The Mechanism Of Hydrogen Reduction Process Of Tungsten Oxide Is Calculated Based On DFT

The hydrogen reduction of tungsten oxide is now the most widely used industrial technology for preparing ultra fine tungsten powder.A lot of works have been done by researchers to clarify the technology of producing nano tungsten powder,but there are still lots of contoversies on the mechanism of adsorption among the reduction process.As a result,it's reasonable to make use of crystal structure of tungsten oxides to study the mechnism of hydrogen reduction of tungsten oxides.This paper present the work on crystal structure of yellow tungsten oxide,blue tungsten oxide and violet tungsten oxide,and the mechanism of hydrogen redcution on their crystal surface.All the calculations were performed whtin the framwork of density functional theory implemented in CASTEP runned on Shenzhen supercomputing center.The results are as follows:When the distance between H₂ and WO₃?001?surface is bigger than 0.8?,the interaction force between them is so small that it's hard for hydrogen to chemically adsorb on surface but physically adsorb on WO₃?001?surface.On the contrary,if the distance between them is smaller than 0.8?,the chemical adsorption appear in which hydrogen molecule will dissosiate into two hydrogen atom bonding with W or O.The hydrone appears when hydrogen adsorb on W₁₈O₄₉?010?O-terminated surface as O-H-O_1c configuration,however,the hydrone still bond with the surface as O atom in hydrone bonding with W in surface due to its under coordination.The hydroxyl appear s when the hydrogen adsorb on the surface as O-H₂-O_3c configuration which means the generation of hydrate?WO₂?OH?₂?.During the hydrogen adsorption process on W₁₈O₄₉?010?WO-terminated surface with configuration WO-H₂-O_3c and WO-H₂-O_2c,lots of W-O bond in crystal break and W-W bond generate.The structure of crystal changes notably into much more stable state and total energy of whole crystal system decrease substantially.During the hydrogen adsorption process on W₂₀O₅₈?010?WO-terminated surface with WO-W_H-O_H configuration,the original W-O bonds break and structure of oxygen vacancies change enormously as new W-O bonds and W-W bonds emmerging.While hydrogen adsorbing on the same surface with configuration WO-W_2H-O_2H,the hydrone separated from surface appear as hydrogen bonding with oxygen during which process the W-O bonds break and tungsten oxide is reduced to ultra fine tungsten powder.The generated hydrone still bond with surface while hydrogen adsorb on 1-coordinated O and 2-coordinated O on W₂₀O₅₈?010? O-terminated surface.It may be because of the stronger W-O bond near near O vancancy and the hydrone generated near O vacancy separates from surface and hydrogen reduction of tungsten oxide proceeds.