Yves Gingras
email: gingras.yves@uqam.ca

Kristoff Talin
email: christophe.talin@univ-lille.fr

More religion means less science

published or not. The documents may come

More religion means less science: An International comparison of the relations between religious beliefs and levels of and attitudes to scientific knowledge

Yves Gingras, Kristoff Talin

page 1

Introduction

Since the early 1980s, there has been a new trend promoting "dialogue" between science and religion, claiming that conflicts between these two modes of thought have been greatly exaggerated. These ideas have stimulated new research to see whether or not scientists perceive any conflict between science and religion. For instance, Ecklund and Park [START_REF] Ecklund | Conflict Between Religion and Science Among Academic Scientists? Journal for the Scientific Study of Religion[END_REF] have conducted interviews with university scientists. Their results show that most respondents do not perceive any conflict between science and religion. When scientists are more integrated, through their practices, with their religion, they are even less likely to assert the existence of such a conflict. According to the authors, these results contradict earlier findings and show that religion and science are not incompatible. They extended their analysis to eight countries (France, Hong Kong, India, Italy, Taiwan, Turkey, United Kingdom, United States) thus providing a comparative perspective [START_REF] Ecklund | Religion among Scientists in International Context: A New Study of Scientists in Eight Regions[END_REF]. Based on a survey of physicists and biologists the authors reaffirm their previous results and conclude that most scientists consider religion and science as operating in separate spheres.

Ecklund's team [START_REF] Ecklund | Religion among Scientists in International Context: A New Study of Scientists in Eight Regions[END_REF] also show that scientists are much less religious -in terms of practices and beliefs -than ordinary citizens. This is, of course, consistent with the many analysis conducted since the beginning of the 20 th century. In 1914, for example, the American psychologist James H. Leuba conducted a survey [START_REF] Leuba | The Belief in God and Immortality: A Psychological, Anthropological and Statistical Study[END_REF] in which he showed that only 27% of the American scientific elite at that time believed in the existence of a personal God. He updated his survey in 1933 and showed that this percentage had fallen to 15% [START_REF] Leuba | Religious beliefs of American scientists[END_REF]. Fifty years later, a new survey, based on Leuba's method for purposes of comparison, was conducted among American scientists [START_REF] Larson | Leading scientists still reject God[END_REF]. The results confirmed the decline: from 15% in 1933, the proportion of believers in a personal God had declined to 7%. The belief rate of American scientists in a personal God thus fell by 50% once, between 1914 and 1933, and then by half again between 1933 and 1998. More generally, the religious sphere is still characterized by a marked decline in traditional forms of practice (belonging to a religion, attending religious services, prayer [START_REF] Dargent | Recul du catholicisme, croissance des non-affiliés et des minorités religieuses[END_REF]) and the emergence of new forms of religious expression (belief in parasciences, the development of "emotional forms" [START_REF] Dargent | Quatre croyances religieuses en progression[END_REF]). In a recent study, Inglehart [START_REF] Inglehart | Giving Up on God. The Global Decline of Religion[END_REF] observed that 43 out of 49 countries he studied saw a decline in religion between 2007 and 2019, the most dramatic shift noted being among the American public.

Research on perceptions of conflict conducted among American undergraduate students by Scheitle [START_REF] Scheitle | College Students' Perception of Religion and Science: Conflict, Collaboration, or Independence? A Research Note[END_REF] shows results quite similar to those of Ecklund [START_REF] Ecklund | Religion among Scientists in International Context: A New Study of Scientists in Eight Regions[END_REF]. The majority of students do not see the religious and scientific spheres as being in conflict. There are, however, interesting variations according to the level of religious integration: on one hand, highly integrated students -as well as those who are the most religiously conservative -are more likely to see a conflict between religion and science; on the other hand, at equal levels of religious integration, students in a religious institution are less likely to see a conflict between science and religion than students in a secular school. These results suggest that enrollment in a religious institution may help reduce the perception of tensions between religion and science.

In Belgium, a survey conducted in 2011, among a representative sample of high school students in their final year, also gives similar results [START_REF] Wolfs | Sciences, religions et identités culturelles : quels enjeux pour l'éducation[END_REF]. The interest of this research is that it highlights different types of conceptions of science that are strongly correlated with what page 3 the author calls the "register of students' convictions". It is possible to position these different types on a continuum where at one end we have a high degree of adherence to religious values -as well as a rejection of rationalist criticism -associated with a very weak recognition of the autonomy and specificity of science. At the other end of the spectrum, we find agnostic or atheist students who see science as very autonomous from religion.

Finally, Evans [START_REF] Evans | Epistemological and Moral Conflict Between Religion and Science[END_REF] shows that, in the United States, levels of religious integration and opinions about science are correlated. The most integrated members of the different Protestant movements, like conservative Catholics, side in favor of religion if a conflict between science and religion arises over their world view. These two groups also try to limit the influence of scientists on moral issues in the public sphere. In a subsequent article, Evans [START_REF] Evans | The Growing Social and Moral Conflict Between Conservative Protestantism and Science[END_REF] shows that these conclusions are reinforced when the respondent belongs to a religious group that promote a fundamentalist reading of the Bible.

Most of these studies inquired about how scientists, or college and university students, perceive the possible relations between science and religion. One limitation of these studies based only on representations is that given the distinction between facts and norms, and between reality and representation of reality, they do not prove that conflicts did not or could not in fact arise in certain social contexts. Another limitation is that the philosophical question of the epistemic difference between science and religion cannot be reduced to that of knowing what scientists think the relations between these two domains are or should be. For example, it is well known that specific conflicts between specific sciences (astronomy, geology, biology) and specific religions (Christianism, Islam) have existed at different times and places since the 17 th century despite discourses alleging that 'well understood' religions cannot 'really' conflict with 'true' science [START_REF] Gingras | Science and religion. An impossible dialogue[END_REF].

A different approach to the study of the relations between science and religion, that goes beyond the analyses of representations or perceptions of these relations, consists in finding independent measures of religious affiliations and practices on the one hand and of level of scientific knowledge and attitudes toward science on the other and then looking at the possible correlations between them.

Starting from the hypothesis that beliefs (scientific or religious) have cognitive effectsotherwise one might wonder whether they are really sincere and not simply superficial beliefs -we wanted to see if, at the macro-social level of the general population of different countries, knowledge of and attitudes towards science vary according to the type and level of religious belief in addition to the usual sociodemographic variables. For even if someone may personally think that there is or should be no conflicts between science and religion, it may actually be the case that, there could indeed exist, at the macro-social level, negative correlations between intense beliefs about religion and the level of knowledge of and attitudes toward science.

Data sources

In order to better understand the ways in which religious beliefs and scientific knowledge are articulated in contemporary Western societies, we have conducted a secondary analysis of existing European and American surveys, whose wealth of data has been under-exploited. These surveys are: In all these surveys, the religious identity is self-declared by the respondents. Thus, a "Catholic", a "Protestant" an "Evangelic" or "Born again Christian" etc. is a person who declared that particular identity. Likewise, the intensity of adhesion to these different religions is self-declared by responding to questions on the frequency of practices like going (regularly or not) to a church, following rites, etc.

In the following section, we first present the results of the analysis of the links between religious practices and beliefs and scientific knowledge. Section 2 deals with the influence of socio-demographic variables on these relationships. Section 3 discusses the links between representations of science and of its social effects (positive or negative) and religious practices and beliefs. In the conclusion, we briefly recall the main findings and limits of these surveys and suggest possible explanations of the correlations observed.

Links between practices, religious beliefs and scientific knowledge in Europe and the United States

This section presents the results of the analysis of the links between religious practices and beliefs and scientific knowledge based on the European (section 1.1) and American (section 1.2) surveys. In both cases, we observe negative correlations between the level of scientific knowledge and the intensity of religious practices and beliefs.

