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Chemoselective hydrogenation of citral is studied over platinum catalyst supported on titanium dioxide nanoparticles and nanowires. The support is found to have considerable effect on both selectivity and activity. Because of the presence of weak basic sites on the nanowire support, the platinum catalyst shows significantly higher activity and better selectivity towards citronellal than that obtained by the catalyst based on TiO 2 nanoparticles having mainly medium strong basic sites. Furthermore, addition of tin promoter to the platinum catalyst decreases the initial rate of reaction and increases the selectivity towards unsaturated alcohols such as nerol and geraniol. The catalytic activity studies are complemented by chemical composition, surface adsorption and structural analyses of the applied catalyst materials assessed by the means of X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, temperature programmed reduction, H 2 and CO 2 desorption, CO chemisorption, electron microscopy and X-ray diffraction, respectively. [ABSTRACT FROM AUTHOR]

The enantioselective hydrogenation of ethyl benzoylformate over (−)-cinchonidine (CD)-modified Pt/AlO catalyst in semi-batch and continuous fixed bed reactors was studied as a function of the modifier concentration and reaction temperature. The kinetic results from the semibatch reactor showed a higher enantioselectivity and lower initial rate as the amount of modifier was increased. The results from the fixed bed reactor demonstrates that continuous enantioselective hydrogenation is possible and that continuous feeding of (−)-CD is needed to maintain a high steady-state enantioselectivity. [ABSTRACT FROM AUTHOR]

A kineticmodel was developed for the enantioselective hydrogenationof ethyl benzoylformate (EBF) on a modified Pt/Al2O3catalyst. This model was based on the assumption of differentnumbers of sites for the adsorption of carbonyl groups from EBF aswell as for the modifier ((−)-cinchonidine) adsorbed in a flat(actor) and tilted (spectator) modes. Density functional theory calculationswere applied to study the energetics of EBF adsorption on Pt(1 1 1)in order to estimate the number of adsorption sites needed. The hydrogenationrate constants were determined along with the adsorption parametersby nonlinear regression analysis. A comparison between the model andthe experimental data revealed very good correspondence. [ABSTRACT FROM AUTHOR]

Solvent effects in the enantioselective hydrogenation of ethyl benzoylformate (EBF) to ( R)-ethyl mandelate over (−)-cinchonidine (CD)-modified Pt/AlO catalyst were studied in a semi-batch reactor. Solvents of different nature were used: protic (2-propanol, 1-propanol, 1-octanol and ethanol), aprotic polar (methyl acetate, acetone, ethyl acetate and tetrahydrofuran) and apolar solvents (methyl cyclohexane and toluene). The effects of pure solvents and binary solvent mixtures on hydrogenation rates and enantioselectivity were investigated. The highest enantiomeric excess ( ee) of 72 % was obtained in ethyl acetate, decreasing nonlinearly with increasing dielectric constant (ε) being close to 20 % in ethanol. The highest value of the initial hydrogenation rate was obtained in the apolar solvents (21 mmol dm ming) while the lowest one was observed in tetrahydrofuran (2 mmol dm min g). A kinetic model was proposed for the enantioselectivity dependence on dielectric constant based on Kirkwood treatment. The non-linear dependence of ee on (ε) was included in the model to describe quantitatively the variation of ee in different solvents. The results showed a good fit for ee as a function of ε. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The basic N-functionalized vapor-grown carbon nanofibers (N-VGCF) were synthesized by post-treating oxidized VGCFs in gaseous NH3 at high temperature (ammonolysis) prior to Pd addition by sol immobilization. The catalysts were characterized by nitrogen adsorption, hydrogen temperature programmed desorption, adsorption microcalorimetry and by SEM and TEM. Catalytic activity was evaluated in a model reaction, synthesis of (R)-1-phenylethyl acetate starting from hydrogenation of acetophenone to racemic 1-phenylethanol over Pd supported on N-VGCFs, at 70°C under atmospheric hydrogen pressure in toluene, followed by acylation over an immobilized lipase in the same reaction pot. The main parameters investigated in this work were the role of the basic N-VGCF supports as well as the reduction procedure of the supported Pd catalysts (Pd-N-VGCF). The results revealed that the catalytic activity of the Pd-N-VGCF catalysts was highly dependent on the reduction procedure. The highest desired product yield, 35%, was obtained over a Pd-N-VGCF catalyst when the support was treated at 400°C with gaseous ammonia prior to Pd addition. [Copyright &y& Elsevier]

