Active Hydrogenation Catalysts Research Articles

Selective conversion of concentrated glucose to 1,2-propylene glycol and ethylene glycol by using RuSn/AC catalysts

A series of RuSn/AC catalysts with 5% Ru and 1–6% Sn loadings were synthesized for converting concentrated (10 wt%) sugars to 1,2-propylene glycol (1,2-PG) and ethylene glycol (EG) in a semi-continuous autoclave reactor. The catalysts structure and the product distributions are found to be highly dependent on the tin loading. At tin contents below 2%, RuSn alloy was formed coexisting with small amounts of highly dispersed SnO2 in the catalyst, and hexitols were the main products due to the high activity of catalysts for hydrogenation. At a tin content above 5%, more SnO2 species were present and covered RuSn alloy particles, leading to notable amounts of humins in the reaction due to the depressed hydrogenation activity. As for the optimal catalyst of 5%Ru3%Sn/AC, 77% of tin formed RuSn alloy with ruthenium and 23% of tin existed in the form of highly dispersed SnO2 under reaction conditions. The catalyst gave 25% and 26.9% yields of 1,2-PG and EG in the glucose conversion at 513 K for 10 min. The glycols yield was insensitive to the feeding rate of glucose, which could be increased to 10 mL/min with a glycols productivity of nearly 180 g L−1 h−1. The catalysts structure and reaction networks were proposed according to pseudo in situ characterizations and conditional experiments. The highly dispersed SnO2 was effective to sugar isomerization and the RuSn alloy played the major role in retro-aldol condensation and hydrogenation reactions. Over the 5%Ru3%Sn/AC catalyst, the rates of cascade reactions of isomerization, retro-aldol condensation and hydrogenation matched well due to the balanced activity of RuSn alloy and highly dispersed SnO2, which afforded a high yield of 1,2-PG and EG.

Hydrogenation of alkenes and alkynes catalysed by NˆO (imino)phenol palladium(II) complexes: Structural, kinetics and chemoselectivity studies

Reactions of 2-(2-methoxyethylimino)ethyl)phenol (HL1), 2-(2-hydroxyethylimino)ethyl)phenol (HL2), 2-(2-aminoethylimino)ethyl)phenol (HL3) and 2-(2-hydroxyethylimino)methyl)phenol (HL4) with [PdCl2(COD)] afforded the neutral palladium complexes [PdCl2(HL1)] (1), [PdCl2(HL2)] (2), [PdCl2(HL3)] (3), [PdCl2(HL4)] (4) respectively. Treatment of complex 1 with PPh3 gave the cationic complex [Pd(HL1)ClPPh3]+ (5), while reactions of 4 with Pd(OAc)2, in the presence of PPh3 and p-TsOH produced the corresponding palladium complex, [Pd(L1) (OTs) (PPh3)] (6). The molecular structure of 4a (derivative of 4) contained two bidentate anionic ligands (L4). Complexes 1–6 formed active catalysts in hydrogenation of alkenes and alkynes, in which the catalytic activities were largely dependent on the pendant donor atom of the ligand motif. Isomerization reactions were dominant in terminal alkenes hydrogenation reactions, while hydrogenation of alkynes to alkanes occurred in two steps via alkene intermediates. Kinetics data were consistent with homogeneous active species. Density functional theory studies supported the hemi-labile nature of the ligands, and offered insights into the catalytic activity trends observed.

Obtaining of highly-active catalysts of unsaturated compounds hydrogenation by using supercritical carbon dioxide

Polymer frameworks have been for the first time impregnated with rhodium and palladium compounds in a supercritical carbon dioxide medium. The polymeric carriers were the mesoporous phenol-formaldehyde resin and cross-linked dendrimer networks, based on poly(propylene imine) and poly(amido amine) dendrimers. The metal compounds were rhodium acetylacetonate and palladium carboxylates including their fluoro-substituted derivatives and palladium hexafluoroacetylacetonate. Using the IR-spectroscopy method, we have shown that the metal content in the polymers was in the range of 0.3–2.0 wt.% depending on the polymer nature, cross-linking agent type and cross-linking degree. We have obtained the samples of polymer supports with nanosized metal particles through hydrogen reduction of immobilized rhodium and palladium compounds at P(H2) = 6–10 MPa, T = 60 °C, 4 h time. The average rhodium particle size was 1–2 nm. It has been shown that the obtained nanocomposites were extremely active catalysts for hydrogenation of unsaturated hydrocarbons.

Pt Single Atoms Embedded in the Surface of Ni Nanocrystals as Highly Active Catalysts for Selective Hydrogenation of Nitro Compounds.