Europe

The level of scientific knowledge was measured by a series of 13 factual questions. Each respondent was given a score between 0 and 13 depending on the number of correct answers.

Figure 1 shows the distribution of correct answers for all respondents to the 2005 Eurobarometer questionnaire. The average is 8.24, or 63%, with an asymmetric Gaussian distribution to the right. Depending on the point of view taken, one could emphasize the relatively good knowledge of basic scientific facts or, on the contrary, insist that a quarter of the sample had less than 50% of correct answers. But what interests us here is less the level of knowledge per se, than its possible relation with other variables, particularly those related to religious practices and beliefs. It has long been known that the level of knowledge is strongly associated with the level of education. Not surprisingly, therefore, the average number of correct answers is lower for those with only a high school education than for those with a university degree. But what about the relationship with religious affiliation? Table 1 shows that there are significant variations in the level of scientific knowledge according to the declared religion. Those with no religion have the highest average, followed by Protestants and other religions (mostly Asian). All three groups score higher than the average of the whole sample. On the other hand, and in descending order, Catholics, Orthodox and Muslims score below average. Religion and level of scientific knowledge are therefore strongly correlated (Unless otherwise indicated, F-test are significant at the 0.000 level for all the tables included in this paper). 2 shows, the less Europeans practice any religion, the higher their scientific knowledge score, with a difference of almost three standard deviations between non-practitioners and weekly practitioners. The practice indicator, which is a synthetic measure of the level of integration into a religion [START_REF] Michelat | Classe, religion et comportement politique[END_REF], is therefore negatively correlated with the level of scientific knowledge: the more individuals practice their religion, the lower their knowledge score. This variation is valid for all religions except for Muslims (Table 4). This result can probably be attributed to the small number of Muslims in the sample. Moreover, the results for Protestantism seem particularly significant. They are consistent with the thesis well known to sociologists of science, which associates the vigorous development of science in 17th century England with scholars belonging more often to Protestant sects [START_REF] Cohen | Puritanism and the Rise of Modern Science: The Merton Thesis[END_REF]. Among religious individuals, Protestants have the highest level of scientific knowledge. Nevertheless, Protestants that practice the least still have a lower average than those declaring themselves to be without any religion. The indicator of belief in God measures a more subjective and less ritualistic dimension of religious feeling. One in two respondents believe in the existence of a God, one in three say there is a spiritual or living force, and 15% believe in neither (Table 5). Of course, subjective beliefs are strongly correlated with the religion to which one belongs (Table 6). However, minority groups -sometimes unexpected -do exist. For example, 10%

of Protestants say they have no subjective belief in a God, while 39% of those without religion believe in a spiritual or living force. It is likely that in these cases, respondents were expressing a purely cultural conception of their religious identity. On the basis of these European data, and as a partial conclusion, we can say that belonging to a religion, having a high level of religious practice and believing in God correlate with lower levels of scientific knowledge. Now let us look at the situation in USA.

United States

In the Pew Research U.S. survey, the level of scientific knowledge is gauged by a group of nine questions. For each of them, respondents were asked to choose the correct answer. On average, 52% of respondents answered correctly, but the dispersion of responses, depending on the question, is significant and follow a normal distribution. For example, while 75% were able to identify carbon dioxide as the gas produced as a result of combustion, only 37% identified nitrogen as the most common gas in the earth's atmosphere.

By counting all of the correct answers, a cumulative index can be constructed ranging from 0 (no correct answers) to 9 (all correct answers). 34% scored less than 4, while 26% scored between 4 and 5 and 40% scored 6 or higher (Figure 2).

Figure 2 Number of correct answers on the scientific knowledge scale (N=2537, percent)

As was the case in European Union countries, the level of scientific knowledge of Americans correlates with their religious practices and beliefs (Table 8, For the purposes of our analysis, the religions analyzed include only the five groups mentioned. Minority religions were excluded because of small numbers that do not allow for robust statistical analyses. In this table, religious integration is measured using an index composed of three variables (the importance of religion in life, the frequency of religious practice and the intensity of prayer).

Individuals with high religious integration attend religious services at least once a week, pray daily and say that religion is very important in their lives. Those with low religious integration say that religion is of little or no importance in their lives, pray rarely or never, These results show that the more people are integrated into a religion, the less they perform in terms of scientific knowledge. Moreover, all indicators of the level of religious practiceprayer and the importance of religion in daily life -vary in the same direction: the more an individual practices, prays or is religious, the lower his or her scientific knowledge score.

The combination of two variables -the religion to which one belongs and the level of religious integration -offers significant contrasts (Table 9. The numbers for the statistical crossover "none with high integration", "agnostic with high integration" and "atheist with intermediate or high integration" are too small to be included in the table. This makes sense, as it is unlikely that a person calling him/herself an atheist or agnostic would consider him/herself highly integrated into a religion. Moreover, since the responses "rarely" and "never" were grouped together in the category "weak" integration, this also explains why the boxes for atheists, agnostics and people without religion but with weak or intermediate integration are not completely empty). Whether the individual is Catholic, Protestant, without religion, agnostic or atheist, the level of religious integration is related to or her level of scientific knowledge. The more integrated an individual, the lower his or her knowledge score.

page 15 The Pew Research Center survey asks a question specifically about the Evangelical movement that is absent from the European data and thus offers another interesting measure:

"Would you describe yourself as an Evangelical Christian or a "born-again" Christian?" It is designed to determine how closely aligned an individual is to the evangelical movements in the United States that are characterized by an emphasis on the Holy Spirit and its spiritual dimension. 48% of respondents define themselves in this way. The majority of them are Protestant (86%) and 12% are Catholic. Belonging is also related to the variables of practice, prayer or the importance of religion in life. Thus, Evangelicals attend more church services than non-evangelicals (46% versus 21% go every week (Cramer's V= 0,27)), and pray more (71% versus 45% do so every day (Cramer's V= 0,27)). Consequently, 72% of them consider religion to be very important in their life (versus 32% for non-evangelicals (Cramer's V= 0,40)).

Being Evangelical is therefore likely to reinforce the influence of the other religious variables. This hypothesis is confirmed by Tables 10 and11, which show that membership in an Evangelical movement, regardless of the degree of practice and the frequency of prayer, is associated with less scientific knowledge. The importance accorded religion, a measure of the subjective dimension of religion, and membership in an Evangelical group is also related the level of scientific knowledge (Table 12). As with religious practice and prayer, Evangelicals, regardless of the importance accorded religion, perform less well than non-Evangelicals. As we observed in the European data, all of these results for Americans confirm the existence of a negative correlations between declared religions and level of religious practice on the one hand and the level of scientific knowledge on the other.

The effect of age, level of education and gender on the level of scientific knowledge

Now let's see how socio-demographic variables affect this conclusion. The control variables included in the surveys used in this paper were: age, gender (female and male) and level of education. Unfortunately, the data do not include level of revenue. This is a limitation but the effect of revenue is indirectly included through the level of education, which is well known to be strongly correlated with it. We will first analyze the European data (section 2.1) and then the American data (section 2.2).

The European Union

The analysis of the European Union data can be summarized thus:

-Overall, men scored higher on the knowledge scale than women (8.77 The score differences between the least and most educated individuals are very large (6.69 versus 8.49). These results are not surprising insofar as the cognitive dimension of a societal phenomenon is very often related to the time spent in school. However, this variable does not eliminate the correlation between religion and the level of scientific knowledge (Table 14). Those without religion, even the least educated (having left school before the age of 16) have a higher score of scientific knowledge than the most educated Muslims (having left school at 20 or older).

Table 15, measure the "added value" of a change in the level of education on the level of knowledge for each declared religion. We observe that the effect of a change in level of education on the knowledge score is higher for Muslims, and much less lower for Protestants and non-religious people. This interesting result could be related to the extent to which each religion deny or limit the interpretive autonomy of individuals in matter of religious precepts and scientific theories. In all cases however, it remains that a higher level of education lead to a higher score of knowledge, though the effect of each education scale is different for each religion. The religion to which one belongs is therefore, all other things being equal, more statistically explanatory of the score of scientific knowledge, as measured by the questionnaire, than the age of graduation. Although the level of education has a strong influence on the results, it does not cancel out the specific effect of belonging to a religion.

