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Dive into the research topics where Y. Y. Yeo is active.

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Featured researches published by Y. Y. Yeo.


Journal of Chemical Physics | 1997

Calorimetric heats for CO and oxygen adsorption and for the catalytic CO oxidation reaction on Pt{111}

Y. Y. Yeo; L. Vattuone; D.A. King

Single crystal adsorption calorimetry was applied to investigate the heats of adsorption of CO and oxygen and the reaction heats for the CO oxidation process on Pt{111} at room temperature. Both sticking probabilities and heats of adsorption for CO and oxygen are presented as a function of coverage. These results are used to interpret the subsequent measurements taken for the CO oxidation process on the same surface. The initial heats of adsorption of CO and oxygen on Pt{111} are 180±8 and 339±32 kJ/mol, respectively. In addition the pairwise lateral repulsive interaction between CO molecules in a (√3×√3)R30° ordered layer at θ=1/3 is found to be 4 kJ/mol. A detailed Monte Carlo modeling of the dissociative adsorption and sticking probability of oxygen on Pt{111} is performed. The initial rapid fall in heat is attributed to adsorption on defect sites, and subsequent adsorption on the planar {111} surface proceeds with a third neighbor interaction energy between the oxygen adatoms ω3∼22 kJ/mol. When gaseou...


Journal of Chemical Physics | 1996

Energetics and kinetics of CO and NO adsorption on Pt{100}: Restructuring and lateral interactions

Y. Y. Yeo; L. Vattuone; David A. King

Calorimetric heats of adsorption and sticking probabilities are reported for NO and CO on both the reconstructed hex and the unreconstructed (1×1) surfaces of Pt{100} by single crystal adsorption calorimetry (SCAC), at room temperature. The hex surface reverts to the (1×1) structure during adsorption of both gases, as previously reported. The initial heat of adsorption on the (1×1) surface is 215 kJ/mol for CO and 200 kJ/mol for NO. Adsorbate–adsorbate interactions determine not only the dependence of the heat of adsorption on coverage but also the formation of different ordered structures. A model is suggested to explain the observed dependence of the differential heat on coverage and the LEED patterns, and a Monte Carlo simulation is performed to derive the corresponding differential heat, thus allowing estimates to be made of the magnitude of adsorbate–adsorbate interactions. For CO adsorption, the critical contribution is the pairwise interaction energy ed between molecules in nnn sites while for NO t...


Science | 1995

Calorimetric Measurement of the Energy Difference Between Two Solid Surface Phases

Y. Y. Yeo; C.E. Wartnaby; D.A. King

A recently designed single-crystal surface calorimeter has been deployed to measure the energy difference between two solid surface structures. The clean Pt{100} surface is reconstructed to a stable phase in which the surface layer of platinum atoms has a quasi-hexagonal structure. By comparison of the heats of adsorption of CO and of C2H4 on this stable Pt{100}-hex phase with those on a metastable Pt{100}-(1x1) surface, the energy difference between the two clean phases was measured as 20 � 3 and 25 � 3 kilojoules per mole of surface platinum atoms.


Surface Science | 1996

An improved single crystal adsorption calorimeter

A. Stuck; C.E. Wartnaby; Y. Y. Yeo; J.T. Stuckless; N. Al-Sarraf; D.A. King

Abstract Significant improvements to the single crystal adsorption calorimeter (SCAC) of Borroni-Bird and King are described. The calorimeter comprises a pulsed molecular beam source, an ultrathin single crystal and an infrared detector. It is calibrated using a chopped laser beam, and the amount of gas adsorbed or reacted per pulse is measured using the King and Wells reflection detector technique. Refinements in the molecular beam system, the optical calibration system, flux calibration system and sticking probability measurement technique have been made. The calorimeter response is accurately linear over a useful energy range; the detection limit is estimated as 10 kJ mol−1; and the accuracy in heats of adsorption for heats above ∼ 80 kJ mol−1 is estimated as ∼ 6%. Comparisons of calorimetric heats with isosteric heats and with desorption energies obtained for reversible systems, such as CO on Ni and Pt single crystal surfaces, generally yield good agreement and give support to the estimate for the absolute accuracy of the instrument.


Surface Science | 2000

Energetics and kinetics of the interaction of acetylene and ethylene with Pd{100} and Ni{100}

L. Vattuone; Y. Y. Yeo; Rickmer Kose; D.A. King

Abstract The adsorption and reactions of C2H4and C2H2on Ni{100} and Pd{100} at room temperature have beeninvestigated by single-crystal adsorption calorimetry (SCAC). On Ni{100}, the initial heats of adsorption are 203and 264 kJ mol−1, respectively. From the correlation of the heat changes with the stable species formed (CH and/orCCH), a mean value of #204 kJ mol−1 is extracted for the NiMC bond energy. On Pd{100} acetylene adsorbsmolecularly in a rehybridized state with initial heat of 112 kJ mol−1, corresponding to a PdMC bond energy of#177 kJ mol−1. The kinetics of adsorption are similar for C2H2on Ni{100} and Pd{100} and C2H4on Ni{100},exhibiting precursor-mediated adsorption with high initial sticking probability, while C2H4adsorbs reversibly onPd{100} at room temperature. Nickel and palladium surfaces are known to favour the cleavage of CMC bonds,whereas platinum surfaces do not. This is not related to diVerences in metalMcarbon bond energies, and must insteadbe attributed to a kinetic origin.


