A study on the reactivity of Ce-based Claus catalysts and the mechanism of its catalysis for removal of H_2S contained in coal gas

摘要

In this study, Claus reaction was applied for the selective removal of H_2S contained in the gasified coal gas, and the characteristics of Claus reaction over the Ce-based catalysts were investigated to propose the reaction mechanism. The Ce-based catalysts showed a high activity on Claus reaction. Specially, Ce_(0.8)Zr_(0.2)O_2 catalyst had a higher activity than CeO. On the basis of our experimental results, it was proposed that the selective oxidation of H_2S was carried out by the lattice oxygen in the Ce-based catalysts and that the reduction of SO_2 was performed by the lattice oxygen vacancy in the reduced catalyst. Since the mobility of the lattice oxygen in Ce_(0.8)Zr_(0.2)O_2 composite catalyst was better than the one in CeO_2, Ce_(0.8)Zr_(0.2)O_2 provided more lattice oxygen for the selective oxidation of H_2S. It was presumed that the reaction mechanism to convert H_2S and SO_2 into elemental sulphur over our prepared catalysts was different from the mechanism over the solid-acid catalysts. It is believed that Claus reaction over the Ce-based catalysts was carried out by the redox mechanism. Since the moisture was contained in the major components, CO and H, of the gasified fuel gas, the effects of CO and H_2O on the catalytic reaction were investigated over a Ce-based catalyst. The conversion of H_2S and SO_2 was decreased in Claus reaction over the Ce-based catalysts as the concentration of either H_2O or CO in the gasified coal gas was increased. Under the circumstances of the coexistence of both moisture and CO, however, the conversion was increased as the concentration of CO was increased. The reactivity of Claus reaction was varied in terms of the concentration ratio of CO to H_2O. The maximum conversion of H_2S and SO_2 was achieved in the condition of that the concentration of CO contained in the reacting gas was higher than the one of H_2O. The conversions of H_2S and SO_2 did not match to the stoichiometric ratios of Claus reaction. The higher conversion of H_2S was obtained in the higher concentration of H_2O, while the higher conversion of SO_2 was achieved in the higher concentration of CO. It was another evidence to indicate that the Claus reaction over the Ce-based catalysts was carried out by the redox mechanism.