Dissociative chemisorption of methane on clean and oxygen precovered Pt(111)

Effects of adsorbed oxygen on dissociative chemisorption of methane molecules on a platinum (111) surface have been studied by using molecular beam surface scattering. It has been found that for an oxygen precoverage of 0.42 ML on Pt(111), and for the clean surface, an increase in translational energy (En) of CH4 and in surface temperature (Ts) of the sample strongly enhance the methane activation in the range of parameters studied, 60 < En < 125 kJ/mol and 300 K < Ts < 750 K. However, the absolute dissociation probability of CH4 is always much smaller for the oxygen precovered surface than for the clean surface. Clearly, oxygen poisons the CH activation. This poisoning of the surface implies that oxygen sterically blocks the active surface sites for dissociative chemisorption of CH4 or it inhibits the dissociation electronically. Despite of surface poisoning, the CH4 activation mechanism is probably the same for the clean and oxygen covered Pt(111) surfaces.