Alkoxylation Reaction of Alcohol on Silica Surfaces Studied by Sum Frequency Vibrational Spectroscopy
Ting Luo, Ruidan Zhang, Wei-Wang Zeng, Chuanyao Zhou, Xueming Yang, Zefeng Ren
Abstract
The interactions between adsorbed alcohols and oxide surfaces have attracted great interest because of their wide existence in nature and industry. Here we investigated the adsorption behaviors of alcohol on silica by surface-sensitive sum frequency vibrational spectroscopy (SFVS) under near-ambient pressure of alcohol and high-temperature conditions. A novel infrared spectral normalization method under high pressure was proposed in internal heterodyne phase-resolved SFVS measurements. The investigation of methanol adsorption on silanol and siloxane sites of silica indicates that the alkoxylation reactions proceed on both sites but preferentially on the siloxane sites at room temperature. The elevated temperature can improve the efficiency of the alkoxylation reactions. Our results not only provide direct evidence of the formation of alkoxy groups on silica-based materials in catalysis but also give guidelines for improving its catalytic activity based on the different reaction processes on two types of terminal sites on silica surfaces.