Methane dissociation on Pt(1 1 1), Ir(1 1 1) and PtIr(1 1 1) surface: A density functional theory study

A periodic density functional theory (DFT) was utilized to calculate the dissociation process of methane (CH4) on Pt(1 1 1), Ir(1 1 1) and PtIr(1 1 1) surfaces. As compared to the adsorption energy, the most stable configurations of methane, methane dissociation species and co-adsorption of CHx (x = 0–3) with H were obtained. The kinetic results of the CH4 dissociation indicated that the dissociating of CH4 into CH3 and H is the rate-limiting step on the PtIr(1 1 1) and Ir(1 1 1) surfaces. CH was the most abundant species that was difficult to dehydrogenate into C and H. Particularly, the activation barrier for CH3 → CH2 + H and CH2 → CH + H on the Pt(1 1 1) surface is 3.5 and 1.4 times, respectively, higher than that on the PtIr(1 1 1) surface. According to the thermodynamics principles, the successive dehydrogenation of CH4 preferred to take place on the PtIr surface.