In-SituObservation of π-Allylc-C6H9Intermediate during High-Pressure Cyclohexene Catalytic Reactions on Pt(111) Using Sum Frequency Generation Vibrational Spectroscopy

Yang, Minchul; Chou, Kuang-Chao; Somorjai, Gábor A.

doi:10.1021/jp034355r

Cited by 39 publications

(89 citation statements)

References 36 publications

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“…7a). SFG studies indicate -allyl (C 6 H 9 ) species are present on the surface (32,44). The addition of CO causes all catalytic activity to cease and orders the surface (Fig.…”

Section: Co Bond Activation Over Platinum Single Crystal Surfacesmentioning

confidence: 99%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

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

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The surface science of heterogeneous metal catalysis uses model systems ranging from single crystals to monodispersed nanoparticles in the 1-10 nm range. Molecular studies reveal that bond activation (C-H, H-H, C-C, CAO) occurs at 300 K or below as the active metal sites simultaneously restructure. The strongly adsorbed molecules must be mobile to free up these sites for continued turnover of reaction. Oxide-metal interfaces are also active for catalytic turnover. Examples using C-H and CAO activation are described to demonstrate these properties. Future directions include synthesis, characterization, and reaction studies with 2D and 3D monodispersed metal nanoclusters to obtain 100% selectivity in multipath reactions. Investigations of the unique structural, dynamic, and electronic properties of nanoparticles are likely to have major impact in surface technologies. The fields of heterogeneous, enzyme, and homogeneous catalysis are likely to merge for the benefit of all three.catalytic bond activation ͉ high selectivity catalyst design ͉ molecular ingredients of catalysis M etal containing catalysts are clusters of 1-10 nm in size. These are grouped into three types: heterogeneous catalysts that are embedded in high surface area supports, usually oxides, to optimize their surface area and thus the number of molecules they produce per second and also to optimize their thermal and chemical stability. They are used mostly at high temperatures (400-800 K) and in the presence of vapor phase reactants and product molecules. Enzyme catalysts operate in solution, mostly in water near 300 K, and the metal-containing active sites are surrounded by proteins that maintain structural mobility (1). Homogeneous catalysts function in the same solution in which the reactant and product molecules are dissolved, mostly in organic solvents, and used in the 300-500 K temperature range. Because of the different operating conditions and for reasons of history, the three fields of catalysis developed independently and became separate fields of science within different subdisciplines of chemistry. Heterogeneous catalysis was practiced mostly by physical chemists and chemical engineers, enzyme catalysis by biochemists, and homogeneous catalysis by inorganic and organometallic chemists.Catalytic reactions are distinguished from stoichiometric reactions by having many turnovers per reacting active site producing 10 2 to 10 6 molecules per site. Some of these catalytic reactions are very fast. For instance, the catalytic oxidation of carbon monoxide (CO) produces thousands of CO 2 molecules per metal surface site per second above ignition where the exothermicity of the process makes it self-sustaining in temperature and the reaction rate is only limited by the speed of transport of molecules to and from the catalyst surface (2-4). Ethylene hydrogenation, another exothermic reaction, turns over to produce ethane Ϸ10 times per metal surface site per second at 300 K on Pt(111) (5). The catalytic conversion of n-hexane to benzene or to branched...

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“…7a). SFG studies indicate -allyl (C 6 H 9 ) species are present on the surface (32,44). The addition of CO causes all catalytic activity to cease and orders the surface (Fig.…”

Section: Co Bond Activation Over Platinum Single Crystal Surfacesmentioning

confidence: 99%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

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

Self Cite

245

187

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“…Upon adsorption of cyclohexene to the platinum surface at pressures below 1 Torr at 300 K, the molecule quickly undergoes partial dehydrogenation to form the p-allyl species (C 6 H 9 ) [19]. This species is very stable on the surface but has been shown to further dehydrogenate as the temperature is increased above 300 K. At pressures above 1 Torr the most stable surface species is the 1,4 cyclohexadiene molecule.…”

