Study On Porous Metal Oxides Synthesized By Thermal Decomposition Of MOFs For Catalytic Combustion Of Benzene

The emission of benzene in volatile organic compounds（VOCs）has a serious impact on human health and the ecological environment.Catalytic combustion technology is currently one of the most effective methods to control VOCs,which has the advantages of high efficiency,energy saving,low light-off temperature and environmental protection.The key is to obtain efficient catalysts.In addition to supported catalysts,which is more researched,how to obtain highly active and highly stable porous metal oxides as catalysts for catalytic combustion of VOCs has also attracted more and more attention from many researchers.In this paper,Ce-MOF,MIL-101（Cr）and（Ce,Cr）-MOF were prepared by high temperature one-step hydrothermal method,and CeO₂,Cr₂O₃ and CeCrO_x were obtained by thermal decomposition of the above-mentioned precursors.The effect of thermal decomposition temperature on the structure of porous metal oxides and catalytic combustion performance of low-concentration benzene were studied.A series of characterization techniques are used to study the crystal structure,particle size,morphology,valence state and benzene adsorption and desorption properties of the catalysts.The main results are as follows:1.Ce-MOF was prepared as a precursor by using a high temperature one-step hydrothermal method,and a series of porous CeO₂ with different structures were obtained by thermal decomposition of it at different temperatures.The effect of the thermal decomposition temperature of Ce-MOF on the structure and morphology of CeO₂ was studied,and an in-depth study on the catalytic performance of porous CeO₂and its supported Pt nanocrystalline catalyst for catalytic combustion of benzene was studied.The results show:when the decomposition temperature is 400℃,it is the threshold value of the decomposition temperature of MOF.Above the threshold,the products formed are CeO2.At this temperature,the material shows the best structural characteristics and performance for catalytic combustion of benzene.The SBET and Vp of CeO₂（400）are the highest,reaching 114 m²/g and 0.152 cm³/g,respectively.Research shows:CeO₂（400）and Pt/CeO₂（400）achieve complete catalytic oxidation of benzene at 260℃ and 200℃,respectively.The high activity of the porous CeO₂-based catalyst is mainly due to the（200）crystal plane of CeO₂ exposed,which contributes to the formation of surface lattice defects and the generation of active oxygen,as well as the strong interaction of Pt-O-Ce between Pt and CeO₂（400）improves the performance of the catalyst for catalytic combustion of benzene.2.MIL-101（Cr）was prepared as a precursor,and a series of porous metal oxides Cr₂O₃ are obtained through high-temperature thermal decomposition,and a series of PtO_x（x=0,2）/Cr2O3 nanocrystalline catalysts were prepared,their catalytic combustion performance of Cr₂O₃ and its supported Pt catalyst for low-concentration benzene was studied.MIL-101（Cr）began to form Cr₂O₃ at 298℃ and completely forms mesoporous Cr₂O₃ at 400℃.As a catalyst,it completely catalyze benzene at about 310℃ and as a support,0.2%Pt/Cr₂O₃ catalyst achieves complete degradation of benzene at 185℃,showing very high catalytic activity.The high dispersion of Pt on Cr₂O₃,the coexistence of Cr ions in multiple oxidation states,a suitable concentration of Pt²⁺,and more oxygen vacancies,promote the interaction between PtO_x and Cr₂O₃,and make performance of the catalyst excellent for catalytic combustion of benzene.3.（Ce,Cr）-MOF was prepared by high-temperature hydrothermal method,and the bimetallic composite oxide formed by thermal decomposition at different temperatures was directly used as a catalyst.The catalytic combustion performance of low-concentration benzene on CeCrO_x with different structures and different ratios of Ce and Cr was investigated.The results show that the interaction between Cr O_x and CeO₂is very important to the redox performance and catalytic activity.At the same time,CeCrO_x（4:1）has the highest redox performance and catalytic activity,which achieves completely degradation of benzene at about 230℃.Compared with the single CeO2 and Cr2O3,Ce,Cr composite metal oxide exhibits good catalytic activity.Compared with the three catalysts supported with 0.2%Pt,Pt/CeCrO_x（4:1）shows the best activity,which achieves the complete degradation of benzene at 180℃.