Efficient catalytic oxidation of VOCs by a Pd-Pt/SiO2 catalyst: The cooperative catalysis of dual metal sites

Volatile organic compounds (VOCs) are one of the main pollutants produced in industrial processes. Catalytic oxidation is an effective method to eliminate VOCs, and the key lies in designing efficient metal catalyst. In this work, Pd-Pt/SiO2 bimetallic catalysts were designed and prepared by the immobilization method, and their performances for toluene oxidation were evaluated. The addition of Pt into the catalyst elevated markedly the reduction of Pd active sites, leading to abundant electron-deficient Pd0 and electron-rich Pt0 in the Pd2Pt1 catalyst, which were confirmed by TEM, CO pulse adsorption and in-situ XPS. As revealed by O2-TPD and toluene-TPD characterization, the cooperative effect of electron-deficient Pd0 and electron-rich Pt0 in Pd2Pt1 catalyst facilitated the activation of O2 and toluene, thus enhanced greatly its activity. A conversion of 90% (T90) for toluene was achieved over Pd2Pt1 catalyst at 165 ℃, and the apparent activation energy (Ea) over Pd2Pt1 catalyst was lower than that over other Pd-Pt bimetallic and monometallic Pd or Pt catalysts. Additionally, the reaction mechanism was studied by In-situ DRIFTS, the results showed that the toluene oxidation passed successively benzyl alcohol, benzaldehyde, benzoic acid and maleic anhydride, then maleic anhydride was further oxidized to CO2 and water.