Adsorption of Reaction Species on Pd−Carbon for Liquid-Phase Hydrogenation of <i>o</i>-Nitrophenol

Choudhary, Vasant R.; Sane, M. G.

doi:10.1021/ie990055d

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“…The models are derived for the adsorption of ONP controlling, adsorption of H 2 controlling, and surface reaction controlling for single and dual-site mechanisms from the basic principles of Langmuir's adsorption theory. It may be noted that the adsorption of ONP is higher than OAP or water. , Also, the adsorption of hydrogen on a Pd catalyst has been reported to be strong . The hydrogenation reaction is therefore expected to be mostly governed by the adsorption of one of the reactants (ONP or H 2 ) or the surface reaction between the adsorbed reactants.…”

Section: Resultsmentioning

confidence: 99%

Kinetics of Hydrogenation of o-Nitrophenol to o-Aminophenol on Pd/Carbon Catalysts in a Stirred Three-Phase Slurry Reactor

Choudhary

Sane

Tambe

1998

Ind. Eng. Chem. Res.

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Kinetics of the hydrogenation of o-nitrophenol to o-aminophenol over a Pd/carbon (4.82 wt % Pd) catalyst (particle size 30 μm) in an agitated three-phase slurry reactor has been investigated in the chemical control regime at different temperatures (293−328 K), with initial concentration of o-nitrophenol (0.072−0.36 mol dm-3 ) and H2 pressures (442−1476 kPa), using methanol as a reaction medium. To confirm the absence of gas−liquid, liquid−solid, and intraparticle mass-transfer effects on the reaction, the effects of stirring speed (260−1290 rpm), catalyst loading (0.05−1.0 g dm-3), and catalyst particle size (30−165 μm) on the initial reaction rate at the maximum temperature (328 K) and o-nitrophenol concentration (0.36 mol dm-3) have been thoroughly studied. For a catalyst particle size of ≤45 μm and a stirring speed of ≥850 rpm, the reaction rate is not influenced by the mass-transfer processes. Effective intraparticle diffusivity of o-nitrophenol has been determined from the effectiveness factor of the catalyst for its different particle sizes. The observed large tortuosity factor (τ = 22.9 av) and activation energy (28.9 kJ mol-1) for the diffusion indicated a strong influence of adsorption and surface diffusion of o-nitrophenol on the catalyst. From the power law analysis of the initial rate data, the reaction order is found to be 0.53 ± 0.03 for o-nitrophenol in its concentration below 0.18, 0.22, 0.23, and 0.25 mol dm-3 at 293, 308, 318, and 328 K, respectively, and from 0.54 (at 293 K) to 1.0 (at 328 K) for hydrogen. However, the reaction is found to be zero-order for the higher o-nitrophenol concentration (>0.25 mol dm-3). The reaction kinetic data (including the initial rate data) could be fitted well to a Hougen−Watson-type model on the basis of the mechanism involving single-site surface reaction control with all the reaction species molecularly adsorbed. The activation energy for the initial reaction obtained from the power law analysis (70.2 kJ mol-1) is found to agree with that (68.0 kJ mol-1) obtained from the Hougen−Watson model.

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Section: Resultsmentioning

confidence: 99%