High-pressure H2 Research Articles

Ultraselective carbon hollow fiber membrane for H2 extraction from blended natural gas

Blending hydrogen into natural gas (H2NG) pipelines is a feasible solution for low-cost hydrogen delivery while purifying H2 at end-use remains challenging due to its high pressure and low H2 concentration. Herein, biomass-derived carbon hollow fiber membranes (CHFMs) with ultrahigh H2/CH4 separation factor of 4149.0 under a simulated H2NG (10 mol% H2/90 mol% CH4) at 30 bar were reported, and the separation performance maintained within 150 h in a dynamic durability test. Furthermore, the CHFMs showed good stability under fluctuating temperature feeds (up to 100 °C). To evaluate the feasibility of the CHFMs for H2 extraction from H2NG, a three-stage membrane system was designed based on the mixed gas separation performances. It suggested that 99.99 mol% H2 can be achieved with a 90 % recovery, and the specific H2 purification cost was 0.245 $/Nm3 for a 1.8 × 105 Nm3/h production scale, which provides the possibility of hydrogen extraction from H2NG pipelines.

(Invited) A Hybrid Electrochemical and Catalytic Compression System for Direct Generation of High-Pressure Hydrogen at 350 Atmospheric Pressure

Hydrogen is becoming the center piece in the global de-carbonatization efforts in multiple industrial sectors. Gaseous hydrogen at high pressures in gas tanks is the most common approach for H2 storage, transportation and hydrogen refueling for fuel cell vehicles. Gaseous hydrogen at high pressures is also heavily used in the Haber process for ammonia production and hydro-cracking of heavy petroleum. In the long term, low-cost high pressure H2 will also play a critical role in the future long-duration grid storage for deep decarbonization and improved resilience.In this talk, I will share some recent development on a hybrid electrochemical/catalytic approach for direct generation of high-pressure H2 in collaboration with Pacific Northwest National Laboratory (PNNL). The hybrid system oxidizes water to oxygen at the anode, reduces V3+ to V2+ at the cathode, and stores proton in the catholyte during the “electrochemical charging” step. We demonstrated that the charged catholyte is then capable of generating H2 at >350 bar in the subsequent “catalytic discharging” step without any additional energy input. This concept leverages the electrochemical Nernst potential difference between the redox couple (V2+/3+) and the hydrogen evolution reaction and delivers a unique system that is capable of generating H2 at demand and at high pressure without any mechanical or electrochemical compression. We estimate a cost of <$0.19/kg-H2 for compression, representing >80% of the cost reduction compared to the traditional multi-stage compressor approach.

Selective Cleavage of Cβ-O-4 Bond for Lignin Depolymerization via Paired-Electrolysis in an Undivided Cell.

The cleavage of C-O bonds is one of the most promising strategies for lignin-to-chemicals conversion, which has attracted considerable attention in recent years. However, current catalytic system capable of selectively breaking C-O bonds in lignin often requires a precious metal catalyst and/or harsh conditions such as high-pressure H2 and elevated temperatures. Herein, we report a novel protocol of paired electrolysis to effectively cleave the Cβ-O-4 bond of lignin model compounds and real lignin at room temperature and ambient pressure. For the first time, "cathodic hydrogenolysis of Cβ-O-4 linkage" and "anodic C-H/N-H cross-coupling reaction" are paired in an undivided cell, thus the cleavage of C-O bonds and the synthesis of valuable triarylamine derivatives could be simultaneously achieved in an energy-effective manner. This protocol features mild reaction conditions, high atom economy, remarkable yield with excellent chemoselectivity, and feasibility for large-scale synthesis. Mechanistic studies indicate that indirect H* (chemical absorbed hydrogen) reduction instead of direct electron transfer might be the pathway for the cathodic hydrogenolysis of Cβ-O-4 linkage.

Modeling of the Time-Dependent H2 Emission and Equilibrium Time in H2-Enriched Polymers with Cylindrical, Spherical and Sheet Shapes and Comparisons with Experimental Investigations.

