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Vladimir P. Zhdanov - One of the best experts on this subject based on the ideXlab platform.

  • Perturbation of period-2 oscillations in catalytic reactions accompanied by Surface Restructuring
    Physical Review E, 2003
    Co-Authors: Vladimir P. Zhdanov
    Abstract:

    We present Monte Carlo simulations illustrating the effect of periodic forcing on period-2 oscillations related to the interplay of catalytic reaction and Surface Restructuring. The oscillations are found to be fairly stable if the external frequency equals the main internal frequency. In contrast, perturbations with other frequencies may easily change the type of oscillation. In particular, perturbations with double frequency convert period-2 oscillations into period-1 oscillations with the imposed frequency.

  • Oscillations in the NO-CO Reaction on Pt(100): NO Decomposition on Island Boundaries
    Catalysis Letters, 2002
    Co-Authors: Vladimir P. Zhdanov
    Abstract:

    We present the first Monte Carlo simulations of kinetic oscillations in heterogeneous catalytic reaction with one of the key reaction steps occurring on the boundaries between the islands formed due to adsorbate-induced Surface Restructuring. Specifically, we treat NO reduction by CO on the Pt(100) Surface with NO decomposition on the interface between the “hex” and (1× 1) phases. For this scenario, in agreement with experiment, our model predicts damped oscillations with correlation between broad maxima in the CO_2-formation rate and minima in the (1 × 1) area.

  • Kinetic oscillations on nm-sized catalyst particles: Surface Restructuring
    Surface Science, 2002
    Co-Authors: Vladimir P. Zhdanov, Bengt Herbert Kasemo
    Abstract:

    Abstract We present Monte Carlo simulations of kinetic oscillations in the CO–O 2 reaction occurring on a (1 0 0) facet of a nm-sized supported Pt particle. The model includes the conventional Langmuir–Hinshelwood mechanism of CO oxidation and CO- and O-induced Restructuring of the facet. The facet size is varied from 50×50 to 5×5. With decreasing size, oscillations become more irregular. More or less regular oscillations accompanied by formation of CO islands are found for the sizes down to 15×15. Practically, this means that for observation of such oscillations the particle diameter should be above ≃4 nm. These findings are in agreement with available experimental data.

  • Catalytic reactions, Surface Restructuring, and pattern formation
    Surface Science, 2001
    Co-Authors: Vladimir P. Zhdanov
    Abstract:

    Abstract We present Monte Carlo simulations of the island formation during heterogeneous catalytic A+B→C reaction occurring under the steady-state conditions via the Eley–Rideal mechanism in the case when adsorbed A particles are able to change the Surface structure. The island formation is demonstrated to be crucially dependent on the details of the mechanism of A diffusion. In the favourable situation, the dependence of the average linear island size on the rate of A diffusion is found to be logarithmic.

  • Surface Restructuring and aperiodic kinetic oscillations in heterogeneous catalytic reactions
    Physica D: Nonlinear Phenomena, 2000
    Co-Authors: Vladimir P. Zhdanov
    Abstract:

    Abstract We present comprehensive Monte Carlo simulations of aperiodic kinetic oscillations in catalytic reactions accompanied by adsorbate-induced Surface Restructuring. Our analysis, focused on the NO–H 2 reaction on Pt(1 0 0), is based on a lattice-gas model describing Surface Restructuring in terms of the statistical theory of first-order phase transitions. The oscillations predicted are proved to be robust. In particular, the type of irregularities observed in the reaction kinetics is nearly independent of the used boundary conditions and does not change upon increasing the rate of adsorbate diffusion. On the other hand, the kinetics are found to be very sensitive to small perturbations in the arrangement of adsorbed particles. Specifically, the divergence of the kinetic curves corresponding to slightly different initial conditions occurs very rapidly. The latter indicates that the oscillations obtained can be classified as chaotic.

Zhan Chen - One of the best experts on this subject based on the ideXlab platform.

