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Abstract
We investigated the adsorption and reaction of methanol on continuous and discontinuous films of samarium oxide (SmOx) 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 SmOx 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 SmOx structures influence the chemical behavior. Over repeated TPD experiments, a SmOx 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 SmOx films or as OH groups on the SmOx surfaces.
Highlights
Rare earth oxides (REOs), especially the oxides of lanthanum and cerium, find their main applications as catalysts in the chemical industry
In a previous study combining scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) we have demonstrated that a high-quality Sm2 O3 (111) thin film can be grown on
By combining temperature-programmed desorption (TPD), infrared reflection-absorption spectroscopy (IRRAS), and LEED with structural information previously determined by STM, we find strong correlations between the samarium oxide (SmOx) /Pt(111) film structure and its chemical properties
Summary
Rare earth oxides (REOs), especially the oxides of lanthanum and cerium, find their main applications as catalysts in the chemical industry. The other oxides of the rare earth elements have shown promising potential in diverse fields like microelectronics [3] or in heterogeneously catalyzed reactions for which the selective formation of an intermediate product has increased importance. In their stable forms under atmospheric conditions CeO2 , Pr6 O11 and Tb4 O7 have shown superior lattice oxygen mobility and a number of stable intermediate crystallographic phases This property makes them good catalysts for total oxidation reactions and ceria has been studied extensively in the field of surface science. By combining temperature-programmed desorption (TPD), infrared reflection-absorption spectroscopy (IRRAS), and LEED with structural information previously determined by STM, we find strong correlations between the SmOx /Pt(111) film structure and its chemical properties
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