Solvent-free Hydrogenation Research Articles

Efficient Solvent‐Free Hydrogenation of Ketones over Flame‐Prepared Bimetallic Pt–Pd/ZrO2 Catalysts

Named and flamed: Bimetallic Pt-Pd/ZrO(2) catalysts with different Pt/Pd atomic ratios and high dispersion of the metal nanoparticles are prepared by a single-step flame-spray pyrolysis. The catalysts show excellent activity and tunable product selectivity for the solvent-free hydrogenation of the ketone model compounds cyclopentanone and acetophenone.

Facile Synthesis of Branched Ruthenium Nanocrystals and Their Use in Catalysis

Our novel and facile synthesis of ruthenium nanostars opens the door to the shape control of previously inaccessible sophisticated and monodisperse ruthenium nanomaterials. The metallic state and hexagonal close-packed (hcp) structure of the Ru nanostars, which are approximately 15 nm across, were determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). These materials can also act as seeds for the first preparation of ruthenium nanourchins. In addition, we have shown that they are as catalysts for the activation of CO and C═C bonds, since Fischer–Tropsch and solvent-free hydrogenation reactivities were observed on these unsupported materials.

Solvent-Free Hydrogenation and Suzuki–Miyaura Coupling Using Pd/C

Key words palladium - cross-coupling - Suzuki–Miyaura coupling - hydrogenation

Rhodium(0) Nanoparticles Supported on Nanocrystalline Hydroxyapatite: Highly Effective Catalytic System for the Solvent-Free Hydrogenation of Aromatics at Room Temperature

The hydrogenation of aromatics under mild conditions remains a challenge in the fields of synthetic and petroleum chemistry. Described herein is a new catalytic material that shows excellent catalytic performance in terms of activity, selectivity, and reusability in the hydrogenation of aromatics in solvent-free systems under mild conditions. The catalyst, consisting of rhodium nanoparticles supported on nanocrystalline hydroxyapatite, can quantitatively hydrogenate neat benzene to cyclohexane with exceptionally high rates (initial TOF > 10(3) h(-1)) at 298 K and 3 bars of initial H(2) pressure. This new material maintains its inherent catalytic activity after several reuses. Importantly, catalyst preparation does not require elaborate procedures because the active metal nanoparticles are readily formed from the in situ reduction of Rh(3+)-exchanged hydroxyapatite while submerged in the aromatic solvent at room temperature under 3 bars of H(2) pressure.

Ruthenium(0) Nanoclusters Stabilized by a Nanozeolite Framework: Isolable, Reusable, and Green Catalyst for the Hydrogenation of Neat Aromatics under Mild Conditions with the Unprecedented Catalytic Activity and Lifetime

The hydrogenation of aromatics is a ubiquitous chemical transformation used in both the petrochemical and specialty industry and is important for the generation of clean diesel fuels. Reported herein is the discovery of a superior heterogeneous catalyst, superior in terms of catalytic activity, selectivity, and lifetime in the hydrogenation of aromatics in the solvent-free system under mild conditions (at 25 degrees C and 42 +/- 1 psig initial H(2) pressure). Ruthenium(0) nanoclusters stabilized by a nanozeolite framework as a new catalytic material is reproducibly prepared from the borohydride reduction of a colloidal solution of ruthenium(III)-exchanged nanozeolites at room temperature and characterized by using ICP-OES, XRD, XPS, DLS, TEM, HRTEM, TEM/EDX, mid-IR, far-IR, and Raman spectroscopy. The resultant ruthenium(0) nanoclusters hydrogenate neat benzene to cyclohexane with 100% conversion under mild conditions (at 25 degrees C and 42 +/- 1 psig initial H(2) pressure) with record catalytic activity (initial TOF = 5430 h(-1)) and lifetime (TTO = 177 200). They provide exceptional catalytic activity not only in the hydrogenation of neat benzene but also in the solvent-free hydrogenation of methyl substituted aromatics such as toluene, o-xylene, and mesitylene under otherwise identical conditions. Moreover, they are an isolable, bottleable, and reusable catalyst in the hydrogenation of neat aromatics. When the isolated ruthenium(0) nanoclusters are reused, they retain 92% of their initial catalytic activity even for the third run in the hydrogenation of neat benzene under the same conditions as those of the first run. The work reported here also includes (i) far-infrared spectroscopic investigation of nanozeolite, ruthenium(III)-exchanged-nanozeolite, and ruthenium(0) nanoclusters stabilized by a nanozeolite framework, indicating that the host framework remains intact after the formation of a nanozeolite framework stabilized ruthenium(0) nanoclusters; (ii) the poisoning experiments performed by using tricyclohexylphosphine (P(C(6)H(11))(3)) and 4-ethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane PC(6)H(11)O(3) to examine whether the ruthenium(0) nanoclusters are encapsulated in the cages or supported on the external surface of nanozeolite; (iii) a summary section detailing the main findings for the "green chemistry"; and (iv) a review of the extensive literature of benzene hydrogenation, which is also tabulated as part of the Supporting Information .