Single-atom catalysts exhibit high selectivity in hydrogenation due to their isolated active sites, which ensure uniform adsorption configurations of substrate molecules. Compared with the achievement in catalytic selectivity, there is still a long way to go in exploiting the catalytic activity of single-atom catalysts. Herein, we developed highly active and selective catalysts in selective hydrogenation by embedding Pt single atoms in the surface of Ni nanocrystals (denoted as Pt1/Ni nanocrystals). During the hydrogenation of 3-nitrostyrene, the TOF numbers based on surface Pt atoms of Pt1/Ni nanocrystals reached ∼1800 h-1 under 3 atm of H2 at 40 °C, much higher than that of Pt single atoms supported on active carbon, TiO2, SiO2, and ZSM-5. Mechanistic studies reveal that the remarkable activity of Pt1/Ni nanocrystals derived from sufficient hydrogen supply because of spontaneous dissociation of H2 on both Pt and Ni atoms as well as facile diffusion of H atoms on Pt1/Ni nanocrystals. Moreover, the ensemble composed of the Pt single atom and nearby Ni atoms in Pt1/Ni nanocrystals leads to the adsorption configuration of 3-nitrostyrene favorable for the activation of nitro groups, accounting for the high selectivity for 3-vinylaniline.

Pd/UiO-66(Hf): A highly efficient heterogeneous catalyst for the hydrogenation of 2,3,5-trimethylbenzoquinone

The conversion of 2,3,5-trimethylbenzoquinone (TMBQ) to 2,3,5-trimethylhydroquinone is regarded as one of the most important reactions for the production of vitamin E. Here, we report on a Hf-based metal–organic framework (MOF), UiO-66(Hf), with supported palladium nanoparticles as a highly active, selective, and recyclable catalyst for the direct hydrogenation of TMBQ with H2 under mild reaction conditions. The developed Pd/UiO-66(Hf) catalyst exhibited a marked increase in activity compared with its Pd/UiO-66(Zr) counterpart and conventional Pd/C catalysts. Its excellent catalytic performance is ascribed to the large number of acid sites in the UiO-66(Hf) framework, which promote hydrogenation.

Hydrogenation of Nickel Octaethylporphyrin over Dispersed MoS2 Catalysts Formed In Situ

AbstractHydrogenation of nickel octaethylporphyrin (Ni‐OEP) over dispersed MoS2 catalysts was studied in a batch autoclave at relatively low temperatures ranging from 553 K to 593 K. In spite of the transformation of catalytic species, invariant rate constants are acceptable to analyze the kinetics in the given temperature range. It turns out that the first hydrogenation of Ni‐OEP is the rate limiting step when the dispersed catalysts are present. With the combined analysis of XRD and XPS patterns, Ni species deposited on the surface of the catalysts were determined. As much as 66.7% of nickel exists in the mixed “NiMoS” phase, and a small amount of sulfided phase of nickel is implied. The influence of metal deposits on the catalytic activity of catalysts for hydrogenation was evaluated using anthracene as the model compounds. The conversion of anthracene over MoS2 shows to be promoted with Ni‐OEP added. It is suggested that Ni‐OEP could be hydrogenated and involved with the formation of active catalytic species. As a result, Ni‐OEP could cooperate with the dispersed MoS2 catalyst for catalyzing the anthracene hydrogenation.

Rationalizing the Reactivity of Bimetallic Molecular Catalysts for CO2 Hydrogenation

We have recently reported the heterobimetallic nickel–gallium complex, NiGaL (where L represents the tris(phosphinoamido)amine ligand, [N(o-(NCH2Pi-Pr2) C6H4)3]3–), which is the most active Ni-based molecular catalyst for CO2 hydrogenation to date. Understanding the reaction mechanism of this catalytic system and identifying the factors that govern its catalytic activity are important in order to design even more efficient base–metal catalysts. Here, we present a computational study of possible reaction pathways for CO2 hydrogenation catalyzed by NiGaL. The most favorable predicted pathway for formate production agrees well with key experimental observations and is defined by four elementary steps: (1) H2 binding to the Ni center, (2) deprotonation of the H2 adduct, (3) hydride transfer to CO2 to form a formate adduct, and (4) formate release to regenerate NiGaL. The overall catalytic process has two main time periods: an induction period, during which the deprotonation of the H2 adduct by exogenous base ...

