Catalytic Activity of Supported Platinum and Metal Oxide Catalysts for Toluene Oxidation

Abstract

Oxidation of toluene has been investigated over supported platinum as well as over a variety metal oxide (M x O y ) catalysts dispersed on high surface area γ-Al2O3. Catalysts were characterized with respect to their specific surface area (BET), metal dispersion (selective chemisorption of CO), phase composition and M x O y crystallite size (XRD) and reducibility (H2-TPR). Catalytic performance for the title reaction was investigated in the temperature range of 100–500 °C, using a feed composition consisting of 0.1% toluene in air. For Pt/M x O y catalysts, it has been found that catalytic performance depends on the nature of the support, with Pt/CeO2 being the most active catalyst at low temperatures. The intrinsic reaction rate per surface platinum atom does not depend on Pt loading (0.5–5 wt%), at least for Pt/Al2O3. Reducible metal oxides, such as ceria, are active for the title reaction and catalytic performance is improved significantly with increase of specific surface area (SSA). However, the intrinsic reaction rate per unit surface area is invariant with SSA. Dispersion of M x O y on high surface area inert supports, such as Al2O3, results in materials with relatively high catalytic activity, which seems to correlate well with the reducibility of metal oxides. Catalytic performance of M x O y /Al2O3 catalysts can be optimized by proper selection of M x O y loading. Best performing catalysts of this series include 60% MnO, 90% CeO2 and 5% CuO on Al2O3 which, under the present experimental conditions, are able to completely convert toluene toward CO2 at temperatures lower than 350 °C. Dispersion of Pt on M x O y /Al2O3 catalysts improves significantly the catalytic performance of irreducible M x O y but does not alter appreciably the activity of reducible M x O y /Al2O3 catalysts.