Effect of washcoat modification with metal oxides on the activity of a monolithic Pd-based catalyst for methane combustion

The deposition of Ni, Co, Ce or Fe oxides onto the washcoat surface in the 0.5%Pd/Al2O3 catalyst enhances conversion of CH4. Catalytic activity of the I'd-catalysts containing cobalt oxide depends on the incorporated amount of cobalt oxide and the method of incorporation. The highest activities were those of the 0.5%Pd/0.3%Co/Al2O3 and 1%Pd/0.3%Co/Al2O3 catalysts (cobalt oxide deposited onto the surface of Al2O3) and the 0.5%Pd/5%CO3O4-Al2O3 catalyst (mixed washcoat). Total SSA, Pd dispersion and Pd crystallite size in the x%Pd/y%Co/Al2O3 Catalysts depend on the incorporated amount of PdO and cobalt oxide. Pd dispersion in the 1%Pd/Al2O3 catalyst increases from 4% to 20% upon deposition of 14 wt.% Co3O4 (by mass Al2O3) onto the Al2O3 surface (1%Pd/0.3%Co/Al2O3). This increase in Pd dispersion influence the increase in the activity of the 1%Pd/Al2O3 catalyst. On the surface of the 0.5%Pd/5%CO3O4Al2O3 catalyst Pd occurs mainly in the form of PdO and displays considerable mobility underconditions of temperature variations-cyclically undergoing reduction and oxidation. At 500 degrees C, in vacuo, the reduction was irreversible and parallelled by the agglomeration of metallic Pd crystallites. At room temperature, cobalt occurred on the catalyst surface in the form of Co+2 ions (CoAl2O4) and was reduced to Coo at 500 degrees C (in vacuo). Up to 500 degrees C, the reduction of Co was reversible. (C) 2008 Elsevier B.V. All rights reserved.