Hydrogen Transfer Process Research Articles

Magnetic Fe3O4 nanoparticles and ZrO2-doped mesoporous MCM-41 as a monolithic multifunctional catalyst for γ-valerolactone production directly from furfural

A magnetically-recoverable multifunctional catalyst (Fe3O4/ZrO2@MCM-41) was tailored by the impregnation of ZrO2 supported on mesoporous MCM-41 coated Fe3O4 nanoparticles, which successfully served as a monolithic catalyst for the cascade conversion of furfural (FAL) giving high yield to γ-valerolactone (GVL), a versatile platform molecule. The ordered hexagonal framework of the parent MCM-41 well reserved after the embedding of Fe3O4 and ZrO2. The incorporation of Fe3O4 could not only impart the catalyst with a strong magnetism, but also tune its acidity to promote GVL production. An impressive yield of 85% was accomplished straight from FAL processing with iso-propanol as a hydrogen donor and solvent. The kinetic study demonstrated higher activation energy for levulinate-to-GVL step (86.9 kJ/mol) than FAL transfer hydrogenation (35.0 kJ/mol) and subsequent alcoholysis process (51.0 kJ/mol). The catalyst could be fully recovered by an external magnetic field and showed good reusability. The sustainability of this conversion represents greatly improved by the process intensification based on one-pot reaction, magnetically-recoverable multifunctional catalyst, and mild operating conditions without using gaseous hydrogen.

Mechanical insight into the formation of H2S from thiophene pyrolysis: The influence of H2O

The thermal utilization of waste rubber is accompanied by the release of sulfur, and the release of H2S to the gas phase is one of the crucial issues. In this work, density functional theory (DFT) calculations and wave function analysis were employed to explore the possible formation pathways of H2S and its precursor (·SH radical) during the pyrolysis of thiophene in the presence of H2O. It indicates that H2O affects the decomposition of thiophene and the formation of H2S in two patterns. First, H2O can participate in the hydrogen transfer process by acting as a catalyst or generating weak hydrogen bonds with thiophene. In this way, the hydrogen transfer reactions are promoted with lower energy barriers, and thus the formation of H2S is facilitated by H2O without changing the pyrolysis pathways. Secondly, H2O can saturate the thiophene ring by addition reactions and alter the generation pathways of H2S significantly. The energy barriers can be decreased with one or two CC bonds of thiophene being saturated. The completely saturated thiophene results in a greater decline of the overall energy barriers for H2S formation. H2O provides the H atom for H2S in the second pattern. Due to the combination of the two influence patterns, the release of H2S can be promoted greatly in the presence of H2O. The present study aims to lay a foundation for the clean thermal utilization of thiophene/rubber and to inspire the advance of desulfurization techniques.

Postsynthetic Modification of Half-Sandwich Ruthenium Complexes by Mechanochemical Synthesis

A mild and environmentally friendly method to synthesize half-sandwich ruthenium complexes through the Wittig reaction between an aldehyde-tagged half-sandwich ruthenium complex and phosphorus ylide mechanochemically is reported herein. The mechanochemical synthesis of valuable half-sandwich ruthenium complexes resulted in a fast reaction, good yield with simple workup, and the avoidance of harsh reaction conditions and organic solvents. The synthesized half-sandwich ruthenium complexes exhibited high catalytic activity for transfer hydrogenation of ketones using 2-propanol as the hydrogen source and solvent. Density functional theory was carried out to propose a mechanism for the transfer hydrogenation process. The modeling suggests the importance of the labile p-cymene ligand in modulating the reactivity of the catalyst.

Insights into the Interfacial Effects in Heterogeneous Metal Nanocatalysts toward Selective Hydrogenation.

