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

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.