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The distortionless enhancement by polarisation transfer (DEPT) nuclear magnetic resonance (NMR) technique, combined with magnetic resonance imaging (MRI), has been used to provide the first in situ spatially-resolved and quantitative measurement of chemical conversion and selectivity within a fixed-bed reactor using natural abundance 13C NMR. The Royal Society of Chemistry 2005.

Core@shell Fe@FexOy nanoparticles (NPs) have attracted a great deal of interest as potential magnetic supports for catalytic metals via galvanic exchange reactions. In this study Fe@FexOy/Pd bimetallic NPs were synthesized through galvanic exchange reactions using 50:1, 20:1 and 5:1 molar ratios of Fe@FexOy NPs to Pd(NO3)2. The resulting Fe@FexOy/Pd NPs have Pd NPs on the Fe oxide surfaces, and still retain their response to external magnetic fields. The materials could be recovered after the reaction by an external magnetic field, and agitation of the solution via a magnetic field led to improvements of mass transfer of the substrates to the catalyst surface for hydrogenation reactions. The Fe@FexOy/Pd NPs derived from the 5:1 molar ratio of their respective salts (Fe:Pd) exhibited a higher catalytic activity than particles synthesized from 20:1 and 50:1 molar ratios for the hydrogenation of 2-methyl-3-buten-2-ol. The highest turnover frequency reached 3600?h?1 using ethanol as a solvent. In situ XANES spectra show that the Fe@FexOy NPs in the Fe@FexOy/Pd system are easily oxidized when dispersed in water, while they are very stable if ethanol is used as a solvent. This oxidative stability has important implications for the sustainable use of such particles in real world applications.

The activity and selectivity of structure-sensitive reactions are strongly correlated with the shape and size of the nanocrystals present in a catalyst. This correlation can be exploited for rational catalyst design, especially if each type of surface atom displays a different behavior, to attain the highest activity and selectivity. In this work, uniform Pd nanocrystals with cubic (in two different sizes), octahedral, and cuboctahedral shapes were synthesized through a solution-phase method with poly(vinyl pyrrolidone) (PVP) serving as a stabilizer and then tested in the hydrogenation of 2-methyl-3-butyn-2-ol (MBY). The observed activity and selectivity suggested that two types of active sites were involved in the catalysis-those on the planes and at edges-which differ in their coordination numbers. Specifically, semihydrogenation of MBY to 2-methyl-3-buten-2-ol (MBE) occurred preferentially at the plane sites regardless of their crystallographic orientation, Pd(111) and/or Pd(100), whereas overhydrogenation occurred mainly at the edge sites. The experimental data can be fit with a kinetic modeling based on a two-site Langmuir-Hinshelwood mechanism. By considering surface statistics for nanocrystals with different shapes and sizes, the optimal catalyst in terms of productivity of the target product MBE was predicted to be cubes of roughly 3-5 nm in edge length. This study is an attempt to close the material and pressure gaps between model single-crystal surfaces tested under ultra-high-vacuum conditions and real catalytic systems, providing a powerful tool for rational catalyst design.

Abstract: The hypotheses about reasons for the inverse dependence of the turnover frequency of hydrogenation of unsaturated compounds (alkyne, alkynol, olefin) on the catalyst concentration were discriminated by kinetic methods combined with electron microscopy. The reasons are: dissociation of polycrystalline Pd–P particles, equilibrium shift (stabilized cluster–cluster + stabilizer), and aggregation–disaggregation of Pd–P particles, the latter being the main reason for the concentration range 0.125–1 mmol/L. The effect of aggregation–disaggregation of Pd–P particles on the catalyst activity differs depending on the substrate. The proposed kinetic model was shown to be consistent with the experimental data for styrene hydrogenation used as an example. The rate constants of some stages were determined.

Processes for converting an olefin reactant into a diol compound are disclosed, and these processes include the steps of contacting the olefin reactant and a supported chromium catalyst comprising chromium in a hexavalent oxidation state to reduce at least a portion of the supported chromium catalyst to form a reduced chromium catalyst, and hydrolyzing the reduced chromium catalyst to form a reaction product comprising the diol compound. While being contacted, the olefin reactant and the supported chromium catalyst can be irradiated with a light beam at a wavelength in the UV-visible spectrum. Optionally, these processes can further comprise a step of calcining at least a portion of the reduced chromium catalyst to regenerate the supported chromium catalyst.

The main challenge in the hydrogenation of alkynes into (E)- or (Z)-alkenes is to control the selective formation of the alkene, avoiding the over-reduction to the corresponding alkane. In addition, the preparation of recoverable and reusable catalysts is of high interest. In this work, we report novel nickel nanoparticles (Ni NPs) stabilized by three different imidazolium-amidinate ligands (ICy·(Ar)NCN; L1: Ar = p-tol, L2: Ar = p-anisyl and L3: Ar = p-ClC6H4). The as-prepared Ni NPs were fully characterized by (HR)-TEM, XRD, WASX, XPS and VSM. The nanocatalysts are active in the hydrogenation of various substrates. They present a remarkable selectivity in the hydrogenation of alkynes towards (Z)-alkenes, particularly in the hydrogenation of 3-hexyne into (Z)-3-hexene under mild reaction conditions (room temperature, 3% mol Ni and 1 bar H2). The catalytic behaviour of Ni NPs was influenced by the electron donor/acceptor groups (-Me, -OMe, -Cl) in the N-aryl substituents of the amidinate moiety of the ligands. Due to the magnetic character of the Ni NPs, recycling experiments were successfully performed after decantation in the presence of an external magnet, which allowed us to recover and reuse these catalysts at least 3 times preserving both activity and chemoselectivity.

