A novel method for isolation of monodispersed Pd nanoparticles from a reverse microemulsion was developed using hydrocarbon evaporation and methanol-assisted particle purification from a surfactant. Fcc Pd nanoparticles of 6, 8, 11, and 13 nm in diameter were isolated from water/AOT/isooctane mixture and used to study a size effect during solvent-free hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol. The initial TOF calculated per mole of surface palladium atoms was duplicated when particle size was increased from 6 to 13 nm but remained constant when accounted per number of specific Pd atoms on Pd(111) facets. Selectivity to olefinic alcohol was not size-dependent, but an increase in particle size decreased the byproduct ratio of dimers to saturated alcohol. Acetylenic alcohol hydrogenation is shown to be a structure-sensitive but size-independent reaction for Pd particles with size of 6–13 nm. The work shows also that the Pd size controlled the reaction rate and the byproduct distribution. © 2007 Elsevier, reprinted with permission.
An innovative structured catalyst based on sintered metal fibers (SMFs) coated by a grain-structured ZnO layer was developed for the selective 3-phase hydrogenation of functionalized alkynes. The catalyst was synthesized by the deposition of Pd0-sol with 7-nm nanoparticles stabilized by molybdate anions on ZnO/SMF after reduction in hydrogen at 773 K. The crystallites of PdZn alloy (24 nm) were formed by high-temperature treatment in hydrogen and contained partly Pd(0) nanoparticles. Pd/ZnO/SMF (0.2 wt% Pd, 6 wt% ZnO) allowed >95% yield of 2-methyl-3-buten-2-ol (MBE) during 2-methyl-3-butyn-2-ol hydrogenation at 308 K and 5 bar pressure using water as the solvent and adding a small amount of quinoline. The consecutive reaction of MBE hydrogenation was suppressed due to the presence of PdZn in the active phase. The catalyst activity of the catalyst was an order of magnitude higher compared with that of commercial Lindlar catalyst (Pd, Pb/CaCO3), which quickly deactivated in aqueous media due to irreversible chemical transformations of the CaCO3 support. The structured catalyst developed in this study could be reused after ultrasonic regeneration, retaining the original selectivity and most of its initial activity. The catalyst showed high mechanical stability, precluding leaching of its components during the reaction. Due to easy shaping, high permeability, and low pressure drop during the fluid passage, the structured Pd/ZnO/SMF catalyst is suitable for a continuously operated staged bubble column reactor. © 2007 Elsevier, reprinted with permission.
The structure sensitivity of a liquid-phase 1-hexyne hydrogenation was studied using monodispersed nonsupported Pd nanoparticles of 6, 8, 11, 13, and 14 nm diameter. The particles were prepared via a reverse microemulsion water/AOT/isooctane. The size was varied by the water-to-surfactant ratio. A 15-fold TOF increase was observed with increase of the particle diameter from 11 to 14 nm. For particles above 14 nm, TOF approached the value of the Pd black catalyst. It was observed that the selectivity toward 1-hexene did not vary with the particle size and was 96.5% at the conversion of 1-hexyne of 85%. The byproduct distribution was characterized by the ratio of selectivities to 2-hexenes/n-hexane and decreased 5-fold with particle diameter from 6 to 11 nm but remained constant for bigger particles. The experimental results indicate a predominance of a “geometric” nature of the size effect observed during selective 1-hexyne hydrogenation, suggesting that an ensemble of neighboring Pd surface atoms constitutes the active center responsible for hydrogenation. © 2007 American Chemical Society, reprinted with permission.
Monodispersed Pd-nanoparticles prepared via a modified microemulsion method were deposited on active carbon fibers (ACF) fabrics and studied in a semi-batch 1-hexyne liquid-phase hydrogenation. The catalyst Pd(0.45 wt%)/ACF demonstrated >96% selectivity to 1-hexene up to 90% of conversion. Initial activity at 303 K, 1.3 MPa pressure, in n-heptane as a solvent was . Assuming a Langmuir–Hinshelwood kinetics with a weak hydrogen adsorption a kinetic model was developed. It was shown to be consistent with the experimental data and allowed determining the main kinetic parameters. © 2006 Elsevier, reprinted with permission.
An innovative staged bubble column reactor (SBCR) with a structured catalyst based on sintered metal fibers (SMFs) coated with a thin ZnO layer has been designed for continuous three-phase hydrogenations. ZnO/SMF thin plates (thickness ≈ 0.3 mm) were found to be suitable stages for the SBCR because of their rigid open structure with high porosity (>90%) and good adhesion of ZnO. The hydrodynamic characteristics of the SBCR, including pressure drop and residence time distribution, were investigated at varying superficial liquid (uL0 ≤ 0.6 cm/s) and gas (uG0 ≤ 10 cm/s) velocities for different gas/liquid systems. A semiempirical model was developed for describing the influence of the superficial fluid velocities as well as the gas and liquid physical properties on the pressure drop during SBCR operation and was found to be consistent with experiments. © 2007 American Chemical Society, reprinted with permission.
