3 years ago

Structure and Reactivity of sol–gel V/SiO 2 Catalysts for the Direct Conversion of Methane to Formaldehyde

Cristina V. Loricera, Adel A. Ismail, M. Consuelo Alvarez-Galvan, Saleh A. Al-Sayari, Jose Luis G. Fierro, Rut Guil-Lopez

Abstract

Vanadium oxide-silica catalysts prepared by the sol–gel method were characterized by different techniques (nitrogen adsorption–desorption isotherms, scanning electron microscopy, X-ray diffraction, temperature-programmed reduction, Raman spectroscopy and X-ray photoelectron spectroscopy) and applied in the direct conversion of methane to C1 oxygenates. The addition of a small amount of nitric oxide to the reaction mixture reduced the energy barrier for H-abstraction, increasing the methane conversion and formaldehyde yield. Correlations between the characterization and activity results indicate that the reaction occurs on tetrahedrally coordinated vanadium sites, as the maximum formaldehyde yield was found for the catalyst with a vanadium content of 1.5 wt%, which has a high surface density of well-dispersed tetrahedrally coordinated monomeric or slightly oligomerized VO4 species. On the other hand, a high space velocity and CH4:O2 ratio decrease the subsequent oxidation to carbon oxides, increasing oxygenate formation.

Publisher URL: https://link.springer.com/article/10.1007/s11244-017-0809-x

DOI: 10.1007/s11244-017-0809-x

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