Preparation Of Cerium-based Semiconductor Materials And Its Catalytic CO₂ Fixation Research

With the development of industrial,there is an increasing demand for fossil fuels,releasing large amounts of carbon dioxide（CO₂）which is one of the major greenhouse gases,leading to the greenhouse effect,causing global warming,melting polar ice,rising sea levels and other environmental problems that ultimately affect plants and animals.And fossil fuels as a kind of non-renewable resources are gradually depleted,which caused the energy crisis and environmental issues has attracted more and more attention of scientists.The use of solar photocatalytic reduction of CO₂ hydrogenation not only can reduce the content of CO₂in the atmospheric,but also can produce many high value-added products,such as CH₄,C₂H₆,CO,etc.And it can solve the crisis of energy and the environmental problems simultaneously,which is considered to be a very promising technology.In recent years,many studies have shown that basic oxides have a strong adsorption capacity for CO₂,and their photocatalytic ability can be enhanced by different modification methods.Therefore,two kinds of modification methods which one is doping Zr⁴⁺on the basis of cerium-based and supporting noble metal Pd nanoparticles and the other one is Cu₂O-loaded heterostructure catalysts were used to study the photocatalytic performance of CO₂hydrogenation.In this paper,Ce（NO₃）₂?6H₂O was used as a starting material to prepare CeO₂nanomaterials and Zr-CeO₂ semiconductors by hydrothermal method.Loading Pd nanoparticles of Zr-CeO₂ semiconductors was prepared by glucose reduction method and applied in photocatalytic CO₂ reduction hydrogenation reaction.The results showed that the shape of prepared catalysts were nanorods.The yield of CH₄ and CO increased firstly and then decreased with the increase of Zr⁴⁺under the condition of UV light irradiation.The products yield of CH₄ and CO reached 196.76μmol/g and 37.43μmol/g respectively when the catalyst was 1.0%Pd/1.5%Zr-CeO₂.This is because of the synergistic effect of Zr-Pd contributes to the photocatalytic CO₂ hydrogenation reaction.Doping Zr⁴⁺can effectively inhibit the recombination of photogenerated electron holes,but also enhance the absorption of UV light by the catalysts.And because the radius of Zr⁴⁺is smaller than the radius of Ce³⁺/Ce⁴⁺ion,doping Zr⁴⁺is easy to form oxygen vacancy,which is benefit for activating reactants.Pd nanoparticles have the effect of aggregating electrons and are the active sites for the adsorption of CO₂.In addition,in order to make the catalyst respond to visible light,we prepared Cu₂O/CeO₂ photocatalyst and tested its photocatalytic reduction of CO₂ hydrogenation.The results show that under the irradiation of visible light,the products are CH₄ and CO.The yield increased firstly and then decreased in the use of 6.0%Cu₂O/CeO₂ catalyst showed the best activity,the highest yield of CH₄ and CO reached 109.43μmol/g和30.36μmol/g.N-type semiconductor CeO₂ and P-type semiconductor Cu₂O form a heterojunction photocatalyst that not only accelerate the separation of photogenerated carriers,but also extend the photo-response range of CeO₂ to the visible region.CeO₂ itself has more basicity,which is beneficial for adsorption of CO₂,which showed higher photocatalytic activity.Through this study,it can be seen that the basic oxide CeO₂ has excellent optical properties in the photocatalytic CO₂ hydrogenation reaction,and has a very great potential application.