Enhancement and sulfur poisoning mechanism of Ce doped ZrO2 catalyst in COS hydrolysis at low-temperature

Abstract

In order to achieve efficient and longer-lifespan removal of carbonyl sulfide (COS), a high-performance catalyst for hydrolysis is needed urgently. In this study, Ce doped ZrO2 oxides are used to remove COS with or without H2O. The results showed that the doping of Ce significantly improves the removal of COS by ZrO2 and obtains a sulfur capacity of 155.4 mgS/g at 70 °C, but there is still accompanied by sulfur poisoning. The characterization reveals that CeO2 has a cubic phase, ZrO2 has a mixed phase of tetragonal and monoclinic, and Ce-doped Zr with different ratio of Ce/Zr forms a Ce-Zr solid solution. Ce and Ce-Zr oxides have Ce3+/Ce4+ pairs, adsorbed oxygen species and surface oxygen vacancies, while ZrO2 has adsorbed oxygen and surface oxygen vacancies, the presence of which can promote the dissociation of H2O and surface adsorption of COS. ZrO2 has abundant medium-strong basicity while CeO2 has abundant weak and strong basicity, and different proportions of Ce/Zr adjust the surface basic strength, basic amount and surface redox property of Ce-Zr solid solution, which changes the adsorption and hydrolysis of COS and H2O and related oxidation reactions on Ce and Zr, thereby changing the sulfur poisoning. Ce has abundant –OH groups, which can rapidly adsorb COS, leading to hydrolysis and direct oxidation of COS in the absence of H2O, while the OH groups on ZrO2 promote the hydrolysis of COS to H2S. Although suitable Ce-doped ZrO2 improves the removal efficiency of COS, it still inevitably leads to the sulfur poisoning, but the presence of Zr could change the sulfation degree of CeO2 and the Claus reaction.