Section: 24mentioning

confidence: 99%

Scanning Tunneling Microscopy (STM) at High Pressures. Adsorption and Catalytic Reaction Studies on Platinum and Rhodium Single Crystal Surfaces

2006

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In this paper, we review the experimental results that were obtained using our high pressure-high temperature STM system (HP/HT STM) for studies of gas adsorption in a broad pressure range. Measurements are carried out in equilibrium with the gas phase. We discovered ordered surface structures of adsorbates that do not exist at low pressures. It appears that small increases in coverage due to increased ambient pressures cause ordering due to repulsive adsorbate-adsorbate interactions. Adsorption isotherms, one of the oldest fields of surface thermodynamics, can be revisited using HP/HT STM to obtain molecular surface structures and surface phase diagrams as the gas pressure is altered.

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“…Cyclohexene adsorption under UHV conditions has been extensively studied on the Pt(111) and Pt(100) surfaces using thermal desorption spectroscopy (TDS) [23][24][25], reflection adsorption infrared spectroscopy (RAIRS) [23], electron energy loss spectroscopy (EELS) [23], bismuth post dosing TDS (BPTDS) [5,25], laser-induced thermal desorption (LITD) [24], high-resolution electron energy loss spectroscopy (HREELS) [23,24], and SFG [26][27][28][29][30][31]. Briefly, cyclohexene exists in a di-r form on the Pt(100) and Pt(111) surfaces at 100 K. Di-r cyclohexene is transformed to p-allyl c-C 6 H 9 as the surface temperature is increased to 200 K. Dehydrogenation and benzene desorption results from further increasing the surface temperature [23].…”

Section: Sum-frequency Generation Vibrational Spectroscopy Studies Onmentioning

confidence: 99%

“…1,4-Cyclohexadiene and 1,3-cyclohexadiene were found to co-exist on Pt(111) at 303 K in the presence of excess hydrogen (15 Torr) and very quickly hydrogenate to p-allyl c-C 6 H 9 at 323 K. p-allyl c-C 6 H 9 dehydrogenates to 1,3-cyclohexadiene when the surface temperature is increased to 400 K [26]. Investigations of cyclohexene hydrogenation/dehydrogenation on the Pt(111) surface have also included kinetic measurements.…”

Section: Sum-frequency Generation Vibrational Spectroscopy Studies Onmentioning

confidence: 99%

Molecular surface science of C–H bond activation and polymerization catalysis

et al. 2006

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Surface science studies of heterogeneous catalysis use model systems ranging from single crystals to monodispersed nanoparticles in the 1-10 nm range. Molecular studies reveal that bond activation (C-H, H-H, C-C, C " O) occurs at 300 K or below as the active metal sites simultaneously restructure. The strongly adsorbed molecules must be mobile to free up these sites for continued turnover of reaction. Oxide-metal interfaces are also active for catalytic turnover. Examples using C-H and C = O activation are described to demonstrate these properties. Polymerization catalysis demonstrates a strong dependence upon catalyst surface structure, which allows for the selectivity to be tuned by the choice of Ziegler-Natta surface preparation. Novel preparation methods of model catalyst arrays in two and three dimensions are opening the door to a complete understanding of catalytic reaction selectivity.

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In-SituObservation of π-Allylc-C₆H₉Intermediate during High-Pressure Cyclohexene Catalytic Reactions on Pt(111) Using Sum Frequency Generation Vibrational Spectroscopy

Cited by 39 publications

References 36 publications

Clusters, surfaces, and catalysis

Clusters, surfaces, and catalysis

Scanning Tunneling Microscopy (STM) at High Pressures. Adsorption and Catalytic Reaction Studies on Platinum and Rhodium Single Crystal Surfaces

Molecular surface science of C–H bond activation and polymerization catalysis

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