Preparation of nitrogen-doped carbon supported cobalt catalysts and its application in the reductive amination

Phase transition induced hydrogen activation for enhanced furfural reductive amination over a CoCu bimetallic catalyst

The synthesis of primary amines from renewable biomass and its derivatives through reductive amination has garnered significant attention. How to construct efficient non-noble-metal catalysts that enable low-temperature catalysis still remains challenging. Herein, we report a Cu-doped Co@CoO x heterostructure catalyst that features structural Co-CoCuO x bifunctional sites, which enable room temperature reductive amination of various aldehydes with 1.57-45 times higher efficiency than Co@CoO x , outperforming many reported non-noble and even noble metal catalysts. Experiments and DFT calculations indicate that Cu doping leads to a phase transition of Co from hcp to fcc, while electrons are transferred from Cu to Co, forming a dual active site with electron-rich Co closely interacting with CoCuO x . These electron-rich Co sites demonstrate excellent activity in the activation and dissociation of hydrogen, while the CuO x component facilitates hydrogen spillover at the CoCuO x interface, thus resulting in a highly efficient cooperative effect for the furfural (FAL) reductive amination. This work provides general guidance for the rational design of high-performance reductive amination catalysts for biomass upgrading.

Reductive Amination of Aldehyde and Ketone with Ammonia and H2 by an In Situ-Generated Cobalt Catalyst under Mild Conditions

Herein, we present the simplest approach for the synthesis of primary amines via reductive amination using H2 as a reductant and aqueous ammonia as a nitrogen source, catalyzed by amorphous Co particles. The highly active Co particles were prepared in situ by simply mixing commercially available CoCl2 and NaBH4/NaHBEt3 without any ligand or support. This reaction system features mild conditions (80 °C, 1-10 bar), high selectivity (99%), a wide substrate scope, simple operation, and easy separation of the catalyst. The successful large-scale application of this reaction in the production of primary amines suggests its potential industrial interest.

Employing Ammonia for the Synthesis of Primary Amines: Recent Achievements over Heterogeneous Catalysts

Primary amines represent highly privileged chemicals for synthesis of polymers, pharmaceuticals, agrochemicals, coatings, etc. Consequently, the development of efficient and green methodologies for the production of primary amines are of great importance in chemical industry. Owing to the advantages of low cost and ease in availability, ammonia is considered as a feasible nitrogen source for synthesis of N-containing compounds. Thus, the efficient transformation of ammonia into primary amines has received much attention. In this review, the commonly applied synthetic routes to produce primary amines from ammonia were summarized, including the reductive amination of carbonyl compounds, the hydrogen transfer amination of alcohols, the hydroamination of olefins and the arylation with ammonia, in which the catalytic performance of the recent heterogeneous catalysts is discussed. Additionally, various strategies to modulate the surface properties of catalysts are outlined in conjunction with the analysis of reaction mechanism. Particularly, the amination of the biomass-derived substrates is highlighted, which could provide competitive advantages in chemical industry and stimulate the development of sustainable catalysis in the future. Ultimately, perspectives into the challenges and opportunities for synthesis of primary amines with ammonia as N-resource are discussed.

New Insights into N-Doped Porous Carbons as Both Heterogeneous Catalysts and Catalyst Supports: Opportunities for the Catalytic Synthesis of Valuable Compounds

Among the vast class of porous carbon materials, N-doped porous carbons have emerged as promising materials in catalysis due to their unique properties. The introduction of nitrogen into the carbonaceous matrix can lead to the creation of new sites on the carbon surface, often associated with pyridinic or pyrrolic nitrogen functionalities, which can facilitate various catalytic reactions with increased selectivity. Furthermore, the presence of N dopants exerts a significant influence on the properties of the supported metal or metal oxide nanoparticles, including the metal dispersion, interactions between the metal and support, and stability of the metal nanoparticles. These effects play a crucial role in enhancing the catalytic performance of the N-doped carbon-supported catalysts. Thus, N-doped carbons and metals supported on N-doped carbons have been revealed to be interesting heterogeneous catalysts for relevant synthesis processes of valuable compounds. This review presents a concise overview of various methods employed to produce N-doped porous carbons with distinct structures, starting from diverse precursors, and showcases their potential in various catalytic processes, particularly in fine chemical synthesis.

