Preparation And Catalytic Performance Of M/Ti_1-xZr_xO₂/GE?M=Pt?Pd?Ru? DOC Catalyst

Diesel vehicles have low fuel consumption,high thermal efficiency and good stability,so they are widely used in transportation,mining industry and engineering machinery,and environmental problems caused by diesel vehicle exhaust emissions have also attracted attention.As an important part of the diesel vehicle exhaust gas treatment system,the catalytic oxidation device?DOC?of diesel vehicles can effectively oxidize carbon monoxide?CO?,hydrocarbons?HC?and nitrogen oxides?NOx?in the exhaust gas to CO₂,H₂O and NO₂.At present,most of the existing commercial diesel DOC catalysts are based on Pt/Al₂O₃ and Pt-Pd/ZrO₂-CeO₂-Al₂O₃catalysts,which can achieve high catalytic activity,but their low-temperature processing ability and sulfur resistance are generally low.In view of the low exhaust temperature of diesel vehicles,excessive incomplete HC during cold starts,and the high sulfur content of fuels in China,the new DOC catalyst needs to have the capability of rapid ignition at low temperatures and good sulfur resistance.As an effective anti-sulfur component,TiO₂ has been applied to the research of new automobile exhaust catalysts.However,TiO₂ has defects such as poor thermal stability and so on.ZrO₂ is a metal oxide that has both redox properties and acidity and alkalinity.Compounding it with TiO₂ can improve the specific surface area,thermal stability,and surface acidity and alkalinity of the composite.Graphene is a two-dimensional layered material with excellent physical and chemical properties.The surface of graphene obtained from the reduction of graphene oxide has defects and incompletely reduced oxygen-containing groups,which can be used as anchor points for metals or metal oxides and enhanced the interaction of graphene with metals or metal oxides.In this paper,graphene oxide?GO?is added as a functional additive to modify the ZrO₂ and TiO₂ composite oxide carrier.Subsequently,platinum group metals Pt,Pd and Ru with excellent oxidation performance are loaded.Designed to produce a new DOC catalyst M/Ti_1-xZr_xO₂/GE with high low temperature activity and good sulfur resistanceand?abbreviated as M/TxZyG;M stands for precious metals,M=Pt,Pd,Ru;T stands for TiO₂,Z stands for ZrO₂,G stands for GO,x/y stands for Ti/Zr feed molar ratio?.By systematically characterizing the microstructure and morphology of the catalyst,the interaction between the catalyst carrier and the active components and its effect on the DOC catalytic activity are explored.The main research contents are as follows:?1?The effect of catalyst preparation conditions on catalytic performance.First,taking CO oxidation as the target reaction,the effects of hydrothermal time,hydrothermal temperature and GO doping amount during the synthesis process of TxZyG composite carrier under the condition of fixed Ti/Zr=3/1 and Ru loading and calcination temperature of Ru/TxZyG catalyst on the performance of catalytic oxidation of CO.The optimal catalyst preparation conditions were as follows:carrier hydrothermal time 24 h,hydrothermal temperature 120?,GO doping amount 0.8wt.%,Ru loading 1.0 wt.%,and calcination temperature 400?.Subsequently,under the optimal preparation conditions,TxZyG composite oxide supports with different Ti/Zr feed ratios were synthesized and impregnated with the active component Ru to obtain Ru/TxZyG series catalyst?x/y=3/1,2/1 1/1 and 1/2?.Explore the effect of different molar ratios of Ti/Zr on CO and C₃H₈ oxidation activity.Ru/T1Z2G showed the best catalytic activity,achieving 50%CO and C₃H₈ conversion at 125 and 226?,and 90%CO conversion and C₃H₈ complete conversion at 274?and 440?,respectively.?2?The effect of precious metal components on catalytic performance.The TIZ2G carrier was prepared hydrothermally under optimal conditions,and the precious metal components Pt,Pd,Ru were impregnated separately to obtain M/T1Z2G series catalysts,and their effects on CO and C₃H₈ oxidation activity were investigated respectively.The overall oxidation activity of Pt/T1Z2G catalyst is the best.It achieves 50%and 90%CO conversion at 135 and 200 C,respectively,and converts 50%C₃H₈ at 216?,and the complete conversion of C₃H₈ at 460?.This is because Pt has the best dispersibility on the T1Z2G carrier,and the pore size is suitable,which is beneficial to the diffusion of the reactants CO and C₃H₈ and accelerates the reaction rate.?3?Research on the sulfur-resistant performance and stability of a series of M/T1Z2G?M=Pt,Pd,Ru?catalysts.The M/T1Z2G catalyst was synthesized by optimized preparation conditions,and the CO and C₃H₈ oxidation activities of the catalyst were investigated under SO₂ conditions.The M/T1Z2G catalyst showed good sulfur resistance.The CO activity decreased only slightly after 3 hours of passing 100ppm SO₂,which is due to the platinum group metal M interacts strongly with the carrier.Moreover,SO₂ greatly promotes the oxidation of C₃H₈.The possible reason is that SO₂forms new active sites at the interface between the precious metal and the carrier to promote C₃H₈ adsorption.At the same time,M/T1Z2G catalyst has good thermal stability,which could stated high catalytic activity after 12 hours of continuous reaction.