Preparation And Photocatalytic Properties Of Tungsten Oxide For CO₂ Reduction

Since China put forward the low-carbon goal of"carbon peak and carbon neutrality"in 2020,as the largest coal consumer in the world,the issue of carbon dioxide which is related to energy conservation and emission reduction has exposed to people's vision.Many issues about how to reduce carbon emissions,promote the conversion of carbon dioxide,increase the proportion of renewable energy and improve energy efficiency and other aspects has been discussed.According to annual report of CCUS,“Carbon dioxide capture,utilization and storage”technology is the only technology choice to realize low carbon utilization of fossil energy in China.In this paper,CO₂ is selected as model small molecules,and the renewable solar energy is used to convert them into industrial products with added value.This approach takes into account many aspects,develops rapidly and has broad prospects.Although photocatalytic small molecule activation has attracted much attention,the efficiency of most catalysts is still low at present.The mainly reasons as following:firstly,CO₂ is symmetrical non-polar molecules,which is difficult to be adsorbed;Secondly,two molecules'bond energy is too high to be activated;The potential required for CO₂ reduction products is very close and the product selectivity is poor.Based on various reasons,tungsten oxide material with appropriate valence band conduction band position was selected as the base material in this paper.The main contents of the study are as follows:(1)Tungsten oxide material with hexagonal mesoporous structure was prepared by self-assembly hydrothermal synthesis method.The mesoporous structure realized the effective adsorption of carbon dioxide.The material can be used as an"electronic container"with good electron storage capacity,and the hexagonal pore is conducive to the transfer of protons and electrons.The mesoporous tungsten oxide could converse carbon dioxide into carbon monoxide and methane.After 3 hours of illumination,the maximum yield of carbon monoxide is about 3.3?mol·g^-1,which is more than three times of commercial tungsten oxide and about 4 times of non-mesoporous tungsten oxide,and the methane yield is 1.91?mol·g^-1,which is 2.2 times of non-mesoporous tungsten oxide.In addition to,the catalytic performance of mesoporous tungsten oxide is reduced by the comparison of loaded noble metal Pt,while the performance of non-mesoporous tungsten oxide is slightly improved.It is finally confirmed that the fundamental reason for CO₂ activation lies in the mesoporous structure of tungsten oxide itself.It is proved that the mesoporous structure of tungsten oxide is the root cause of carbon dioxide activation by comparison of loaded metal Pt or not.(2)Ultrathin 2D structure tungsten oxide material(R-WO₃)is synthesized by the hydrothermal method to explore the photocatalysis CO₂ reduction.The R-WO₃ has high specific surface area,abundant surface defect sites and low price of tungsten atoms and surface hydroxyl radicals,through the synergy of many factors,CO₂ is effectively adsorbed and activated.In CO₂-TPD,chemical absorption peak intensity is much higher than physical adsorption peak.Ultrathin material shortens the carrier migration distance and reduces the carriers'recombination rate.Besides,it improves the utilization efficiency of light energy.Methane was finally synthesized by activated hydrogenation with the highest yield of 0.37?mol·g^-1h^-1.It provides some reference for the generation of high value-added CO₂ reduction products,which further verified the unique application of two-dimensional materials in the activation of small molecules.