Cu-exchanged zeolites possess active sites that are able to cleave the C-H bond of methane at temperatures ≤200 °C, enabling its selective partial oxidation to methanol. Herein we explore this process over Cu-SSZ-13 materials. We combine activity tests and X-ray absorption spectroscopy (XAS) to thoroughly investigate the influence of reaction parameters and material elemental composition on the productivity and Cu speciation during the key process steps. We find that the Cu moieties responsible for the conversion are formed in the presence of O and that high temperature together with prolonged activation time increases the population of such active sites. We evidence a linear correlation between the reducibility of the materials and their methanol productivity. By optimizing the process conditions and material composition, we are able to reach a methanol productivity as high as 0.2 mol CHOH/mol Cu (125 μmol/g), the highest value reported to date for Cu-SSZ-13. Our results clearly demonstrate that high populations of 2Al ZCu sites in 6r, favored at low values of both Si:Al and Cu:Al ratios, inhibit the material performance by being inactive for the conversion. Z[CuOH] complexes, although shown to be inactive, are identified as the precursors to the methane-converting active sites. By critical examination of the reported catalytic and spectroscopic evidence, we propose different possible routes for active-site formation.

The direct conversion of methane to methanol (MTM) is a reaction that has the potential to disrupt a great part of the synthesis gas-derived chemical industry. However, despite many decades of research, active enough catalysts and suitable processes for industrial application are still not available. Recently, several copper-exchanged zeolites have shown considerable activity and selectivity in the direct MTM reaction. Understanding the nature of the active site in these materials is essential for any further development in the field. Herein, we apply multivariate curve resolution analysis of Xray absorption spectroscopy data to accurately quantify the fraction of active Cu in Cu-MOR (MOR = mordenite), allowing an unambiguous determination of the active site nuclearity as a dicopper site. By rationalizing the compositional parameters and reaction conditions, we achieve the highest methanol yield per Cu yet reported for MTM over Cu-zeolites, of 0.47 mol/mol.

This communication reports the discovery of several small-pore Cu-zeolites and zeotypes that produce methanol from methane and water vapor, and produce more methanol per copper atom than Cu-ZSM-5 and Cu-mordenite. The new materials include Cu-SSZ-13, Cu-SSZ-16, Cu-SSZ-39, and Cu-SAPO-34.

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The author`s contribution Several people contributed to the Papers and manuscripts in this thesis. A description of Wegard Skistad`s contribution to each work is presented below. Paper I: Wegard Skistad has synthesized EU-1 and ZSM-48 catalysts, contributed to the characterization of the catalysts, interpretation of the results, and preparation of the manuscript. Paper II: Wegard Skistad has synthesized the catalysts and performed low pressure catalytic tests. He has contributed to the characterization of the catalysts, planning of the experiments, interpretation of the results, and preparation of the manuscript. Paper III: Wegard Skistad has synthesized TNU-9 and IM-5 catalysts, contributed to the characterization of the catalysts, interpretation of the results, and preparation of the manuscript. Paper IV: Wegard Skistad has synthesized TNU-9 and IM-5 and characterized the materials. He built a methanol pulse dosing system and performed the Raman spectroscopic investigation together with Francesca Bonino (University of Turin). He has contributed to the planning of the experiments, interpretation of the results, and preparation of the manuscript.