Effect of palladium surface structure on direct NO decomposition over supported palladium catalysts

摘要

The effect of metal surface structure on the catalytic activity of palladium for direct NO decomposition was investigated by using both single-crystal model catalysts and conventional Pd/Al_2O_3 catalysts. Adsorption, dissociation and desorption measurements of NO on Pd (111), (100) and (311) single crystal surfaces showed that only NO species adsorbed on the two-fold bridge site of the (100) step on the Pd (311) surface can be dissociated, suggesting the participation of the step sites in NO decomposition. The turnover frequency (TOF) on Pd/Al_2O_3 was significantly dependent on palladium precursor used for catalyst preparation, namely Pd (N) /Al_2O_3 prepared from palladium nitrate showed the highest TOF. From the measurement of FT-IR spectra of adsorbed NO, a good correlation was found between the proportion of the step sites on the palladium surface and the TOF for NO decomposition on Pd/Al_2O_3. Taking into account the results obtained for single-crystal model catalysts, it was concluded that the step sites act as the catalytically actives sites for direct NO decomposition on Pd/Al_2O_3.