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

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.

Methanol Adsorption and Oxidation on Reduced and Oxidized TbOx(111) Surfaces

“…As a final comparison, we have recently reported that continuous thin films of Sm 2 O 3 (111) highly active toward promoting the complete dehydrogenation of adsorbed CH 3 OH, with the CO and H 2 products desorbing near 600 K. 25 The high activity of Sm 2 O 3 (111) for promoting CH 3 OH conversion to CO and H 2 is similar to that of reduced CeO x (111) surfaces while being quite distinct from the low reactivity of Tb 2 O 3 and Pr 2 O 3 toward CH 3 OH. Unlike the Ce, Pr, and Tb oxide systems, samaria does not form a stable dioxide and yet exhibits high activity toward CH 3 OH.…”

“…Only a few studies by Mullins et al dealt with thin films of dysprosium and praseodymium oxides as supports for metal particles, , and nearly 20 years ago thin samarium oxide films and their interaction with CO were studied on Ru(0001) . Recently, we contributed work on the growth and structural properties of samaria thin films and their reactivity toward methanol adsorption and terbia thin films grown on Pt(111) and Cu(111) single crystals, respectively. Thin films of PrO x and CePrO x have also been studied on silicon surfaces .…”

Support effects in iridium-catalyzed aerobic oxidation of benzyl alcohol studied by modulation-excitation attenuated total reflection IR spectroscopy

“…The original band at 1016 cm -1 is assigned to adsorbed alkoxide species (benzyloxy) bound to the metal surface (Ir), while bands at higher wavenumber originate from alkoxide adsorbed on metal cations of the titania overlayer due to oxygen vacancies [59]. The H 2 pretreatment at high temperature leads to a reduction of TiO 2 to TiO x in the titania layer covering the Ir particles [29,36].…”

“…Thus the Ir particles completely covered by the titania overlayer enhanced the second oxidative dehydrogenation, that is the reaction of the intermediate alkoxide to BAL. A new band at 1098cm -1 emerged due to the formation of on-top alkoxy species on the metal cation of the titania support[59]. The oxygen vacancy of Ti cations seems to be filled with the adsorbed alkoxy species (C 6 H 5 CH 2 O-) to balance the charge.…”