Study On The New And Efficient Catalysts With Wide Operating Temperature For Selective Catalytic Reduction Of NO

In recent years,with the development of industry and automobile industry,nitrogen oxides?NOx?pollution,which is one of atmospheric pollutants,has become more and more serious.The elimination of nitrogen oxides has become a problem that needs to be solved as humans attach importance to environmental pollution.Selective catalytic reduction of NOx by hydrocarbons has attracted widespread attention as one of the most promising methods to remove NOx.Due to its abundant raw materials,convenient storage and transportation,and high reactivity among many hydrocarbon reductants,Propylene?C₃H₆?has become one of the research hotspots for the selective catalytic reduction of hydrocarbons.Molecular sieve catalysts have the advantages of high catalytic activity,large area for comparison,good thermal stability,and relatively long service life,which have attracted extensive attention of researchers.Therefore,this article aims to improve the low-temperature activity of the catalyst and widen the operating temperature window of the catalyst by designing and synthesizing novel high-efficiency wide-temperature molecular sieve catalysts.In this paper,C₃H₆ was used as the reducing agent to remove NOx under the conditions of excess oxygen.A Cu-based three-way molecular sieve catalyst and a Mn-based three-way molecular sieve catalyst were designed and synthesized and compared the different synthetic methods for the influence of the molecular sieve catalyst.At the same time,the structure of the catalyst was characterized by XRD,BET,SEM,TPD,TPR.Specifically include the followings:?1?The catalytic performance of the molecular sieve catalyst was regulated by supporting active components and auxiliaries.The Cu-based three-way molecular sieve catalyst was prepared by impregnation method.Its catalytic performance in selective catalytic reduction of NO with C₃H₆ was investigated.The results showed that the7%Cu-3%Zr-3%Ag/ZSM-5 molecular sieve catalyst has good catalytic performance.The NO conversion at 300°C reaches 92%.The operating temperature window T₅₀0 is255-500?,which is comparable to 7%Cu-3%Zr/ZSM-5 catalyst,NO conversion increased by 12%,operating temperature window widened 7?,compared with 7%Cu/ZSM-5 catalyst,NO conversion increased by 19%,operating temperature window widened 60?.The XRD characterization results showed that the metal oxide on the catalyst was in an amorphous state,which was helpful to stabilize the structure of the catalyst and the ZSM-5 zeolite catalyst also maintained better micropore characteristics.The BET characterization results showed that the specific surface area,average pore size,and pore volume of the catalyst gradually decreased with the increase of the doping content of the active components and additives.The SEM results showed that the metal loading affected the physical structure of the catalyst.After the metal loading,the catalyst surface was loaded with metal particles,the crystal was damaged,and the relative crystallinity decreased.The TPD results indicated that that the introduction of Zr and Ag were beneficial to increase the acidity of the catalyst and increase the weak acid and moderate acid sites of the catalyst.The TPR results showed the introduction of Zr can also increase the interaction between the active component,additive and support.The introduction of Ag is not only beneficial to the low-temperature reduction peak of H₂-TPR,but also to the low-temperature activity of the catalyst.2)The Mn-based three-way molecular sieve catalyst was prepared by impregnation method and the amount of active components and additives were optimized,its catalytic performance in the selective catalytic reduction of NO with C₃H₆ was investigated.The catalytic performance evaluation results showed that 20%Mn-7%La-5%Ce/ZSM-5 and20%Mn-7%Ce-1%Zr/ZSM-5 molecular sieve catalysts had good catalytic performance.The NO conversion of 20%Mn-7%La-5%Ce/ZSM-5 at an optimum activation temperature of 200°C was 96%,and the operating temperature window T₅₀ was 150-390°C.The NO conversion of 20%Mn-7%Ce-1%Zr/ZSM-5 at the optimal reaction temperature of 200°C was 87%,and the operating temperature window T₅₀ was 150-380°C.The catalytic performance of the 20%Mn-7%La-5%Ce/ZSM-5 molecular sieve catalyst was better than that of 20%Mn-7%Ce-1%Zr/ZSM-5,but all were Mn-based three-way molecular sieve catalysts with excellent NO removal.The XRD results indicated that the metal oxide on the catalyst was amorphous.The BET results showed that the specific surface area,average pore diameter,and pore volume of the catalyst decrease with the aggregation of fine particles of the metal oxide.The SEM results showed that the metal oxide fine particles formed by the active components and additives accumulated on the surface of catalyst and innsided the tunnel.The TPD results indicated that La,Ce and Zr could both enhance the weak and moderate acid sites of the catalyst,thereby increasing the amount of weak acid and medium-strong acid and also moved the medium-strong acid center to low temperatures,further increasing the weak acid sites of the catalyst.The TPR results indicated that the La accelerates the peak temperature of the H₂-TPR reduction of the catalyst to the high temperature region,which enhances the interaction between the active component,auxiliary agent and support,and contributed to the stability of the catalyst structure.Ce shiftd the peak temperature of the H₂-TPR reduction of the catalyst toward the low temperature region,enhanced the redox ability of the catalyst,and increased its catalytic activity.Zr could not only enhance the interaction between the active components,auxiliaries and carriers,but also increase the redox ability of the catalyst.?3?The Cu-Zr-Ag/ZSM-5 molecular sieve catalyst was prepared by sol-gel method,and its catalytic performance in selective catalytic reduction of NO with C₃H₆ was investigated.The results of catalytic performance evaluation showed that compared with the 7%Cu-3%Zr-3%Ag/ZSM-5 catalyst prepared by impregnation method,the best formula of Cu-Zr-Ag/ZSM-5 molecular sieve catalyst prepared by sol-gel method was10%Cu-1%Zr-1%Ag/ZSM-5.The NO conversion of the 10%Cu-1%Zr-1%Ag/ZSM-5molecular sieve catalyst prepared by sol-gel method at an optimum activation temperature of 300°C is 88%,and its operating temperature window T₅₀0 is 265-500°C.Compared to the7%Cu-3%Zr-3%Ag/ZSM-5 catalyst prepared by the impregnation method,the NO conversion rate is reduced by 4%,and the operating temperature window is reduced by10°C Although the NO conversion rate was slightly reduced,the loadings of the promoters Zr and Ag were both reduced by 2%,and the catalyst cost was correspondingly reduced,which had important guiding significance for the industrial application of the catalyst.?4?The Mn-La-Ce/ZSM-5 moleculr sieve catalyst was prepared by sol-gel method,and its catalytic performance in selective catalytic reduction of NO with C₃H₆ was investigated.The results of catalytic performance evaluation showed that the optimal formula of Mn-La-Ce/ZSM-5 molecular sieve catalyst prepared by sol-gel method is25%Mn-10%La-5%Ce/ZSM-5.The NO conversion of the 10%Cu-1%Zr-1%Ag/ZSM-5molecular sieve catalyst prepared by sol-gel method at the optimal reaction temperature reached 98%,and the operating temperature window T₅₀ is 150-390°C.Compared to the20%Mn-7%La-5%Ce/ZSM-5 catalyst prepared by the impregnation method,the NO conversion is increased by 2%,and the operating temperature window remained unchanged.Although the loading of the Mn and La increased,the catalysts had improved activity in low temperature areas,which can provide basic data for the study of the low temperature activity of the catalyst.