Abstract
Direct functionalization of methane in natural gas is of paramount importance but faces tremendous challenges. We reported a nickel-modified copper zeolite catalyst for the selective oxidation of methane into methanol. Using H(2)O(2) as an oxidant in the liquid phase at 80 °C, Cu(1)Ni(0.75)/ZSM-5 catalyst presented a relatively high methanol yield of 82 162 μmol g(cat) (-1) h(-1) (with a methanol selectivity of ∼74%). Combining series of designed experiments and thorough characterization analysis, including electron microscopy, X-ray photoelectric spectroscopy, Fourier transform infrared reflection as well as in situ diffuse reflectance infrared Fourier transform spectroscopy, abundant Cu(I) active sites were found on Ni-Promoted Cu/ZSM-5, differing from the dominating Cu(II) active sites over Cu/ZSM-5. Cu(I) active sites had an excellent ability to promote CH(4) adsorption, CH(4) activation and CH(3)OH generation compared to Cu(II) active sites. This work elucidates a constellation of insightful and potent perspectives for further improvement of metal-zeolite catalysts for the direct oxidation of methane to methanol.