Single-step methane to methanol over lanthanum cerium oxide: The crucial role of surface reactive oxygen and carbonate species

Abstract

The single-step conversion of methane to methanol (MTM) represents an attractive route for the valorization of low-concentration coalbed methane (CBM). In this work, the effects of surface reactive oxygen and carbonate species on the catalytic performance of LaCeOx materials for MTM reaction was investigated. Lanthanum cerium oxide with different crystal structure were prepared by adjusting the ratio of La to Ce. Under low methane concentration (8 vol.%), La5Ce1 sample with defective fluorite phase exhibited the best methanol site-time yield to 20 μmol gcat−1h−1. The more oxygen vacancies on defective fluorite phase promote the generation of reactive oxygen species. Moreover, it was also found that the incorporation of Ce weakened the adsorption of surface carbonate. The more moderately adsorbed carbonate on La2Ce1 sample enhanced the methanol selectivity. In-situ diffuse reflectance Fourier transform infrared spectroscopy (In-situ DRIFTS) further revealed the different methane to methanol pathway over La5Ce1 and La2Ce1 sample. Reactive oxygen species were attributed to the site for methane activation and CH3O* was the intermediate group of methanol. This study provides a new point that the oxygen species of lanthanum-cerium oxide could be regulated to promote their performance for MTM reaction, and we believed that the as-discussed oxide could be employed as the host materials for active phases as well.