The effect of preparation and steaming on the catalytic properties of Cu- and Co-ZSM-5 in lean NOX reduction

Overexchange of H-ZSM-5 zeolite (Si/Al=80) with copper and cobalt was easily performed at 50 and 80 degrees C. With copper acetate solution it was related to the formation of a precipitate identified as copper hydroxyacetate, Cu-2(OH)(3)(OAc). H2O. Under the same conditions the overexchange with cobalt acetate solution did not cause the formation of any precipitate. The initial catalytic activity in lean NOx reduction of Cu-ZSM-5 catalysts was not influenced by the formation of copper hydroxyacetate, but for both Cu-ZSM-5 preparations a change of the nature of copper species was evidenced after temperature programmed reaction test at spark ignition engine exhaust. Similar modifications were found for Co-ZSM-5 samples after catalytic test at the exhaust of a methane fuelled engine. The very demanding conditions of experiments with engine exhaust gas resulted in lower performances of both Cu- and Co-ZSM-5 catalysts in comparison to those reported for less severe conditions.