Hydrogen Transfer on Metal Surfaces

Christmann, K.

doi:10.1002/9783527611546.ch25

Cited by 5 publications

(5 citation statements)

References 132 publications

(158 reference statements)

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“…For this purpose, knowledge of the stoichiometric interactions between Pd metal sites and the reactants, namely, H 2 and 2,4-DNT, is necessary. The activation of H 2 by Pd metal sites was investigated earlier by Paal and Menon (1983), Geus (1988), Christmann (1988), Burch (1980), and Engel and Kuipers (1979), in which it is proposed that Pd can form hydrides of the form shown in eq 1. Although the formation of these hydrides (R and β hydrides differing in hydrogen content are known to form with Pd surfaces) involves a L-H type mechanism, it is well understood that dissolved H 2 on Pd metal surface can have a dramatic influence on the reaction rate since Pd can act as an H 2 reservoir for reactive species (Benedetti et al, 1995).…”

Section: Resultsmentioning

confidence: 97%

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al₂O₃ Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Rajashekharam

Nikalje

Jaganathan

et al. 1997

Ind. Eng. Chem. Res.

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The kinetics of hydrogenation of 2,4-dinitrotoluene (2,4-DNT) using a 5% Pd/Al 2 O 3 catalyst was studied in a semibatch slurry reactor in a temperature range of 323-363 K. Experimental data on the concentration-time and H 2 consumption-time profiles were obtained, and the effects of 2,4-DNT concentration, H 2 pressure, and catalyst loading were studied under both isothermal and nonisothermal conditions. A fundamental approach based on a molecular level description of the catalytic cycle has been used to derive the rate models. Several rate forms were derived considering different types of interactions, but the rate equations derived assuming that the reaction between the transient molecular species formed due to the interactions of H 2 and liquid phase components on different sites of Pd catalyst were found to best represent experimental data. The overall hydrogenation rate was found to vary by approximately second order with respect to catalyst loading, and this trend is adequately explained by the kinetic model proposed. It was found that the intraparticle diffusional effects were important for particle sizes (d p ) > 3 × 10 -4 m, but the external mass-transfer (gas-liquid and liquid-solid) effects were unimportant. For a complex rate equation observed, an approximate expression for the overall effectiveness factor was derived and the experimental data for different particle sizes were found to agree with the predictions of the model incorporating intraparticle diffusion effects. Under certain conditions, a significant temperature rise was observed and the increase in temperature was found to vary with time and the initial set of conditions. A mathematical model to predict the temperature and concentration profiles in a semibatch reactor under nonisothermal conditions has been proposed. A comparison of the experimental data with model predictions showed an excellent agreement.

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Section: Resultsmentioning

confidence: 97%

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al₂O₃ Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Rajashekharam

Nikalje

Jaganathan

et al. 1997

Ind. Eng. Chem. Res.

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“…In two reactions, we first pretreated the metal powders in a dry state with H 2 gas for 16 h at 50 °C before adding a buffer/NAD + solution. Chemisorption and dissociation of H 2 is feasible at these temperatures [51–53]. This approximates the situation in serpentinizing systems, where H 2 is being produced continuously, such that the minerals could be constantly hydrogenated (i.e.…”

Section: Resultsmentioning

confidence: 99%

“…2C), but it employs the most straightforward hydrogenation mechanism, additionally backed up by the results of the experiments with heavy water. Known to enable the dissociation of H 2 [15,[64][65][66][67], Ni was able to reduce NAD + under H 2 gas and showed the strongest positive response to pretreatment with H 2 gas out of the three metals. This suggests that Ni-bound hydrides are transferred to NAD + to produce mainly 1,4-NADH (s. Fig.…”

