Preparation Of Pt-based Catalysts And Their Performances In Catalytic Oxidation Of Toluene

As the main air pollutants,volatile organic compounds（VOCs） not only cause serious harm to health and life,but also cause serious environmental problems such as photochemical smog and acid rain.Catalytic oxidation method is an effective method for the treatment of VOCs,which has the advantages of low energy consumption,high purification efficiency,heat recovery and no secondary pollution,and has broad application prospects.Therefore,the design and preparation of catalysts with high activity and long life have become the core of VOCs treatment.Currently,VOCs catalytic oxidation reactions mainly catalyzed by noble metal,single metal oxide and composite metal oxides.Pt-based catalysts,owing to high catalytic activity,strong anti-deactivation and regeneration performance,are considered to be the preferred catalysts for the catalytic oxidation of VOCs.Whereas the noble metal reserves are limited and expensive.Therefore,the development of supported noble metal catalysts to improve catalytic efficiency is one of the important goals of research.In this paper,Pt nanoparticles are supported on CoO_x and Co-Ce composite metal oxides,and the application of Pt-based catalysts in the catalytic oxidation of toluene is investigated.At the same time,the physicochemical properties of the catalysts are examined in detail by various characterization methods and reasons for the difference in Pt-based catalyst activity.The polyhedral structure CoO_x was successfully synthesized by the MOF template method.The toluene catalytic oxidation activity of CoO_x and Co₃O₄ which obtained by the co-precipitation method was compared.The results show that the CoO_x catalyst displays better catalytic performance,which may be related to its unique polyhedral structure,high concentration of Co³⁺ions on the surface and richer surface active oxygen species.In addition,Pt/CoO_x catalysts were prepared using CoO_x as the carrier and Pt nanoparticle solution and chloroplatinic acid solution as Pt precursors,respectively.The toluene activity test showed that the Pt_nano/CoO_x catalyst obtained with Pt nanoparticle solution as the Pt precursor had the best toluene catalytic activity,and its T₉₀ was 177℃.The distribution and existence of Pt particles in the catalyst were studied by TEM,H₂-TPR,etc.The Pt_nano/CoO_x catalyst has better Pt particle dispersion and more Pt species in metal form.The stability test of the catalyst showed that no significant decrease in catalytic efficiency was observed within 48 hours of continuous operation,so the Pt_nano/CoO_x catalyst showed excellent stability for toluene oxidation oxidation.The reaction kinetics under the condition of no interference from diffusion shows that the rate equation of toluene on Pt_nano/CoO_x catalyst is r = k·Ptoluene,which is only related to the partial pressure of toluene and is a first-order reaction.Oxygen supplementation experiments confirm that gaseous oxygen can dissociate during the reaction and activate on the catalyst surface to form an oxygen cycle.At the same time,the migration of lattice oxygen promotes the formation of surface adsorbed oxygen.Cobalt-based metal organic framework and cerium were combined by one-step liquid phase method to synthesize Co-Ce composite metal oxide with polyhedral structure.Pt_nano/Ce_yCoO_x catalysts with different cobalt-cerium ratios were obtained by loading Pt nanoparticles on the oxide.Pt_nano/Ce_0.2CoO_x catalyst showed the best catalytic performance for toluene,with T₉₀ of 173℃,which was better than the previous catalysts.The strong interaction between Co and Ce,better low temperature reduction performance and highly defective structure may be the reason for its better toluene oxidation activity.In addition,Pt_nano/Ce_0.2CoO_x catalyst has excellent water resistance and catalytic stability,and has broad application prospects.