Abstract: The effect of the composition of the catalytic system and reaction conditions on the properties of phosphorus-modified palladium catalysts in hydrogenations of alkynols was studied. Modification with phosphorus increased the activity and turnover number of palladium catalysts in the hydrogenation of the model compound 2-methyl-3-butyn-2-ol (MBY) without any reduction in the selectivity to 2-methyl-3-butene-2-ol at 95–98percent MBY conversion. The promoting effect of phosphorus on the properties of the palladium catalyst is caused not only by an increase in the particle size, but also, probably, by a change in the energy of interaction of reagents with the active sites. Hypotheses on the nature of the carriers of catalytic activity in Pd–P particles were discriminated using kinetic methods with the differential selectivity of catalytic systems as the main measured parameter under the conditions of competition between two alkynols. The hydrogenation of acetylenic alcohols involves only one of the two potentially active forms in Pd–P nanoparticles—Pd(0) clusters, whereas the hydrogenation of the resulting allyl alcohols involves both Pd(0) clusters and palladium phosphides.

To achieve high catalytic activities and long-term stability to produce higher alcohols via CO hydrogenation, the catalytic activities were tuned by controlling the loading amounts of γ-alumina nanorods and Al3+ ions added to modify Cu-Zn catalysts promoted with Li. The selectivity of higher alcohols and the CO conversion to higher alcohols over a Li-modified Cu0.45Zn0.45Al0.1 catalyst supported on 10% nanorods were 1.8 and 2.7 times higher than those with a Cu-Zn catalyst without nanorods and Al3+ ions, respectively. The introduction of the thermally and chemically stable γ-Al2O3 nanorod support and of Al3+ to the modified catalysts improves the catalytic activities by decreasing the crystalline size of CuO and increasing the total basicity. Along with the nanorods, a refractory CuAl2O4 formed by the thermal reaction of CuO and Al3+ enhances the long-term stability by increasing the resistance to sintering of the catalyst.

Finely divided polymer-stabilized PdZn bimetallic nanoclusters are prepared by the polyol method. TiO2 matrix-impregnated nanoclusters coated on the inner surface of a capillary microreactor are used as catalysts for the selective hydrogenation of 2-methyl-3-butyn-2-ol. The effect of the activation conditions (duration, temperature, and gas medium composition) on the physicochemical and catalytic properties of the coatings is studied. It is shown that their catalytic activities decrease and the reaction’s selectivity increases with an increase in the reaction time and the time of hydrogen reduction at 573 K. The highest selectivity (96.5% at a conversion rate of 99%) is reached on the coatings reduced with hydrogen for 6 h. The coatings remain highly active and stable for 1 month in the continuous flow mode of the reaction. Kinetic simulation showed that a high selectivity level is ensured by a decrease in the rate constants of hydrogenation of 2-methyl-3-buten-2-ol and the ratio of the alkene/alkyne adsorption constants after reductive treatment.

Graphitic carbon nitride (g-C3N4) exhibits unique properties for the preparation of single-atom heterogeneous catalysts (SAHCs) due to the presence of sixfold nitrogen-based coordination sites in the lattice. Despite the potential to profoundly affect the metal stabilisation and resulting catalytic properties, no work has previously investigated the effect of modifying the carrier composition. Here, we study the impact of doping carbon in g-C3N4 on the interaction with palladium. This is achieved by introducing carbon-rich heterocycles (barbituric acid or 2,4,6-triaminopyrimidine) during the synthesis of bulk and mesoporous g-C3N4. Palladium is subsequently introduced via microwave-irradiation-assisted deposition, which emerges as a highly effective route for the dispersion of single atoms. Detailed characterisation confirms the controlled variation of the C/N ratio of the lattice and reveals the complex interplay with the crystal size, surface area, amount of defects, basic properties and thermal stability of the carrier. Atomic dispersions of palladium with similar surface densities could be obtained on both the stoichiometric and carbon-doped carriers in mesoporous form, but appreciable differences are observed in the ratio of Pd2+/Pd4+. The latter, which provides a measure of the degree of electron transfer from the metal to the carrier, is found to correlate with the activity in the continuous flow semi-hydrogenation of 2-methyl-3-butyn-2-ol. Density functional theory calculations support the decreased adsorption energy of palladium upon doping with carbon and reveal the potentially significant impact of oxygen-containing defects. The findings demonstrate the importance of understanding the metal-carrier interaction to optimise the catalytic efficiency of SAHCs.

