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Literatura académica sobre el tema "Catalyseur à atomes isolés"
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Artículos de revistas sobre el tema "Catalyseur à atomes isolés"
Meyer, Olivier, Stéphane Chevalier, Raphaël Weil, André Loupy, François Maurel y Arlette Fourrier-Lamer. "Chimie de synthèse : paramètres diélectriques de systèmes isolés et de mélanges réactionnels. II : saponification d'un ester en présence d'un catalyseur de transfert de phase". Annales de Chimie Science des Matériaux 29, n.º 4 (31 de julio de 2004): 89–103. http://dx.doi.org/10.3166/acsm.29.4.89-103.
Texto completoTesis sobre el tema "Catalyseur à atomes isolés"
Rivera, Cárcamo Camila. "Atomes isolés supportés sur des matériaux carbonés pour la catalyse de réactions d'hydrogénation". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30174.
Texto completoThis research work focuses on the preparation of carbon-based single atom (SA) catalysts and their applicability on hydrogenation reactions. Chapter 1 correspond to a comprehensive review over experimental and computational studies aiming at: i) preparing SAC on carbon materials, ii) understanding the metal-support interactions in SAC, and iii) studying how this relates to catalytic performances. In Chapter 2 we were able to understand the possibility of producing different Ru@fullerene nanostructures that can be nanometrically modulated by varying the conditions during their synthesis, solvent and Ru/C60 ratio, through well-defined nanoparticles (NP) to very small clusters and even single atoms (SA) with a high metallic loading (~ 6-20wt%). We applied these nanostructures as catalysts in the hydrogenation of nitrobenzene, finding that Ru SA is less efficient than Ru NP, performance that was also studied by DFT calculations. Chapter 3, details a new and straightforward protocol for the creation of vacancies over carbonaceous supports. We propose that is possible to create defects/vacancies over the supports by a controlled subsequent two-steps process, which comprises the subsequent creation and composition of surface oxygen groups. Magnetic characterization reflexed the presence of this reactive species with a paramagnetic behavior raising form possible radicals species on the surface. Afterwards, we showed that was possible to use such defects as anchoring point to successfully stabilize single metallic atoms (Ru, Pd, Pt, Ni, Cu, Co, Ir) with a loading up to ~ 1.6wt%. Also, by improving this method, we arrived to be capable to control the ratio SA/NP for a given metallic loading ranging from 10 to 200. Chapter 4, through a combined experimental-theoretical study, we provide an explanation of the influence of structural characteristics of Pd/C catalysts for alkene hydrogenation. Highly dispersed Pd nanoparticles (PdNP) are necessary to activate dihydrogen. A high concentration of surface defects on the carbon support is necessary to stabilize Pd single atoms (PdSA), which coexist with PdNP on Pd/C catalysts. A high concentration of oxygenated surface groups is also necessary on the carbon support to allow hydrogen spillover. We demonstrate that such combination allows a cooperative catalysis to operate between PdNP and PdSA that involve the formation of PdSA-H species, which are much more active than PdNP-H for alkene hydrogenation but also isomerization. Indeed, for myrcene hydrogenation activity variations of several orders of magnitude were measured as a function of the value of this ratio SA/NP. We show that the control of this ratio allows the development of a new generation of highly active catalysts integrating the ultra-rational use of precious metals in short supply. Finally, Chapter 5, focuses on the catalytic performance of SA catalysts in carbon dioxide hydrogenation. The results show highest activity for Pt as well as 99% selectivity to CO. On the other hand, Ru catalysts had highest selectivity to CH4
Yan, Yilong. "Catalytic hydrogenation properties of MXenes promoted by single metal atoms". Electronic Thesis or Diss., Lyon 1, 2024. http://www.theses.fr/2024LYO10190.
