysts obtained at mixing ratios 2:8 and 1:9. Interestingly, for each Fig. 2. Methanation rate for the three mixing series from homemade supports, as a function of the anatase content in the samples (red, blue, and purple data points). In each plot, the activity of R100 (0% anatase) and A100 (100% anatase) are shown with black dots. The dotted line indicates the calculated weighted average of R100 and A100 activities as if they were mixed at various ratios and under the hypothesis that they act independently at their respective rates. The error bars represent the statistic error (repeatability) of the catalytic testing procedure for one prepared catalyst. For R100 and A100, the error bar ranges also account for the preparation (reproducibility); two same catalysts were prepared separately with different batches of pure homemade TiO 2 and tested. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) mixing ration, the synergy was systematically slightly more important for the catalysts of the mixing 1 series as compared to mixing 2.

Catalyst characterization

After impregnation of the colloidal suspension, RuO 2 nanoparticle are dispersed over the support particles (Fig. 3, top). After annealing, however, drastic modifications occur (Fig. 3, center) . On anatase TiO 2 , heavy sintering of RuO 2 is observed. On rutile TiO 2 , RuO 2 spreads in the form of thin layers on the surface of the particles or is "sandwiched" between sintered rutile TiO 2 rods. Upon reduction, large chunks of Ru are detected on anatase TiO 2 , while small Ru particles are found on the surface of rutile TiO 2 rods, along with some RuO 2 which remains trapped in the sintered support (Fig. 3, bottom). These modifications are described in details in our previous work [24]. Also, when a mixture of anatase TiO 2 and rutile TiO 2 is used as a support for RuO 2 nanoparticles, RuO 2 migrates towards the rutile TiO 2 particles (supplementary information, Fig. S1). Here, the impact of these phenomena is inspected in details for different mixing ratios and mixing procedures.

The textural properties of the catalysts analyzed by N 2 physisorption are summarized in Table 2. The texture of the starting anatase and rutile supports (specific surface areas of ∼ 140 m 2 g -1 and 80 m 2 g -1 , respectively) is affected by the catalyst preparation, leading to corresponding Ru/TiO 2 catalysts with specific surface areas of ∼60 m 2 g -1 and ∼30 m 2 g -1 , respectively. Expectedly, the mixing of both catalysts after annealing (mixing 3) produces catalysts with specific surface areas corresponding exactly to the weighted averages of the specific surface areas of the separate catalysts. It is noteworthy, however, that two other series of samples (mixing pure supports first and mixing before annealing) show similar specific surface areas, pointing to an absence of impact of the mixing stage to the TiO 2 sintering behavior. On the other hand, it is notable that, while the pore volumes are similar for the catalysts mixed before annealing (Mixing 2) and after annealing (Mixing 3), the catalysts prepared by mixing the pure supports prior to the RuO 2 NPs deposition (Mixing 1) systematically present smaller pore volumes. We put forward that a better degree of mixing of rutile and anatase particles is obtained in aqueous suspension as compared to mechanical grinding, which leads to a tighter contact among particles in the aggregates and smaller interparticle porosity.

A factor influencing catalytic activity is the Ru dispersion, namely the proportion of Ru atoms effectively accessible on the surface of the catalyst and thus potentially active in the reaction. Ru dispersion has been measured by H 2 chemisorption for the catalysts made from pure anatase and rutile TiO 2 supports as well as for the mixtures (Fig. 4).

The anatase supported Ru catalyst displayed a much lower dispersion than the catalyst prepared from pure rutile. This is explained by a heavy sintering of RuO 2 when supported on anatase (Fig. 3). On rutile, TEM reveals that RuO 2 was in part highly dispersed at the surface of rutile rods (stabilized through epitaxial interactions) and in part trapped ("sandwiched") between rutile rods that tend to sinter during annealing (Fig. 3). Both phenomena are expected to have opposite effect on the dispersion value. Yet the dispersion value for rutile supported catalyst (R100) reached ∼14%, significantly higher than that of the anatase supported catalyst (A100).

Catalysts from the mixing 3 series tend to exhibit Ru dispersion in the vicinity of the value expected for a simple mechanical mixture of R100 and A100. Catalysts from mixing 2 and mixing 1 series tend to exhibit higher dispersion. It is reasonable to consider that the "sandwiching" effect observed for R100 would be reduced in the case of an intimate mixture between anatase and rutile. Also, the migration of RuO 2 from anatase TiO 2 towards rutile TiO 2 -discussed in details in our previous study [24] is expected to occur in these samples, which should favor a better dispersion.

