| Volatile organic compounds(VOCs)are one of the important precursors of atmospheric compound pollution,and they are hazardous for the environment and human health.Therefore,the removal of VOCs plays a key role in solving air pollution.Catalytic oxidation method has attracted much attention in the field of VOCs removal because of its high efficiency and no secondary pollution.Mn-based catalysts have the advantages of multivalence,strong electron transfer ability and good redox performance,which show good catalytic performance in the field of VOCs elimination and cause extensive research.However,how to further improve the catalytic performance of Mn-based catalysts and clarify the mechanism of its oxidation of VOCs are also a key issue that needs to be resolved in the current field of VOCs elimination.Mn-based catalysts as the research object was used in this thesis.The surface structure and active sites of the Mn-based catalysts were adjusted by modifying and doping with other metals to optimize its catalytic activity;the relationship between the structure and catalytic performance of the Mn-based catalysts was systematically studied;the consumption and replenishment of oxygen species in toluene oxidation were deeply investigated,and the reaction pathway of toluene oxidation was explored by in-situ DRIFTS,then the understanding of the reaction mechanism of toluene oxidation with Mn-based catalysts was deepened.The specific research content and results are as follows:(1)The nanosheet MnO2 catalyst was modified by tetramethylammonium hydroxide(TMAOH)and tetrapropylammonium hydroxide(TPAOH)to study the effect of MnO2 modified by TM(P)AOH on its structure and catalytic performance.It could be found that the TM(P)AOH modification significantly broadened the pore size distribution range of MnO2,increased the pore volume,specific surface area and surface roughness,and also weakened the interaction force between Mn and O,which was beneficial to improve its catalytic activity of toluene oxidation.Among them,MnO2 modified by TPAOH exhibited the best catalytic activity,with T50 and T90 of 207 and 223℃,respectively.(2)Doping metal Cu2+ into nanosheet MnO2 could adjust its low-temperature redox ability and catalytic activity of toluene oxidation.An appropriate amount of Cu2+(≤0.10:1)doping could improve the concentration of oxygen vacancy and the low-temperature redox ability,thereby enhancing the activity of MnO2 in the catalytic oxidation of toluene.Among them,when the doping amount of Cu2+was 0.10:1,the MnO2 catalyst exhibited the highest catalytic activity,with the T50 and T90 of 200 and 216℃,respectively.Although the higher Cu2+doping amount(0.12:1)further increased the concentration of oxygen vacancy on MnO2,part of nanosheets of MnO2 was aggregated and their redox ability was reduced,which in turn led to a decrease in their catalytic activity of toluene oxidation.(3)Based on the reaction mechanism that oxygen species on MnO2 could participate in the toluene oxidation(MvK mechanism),alkaline(earth)metal(Ca2+,Na+)doping was used to adjust the amount of active oxygen species on the nanosheet MnO2,and its catalytic performance of toluene oxidation was investigated.It could be found that Ca2+ and Na+ doping increased the amount of active oxygen species on MnO2.Compared with undoped MnO2(6.3 mmol/g),the active oxygen species amount of MnO2 doped with Na+and Ca2+(according to H2-TPR quantitative results)increased to 8.9 and 9.7 mmol/g,respectively.The T50 of MnO2 was reduced by 13℃ after Na+doping,and the T50 was reduced by 24℃ after Ca2+doping.(4)The spinel CoMn2O4 catalyst and the oxide Co3O4/MnOx catalyst were prepared by the sol-gel method and the impregnation method,respectively,and the reasons for the difference in the catalytic performance between two catalysts were inversigated.It could be found that CoMn2O4 had higher catalytic activity than Co3O4/MnOx oxide,with T50 and T90 of 202 and 210℃,respectively.This was mainly due to the abundant defects,large specific surface area and high mobility of oxygen species in CoMn2O4.In situ mass spectrometry studies showed that the surface lattice oxygen on the CoMn2O4 catalyst first reacted with toluene,and then gaseous oxygen was added to the bulk lattice.The migration rate of lattice oxygen from bulk to the surface increaseed with the reaction temperature(200-250℃),thereby accelerating the catalytic reaction,while the oxide Co3O4/MnOx activated gaseous oxygen only on the catalyst surface at relatively high temperature.(5)Based on the formation of defects in the CoMn2O4 catalyst and the rapid migration of oxygen species,the CoMn2O4 supported Pt catalyst was prepared by the in-situ liquid phase reduction method.And the effect of CoMn2O4 supported Pt on the adsorption-activation of reactants and the catalytic performance of toluene oxidation was systematically studied.It could be found that loading Pt increased the adsorption sites of toluene on CoMn2O4,enhanced the interaction between CoMn2O4 and toluene,and promoted the activation of gaseous oxygen and the mobility of surface lattice oxygen,thereby significantly improving the catalytic performance of toluene oxidation.Compared with CoMn2O4,the T50 and T90 of the PtCoMn2O4 catalyst were reduced by 69 and 61℃,respectively. |