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The addition of other variables into the regression analysis does not change the previous results. Thus, taking gender (female or male), age and intensity of religious practice into account induces only minor variations (Table 17). consistent with what we know of the the particular characteristics of a Protestantism which, at the doctrinal level, allows for a great freedom of individual thought and was never systematically opposed to science and the autonomy of the scientific sphere with regards to the religious sphere.

In summary, the regression analyses confirm the previous results; religion and education level are important explanatory variables of scientific knowledge and they overshadow the other socio-demographic variables. While the level of education is positively correlated with higher knowledge scores, a strong religious identity is, in contrast, postiviely correlated with lower knowledge scores.

The United States

For the United States, Table 18 shows that, as could be expected from the above results, the level of education modulates the effect of religious affiliation on knowledge scores. Since the age of graduation is strongly positively correlated with the scientific knowledge score, the following hypothesis can be advanced: within the same religious group, respondents with a high level of education will have more knowledge than those with a low level of education.

Regardless of the group considered, this hypothesis holds true. Indeed, when the respondent has a low level of education, the score is between 1.30 and 2.18 times lower than if he or she has a bachelor's degree or higher.

page 23 A complementary hypothesis can be formulated: if the level of education is more predictive of the scientific knowledge score than the religious group to which one belongs, then agnostic or atheist individuals with a low level of education should have a lower score than Catholics or Protestants who have a high level of education. The results show that this hypothesis does not hold true, and it can therefore be concluded that belonging to a religious group is more explanatory of the knowledge score measured than the level of education.

The addition of the level of religious integration in the analysis slightly changes the intensity of the results, but does not change the direction of the relationship (Table 19).

From these results, it is possible to conclude that:

-The addition of the level of integration does not change the direction of the relationship:

atheists or agnostics with a low level of integration and a low level of education perform better than highly integrated Catholics or Protestants with a high level of education;

Table 20 shows that these graduation ratios are highest for groups 3, 4 and 5, i.e. the groups with the least religious integration. In other words, the stronger the religious integration, the smaller the effect of degree level on knowledge level. Respondents who declare themselves to be Catholic or Protestant, but with a low level of religious practice and prayer activity (group 3) are more "culturally religious" than "religious by conviction". We can therefore conclude that the variable "religion" is not central to their lives.

In this case, as for people without religion, the level of education is more explanatory of scientific knowledge than the religious variable. For those who report having no religion, but who have an intermediate level of integration (group 4), the level of education is less explanatory of their score of scientific knowledge than for respondents in group 5. It can therefore be concluded that educational level is less predictive of the scientific literacy score than religious group affiliation.

Socio-demographic and religious determinants of representations of science

Having highlighted the links between religious beliefs and the level of scientific knowledge, the next section will analyses the relations between these beliefs and attitudes (positive or negative), towards science, first in European countries (section 3.1) and then in the United States (section 3.2).

Representations of science in the European Union

In order to identify the representations of science present among the people of the European Union, the Eurobarometer asks a series of questions on the social impact of scientific developments and opinions on science, technology and the environment. The questionnaire also includes a question on the degree of scientificity of various disciplines. We have not analyzed it here, as it is not very informative with regards to the relationship between science and religion. Respondents were asked to rank 13 professions or organizations to determine those which were best qualified to explain the impact of scientific developments on society (Table 21). Perceptions of course vary according to socio-demographic variables but here we focus on the religious variable.

page 27 In short, religion has an influence on the individuals or organizations deemed most competent to explain the impact of scientific and technological developments on society. Admittedly, the age of school leaving also affects opinions, but it never cancels out the effect of religion.

Representations of science in the United States

In the survey conducted in the United States, the questions concerning the representations of science are very different from those asked in the European Union analyzed above. It is therefore not possible to compare the results directly. However, as our focus is less on representations as such than on the possible relations between them and religious beliefs and practices, these differences do not create methodological problems. Thus, the correlations page 29

observed can be analyzed in the same way in both cases, even though the dimensions they measure may be different.

Seven questions, representing 11 variables, delineate the scope of our analysis. The first provides an overall view of the contribution (positive or negative) of science to society. 90%

of the respondents believe that science has made life easier for most people, while only 10% believe the opposite. It should be noted in passing that, as the questions asked to assess the level of knowledge of Americans are different from those asked Europeans by the Eurobarometer, the fact that the relationship observed between the level of knowledge and religious beliefs is more or less the same in the two surveys strongly suggest that the two indicators of the level of knowledge do indeed assess the same underlying reality.

While age has little effect on results, women (88%) are less optimistic than men (93%). This difference between men and women remains, regardless of the level of education. The level of education is fairly strongly correlated with the overall perception of science. The higher the level of education, the more positive the perception of science is. For example, while 85% of the less educated believe that science has made life easier for most people, 96% of those with a bachelor's degree or higher agree with that statement.

Similarly, 91% of Americans surveyed said that science has had a mostly positive effect on health. This quasi-consensus is less clear-cut for the effect on the environment (76%) and on food (71%). For these two items, there is a critical minority who doubt the prevailing positivism about the benefits of science.

Unsurprisingly, responses to these three variables are closely correlated. A synthetic index of the positive effects of science shows that the average response is 2.36 out of a maximum of 3. We observe that 59% of the respondents think that science always has positive effects and only 6% think that it has none. Opinion is therefore overwhelmingly positive.

These answers are highly correlated with the previous question about whether or not science has made life easier. For example, 62% of respondents who say that science has made life easier consider that science has had three positive effects while only 19% of those who say that science has made life more difficult think so. Note that men are significantly more likely than women to attribute positive consequences to science (Table 23). Moreover, as age increases, the probability of being positive about the consequences of science increases. While only 48% of 18-29 years-old have three positive elements, 70% of those 65 and older have three. This likely reflects the greater sensitivity of youth to environmental issues. Similarly, but with less amplitude, those with higher levels of education are also more positive. Religious affiliation also plays a role: atheists and agnostics have a much more positive view of the effects of science than do Catholics and Protestants.

Similarly, the level of religious integration and whether or not one is evangelical significantly affects attitudes towards science.

Views regarding the use of animals for scientific research divided respondents into two groups. While 47% support it, 53% oppose it (Table 24). Those who say that science has made life easier are more supportive of the use of animals (49% versus 35%). Similarly, those who think science has had three positive effects are more supportive of animal use than those who say science has had no positive effects (54% versus 25%). Furthermore, the ethical choice of whether or not to use animals varies according to socio-demographic and religious criteria.

While age does not appear to be a discriminating factor, men are more favorable to the use of animals for research purposes than women (59% versus 37%), as are the most highly educated (58% versus 41%). Finally, atheists stand out in clearly approving more than all other groups the use of animals (58%).

As was the case for the level of scientific knowledge, representations of science are affected not only by the individual's socio-demographic but also by their religious identity.

Conclusion

This secondary analysis of previous American and European surveys has shown that, everything being equal, there exists strong correlations between knowledge and representation of science on one hand and religion identity and practices on the other. For although the level of education obviously affects that relation it does not, however, cancel out the specific influence of the religion that is declared and practiced. One limitation of our page 33

regression analyses is that it does include the level of economic revenue and thus cannot measure the specific effect of that variable on the score of scientific knowledge. However, given that revenue is strongly correlated with the level of education, we do not expect that this variable would, if added, cancel the effect of religion, as revenue is already implicitly present in the education variable. But that must remain a hypothesis that could be tested with new data sets.

