Reaction mechanism and structure of activated complex of CO2 formation in CO oxidation on Pd(1 1 0) and Pd(1 1 1) surfaces

Nakao, Kenji; Ito, Shin Ichi; Tomishige, Keiichi; Kunimori, Kimio

doi:10.1016/j.cattod.2005.10.043

Cited by 22 publications

(19 citation statements)

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“…technique [6][7][8][9][10][11][12][13][14]. Analysis of the vibrational states can give the information on the structure of the activated CO 2 complex (i.e., the dynamics of CO oxidation) from which the gas-phase molecules desorbed.…”

Section: Molecules Have Been Performed By Infrared Chemiluminescence mentioning

confidence: 99%

“…On the other hand, the reaction is also of scientific interest because the total reaction can be divided into a few elementary steps and the theoretical approaches can be applied to the reaction to describe the kinetics of the surface-catalyzed reaction. In contrast, in order to elucidate the dynamics of the surface-catalyzed reaction, it is effective to investigate internal (vibrational and rotational) [6][7][8][9][10][11][12][13][14] and translational [15] energy of product molecules. Measurements of the vibrational and rotational states of the product CO 2 …”

Section: Introductionmentioning

confidence: 99%

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CO oxidation on Pd(1 1 1), Pt(1 1 1), and Rh(1 1 1) surfaces studied by infrared chemiluminescence spectroscopy

et al. 2007

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Section: Molecules Have Been Performed By Infrared Chemiluminescence mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

CO oxidation on Pd(1 1 1), Pt(1 1 1), and Rh(1 1 1) surfaces studied by infrared chemiluminescence spectroscopy

et al. 2007

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“…3A. The structure of the transition state can be inferred from energy-and angle-resolved reactive desorption spectroscopy experiments (33,34) (32, 36). As the distance OC⅐⅐⅐O Ϫ decreases and the angle ЄOCO straightens along a reaction path, the bottom of the ionization continuum of OC⅐⅐⅐O Ϫ , set by the ground-state adiabatic potential of OC⅐⅐⅐O, descends upon the discrete anion levels to devour them.…”

Section: Microscopic Paths That Contribute To Chemicurrentmentioning

confidence: 99%

Chemistry of fast electrons

Maximoff

Head‐Gordon

2009

Proc. Natl. Acad. Sci. U.S.A.

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A chemicurrent is a flux of fast (kinetic energy տ 0.5؊1.3 eV) metal electrons caused by moderately exothermic (1؊3 eV) chemical reactions over high work function (4؊6 eV) metal surfaces. In this report, the relation between chemicurrent and surface chemistry is elucidated with a combination of top-down phenomenology and bottom-up atomic-scale modeling. Examination of catalytic CO oxidation, an example which exhibits a chemicurrent, reveals 3 constituents of this relation: The localization of some conduction electrons to the surface via a reduction reaction, 0.5 O2 ؉ ␦e ؊ 3 O ␦ ؊ (Red); the delocalization of some surface electrons into a conduction band in an oxidation reaction, O ␦ ؊ ؉ CO 3 CO 2 ␦ ؊ 3 CO2 ؉ ␦e ؊ (Ox); and relaxation without charge transfer (Rel). Juxtaposition of Red, Ox, and Rel produces a daunting variety of metal electronic excitations, but only those that originate from CO2 reactive desorption are long-range and fast enough to dominate the chemicurrent. The chemicurrent yield depends on the universality class of the desorption process and the distribution of the desorption thresholds. This analysis implies a power-law relation with exponent 2.66 between the chemicurrent and the heat of adsorption, which is consistent with experimental findings for a range of systems. This picture also applies to other oxidationreduction reactions over high work function metal surfaces.heterogeneous catalysis ͉ hot electrons ͉ metal surfaces ͉ surface science ͉ transition metals T he significance of electronic excitations on metal surfaces was probably first recognized within the photoelectric effect (1, 2) and has been reaffirmed ever since. Photoelectrons are emitted into the vacuum from metal surfaces upon exposure to light, the energy quantum of which exceeds an exit thresholdthe work function. Just as light ejects photoelectrons that map the surface, chemical reactions of exothermicity exceeding the work function eject exoelectrons (3) that map the chemistry on low work function (Շ3 eV) metal surfaces. Low work function metal substrates (e.g., groups IA, IIA, and IIIA) are too reactive to be practical for catalysis unlike their noble or late transition d-metal counterparts, which support rich chemistry, often of industrial significance. These more interesting substrates have work functions of 4Ϫ6 eV (4), too high for exoelectrons to emerge. But electronic excitations in metals are omnipresent: Any surface movement invokes, by virtue of Anderson's orthogonality catastrophe, sub-work function electronic excitations (5) that stay inside the metal-unseen unless looked for-and ultimately dissolve in the sea of thermal conduction electrons, phonons, and photons.Experimental evidence of internal metal excitations associated with chemistry on high work function metal surfaces has emerged only recently. A pattern in quenching of NO molecules ro-vibrationally excited by 2.9Ϫ3.8 eV near an Au(111) surface (6) alludes to the involvement of sub-work function electronic excitations. Involvement of the Au(111) surface...