In this work, we introduce a new procedure for the protection and deprotection process of various types of alcohols and phenols by HMDS in the presence of nano magnetic sulfated zirconia (Fe3O4@ZrO2/SO42?) as a solid acid catalyst under very mild and solvent-free condition. This method has interesting advantages like short reaction times and a simple workup process. With regard to some outstanding benefits of this new heterogeneous catalyst such as excellent yield, reusability of the catalyst and easy thermal stability, high acidity, strong and excellent magnetic properties, this method can be very interesting in aspect of green chemistry Principles.

The two catalysts Pd3Sn/TiO2 and Pd3Sn/ZnO were prepared via a one-pot procedure based on the “polyol method” with the addition of a capping agent (polyvinylpyrrolidone) to control the particle size distribution. The same procedure was used to prepare Pd/TiO2 and Pd/ZnO for comparison. All four catalysts showed high activity and selectivity for the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) in the liquid phase under identical conditions. However, Pd3Sn/TiO2 and Pd3Sn/ZnO show selectivities to alkene significantly higher than that of the Pd catalysts. Specifically, the selectivity increases from 96.4% to 97.4% on TiO2 support, and 96.2% to 97.6% on ZnO support, at 90% conversion. Transition electron microscopy shows nanoparticles evenly dispersed on the support, with mean particle sizes as low as 4.1 (±0.8) nm when Sn is incorporated into the catalyst. Unsupported Pd3Sn was prepared using the same method and characterised by powder X-Ray diffraction followed by the Rietveld refinement. Pd3Sn was found to be single-phase and isostructural to Pd metal with a face centred cubic unit cell.

Low power consumption and minimal potential hazards are ultimate goals for the modern development of chemical manufact? however, it often reduces the selectivity of chemical reactions by implementing a new reaction system. A nanocatalyst design is reported for achieving efficient and selective alkyne semihydrogenation through the photocatalytic hydrogen transfer from water, which avoids the use of a heat source and explosive H2. The PdPt catalytic sites that are implemented on the TiO2 photocatalyst hold the key to achieving both high activity and selectivity. As compared with pure Pd or Pt, the alloy cocatalysts can better harness H diffusion/desorption for selective semihydrogenation as well as suppress competitive H2 evolution. This work opens up new possibilities for green and selective alkyne semihydrogenation and highlights the importance of lattice engineering to catalytic selectivity.

The reaction of alkynes with hydrogen under atmospheric pressure in the presence of nickel nanoparticles as a catalyst led to the exhaustive hydrogenation of the triple bond.

A 2.5 wt.% Pd/ZnO catalytic coating has been deposited onto the inner wall of capillary reactors with a diameter of 0.53 and 1.6 mm. The coatings were characterised by XRD, SEM, TEM and elemental analysis. The performance of catalytic reactors was studied in solvent-free hydrogenation of 2-methyl-3-butyn-2-ol. No mass transfer limitations was observed in the reactor with a diameter of 0.53 mm up to a catalyst loading of 1.0 kg(Pd) m?3. The activity and selectivity of the catalysts has been studied in a batch reactor to develop a kinetic model. The kinetic model was combined with the reactor model to describe the obtained data in a wide range of reaction conditions. The model was applied to calculate the range of reaction conditions to reach a production rate of liquid product of 10–50 kg a day in a single catalytic capillary reactor.

The kinetics of 1,1-dimethylpropyl peroxy radicals recombination in polar solvents - water, methanol, and their mixtures - was studied by EPR spectroscopy in combination with the stopped-flow method, and the rate constants of this reaction were determined. Peroxyl radicals were generated by mixing solutions of Ce4+ sulfate and 1,1-dimethylpropyl hydroperoxide. The observed EPR signal of the peroxyl radical is a singlet with a g-factor of 2.015 ± 0.001, and a line width of ΔH = (1.36 ± 0.02) × 10-3 T for methanol and ΔH = (9.7 ± 0.2) × 10-4 T for water. The measured rate constants of (CH3)2C(O2 ·)CH2CH3 radical recombination at 298 K are 2k t = (3.9 ± 0.4) × 104 L mol-1 s-1 for water and 2k t = (5.2 ± 0.5) × 103 L mol-1 s-1 for methanol. A linear relationship between ln(2kt ) and the Kirkwood function (?-1)/(2? + 1), where e is the dielectric constant of the medium, has been established, indicating an important role of nonspecific solvation in the recombination of tertiary peroxyl radicals.

Pd nanoparticles were easily immobilized onto titanate nanotubes by a straightforward procedure. The material (0.50 wt % Pd) was used as catalyst in the continuous-flow, liquid-phase hydrogenation reaction of unsaturated C-C bonds and it showed excellent performance and durability under very mild conditions (room temperature, 1-2 bar H2, residence time 13-36 s). In particular, very high productivity was obtained in the synthesis of the perfumery component cis-3-hexen-1-ol (40.6 mol gPd-1 h-1) without additives or metal contamination, with clear benefits in terms of process economy and environmental impact compared with conventional catalysts. The catalyst performance is discussed in the light of comparable systems.