Ruthenium p‐Cymene Iminophosphonamide Complexes: Activation under Basic Conditions and Transfer Hydrogenation Catalysis

Complex [(η6‐Cym)RuCl(NPN)] {Cym = p‐cymene; NPN = (pTolN)2PPh2} (1) yields a thermally sensitive hydride derivative [(η6‐Cym)RuH(NPN)] (2) by reaction with iPrOH in the presence of a strong base, via an observable isopropoxide intermediate [(η6‐Cym)Ru(OiPr)(NPN)] (3), or with NaBHEt3 in toluene. Partial conversion also occurs in iPrOH in the absence of base. 2 is stabilized by dihydrogen bonding with isopropyl alcohol, but attempts to isolate it induce isomerization by hydride migration to a ring CH position to yield a 16‐electron cyclohexadienyl derivative [{η5‐p‐C6H5(Me)(iPr)}Ru(NPN)], which has been crystallographically characterized as a disordered mixture of two regioisomers (4/4′). Complex 2 is able to release H2 upon treatment with medium strength proton donors (fluorinated alcohols), but also slowly with iPrOH. 2 is an active catalyst for the transfer hydrogenation of acetophenone to phenylethanol in isopropyl alcohol. The catalytic transformation is first order in acetophenone and first order in catalyst, with k = 117 ± 10 m–1 h–1 at 40 °C. The temperature dependence of the rate constant (25–80 °C) gave the activation parameters ΔH‡ = 9.6 ± 1.3 kcal mol–1 and ΔS‡ = –31 ± 4 cal mol–1 K–1. DFT calculations have validated the slow isomerization of 2 to 4/4′ (high energy TS), the preference of the cyclohexadienyl system for 4/4′ relative to the other isomers 4Me and 4iPr, where the hydride has migrated to the CMe or CiPr position, and suggest that the hydrogen transfer mechanism involves outer sphere hydride transfer to the ketone substrate with H‐bonding assistance of isopropyl alcohol to yield a σ complex intermediate [(η6‐Cym)Ru+(NPN){H‐C(Me)(Ph)O–}].

Catalytic carpets: Pt@MIL-101@electrospun PCL, a surprisingly active and robust hydrogenation catalyst

Metal Organic Frameworks (MOFs) have been explored widely to create heterogeneity in a catalytic system. Catalytic applications require the use of stable catalysts with no leaching and easy recovery. In this regard, Pt@MIL-101 is embedded in a poly-є-caprolactone (PCL) matrix by means of electrospinning to create a “catalytic carpet” which is highly efficient and can be recovered within seconds after catalysis. The obtained composite material is completely intact with a homogeneous distribution of the Pt@MIL-101 throughout the electrospun PCL fiber matrix. The catalytic carpet was examined in the hydrogenation of cyclohexene and full conversion was obtained in just 90 min. Remarkably, a very large fraction (>65%) of the total Pt-atoms participate in the reaction. Reusability tests showed that the material could be recycled for at least 4 runs without detectable Cr and Pt leaching displaying the durability of the catalytic carpets. Complete recovery is achieved with zero weight loss while fully preserving the crystalline structure.

Supported Ultrafine NiCo Bimetallic Alloy Nanoparticles Derived from Bimetal–Organic Frameworks: A Highly Active Catalyst for Furfuryl Alcohol Hydrogenation

Highly dispersed NiCo bimetallic alloy nanoparticles have been successfully immobilized on the SiO2 frameworks by using heteronuclear metal–organic frameworks (MOFs) as metal alloy precursors. Catalyst characterizations revealed that the average size of NiCo alloy particles was less than 1 nm, with a total metal loading of about 20 wt %. As compared to individual Ni or Co MOF-derived catalysts and the catalysts prepared by the conventional impregnation method, the ultrafine NiCo/SiO2-MOF catalyst showed a much better catalytic performance in the catalytic hydrogenation of furfuryl alcohol (FA) to tetrahydrofurfuryl alcohol (THFA) under mild conditions, giving 99.8% conversion of FA and 99.1% selectivity to THFA. It was found that a significant synergistic effect existed between Co and Ni within the subnanometer NiCo/SiO2-MOF catalyst, which was 2 and 20 times more active than Ni/SiO2-MOF and Co/SiO2-MOF, respectively.

Nuclearity effects in supported, single-site Fe(ii) hydrogenation pre-catalysts.

Dimeric and monomeric supported single-site Fe(ii) pre-catalysts on SiO2 have been prepared via organometallic grafting and characterized with advanced spectroscopic techniques. Manipulation of the surface hydroxyl concentration on the support influences monomer/dimer formation. While both pre-catalysts are highly active in liquid-phase hydrogenation, the dimeric pre-catalyst is ∼3× faster than the monomer. Preliminary XAS experiments on the H2-activated samples suggest the active species are isolated Fe(ii) sites.

