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A set of graphitic carbon nitride samples was prepared using a straightforward experimental procedure without templates and any subsequent treatments. The materials were studied in‐depth using a range of physical and chemical methods such as X‐ray diffraction, FTIR spectroscopy, elemental analysis (CHN), nitrogen physisorption, SEM, XPS, TPD CO2. The resulting g‐C3N4 was shown to be highly efficient in carboxymethylation of cinnamyl alcohol with dimethyl carbonate yielding up to ca. 82 % of the desired cinnamyl methyl carbonate. In the studied conditions, an increase in the surface N atomic content leads to an increase in selectivity towards the desired carbonate, while a higher surface O content was beneficial for side products. Metal‐free graphitic carbon nitride was shown to be one of the most productive (ca. 2 mol/h kgcat) in the investigated reaction among studied heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

The selective oxidation of glucose to gluconic acid with hydrogen peroxide was studied using different heterogeneous catalysts with alumina (Al2O3) and titanium silicate (TS‐1, TiMWW) as supports and different noble (Au, Pd) and non‐noble metals (Fe, W) as the catalytically active phases. Supported tungsten oxide catalysts showed a moderate selectivity and activity compared to palladium and iron catalysts. The best performance in the selective oxidation of glucose among the studied catalysts was displayed by gold on alumina. For this kind of catalyst, the structure sensitivity in glucose oxidation was explored, revealing a maximum rate shifted to larger gold particle sizes at higher temperatures in comparison with other studies involving activation of molecular oxygen on gold particles. A significant change in the apparent activation energy was established while changing the particle size of gold. These changes of the activation energy were adequately explained by a theoretical model for the cluster size dependence of the apparent activation energy. [ABSTRACT FROM AUTHOR]

Despite a large number of studies focusing on single‐ site (surface organometallic, single‐atom and single‐atom alloy) catalysts much less attention is devoted to kinetic analysis of such reactions. This mini‐review addresses some kinetic features of single‐site catalysis including both qualitative and quantitative aspects. [ABSTRACT FROM AUTHOR]

Several bimetallic Ni Co catalysts supported on θ-Al2O3 together with 10 wt% Ni and 10 wt% Co on θ-Al2O3 were prepared via the incipient wetness method, characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy, temperature programmed reduction, temperature programmed CO2 desorption, Fourier Transformed Infrared Spectroscopy (FTIR) with pyridine adsorption-desorption and tested in dry methane reforming at 700°C in a fixed bed reactor. According to XRD the metal oxide crystallite sizes decreased from 20 nm for 10 wt% Co/θ-Al2O3 to 13 nm for 5 wt% Ni-5 wt% Co/θ-Al2O3, which also showed formation of a mixed oxide alloy. The unit cell parameters for spinel in the fresh catalyst and fcc metal formed during the reaction followed the Vegard’s rule. Although monometallic 10 wt% Co/ θ-Al2O3 exhibited high hydrogen consumption, desorption temperature was also high resulting in a rather low activity of 10 wt% Co/θ-Al2O3 in comparison to bimetallic 5 wt% Ni5 wt% Co/θ-Al2O3. The latter exhibited the highest initial activity for hydrogen formation due to its relatively small metal particle size. This catalyst suffered, however, from extensive coking. The most stable catalyst was 10 wt% Ni/θ-Al2O3 for which the hydrogen yield decreased form 56% to 45% during 100 h time-on-stream. For this s catalyst no sintering occurred, opposite to 10 wt% Co/θ-Al2O3. [ABSTRACT FROM AUTHOR]

Recent developments in sugar transformations to methyl lactate and lactic acid are critically summarized. The highest yield of methyl lactate from glucose obtained over Sn(salen)/octylmethyl imidazolium bromide catalyst was 68 % at 160 °C whereas the highest yield of lactic acid of 58 % was achieved over hierarchical Lewis acidic Sn‐Beta catalysts at 200 °C under inert atmosphere. In addition to the desired products also humins are formed in water whereas in methanol alkyl glucosides‐ and ‐fructosides as well as acetals were generated, especially in the presence of Brønsted‐acidic sites. The main challenges limiting the industrial feasibility of these reactions are incomplete liquid phase mass balance closure, complicated product analysis and a lack of kinetic data. In addition to reporting optimized reaction conditions and catalyst properties also catalyst reuse and regeneration as well as kinetic modelling and continuous operation are summarized. [ABSTRACT FROM AUTHOR]