A continuously working capillary microreactor with a catalytic coating based on mesoporous titanium dioxide with embedded Pd nanoparticles was tested in a reaction of the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBI). The catalytic coatings were obtained by the supporting of a carrier sol, which contained colloidal Pd nanoparticles, onto the internal wall of a quartz capillary with a diameter of 250 μm in the dynamic mode. The effects of the concentration of MBI in methanol (0.05–0.2 mol/L), the partial pressure of hydrogen (0.28–1.0 atm), and the reaction temperature (308–333 K) on the catalyst activity and the selectivity of reaction were studied. High selectivity for the formation of the semi-hydrogenated product 2-methyl-3-buten-2-ol was reached at 313 K in an atmosphere of pure hydrogen. At a conversion of 99.9%, the selectivity was 92.3%, which is 15.5% higher than that in a batch reactor. The rate of hydrogenation on the Pd/TiO2 coating was higher by one order of magnitude than that on a commercial Lindlar catalyst. The coating remained stable upon the continuous passage of the flow of a reaction mixture for 500 h.

A variety of metal nanoparticle (NP)/tetraalkylphosphonium ionic liquid (IL) composite systems were evaluated as potential catalysts for the deep hydrogenation of aromatic molecules. Particles were synthesized by reducing appropriate metal salts by LiBH4 in a variety of ILs. Gold NPs were used as probes to investigate the effect of both chain lengths of the alkyl substituents on the phosphonium cation and the nature of anions, on the stability of NPs dispersed in the ILs. The presence of three medium-to-long alkyl chains (such as hexyl) along with one long alkyl chain (such as tetradecyl) in the IL, coupled with highly coordinating anions (such as halides, or to a smaller extent, bis-triflimides) produced the most stable dispersions. These ILs also showed maximum resistance to heat-induced sintering; for example, TEM studies of Pt NPs heated under hydrogen to 120 °C showed only moderate sintering in trihexyl(tetradecyl)phosphonium chloride and bis(triflimide) ILs. Finally, olefinic hydrogenations, aromatic hydrogenations, and hydrodeoxygenation of phenol were carried out with Ru, Pt, Rh and PtRh NPs using hydrogen at elevated pressures. From preliminary studies, Ru NPs dispersed in trihexyl(tetradecyl)phosphonium chloride emerged as the catalyst system of choice. The presence of borate Lewis-acid by-products in the reaction medium (from the borohydride reduction step) allowed for partial phenol hydrodeoxygenation.

The rhodium complex [Rh(cod)Cl(N-tBuBzPTA)]PF6 (2) was obtained by reacting the appropriate Rh(I) precursor with the lower-rim PTA derivative [N-tBuBzPTA]PF6 (tBuBz = 4-tert-butylbenzyl; PTA = 1,3,5-triaza-7-phosphaadamantane). The solubility and stability in water of 2 were increased in the presence of native-β-cyclodextrin (β-CD). The interaction of 2 with mono-amino β-cyclodextrin (β-CDNH2, 2 equiv.) led to a supramolecular Rh assembly (3), identified by 31P, 1H and 2D T-ROESY NMR experiments. The catalytic activity of 3 was evaluated in the water-phase hydrogenation of unsaturated and allylic alcohols and preliminary results are presented here.

Selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-butene-2-ol (MBE) over Pd supported on hypercrosslinked polystyrene was studied in polar (ethanol, isopropanol, water) and non-polar (cyclohexane, toluene, octane, hexane, heptane and m-xylene) solvents. The catalytic activity and selectivity were found to be strongly affected by solvent properties such as dipole moment and dielectric constant, but cannot be explained by solvent polarity only. Hydrogen solubility and solvent-catalyst interaction also influential factors. The catalyst activity decreases in the series: alcohols > cyclohexane > water/ethanol mixture > octane ≥ hexane ≥ xylene > toluene > heptane. The highest values of MBE selectivity of 99.6% and 98.7% at 95% MBY conversion were obtained in toluene and in ethanol, respectively.

The effects of poisoning of Pd catalysts with Bi and annealing in a polyol (ethylene glycol) were studied on the semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY). An increase in the Pd:Bi ratio from 7 to 1 in the Bi-poisoned catalysts decreased the hydrogenation activity due to blocking of active sites, but increased maximum alkene yield from 91.5% for the Pd catalyst to 94-96% for all Bi-poisoned Pd catalysts, by decreasing the adsorption energy of alkene molecules and suppressing the formation of β-hydride phase. Annealing of the catalysts induced the formation of intermetallic phases and decreased its activity due to sintering of the catalytic particles and low activity of intermetallic compounds. Langmuir-Hinshelwood kinetic modelling of the experimental data showed that poisoning of Pd with Bi changed the relative adsorption constants of organic species suggesting ligand effects at high Bi content.

In order to better respond to environmental standards, the development of metal nanoparticles using green approaches has exponentially grown for the last decade. Cyclodextrins, which are cyclic oligosaccharides composed of 6(α), 7(β) or 8(γ) glucopyranose units, have appeared to be interesting candidates for the synthesis of metal nanoparticles. Indeed, through the ability to form inclusion complexes or supramolecular adducts with organic molecules or metal precursors, cyclodextrins can be successfully employed to stabilize size-controlled zerovalent metallic nanoparticles active for hydrogenation reactions carried out in aqueous or gas-phase media. In this summary of our works, we report that cyclodextrins could be used in various forms and environments: (i) in free form, (ii) in complexed form with appropriate guests molecules, (iii) in combination with polymer matrices, (iv) in thermosensitive hydrogels and (v) immobilized onto porous carbons supports. All these studies highlight the fact that cyclodextrins can be seen as multi-task agents for nanocatalysis.

