Ce-based Metal Oxide Catalysts Prepared Using MOF As Precursors For Catalytic Oxidation Of Toluene

Volatile organic compounds（VOCs）are common pollutants in the atmosphere and have serious harm to the environment and human body.How to remove VOCs is one of the research hotspots of air pollution prevention at present.Among many removal methods,catalytic oxidation is considered to be an effective method to treat VOCs because of its advantages such as low energy consumption and high efficiency.MOFs（metal organic frameworks）have a high specific surface area.The oxide catalysts formed by their pyrolysis retain the advantages of high specific surface area and three-dimensional mesoporous structure,which makes the catalysts show good activity.Cerium based oxides have good oxygen storage capacity,rich acid sites and good oxidation-reduction capacity.Therefore,in this paper,a series of Ce-based metal oxide catalysts were prepared by water bath method combined with sacrificial Ce-MOF template method,and their catalytic performance for the degradation of toluene was studied.The specific research contents and results are as follows:A series of CeO₂catalysts doped with different elements（Mn,Cu,Co）were prepared by water bath method and sacrificial Ce-MOF template method,and their structures were characterized by XRD and SEM.Based on the catalytic oxidation of toluene tests,It was found that when the doping amount of elements was 2%,the catalytic performance was the best,and CeCo_0.02O_xshowed the best catalytic performance,When the degradation rate of toluene is 90%,the corresponding temperature T_90%is 226℃.The best material system for catalytic oxidation of toluene was selected on the basis of the experimental process:Ce/Co system,and the changing law of the physicochemical properties of the catalyst on doping elements and the mechanism of catalytic oxidation of toluene were explored through XRD,SEM,TEM,N₂adsorption and desorption test,H₂-TPR,O₂-TPD,XPS and In situ DRIFTS.The results showed that after doping Co,a homogeneous CeCo_aO_xsolid solution was formed,and there was a strong interaction between Ceand Co,forming Ce⁴⁺+Co²⁺（?）Ce³⁺+Co³⁺redox cycles,which promoted the formation of more Ce³⁺and oxygen vacancies.At the same time,with the increase of the content of doped Co,the size of the catalyst decreased gradually;The average pore size gradually decreased from 6.8915 nm to 6.235 nm;The specific surface area of catalyst gradually increased from 118.19 m³/g to 122.85 m³/g.In the test of catalytic toluene,the catalyst CeCo_0.02O_xshowed the best catalytic performance,T_10%,T_50%and T_90%were 140℃,205℃and 226℃,respectively,which were 61℃,12℃and 14℃lower than the pure phase CeO₂,and still had good catalytic activity at high air speed,and had good stability and cycling performance.A series of Y wt.%Pt/CeCo_0.02O_x（Y=0.5,1.0,1.5,2.0）catalysts were prepared by sodium borohydride reduction method,and they were characterized and tested.The results show that after loading Pt elemental,Pt particles are uniformly distributed on the surface of the catalyst,and the specific surface area and average pore size of the catalyst gradually decrease with the increasing content of Pt elemental.The SMSI effect of metal-support strong interaction between Pt particles and CeCo_0.02O_xenhances the flow of oxygen in the catalyst and promotes the redox cycle of Ce⁴⁺+Co²⁺（?）Ce³⁺+Co³⁺.The catalyst 2 wt.%Pt/CeCo_0.02O_xshowed the best catalytic performance,T_10%,T_50%and T_90%were 132℃,152℃and 157℃,respectively,which were 8℃,73℃and 69℃lower than the catalyst CeCo_0.02O_x.At the same time,the influence of different loading positions of Pt particles on the catalytic performance was explored,and it was found that the Pt elemental were more evenly distributed on the surface of the catalyst and the internal lattice gap had better performance than when only distributed on the surface of the catalyst.In situ DRIFTS were carried out on the catalyst CeCo_0.02O_xand 2wt.%Pt/CeCo_0.02O_x,and the results showed that toluene was rapidly adsorbed on the surface of the catalyst,and then oxidized to intermediate species such as benzaldehyde and benzoic acid,and finally completely oxidized to CO₂and H₂O.The addition of Pt elemental accelerated the conversion rate of toluene to intermediate,but did not change the conversion path of toluene.