The major conclusion is thus that the "no religion" and Protestants tend to score better on the standard tests of scientific knowledge than Catholics, Orthodox or Muslims and that the result depend not only on the religious identity of respondents but also on the intensity of their religious practices. This latter association suggests that the more a religion exercises a strong imprint on its adepts, the less scientifically literate they tend to be. Representations of science also vary according to socio-demographic and religious variables and the latter are still negatively correlated with having positive attitudes towards science. Thus, the least religious Europeans and Americans also have the most positive representations of science and its social impacts. Now, it is well known that correlation studies cannot identify causal links. However, it is also obvious that in the socialization process of individuals within families, religious education comes many years before scientific education. That temporal succession strongly suggests the most likely direction of the causal link. At the individual level, however, particular life experiences may later reverse the causality and scientific training may in turn feedback on religious conceptions and lead to abandoning some religious beliefs learned in a younger age that could then be seen as competing or in contradiction with the scientific knowledge acquired.

Most papers concluding that there is no necessary or even real conflict between science and religion are based on questions asking explicitly if there are or should be such conflicts. But the very asking of such questions may in fact bias the situation, given the tendency of most people to try to avoid conflict, and also the tendency to mix factual and normative questions.

In contrast to such approaches, our analysis does not suffer from these limitations at it finds the links between religion and knowledge and attitudes towards science indirectly through statistical analysis of independent variables. It should also be noted that, to our knowledge, no study based on large-scale, empirical data, such as those analyzed here, highlights the opposite relation, namely that, at the macro-sociological level, religious beliefs and practices are positively correlated with what can be called the scientific attitude, here measured through knowledge scores and representations of the effects of science in society. Finally, it bears repeating that the existence of such macro-social realities does not exclude the obvious fact that some scientists can in their conscience positively associates science and their personal religious beliefs and practices and even promotes a "dialogue" between science and religion [START_REF] Gingras | Science and religion. An impossible dialogue[END_REF].

page 5 -

 5 the Eurobarometer surveys conducted in 2005 and 2010 in European Union member countries. That is, the 25 countries in 2005 plus Romania and Bulgaria (members in 2007) and Croatia (member in 2013). The first, No. 63.1, dates from 2005 and covers Europeans, science and technology [14]. The second, No. 73.1, dates from 2010 and focuses on biotechnology [15]. The data include variables on religious adherence, levels of religious practice and belief in the existence of a God. This makes it possible to take account of different dimensions of the relationship to religion. The knowledge and representation of science are approached through different questions on basic scientific facts and scales of attitudes toward science; the survey conducted by the Pew Research Center in 2018 in the United States [16]. This data set tells us about religious affiliation, the intensity of religious practice, the frequency of prayer, and the importance of religion in daily life. Scientific knowledge is measured using a series of nine variables to construct a scientific knowledge score.

Figure 1

 1 Figure 1 Number of correct answers on the scientific knowledge scale (N=27909, in percent)

Table 1 Average score on the scientific knowledge scale according to declared religious affiliation Mean Number Overall sample 8,24 27384

 1

	No religion	9,56 4653
	Protestant	9,06 3958
	Other religions 8,82 1705
	Catholic	7,91 13076
	Orthodox	6,80 3694
	Muslim	6,00	298
	In addition to religious affiliation, survey data allow us to measure intensity of practice,
	which is a relevant indicator of religious integration. One might, for example, declare oneself
	Catholic and never go to Church. Such an individual is clearly different from a declared
	Catholic who attends Church weekly. As Table

Table 2 Average score on the scale of scientific knowledge according to the intensity of religious practice Mean Number Complete sample 8,25 27661 At

 2

	least once a week	7,18	5271
	About once a month	7,85	2458
	Two to three times a year	8,18	7165
	Less often	8,67	6016
	Never	8,91	6751

Table 3

 3 that joins religion and practices versus no religion, confirm the same trend.

	page 9

score on the scale of scientific knowledge according to religion and level of practice

		Mean	Number
	Complete sample	8,13	24301
	Religious, practicing	7,87	18261
	Religious, non-practicing	8,16	2652
	No religion	9,50	3388

Table 4 Average score on the scale of scientific knowledge according to religion and level of practice

 4

	Mean	Number

Table 5 Percentage of subjective beliefs in a God (Vertical percentages)

 5

	Percentage	Respondents

Table 6 Subjective beliefs in a God according to declared religion (N=25092, horizontal percentages)

 6

		I believe	I believe that there is a	I don't believe in God
		there is a	spiritual or living force	or a spiritual force
		God
	Complete sample	56	29	15
	Catholic	71	23	6
	Orthodox	74	23	3
	Protestant	48	42	10
	Muslim	74	20	6
	No religion	6	39	56
	Cramer's V = 0,43

Table 7

 7 Interestingly, the belief in a God or spiritual force also affects the level of knowledge of persons without religion. Hence, those without a religion who believe in God score significantly lower(8.38) than those who declare themselves to be non-believers (9.69).

shows that belief in a God or in a spiritual force, is correlated with level of scientific knowledge. For example, non-believing Protestants score highest among respondents who page 11 declare a religion.

Table 7 Average score on the scale of scientific knowledge according to the typology religion and belief

 7

	Mean	Number

Table 8 Average score for correct answers to knowledge questions based on different measures of the degree of identification with a religion

 8

	page 13

Table 9 Mean score for scientific knowledge by religion and level of religious integration

 9

	(N=2037)
	Complete sample	4,49
	Strong Catholic Integration	4,39
	Intermediate Catholic Integration	3,98
	Weak Catholic Integration	4,52
	Strong Protestant Integration	4,00
	Intermediate Protestant Integration	4,10
	Weak Protestant Integration	4,54
	No Integration Intermediate	3,78
	No Integration Weak	4,67
	Agnostic Intermediate Integration	6,04
	Agnostic Weak Integration	6,29
	Atheist Weak Intégration	7,16

Table 10 Average score for scientific knowledge according to religious practice and evangelical

 10

	affiliation (N=1490)
	Complete Sample	4,09
	Weekly Practice, Non-Evangelical	4,49
	Weekly Practice, Evangelical	3,96

Table 11 Average score for scientific knowledge according to prayer and evangelical affiliation

 11

	(N=1338)
	Complete sample	4,17
	Daily Prayer, Non-Evangelical	4,31
	Daily Prayer, Evangelical	3,76

Table 12 Mean score for scientific knowledge according to the importance given to religion and Evangelical affiliation (N=1483))

 12

	Complete Sample

Table 13 Average score of correct answers to the question on scientific knowledge by age of graduation

 13

	versus 7.81). This

Table 14 Mean Score by Religion and Age of Graduation

 14

	Religion	Level of Education	Mean	Number
	Catholic	16 years or less	6,48	4538
		17-19 years	8,32	4548
		20 years or more	9,34	2670
	Orthodox	16 years or less	4,96	1171
		17-19 years	6,95	1264
		20 years or more	8,40	887
	Protestant	16 years or less	7,89	1126
		17-19 years	8,73	889
		20 years or more	9,92	1609
	Muslim	16 years or less	3,69	119
		17-19 years	6,59	88
		20 years or more	8,15	47
	No religion 16 years or less	8,44	871
		17-19 years	9,22	1616
		20 years or more	10,38	1591

Table 15 Added value of the level of education on the level of knowledge according to religion

 15

		(N=23034)
	Muslim	4,46
	Orthodox	3,44
	Catholic	2,86
	Protestant	2,03
	No Religion	1,94
	We did a logistic regression on the Eurobarometer data taking the scientific knowledge score
	as a dependent variable and the age of graduation and the respondent's religion as
	independent variables. We chose to test a model where "the non-religious" with a "school-
	leaving age above 19 years" are the reference group. The choice of this group is explained
	by the fact that it is composed of individuals most likely to have a high score of scientific
	knowledge. It should be noted that choosing another benchmark does not change the results.

score. The decrease is negligible for Protestants and four times greater for Catholics. The maximum effect is observed for Muslims and Orthodox (Table

16

). In sum, the Eurobarometer surveys indicate that among the main religions, only Protestant membership does not significantly affect the score of scientific knowledge.

