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Gunther Rupprechter - One of the best experts on this subject based on the ideXlab platform.
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sum frequency generation and polarization modulation infrared reflection absorption spectroscopy of functioning model catalysts from ultrahigh vacuum to ambient pressure
Advances in Catalysis, 2007Co-Authors: Gunther RupprechterAbstract:Abstract It has long been debated whether the results of classical surface science investigations carried out under ultrahigh vacuum (UHV) can be truly transferred to heterogeneous catalysis, which is normally carried out at ambient or even higher pressures. In an effort to answer this question, several surface-sensitive methods have been developed that can operate in a pressure range from UHV to 1 bar. By the application of characterization methods to single-Crystal Surfaces as well as supported nanoparticles while they are functioning as catalysts, the pressure and materials gaps between surface science and heterogeneous catalysis can be simultaneously bridged. Vibrational spectroscopy techniques, like infrared-visible (IR-vis) sum frequency generation (SFG), and polarization–modulation IR reflection absorption spectroscopy (PM-IRAS) have been applied to characterize the adsorption, coadsorption, and reaction of small molecules on transition metal Surfaces (palladium, platinum, rhodium, gold, ruthenium, etc.) at pressures ranging from UHV to 1 bar. The goal of these investigations at mbar pressures is to elucidate the elementary steps of heterogeneous catalytic reactions. The investigations considered here include CO adsorption and dissociation, CO oxidation and hydrogenation, ethene adsorption and hydrogenation, and methanol decomposition and partial oxidation taking place on low-index single-Crystal Surfaces, defect-rich (stepped or ion-bombarded) single-Crystal Surfaces, and oxide-supported metal nanoparticles. When available, complementary structural information determined by high-pressure scanning tunneling microscopy (HP-STM) and compositional analysis by high-pressure photoelectron spectroscopy (HP-XPS) is included. The implications of the high pressure results on the mechanisms of catalytic reactions are discussed, and potential future research directions are suggested.
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surface vibrational spectroscopy on noble metal catalysts from ultrahigh vacuum to atmospheric pressure
ChemInform, 2005Co-Authors: Gunther RupprechterAbstract:There is a long-standing question whether results of studies of surface processes under ultrahigh vacuum (UHV) can be truly transferred to the conditions of heterogeneous catalysis. Several in-situ surface-sensitive methods have been developed that can operate in a pressure range from UHV to ambient conditions, that may help to answer this question. By applying in-situ methods to single-Crystal Surfaces as well as supported nanoparticles, the pressure and materials gaps between surface science and heterogeneous catalysis can be simultaneously bridged. Vibrational spectroscopy techniques, i.e. IR-vis sum frequency generation (SFG) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) are applied to study the adsorption, coadsorption and reaction of small molecules on transition metal Surfaces (Pt, Rh, Pd, Au, Ru) from UHV to 1 bar. The goal of these in-situ studies at mbar pressures is, of course, to elucidate the elementary steps of heterogeneous catalytic reactions. Case studies include CO adsorption and dissociation, CO oxidation and hydrogenation, ethylene adsorption and hydrogenation, and methanol decomposition on low-index single-Crystal Surfaces, defect-rich (stepped or ion-bombarded) single-Crystal Surfaces, as well as oxide supported metal nanoparticles. The potential of polarization-dependent SFG to determine the molecular orientation of adsorbates and of time-resolved broadband SFG is demonstrated. If available, complementary structural information by high-pressure scanning tunneling microscopy (HP-STM) and compositional analysis by high-pressure photoelectron spectroscopy (HP-XPS) was also included. Implications of the described results on the mechanism, activity and selectivity of catalyzed reactions are discussed.
