Interinfluence between Reactions on the Catalyst Surface and Reactions in the Gas Phase during the Catalytic Oxidation of Methane with Air

Abstract

Direct catalytic oxidation of CH4 with air was studied using a wire-mesh reactor and a quartz tube reactor. Two types of nickel-containing catalysts (nickel and Monel 400 alloy) in the form of wire-mesh were used. The wire-mesh reactor features the minimisation of the thermally induced gas-phase reactions by rapidly quenching the products leaving the mesh catalyst surface. The wire-mesh reactor can be used as a differential reactor for the study of both exothermic and endothermic reactions, with the reactions on the catalyst surface not controlled by heat transfer. Increasing total gas flow rate passing through the mesh catalyst caused not only increases in overall reaction rates but also changes in the product selectivities. With the reduction of the thickness of the gas film around the catalyst wires, the coupling of the CH3 radicals desorbed from the catalyst surface becomes an important route of C2H6 formation during the catalytic oxidation of CH4 with air, even at 950°C. The reactor has proved to be a powerful tool in understanding the reactions on the catalyst surface without the complications caused by the reactions in the gas phase. Comparison of the results from the wire-mesh reactor with those from the quartz tube reactor indicates that the reactions in the gas phase inhibited the reactions on the catalyst surface. The interinfluence between the surface-catalysed reactions and the gas-phase reactions must be considered in evaluating the intrinsic reactions on the catalyst surface.