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Selectivity enhancement by catalyst deactivation in the liquid phase has been investigated in this work with batchwise nerol hydrogenation over Rh/Al2O3 catalyst in 2-pentanol as a model system. The desired product is an unsaturated alcohol citronellol. Besides hydrogenation, isomerization of nerol to citronellal as well as hydrodeoxygenation reactions also took place. Other possible products were the undesired product of complete hydrogenation, 3,7-dimethyloctanol, and cis-3,7-dimethyl-2-octenol. The selectivity enhancement of citronellol as a function of nerol conversion was observed at higher reaction temperatures, with higher initial nerol concentrations and under lower hydrogen pressures. Under these conditions the final conversions even after prolonged reaction times were lower than 100% due to catalyst deactivation. Additionally, nearly 3-fold selectivity enhancement to citronellol compared to that of the fresh catalyst was achieved in the second reuse of the same catalyst. The main reason for the catalyst deactivation is most probably decarbonylation of nerol.

Kinetic studies of catalytic three-phase systems are traditionally performed in autoclaves operating batchwise, and the results are described with rate equations based on the simple Langmuir−Hinshelwood concept. This is not sufficient, as complex organic molecules react on the catalyst surface, and more advanced kinetic models and experimental techniques are needed. Semicompetitive and multicentered adsorption models have been applied to kinetic data, and transient step−response experiments have been carried out for various industrially relevant three-phase systems. The theoretical basis of the advanced kinetic concept is described and successfully applied to several industrially relevant processes, such as hydrogenation of aromatic components and aldehydes on commercial catalysts and enantioselective hydrogenation on modified catalyst surfaces.

Kinetic experiments in selective isomerization of technical grade (~55%) linoleic acid to cis-9,trans-11-conjugated linoleic acid (B) and trans-10,cis-12-conjugated linoleic (E) acid isomers were performed batchwise at 165 °C over two series of supported metal catalysts, i.e., hydrogen preactivated and nonpreactivated. Activated carbon- and aluminium oxide-supported Ru, Pd, Os, Ir, and Pt−Rh catalysts with 5 wt % metal loading were screened. Catalyst characterization was done by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy−energy-dispersive X-ray analysis (SEM−EDX), temperature-programmed desorption of hydrogen (H2-TPD), direct current plasma atomic emission spectrometry (DCP-AES), and nitrogen adsorption techniques. Over such catalysts, the reaction scheme involves six steps:  (1) double bond migration of linoleic acid to conjugated linoleic acid, (2) positional and geometric isomerization of conjugated linoleic acid, (3) double bond hydrogenation of linoleic acid to monoenoic acids, (4) double bond hydrogenation of conjugated linoleic acid to monoenoic acids, (5) positional and geometric isomerization of monoenoic acids, and (6) double bond hydrogenation of monoenoic acids to stearic acid. Over Ru/C catalyst, chemisorbed hydrogen on the metal surface dramatically increased the linoleic acid isomerization rate in a diluted system as an astoichiometric component-enhancing double bond migration but decreased the isomerization rate by promoting deactivation in a solvent-free system. Over Ru/Al2O3 catalyst, on the other hand, dissociated hydrogen increased the isomerization rate for both the diluted and nondiluted systems. The effect of eliminating the solvent was an increase of the turnover frequency (TOF) at 165 °C by a factor of 12 with respect to that shown in a diluted system. At the same conversion carbon- and aluminium oxide-supported Ru catalyst showed higher selectivity toward B and E than carbon-supported Pd, Os, Ir, and Pt−Rh catalysts.

A spontaneous reaction involving a sparingly soluble solid compound 1,2,4-triazole as sodium salt and a complex substituted aliphatic halide was studied. Kinetic experiments were performed in the temperature interval 120−170 °C. A part of the study was focused on the solubility of different compounds and the impact of triazole concentration on the reaction. On the basis of the experimental data, a mathematical model was developed, and the parameters in the model were estimated by nonlinear regression. On the basis of the consistency of the data, rather accurate values for the parameters were calculated from the experimental values and compared to the estimated ones. The model can be used as a helpful tool in developing industrial applications.

