MORDENITE ACIDITY - DEPENDENCE ON THE SI/AL RATIO AND THE FRAMEWORK ALUMINUM TOPOLOGY .1. SAMPLE PREPARATION AND PHYSICOCHEMICAL CHARACTERIZATION

A series of dealuminated mordenites (with Si/Al(f) ratios between 7 and 48) was prepared by acid leaching and characterized by using different physicochemical methods. The Al content of the framework and the distribution of the tetrahedral and octahedral aluminum were determined by Al-27 MAS NMR measurements and chemical analysis. Attempts to quantify the number of SiOH defect groups by Si-29 MAS NMR measurements (following a procedure given in the literature) failed. The number of silanol groups (and Bronsted sites) were determined using H-1 MAS NMR investigations. The micro- and mesopore volumes of the samples were derived from measurements of the benzene adsorption isotherms. It was found that low dealumination of the H-mordenites transforms small- into large-port mordenites. The micropore volume diminished again at a high degree of dealumination.