Structure, morphology, and catalytic activity of β zeolite synthesized in a fluoride medium for asymmetric hydrogenation

Abstract

A series of beta (β) zeolites has been synthesized in a fluoride medium and characterized by different techniques. XRD showed that the majority of F-Si-β, F-Pt-β, F-Pd-β, and F-W-β materials consisted of polymorph A. W and Al were incorporated into the framework of β, while Pt and Pd existed on the surface of β in the form of PtOx or PdOx oxides. The framework structures of F-Si-β, F-Pt-β, and F-Pd-β were almost identical, as proven by 29Si MAS NMR and FTIR spectra. The relative coverage of surface -OH groups decreased in the sequence H-β>H-ZSM-5>F-Al-β>F-W-β>F-Pd-β> F-Pt-β>F-Si-β(1)>F-Si-β(2). SEM revealed an especially uniform crystalline morphology of F-Si-β(2) nucleated spontaneously and a mixed morphology of F-Si-β(1), F-W-β, F-Pt-β, and F-Pd-β induced by seeding H-β. The reduced F-Pt-β and F-Pd-β were catalytically active for the asymmetric hydrogenation of tiglic acid with an appreciable enantiomeric excess value of about 9-11% without adding chiral modifiers. © 2003 Elsevier Inc. All rights reserved.