Experimental and theoretical study about sulfur deactivation of Ni/ CeO2 and Rh/CeO2 catalysts

Abstract

Sulfur deactivation of Ni/CeO2 and Rh/CeO2 catalysts were examined through an experimental and theoretical study. These catalysts were characterized by N2 adsorption, X-ray diffraction, temperature programmed reaction, thermogravimetric analysis, Uv-visible spectroscopy and Raman spectroscopy, and tested under the methane dry reforming reaction in the presence of H2S. On the other hand, different possible interactions of sulfur with Rh, Ni or surface sites of the CeO2 support were evaluated by performing energy calculations with the density functional theory (DFT). Overall, the results indicate that tolerance to sulfur of Rh/CeO2 catalyst is higher than that of Ni/CeO2 one. In this sense, TPR measurements show that reduction of CeO2 is promoted by the presence of Rh. This effect, probably caused by hydrogen spillover to CeO2 support during the reduction of RhOx species, could be linked to a high oxygen donation capacity of Rh/CeO2 catalysts. Accordingly, the O2- species existing on Rh/CeO2 catalysts, revealed by Raman spectra of these samples, could favor sulfur oxidation and prevent Rh-S interactions. Likewise, the theoretical calculations show that desorption of S-O species from Rh/CeO2 system is more favorable than that from Ni/CeO2 one. Therefore, our experimental and theoretical study about sulfur deactivation of Ni and Rh supported on CeO2 allow us to postulate that Rh can help to desorb SOx species formed on the support, retarding sulfur poisoning of the Rh/CeO2 catalysts.