Heterogeneous metal catalysts are distinguished by their structure inhomogeneity and complexity. The chameleonic nature of heterogeneous metal catalysts have prevented us from deeply understanding their catalytic mechanisms at the molecular level and thus developing industrial catalysts with perfect catalytic selectivity toward desired products. This Perspective aims to summarize recent research advances in deciphering complicated interfacial effects in heterogeneous hydrogenation metal nanocatalysts toward the design of practical heterogeneous catalysts with clear catalytic mechanism and thus nearly perfect selectivity. The molecular insights on how the three key components (i.e., catalytic metal, support, and ligand modifier) of a heterogeneous metal nanocatalyst induce effective interfaces determining the hydrogenation activity and selectivity are provided. The interfaces influence not only the H2 activation pathway but also the interaction of substrates to be hydrogenated with catalytic metal surface and thus the hydrogen transfer process. As for alloy nanocatalysts, together with the electronic and geometric ensemble effects, spillover hydrogenation occurring on catalytically "inert" metal by utilizing hydrogen atom spillover from active metal is highlighted. The metal-support interface effects are then discussed with emphasis on the molecular involvement of ligands located at the metal-support interface as well as cationic species from the support in hydrogenation. The mechanisms of how organic modifiers, with the ability to induce both 3D steric and electronic effects, on metal nanocatalysts manipulate the hydrogenation pathways are demonstrated. A brief summary is finally provided together with a perspective on the development of enzyme-like heterogeneous hydrogenation metal catalysts.

Hf-MOF catalyzed Meerwein−Ponndorf−Verley (MPV) reduction reaction: Insight into reaction mechanism

Hf-MOF-808 exhibits excellent activity and specific selectivity on the hydrogenation of carbonyl compounds via a hydrogen transfer strategy. Its superior activity than other Hf-MOFs is attributed to its poor crystallinity, defects and large specific surface area, thereby containing more Lewis acid-base sites which promote this reaction. Density functional theory (DFT) computations are performed to explore the catalytic mechanism. The results indicate that alcohol and ketone fill the defects of Hf-MOF to form a six-membered ring transition state (TS) complex, in which Hf as the center of Lewis stearic acid coordinates with the oxygen of the substrate molecule, thus effectively promoting hydrogen transfer process. Other reactive groups, such as –NO2, C = C, -CN, of inadequate hardness or large steric hindrance are difficult to coordinate with Hf, thus weakening their catalytic effect, which explains the specific selectivity Hf-MOF-808 for reducing the carbonyl group.

Hydrogen-free hydrogenation of furfural to furfuryl alcohol and 2-methylfuran over Ni and Co-promoted Cu/γ-Al2O3 catalysts

Catalytic transformation of furfural to furfuryl alcohol and 2-methylfuran without H2 supply toward transfer hydrogenation process using 2-propanol as a H2 source was systematically investigated over the bimetallic NiCuAl and CoCuAl catalysts in comparison with the monometallic CuAl, NiAl, and CoAl catalysts. The XRD analysis confirmed the generation of Ni-Cu and Co-Cu alloys after the reduction in presence of H2. The interaction between Cu and Ni or Co resulted in a simplicity of the reduction behavior of Ni and Co species observed in H2-TPR experiments. It was evident from pyridine adsorption FTIR analysis that the formation of bimetallic Ni-Cu and Co-Cu alloys apparently improved the stronger Lewis acidic sites. The influences of reaction temperature and time were examined and optimized to maximize the yields of furfuryl alcohol and 2-methylfuran. The highest two major products yield and selectivity with lower by-products were obtained over the NiCuAl and CoCuAl catalysts compared with the CuAl and NiAl catalysts. The superior performance of the bimetallic catalysts was attributed to the stronger Lewis acidic centre on the catalyst surface. The CoCuAl catalyst was found to have lower catalyst deactivation and carbon deposition among the CuAl and NiCuAl catalysts under H2-free atmosphere.

The effect of introducing Ga on the ZSM-5-catalyzed methanol to aromatics reaction: taking methylcyclopentane to benzene as an example.

