Study On Catalytic Combustion Of CVOCs Over Rhodium-supported Monolithic Catalysts

Accompanied with China's increasing economy in recent years,environmental problems have been much concerned.The release of volatile organic compounds(VOCs)is one of the main cause of the environmental pollution,among which chlorine volatile organic compounds(CVOCs)are considered as the pollutants demanding preferential control.With advantages such as high efficiency and lowenergy consumption,catalytic combustion is considered as one of the most promising technology to the abatement of CVOCs,with the core being the highly efficient catalysts.The currently employed catalysts mainly include noble metal catalysts(Pt,Pd,Au,Rh,Ru)and non-noble metal catalysts with transition metal(V,Ce,Mn,Co,Cr,Cu).ost of the catalysts reported in literature are powdered catalysts,which are used to study the relationship between the catalyst structure and catalytic performance.Monolithic catalysts are more suitable in the practical applications,however,the preparation of monolithic catalysts is quite complicated,which involves coating and adhesive,and therefore the performance of the monolithic catalyst would be different from the powdered catalyst with the same composition.The goal of this thesis is the development of monolithic catalysts with easy preparation and high efficiency.We prepared multi-component metal catalysts for CVOCs combustion,which combined the advantages of noble metal catalysts(high activity)and non-noble metal catalysts(high stability).By taking dichloromethane and 1,2-dichloroethane as the model reactants,the relationship between the activity and the catalyst structure was illustrated by various characterizations.The detailed contents are as follows:1.A series of Rh catalysts supported on Al2O3 powder were prepared by an impregnation method.Then a series of Rh/Al2O3-Cr2O3 monolithic catalysts were prepared by a coating method using Rh/Al2O3 and Cr2O3 as the active components,aluminum gel as the adhesive and cordierite honeycomb ceramic as the support.These catalysts with different Rh contents were tested for catalytic combustion of dichloromethane and 1,2-dichloroethane.It was found that the 0.4 Rh/A12O3-Cr2O3(Rh content:0.4 g/L)had the highest activity and no chlorine-containing by-products were formed.However,It's stability is not so good.The catalysts were characterized by various techniques such as XRD,H2-TPR,NH3-TPD and BET.The results showed that the addition of Rh improved the surface acidity and redox performance of the catalyst,and further improve the activity of the catalyst.It was believed that the activity of the catalyst was closely related to its reducibility and surface acidity.Moreover,the addition of Cr2O3 was beneficial to the further oxidation of CH3Cl intermediate and thus improve the selectivity.2.Based on the above method,catalysts with CeO2 as the second active component instead of Cr2O3 were prepared.The effects of the carrier properties,the calcination temperature and the Rh contents on the catalytic performance were investigated.It was found that the 0.4Rh/Al2O3-CeO2(Rh contents:0.4 g/L)catalyst possessed the best performance,high stability and no chlorine-containing by-products were formed,but its activity was lower than that of the Rh/Al2O3-Cr2O3 catalyst.The results revealed that the catalytic performance for the combustion of dichloromethane is related to the synergistic effect of the redox property and the acidity of the catalyst.The surface acidic sites in the catalyst were the active centers of the decomposition of dichloromethane,and the redox property of the catalyst is beneficial to the deep oxidation of dichloromethane and thus inhibiting the production of CH3Cl.The presence of CeO2 in the catalyst not only improved the catalytic activity in decomposition of dichloromethane,but also inhibited the formation of CH3Cl.