Deactivation and regeneration of Pt/γ-alumina and Pt/ceria–alumina catalysts for methane combustion in the presence of H<sub>2sub>S
摘要
Ceria has been widely explored as an additive in alumina-supported precious metal catalysts due to a number of unique properties. The success of ceria and ceria-based materials is mainly attributed to the unique combination of an elevated oxygen transport capacity coupled with the ability to shift easily between reduced and oxidised sates. In this study the influence of CeO<sub>2sub> addition to a Pt/Al<sub>2sub>O<sub>3sub> catalyst for low temperature (<540°C) methane oxidation in an oxidising environment has been investigated. The resistance to H<sub>2sub>S-poisoning and influence on catalyst regeneration by oxidation or reductive treatments has been studied. The addition of CeO<sub>2sub> to the support creates an increase in the level of activity based primarily on the oxygen storage capacity offered by the cerium oxide, causing an increase in oxygen activation. The ceria–alumina-supported catalyst showed a greater shift to poorer activity upon exposure to H<sub>2sub>S. It appears sulphur compounds react with the oxygen storage component causing a decrease in oxygen transfer, removing any benefit offered by the ceria. However, the level of Pt-agglomeration and support changes were reduced with the incorporation of ceria, emphasising the stabilising effect and promotion of metal particle dispersion associated with ceria. In order to obtain the maximum benefit of ceria addition to the support structure in terms of activity a reductive pretreatment is required. Upon exposure to a reducing atmosphere, it appears a Pt–CeO<sub>2sub> interaction generates greater levels of activity.