Section: Discussionmentioning

confidence: 99%

Role of geochemical protoenzymes (geozymes) in primordial metabolism: specific abiotic hydride transfer by metals to the biological redox cofactor NAD⁺

et al. 2022

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Hydrogen gas, H2, is generated in serpentinizing hydrothermal systems, where it has supplied electrons and energy for microbial communities since there was liquid water on Earth. In modern metabolism, H2 is converted by hydrogenases into organically bound hydrides (H–), for example, the cofactor NADH. It transfers hydrides among molecules, serving as an activated and biologically harnessed form of H2. In serpentinizing systems, minerals can also bind hydrides and could, in principle, have acted as inorganic hydride donors—possibly as a geochemical protoenzyme, a ‘geozyme’— at the origin of metabolism. To test this idea, we investigated the ability of H2 to reduce NAD+ in the presence of iron (Fe), cobalt (Co) and nickel (Ni), metals that occur in serpentinizing systems. In the presence of H2, all three metals specifically reduce NAD+ to the biologically relevant form, 1,4‐NADH, with up to 100% conversion rates within a few hours under alkaline aqueous conditions at 40 °C. Using Henry's law, the partial pressure of H2 in our reactions corresponds to 3.6 mm, a concentration observed in many modern serpentinizing systems. While the reduction of NAD+ by Ni is strictly H2‐dependent, experiments in heavy water (2H2O) indicate that native Fe can reduce NAD+ both with and without H2. The results establish a mechanistic connection between abiotic and biotic hydride donors, indicating that geochemically catalysed, H2‐dependent NAD+ reduction could have preceded the hydrogenase‐dependent reaction in evolution.

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“…To represent the catalytic hydrogenation steps, several forms of rate equations were considered. Several authors have reported the activation of hydrogen in the presence of palladium metal − in which the hydrogen may be present as an α-hydride (Pd(H) 2 ) or a β-hydride (Pd(H)) species and where the metal surface influences the reaction rate dramatically . Such molecular level approach for activation of the Shiff base and aromatic ring in the presence of the palladium metal surface are not well documented in the literature.…”

Section: Resultsmentioning

confidence: 99%

Kinetic Modeling of Reductive Alkylation of Aniline with Acetone Using Pd/Al₂O₃ Catalyst in a Batch Slurry Reactor

Roy¹,

Jaganathan²,

Chaudhari³

2005

Ind. Eng. Chem. Res.

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The kinetics of reductive alkylation of aniline with acetone was studied in a slurry reactor under isothermal conditions in a temperature range of 378-408 K using 3% Pd/Al 2 O 3 catalyst. Experimental data on concentration-time as well as hydrogen consumption-time profiles were obtained to study the effect of concentration of aniline, catalyst loading, and partial pressure of hydrogen. Separate controlled experiments were performed to understand the nature of the condensation reaction between aniline and acetone, which forms the Shiff's base intermediate. From the concentration-time profiles and the effect of reaction conditions, it was found that the noncatalytic equilibrium formation of the Shiff base intermediate was the slowest step in the multistep reaction sequence. Several rate equations were considered to fit the batch slurry reactor data, and rate models based on competitive dissociative adsorption of hydrogen and the reactive substrates in the rate-limiting catalytic steps were found to represent the experimental data. The kinetic parameters were evaluated by fitting the integral batch reactor data at different temperatures. The activation energies, heat of adsorption, and entropy of adsorption of all the reactant species were also evaluated.

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Hydrogen Transfer on Metal Surfaces

Cited by 5 publications

References 132 publications

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al₂O₃ Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al₂O₃ Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Role of geochemical protoenzymes (geozymes) in primordial metabolism: specific abiotic hydride transfer by metals to the biological redox cofactor NAD⁺

Kinetic Modeling of Reductive Alkylation of Aniline with Acetone Using Pd/Al₂O₃ Catalyst in a Batch Slurry Reactor

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Hydrogen Transfer on Metal Surfaces

Cited by 5 publications

References 132 publications

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al2O3 Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al2O3 Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Role of geochemical protoenzymes (geozymes) in primordial metabolism: specific abiotic hydride transfer by metals to the biological redox cofactor NAD+

Kinetic Modeling of Reductive Alkylation of Aniline with Acetone Using Pd/Al2O3 Catalyst in a Batch Slurry Reactor

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Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al₂O₃ Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Hydrogenation of 2,4-Dinitrotoluene Using a Pd/Al₂O₃ Catalyst in a Slurry Reactor: A Molecular Level Approach to Kinetic Modeling and Nonisothermal Effects

Role of geochemical protoenzymes (geozymes) in primordial metabolism: specific abiotic hydride transfer by metals to the biological redox cofactor NAD⁺

Kinetic Modeling of Reductive Alkylation of Aniline with Acetone Using Pd/Al₂O₃ Catalyst in a Batch Slurry Reactor