Research On Cobalt-based Catalyst For Catalytic Combustion Of Methane In The Exhaust Of Compressed Natural Gas Vehicle

With the adjustment of energy structure and the increasingly serious air pollutionproblem，the development of alternative fuel vehicles is becoming an inevitable trend.Compared with traditional gasoline cars, compressed natural gas （CNG） vehiclesdischarge less HC, CO and NO_x. However the unconverted methane emission is tentimes than gasoline vehicles, so to develop an efficient and low cost catalyst formethane combustion has scientific significance and practical value. In this thesis, basedon Co₃O₄we have studied the influence of preparation methods and process parameterson catalytic performance of methane. Based on the results of powder samples in ourlaboratory, we have investigated the catalytic performance of Co-based honeycombsamples and prepared the catalytic converter for the evaluation on the engine bench. Themain results are summarized as follows:According to this research, the calcination temperature has important influence onstructure of Co₃O₄. With calcination temperature increasing from400to800℃, thedegree of crystallization of Co₃O₄increased, BET surface area decreased from40to2m²/g, the average crystallize particle size increased from21nm to193nm. Meanwhile,the lattice defects of Co₃O₄reduced, vibration of Co-O became strong, reducibility oflattice oxygen reduced and the ratio of lattice oxygen reduced from60%to44%. Thecombination of the above phenomena resulted in the decrease of catalytic performanceof Co₃O₄. The Co₃O₄/γ-Al₂O₃catalyst prepared by the combination of urea combustionand impregnation exhibited excellent catalytic performance of methane combustionbecause of the high cobalt species dispersion, more active sites, more lattice defects andthe existence of Co³⁺on the support surface.Because the zeolite has special pore structure and high surface area, the dispersionof cobalt species was well and it can be reduced easily at low temperature.Consequently, the zeolite supported Co₃O₄catalyst showed more excellent catalyticperformance than the oxide supported samples. Particularly Co/SBA-15and Co/ZSM5exhibited the best catalytic activity.Based on the results of our previous experiments, we preparedPd/Co₅MnO_x-Al₂O₃/cordierite catalyst and tested its performance on CNG engine bench. When the engine speed was2000r/min, torsion was21.4Nm and excess air ratio was1.0, the highest removal rate of methane reached55.30%, NMHC conversion wasbetween30⁸0%and the CO conversion was almost100%.