Study On The Performance Of Noble Metal Modified Ta Or Nb Doped TiO₂ Catalyst For Photocatalytic Oxidation Of Ethanol

Ethanol can be converted from CO₂ and H₂O under sunlight,so it is called"liquid sunlight".It is of great theoretical significance and practical value to study the new process of ethanol synthesis and conversion due to the important role of ethanol in solar energy conversion and global carbon cycle chain.The conventional thermal processes of ethanol conversion are relatively mature,but the high reaction temperature or pressure leads to more byproducts and difficulty in product separation,and even more some processes may cause environmental pollution.Therefore,it has potential application value to study the new photocatalytic partial oxidation of ethanol at room temperature.In this paper,two series catalysts of Ta doped TiO₂ and Nb doped TiO₂ were prepared,and Au and Cu-modified（Au@Ta-TiO₂ and Cu@Ta-TiO₂ ）catalysts were prepared by metal deposition method using 5%Ta-TiO₂ as the support.The influences of doping amount of Ta and Nb,temperature of calcination and precious metal content were investigated,and the catalysts were characterized by means of XRD,FTIR,UV-vis DRS,XPS,TEM and H₂ -TPR methods.The performance of photocatalytic partial oxidation of ethanol in25℃～45℃under visible light irradiation was investigated,and the photocatalytic reaction mechanism of the catalyst was analyzed based on the characterization results.The results are as follows.1.TiO₂ doped with Ta and Nb can significantly improve the photocatalytic activity of the catalyst,and Ta is better than Nb.The surface hydroxyl groups increased after doping,which promoted the conversion of ethanol and the selectivity of acetaldehyde.The doping reduced the band gap of the catalyst and enhanced the absorption of visible light.The catalyst with 5%Ta or Nb and 500℃calcination temperature has the best activity.2.5%Ta-TiO₂ is the carrier supporting Au,and the ethanol reaction conversion rate is significantly improved.This can be attributed to the fact that Au make the band of TiO₂ bend to form a shallow potential（Schottky barrier）that traps electrons at the interface between the two.It hinders the recombination of photo-generated electrons and holes.In addition,The surface plasmon resonance（LSPR）of Au nanoparticles also enhances the response of the catalyst to visible light.and the main products were acetaldehyde,ethylene,ethyl formate and CO₂ .The negatively charged gold nanoparticles under irradiation promoted the breakage of C-H bond in ethanol molecule,which is conducive to the dehydration and complete oxidation of ethanol,leading to the decrease of acetaldehyde selectivity and increase of ethylene and CO₂ selectivity.3.The ethanol conversion increased on the catalyst with Cu supported on5%Ta-TiO₂ ,Cu is oxidized to Cu O and Cu₂ O on the surface of the catalyst,forming a p-n heterojunction,thereby increasing the photocatalytic activity of the catalyst.and the main products included acetaldehyde,ethylene and CO₂ .The selectivity of CO₂ increased while the selectivity of acetaldehyde decreased.The copper species is beneficial to the complete oxidation of ethanol.