Table 16 Logistic regression analysis by religion and school-leaving age

 16

	Parameter	Pr > |t|
	values

Reference group: no religion, education 19 years or older

		9.74757	<.0001
	Catholic	-1.24116	<.0001
	Orthodox	-2.33504	<.0001
	Protestant	-0.31448	<.0001
	Muslim	-3.19462	<.0001
	Education 16 years or less	-2.46421	<.0001

Table 17 Logistic regression by religion, age, school leaving age, gender and religious practice

 17

	Parameter	Pr > |t|
	Values

model, is no longer determinant in this model, which includes more variables. Subject to the "competition" of other variables, the specificity of Protestantism fades away; this seem

Table 18 Mean score for scientific knowledge by education level controlled by religious belonging (N=2262)

 18

		Entire Sample	4,00
	Protestant or Catholic	Bachelor's degree or higher Post-Secondary Education	5,49 4,16
		High school or less	3,00
		Entire Sample	4,21
	No religion	Bachelor's degree or higher Post-Secondary Education	6,06 4,86
		High school or less	2,78
		Entire Sample	6,63
	Agnostic or Atheist	Bachelor's degree or higher Post-Secondary Education	7,23 6,60
		High school or less	5,58

Table 20 Bachelor's degree or higher / Secondary or less for the seven "religious" groups (N=2037)

 20

	Group 1 : Catholic or protestant, strong integration	1,84
	Group 2 : Catholic or protestant, intermediate integration	1,77
	Group 3 : Catholic or protestant, weak integration	2,44
	Group 4 : No religion, intermediate integration	2,12
	Group 5 : No religion, weak integration	2,26
	Group 6 : Agnostic or atheist, intermediate integration	1,57
	Group 7 : Agnostic or atheist, weak integration	1,25

Table 21 Persons or organizations best qualified to explain the impact of science and technology on society (Percentage of mentions)

 21 As shown in Table22, the religion to which one belongs has an effect on the individuals or

	Complete Sample	18
	University scientists	53
	Television journalists	34
	Scientists in the private sector	28
	Print journalists	27
	Physicians	23
	Environmental organizations	20
	Consumer groups	12
	Writers and intellectuals	10
	The government	6
	Industry	6
	Politicians	5
	Representatives of religious groups	2
	The army	2
	organizations considered most qualified to explain social impact of scientific or technological
	developments:
	-Among the less educated, Orthodox individuals value university scientists and physicians,
	while Protestants and no religion tend to rely on consumer groups;
	-Orthodox and no religion, at an intermediate level of education, value university scientists,
	while Protestants and Muslims value print journalists;
	-Perhaps the most surprising variations are those affecting respondents with the highest
	school-leaving age. The no religion groups clearly favor -as do Orthodox and Muslims -
	university scientists. It can also be deduced from this table that, for all religions, schooling

Table 22 Individuals or organizations most qualified the impact of science and technology on society by education and religion of respondents (Percentage)

 22

			Television	University	Print	Physician	Scientists in	Environmental	Consumer
			journalists	scientists	journalists	s	the private	organizations	groups
							sector
	16	Mean	40	39	26	24	22	15	11
	years	Catholic	40	38	26	23	22	16	9
	or less	Orthodox	42	47	21	28	22	12	5
		Protestant	40	32	27	26	19	15	17
		Muslim	38	23	21	13	7	8	7
		No religion	35	42	27	25	24	18	19
	17-19	Mean	35	55	27	24	30	20	11
	years	Catholic	36	55	26	23	30	21	11
		Orthodox	39	60	29	24	35	16	6
		Protestant	37	44	32	27	26	20	14
		Muslim	42	31	38	18	11	9	8
		No religion	27	61	25	23	30	21	14
	20	Mean	30	62	31	22	32	23	16
	years	Catholic	29	61	31	22	33	25	14
	or	Orthodox	30	71	26	27	43	21	6
	more	Protestant	34	53	33	23	26	20	21
		Muslim	34	72	26	21	36	15	11
		No religion	26	68	31	20	31	26	19

Table 23 Number of positive elements according to socio-demographic and religious criteria (Horizontal percentages)

 23

			Number of positive elements
		0	1	2	3
	Complete sample	6 %	12 %	24 %	59 %
	Sex
	Male	5	10	23	62
	Female	6	13	25	55
	Age
	18-29	5	14	33	48
	30-49	6	10	27	57
	50-64	7	13	19	61
	65 and over	4	9	17	70
	Diploma
	High school or less	9	12	23	56
	Post-secondary education	4	12	29	54
	Bacherlor's degree or more	2	10	21	67
	Religion
	Catholic	5	10	23	62
	Protestant	5	11	22	62
	No religion	9	16	27	48
	Agnostic	1	6	24	69
	Atheist	2	6	16	76
	Religious integration
	Weak	3	10	22	65
	Intermediate	7	12	24	57
	Strong	5	12	27	56
	Evangelist
	Yes	7	11	24	58
	No	4	11	20	66

Table 24 Favorable or unfavorable to the use of animals for research based on socio- demographic and religious variables (Horizontal percentages)

 24

		Favorable	Opposed
	Total	47	53
	Sex
	Male	59	41
	Female	37	63
	Age
	18-29	45	55
	30-49	51	49
	50-64	45	55
	65 and over	48	52
	Diploma
	Bachelor's degree or	58	42
	higher
	Postsecondary education	46	54
	High school or less	41	59
	Religion
	Catholic	49	51
	Protestant	50	50
	No religion	37	63
	Agnostic	47	53
	Atheist	68	32
	Religious integration
	Strong	51	49
	Intermediate	43	57
	Weak	54	46
	Evangelist
	Yes	52	48
	No	48	52

-Regardless of the group considered, within the group, those with the lowest level of education have also the lowest score of scientific knowledge (the amplitude of the ratio of Bachelor's degree or higher / Secondary or lower varies between 1.25 and 2.44).


Nassim Bouchoul

Elodie Fourré

Jean-Michel Tatibouët

Alysson Duarte

Nathalie Tanchoux

Catherine Batiot-Dupeyrat
email: catherine.batiot.dupeyrat@univ-poitiers.fr

Structural modifications of calcium based catalysts by non-thermal plasma in the CO2 reforming of CH4 and the influence of water

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Structural modifications of calcium based catalysts by non-thermal plasma in the CO2 reforming of CH4 and the influence of water

Introduction

Valorization of CO2 is a major subject of investigation since decades and is of upper importance nowadays, especially after the alarming reports issued from the COP24. The simultaneous conversion of carbon dioxide and methane is an important topic since it allows the valorization of those two greenhouse gases into syngas, a feedstock for methanol synthesis and for light hydrocarbons production via Fischer Tropsch reaction [1]. The conventional catalytic method for CH4 reforming is performed at elevated temperature since the reaction is highly endothermic (H°= 247 kJ.mol -1 ) [2]. The high energy consumption associated with the catalyst deactivation due to carbon deposition, make the process little attractive for industrial application [3].

The concomitant activation of methane and carbon dioxide under plasma discharge has been the subject of many publications, using several types of plasma (dielectric barrier discharges: DBD, microwave: MW and gliding arc: GA) and different experimental conditions (reactant flow, ratio CH4/CO2, dilution by rare gases etc.) [4][5][6]. However, the reported studies showed that the selectivity towards targeted products was often difficult to achieve due to the occurrence of a large number of reactions in the gaseous phase under plasma discharge [7].

