Potassium Adsorption on Pt(111) and its Effect on Co Chemisorption

ABSTRACTTemperature programmed desorption (TPD) and secondary ion mass spectrometry (SIMS) have been used to study the chemisorption properties of carbon monoxide on potassium predosed Pt. SIMS cluster ions (such as K+, K2+, KO+ and KCO+) were monitored to probe, K-CO interactions. Large changes in the SIMS yields are observed as the potassium coverage is varied. The SIMS results are correlated with previous work function change and TPD studies. Temperature programmed secondary ion mass spectrometry of potassium-containing ions indicates a local interaction between potassium and CO molecules.As typically observed on transition metal surfaces, two different CO TPD states are observed. The lower temperature state shifts to higher temperatures with increasing potassium coverage and to lower temperatures with increasing CO exposure. The high temperature CO state builds in with increasing potassium coverage and is accompanied by simultaneous potassium desorption. Evidence for the occurrence of both long-range (indirect) and short-range (direct) potassium effects on adsorbed CO is presented.