Hydrogenation of ethylene over platinum (111) single-crystal surfaces

Zaera, Francisco; Somorjai, G. A.

doi:10.1021/ja00320a013

Cited by 352 publications

(274 citation statements)

References 9 publications

(13 reference statements)

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“…Based on the literature for Pt single crystals [13][14][15] , traditionally prepared supported Pt catalysts 18,19 , supported Pt nanoparticles 9,20 , Pt NP arrays 16,17 , and Pt nanowires 16 , an average TOF (after being corrected to the conditions reported in this paper in the same manner as described in Section 3.2) was 8.7 s -1 . Using this value as a normalization factor, dispersions were estimated from ethylene hydrogenation as a chemical probe technique (Table 2).…”

Section: Estimation Of Metallic Surface Area By Ethylene Hydrogenationmentioning

confidence: 97%

“…In addition to initial catalytic activity, the capping agents also caused Pt to 13 , Pt(100)-(5x20) 14 , Pt (210) 15 were 4.5, 2.7, and 5.8 s -1 , respectively, after correcting (to 20°C with reported activation energies or, if none given, assuming 10 kcal mol -1 and zero and first order dependence upon ethylene and hydrogen, respectively) to the conditions used in this paper. Similar results were also reported over Pt NP arrays and nanowires.…”

Section: Ethylene Hydrogenation Activitymentioning

confidence: 99%

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Effect of organic capping layers over monodisperse platinum nanoparticles upon activity for ethylene hydrogenation and carbon monoxide oxidation

Kuhn

Tsung

Huang

et al. 2009

Journal of Catalysis

171

149

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The influence of oleylamine (OA), trimethyl tetradecyl ammonium bromide (TTAB), and polyvinlypyrrolidone (PVP) capping agents upon the catalytic properties of Pt/silica catalysts was evaluated. Pt nanoparticles of 1.5 nm in size were synthesized by the same procedure (ethylene glycol reduction under basic conditions) with the various capping agents added afterwards for stabilization.Before examining catalytic properties for ethylene hydrogenation and CO oxidation, the Pt NPs were deposited onto mesoporous silica (SBA-15) supports and characterized by transmission electron microscopy (TEM), H 2 chemisorption, and elemental analysis (ICP-MS). PVP and TTAB capped Pt yielded mass normalized reaction rates that decreased with increasing pretreatment temperature and was attributed to partial coverage of the Pt surface with decomposition products from the organic capping agent. Once normalized to the Pt surface area, similar intrinsic activities were obtained regardless of the pretreatment temperature, which indicated no influence on the nature of active sites. Consequently, a chemical probe technique using intrinsic activity for ethylene hydrogenation was demonstrated as an acceptable method for estimating the metallic surface areas of Pt. Amine (OA) capping exhibited a detrimental influence on the catalytic properties as severe deactivation and low activity were observed for ethylene hydrogenation and CO oxidation, respectively. These results were consistent with amine groups being strong poisons for Pt surfaces and revealed the need to consider the effects of capping agents to stabilize nanoparticles on the catalytic properties.

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Section: Estimation Of Metallic Surface Area By Ethylene Hydrogenationmentioning

confidence: 97%

Section: Ethylene Hydrogenation Activitymentioning

confidence: 99%

Effect of organic capping layers over monodisperse platinum nanoparticles upon activity for ethylene hydrogenation and carbon monoxide oxidation

Kuhn

Tsung

Huang

et al. 2009

Journal of Catalysis

171

149

View full text Add to dashboard Cite

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“…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)(3)(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 isomers, a complex but important reaction that produces high-octane gasoline, has a turnover rate of 10 Ϫ2 product molecules per platinum surface site per second at Ϸ600 K (6).…”

mentioning

confidence: 99%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

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

240

186

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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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“…It is currently not completely understood why this is the case. One hypothesis is that the ethylene actually adsorbs on top of the layer of ethylidyne [109,110] rather than directly onto the platinum. Another hypothesis is that the ethylene can compress the ethylidyne (which has been shown to be highly mobile on the surface) and adsorb on the platinum sites freed.…”

Section: Ethylene Hydrogenationmentioning

confidence: 99%