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

Abstract

The stability of Rh(0.6)/La 2O 3 and Rh(0.6)/La 2O 3(27)·SiO 2 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/La 2O 3·SiO 2 showed a constant activity after 50 h on stream and that it was made up of La 2Si 2O 7 with very low crystallinity and SiO 2. On the other hand, Rh/La 2O 3 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.