ZIRCONIA-SUPPORTED COPPER-CATALYSTS FOR NO-CO REACTIONS - SURFACE COPPER SPECIES ON ZIRCONIA

Cu/ZrO2 catalysts show high activity for the NO-CO reaction, even at l ow temperature (100-200 degrees C). The structure and reduction behavi our of ZrO2-supported Cu species have been characterized by means of X -ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), FTIR and temperature-programmed reduction (TP R). It was found that highly dispersed Cu2+ species in an octahedral s ymmetry dominated at a Cu content lower than 1 wt% and that the amount of the Cu2+ species was saturated at 1 wt.% Cu. On the other hand, Cu oxide clusters were exclusively formed upon additional Cu incorporati on after 1 wt.%. The highly dispersed Cu2+ species were produced by re action with the terminal OH groups of the ZrO2 surface. The highly dis persed Cu2+ species were reduced by CO at a much lower temperature tha n Cu oxide clusters and produced highly dispersed Cu+ species at 100 d egrees C, which subsequently formed Cu-0 species at 170-180 degrees C. It is concluded that the high catalytic activity of Cu/ZrO2 for NO-CO reactions at low temperature is brought about by the formation of hig hly active Cu-0 species on low-temperature reduction of the Cu2+ speci es interacting with the ZrO2 surface, and that the activity of the Cu- 0 species is lost by agglomeration into Cu metal particles.