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Title: Effect of Alumina and Titania on the Oxidation of CO over Au Nanoparticles Evaluted by 13C Isotopic Transient Analysis

Abstract

Titania- and alumina-supported Au nanoparticles were synthesized by a deposition-precipitation method and subsequent thermal treatment in He. X-ray absorption spectroscopy at the Au-L{sub III} edge revealed that the as-prepared Au/TiO{sub 2} sample contained cationic Au that was reduced to a predominately metallic state after treatment in He at 623 K. Scanning transmission electron microscopy showed the Au to be highly dispersed over both the metal oxides, with an average particle size of 3.3 nm for Au/TiO{sub 2} and 2.5 nm for Au/Al{sub 2}O{sub 3}. The global rate, apparent activation energy, and orders of reaction with respect to CO and O{sub 2} of CO oxidation were different for the two metal oxide-supported samples. Steady-state isotopic transient kinetic analysis was used to explore the intrinsic turnover frequency (TOF{sub intr}) and coverage of active carbon-containing intermediates ({theta}{sub COx}) that led to carbon dioxide during CO oxidation. After correcting for CO{sub 2} readsorption, the TOF{sub intr} was found to be independent of temperature, approximately 3.4 s{sup -1} for Au/TiO{sub 2} (261-303 K) and 2.1 s{sup -1} for Au/Al{sub 2}O{sub 3} (272-343 K). At 293 K, the coverage of active carbon-containing intermediates was greater over Au/TiO{sub 2} than over Au/Al{sub 2}O{sub 3}. The higher coveragemore » of species-forming product on Au/TiO{sub 2} is attributed to the greater availability of active surface oxygen on a titania catalyst compared with an alumina catalyst.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
914113
Report Number(s):
BNL-78681-2007-JA
Journal ID: ISSN 0021-9517; JCTLA5; TRN: US200804%%316
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Catal.; Journal Volume: 238; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CARBON MONOXIDE; OXIDATION; CATALYTIC EFFECTS; TITANIUM OXIDES; ALUMINIUM OXIDES; GOLD; ACTIVATION ENERGY; CATALYSIS; REACTION INTERMEDIATES; national synchrotron light source

