Continuous Flow Hydrogenation Research Articles

Interfacial acidity in ligand-modified ruthenium nanoparticles boosts the hydrogenation of levulinic acid to gamma-valerolactone

Supported Ru-HHDMA nanoparticles are superior catalysts for the continuous-flow hydrogenation of levulinic acid to γ-valerolactone due to the bifunctional nature of the metal–ligand interface.

Grafted Polymethylhydrosiloxane on Hierarchically Porous Silica Monoliths: A New Path to Monolith-Supported Palladium Nanoparticles for Continuous Flow Catalysis Applications.

Polymethylhydrosiloxane has been grafted on the surface of a hierarchically porous silica monolith using a facile catalytic reaction between Si-H and silanol to anchor the polymer. This easy methodology leads to the functionalization of the surface of a silica monolith, where a large amount of free Si-H bonds remain available for reducing metal ions in solution. Palladium nanoparticles of 15 nm have been synthesized homogeneously inside the mesopores of the monolith without any stabilizers, using a flow of a solution containing Pd2+. This monolith was used as column-type fixed bed catalyst for continuous flow hydrogenation of styrene and selective hydrogenation of 3-hexyn-1-ol, in each case without a significant decrease of the catalytic activity after several hours or days. Conversion, selectivity, and stereoselectivity of the alkyne hydrogenation can be tuned by flow rates of hydrogen and the substrate solution, leading to high productivity (1.57 mol g(Pd)-1 h-1) of the corresponding cis-alkene.

Batch and Continuous Flow Hydrogenation of Liquid and Gaseous Alkenes Catalyzed by a Silica‐grafted Iridium(III) Hydride

The silica‐grafted hydride complex [IrH(SBA‐15)(PCP)] (2a; PCP = 1,3‐bis((di‐tert‐butylphosphino)methyl)benzene) hydrogenates alkenes under ambient condition without prior activation. Compared to its POCOP analogue (POCOP = 1,3‐bis((di‐tert‐butylphosphino)oxy)benzene), the activity of catalyst 2a is significantly improved with liquid substrates and exceptionally boosted with ethene and propene. Under gas flow conditions, catalyst 2a hydrogenates ethene with a remarkable turnover frequency of 0.95 s−1. A stability test indicates that the conversion is constant for at least 1 week.

Efficient Batch-Mode Parahydrogen-Induced Polarization of Propane.

We report on a simple approach for efficient NMR proton hyperpolarization of propane using the parahydrogen-induced polarization (PHIP) technique, which yielded ≈6.2 % proton polarization using ≈80 % parahydrogen, a record level achieved with any hyperpolarization technique for propane. Unlike in previously developed approaches designed for continuous-flow operation, where reactants (propene and parahydrogen) are simultaneously loaded for homogeneous or heterogeneous pairwise addition of parahydrogen, here a batch-mode method is applied: propene is first loaded into the catalyst-containing solution, which is followed by homogeneous hydrogenation via parahydrogen bubbling delivered at ≈7.1 atm. The achieved nuclear spin polarization of this contrast agent potentially useful for pulmonary imaging is approximately two orders of magnitude greater than that achieved in the continuous-flow homogeneous catalytic hydrogenation, and a factor of 3-10 more efficient compared to the typical results of heterogeneous continuous-flow hydrogenations.

Magnetic Co@g-C3N4 Core-Shells on rGO Sheets for Momentum Transfer with Catalytic Activity toward Continuous-Flow Hydrogen Generation.