XRD patterns of all catalysts are presented in the supplementary information, Fig. S2-4. For conciseness, only the patterns of the catalysts prepared with the mixing ratio 2:8 rutile:anatase using the three mixing procedures are compared in Fig. 5. As expected, the patterns mainly show the presence of anatase and rutile TiO 2 phases (with a small amount of brookite phase in some cases) and in some catalysts, the presence of RuO 2 can be detected as a shoulder to the rutile TiO 2 peaks. The intensities of the rutile and anatase TiO 2 peaks consistently follow the nominal composition (Fig. S2-4). XRD peaks associated with RuO 2 are visibly more pronounced on the catalyst prepared by mixing after annealing (Fig. 5). While RuO 2 peaks are too small in intensity to be refined using a pattern matching method, the position and width of the main TiO 2 and RuO 2 peaks for each catalyst could be obtained after deconvolution. Results are reported in Table S3. Overall, TiO 2 peak positions and widths (2θ and FWHM) do not evolve when the mixing order or the anatase/rutile ratio is changed; mixing order or anatase/ rutile ratio do not influence the TiO 2 sintering in comparison to what already occurs on pure homemade TiO 2 supported RuO 2 catalysts, nor do they influence the crystal structure (cell parameters) of the TiO 2 supports.

On the other hand, the RuO 2 peak positions appear to evolve. For a better visualization of the shifts in RuO 2 peak positions, the 110 2θ positions were subtracted from the 101 2θ positions and compared with the expected value (2θ 101 -2θ 110 = 7.024°for RuO 2 as per ICDD 01-070-2662), as shown in Fig. 6(a). The mixing 3 series of catalysts show values close to this expected value. Upon annealing prior to mixing, the Surface area (m 2 g -1 )

Pore volume (cm Table 2 Textural properties of the homemade anatase and rutile TiO 2 supports and of the catalysts obtained from them (N 2 physisorption). Catalysts are characterized after annealing, prior to reduction and methanation.

RuO 2 nanoparticles grow into larger RuO 2 crystals independently from the support on anatase TiO 2 , while they transform into epitaxial layer over rutile TiO 2 in strong interaction with the support [24]. When these two catalysts were mixed (mixing 3) two RuO 2 peaks can expected: one which is thin and non-shifted (on anatase), and one which is broad and shifted toward TiO 2 rutile peak positions (on rutile). The former dominates the diffractogram and relatively broad un-shifted peaks are observed.

On the contrary, the mixing 2 and 1 series clearly show significantly higher values for the RuO 2 2θ 101 -2θ 110 difference, attesting of a change in the RuO 2 structure towards rutile TiO 2 structure. In these samples, both RuO 2 peaks are shifted towards the associated rutile TiO 2 peaks. This is consistent with the fact that RuO 2 nanoparticles are able to migrate from anatase TiO 2 to rutile TiO 2 during annealing and to form epitaxial layers. The effect is larger for mixing 1 than mixing 2. We hypothesize that this results from a better degree of mixing with higher proximity between rutile and anatase particles at the wet step of the preparation, which may facilitate RuO 2 nanoparticles migration.

In comparison, Fig. 6(b) shows the values of the difference in 2θ 101 and 2θ 110 positions of rutile TiO 2 , which always remain close to the expected value of 8.639°(as per ICDD 00-021-1276), attesting that the support is not affected by these phenomena.

The size of RuO 2 is difficult to evaluate by XRD due to the low peak intensity, their overlapping with rutile TiO 2 peaks, as well as the fact that RuO 2 is well known to present numerous defects which enlarge the XRD peaks by itself [40].

Interpretation of the synergistic effect

Based on the catalytic activities of the mixing 3 series that systematically fall on the weighted average activity of the R100 and A100 at all mixing ratios, the synergy in the catalytic activities clearly does not simply come from the co-presence of the two different TiO 2 phases during the reaction. Instead, the synergy observed for mixing 1 and 2 is the result of the co-existence of the two different TiO 2 phases during annealing. The co-existence of rutile and anatase supports in the annealing step dictates the localization and morphology of the RuO 2 and then Ru particles that are stabilized on the support upon reduction.