Acylation of ( R,S)-1-phenylethanol, which is a product of acetophenone hydrogenation, over a Pd-supported catalyst, was studied in ethyl acetate with an immobilized lipase. It was demonstrated that in the presence of hydrogen and Pd/C in the reaction medium the ( R,S)-1-phenylethanol acylation rate is not hindered, whereas the selectivity was strongly altered in the latter case, leading to significant amounts of side products. [ABSTRACT FROM AUTHOR]

Abstract: One-pot synthesis of R-1-phenylethyl acetate was investigated starting from hydrogenation of acetophenone over a metal-supported catalyst followed by acylation of the formed R-1-phenylethanol over an immobilized lipase. The most promising catalyst for the hydrogenation step was Pd/Al2O3, which in combination with an immobilized lipase yielded maximally 22% R-1-phenylethyl acetate. The support acidity had a crucial effect on the selectivity towards the desired product. [Copyright &y& Elsevier]

Abstract: The kinetics in the one-pot synthesis of R-1-phenyl ethylacetate starting from acetophenone have been systematically investigated by using different amounts of hydrogenation catalyst and an immobilized enzyme simultaneously. The kinetic results revealed that there is interference between their catalytic performance indicating that these catalysts were not acting independently but in concert. The reaction mechanism was very complex, since besides the consecutive reactions, hydrogen-acylation, also dehydration of an intermediate product, (R,S)-1-phenylethanol occurred leading to styrene and its instantaneous hydrogenation to ethyl benzene. This work presents the kinetic regularities, quantitative understanding of which remains a challenge. [Copyright &y& Elsevier]

Abstract: One-pot synthesis of R-1-phenylethyl acetate starting from acetophenone hydrogenation was studied over supported palladium catalysts in combination with an immobilized lipase. Ethyl acetate was used as an acyl donor and the experiments were carried out under 1bar hydrogen at 70°C. In this work, the effect of support acidity was systematically investigated by using two mesoporous Pd–H–MCM-41 and Pd–Si–MCM-41 catalysts as hydrogenation catalysts. Furthermore their performance was compared with the performances of Pd–SiO2 and Pd–Al2O3. The catalysts acidity was determined by pyridine adsorption while the metal crystallite sizes were measured by XRD technique. The initial hydrogenation rates of acetophonene decreased with increasing Pd crystallite sizes. Initially both R- and S-1-phenylethanol were formed with the same rates. After prolonged reaction times activities of both hydrogenation catalyst and lipase declined. The former catalyst deactivated due to formation of acetic acid via deacylation reaction, whereas ethanol formed as a stoichiometric product in acylation decreased the lipase activity. The formation of ethylbenzene via dehydration of an intermediate alcohol, (R,S)-1-phenylethanol was enhanced by acidic catalysts. The most selective catalyst for one-pot synthesis of R-1-phenylethylacetate was a slightly acidic Pd–Al2O3 in combination with lipase. A reaction network was proposed based on the kinetic data. [Copyright &y& Elsevier]

Abstract: Kinetics for citral hydrogenation was investigated over a Ni/Al2O3 catalyst both in semibatch and in batch mode with respect to the liquid phase. In the former case the liquid phase was pumped out from the reactor continuously, while the amount of catalyst was kept constant during the hydrogenation in the latter case. The idea with liquid phase drainage was to increase the catalyst bulk density with increasing reaction time. The effect of increasing catalyst bulk density on reaction kinetics and selectivity was investigated both qualitatively and quantitatively. The main parameters were hydrogen pressure (5–21bar) and temperature (50–90°C). The product selectivity, which should theoretically be independent on the changes in catalyst bulk density, varied with varying catalyst bulk density, especially at higher reaction temperatures due to catalyst deactivation. The simplified kinetic model with lumped kinetic and deactivation parameters was applied to the experimental data being able to explain results obtained under semibatch conditions with continuous liquid phase drainage out of the reactor. [Copyright &y& Elsevier]

