Optimization of zeolite Beta by steaming and acid leaching for the acylation of anisole with octanoic acid: a structure–activity relation

This paper presents a catalytic and spectroscopic study of the dealumination of a commercial zeolite, Beta (Zeolyst). After dealumination by hydrochloric or oxalic acid and steaming (up to 973 K), increased activity and selectivity were found in the acylation of anisole with octanoic acid. The treatments led to the extraction of aluminum from the crystallographic T-sites in the framework structure, giving amorphous extraframework aluminum(–silicon)–oxide species in the case of steaming, while treatment with mineral acids or complexing agents removed framework and extraframework aluminum from the zeolite. 27Al MQ MAS NMR revealed a changing of the aluminum coordinations and a shift from framework to extraframework species after steaming. Steaming removes aluminum from other crystallographic T-sites than acid leaching. Using nitrogen physisorption, no differences in the texture properties could be observed and XRD showed that the crystallinity was preserved, indicating high stability of the commercial zeolite Beta. The nature of the enhanced activity is suggested to result from higher accessibility of the active sites that are proposed to be associated with framework-connected aluminum atoms.