Recent Catalytic Advances on the Sustainable Production of Primary Furanic Amines from the One-Pot Reductive Amination of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (5-HMF) represents a well-known class of lignocellulosic biomass-derived platform molecules. With the presence of many reactive functional groups in the structure, this versatile building block could be valorized into many value-added products. Among well-established catalytic transformations in biorefinery, the reductive amination is of particular interest to provide valuable N-containing compounds. Specifically, the reductive amination of 5-HMF with ammonia (NH₃ ) and molecular hydrogen (H₂ ) offers a straightforward and sustainable access to primary furanic amines [i. e., 5-hydroxymethyl-2-furfuryl amine (HMFA) and 2,5-bis(aminomethyl)furan (BAMF)], which display far-reaching utilities in pharmaceutical, chemical, and polymer industries. In the presence of heterogeneous catalysts contanining monometals (Ni, Co, Ru, Pd, Pt, and Rh) or bimetals (Ni-Cu and Ni-Mn), this elegant pathway enables a high-yielding and chemoselective production of HMFA/BAMF compared to other synthetic routes. This Review aims to present an up-to-date highlight on the supported metal-catalyzed reductive amination of 5-HMF with elaborate studies on the role of metal, solid support, and reaction parameters. Besides, the recyclability/adaptability of catalysts as well as the reaction mechanism are also provided to give valuable insights into this potential 5-HMF valorization strategy.

In-situ reconstruction of CoBOx enables formation of Co for synthesis of benzylamine through reductive amination

Cobalt (Co) as a substitute of noble-metal catalysts shows high catalytic capability for production of the widely used primary amines through the reductive amination. However, the synthesis of Co catalysts usually involves the introduction of organic compounds and the high-temperature pyrolysis, which is complicated and difficult for large-scale applications. Herein, we demonstrated a facile and efficient strategy for the preparation of Co catalysts through the in situ reconstruction of cobalt borate (CoBO_x) during the reductive amination, delivering a high catalytic activity for production of benzylamine from benzaldehyde and ammonia. Initially, CoBO_x was transformed into Co(OH)₂ through the interaction with ammonia and subsequently reduced to Co nanoparticles by H₂ under the reaction environments. The in situ generated Co catalysts exhibited a satisfactory activity and selectivity to the target product, which overmatched the commonly used Co/C, Pt or Raney Ni catalysts. We anticipate that such an in situ reconstruction of CoBO_x by reactants during the reaction could provide a new approach for the design and optimization of catalysts to produce primary amines.

Ambient-Temperature Reductive Amination of 5-Hydroxymethylfurfural Over Al2 O3 -Supported Carbon-Doped Nickel Catalyst

An efficient catalytic system for the conversion of 5-hydroxymethylfurfural (HMF) into N-containing compounds over low-cost non-noble-metal catalysts is preferable, but it is challenging to reach high conversion and selectivity under mild conditions. Herein, an Al₂ O₃ -supported carbon-doped Ni catalyst was obtained via the direct pyrolysis-reduction of a mixture of Ni₃ (BTC)₂  ⋅ 12H₂ O and Al₂ O₃ , generating stable Ni⁰ species due to the presence of carbon residue. A high yield of 96 % was observed in the reductive amination of HMF into 5-hydroxymethyl furfurylamine (HMFA) with ammonia and hydrogen at ambient temperature. The catalyst was recyclable and could be applied to the ambient-temperature synthesis of HMF-based secondary/tertiary amines and other biomass-derived amines from the carbonyl compounds. The significant performance was attributable to the synergistic effect of Ni⁰ species and acidic property of the support Al₂ O₃ , which promoted the selective ammonolysis of the imine intermediate while inhibiting the potential side reaction of over-hydrogenation.