Magnetic core-shell structures provide abundant opportunities for the construction of multifunctional composites. In this article, magnetic core-shells were fabricated with Co nanoparticles (NPs) as cores and g-C3N4 as shells. In the fabrication process, the Co@g-C3N4 core-shells were anchored onto the rGO nanosheets to form a Co@g-C3N4-rGO composite (CNG-I). For hydrogen generation from the hydrolysis of NaBH4 or NH3BH3, the Co NP cores act as catalytic active sites. The g-C3N4 shells protect Co NPs cores from aggregating or growing. The connection between Co NPs and rGO was strengthened by the g-C3N4 shells to prevent them from leaching or flowing away. The g-C3N4 shells also work as a cocatalyst for hydrogen generation. The magnetism of Co NPs and the shape of rGO nanosheets achieve effective momentum transfer in the external magnetic field. In the batch reactor, a higher catalytic activity was obtained for CNG-I in self-stirring mode than in magneton stirring mode. In the continuous-flow process, stable hydrogen generation was carried out with CNG-I being fixed and propelled by the external magnetic field. The separation film is unnecessary because of magnetic momentum transfer. This idea of the composite design and magnetic momentum transfer will be useful for the development of both hydrogen generation and multifunctional composite materials.

Continuous flow hydrogenation of nitroarenes, azides and alkenes using maghemite–Pd nanocomposites

Maghemite-supported ultra-fine Pd (1–3 nm) nanoparticles, prepared by a simple co-precipitation method, find application in the catalytic continuous flow hydrogenation of nitroarenes, azides, and alkenes.

Magnetic catalysts as nanoactuators to achieve simultaneous momentum-transfer and continuous-flow hydrogen production

A catalytically active and super paramagnetic Co–carbon–rGO composite was synthesized and used as a nanoactuator to achieve simultaneous momentum-transfer and hydrolysis of NaBH4 or H3NBH3 for hydrogen production.

Flow hydrogenation of p-nitrophenol with nano-Ag/Al2O3

Herein, we report the first continuous-flow hydrogenation of p-nitrophenol to p-aminophenol with molecular hydrogen, as a reducting agent.

A General, Green Chemistry Approach for Immobilization of Inorganic Catalysts in Monolithic Porous Flow-Reactors

A general, green chemistry approach is developed for the immobilization of inorganic catalysts in monolithic porous flow-reactors for continuous flow reactions, in which pyrogallol (PG) acts as an assistant layer for the in situ immobilization of various catalysts on the inner pore surface of the flow-reactor. Au nanoparticles (AuNPs), Al2O3, and phosphotungstic acid (HPW) are selected as examples of noble metals, metal oxides, and polyoxometalate (POM) type catalysts, respectively, and the corresponding flow-reactors show high catalytic performance in continuous flow hydrogenation reactions, esterification reactions, and Knoevenagel reactions, respectively. These reactions are important in the treatment of environmental contaminants and in the chemical industry. In addition, multiple monolithic flow-reactors can be assembled together for efficient performance of multi-step cascade reactions.

Continuous-Flow Hydrogenation with Supported Platinum Nanoparticles

Continuous-Flow Hydrogenation with Supported Platinum Nanoparticles

ChemInform Abstract: The Expanding Utility of Continuous Flow Hydrogenation

AbstractReview: 79 refs.

The expanding utility of continuous flow hydrogenation.

There has been an increasing body of evidence that flow hydrogenation enhances reduction outcomes across a wide range of synthetic transformations. Moreover flow reactors enhance laboratory safety with pyrophoric catalysts contained in sealed cartridges and hydrogen generated in situ from water. This mini-review focuses on recent applications of flow chemistry to mediate nitro, imine, nitrile, amide, azide, and azo reductions. Methodologies to effect de-aromatisation, hydrodehalogenation, in addition to olefin, alkyne, carbonyl, and benzyl reductions are also examined. Further, protocols to effect chemoselective reductions and enantioselective reductions are highlighted. Together these applications demonstrate the numerous advantages of performing hydrogenation under flow conditions which include enhanced reaction throughput, yields, simplified workup, and the potential applicability to multistep and cascade synthetic protocols.

Continuous-flow catalytic hydrogenation of 3a,6-epoxyisoindoles

Selective catalytic (10% Pd/C) hydrogenation of the double bond in the oxabicyclo[2.2.1]heptene fragment of substituted fused 1-oxo-3a,6-epoxyisoindoles is described. A continuous-flow hydrogenation device that incorporates in situ hydrogen generation by electrolysis of water was used. Changing the hydrogen source from water to deuterium oxide provides possibility to synthesize deuterated oxoepoxyisoindolones. Hydrogenation is stereoselective to give exclusively exo-cis deuterated derivatives.