Texto completoTwo-dimensional materials attract considerable interest due to their distinctive properties. MXenes, derived from MAX phases through the selective etching of the A element (e.g. Al, Ga or Si), exhibit a wide range of chemistries and potential catalytic applications. These materials possess the chemical formula Mn+1XnTx, where M represents an early transition metal, X is either C or N, and Tx denotes surface terminations (e.g. -O, -OH, -F). Single-atom catalysts (SACs), which comprise isolated metal atoms on supports such as metal oxides or carbon, offer high atomic efficiency and possess distinctive electronic properties with respect to nanoparticulate counterparts. Nevertheless, ensuring their stability remains a significant challenge. MXenes present a renewed opportunity to anchor metal atoms and enhance catalytic performance. In this research work, we investigated the potential of MXenes, specifically Ti3C2Tx and Mo2Ti2C3Tx, as full-fledged catalysts or catalyst supports for the stabilization of single metal atoms employed in hydrogenation reactions. A particular focus was put on MXene delamination and unstacking via solid intercalation for effective application in gas-phase catalysis. Numerous characterization techniques were employed, including XPS, XRD, STEM, and SEM.The investigation started with an evaluation of the stability of Pt and Pd single atoms on Ti3C2Tx MXene, employing the conventional wet impregnation method with chloride salts as the precursors. First, the impact of the MXene preparation methodology (HF versus LiF-HCl etchants) on the surface structure/composition and metal dispersion/oxidation state is investigated. Second, the catalytic hydrogenation performances of these materials are presented. While the bare MXene is inactive, Pt/Ti3C2Tx SACs, obtained for low metal content, exhibit an exceptional selectivity towards 2-butene, with no butane formation, in the hydrogenation of butadiene, herein considered as a model reaction. Furthermore, in the reduction of CO2 to CO through reverse water-gas shift at high pressure, which is relevant to clean-energy applications, these catalysts demonstrate up to 99% selectivity and enhanced Pt-molar activity in comparison to oxide-supported references. To further enhance performance, we employed the Mo2Ti2C3Tx MXene, which possesses inherent hydrogenation properties, with the objective of exploiting the synergy between Pt atoms and surface carbidic Mo atoms. The use of the Pt(NH3)4(NO3)2 precursor enabled the achievement of a higher loading of atomically dispersed Pt (up to 2.3 wt%). The Pt/Mo2Ti2C3Tx SACs demonstrate remarkable catalytic activity for CO2 hydrogenation, even higher than the MXene alone, producing CO and smaller amounts of methane and methanol. Following impregnation, single Pt atoms bear a +2 charge like in the precursor, but undergo partial reduction upon exposure to H2 flow at 400 °C, thereby replacing surface Mo atoms or filling surface Mo vacancies – as supported by EXAFS. The addition of platinum increases the activity of the MXene mostly by facilitating H2 dissociation, as suggested by DFT modeling, but has little effect on the SAC selectivity. To investigate the thermal stability of the catalysts and their evolution under reaction conditions, advanced characterization techniques, including in situ XRD, TG-DTA-MS, operando XAS, NAP-XPS, and isotopic temperature-programmed experiments were employed. The Mo2Ti2C3Tx MXene exhibits high thermal stability up to ca. 600 °C under argon or hydrogen flow. At 400 °C under hydrogen, part of MoIV ions undergo reduction to MoII owing to surface defunctionalization. At 600 °C, a carbon-deficient stoichiometry of Mo2Ti1.9C2.6O0.3 is obtained. The formation of stable structures with anchoring of Pt single atoms, mostly in the Mo-rich surface layers, occur at temperatures approaching 200 °C. This leads to a high thermal stability of the SACs under reaction conditions
Ferré, Géraldine. "Étude des propriétés dynamiques du catalyseur Pt/CeO2". Thesis, Lyon, 2019. https://n2t.net/ark:/47881/m6qj7gnq.