  • In Situ Probing the Surface Restructuring of Antibiofouling Amphiphilic Polybetaines in Water
    ACS Macro Letters, 2013
    Co-Authors: Chuan Leng, Katherine A. Gibney, Yuwei Liu, Gregory N. Tew, Zhan Chen
    Abstract:

    Antibiofouling materials have a wide range of applications in biomedical devices and marine coatings. Due to the amphiphilic nature of proteins and organisms, amphiphilic materials have been designed to resist their unspecific adsorption. Surface Restructuring behavior of amphiphilic materials in water is believed to play a key role in the antibiofouling mechanisms. In this work, the Surface structures of several amphiphilic polybetaine coatings in water have been probed in situ using sum frequency generation (SFG) vibrational spectroscopy. These are novel polybetaines constructed from functionalized polynorbornenes. The polybetaines with oligo(ethylene glycol) (OEG), octyl (C8), or fluorinated (F13) side chains exhibit different Surface Restructuring behaviors upon contacting water due to their different Surface hydrophobicity. The OEG and C8 chains were present and ordered at the water interface, while the F13 chain withdrew from water. The hydrophilic betaine group extended into the water and formed hy...

  • Phenolic resin Surface Restructuring upon exposure to humid air: a sum frequency generation vibrational spectroscopic study.
    The journal of physical chemistry. B, 2009
    Co-Authors: Jianglong Han, Nick Evan Shephard, Susan M. Rhodes, Alex D. Martin, Gi Xue, Zhan Chen
    Abstract:

    Epoxy and phenolic resins are extensively used for modern microelectronics, for example, as packaging materials. Humidity may greatly alter or degrade their function and application, leading to failure of the device. A nonlinear optical laser technique, sum frequency generation (SFG) vibrational spectroscopy, was used to investigate the molecular Surface structures of the epoxy and phenolic resins after exposure to humid air. It was found that the adsorbed water molecules at the phenolic resin Surface can induce substantial Surface Restructuring. The Surface phenyl groups were reoriented closer to a perpendicular position to the Surface after exposure to humid air from a more parallel position in air. Epoxide group Surface Restructuring was not observed.

  • Surface Restructuring behavior of various types of poly(dimethylsiloxane) in water detected by SFG.
    Langmuir : the ACS journal of surfaces and colloids, 2004
    Co-Authors: Chunyan Chen, Jie Wang, Zhan Chen
    Abstract:

    Surface structures of several different poly(dimethylsiloxane) (PDMS) materials, tetraethoxysilane-cured hydroxy-terminated PDMS (TEOS−PDMS), platinum-cured vinyl-terminated PDMS (Pt−PDMS), platinum-cured vinyl-terminated poly(diphenylsiloxane)-co-poly(dimethylsiloxane) (PDPS-co-PDMS), and PDMS-co-polystyrene (PDMS-co-PS) copolymer in air and water have been investigated by sum frequency generation (SFG) vibrational spectroscopy. The SFG spectra collected from all PDMS Surfaces in both air and water are dominated by methyl group stretches, indicating that all the Surfaces are mainly covered by methyl groups. Other than Surface-dominating methyl groups, some −Si−CH2−CH2− moieties on the Pt−PDMS Surface have also been detected in air, which are present at cross-linking points. Information about the average orientation angle and angle distribution of the methyl groups on the PDMS Surface has been evaluated. Surface Restructuring of the methyl groups has been observed for all PDMS Surfaces in water. Upon cont...

  • Surface Restructuring of polystyrene polymethacrylate blends in water studied by atomic force microscopy
    Langmuir, 2004
    Co-Authors: Sara E. Woodcock, Chunyan Chen, Zhan Chen
    Abstract:

    Blends of poly(n-butyl methacrylate) (PBMA)/polystyrene (PS) and poly(n-octyl methacrylate) (POMA)/ PS were imaged with atomic force microscopy in both ambient and aqueous environments. The Surfaces of the blends were monitored over time under water, and most PBMA/PS and POMA/PS samples showed no Surface Restructuring. A morphology change, however, was observed for high ratios of POMA and specific ratios of PBMA in the blend. For the blend of 60% PBMA and 40% PS, the Surface was pitted in air with depths of 60 nm. In water, as the exposure time increased, islands replaced the holes on the Surface. The height of these islands averaged 50 nm. At high ratios of POMA, in POMA/PS blends, the Surface structure also changed when contacted with water. The structural changes that were observed for all of these select blends were reversible after the Surface was dried and reimaged in air. Sum frequency generation vibrational spectroscopy was used to give insight into the functional groups and Surface chemical composition of the blends in air and water.