Naphthenes are key intermediates in the formation of aromatic compounds during the methanol to aromatics (MTA) reaction, and the dehydrogenation process is more important than the hydrogen transfer process. Theoretical studies were performed to investigate the methylcyclopentane, which represents a naphthene, to benzene MTA process catalyzed by ZSM-5 before and after introducing Ga, showing that Ga-ZSM-5 was more favorable for carrying out the reaction than two H-type ZSM-5 (H-Z1 and H-Z2) models. H-Z1 and H-Z2 are favorable for the transfer of H during ring expansion reactions and the reformation of Brønsted acids, but the dehydrogenation reactions involving H-Z1 and H-Z2 require high free-energy barriers to be overcome. Although introducing Ga to ZSM-5 is not conducive to the transfer of H after dehydrogenation, it can reduce the extremely high dehydrogenation free-energy barrier compared with H-Z1 and H-Z2; this is mainly because Ga at dehydrogenation active centers, [GaH]2+, can accept electrons and donate them to the H atoms of [GaH]2+, giving H negative charge and making it easy to combine with positive B-acid H atoms that come from methylcyclopentane, cyclohexene, and cyclohexadiene to produce H2. Also, analysis of the transition state structures of all DH processes shows that Ga-ZSM-5 is more favorable for promoting the combination of H to produce H2 than H-Z1 and H-Z2.

Istraživanje performansi višestepene adsorpcione toplotne pumpe na bazi vodonika

Metal hydrides are broadly investigated, for more than three decades, towards its application for cooling and heating applications. As a continuation of those works, in the present study, authors have investigated the performance of a multi-stage sorption heat pump for multiple cooling and heating outputs. The metal hydrides selected for the present study are Ti0.98Zr0.02V0.43Fe0.09Cr0.05Mn1.5, MmNi4.7Al0.3, LaNi4.8Al0.2 and Zr0.9Ti0.1 Cr0.9Fe1.1, with the operating temperature range as 20°C for cooling output, 45°C for heating output and 140°C for heat supply. The system produces three cooling and four heating outputs with only one heat input. The performance of the system is investigated, via finite volume approach, in terms of hydrogen interaction within the coupled beds, bed temperature variations and heat interactions during hydrogen transfer processes. The minimum temperature observed during the cooling process is 0.5°C, whereas the maximum temperature observed during the heating process is 60°C, which shows that the obtained temperature is capable of space air-conditioning. On the other hand, the maximum cooling and heating outputs, at a particular instant of time, are estimated at 361 W and 402 W, respectively with a heat supply of 23 W.

A Compartmentalized‐type Bifunctional Magnetic Catalyst for One‐pot Aerobic Oxysulfonylation and Asymmetric Transfer Hydrogenation

AbstractUtilization of the confined cavity of the mesoporous silica, the exploration of the synergetic catalysis process for sequential organic transformations has great significance in asymmetric catalysis. In this study, the yolk‐shell‐structured magnetic nanoparticles with the chiral Ru/diamine species within the nanochannels of the outer mesoporous silica shell and the FeCl3 species on the inner magnet core are fabricated. The electron microscopy images and the structural characterizations disclose the uniformly distributed magnetic nanoparticles with the well‐defined single‐site ruthenium/diamine active centers onto the outer silica shell. As a yolk‐shell‐structured bifunctional magnet catalyst, the FeCl3 species enables an efficient aerobic oxysulfonylation between aryl‐substituted terminal alkynes and sodium sulfinates to the β‐keto sulfones intermediates, and the ruthenium/diamine species sequentially reduces the in‐situ generated intermediate to the chiral β‐hydroxysulfones products. As we envision, this one‐pot aerobic oxysulfonylation/asymmetric transfer hydrogenation process affords various chiral β‐hydroxysulfones in high yields with excellent enantioselectivities. Furthermore, this magnetic catalyst can also be conveniently recovered via an additional outer magnet and repeatedly recycled, showing a potential application in industrial interest.

A novel interaction mechanism in lignin pyrolysis: Phenolics-assisted hydrogen transfer for the decomposition of the β-O-4 linkage

