Structure and Reactivity of sol–gel V/SiO2 Catalysts for the Direct Conversion of Methane to Formaldehyde

[EN] 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 VO species. On the other hand, a high space velocity and CH:O ratio decrease the subsequent oxidation to carbon oxides, increasing oxygenate formation.This work was supported by Najran University, Najran, The Kingdom of Saudi Arabia. This is a post-peer-review, pre-copyedit version of an article published in Topics in Catalysis. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11244-017-0809-