Seeding Growth of Pd/Au Bimetallic Nanoparticles on Highly Cross-Linked Polymer Microspheres with Ionic Liquid and Solvent-Free Hydrogenation

We developed a method to immobilize Pd/Au bimetallic nanoparticles (NPs) on highly cross-linked polymer microspheres. In this route, the cross-linker divinylbenzene and ionic liquid (IL) 1-vinyl-3-...

Supercritical CO2-facilitating large-scale synthesis of CeO2 nanowires and their application for solvent-free selective hydrogenation of nitroarenes

Ceria nanowires were synthesized on a large scale by a simple, efficient, and environmentally benign strategy using supercritical (SC) CO2 expanded ethanol as reaction medium. Morphological characterization by SEM and TEM showed that most of the nanowires were bundles composed of individuals oriented parallel to each other throughout the whole length of the nanowires. Statistical data from AFM measurements showed that approximately 10% ceria nanowires (bundles/individuals) were ultrafine ones with diameters less than 5 nm. The effects of precursor concentration, reaction time and CO2 pressure on the formation of nanowires were studied, and it was found that SC CO2 played a key role in the evolution of the nanowires. As such, a possible formation mechanism for the as-prepared nanowires was provided. Moreover, the synthesis strategy was proved to be applicable to other rare earth oxide (La2O3, Eu2O3) nanowire preparation. Additionally, we successfully decorated ceria nanowires with ultrafine Pt nanoparticles via a sonication-facilitating deposition method. The as-prepared Pt-CeO2 showed superior catalytic activity and good selectivity for the solvent-free hydrogenation of nitrobenene and o-chloronitrobenzene.

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 ∼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 (∼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.

A Concept of Supported Amino Acid Ionic Liquids and Their Application in Metal Scavenging and Heterogeneous Catalysis

Novel supported task-specific ionic liquids have been developed for the first time via the ionic-pair coupling of imidazolium cation of the modified polystyrene support with L-proline. The materials have shown an efficient metal scavenging ability (e.g., CuI, Pd(OAc)2, Pd0, and IrCl3) without the aid of a nonimmobilized ionic liquid, which relies on the highly synergistic effect of the coordination with the nitrogen atom and the COO- group of the L-proline moiety, electrostatic forces, and steric protection. The resulting metal-soaked supported ionic liquids can be used as efficient heterogeneous catalysts. These materials have been investigated in the CuI-catalyzed N-arylation of nitrogen-containing heterocycles and exhibit much higher catalytic activity and a more extensive structural range of aryl and heteroaryl halides than those exhibited by free L-proline in combination with CuI both in the ionic liquid ([BMIM][BF4]) and in the corresponding homogeneous reaction conditions. The CuI-soaked catalyst 4a-2 can be recycled for nine runs at least without any considerable loss of activity. To the best of our knowledge, our catalytic process is among the most efficient approaches to the N-arylation of imidazoles with aryl halides so far reported. Furthermore, the Pd-soaked material 4a-2 also shows higher catalytic activity in the solvent-free hydrogenation of styrene to ethylbenzene. This new concept is generally applicable and may easily be extended to other supported task-specific ionic liquids.

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.

The advantages and future potential of single-site heterogeneous catalysts

Using open-structure (nanoporous) solids, advantage may be taken of single-site catalytically active centres to effect an enormous range of conversions of organic compounds where regio-selectivity and shape-selectivity loom large. When the single-site active centres are accommodated within a well-defined nanospace (typically pores of ca 30 A diameter), uniquely powerful enantio-selective conversions may also be achieved; thus organometallic complexes, composed of cheap (nitrogen-based) chiral ligands anchored to the concave walls of the nanoporous solid, are especially powerful enantio-selective hydrogenation catalysts for pharmaceutically significant precursor species. The design, characterization and performance of single-site nanoporous catalysts are described and their application in (1) aerobic, shape-selective oxidation of cyclohexane to adipic acid; (2) region-specific oxidation of linear alkanes; (3) bromine-free synthesis of terephthalic acid from p-xylene using air as oxidant; (4) the in situ generation of hazardous reagents for Baeyer–Villiger oxidation of ketones to lactones and for the epoxidation of olefins; and (5) the single-step production of e-caprolactam from cyclohexanone are outlined. Atomically engineered, multinuclear nanoparticle (bimetallic) catalysts are also described and their application in (1) one-step, solvent-free hydrogenation of polyenes; (2) asymmetric synthesis of pharmaceutical intermediates; (3) region-selective and stereo-selective allylic aminations; (4) single-step hydrogenation of dimethyl tererpthalate to 1,4-cyclohexane-dimethanol; and (5) renewable nylons from glucose and its biocatalytic derivatives is summarized. The key features of these solid catalysts (which facilitate separation of products from reactants) are that (a) they dispense with the use of corrosive reagents (and often of solvents); (b) permit the replacement of aggressive oxidants (e.g. HNO3, CrO3, etc) or even H2O2 and alkyl hydroperoxides, with molecular oxygen as the oxidant, thereby facilitating use of low-temperature and otherwise environmentally benign processes; (c) they are generally stable and recyclable and require no chemical initiators; and (d) they offer significant processing advantages in large scale and industrial operations when compared to homogeneous catalysts, especially in the generation of vital intermediates (surfactants, detergents, pharmaceuticals, polymers, perfumes and cosmetics). Typically, just one of the products (nylon-6), made by the “green”, environmentally benign bifunctional catalysts described herein, is in great demand industrially for the manufacture of (i) apparel and other textiles; (ii) floor coverings; (iii) industrial yarns; (iv) engineering plastics and (v) films for food and industrial packaging.