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molecular studies of catalytic reactions on Crystal Surfaces at high pressures and high temperatures by infrared visible sum frequency generation sfg surface vibrational spectroscopy
Journal of Physical Chemistry B, 1999Co-Authors: G A Somorjai, Gunther RupprechterAbstract:Infrared−visible sum frequency generation (SFG) is a surface-specific vibrational spectroscopy that can operate in a pressure range from ultrahigh vacuum (uhv) to atmospheric pressures. SFG is therefore one of the few surface science techniques that permits atomic scale monitoring of surface species during catalytic reactions at high pressures (around 1 atm) and high temperatures. Using single-Crystal Surfaces of transition metals, platinum and rhodium, reaction rates can be simultaneously determined by gas chromatography, and correlations between the concentration of adsorbates under reaction conditions and the observed turnover numbers can help to elucidate the reaction mechanism. To bridge the gap to traditional surface science experiments, SFG is also employed under uhv or low pressures. The technique has been successfully applied to the adsorption and oxidation of CO, hydrocarbon conversion such as ethylene hydrogenation and cyclohexene hydrogenation and dehydrogenation on Pt(111). The experiments de...
Gabor A. Somorjai - One of the best experts on this subject based on the ideXlab platform.
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furan hydrogenation over pt 111 and pt 100 single Crystal Surfaces and pt nanoparticles from 1 to 7 nm a kinetic and sum frequency generation vibrational spectroscopy study
Journal of the American Chemical Society, 2010Co-Authors: Christopher J Kliewer, Cesar Aliaga, Marco Bieri, Wenyu Huang, Chiakuang Tsung, Jennifer B Wood, Kyriankos Komvopoulos, Gabor A. SomorjaiAbstract:Sum frequency generation surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to systematically study the adsorption and hydrogenation of furan over Pt(111) and Pt(100) single-Crystal Surfaces and size-controlled 1.0-nm, 3.5-nm and 7.0-nm Pt nanoparticles at Torr pressures (10 Torr of furan, 100 Torr of H2) to form dihydrofuran, tetrahydrofuran, and the ring-cracking products butanol and propylene. As determined by SFG, the furan ring lies parallel to all Pt Surfaces studied under hydrogenation conditions. Upright THF and the oxametallacycle intermediate are observed over the nanoparticle catalysts under reaction conditions. Butoxy increases in surface concentration over Pt(111) with increasing temperature in agreement with selectivity trends.
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structure effects of benzene hydrogenation studied with sum frequency generation vibrational spectroscopy and kinetics on pt 111 and pt 100 single Crystal Surfaces
Journal of Physical Chemistry B, 2006Co-Authors: Kaitlin M Bratlie, Christopher J Kliewer, Gabor A. SomorjaiAbstract:Sum frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have identified at least two reaction pathways for benzene hydrogenation on the Pt(100) and Pt(111) single-Crystal Surfaces at Torr pressures. Kinetic studies at low temperatures (310−370 K) show that benzene hydrogenation does not proceed through cyclohexene. A Langmuir−Hinshelwood-type rate law for the low-temperature reaction pathway is identified. The rate-determining step for this pathway is the addition of the first hydrogen atom to adsorbed benzene for both single-Crystal Surfaces, which is verified by the spectroscopic observation of adsorbed benzene at low temperatures on both the Pt(100) and Pt(111) Crystal faces. Low-temperature SFG studies reveal chemisorbed and physisorbed benzene on both Surfaces. At higher temperatures (370−440 K), hydrogenation of benzene to π-allyl c-C6H9 is observed only on the Pt(100) surface. Previous single-Crystal studies have identified π-allyl c-C6H9 as...
G A Somorjai - One of the best experts on this subject based on the ideXlab platform.
