Simulation Calculation Of Chemisorption Behaviors Of Tungsten Carbide Based On Density Function Theory

WC has almost the same catalysis capacity as Pt, so it is hopeful to use WC to replace Pt to deal with the difficult of decrease of Pt's reserves. In this paper, the chemisorption energy, length of C-O bond, C-Pt bond, C-W bond, population analysis, density of state(DOS) of CO-Pt adsorption system, CO-WC adsorption system, and CO/O-WC co-adsorption system are studied by generalized gradient approximation(GGA) based on density function theory(DFT). The results show that when the coverage is 0.25ML, the preference sites of CO chemisorption on Pt are the bridge site of Pt(100), short bridge site of Pt(110), hcp hollow site of Pt(111), respectively; the chemisorption energies are 2.11eV, 2.37eV, 1.96eV, respectively. As to CO-WC system, when the coverage is 0.25ML, the preference sites of CO chemisorption on WC are the top site of WC(0001), long bridge site of WC( 011 1), hollow site of WC( 101 0), respectively; the chemisorption energies are 1.64eV, 2.90eV, 3.51eV, respectively. There exists electron transfer between CO molecule and metal atoms during the adsorption. After adsorption, C-O bond is weaken, its bond length is longer than before, the interactions of inner Pt atoms and W atoms are weaken too, their populations have an obvious decrease. According to the DOS analysis, when CO adsorbs to the Pt surface, its 4σ, 1π, 5σ, 2π* molecular orbitals participate in the bonding process, as to CO-WC system, its adsorption action is stronger, the low energy 3σmolecular orbital of CO also participate in the bonding process besides its 4σ, 1π, 5σ, 2π* molecular orbitals.The study on the CO/O-WC co-adsorption system shows that the difference of chemisorption energy of CO adsorbing on different sites on WC(0001) is very small which means that CO molecule can move along the surface without difficulty. While the most chemisorption energy of O adsorbing on WC(0001) is up to 6.20eV, meaning that it is hard for O to move along the surface after the adsorption. So it can conjecture the process of CO's oxidation on WC surface like this: firstly, O adsorbs on hcp site of WC(0001) surface stably, then CO molecule adsorbs on other sits of WC(0001) surface and moves along the surface until it contacts O on the top site near to O, at last the oxidation reaction happens.The simulation calculation of electron structure of WC can explain catalysis mechanism of WC to a certain extant. According to the DOS results, it shows that the electron structure of WC has remarkable resemblance to electron structure of Pt after W and C formed WC. Besides, both WC and Pt have sub-shell unoccupied orbital, which is good to adsorption of CO. While the d bond of WC is wider than that of Pt, maybe this is the reason why the catalysis activity of WC is not completely same as that of Pt.