Time-dependent emitted H2 content modeling via a reliable diffusion analysis program was performed for H2-enriched polymers under high pressure. Here, the emitted hydrogen concentration versus elapsed time was obtained at different diffusivities and volume dimensions for cylinder-, sphere- and sheet-shaped specimens. The desorption equilibrium time, defined as the time when the H2 emission content is nearly saturated, was an essential factor for determining the periodic cyclic testing and high-pressure H2 exposure effect. The equilibrium time in the desorption process was modeled. The equilibrium time revealed an exponential growth behavior with respect to the squared thickness and the squared diameter of the cylinder--shaped specimen, while it was proportional to the squared diameter for the sphere-shaped specimen and to the squared thickness for the sheet-shaped specimen. Linear relationships between the reciprocal equilibrium time and diffusivity were found for all shaped polymers. The modeling results were confirmed by analysis of the solutions using Fick's second diffusion law and were consistent with the experimental investigations. Numerical modeling provides a useful tool for predicting the time-dependent emitted H2 behavior and desorption equilibrium time. With a known diffusivity, a complicated time-dependent emitted H2 behavior with a multi-exponential form of an infinite series could also be predicted for the three shaped samples using a diffusion analysis program.

Development of a high-pressure 700 bar metal hydride hydrogen compressor

HySA Systems and TF Design have recently developed a single-stage prototype high-pressure metal hydride hydrogen compressor (MHHC) which is able to compress hydrogen from 100 to >700 bar at the working temperatures from 20 to 150 °C, with estimated productivity about 1 Nm3/h. The MHHC comprises of two 2 m-long fibre-wound high-pressure MH containers developed by the authors earlier and assembled in two modules operating in a mode of a cyclic lower-pressure H2 absorption (on cooling) and high-pressure H2 desorption (on heating). The containers operate using a self-developed multicomponent C14 Laves type Ti–based AB2 intermetallic alloy. The article considers phase-structural and hydrogen sorption properties of the utilized metal hydride material, hydrogen compression performances of the metal hydride container, as well as layout and the expected performance characteristics of the compressor assembly.

Impact of mixing low-reactivity gases on the mechanism of hydrogen spontaneous combustion: A ReaxFF MD study

The phenomenon of spontaneous combustion during the release of high-pressure H2 is critical to the safe storage and transportation. Besides physical methods to suppress self-ignition, the approach of mixing low-reactivity gases has gained increasing attention. Previous work has mainly focused on the flow, physical heating effects, and boundary conditions of self-ignition in mixed gases, while the intrinsic chemical reaction mechanisms of spontaneous combustion remain underexplored. To clear this issue, this work uses the ReaxFF MD simulation method to study the spontaneous combustion process of H2/CO and H2/CH4 mixtures with various concentrations. The results indicate that: (1) in pure H2, H2/CO, and H2/CH4 systems, the primary initial reaction mechanism is H2+O2HO2+H. Additionally, in some mixed systems, CO + O2CO2+O and CH4+O2CH3+HO2 may also serve as initial reaction mechanisms. (2) Under fuel-lean combustion conditions, the RIDTs of the systems decrease, supporting the viewpoint that self-ignition typically occurs first in fuel-lean regions. The addition of CO and CH4 increases the RIDTs, which helps inhibit the development of self-ignition. (3) In H2-rich environments, CO combusts to CO2 through the formation of HOCO, while CH4 undergoes dehydrogenation and oxidation processes through intermediates such as CH3, CH3O, and HCHO, leading to the formation of CO and CO2. The combustion of H2 is also influenced by these processes. (4) The addition of CO and CH4 increases the activation energy of H2 combustion, raising the reaction energy barrier that must be overcome for spontaneous combustion. This effectively helps to suppress the occurrence and development of self-ignition during the release of high-pressure gases.

Effect of the reorganization of acid sites induced by metal species on TiO2 supports on the conversion of furfural to acetals and ethers

For the catalytic hydrogenation of furfural (FFR) over supported metal catalysts, acetals and ethers were often observed as by-products when alcohols were used as solvents. The presence of specific acid sites on the catalyst led to the conversion of FFR to acetals and ethers. To understand the effect of the interaction between metal species and oxide supports on the acid properties of catalysts and the conversion of FFR to acetals and ethers, anatase TiO2 (TiO2-A), rutile TiO2 (TiO2-R) and these TiO2 supported Ni catalysts were studied as models. The relationship between the acid properties of these samples and FFR conversion pathways in isopropanol was revealed. The interaction between Ni species and TiO2 supports was found to selectively remove Brønsted acid sites on the TiO2 supports in the absence of H2, thereby inhibiting the conversion of FFR to acetals and ethers in N2. However, the presence of high-pressure H2 during the reaction induced the formation of new Brønsted acid sites on Ni/TiO2 catalysts via hydrogen spillover, promoting the acetalization of FFR to acetals and the hydrogenolysis of acetals to ethers. The Ni/TiO2-A catalyst exhibited higher activity in catalyzing the conversion of FFR to acetals and ethers compared to the Ni/TiO2-R catalyst. This work provides reference information for the selective regulation of acid-catalyzed reaction pathways of FFR in alcohols.

