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Title: Rh-Promoted Methanol Decomposition on Cerium Oxide Thin Films

Abstract

Methanol adsorption and reaction have been studied on Rh-deposited cerium oxide thin films under UHV conditions using temperature-programmed desorption and synchrotron soft X-ray photoelectron spectroscopy. The methanol behavior was examined as a function of the Ce oxidation state, methanol exposure, and Rh particle size and coverage. When Rh nanoparticles were deposited on the ceria films, methanol decomposed on Rh to CO and H below 200 K. H atoms recombined and desorbed between 200 and 300 K. CO evolved from Rh deposited on fully oxidized ceria between 400 and 500 K. However, on reduced ceria films, the CO on Rh further decomposed to atomic C. Methanol adsorbed on the ceria films deprotonated to form methoxy as the only intermediate on the surface. This methoxy decomposed and desorbed as CO and H2 at higher temperatures regardless of the ceria oxidation state. Compared with the methanol reaction on Rh-free ceria thin films, formaldehyde formation from methoxy was completely suppressed after Rh deposition. Our results indicate that Rh can promote the decomposition of methoxy adsorbed on the ceria and that decomposition of methoxy intermediates occurred at the metal/oxide interfaces. On the other hand, the reduced ceria can promote total methanol decomposition on Rh.

Authors:
;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
913980
Report Number(s):
BNL-78548-2007-JA
Journal ID: ISSN 1089-5647; JPCBFK; TRN: US0801447
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Phys. Chem. B; Journal Volume: 110
Country of Publication:
United States
Language:
English
Subject:
10 SYNTHETIC FUELS; 43 PARTICLE ACCELERATORS; ADSORPTION; ATOMS; CERIUM OXIDES; DEPOSITION; DESORPTION; FORMALDEHYDE; METHANOL; PARTICLE SIZE; SYNCHROTRONS; THIN FILMS; X-RAY PHOTOELECTRON SPECTROSCOPY; national synchrotron light source