BACKGROUND Inulin is a valuable source of high purity fructose. The conversion of inulin to fructose utilizing an advanced sulfonic ion‐exchange resin was previously investigated in detail in a batch reactor study, where a detailed mechanistic model for the reaction kinetics was demonstrated (J Chem Technol Biotechnol 2018;93:224–232). The same catalyst was employed in tailor‐made continuous fixed‐bed reactors in the current work in order to study the feasibility of continuous operation. RESULTS: Two types of reactors were utilized: a single‐bed reactor and a multibed reactor with sample withdrawal between catalyst beds. The results from the single‐bed reactor allowed optimal reaction conditions to be determined which were extrapolated and used for experiments in the multiple‐bed reactor. High yields of fructose (75%) were obtained with the multiple‐bed reactor without any degradation products. Detailed flow characterization was performed on the reactor system and residence time distribution results were merged with the detailed model for the chemical kinetics obtained from batch reactor studies taking into account mass transfer limitations, in order to obtain a rigorous model for the performance of the continuous reactor. The fit of the mathematical model to the experimental data was very good and this provides a useful tool for further development and scale‐up purposes. CONCLUSIONS: The results of the two related studies highlight the potential of new reactor design strategies towards the realization of more efficient, sustainable and green processes, which can easily be scaled‐up and implemented in bio‐based industry. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Inulin can be extracted from the non-edible chicory root and high purity fructose can be obtained from hydrolysis of inulin and used as a valuable platform molecule for further valorization. Heterogeneous catalysts are sought as alternatives to mineral acids because of costly separation and severe corrosion problems. In this work, hydrolysis of inulin was performed in a batch reactor with an advanced sulfonic resin (Smopex-101) employing HCl as a reference catalyst, at 75-95 °C and pH ranging from 1 to 2. RESULTS The reaction was shown to proceed predominantly via an end-biting mechanism. The activity of the heterogeneous catalyst was on par with the reference catalyst, with the special advantage that Smopex-101 was more selective towards monomer formation at milder reaction conditions. Mathematical modelling of the kinetics was successfully performed with a recently developed model incorporating a reaction mechanism based on an autocatalytic effect. CONCLUSIONS The current work demonstrates that high purity fructose can be obtained by hydrolysis of inulin employing a heterogeneous catalyst at ambient pressure. The results can be utilized directly for optimization and design purposes and they open up novel possibilities in production and process design, i.e. batch or possibly continuous operation without the need for costly separation and corrosion problems commonly encountered with homogeneous catalysts. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Heterogeneously catalyzed one-pot reactions combining individual reaction steps into sequences enhance the efficiencies of overall chemical processes by reducing costs, time, and labor efforts. This minireview focuses on the production of chiral compounds by using dynamic kinetic resolution (DKR) and related sequential reactions, utilizing heterogeneous and immobilized metal catalysts and enzymes. Enzymes, especially lipases, often possess high chemical, stereo-, and regiospecificities under mild reaction conditions. Supported transition-metal catalysts are effective and widely used for various chemical transformations including racemization and hydrogenation reactions. This minireview discusses both the early and important applications, as well as modern state-of-the-art processes, in which different catalyst combinations are utilized. Also catalyst compatibility issues, including catalyst inhibition and applicability are addressed with specific focus on the racemization catalysts applied in DKRs. Finally, some examples on the utilization of heterogeneous catalysts in flow reactors are presented. [ABSTRACT FROM AUTHOR]

Amidation of renewable feedstocks, such as fatty acids, esters, and Chlorella alga based biodiesel, was demonstrated with zeolites and mesoporous materials as catalysts and ethanolamine, alaninol, and leucinol. The last two can be derived from amino acids present in alga. The main products were fatty alkanol amides and the corresponding ester amines, as confirmed by NMR and IR spectroscopy. Thermal amidation of technical-grade oleic acid and stearic acid at 180 °C with ethanolamine were non-negligible; both gave 61 % conversion. In the amidation of stearic acid with ethanolamine, the conversion over H-Beta-150 was 80 % after 3 h, whereas only 63 % conversion was achieved for oleic acid; this shows that a microporous catalyst is not suitable for this acid and exhibits a wrinkled conformation. The highest selectivity to stearoyl ethanolamide of 92 % was achieved with mildly acidic H-MCM-41 at 70 % conversion in 3 h at 180 °C. Highly acidic catalysts favored the formation of the ester amine, whereas the amide was obtained with a catalyst that exhibited an optimum acidity. The conversion levels achieved with different fatty acids in the range C12-C18 were similar; this shows that the fatty acid length does not affect the amidation rate. The amidation of methyl palmitate and biodiesel gave low conversions over an acidic catalyst, which suggested that the reaction mechanism in the amidation of esters was different. [ABSTRACT FROM AUTHOR]

Abstract: The impact of nanoparticle size effects in heterogeneous catalytic kinetics over supported metal catalysts is discussed taking into account different activities of edges and terraces. Kinetic equations for the Eley–Rideal mechanism as well as for the two-step sequence were derived, analyzed and compared with experimental data for ethene hydrogenation. Quantitative description for selectivity in a consecutive reaction of pyrrole hydrogenation/ring opening as function of the metal cluster size is provided demonstrating good correspondence between theory and experiments. [ABSTRACT FROM AUTHOR]