Here, a systematic study of magnetite nanoparticle (NP) formation in the presence of functional polyphenylenepyridyl dendrons and dendrimers of different generations and structures (such as focal groups, periphery and a combination of phenylene and pyridyl moieties) has been reported. For certain dendron/dendrimer concentrations and structures, well-dispersible, multi-core, flower-like crystals are formed which display ferrimagnetic-like behavior. It is noteworthy that the least complex second generation polyphenylenepyridyl dendrons with a carboxyl focal group already allow formation of flower-like crystals. Magnetically recoverable catalysts were obtained via Pd NP formation in the dendron/dendrimer shells of magnetite NP and tested in selective hydrogenation of dimethylethynylcarbinol to dimethylvinylcarbinol. Dependences of catalytic activity and selectivity on the dendron/dendrimer generation and structure, type of Pd species, and Pd NP size have been demonstrated. High selectivity and activity of these catalysts along with easy catalyst recovery and successful repeated use make them promising in catalytic hydrogenation.

Selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-butene-2-ol (MBE) over Pd supported on hypercrosslinked polystyrene was studied in polar (ethanol, isopropanol, water) and non-polar (cyclohexane, toluene, octane, hexane, heptane and m-xylene) solvents. The catalytic activity and selectivity were found to be strongly affected by solvent properties such as dipole moment and dielectric constant, but cannot be explained by solvent polarity only. Hydrogen solubility and solvent. catalyst interaction also influential factors. The catalyst activity decreases in the series: alcohols > cyclohexane > water/ethanol mixture > octane ≥ hexane ≥ xylene > toluene > heptane. The highest values of MBE selectivity of 99.6% and 98.7% at 95% MBY conversion were obtained in toluene and in ethanol, respectively.

(Figure Presented) Here we report control of iron oxide and palladium nanoparticle (NP) formation via stabilization with polyphenylenepyridyl dendrons of the second and third generations with dodecyl periphery. These nanomaterials are developed as magnetically recoverable catalysts. To accurately assess the influence of the dodecyl exterior for the same dendron generation, we also designed a second generation dendron with partial dodecyl periphery. For all dendrons studied, the multicore iron oxide mesocrystals were formed, the sizes and morphology of which were controlled by the dendron generation. Analysis of the static and dynamic magnetic properties, in combination with transmission electron microscopy observations, demonstrate that magnetism is sensitive on the structure-directing capabilities of the type of the dendron which was employed for the mesocrystal stabilization. Close proximity of single cores in such multicore mesocrystals promotes the coupling of the neighboring magnetic moments, thus boosting their magnetization and allowing easy crossover between superparamagnetic and ferrimagnetic behaviors at room temperature. The particularly dramatic role of the dendron structure was also witnessed via the Pd NP formation, which was found to depend on both the dendron generation and its dodecyl periphery. In the case of the catalyst based on the second generation dendron with full dodecyl periphery, no Pd NPs were observed by TEM indicating that these species are of a subnanometer size and are not visible on or near the iron oxide NPs. For the catalyst based on the second generation dendron with partial dodecyl periphery, hydrogen reduction leads to much larger Pd NPs (2.7 nm) due to an unimpeded exchange of Pd species between dendrons and nondense dendron coating with asymmetrical dendrons. The third generation dendron with full dodecyl periphery allows nearly monodisperse 1.2 nm Pd NPs in the shells of iron oxide mesocrystals and the best catalytic properties in selective hydrogenation of dimethylethynylcarbinol. This study suggests a robust approach to control NP formation in magnetically recoverable catalysts for a wide variety of catalytic reactions using dendrons combining rigidity and flexibility in one molecule.

Palladium nanoparticles of 3.2?±?0.9?nm size were generated within 12–18 mesh pellets of hybrid zirconia/polyvinyl alcohol matrix, to afford a 0.03–0.1% Pd loading (w/w). The material was used in the catalytic, continuous flow hydrogenation reaction of multiple C[dbnd]C and C[tbnd]C bonds and nitrobenzene, showing good selectivity at full conversion and excellent resistance over prolonged time-on-stream under room temperature and 1–2?bar H2gas. No metal leaching in solution was detected as well as no additives nor regeneration steps were needed for use in hydrophilic solvents.

