Promotion of CO and CO2 Hydrogenation over Rh by Metal Oxides: The Influence of Oxide Lewis Acidity and Reducibility

Boffa, A. B.; Lin, Chenxi; Bell, Alexis T.; Somorjai, Gábor A.

doi:10.1006/jcat.1994.1280

Cited by 211 publications

(136 citation statements)

References 0 publications

Supporting

Mentioning

119

Contrasting

Unclassified

Order By: Relevance

“…CO and CO 2 hydrogenation to methane over a Rh foil decorated with submonolayer quantities of TiO x , VO x , ZrO x , NbO x , TaO x , and WO x were carried out (45). The rate of methane formation was measured at 1 atm (1 atm ϭ 101.3 kPa), and the state of the working catalyst was characterized by x-ray photoelectron spectroscopy immediately after reaction.…”

Section: Reactivity Of Oxide-metal Interfacessupporting

confidence: 42%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

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

245

187

View full text Add to dashboard Cite

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...

show abstract

Section: Reactivity Of Oxide-metal Interfacessupporting

confidence: 42%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

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

245

187

View full text Add to dashboard Cite

show abstract

“…It has been a longstanding observation in the field of heterogeneous catalysis that the oxide onto which the metal nanoparticles are deposited can dramatically change the activity and selectivity in certain reactions even though the oxide itself is not active in catalysis [50,51,52 ] . Recently studies, which detected hot electron formation at metal surfaces helped to explain these curious findings [53][54][55] .…”

Section: Oxide Metal Interfaces Are Catalytically Activementioning

confidence: 46%

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Somorjai

Park

2008

The Journal of Chemical Physics

View full text Add to dashboard Cite

Vacuum studies of metal single crystal surfaces using electron and molecular beam scattering revealed that the surface atoms relocate when the surface is clean (reconstruction) and when it is covered by adsorbates (adsorbate induced restructuring).It was also discovered that atomic steps and other low coordination surface sites are active for breaking chemical bonds (H-H, O=O, C-H, C=O and C-C) with high reaction probability. Investigations at high reactant pressures using sum frequency generation (SFG) -vibrational spectroscopy and high pressure scanning tunneling microscopy (HPSTM) revealed bond breaking at low reaction probability sites on the adsorbatecovered metal surface, and the need for adsorbate mobility for continued turnover. Since most catalysts (heterogeneous, enzyme and homogeneous) are nanoparticles, colloid synthesis methods were developed to produce monodispersed metal nanoparticles in the 1-10 nm range and controlled shapes to use them as new model catalyst systems in twodimensional thin film form or deposited in mesoporous three-dimensional oxides. Studies of reaction selectivity in multipath reactions (hydrogenation of benzene, cyclohexene and crotonaldehyde) showed that reaction selectivity depends on both nanoparticle size and shape. The oxide-metal nanoparticle interface was found to be an important catalytic site because of the hot electron flow induced by exothermic reactions like carbon monoxide oxidation.

show abstract

“…The oxide-metal interface is one of the major factors which determines the activity and selectivity of the heterogeneous catalysts [19][20][21] . It was observed that during certain reactions the oxide onto which the metal nanoparticles are deposited can dramatically change activity and selectivity even though the oxide itself is not active in catalysis 22,23 .…”

mentioning

confidence: 49%

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO₂Schottky Diodes during Catalytic CO Oxidation

et al. 2008

View full text Add to dashboard Cite

Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO 2 diodes.Although Au/TiO 2 diodes are not catalytically active, platinum nanoparticles on Au/TiO 2 exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO 2 . The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting inballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (Tetradecyltrimethylammonium Bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O 2 and 40 Torr CO at 373~513 K. We found that chemicurrent yield varies with each capping agent, but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.

show abstract

Promotion of CO and CO2 Hydrogenation over Rh by Metal Oxides: The Influence of Oxide Lewis Acidity and Reducibility

Cited by 211 publications

References 0 publications

Clusters, surfaces, and catalysis

Clusters, surfaces, and catalysis

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO₂Schottky Diodes during Catalytic CO Oxidation

Contact Info

Product

Resources

About

Promotion of CO and CO2 Hydrogenation over Rh by Metal Oxides: The Influence of Oxide Lewis Acidity and Reducibility

Cited by 211 publications

References 0 publications

Clusters, surfaces, and catalysis

Clusters, surfaces, and catalysis

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO2Schottky Diodes during Catalytic CO Oxidation

Contact Info

Product

Resources

About

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO₂Schottky Diodes during Catalytic CO Oxidation