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Title: Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study

Abstract

A tandem experimental and theoretical investigation of a mesoporous ceria catalyst reveals the properties of the metal oxide are conducive for activity typically ascribed to metals, suggesting reduced Ce 3+ and oxygen vacancies are responsible for the inherent bi-functionality of CO oxidation and dissociation of water required for facilitating the production of H 2. The degree of reduction of the ceria, specifically the (1 0 0) face, is found to significantly influence the binding of reagents, suggesting reduced surfaces harbor the necessary reactive sites. The metal-free catalysis of the reaction is significant for catalyst design considerations, and the suite of in situ analyses provides a comprehensive study of the dynamic nature of the high surface area catalyst system. Finally, this study postulates feasible improvements in catalytic activity may redirect the purpose of the water-gas shift reaction from CO purification to primary hydrogen production.

Authors:
 [1];  [2];  [1];  [3];  [3];  [4];  [5];  [6];  [1];  [5];  [5];  [1]
  1. Univ. of Connecticut, Storrs, CT (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States); State Univ. of New York at Stony Brook, Stony Brook, NY (United States)
  3. Aarhus Univ. (Denmark)
  4. Technical Univ. of Catalonia- BarcelonaTech, Barcelona (Spain)
  5. Brookhaven National Lab. (BNL), Upton, NY (United States)
  6. Univ. of Connecticut, Storrs, CT (United States); Tanta Univ., Tanta (Egypt)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1368675
Alternate Identifier(s):
OSTI ID: 1401890
Report Number(s):
BNL-114017-2017-JA
Journal ID: ISSN 1867-3880; R&D Project: CO040; KC0302010
Grant/Contract Number:
SC00112704; SC0012704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ChemCatChem
Additional Journal Information:
Journal Volume: 9; Journal Issue: 8; Journal ID: ISSN 1867-3880
Publisher:
ChemPubSoc Europe
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ceria; water-gas-shift; hydrogen; fuel cells; metal-free catalysis

Citation Formats

Guild, Curtis J., Vovchok, Dimitriy, Kriz, David A., Bruix, Albert, Hammer, Bjørk, Llorca, Jordi, Xu, Wenqian, El-Sawy, Abdelhamid, Biswas, Sourav, Rodriguez, Jose A., Senanayake, Sanjaya D., and Suib, Steven L. Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study. United States: N. p., 2017. Web. doi:10.1002/cctc.201700081.
Guild, Curtis J., Vovchok, Dimitriy, Kriz, David A., Bruix, Albert, Hammer, Bjørk, Llorca, Jordi, Xu, Wenqian, El-Sawy, Abdelhamid, Biswas, Sourav, Rodriguez, Jose A., Senanayake, Sanjaya D., & Suib, Steven L. Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study. United States. doi:10.1002/cctc.201700081.
Guild, Curtis J., Vovchok, Dimitriy, Kriz, David A., Bruix, Albert, Hammer, Bjørk, Llorca, Jordi, Xu, Wenqian, El-Sawy, Abdelhamid, Biswas, Sourav, Rodriguez, Jose A., Senanayake, Sanjaya D., and Suib, Steven L. Mon . "Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study". United States. doi:10.1002/cctc.201700081. https://www.osti.gov/servlets/purl/1368675.
@article{osti_1368675,
title = {Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study},
author = {Guild, Curtis J. and Vovchok, Dimitriy and Kriz, David A. and Bruix, Albert and Hammer, Bjørk and Llorca, Jordi and Xu, Wenqian and El-Sawy, Abdelhamid and Biswas, Sourav and Rodriguez, Jose A. and Senanayake, Sanjaya D. and Suib, Steven L.},
abstractNote = {A tandem experimental and theoretical investigation of a mesoporous ceria catalyst reveals the properties of the metal oxide are conducive for activity typically ascribed to metals, suggesting reduced Ce3+ and oxygen vacancies are responsible for the inherent bi-functionality of CO oxidation and dissociation of water required for facilitating the production of H2. The degree of reduction of the ceria, specifically the (1 0 0) face, is found to significantly influence the binding of reagents, suggesting reduced surfaces harbor the necessary reactive sites. The metal-free catalysis of the reaction is significant for catalyst design considerations, and the suite of in situ analyses provides a comprehensive study of the dynamic nature of the high surface area catalyst system. Finally, this study postulates feasible improvements in catalytic activity may redirect the purpose of the water-gas shift reaction from CO purification to primary hydrogen production.},
doi = {10.1002/cctc.201700081},
journal = {ChemCatChem},
number = 8,
volume = 9,
place = {United States},
year = {Mon Jan 23 00:00:00 EST 2017},
month = {Mon Jan 23 00:00:00 EST 2017}
}

