Synthesis Of Spinel-type Composite Metal Oxides And Their Catalytic Performance For Degradation Of Volatile Organic Compounds

In the past few decades,a variety of control technologies have been used to remove VOCs,such as catalytic oxidation,plasma technology,photo catalytic oxidation and adsorption removal.Catalytic oxidation has been used in emission reduction for more than 60 years and has been proven to be an effective technology.Compared with other technologies,catalytic oxidation can completely oxidize toluene to carbon dioxide and water at a lower temperature,and has the advantages of lower operating temperature,no secondary pollution.Studies have shown that the activity of metal catalysts is mainly governed by the intrinsic properties,the number of the active sites and morphology of carrier,which are affected by the preparation method,precursors and the state of the active metal sites（loading,dispersion,size,and valence）.Compared with single-component catalysts,multi-component catalysts exhibit better catalytic performance.Modification of single-component catalysts with different kinds of rare earth metals,alkali metals or transition metals can improve the catalytic performance by stabilizing metal activity,improving the amount of free oxygen and the fluidity of bulk oxygen.In this work,we developed a series of spinel-type composite metal oxides as catalysts for degradation of volatile organic pollutions,and spinel-type metal oxides were modified through morphology adjustment,attapulgite loading and other metal oxides impregnation,and thus exhibited highly enhanced performance for lower temperature catalytic oxidation.XRD,TEM,SEM,BET,XRF,XPS,H₂-TPR and other characterization methods were used to explore the structure of the catalyst and its reaction mechanism.The difference in activity between the catalysts prepared in the experiment was compared through catalytic acyivity measurements.The main research contents of this work are as follows:（1）In this work,a series of spinel CuM₂O₄（M=Mn,Fe and Al）catalysts were prepared by sol-gel method to investigate the degradation of VOCs,and CuMn₂O₄ was selected as the research object,the molar ratio of Cu to Mn were studied,and modify CeO₂ to improve its catalytic performance.By characterizing the structure,activity and surface element types of CeO₂-CuMn₂O₄ and using toluene as the probe molecule,the catalytic activity of the catalyst was tested.The results showed that the temperature at which CeO₂-CuMn₂O₄ converts toluene to 90%and 100%are 200°C(T₉₀%)and 240°C(T_100%)respectively,and the CO₂ yield reaches100%at 248°C.（2）In this work,attapulgite was used to support metal oxides to change the adsorption performance and the number of active sites of the catalyst in the catalytic degradation process of toluene,in order to improve the adsorption performance of the catalyst and the dispersion of active components,thereby enhancing the catalytic performance of the catalyst.This work studied the effective degradation of toluene by a series of single-active component catalysts,dual-active component catalysts and three-active component catalysts.The catalysts were characterized by XRD,nitrogen adsorption and desorption,TEM,XRF,XPS,and H₂-TPR.The study found that the three-active component catalyst CeO₂-CuMn O_x-ATP exhibited the best toluene catalytic performance.When the actual loading is72.19%,it can reach 90%degradation at 175℃ and 100%at 200℃.（3）In order to expose more active sites of the prepared supported catalyst and thus more fully react with toluene,the nano-flower-like spinel Co Mn₂O₄,which have more specific surface area than the layered CuMn₂O₄spinel,was selected as the carrier and loaded different metal oxides by impregnation,we studied a series of two-step synthesis of composite metal oxides NiO-Co Mn₂O₄,Cu O-Co Mn₂O₄,Fe₂O₃-Co Mn₂O₄,CeO₂-Co Mn₂O₄,and characterized their toluene catalytic performance.XRD,nitrogen adsorption and desorption experiments,SEM,XPS,H₂-TPR were carried out a series of characterization of the catalyst.The study show that NiO-Co Mn₂O₄ exhibits the best catalytic activity for toluene when the loading is 50%,and the complete degradation of toluene can be achieved at190℃.