Green Ironmaking at Higher H2 Pressure: Reduction Kinetics and Microstructure Formation During Hydrogen-Based Direct Reduction of Hematite Pellets

Hydrogen-based direct reduction (HyDR) of iron ores has attracted immense attention and is considered a forerunner technology for sustainable ironmaking. It has a high potential to mitigate CO2 emissions in the steel industry, which accounts today for ~ 8–10% of all global CO2 emissions. Direct reduction produces highly porous sponge iron via natural-gas-based or gasified-coal-based reducing agents that contain hydrogen and organic molecules. Commercial technologies usually operate at elevated pressure, e.g., the MIDREX process at 2 bar and the HyL/Energiron process at 6–8 bar. However, the impact of H2 pressure on reduction kinetics and microstructure evolution of hematite pellets during hydrogen-based direct reduction has not been well understood. Here, we present a study about the influence of H2 pressure on the reduction kinetics of hematite pellets with pure H2 at 700 °C at various pressures, i.e., 1, 10, and 100 bar under static gas exposure, and 1.3 and 50 bar under dynamic gas exposure. The microstructure of the reduced pellets was characterized by combining X-ray diffraction and scanning electron microscopy equipped with electron backscatter diffraction. The results provide new insights into the critical role of H2 pressure in the hydrogen-based direct reduction process and establish a direction for future furnace design and process optimization.Graphical

Mild Photochemical Reduction of Alkenes and Heterocycles via Thiol-Mediated Formate Activation.

The reduction of alkenes to their respective alkanes is one of the most important transformations in organic chemistry, given the abundance of natural and commercial olefins. Metal-catalyzed hydrogenation is the most common way to reduce alkenes; however, the use of H2 gas in combination with the precious metals required for these conditions can be impractical, dangerous, and expensive. More complex substrates often require extremely high pressures of H2, further emphasizing the safety concerns associated with these hydrogenation reactions. Here we report a safe, cheap, and practical photochemical alkene reduction using a readily available organophotocatalyst, catalytic thiol, and formate. These conditions reduce a variety of di-, tri-, and tetra-substituted alkenes in good yield as well as dearomatize pharmaceutically relevant heterocycles to generate sp3-rich isosteres of benzofurans and indoles. These formal-hydrogenation conditions tolerate a broad range of functionalities that would otherwise be sensitive to typical hydrogenations and are likely to be important for industry applications.

The Impact of Impurity Gases on the Hydrogen Embrittlement Behavior of Pipeline Steel in High-Pressure H2 Environments.

The use of hydrogen-blended natural gas presents an efficacious pathway toward the rapid, large-scale implementation of hydrogen energy, with pipeline transportation being the principal method of conveyance. However, pipeline materials are susceptible to hydrogen embrittlement in high-pressure hydrogen environments. Natural gas contains various impurity gases that can either exacerbate or mitigate sensitivity to hydrogen embrittlement. In this study, we analyzed the mechanisms through which multiple impurity gases could affect the hydrogen embrittlement behavior of pipeline steel. We examined the effects of O2 and CO2 on the hydrogen embrittlement behavior of L360 pipeline steel through a series of fatigue crack growth tests conducted in various environments. We analyzed the fracture surfaces and assessed the fracture mechanisms involved. We discovered that CO2 promoted the hydrogen embrittlement of the material, whereas O2 inhibited it. O2 mitigated the enhancing effect of CO2 when both gases were mixed with hydrogen. As the fatigue crack growth rate increased, the influence of impurity gases on the hydrogen embrittlement of the material diminished.

Water-assisted hydrogenation of aromatics under ambient conditions over Ru catalyst: A combined experimental and computational investigation

Conventional hydrogenation of lignin-derived compounds requires high H2 pressures and temperatures, and yet, achieving the desired conversion and selectivity remains a challenge. Herein, a novel reaction system with a ruthenium catalyst and water as a solvent is developed for the selective hydrogenation of lignin-derived aromatics to corresponding ring-saturated products under ambient conditions (room temperature, and 1 bar H2 pressure). Using a synergistic combination of catalytic experiments, advanced characterization techniques and quantum mechanical simulations, we elucidate that Ru catalyst switches its selectivity from deoxygenation in gas phase to ring hydrogenation in the condensed phase. Water partially dissociates and adsorbs on the catalyst surface as a combination of hydroxyl fragments, H atoms, and physisorbed molecules, and this is critical for Ru to flip its selectivity in the aqueous phase. Experimental results demonstrate a high conversion (>99 %) and >75 % selectivity towards the total hydrogenated products in the presence of water, corroborating the computational results in which kinetic free energy barriers for direct hydrogenation steps reduced to 70 kJ/mol and barrier for direct dehydroxylation increased from 63 kJ/mol to 202 kJ/mol in the case of phenol. Furthermore, H from dissociated water molecules is utilized in the hydrogenation and water also gets regenerated utilizing external hydrogen supply, thus acting as a shuttler for the external hydrogen.

