Preparation Of Supported Polyoxometalate-Ionic Liquid Catalyst And Its Oxidative Desulfurization Performance Investigation

In order to produce clean fuels,the Chinese government stipulates that the sulfur content of national VI（B）gasoline should not exceed 10μg/g.Among various desulfurization technologies,hydrodesulfurization（HDS）is currently the most widely used and relatively mature desulfurization technology in industry.However,due to its harsh reaction conditions（300～400℃,3～13 Mpa）and the need to consume H₂,non hydrodesulfurization technology has become a current research hotspot.Oxidative desulfurization（ODS）has attracted researchers’interest due to its mild reaction conditions and high desulfurization efficiency for difficult to remove thiophene sulfides.Polyoxometalates（POMs）are widely used in the catalytic field due to their simple synthesis,strong acidity,and high thermal stability.Ionic liquid（IL）has become a novel green solvent due to its lower melting point,lower vapor pressure,and good conductivity.Polyoxometalate-ionic liquid（POM-IL）can preserve the characteristics of POM and IL while solving the problem of POM itself being easily soluble in organic solvents.However,it still has drawbacks such as small specific surface area and difficulty in recycling.By selecting a suitable support to load POM-IL onto the support,it is possible to solve the above problems and improve its catalytic oxidation desulfurization efficiency.This paper successfully designed and prepared a supported POM-IL oxidative desulfurization catalyst:[C₁₂mim]₃（NH₄）₃Mo₇O₂₄/2D Ni-MOF.The catalyst was successfully synthesized by verification of FT-IR,XRD,XPS and other characterization.The contact angle test results showed that the catalyst has amphiphilicity.According to the N₂adsorption-desorption isotherm,it can be seen that both the support and the catalyst are mesoporous structure.The characterization results of FESEM and TEM demonstrate that2D Ni-MOF is a stacked structure composed of two-dimensional nanosheets,and the structure of the supported catalyst remains basically unchanged.When the catalyst is used for oxidative desulfurization,under the optimal conditions of T=70℃and n（O/S）=5,DBT can be completely oxidized to DBTO₂within 40 min,and the catalytic performance can still reach over 90%after the catalyst is recycled for 26 cycles.Although[C₁₂mim]₃（NH₄）₃Mo₇O₂₄/2D Ni-MOF is an amphiphilic catalyst,and 2D Ni MOF has a mesoporous structure that can completely oxidize DBT to DBTO₂within 40min,the pore size of 2D Ni MOF is relatively small（5.6 nm）.For larger molecules such as thiophene,larger pore sizes are easier to remove.Hexagonal boron nitride（h-BN）is a two-dimensional layered structure similar to graphene,with thermal conductivity,high stability,and oxidation resistance.h-BN also has strong hydrophobicity and a larger pore size（17.4 nm）.In addition,replacing[C₁₂mim]₃（NH₄）₃Mo₇O₂₄with[C₁₂mim]₃PMo₆W₆O₄₀as the active component,the catalyst has a bimetallic catalytic center.A novel hydrophobic catalyst[C₁₂mim]₃PMo₆W₆O₄₀/h-BN was obtained by loading[C₁₂mim]₃PMo₆W₆O₄₀on h-BN with hydrophobicity.The characterization results of FT-IR,XRD,XPS confirmed that the structures of POM,IL,and support were fully preserved during the synthesis process,and the catalyst was successfully synthesized.According to the N₂adsorption-desorption isotherm,h-BN has a layered structure,its average pore size is mesoporous,and the supported catalyst also shows a similar structure to h-BN.The TEM characterization results indicate that h-BN is a typical two-dimensional layered nanosheet structure,and the surface morphology of the supported catalyst has not changed much.When the catalyst is used for oxidative desulfurization,under the optimal conditions of T=60℃and n（O/S）=5,DBT can be completely oxidized to DBTO₂within 20 min,and the catalytic performance can still reach over 90%after the catalyst is recycled for 20 times.