The Study Of Catalytic Diesel Soot Oxidation Performance On MnO_x-CeO₂ Complex Oxides

Nowadays, diesel motor vehicles are widely used in many countries all over the word for their good performance and high fuel economy, also because of the advantage of saving energy and environmental protection, however, serious environmental impact are brought out because of pollutans especially soot from exhaust. Diesel Particulat Filter (DPF) as one kind of after-treatment technology is widely applied for its effective and functional method for soot elimination, but precious metal catalyst are needed to be coated on the wall in the DPF, while because precious metals resources are growing shortages and expensive, other alternative metal or metal (composite) oxides are anticipated by many frontier researchers. Based on these points, MnOx-CeO2 was applied as the research object in this paper to study the performance of catalytic soot combustion.Mn was introduced into CeO2 in order to improve oxygen storage and redox performance, and applied for catalytic oxidation of diesel soot, BET specific surface area (BET), X-Ray diffraction (XRD), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD), X-ray Photoelectron (XPS), In-situ Diffuse Fourier Transorm Infrared Spectroscopy (In-situ DRIFTS) are used to study the correlation between catalyst features and soot oxidation activity. In addition, considering the characteristics of diesel exhaust, NO was introduced in the reaction atmosphere of TPO and In-situ DRIFTS test in order to explore the correlation between morphology and evolution of NO/O2 and soot oxidation, and then the mechanism was inferred.The main conclusion were concluded after the study:1) With Mn introduced into CeO2 by coprecipitation method, MnOx-CeO2 still has formed a cubic phase fluorite structure, redox ability was improved greatly, and more oxygen vacancies were produced compared with CeO2, thus being good for the adsorption, activation and migration of gas oxygen on the catalyst, also rich surface oxygen species are formed (O2-,O-,O2-).2) MnOx(z)-CeO2 series catalysts could obviously reduce the light-off temperature of soot compared with pure MnOx and CeO2, with oxygen existed, the activity of catalysts were correlated well with the atomic adsorptive oxygen(O-); While NO was added into the reation atmosphere, the activity was greatly improved, which had close association performance with the high NO oxidation ability and NOx storage ability.3) NO could be oxidized to NO2-, NO3- by surface oxygen species (O2-, O-, O2-) on MnOx, CeO2 and MnOx-CeO2 catalysts, while the introduction of O2 gas would improve the NO oxidation ability to NO2-, NO3-, the soot oxidation could be improved because of high NO3- storage ability by MnOx-CeO2 complex oxides 4) During the soot catalytic oxidation reaction, carbon oxygen intermediate species C(O) gengrated on MnOx(z)-CeO2 series catalysts could not only react with O2, NO2 gas phase to produce CO2, also with the NO3" stored on the catalyst surface directly.