Evaluation of Surface Properties of Solid Acids by the Adsorption of Inert Gases

点击翻译按钮获取中文摘要

Chemically inert gases like argon and nitrogen are to be polarized state when they are approached to a polarized sites, and there is an electrostatic interaction between them. The most polarized sited on a solid acid is expected to be acid sites. This interaction between the polarized acid sites and induced dipole of argon or nitrogen is acid-base like interaction. It can be easily expected that the strength of the interaction will depend on the acid strength.It was shown that the heat of adsorption of argon obtained by applying the Henry-type adsorption isotherms was an indicator of the relative acid strength of solid acids of proton-type mordenite, beta, ZSM-5, sulfated zirconia, and silica-alumina.The adsorption isotherm was not Henry-type in particular, and the obtained heat of adsorption of argon was approximate value. As the result of detailed research, it was clarified that the heat of argon adsorption obtained by applying Lngmuir-type adsorption isotherms indicated the relative acid strength and the calculated adsorption amount saturation was equal to the number of acid sites. Additionally, temperature dependence of adsorption amount related to the pore size of solid acids.For the purpose to determine the distribution of acid strength of the acid sites, the Clausius-Clapeyron equation was applied to the isothermos of argon and nitrogen adsorption measured at various temperatures. The obtained data of argon adsorption indicated the distribution of avid strength. The much larger heat of nitrogen adsorption was measured on several solid acid which has Lewis-type acid sites. This result indicates that the type of acid sites is possible to distinguish by comparison of the adsorption heat of nitrogen with that of argon.