Direct Catalytic Oxidation of Low-Concentration Methane to Methanol in One Step on Ni-Promoted BiOCl Catalysts

The direct oxidation of low-concentration methane (CH4) to methanol (CH3OH) is often regarded as the "holy grail". However, it still is very difficult and challenging to oxidize methane to methanol in one step. In this work, we present a new approach to directly oxidize CH4 to generate CH3OH in one step by doping non-noble metal Ni sites on bismuth oxychloride (BiOCl) equipped with high oxygen vacancies. Thereinto, the conversion rate of CH3OH can reach 39.07 μmol/(gcat·h) under 420 °C and flow conditions on the basis of O2 and H2O. The crystal morphology structure, physicochemical properties, metal dispersion, and surface adsorption capacity of Ni-BiOCl were explored, and the positive effect on the oxygen vacancy of the catalyst was proved, thus improving the catalytic performance. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was also performed to study the surface adsorption and reaction process of methane to methanol in one step. Results demonstrate that the key to keep good activity lies in the oxygen vacancies of unsaturated Bi atoms, which can adsorb and active CH4 and to produce methyl groups and adsorbing hydroxyl groups in methane oxidation process. This study broadens the application of oxygen-deficient catalysts in the catalytic conversion of CH4 to CH3OH in one step, which provides a new perspective on the role of oxygen vacancies in improving the catalytic performance of methane oxidation.