Catalytic wet air oxidation of succinic acid over Ru and Pt catalysts supported on CexZr1-xO2 mixed oxides
Résumé
Different CexZr1 - xO2 mixed oxides, prepared by co-precipitation and Ce(x)Zri(1 - x)O(2)-supported platinum and ruthenium catalysts, synthesised by impregnation, were investigated in the catalytic wet air oxidation (CWAO) of succinic acid at 190 degrees C under 50 bar total pressure. The catalytic activity of these solids, was demonstrated to be strongly influenced by the Ce content in the CexZr1 - O-x(2) support. The higher the Ce content in the mixed oxide support, the higher the succinic acid removal rate. The ruthenium catalysts exhibited the best performances in terms of succinic conversion at a given time of reaction; but, when the activity was expressed per mole of metal, the platinum catalysts were observed to perform better (435 mol(acid) h(-1) mol(pt)(-1)). Upon recycling reactions, the Ce0.9Zr0.1O2 support and the 0.5 wt% Ru/Ce0.9Zr0.1O2 catalyst maintained some good performances even though the conversion of succinic acid gradually decreased. It was demonstrated that the leaching of the metallic phase, the formation of carbonaceous deposits on the catalyst surface and the decrease of the specific surface area did not play a major role in the deactivation, which was more likely related to modifications of the chemical state of the active phase. Finally, the reaction was shown to be +0.1 order with respect to succinic acid and +0.4 order with respect to oxygen, indicating some major changes in the reaction kinetics and mechanism of the reaction over such catalysts containing ceria. (C) 2014 Elsevier B.V. All rights reserved.