Hydroconversion of lignin-derived platform compound guaiacol to fuel additives and value-added chemicals over alumina-supported Ni catalysts

Hydroconversion of guaiacol (GUA) over γ-Al2O3 and phosphatized-γ-Al2O3 (γ-Al2O3(P)) supported Ni catalysts was initiated by Lewis-sites and active Ni sites. Conversion proceeded via transmethylation and hydrodemethylation/hydrodemethoxylation as major and minor pathways, respectively, resulting in mainly catechol and methylcatechols, and via series of consecutive hydrodehydroxylation (HDHY) and ring hydrogenation (HYD) reactions leading to partially and fully deoxygenated, saturated, and unsaturated products. High Ni-loading and high H2 pressure promoted the formation of cyclohexane and methyl-substituted cyclohexanes; however, above 300 °C the hydrogenation–dehydrogenation equilibrium favored the formation of benzene and methyl-substituted benzenes. Ni/γ-Al2O3(P) showed suppressed HYD/HDHY activity resulting in pronounced formation of catechol and/or phenol and their methyl-substituted derivatives. Surface phenolate species were substantiated as surface intermediates of hydrodeoxygenation. Phosphatizing reduced the concentration of both basic OH and Lewis acid (Al+) – Lewis base (O–) pair surface sites of the γ-Al2O3 support and, thereby, suppressed phenolate formation and hydrodeoxgenation.

Elucidation of the Pyridine Ring-Opening Mechanism of 2,2'-Bipyridine or 1,10-Phenanthroline Ligands at Re(I) Carbonyl Complexes.

The cleavage of the C-N bonds of aromatic heterocycles, such as pyridines or quinolines, is a crucial step in the hydrodenitrogenation (HDN) industrial processes of fuels in order to minimize the emission of nitrogen oxides into the atmosphere. Due to the harsh conditions under which these reactions take place (high temperature and H2 pressure), the mechanism by which they occur is only partially understood, and any study at the molecular level that reveals new mechanistic possibilities in this area is of great interest. Herein, we unravel the pyridine ring-opening mechanism of 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen) ligands coordinated to the cis-{Re(CO)2(N-RIm)(PMe3)} (N-RIm= N-alkylimidazole) fragment under mild conditions. Computational calculations show that deprotonation of the pyridine ring, once dearomatized, is crucial to induce ring contraction, triggering extrusion of the nitrogen atom from the ring and cleavage of the C-N bond. It is noteworthy that different products (regioisomers) are obtained depending on whether the ligand used is bipy or phen due to the additional rigidity and stability conferred by the central ring of the phen ligand, an issue also addressed and clarified computationally. Strong support for the proposed mechanism is provided by the characterization and isolation, including three single-crystal X-ray diffraction structures, of several of the proposed reaction intermediates.

High-rate etching of silicon oxide and nitride using narrow-gap high-pressure (3.3 kPa) hydrogen plasma

We investigated the etching behavior of silicon oxide (SiO x ) and silicon nitride (SiN x ) in narrow-gap, high-pressure (3.3 kPa) hydrogen (H2) plasma under various etching conditions. Maximum etching rates of 940 and 240 nm min−1 for SiO x and SiN x , respectively, were obtained by optimizing the H2 gas flow rate. The dependence of the etching rate on gas flow rate implied that effective elimination of etching products is important for achieving high etching rates because it prevents redeposition. The sample surfaces, especially the oxide surfaces, were roughened and contained numerous asperities after etching. Etching rates of both SiO x and SiN x decreased as the temperature was raised. This suggests that atomic H adsorption, rather than H-ion bombardment, is an important step in the etching process. X-ray photoelectron spectroscopy revealed that the etched nitride surface was enriched in silicon (Si), suggesting that the rate-limiting process in high-pressure H2 plasma etching is Si etching rather than nitrogen abstraction. The etching rate of SiO x was three times higher than that of SiN x despite the higher stability of Si–O bonds than Si–N ones. One reason for the etching difference may be the difference between the bond densities of SiO x and SiN x . This study presents a relatively non-toxic, low-cost, and eco-friendly dry etching process for Si-based dielectrics using only H2 gas in comparison with the conventional F-based plasma etching methods.

