8 research outputs found
Polypropylene cracking on embryonic and ZSM-5 catalysts : an operando study
Get PDFInternational audienceA series of ZSM-5 zeolites (embryonic, microporous, hierarchical) is studied in the catalytic cracking of polypropylene in the framework of its chemical recycling. Two important zeolite features impact their catalytic performances and allow their design as efficient catalysts: porosity and acidity. They also play a key role in catalyst deactivation and regeneration. A detailed thermogravimetric and spectroscopic (operando FT-IR) analysis of the reaction, including catalyst coking and regeneration, shows the emergence of rules to design fit-for-purpose catalysts to be used in existing or grass-roots FCC units
Prebiotic synthesis of Ribonucleotides on mineral surfaces
No full textDans le contexte prébiotique du " monde ARN ", les ribonucléotides sont considérés comme étant les premières espèces à avoir émergé sur Terre. En milieu aqueux, leur formation est défavorable thermodynamiquement. Les voies de synthèse de nucléotides décrites en phase homogène impliquent l'utilisation des molécules activées. En 1951, Bernal a introduit une autre voie de synthèse impliquant des surfaces minérales. Cependant, dans cette voie, les effets thermodynamique et/ou catalytique des surfaces minérales restent inexplorés. Dans le cadre de l'hypothèse de Bernal, notre travail présente pour la première fois une étude in-situ de la réactivité thermique des " briques élémentaires " des nucléotides adsorbés sur des surfaces minérales avec comme objectif de réaliser la synthèse des nucléotides sans activation chimique. Ce travail a montré dans un premier temps que les surfaces minérales sont capables de déclencher la formation de polyphosphates inorganiques à partir de monophosphates à des températures modérées. D'autre part, l'adsorption du ribose sur la surface de la silice a permis d'améliorer sa stabilisation thermique : alors qu'il est instable dès 90°C en milieux aqueux, il devient stable jusqu'à 200°C après adsorption sur la silice. Dans un deuxième temps, nous avons mis en évidence la formation de PRPP, un intermédiaire réactionnel très important, par co-adsorption du ribose avec du phosphate inorganique sur la surface de la silice. Enfin, on a pu montrer la glycosylation de l'adénine et la formation après co-adsorption de ses composants sur les deux surfaces minérales utilisées. Une étude préliminaire suggère même la possibilité de dimérisation des nucléotides.In the « RNA world» prebiotic scenario, ribonucleotide polymers are considered as the first biochemical species to have emerged. However, in aqueous solution, their formation through conventional mechanisms of condensation is thermodynamically forbidden. Several synthesis pathways of nucleotides have been described in aqueous solution; most often, they involve chemically activated molecules. Another pathway to nucleotides implies mineral surfaces, which have been considered in prebiotic processes at least since the work of Bernal in 1951. However, these studies have hardly tried to understand surface-molecule interactions and consequently, thermodynamic and/or catalytic effects of mineral surfaces are not well rationalized. In the context of Bernal's hypothesis, we present for the first time an in-situ study of the thermal reactivity of nucleotides “building blocks” adsorbed on mineral surfaces (amorphous silica, saponite) emphasizing the synthesis of nucleotides without chemical activation. In our work, we first show that mineral surfaces are able to trigger the formation of inorganic polyphosphates from monophosphates at moderate temperatures. On the other hand, adsorption of ribose on silica surface improves its thermal stabilization. While ribose decomposes at 90°C in aqueous solutions, it is stable up to 200°C on silica (in the presence of ZnCl2). Secondly, we have demonstrated the formation of PRPP, as important reaction intermediate, by co-adsorption of ribose and inorganic phosphate on the silica surface. Finally, we showed the glycosylation of adenine to adenosine and the formation of AMP (i.e. simultaneous glycosylation and phosphorylation) after co-adsorption of their components on both mineral surfaces employed. A preliminary study even suggests that nucleotide dimerisation can occur in the same conditions