Abstract Pyrolysis of lignin involves complex unimolecular decomposition and bimolecular interaction mechanisms. Unimolecular decomposition of lignin model compounds has been widely investigated, while bimolecular interactions are far from well elucidated. Currently, only two radical reaction-based interactions, i.e., hydrogen abstraction and hydrogen-bond-induced homolysis mechanisms, have been proposed to explain the interactions in the lignin pyrolysis process, which ignores the concerted reaction-based interactions involving the pyrolytic products of lignin. Particularly, a large number of phenolics are produced in the pyrolysis of lignin, which can further affect the concerted pyrolysis reactions of lignin. In the present work, a novel interaction mechanism, phenolics-assisted hydrogen transfer (phenolics-AHT) process for the concerted reactions, is confirmed and carefully investigated. Phenylethyl phenyl ether (PPE), a typical β-O-4 lignin dimer, is used as the model compound to reveal the phenolics-AHT mechanism in the lignin pyrolysis system. Density functional theory (DFT) calculation, electrostatic potential (ESP) analysis, and fast pyrolysis experiment results are combined to reveal that the phenolic products participate in the hydrogen transfer process of the concerted Maccoll elimination reaction by means of their phenolic hydroxyl structures and significantly reduce the energy barrier, thus promoting the cleavage of the β-O-4 linkage. On the contrary, phenolics-AHT has no obvious effect on the concerted retro-ene fragmentation. At medium pyrolysis temperatures, the hydrogen transfer processes induced by phenolic products play a more significant role in the dissociation of the β-O-4 linkage than the hydrogen abstraction induced by radicals, due to the limited amount of free radicals. In addition, DFT calculation results further suggest that decarbonylation, decarboxylation, dehydration, tautomerism, and other concerted reactions can also be promoted by phenolics-AHT.

Reduction of Nitroarenes via Catalytic Transfer Hydrogenation Using Formic Acid as Hydrogen Source: A Comprehensive Review

AbstractThe reduction of nitroarenes to the corresponding aromatic amines is one of the most popular reactions in organic synthesis with significant application in pharmaceutical and manufacture industry. In the last decades, many efforts have been devoted to the design highly effective, chemoselective, low‐cost and eco‐friendly protocols. In this sense, the reduction of nitroarenes via transfer hydrogenation using formic acid as hydrogen source has gained great relevance with tremendous advance over the last year as an attractive and competitive strategy to classical protocols. The efforts have mainly been focused on the discovery of efficient catalyst based on advanced mesoporous support material loaded with transition metals or metallic nanoparticles, the optimization conditions for non‐supported catalyst as well as convenient energy source to achieve an efficient and selective catalytic transfer hydrogenation (CTH) at room temperature. In the present review, several examples of reduction of nitroarenes using formic acid are shown as well as a comprehensive discussion about the role of catalyst, energy source and mechanism of reaction in the transfer hydrogenation process.

The Role of Imidazolium-Based Surface-Active Ionic Liquid to Restrain the Excited-State Intramolecular H-Atom Transfer Dynamics of Medicinal Pigment Curcumin: A Theoretical and Experimental Approach.

The naturally occurring polyphenolic compound curcumin has shown various medicinal and therapeutic effects. However, there are various challenges associated with curcumin, which limits its biomedical applications, such as its high degradation rate and low aqueous solubility at neutral and alkaline pH. In the present study, efforts have been directed towards trying to resolve such issues by encapsulating curcumin inside the micelles formed by imidazolium-based surface-active ionic liquid (SAIL). The shape and size of the micelles formed by the SAIL have been characterized by using DLS analysis as well as TEM measurements. The photo-physics of curcumin in the presence of ionic liquid (IL) and also with the addition of salt (NaCl) has been explored by using different optical spectroscopic tools. The time-dependent absorption studies have shown that there is relatively higher suppression in the degradation rate of curcumin after encapsulation by the imidazolium-based SAIL in an aqueous medium. The TCSPC studies have revealed that there is deactivation in the nonradiative intramolecular hydrogen transfer process of curcumin in the presence of IL micelles as well as with the addition of salt. Furthermore, the time-dependent fluorescence anisotropy measurement has been carried out to figure out the location of curcumin inside the micellar system. In order to correlate all experimental findings, density functional theory (DFT) and classical molecular dynamics (MD) simulations at neutral pH media have been performed. It has been found that the van der Waals force of interactions plays a major role in the stabilization of curcumin in the micelles rather than the coulombic forces. It also has been observed that the van der Waals interactions remain unaffected in the presence of salt. However, as revealed by the MD simulation results, the micelles are found to be more compact in size after the addition of salt. The RMSD results show that the micelles formed by the SAIL achieve greater stability after a particular time constraint. Our results have divulged that the SAIL could act as a promising drug delivery system.