Pd nanoparticles (2 nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly-2-vinylpyridine were studied in 2-butyne-1,4-diol partial hydrogenation. Both unsupported micelles (0.6 kgPd/m3) and supported ones on γ-Al2O3 (0.042 wt.% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol up to 94% conversion. The only side product observed was 2-butane-1,4-diol. The catalysis was ascribed to Pd nanoparticles’ surface modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). TOFs over the unsupported and supported catalysts were found to be 0.56 and 0.91 s−1(at 323 K, 0.6 MPa H2 pressure, solvent 2-propanol/water = 7:3), respectively. Reaction kinetics fit the Langmuir–Hinshelwood model assuming weak hydrogen adsorption. The experiments on the catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles slightly desorbed (less then 5%) during the catalytic run. © 2004 Elsevier, reprinted with permission.
Selective dehydrolinalool (3,7-dimethyloct-6-ene-1-yne-3-ol, DHL) hydrogenation to linalool (3,7-dimethylocta-1,6-diene-3-ol, LN, a fragrant substance) was studied with Pd nanoparticles formed in poly(ethylene oxide)-block-poly-2-vinylpyridine (PEO-b-P2VP) micelles with varying solvent composition (‘isopropanol (i-PrOH):water’ ratio) and the pH of the reaction medium. According to transmission electron microscopy (TEM) and atomic force microscopy (AFM), isopropanol fraction and KOH loading control the micellar characteristics governing catalytic properties. The larger and denser the micelles, the slower the reaction due to internal diffusion limitations within the micelles. Denser micelle cores provide better modification of the Pd nanoparticle surface with pyridine units and higher selectivity. The highest selectivity (99.4%) was obtained at pH of 9.4 and 95 vol.% of isopropanol. The highest observed TOF value was found to be 24.4 s−1 at pH of 13.0 and 70 vol.% of isopropanol. KOH and isopropanol were shown both to affect the micelle characteristics and act as modifiers of the catalyst surface. The hydrogenation kinetics was studied and zero order with respect to dehydrolinalool was found. © 2004 Elsevier, reprinted with permission.
In this article we finalize our experimental and theoretical studies on the (η2-C60)Pd(PPh3)2 palladium–phosphine fullerene complex. Full scale ab initio quantum-chemical calculations up to the B3LYP/SDDALL level of theory have been performed to determine the structure and electronic spectrum of (η2-C60)Pd(PPh3)2. Based on the results of calculations and experimental data we conclude that the preliminary interaction of the catalyst with the substrate facilitates the interaction of the substrate–catalyst complex with H2 by decreasing the energy barrier. In conclusions we summarize the results of our studies of the structure and electronic spectrum of the investigated complex, the kinetics of catalytic reactions, the influence of the solvents on the catalyst’s activity in the heterogeneous phase, and provide the possible mechanism of catalytic reaction. © 2004 Wiley Periodicals, reprinted with permission.
Extraction of biologically active substances is the main stage in the production of drugs from
natural compounds. With only a few exceptions, the process is performed by poorly efficient,
labor- and time-consuming (up to two weeks) methods based on percolation and maceration. In connection with this, intensification of the extraction stage, as well as increase in the final product quality, are tasks of special importance for the pharmaceutical industry. It was demonstrated that using various physical factors, including physical treatments (ultrasound, electrothermal processes, electroflotation, etc.), provides significant acceleration of the extraction process and a considerable decrease in the amount of structural metals used in the equipment and in the energy consumed in the process. The purpose of this work was to study the ultrasound-stimulated extraction of biologically active substances from raw plant materials and ways of acoustic energy dissipation in the system. © 2000 Springer, reprinted with permission.
Hydrogenation of triple bond of dehydrolinalool to double one of linalool was studied with Pd colloids prepared in polystyrene-poly-4-vinylpyridine micelles in toluene and deposited on Al2O3. The high selectivity (99.8%) of this catalyst is explained by durable modification of the Pd nanoparticle surface with 4-vinylpyridine units. The activity of Pd catalyst studied is determined by high reactivity of small Pd nanoparticles. The influence of solvent nature on catalytic properties of Pd colloidal catalyst is studied. Maximum relative rate was found to be in methanol, but the highest selectivity was achieved in toluene because the latter is a selective solvent for polystyrene-poly-4-vinylpyridine micelles and provides the better accessibility of reactive sites. © 1999 Elsevier, reprinted with permission.
Catalytic properties of Pd–fullerene complex η2-C60Pd(PPh3)2 have been studied in the hydrogenation of acetylenic alcohols. The kinetics of the homogeneous hydrogenation has been investigated under static conditions. The catalyst quantity and the initial concentration of acetylenic alcohol have been varied. Physico-chemical properties of Pd–fullerene complex have been studied using methods of NMR, IR- and UV-spectroscopies. Using experimental results and physico-chemical investigations, the mathematical model of the process and the reaction mechanism have been offered. © 1999 Elsevier, reprinted with permission.