Study On The Hydrogen Molecule Diffusion In Tungsten Oxides Simulation And Hydrogen Reduction Mechanism Of Tungsten Oxide

The thermodynamic process of tungsten oxide hydrogen reduction,such as what phases will appear in the reaction and the related reaction equations,has been basically studied.However,due to the small hydrogen molecules that are difficult to be monitored in real time,the dynamic characteristics of tungsten oxide hydrogen reduction are still not very clear,and the evolution process of micro morphology in the reduction process has not been described in detail.In this paper,the diffusion process of hydrogen molecules from the surface of WO₃?001?,W₂₀O₅₈?010?and W₁₈O₄₉?010?to their inside is studied by density functional theory.The transition states of each diffusion process are calculated by DMol3 module,and the property changes caused by the diffusion of hydrogen molecule are discussed.In addition,hydrogen reduction blue tungsten oxide were carried out,XRD and FE-SEM analysis were applied to study the influence of temperature and hydrogen flow rate on particle morphology and particle size in the process of hydrogen reduction of blue tungsten oxide.?1?The hydrogen molecule diffused in tungsten oxides without chemical adsorption or chemical reaction.In the diffusion process,hydrogen molecules are always negatively charged because of obtaining electrons.From the properties analysis of structures,it can be concluded that the density of state of hydrogen molecules in the transition state structures have more peaks which indicates that the hydrogen molecules in transition state structures has the strongest interaction with the surrounding w atom and O atom in the diffusion process,and the transition state structure has highest total energy in the diffusion process.?2?The activation energy of hydrogen molecule diffuses from the surface to the first layer vacancy in WO₃ is 2.02ev,and the activation energy of hydrogen molecule diffuses from the first layer vacancy to the second layer vacancy is 0.924ev.The activation energy of hydrogen molecules diffuses from the surface to the vacancy H in W₂₀O₅₈ is 2.092ev,the activation energy of hydrogen molecules diffuses from the vacancy H to the vacancy h in W₂₀O₅₈ is 1.832ev.The activation energy of hydrogen molecule diffuses from the surface to vacancy A in W₁₈O₄₉ is 2.024ev,and the activation energy of hydrogen molecule diffuses from the surface to the vacancy B in W₁₈O₄₉ is1.790ev.It shows that hydrogen molecules couldn't diffuse inside tungsten oxides spontaneously.And the activation energy required for hydrogen molecule diffusion in violet tungsten is the lowest.?3?During the hydrogen reduction of blue tungsten,the micro morphology changes as follows:hydrogen combines with O atom in blue tungsten,resulting in W-O bond breaking,forming porous block structure.With the reaction going on,new growth nuclei are gradually formed outside the block structure and on the surface.The longer the reaction time is,the less the block structure is,and more and more fine particles are scattered.The fine particles gradually grow up,and finally form reduction products with different particle sizes.?4?The particle size of W powder increased with the increase of temperature.?5?The larger the hydrogen flow rate is,the faster the hydrogen reduction rate is.However,the hydrogen flow rate has a negative correlation with the particle size of W powder and a positive correlation with the standard deviation of the particle size of W powder.