A parallel throughput screening system coupled with GC/MS analysis system was constructed. The system consists of six parallel tubes which can be filled with catalyst materials (particles, nets, monoliths). Different catalyst materials, particle sizes and temperatures were evaluated in catalytic three-phase hydrogenation of citral over Ni/SiO2 catalyst. The reactor system showed good reproducibility. [ABSTRACT FROM AUTHOR]

Synthesis of fine and specialty chemicals involving heterogeneous catalysts is discussed according to the type of reactions (e.g., hydrogenation, oxidation, isomerization, etc.) for various biomass derived feedstocks (carbohydrates, lignans, phenols, flavonoids, tannins, and stilbenes, tall oil, and fatty acids). [ABSTRACT FROM AUTHOR]

Abstract: Solvent effects and catalyst stability were studied in the three-phase hydrogenolysis of the natural occurring lignan hydroxymatairesinol to matairesinol. To study the solvent effects, the reaction was carried out over a Pd/C catalyst in a variety of solvents, including ethanol, 2-propanol, tert-butanol, 2-pentanol, as well as in a mixture of 2-propanol and water (50:50, v/v). Over 70% of the hydroxymatairesinol was converted in 4h when ethanol, 2-propanol, and 2-pentanol were used as solvents. The reaction was significantly retarded by mixing 2-propanol with water and the lowest activity was obtained in tert-butanol. Alcohols with shorter carbon chains were also interacting with the reactant resulting in lower selectivity; the byproducts 7-ethoxymatairesinol and 7-isopropoxymatairesinol were obtained in ethanol (the lowest selectivity) and in 2-propanol, respectively. Hydrogenolysis in 2-propanol over palladium impregnated activated carbon, and two Beta zeolites (H-Beta-300 and H-Beta-150, SiO2/Al2O3 molar ratio 300 and 150) was also investigated with respect to deactivation; consecutive experiments were performed with the catalysts being filtered, washed, dried, and re-reduced in between the runs. The catalysts were prone to deactivation caused by fouling; long chain alkanes and aromatic components were blocking the active sites. The decrease in activity was the largest for the Pd-H-Beta-300 catalyst. [Copyright &y& Elsevier]

Abstract: Citral hydrogenation was studied over a Pt/Al2O3 catalysts in cyclohexane and in 2-pentanol. Several kinetic trends, which were correlated to catalyst deactivation, were achieved. Accumulation of trans isomers in both citral and in unsaturated alcohols was visible under deactivating conditions. The further hydrogenation of citronellal was nearly totally inhibited due to catalyst deactivation, whereas nerol, geraniol and citronellol formation were enhanced at higher temperatures and pressures. The main unusual kinetic phenomena in citral hydrogenation in 2-pentanol were, first, a maximum observed in the initial hydrogenation rates as a function of temperature caused by catalyst deactivation and, second, a minimum in citral conversion after prolonged reaction times. The reason for these unusual kinetic phenomena is decarbonylation reaction occurring during hydrogenation, i.e. formation of CO, which was confirmed by temperature programmed desorption of geraniol from a reduced Pt/Al2O3 catalyst. [Copyright &y& Elsevier]

Chemoselective hydrogenation of nerol was investigated over Pt/SiO2, Pt/H-Y and Pt/H-MCM-41 catalysts. The initial total reaction rates decreased in following order: Pt/H-Y > Pt/SiO2 > Pt/H-MCM-41. Nerol hydrogenation was found to be an apparent structure sensitive reaction. The selectivities to citronellol at 30% conversion of nerol were 65%, 55% and 25% over Pt/SiO2, Pt/H-MCM-41 and Pt/H-Y, respectively. [ABSTRACT FROM AUTHOR]