Citation Formats

Zhou,J., and Mullins, D.. Rh-Promoted Methanol Decomposition on Cerium Oxide Thin Films. United States: N. p., 2006. Web. doi:10.1021/jp061985v.
Zhou,J., & Mullins, D.. Rh-Promoted Methanol Decomposition on Cerium Oxide Thin Films. United States. doi:10.1021/jp061985v.
Zhou,J., and Mullins, D.. Sun . "Rh-Promoted Methanol Decomposition on Cerium Oxide Thin Films". United States. doi:10.1021/jp061985v.
@article{osti_913980,
title = {Rh-Promoted Methanol Decomposition on Cerium Oxide Thin Films},
author = {Zhou,J. and Mullins, D.},
abstractNote = {Methanol adsorption and reaction have been studied on Rh-deposited cerium oxide thin films under UHV conditions using temperature-programmed desorption and synchrotron soft X-ray photoelectron spectroscopy. The methanol behavior was examined as a function of the Ce oxidation state, methanol exposure, and Rh particle size and coverage. When Rh nanoparticles were deposited on the ceria films, methanol decomposed on Rh to CO and H below 200 K. H atoms recombined and desorbed between 200 and 300 K. CO evolved from Rh deposited on fully oxidized ceria between 400 and 500 K. However, on reduced ceria films, the CO on Rh further decomposed to atomic C. Methanol adsorbed on the ceria films deprotonated to form methoxy as the only intermediate on the surface. This methoxy decomposed and desorbed as CO and H2 at higher temperatures regardless of the ceria oxidation state. Compared with the methanol reaction on Rh-free ceria thin films, formaldehyde formation from methoxy was completely suppressed after Rh deposition. Our results indicate that Rh can promote the decomposition of methoxy adsorbed on the ceria and that decomposition of methoxy intermediates occurred at the metal/oxide interfaces. On the other hand, the reduced ceria can promote total methanol decomposition on Rh.},
doi = {10.1021/jp061985v},
journal = {J. Phys. Chem. B},
number = ,
volume = 110,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • No abstract prepared.
  • The adsorption and reaction of CO on Rh-loaded ceria was studied by soft x-ray photoelectron spectroscopy. The system was studied as a function of the degree of oxidation of the ceria and different preparations of the Rh. Molecular CO and atomic C on Rh are readily distinguished in the C 1s spectra. CO adsorbed directly on ceria, possibly as carbonate or carboxylate, is also observed in the C 1s spectra. The degree of dissociation of CO on Rh deposited on ceria (Rh/CeO{sub x}) is directly dependent on the degree of oxidation of the ceria. Nearly total decomposition can occur ifmore » the ceria substrate is highly reduced. Molecular CO also persists to a higher temperature on Rh deposited on reduced ceria compared with Rh on oxidized ceria. The degree of dissociation does not depend on the amount of Rh deposited or on the annealing treatment after deposition.« less
  • Highlights: • Thin films of ceria doped by rhodium deposited by RF magnetron sputtering. • Concentration of rhodium has great impact on properties of Rh–CeO{sub x} thin films. • Intensive oxygen migration in films with low concentration of rhodium. • Oxygen migration suppressed in films with high amount of Rh dopants. - Abstract: Ceria containing highly dispersed ions of rhodium is a promising material for catalytic applications. The Rh–CeO{sub x} thin films with different concentrations of rhodium were deposited by RF magnetron sputtering and were studied by soft and hard X-ray photoelectron spectroscopies, Temperature programmed reaction and X-ray powder diffractionmore » techniques. The sputtered films consist of rhodium–cerium mixed oxide where cerium exhibits a mixed valency of Ce{sup 4+} and Ce{sup 3+} and rhodium occurs in two oxidation states, Rh{sup 3+} and Rh{sup n+}. We show that the concentration of rhodium has a great influence on the chemical composition, structure and reducibility of the Rh–CeO{sub x} thin films. The films with low concentrations of rhodium are polycrystalline, while the films with higher amount of Rh dopants are amorphous. The morphology of the films strongly influences the mobility of oxygen in the material. Therefore, varying the concentration of rhodium in Rh–CeO{sub x} thin films leads to preparing materials with different properties.« less
  • The role of trivalent rare-earth dopants in ceria epitaxial films on surface ion exchange reactivity and ion conductivity has been systematically studied. Single-crystal epitaxial films with unique crystal orientation and micro-structure nature have allowed us to rule out the influence of structural defects on both transport and surface ion exchange properties. The films conductivities were larger than those reported in literature for both polycrystalline ceramic pellets and crystalline films. An increase in oxygen vacancies and Ce 3+ concentration while decreasing the dopant ionic radius from La 3+ to Yb 3+ was observed, thus explaining the measured increased activation energy andmore » enhanced surface reactivity. The more significant ability of smaller dopant ionic radius in releasing the stress strength induced by the larger Ce 3+ ionic radius allows promoting the formation of oxygen vacancies and Ce 3+, which are two precious species in determining the efficiency of ion transport and surface ion exchange processes. This can open new perspectives in designing ceria-based materials in tailoring functional properties, either ion migration or surface reactivity, by rational cation substitutions.« less
  • Formaldehyde adsorption and reaction have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The formaldehyde behavior was examined as a function of temperature, exposure and Ce oxidation state. Formaldehyde chemisorbs on fully oxidized CeO{sub 2} as dioxymethylene, CH{sub 2}O{sub 2}. The dioxymethylene decomposes and desorbs as formaldehyde between 200 K and 400 K. No other products are formed. On reduced ceria, formaldehyde also adsorbs as dioxymethylene. In addition to the formaldehyde desorption between 200 K and 400 K, a more strongly bound form of dioxymethylene is formed that produces formaldehyde at 440more » K. Above 400 K, some of the dioxymethylene reacts to form formate and methoxy on the surface. These species decompose to produce H{sub 2}, CO and CH{sub 2}O above 500 K.« less