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Title: Importance of Low Dimensional CeO x Nanostructures in Pt/CeO x –TiO 2 Catalysts for the Water–Gas Shift Reaction

Abstract

CO 2 and H 2 production from the water–gas shift (WGS) reaction was studied over Pt/CeO x–TiO 2 catalysts with incremental loadings of CeO x, which adopts variations in the local morphology. The lowest loading of CeO x (1 wt % to 0.5 at. %) that is configured in its smallest dimensions exhibited the best WGS activity over larger dimensional structures. We attribute this to several factors including the ultrafine dispersed one-dimensional nanocluster geometry, a large concentration of Ce 3+ and enhanced reducibility of the low loadings. We utilized several in situ experiments to monitor the active state of the catalyst during the WGS reaction. X-ray diffraction (XRD) results showed lattice expansion that indicated reduced ceria was prevalent during the WGS reaction. On the surface, Ce 3+ related hydroxyl groups were identified by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced reducibility of the catalyst with the introduction of ceria was further revealed by H 2-temperature programed reduction (H 2-TPR) and good thermal stability was confirmed by in situ environmental transmission electron microscopy (ETEM). Finally, we also investigated the formation of the low dimensional structures during catalyst preparation, through a two-stage crystal growth of ceria crystallite on TiO 2more » nanoparticle: fine crystallites ~1D formed at ~250 °C, followed by crystal growth into 2D chain and 3D particle from 250–400 °C.« less

Authors:
; ; ; ORCiD logo; ; ; ; ; ORCiD logo
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:
1347370
Report Number(s):
BNL-113651-2017-JA
Journal ID: ISSN 1932-7447; R&D Project: CO009; KC0302010
Grant/Contract Number:
SC00112704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 12; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Luo, Si, Barrio, Laura, Nguyen-Phan, Thuy-Duong, Vovchok, Dimitriy, Johnston-Peck, Aaron C., Xu, Wenqian, Stach, Eric A., Rodriguez, José A., and Senanayake, Sanjaya D.. Importance of Low Dimensional CeO x Nanostructures in Pt/CeO x –TiO 2 Catalysts for the Water–Gas Shift Reaction. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.6b12285.
Luo, Si, Barrio, Laura, Nguyen-Phan, Thuy-Duong, Vovchok, Dimitriy, Johnston-Peck, Aaron C., Xu, Wenqian, Stach, Eric A., Rodriguez, José A., & Senanayake, Sanjaya D.. Importance of Low Dimensional CeO x Nanostructures in Pt/CeO x –TiO 2 Catalysts for the Water–Gas Shift Reaction. United States. doi:10.1021/acs.jpcc.6b12285.
Luo, Si, Barrio, Laura, Nguyen-Phan, Thuy-Duong, Vovchok, Dimitriy, Johnston-Peck, Aaron C., Xu, Wenqian, Stach, Eric A., Rodriguez, José A., and Senanayake, Sanjaya D.. Wed . "Importance of Low Dimensional CeO x Nanostructures in Pt/CeO x –TiO 2 Catalysts for the Water–Gas Shift Reaction". United States. doi:10.1021/acs.jpcc.6b12285. https://www.osti.gov/servlets/purl/1347370.
@article{osti_1347370,
title = {Importance of Low Dimensional CeO x Nanostructures in Pt/CeO x –TiO 2 Catalysts for the Water–Gas Shift Reaction},
author = {Luo, Si and Barrio, Laura and Nguyen-Phan, Thuy-Duong and Vovchok, Dimitriy and Johnston-Peck, Aaron C. and Xu, Wenqian and Stach, Eric A. and Rodriguez, José A. and Senanayake, Sanjaya D.},
abstractNote = {CO2 and H2 production from the water–gas shift (WGS) reaction was studied over Pt/CeOx–TiO2 catalysts with incremental loadings of CeOx, which adopts variations in the local morphology. The lowest loading of CeOx (1 wt % to 0.5 at. %) that is configured in its smallest dimensions exhibited the best WGS activity over larger dimensional structures. We attribute this to several factors including the ultrafine dispersed one-dimensional nanocluster geometry, a large concentration of Ce3+ and enhanced reducibility of the low loadings. We utilized several in situ experiments to monitor the active state of the catalyst during the WGS reaction. X-ray diffraction (XRD) results showed lattice expansion that indicated reduced ceria was prevalent during the WGS reaction. On the surface, Ce3+ related hydroxyl groups were identified by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced reducibility of the catalyst with the introduction of ceria was further revealed by H2-temperature programed reduction (H2-TPR) and good thermal stability was confirmed by in situ environmental transmission electron microscopy (ETEM). Finally, we also investigated the formation of the low dimensional structures during catalyst preparation, through a two-stage crystal growth of ceria crystallite on TiO2 nanoparticle: fine crystallites ~1D formed at ~250 °C, followed by crystal growth into 2D chain and 3D particle from 250–400 °C.},
doi = {10.1021/acs.jpcc.6b12285},
journal = {Journal of Physical Chemistry. C},
number = 12,
volume = 121,
place = {United States},
year = {Wed Mar 15 00:00:00 EDT 2017},
month = {Wed Mar 15 00:00:00 EDT 2017}
}

