Support effect on oxidation resistance of precious metal catalysts as examined by N2O decomposition

The support effect on both steps of oxidation and reduction of precious metal catalysts was investigated by using pulse reaction of N2O decomposition below 573 K over Pt and Pd catalysts supported on a series of oxides. Oxygen uptake was calculated from the amount of N-2 formed and from white line intensity of Pt L-III-edge XANES after the pulse reaction. Although the oxygen uptake ratio to the surface metal atoms scarcely varied with the dispersion of precious metal, it varied with the support materials. At low temperature (<= 373 K), the oxygen uptake decreased as the acid strength of support materials enhanced, indicating that the acidic support materials depress the oxidation step of precious metal. On the other hand, at higher temperature (>= 473 K), the oxygen uptake calculated from N-2 formed was larger on acidic support than those on the supports with moderate acid strength. However, the oxygen uptake calculated from white line intensity clearly decreased as the acid strength of support materials enhanced. This contradiction was interpreted by the desorption of oxygen, i.e., the reduction of metal oxide, during the period between the pulses. Thus, it was concluded that the acidic support affected the oxidation state of precious metal through not only the depression of oxidation step but also the promotion of the reduction step. (C) 2007 Elsevier B.V. All rights reserved.