Solvent-Free Hydrogenation of 5-Hydroxymethylfurfural and Furfural to Furanyl Alcohols and their Self-Condensation Polymers

2,5-Bis(hydroxymethyl)furan (BHMF) as well as furfuryl alcohol (FFA) are considered as highly valuable biomass-derived alcohols resembling aromatic monomers in polymer synthesis. Herein, a series of cobaltic nitrogen-doped carbon (Co-NC) catalysts calcinated at different temperatures were synthesized and tested for the solvent-free hydrogenation of 5-hydroxymethylfurfural (HMF) to prepare BHMF. It was found that the Co-NC catalyst calcinated at 600 °C (Co-NC-600) exhibited a superior catalytic activity in the hydrogenation reaction mainly due to the doping of graphitic N, which probably facilitated the polarization of H₂ to afford H⁺ and H^- . Consequently, Co-NC-600 offered a high BHMF/FFA yield greater than 90 % with a nearly complete conversion of HMF/furfural (FF) at the optimal conditions (80 °C, 4 h, and 5 MPa H₂ ). After the hydrogenation reaction, Co-NC catalyst was facilely recycled by magnetic separation, and the obtained BHMF/FFA was then successfully transformed into hypercrosslinked polymers with an excellent CO₂ /H₂ storage capacity comparable to aromatic hydroxymethyl polymers. Therefore, this is a novel and facile two-step pathway for the conversion of biomass-derived HMF/FF towards functional polymers from both industrial and environmental perspectives.

Advances in the Catalytic Reductive Amination of Furfural to Furfural Amine: The Momentous Role of Active Metal Sites

One-pot synthesis of sustainable primary amines by catalytic reductive amination of bio-based carbonyl compounds with NH₃ and H₂ is emerging as a promising and robust approach. The primary amines, especially furfuryl amine (FUA) derived from furfural (FUR), with a wide range of applications from pharmaceuticals to agrochemicals, have attracted much attention due to their versatility. This Review is majorly comprised of two segments on the reductive amination of FUR to FUA, one with precious (Ru, Pd, Rh) and the other with non-precious (Co, Ni) metals on different supports and in various solvent systems in the presence of NH₃ and H₂ . The active metal sites generated on multiple supports are accentuated with experimental evidence based on CO-diffuse reflectance infrared Fourier-transform spectroscopy, H₂ temperature-programmed reduction, X-ray photoelectron spectroscopy, and calorimetry. Moreover, this Review comprehensively describes the role of acidic and basic support for the metal on the yield of FUA. Overall, this Review provides an insight into how to design and develop an efficiently robust catalyst for the selective reductive amination of a broad spectrum of carbonyl compounds to corresponding amines.

Primary amine synthesis by hydrogen-involving reactions over heterogeneous cobalt catalysts

Co/SiO2 exhibited high selectivity for primary amines in hydrogenation of nitriles and reductive amination of carbonyl compounds.

Modulated electronic structure of Pd nanoparticles on Mg(OH)2 for selective benzonitrile hydrogenation into benzylamine at a low temperature

Pd nanoparticles with enriched electronic density anchored on Mg(OH)2 realize selective benzonitrile hydrogenation to benzylamine at low temperature in the absence of additives, in an atom-economical and green approach for synthesis of highly value-added primary amines.

In–Co–Zn/C–N catalysts derived from ZIFs for selective hydrogenation of CO2 into methanol

In2O3 combines ZIF derived Co–Zn/C–N catalyst perform a CO2 conversion of 7.0% with methanol selectivity over 77% and the STY of methanol is 3.3 mmol gcat−1 h−1 under the condition of CO2/H2 = 3 : 1, 2 MPa, 300 °C and GHSV = 6 L gcat−1 h−1.

Nanoparticles and single atoms of cobalt synergistically enabled low-temperature reductive amination of carbonyl compounds

Low-temperature and selective reductive amination of carbonyl compounds is a highly promising approach to access primary amines. However, it remains a great challenge to conduct this attractive route efficiently over earth-abundant metal-based catalysts. Herein, we designed several Co-based catalysts (denoted as Co@C–N(x), where x represents the pyrolysis temperature) by the pyrolysis of the metal–organic framework ZIF-67 at different temperatures. Very interestingly, the prepared Co@C–N(800) could efficiently catalyze the reductive amination of various aldehydes/ketones to synthesize the corresponding primary amines with high yields at 35 °C. Besides non-noble metal and mild temperature, the other unique advantage of the catalyst was that the substrates with different reduction-sensitive groups could be converted into primary amines selectively because the Co-based catalyst was not active for these groups at low temperature. Systematic analysis revealed that the catalyst was composed of graphene encapsulated Co nanoparticles and atomically dispersed Co–N_x sites. The Co particles promoted the hydrogenation step, while the Co–N_x sites acted as acidic sites to activate the intermediate (Schiff base). The synergistic effect of metallic Co particles and Co–N_x sites is crucial for the excellent performance of the catalyst Co@C–N(800). To the best of our knowledge, this is the first study on efficient synthesis of primary amines via reductive amination of carbonyl compounds over earth-abundant metal-based catalysts at low temperature (35 °C).

