Oxidation of Methane to Methanol by Water Over Cu/SSZ‐13: Impact of Cu Loading and Formation of Active Sites

Cu/SSZ‐13 catalysts with different Cu loadings (1–5 wt.%) were prepared by conventional impregnation via a slow step‐dry process for the direct conversion of methane to methanol. Catalytic performance of the catalysts is found to depend on the Cu loading in both stepwise and continuous processes and 2 wt.% Cu presents the best performance. CuO nanoparticles, CuxOy clusters and monomeric [CuOH]+ species are found on Cu/SSZ‐13 based on HRTEM, HAADF‐STEM, DR UV‐vis and FTIR spectroscopies. The high coverage of CuO nanoparticles on 5 wt.% Cu/SSZ‐13 results in the loss of catalytic reactivity in spite of the existence of active CuxOy and [CuOH]+ sites. Besides, it is proposed that the formation of [Cu2O2]2+ and [Cu2O]2+ active sites involves [CuOH]+ intermediates. We further found that improved catalytic performance in cyclic stepwise process involves the re‐dispersion of CuO nanoparticles and/or large clusters as well as the re‐oxidation of Cu(I) cations from self‐reduction of [CuOH]+ species. Structure‐activity relationship: Formation of active sites over impregnated Cu/SSZ‐13 catalyst involves the re‐dispersion of CuO and re‐oxidation of Cu(I) species in methane‐to‐methanol reaction with water as oxidant.