Microcalorimetry on Cu-MCM-22 Reveals Structure-Activity Relationships for the Methane-to-Methanol Reaction

Abstract

With a stepwise mechanism for direct methane activation to methanol (MTM) over Cu-zeolites, it is possible to produce methanol with high selectivity. With this study, we apply adsorption/desorption experiments with n-propylamine, NH3, and CH4 as powerful techniques to learn more about the acidity and nature of the Cu-sites within a hitherto untested material for MTM, namely, MCM-22. The Cu-exchanged zeolites have a moderate performance in MTM (∼0.10 molMeOH/molCu), and upon comparing to the activity of other zeolite frameworks, we use the results found for MCM-22 to search for structure–activity relationships. We show with CO-adsorption FT-IR spectroscopy experiments that there is more than one distinct Cu-site within MCM-22, where one of which is likely linked with inactive Cu species. NH3 adsorption/desorption experiments disclose that the Brønsted acid sites before Cu exchange are few and heterogeneous in strength, leading to a low number of C–H-activating Cu-oxo species.