Roles of desorbed radicals and reaction products during the oxidation of methane using a nickel mesh catalyst

Abstract

Partial oxidation of methane with air was studied in a quartz tube reactor and a wire-mesh reactor at 850–950 °C using pure nickel mesh as a catalyst. In the wire-mesh reactor, only the mesh catalyst itself was heated, giving more direct information on the reactions on the catalyst surface. In the quartz tube reactor, reactions took place both on the catalyst surface and in the gas phase. The use of a non-porous mesh as the catalyst at short contact times allowed for the elimination of mass transfer limitations for radicals, which would be considered as “irreducible” with porous catalysts at high temperature. Our experimental results demonstrated that the desorption of radicals from the catalyst surface at short contact times competed well with other reactions (including oxidation reactions) involving the radicals on the catalyst surface or within the gas film surrounding the wires. The desorbed radicals played an important role by participating in the subsequent reactions in the gas phase and/or on the catalyst surface. The use of two pieces of meshes (5 mm apart) in the quartz tube reactor at high gas flow rates indicated that the desorbed radicals could decrease the apparent catalyst activity due to the re-formation of CH 4 from the radicals desorbed from the catalyst surface. The reactions in the quartz tube reactor at least partly represent the reactions inside a porous catalyst. Our study has thus given further insights into the fundamental reactions taking place inside the pores in a porous catalyst.