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The synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol was studied over a ceria- zirconia mixed metal oxide. When using oxygen-18 labeled ceria-zirconia, no oxygen-18 labeled DMC or water was observed. On the other hand, using oxygen-18 labeled methanol led almost exclusively to the formation of double labeled DMC, CH 3 18 O (C 16 O) 18 OCH 3. These results were used to further elaborate the proposed reaction mechanisms for DMC synthesis. The rate-controlling step identified was that of a nucleophilic attack of gas phase methanol on surface monomethyl carbonate species to form DMC. [Display omitted] • Dimethyl carbonate synthesis over oxides does not follow a Mars-Van Krevelen route. • The rate controlling step is a nucleophilic attack of methanol/methoxy species. • Zirconia promotion of ceria weakens the methyl carbonate species metal‑oxygen bond. [ABSTRACT FROM AUTHOR]

• Flame Sprayed Pyrolysis (FSP) cerium-zirconium oxides show high catalytic activities. • Coprecipitated (CP) and FSP mixed oxides exhibits different surface properties. • FSP enables a surface enrichment in cerium oxide at the top layer. • Cerium enrichment gives higher concentration of adsorbed methanol at the surface. The direct synthesis of Dimethyl carbonate (DMC) from methanol and CO 2 is a green process which allows CO 2 valorization. Among efficient catalysts, ceria, zirconia and cerium-zirconium mixed oxides are often reported as the most active catalysts. In a recent report, we discovered that cerium-zirconium mixed oxides prepared by Flame Spray Pyrolysis (FSP) show greater catalytic activities than those prepared by precipitation, although both exhibit very similar surface area and bulk features. The objective of this study was to find out the origins of the superior catalytic activities obtained by flame spray pyrolysis synthesis method by a deeper analysis of bulk and surface properties. We have opted to focus on mixed ceria-zirconia of equimolar composition (Ce 0.5 Zr 0.5 O 2) as it exhibits maximum catalytic activity for both synthesis methods. Combining bulk and surface characterization as well as surface adsorption measurements using probe molecules, we propose that flame spray pyrolysis enables a surface enrichment in cerium oxide still in interaction with zirconium oxide that leads to a high concentration of adsorbed methanol at the surface, which might explain the greater activity of the catalysts prepared using this method. Beyond the application of DMC synthesis, we can anticipate that Flame Spray Pyrolysis synthesis should generate relative high surface area mixed oxides with different catalytic performances with respect to mixed oxides prepared at lower temperature owing their metastable nature. [ABSTRACT FROM AUTHOR]

Abstract: Ceria-based catalysts have been assessed for internal methane reforming at low temperature (400–600°C) in Solid Oxide Fuel Cell (SOFC). A combinatorial library of 15 metal (Cu, Pt, Ni) supported ceria was prepared using wet impregnation method. The ceria-based oxides are undoped or doped with metal transition (Zr) or by rare earth (Gd or Pr). The effect of the metal, the dopant and the surface area on the catalytic performances was investigated in high-throughput manner using a 16-parallel reactor. The catalysts were assessed in two different conditions, (i) in CH4 rich condition and (ii) in model reformate condition. Catalytic performances are very metal depending. In dry conditions, Cu-based catalysts do not produce H2 whereas Ni-catalysts are very active despite low carbon balance. However, when water and CO2 are added in the feed, the nature of the ceria plays an important role in the catalytic performances. At low temperature (T <550°C), most of Ni/ceria catalysts are not active under reformate conditions at low temperature while Pt catalysts appear more robust with respect to the conditions. From unsteady state parallel studies, we suggest that surface hydroxyl on ceria are the active species. [ABSTRACT FROM AUTHOR]

An accelerated investigation of various ceria-supported platinum catalysts by means of parallel synthesis and testing reactors is reported. The aim is to discover new catalysts for purifying hydrogen for fuel cells and other applications by studying three reactions: selective CO oxidation in the absence and in the presence of hydrogen (SelOx), water–gas shift (WGS), and reverse water–gas shift (RWGS). A set of catalysts is prepared by impregnating platinum on various doped ceria supports. These catalysts display, despite their nearly identical X-ray crystal structures, diverse redox/acidic/basic properties and different selectivities in the three test reactions. The best SelOx catalysts are also the most active for WGS/RWGS equilibration. In contrast to the conventional two-stage approach of discovery screening followed by lead optimization, we demonstrate that it is possible to extract valuable mechanistic information directly from the discovery stage. Specifically, we elucidate the elementary steps coupling the SelOx and WGS processes and gain insight as to the combined effects of hydrogen presence and cation doping on the CO oxidation reaction. [Copyright &y& Elsevier]