Effect of the support on the catalytic stability of Rh formulations for the water-gas shift reaction

The stability of Rh(0.6)/La2O3 and Rh(0.6)/La2O3(27)·SiO2 catalysts used in the water–gas shift reaction (WGSR) was studied. In order to understand the different behavior of the two formulations, XRD, Raman spectroscopy and operando-DRIFTS were employed. It was demonstrated that Rh/La2O3·SiO2 showed a constant activity after 50 h on stream and that it was made up of La2Si2O7 with very low crystallinity and SiO2. On the other hand, Rh/La2O3 after use evolved to a mixture of oxycarbonates and lanthanum hydroxide evidenced by XRD and confirmed by Raman spectroscopy. This solid suffered a significant deactivation which was assigned to the formation of very small amounts of formate and carbonate residues. These residues disappeared after being burnt in air at 673 K and the initial catalytic activity was restored. The results obtained were useful to explain the reasons for the different stability of the two formulations and could have implications for the design of active catalysts used in the WGSR and in the processes in which it is involved

CO2 hydrogenation with shape-controlled Pd nanoparticles embedded in mesoporous silica: Elucidating stability and selectivity issues

International audienceShape-controlled Pd nanocubes and nanopolyedra particles wereembedded inmesoporous silica shells and their catalytic properties for the CO2 hydrogenation were compared to a reference Pd/SiO2 catalyst prepared by wetness impregnation.Whereas the Pd impregnated silica exhibits a strong deactivation, the activity of both embedded solids is remarkably stable. This difference is due to a significant Pd particles sintering in the referencecatalyst while no increase of particle size is observed for the core@shell solids. CH4 selectivity is shown to be correlated to the mean coordination number of surface atoms which controls the adsorption strength of CO as intermediate species