Controlling N-doping type in carbon to boost single-atom site Cu catalyzed transfer hydrogenation of quinoline

Single-atom site (SA) catalysts on N-doped carbon (CN) materials exhibit prominent performance for their active sites being M-Nx. Due to the commonly random doping behaviors of N species in these CN, it is a tough issue to finely regulate their doping types and clarify their effect on the catalytic property of such catalysts. Herein, we report that the N-doping type in CN can be dominated as pyrrolic-N and pyridinic-N respectively through compounding with different metal oxides. It is found that the proportion of distinct doped N species in CN depends on the acidity and basicity of compounded metal oxide host. Owing to the coordination by pyrrolic-N, the SA Cu catalyst displays an enhanced activity (two-fold) for transfer hydrogenation of quinoline to access the valuable molecule tetrahydroquinoline with a good selectivity (99%) under mild conditions. The higher electron density of SA Cu species induced by the predominate pyrrolic-N coordination benefits the hydrogen transfer process and reduces the energy barrier of the hydrogenation pathway, which accounts for the improved catalytic effeciency.

Efficient Quantum Mechanical Calculations of Mode-Specific Tunneling Splittings upon Fundamental Excitation in the Dimer of Formic Acid.

The formic acid dimer (FAD) is an important benchmark system for understanding the double hydrogen transfer process. Most recently, Zhang et al. measured a few tunneling splittings upon fundamental excitation of FAD precisely (Zhang, Y. et al. J. Chem. Phys. 2017, 146, 244306); however, relevant theoretical studies are very limited. Here, we present a multidimensional quantum dynamics study on mode-specific tunneling splittings upon fundamental excitation in FAD with an efficient theoretical scheme developed by our group in which the process-oriented basis function customization strategy is combined with the preconditioned inexact spectral transform method. Various mode-specific tunneling splittings upon fundamental excitation are systematically calculated, and interesting mode-specific excitation effects on tunneling rate are identified. In particular, the calculated tunneling splittings for the ν22 and ν21 states are in good agreement with experiment, and the remarkable mode-specific suppression effects upon excitation should result from that the antisymmetric vibrational modes hinder the concerted double H-transfer. The present work is helpful to acquire a better understanding of the mode-specific excitation effects on tunneling processes.

Ruthenium‐Catalyzed Dehydrogenation of Alcohols with Carbodiimide via a Hydrogen Transfer Mechanism

Ruthenium‐catalyzed oxidative dehydrogenation of alcohols using carbodiimide as an efficient hydrogen acceptor has been developed. The protocol exhibits wide substrate scope with good to excellent yields. The results of the kinetic analysis indicated that the reaction mechanism includes the hydrogen transfer process and that the addition of carbodiimide is essential for the reaction system, and the resulting amidine also could react as a hydrogen acceptor.

Desaturation via Redox-Neutral Hydrogen Transfer Process: Synthesis of 2-Allyl Anilines, Mechanism and Applications.

SummaryAn unprecedented desaturation method via redox-neutral hydrogen transfer process has been disclosed under mild conditions for the selective formation of terminal alkene with alkyl diazo compounds and aza-o-QMs. The control experiments and DFT calculations suggest that the visible light was introduced as a key parameter to enhance the reactivity via a radical process in the formation of closed-shell cyclopropane intermediate, followed by a ring opening and redox-neutral hydrogen transfer process to give the desaturated product. The high regioselectivity in this transformation is enabled by the internal amino species as an ancillary group (AG) in the final olefin formation step. This method provides a missing link in the expeditious preparation of synthetically useful 2-allyl anilines with broad substrate generality. Further applications of these generated products in N-heterocycle construction, including 5- and 6-membered rings with structural diversity, have been tactfully explored, which highlight the potential in methodology development and drug discovery.

Ground state potential energy surface of methanimine plus 3NH reaction: Rates of atmospheric reactions and validated mechanisms

Methanimine (H2CNH) and imidogen (NH) are well known interstellar species and also are essential for biomolecules. In this work, the elementary reactions of H2CNH + 3NH are studied on the triplet ground state of the potential energy surface at the atmospheric conditions. Thermodynamic (enthalpy, free energy, and entropy in the standard condition) and kinetic (rate constant) parameters are computed by using the DFT-M06-2X, MP2, and CCSD(T) methods in connection with the aug-cc-pVTZ basis set. For all pathways, the rate constants were calculated in the temperature range 300–3000 K and at the atmospheric pressure by using the conventional transition state and RRKM theories at the M06-2X/aug-cc-pVTZ level. The addition processes that lead to forming the stable adducts, are thermodynamically favorable, while the hydrogen transfer processes are kinetically favorable. So, the H2CN + NH2 and trans-HNCH + NH2 adducts are kinetically main product channels, and production of the H3CNNH is the main reaction in the thermodynamic viewpoint.