The kinetics of the gas-phase hydrogenation of o-xylene over Pt/alumina catalysts was studied at 430–520 K, a hydrogen partial pressure of 0.19–0.36, and an o-xylene partial pressure of 0.04–0.10. The catalysts were characterized by H2/o-xylene TPD, H2 chemisorption, energy-dispersive X-ray analysis, and XPS. The stereoisomers, cis- and trans-1,2-dimethylcyclohexane, were the only reaction products. A reversible maximum in the o-xylene hydrogenation activity vs temperature was observed; it was explained by a decrease in the surface concentration of o-xylene at higher temperatures. The hydrogenation rate was independent of the o-xylene concentration, whereas the reaction orders with respect to hydrogen varied from 0.9 to 3 in the temperature range investigated. The stereoselectivity of the products was found to depend on temperature, reactant concentrations, and platinum precursor. The catalyst prepared from a chlorine-containing precursor exhibited a lower hydrogenation activity and selectivity toward the trans isomer. Chlorine remained on the catalyst surface, even after reduction at 673 K. Dehydrogenation and configurational isomerization of cis- to trans-1,2-dimethylcyclohexane took place at the same time as hydrogenation. Dehydrogenation and configurational isomerization reactions are enhanced by the presence of residual chlorine on the catalyst surface. The reaction pathway is proposed. [Copyright &y& Elsevier]

Selective hydrogenation of citral was investigated at 70 °C in four different alcohols over Ru, Rh and Ni supported catalysts. The main aim was to suppress the side reaction, like acetalization and cyclization of citronellal. Acetalization could be suppressed either by using chloride-free catalyst precursors and other supports than active carbon or by using longer chained alcohols, like 2-pentanol and 2-methyl-2-propanol as solvents. The highest maximum selectivity to citronellol (92%) was obtained in citral hydrogenation in ethanol over Ni/Al2O3 catalyst, which was pre-reduced ex situ at 350 °C and in situ at 350 °C for 2 h in ethanol. The acidic alumina support was covered by spillover hydrogen, suppressing the acetalization reaction. Citronellal cyclization increased with the increasing solvent hydrophobicity and was also larger over active carbon supported Ru catalyst. [Copyright &y& Elsevier]

[Display omitted] • Review on the effect of the metal particle shape in catalysis. • Discussion on preparation methods to cubic, spherical, tetrahedral or octahedral shape particles. • Nanoparticle shape influences selective hydrogenation of carbon-carbon triple and double bonds. • Depending on the shape deactivation can change selectivity. The effects of the metal particle size and shape (e.g. cubic, spherical, tetrahedral or octahedral) on catalytic activity, selectivity and stability were elucidated in selective hydrogenation of carbon-carbon triple and double bonds, and carbonyl bonds as well as in hydroisomerization, and hydrodeoxygenation. In several reactions, clear effects of the nanoparticles size and shape on catalytic behavior were demonstrated, e.g. cubic particles exhibited high turn-over frequencies in acetylene and stilbene hydrogenation. Furthermore, high index Pt(111) and Pd(111) facets were more selective towards hydrogenation of buta-1,3-diene and acetylene, respectively in comparison with other facets. Coking was observed to change selectivity, especially in acetylene hydrogenation due to formation of the Pd carbide phase. In hydrogenation of 2-methyl-3-butyn-2-ol to the corresponding alkenol, structure sensitivity was absent below 50 % conversion due to a high coverage of the reactant caused by strong adsorption of alkynol, while above 50 % conversion the reaction was structure sensitive. The highest selectivity to alkynol semihydrogenation was obtained with 18 nm cubic Pd particles exhibiting a low amount of edge surface sties. Furthermore, Pt(111) planes exhibited the highest selectivity towards cinnamylalcohol formation in hydrogenation of cinnamaldehyde, even in some cases Pt(100) particles supported on carbon exhibited the highest turnover frequency. Small octahedral Pt(111) particles were selective in hexadecane hydroisomerization. These data were also supported by different catalyst characterization results, such as in-situ XRD, temperature programmed desorption as well as theoretical DFT calculations and kinetic modelling. Structure selectivity is reaction specific and rationalization of the results is typically restricted to a specific reaction requiring further studies for various heterogeneous catalytic reactions. [ABSTRACT FROM AUTHOR]