Abstract: A quantitative thermodynamic approach is considered with the aim to describe the size-dependent Langmuir–Hinshelwood mechanism and the two-step catalytic cycle. The general treatment takes into account surface energy excess due to an intrinsic increase in chemical potential with size decrease as well as the changes in chemical potential upon adsorption. Numerical simulations as well as qualitative analysis show that for catalytic reactions over nanoparticles not only the rates but also reaction orders can vary depending on the size of nanoclusters. Comparison with experimental data is given. [Copyright &y& Elsevier]

Abstract: This paper describes the application of LFER to understand the mechanism of the perhydrolysis of carboxylic acids over homogeneous and heterogeneous catalysts. Several experiments were carried out with different linear carboxylic acids: formic, acetic, propionic and butyric acids; using sulfuric acid and Amberlite IR-120 as catalyst and different reaction temperatures. From the experiments, the apparent rate constants decrease in the following order: k app (PFA)> k app (PAA)> k app (PPA)> k app (PBA), in both catalytic system. Furthermore, it was found that this reaction follows Taft and Charton correlations, which implies that the steric effect of the substituent governs that reaction and the mechanism is similar between the different carboxylic acids. Comparison between homogeneous and heterogeneous catalytic system was carried out based on the analysis of the kinetic expression. [Copyright &y& Elsevier]

The nonlinear behavior of modifier mixtures has been discussed for heterogeneous enantioselective catalysis. A kinetic model is developed, which is based on molecular mechanism. Numerical calculations as well as comparison with experimental data on ketopantolactone, isophorone and 4-methoxy-6-methyl-2-pyrone hydrogenation demonstrate applicability of the model to explain nonlinear phenomenon. Within the framework of the advanced model, which has several simplifications, an attempt is made to analyze striking nonlinear phenomena in terms of rate constants and adsorption enthalpies. In order to account for this behavior solely based on adsorption enthalpy (i.e., neglecting the possible difference between adsorption entropy) corresponding difference between two modifiers should be 8–17 kJ mol−1. Alternatively, the reaction rates should have two to three orders of magnitude difference over different modifiers in order to observe strong nonlinear phenomena in a system with modifier mixtures. [ABSTRACT FROM AUTHOR]

Abstract: Ethyl pyruvate (EP) was hydrogenated in the presence and absence of cinchonidine (CD) over a broad concentration range of EP (0.01–2.0 mol L−1) using a commercial 5% Pt/Al2O3 catalyst (Strem). Ligand acceleration (LA) could be observed at a higher concentration (0.3–2.0 mol L−1), whereas at lower concentration, both enantioselective and racemic reactions have very similar reaction rates. Regardless of LA, a constant () enantiomeric excess (ee) could be obtained. As CD concentration was increased, the ee increased from 0 to 80%, while the hydrogenation rate remained constant at a low EP concentration (0.01 mol L−1). Continuous fixed-bed reactor experiments revealed that LA can be linked to catalyst deactivation. In particular, EP causes catalyst deactivation, which is faster at higher reactant concentrations. CD restores catalyst activity and suppresses catalyst deactivation, resulting in higher reaction rates compared with racemic reactions carried out without CD. [Copyright &y& Elsevier]

Abstract: Complex reaction schemes in heterogeneous, homogeneous or enzymatic catalysis often contain reaction routes, which do not result in chemical transformations. Existence of these empty routes imposes thermodynamic constraints on the values of kinetic parameters, e.g. rate coefficients in the steps, which constitute the empty routes. Thermodynamic analysis is presented in connection with reaction of 7,8-dihydrofolate and NADPH to form 5,6,6,8-tetrahydrofolate and NADP, catalyzed by dihydrofolate reductase. [Copyright &y& Elsevier]

Review: 43 refs. [ABSTRACT FROM AUTHOR]

Review: 122 refs. [ABSTRACT FROM AUTHOR]

Structure sensitivity in heterogeneous catalytic oxidative dehydrogenation of lignan hydroxymatairesinol (HMR) extracted from Norway spruce knots was investigated over a series of alumina-supported gold catalysts. A mathematical model was developed based on the concept of noncompetitive adsorption of reactants. The model, being consistent with kinetic regularities, such as reaction orders in reactants, explains well the dependence of catalytic activity on the gold cluster size. [ABSTRACT FROM AUTHOR]