Formation and Fate of Formaldehyde in Methanol-to-Hydrocarbon Reaction: In Situ Synchrotron Radiation Photoionization Mass Spectrometry Study.

HCHO has been confirmed as an active intermediate in the methanol-to-hydrocarbon (MTH) reaction, and is critical for interpreting the mechanisms of coke formation. Here, HCHO was detected and quantified during the MTH process over HSAPO-34 and HZSM-5 by in situ synchrotron radiation photoionization mass spectrometry. Compared with conventional methods, excellent time-resolved profiles were obtained to study the formation and fate of HCHO, and other products during the induction, steady-state reaction, and deactivation periods. Similar formation trends of HCHO and methane, and their close correlation in yields suggest that they are derived from disproportionation of methanol at acidic sites. In the presence of Y2 O3 , the amount of HCHO changes, affecting the hydrogen-transfer processes of olefins into aromatics and aromatics into cokes. The yield of HCHO affects the aromatic-based cycle and the formation of ethylene, indicating that ethylene is mainly formed from the aromatic-based cycle.

Theoretical insight into the solvent effect on the stoichiometric reduction of carbonyl compounds by ammonia borane and N‐methyl amine borane

AbstractFor the traditional reduction of ketones and aldehydes, NH3BH3 (AB) and N‐methyl amine borane (M nAB) have been effective reducing agents. However, the reaction process is indefinite and different mechanisms have been proposed; also the solvent effect, which is closely related to the mechanism, has not been considered seriously. Here we employ density functional theory to carry out a comprehensive study on the mechanism. The calculated free energy of the concerted double hydrogen transfer process is lower than the hydroboration mechanism by 4.7 kcal/mol, which indicates that reduction of carbonyl by AB is likely due to be the concerted double hydrogen transfer in both aprotic (tetrahydrofuran) and protic (MeOH) solvents. For the reduction by M nAB, the corresponding free energies of all reactions are higher than those of AB. Meanwhile, the reduction of benzaldehyde by M nAB (n = 1, 2) also favors a concerted double hydrogen transfer rather than hydroboration.

Catalytic reduction of 1,4‐benzoquinone to hydroquinone via [FeFe]‐hydrogenase model complexes under mild conditions

AbstractBACKGROUNDHydroquinone (HQ) is an important fine chemical raw material and intermediate, which is widely used in chemistry industry. It is great significance to develop a new environmentally‐friendly synthesis method to produce HQ.RESULTSThree [FeFe]‐hydrogenase model complexes (μ‐budt)[Fe(CO)3]2[1; budt = SCH(CH3)CH2CH2)S], (μ‐budt)[Fe(CO)3][Fe(CO)2PPh3](2), and (μ‐bust)[Fe(CO)3]2 [3; bust = SCH(CH3)CH2CH2)S(O)] were synthesized by direct CO/L substitution or sulfur based oxygenation. The synthesized new complexes were fully characterized by FT‐IR, 1H NMR, 13C NMR and X‐ray crystallography. The electrochemical properties of these model complexes were investigated by cyclic voltammetry in CH2CI2 to evaluate the redox properties of the iron atoms. It was indicated that these new complexes are not only electrochemical catalysts for proton reduction of hydrogen, but also efficient catalysts for catalytic the transfer hydrogenation of BQ (1, 4‐benzoquinone) to prepare HQ under mild conditions. Especially,complex 2 exhibited the highest catalytic activity for reduction of BQ with methanol as the proton source, which gave a BQ conversion of 91 % and 72 % selectivity for HQ.CONCLUSIONSThe complex 2 can be a new type catalyst for catalytic reduction of BQ to HQ under mild reaction conditions. In addition, the Kinetics and mechanism were also investigated for a proposed transfer hydrogenation process. © 2019 Society of Chemical Industry