The Toluene Catalytic Oxidation Over Mn-Ce Mixed Oxides Synthesized Using Metal-organic Framework As Sacrificial Template

As the key precursor of O₃ and PM_2.5 pollutants,Volatile Organic Compounds?VOCs?have a serious impact on human health and environment.Among all the mainstream technologies,catalytic combustion is widely used for VOCs treatment in our country.Mn-Ce mixed oxides have attracted much attention for VOCs catalytic combustion due to its excellent characteristics of CeO₂ and transition metal.Using toluene as target pollutant,this paper focused on controllable synthesis of MnO_x-CeO₂?CeO₂-MnO_x?mixed oxides by using MOFs sacrificial template method.The catalysts exhibited well-dispersed active site,controllable morphology and well-dispersed nano particles.The effect of calcination temperature on MOFs sacrificial template was investigated.The influence of mass fraction of active components of catalysts on their activity for toluene catalytic oxidation was also studied.Moreover,research of the structure-activity relationship between mixed oxides catalysts and toluene oxidation was conducted.In C hapter two,CeBTC template was prepared using self-assembly method.And a serious of MnO_x-CeO₂ mixed oxides?Mn%=1%,3%,5%,8%,10%?was synthesized by using MOFs sacrificial template method.The effect of calcination temperature on MOFs sacrificial template was investigated.The influence of mass fraction on the reaction of toluene catalytic oxidation was also studied.Results showed that the optimal calcination temperature of Ce BTC was 300 ^oC.The as-synthesis catalysts exhibited well-dispersed active site,controllable morphology and well-dispersed nano particles.Results of characterization including Raman,XPS and H₂-TPR revealed that the interaction between Mn species and CeO₂ could weaken Ce-O chemical bond and further enhanced the reducibility of surface oxygen.When Mn mass fraction rea ched 5%,which content was close to monolayer dispersion threshold,the catalyst showed the highest catalytic activity.And threshold effect existed in the catalytic system.In C hapter three,MnBTC template was prepared using self-assembly method.And a serious of CeO₂-MnO_x mixed oxides?Ce%=1%,3%,5%,8%,10%?was synthesized by using MOFs sacrificial template method.The effect of calcination temperature on MOFs sacrificial template was investigated.The influence of mass fraction on the reaction of tolue ne catalytic oxidation was also studied.Results showed that the optimal calcination temperature of MnBTC was 300 ^oC.The as-synthesis catalysts exhibited well-dispersed active site,controllable morphology and well-dispersed nano particles.Results of characterization revealed that the interaction between Ce species and MnO _x could weaken Mn-O chemical bond and further enhanced the reducibility of surface oxygen.When Ce mass fraction reached3%,which content was close to monolayer dispersion threshold,the catalyst showed the highest catalytic activity.And threshold effect existed in the catalytic system.In C hapter four,the characterization of active components were conducted using XPS and UV-vis,to explain the threshold effect in toluene oxidation and to illuminate structure-activity relationship in the system.Results showed that,in MnO _x-CeO₂ system,the monolayer dispersion threshold of Mn was 6.2%,while in CeO₂-MnO_x system,the monolayer dispersion threshold of Ce was 3.2%.The strong interaction between supporter and surface compound could be demonstrated by embedding model.And the embedding model could be used for explaining the essential mechanism of catalytic oxidation,in which the correlation of oxygen-related parameters and electron transfer was elaborated.