Study On Performance Of Photocatalytic Partial Oxidation Of Ethanol By Ag Modified Rare Earth Nd Or Eu Doped TiO₂

Ethanol is one of the most important compounds in the future solar energy conversion and global carbon cycle chain,which has been called"liquid sunshine"in recent years.The photocatalytic conversion of ethanol to other chemicals is an important path in the global carbon cycle.It has been a hot research topic in recent years and thus has a certain scientific significance and practical application value.In this study,Nd and Eu doped catalysts Nd-TiO₂ and Eu-TiO₂,respectively,were prepared by the wet chemical method,and the catalysts Ag/Nd-TiO₂ and Ag/Eu-TiO₂ with metallic Ag nanoparticles supported on Nd-TiO₂ and Eu-TiO₂,respectively,were prepared by the metal deposition method,and characterized by a series methods.The effects of rare earth doping amount,calcination temperature and metal loading on the crystal structure,morphology,optical absorption properties,surface functional groups,energy band structure and surface element microenvironment of the catalyst were studied.The catalytic performance of photocatalytic partial oxidation of ethanol under simulated sunlight and different operating conditions was investigated.The main results are as follows1、The main products were acetaldehyde,ethyl formate,ethylene and CO₂,of which acetaldehyde accounted for more than 80%.Nd-O-Ti and Eu-O-Ti structures were formed on the surface of Nd-TiO₂ and Eu-TiO₂ catalysts.Compared with undoped TiO₂,the surface hydroxyl groups were increased and the visible light absorption was slightly enhanced.The doping amount and calcination temperature had influence on the structure and performance of the catalyst.With the increase of Nd or Eu doping content,the crystal size first decreased and then increased,the band gap decreased gradually,the ethanol conversion increased at first and then decreased,and the selectivity of acetaldehyde decreased at first and then increased.Among them,the catalyst with the calcination temperature 500℃and doping amount of 5%exhibited the best photocatalytic activity.2、There existed two valence states of Ag⁰ and Ag⁺¹ in Ag/Nd-TiO₂ and Ag/Eu-TiO₂.After loading Ag,the light absorption bandwas extended to the visible light region,and the catalytic performance is obviously improved.With the increase of Ag loading,the specific surface area of the catalyst gradually increased,the rate of charge transfer increased,and the ethanol conversion,ethylene selectivity as well as ethyl formate selectivity increased at first and then decreased,while the acetaldehyde selectivity decreased at first and then increased.Compared with the unsupported catalyst,the ethanol conversion was doubled,and the optimum Ag loading was 5%.3、The flow rate of feed gas,oxygen concentration and light intensity had significant effects on the reaction performance,the flow rate was negatively correlated with ethanol conversion,and the light intensity and oxygen concentration were positively correlated with ethanol conversion.With the increase of oxygen concentration,the selectivity of acetaldehyde decreased,the selectivity of ethylene increased,and ethyl formate had no obvious change.With the increase of flow rate of the feed gas,the selectivity of acetaldehyde increased at first and then decreased,while the selectivity of ethyl formate and ethylene decreased at first and then increased.With the increase of light intensity,the selectivity of acetaldehyde decreased at first and then increased.Ethyl formate and ethylene were formed when the light intensity was 91.98 mw/cm² and 62.77 mw/cm².The reaction mechanism was proposed:Ethanol was oxidized to ethoxy which was further oxidized to acetaldehyde.Acetaldehyde was oxidized to methyl and formaldehyde.Methyl reacted with hydroxyl groups and then was oxidized to formaldehydes.Ethyl formate was obtained by the reaction between formaldehyde group and ethoxy group.