Pd-based monolithic catalysts on metal supports for catalytic combustion of methane

Monolithic Pd-based catalysts on heat-resisting foil supports, with different washcoats, were investigated for catalytic activity in the combustion of methane. Palladium was deposited either onto pure aluminium oxide (Pd/Al2O3) or onto Al2O3 modified with 9 wt.% of SiO2 and 0.8 wt.% of La2O3 (Pd/Al2O3-SiO2) or with ZrSiO4 (Pd/Al2O3-ZrSiO4). The modification of the Al2O3 washcoats was found to increase the conversion of methane and to enhance the thermal resistance of the catalysts. XPS, XRD and TEM examinations have shown that PdO well dispersed on the washcoat surfaces is the active form of palladium in the Pd/Al2O3, Pd/Al2O3-SiO2 and Pd/Al2O3-ZrSiO4 catalysts. XPS examinations of the same catalysts after 20-h run have revealed an over twofold increase in surface Pd concentration measured in terms of the Pd/Al ratio, which substantiates an activation of the catalysts. Heating to 1060 °C deactivated all the catalysts due to the agglomeration of crystallites on their surfaces and decomposition of PdO to metallic Pd. The incorporation of additives into the pure Al2O3 washcoat noticeably reduced crystallite growth at high temperatures. As a result, the deactivation of the Pd/Al2O3-ZrSiO4 and Pd/Al2O3-SiO2 catalysts was much lower than that of the Pd/Al2O3 catalyst.