Lanthanum-doped Amorphous TiO₂ Photocatalytic Oxidation Desulfurization Catalyst

In this paper,amorphous and crystalline TiO₂ photocatalysts were prepared by hydrolysis and calcination using butyl titanate and anhydrous ethanol as raw materials.Amorphous TiO₂ was doped with lanthanum nitrate as the source of lanthanum to prepare different doping amount of La-TiO₂photocatalyst.XRD,FT-IR,UV-Vis,PL,XPS and SEM methods were used to analyze the crystal structure,surface functional groups,light absorption performance,photogenerated electron-hole pair recombination rate,surface element status and surface morphology of the prepared catalyst.Using the mixture of dodecane and dibenzothiophene（DBT）as model fuel,the photocatalytic oxidation desulfurization（PODS）performance of the prepared catalyst was evaluated,and the process conditions were optimized.Finally,the catalytic reaction mechanism was explored.The main research results are as follows:（1）When the calcination temperature was 100℃,amorphous TiO₂photocatalyst was prepared.When the calcination temperature was raised to500℃,the crystal shape of the TiO₂ photocatalyst changed from amorphous structure to anatase.When the calcination temperature was raised to 700℃,rutile TiO₂ appeared.Compared with crystalline TiO₂,amorphous TiO₂ has surface hydroxyl groups,stronger absorption intensity in the ultraviolet region,and lower photogenerated electron-hole pair recombination rate.Under the conditions of UV irradiation for 4 h,the amount of catalyst is 1%（based on the quality of model fuel）,the O/S molar ratio of oxidant to model fuel is 20:1,and the volume ratio of extractant to model fuel is 1:1,the desulfurization rate can reach 84.8%using amorphous TiO₂ as photocatalyst.The catalytic reaction mechanism was proposed,and it was considered that the hole（h⁺）in the amorphous TiO₂ valence band reacted with OH^-and H₂O to generate hydroxyl radical（·OH）,and the electron（e^-）in the conduction band combined with O₂ to form superoxide radical（·O₂^-）.These radicals oxidize DBT⁺to form DBTO and DBTO₂,which are then extracted with methanol.（2）TiO₂ doped with lanthanum still has an amorphous structure.Compared with amorphous TiO₂,the spectral absorption range of 0.5%La-TiO₂ photocatalyst becomes wider,the band gap becomes narrower,and the photogenerated electron-hole pair recombination rate decreases.Under the conditions of UV irradiation for 4 h,the amount of catalyst is 1%（based on the quality of model fuel）,the O/S molar ratio of oxidant to model fuel is20:1,and the volume ratio of extractant to model fuel is 1:1,using 0.5%La-TiO₂ as photocatalyst,the desulfurization rate can reach 95.1%,which is 10.3%higher than that of amorphous TiO₂.The catalytic reaction mechanism is proposed.It is believed that the introduction of lanthanum narrows the band gap of amorphous TiO₂,which is beneficial to the electron transition in the valence band and generates more electron-hole pairs.The effective electron-hole pairs can further react to generate hydroxyl radicals（·OH）and superoxide radicals（·O₂^-）,which can oxidize DBT⁺to produce sulfones（DBTO,DBTO₂）,which are finally extracted by methanol.