Synthèse prébiotique de Ribonucléotides sur des surfaces minérales
Get PDFIn the « RNA world» prebiotic scenario, ribonucleotide polymers are considered as the first biochemical species to have emerged. However, in aqueous solution, their formation through conventional mechanisms of condensation is thermodynamically forbidden. Several synthesis pathways of nucleotides have been described in aqueous solution; most often, they involve chemically activated molecules. Another pathway to nucleotides implies mineral surfaces, which have been considered in prebiotic processes at least since the work of Bernal in 1951. However, these studies have hardly tried to understand surface-molecule interactions and consequently, thermodynamic and/or catalytic effects of mineral surfaces are not well rationalized. In the context of Bernal's hypothesis, we present for the first time an in-situ study of the thermal reactivity of nucleotides “building blocks” adsorbed on mineral surfaces (amorphous silica, saponite) emphasizing the synthesis of nucleotides without chemical activation. In our work, we first show that mineral surfaces are able to trigger the formation of inorganic polyphosphates from monophosphates at moderate temperatures. On the other hand, adsorption of ribose on silica surface improves its thermal stabilization. While ribose decomposes at 90°C in aqueous solutions, it is stable up to 200°C on silica (in the presence of ZnCl2). Secondly, we have demonstrated the formation of PRPP, as important reaction intermediate, by co-adsorption of ribose and inorganic phosphate on the silica surface. Finally, we showed the glycosylation of adenine to adenosine and the formation of AMP (i.e. simultaneous glycosylation and phosphorylation) after co-adsorption of their components on both mineral surfaces employed. A preliminary study even suggests that nucleotide dimerisation can occur in the same conditions.Dans le contexte prébiotique du " monde ARN ", les ribonucléotides sont considérés comme étant les premières espèces à avoir émergé sur Terre. En milieu aqueux, leur formation est défavorable thermodynamiquement. Les voies de synthèse de nucléotides décrites en phase homogène impliquent l'utilisation des molécules activées. En 1951, Bernal a introduit une autre voie de synthèse impliquant des surfaces minérales. Cependant, dans cette voie, les effets thermodynamique et/ou catalytique des surfaces minérales restent inexplorés. Dans le cadre de l'hypothèse de Bernal, notre travail présente pour la première fois une étude in-situ de la réactivité thermique des " briques élémentaires " des nucléotides adsorbés sur des surfaces minérales avec comme objectif de réaliser la synthèse des nucléotides sans activation chimique. Ce travail a montré dans un premier temps que les surfaces minérales sont capables de déclencher la formation de polyphosphates inorganiques à partir de monophosphates à des températures modérées. D'autre part, l'adsorption du ribose sur la surface de la silice a permis d'améliorer sa stabilisation thermique : alors qu'il est instable dès 90°C en milieux aqueux, il devient stable jusqu'à 200°C après adsorption sur la silice. Dans un deuxième temps, nous avons mis en évidence la formation de PRPP, un intermédiaire réactionnel très important, par co-adsorption du ribose avec du phosphate inorganique sur la surface de la silice. Enfin, on a pu montrer la glycosylation de l'adénine et la formation après co-adsorption de ses composants sur les deux surfaces minérales utilisées. Une étude préliminaire suggère même la possibilité de dimérisation des nucléotides
Thermal Behavior of d -Ribose Adsorbed on Silica: Effect of Inorganic Salt Coadsorption and Significance for Prebiotic Chemistry
