Research On The Effect Of NO On Soot Oxidation Over LaMnO₃and La_0.8K_0.2MnO₃Peravsk-type Catalysts

Nowadays，the diesel motor vehicle not only has good power and economy, but also hasthe advantages of energy saving and environmental protection, thus have been widely used incountries around the world. However, major pollutants discharged in exhaust gas of the dieselmotor vehicle, such as particle matter （PM）, nitrogen oxides （NOx）, carbon monoxide （CO）and hydrocarbons （CH）, have great pollution on the urban environment and generate seriousharm to human health at the same time. In exhaust gas post-treatment technology, dieselparticulate filter （DPF） serving as a most effective and practical method for eliminating PM inthe exhaust gas of the diesel vehicle is widely used in a diesel vehicle exhaust gas treatmentdevice, but a noble metal catalyst is required to be coated on the inner wall of the DPF, andthe noble metal resources are becoming scarce and expensive. LaMnO₃with perovskitestructure has higher catalytic activity because the A position part is replaced, thus has becomea research hot topic of the diesel vehicle catalyst.La0.8MnO3and La_0.8K_0.2MnO₃perovskite-type catalysts were prepared using the citricacid sol-gel method. TPO tests were performed to evaluate the catalyst activity for sootoxidation in three different gas atmosphere （10%O2,10%O2+2500ppmNO and10%O2+2500ppmNO2）. X-Ray diffraction （XRD）, Temperature Programmed Reduction（TPR）, Temperature Programmed Desorption （TPD）, X-ray Photoelectron （XPS）, In-situDiffuse Fourier Transorm Infrared Spectroscopy （In-situ DRIFTS） are used to study thecorrelation between catalyst features and soot oxidation activity.Through study, the following main conclusions can be drawn:1) LaMnO₃andLa_0.8K_0.2MnO₃perovskite catalysts are prepared by a citric acid complexing method; dopingof K+to replace La3+can cause the local charge imbalance, and can cause the expansion ofunit cells and the increase of oxygen vacancies at the same time, thereby facilitating theadsorption, activation and migration of gaseous oxygen on the catalyst surface; by using theLaMnO₃and La_0.8K_0.2MnO₃perovskite catalysts in10%O2gas atmosphere, the ignitiontemperature of soot decrease by103°C and125°C, respectively; and the content of oxygenweakly adsorbed on the surface is closely related to the catalytic activity and the deepoxidation of the soot; and2) the partial oxidation of NO to form NO2can promote thecombustion of the soot, and can also promote the generation of reactive oxygen; becauseLa_0.8K_0.2MnO₃has more oxygen vacancies than LaMnO₃and NO and O2have a similarelectron structure, NO is easily adsorbed by the oxygen vacancies of the catalyst and exists inthe form of adsorption, thus weakening the interaction between lattice oxygen and metal ions, promoting the overflow and the conversion of partial lattice oxygen to reactive oxygen, andpromoting the circulated regeneration of the oxygen vacancies. In NO+O2gas atmosphere,La_0.8K_0.2MnO₃has more significant activity in catalyzing the soot.