It is important to note that the activation energies for all catalysts were similar (Table 3 and Fig. S5-7). This indicates that the rate determining pathway of the catalytic reaction and the nature of the active sites are the same for all catalysts. It must be recalled that the rate limiting step in CO 2 methanation is the dissociation of adsorbed CO (formed after a first rapid dissociation of CO 2 ) [3,10,41]. Thus the factor dictating the activity of the catalysts is the number of surface sites able to catalyze the dissociation of adsorbed CO. This is obviously influenced by the dispersion, i.e. the available metallic surface. However, it may also depend on Ru particle size (the number of sites that turn out to be active in the reaction depend on the curvature of the particle [42]) or on the formation of specific sites at the interface between the metallic particles and the support (e.g. oxygen vacancy located at the metal-support interface, which are often proposed to take an active part in the rate limiting step [43,44]).

In an attempt to explain the performance of the catalysts by the dispersion of the active phase, the methanation activity has been normalized by the amount of surface accessible Ru atoms (probed by H 2 - chemisorption). This provides the apparent TOF, here defined as the number of methane molecule produced per surface Ru atom and per second (Fig. 7). A100 has a specific activity 3-times higher than R100 and its dispersion is 3 times lower. Thus, the TOF of A100 is about 1 order of magnitude higher than that of R100. This shows that activity is not simply governed by dispersion. Indeed, in such case, the TOF would be the same for both catalysts. Instead, such marked difference in TOF points to a marked difference in the speciation of surface Ru atoms in both catalysts. For a given surface of Ru atoms, those that are found on the large Ru aggregates formed on anatase supported catalysts are ∼10 times more abundant than those found on the smaller Ru particles formed on rutile supported catalysts.

Consistent with the migration of ruthenium from anatase particles to rutile particles, TOF values were systematically found in the interval between the extreme values of R100 and A100. TOF tends to increase as the anatase content increases (Fig. 7). No clear delineation can be drawn between the catalysts from the three mixing series. The TOF values land in the same area, not far from the theoretical line, but systematically lower (closer to R100 than A100). Within the hypothesis that all the RuO 2 migrates towards rutile and subsequently forms identical rutile-supported Ru nanoparticles, in all catalysts prepared by support mixing before annealing, one should expect a constant TOF, close to that obtained for R100. However, as mentioned above, it is clear that the intrinsic activity of surface Ru is also affected by other factors like the particle size or the nature of the interaction with the support. As Ru concentrates on rutile particles (especially in anataserich mixtures), the Ru particles size is expected to be affected, potentially leading to a different TOF. Also, if a fraction of the Ru did not migrate and still formed large Ru chunks as those formed in A100, the measured dispersion (and the corresponding TOF) should be an average of both types of active species. Finally, let us remember that rutile rods stacking with the sandwiching of RuO 2 was clearly observed. It is possible that mixed support tend to minimize this phenomenon. Taking into consideration the absence of clear trend in this set of data, no hasty conclusion should be drawn on the TOF.

At this point, we conclude that the beneficial effect of mixing Table 3 Summary of activation energies (Ea) of the catalysts prepared from home-made supports (see also Arrhenius plots in Fig. S5-7).

anatase and rutile in the preparation of Ru/TiO 2 catalysts arises from the co-presence of the two crystalline phases during annealing. RuO 2 does migrate from anatase TiO 2 to rutile TiO 2 support particles during the annealing step. Simultaneously, the loss of Ru through the TiO 2 -RuO 2 -TiO 2 particle stacking on the (110) facets may be partly prevented by the mixing of rutile and anatase TiO 2 particles, especially when diluting rutile in large proportions of anatase. Thus, the superior activity of catalysts based on mixed supports may be explained by a higher amount of surface Ru as compared to R100. However, it is not excluded that more active (larger) Ru metallic particles are formed due to the accumulation of higher Ru content on rutile particles. The heavy sintering observed with the homemade supports complicates drawing conclusions.

