Design And Preparation Of Transition Metal Integrated Composite Catalytic Materials And Catalytic Combustion Of Toluene

Volatile organic compounds（VOCs）pose a serious threat to human health and ecological environment because of their toxicity and carcinogenicity.As an effective VOCs end treatment technology,catalytic combustion can completely oxidize and decompose VOCs into non-toxic and harmless CO₂and H₂O at lower temperature（compared with RCO technology）under the action of heterogeneous catalyst.The heterogeneous catalyst involved is the key of catalytic combustion technology,and its performance determines the treatment efficiency and energy consumption of VOCs.As we all know,precious metals such as Pt and Pd have been widely recognized for their excellent catalytic activity at low temperature,but their large-scale applications in VOCs treatment are seriously limited by various shortcomings such as high cost and easy poisoning.Accordingly,the application of non-noble metal catalysts to the catalytic combustion of VOCs has high research value.The catalytic efficiency of transition metals is generally low due to the limitation of their intrinsic activity.In this thesis,through the construction of non-noble metal synergistic system and the development of efficient transition metal integrated catalysts,a series of supported oxidation catalysts with low cost and high activity were synthesized and the effects of active metal concentration,dispersion and bimetal coordination on the catalytic activity were studied.The prepared catalysts showed excellent catalytic performance for VOCs treatment such as toluene catalytic combustion.The specific research contents are as follows:（1）A series of supported Al₂O₃catalysts with different cobalt content were prepared by hydrothermal synthesis,coprecipitation and heat treatment.The Co modified Al OOH multilayer two-dimensional nanowires still maintain a good layer stacking structure after heat treatment,and the adjustment of cobalt content can effectively control the morphology and structure of the materials.The physical and chemical properties of the prepared catalysts were verified by various characterization methods,and the morphology and structure of active cobalt oxide on the surface of alumina were studied.The catalytic results of toluene showed that the optimal catalyst Al Co3O showed better catalytic activity for toluene combustion at low temperature(T₁₀₀=330°C)and excellent catalytic stability compared with commercial 5%Pd/C noble metal catalysts,while Al Co1O with less cobalt content and Al Co6O with higher cobalt loading had lower catalytic activity for toluene,which may be attributed to the excellent activity characteristics and exposure degree of active cobalt oxide under specific content conditions.The advantage of this series of catalysts is that the active material on the surface of the carrier is highly dispersed and the internal diffusion effect of toluene can be partially eliminated,thus improving the catalytic combustion performance of toluene.（2）Limited by the intrinsic activity of single metal,the reasonable action of bimetal on alumina carrier is used to further improve the catalytic activity of the catalyst.Ni-doped Al OOH nanoflowers were prepared by hydrothermal method.The transition metal cations(Cu²⁺,Co²⁺)were adsorbed and modified by metal ions with strong surface active hydroxyl groups.Finally,Ni-M bimetal oxide modified Al₂O₃catalysts were obtained by high temperature calcination.The nickel oxide supported by the prepared catalyst exists on the surface of alumina in the form of nanoparticles,while the adsorbed second metal still shows a good dispersion state after high temperature treatment.Various characterization methods have proved that the modified Ni-M bimetal has a strong interaction,and the morphology of the catalyst is good.The transition metal oxides uniformly loaded on the nano-flower can provide more active sites,which eliminates the internal diffusion process and the synergism between bimetals further improves the activity of the catalyst.Therefore,the optimal catalyst Al₂O₃（Ni）-Co can completely degrade toluene at 300°C.However,the catalytic activity of Al₂O₃（Ni）-Cu is slightly lower.（3）In order to better load the bimetal on the specific limited space on the carrier to strengthen the interaction between bimetal and further improve the atomic efficiency of metal active substances exposed on the catalyst surface,this chapter uses the in-situ modification of mesoporous molecular sieves to synthesize active metal mesoporous packaging catalysts in order to obtain surface functional mesoporous materials with transition metal monolayer dispersion by using space limitation and host-guest effect.Firstly,Cu-Co bimetallic ions were embedded in HMS nanopores by micellar template induction method（S⁰M⁺I^-）.The atomic ratio of Cu-Co was controlled to Cu:Co=1:1/2/3/4,and then calcined at high temperature to prepare mesoporous silica catalysts modified by bimetallic Cu-Co oxides.The characterization method proves that the Co-Cu bimetal is highly dispersed in the mesoporous domain space with strong interaction.The prepared mesoporous catalysts have rich nano-pores,highly dispersed bimetallic active metals provide abundant catalytic active sites in the process of VOCs catalysis,and the strong synergism between bimetals greatly improves the catalytic activity of toluene combustion.The results show that the temperature of complete catalytic elimination of toluene by the optimal catalyst 1Cu3Co/NS-MS-s is reduced to 240°C which is much lower than that of the synthesized single metal Cu/Co and other Co-Cu co-modified catalysts.