Non-thermal plasma combined with a catalytic material has been widely investigated over the years for CO2/CH4 reaction [8,9]. From the published data and different effects reported, it appeared that non thermal plasma induces modification of the catalytic substrate, but very few deep analysis of the catalysts modification under plasma discharge has (ever) been made and further investigations are essential to fully understand this process. In fact, by coupling a catalyst with a plasma, the reactants conversion could be increased in some cases [10], but as indicated by J.C. Whitehead, the interaction between the plasma and the catalyst was difficult to understand [11]. Tu et al. [12] showed that the use of Ni/Al2O3 catalyst (exhibiting high efficiency in classical catalytic process) limited the reactant conversion when coupling with plasma due to the modification of the plasma discharge at the surface of conductive Ni species.

When nonthermal plasma was combined with La2O3 deposited over alumina balls, the CO2 conversion was significantly increased while CH4 conversion was not modified as soon as the reaction was performed at 400°C [13]. The selectivity to CO was improved in the presence of the catalyst and the formation of surface oxycarbonate species was identified. From these results, new studies on the use of oxides, in particular those prone to carbonation, are of particular importance. Not only the carbonation step could favor the activation of CO2 but also it could be a way to trap CO2 in flue gas.

Calcium oxide, CaO, is a well-known sorbent and was largely used for CO2 capture at high temperature [14]. Moreover, it was shown that the addition of steam in carbonation procedure increases significantly the performances for CO2 capture [15]. In this study, the influence of calcium based oxides for CH4 and CO2 transformation was investigated, with a strong focus on catalyst structural modifications under plasma discharge, in the presence (or not) of water.

Experimental part

The coaxial dielectric barrier discharges (DBD) reactor, represented in figure 1, is described in previous work [16]. The reaction was carried out at room temperature and atmospheric pressure.

A total flow rate of 40 mL.min -1 was set, consisting in 75 % helium and 25 % CH4/ CO2. The mixture of methane and carbon dioxide was fixed at a ratio CH4/CO2= 2, the reactants being diluted with helium in order to favor the reactivity under plasma discharge [17]. The calcium oxides (ACROS supplier) were sieved between 355 and 650µm and introduced into the reactor in order to completely fill the plasma zone. A catalyst Ca(OH)2+H2O (18wt%) was also prepared by adding liquid water to the powder Ca(OH)2. The residence times in the reactor were 1.8 s without catalyst and 1.6 s in the presence of a catalyst. The water phase was introduced into the feed at a rate of 0.1g.h -1 (which corresponds to about 5 vol %).

The calcination of CaO material at 800°C was achieved under a dry air flow at a rate of 10°C.min -1 , during 2 hours. The sample was cooled down to ambient with dry air. Before and after plasma treatment, the sample was in contact to ambient air and surface modification due to exposure to ambient air is taken into account in the results.

A function generator (TG1010A Aim-TTi, Thurlby Thandar Instruments Brand) was connected to an amplifier (Trek, 20/20) to generate a sinusoidal signal between the electrodes. The discharge power was set at 8W (constant frequency of 800 Hz and voltage of 13.5 kV) and was calculated from the Manley method, a well-known procedure based on the analysis of Lissajous graphs [START_REF] Manley | The Electric Characteristics of the Ozonator Discharge[END_REF]. Two high voltage probes (PMK, model PHV4-2757) connected to an oscilloscope (waveRunner 62 Xi, Lecroy) were used to measure the signals.

Characterizations of the oxides were performed before and after the plasma treatment. It consisted in BET analysis (Micromeritics Flowsorb II 2300 equipment at -196°C) for surface area calculations and thermogravimetric analysis (SDTQ600TA analyzer under a 100mL/min flow of air up to 1173K). The diffraction patterns (Siemens D-5005 X-Ray diffractometer with CuK=1.5417Å, operating at 40kV and 30mA) were recorded in the 2 range of 10-90° with a step interval of 0.02° and period of 1s.

Infrared spectra were collected for the solid samples before and after plasma treatment on a Perkin Elmer FT-IR (Spectrum One) operating in the range 4000-650 cm -1 . The spectra were normalized for comparison.

The reaction was carried out for one hour and gases were analyzed by on-line gas chromatography, detailed in [19]. A margin error of ±3% was evaluated from 3 successive experiments, in between which the electrode was cleaned and catalyst changed.

Yields, conversion and selectivities was calculated from:

𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 𝑋 (%) =

Results and discussion

2.1.CH4 and CO2 transformation on calcium oxide with and without water addition

In a first time, experiments were conducted using CaO, calcined at 800°C in order to remove as much as possible carbonate species. The introduction of water leads to a slight increase of methane conversion while CO2 conversion is not modified by the presence of water whatever the temperature: 100, 200 or 300°C (Fig. 2). The yield of CO is increased significantly in the presence of water and the carbon balance is also improved. The formation of hydrocarbons is favored under the experimental conditions used (excess of methane) and the presence of methyl radicals generated under plasma discharge leads to the production of ethane, ethylene and propane, ethane being the main product formed (approximately 90% of hydrocarbons quantity).

The carbon balance is always lower than 100% particularly at the highest temperature since the formation of ethylene (a precursor of coke) is favored at high temperature. Moreover the formation of heavy products, in an excess of methane is also probable [13]. It appears that the presence of water has no significant influence on hydrocarbons and global oxygenates yields (Fig. 3). The production of oxygenates is low whatever the reaction temperature, with and without water. However a small increase of methanol selectivity is observed in the presence of water (Table 2). The other oxygenates quantified were ethanol, acetaldehyde, acetone and formaldehyde. Bogaerts et al. [20] performed chemical kinetics calculations and showed that methanol selectivity can be increased by more than a factor 4 when 32% of water was added in the feed. The differences observed could result from the higher energy density used in our study: 12kJ/L against 3 kJ/L in ref [20]. At this energy density, methanol would readily be decomposed under the plasma discharge as soon as it is formed, by electron impact dissociation. Moreover the reaction of CO2 and water with the solid could also explain the lower methanol selectivity since part of CO2 and H2O is consumed through hydroxylation and carbonation of CaO (see TGA analysis below).

From the coefficient R (Fig. 3), corresponding to the ratio between the CO formed (COf) and the CO2 transformed (CO2t), it was possible to estimate if CO comes only from direct CO2 dissociation or from both methane partial oxidation and CO2 splitting. The results show that, at 100°C, the ratio is always higher than unity proving that CO is formed by the two reactions.

Moreover, the presence of water leads to a R value close to 2, which is higher than without water (Rmax=1.5) suggesting the formation of CO through methane water reforming (CH4 + H2O → CO+H2) which is corroborated by the increased methane conversion with water. The molar ratio H2/CO is far from unity which indicates that hydrogen from methane is mainly converted into H2O whatever the reaction temperature and even when water is introduced into the gas feeds.

2.2.TGA analysis of CaO

The thermogravimetric analysis performed after one hour of reaction under plasma at 100, 200 and 300°C are shown in Fig. 4. Two weight losses between 400-450°C and 600-760°C are attributed to the decomposition of Ca(OH)2 to CaO [21] and the decomposition of CaCO3 to CaO respectively. The coupling of TGA with mass analysis confirmed that the first weight loss corresponds to water elimination (m/z=18) and the second one to CO2 elimination (peak corresponding to m/z = 44). Note that before reaction, TGA analysis of CaO exhibited a weight loss at high temperature showing that the carbonation of CaO had proceeded by atmospheric CO2 after calcination under air at 800°C (Fig. 4a). The amount of CaCO3 in the starting material was estimated at 2.4wt%. After reaction without water, no significant differences were observed in the TGA profile suggesting that no structural modifications of the material had occurred. As soon as water was added in the gas feed, the weight loss of 6.2% at 400-450°C showed that Ca(OH)2 was formed under plasma discharge and the carbonation was not favored. At 200°C, the hydroxylation of CaO was very small in the presence of water in the feed while it proceeded readily without water. At this temperature, the carbonation of CaO is not favored, while at 300°C a weight loss of 7.5 wt% is obtained without water and corresponds to 8.7wt% with water. It is known that high temperature favors CO2 sorption [22], but it was also reported that water vapor has a positive effect for CaO carbonation in the temperature range of 250-400°C due the occurrence of a two-step route when H2O vapor is used: CaO →Ca(OH)2 → CaCO3.