An earth-abundant Co-based catalyst, Co@C–N(800), could efficiently catalyze the reductive amination of carbonyl compounds into primary amines at 35 °C owing to the synergistic effect of Co nanoparticles and atomically dispersed Co–N_x sites.

Highly active heterogeneous hydrogenation catalysts prepared from cobalt complexes and rice husk waste

Highly active heterogeneous catalysts for the hydrogenation of nitro compounds were made by pyrolysis of rice husk waste impregnated with cobalt complexes followed by base-treatment. The catalysts show high selectivity and broad substrate scope.

Earth-abundant Metal-catalyzed Reductive Amination: Recent Advances and Prospect for Future Catalysis

Nitrogen-containing compounds, as an important class of chemicals, have been used widely in pharmaceuticals, materials synthesis. Transition metal-catalyzed reductive amination of an aldehyde or a ketone with ammonia or an amine has been proved to be an efficient and practical method for the preparation of nitrogen-containing compounds in academia and industry for a century. Given the above, several effective methods using transition metals have been developed in recent years. Noble transition metals like Pd, Pt, and Au-based catalysts have been predominately used in reductive amination. Because of their high prices, strict official regulations of residues in pharmaceuticals, and deleterious effects on the biological system, their industrial applications are severely hampered. With the increasing sustainable and environmental problems, the Earth-abundant transition metals including Ti, Fe, Co, Ni, and Zr have also been investigated for the reductive amination reaction and showed great potential to the advancement of sustainable and cost-effective reductive amination processes. This critical review will mainly summarize the work using Earth-abundant metals. The effects of different transition metals used in catalytic reduction amination were discussed and compared, and some suggestions were given. The last section highlights the catalytic activities of bi- and tri-metallic catalysts. Indeed, this latter family is very promising and simultaneously benefits from increased stability, and selectivity, compared to monometallic NPs, due to synergistic substrate activation. Few comprehensive reviews focusing on Earth-abundant transition metals catalyst has been published since 1948, although several authors reported some summaries dealing with one or the other part of this aspect. It is hoped that this critical review will inspire researchers to develop new efficient and selective earth-abundant metal catalysts for highly, environmentally sustainable reductive amination methods, as well as improve the pharmaceutical industry and related chemical synthesis company traditional method with the utilization of the green method widely.

Co-Catalyzed Synthesis of Primary Amines via Reductive Amination employing Hydrogen under very mild Conditions

Nanostructured and reusable 3d-metal catalysts that operate with high activity and selectivity in important chemical reactions are highly desirable. Here, a cobalt catalyst was developed for the synthesis of primary amines via reductive amination employing hydrogen as the reducing agent and easy-to-handle ammonia, dissolved in water, as the nitrogen source. The catalyst operates under very mild conditions (1.5 mol% catalyst loading, 50 °C and 10 bar H₂ pressure) and outperforms commercially available noble metal catalysts (Pd, Pt, Ru, Rh, Ir). A broad scope and a very good functional group tolerance were observed. The key for the high activity seemed to be the used support: an N-doped amorphous carbon material with small and turbostratically disordered graphitic domains, which is microporous with a bimodal size distribution and with basic NH functionalities in the pores.

Single-Crystal Cobalt Phosphide Nanorods as a High-Performance Catalyst for Reductive Amination of Carbonyl Compounds

The development of metal phosphide catalysts for organic synthesis is still in its early stages. Herein, we report the successful synthesis of single-crystal cobalt phosphide nanorods (Co₂P NRs) containing coordinatively unsaturated Co-Co active sites, which serve as a new class of air-stable, highly active, and reusable heterogeneous catalysts for the reductive amination of carbonyl compounds. The Co₂P NR catalyst showed high activity for the transformation of a broad range of carbonyl compounds to their corresponding primary amines using an aqueous ammonia solution or ammonium acetate as a green amination reagent at 1 bar of H₂ pressure; these conditions are far milder than previously reported. The air stability and high activity of the Co₂P NRs is noteworthy, as conventional Co catalysts are air-sensitive (pyrophorous) and show no activity for this transformation under mild conditions. P-alloying is therefore of considerable importance for nanoengineering air-stable and highly active non-noble-metal catalysts for organic synthesis.

