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

化学惰性气体，如氩气和氮气，当它们接近极化位置时，它们之间存在静电相互作用，处于极化状态。固体酸上极化程度最高的位置被认为是酸位。这种极化酸位与氩或氮的诱导偶极子之间的相互作用是类似酸碱的相互作用。可以很容易地预料，相互作用的强度将取决于酸的强度。结果表明，采用亨利等温线计算的氩的吸附热可作为质子型丝光沸石、β、ZSM-5、硫酸氧化锆和硅铝等固体酸的相对酸强度指标。吸附等温线不属于亨利型，所得氩的吸附热为近似值。详细研究表明，采用langmuir型吸附等温线得到的氩吸附热表明，相对酸强度和计算的吸附量饱和等于酸位数。此外，吸附量的温度依赖性与固体酸的孔径有关。为了确定酸位的酸强度分布，将Clausius-Clapeyron方程应用于不同温度下测得的氩、氮吸附等温线。所得的氩气吸附数据表明了氩气强度的分布。在几种具有lewis型酸位的固体酸上测得更大的氮吸附热。这一结果表明，通过比较氮气和氩气的吸附热，可以区分酸位的类型。

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.