A knitted silica fiber was prepared and employed as a support material for platinum catalysts. Different knitted silica-fiber supported platinum catalysts were prepared using several platinum precursors. The catalysts were characterized by N2 physisorption, H2 adsorption, NH3/H2/o-xylene temperature-programmed desorption, scanning electron microscopy−energy-dispersive X-ray analysis, and X-ray photoelectron microscopy. Catalyst activity was investigated in the gas-phase hydrogenation of o-xylene at 360−460 K with o-xylene and hydrogen partial pressures of 0.06 and 0.36−0.73 bar. High o-xylene conversions (up to 99%) to cis- and trans-1,2-dimethylcyclohexane were achieved. The specific surface area and pore volume of the support and the platinum precursor affected the catalyst performance. A catalyst prepared from platinum nitrate with a metal loading of 5 wt % exhibited the highest hydrogenation activity. A maximum in hydrogenation activity vs temperature was observed, which was caused by decreased surface o-xylene coverage with a temperature increase. Residual surface chlorine was found to affect both the catalyst activity and the product stereoselectivity. The selectivity toward the formation of trans-1,2-dimethylcyclohexane is increased at higher operation temperatures.

Although research interest on anticarcinogenic and other physiological effects of the cis-9,trans-11 and trans-10,cis-12 positional and geometric conjugated dienoic isomers of linoleic acid (cis-9,cis-12-octadecadienoic acid) on animals and humans has been growing explosively for the past decade, no strikingly efficient process for conjugated linoleic acid (CLA) synthesis has been reported. After development of a new heterogeneously catalytic pathway for isomerization of linoleic acid, several supported metal catalysts have been screened, and in present paper the conjugation reaction of linoleic acid to cis-9,trans-11- and trans-10,cis-12-CLA over 5 wt % Ru/C and 5 wt % Ru/Al2O3 catalysts in a diluted system was studied in the temperature range 76−165 °C. Catalyst characterization was done by X-ray powder diffraction, hydrogen temperature-programmed desorption (H2-TPD), and nitrogen adsorption techniques. Reactions taking place were isomerization of linoleic acid to CLA, hydrogenation of linoleic acid and CLA to monounsaturated octadecenoic acids (oleic acid, elaidic acid, and cis- and trans-vaccenic acid), and further hydrogenation of monounsaturated acids to stearic acid (n-octadecanoic acid), with conjugation and hydrogenation being two competing parallel reactions. Rate enhancement was obtained by applying a technique of catalyst preactivation under hydrogen, but increased coverage of hydrogen on the Ru surface also restrained the isomerization selectivity. At similar conditions, Ru/C showed a higher turnover frequency than Ru/Al2O3, 3.27 × 10^-4 and 1.53 × 10^-4 s^-1, respectively, and H2-TPD measurements indicated that the former had a higher hydrogen storage capacity than the latter. Ru/Al2O3, on the other hand, exhibited a higher selectivity for the cis-9,trans-11- and trans-10,cis-12-CLA isomers than Ru/C. The selectivities were very sensitive to the reactant to catalyst mass ratio, and experiments over varied particle size ranges indicated that the conjugation reactions were close to the intrinsic kinetic regime. Hydrogenation selectivity and competitive adsorption between reactant and solvent were minimized by the use of nonpolar solvents such as n-nonane and n-decane, whereas protic solvents such as 1-propanol and 1-octanol exhibited lowered selectivity toward CLA. The CLA isomer composition was studied for the use of pure linoleic acid and cis-9,trans-11-, trans-10,cis-12-, and trans-9,trans-11-CLA isomers as reactants. The surface area of Ru/C decreased slightly from 841 to 749 m²/g while repeating the isomerization reaction over the same catalyst sample five times, and the catalytic performance did not indicate any deactivation.

