No abstract

8473support of the Basic Research Fund administered by the Israeli Academy of Sciences, the contribution of David Yogev to the design of the system and preliminary measurements, and the help of Ofra Levi in some of the calculations. R e t r y NO. Ag, 7440-22-4. References and Notes(1) Yogev, D.; Efrima, S.A series of dealuminated mordenites (with Si/Alf ratios between 7 and 48) was prepared by acid leaching and characterized by using different physicochemical methods. The A1 content of the framework and the distribution of the tetrahedral and octahedral aluminum were determined by 27Al MAS NMR measurements and chemical analysis. Attempts to quantify the number of SiOH defect groups by ' %i MAS NMR measurements (following a procedure given in the literature) failed. The number of silanol groups (and Bransted sites) were determined using 'H 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.

H-ZSM-5 zeolite was dealuminated by steaming under "mild" and "severe" conditions at 675 and 975 K for 71.5 and 0.5 h, respectively. It resulted in a comparable number of Al atoms released from the zeolite framework, although of their different nature. The "mild" zeolite steaming yielded Al species easily removable from the zeolite by an acid leaching, in contrast to the zeolite steamed at "severe" conditions. The extra-framework Al species contributed to both a substantially higher para-selectivity in toluene disproportionation and its alkylation with ethylene and to an increased rate of side reactions leading to the zeolite deactivation by coke formation in toluene alkylation with ethylene.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mordenite Acidity:Dependence on the Si/Al Ratio and the Framework Aluminum Topology. Part 1. Sample Preparation and Physicochemical Characterization.-A series of dealuminated mordenites with Si/Al ratios between 7 and 48 is prepared by acid leaching (8 N HNO3, 338-385 K, 8-24 h) of commercial Na-mordenite and characterized by 27Al, 29Si, and 1H MAS NMR, and benzene adsorption or ammonia desorption measurements. The micro-and mesopore volumes increase with increasing dealumination up to a maximum at Si/Al ∼ =18 and then decrease slowly. The dealumination procedure increases the adsorption capacity for benzene. -(STACH, H.; JAENCHEN, J.; JERSCHKEWITZ, H.-G.; LOHSE, U.; PARLITZ, B.; ZIBROWIUS, B.; HUNGER, M.; J.