Active Hydrogenation Catalysts Research Articles

The influence of metal selection on catalyst activity for the liquid phase hydrogenation of furfural to furfuryl alcohol

In this work the replacement of toxic chromium containing catalysts for the selective hydrogenation of furfural to furfuryl alcohol was investigated. The initial focus was on the synthesis of monometallic catalysts by wet impregnation and concentrated on the employment of metals such as platinum, palladium, copper and nickel. Experiments were conducted using ethanol as the solvent which was found to have a negative effect on the selectivity to the desired product, furfuryl alcohol, with high quantities of 2-Furaldehyde diethyl acetal and difurfuryl ether formed. Consequently, toluene was selected as an alternative solvent facilitating selectivity to furfuryl alcohol only. It was found that platinum was the most promising metal of those studied as it displayed higher selectivity to furfuryl alcohol and was subsequently employed for the synthesis of bimetallic catalysts. The bimetallic catalysts were synthesised by surface reactions using a variety of promoter metals selected according on their electronegativity. It was found that, while the selectivity of all catalysts to furfuryl alcohol was close to 100%, the conversion was influenced significantly by the second metal and followed the order tin>molybdenum>manganese>barium>iron>nickel. The purpose of the research was to produce an active catalyst for the liquid phase hydrogenation under suitable industrial conditions with the results presented here conducted at 100°C and 20bar hydrogen pressure. Furfural conversion of 47% and close to 100% selectivity to furfuryl alcohol was achieved using a 0.6%Pt0.4%Sn/SiO2 catalyst.

ChemInform Abstract: Fabrication of Ultrafine Palladium Phosphide Nanoparticles as Highly Active Catalyst for Chemoselective Hydrogenation of Alkynes.

AbstractThe title catalyst is applied for the hydrogenation of terminal and internal alkynes to produce the corresponding alkenes with high yields and chemoselectivity.

Neutral and cationic (pyrazolylmethyl)pyridine palladium(II) complexes: kinetics and chemoselectivity studies in hydrogenation of alkenes and alkynes

Reactions of (3,5-dimethylpyrazolylmethyl)pyridine (L1) and (3,5-diphenylpyrazolylmethyl)pyridine (L2) with either [PdCl2(NCMe)2] or [PdClMe(COD)] afforded the respective neutral palladium complexes, [PdCl2(L1)] (1), [PdCl2(L2)] (2) and [PdClMe(L1)] (3). Treatment of complex 1 with equimolar amounts of PPh3 or PPh3/NaBAr4 produced the corresponding cationic complexes [Pd(L1)ClPPh3]Cl (4) and [Pd(L1)ClPPh3]BAr4 (5), respectively. Complexes 1–5 formed active catalysts in hydrogenation of alkenes and alkynes. Isomerization reactions were predominant in the hydrogenation reactions of terminal alkenes, while hydrogenation of alkynes involved a two-step process via alkene intermediates prior to the formation of the respective alkenes. The lack of induction periods in the hydrogenation reactions in addition to pseudo-first-order kinetics with respect to the substrates established the homogeneous nature of the active species.

Highly stable and sub-3 nm Ni nanoparticles coated with carbon nanosheets as a highly active heterogeneous hydrogenation catalyst

An efficient catalyst of Ni/C hybrid nanosheets was prepared via a facile and simple procedure. The highly dispersed and sub-3nm Ni nanoparticles (NPs) were coated with the carbon nanosheets which can prevent the aggregation and growth of the Ni NPs. The Ni/C hybrid nanosheets exhibited high activity for the catalytic reduction of 4-nitrophenol (4-NP), which was much higher than many noble metal NPs. Additionally, the magnetic Ni/C hybrid nanosheets showed good separation ability and reusability.

Zirconium-Catalyzed Imine Hydrogenation via a Frustrated Lewis Pair Mechanism

Zirconium-based frustrated Lewis pairs (FLPs) are active imine hydrogenation catalysts under mild conditions. Complexes of the type [CpR2ZrOMes][B(C6F5)4] utilize the imine substrate itself as the Lewis base component of the FLP. Catalyst performance is a function of ligand structure; in general more bulky, more electron rich cyclopentadienyl derivatives give the best results. However, Cp* derivatives are not catalytically active, being stable after initial heterolytic cleavage of H2; this allows experimental verification of the competence of the zirconocene–imine pair in FLP-type heterolytic H2 cleavage. Enamines and protected nitriles are also hydrogenated if an additional internal phosphine base is used.

