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

化学惰性气体如Ar和N在接近极化位置时处于极化状态，它们之间存在静电相互作用。在固体酸上极化最强的部位应该是酸性部位。这种极化酸位与诱导的Ar或N的偶极相互作用是类酸碱相互作用。结果表明，应用Henry吸附等温式得到的Ar的吸附等温热是质子型丝光沸石、β、ZSM-5、硫酸氧化锆酸和硅铝固体酸相对酸强度的指标，吸附等温线不是Henry-型的，所得到的Ar的吸附热是近似值。研究表明，应用Lngmuir型吸附等温式得到的Ar吸附等温热反映了相对酸强度，计算出的吸附量饱和度等于酸中心个数。此外，吸附量的温度依赖性与固体酸的孔径大小有关。为了确定酸中心的酸强度分布，用Clausius-Clapeyron方程测定了不同温度下的Ar和N的吸附等温线。所获得的Ar吸附数据表明了吸附强度的分布。在几种具有Lewis酸中心的固体酸上测得了更大的氮吸附热。这一结果表明，可以通过比较氮和氩的吸附热来区分酸中心的类型。

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.