Au@Pd bimetallic nanoparticles (NPs) catalysts were synthesized by a seeding growth method using bayberry tannin grafted collagen fiber (BT-CF) as the matrix. In this method, Au3+ was first reductively adsorbed onto BT-CF to form Au NPs, and then they serve as the seeds for the over growth of Pd shell. The morphology of BT-CF-Au@Pd catalyst was observed by TEM and SEM, and the core-shell structure of the Au@Pd was confirmed by EDS and XRD. It was found that the as-prepared BT-CF-Au9@Pd3 catalyst showed excellent synergy effect in liquid-phase hydrogenation of cyclohexene, whose reaction time was three times faster than that catalyzed by BT-CF-Pd catalyst under the same conditions. Meanwhile, the BT-CF-Au9@Pd3 catalyst could be re-used four times without significant loss of activity. In the fourth run, the substrate conversion was still as high as 92.70%, much better than that by using commercial Pd/C catalyst (42.60%). Additionally, BT-CF-Au9@Pd3 catalyst exhibited high hydrogenation activity to various alkenes and nitro-compounds. For example, the TOF of allyl alcohol, styrene and nitrobenzene hydrogenations reached 10,980, 14,732 and 1379 mol mol-1 h-1, respectively.

For the first time we report syntheses of a family of functional polyphenylenepyridyl dendrons with different generations and structures such as focal groups, periphery, and a combination of phenylene and pyridyl moieties in the dendron interior using a Diels-Alder approach and a divergent method. The dendron structure and composition were confirmed using NMR spectroscopy, MALDI-TOF mass spectrometry, FTIR, and elemental analysis. As a proof of concept that these dendrons can be successfully used for the development of nanocomposites, synthesis of iron oxide nanoparticles was carried out in the presence of thermally stable dendrons as capping molecules followed by formation of Pd NPs in the dendron shells. This resulted in magnetically recoverable catalysts exhibiting exceptional performance in selective hydrogenation of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol (DMVC).

In this study, the homogenous Pd nanoparticles (Pd NPs) were first prepared with bayberry tannin (BT) as the stabilizers. Subsequently, the obtained bayberry tannin-stabilized Pd nanoparticles (BT-Pd) were immobilized onto γ-Al2O3 to prepare heterogeneous γ-Al 2O3-BT-Pd catalysts. Fourier Transformation Infrared Spectrum (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses confirmed that the Pd NPs were well stabilized by the phenolic hydroxyl groups of BT. Transmission Electron Microscopy (TEM) observation indicated that the diameter of the Pd NPs can be effectively controlled in the range of 4.2-16.0 nm by varying the amount of BT. It is found that the γ-Al2O 3-BT-Pd catalysts exhibit highly activity for various olefin hydrogenations. For example, the initial TOF (turnover frequency) of the γ-Al2O3-BT-Pd in the allyl alcohol hydrogenation is as high as 12804 mol·mol-1·h-1. Furthermore, the γ-Al2O3-BT-Pd can be reused 5 times without significant loss of activity, exhibiting a superior reusability as compared with conventionally prepared γ-Al2O3-Pd catalysts.

A thermoregulated catalytic process has been elaborated using a ruthenium-nanoparticle catalyst embedded into a supramolecular cyclodextrin-based hydrogel matrix. Upon heating, the gel phase turned into a sol phase in which alkenes could be efficiently hydrogenated. Upon cooling, the reaction products and the metallic catalyst could be easily separated. The reusability of the system was clearly demonstrated. Copyright

Gold and palladium nanoparticles were prepared by lithium borohydride reduction of the metal salt precursors in tetraalkylphosphonium halide ionic liquids in the absence of any organic solvents or external nanoparticle stabilizers. These colloidal suspensions remained stable and showed no nanoparticle agglomeration over many months. A combination of electrostatic interactions between the coordinatively unsaturated metal nanoparticle surface and the ionic-liquid anions, bolstered by steric protection offered by the bulky alkylated phosphonium cations, is likely to be the reason behind such stabilization. The halide anion strongly absorbs to the nanoparticle surface, leading to exceptional nanoparticle stability in halide ionic liquids; other tetraalkylphosphonium ionic liquids with non-coordinating anions, such as tosylate and hexafluorophosphate, show considerably lower affinities towards the stabilization of nanoparticles. Palladium nanoparticles stabilized in the tetraalkylphosphonium halide ionic liquid were stable, efficient, and recyclable catalysts for a variety of hydrogenation reactions at ambient pressures with sustained activity. Aerial oxidation of the metal nanoparticles occurred over time and was readily reversed by re-reduction of oxidized metal salts. Stable morsels of metal: Palladium nanoparticles stabilized in tetraalkylphosphonium halide ionic liquids are stable, efficient, and recyclable catalysts for a variety of hydrogenation reactions at ambient pressures with sustained activity (see picture). Copyright

As benchmarks for judging the catalytic power of sulfate monoesterases, we sought to determine the rates of spontaneous hydrolysis of unactivated alkyl sulfate monoesters by S-O bond cleavage. Neopentyl sulfate proved to be unsuitable for this purpose, since it was found to undergo hydrolysis by a C-O bond cleaving mechanism with rearrangement of its carbon skeleton. Instead, we examined the temperature dependence of the spontaneous hydrolyses of aryl sulfate monoesters, which proceed by S-O cleavage. Extrapolation of a Bronsted plot [log(k25N) = (-1.81 ± 0.09) pKaLG + (3.6 ± 0.7)] based on the rate constants at 25 °C for hydrolysis of a series of sulfate monoesters to a pKaLG value of 16.1, typical of an aliphatic alcohol, yields k25N = 3 × 10 -26 s-1. Comparison of that value with established k cat values of bacterial sulfatases indicates that these enzymes produce rate enhancements (kcat/kuncat) of up to 2 × 1026-fold for the hydrolysis of sulfate monoesters. These rate enhancements surpass by several orders of magnitude the ～10 21-fold rate enhancements that are generated by phosphohydrolases, the most powerful biological catalysts previously known. The hydrolytic rates of phosphate and sulfate monoesters are compared directly, and the misleading impression that the two classes of ester are of similar reactivity is dispelled.

