Study On Catalystswith Molecular Sieve As Support For Selective Catalytic Reduction Of NO_x Under Lean-burn Conditions

With the fast development of global automobile industry, the pollution caused by automobile exhaust has become more and more severe, especially NOx pollution, so people pay more attention to decrease the emission of NOx. The traditional three-way catalyst would be ineffective under lean-burn condition, thus a new type of catalyst for automobile exhaust purification under lean-burn condition is urgently needed to be developed .In this thesis, a series of (Fe-)Ag/SAPO-11 and (Fe-)Cu/SAPO-11 catalysts have been prepared by wet impregnation and co-impregnation methods, using silicoaluminophosphates SAPO-11 as support due to its proper pore structure, mid-strong acid site, good thermal and hydrothermal stability. By combining the catalytic performances and the results of catalysts characterizations, the catalysts activity and structure as well as the reactive mechanism have been investigated.The results from activity evaluation show that the catalysts using SAPO-11 as support have a good reactivity. In the present of the vapor gas, the NO conversion upon 3wt%Cu/SAPO-ll, 5wt%Ag/SAPO-ll, 3wt%Cu-7wt%Fe/SAPO-ll and Fe/SAPO-11 catalysts is 68.0%, 67.8% , 58.9%and 40% respectively under thereactive temperature of 350℃, and CsHe is almost converted to CO and CO2, whilethe Fe catalyst show lower catalytic activity, partly due to the replacement of Fe ion of Al ion located in the framework of SAPO-11, this could lead to the decrease of the amount of Bronsted acid from SAPO-11 support to some extent. Hence the Fe/SAPO-11 catalyst has a poorer reactive activity compared with Ag(Cu)/SAPO-11 catalyst.The results from XRD and BET characterizations of the above catalysts testify that, after the active species are loaded into the SAPO-11 support, the crystallization and framework of SAPO-1 1 support could be partly influenced with the decreasing inthe order of Fe/SAPO-11>Cu-Fe/SAPO-11>Cu/SAPO-11 Ag/SAPO-11, which iscorresponding to the results of catalysts active evaluation. The XPS results illustrate that Ag(Cu)/SAPO-11 catalyst possess the bi -functional property, which the Bronsted acidic sites from SAPO-11 support is responsible for the activation of NO, and Ag(Cu) component is responsible for the catalytic reduction of the active NO by C3H6, and theactive site could be denoted as Ag - O - O -Si and Cu - O - Sirespectively on Ag/SAPO-11 and Cu/SAPO-11 catalysts. Additionally the reactive mechanism could also be deduced by XPS characteristic results.