Methanol Adsorption and Reaction on Samaria Thin Films on Pt(111)

We investigated the adsorption and reaction of methanol on continuous and discontinuous films of samarium oxide (SmO) grown on Pt(111) in ultrahigh vacuum. The methanol decomposition was studied by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), while structural changes of the oxide surface were monitored by low-energy electron diffraction (LEED). Methanol dehydrogenates to adsorbed methoxy species on both the continuous and discontinuous SmO films, eventually leading to the desorption of CO and H₂ which desorbs at temperatures in the range 400-600 K. Small quantities of CO₂ are also detected mainly on as-prepared Sm₂O₃ thin films, but the production of CO₂ is limited during repeated TPD runs. The discontinuous film exhibits the highest reactivity compared to the continuous film and the Pt(111) substrate. The reactivity of methanol on reduced and reoxidized films was also investigated, revealing how SmO structures influence the chemical behavior. Over repeated TPD experiments, a SmO structural/chemical equilibrium condition is found which can be approached either from oxidized or reduced films. We also observed hydrogen absence in TPD which indicates that hydrogen is stored either in SmO films or as OH groups on the SmO surfaces.