Mixture of commercial anatase and rutile TiO 2

In order to consolidate our interpretation of the synergy effect between anatase and rutile, a second set of experiments was carried out with commercial TiO 2 supports that do not sinter. Unlike the homemade supports, the commercial supports are stable after a 450 °C thermal treatment, even in the presence of Ru (see Section 3.2.2.). We study catalysts prepared by the mixing at the beginning or at the end of the preparation (mixing 1 and mixing 3) recalling that mixing 2 was shown to be equivalent to mixing 1. We compare them to the catalysts made from the pure commercial supports CR100 and CA100.

It should be noted that the catalytic activities of the catalysts prepared from the commercial anatase and rutile supports (CA100 and CR100) show completely opposite trend from what we have observed for A100 and R100: the catalytic activity of the catalyst based on commercial rutile TiO 2 is much higher than that based on commercial anatase TiO 2 (Fig. 8). CR100 was also more active than the catalyst based on the commercial P25 support [24]. This is consistent with earlier reports by Lin et al., who identified a non-sintering rutile TiO 2 support as the most promising for the design of methanation catalysts [28]. Indeed, in the case of stable rutile support, the interaction between RuO 2 and rutile TiO 2 is still favorable, but no Ru is lost by "sandwiching" between rutile TiO 2 rods.

Activity of the catalysts obtained by mixing (mixing 1 vs. mixing 3)

As expected, when the rutile TiO 2 -supported and anatase TiO 2supported Ru catalysts were mixed together after annealing, the catalytic activities of the mixed catalysts corresponded exactly to the weighted average activity of the two separately prepared CR100 and CA100 (Fig. 8, right). This is the same trend seen in the case of homemade TiO 2 supports and it indicates that the co-presence of rutile and anatase phases during reaction does not have any effect on the

activity.

When the mixing was done early in the preparation, the effect of synergy was observed (Fig. 8, left), confirming the beneficial effect of the co-presence of rutile and anatase during the annealing step. The catalytic activity reached the same activity as CR100 when the mixing ratio was 50% rutile to 50% anatase (C(R + A)55), significantly higher than the value expected for a simple mechanical mixture.

Catalysts characterization

N 2 -physisorption analysis confirmed that both commercial anatase and rutile TiO 2 particles are not subjected to sintering upon annealing, with or without the presence of RuO 2 NPs, as shown in Table 4. The specific surface areas of the mixture of rutile and anatase phases at different catalyst preparation stages were unaffected and remained similar to the weighted averages of 50:50 mixture (33 m 2 g -1 ) and 20:80 mixture (38 m 2 g -1 ). Pore volumes were also unaffected by mixing at different stages.

The Ru dispersion on the commercial rutile TiO 2 is much higher than on the commercial anatase TiO 2 (Fig. 9). This again points to the heavy sintering of RuO 2 on anatase while a much better dispersion is obtained on rutile, thanks to the epitaxial stabilization effect. Dispersion for the mixing 3 series expectedly falls close to the values expected (weighted average) for simple mechanical mixtures of CR100 and C-A100. On the other hand, the mixing 1 series appears to exhibit relatively high dispersion, clearly above that expected for mechanical mixture. Again, this points to a better dispersion when RuO 2 has the opportunity to migrate towards rutile during the annealing phase, while it sinters heavily when the only available support surface is anatase. Note that the dispersion obtained for C(R + A)55 is similar to that of R100. In the case of a quantitative migration of RuO 2 towards rutile, this suggests that similar Ru particles, with similar size are stabilized.

The XRD patterns of CR100 and CA100 are shown in Fig. 10. Similar behavior as the homemade TiO 2 supports was observed. On rutile TiO 2 support, only a slight broadening at each shoulder of rutile TiO 2 (110) and (101) peaks can be seen. On the other hand, on anatase TiO 2 support, RuO 2 (110) and (101) peaks are clearly visible, confirming the crystal growth of large RuO 2 crystals as on the homemade anatase TiO 2 .

The XRD patterns of all commercial TiO 2 supported catalysts mixed at different stages of mixing in various ratios are shown together in Fig. 10 and the corresponding deconvolution results of the main TiO 2 peaks and RuO 2 peaks are summarized in Table S4. The difference in the positions of the 110 and 101 peaks of RuO 2 and rutile TiO 2 is plotted in Fig. 11. The same tendency was observed as in the previous section: (i) the 110 and 101 rutile TiO 2 peak positions remain constant regardless of the mixing order, and (ii) the shift in 110 and 101 RuO 2 peak positions towards 110 and 101 rutile TiO 2 peak positions is apparent for mixing 1 but not for mixing 3.