Kinetics in the hydrodeoxygenation of stearic acid was investigated over Ni-γ-Al 2 O 3 catalyst. The main variables were catalyst prereduction mode, reaction atmosphere and hydrogen pressure in the total pressure range of 7–30 bar. The results revealed that high conversion, 99% in 360 min and high selectivity to heptadecane, 97% were achieved at 300 °C under 30 bar total pressure. The yield of an intermediate hydrogenation product, stearyl alcohol increased with increasing hydrogen pressure as expected. Higher reaction rates and conversion levels were also achieved with the prereduced catalyst and carrying out the reaction in the presence of hydrogen. As a comparison to stearic acid, hydrodeoxygenation of tall oil fatty acids, an industrial feedstock was successfully demonstrated with Ni-γ-Al 2 O 3 under the same conditions. A kinetic model including the pressure effect was derived and applied for data with Ni-γ-Al 2 O 3 as well as for Pd/C, Ni-H-Y-80 and Ni/SiO 2 catalysts. The model described well the kinetic data. [ABSTRACT FROM AUTHOR]

Heterogeneous supported metal catalysts were applied for the isomerization reaction of linoleic acid (cis-9,cis-12-octadecadienoic acid) to conjugated linoleic acid (CLA) between 80 and 120 °C in a diluted system. Ru, Ni, Pd, Pt, Rh, Ir, Os, and bimetallic Pt-Rh supported by activated carbon, Al2O3, SiO2Al2O3, MCM-22, H-MCM-41, H-Y, and H-β were screened. Catalyst characterization was done by XRD, X-ray fluorescence, XPS, H2-TPD, DCP-AES, and nitrogen adsorption techniques. The isomerization reaction was conducted batchwise in both 1-octanol and n-decane as solvents. Reactions taking place were the isomerization of linoleic acid to CLA, hydrogenation of linoleic acid and CLA to monounsaturated octadecenoic acids (oleic acid, elaidic acid, cis-vaccenic acid, and trans-vaccenic acid), as well as the further hydrogenation of monounsaturated acids to stearic acid (n-octadecanoic acid) with isomerization and hydrogenation being two competing parallel reactions. The isomerization reaction was enhanced by catalyst preactivation under hydrogen. The presence of chemisorbed hydrogen increased the conversion but reduced the isomerization selectivity. Ru and Ni showed the best isomerization properties whereas Pd favored the double bond hydrogenation reaction. [Copyright &y& Elsevier]

Highlights: [•] Hydrolytic hydrogenation of hemicellulose arabinogalactan. [•] Beta zeolites with different acidity. [•] Substantial homogeneous hydrolysis. [•] Prevention of side reactions on Ru/beta. [ABSTRACT FROM AUTHOR]

Abstract: When in a pure form, carbon nanotubes are known to be stable in air up to ∼800K making them attractive for a large variety of applications. In this work, we report a significant decrease of ignition temperature (in some cases occurring at ∼500K) and a reduction in the apparent activation energy for oxidation in air as a result of impregnation with nanoparticles (<2nm) of metal (Pt, Pd, Ni and Co) acetylacetonates or by decoration with corresponding oxides. Surprisingly, defects introduced by partial oxidation of the carbon nanotubes do not in practice have any influence on the enhancement of further oxidation. Reduction temperatures of metal oxides with H2 were close to those of other carbon supported catalyst materials. However, the carbon nanotubes showed a tendency for low temperature gasification in the presence of hydrogenation catalyst metals (Pt, Pd). [Copyright &y& Elsevier]

Abstract: The hydrolytic hydrogenation of hemicellulose arabinogalactan, into sugars, sugar alcohols and furfurals was carried out in a batch reactor using modified mesoporous MCM-48 material incorporated with ruthenium metal into the framework. The bi-functional catalytic materials, MCM-48 and Ru–MCM-48 were synthesized, characterized and investigated in the title reaction at total pressure of 20bar hydrogen, using an initial arabinogalactan concentration of 0.4wt%, at 458K. The transformation of the hemicellulose consists of arabinogalactan hydrolysis to the monosaccharides, l-arabinose and d-galactose followed by the subsequent hydrogenation to sugar alcohols, arabitol and galactitol or dehydration of the monomers to furfural and 5-hydroxymethylfurfural. The yields of the main products, i.e. sugars, sugar alcohols and furfurals were varied depending on the strength of the acid sites and the presence of metal in the structure of the ruthenium modified catalyst. Ru–MCM-48 displayed high catalytic activity and the sugar alcohols were obtained selectively from the hemicellulose. The catalytic performance of the mesoporous MCM-48 catalysts with respect to the catalyst structure, acidity and presence of the metal was evaluated. [Copyright &y& Elsevier]