Insights into the selective hydrogenation of levulinic acid to γ-valerolactone using supported mono- and bimetallic catalysts

Hydrogenation of levulinic acid (LA) towards γ-valerolactone (GVL) is one of the most promising reactions in the field of biomass valorization to fine chemicals and liquid transportation fuels. Bimetallic Ni-Pt and Ni-Ru supported on ZrO2 and γ-Al2O3 were successfully utilized in this work as highly active and GVL-selective catalysts for the solvent-free hydrogenation of levulinic acid (LA) using formic acid (FA) as a hydrogen source in a microwave reactor, with results further translated into a continues flow system to prove the reaction mechanism. The supported bimetallic catalysts and their corresponding monometallic counterparts were characterized using N2-sorption, elemental analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Under microwave irradiation, 100% selectivity to GVL was achieved using both mono- and bimetallic catalysts. Bimetallic Ni-Ru supported on γ-Al2O3 shows the highest LA conversion (71%) among the studied catalysts. This high activity is attributed to a larger Ru° concentration on the surface of γ-Al2O3 in comparison to ZrO2 as well as to the textural properties of γ-Al2O3 (i.e., surface acidity, specific surface area). In contrast, ZrO2‐based catalysts exhibited a higher stability with respect to γ-Al2O3-based after four consecutive runs of reaction.

Nickel-Catalyzed Asymmetric Alkene Hydrogenation of α,β-Unsaturated Esters: High-Throughput Experimentation-Enabled Reaction Discovery, Optimization, and Mechanistic Elucidation.

A highly active and enantioselective phosphine-nickel catalyst for the asymmetric hydrogenation of α,β-unsaturated esters has been discovered. The coordination chemistry and catalytic behavior of nickel halide, acetate, and mixed halide-acetate with chiral bidentate phosphines have been explored and deuterium labeling studies, the method of continuous variation, nonlinear studies, and kinetic measurements have provided mechanistic understanding. Activation of molecular hydrogen by a trimeric (Me-DuPhos)3Ni3(OAc)5I complex was established as turnover limiting followed by rapid conjugate addition of a nickel hydride and nonselective protonation to release the substrate. In addition to reaction discovery and optimization, the previously unreported utility high-throughput experimentation for mechanistic elucidation is also described.

Half-Sandwich Ruthenium Complexes with Schiff-Base Ligands: Syntheses, Characterization, and Catalytic Activities for the Reduction of Nitroarenes

A series of ruthenium(II) p-cymene complexes containing Schiff-base ligands [Ru(p-cymene)LCl] [HL = pyridyl-salicylimine (2a–2d); HL = thiazol-salicylimine (2e–2h); HL = benzothiazol-salicylimine (2i–2l)] have been synthesized and characterized. All Schiff-base ligands and half-sandwich ruthenium complexes were fully characterized by 1H and 13C NMR spectra, mass spectrometry, and infrared spectrometry. The molecular structures of ruthenium complexes 2b and 2k were further confirmed by single-crystal X-ray diffraction methods. Furthermore, these half-sandwich ruthenium complexes are active catalysts for the mild hydrogenation of nitroarenes to aromatic anilines in the presence of sodium tetrahydroborate reducing agent in water. The most efficient catalyst, 2b, was found be compatible with nitroarenes of various functional groups.

Improved Catalytic Activity and Stability of a Palladium Pincer Complex by Incorporation into a Metal-Organic Framework.

A porous metal-organic framework Zr6O4(OH)4(L-PdX)3 (1-X) has been constructed from Pd diphosphinite pincer complexes ([L-PdX](4-) = [(2,6-(OPAr2)2C6H3)PdX](4-), Ar = p-C6H4CO2(-), X = Cl, I). Reaction of 1-X with PhI(O2CCF3)2 facilitates I(-)/CF3CO2(-) ligand exchange to generate 1-TFA and I2 as a soluble byproduct. 1-TFA is an active and recyclable catalyst for transfer hydrogenation of benzaldehydes using formic acid as a hydrogen source. In contrast, the homogeneous analogue (t)Bu(L-PdTFA) is an ineffective catalyst owing to decomposition under the catalytic conditions, highlighting the beneficial effects of immobilization.

