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 foun d to have an activity in the decomposition of N2O comparable to that o f Cu-ZSM-5, but a higher stability at high N2O concentrations. Zirconi a promotes the activity of supported copper species and plays a cataly tic role itself, but the tetragonal crystalline form of zirconia is mo re effective in the promotion than the monoclinic form. Characterizati on of the samples by ESR, IR (CO chemisorption) and oxygen thermodesor ption suggests that during dehydroxylation of zirconia at temperatures in the 400-500 degrees C range Cu-1 species form which are stable aga inst consecutive reoxidation, when the zirconia surface is not rehydro xylated. It is suggested that the good behavior of Cu-ZrO2 catalysts i n 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 com petition with N2O for chemisorption on copper ions.