Controllable Preparation Of Co₃O₄ Catalysts With Tunable Morphology And Study On The Catalytic Oxidation Of Toluene

Volatile organic compounds?VOCs?are considered as one of the major air pollutants,which not only threaten the environment but also do harm to our human health,because many of them?e.g.toluene?are toxic and carcinogenic.In order to minimize the negative impact of VOCs,it is urgent to control VOCs pollution.Catalytic oxidation technology is one of the most effective ways of solving a VOCs emission problem due to its high removal efficiency and no secondary pollution.One crucial factor of catalytic oxidation technology is the exploration of high-performance catalysts.In recent years,Metal-organic frameworks?MOFs?have gained great attention due to their outstanding structural properties such as ultrahigh porosities and surface areas.The MOFs-derived materials could partly reserve the structural properties from their precursors,show high stability and more active sites,exhibiting great potential for practical applications.In this paper,toluene is used as the target pollutant,Co₃O₄catalysts with different morphologies are prepared by one-step pyrolysis were successfully prepared with Co?OH?₂ or MOFs materials as the source of Co element and template,and the structural properties were further investigated.The catalytic oxidation performance of different morphology Co₃O₄ catalysts for toluene was investigated.First,ZIF-67 template with different morphologies was prepared using surfactant-assisted hydrothermal method.And Co₃O₄ catalysts was synthesized by using ZIF-67sacrificial template method.The effect of calcination temperature on ZIF-67 template was investigated.The influence of catalyst morphology on the reaction of toluene catalytic oxidation was also studied.Results showed that the optimal calcination temperature of ZIF-67 was 300 ^oC.The as-synthesis catalysts showed well-dispersed active site,porous hollow structure and controllable morphology.Results of characterization demonstrated that the morphologies had a significant influence on the catalytic performance of the Co₃O₄.The Co₃O₄ truncated nanocubes?i.e.Co₃O₄-TC?with mainly exposed{110}planes exhibited the best toluene oxidation activity(T₉₀=230°C).The superior catalytic activity of Co₃O₄ truncated nanocubes might be associated with the high exposure of{110}crystal plane,abundant surface adsorbed oxygen species and good low-temperature reducibility.Through the experimental research in Chapter 3,it is found that 2-methylimidazole also plays an important role in the hydrothermal reaction.Therefore,on the basis of the third chapter,it was further optimized.By controlling the ratio of Co²⁺to 2-methylimidazole,different precursors were successfully prepared.Co₃O₄ catalysts with different morphologies were prepared for the sacrificial template and applied to the catalytic oxidation of toluene.The activity results show that the morphologies had a significant influence on the catalytic performance of the Co₃O₄,and the flower-shaped Co₃O₄ catalyst has the best catalytic performance(T₉₀=208°C).The characterization results show that exposed{110}plane,specific surface area,redox properties and surface oxygen vacancies play an important role in enhancing the catalytic performance of the flower-like Co₃O₄ catalyst.