Citation Formats

Calla,J., Bore, M., Datye, A., and Davis, R. Effect of Alumina and Titania on the Oxidation of CO over Au Nanoparticles Evaluted by 13C Isotopic Transient Analysis. United States: N. p., 2006. Web. doi:10.1016/j.jcat.2006.01.009.
Calla,J., Bore, M., Datye, A., & Davis, R. Effect of Alumina and Titania on the Oxidation of CO over Au Nanoparticles Evaluted by 13C Isotopic Transient Analysis. United States. doi:10.1016/j.jcat.2006.01.009.
Calla,J., Bore, M., Datye, A., and Davis, R. Sun . "Effect of Alumina and Titania on the Oxidation of CO over Au Nanoparticles Evaluted by 13C Isotopic Transient Analysis". United States. doi:10.1016/j.jcat.2006.01.009.
@article{osti_914113,
title = {Effect of Alumina and Titania on the Oxidation of CO over Au Nanoparticles Evaluted by 13C Isotopic Transient Analysis},
author = {Calla,J. and Bore, M. and Datye, A. and Davis, R.},
abstractNote = {Titania- and alumina-supported Au nanoparticles were synthesized by a deposition-precipitation method and subsequent thermal treatment in He. X-ray absorption spectroscopy at the Au-L{sub III} edge revealed that the as-prepared Au/TiO{sub 2} sample contained cationic Au that was reduced to a predominately metallic state after treatment in He at 623 K. Scanning transmission electron microscopy showed the Au to be highly dispersed over both the metal oxides, with an average particle size of 3.3 nm for Au/TiO{sub 2} and 2.5 nm for Au/Al{sub 2}O{sub 3}. The global rate, apparent activation energy, and orders of reaction with respect to CO and O{sub 2} of CO oxidation were different for the two metal oxide-supported samples. Steady-state isotopic transient kinetic analysis was used to explore the intrinsic turnover frequency (TOF{sub intr}) and coverage of active carbon-containing intermediates ({theta}{sub COx}) that led to carbon dioxide during CO oxidation. After correcting for CO{sub 2} readsorption, the TOF{sub intr} was found to be independent of temperature, approximately 3.4 s{sup -1} for Au/TiO{sub 2} (261-303 K) and 2.1 s{sup -1} for Au/Al{sub 2}O{sub 3} (272-343 K). At 293 K, the coverage of active carbon-containing intermediates was greater over Au/TiO{sub 2} than over Au/Al{sub 2}O{sub 3}. The higher coverage of species-forming product on Au/TiO{sub 2} is attributed to the greater availability of active surface oxygen on a titania catalyst compared with an alumina catalyst.},
doi = {10.1016/j.jcat.2006.01.009},
journal = {J. Catal.},
number = 2,
volume = 238,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Transient studies on the oxidation of CO over Au/TiO{sub 2} have been performed at 243-363 K using a time-resolved fast-scanning Fourier transform infrared (FTIR) spectrometer coupled with a quadrupole mass spectrometer. Different CO-O{sub 2} interactions were performed by stepping CO into a steady-state He flow, O{sub 2} into a steady-state CO flow, CO into a steady-state O{sub 2} flow, and CO/O{sub 2} into an He flow. The CO oxidation reaction occurs at all temperature ranges investigated whether CO is preadsorbed or O{sub 2} is preadsorbed, indicating that there is no competition between CO and O{sub 2} for adsorption at amore » temperature range of 243-363 K (noncompetitive adsorption). It suggests that CO and O{sub 2} adsorption occurs on two different types of sites. When there is no O{sub 2} present in step feed (i.e., step CO into He), CO immediately builds up on the surface (rapid adsorption of CO) and desorbs slowly after cutting off CO flow. However, when O{sub 2} is present in the step feed (i.e., step CO/O{sub 2} into He), adsorbed CO reacts with adsorbed oxygen immediately (fast surface reaction), whereas CO{sub 2} product desorption monitored by mass spectroscopy appears to be very slow. Slow desorption of CO{sub 2} product is claimed to be the rate-limiting step of CO oxidation over Au/TiO{sub 2} at a temperature range of 243-273 K.« less
  • Alumina-supported Au nanoparticles were prepared by a deposition-precipitation method using HAuCl{sub 4} and a thermal treatment in He. X-ray absorption spectroscopy at the Au L{sub III} edge revealed that the Au particles were predominantly metallic with an average size of 1.2 nm. The kinetics of CO oxidation were measured with various amounts of co-fed H2O in the presence and absence of H2. Co-feeding H2O significantly increased the rate of CO oxidation, with rates similar to that observed during selective CO oxidation in H2. The order of reaction with respect to CO decreased from 0.32 to 0.18 by the addition ofmore » water vapor. In contrast, the O2 order increased from 0.36 to 0.48 in the presence of H2O. The temperature dependence of the rate changes with water concentration. Although values of the kinetic parameters determined in the presence of H2 were different from those in the presence of co-fed H{sub 2}O, the general trends were similar. These results suggest that the presence of H{sub 2}O or H{sub 2} and O{sub 2} have similar promotional effects during CO oxidation on Au/Al{sub 2}O{sub 3}.« less
  • Titania and titania modified with 3 and 12 {mu}mol Ce/m{sup 2} surface area of the titania were prepared and were used as supports for copper oxide. Preparations with 3 and 12 {mu}mol CuO{sub x}/m{sup 2} surface area of the support were tested for the combustion of CO, ethyl acetate, and ethanol. The results show that the Ce-doped titania surface is good as support for CuO{sub x} and that the cerium not only enhances the activity of the copper species, but also stabilizes the surface area of the TiO{sub 2} support in the presence of copper oxide. Additions of Al, K,more » and La are also found to stabilize the TiO{sub 2} support but, compared with Ce, these elements do not to the same extent enhance the activity of the copper species. Acetaldehyde is observed to ban an intermediate in the combustion of both ethanol and ethyl acetate over Cu-Ce-Ti-O catalysts. Since acetaldehyde is more harmful than any of the reactants and also is photochemically active, it is in applications important to assure that the combustion is complete. Cu-Ce-Ti-O catalysts show good performance not only for feeds without water vapor, but also for humid feeds. Although the concentrations of intermediates are affected by the addition of water, there is little effect on the temperature required for obtaining complete conversion to carbon dioxide and water. Characterization with XRD, FT-Raman, TPR, and XPS indicates that the dispersed copper species are in the form of patches or a bidimensional layer which interacts with the surface of the support. When the content of cerium and copper is low, other types of dispersed copper species are present, which possibly are monomers or dimers. The copper species are predominantly Cu{sup 2+} species.« less
  • The reduction of NO with CO on a perovskite catalyst, LaCoO[sub 3], was investigated by means of steady state isotopic transient kinetic analysis (SSITKA). Steady state reactions were carried out at temperature of 300--700 C, while the isotopic transient experiments were carried out at temperatures of 500--700 C. Isotopic switches of [sup 12]CO to [sup 13]CO or [sup 14]NO to [sup 15]NO were performed after the reaction reached steady state. In order to determine the effect of readsorption, experiments at various temperatures were carried out as a function of space velocity. The SSITKA results for NO reduction with CO indicatedmore » that all the species (reactants and products) had measurable surface lifetimes and concentrations on the catalyst surface at various temperatures. Both the steady state and the SSITKA results were consistent with N[sub 2]O being a precursor in the formation of N[sub 2] at temperature below 600 C. SSITKA results indicated that the entire catalyst surface was involved in the reaction, and that, at high temperature, CO[sub 2] desorption became limiting for the overall reaction. This was most likely due to the rapid formation and slow decomposition of carbonates on the surface.« less