Synergistic effect of Pd/CZO catalysts and an electric field on complete combustion of lean and humid methane at low temperatures†

The elimination of unburned methane produced by internal combustion engines is extremely important because of the strong greenhouse effect of methane. Difficulties in controlling unburned methane arise from its characteristics, such as its difficulty of adsorption, low exhaust gas temperatures in an efficient engine, low concentrations of unburned emitted methane, and the coexistence of steam and residual oxygen as coexisting substances in the exit gas. Results of the present study demonstrate that the removal activity of methane by complete combustion was improved dramatically at low temperatures by the application of a DC electric field to the Pd/Ce_xZr_1−xO₂ catalyst system, even under a humid atmosphere. Specifically, 1 wt% Pd/Ce_0.25Zr_0.75O₂ showed very higher methane conversion under humid conditions than under dry conditions at 473 K in the presence of an electric field. To elucidate the reaction mechanisms involved in this process of steam adsorption, we conducted partial pressure dependence tests and activity tests with steam under an electric field.