Journal of Chemical Physics | 1997

Calorimetric investigation of NO and CO adsorption on Pd{100} and the influence of preadsorbed carbon

Y. Y. Yeo; L. Vattuone; D.A. King

The coverage dependencies of the differential heats of adsorption for CO and NO on Pd{100}, at room temperature, are reported using single crystal adsorption calorimetry (SCAC). The initial heat for CO is 165 kJ/mol, falling markedly with increasing coverage due to anomalously strong repulsive interactions between molecules. The formation of a c(2×4) overlayer at half monolayer coverage places severe constraints on the magnitudes of lateral interactions between adsorbates which can fit the data. A realistic lateral interaction model is proposed. The influence of predosed carbon on the heat of adsorption of CO was also investigated. As little as 0.05 ML of C causes a decrease in the initial heat of about 20 kJ/mol; 0.2 ML reduces the heat to 120 kJ/mol. The results suggest long range interactions between C atoms and CO molecules. The initial heat for NO is 155 kJ/mol, decreasing smoothly to about 105 kJ/mol at saturation. The coverage dependencies of the sticking probabilities for both NO and CO exhibits p...


Chemical Physics Letters | 1996

Microcalorimetric study of ethylene adsorption on the Pt{111} surface

Y. Y. Yeo; A. Stuck; C.E. Wartnaby; D.A. King

Abstract The reaction of C 2 H 4 on Pt{111} at 300 K has been investigated by single crystal adsorption calorimetry. The initial heats of adsorption and the initial sticking probability are 174 kJ/mol and 0.67 respectively. The adsorption heat versus coverage data shows a remarkable minimum which serves as a basis for a mechanism involving ethylidene (CHCH 3 ) as an intermediate for the formation of ethylidyne (C 2 H 3 ) on the Pt{111} surface. The coverage-dependent sticking probability strongly indicates that adsorption is precursor mediated and is well-fitted by the King and Wells expression. From the structure of the decomposition species known to form on the Pt{111} surface, the average CPt bond strength is found to be about 245 kJ/mol, although the actual value is found to be species-dependent.


Journal of Chemical Physics | 1995

Calorimetric measurement of catalytic surface reaction heat: CO oxidation on Pt{110}

C.E. Wartnaby; A. Stuck; Y. Y. Yeo; D.A. King

The technique of single crystal adsorption microcalorimetry has for the first time been applied to the study of a catalytic reaction, namely the oxidation of CO on a Pt{110} substrate at room temperature. By comparing the measured heat deposited in the crystal with that expected for the reaction, the excess energy removed by the desorbing CO2 molecules can be deduced. It is found that when CO is dosed onto a saturated oxygen overlayer, the product CO2 molecules remove only 9±17 kJ mol−1 more energy than expected for thermally accommodated molecules. However, when oxygen is dosed onto a CO overlayer, the product CO2 molecules remove 52±21 kJ mol−1 of excess energy. We suggest that the more highly excited CO2 molecules are formed by reaction of CO molecules with ‘‘hot’’ oxygen adatoms produced by the dissociation process and not thermally accommodated to the surface.


Journal of Chemical Physics | 1996

Adatom bond energies and lateral interaction energies from calorimetry: NO, O2, and N2 adsorption on Ni{100}

L. Vattuone; Y. Y. Yeo; David A. King

Heats of adsorption and sticking probabilities have been measured for NO and O2 on clean and oxygen precovered Ni{100} at room temperature by single crystal adsorption calorimetry (SCAC). Adsorption is initially dissociative for both species and the initial heat of adsorption is 536 kJ/mol for O2 and 426 kJ/mol for NO. From these data the initial heat of dissociative adsorption of N2 on Ni{100} is estimated to be 136 kJ/mol. With increasing coverage the adsorption heat for both NO and O2 decreases due to repulsive interactions between adsorbed adatoms; the magnitude of the pairwise repulsive interactions between oxygen adatoms in nnn sites is estimated to be about 40 kJ/mol by fitting the experimental data for O2 dissociative adsorption with a Monte Carlo simulation. The pairwise repulsive interaction between nitrogen and oxygen and between nitrogen adatoms in nnn sites is obtained as about 100 kJ/mol. Due to the high magnitude of lateral repulsive interactions between adatoms, a critical coverage of NO i...


Catalysis Letters | 1996

Lateral interactions as the determinant in the switch from dissociative to molecular chemisorption: NO on Ni{100}

L. Vattuone; Y. Y. Yeo; David A. King

Lateral interactions between adatoms on a solid surface play a key role in determining whether adsorption takes place dissociatively or non-dissociatively, as revealed by single crystal adsorption calorimetry. With NO on Ni{100}, adsorption occurs dissociatively at low coverage, while at higher coverage strong interatomic repulsions reverse the relative stability and the molecularly adsorbed state is then more stable than the dissociated state. Essentially, above a critical adatom coverage the adsorption heat for further dissociative adsorption is lower than that for non-dissociative adsorption, due to strong repulsive interactions between adatoms on the surface. By changing the oxygen adatom precoverage it is possible to control the relative amounts of dissociated and molecularly adsorbed NO. This result has important general consequences for the control of catalytic reactions.

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D.A. King

University of Cambridge

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L. Vattuone

University of Cambridge

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A. Stuck

University of Cambridge

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Rickmer Kose

University of Cambridge

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J Gu

University of Cambridge

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L Mao

University of Cambridge

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N. Al-Sarraf

University of Cambridge

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