Catalytic Performance Of Pt-based Supported Catalysts And Co-based Composite Catalysts Towards Benzene Oxidation

Benzene is widely applied in industrial production,but direct release to the surrounding area without any post-processing operation will pose a great threat to both the environment and the health of human beings,due to its high volatile and toxic properties.Catalytic oxidation is the one of most potential method for benzene removal among many end-of-pipe treatment techniques,since it can utilize oxygen in the air as the oxidizer to complete benzene oxidation on the surface of the catalyst at suitable temperature.The core for this method is to develope durable and high-efficiency catalysts.Noble metal supported catalysts and transition-metal-based oxides are two typical catalysts that are widely used in this field.The former generally exhibits superior and stable catalytic performances,but it suffers from the high-price and the scarcity of resources.While the latter owns the characteristics of low prices and abundant resources,its catalytic performance is typically lower than that of the former.For precious metal supported catalysts,the selection of high-efficiency support is an essential part,and some natural supports can be ultilized since they possess porous structure,excellent physiochemical-stability and low price.Therefore,applying natural materials as supports is significance for value-added of natural products,green manufacturing of catalysts and reducing the overall cost of the catalysts.Besides that,the development of relatively inexpensive and abundant composite transition-metal oxides seems an attractive strategy for potentially replacing noble-metal supported catalysts,because their catalytic performance towards benzene oxidation can be highly enhanced due to the synergistic effects of different metal ions or metal oxides.Firstly,in chapter 2,diatomite supported Pt(Pt/diatomite)catalysts were synthesized by combining natural diatomite support and bio-reduction method.Under the high space velocity(SV)of 60000 h-1,0.3%Pt/diatomite catalyst can achieve 100%benzene conversion at 210℃,which was 30℃ lower than that of 0.3%Pt/SiO2.Besides,0.3%Pt/diatomite was catalytically stable and durable through 60 h time onstream,water vapor and carbon dioxide effect experiments.Through XPS,H2-TPR,H2TPD,TEM,and in situ DRIFTS of CO adsorption analysis,it was found that the high catalytic oxidation activity of 0.3%Pt/diatomite is attributed with more surface absorbed oxygen,good Pt dispersion and strong interactions between Pt and diatomite.Moreover,in situ DRIFTS of benzene oxidation experiments revealed that benzene was first oxidized to hydrocarbon fragments,and subsequently transformed to water and carbon dioxide.Secondly,carbon-based materials were typically used as efficient supports to anchore nanoparticles with high dispersion because they have abundant functional electrophilic oxygen groups.Thus,in chapter 3,expanded graphite with excellent thermal stability was applied as catalyst carrier,while normal graphite and activated carbon were used as reference supports.Through ICP-OES,TEM and XPS analysis,it can be confirmed that Pt(0.5%)were successfully decorated at the surface of the three carbon-based supports through a photo-induced strategy.Benzene catalytic oxidation evaluation experiment was carried out to evaluate the performance of the as-obtained three carbon supported Pt catalysts,and the results showed that 0.5%Pt/EG was the best,because it can achieve 100%benzene conversion at 180℃ under the high SV of 120000 h-1,which was 20 and 60℃ lower than that of Pt NPs supported on GP and AC.Besides that,0.5%Pt/EG was catalytically stable and durable through 100 h time onstream,water vapor and carbon dioxide effect experiments.Through benzene-TPD,O2TPD and EIS analysis,it was found that the adsorption capacity and the electron transfer property caused by the Pt nanoparticles and EG support led to a good catalytic performance.Single transition metal oxide suffers from bad catalytic performance.Therefore,in chapter 4,solid solution catalyst in the form of porous coral-like cobalt-manganese oxide(CoMnOx)with high surface area was synthesized through annealing Co-Mn-1,3propanediol precursors at high temperature in air.By utilizing the synergistic effects of Co and Mn ions,the as-obtained CoMnOx showed the best benzene catalytic activity under the SV of 20000 h-1,and it can completely remove benzene at 210℃,which was 30 and 50℃ lower than that of the referenced Mn3O4 and Co3O4 samples prepared by the same methods.According to BET,H2-TPR,O2-TPD,and XPS analysis,the asobtained CoMnOx catalyst demonstrated the highest BET surface area,better lowreducibility temperature,and high content of absorbed oxygen groups when compared to Mn3O4 and Co3O4,which make significant contributions to its catalytic benzene oxidation activity,From the analysis of in situ DRIFTS of benzene oxidation experiments,it can be observed that the benzene molecules can absorb on the catalyst surface through three ways including physical adsorption,Br?nsted acid sites and alkoxide species(C-O-metal),and finally oxidize to water and carbon dioxide.Lastly,composite oxide with rich interfaces is an attractive strategy to further enhance the catalytic performance of transition-metal-based oxide.In chapter 5,CuO/CO3O4 catalysts with nanosheet-like heterostructures were fabricated by etching a meta-organic framework(ZIF-67)using copper nitrate,followed by annealing treatment.The obtained CuO/CO3O4 sample exhibited superior catalytic performance for benzene oxidation,similar with the commercial 1%Pt/Al2O3 catalyst,since it can effectively eliminate benzene at a temperature of 250℃ under a high SV of 60000 h-1,which was 30 and 70℃ lower than that of pure Co3O4 and CuO,respectively.Furthermore,the CuO/Co3O4 catalyst also presented excellent recyclability and good catalytic stability through 10 repeated cycles and 100 h on-stream test.Based on H2TPR and XPS results,the interfacial effects in the CuO/Co3O4 heterostructures were beneficial for boosting low-temperature reducibility and increasing surface-adsorbed oxygen species.According to benzene-TPD,O2-TPD and EIS tests,it was found that the CuO/Co3O4 catalyst owned better reactant adsorption and electron transfer properties.Those above-mentioned interfacial effects arose from CUO/Co3O4 catalyst are the reasons for the superior benzene catalytic performances.Furthermore,in situ DRIFTS demonstrated that phenol and carbonate species were the main intermediates during the benzene oxidation process.