Continuous-flow hydrogenation of olefins and nitrobenzenes catalyzed by platinum nanoparticles dispersed in an amphiphilic polymer

Continuous-flow hydrogenation of olefins and nitrobenzenes with ARP-Pt.

Hydrodeoxygenation of the aqueous fraction of bio-oil with Ru/C and Pt/C catalysts

In this paper we discuss the continuous flow hydrogenation of the water soluble fraction of bio-oil (WSBO) with Ru/C and Pt/C catalysts. Temparatures higher then 125°C lead to homogeneous reactions within the aqueous phase of bio-oil. Low temperature hydrogenation (LTH) at 125°C over Ru/C catalyst and with WHSV of 1.5–3h−1 was required to stabilize the bio-oil so higher temperature hydrogenation (HTH) could occur. The main products from LTH were ethylene and propylene glycols and sorbitol. At these temperatures only small amounts of acetic acid (AA), levoglucosan, furanone, phenol and phenol substitutes were hydrogenated. In the HTH step, the sorbitol was hydrogenated to mono-alcohols and diols by hydrogenolysis and secondary hydrogenation reactions. Up to 45% carbon in WSBO was converted to useful products (gasoline-cuts and diols) in the HTH step over Pt/C catalyst at 250°C and WHSV of 3h−1. The reactions product distribution can be controlled by modifying operating pressure and temperature. The production of gasoline range compounds (C4–C6 alkanes and C1–C6 alcohols) is favoured at low pressure (750psi). Increasing the reaction pressure decreased the amount of carbon that was converted into gas phase products.

ChemInform Abstract: Chemoselective Flow Hydrogenation Approaches to Isoindole‐7‐carboxylic Acids and 7‐Oxa‐bicyclo[2.2.1]heptanes.

AbstractTwo series (VI) and (XI) of norcantharidin analogues are synthesized using continuous flow hydrogenation in key steps.

Catalytic Flow Hydrogenation of Aromatic Nitro Compounds Using Polysilane-Supported Palladium

Continuous-flow hydrogenation of aromatic nitro compounds was successfully performed by using polysilane-supported palladium catalysts to afford the corresponding amino compounds in high yields. Productivity was high, and a wide variety of nitro compounds were applicable under the continuous-flow conditions. It is noted that no leaching of palladium was observed by inductively coupled plasma analysis.

Continuous flow hydrogenation reactions by Pd catalysts onto hybrid ZrO2/PVA materials

Palladium nanoparticles of 3.2±0.9nm 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 CC and CC bonds and nitrobenzene, showing good selectivity at full conversion and excellent resistance over prolonged time-on-stream under room temperature and 1–2bar H2 gas. No metal leaching in solution was detected as well as no additives nor regeneration steps were needed for use in hydrophilic solvents.

ChemInform Abstract: Synthesis of 3‐Arylated 3,4‐Dihydrocoumarins: Combining Continuous Flow Hydrogenation with Laccase‐Catalyzed Oxidation.

AbstractA flow hydrogenation/laccase catalyzed oxidation/Michael addition sequence for the conversion of coumarin derivatives into the title compounds.

Process Intensification for the Continuous Flow Hydrogenation of Ethyl Nicotinate

Here we report a process intensification study for the selective, partial, and full hydrogenation of ethyl nicotinate using a trickle bed reactor for meso-flow transformations (HEL FlowCAT). The process achieved a throughput of 1219 g d–1 (78 g h–1 of product per g of active catalyst) for the partial hydrogenation to ethyl 1,4,5,6-tetrahydropyridine-3-carboxylate, whereas the productivity for the full hydrogenation process reached a 1959 g d–1 of throughput (408 g h–1 of product per g of active catalyst) on this laboratory-scale flow chemistry platform.