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  • Periodic density functional theory calculations and microkinetic modeling are used to investigate the associative carboxyl pathways of the water-gas shift (WGS) reaction at the Pt/CeO 2 (111) interface. Analysis of a microkinetic model based on parameters obtained from first principles suggests that the turnover frequencies for the CO-assisted associative carboxyl mechanism are comparable to experimental results. However, this microkinetic model containing various associative carboxyl pathways at interface sites cannot explain the experimentally observed activation barriers and reaction orders of Pt/CeO 2 catalysts. Considering furthermore that a model of an associative carboxyl mechanism with redox regeneration, also derived from first principlesmore » and recently published by us, accurately predicts all kinetic parameters while displaying a 2 orders of magnitude higher turnover frequency, we conclude that at Pt/CeO 2 interface sites, the WGS reaction follows a bifunctional Mars-van Krevelen mechanism in which support oxygen vacancies facilitate water dissociation.« less
  • Alumina-supported platinum catalysts, both with and without ceria, were prepared by supercritical fluid deposition and evaluated for activity for water-gas shift reaction. The organometallic precursor, platinum(II) acetylacetonate, was deposited from solution in supercritical carbon dioxide. Analysis of the catalysts by high resolution scanning transmission electron microscopy indicated that platinum was present in the form of highly dispersed metal nanoparticles. Pretreatment of the alumina-supported ceria in hydrogen prior to the deposition of the platinum precursor resulted in more platinum nucleated on ceria than non-pretreated alumina-supported ceria but varied in both particle size and structure. The ceria-containing catalyst that was not pretreatedmore » exhibited a more uniform particle size, and the Pt particles were encapsulated in crystalline ceria. Reaction rate measurements showed that the catalyst was more active for water-gas shift, with reaction rates per mass of platinum that exceeded most literature values for water-gas shift reaction on Pt-CeO x catalysts. The high activity was attributed to the significant fraction of platinum/ceria interfacial contact. We found that these results show the promise of supercritical fluid deposition as a scalable means of synthesizing highly active supported metal catalysts that offer efficient utilization of precious metals.« less
  • We used scanning tunnelling microscopy to study the morphology of an overlayer of ceria in contact with a TiO 2(110) substrate. Two types of domains were observed after ceria deposition. An ordered ceria film covered half of the surface and high-resolution imaging suggested a near-c(6 × 2) relationship to the underlying TiO 2(110)-(1 × 1). For the other half of the surface, it comprised CeO x nanoparticles and reconstructed TiOx supported on TiO 2(110)-(1 × 1). Exposure to a small amount of gold resulted in the formation of isolated gold atoms and small clusters on the ordered ceria film andmore » TiO 2(110)-(1 × 1) areas, which exhibited significant sintering at 500 K and showed strong interaction between the sintered gold clusters and the domain boundaries of the ceria film. The Au/CeO x/TiO 2(110) model system proved to be a good catalyst for the water–gas shift (WGS) exhibiting much higher turnover frequencies (TOFs) than Cu(111) and Pt(111) benchmarks, or the individual Au/TiO 2(110) and Au/CeO 2(111) systems. Finally, for Au/CeO x/TiO 2(110) catalysts, there was a decrease in catalytic activity with increasing ceria coverage that correlates with a reduction in the concentration of Ce 3 + formed during WGS reaction conditions.« less
  • In this study, scanning tunnelling microscopy has been used to study the morphology of an overlayer of ceria in contact with a TiO 2(110) substrate. Two types of domains were observed after ceria deposition. An ordered ceria film covered half of the surface and high-resolution imaging suggested a near-c(6 × 2) relationship to the underlying TiO 2(110)-(1 × 1). The other half of the surface comprised CeO x nanoparticles and reconstructed TiOx supported on TiO 2(110)-(1 × 1). Exposure to a small amount of gold resulted in the formation of isolated gold atoms and small clusters on the ordered ceriamore » film and TiO 2(110)-(1 × 1) areas, which exhibited significant sintering at 500 K and showed strong interaction between the sintered gold clusters and the domain boundaries of the ceria film. The Au/CeO x/TiO 2(110) model system proved to be a good catalyst for the water–gas shift (WGS) exhibiting much higher turnover frequencies (TOFs) than Cu(111) and Pt(111) benchmarks, or the individual Au/TiO 2(110) and Au/CeO 2(111) systems. For Au/CeO x/TiO 2(110) catalysts, there was a decrease in catalytic activity with increasing ceria coverage that correlates with a reduction in the concentration of Ce 3+ formed during WGS reaction conditions.« less
  • An FTIR and quadruple mass spectroscopic study of the water-gas shift (WGS), the reverse WGS reactions, and the adsorption of the individual molecules involved has been carried out on Au/Fe{sub 2}O{sub 3} and Au/TiO{sub 2} catalysts. The chemisorptions and the reactions on the two catalysts have been compared with the aim of gaining a better understanding of the role played by the two phases present in these catalysts and of the synergistic interplay between them in gold catalysts tested for a low-temperature water-gas shift reaction. Evidences are reported that H{sub 2} is dissociated already at room temperature on both themore » catalysts on gold sites, giving rise to hydrogen atoms that can react with adsorbed oxygen atoms or spillover on the supports where they can reduce the support surface sites. It is shown that CO is adsorbed molecularly on different surface sites, on the support cations, on Au{sup 0} sites exposed at the surface of small three-dimensional particles and also on Au{sup {delta}{minus}} sites exposed at the surface of negatively charged clusters. The CO formed in the reverse WGS reaction appears chemisorbed only on the Au{sup 0} sites. The support sites and the Au{sup {delta}{minus}} sites, where the CO appears as more strongly bonded, are present but not accessible to the CO formed by CO{sub 2} reduction, probably because these sites are covered by water. Water and OH groups are adsorbed on the supports, on gold sites, and at the interface between them. The effects of CO coadsorption on water dissociation and of H{sub 2} dissociation on CO{sub 2} reduction have been evidenced. The close similarity of the catalytic activity of the two examined samples indicates that the active sties for hydrogen dissociation and for water-CO reactive interactions are located at the surface of the metallic gold small particles where the reaction can take place by a red-ox regenerative mechanism.« less