High-Performance Pd-Pt/α-MnO2 Catalysts for the Oxidation of Toluene

Abstract

Herein, α-MnO2-supported Pt-Pd bimetal (xPd-yPt/α-MnO2; x and y are the weight loadings (wt%) of Pd and Pt, respectively; x = 0, 0.23, 0.47, 0.93, and 0.92 wt%; and y = 0.91, 0.21, 0.46, 0.89, and 0 wt%) catalysts were prepared using the polyvinyl alcohol-protected NaBH4 reduction method. The physicochemical properties of the catalysts were determined by means of various techniques and their catalytic activities for toluene oxidation were evaluated. It was found that among the xPd-yPt/α-MnO2 samples, 0.93Pd-0.89Pt/α-MnO2 showed the best catalytic performance, with the toluene oxidation rate at 156 °C (rcat) and space velocity = 60,000 mL/(g h) being 6.34 × 10−4 mol/(g s), much higher than that of 0.91Pt/α-MnO2 (1.31 × 10−4 mol/(g s)) and that of 0.92Pd/α-MnO2 (6.13 × 10−5 mol/(g s)) at the same temperature. The supported Pd-Pt bimetallic catalysts possessed higher Mn3+/Mn4+ and Oads/Olatt molar ratios, which favored the enhancement in catalytic activity of the supported Pd-Pt bimetallic catalysts. Furthermore, the 0.47Pd-0.46Pt/α-MnO2 sample showed better resistance to sulfur dioxide poisoning. The partial deactivation of 0.47Pd-0.46Pt/α-MnO2 was attributed to the formation of sulfate species on the sample surface, which covered the active site of the sample, thus decreasing its toluene oxidation activity. In addition, the in situ DRIFTS results demonstrated that benzaldehyde and benzoate were the intermediate products of toluene oxidation.