Interpretation of the synergistic effect

Synergy is confirmed: when a mixture of anatase and rutile is present during annealing, the specific activity is much higher than the expected value for simple mechanical mixtures. This is clearer in the present case because no support sintering is occurring. So the beneficial effect of support blending is not merely related to the absence of Ru "sandwiching". In theory, it can be the effect of two phenomena that are related to the migration of RuO 2 from anatase TiO 2 to rutile TiO 2 .

Firstly, RuO 2 can migrate towards rutile TiO 2 when present, be stabilized via epitaxial interactions andunlike when on anataseremain highly dispersed after annealing and reduction. We propose to call this a "migration effect" which simply relates to the localization of ruthenium: on anatase it forms large chunks of RuO 2 with low specific activity but on rutile it forms dispersed Ru nanoparticles with high specific activity. Secondly, the higher concentration of Ru found on the rutile particles after migration can lead to larger Ru particles. We propose to call this a "concentration effect", accounting for the fact that in a certain size range (a few nanometers)larger Ru particles can have higher intrinsic activity. So even if dispersion is slightly lower than in R100, the activity can in principle be as high or even higher, simply because the morphology of the stabilized particles is different.

In attempt to discriminate between both effects, the apparent TOF was calculated by normalizing the activity by the amount of surface Ru (Fig. 12). It is noteworthy that the TOF for the pure commercial support Summary of activation energies (Ea) of the catalysts prepared from commercial supports (see also Arrhenius plots in Fig. S8-9). is different from that reported for the pure homemade supports. This again points to an influence of the interaction of the Ru nanoparticles with the TiO 2 supports (which can be linked to the formation of active sites). It would not be surprising that the nature of such interactions is different in the catalysts which undergo severe support modifications (sintering) vs. in the catalysts based on very stable supports. Nevertheless, the activation energies of the catalysts supported on commercial TiO 2 (Table 5 and Fig. S8-9) were similar to the catalysts supported on homemade TiO 2 (Table 3) at all different ratios of mixing at different steps. This indicates that the rate determining pathway of the catalytic reaction is the same for all catalysts.

For the catalysts prepared by mixing the final catalysts (Mixing 3), the TOF was close to the expected value for a simple mechanical mixture (as expected). For the catalyst prepared by mixing the pure supports before RuO 2 deposition and annealing (Mixing 1), the TOF values fell between the values of catalysts from Mixing 3 and that of CR100. This suggests that the main effect of synergy is simply related to the better Ru dispersion after migration towards rutile TiO 2 (migration effect) and not to the formation of another type of Ru particles that would exhibit a higher surface density of active sites (concentration effect). Fig. 13 sums up the interpretation that the non-sintering rutile TiO 2 support contributes to stabilize high Ru dispersion which leads to high methane production rate.

Conclusion

Ru/TiO 2 catalysts were prepared by a colloidal method, using RuO 2 nanoparticles in suspension as the precursor for the active phase and using mixtures of rutile and anatase TiO 2 as supports. The mixing of the two supports was done in various ratios and at different stages of catalyst preparation, i.e. before or after RuO 2 deposition, and after annealing. The catalysts were studied in the methanation of CO 2 after undergoing a thermal reduction under H 2 . Activity depended markedly on the crystalline structure of the support. Catalysts prepared from mixed supports behaved differently, depending on the step at which rutile and anatase TiO 2 are combined. If the mixing is done after annealing, the activity simply corresponds to the weighted average activity of the two catalysts prepared from pure supports. The co-existence of rutile and anatase TiO 2 crystal phases during the reaction itself do not affect the catalytic performance. If, on the opposite, the mixing is done prior to annealing, a synergy is obtained: the catalyst based on a mixed support is significantly more active than the weighted average activity of the two catalysts prepared from pure supports. Characterization indicates that RuO 2 nanoparticles migrate towards the rutile TiO 2 phase to be stabilized by epitaxy. The stabilized RuO 2 phase located on rutile TiO 2 is then transformed into reduced Ru species exhibiting a high dispersion and high specific activity. In the catalysts prepared from homemade rutile and anatase TiO 2 supports, the blending is also beneficial to impede the negative effect of support sintering and especially the loss of Ru in TiO 2 -RuO 2 -TiO 2 "sandwich" structures. When thermally stable supports are used, the activity of the catalysts obtained by mixing the supports before annealing tend to reach the activity of the catalysts based on pure rutile. All in all, nonsintering rutile TiO 2 appears to be the best support to prepare highly active Ru/TiO 2 CO 2 methanation catalysts. Fig. 13. Graphical representation and TEM images of Ru/TiO 2 methanation catalysts prepared from commercial supports; comparison between the catalysts based on pure rutile and those based on a mixture of anatase and rutile using either the "mixing1" or the "mixing 3" procedures. Mixing 1 permits the migration of RuO 2 towards the rutile TiO 2 particles and leads a situation similar to that obtained with pure rutile TiO 2 (anatase particles are spectators).

