CO Adsorption on the Model Catalyst Pd/CeO_2-x(111)/Rh(111)

Abstract

X-ray photoelectron spectroscopy (XPS) has been used to investigate the stoichiometry of CeO 2-x (111) ultrathin films grown on Rh(111), as well as the modification of the average Ce oxidation state by Pd and CO at room temperature. The stoichiometry of three-layer CeO 2-x (111) has been varied between CeO 1.91 and CeO 1.61 by altering the oxygen pressure during Ce deposition. Pd deposition induces a change in the Ce oxidation state that is highly dependent on the initial stoichiometry of the CeO 2-x films. The difference in behavior of CeO 2-x thin films with different oxidation states is ascribed to the presence of a Ce 2 O 3 (0001) termination of the more reduced thin films. CO adsorbs only in the presence of Pd, independent of the stoichiometry of the original film, without changing the oxidation state of the CeO 2-x thin film.

Structure, Morphology and Reducibility of Epitaxial Cerium Oxide Ultrathin Films and Nanostructures

“…Indeed, it is also possible to grow films at reduced oxygen pressures to obtain CeO 2- x films with 0 < x < 1/2 [27,29,46]. …”

Reducible Oxides as Ultrathin Epitaxial Films

“…The repeating unit along the (111) direction is an O-Ce-O triple layer, which in the following will be referred to as a monolayer (ML). Cerium oxide ultrathin films exposing the (111) surface can be obtained by epitaxial growth on metallic single crystal substrates with six-fold surface symmetry such as (111) surfaces of cubic structures [12][13][14][15][16][17][18], or hcp (0001) surfaces [14,19,20]. The lattice mismatch between cerium oxide and most of the metal substrates is quite large and it amounts to approximately 30-40%.…”

“…The results of the early studies provided a strong motivation for subsequent works, using more controlled growth procedures, combined with a variety of techniques for surface characterization down to the atomic level. Cerium oxide ultrathin films with the (111) fluorite structure were grown on Pt(111) [17,21,28,29], Rh(111) [15,16], Ru(0001) [14,20], Ni(111) [14], Cu(111) [30,31], Au(111) [32], Pd(111) [33] and Re(0001) [34] substrates. On one side these studies confirmed the enhanced reactivity of bidimensional cerium oxide films compared to the clean substrates and the importance of metal-oxide interface sites [31,35], on the other they clarified important fundamental aspects linked to the reducibility of low-dimensional supported cerium oxide systems [15,29,30].…”

Влияние Адсорбированных Молекул СО На Электронное Состояние Нанопленок Иттербия, Выращиваемых На Кремниевых Подложках

“…В частности, довольно много работ посвящено изучению адсорбционных свойств таких структур. При этом в значительной части из них в качестве адсорбата используется монооксид углерода (угарный газ СО) [3][4][5][6][7][8]. Недостатком этих работ является то, что в них не проводилось систематическое изучение типа связи молекул СО с поверхностью нанообъектов, размерных зависимостей адсорбционных свойств последних и возможного влияния адсорбата на свойства их объема.…”