Site Selective Detection of Methane Dissociation on Stepped Pt Surfaces

We report a combined experimental and theoretical study comparing methane dissociation on three di erent platinum surfaces Pt(111), Pt(211), and Pt(110)-(1 × 2). Re ection absorption infrared spectroscopy (RAIRS) was used to detect chemisorbed methyl species formed by dissociative chemisorption of CH4 on speci c surface sites and to measure surface- site-speci c sticking coe cients of CH4 on the terrace, step, and ridge sites as function of incident translational energy. Methane dissociation is observed to be direct on all sites and di usion of the chemisorbed methyl species is absent for surface temperature below 150 K. The experimental data are compared with the results of density functional (DFT) calculations that give minimum energy barriers for CH4 chemisorption that properly account for the experimental relative site-speci c reactivities. Also in agreement with experiments, DFT results predict a negligible e ect of co-adsorbed H and CH3 species on the vibrational frequency of a methyl group chemisorbed on terrace and step sites of Pt(211). However, the origin of the red-shift of the RAIRS peak of CH3 chemisorbed on terrace sites compared with that on step sites of Pt(211) remains elusive and still demands further investigation.