Combustion Synthesis Of Mixed Metal Oxides Catalysts For Selective Catalytic Reduction

Vehicle emissions consist approximately 1/3 of the total NO_x emission in China mainland.With the motor vehicle emission regulations becoming more and more stringent,performance requirements for automotive catalyst come mainly from two aspects:diesel engine cold starting and idling exhaust temperature is low,usually below 250 deg C;the actual temperature field in the reactor of catalyst is not uniform,the high temperature region will be from 430 deg C to 530 deg C;DPF regeneration will also produce high temperature exhaust.This requires that the catalyst has good performance at both low temperature and high temperature.This paper used the catalyst solution combustion method,in turn supported manganese element and erbium element in vanadium catalysts,developed a compound metal oxide catalyst for wide temperature window,and tested the properties and physicochemical characterization.The main contents of this paper are as follows:?1?Effect of doping manganese on the performance of catalyst and its physical and chemical characterizationTiV_0.1Ox and a series of TiV_0.1Mn_rOx?r=0.05,0.1,0.15?catalysts were prepared by solution combustion method.The performance results show that the introduction of manganese element can effectively improve the low temperature activity of the catalyst,but also reduce its high temperature activity.When r=0.1,the performance of TiV_0.1Mn_0.1O_x catalyst is the best,and the activity and selectivity of the catalyst is more than 80%between 190 and 440 deg C.BET characterization showed that there was no apparent surface area,pore volume and pore size change.The TiO₂ diffraction peaks were found in the XRD spectra,indicating that the active components were highly dispersed on the surface.The NH₃-TPD curve showed that four kinds of catalyst surface acid content are similar,with the increase of Mn content,the distribution to the low concentration of acid.The TEM images show that some of the catalysts are sintered,but the pore structure is rich.?2?Effect of doping erbium on the performance of catalyst and its physical and chemical characterizationA series of TiV_0.1Mn_0.01Er_mO_x?m=0.005,0.01,0.015,0.02?catalysts were prepared by solution combustion method.The performance shows that proper erbium element load not only can improve the low temperature performance,but also can improve the high temperature performance,while more erbium elements will only enhance the high temperature performance,but lower the low temperature performance.The optimal TiV_0.1Mn_0.01Er_0.01O_x catalyst has an active temperature window from 160deg C to 470 deg C.The BET characterization showed that the specific surface area increased with the addition of Er element.The TiO₂ diffraction peaks were found in the XRD spectra,indicating that the active components showed no definite shape distribution on the surface of the carrier.The NH₃-TPD curve showed that TiV_0.1Mn_0.01Er_0.01O_x is greater than the total acidity of TiV_0.1Mn_0.1O_x catalyst in the entire temperature distribution was also higher than that of TiV_0.1Mn_0.1O_x catalyst.The TEM images show that pore structure is rich.?3?SCR reaction mechanism over TiV_0.1Mn_0.01Er_0.01O_x catalystIn situ DRIFTS method was applied to the study on the mechanism of TiV_0.1Mn_0.01Er_0.01O_x catalyst.Results showed The catalyst surface is rich in Bronsted acid sites and Lewis acid sites,NH₃ adsorption formation of NH₄⁺and coordinated NH₃,the Lewis locus was higher,play a leading role;NO on the surface of the catalyst while the formation of monodentate,bidentate and Bridge nitrate,the nitrate content of three kinds of similar,participate in the SCR reaction in this paper;that is NH₃ activated and the gas phase reaction of NO,but also NO oxidized to nitrate in the reaction.Therefore,it is reasonable to say that not only activated NH₃ reacted with NO gas phase,but also nitrate formed by absorbed NO participated in the reaction,that occur at the same time Eley-Rideal reaction mechanism and Langmuir-Hinshelwood reaction mechanism over TiV_0.1Mn_0.01Er_0.01O_x catalyst.