Chemoselective Hydrogenation of Substituted Nitroaromatics Using Novel Water‐Soluble Iron Complex Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chemoselective hydrogenation of substituted nitroaromatics using novel water-soluble iron complex catalysts.

Chemoselective hydrogenation of substituted nitroaromatic compounds by water-soluble iron complex catalysts with molecular hydrogen has been reported for the first time. This biphasic catalyst presents an opportunity for a solvent-free hydrogenation. This catalyst system provides a low-cost, efficient alternative to the selective but environmentally unacceptable stoichiometric reductions as well as the supported noble metal catalysts used for hydrogenation. An efficient recycling strategy has resulted in a cumulative turnover number above 6000.

New Catalysts for Clean Technology

AbstractFor Abstract see ChemInform Abstract in Full Text.

New catalysts for clean technology

The preparation, characterisation and catalytic performance of both bimetallic nanoparticles and chiral homogeneous catalysts anchored along the interior walls of mesoporous silica (MCM-41) are described. The bimetallic nanoparticles are prepared from Ru 6Pd 6 and Ru 6CSn carbonyl clusters and the resulting MCM derivatives are characterised by a number of methods, including EXAFS, FTIR and STEM. The solvent-free hydrogenation of naphthalene and cyclic polyenes using these catalysts are described, with the Ru 6CSn based catalyst giving a 90% selectivity for the corresponding monoenes while the Ru 6Pd 6 produces the fully hydrogenated product in high yield. The homogeneous catalysts 1-[-( R)-1′-2-bis(diphenylphosphino)ferrocenyl]ethyl-N-N′-dimethylethylenediamine palladium dichloride was heterogenised by anchoring along the inside walls of MCM-41. The catalysed reaction between cinnamylacetate and benzylamine was studied and the catalyst produced 51% of the branched chain product possibly with 100%ee.

Liquefaction studies of some Indonesian low rank coals

One sub-bituminous and five brown coals from South Banko and Kalimantan, Indonesia have been evaluated under a range of liquefaction conditions for the provision of liquid fuels. The coals were reacted with hydrogen using various catalysts in the presence and absence of a donor solvent, both with and without added sulfur-containing compounds. In addition, the coals have been reacted with CO/H 2O in the presence and absence of an added alkali catalyst, sodium aluminate. The results confirm the effectiveness of Ni/Mo in the absence of added S, and Mo in the presence of S, as catalysts for solvent-free hydrogenation of low rank coals. The most interesting finding for the CO/H 2O reactions was that Tanito Harum, a sub-bituminous coal, gave as high a conversion as any of the low rank coals.

Relation between release of conversion products in coal liquefaction and cross-linking

A study was made of the relation between the release of coal conversion products and cross-linking, using catalytic solvent-free hydrogenation in order to avoid problems in data interpretation caused by the presence of solvent. Twenty-five subbituminous and bituminous coals were hydrogenated in the absence of solvent at 5 and 10 MPa H 2 (cold), temperatures of 300, 350 and 400 °C and reaction time 30 min, with molybdenum sulfide as catalyst supported on the coal. The low-rank coals selected were more reactive than the bituminous ones. The subbituminous coals gave a maximum liquids production at 350 °C. At 400 °C the liquids yield decreased but the oil yield increased. Liquids from the hydrogenation of subbituminous coals were less asphaltenic than those from the bituminous ones. The residual chars were characterized by the extent of swelling in pyridine. For the subbituminous coals the swelling decreased with increasing conversion, reaching maximum cross-linking at the most severe conditions in most instances. The bituminous coals showed a different behaviour at low conversion, but at higher conversion the relation between conversion and swelling appeared to be similar to that for the subbituminous coals.