差热-色谱联用法测吸附热——吡啶在γ-Al_2O_3及NaX沸石上吸附热研究

DTA-GC Combination for Measuring Adsorption Heat——The Investigation of Differential Heat of Adsorption for Pyridine on γ-Al_2O_3 and NaX Zeolites

测量和研究吸附热对探讨多相催化过程及固体催化剂表面活性中心、结构和吸附特性等均有重要意义。本文参照Richardson及杨梦彦的方法,将差热技术与色谱技术相结合,建立了适于测定气-固不可逆吸附的微分吸附热的量热系统。用它测定了吡啶在γ-Al_2O_3及分子筛NaX沸石上的微分吸附热并初步探讨了它们的表面酸性。 1

The differential heats of adsorption for pyridine on γ-Al_2O_3 and NaX zeolites at 170℃～270℃ have been measured by a DTA-GC adsorption calorimetric system we designed. It is verified that the acidic sites on the surface of γ-Al_2O_3 are mainly L-acid sites. The acid amount would be reduced and the acid strength would be decreased as the temperature is raised. The decreasing extent of the acid strength at one adsorption site is not the same as that at another. There are two types of acidic sites which adsorb pyridine irreversibly and reversibly on the surface of NaX zeolite. The stronger type is the non-active L-acid site and the weaker one the active B-acid site. The Influence of the temperature variation upon the two types of acidic sites is not the same. The calculation result shows that the total adsorption sites in β-cages and octahedral zeolite cages are partly occupied by H_2O molecules.