A new synthetic smectite-like vanadosilicate containing V3+ in the framework

Abstract

A new synthetic smectite-like vanadosilicate, named Vanadosilicate Araraquara Madrid (VAM), containing V3+ was prepared by a hydrothermal method and its behavior as catalyst for methanol oxidation was investigated by X-ray Absorption Spectroscopy (XAS) under operando conditions. The samples were characterized by powder X-ray Diffraction (XRD), Scanning and Transmission Electronic Microscopy (SEM and TEM), CHN chemical analysis, as well as Nuclear Magnetic Resonance spectroscopy, Ultraviolet–visible spectroscopy (UV–Vis) and XAS. The use of VCl3 as a source of vanadium in low oxidation state (V3+) together with a mixture of hexamethyleneimine (HMI) and N,N,N-trimethyl-1-adamantamonium hydroxide (TMAdaOH) and the preparation of the synthesis mixture under inert atmosphere are mandatory for an efficient formation of this smectite-like vanadosilicate. XRD analyses show the synthetic smectite-like vanadosilicate to be impurity free and dioctahedral smectite peaks were observed. TEM observations together with EDS analyses indicate that the chemical composition is consistent with the dioctahedral structure. XAS measurements have revealed that six-coordinated vanadium is present on VAM, in an environmental similar to that reported for roscoelite mineral. The catalytic properties of this material were evaluated during methanol transformation under operando conditions. The reaction mechanism under different atmospheres was investigated and the results indicated that the process under He leads to the formation of H2 and CO, while the presence of oxygen shifts the mechanism toward the partial oxidation of methanol.