Silver as a Promoter for the Catalytic Decomposition of NO_x under Oxygenexcess Condition: Evidence for Oxygen Spillover from Noble Metals to Silver

摘要

Metallic silver as an effective additive in noble metal based catalysts enahnces the migration of the tightly bound oxygen on noble metal atoms, as evidenced by TDS and photoemisison electron microscopy (PEEM) observations. The atual spillover of oxygen and the unique thermal redox properties of silver results in a significant lowering of the temperature for the removal of the surface oxygen, which keeps the noble metal sites available for the adsorption of reactants, particularly in the presence of excess oxygen, and leads to an increase of the activity. For the catalytic decomposition of NO over the Al_2O_3-supported 1 percent Pd catalyst, the presence of 0.1 percent Ag as a promoter resulted in about 18 percent increase of the conversion of NO to N_2 at 873K.