Enhancing the catalytic activity of Ru NPs deposited with carbon species in yolk–shell nanostructures

An efficient H2 pyrolysis method was developed to remove stabilizers on metal surfaces with Ru–poly(amindoamine) as the model. Ru NPs after pyrolysis with the TOF as high as 20 300 h−1 are among the most active solid catalysts for toluene hydrogenation. The high catalytic activity could be mainly attributed to the high exposure degree and accelerating effect of C and N residues at the Ru surface.

Pd–Ru/TiO2 catalyst – an active and selective catalyst for furfural hydrogenation

The selective hydrogenation of furfural at ambient temperature has been investigated using a Pd/TiO2 catalyst.

Cu(ii)/Cu(0)@UiO-66-NH2: base metal@MOFs as heterogeneous catalysts for olefin oxidation and reduction.

Two copper-loaded MOF materials, namely Cu(ii)@Ui-O-66-NH2 (1) and Cu(0)@UiO-66-NH2 (2), are reported. They can, respectively, serve as highly efficient heterogeneous catalysts for olefin oxidation and hydrogenation under mild conditions. Complete styrene hydrogenation occurs in 15 min at ambient temperature with quantitative yield.

Ruthenium complexes bearing an unsymmetrical pincer ligand with a 2-hydroxypyridylmethylene fragment: active catalysts for transfer hydrogenation of ketones

Five ruthenium(ii) complexes were synthesized, including (HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)Cl2 (3), [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2Cl][PF6] (4) and [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2OH][PF6] (5) bearing an unsymmetrical pincer NNN ligand with a 2-hydroxypyridylmethylene fragment, and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][Cl]2 (6) and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][PF6]2 (7) containing 2-methoxypyridylmethylene moieties. 4 reacts with H2O at room temperature to give 5 whose crystal structure reveals the existence of intramolecular hydrogen-bonding between its two -OH groups. 3 exhibits high catalytic activity for transfer hydrogenation of ketones.

A 2-(2’-pyridyl)quinoline ruthenium(II) complex as an active catalyst for the transfer hydrogenation of ketones

AbstractThe ruthenium(II) complex cis-[RuCl2(PPh3)2(L1)] (1) where L1 = 2-(2’-pyridyl)quinoline was obtained in high yield from the reaction of [RuCl2(PPh3)3] with L1. The new compound was characterized by different spectroscopic methods including FT-IR, UV-Vis, NMR (1H, 31P) spectroscopy along with a mass spectrometric analysis (ESI-MS) and conductivity measurements. 31P NMR spectroscopy provided evidence that the two PPh3 ligands are orientated trans to each other in an octahedral environment. Complex (1) was tested in the transfer hydrogenation of various ketones in 2-propanol at 82 oC. The catalytic activity of (1) displayed quantitative conversions for benzophenone and 4-chloroacetophenone.

Catalysts for selective hydrogenation of aromatic nitrocompounds and hydrocarbons

The liquid-phase hydrogenation of nitrocompounds and aromatic hydrocarbons at the elevated pressure of hydrogen on the mono- and bimetallic supported catalysts was studied. The optimumtechnological parameters of reactions for obtaining a high yield of target products were determined. It was shown that the mechanism of transforming aromatic nitro compounds – hydrogenation and it was identical for all solvents. It was studied the influence of the added hydrogenation reaction product (p-aminophenol) during p-nitrophenol hydrogenation for determination the cause of reducing of velocity of hydrogenation. It was revealed that the monometallic Rh/Al2O3 or bimetallic catalysts of Rh-Pt/Al2O3 composite are the most active catalysts for hydrogenation of aromatic hydrocarbons. The catalysts applied on aluminum oxide are more active and selective, than the catalysts applied on a silica gel.

Magnetic NiO nanoparticles confined within open ends MWCNTs: a novel and highly active catalyst for hydrogenation and synthesis of imines

The novel catalyst is highly active for hydrogenation and synthesis of imines.

Fabrication of Ultrafine Palladium Phosphide Nanoparticles as Highly Active Catalyst for Chemoselective Hydrogenation of Alkynes.