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“…So far, a wide variety of Pd nanocrystals with different shapes including cubes, bars, octahedra, plates, icosahedra, and pentagonal rods have all been prepared by carefully controlling reaction conditions such as temperature, reductants, capping agents, and concentrations of reagents and ionic species [27][28][29][30][31][32][33][34][35][36][37][38]. Nanoscale cubes and bars of Pd enclosed by {100} facets have received particular attention because these facets have been demonstrated to have a higher catalytic activity than {111} facets in some important reactions such as CO oxidation [39][40][41][42][43][44][45]. To this end, we and other groups have developed a simple strategy for the large-scale synthesis of Pd cubes and bars with sharp corners by introducing Br -as a capping agent and by taking advantage of its selective adsorption on {100} facets [27,28].…”

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confidence: 99%

Synthesis of Pd nanocrystals enclosed by {100} facets and with sizes <10 nm for application in CO oxidation

et al. 2010

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The catalytic activity of noble-metal nanocrystals is mainly determined by their sizes and the facets exposed on the surface. For single crystals, it has been demonstrated that the Pd(100) surface is catalytically more active than both Pd(110) and Pd(111) surfaces for the CO oxidation reaction. Here we report the synthesis of Pd nanocrystals enclosed by {100} facets with controllable sizes in the range of 6-18 nm by manipulating the rate of reduction of the precursor. UV-vis spectroscopy studies indicate that the rate of reduction of Na 2 PdCl 4 can be controlled by adjusting the concentrations of Br -and Cl -ions added to the reaction mixture. Pd nanocrystals with different sizes were immobilized on ZnO nanowires and evaluated as catalysts for CO oxidation. We found that the activity of this catalytic system for CO oxidation showed a strong dependence on the nanocrystal size. When the size of the Pd nanocrystals was reduced from 18 nm to 6 nm, the maximum conversion rate was significantly enhanced by a factor of ~10 and the corresponding maximum conversion temperature was lowered by ~80 °C . KEYWORDS

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Reaction mechanism and structure of activated complex of CO2 formation in CO oxidation on Pd(1 1 0) and Pd(1 1 1) surfaces

Cited by 22 publications

References 25 publications

CO oxidation on Pd(1 1 1), Pt(1 1 1), and Rh(1 1 1) surfaces studied by infrared chemiluminescence spectroscopy

CO oxidation on Pd(1 1 1), Pt(1 1 1), and Rh(1 1 1) surfaces studied by infrared chemiluminescence spectroscopy

Chemistry of fast electrons

Synthesis of Pd nanocrystals enclosed by {100} facets and with sizes <10 nm for application in CO oxidation

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