Effect Of Metal Doping For Performance Of NO Oxidation Over Mn And Cr Based Supported Catalyst

In the lean burn automobile exhaust catalytic purification technology, NO catalytic oxidation catalyst plays an important role. Increasing the proportion of NO2 in lean-burn vehicles exhaust helps to improve activity of selective catalytic Reduction(SCR) catalyst at low temperature, adsorption properties of NOx storage reduction(NSR) catalyst, and continuous regeneration of diesel particulate filters( DPF) and particle oxidation catalyst( POC).The main contents of this paper:(1) Investigate the preparation conditions and performance of Al2O3-TiO2 catalyst support. The Al2O3- TiO2 is prepared in different coating ratio, pH value and coated times by the sol-gel method. Then, the loading10% Mn catalyst is characterized by means of catalytic activity evaluation;(2)Investigate the performance of A-Mn/ Al2O3-TiO2 catalysts(A=Ce, Co, Cu, Fe). The best metal doped is selected to study the doping ratio, dipping sequence of the active ingredient and sulfur resistance of the catalyst;(3) Investigate the performance of xCr/Al2O3-TiO2 catalysts(x=5~20%C) and select the best catalyst to study the performance of B-Cr/ Al2O3-TiO2 catalysts(B=Ce, Co, Mn). The best metal doped is selected to study the calcination temperature and sulfur resistance of the catalyst. The main experimental results are as follows:1) The results indicated that the catalyst had good activity(the rate of NO conversion is 63%) when 1/16 TiO2 covered and pH=3. The TiO2 formed relatively thin layer on the surface of Al2O3 not only improves the thermal stability of the support, but also contributes to the catalytic oxidation of NO. When the cladding is two the surface area of catalyst support increased significantly from197.97 m2·g-1 to237.41 m2·g-1. It may be that the addition of double amount of PEG contributes to theaccumulation and formation of new holes. More binding sites for the metal active components are formed to enhance the catalytic activity of the catalyst.2) In a series of metal-doped catalyst(Ce, Co, Cu, Fe-Mn/Al2O3-TiO2), Co doping makes the low-temperature activity of the catalyst to increase and contribute to the active ingredient MnOx dispersed on the catalyst surface. XPS results show that Mn presents on the surface of Mn/Al2O3-TiO2 catalyst mainly in the form of Mn3+. After Co doping, the content of Mn3+ decline and Mn4+ risen. The order of performance of catalyst are positively correlated by ratio of the surface chemisorbed oxygen and Mn4+.Thus indicating that MnO2 and surface chemisorbed oxygen may plays the major role in the reaction of NO oxidation for Co-Mn/Al2O3-TiO2 catalyst.3) In a series of different Cr loading of Cr/Al2O3-TiO2 catalyst, the activity of Cr/Al2O3-TiO2 catalysts corresponds to the order of 10%> 15%> 20%> 5%. In the whole temperature range of reaction, the activity of B-Cr/Al2O3-TiO2 catalyst corresponds to the order of Co-Cr > Cr > Ce-Cr > Mn-Cr. The activity of catalyst with Co doping has been significantly improved. The activity of Co-Cr/Al2O3-TiO2 catalyst activity firstly increase and then decrease with the grow of calcination temperature. The XPS results show that Cr presents on the surface of Co-Cr/Al2O3-TiO2 catalyst mainly in the form of Cr6+with the increase of calcination temperature(450~550 ℃). And the performance of presulfided catalyst decrease with the amount of Cr6+ decrease. The results show that the Cr6+ may plays the major role in the reaction of NO oxidation for Co-Cr/Al2O3-TiO2 catalyst.