[ReBr2(NO)(CH3CN)(PTA)2] (PTA = 1, 3, 5-triaza-7-phosphaadamantane) catalyzes the alcoholysis of ammonia-borane and amine-boranes and the catalytic transfer hydrogenations of various terminal olefins. Excellent yields were achieved at 70 °C in isopropanol using tBuOK as a co-catalyst affording TOF values up to 396 h-1.

A new triphenylphosphane based on a β-cyclodextrin skeleton (PM-β-CD-OTPP) was synthesized. This ligand can be dispersed in water by using the nanoprecipitation method. Transmission electron microscopy and NMR spectroscopy showed that PM-β-CD-OTPP is aggregated in water and forms a stable dispersion. Its aqueous solubility can be dramatically increased in the presence of selected water-soluble guests by formation of inclusion complexes. Associated to a rhodium precursor, PM-β-CD-OTPP is able to generate soluble rhodium species in water. In addition, NMR experiments showed that the cyclodextrin cavity remains accessible for a guest even when PM-β-CD-OTPP is coordinated to rhodium. Finally, this ligand was efficient for rhodium-catalyzed hydrogenation and hydroformylation performed in aqueous medium.

Acid-washed (pH 4 and pH 6) bentonite earth cleaves the tetrahydropyranyl ethers to the corresponding alcohols in good yield under mild conditions.

The homogeneous ruthenium complexes were immobilized onto tannin grafted micelle templated silica (MTS-BT) to prepare heterogeneous MTS-BT-Ru catalysts. The catalyst was found to be highly active in liquid phase hydrogenation of olefins. The heterogenized Ru complexes also exhibited excellent stability, reusability and catalytic efficiency. Furthermore, this methodology could extend to heterogenize other complexes to improve their reusability and stability. Crown Copyright

A new diphenylphosphane based on a β-cyclodextrin skeleton that exhibits a dual solubility in water and in organic solvent was synthesised. Interestingly, a solvent-dependent conformation change was evidenced by NMR spectroscopy studies; the self-inclusion of a phenyl group of the phosphane moiety into cyclodextrin cavity observed in water disappeared in organic solvents due to a change in conformation. Hydrogenation or hydroformylation reactions performed in water and in organic solvents showed that this ligand was able to stabilise catalytically active rhodium species in solution. In the case of the hydroformylation reaction, it was demonstrated that regioselectivity was influenced by the solventdependent conformation of the ligand.

Continuous flow capillary microreactors with embedded monometallic (Pd) or bimetallic (Pd25Zn75) catalysts have been tested in the selective hydrogenation of alkyne reagents. The catalysts were prepared in two steps. At first, polymer- stabilized metal nanoparticles (either Pd or Pd 25Zn75) were prepared by the reduction by solvent method. Then, a solution of colloidal nanoparticles with a desired concentration was added into a titania sol, which was destabilized by solvent evaporation during dip-coating of the inner wall of a fused silica capillary with an internal diameter of 250 μm. The wall-coated microreactors were tested in the hydroge- nation of 2-methyl-3-butyne-2-ol (0.011-0.45 M solution in methanol) in the 328-337 K temperature range. The highest selectivity towards the alkene product of 90% was obtained at 99.9% conversion on the Pd25Zn 75/TiO2 catalyst. The selectivity was further increased to 97% by addition of pyridine into the reactant solution. No deactivation of the wall-coated catalysts was observed during one month of continuous operation at 333 K.

Iron nanoparticles prepared by reducing FeCl3 with three equivalents of EtMgCl in THF are effective catalysts for the hydrogenation of alkenes and alkynes under moderate conditions.

Photolysis of substituted thiophene-S-oxides in solution results in the formation of either the corresponding thiophene or furan, in addition to uncharacterized materials. No good rationalization is available for the choice of which pathway may predominat

(Chemical Equation Presented) Sugar snap P: An N,P heterobidentate supramolecular ligand was synthesized in water by mixing a monoamino-β- cyclodextrin with an appropriate phosphane. The resultant assembly was used with a platinum(II) salt in aqueous medium to catalyze the hydrogenation of an allylic alcohol (see picture).

In this article, a new route for conversion of camptothecin to 7-ethylcamptothecin and 7-propylcamptothecin is described. Compared with previous reports, the reaction time of the new synthetic route was greatly shortened to 30 min, and the products were obtained in high yield. Copyright Taylor & Francis Group, LLC.

