Compensation Phenomena in Heterogeneous Catalysis: General Principles and a Possible Explanation

Bond, Geoffrey C.; Keane, Mark A.; Kral, H.; Lercher, Johannes A.

doi:10.1081/cr-100100264

Cited by 263 publications

(236 citation statements)

References 131 publications

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“…The same results are found for the conversion of neopentane (2,2-dimethylbutane) to isopentane (isomerization) or isobutane and methane (hydrogenolysis) [24][25][26][27]. In addition to the correlation between the order in P H 2 and E app , the compensation relation is regularly observed for hydrogenolysis reactions [28][29][30]. The compensation relation denotes a linear relationship between the apparent activation energy and the preexponential factor.…”

Section: Introductionsupporting

confidence: 54%

“…The observation that all Arrhenius parameters for all catalysts obey the Constable-Cremer relation [31] indeed suggest that compensation behavior is present. According to the standards set by Bond et al [32], the range in E app should ideally be at least 50% of the smallest E app measured, which is close to the value of 40% for the results presented in this study.…”

Section: Kineticsmentioning

confidence: 99%

“…One mechanism that can account for the compensation relation involves changes in the surface coverage or binding energies of the reactants as extensively discussed by Bond et al [32]. These changes can alter the kinetic parameters, even if the true activation energy remains constant.…”

Section: Introductionmentioning

confidence: 99%

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In situ X-ray absorption spectroscopy as a unique tool for obtaining information on hydrogen binding sites and electronic structure of supported Pt catalysts: towards an understanding of the compensation relation in alkane hydrogenolysis

Koningsberger

Oudenhuijzen

Graaf

et al. 2003

Journal of Catalysis

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L 2 and L 3 X-ray absorption near edge spectra (XANES) on supported Pt particles, with and without chemisorbed hydrogen, are shown to reflect the type of hydrogen-binding site on the Pt surface. FEFF8 ab initio multiple scattering calculations are used to determine XANES spectral fingerprints for the atop vs threefold H binding sites on Pt. Comparison of the experimental XANES data with the theoretical fingerprints, and further theoretical results, show that the acid/base properties of the support have a profound influence on the hydrogen coverage, and therefore on the mode of hydrogen adsorption on the Pt surface. As the electron richness of the support oxygen atoms increases (i.e., with increasing alkalinity of the support), the H coverage increases and the hydrogen-binding site of the strongly adsorbed hydrogen changes from atop to threefold. This site change is primarily responsible for the observed changes in previously reported kinetic data, which show an increase in negative order (roughly from −1.5 to −2.5) in hydrogen partial pressure for neopentane hydrogenolysis with increasing support alkalinity. This change in negative order directly reflects the greater number of vacant Pt sites that must be available to allow adsorption of the neopentane. A compensation relation is found in the kinetic data of Pt on different supports resulting directly from this change in hydrogen coverage. This implies that the experimentally determined kinetic parameters are apparent values. These apparent values are correlated to the intrinsic kinetic parameters via the thermodynamic properties of the sorption of the reactants, described by the Temkin equation. The TOF of neopentane hydrogenolysis over several catalysts, measured in previous work, decreases with the increasing alkalinity of the support. This can now be directly explained as the result of the change in hydrogen coverage using a Frumkin isotherm, implying that the neopentane adsorption becomes weaker with increased hydrogen coverage. These conclusions, that hydrogen drives the catalysis, are further supported by density functional calculations on small Pt 4 clusters, which show that the acid/base properties of the support have a much larger direct influence on Pt-H bonding than on Pt-CH n bonding.

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Section: Introductionsupporting

confidence: 54%

Section: Kineticsmentioning

confidence: 99%

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In situ X-ray absorption spectroscopy as a unique tool for obtaining information on hydrogen binding sites and electronic structure of supported Pt catalysts: towards an understanding of the compensation relation in alkane hydrogenolysis

Koningsberger

Oudenhuijzen

Graaf

et al. 2003

Journal of Catalysis

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“…The existence of linear relationships between adsorption enthalpy and entropy, and the carbon number has been demonstrated numerously [3,[25][26][27]. Among all zeolites, ZSM-5 is undoubtedly the most studied one, both from the adsorption and catalysis point of view.…”

Section: Chain Length Induced Selectivity Reversal In Zsm-5mentioning

confidence: 99%

Adsorption and Reaction in Confined Spaces

Denayer¹,

Daems²,

Baron³

2006

Oil & Gas Science and Technology - Rev. IFP

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Résumé -Adsorption et réaction dans des espaces confinés -L'adsorption de molécules dans des matériaux microporeux cristallins implique des interactions énergétiques et entropiques spécifiques. L'assemblage moléculaire dans ces espaces confinés résulte dans des effets de sélectivité complètement différents des ceux qu'on observe traditionnellement avec des solides amorphes ou mésoporeux. Quelques exemples d'effets entropiques ou d'assemblage moléculaire dans l'adsorption d'hydrocarbures dans des zéolites sont présentés. Abstract -Adsorption and Reaction in Confined Spaces

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“…Since it was first described in the 1920s, 527-530 the origin of this so-called compensation effect has been the subject of a lot of debate. 531 Haag et al 130 showed that the true activation energy of the cracking reaction is virtually invariant with alkane chain length despite the rapid decrease in the apparent activation energy. The reason for the rapid decrease in apparent activation energy and increase in preexponential factor with chain length is that the enthalpy of adsorption dominates the former and the entropy of adsorption the latter at the catalytic cracking conditions applied.…”

Section: Reactant Shape Selectivitymentioning

confidence: 99%