FTIR Evidence of Different Bonding of Methane to OH Groups on H–ZSM-5, HY, and SiO2

Low-temperature adsorption of CH4 and 15N2 on H–ZSM-5, SiO2, and HY is comparatively studied. Partly and fully deuteroxylated samples were also investigated. It was established that methane forms H bonds simultaneously with oxygen and hydrogen from the Si–OH groups, which reflects in enhanced shift of the OH modes to lower frequency as compared to the case if methane was bound to the proton only. In contrast, methane is attached to highly acidic hydroxyls forming a bond mainly with the proton. At high methane equilibrium pressure, a second methane molecule is bound to the same acidic OH group.