Modified zeolites. Part 1.—Dealuminated mordenites and their silanation

Abstract

A series of partially dealuminated H-mordenites having different ratios SiO₂/Al₂O₃ has been prepared from Na-mordenite by various treatments with acid. From these a series of dealuminated Na-mordenites has been made by treating the corresponding H-mordenites with dilute NaOH. The loss of water, including that from the groups [graphic omitted] and the “nests” of hydroxyls, H₄O₄, has been investigated as a function of temperature for the dealuminated forms. This showed at 360°C the existence of some OH groups not originating from [graphic omitted]. Such groups were attributed to —OH originating from nests. The silanation of the dealuminated H- and Na-mordenites was investigated quantitatively. In the mordenites free of zeolitic water the ratios H₂(evolved)/SiH₄(chemisorbed) were always between 1.5 and 2 and each ratio usually remained reasonably constant over the course of a run. This suggested a rather constant ratio of primary chemisorption to secondary reaction during many runs. The ratio increased above 2 only if zeolitic water was also present. No evidence was found for a significant amount of the reaction [graphic omitted] in which SiH₄ interacts with intact “nests”, H₄O₄, to regenerate defect-free framework. The Elovich equation appeared able to represent the kinetics of chemisorption of SiH₄.