Chemisorption of CO and mechanism of CO oxidation on supported platinum nanoclusters

Handle URI:
http://hdl.handle.net/10754/561737
Title:
Chemisorption of CO and mechanism of CO oxidation on supported platinum nanoclusters
Authors:
Allian, Ayman Daoud; Takanabe, Kazuhiro ( 0000-0001-5374-9451 ) ; Fujdala, Kyle L.; Hao, Xianghong; Truex., Timothy J.; Cai, Juan; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique
Abstract:
Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O-18O2-16O 2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevant O2 activation steps involve direct O2* (or O2) reactions with CO* to form reactive O*-O-C*=O intermediates that decompose to form CO 2 and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O2. These CO-assisted O2 dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassisted O2 dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O2 reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with 12CO- 13CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at saturation coverages do not depend on Pt cluster size in a range that strongly affects the coordination of Pt atoms exposed at cluster surfaces. These data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size. Theoretical estimates of rate and equilibrium constants for surface reactions and CO adsorption show that both parameters increase as the coordination of exposed Pt atoms decreases in Pt201 cluster surfaces; such compensation dampens but does not eliminate coordination and cluster size effects on measured rate constants. The structural features and intrinsic non-uniformity of cluster surfaces weaken when CO forms saturated monolayers on such surfaces, apparently because surfaces and adsorbates restructure to balance CO surface binding and CO-CO interaction energies. © 2011 American Chemical Society.
KAUST Department:
Biological and Environmental Sciences and Engineering (BESE) Division; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC); Catalysis for Energy Conversion (CatEC)
Publisher:
American Chemical Society (ACS)
Journal:
Journal of the American Chemical Society
Issue Date:
30-Mar-2011
DOI:
10.1021/ja110073u
PubMed ID:
21366255
Type:
Article
ISSN:
00027863
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC); Biological and Environmental Sciences and Engineering (BESE) Division

Full metadata record

DC FieldValue Language
dc.contributor.authorAllian, Ayman Daouden
dc.contributor.authorTakanabe, Kazuhiroen
dc.contributor.authorFujdala, Kyle L.en
dc.contributor.authorHao, Xianghongen
dc.contributor.authorTruex., Timothy J.en
dc.contributor.authorCai, Juanen
dc.contributor.authorBuda, Corneliuen
dc.contributor.authorNeurock, Matthewen
dc.contributor.authorIglesia, Enriqueen
dc.date.accessioned2015-08-03T09:03:28Zen
dc.date.available2015-08-03T09:03:28Zen
dc.date.issued2011-03-30en
dc.identifier.issn00027863en
dc.identifier.pmid21366255en
dc.identifier.doi10.1021/ja110073uen
dc.identifier.urihttp://hdl.handle.net/10754/561737en
dc.description.abstractKinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O-18O2-16O 2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevant O2 activation steps involve direct O2* (or O2) reactions with CO* to form reactive O*-O-C*=O intermediates that decompose to form CO 2 and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O2. These CO-assisted O2 dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassisted O2 dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O2 reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with 12CO- 13CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at saturation coverages do not depend on Pt cluster size in a range that strongly affects the coordination of Pt atoms exposed at cluster surfaces. These data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size. Theoretical estimates of rate and equilibrium constants for surface reactions and CO adsorption show that both parameters increase as the coordination of exposed Pt atoms decreases in Pt201 cluster surfaces; such compensation dampens but does not eliminate coordination and cluster size effects on measured rate constants. The structural features and intrinsic non-uniformity of cluster surfaces weaken when CO forms saturated monolayers on such surfaces, apparently because surfaces and adsorbates restructure to balance CO surface binding and CO-CO interaction energies. © 2011 American Chemical Society.en
dc.publisherAmerican Chemical Society (ACS)en
dc.titleChemisorption of CO and mechanism of CO oxidation on supported platinum nanoclustersen
dc.typeArticleen
dc.contributor.departmentBiological and Environmental Sciences and Engineering (BESE) Divisionen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical Science Programen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.contributor.departmentCatalysis for Energy Conversion (CatEC)en
dc.identifier.journalJournal of the American Chemical Societyen
dc.contributor.institutionDepartment of Chemical Engineering, University of California, Berkeley, CA 94720, United Statesen
dc.contributor.institutionNanostellar, Inc., 3696 Haven Avenue, Redwood City, CA 94063, United Statesen
dc.contributor.institutionDepartments of Chemical Engineering and Chemistry, University of Virginia, Charlottesville, VA 22904, United Statesen
dc.contributor.institutionDivision of Chemical Sciences, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United Statesen
dc.contributor.institutionGlobal Pharmaceutical Research and Development, Abbott Laboratories, 1401 Sheridan Rd., North Chicago, IL 60064, United Statesen
dc.contributor.institutionPrecursor Energetics, 3221 Scott Blvd., Santa Clara, CA 95054, United Statesen
dc.contributor.institutionAlternative Energy Products, Applied Materials, 3340 Scott Blvd., Santa Clara, CA 95052, United Statesen
kaust.authorTakanabe, Kazuhiroen

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