Palladium Nanohexagons and Nanospheres in Selective Alkyne Hydrogenation

Palladium nanohexagons were prepared using a seed-mediated method. Their catalytic performance in 2-methyl-3-butyn-2-ol hydrogenation was compared to the one of monodispersed Pd nanospheres. Quantitative correlations between initial turnover frequencies (TOFs) and nanoparticle surface compositions showed independence of TOFs calculated per atoms on Pd(111) facets on particle size and shap

Recent Advances in the Liquid-Phase Synthesis of Metal Nanostructures with Controlled Shape and Size for Catalysis

Recent advances in the liquid-phase synthesis of metal nanostructures of different sizes and shapes are reviewed regarding their catalytic properties. The controlled synthesis of nanostructures is based on the colloid chemistry techniques in the solution, which use organic nanoreactors and a variety of stabilizers. Their catalytic activity and selectivity depend on the particle’s shape and size, as shown for Suzuki and Heck coupling, hydrogenations, hydrogenolysis, oxidations, and electron-transfer reactions. The knowledge of a reaction’s structure-sensitivity relationship is important for the rational catalyst design in view of process intensification. Nanostructures can be used per se and in supported form to meet the requirements of an eventual process

Palladium Nanohexagons and Nanospheres in Selective Alkyne Hydrogenation

Palladium nanohexagons were prepared using a seed-mediated method. Their catalytic performance in 2-methyl-3-butyn-2-ol hydrogenation was compared to the one of monodispersed Pd nanospheres. Quantitative correlations between initial turnover frequencies (TOFs) and nanoparticle surface compositions showed independence of TOFs calculated per atoms on Pd(111) facets on particle size and shape

Monodispersed Pd Nanoparticles for Acetylene Selective Hydrogenation: Particle Size and Support Effects

Monodispersed Pd nanoparticles (8, 11, and 13 nm in iameter) as confirmed by high resolution transmission electron microscopy were prepared via the reverse microemulsion method and deposited on structured supports consisting of carbon nanofibers (CNF) grown on sintered metal fibers (SMF). The CNF/SMF supports were subjected to oxidative treatments to introduce O-functional groups on the CNF surface. These groups were characterized by temperature-programmed decomposition (TPD) and X-ray photoelectron spectroscopy. The catalysts were used to study (a) the effect of Pd size and (b) the effect of the support nature on the selective acetylene hydrogenation. Antipathetic size dependence of TOF disappeared at particle size bigger than 11 nm. Initial selectivity to ethylene was found size-independent. The deactivation due to coke deposition was faster for smaller particles. The structure-sensitivity relations for the catalysts investigated are discussed in terms of “geometric” and “electronic nature” of the size effect and rationalized regarding Pd-Cx phase formation which is size-dependent. Supports with increased acidity diminished the formation of coke and changed the byproduct distribution toward ethane

Synthesis of monodispersed palladium nanoparticles to study structure sensitivity of solvent-free selective hydrogenation of 2-methyl-3-butyn-2-ol

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

Kinetics of the solvent-free hydrogenation of 2-methyl-3-butyn-2-ol over a structured Pd-based catalyst

The solvent-free selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) was studied over a Pd/ZnO structured catalyst and compared to its behavior in water-assisted conditions. The catalytic behavior was correlated with the surface properties of the catalysts which were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The catalyst showed high selectivity and stability with the performance being superior to that of the industrial Lindlar catalyst (50%). The addition of a sulphur-containing modifier in the reaction mixture was found to affect the activity and to hinder the over-hydrogenation reaction. The MBE yield of similar to 97% was attained at MBY conversion >99%. The reuse of the catalyst showed that it deactivated by a 38% and that its selectivity slightly increased (similar to 0.5%) over 10 runs. The reaction kinetics was modeled using a Langmuir-Hinshelwood mechanism considering competitive adsorption for the organic species and dissociative adsorption for hydrogen. The kinetic experiments were planned and the results analyzed following a design of experiments (DOE) methodology. This approach led not only to a robust model that predicts the reaction rate in a wide range of reaction conditions but also to the determination of its kinetic parameters. (C) 2008 Elsevier B.V. All rights reserved

Palladium nanoparticles stabilized in block-copolymer micelles for highly selective 2-butyne-1,4-diol partial hydrogenation

Pd nanoparticles (2 nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly(2-vinylpyridine) were studied in partial hydrogenation of 2-butyne-1,4-diol. Both unsupported micelles (0.6 kg Pd/m3) and supported ones on g-Al2O3 (0.042% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol, with up to 94% conversion. The only side product obsd. was butane-1,4-diol. The catalysis was ascribed to the surface of Pd nanoparticles modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). The TOF [turnover frequency] over unsupported and supported catalysts was 0.56 and 0.91 s-1 (at 323 K, 0.6 MPa H2 pressure, solvent 2-propanol/water = 7:3), resp. Reaction kinetics fit the Langmuir-Hinshelwood model assuming weak hydrogen adsorption. Expts. on catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles desorbed by less then 5% during the catalytic run. [on SciFinder (R)

Three-Phase Catalytic Hydrogenation of a Functionalized Alkyne: Mass Transfer and Kinetic Studies with in Situ Hydrogen Monitoring

Systematic studies of mass transfer interactions with intrinsic reaction kinetics were performed for the threephase selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) over a modified Pd/CaC${O}_{3}$ catalyst under solvent free conditions. Hydrogen concentration in the liquid phase (${C}_{H2,b}$) was monitored in situ during the catalytic reaction by means of the Fugatron” analyzer. Reactions were carried out in an autoclave at different stirring rates at two concentrations of hydrogen (5 and 13 mol ·${m}^{-3}$ For stirring speeds higher than 1500 rpm no influence of gas-liquid mass transfer was observed. Hydrogen liquid-solid (L-S) mass transfer was found to be negligible, whereas the MBY mass L-S transfer becomes important at high MBY conversions at high hydrogen concentration. Low stirrer speed caused the reaction rate and MBE selectivity to decrease. No internal mass transfer limitations were observed, and conditions for the kinetic regime were found. The kinetics modeled ollowed the Langmuir-Hinshelwood mechanism and was consistent with the experimental data

High‐Indexed Pt3Fe Nanocatalysts and Their Enhanced Catalytic Performance in Dual Organic Reactions

The synthesis of noble metal nanocrystals terminated with high‐index facets has received increasing attention due to the remarkable improvement in their catalytic performance. Introducing a transition metal to noble metals (bimetallic nanocrystals) could result in a reduced cost and potentially improve properties. Keeping in mind both of these advantages, we have developed a new synthetic approach to fabricate size‐controlled Pt3Fe concave nanocubes using a high‐temperature organic solution system containing oleylamine and oleic acid. It further demonstrates that the particle size and concavity could be controlled by a number of parameters such as the ratio of oleylamine and oleic acid, the physicochemical properties of the metal carbonyl, the metal valence in the precursor, and the ratio of metal precursors. Catalytic tests show that the high‐index‐surface‐terminated ≈12 nm Pt3Fe concave nanocubes exhibit superior performance in both the hydrogenation of styrene and reduction of 4‐nitrophenol in comparison with their counterparts.Monodisperse Pt3Fe concave nanocubes with high‐index surfaces and a combination of sub‐facets {hk0} were synthesized using a high‐temperature solution approach, and show the highest turnover frequency for the hydrogenation of styrene and a promoted reaction rate for 4‐nitrophenol reduction in comparison with their counterparts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113773/1/cnma201500048-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/113773/2/cnma201500048.pd