The kinetics of the liquid-phase hydrogenation of naphthalene and tetralin (1,2,3,4-tetrahydronaphthalene) in decane was studied on a commercial nickel catalyst at 80−160 °C and 20−40 bar in a CSTR. The proposed kinetic model assumes three adsorption modes (π-, π/σ-, and σ-adsorption), of which two are associative and one is dissociative. The associatively adsorbed aromatic compounds are assumed to be active in hydrogenation, whereas the dissociative adsorption leads to coke formation. Moreover, it is proposed that naphthalene adsorption occurs on a single active site, whereas tetralin adsorption requires an ensemble of Ni atoms. This explains the nonlinear decrease in the tetralin hydrogenation rate with catalyst deactivation, whereas the naphthalene hydrogenation decreases linearly. The proposed reaction and deactivation mechanism is able to describe the main features of the observed kinetics, including the formation of octalins (octahydronaphthalene), changes in the cis-to-trans selectivity of decalin (decahydronaphthalene), and the difference between the naphthalene and tetralin hydrogenation and deactivation rates.

The isomerization reaction of 2,4,4-trimethyl-1-pentene to 2,4,4-trimethyl-2-pentene was studied. In contrast to the general rule for alkene stability, an excess of the R-alkene (2,4,4-trimethyl-1-pentene) was observed in the thermodynamic equilibrium. The result is explained in terms of the molecular structure: the large and bulky substituents in 2,4,4-trimethyl-2-pentene cause steric tension and make the molecule less stable. A reaction enthalpy of 3.51 ( 0.03 kJ mol -1 , i.e., endothermic reaction, and a reaction entropy of -0.47 ( 0.10 J mol -1 K -1 were determined from the experimental data of the isomerization reaction.

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The hydrogenation reactivity of some aromatic compounds used to model diesel fractions was examined under sulfur-free conditions. Reactions of toluene, 1,2,3,4-tetrahydronaphthalene (tetralin), and naphthalene, separately and as mixtures, were studied using a commercial Ni/ Al 2 O 3 catalyst. The reactivity decreased in the following order: naphthalene . tetralin > toluene. Because of competitive adsorption and subsequent inhibition, naphthalene severely reduced the other hydrogenation rates in mixtures, whereas the hydrogenation rate of naphthalene was little affected by the concentration of toluene or tetralin. A kinetic model based on the general form of the Langmuir-Hinshelwood equation was developed. The activation energies of toluene, tetralin, and naphthalene were found to be 52.9, 40.4, and 58.7 kJ/mol, respectively, and the reaction orders of the monoaromatic and diaromatic compounds were about 1.4 and 2.1, respectively. Furthermore, simulations showed that the reaction kinetics in mixtures can be successfully described with models based on single-compound experiments, if surface-concentration terms (K i c i ) for all aromatics are included in the rate equations.

Isooctenes (2,4,4-trimethyl-1-pentene, TMP-1, and 2,4,4-trimethyl-2-pentene, TMP-2) were hydrogenated to isooctane (2,2,4-trimethylpentane) using a commercial Pt/Al 2 O 3 catalyst in a three-phase laboratory-scale reactor. The terminal double bond in TMP-1 was hydrogenated substantially faster than the internal double bond in TMP-2, and double bond isomerization was found to be of no importance. Furthermore, strong catalyst deactivation through the formation of carbonaceous deposits was observed under the applied reaction conditions. Kinetic models, which were formulated on the basis of the Horiuti-Polanyi mechanism, described the experimental data accurately and with physically reasonable parameter values (E a 49 kJ/mol for TMP-1 and 65 kJ/mol for TMP-2). Catalyst deactivation was successfully described with the first-order equation, in which the deactivation constant was dependent on the alkene-to-hydrogen ratio. Features in which the studied Pt catalyst deviates from Ni and Co include higher activation energies, stronger hydrogen adsorption, and more severe catalyst deactivation.

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