Preparation Of Rare Earth Metal Modified Cerium-based Metal Oxides And Research On Catalytic Oxidation Of Toluene

Industrial Volatile Organic Compounds?VOCs?are emitted from a large variety of sources,such as transports and industry?outdoor sources?as well as form household products.VOCs are harmful to human health and the environment because of they are actually important precursors of atmospheric particles and O₃.Among them,toluene is one of the important and typical kinds of VOCs widely used as an industrial feedstock and as a solvent that is hard to be eliminated catalytic.Up until now,catalytic combustion is believed to be an of the most efficient pathways in eliminating toluene.Therefore,synthesizing a catalyst with good activity and stability is the first task to remove volatile organic pollutants?VOCs?such as toluene.This study aims to prepare a highly active catalyst for the removal of toluene from the air.At the same time,the process and mechanism for the removal of toluene from catalytic materials are discussed.The following are the results obtained by the study:Firstly,Pt/Eu₂O₃-CeO₂ catalyst was prepared by active agent-inducing soft template method.By adjusting the Eu/Ce molar ratio,Pt/EC-x catalysts with different Eu contents were successfully synthesized.Based on this,the catalytic oxidation performance was studied.It was found that Pt/EC-x catalyst has good stability and catalytic activity,and the catalyst activity shows an increasing trend with the increase of reaction temperature.Among them,Pt/EC-2.5 catalyst shows the best catalytic activity,Pt/EC-2.5(T₉₀)temperature is 180°C.In addition,to better understand the structure and possible metal-support interaction of the Pt/EC,the catalysts were characterized by SEM,TEM,XRD,XPS,BET,and in suit DRIFTS.BET studies indicate that some of the pores are clogged the reason for this behavior is that partial blocking of pores induced be usage of Eu.XPS results show that the Ce³⁺contents in Pt/EC-x catalysts are higher than those of Pt/CeO₂ samples reveal that the template method can create more oxygen vacancies than sol-gel.H₂-TPR results show that the total H₂ consumption?0.84 mmol/g?of Pt/EC-2.5 was much higher than other samples,indicating that the former possessed a more amount of adsorbed oxygen species on Pt/EC-2.5Secondly,a novel porous material CuO-MO_x-Ce O?M=Y,Eu,Ho,Sm?with specific surface area of 70-95 m²/g was further prepared by sol-gel method.Compared with CuCeO_x,CuO-MO_x-CeO_x samples exhibit considerable activity and stability for toluene combustion.Among them,the toluene conversion rate of CuHoCeO_x catalyst at 220°C and the space velocity of 50000h^-1is close to 100%.The results show that rare earth metal doping can greatly increase the specific surface area,reducibility and migration rate of adsorbed oxygen on the surface of porous metal oxides.At the same time,the synergetic effect between Ho and CuCe O_x framework is inclined to enhance the oxygen vacancies over the materials,which is beneficial for toluene combustion,?The Ho element is coordinated with two oxygen atoms and occupied a site of Ce atom,which changes the Pi-bond of Ce in binary oxides samples?.Through in-situ DRIFTS analysis,we proposed the oxidation of toluene over the CuHoCeO_x binary oxides samples involves a Mars-van Krevelen mechanism.The toluene is converted into aldehydes or ketones as intermediates.