On the apparent compensation effect

Schwab, Georg‐Maria

doi:10.1016/0021-9517(83)90079-9

Cited by 44 publications

(21 citation statements)

References 4 publications

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“…This phenomenon is known as the ''compensation effect'' or ''isokinetic relationship'' and is observed with many reactions [74][75][76][77][78][79][80]. Associated with this actuality is a temperature at which the rates of product formation are equivalent, and this is commonly referred to as the ''isokinetic temperature'', but is also referred to as an ''isocatalytic temperature'' [77].…”

Section: Isokinetic Relationshipmentioning

confidence: 96%

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

et al. 2010

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Twelve phosphomolybdate compounds were synthesized via cationic exchange and were of the form: M x H 3-3x [PMo 12 O 40 ] (M = Al, La or Ce; 0 B x B 1). These compounds were analyzed by XRD and adsorption isotherm. Aluminum addition causes a primitive cubic phase, while lanthanum and cerium yield body-centered structures. La and Ce addition reduces surface area of phosphomolybdate structure. Temperature-programmed experiments for the selective oxidation of isobutane yielded methacrolein, 3-methyl-2-oxetanone (lactone), acetic acid (not with aluminous compounds), propene (only with aluminous compounds), carbon dioxide and water. The preference for propene rather than acetic acid formation with Al 3? may be due to the smaller cation size, or primitive cubic structure. These products form via two distinct reaction processes, labeled categories 1 and 2. Category 1 formation is associated with isobutane forming products on the surface, but reaction rate determined by bulk migration of charged particles. Category 2 formation is concerned with isobutane penetrating deep within the bulk of the substrate and forming products which subsequently desorb in a series of bell-shaped humps. Methacrolein forms via both category 1 and 2, whilst all other products form via category 2 exclusively. Kinetic analysis showed apparent activation barriers for category 1 methacrolein formation range from 67 ± 2 kJ mol -1 to [350 kJ mol -1 , and occur in groups with small, medium and large activation barriers. The addition of ?3 metal cations to the phosphomolybdate anion increase thermal stability, significantly decreasing deactivation; IR spectroscopy shows that the Keggin structure remains intact during temperature-programmed experiments with the Al, La and Ce salts.

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Section: Isokinetic Relationshipmentioning

confidence: 96%

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

et al. 2010

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“…In his last paper Schwab [7], the co-inventor of the Theta-Rule, refers to his own review of 1950 [lo] which "gives many examples of such an agreement" between isokinetic and preparation temperatures, contradicting the examples quoted by Cremer [ 1 I]. The two reviews form the basis of descriptions in textbooks.…”

Section: Me Theta-rulementioning

confidence: 98%

“…(7) for n = 1: -dkldt a k , K" (7) k a exp -k , t (10) where k , is the rate constant of the deactivation process, dependent on temperature, rn is the exponent and t the time. As a rule, relative activity is used instead of the rate constant k .…”

Section: Time Dependencementioning

confidence: 99%

“…In this temperature range, the catalyst with the highest activity ( = rate constant) has the smallest activation energy according to the energetic concept (potential energy profile) which is assumed to have a universal validity. Therefore, the activation energy is used as a general activity index [7] and assumes a fundamental importance for the interpretation of catalytic effects [lo, 15 -171. The identical use of O for the preparation and/or the isokinetic temperature, which is still common in the current literature [18], impedes the testing of the presented results and interpretations.…”

Section: Validity Rangementioning

confidence: 99%

“…This is one reason for testing its applicability. The second reason is the assertion of Schwab [7] in his last paper that "the compensation effect and the Theta-Rule are artefacts", a statement which indicates the need for an examination of the original literature.…”

Section: Introductionmentioning

confidence: 96%

See 2 more Smart Citations

Thermal deactivation of heterogeneous catalyst, part 1. The theta‐rule ‐ a critical review

Kral

1988

Chem Eng & Technol

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Thermal deactivation can be described either by deactivation kinetics or by the isokinetic effect. The latter expression is used synonymously with the "compensation effect" and the "ThetaRule". An examination of the original literature shows that only the compensation effect is applicable to thermal deactivation but not the Theta-Rule. The introduction of the preparation temperature as a parameter of the compensation effect results in a "modified Theta-Rule", which describes the experimental data and is proposed for the non-separable kinetics. The consequence of the observed deviations from the validity range of the Theta-Rule is that the activation energy cannot be used as a universal activity criterion.

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Thermally stimulated current studies on molecular relaxation and blow moulding of poly(ethylene terephthalate)

Satoto¹,

Morikawa²,

Hashimoto³

1999

Polym. Int.

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The thermally stimulated current (TSC) technique has been used to investigate molecular relaxation in poly(ethylene terephthalate) (PET) films unstretched and biaxially stretched at 90 and 95 °C. Unstretched PET films show two peaks at 77 and 90 °C corresponding to α and ρ relaxation processes, respectively. The α relaxation is associated with the main glass transition of the material. The ρ peak with lower intensity is attributable to permanent dipoles. Both biaxially stretched samples show one TSC peak at 95 °C, supposed to correspond to ρ relaxation. The disappearance of the α peak, accompanied by the displacement of the ρ peak to higher temperature, is the result of the higher thermal stability of the permanent dipoles, which is strongly influenced by the stiffening of amorphous parts and the crystallization by stretching. In both stretched samples, the continuous distribution of pre‐exponential factors over activation energies observed might correspond to a single relaxation mode. The kinematics of stretching PET has been discussed in terms of activation energy and temperature dependence of relaxation time. © 1999 Society of Chemical Industry

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On the apparent compensation effect

Cited by 44 publications

References 4 publications

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

Thermal deactivation of heterogeneous catalyst, part 1. The theta‐rule ‐ a critical review

Thermally stimulated current studies on molecular relaxation and blow moulding of poly(ethylene terephthalate)

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