(573g) Methane to Methanol Conversion in Small Pore Zeolites
CuxOy clusters embedded in different zeolite frameworks have shown significant activity in converting methane to methanol. However, depending on the zeolite structure and the exact synthesis and preparation protocols, different sites have been claimed in the literature to be most favorable. Here we develop a thermodynamic model to identify the most stable CuxOy under various conditions in the zeolite SSZ-13. We find Cu2O2 clusters anchored at defect sites in zeolites to be most stable. We discuss the impact on several parameters on their formation and give guidelines what parameters might influence the CuxOy distribution in the material. Furthermore we compare modeled UV-vis and Raman spectra to experiment and find excellent agreement for the suggested site with experimental measurements.
Additionally several studies indicate that confinement influences the activation enthalpies for this reaction in zeolites. To simplify the problem we focus on a more simple and better-understood Fe-oxo center, that also shows activity for the given reaction. We find that confinement stabilizes a methyl radical significantly more than the initially adsorbed methane molecule, which significantly lowers activation energies. We furthermore generalize these results to arrive at statements about the impact of confinement methane to methanol conversion and also other reactions.