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single Crystal Surfaces
Handbook of Heterogeneous Catalysis, 2008Co-Authors: Anderson L Marsh, Fabio H Ribeiro, G A SomorjaiAbstract:The sections in this article are Introduction Techniques Examples of Studies with Single Crystals The Active Site Model of a Catalytic Surface Catalysis over an Adsorbed Overlayer Structure-Sensitive or Structure-Insensitive Reactions Single Crystals are the Standard in Catalysis Examples of Complex Model Catalyst Systems The Future Keywords: single Crystals; industrial catalysts; turnover rate; standard reference rate
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molecular surface chemistry by metal single Crystals and nanoparticles from vacuum to high pressure
Chemical Society Reviews, 2008Co-Authors: G A Somorjai, Jeong Young ParkAbstract:Model systems for studying molecular surface chemistry have evolved from single Crystal Surfaces at low pressure to colloidal nanoparticles at high pressure. Low pressure surface structure studies of platinum single Crystals using molecular beam surface scattering and low energy electron diffraction techniques probe the unique activity of defects, steps and kinks at the surface for dissociation reactions (H–H, C–H, C–C, OO bonds). High-pressure investigations of platinum single Crystals using sum frequency generation vibrational spectroscopy have revealed the presence and the nature of reaction intermediates. High pressure scanning tunneling microscopy of platinum single Crystal Surfaces showed adsorbate mobility during a catalytic reaction. Nanoparticle systems are used to determine the role of metal–oxide interfaces, site blocking and the role of surface structures in reactive surface chemistry. The size, shape and composition of nanoparticles play important roles in determining reaction activity and selectivity and is covered in this tutorial review.
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molecular studies of catalytic reactions on Crystal Surfaces at high pressures and high temperatures by infrared visible sum frequency generation sfg surface vibrational spectroscopy
Journal of Physical Chemistry B, 1999Co-Authors: G A Somorjai, Gunther RupprechterAbstract:Infrared−visible sum frequency generation (SFG) is a surface-specific vibrational spectroscopy that can operate in a pressure range from ultrahigh vacuum (uhv) to atmospheric pressures. SFG is therefore one of the few surface science techniques that permits atomic scale monitoring of surface species during catalytic reactions at high pressures (around 1 atm) and high temperatures. Using single-Crystal Surfaces of transition metals, platinum and rhodium, reaction rates can be simultaneously determined by gas chromatography, and correlations between the concentration of adsorbates under reaction conditions and the observed turnover numbers can help to elucidate the reaction mechanism. To bridge the gap to traditional surface science experiments, SFG is also employed under uhv or low pressures. The technique has been successfully applied to the adsorption and oxidation of CO, hydrocarbon conversion such as ethylene hydrogenation and cyclohexene hydrogenation and dehydrogenation on Pt(111). The experiments de...
Christopher J Kliewer - One of the best experts on this subject based on the ideXlab platform.
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furan hydrogenation over pt 111 and pt 100 single Crystal Surfaces and pt nanoparticles from 1 to 7 nm a kinetic and sum frequency generation vibrational spectroscopy study
Journal of the American Chemical Society, 2010Co-Authors: Christopher J Kliewer, Cesar Aliaga, Marco Bieri, Wenyu Huang, Chiakuang Tsung, Jennifer B Wood, Kyriankos Komvopoulos, Gabor A. SomorjaiAbstract:Sum frequency generation surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to systematically study the adsorption and hydrogenation of furan over Pt(111) and Pt(100) single-Crystal Surfaces and size-controlled 1.0-nm, 3.5-nm and 7.0-nm Pt nanoparticles at Torr pressures (10 Torr of furan, 100 Torr of H2) to form dihydrofuran, tetrahydrofuran, and the ring-cracking products butanol and propylene. As determined by SFG, the furan ring lies parallel to all Pt Surfaces studied under hydrogenation conditions. Upright THF and the oxametallacycle intermediate are observed over the nanoparticle catalysts under reaction conditions. Butoxy increases in surface concentration over Pt(111) with increasing temperature in agreement with selectivity trends.
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structure effects of benzene hydrogenation studied with sum frequency generation vibrational spectroscopy and kinetics on pt 111 and pt 100 single Crystal Surfaces
Journal of Physical Chemistry B, 2006Co-Authors: Kaitlin M Bratlie, Christopher J Kliewer, Gabor A. SomorjaiAbstract:Sum frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have identified at least two reaction pathways for benzene hydrogenation on the Pt(100) and Pt(111) single-Crystal Surfaces at Torr pressures. Kinetic studies at low temperatures (310−370 K) show that benzene hydrogenation does not proceed through cyclohexene. A Langmuir−Hinshelwood-type rate law for the low-temperature reaction pathway is identified. The rate-determining step for this pathway is the addition of the first hydrogen atom to adsorbed benzene for both single-Crystal Surfaces, which is verified by the spectroscopic observation of adsorbed benzene at low temperatures on both the Pt(100) and Pt(111) Crystal faces. Low-temperature SFG studies reveal chemisorbed and physisorbed benzene on both Surfaces. At higher temperatures (370−440 K), hydrogenation of benzene to π-allyl c-C6H9 is observed only on the Pt(100) surface. Previous single-Crystal studies have identified π-allyl c-C6H9 as...
