Mn-Fe/V-W/CeO₂/TiO₂ Composite Catalyst Preparation And Denitration Performance

Nitrogen oxide NO_x ?NO, NO₂, N₂O? is one of the main atmospheric pollutants, through physical and chemical action, can lead to a series of environmental problems,such as photochemical smog, acid rain and the hole in the ozone layer and so on, intensify the greenhouse effect, and cause great harm for human health, environment and production activities.Now selective catalytic reduction ?SCR? is a mature and efficient one of the main denitration technology, its core technology is the catalyst.In recent years, for ammonia selective catalytic reduction of NOx ?NH₃-SCR? reaction at low temperature, composite catalysts which exhibit excellent catalytic activity get extensive attention of the researchers.A series of TiO₂-supported manganese oxide with different transition metal oxides?Ce?Fe?V?Cu? catalysts were prepared by ultrasonic impregnation method in this experiment and were evaluated for the selective catalytic reduction of NO with NH₃.Results show that in contrast to the V-Mn-Ce/TiO₂ and Cu-Mn-Ce/TiO₂ catalyst, denitration performance of Fe-Mn-Ce/TiO₂ catalyst whose denitration rate is above 70% is better betwween 150? and 400?. Catalysts were characterized by BET?NH₃-TPD?H₂-TPR?XRD?SEM and XPS, then the results showed that the bigger the specific surface area of the catalyst, the bigger the stripping peak area of catalyst NH₃-TPD and the more the number of' stripping peak. the higher the activity; the active component on the surface of the catalyst exist in the form of particles, particles on the surface of the catalyst is more small and well-distributed , the denitration activity is relatively high.The presence form of Mn element on the surface of the catalyst has the great influence on the denitration performance.when Mn content of high valence state in the catalyst increases, the denitration performance will improve accordingly.By orthogonal design experimental, on the basis of the highest active of Fe?0.1?-Mn-Ce/TiO₂ catalyst, the content of V2O5 , WO₃, ?Mn/Ce/Fe? and the effect of calcination temperature were investigated.Through the denitration activity and specific surface area test, the optimal formula of compound catalysts and experimental conditions were selected: the content of V₂O₅ is 1%;the content of WO₃ is 10%; the content of Mn-Ce-Fe were 0.03mol,0.00525mol,0.0075mol; Calcination temperature is 400?. Composite catalyst was prepared in the best experimental conditions ,whose denitration activity is around 90%between 150? and 300?. Catalysts were characterized by BET, NH₃-TPD, H₂, TPR, XRD,SEM, XPS, and the study found that the specific surface area of the catalyst is 52.3m2/g and is the largest in the same series catalyst, its activity is the highest.The intensity of NH₃-TPD stripping peak is the highest and the quantity of stripping peak is the most, stripping area is the largest and the quantity of acid is biggest. The intensity of H₂-TPR reduction peak is highest, the peak area is largest.Active component of catalyst has high dispersibility and evenly distuibuted and grain size is small and there is a certain porosity, these are beneficial to adsorption of NH₃ and promote the catalytic reaction. The presence form of Mn element on the surface of the catalyst is mainly high valence state(Mn⁴⁺ and Mn³⁺).For denitration reaction at low temperature, Mn³⁺ is advantageous to the selectivity of SCR, and Mn⁴⁺ is advantageous to catalytic coversion of NOx and therefore Mn⁴⁺ and Mn³⁺ exist at the same time and are more conducive to raising the denitration activity.Surface vanadium species mainly exists in the form of V⁴⁺, and the ratio of V⁴⁺/V⁵⁺ is largest, thus improving on the activity of denitration. W⁶⁺ content on the surface is slightly higher than W⁵⁺ content, which enhance the B acid. Fe²⁺content on the surface is higher than Fe³⁺ content, Fe²⁺ exists in the form of FeO, while FeO is p-type semiconductor, hole conduction and this is ad-vantageous to adsorption of oxygen and the catalytic reaction, thus enhancing on the activity of denitration.The majority of Ce⁴⁺ is more on the surface of the catalyst, conversion between Ce³⁺ and Ce⁴⁺ promotes the catalytic reaction.Surface lattice oxygen and chemical adsorption oxygen are participation in the redox reaction and promote the catalytic cycle, thus enhancing on the activity of denitration.