No full textInternational audienceUnderstanding ribose reactivity is a crucial step in the “RNA world” scenario because this molecule is a component of all extant nucleotides that make up RNA. In solution, ribose is unstable and susceptible to thermal destruction. We examined how ribose behaves upon thermal activation when adsorbed on silica, either alone or with the coadsorption of inorganic salts (MgCl2, CaCl2, SrCl2, CuCl2, FeCl2, FeCl3, ZnCl2). A combination of 13C NMR, in situ IR, and TGA analyses revealed a variety of phenomena. When adsorbed alone, ribose remains stable up to 150 °C, at which point ring opening is observed, together with minor oxidation to a lactone. All the metal salts studied showed specific interactions with ribose after dehydration, resulting in the formation of polydentate metal ion complexes. Anomeric equilibria were affected, generally favoring ribofuranoses. Zn2+ stabilized ribose up to higher temperatures than bare silica (180 to 200 °C). Most other cations had an adverse effect on ribose stability, with ring opening already upon drying at 70 °C. In addition, alkaline earth cations catalyzed the dehydration of ribose to furfural and, to variable degrees, its further decarbonylation to furan. Transition-metal ions with open d-shells took part in redox reactions with ribose, either as reagents or as catalysts. These results allow the likelihood of prebiotic chemistry scenarios to be evaluated, and may also be of interest for the valorization of biomass-derived carbohydrates by heterogeneous catalysi
Synthesis of Embryonic Zeolites with Controlled Physicochemical Properties
No full textInternational audienceColloidal zeolite precursors, with a sharp particle size distribution (ca. 3-5 nm) and identical chemical composition, the so-called embryonic zeolites (EZs), are prepared by a strict control of aluminosilicate precursors polymerization in zeoliteyielding systems. The organic structure directing agent (OSDA) acts as a sacrificial template and is eliminated by high temperature combustion after the synthesis. Physicochemical properties of the EZs, such as pore size and volume and specific surface area are determined by the size of the OSDA and the synthesis conditions employed; i.e. the larger the OSDA, the higher the microporous volume and the specific surface area of the derived EZs. The EZs belong to the family of extra-large microporous (1-2.5 nm) materials. Upon calcination EZs retain their structure/porosity, and most of their aluminum remains in tetrahedral coordination to provide BrØnsted acidity. Pyridine adsorption shows a lower acidic strength for embryonic zeolites with respect to their crystalline counterparts (zeolites). An appropriate combination of extra-large micropores (1-2.5 nm) and Brønsted acid sites (~25µmol.g-1) leads to improved catalytic performances in the dealkylation of TiPBz, a proxy for bulky molecules reacting only on the external surface of crystalline zeolites. By varying the size of the OSDA for synthesizing the EZ, materials with controlled porosity, acidity, accessibility, and catalytic activity are prepared and their properties extend those of existing crystalline zeolites
Synthesis of Embryonic Zeolites with Controlled Physicochemical Properties
No full textInternational audienceColloidal zeolite precursors, with a sharp particle size distribution (ca. 3-5 nm) and identical chemical composition, the so-called embryonic zeolites (EZs), are prepared by a strict control of aluminosilicate precursors polymerization in zeoliteyielding systems. The organic structure directing agent (OSDA) acts as a sacrificial template and is eliminated by high temperature combustion after the synthesis. Physicochemical properties of the EZs, such as pore size and volume and specific surface area are determined by the size of the OSDA and the synthesis conditions employed; i.e. the larger the OSDA, the higher the microporous volume and the specific surface area of the derived EZs. The EZs belong to the family of extra-large microporous (1-2.5 nm) materials. Upon calcination EZs retain their structure/porosity, and most of their aluminum remains in tetrahedral coordination to provide BrØnsted acidity. Pyridine adsorption shows a lower acidic strength for embryonic zeolites with respect to their crystalline counterparts (zeolites). An appropriate combination of extra-large micropores (1-2.5 nm) and Brønsted acid sites (~25µmol.g-1) leads to improved catalytic performances in the dealkylation of TiPBz, a proxy for bulky molecules reacting only on the external surface of crystalline zeolites. By varying the size of the OSDA for synthesizing the EZ, materials with controlled porosity, acidity, accessibility, and catalytic activity are prepared and their properties extend those of existing crystalline zeolites
