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Title: Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions

Abstract

We compare the activity and relevant gold species of nanostructured gold-cerium oxide and gold-iron oxide catalysts for the CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze the water-gas shift reaction. Gold species weakly bound to ceria (doped with lanthana) or iron oxide can be removed by sodium cyanide at pH {>=}12. Both parent and leached catalysts were investigated. The activity of the leached gold-iron oxide catalyst in CO oxidation is approximately two orders of magnitude lower than that of the parent material. However, after exposure to H{sub 2} up to 400 C gold diffuses out and is in reduced form on the surface, a process accompanied by a dramatic enhancement of the CO oxidation activity. Similar results were found with the gold-ceria catalysts. On the other hand, pre-reduction of the calcined leached catalyst samples did not promote their water-gas shift activity. UV-Vis, XANES and XPS were used to probe the oxidation state of the catalysts after various treatments.

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929972
Report Number(s):
BNL-80577-2008-JA
TRN: US200822%%949
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Topics in Catalysis; Journal Volume: 44; Journal Issue: 39449
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COMPARATIVE EVALUATIONS; CATALYST SUPPORTS; GOLD; CERIUM OXIDES; IRON OXIDES; OXIDATION; CARBON MONOXIDE; WATER GAS; SHIFT PROCESSES; NANOSTRUCTURES; national synchrotron light source

Citation Formats

Deng,W., Carpenter, C., Yi, N., and Flytzani-Stephanopoulos, M. Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions. United States: N. p., 2007. Web. doi:10.1007/s11244-007-0293-9.
Deng,W., Carpenter, C., Yi, N., & Flytzani-Stephanopoulos, M. Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions. United States. doi:10.1007/s11244-007-0293-9.
Deng,W., Carpenter, C., Yi, N., and Flytzani-Stephanopoulos, M. Mon . "Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions". United States. doi:10.1007/s11244-007-0293-9.
@article{osti_929972,
title = {Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions},
author = {Deng,W. and Carpenter, C. and Yi, N. and Flytzani-Stephanopoulos, M.},
abstractNote = {We compare the activity and relevant gold species of nanostructured gold-cerium oxide and gold-iron oxide catalysts for the CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze the water-gas shift reaction. Gold species weakly bound to ceria (doped with lanthana) or iron oxide can be removed by sodium cyanide at pH {>=}12. Both parent and leached catalysts were investigated. The activity of the leached gold-iron oxide catalyst in CO oxidation is approximately two orders of magnitude lower than that of the parent material. However, after exposure to H{sub 2} up to 400 C gold diffuses out and is in reduced form on the surface, a process accompanied by a dramatic enhancement of the CO oxidation activity. Similar results were found with the gold-ceria catalysts. On the other hand, pre-reduction of the calcined leached catalyst samples did not promote their water-gas shift activity. UV-Vis, XANES and XPS were used to probe the oxidation state of the catalysts after various treatments.},
doi = {10.1007/s11244-007-0293-9},
journal = {Topics in Catalysis},
number = 39449,
volume = 44,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {l_brace}Au+AuO{sub x}{r_brace}-CeO{sub 2} catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 C, a complete AuO{sub x}{yields}Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO{sub 2}(111) single crystal corroborate that cationic Au{sup {delta}} species cannot be the key sites responsible for the WGS activity at high temperatures. The rate determining steps for the WGS seem to occur at the gold-ceria interface, with themore » active sites involving small gold clusters (<2 nm) and O vacancies.« less
  • X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO{sub 2}(111) surfaces. Upon adsorption on CeO{sub 2}(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500-800 K) leads to partial reduction of the ceria substrate with the formation of Ni{sup 2+} species that exists as NiO and/or Ce{sub 1-x}Ni{sub x}O{sub 2-y}. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species onmore » CeO{sub 2}(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce{sup +3} cations, CO dissociates on the surface at 300 K forming NiC{sub x} compounds that may be involved in the formation of CH{sub 4} at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO{sub 2}(111) surfaces are able to catalyze the production of methane from CO and H{sub 2}, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO{sub 2}(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water-gas shift reaction.« less
  • X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO2(111) surfaces. Upon adsorption on CeO2(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500 800 K) leads to partial reduction of the ceria substrate with the formation of Ni2? species that exists as NiO and/or Ce1-xNixO2-y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO2(111) which are clearly distinguishablemore » from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce?3 cations, CO dissociates on the surface at 300 K forming NiCx compounds that may be involved in the formation of CH4 at higher temperatures. At medium and large Ni coverages ([0.3 ML), the Ni/CeO2(111) surfaces are able to catalyze the production of methane from CO and H2, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (\0.3 ML), the Ni/CeO2(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water gas shift reaction.« less
  • Combined in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies have been conducted to follow gold structural changes of low-content (<1%Au) gold-ceria catalysts in water-gas shift (WGS) reaction tests at 100 and 200 C; and after heating the used catalysts in oxygen gas at 150 C. Gold in the fresh (400 C-calcined) material was atomically dispersed in cerium oxide. Under WGS reaction conditions, reduction of the oxidized gold species was observed, accompanied by gradual gold aggregation. The Au-Au coordination number is zero for the fresh material, but increases with the reaction temperature, to 6.5more » {+-} 2.4 (after use at 100 C) and to 8.7 {+-} 1.5 (after 200 C) in a gas mixture containing 5% CO- 3% H2O in helium. The second important parameter is the reaction gas composition which determines the extent of Au-O reduction. The lower the reduction potential of the reaction gas mixture, the more oxidized the gold is in the used catalyst, and the higher its activity. The maximum activity of Au-CeO2 was that of the fully dispersed Au-O-Ce fresh material. Loss of surface oxygen took place during reaction, as measured by H2-TPR of the used samples, and it was commensurate with the activity loss. Attempts to reoxidize and redisperse the gold by heating in oxygen gas at 150 C were not effective. However, we report here that complete recovery of the surface oxygen amount and redispersion of gold in ceria was possible after a 400 C- oxygen treatment of both the 100 C- and 200 C- used catalyst samples, with concomitant recovery of the initial catalyst activity. These tests were conducted by consecutive H2-TPR/steady-state catalyst activity measurements in the same microreactor.« less