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Recent developments in transformations of biobased 5‐hydroxymethylfurfural to 2,5‐dimethylfuran, a potential liquid fuel, are critically summarized. The highest yield of 2,5‐dimethylfuran (more than 98 %) from 5‐hydroxymethylfurfural are obtained over bimetallic Cu−Co supported on carbon at 180 °C under 5 bar hydrogen in 2‐propanol and over Ni supported on mesoporous carbon at 200 °C under 30 bar hydrogen in water in a batch reactor. The desired catalyst should have relatively high metal dispersion and some acidity to facilitate both hydrogenation and hydrogenolysis. However, overhydrogenation and overhydrogenolysis forming 2,5‐dimethyltetrahydrofuran and methylfuran, respectively, should be suppressed. Furthermore, a hydrophobic support is more selective than oxide‐based support. After a careful adjustment of the residence time in a continuous reactor it is also possible to produce high yields of 2,5‐dimethylfuran even over Pt/C. The main challenges limiting the industrial feasibility of these reactions are relatively low initial reactant concentration, catalyst deactivation by sintering, leaching and coking. In addition to selection of optimum reaction conditions and catalyst properties, kinetic modelling was also summarized. [ABSTRACT FROM AUTHOR]

A range of heterogeneous ‐SO3H functionalized catalysts including carbon and halloysite nanotubes, commercial K10 clay, Amberlyst‐15 etc. was investigated for the first time using as a model the Prins‐Ritter reaction of (−)‐isopulegol with benzaldehyde and acetonitrile producing 4‐amido derivatives of octahydro‐2H‐chromenes (as (S)‐ and (R)‐diastereomers). A strong effect of water addition prior the reaction on the overall selectivity and the ratio of isomers in the case of heterogeneous and homogeneous (p‐toluenesulfonic acid) catalysis was found for the first time. The yield of the (R)‐diastereomer sharply increased with increasing amount of added water, while the S‐isomer prevailed with a minimum amount of added water. Experimental results and DFT calculations clearly indicate a kinetic control for R‐amide formation. Typically synthesis of 4‐amidooctahydro‐2H‐chromenes requires subzero temperatures and toxic catalysts, which were avoided in the current work. Nevertheless, the yield of the desired products (up to 83 %) at 30 °C after water addition exceeded the values reported previously. Thus, adding water is a simple and a very effective method for controlling both the yield and stereoselectivity of the Prins‐Ritter reaction products under mild conditions. [ABSTRACT FROM AUTHOR]

Kinetics and thermodynamics of α-pinene oxide isomerization was investigated both theoretically and experimentally in different solvents in the temperature range of 50-140 °C using different zeolites, iron modified zeolites, Fe-H-MCM-41 and micro-mesoporous ZSM-5 derived catalysts. The aim was to elucidate the effect of solvent basicity and polarity on the product distribution in this reaction giving as the main value-added products campholenic aldehyde and trans-carveol, which are used as fragrances and perfumes. A generic kinetic first order model was developed composed of both parallel and consecutive routes. A thermodynamic analysis showed that product selectivity is determined by kinetic control and not by thermodynamics. Formation of campholenic aldehyde was favored in non-polar solvents, whereas basic solvents promoted formation of trans-carveol independent on temperature.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Activity of heterogeneous catalysts for synthesis of Guerbet alcohols from hexanol was evaluated. Commercial synthetic hydrotalcite (HT) was used in the aldol condensation reaction, which is a part of the Guerbet reaction network. HTs were calcined at different temperatures in order to modify their basicity and additionally, NaOH was applied in some experiments as a homogeneous base. The homogeneous base proved to be more efficient in aldol condensation experiments, while HT also performed in an acceptable way. Bi-functional metal containing HTs were synthesized by wet impregnation and co-precipitation methods employing different active metals. The materials were characterized with a number of methods, including CO2-TPD, pyridine-FTIR, nitrogen physisorption, transmission electron microscopy, SEM-EDX and XRD. Copper containing catalysts produced hexyl-hexanoate with a very high selectivity, while Ni-containing counterparts exhibited the highest selectivity towards the Guerbet alcohol. The co-precipitated catalysts were more active in the current study than the ones produced by wet-impregnation. Nevertheless, synthesis of Guerbet alcohols from hexanol with a one-pot method proved to be challenging, with the best yield of the Guerbet product in 24 h being 5%. This is proposed to be largely due to thermodynamic limitations, which was confirmed by calculations of thermodynamics. [ABSTRACT FROM AUTHOR]

The ethyl ester of levulinic acid, ethyl levulinate is a completely bio-based chemical made from levulinic acid, which is a hydrolysis product of cellulose and bio-ethanol. The very precise kinetics of levulinic acid esterification with ethanol was studied in an isothermal batch reactor in the presence of homogeneous (H2SO4) and heterogeneous catalysts (cation exchange resin Smopex-101). The temperature interval of the experiments was 50-70 °C. A kinetic model was proposed for both kinds of catalysts, adopting equilibrium rate expressions in any case. The different role of the catalyst used was considered separately, while a unique equilibrium constant was assumed for each system. The kinetic parameters were successfully determined by non-linear regression analysis. The model gave a very good description to the experimental data. The heterogeneous catalyst was used to demonstrate the feasibility of continuous operation in isothermal fixed bed reactors. The catalyst showed a good stability and high conversions of levulinic acid were obtained in the laboratory-scale fixed bed reactor. The model was able to predict both dynamic and steady-state experimental data. [ABSTRACT FROM AUTHOR]

The purpose of this work was to investigate biomass-derived ethanol dehydrogenation into acetaldehyde using several mono- and multicomponent (CuO, ZnO and Cr 2 O 3 )-containing catalysts supported on industrial size Al 2 O 3 beads. The catalysts, prepared with either solution combustion or incipient wetness method, were characterized by using various physico-chemical methods, such as EDXA, SEM-EDXA, TEM, XRD, XPS, pyridine adsorption desorption FTIR, and ζ-potential measurements. The results revealed that the multicomponent catalysts exhibited superior activity compared to the metal oxide catalysts containing only one metal oxide. In addition, the most selective catalyst towards acetaldehyde formation, with 50% selectivity at 55% conversion of ethanol at 300 °C and WHSV 1 h −1 was CuO Cr 2 O 3 /Al 2 O 3 prepared by using the solution combustion method, indicating that this inexpensive and rapid catalyst preparation method is promising for other applications. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of multi-component cobalt based catalysts with different metal precursors and thermal treatment was performed. A special emphasis was put on promotion with ceria. Catalysts, which were synthesized from thermally pre-activated CoCO3·mCo(OH)2·nH2O as a precursor and thereafter underwent reduction in flowing hydrogen, have a clear tendency for decomposition of mixed aluminum–cobalt containing complexes, inevitably formed during thermal treatment. The catalysts were tested in steam reforming of hydrocarbons. The size of metal particles in reduced catalysts was determined by TEM and related to catalytic activity.Graphical Abstract: [ABSTRACT FROM AUTHOR]