Isokinetic behaviour in gas phase catalytic haloarene hydrodehalogenation reactions: Mechanistic considerations

Keane, Mark A.; Larsson, Ragnar

doi:10.1016/j.molcata.2006.01.017

Cited by 9 publications

(11 citation statements)

References 31 publications

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“…The basis for the SET model is the occurrence of a state of resonance between a vibrational mode of the catalyst system and a complementary vibrational mode of the reacting molecule. We identified the critical reactant vibrational mode as an out-of-plane C-H vibration with optimum resonance energy transfer from the catalyst (Ni-H) vibrational mode [1,3]. We have now extended that work and report here an SET analysis of the hydrogenolytic cleavage of oxygenated functional groups from the aromatic ring.…”

Section: Introductionmentioning

confidence: 79%

“…In a series of earlier studies [1][2][3], we examined the isokinetic effect for the reductive cleavage of C-X bonds in a range of haloarenes over supported Ni catalysts. An isokinetic response occurs where the Arrhenius plots (ln k vs. 1/T) for a series of related reactions intersect at a common temperature (the isokinetic temperature, T iso ).…”

Section: Introductionmentioning

confidence: 99%

“…An isokinetic response occurs where the Arrhenius plots (ln k vs. 1/T) for a series of related reactions intersect at a common temperature (the isokinetic temperature, T iso ). We demonstrated that the T iso for hydrodehalogenation could be accounted for using the Selective energy transfer (SET) model [1]. The basis for the SET model is the occurrence of a state of resonance between a vibrational mode of the catalyst system and a complementary vibrational mode of the reacting molecule.…”

Section: Introductionmentioning

confidence: 99%

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Application of the Selective Energy Transfer Model to Account for an Isokinetic Response in the Gas Phase Reductive Cleavage of Hydroxyl, Carbonyl and Carboxyl Groups from Benzene Over Nickel/Silica

Keane

Larsson

2009

Catal Lett

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The gas phase hydrodeoxygenation of a series of aromatic alcohols, aldehydes and acids has been examined over Ni/SiO 2 . Compensation behaviour is established with an isokinetic temperature (518 ± 21 K) that is consistent with with the point of intersection of the Arrhenius lines. This is accounted for using the Selective Energy Transfer model that is based on resonance between the catalytic Ni-H vibration and out-of plane C-H vibrations of the aromatic reactants with a transferral of resonance energy from the catalyst to generate the ''activated complex''. The calculated wave number of this vibration mode is 720 ± 29 cm -1 with an associated anhamonicity of -3.3 ± 0.9 cm -1 . Our analysis suggests that the oxygenated aromatic is weakly adsorbed on the catalyst and surface mobility facilitates reaction with adsorbed hydrogen atoms.

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Section: Introductionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Application of the Selective Energy Transfer Model to Account for an Isokinetic Response in the Gas Phase Reductive Cleavage of Hydroxyl, Carbonyl and Carboxyl Groups from Benzene Over Nickel/Silica

Keane

Larsson

2009

Catal Lett

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“…Perhaps of morphological nature, perhaps composition of the catalyst or reactant (in Ref. [ 14 ], where a difference of ∆ln k iso = 0.75 was found between two groups of reactions, with seven and five members, respectively, we concluded that the difference originated from positions of substituents in the molecules that reacted—in one case ortho -positions, in the other meta - or para -positions). Incidentally, one notes that the combination of Equations (7) and (8) gives the so called Compensation effect.…”

Section: Discussionmentioning

confidence: 76%

“…One notes that three of these lines (red-colored) cut in one and the same point, with a mean value of 1000/T = 1.376 ± 0.005 K −1 corresponding to T iso = 727 ± 4 K (had a few more catalysts been included in the investigation, one might very well have found a “mate” to the upper line that most probably would have cut the other one at a similar temperature. This is not uncommon [ 12 , 13 , 14 ].…”

Section: Discussionmentioning

confidence: 99%

Propane Dehydrogenation Catalyzed by ZSM-5 Zeolites. A Mechanistic Study Based on the Selective Energy Transfer (SET) Theory

Larsson

2015

Molecules

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Experimentally determined activation energies of propane dehydrogenation catalyzed by ZSM-5 zeolites have been used to test the SET theory. The basis of this theory is that the catalyst system transfers vibrational energy via a resonance process to a specific vibration mode of the reacting molecule. Being excited up to a certain number of vibrational quanta the molecule is brought to reaction. By analyzing the above-mentioned activation energies we found the wave number of this “specific mode” to be 1065 cm−1. This is very close to the rocking vibration of propane (1053 cm−1). We suggest that the propane molecule reacts when excited so that the CH3 group has been forced towards a flat structure with a carbon atom hybridization that is more sp2 than sp3. Consequently there is no way for three H-atoms to bind to the carbon and one of them must leave. This is the starting point of the reaction. The isokinetic temperature of the system was found as Tiso = 727 ± 4 K. From the SET formula for Tiso when both energy-donating (ω) and energy-accepting (ν) vibrations have the same frequency, viz., Tiso = Nhcν/2R, we obtain ν = ω = 1011 ± 6 cm−1. This agrees rather well with the CH3 rocking mode (1053 cm−1) and also with asymmetric “TO4” stretching vibrations of the zeolite structure (ω).

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Supported Transition Metal Catalysts for Hydrodechlorination Reactions

2011

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As halogenated waste is xenobiotic with no analogous compounds in nature, there is no natural means of ameliorating the negative environmental impact caused by halo‐organic emissions. The presence of organo‐halogens in effluent discharges is of increasing concern, owing to the mounting evidence of adverse stratospheric ozone, ecological effects, and the impact on public health. There is a pressing need, driven by legislative and financial imperatives, to develop robust and efficient treatment technologies. This Review considers the application of catalytic hydrodechlorination (HDC) as a progressive approach to the conversion and recycling of toxic chloro‐compounds. An overview of the existing treatment technologies is provided with an assessment of the benefits of catalytic HDC over separation/oxidation methodologies. Taking the transformation of chloro‐aromatics, the catalytic HDC of liquid and gas phase reactants is considered in turn with a critical analysis of the pertinent literature. Two “case studies” are considered in detail: i) the liquid phase HDC of chlorophenols over alumina supported palladium, focusing on the critical process and catalyst structural characteristics that influence HDC performance; ii) the gas phase conversion of a range of halogenated (Cl and Br) aromatics over silica supported nickel with an examination of the dehalogenation activity/selectivity response as a function of the nature of the aromatic reactant.

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Isokinetic behaviour in gas phase catalytic haloarene hydrodehalogenation reactions: Mechanistic considerations

Cited by 9 publications

References 31 publications

Application of the Selective Energy Transfer Model to Account for an Isokinetic Response in the Gas Phase Reductive Cleavage of Hydroxyl, Carbonyl and Carboxyl Groups from Benzene Over Nickel/Silica

Application of the Selective Energy Transfer Model to Account for an Isokinetic Response in the Gas Phase Reductive Cleavage of Hydroxyl, Carbonyl and Carboxyl Groups from Benzene Over Nickel/Silica

Propane Dehydrogenation Catalyzed by ZSM-5 Zeolites. A Mechanistic Study Based on the Selective Energy Transfer (SET) Theory

Supported Transition Metal Catalysts for Hydrodechlorination Reactions

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