The present invention provides an improved process for the production of tertiary amyl hydroperoxide by the liquid phase oxidation of isopentane in presence of air or molecular oxygen as oxidant using the oxides of Group IIA metals such as magnesium, calcium, strontium and barium in high pressure reactor under stirring conditions at a temperature ranging between 110°-180° C. and at moderate pressures for a period of 0.1-12 h. The catalyst reused for sevral times without affecting its catalytic performance. The present invention produces a tertiary amyl hydroperoxide with 40-60% selectivity and tertiary amyl alcohol, which has a numerius industrial applications.

The present invention provides an improved process for the production of tertiary amyl hydroperoxide by the liquid phase oxidation of isopentane in presence of air or molecular oxygen as oxidant using the oxides of Group IIA metals such as magnesium, calcium, strontium and barium in high pressure reactor under stirring conditions at a temperature ranging between 110°- 180oC and at moderate pressures for a period of 0.1- 12 h. The catalyst reused for several times without affecting its catalytic performance. The present invention produces a tertiary amyl hydroperoxide with 40-60 % selectivity and tertiary amyl alcohol, which has a numerius industrial applications.

Hydroxyl radicals, generated by photolysis of H2O2. were reacted with n-pentane and isopentane in air in the absence of nitrogen oxides. The observed product distributions were compared with similar data derived by computer simulations, based on the known reaction mechanisms, to determine relative probabilities for hydrogen abstraction at different sites of the parent compounds and to estimate branching ratios and relative rate coefficients for cross-combination reactions between different peroxy radicals. For n-pentane. the distribution of the pentanols indicates probabilities for hydrogen abstraction, in percent, of q1= 9.1 ± 0.7. q 2 = 56.1 ± 1.8, and q3 = 34.8 ± 1.3. which agree with predictions based on the algorithm proposed by Atkinson. Branching ratios needed to harmonize calculated and observed product distributions are somewhat larger than, although still within the error ranges of. the values found by us previously Comparison between experimental and calculated data confirms the isomerization and decomposition constants recently established for the three pentoxyl radical isomers. The product distribution for isopentane. which is dominated by acetone, acetaldehyde. 2-methyl-butan-2-ol. and 2-methyl-butan-2-hydroperoxide, is in harmony with the predicted oxidation mechanism. Probabilities for hydrogen abstraction from isopentane were estimated to occur to 12% at the primary. 28% at the secondary, and 60% at the tertiary sites, again in agreement with predictions based on the algorithm of Atkinson.

Cerium(III) triflate deprotects p-methoxybenzyl ethers of simple alcohols better than the cerium(III) chloride/sodium iodide system. It can be used in 1% M instead of equimolecular amounts, giving better yields. Aromatic alcohols rearrange, but the addition of a scavenger overcomes this drawback. Unfortunately, unsaturated alcohols are deprotected with decomposition, probably due to side electrophilic additions to double bonds. A comparison between the mechanisms of cerium triflate and cerium chloride is reported. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Hydrolyses of benzaldehyde acetals, PhCH(OR)2, are specific hydrogen-ion catalyzed when R = methyl, n-butyl, but with secondary and tertiary alkyl derivatives, R = i-propyl, s-butyl, t-butyl, t-amyl, hydrolyses are general-acid catalyzed. The Broonsted α values for both secondary and tertiary alkyl groups are in the range: α = 0.57-0.61. A simple iterative procedure was developed to estimate the individual rate constants for general-acid catalysis by the diacid and monoacid forms of succinic acid buffer. Plots of log kobs (at [buffer] = 0 M) against pH are linear for the secondary and tertiary acetals, and plots of log kH for the H3O+-catalyzed reaction, 13C and 1H chemical shifts, and 1JCH coupling constants against the Charton steric parameter, v, for alkoxy groups are linear. The second-order rate constant, kH, increases about 100-fold on going from R = Me to R = t-amyl, indicating the significant role of steric effects on reactivity. Steric effects upon 13C NMR chemical shifts and coupling constants indicate that increasing the bulk of the alkoxy moiety increases the electron density at the carbon reaction center, which accelerates hydrolysis. Analysis of the Jencks-More-O'Ferrall free energy diagram for the reaction provides support for concerted proton transfer and C-O bond breaking in the transition state for hydrolyses of benzaldehyde acetals with secondary and tertiary alkyl groups in contrast to specific hydrogen catalysis with R = Me and n-Bu. All our results are consistent with rate-determining acid hydrolysis of benzaldehyde dialkyl acetals to hemiacetal intermediates that breakdown rapidly to benzaldehyde.

The invention concerns a method for preparing a benzylic-type ether from an aromatic compound. The inventive method for preparing a benzylic-type ether from an aromatic compound is characterised in that it consists in: in a first step, acylating an aromatic compound by reacting said aromatic compound with an acylating agent, in the presence of an efficient amount of zeolite or a Friedel-Crafts catalyst leading to a ketonic compound; in a second step, reducing the carbonyl group into carbinol leading to a benzylic alcohol; in a third step, etherifying the hydroxyl group, by reacting the benzylic alcohol with another alcohol, in the presence of an efficient amount of zeolite.

Tertiary alcohols can be prepared by the hydration of tertiary olefins having the same number of carbon atoms on an acidic ion exchanger using special structured multi-purpose packings for heterogeneous reactive rectification. An excellent yield and purity of the alcohol and an extended service life of the catalyst are achieved.