Abstract: Three Pt catalysts exhibiting similar metal particles size (<2nm) were prepared on mesoporous supports differing by their chemical composition and tested in the liquid phase hydrogenation of cinnamaldehyde. The hydrogenation of the Cs favored with Pt/SBA-15 and Pt/Al-SBA-15, with significantly higher reaction rates on the latter catalyst. The acidic support changes the adsorptive properties of the platinum nanoparticles, modifying their surface electron density and possibly their morphology. In contrast, Pt/Al2O3 was the most selective catalyst of the series toward cinnamyl alcohol, with Ce:glyph name="dbnd" />O hydrogenations taking place at the same rate. The presence of Lewis acidic sites close to the particles is assumed to favor the adsorption of molecules via their polar Cven if cinnamaldehyde hydrogenation does not require acidic sites to be performed, the composition and acidity of the support significantly influence the reaction rate and selectivity. [Copyright &y& Elsevier]

The continuous enantioselective hydrogenation of 1-phenyl-1,2-propanedione was investigated in fixed-bed reactor at 25 °C and 5 bar H2 over a knitted Pt silica fibre catalyst modified with (−)-cinchonidine. Transient data were quantitatively modelled based on the reaction mechanism which assumes two parallel and tilted adsorption modes for the modifier and two distinct adsorption modes for 1- and 2-carbonyls, each of them requiring different number of surface sites. A dynamic axial dispersion model described the tube reactor with the Peclet number estimated from the separate impulse experiments carried out with an inert tracer. The modelling revealed that inclusion of sorption dynamics of components is of critical importance for the adequate description of transient data. [Copyright &y& Elsevier]

The isomerization reaction of linoleic acid (cis-9,cis-12-octadecadienoic acid) to conjugated linoleic acids (CLA) was studied. A new heterogeneously catalytic pathway was developed for synthesis of CLA at mild reaction conditions (80–120°C) over Ru/C and Ni/H–MCM-41 catalysts in a diluted system. The isomerization reaction was tested in 1-octanol and n-decane. Solvents with low polarity were selected to afford good reactant adsorption on the catalyst surface and a high solvent-to-reactant ratio was used to prevent potential side reactions. Catalyst characterization was done by X-ray powder diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, hydrogen temperature-programmed desorption, direct current plasma atomic emission spectrometry, and BET techniques. The reactions taking place were isomerization of linoleic acid C18:2, hydrogenation of C18:2 acids to C18:1 monounsaturated octadecenoic acids (oleic acid, elaidic acid, cis-vaccenic acid and trans-vaccenic acid), and further hydrogenation of C18:1 acids to C18:0 stearic acid (n-octadecanoic acid) where isomerization and hydrogenation were two competing parallel reactions. The isomerization reaction was enhanced by preactivation of the catalysts under hydrogen, but such a treatment also increased the side reaction double-bond hydrogenation. [Copyright &y& Elsevier]

This work concerned the pathway from intrinsic kinetics to diffusion-affected kinetics in catalytic hydrogenation. Kinetics and mass transfer effects in the liquid-phase hydrogenation process of an aldol (2,2-dimethylol-1-butanal) to the corresponding triol (trimethylolpropane) were studied in a semibatchwise operating autoclave, where finely dispersed and large catalyst particles were used. The intrinsic hydrogenation kinetics was determined with the crushed catalyst particles at 40–80 bar H2 and 50–90°C in isobaric experiments. A kinetic model based on competitive adsorption and surface reaction between the aldol and hydrogen was successfully fitted to the experimental data. Physical measurements of the density, viscosity as well as hydrogen solubility in the reaction mixture were carried out. The measurements revealed that the governing factor in the physical data is the temperature dependence, while the composition dependence during the hydrogenation is a minor factor under the actual experimental conditions. The models for intrinsic kinetics, physical properties and mass transfer effects were combined to describe the behaviour of large catalyst particles. It turned out that the theoretically developed model agreed well with experimental observations made with large-size catalyst particles. The approach is suitable for the scale-up of catalytic hydrogenation processes. [Copyright &y& Elsevier]