Tin-palladium supported on alumina as a highly active and selective catalyst for hydrogenation of nitrate in actual groundwater polluted with nitrate

We developed SnPd/Al2O3 showing high catalytic performance for the hydrogenation of NO3− in actual groundwater polluted with NO3−.

Methanol synthesis via CO2 hydrogenation over CuO–ZrO2 prepared by two-nozzle flame spray pyrolysis

Controlled CuO–ZrO2 particle synthesis by tuning the flame spray pyrolysis conditions allow generating highly active and methanol selective CO2 hydrogenation catalysts.

Cobalt-based nanoparticles prepared from MOF-carbon templates as efficient hydrogenation catalysts.

The development of efficient and selective nanostructured catalysts for industrially relevant hydrogenation reactions continues to be an actual goal of chemical research. In particular, the hydrogenation of nitriles and nitroarenes is of importance for the production of primary amines, which constitute essential feedstocks and key intermediates for advanced chemicals, life science molecules and materials. Herein, we report the preparation of graphene shell encapsulated Co3O4- and Co-nanoparticles supported on carbon by the template synthesis of cobalt-terephthalic acid MOF on carbon and subsequent pyrolysis. The resulting nanoparticles create stable and reusable catalysts for selective hydrogenation of functionalized and structurally diverse aromatic, heterocyclic and aliphatic nitriles, and as well as nitro compounds to primary amines (>65 examples). The synthetic and practical utility of this novel non-noble metal-based hydrogenation protocol is demonstrated by upscaling several reactions to multigram-scale and recycling of the catalyst.

Hydroxide‐Membrane‐Coated Pt3Ni Nanowires as Highly Efficient Catalysts for Selective Hydrogenation Reaction

AbstractRational design of effective catalysts with both high activity and selectivity is highly significant and desirable for hydrogenation reaction. In this paper, for the first time an efficient approach to controllably construct 1D metal nanowires (NWs) coated with hydroxide (NixM(OH)2 (M = Mn, Fe, Co, Cu, and Al)) membranes as highly active and selective hydrogenation catalysts is reported. The optimized Ni32Cu(OH)2 membrane coated Pt3Ni nanowires show much enhanced selectivity of 87.9% for the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde instead of hydrocinnamyl alcohol, in contrast with the pristine Pt3Ni nanowires and Pt3Ni nanowires on Ni(OH)2 membranes. The enhanced selectivity of Pt3Ni@Ni32Cu(OH)2‐2 NWs is ascribed to confinement/poisoning effects of the coated Ni32Cu(OH)2 membranes as well as the intimate interaction between the Pt3Ni NWs and Ni32Cu(OH)2 membranes, as confirmed by X‐ray photoelectron spectroscopy. The coated structures also show good stability after five recycle runs. The present work highlights the importance of surface engineering for the design of multicomponent composites with desirable activity and selectivity toward hydrogenation reaction and beyond.

Immobilized phosphine–phosphite rhodium complexes: highly active and enantioselective catalysts for asymmetric hydrogenation under continuous flow conditions

The asymmetric hydrogenation of benchmark substrates dimethyl itaconate and (Z)-α-acetamidocinnamic acid methyl ester with chiral pentane-2,4-diyl-based phosphine–phosphite Rh complexes immobilized on the support with heteropolyacid (phosphotungstic acid) as anchoring agent has been studied. The complexes have been supported on commercially available Al2O3 by the Augustine method. The novel heterogeneous catalysts were applied in a high-throughput flow reactor. The effect of the pressure, temperature, substrate concentration, and flow rate was thoroughly screened to optimize reaction conditions. The immobilized catalysts proved to be remarkably stable and could be used 6 h in the microfluidic-based reactor without a significant loss of activity and selectivity. Furthermore, under optimized conditions, the hydrogenation product could be obtained with high activity (TOF >2000 h−1) and enantioselectivity (up to 99% ee). As the first precedent, the potential of supported Rh(P-OP)-complexes under flow conditions has been presented.

Effect of Vanadium Introduction on the Activity of NiMo/Al2O3 Catalysts in the Hydrotreating of Diesel Fractions

The influence of the introduction of V2O5 into NiMo/Al2O3 catalysts on their activity in hydrodesulfurization (HDS) and hydrogenation reactions of the components of petroleum fractions has been studied. The activity of the synthesized catalysts has been determined in the straight-run diesel and light coker gas oil hydrotreating processes in a flow-through unit under hydrogen pressure. The most active catalyst for HDS and hydrogenation of polycyclic aromatic hydrocarbons has been synthesized using VMo12 heteropoly compounds: the activity increases by 6–10 and 11–13 wt % in HDS and PAH hydrogenation, respectively, at different temperatures. It has been shown that the activity of the regenerated catalyst further impregnated with the vanadium compound in HDS and PAH hydrogenation increases by 2–5 rel. %, as compared to the regenerated catalyst.

