The Effect Mechanism Of SO₂ And H₂O On Lanthanide Based Perovskite Catalysts For Simultaneous Catalytic Oxidation Of NO And Toluene

Diesel engines are widely used in various construction machinery and vehicles because of their strong power,high efficiency and energy saving.However,pollutants such as nitrogen oxides（NO_x）and volatile organic compounds（VOCs）emitted by diesel engines cause environmental problems such as haze and ground-level ozone,which have attracted widespread attention from the society.Therefore,it is particularly important to develop the corresponding processing technology.The technical route of Diesel Oxidation Catalysis（DOC）+Diesel Particulate Filter（DPF）+Selective Catalytic Reduction（NH₃-SCR）is an effective purification method for diesel engine exhaust,and DOC technology as a key part can not only convert low-concentration VOCs into CO₂and H₂O,but the oxidation of NO to NO₂is beneficial to the NH₃-SCR reaction.La FeO₃perovskite composite oxide has become a very potential oxidation catalyst due to low cost,stable structure and excellent catalytic activity.However,La FeO₃perovskite catalysts prepared by the traditional method have low specific surface area,which seriously affects the number and active strength of surface active centers,resulting in poor catalytic activity.In addition,SO₂and H₂O have a worse impact on the catalytic performance of lanthanide-based perovskite catalysts,and the effect mechanism of them is unclear.Therefore,the study of the effect mechanism of SO₂and H₂O on the performance of lanthanide-based perovskite catalysts in the catalytic oxidation of NO and toluene has guiding significance to further improving the catalytic performance of the catalysts for the simultaneous catalytic oxidation of NO and toluene.Based on the above problems,this paper prepared a series of A-site doping of different transition metal elements of cerium（Ce）,cobalt（Co）,copper（Cu）and manganese（Mn）modified lanthanide-based perovskites via a citrate sol-gel method using hard template.The catalytic performance of the lanthanum-iron perovskite catalysts for the simultaneous catalytic oxidation of NO and toluene was studied,the interaction mechanism of NO and toluene oxidation was revealed,and the effect mechanism of SO₂and H₂O on the performance of the simultaneous oxidation of NO and toluene was explored.The main conclusions of the paper are as follows:（1）A series of A-site substituted La_0.65X_0.35FeO₃（X=Cu,Ce,Co,Mn）catalysts were synthesized via a sol-gel method using KIT-6 as hard template to investigate the effect mechanism of SO₂on the activity of simultaneous catalytic oxidation of NO and toluene.The results show that the inhibitive effect of H₂O on the catalytic activity of La_0.65X_0.35FeO₃（X=Cu,Ce,Co,Mn）catalysts for the simultaneous catalysis of NO and toluene is due the fact that SO₂is easy to oxidize with the metal sites to form sulfates covering the surface of catalysts,resulting in the active sites are reduced and the pore structure is blocked,thereby inhibiting the oxidation reaction of NO and toluene.However,the A-site doping modification of Co shows excellent catalytic performance(NO conversion is 60.2%at 300℃,T₉₀is 220℃),which may be due to the synergistic effect between Co and Fe that makes the adsorption capacity of SO₂on the catalysts surface worse,and weakening sulfation.（2）Based on the optimization of the preliminary experiment,a series of A-site substituted La_1-xCo_xFeO₃（x=0-0.5）perovskite-type catalysts with three-dimensional porous structure were synthesized via a sol-gel method using KIT-6 as hard template to investigate the reaction mechanism of simultaneous catalytic oxidation of NO and toluene,and the effect mechanism of H₂O,and reveal the reaction mechanism of simultaneous catalytic oxidation of NO and toluene as well as the inhibitive effect of H₂O on reaction.The results demonstrated that different amounts of Co doping can induce the structural distortion,promote the specific surface area,enhance redox property and produce abundant reactive oxygen species,which promotes the catalytic activities for simultaneous catalytic oxidation of NO and toluene in the presence of H₂O.The reaction pathway of simultaneous catalytic oxidation of NO and toluene follows that:Firstly,gaseous NO is absorbed on the surface of La_1-xCo_xFeO₃perovskite catalysts,and then reacts with surface adsorbed oxygen to form NO₂.Meanwhile,absorbed toluene is oxidized by lattice oxygen to form intermediate species which finally completely oxidized into CO₂and H₂O.In addition,NO and toluene have mutual promoted effects in the reaction system,which because adsorbed NO could react with co-adsorbed toluene to form N₂and CO₂.However,H₂O has an inhibitory effect on the catalytic activity of the La_1-xCo_xFeO₃perovskite catalyst for simultaneous catalysis of NO and toluene.This is because H₂O can react directly with oxygen vacancies to generate hydroxyl groups and compete with NO and toluene for adsorption,affected the activation and activation of O₂,decreasing the catalytic activity for the simultaneous catalytic oxidation of NO and toluene.