Catalytic behavior and nature of active sites in copper-on-zirconia catalysts for the decomposition of N2O

Copper-on-zirconia catalysts prepared by a sol-gel technique were found to have an activity in the decomposition of N2O comparable to that of Cu-ZSM-5, but a higher stability at high N2O concentrations. Zirconia promotes the activity of supported copper species and plays a catalytic role itself, but the tetragonal crystalline form of zirconia is more effective in the promotion than the monoclinic form. Characterization of the samples by ESR, IR (CO chemisorption) and oxygen thermodesorption suggests that during dehydroxylation of zirconia at temperatures in the 400-500 degrees C range Cu-1 species form which are stable against consecutive reoxidation, when the zirconia surface is not rehydroxylated. It is suggested that the good behavior of Cu-ZrO2 catalysts in N2O decomposition derives from the stabilization of Cu-1 species by the support. Water in the feed inhibits the surface reactivity due to the modification of the redox properties of copper ions as well as competition with N2O for chemisorption on copper ions.