Behavior of highly dispersed platinum catalysts in liquid-phase hydrogenations

Gutiérrez-Ortiz, M.A.; González‐Marcos, José A.; González-Marcos, M.P.; González‐Velasco, Juan R.

doi:10.1021/ie00018a007

Cited by 7 publications

(7 citation statements)

References 16 publications

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“…For benzene hydrogenation in the gas phase (no water) on Pd, turnover frequencies for Pd/C of 0.003–0.022 s –1 at 673 K have been reported, with benzene hydrogenation rates for Pd only reported at a minimum temperature of 448 K . In cyclohexane solvent, benzene hydrogenation turnover frequencies on Pt have been reported in the range of 1.6–12.4 s –1 at 393–433 K and 2.0 MPa . On a Rh-Pt catalyst, both electrocatalytic and thermal catalytic benzene hydrogenation in the gas phase but “saturated with water vapor” was observed at 50 °C, with benzene conversion detected even at 25 °C .…”

Section: Resultsmentioning

confidence: 99%

A Simple Bond-Additivity Model Explains Large Decreases in Heats of Adsorption in Solvents Versus Gas Phase: A Case Study with Phenol on Pt(111) in Water

2019

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We recently reported the low-coverage heat of adsorption of phenol on Pt(111) facets of a Pt wire in aqueous phase to be approximately 21 kJ/mol (relative to aqueous phenol) on the basis of measurements of the adsorption equilibrium constant. This is much smaller than the heat we reported for gas-phase phenol adsorption at this same low coverage on single-crystal Pt(111) under ultrahigh vacuum (200 kJ/mol) on the basis of adsorption calorimetry measurements. Here we quantitatively analyze the individual contributions that give rise to this 179 kJ/mol difference using a simple pairwise bond-additivity model, taking advantage of experimental data from the literature to estimate the bond energies. The dominant contribution to the lowering in heat when phenol is adsorbed in water is the energy cost to break the strong bond of liquid water to Pt(111) (∼116 kJ per mole of phenol area). The water–phenol bonding is lost on one face of the phenol, and this costs ∼50 kJ/mol, but this is nearly compensated by the new water–water bonding (∼53 kJ/mol of phenol area). The results indicate that the intrinsic bond energy between phenol and Pt(111) is not very different in the gas versus the aqueous phase, provided one takes into consideration the expectation that water forces phenol into islands of high local coverage even at low average coverage (for the same reason that phenol has limited solubility in water). This also explains the lack of a strong coverage dependence in the heat of adsorption when it is measured in aqueous phase, whereas it decreases by ∼57 kJ/mol with coverage when it is measured in gas phase. This bond-additivity analysis presented here can be easily generalized to other adsorbates, surfaces, and solvents. It clarifies why catalysis with molecules such as phenol which have very strong bonding to Pt-group metals can proceed rapidly at room temperature in liquid solvents such as water but would never proceed in the gas phase at room temperature due to irreversible site poisoning.

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Section: Resultsmentioning

confidence: 99%

A Simple Bond-Additivity Model Explains Large Decreases in Heats of Adsorption in Solvents Versus Gas Phase: A Case Study with Phenol on Pt(111) in Water

2019

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“…The reactor disposes of a 45°p itched blade turbine with four blades connected to an electric engine with variable stirring speed up to 750 rpm, an automatic temperature controller up to 673 K, a pressure controller with a top operation pressure of 4 MPa, and a hydrogen flow controller. The schematics of the apparatus has been presented elsewhere (Gutiérrez-Ortiz et al, 1993). The reactor operated in a semicontinuous way, bubbling 50 cm3 min™1 of pure hydrogen in 200 cm3 of the liquid feed.…”

Section: Methodsmentioning

confidence: 99%

Activity and Selectivity of Palladium Catalysts during the Liquid-Phase Hydrogenation of Phenol. Influence of Temperature and Pressure

González‐Velasco¹,

González-Marcos²,

Arnaiz³

et al. 1995

Ind. Eng. Chem. Res.

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“…The experimental set-up for reaction experiments consisted of a 4.5 cm i.d., 300 mL capacity stainless steel batch reactor (Autoclave Engineers, Erie, Pennsylvania, USA). 17 The tank was equipped with a cooling coil, a thermometer pocket, a 4 cm diameter disc turbine impeller with six blades, located at a height of 2.5 cm from the bottom of the reactor, an electric heating mantle, a digital temperature control system and a manometer. A nitrogen purge was used to create an inert atmosphere inside the vessel.…”

Section: Methodsmentioning

confidence: 99%

A kinetic study of the depolymerisation of poly(ethylene terephthalate) by phase transfer catalysed alkaline hydrolysis

López‐Fonseca

González-Marcos

González‐Velasco

et al. 2008

J of Chemical Tech & Biotech

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BACKGROUND: Chemical or tertiary recycling of waste polymers including PET, poly(ethylene terephthalate), leads to the formation of raw starting monomers by different depolymerisation routes. This work was focused on the identification of the catalytic behaviour, if any, of a series of quaternary phosphonium and ammonium salts as phase transfer catalysts for the alkaline hydrolysis of PET, and on the determination of the kinetics of the phase transfer catalysed process.

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Behavior of highly dispersed platinum catalysts in liquid-phase hydrogenations

Cited by 7 publications

References 16 publications

A Simple Bond-Additivity Model Explains Large Decreases in Heats of Adsorption in Solvents Versus Gas Phase: A Case Study with Phenol on Pt(111) in Water

A Simple Bond-Additivity Model Explains Large Decreases in Heats of Adsorption in Solvents Versus Gas Phase: A Case Study with Phenol on Pt(111) in Water

Activity and Selectivity of Palladium Catalysts during the Liquid-Phase Hydrogenation of Phenol. Influence of Temperature and Pressure

A kinetic study of the depolymerisation of poly(ethylene terephthalate) by phase transfer catalysed alkaline hydrolysis

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