Incorporation of Nb(V) into BEA zeolite investigated by XRD, NMR, IR, DR UV–vis, and XPS

Abstract

Nb x SiBEA ( x = 1.0, 1.5 Nb wt%) zeolites are prepared by a two-step postsynthesis method involving first the creation of vacant T-atom sites associated with silanol groups by dealumination of BEA zeolite by nitric acid solution and then by impregnation of the resulting SiBEA zeolite with the niobium ethoxide Nb(OC 2H 5) 5 precursor. The incorporation of Nb into the framework of SiBEA as isolated mononuclear Nb(V) species is evidenced by XRD, 29Si MAS NMR, 1H– 29Si CP-MAS NMR, IR and 1H MAS NMR. DR UV–vis investigation shows that two types of framework mononuclear Nb(V) ions are present, evidenced by two bands at 222 and 236 nm, the intensity of which increases with Nb content. XP spectra with a doublet peaks at BE of 209.6–209.9 eV for Nb 3d 3/2 and of 206.9–207.5 eV for Nb 3d 5/2 show that niobium is present in the framework BEA zeolite as Nb(V).