Partial Oxidation Of Methanol To Methyl Formate Under Visible Light Irradiation On Iron Doped Bismuth Tungstate

Methyl formate（HCOOCH₃）is an important industrial product and can be produced from methanol.In 2021,China’s methanol production capacity was up to 105.75 million tons and the actual output was over 68 million tons,which was a serious overcapacity.Therefore,it is of great economic value to convert methanol to methyl formate with high added value.Photocatalytic partial oxidation of methanol to methyl formate has gradually become a hot research topic due to its mild reaction conditions and high reactivity.However,ultraviolet light is often used in current studies.As the energy of ultraviolet light only accounts for about 4%of the total energy of sunlight while that of visible light accounts for up to 43%,visible light has been used as light source for photocatalytic oxidation of methanol to methyl formate in this study in order to improve the utilization rate of sunlight.In this study,a series of Fe-doped Bi₂WO₆ photocatalysts were successfully prepared via solvothermal method and has investigated the preparation conditions and the influence of surfactants on the structure and properties of Fe-Bi₂WO₆photocatalysts.In addition,the Ag modified Fe-Bi₂WO₆photocatalysts using the best activity 0.75%Fe-Bi₂WO₆support via a metal deposition method were futher synthesized.The catalysts were characterized by XRD,FTIR,UV-Vis DRS,EIS,BET,XPS and TEM.Meanwhile,the photocatalytic performance of the photocatalysts in the photocatalytic partial oxidation of methanol to methyl formate under visible light within the temperature range of 25-45℃were investigated.The results are as follows:1.The source of Fe precursor,hydrothermal temperature and duration had significant effects on the photo absorption,surface hydroxyl group,crystallinity and photocatalytic activity of Fe-Bi₂WO₆ photocatalysts.The screened preparation condition for Fe-Bi₂WO₆ photocatalysts was hydrothermal treatment at 140℃for 20 hours with ferric acetate as iron precursor.2.The surfactants had great influence on the crystallinity,specific surface area,photo absorption and catalytic activity of the sample.Adding CTAB enhanced the photo absorption and the number of hydroxyl groups of the sample.The specific surface area was increased from 21.237 m~2/g to45.92 m~2/g and the catalytic activity was significantly improved as well.The sample with 5%CTAB showed the highest catalytic activity.3.The Fe content had little influence on impedance,but remarkable influence on the number of hydroxyl groups,the recombination of electron-hole pairs and photo absorption.The sample of 0.75%Fe-Bi₂WO₆ had the best catalytic performance with methanol conversion up to 52%,and methyl formate formation rate up to 2.6 mmol/g/h.4.The reducing agent had a significant effect on the performance of samples with Ag nanoparticles supported on Fe-Bi₂WO₆.When Na BH₄ and C₆H₅Na₃O₇ were used as reducing agents,the activity of Ag/Fe-Bi₂WO₆decreased significantly,while when VC was used,the catalytic activity increased significantly.The sample with 1.5%Ag exhibited the best activity when VC is used as reducing agent,with 68%of the methanol conversion and 3.2611 mmol/g/h of the formation rate of methyl formate.