Effect of the support on the catalytic stability of Rh formulations for the water–gas shift reaction Original Research Article

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.