Cucurbit[6]uril-Stabilized Palladium Nanoparticles as a Highly Active Catalyst for Chemoselective Hydrogenation of Various Reducible Groups in Aqueous Media

Herein, we report the synthesis, characterization, and application of uniformly dispersed palladium nanoparticles supported on cucurbit[6]uril. The 2.56 wt% Pd was loaded on cucurbit[6]uril by impregnation method. Cucurbit[6]uril is a macrocyclic compound in which six glycoluril units are joined with twelve methylene bridges which not only act as support but also helped in stabilizing Pd nanoparticles. The synthesized catalyst was thoroughly characterized by various physicochemical methods. The high resolution transmission electron microscopic analysis revealed the uniform distribution of Pd nanoparticles with average size of ∼3 nm over the cucurbit[6]uril surface. Furthermore, the synthesized catalyst was used for the chemoselective hydrogenation of various reducible (epoxide, olefin, carbonyls, nitrile, azo, imines and nitroarenes) groups with excellent conversion, selectivity (> 99%) and high turnover frequency (up to 2,05,882 h−1) in aqueous and in some cases with water-THF mixture. Also, the catalyst was successfully recycled several times (>10 times) without losing any significant conversion and selectivity. Moreover, the leaching results were confirmed by analyzing reaction mixture by inductively coupled plasma atomic emission spectroscopy. Furthermore, the kinetic studies reveal the reaction rate depends on substrate concentration. The reaction mechanism was investigated by studying the reaction through drift FTIR studies.

Microwave-assisted Ni–La/γ-Al2O3 catalyst for benzene hydrogenation

A series of Ni–La/γ-Al2O3 catalysts were prepared by adopting the methods of isometric impregnation and microwave impregnation. The catalysts were characterized with XRD, BET, and SEM, respectively. Inspecting the effects of adding La and the methods of impregnation on the hydrogenation activity of catalysts. The results show that adding a moderate amount of La promotes the dispersing of Ni on the carrier, the methods of microwave impregnation weaks the interaction between Ni and the carrier further, inhibits the formation of NiAl2O4, and the activity of catalyst prepared by the methods of microwave impregnation was significantly higher than that prepared by the methods of isometric impregnation. The hydrogenation activity of the Ni–La/γ-Al2O3 (WB) dipped with n(Ni): n(La) = 4: 1, microwave irradiation time 30 min with power 600W as well as calcined at 400°C exhibited the best performance. The conversion rate is 91.21% with reaction conditions: T = 160°C, p = 0.8 MPa, air speed 5 h–1, n(H2): n(benzene) = 2: 1.

The Catalytic Hydrogenation of Maleic Anhydride on CeO2−δ-Supported Transition Metal Catalysts

The proper selection of transition metals and support is pivotal to the design of active and selective catalysts for maleic anhydride hydrogenation (MAH). Herein, the M/CeO2−δ (M = Co, Ni, Cu, respectively) catalysts with pre-optimised metal loading of 10 wt % were prepared via a wet impregnation method and well characterized to corroborate their MAH performance with the properties of metal, support and the M/CeO2−δ catalysts. The results revealed that the metal dispersion on the catalyst declines in the order of Ni/CeO2−δ > Co/CeO2−δ > Cu/CeO2−δ, similar to the apparent activity for maleic anhydride (MA) transformation to succinic anhydride (SA). The hydrogenolysis of SA to γ-butyrolactone (GBL) occurs on Ni/CeO2−δ and Co/CeO2−δ only when the MA → SA transformation completing. The Ni/CeO2−δ displays superior activity and selectivity to Co/CeO2−δ in both MA → SA and SA → GBL reactions, while the Cu/CeO2−δ and CeO2−δ are both inert for SA → GBL hydrogenolysis. The MA hydrogenation to SA follows the first order kinetic law on the Ni/CeO2−δ and Co/CeO2−δ catalysts yet a more complex kinetic characteristics observed on the Cu/CeO2−δ. The distinct catalytic hydrogenation behaviours of the M/CeO2−δ catalysts are assigned to the synergism of dispersion and electronic configuration of the transition metals and oxygen vacancies.