Study On Catalytic Mechanism Of Tungsten Carbide Based On Density Function Theory

With the development of industry, the demand of precious metals (especially platinum group metals) catalyst is increasing, while their reserves are decreasing year by year. WC has almost the same catalysis with Pt, therefore,to a certain extent, WC may replace Pt to deal with the difficulty of decrease of Pt's reserve.In this paper CO oxidation on Pt(111) and Pt(100) is studied by density functional theory. The low energy pathway and transition state for the reaction are identified, population analysis and density of state are calculated by CASTEP software. It is suggested for the Langmuir-Hinshelwood reaction of catalytic CO oxidation on Pt(111) and Pt(100). The reaction pathway is shown that the CO molecule has to approach the Oa atom, then Oa atom is activated, CO2 is formed in the end. In contrast with the reactant, the bond force of C and Pt in the productant is weakened obviously. In the structure of transition state on the two surface∠O-CO are 111°and 119°, respectively. The bond lengths of CO2 in the productant are 1.20 ? and 1.28 ?, the angle of the bond is 132°. The activation energies are 1.13eV and 0.75eV.The study of CO oxidation on the WC surface shows that CO oxidation on the WC ( 101 0) and WC (0001) surface also follow the Langmuir-Hinshelwood (L-H) mechanism. The reaction processes on metal Pt and WC surface are roughly the same. LDOS and population analysis show that, in the process of CO oxidation on the WC ( 101 0) and WC (0001) surface, the bond between C and Oa in the structure of transition state are weak. Compared to WC ( 101 0) surface, the structure of the final state over WC (0001) Surface, C and two O atoms are closer to the actual CO2 molecules. The activation energy of WC ( 101 0) surface is 1.13eV, which is lower than the energy of WC (0001) surface (2.24eV). The law is similar with Pt (111) and Pt (100) surface. The catalysis mechanism of WC from the view of electron structure is studied. According to the results of density of states, it shows that the electron structure of WC has remarkable resemblance to that of Pt, but the d bond of WC is wider than that of Pt, maybe this is the reason why WC can not compete with Pt.