The hydrogenation kinetics of 2,2-dimethylol-1-butanal (TMP-aldol) and 2,2-dimethylol-1-propanal (TME-aldol) over a supported nickel catalyst were determined with experiments carried out in a batchwise operating autoclave at 50−90 °C and 40−80 bar hydrogen. Water was used as the solvent. TMP- and TME-aldol were hydrogenated with 100% selectivity to the corresponding triols. The effects of the catalyst activation procedure and the formaldehyde concentration on the hydrogenation kinetics were studied with thermogravimetry, X-ray photoelectron spectroscopy, and hydrogenation experiments. Catalyst reduction at a high temperature (400 °C) under hydrogen flow was favorable because of a more effective reduction of nickel oxides. Formaldehyde had a considerable retarding effect on the aldol hydrogenation:  the hydrogenation rate was low until all of the formaldehyde was hydrogenated to methanol. The hydrogenation rate of TME-aldol was found to be significantly lower than that of TMP-aldol at low temperatures and pressures (60 °C and 40 bar), whereas equally high rates for both aldol molecules were observed at the highest temperature and pressure studied. A kinetic model including the inhibitory effect of formaldehyde as well as real hydrogen solubility data was proposed for the aldol hydrogenation. The model is comprised of adsorption, desorption, and surface reaction steps. The rate equations based on the model were able to describe the experimentally recorded hydrogenation kinetics of TMP- and TME-aldol.

Aldols are important intermediates in the production of polyols, which are raw material for lubricants, surface coatings, and synthetic resins. The activities and selectivities of gel-type and macroporous anion-exchange resin catalysts in the aldolization of butyraldehyde with formaldehyde in an aqueous environment were investigated at 60 °C. The experiments were carried out batchwise in a stirred glass reactor, and the reaction products were analyzed with high performance liquid chromatography. Two main products were observed, 2-ethyl-3-hydroxy-2-hydroxy-methylpropanal (trimethylolpropane aldol) and 2-ethylpropenal (ethylacrolein). The product ratio was strongly dependent on the catalyst. The selectivity with respect to trimethylolpropane aldol varied within the range 2.7−7.3 for the catalysts investigated. Systematic kinetic experiments were carried out at 50−70 °C with the gel-type resin catalyst displaying the highest aldol selectivity. A kinetic model based on molecular mechanisms was able to describe the product distribution.

The hydrogenation kinetics of 2,2-dimethylol-1-butanal (TMP-aldol) over a supported nickel catalyst was determined with experiments carried out in a batchwise operating autoclave at 50−90 °C and 40−80 bar hydrogen. The reaction mixture was analyzed with gas and liquid chromatography. It was found that TMP-aldol can be hydrogenated with a 100% selectivity to the corresponding triol, trimethylolpropane. The effects of the catalyst activation procedure and the formaldehyde concentration on the hydrogenation kinetics were studied. The hydrogenation experiments revealed that catalyst reduction at a high temperature (400 °C) under hydrogen flow was favorable for the catalyst performance. The reason was a more effective reduction of nickel oxides which was confirmed with thermogravimetry and X-ray photoelectron spectroscopy. The presence of formaldehyde had a considerable retarding effect on the aldol hydrogenation kinetics:  the hydrogenation rate was low until all of the formaldehyde was hydrogenated to methanol. The retarding effect was more prominent at higher temperatures than at lower temperatures, which indicates that formaldehyde forms oligomers on the catalyst surface as the temperature increases. A kinetic model was proposed for the aldol hydrogenation. The model includes adsorption, desorption, and surface reaction steps as well as the inhibitory effect of formaldehyde on the aldol hydrogenation kinetics. The model was able to describe the experimentally recorded hydrogenation kinetics of TMP-aldol in the presence and in the absence of formaldehyde.

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