Under non-thermal plasma it appears that the addition of water into the feed does not improve significantly the carbonation process at 300°C.

2.3.CH4 and CO2 transformation on calcium based oxides with and without water addition

In a second time, it was interesting to investigate the influence of different starting materials such as CaCO3 and Ca(OH)2 and evaluate the impact of surface carbonate on the efficiency and selectivity of the reaction. Experiments were performed at room temperature and at 100°C in presence of water in order to avoid its condensation at the surface of the solid. The experiments at 100°C without water showed no difference in terms of conversions or selectivity compared to room temperature ones. The results, gathered in Table 1, show that CO2 and CH4 conversions are similar whatever the starting material and CH4 conversion is slightly enhanced in presence of water, as observed on CaO. The different oxides have no or little effect on the syngas production, which is however favored in the presence of water. Higher yields of CO and H2 are obtained, while hydrocarbons (mainly ethane) yield decreased with water.

The yield of oxygenates products is relatively low independently of the material, methanol and formaldehyde are the two main oxygenated products formed (Table 2). Besides methanol and formaldehyde, ethanol, acetaldehyde and acetone were also quantified but low selectivities were obtained.

The selectivity to formaldehyde is higher using CaCO3, Ca(OH)2 and Ca(OH)2+H2O than in the presence of CaO. It was proposed by some authors that formaldehyde is formed under plasma from CO2 and CH2 radicals [23], which generation is favored in presence of carbonate on the material surface. As shown below (TGA analysis), Ca(OH)2 and Ca(OH)2+H2O are carbonated under plasma discharge, so the involvement of carbonate species from the surface of catalyst could be proposed in the reaction mechanism, however only to a small extent.

The addition of water into the feed increases significantly the selectivity to methanol regardless the nature of the material, consequently it seems that the reaction occurs mainly in gaseous phase, through water activation according to the following [24]:

CH4 + He* → CH3  + H + He H2O + e-→ OH  + H  CH3  + OH  →CH3OH
Additionally, the reaction was performed during 2 hours over the material Ca(OH)2+H2O at room temperature (Fig. 5). Carbon dioxide was completely converted during the first minutes of reaction due to carbonation (described below), the yield of CO was stabilized at around 13% after 20 minutes. The carbon balance did not reach 100% and the catalyst took a yellowish color after 2 hours on stream probably due to the presence of adsorbed organic products. Among the products analyzed by pyrolysis coupled with mass spectrometry, many compounds such as C3 aldehydes and C5 ketones were detected.

TGA analysis of CaCO3 and Ca(OH)2

The thermogravimetric analysis of CaO, CaCO3, Ca(OH)2 and hydrated Ca(OH)2 were performed before and after reaction under plasma without and with water (0.1g.h -1 ) (Fig. 6).

Four weight losses were identified in the temperature range: 50-100, 400-450, 600-660 and 660-760°C, attributed to the desorption of water, decomposition of Ca(OH)2 to CaO and from 600°C to the decomposition of CaCO3 to CaO respectively. The transformation of CaCO3 can be divided into two different steps, one from 600-660 corresponding to the desorption of weakly linked CO2 (surface and upper layers) and the second one between 660-760°C corresponding to carbonate in strong interaction with calcium: bulk CaCO3. Note that TGA analysis before reaction, showed that the presence of carbonate species was also visible for CaO, Ca(OH)2 and hydrated Ca(OH)2 due to ambient air contamination. After reaction under plasma, the TGA profile of CaO material is not strongly modified (ambient air contamination) compared to before reaction while as soon as water is introduced with the reactants, the formation of Ca(OH)2 is clearly visible. The hydroxylation of CaO occurs under plasma as soon as water is introduced in the stream, while the carbonation of CaO is not favored. Starting from calcium carbonate, no significant differences are observed in terms of temperature range and weight loss whatever the experimental conditions used. A weight loss of about 42 wt% is obtained (Table 3), a value closed to the theoretical one associated with the CaCO3 decomposition into CaO and CO2: 44 wt%. After reaction under plasma, Ca(OH)2 is modified, the material is partially carbonated and dehydroxylated according to the TGA profile and the values reported in Table 3. The formation of more stable carbonate species occurred under plasma as shown by the removal of carbonate species in the 660-760°C temperature range. The presence of stable CaCO3 is clearly visible when water is introduced in the feed gas, while the amount of Ca(OH)2 is strongly decreased. This result shows that the addition of water in gaseous state favors the carbonation of Ca(OH)2 under the plasma discharge. The better performance of Ca(OH)2 compared to CaO as sorbent for CO2 capture was evidenced under classical carbonation experimental conditions (temperature around 900K) [25,26]. Moreover, the carbonation of CaO was over doubled when steam was introduced, which was attributed to the formation of transient Ca(OH)2 [27,28]. Under non-thermal plasma a different behavior is observable: the introduction of steam do not favor significantly the carbonation of CaO but the formation of Ca(OH)2 is obtained. Starting from Ca(OH)2, the poor carbonation is confirmed under plasma, while the addition of steam to the feed strongly enhanced the carbonation of Ca(OH)2. The addition of water into the solid Ca(OH)2 (18% in wt) improves the carbonation of the material under plasma, while the addition of steam during the reaction favors the formation of Ca(OH)2 instead of CaCO3. It is suggested that the amount of water is too high to allow the carbonation of the Ca(OH)2 phase when performing the reaction under water steam. Indeed the carbonation proceeds rapidly as evidenced in Fig. 5, with water in gas phase CO2 absorption into water is believed to be favored limiting the carbonation of Ca(OH)2. Note that after reaction under plasma, all the physisorbed water was removed most probably due to the increase of temperature into the plasma zone estimated at around 110°C (joule effect).

In order to visualize better the modification of the materials under plasma discharge, the results are gathered as bargraphs corresponding to the amount of the respective phases obtained from TGA analysis (Fig. 7). It clearly shows that carbonation is favored starting from Ca(OH)2, in the presence of water in gaseous phase, proving the beneficial role of hydroxyl group for CO2 absorption under plasma. To better understand the carbonation step under plasma discharge, experiments were performed using Ca(OH)2, H2O under plasma and a flow of CO2, analyzing the exhaust gases.

2.5.Transformation of Ca(OH)2 +H2O under CO2/plasma

The structural modification of Ca(OH)2 +H2O was investigated by analyzing the exit gas using a mass spectrometer, m/z= 18 and m/z=44 corresponding to water and CO2, respectively. A flow of carbon dioxide diluted in helium was introduced at room temperature, without plasma, H2O was released during the first ten minutes on stream while carbon dioxide was retained by the solid (Fig. 8). After ten minutes, CO2 absorption was stopped and the signal corresponding to m/z=44 remained stable. The slow increase of the water signal seemed to indicate that dehydration proceeded slowly from 10 to 60 minutes.

Carbonation of Ca(OH)2,H2O proceeds at room temperature under the flow of CO2 in helium due to the presence of water, which favors CO2 ionization to form CO3 2-, according to [29] :

CO2 + H2O →2H + + CO3 2-
Carbonation proceeds through the following equations:

Ca(OH)2 → Ca 2+ + 2OH - Ca 2+ + CO3 2-→ CaCO3
From equations above, a complete carbonation is possible as soon as water is introduced at least as stoichiometric amount relative to Ca. The carbonation of Ca(OH)2,H2O was confirmed by TGA analysis, exhibiting a weight loss in the temperature range 600-750°C. The carbonation is limited, a weight loss of 17.6% related to CO2 elimination being measured (Table in Fig. 9).