R L Stockbauer - One of the best experts on this subject based on the ideXlab platform.
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comparison of the electronic structure of anatase and rutile tio2 single Crystal Surfaces using resonant photoemission and x ray absorption spectroscopy
Physical Review B, 2007Co-Authors: Andrew G Thomas, W R Flavell, A K Mallick, A R Kumarasinghe, D Tsoutsou, N Khan, C Chatwin, S Rayner, G C Smith, R L StockbauerAbstract:A comparison of the electronic structure of rutile (110), anatase (101), and anatase (001) single-Crystal Surfaces has been made using resonant photoemission and x-ray absorption spectroscopy. Under identical preparative conditions, the anatase (101) surface shows the lowest Ti 3d and 4sp hybridization in the states close to the valence-band maximum of the three Surfaces. It also shows the highest concentration of surface-oxygen vacancies. The effect on the electronic structure of modifying the surface preparative route and thus the concentration of surface-oxygen vacancies is examined. The sigma-antibonding Ti 3d e(g)/O 2p hybridization (probed by XAS) is reduced by the removal of surface-oxygen. Photoemission shows that as the number of surface-defects is increased, the O 2p-Ti 3d t(2g) pi-bonding interaction is disrupted. For the anatase (101) surface it is found that as the number of surface-oxygen vacancies is increased, the Ti 3d and 4sp contributions at the valence-band maximum are reduced. We discuss the correlation between electronic structure and photocatalytic activity of the different polymorphs of TiO2.
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comparison of the electronic structure of anatase and rutile tio2 single Crystal Surfaces using resonant photoemission and x ray absorption spectroscopy
Physical Review B, 2007Co-Authors: Andrew G Thomas, W R Flavell, A K Mallick, A R Kumarasinghe, D Tsoutsou, N Khan, C Chatwin, S Rayner, G C Smith, R L StockbauerAbstract:A comparison of the electronic structure of rutile (110), anatase (101), and anatase (001) single-Crystal Surfaces has been made using resonant photoemission and x-ray absorption spectroscopy. Under identical preparative conditions, the anatase (101) surface shows the lowest $\mathrm{Ti}\phantom{\rule{0.3em}{0ex}}3d$ and $4sp$ hybridization in the states close to the valence-band maximum of the three Surfaces. It also shows the highest concentration of surface-oxygen vacancies. The effect on the electronic structure of modifying the surface preparative route and thus the concentration of surface-oxygen vacancies is examined. The $\ensuremath{\sigma}$-antibonding $\mathrm{Ti}\phantom{\rule{0.3em}{0ex}}3d\phantom{\rule{0.3em}{0ex}}{e}_{g}∕\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p$ hybridization (probed by XAS) is reduced by the removal of surface-oxygen. Photoemission shows that as the number of surface-defects is increased, the $\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p\text{\ensuremath{-}}\mathrm{Ti}\phantom{\rule{0.3em}{0ex}}3d\phantom{\rule{0.3em}{0ex}}{t}_{2g}\phantom{\rule{0.3em}{0ex}}\ensuremath{\pi}$-bonding interaction is disrupted. For the anatase (101) surface it is found that as the number of surface-oxygen vacancies is increased, the $\mathrm{Ti}\phantom{\rule{0.3em}{0ex}}3d$ and $4sp$ contributions at the valence-band maximum are reduced. We discuss the correlation between electronic structure and photocatalytic activity of the different polymorphs of ${\mathrm{TiO}}_{2}$.