Monodisperse palladium phosphide nanoparticles (Pd-P NPs) with a smallest size ever reported of 3.9 nm were fabricated using cheap and stable triphenylphosphine as phosphorous source. After the deposition and calcination at 300 °C and 400 °C, the resulting Pd-P NPs increased in size to 4.0 nm and 4.8 nm, respectively. Notably, the latter NPs probably crystallized with a single phase of Pd3 P0.95, which acted as a highly active catalyst in semi- and stereoselective hydrogenation of alkynes. X-ray photoelectron spectroscopy analysis determined a positive shift of binding energy for Pd(3d) in Pd-P NPs compared to that in Pd on carbon. It indicated the electron flow from metal to phosphorus and the larger electron deficiency of Pd in Pd-P NPs, which suppressed palladium hydride formation and subsequently increased the selectivity. Thus, this result may also indicate the applications of Pd-P and other metal-P NPs in various selective hydrogenation reactions.

Platinum nanoparticles entrapped in zeolite nanoshells as active and sintering-resistant arene hydrogenation catalysts

Pt nanoparticles supported on ZSM-5 nanoshells have been prepared by a mild desilication method. The zeolite support is a ZSM-5 crystal with extremely thin walls (ca. 15nm) that contain meso/microporous defects. The 2–3nm diameter Pt nanoparticles are entrapped and highly dispersed in these ZSM-5 nanoshells. The particles are stable up to 750°C in H2 owing to this immobilization. Catalytic activities for toluene hydrogenation were compared with those of reference Pt-based catalysts. The reaction rates obtained on the novel Pt-ZSM-5 nanoshells catalyst were about 100 times higher than those measured over conventional Pt-ZSM-5 catalysts. The highly defective zeolite nanoshell allowed even bulky molecules such as mesitylene to access all the Pt particles. This was in contrast to Pt nanoparticles encapsulated in ZSM-5 hollow single crystals, which were totally inactive due to molecular sieving. This novel Pt-ZSM-5 nanoshell catalyst shows outstanding sintering-resistance and mass transfer properties owing to its hierarchical design.

Well-dispersed Pt on TiO2: A highly active and selective catalyst for hydrogenation of 3-nitroacetophenone

Pt nanoparticles with size between 2 and 7nm supported on TiO2 were prepared by a deposition–precipitation method. These catalysts were characterized by nitrogen sorption, powder X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The effects of Pt loading and reaction conditions on the hydrogenation properties of 3-nitroacetophenone over Pt/TiO2 were investigated. The results show that the catalytic performance of Pt/TiO2 for 3-nitroacetophenone hydrogenation to 3-aminoacetophenone is better than those of Rh/TiO2 and Rh/SiO2. The specific activity of Pt in the Pt/TiO2 for 3-nitroacetophenone hydrogenation increases nearly two times when the Pt loading in the Pt/TiO2 decreases from 1.5wt% to 0.3wt%. The selectivity to 3-aminoacetophenone can be up to 100% at complete conversion of 3-nitroacetophenone over the 0.3wt% Pt/TiO2 even at high temperature and H2 pressure. The high activity and excellent selectivity of the 0.3wt% Pt/TiO2 are primarily derived from Pt nanoparticles and TiO2 support as well as the interaction between them. The reaction conditions also have a pronounced effect on the catalytic performance. Higher reaction temperature, H2 pressure and polar solvent are favorable for 3-nitroacetophenone hydrogenation to 3-aminoacetophenone over the 0.3wt% Pt/TiO2.

Theoretical Investigation of a Parallel Catalytic Cycle in CO2 Hydrogenation by (PNP)IrH3

The (PNP)IrH3 (2,6-bis(diisopropylphosphinomethyl)pyridine iridium trihydride) complex by Nozaki is a highly active and selective catalyst for CO2 hydrogenation to formic acid in aqueous KOH. Previous theoretical investigations found that regeneration of the catalyst is the rate-determining step in this reaction. In the current article we present results from a computational study using density functional theory in order to consider the possibility of sequential insertion of two CO2 molecules in two Ir–H bonds before the reaction with hydrogen. We found that insertion of a second CO2 molecule is indeed possible; moreover, this sequential insertion allows formation of a more electrophilic iridium monohydride intermediate, and thereby the process of H2 cleavage is facilitated. In addition, we considered the influence of ligands coplanar with the PNP ligand on the energy of CO2 insertion into the (PNP)IrH2X complex and found that σ- and π-donating ligands promote the reaction.