Fig. 1 .

 1 Fig.1. Schematics of mixing anatase and rutile TiO 2 phases at different stages of catalyst preparation. The three routes are denoted "mixing 1", "mixing 2" and "mixing 3" in the following. Methanation step include in-situ reduction of RuO 2 into Ru.

Fig. 3 .

 3 Fig. 3. Selected electron microscopy images representing the catalysts, from top to down, as synthesized, after annealing, and after methanation. (a) TEM images from A100 (catalyst obtained from the homemade pure anatase support), (b) STEM-HAADF and STEM-BF images from R100 (catalyst obtained from the homemade pure rutile TiO 2 support). The scale bars represent 20 nm.

Fig. 4 .

 4 Fig. 4. Ru dispersion (%) obtained by number of surface Ru atoms probed by H 2 chemisorption divided by total number of Ru atoms catalyst determined by ICP-AES. A100 and R100 are shown as references with error ranges determined from several reproduced catalysts. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6 .

 6 Fig. 6. The difference in the XRD 2θ peak positions, 101 and 110, for (a) RuO 2 and (b) rutile TiO 2 . Expected values are taken from ICDD 01-070-2662 for RuO 2 and ICDD 00-021-1276 for rutile TiO 2 . The grouped four data points represent rutile to anatase mixing ratios, 1:9, 2:8, 3:7, 5:5, from left to right.

Fig. 5 .

 5 Fig. 5. XRD patterns of (a) (R + A)28, (b) (R + A)28-BA, (c) (R + A) 28-AA from homemade supports; rutile TiO 2 (▲), anatase TiO 2 (•), brookite TiO 2 (+), and rutile RuO 2 (drawn as dotted lines) peak positions.

Fig. 7 .Fig. 8 . 4 Fig. 9 .

 7849 Fig. 7. Turn over frequencies (TOF) for all catalysts prepared from homemade supports. The TOF is calculated as the methane production rates normalized by the surface Ru (itself probed by H2 chemisorption). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 10 .

 10 Fig. 10. XRD patterns of (a) CR100, (b) CA100, (c) C(R + A)28, (d) C(R + A)55, (e) C(R + A)28-AA, and (f) C(R + A)55-AA obtained from commercial supports; rutile TiO 2 (▲), anatase TiO 2 (•), and rutile RuO 2 (drawn as dotted lines) peak positions.

Fig. 11 .

 11 Fig. 11. The difference in the XRD 2θ peak positions, 101 and 110, for (a) RuO 2 and (b) rutile TiO 2 . Expected values are taken from ICDD 01-070-2662 for RuO 2 and ICDD 00-021-1276 for rutile TiO 2 .

Fig. 12 .

 12 Fig. 12. Turn over frequencies (TOF) or methane production rates normalized per surface Ru probed by H 2 chemisorption for all catalysts concerned in this section. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Acknowledgements

A.K. thanks the European doctoral school IDS FunMat fort the PhD fellowship. The authors acknowledge Wallonie-Bruxelles International, the Ministère Français des Affaires étrangères et européennes and the Ministère de l'Enseignement Supérieur et de la Recherche for their financial support in the framework of the Hubert Curien partnership (Tournesol), as well as Gilles Patriarche from Centre de Nanosciences et de Nanotechnologies, Université Paris-Saclay, C2N -Site de Marcoussi for STEM-HAADF images (Figs. 3b and Fig. S1). Authors also acknowledge the Fondation Collège de France.

Supplementary data

Supplementary data associated with this article can be found, in the online version