Deactivation and regeneration of Pt/γ-alumina and Pt/ceria-alumina catalysts for methane combustion in the presence of H2S

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 CeO2 addition to a Pt/Al2O3 catalyst for low temperature (<540 degreesC) methane oxidation in an oxidising environment has been investigated. The resistance to H2S-poisoning and influence on catalyst regeneration by oxidation or reductive treatments has been studied. The addition Of CeO2 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 H2S. 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-agglorneration 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-CeO2 interaction generates greater levels of activity. (C) 2003 Elsevier B.V. All rights reserved.