Under plasma a different behavior was observed (Fig. 8b). Plasma was switched on after 15 minutes, corresponding to a stable CO2 signal. As soon as plasma was switched on, the concentration of CO2 decreased and an oscillation period occurred from 15 to 35 minutes. The decrease of CO2 signal indicates that carbonation is favored under plasma discharge. Another experiment was performed at lower deposited power (P=4W) and the solid was characterized by TGA analysis after each reaction. According to the weight loss measured (Table in Fig. 9) it is possible to give the molar composition of the material after reaction, it can be summarized It appears clearly that under plasma discharge carbonation of the starting material is improved particularly at low deposited power since 90% of Ca is present as CaCO3 after reaction. It is believed that at low deposited power, the increase of temperature is limited in the catalyst bed and consequently the water added to Ca(OH)2 favors the carbonation. Meanwhile, at higher deposited power, the temperature measured at the exit of the reactor is close to 90°C suggesting that it can reach higher values in the catalyst bed, which leads to water evaporation.

Moreover, it is interesting to observe that the signals of CO2 and H2O evolved in opposite phase during that period: CO2 decrease corresponding to H2O increase. Fig. 8b can be decomposed into three parts: 1) During the first 15 minutes: CO2 sorption proceeds without water elimination, 2) between 15 and 35 minutes: CO2 sorption is accompanied by H2O release, according to a periodic behavior 3) no significant evolution.

The reactions involved during the different stages could be:

1) Ca(OH)2,H2O + CO2 → CaHCO3.OH, H2O
2) Ca(OH)2,H2O + CO2 → CaHCO3.OH + H2O and CaHCO3.OH → CaCO3 + H2O

The water elimination could be due to thermal effect under plasma discharge. The periodic variation of CO2 consumption associated to water release could be explained by diffusion limitations of CO2 into the bulk, by analogy with thermal carbonation of CaO under steam/CO2.

Indeed it was proposed that CaCO3 generated at the surface of the material blocked the contact between the solid and CO2 in gas phase [30]. It appears that the activation of CO2 under plasma discharge favors the carbonation of Ca(OH)2,H2O, it could be suggested that the active oxygen species generated in gas phase through CO2 decomposition could be involved in the carbonation reaction, its diffusion through the CaCO3 layer would facilitate the reaction with Ca 2+ leading to carbonation.

3) No more water is available to favor the carbonation Note that the decomposition of CaCO3 in Ar plasma due to thermal effect has been evidenced by Giammaria et al. [31] at low deposited power, however, the experiments were performed at 630°C while in the present study it was at room temperature.

2.6.Infrared analysis

The infrared spectrum of the different calcium based materials are gathered in Fig. 10. As expected, CaO before reaction exhibited small peaks related to a carbonate contamination. In the low region, CO3 2-out-of-plane-bending-mode ν2 at 870 cm -1 and in-plane bending mode ν4 at 710 cm -1 and in the mid-region, ν3 asymmetric C-O stretch at 1410 cm -1 were identified [32,33]. A similar spectrum was obtained after reaction under plasma without water, corroborating the TGA since no phase transformation had occurred. After plasma reaction in the presence of humidity, a sharp absorption peak is visible at 3630 cm -1 related to the stretching mode of Ca(OH)2 hydroxyl group, supported also the results of TGA analysis. The splitting of the band at 1410 cm -1 generated a band at 1480 cm -1 which was identified as amorphous calcium carbonate [34]. The band at 1080 cm -1 was related to the ν1 symmetric C-O stretch of carbonate and a blurry zone between 2000-2300 cm -1 to the gaseous CO2 [35]. Increasing the temperature inside the plasma reactor led to a loss of the 1480 and 1080 cm -1 vibration bands of carbonate (at 200°C and 300°C) and of the band at 3630 cm -1 related to hydroxyde (at 300°C), indicating a loss of calcium hydroxide, which is in agreement with TGA analysis.

Regarding Ca(OH)2, the plasma treatment led to a decrease of the bands related to carbonate contamination (1430, 870, 710 cm -1 ) and this effect was reversed in presence of humidity where carbonates formation was enhanced. These results are in agreement with TGA analysis where 26.8 wt% are lost under humid conditions against 5.2 wt% under dry conditions. The addition of water on the surface of Ca(OH)2 prior to its treatment under plasma discharge showed evident bands related to water at 3370 cm -1 and 1640 cm -1 corresponding to O-H stretching and O-H bending vibrations, respectively. After plasma treatment, with or without humidity in the gas flow, the water bands completely disappeared leaving only bands related to calcium oxide (3640 cm -1 ) and carbonate (1430, 1080, 870, 710 cm -1 ). Those results were also completely linked with TGA ones, where water weight loss was only visible on the untreated sample.

An additional band at 1800 cm -1 completed the characterization of carbonates on the CaCO3 spectrum, corresponding to the ν1 and ν4 symmetric stretching modes of carbonate, which was also detected on Ca(OH)2 + H2O.

Conclusion

Different calcium based materials, with calibrated grain size, were tested for the transformation of methane and carbon dioxide in a DBD plasma at room temperature, with a constant deposited power fixed at 8 W. This low deposited power excludes the activation of reactants due to thermal effect. It is observed that the conversion of methane and carbon dioxide is not significantly modified whatever the nature of the calcium based material used.

  Nassim Bouchoul, Elodie Fourré, Jean-Michel Tatibouet, Alysson Duarte, Nathalie Tanchoux, Catherine Batiot-Dupeyrat To cite this version: Nassim Bouchoul, Elodie Fourré, Jean-Michel Tatibouet, Alysson Duarte, Nathalie Tanchoux, et al.. Structural modifications of calcium based catalysts by non-thermal plasma in the CO2 reforming of CH4 and the influence of water. Journal of CO2 Utilization, 2020, 10.1016/j.jcou.2019.09.006. hal-02351943

Figure 1 Figure 2 :Figure 3 :Figure 4 :

 1234 Figure 1: Reactor scheme

Figure 5 :Figure 6 :Figure 7 :Figure 8 :- 15 Figure 9 :Figure 10 :Figure 11 :

 56781591011 Figure 5: Transformation of CH4 and CO2 at room temperature over Ca(OH)2+H2O (18 wt% of water), grain size: 355-650µm, P=8W, total flow: 40mL/min, He: 75%. CH4/CO2 =2

Table 1 :

 1 Influence of the nature of calcium based material on product yield (average value,

	The yield of

Table 2 :

 2 Influence of the nature of calcium based material on selectivity to oxygenates (average

	value, reaction time: 30 minutes), grain size: 355-650µm, P=8W, total flow: 40mL/min, He:
	75%, ratio CH4/CO2 =2. Reaction temperature: without water: room temperature, in the
	presence of water: T=100°C

Acknowledgements

The authors grateful acknowledge the ANR for the financial support of the PRC program VALCO2PLAS and the financial support from the European Union (ERDF) and "Région Nouvelle Aquitaine"

for HCOH formation could be suggested but only to a small extent. Over CaO, an increase of the reaction temperature from 100°C to 300°C favors slightly the conversion of methane and the hydrocarbon yield. At 100°C, the addition of water into the feed leads to an increase of methane conversion as CO and oxygenates yields due to the involvement of the water reforming reaction and the formation of OH species by H2O activation under plasma.

The respective contribution of pure plasma reaction and surface catalyst reaction induced by plasma is very difficult to establish. However, it is believed that carbonate species formed at the surface of the catalyst can be involved in the formation of formaldehyde but only to a small extent.

The most significant results obtained within the present study is the deep catalyst modification under plasma: the hydroxylation of CaO proceeded as soon as water was added in the gas flow, while the carbonation was favored over Ca(OH)2. An oscillating phenomena was highlighted under CO2 plasma discharge over Ca(OH)2,H2O resulting in carbonation through simultaneous CO2 capture and H2O release. Moreover an almost complete carbonation of Ca(OH)2,H2O was evidenced after one hour exposure to a mixture He/CO2, under a low energetic plasma: P=4W, exhibiting, for the first time, the potentiality for CO2 capture under plasma.

Material