General Synthesis of Secondary Alkylamines by Reductive Alkylation of Nitriles by Aldehydes and Ketones

The development of C-N bond formation reactions is highly desirable due to their importance in biology and chemistry. Recent progress in 3d metal catalysis is indicative of unique selectivity patterns that may permit solving challenges of chemical synthesis. We report here on a catalytic C-N bond formation reaction-the reductive alkylation of nitriles. Aldehydes or ketones and nitriles, all abundantly available and low-cost starting materials, undergo a reductive coupling to form secondary alkylamines and inexpensive hydrogen is used as the reducing agent. The reaction has a very broad scope and many functional groups, including hydrogenation-sensitive examples, are tolerated. We developed a novel cobalt catalyst, which is nanostructured, reusable, and easy to handle. The key seems the earth-abundant metal in combination with a porous support material, N-doped SiC, synthesized from acrylonitrile and a commercially available polycarbosilane.

Hydrodeoxygenation of sulfoxides into sulfides under mild conditions over a heterogeneous cobalt catalyst

A kind of nitrogen-doped carbon material and Al₂O₃ co-supported Co nanoparticle catalyst (Co–NC/Al₂O₃-500) demonstrated high activity, selectivity and stability for the hydrodeoxygenation of sulfoxides into sulfides.

Transition-Metal-Catalyzed Reductive Amination Employing Hydrogen

The reductive amination, the reaction of an aldehyde or a ketone with ammonia or an amine in the presence of a reducing agent and often a catalyst, is an important amine synthesis and has been intensively investigated in academia and industry for a century. Besides aldehydes, ketones, or amines, starting materials have been used that can be converted into an aldehyde or ketone (for instance, carboxylic acids or organic carbonate or nitriles) or into an amine (for instance, a nitro compound) in the presence of the same reducing agent and catalyst. Mechanistically, the reaction starts with a condensation step during which the carbonyl compound reacts with ammonia or an amine, forming the corresponding imine followed by the reduction of the imine to the alkyl amine product. Many of these reduction steps require the presence of a catalyst to activate the reducing agent. The reductive amination is impressive with regard to the product scope since primary, secondary, and tertiary alkyl amines are accessible and hydrogen is the most attractive reducing agent, especially if large-scale product formation is an issue, since hydrogen is inexpensive and abundantly available. Alkyl amines are intensively produced and use fine and bulk chemicals. They are key functional groups in many pharmaceuticals, agro chemicals, or materials. In this review, we summarize the work published on reductive amination employing hydrogen as the reducing agent. No comprehensive review focusing on this subject has been published since 1948, albeit many interesting summaries dealing with one or the other aspect of reductive amination have appeared. Impressive progress in using catalysts based on earth-abundant metals, especially nanostructured heterogeneous catalysts, has been made during the early development of the field and in recent years.

The Synthesis of Primary Amines through Reductive Amination Employing an Iron Catalyst

The reductive amination of ketones and aldehydes by ammonia is a highly attractive method for the synthesis of primary amines. The use of catalysts, especially reusable catalysts, based on earth-abundant metals is similarly appealing. Here, the iron-catalyzed synthesis of primary amines through reductive amination was realized. A broad scope and a very good tolerance of functional groups were observed. Ketones, including purely aliphatic ones, aryl-alkyl, dialkyl, and heterocyclic, as well as aldehydes could be converted smoothly into their corresponding primary amines. In addition, the amination of pharmaceuticals, bioactive compounds, and natural products was demonstrated. Many functional groups, such as hydroxy, methoxy, dioxol, sulfonyl, and boronate ester substituents, were tolerated. The catalyst is easy to handle, selective, and reusable and ammonia dissolved in water could be employed as the nitrogen source. The key is the use of a specific Fe complex for the catalyst synthesis and an N-doped SiC material as catalyst support.

Catalytic reductive aminations using molecular hydrogen for synthesis of different kinds of amines

Catalytic reductive aminations using molecular hydrogen represent an essential and widely used methodology for the synthesis of different kinds of amines.