Study On Catalytic Reduction Of NO_x With Metal Modified Zeolites

With the rapid development of China's economy and society,environmental pollution caused by pollutants such as nitrogen oxides?NOx?emitted from fixed sources and moving sources is becoming more and more serious.In recent years,the processing methods and technologies for nitrogen oxides have received increasing attention.At present,regarding the treatment of NOx in automotive exhaust gas,the most commonly used method is NH3-Selective Catalytic Reduction?NH₃-SCR?,and the catalyst is one of the key areas of SCR technology research and research and development of new SCR.Catalysts have broad application prospects.In this paper,single metal Cu and single metal Co modified SAPO-34 zeolite catalysts were prepared by impregnation and electroless plating.The catalytic properties of the modified catalysts prepared by these two methods were compared.SEM,BET and XRD were used to characterize the catalysts.Bimetal Cu-Co and polymetallic modified SAPO-34 zeolite catalysts were prepared by impregnation,and the difference and relation between mono metal,bimetallic and polymetallic catalysts were compared.At 400?,propylene gas was used to test the poisoning of SAPO-34molecular sieve catalyst.The catalytic performance of the SAPO-34 molecular sieve catalyst was observed under moderate HC conditions,and its reaction mechanism was analyzed.The main results are as follows:?1?single metal Cu and single metal Co modified SAPO-34 zeolite catalysts were prepared by impregnation and electroless plating.The results showed that the catalytic activity of the metal modified catalyst prepared by the impregnation method was more stable than the metal modified catalyst prepared by the electroless plating method.The Cu modified SAPO-34 zeolite catalyst prepared by impregnation has a wider temperature range than the Co modified SAPO-34 molecular sieve catalyst when the conversion efficiency of NO is higher than 80%.By the SEM characterization of the catalyst,it is found that the white particles on the surface of the modified catalyst prepared by electroless plating are irregular and more than the catalysts prepared by the impregnation method,because the catalysts prepared by the electroless plating process are not as stable as the catalysts prepared by the impregnation method,so these white particles may be accelerating.The catalyst BET found that the surface area and the pore volume of the catalyst prepared by the electroless plating method were smaller than that of the catalyst prepared by the impregnation method.It may be that the electroless plating process took place in the process of plating metal in the catalyst,and the generated material blocked the micropore volume of the catalyst.?2?the catalytic activity of Cu-Co bimetallic modified SAPO-34 molecular sieve catalyst in the SCR catalytic system shows that after the Cu modified molecular sieve catalyst is doped with Co,the ratio of Cu to Co is different,and the performance of the catalyst is very different.The catalytic performance of the Cu:Co=3:1 modified molecular sieve catalyst is better in the bimetallic modification.Yes.?3?after adding third metals in Cu:Co=3:1,the temperature window of the polymetallic modified catalyst was observed.It was found that the catalytic performance of the catalyst added with different third metals was very different.In this experiment,it is determined that M is Fe in Cu-Co-M modified molecular sieve catalyst,and this kind of polymetallic modified catalyst is more ideal than other multi metal modified catalysts.?4?by analyzing and comparing the characterization of BET,XRD,and TPD of single metal,bimetallic and polymetallic modified SAPO-34 zeolite catalysts,it was found that the specific surface area of the catalyst decreased,the strength and concentration of the acid sites decreased,and the specific surface area and acid position of the catalyst for each metal modified SAPO-34 molecular sieve catalyst.And the degree of crystallization will affect the catalytic activity of metal modified SAPO-34 zeolite catalyst.?5?after HC poisoning test,it was found that the conversion efficiency of metal modified SAPO-34 zeolite NO decreased by about 20%after 400 degree propylene poisoning.The effects of propylene gas on the poisoning of metal modified SAPO-34zeolite catalyst can be analyzed by means of SEM,TPD,BET and other characterizations.It is possible that the propylene gas is involved in the catalytic reaction and produces the product covering the active site of the catalyst,which reduces the specific surface area and leads to the reduction of the conversion efficiency of the catalyst NO.