Abstract: Transient techniques are frequently used for catalytic gas-phase processes, but the application of transient techniques on catalytic three-phase systems is very scarce. Transient kinetic experiments provide valuable additional information about the behaviour of complex organic reaction systems, which was illustrated here with continuous enantioselective three-phase hydrogenation of ethyl benzoylformate over supported Pt catalyst particles in a fixed bed. The catalyst stability and the details of the adsorption–desorption behaviour of the reaction participants were revealed by transient experiments. Quantitative modelling of the data was based on kinetic experiments and characterisation of the reactor flow pattern by an inert tracer. Both liquid-phase species and adsorbed surface species were included in the modelling. The model predicted correctly the dynamic behaviour of the complex organic system under transient conditions. The approach is generally applicable to complex organic systems undergoing catalytic transformations. [Copyright &y& Elsevier]

Tetrahydropyrans, compounds with 6-membered oxygen-containing heterocycles, are widely used for the synthesis of biologically active compounds with analgesic, anti-inflammatory or cytotoxic activity. Synthesis of compounds with the desired structure can be realized by several methods, including the acidic catalyzed Prins cyclization of homoallylic alcohol with simple aldehydes. In the current study, synthesis of compounds with the desired tetrahydropyran framework by Prins cyclization of benzaldehyde and alcohols with different structure, namely isopulegol and 3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol, was investigated. Different parent zeolites as well as their metal modified forms and mesoporous materials were employed in the comparative investigation. Activity and selectivity of the tested catalysts were correlated with their physico-chemical properties. The highest conversion and selectivity toward the product with the tetrohydropyran structure was achieved using Ce-MCM-41 in the interactions of isopulegol and benzaldehyde. [ABSTRACT FROM AUTHOR]

Catalytic synthesis of a dioxinol compound, (2 S ,4a R ,8 R ,8a R )-4,4,7-trimethyl-2-phenyl-4a,5,8,8a-tetrahydro-4 H -benzo[d][1,3]dioxin-8-ol, exhibiting analgesic activity was demonstrated over Fe-modified beta zeolite. During interactions between cis-verbenol oxide and benzaldehyde, two main reactions occurred. In the first reaction, namely isomerization of verbenol oxide both cyclopentenic hydroxyketone, oxetane as well as a cyclohexyl compound, (1 R ,2 R ,6 S )-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol were formed. In the second parallel reaction the target compound was generated. The highest yield of the target compound was achieved in the reaction between verbenol oxide and benzaldehyde at their molar ratio of 1:133 with the bifunctional iron modified Fe-H-Beta-150 catalyst at 70 °C giving a much higher yield than reported earlier in the literature, being 46 mol-% at complete conversion of verbenol oxide. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of the lignan oxomatairesinol via oxidative dehydrogenation of the naturally occurring lignan hydroxymatairesinol was studied over gold catalysts supported on C, TiO2, SiO2, Al2O3, and MgO. In order to investigate the reaction performance over the gold catalyst, synthesis of lignan oxomatairesinol was carried out in different organic solvents/water mixtures under synthetic air and nitrogen atmosphere at 373K, and using also isolated hydroxymatairesinol isomers as a starting material. The results were compared with those obtained over palladium catalysts. Synthesized supported gold catalysts as well as the corresponding supports were characterized by TEM, XRD, ICP-OES, CO2-TPD, FTIR (using pyridine as a probe molecule), and XPS. Gold catalysts were shown to display superior performance compared with palladium ones: the activity was 4 times higher, with selectivity toward oxomatairesinol being 100%, while 60–85% were obtained over palladium catalysts. In contrast to palladium, the activity of gold catalysts is high in aerobic conditions and water–propan-2-ol mixture. However, activity and selectivity of gold catalysts were shown to be dependent on the electronic state of the metal and, similar to palladium catalysts, on the support acidity. [Copyright &y& Elsevier]

Abstract: Nine cinchona alkaloid O-ethers together with cinchonidine and cinchonine were studied as chiral modifiers in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione over Pt/Al2O3. The influence of the O-substituent on the reaction rate, selectivity and product distribution was investigated. Apparent rate constants for all hydrogenation steps were calculated using a first-order kinetic approach resulting in a good agreement between the experimentally recorded and predicted concentrations. The experimentally observed structure–selectivity effects indicate that the mechanisms of enantiodifferentiation over the catalyst modified by parent cinchona alkaloids and their ether derivatives differ from each other. Moreover, the modifier structure–selectivity dependence and the solvent effect were different for enantio- and diastereoselection in the 1-phenyl-1,2-propanedione and 1-hydroxyketone hydrogenations. Correlation between the modifier substituent bulkiness and diastereoselectivity of the 1-hydroxyketone hydrogenation was observed. Data on the inversion of enantioselectivity of 1-phenyl-1,2-propanedione hydrogenation, diastereoselectivity and the sense of kinetic resolution of the 1-hydroxyketones were presented. Due to the complexity of the reaction network, several competing mechanistic pathways may be present in a single reaction system. [Copyright &y& Elsevier]