Synthesis and characterisation of chromium-substituted ETS-10

Abstract

A series of microporous chromium-containing ETS-10 (ETCrS-10) with different Cr/Ti molar ratios have been synthesised and characterised by energy dispersive absorption of X-rays (EDAX), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption measurements, diffuse-reflectance ultraviolet spectroscopy (DR-UV), electron paramagnetic resonance (EPR) and ²⁹Si magic-angle-spinning nuclear magnetic resonance (MAS NMR). The diffractograms of the as-synthesised ETCrS-10 materials indicate that the ETS-10 structure has remained intact upon Cr substitution. DR-UV and EPR reveal that the as-prepared ETCrS-10 samples contain Cr³⁺ in octahedral coordination. The resonances in the ²⁹Si MAS NMR spectra of ETCrS-10 are considerably broader than those of ETS-10 and such a broadening may relate to isomorphous substitution of Cr for Ti in the ETS-10 framework. The acid–base properties of ETCrS-10 materials are responsible for the high dehydrogenation activity in the conversion of isopropanol to acetone and dehydration activity in the conversion of tert-butanol to isobutene. Ethanol oxidation over ETCrS-10 yields acetaldehyde as a main product.