Intrinsic reaction kinetics of methane steam reforming on a nickel/zirconia anode

For the purposes of optimising important system parameters in direct intern ally reforming (DIR) solid oxide fuel cell (SOFC) systems, a detailed knowl edge of the methane steam reforming rate on the anode is needed. In order t o shed light on the present poorly understood kinetics, a study of the meth ane steam reforming rate given by a typical thin electrolyte-supported nick el/zirconia SOFC anode has been carried out using a tubular plug flow diffe rential reactor. These tests were essentially gradientless. The reaction ra te was studied as a function of temperature (700-1000 degrees C) and the pa rtial pressure of methane (2-40 kPa), hydrogen (10-70 kPa) and steam (10-70 kPa). The total pressure was nominally 1 arm. The reaction was first order in methane with a weak positive effect of hydrogen, and a stronger negativ e effect of steam, The kinetics were complicated by the fact that reaction orders in hydrogen and steam were either temperature dependent and/or depen ded on the partial pressures of other components in the gas mixture. Furthe rmore, Arrhenius-type plots gave gradients which were dependent on the stea m partial pressure. It is clear from this study that the reaction cannot be represented as simply as is generally attempted in the literature. An impr oved rate equation has been derived. (C) 2000 Elsevier Science S.A. All rig hts reserved.