  • Surface Restructuring of Polystyrene/Polymethacrylate Blends in Water Studied by Atomic Force Microscopy
    Langmuir, 2004
    Co-Authors: Sara E. Woodcock, Chunyan Chen, Zhan Chen
    Abstract:

    Blends of poly(n-butyl methacrylate) (PBMA)/polystyrene (PS) and poly(n-octyl methacrylate) (POMA)/ PS were imaged with atomic force microscopy in both ambient and aqueous environments. The Surfaces of the blends were monitored over time under water, and most PBMA/PS and POMA/PS samples showed no Surface Restructuring. A morphology change, however, was observed for high ratios of POMA and specific ratios of PBMA in the blend. For the blend of 60% PBMA and 40% PS, the Surface was pitted in air with depths of 60 nm. In water, as the exposure time increased, islands replaced the holes on the Surface. The height of these islands averaged 50 nm. At high ratios of POMA, in POMA/PS blends, the Surface structure also changed when contacted with water. The structural changes that were observed for all of these select blends were reversible after the Surface was dried and reimaged in air. Sum frequency generation vibrational spectroscopy was used to give insight into the functional groups and Surface chemical composition of the blends in air and water.

David A. King - One of the best experts on this subject based on the ideXlab platform.

  • site switching and Surface Restructuring induced by no adsorption on pt 110
    Journal of Physical Chemistry B, 1998
    Co-Authors: Wendy A. Brown, R K Sharma, David A. King
    Abstract:

    We present the first infrared vibrational study of the adsorption of NO on Pt(110) over a wide range of temperatures. Adsorption is strongly dependent on both temperature and coverage, with many different species being formed on the Surface. Under all conditions, site switching is observed during NO adsorption: at low coverages bridge-bonded species are formed on the Surface, and at very high coverage NO switches to on-top sites. Other species, not previously reported, are also observed, depending on both adsorption temperature and coverage. The clean Pt(110) Surface exhibits a (1 x 2) Surface reconstruction which can be lifted by the adsorption of NO (or CO), depending on Surface temperature and adsorbate coverage. In contrast to CO adsorption, the on-top Surface species shows different frequencies on the(1 x 2) and(1 x 1) Surface phases, and this is deployed to identify the temperature at which the reconstruction begins to lift.

  • Site switching and Surface Restructuring induced by NO adsorption on Pt{110}
    The Journal of Physical Chemistry B, 1998
    Co-Authors: Wendy A. Brown, R K Sharma, David A. King
    Abstract:

    We present the first infrared vibrational study of the adsorption of NO on Pt(110) over a wide range of temperatures. Adsorption is strongly dependent on both temperature and coverage, with many different species being formed on the Surface. Under all conditions, site switching is observed during NO adsorption: at low coverages bridge-bonded species are formed on the Surface, and at very high coverage NO switches to on-top sites. Other species, not previously reported, are also observed, depending on both adsorption temperature and coverage. The clean Pt(110) Surface exhibits a (1 x 2) Surface reconstruction which can be lifted by the adsorption of NO (or CO), depending on Surface temperature and adsorbate coverage. In contrast to CO adsorption, the on-top Surface species shows different frequencies on the(1 x 2) and(1 x 1) Surface phases, and this is deployed to identify the temperature at which the reconstruction begins to lift.

  • Surface Restructuring dynamics in co adsorption desorption and reaction with no on pt 100
    Principles and Practice of Constraint Programming, 1993
    Co-Authors: A. Hopkinson, David A. King
    Abstract:

    Abstract A detailed experimental molecular beam study of the CO-induced Surface phase transition on Pt{100}, from the clean Surface hex-R0.7° structure of the bulk termination (1 × 1) structure, has recently been completed in our laboratory. In the present work a stepwise mechanistic scheme is presented which accounts for the observed sticking probability dependence on both coverage and substrate temperature, including a strong flux dependence in the net sticking probability, and the behaviour of the desorption spectra. The shift in the highest-temperature peak to lower temperatures with increasing coverage is reproduced, together with zero order desorption kinetics. The model is based on the observed dependence of the (1 × 1) island growth rate from the hex-R phase with an apparent reaction order of 4.1 in the local CO coverage on the hex-R phase, and reproduces the observed hysteresis in the Surface phase transition when Pt{100} is heated or cooled in CO. Kinetic oscillations in the reaction between CO and NO to form CO 2 and N 2 are reproduced by the model within two temperature regimes, in close agreement with experiment. In the higher temperature regime the oscillations are assigned to a new mechanism involving the hex↓(1 × 1) phase transition. As these transitions proceed Surface defects are generated, and these defects are shown to play an important role in the time scale of the oscillations. All the major features of adsorbate-induced Restructuring, desorption and the CO + NO oscillatory reaction are therefore successfully reproduced by this single mechanistic scheme.

  • Surface Restructuring dynamics in CO adsorption, desorption, and reaction with NO on Pt{100}
    Chemical Physics, 1993
    Co-Authors: A. Hopkinson, David A. King
    Abstract:

    Abstract A detailed experimental molecular beam study of the CO-induced Surface phase transition on Pt{100}, from the clean Surface hex-R0.7° structure of the bulk termination (1 × 1) structure, has recently been completed in our laboratory. In the present work a stepwise mechanistic scheme is presented which accounts for the observed sticking probability dependence on both coverage and substrate temperature, including a strong flux dependence in the net sticking probability, and the behaviour of the desorption spectra. The shift in the highest-temperature peak to lower temperatures with increasing coverage is reproduced, together with zero order desorption kinetics. The model is based on the observed dependence of the (1 × 1) island growth rate from the hex-R phase with an apparent reaction order of 4.1 in the local CO coverage on the hex-R phase, and reproduces the observed hysteresis in the Surface phase transition when Pt{100} is heated or cooled in CO. Kinetic oscillations in the reaction between CO and NO to form CO 2 and N 2 are reproduced by the model within two temperature regimes, in close agreement with experiment. In the higher temperature regime the oscillations are assigned to a new mechanism involving the hex↓(1 × 1) phase transition. As these transitions proceed Surface defects are generated, and these defects are shown to play an important role in the time scale of the oscillations. All the major features of adsorbate-induced Restructuring, desorption and the CO + NO oscillatory reaction are therefore successfully reproduced by this single mechanistic scheme.

Peng Chen - One of the best experts on this subject based on the ideXlab platform.

  • Size-dependent catalytic activity and dynamics of gold nanoparticles at the single-molecule level.
    Journal of the American Chemical Society, 2010
    Co-Authors: Xiaochun Zhou, Guokun Liu, Debashis Panda, Peng Chen
    Abstract:

    Nanoparticles are important catalysts for petroleum processing, energy conversion, and pollutant removal. As compared to their bulk counterparts, their often superior or new catalytic properties result from their nanometer size, which gives them increased Surface-to-volume ratios and chemical potentials. The size of nanoparticles is thus pivotal for their catalytic properties. Here, we use single-molecule fluorescence microscopy to study the size-dependent catalytic activity and dynamics of spherical Au-nanoparticles under ambient solution conditions. By monitoring the catalysis of individual Au-nanoparticles of three different sizes in real time with single-turnover resolution, we observe clear size-dependent activities in both the catalytic product formation reaction and the product dissociation reaction. Within a model of classical thermodynamics, these size-dependent activities of Au-nanoparticles can be accounted for by the changes in the adsorption free energies of the substrate resazurin and the product resorufin because of the nanosize effect. We also observe size-dependent differential selectivity of the Au-nanoparticles between two parallel product dissociation pathways, with larger nanoparticles less selective between the two pathways. The particle size also strongly influences the Surface-Restructuring-coupled catalytic dynamics; both the catalysis-induced and the spontaneous dynamic Surface Restructuring occur more readily for smaller Au-nanoparticles due to their higher Surface energies. Using a simple thermodynamic model, we analyze the catalysis- and size-dependent dynamic Surface Restructuring quantitatively; the results provide estimates on the activation energies and time scales of spontaneous dynamic Surface Restructuring that are fundamental to heterogeneous catalysis in both the nano- and the macro-scale. This study further exemplifies the power of the single-molecule approach in probing the intricate workings of nanoscale catalysts.