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  • In this investigation, a similar degree of surface shell reduction among a series of metal promoted ceria catalysts was established by diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and X-ray absorption near-edge spectroscopy (XANES) measurements. Surface formate species were generated by reaction of CO with bridging OH groups associated with the Ce{sup 3+} defect sites. The thermal decomposition of the pseudo-stable formates was followed in the absence of H2O. Decomposition and exchange from H to D of the pseudo-stabilized formate was enhanced by changing the promoter from Au to Pt. Likewise, an increase was observed in both decomposition and exchangemore » rates by increasing the promoter loading from 0.5 to 2.5 wt.%. The results suggest that C{single_bond}H bond breaking is facilitated during this thermal decomposition (i.e., reverse decomposition to CO and {single_bond}OH). Therefore, since the rate limiting step of the forward formate decomposition (i.e., the WGS reaction) is strongly suggested to be associated with C{single_bond}H bond cleaving in the formate intermediate (based on earlier kinetic isotope effect and isotopic tracer studies), the results can explain the promotion in the WGS rates as observed by changing from Au to Pt and by increased promoter loading.« less
  • A similar degree of surface shell reduction of ceria was obtained for a series of metal/ceria catalysts. Surface formate species were generated by reaction of CO with bridging OH groups associated with the Ce{sup 3+} defects. Forward decomposition of the pseudo-stable formates was followed in flowing H{sub 2}O, leading to the production of surface carbonate species. The forward formate decomposition rate was enhanced changing the promoter from Au to Pt, and by increasing the promoter loading (from 0.5 to 2.5%). Results suggest that formate C{single_bond}H bond breaking is not only facilitated by H{sub 2}O, but it is further enhanced bymore » type and loading of metal promoter. From earlier kinetic isotope effect and isotopic tracer studies, the rate-limiting step of the forward formate decomposition (WGS reaction) was considered to be associated with C{single_bond}H bond rupture of the formate. The results can explain the promotion in the WGS rates observed for these samples by changing from Au to Pt and by increasing the promoter loading.« less
  • Model metal/ceria and ceria/metal catalysts have been shown to be excellent systems for studying fundamental phenomena linked to the operation of technical catalysts. In the last fifteen years, many combinations of well-defined systems involving different kinds of metals and ceria have been prepared and characterized using the modern techniques of surface science. So far most of the catalytic studies have been centered on a few reactions: CO oxidation, the hydrogenation of CO 2, and the production of hydrogen through the water–gas shift reaction and the reforming of methane or alcohols. By using model catalysts it is been possible to examinemore » in detail correlations between the structural, electronic and catalytic properties of ceria–metal interfaces. In situ techniques (X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, infrared spectroscopy, scanning tunneling microscopy) have been combined to study the morphological changes under reaction conditions and investigate the evolution of active phases involved in the cleavage of C–O, C–H and C–C bonds. Several studies with model ceria catalysts have shown the importance of strong metal–support interactions. Generally, a substantial body of knowledge has been acquired and concepts have been developed for a more rational approach to the design of novel technical catalysts containing ceria.« less