Energetic Characterization of Faujasite Zeolites Using a Sensor Gas Calorimeter

In addition to the adsorption mechanism, the heat released during exothermic adsorption influences the chemical reactions that follow during heterogeneous catalysis. Both steps depend on the structure and surface chemistry of the catalyst. An example of a typical catalyst is the faujasite zeolite. For faujasite zeolites, the influence of the Si/Al ratio and the number of Na+ and Ca2+ cations on the heat of adsorption was therefore investigated in a systematic study. A comparison between a NaX (Sodium type X faujasite) and a NaY (Sodium type Y faujasite) zeolite reveals that a higher Si/Al ratio and therefore a smaller number of the cations in faujasite zeolites leads to lower loadings and heats. The exchange of Na+ cations for Ca2+ cations also has an influence on the adsorption process. Loadings and heats first decrease slightly at a low degree of exchange and increase significantly with higher calcium contents. If stronger interactions are required for heterogeneous catalysis, then the CaNaX zeolites must have a degree of exchange above 53%. The energetic contributions show that the highest-quality adsorption sites III and III’ make a contribution to the load-dependent heat of adsorption, which is about 1.4 times (site III) and about 1.8 times (site III’) larger than that of adsorption site II.

Experimental Investigations of the Adsorption of NH3 on Silica Gel-Based Adsorbent

The silica gel-water working pair has been commonly used for commercial adsorption chillers due to the environmental benign refrigerant and low desorption temperature (less than 85°C). However, the application has been constrained due to the vacuum working condition and Ice point. This motivates researchers to investigate alternative working pairs. The silica gel-based adsorbents - ammonia working pairs have been found to be the most promising alternative. The isotherms and heats of adsorption of the working pair are essential to be investigated for designing the adsorption reactor and predicting the chiller performance. A novel sensor-gas calorimeter has been used to simultaneously measure the adsorption isotherm and heats of adsorption. The experimental results for adsorption of ammonia on the pure silica gel and silica gel treated with different weight percentage of calcium chlorine are presented.