Study on performance of photocatalytic partial oxidation of CH4 to HCHO on AgCl/ZnO
The photocatalytic partial oxidation of CH4 to CH3OH,HCHO and other products is a potential low-energy CH4 conversion path,which has the problems of high activation difficulty of CH4 and low product selectivity.The design and preparation of high-performance catalysts are crucial to solve these problems.Based on the hydrothermal method,ZnO-x catalysts with different morphologies including granules,nano-flower,nano-flake and agglomerated nanoparticles were prepared by varying Zn precursors.It is found that the morphologies of ZnO-x has a significant effect on photocatalytic partial oxidation of CH4 to HCHO(short for"CH4 photocatalytic oxidation performance").The nAgCl/ZnO-Cl photocatalysts(n is the mole fraction of AgNO3)were further prepared by using ZnO-Cl as the substrate with the best CH4 photocatalytic oxidation performance.The samples were characterized by X-ray diffraction,N2 adsorption/desorption and scanning electron microscopy,etc.The results show that 2.0％AgCl/ZnO-Cl shows the best CH4 photocatalytic oxidation performance.Under the action of 5 mg 2.0％AgCl/ZnO-Cl and reaction conditions of temperature of 25 ℃,O2 pressure of 0.1 MPa,CH4 pressure of 2.9 MPa,H2O volume of 75 mL,light intensity of 450 mW/cm2 and illumination time of 2 h.The total yield of oxygenated liquid products(CH3OH+CH3OOH+HCHO)is 10409 μmol/(g·h),and the total selectivity of oxygenated liquid products is 91.4％,and the main product HCHO is 6271 μmol/(g·h)with HCHO selectivity of 60.2％.Based on radical trapping experiments,it is found that the formation of·O2-and the holes are the key to the activation of CH4 to·CH3,and more importantly,interaction of·O2-and·CH3 becomes the major reaction path.In such a way,the initial product(CH3OOH)can be further oxidized to HCHO,and thus leading to the promotion of HCHO selectivity of nAgCl/ZnO-Cl.
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