Photocatalytic Performance For Direct Conversion Of Low Concentration Gas To Methanol Over Modified Tungsten Oxide

Gas extraction and utilization can reduce the occurrence of gas disasters in coal mines,and at the same time,it can turn waste gas into treasure,increase the supply of clean energy,and reduce greenhouse gas emissions.However,most of the gas extracted during the mine mining process is low-concentration gas(C_CH4<30%),and due to the danger of explosion in its transportation and use,it is difficult to utilization.In the actual production process of the enterprise,a large number of low-concentration gas is often discharged directly into the atmosphere and cannot be used effectively.Therefore,this paper studies the photocatalytic oxidation of low-concentration gas into methanol by using modified WO₃ as catalytic material.It provides new ideas for the safe and clean utilization of low-concentration gas in coal mines,and meantime promotes the safe production of coal mining enterprises.The main work and research results of this paper are as follows:（1）WO₃ nanosheets were firstly synthesized via the hydrothermal method,and the Co₃O₄/WO₃ composite catalysts were prepared by combining the surface impregnation process.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,transmission electron microscopy（TEM）,UV-Vis absorption spectroscopy and other testing methods were used to systematically characterize the crystal structure,microscopic morphology and light absorption properties of Co₃O₄/WO₃.Photocatalytic conversion system of low-concentration gas was constructed by using Co₃O₄/WO₃ composites as photocatalyst and hydrogen peroxide as oxidant.The influence factors of photocatalytic performance for low concentration gas conversion into methanol were systematically explored.The results show that the incorporated Co₃O₄ can significantly improve the photocatalytic conversion of methane.For the simulated gas with a volume fraction of 20%methane,the methane conversion after visible light irradiation for 120 min is 2041μmol/g over3.0%Co₃O₄/WO₃ catalyst under the optimal reaction conditions.The corresponding methanol production and selectivity are 1194μmol/g and 58.5%,which are 4.03 times and 2.39 times that of single WO₃,respectively.It is superior to most of the reported heterogeneous photocatalysts for methane conversion,and the as-synthesized Co₃O₄/WO₃ composite catalysts have good cyclic stability.（2）A series of WO_3-x nanosheets with gradient concentrations of oxygen vacancies were synthesized via the hydrothermal method combined by a heat treatment process.Under simulated sunlight irradiation,the methanol yield of defect-rich WO_3-x-N2.0 is up to 1475μmol/g,and the methanol selectivity can reach 76%,which is obviously better than WO₃ catalyst under the same experimental conditions.In addition,WO_3-x-N2.0exhibits a methanol yield of 396μmol/g and a selectivity of 82%even under NIR light irradiation,suggesting that NIR-light-driven methane conversion can be achieved through the introduction of oxygen defects,which has been rarely reported in the literatures.Transient photocurrent,EIS,PLs and EPR test results show that the introduction of oxygen vacancies can improve the separation efficiency of photogenerated carriers,promote the generation of photoholes to activate CH₄molecules.Meanwhile,the oxygen defects also make WO_3-x possessing near-infrared light absorption,which can effectively enhance the photocatalytic activity of low-concentration gas conversion.This provides important theoretical guidance for designing the photocatalysts with full spectral response and constructing efficient light-driven system for gas conversion to methanol.There are 46 pictures,7 tables and 90 references in this paper.