STUDIES OF MORDENITE BY THE MONTE-CARLO METHOD

A model on the distributions of Al atoms in the framework of parent mo rdenites is suggested. The distribution of Al atoms in the framework o f dealuminated mordenite is determined by both the parent sample and i ts follow-up dealumination. The continuous dealumination is simulated by a discrete stochastic process (Markov chain). The relative populati ons of the building units {Si(n-Al)} and the types of Al atom {Al(m-Al )} for parent mordenites with different Si/Al ratios and the evolution s of the relative populations of {Si(n-Al)} and {Al(m-Al)} during the dealumination can then be calculated by Monte Carlo method. Since the relative populations of both {Si(n-Al)} and {Al(m-Al)} are obtained fr om the same sample space of the Monte Carlo simulation, their correlat ion is established from a reliable theoretical foundation. The former, calculated {Si(n-Al)}, can be compared directly with Si-29 MAS n.m.r. observations of parent and dealuminated mordenites to prove the reaso nability of the present theory. The latter, calculated {Al(m-Al)}, pre dicts the acidic properties of the parent and the dealuminated mordeni tes. The definition of the efficiency parameter of type acid site, whi ch scales the contribution of a type acid site toward the acidity, is introduced. Based on this definition, the acid amount and the efficien cy parameter alpha(O), (introduced by Beaumont and Barthomeuf for fauj asites) in a mordenite sample can be expressed quantitatively. The pre sent theory satisfactorily explains the ammonia t.p.d. acidity measure ment results for both the parent and dealuminated mordenite samples.