Selective oxidation of methane to methanol in oleum over Pd/C catalyst

The selective oxidation of methane to methanol over Pd/C catalysts generated from a PdCl2 precursor was investigated in oleum.Characterization of the catalysts was performed by X-ray diffraction,X-ray photoelectron spectroscopy,high-resolution transmission electron microscopy,and CO adsorption.The major product in the oxidation reaction was methyl bisulfate,which was then hydrolyzed into methanol.Methane conversion of 23.6% with methanol selectivity of 69.5% and yield of 16.4% was achieved under the optimum conditions of 5%Pd/C,30 μmol Pd,reaction temperature 180 ℃,methane pressure 4.0 MPa,reaction time 4 h,and 50% sulfur trioxide concentration.After facile separation with the reactants and pretreatment,the catalyst could be reused several times with considerable stability.The selective oxidation of methane catalyzed by Pd/C catalysts in oleum possibly involved an electrophilic substitute mechanism.The catalytic performance was related to the Pd loading,dispersion,and particle size.