Methanol Desorption from Cu-ZSM-5 Studied by <i>In Situ</i> Infrared Spectroscopy and First-Principles Calculations

Abstract

The dynamic interaction of methanol and its derivatives with Cu-exchanged ZSM-5 during methanol temperature-programmed desorption from 30 to 450 °C has been investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and first-principles calculations. The results emphasize that defects in the framework structure of the zeolite and Brønsted acid sites constitute ion-exchange sites for Cu ions. The Cu sites introduced in ZSM-5 actively interact with methanol adsorbed at moderate temperature, i.e., below 250 °C, and take roles in further oxidation of the adsorbed species to formate and CO. Moreover, spectra recorded at higher temperatures, i.e., above 300 °C, after adsorption of methanol show strong interaction between methoxy groups and the zeolite framework, suggesting that, under mild conditions, proton extraction for methanol production during direct partial oxidation of methane to methanol over Cu-ZSM-5 is necessary.