Catalytic performance of vanadium incorporated MCM-41 catalysts for the partial oxidation of methane to formaldehyde

The catalytic performance of incorporated V-MCM-41 catalysts for the partial direct oxidation of methane to formaldehyde with molecular oxygen has been investigated. V-MCM-41 catalysts containing 0.56-1.86 wt.% V have been prepared by incorporating the vanadium ions into the framework of mesoporous siliceous MCM-41, resulting in a highly ordered structure with large BET surface area and high surface density of isolated vanadium atoms. The structure of the V-MCM-41 catalysts was studied by N₂ physisorption. The influence of the main reaction parameters, i.e. reaction temperature, reaction pressure, CH₄:O₂ ratio, gas hourly space velocity (GHSV) and vanadium content, on the selectivity and space time yield (STY) of formaldehyde were studied. A formaldehyde selectivity of 59.4% using a 0.56 wt.% vanadium loading V-MCM-41 catalyst was achieved at a temperature of 873 K, pressure of 12 psi, CH₄:O₂ molar ratio of 13:1, GHSV of 2.0 × 10⁵ l kg^-1 h^-1. The highest STY_HCHO of 2103 g kg^-1 h^-1 with a high HCHO selectivity of 53.2% was obtained with the V-MCM-41 catalyst containing 1.86 wt.% vanadium loading at 933 K, CH₄:O₂ ratio of 13:1, GHSV of 1.3 × 10 ⁶ l kg^-1 h^-1. The improved catalytic performance of the V-MCM-41 catalysts is related to the highly dispersed vanadium oxide species forming a high concentration of isolated active sites, which are crucial to minimize the consecutive oxidation of formaldehyde to carbon oxides.