Sorption properties of zeolite rho

Abstract

Zeolite rho possesses an unusual combination of selectivity and activity for the synthesis of dimethylamine from ammonia and methanol. Sorption measurements were used to examine the synthesis of zeolite rho and how it evolves to become a superior catalyst, to distinguish various preparations, and to determine the effects of calcination under different conditions. A term “packing ratio” was defined as the ratio of adsorbed weights at equilibrium of different molecules for the same sorption volume and was shown to provide a measure of the steric constraints imposed on guest molecules by the host framework. Statistical analysis of the sorption data for many samples reveals that methanol fills the available framework volume and packs according to its liquid density. Because of this feature, methanol sorption provides a measure of the crystallinity of the rho framework. Larger molecules are constrained by the framework in the order: n-hexane> n-propanol > ethanol > methanol. Reproducible packing ratios, ethanol/methanol and n-propanol/ethanol, were determined for the rho framework. Rates of filling used in conjunction with the packing ratios show the presence of extra-lattice material and its proximity to the double 8-rings of rho.