Study On Suppout Effect Of Ni-based Catalysts For CO₂ Methanation Under Visible Light Irridiation

Producing synthetic natural gas?SNG?by carbon dioxide methanation under visible light irradiation is a hot research topic in recent years.Consuming carbon dioxide can reduce carbon emission and is conducive to environmental protection.The SNG is a kind of clean energy,which can alleviate the current situation of natural gas shortage in China,and has important practical application value.In this study,the catalysts with different Ni content were prepared by loading Ni on titania,titania doped with nitrogen,titania doped with sulfur,?-Al₂O₃ and activated carbon.The catalysts were characterized by the X-ray powder diffraction?XRD?,N₂ adsorption-desorption,H₂ temperature programmed reduction?TPR?,scanning electron microscopy?SEM-EDS?and ultraviolet-visible diffuse reflection spectroscopy?UV-Vis DRS?.The catalytic performance for CO₂ methanation under visible light irradiation was investigated at atmospheric pressure and reaction temperature of 100-180°C.The molar ratio of H₂/CO₂ was 4,catalyst loading was0.02 g and the reactor volume was 23 ml.The specific content and research results of the study are as follows:1.The CH₄ yield was up to 70%for the nickel-base catalyst supported on nano-TiO₂ with the Ni content 70%at 150°C under visible light irradiation for 80min.The catalytic activity decreased significantly when the reaction temperature was below 130°C.2.The Ni catalysts supported on the N or S doped titanium dioxide had larger specific surface area,and the Ni species dispersed well on their surfaces.Thus the catalytic performance was better than that of the undoped catalyst.S doped catalysts?Ni/S-TiO₂?were better than N doped catalysts?Ni/N-TiO₂?,and the CH₄ yield reached 75%at 150°C on Ni/S-TiO₂ with Ni load 60%under visible light irradiation for 55 min.3.Compared with other four kinds of supports,the catalysts supported on activated carbon exhibited the best performance,and those with Ni content in a wide range of 40-70%showed high catalytic activity for CO₂ methanation,CH₄ yield up to84%.The larger specific surface areas of the carbon support enhanced the dispersity of Ni species,while the reducibility of activated carbon ensured that most of the Ni species could exist in a metallic state and thus increased the number of the active sites.There was a very small amount of CO in the reaction products on catalysts supported on activated carbon.4.Compared with other catalysts,the catalytic performances of the catalysts supported on?-Al₂O₃ were relatively poor in the CO₂ methanation reaction,which was related to that the Ni species more easily aggregated on their surfaces.