Analysis of Pt/SnO x; during catalysis of CO oxidation

Abstract

Temperature-programmed reduction using 6 kPa H 2 suggests that a sample consisting of 3% Pt supported directly on SnO 2 is, under the conditions of catalysis of CO oxidation used here, best represented as 3% Pt/SnO x since the support is likely, to be partially reduced, probably in the vicinity of the metal/oxide interface. This metal-support interaction is induced at remarkably low temperatures and suppresses hydrogen adsorption at 196 ±1 K. Catalytic measurements at 421-424 K show that this 3% Pt/SnO x is significantly more active per unit area of Pt than 6% Pt/SiO 2 in catalysing the oxidation of CO. In situ micro-FTIR reveals that while the latter has predominantly linearly bound CO on the surface under reaction conditions, the Pt/SnO x also has a species absorbing at 2168 cm −1 which may be CO on Pt in a positive oxidation state or weakly chemisorbed CO on zero-valent Pt. This may be directly involved in the low temperature oxidation of CO on the Pt/SnO x since, being weakly held, the activation energy for its surface diffusion to the metal/oxide interface will be low. Such mobile species could allow high rates of surface transport and an increase in the fraction of the surface over which the CO oxidation occurs. FTIR also reveals carbonate-type species on the Pt/SnO x surface.