IR observation of activated ether species on acidic OH groups on H-ZSM-5 zeolites

Abstract

IR spectra of ethers adsorbed on zeolite (H-ZSM-5) were analyzed in detail in comparison with those of water and alcohols. Interpretation of complicated features of IR spectra observed for adsorption of water and alcohols on acidic OH groups of zeolite is summarized in relation with the adsorption structure and the potential energy based on the accepted knowledge. Since the presence of Fermi resonance in vibrational modes between acidic OH groups and adsorbed species can be an estimate for the potential energy of the protonated transition state, IR spectra of adsorption of ethers on zeolite were interpreted by changing acidic OH groups to OD. Adsorption of ethers on silanol and acidic OH groups of zeolite resulted in markedly different IR spectra. In addition, the Fermi resonance between OH stretching of acidic OH (shifted below 2000 cm−1) and CH bending vibrations of adsorbed ethers was confirmed, and the observed adsorbed species were co-existent with protonated transition state in equilibrium at 298 K.