Texto completoEuropean regulation against cars’ pollution is more and more tough. Car’s constructors have to develop new solutions to limit the impact on the population. One possible improvement for the actual depollution systems is to start the catalysis at low temperature to reduce the pollution from cold start. The major objective of this thesis’ research has been to understand the evolution of the catalyst Pt/CeO2 during several REDOX cycles in order to improve the oxidation performances of CO, C3H6 and NO at low temperature. To simulate NOXTRAP conditions, gas pulses of rich and lean atmosphere have improved catalytic performances for CO oxidation. In situ characterization aren’t compatible with these kind of activation. Therefore, REDOX sequences have been established with 1 h under reductive atmosphere and 1 h under oxidative atmosphere. Three kind of configurations for the Pt atoms have been observed by MET after theses kind of sequences in function of the temperature: 3D Nps, raft and single atoms. By using various characterization technics: Raman, TPS, CO chemisorption, XANES, XPS, the results demonstrate that the most effective site come from the probable cluster Pt8O14. In this configuration the platinum is in Pt2+ electronic stat with Pt-O-Pt bonds. On this kind of particles, Mars-Van Krevlen mechanism isn’t applicable for CO oxidation. For NO and propene bigger particles are needed for improve performances. The dynamics of formation and dispersion of the particles led to the build of optimum dispersity for the reactions of oxidation and the use of REDOX of activation leads successfully to the formation of active Pt/CeO2 catalyst
Kara, Abdelkader. "Contribution à l'étude expérimentale et théorique de la diffusion élastique d'atomes neutres par des surfaces périodiques et des surfaces avec des défauts isolés". Lille 1, 1985. http://www.theses.fr/1985LIL10031.
Texto completoBerro, Youssef. "Élaboration de formulations catalytiques optimisées pour la valorisation de la biomasse par une approche combinée Théorie/Expérience". Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0137.
Texto completoLignin pyrolysis produces oxygenated bio-oils with poor fuel efficiency. Hence, they are upgraded through hydrodeoxygenation (HDO) leading to the production of oxygen-free molecules and water as by-product. Our objective is to elaborate new catalysts for HDO by combining Density Functional Theory (DFT) calculations with experimental studies. HDO includes two deoxygenation routes: hydrogenation of aromatic ring before C-O cleavage (HYD) or direct C-O cleavage - Direct DeOxygenation (DDO). Fe@silica catalysts show a good activity and selectivity toward aromatics. Thus, our work focused on designing such catalysts that promote DDO in order to increase aromatics production under lower H2 pressure. The adsorption energies of phenol and inhibitors (CO and water) over silica surfaces, having various silanol densities and types, were computed by DFT. Three interaction modes were investigated: “perpendicular O-int”, “flat π-int”, and “flat O-int”. For amorphous silica, the highest adsorption energies were found for the “flat O-int” mode, and a specific interaction of 120 kJ/mol (with a C-Si bond and phenol deformation) was observed for surfaces with a silanol density between 2 and 3.3 OH/nm2. CO competitive adsorption is negligible for all silica surfaces, which make them more attractive than conventional sulfide catalysts. Hence, these results motivated the synthesis of silica-supported catalysts with a silanol density between 2 and 4 OH/nm2. Single iron atom catalysts (SACs) supported on silica were elaborated using non-ionic/metallic surfactants. Iron distribution within mixed P123/CTAF micelles, used as templates, allows the fine dispersion of those atoms within silica mesopores. The lack of iron clusters was confirmed by synchrotrons PDF, STEM mapping, magnetic and NMR measurements. DFT+U calculations confirmed that those atoms are predominately present as high spin Fe(III). This method increases the number of active sites, which improves the catalytic performance. However, the results of catalytic tests were unsatisfactory due to the difficulty of Fe(III) reduction. Metallic (Fe & Cu) and bimetallic (Fe-Cu) catalysts, synthesized by simple impregnation or through the co-precipitation method with thermal decomposition of urea, were tested for guaiacol HDO conversion. Results proved that bimetallic Fe-Cu have a better performance (90% conversion, 70% selectivity) than Fe-based catalysts since Cu incorporation facilitates the reduction of Fe(III)