  • Single-molecule nanocatalysis reveals heterogeneous reaction pathways and catalytic dynamics
    Nature materials, 2008
    Co-Authors: Jason S. Kong, Yun-ting E. Yeh, Peng Chen
    Abstract:

    Nanoparticles are important catalysts for many chemical transformations. However, owing to their structural dispersions, heterogeneous distribution of Surface sites and Surface Restructuring dynamics, nanoparticles are intrinsically heterogeneous and challenging to characterize in ensemble measurements. Using a single-nanoparticle single-turnover approach, we study the redox catalysis of individual colloidal Au nanoparticles in solution, using single-molecule detection of fluorogenic reactions. We find that for product generation, all Au nanoparticles follow a Langmuir-Hinshelwood mechanism but with heterogeneous reactivity; and for product dissociation, three nanoparticle subpopulations are present that show heterogeneous reactivity between multiple dissociation pathways with distinct kinetics. Correlation analyses of single-turnover waiting times further reveal activity fluctuations of individual Au nanoparticles, attributable to both catalysis-induced and spontaneous dynamic Surface Restructuring that occurs at different timescales at the Surface catalytic and product docking sites. The results exemplify the power of the single-molecule approach in revealing the interplay of catalysis, heterogeneous reactivity and Surface structural dynamics in nanocatalysis.

V. P. Zhdanov - One of the best experts on this subject based on the ideXlab platform.

  • Reply to "Comment on 'Surface Restructuring, kinetic oscillations, and chaos in heterogeneous catalytic reactions' ".
    Physical review. E Statistical nonlinear and soft matter physics, 2001
    Co-Authors: V. P. Zhdanov
    Abstract:

    In my numeration, the criticism of my simulations of kinetic oscillations in NO reduction by H2 on Pt(100) [V. P. Zhdanov, Phys. Rev. E 59, 6292 (1999)] by Kuzovkov, Kortlüke, and von Niessen [preceding paper, Phys. Rev. 63, 023101 (2001)] contains 19 comments. I show that four comments are irrelevant. The other 15 comments are wrong, because they either contradict the basic principles of the theory of phase transitions, Monte Carlo simulations, and catalytic chemistry or ignore numerous experimental data on adsorbate-induced Restructuring of the Pt(100) Surface.

  • Monte Carlo simulation of oscillations in the NO–H2 reaction on Pt(1 0 0) ☆
    Applied Catalysis A: General, 1999
    Co-Authors: V. P. Zhdanov, Bengt Herbert Kasemo
    Abstract:

    Abstract We present Monte Carlo simulations of phase separation during kinetic oscillations in catalytic reactions accompanied by adsorbate-induced Surface Restructuring. As an example, we analyze the NO–H 2 reaction on Pt(1 0 0). The lattice-gas model employed to describe Surface Restructuring and the reaction steps takes into account substrate–substrate, substrate–adsorbate and adsorbate–adsorbate lateral interactions. Using a reduced generic mechanism of the reaction, we show the type of spatio-temporal patterns which might be observed on the nm scale.

  • Surface Restructuring, Thermal Desorption, Kinetic Bistability, and Chemical Waves
    Journal of Statistical Physics, 1998
    Co-Authors: V. P. Zhdanov, B. Kasemo
    Abstract:

    Adsorbate-induced Surface Restructuring is treated in the framework of a statistical lattice-gas model taking into account the possibility of formation of a metastable substrate structure on the clean Surface and stabilization of this structure by adsorbate–substrate interaction. With these assumptions, Surface Restructuring is described in terms of the theory of first-order phase transitions. The proposed model is then employed to analyze (i) the influence of adsorbate-induced changes in the Surface on thermal desorption spectra and (ii) the effect of Surface Restructuring on the propagation of chemical waves in the 2A + B_2 → 2AB reaction. The interplay between reaction-diffusion kinetics and Surface Restructuring is shown to result in formation of chemical waves with atomistically sharp spatial features.