Strong resistance to hydrogen embrittlement of high-performance superalloy MP35N under 200 MPa (≈30,000 psi) H2 gas pressure

ABSTRACT Embrittlement of steels and alloys in contact with hydrogen gas under pressure is a key problem in metallurgy with important implications for a future energy economy based on hydrogen. Here we report stress–strain measurements recorded under 200 MPa (∼30,000 PSI) hydrogen gas pressure to evaluate the resistance of MP35N to embrittlement. We find that MP35N with a tensile strength of more than 1800 MPa does not suffer any strength loss, retains a significant amount of ductility and hence appears to be highly resistant to hydrogen embrittlement even under elevated stress when exposed over a time-scale of hours. This exceptional resistance to H-embrittlement seems to be unique among all high-performance steels and alloys of comparable strength and bears on the use of this material for high pressure H2 research devices and storage applications.

Static state synthesis of STT zeolite membranes for high-pressure H2/CH4 separation

STT zeolite membrane with seven-membered rings (7 MR) and nine-membered rings (9 MR) is an ideal alternative for the separation of hydrogen (H2) and methane (CH4). However, the successful synthesis is only possible in rotation conditions, which is difficult to achieve at an industrial scale. Herein we developed a static synthesis approach to prepare high-quality STT zeolite membranes. The precursor transformed in-situ from a liquid state to a semi-solid state to efficiently suppress the nucleation in the bulk gel. This did not affect the growth of the seed layer to form a continuous membrane. The water content was modulated between y = 44 and y = 124 in the molar composition of 1 SiO2: 0.2 TMAdaOH: y H2O. The precursor could be re-used one more time to reduce the total amount of chemical waste. The optimal H2 permeance and H2/CH4 mixture selectivity was up to 6.1 × 10−8 mol m−2 s−1 Pa−1 and 115 at atm pressure. The H2 permeation flux monotonically increased to 2.0 Nm3 m−2 h−1 under feed pressure up to 2.1 MPa. This paves the way for zeolite membranes to high-pressure H2 separation in practical applications.

Electrochemical hydrogenation and oxidation of organic species involving water.

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactionsinvolving waterare summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Enabling one-step regeneration of LiBH4 with self-sustaining hydrogen in its spent fuel – One pathway to storing renewable hydrogen

LiBH4 (LB in short) with a hydrogen capacity as high as 18.5 wt% and a low molecular weight (21.78 g mol−1) is among the most promising candidates for the hydrogen-based economy. However, current major technologies in (re)generation of LB rely heavily on energy-intensive processes, which greatly prohibits practical scaling-up of applications. Here we report a sustainable and effective approach to (re)generate LB via converting renewable H+ in crystalline water into H-, achieving a desirable yield of ∼50%. This one-step synthesis method relies on the reaction between spent fuels, specifically LiBO2·xH2O, and Mg-based alloys to form LB under ambient atmosphere. Notably, our approach surpasses the efficiency of other conventional method, such as LiH-B-H2 and MgH2-LiBO2 systems, which not only bypasses the energy-intensive dehydration procedure of LiBO2·xH2O (∼470 ℃) but also eliminates the use of costly hydrides or high-pressure H2. Our findings indicate that Mg participated in the regeneration process prior to Al in Mg-Al alloys and [BH4]- is gradually evolved from other intermediate species [BHx(OH)4-x]- (x = 0, 1, 2, 3). By combining hydrogen release and efficient storage of hydrogen-rich substrate in a closed materials cycle, this study may shed light on a promising step toward application of renewable hydrogen in a fuel cell-based hydrogen economy.

Hydrogen Spillover Phenomenon at the Interface of Metal-Supported Electrocatalysts for Hydrogen Evolution.

ConspectusHydrogen spillover, as a well-known phenomenon for thermal hydrogenation, generally involves the migration of active hydrogen on the surface of metal-supported catalysts. For thermocatalytic hydrogenation, hydrogen spillover generally takes place from metals with superiority for dissociating hydrogen molecules to supports with strong hydrogen adsorption under a H2 environment with high pressures. The former can bring high hydrogen chemical potential to largely reduce the kinetic barrier of the migration of active hydrogen species from metals to supports. At the same time, the latter can make H* migration thermodynamically spontaneous. For these reasons, hydrogen spillover is a common interfacial phenomenon occurring on metal-supported catalysts during thermocatalysis. Recently, this phenomenon has been observed for the exceptionally enhanced electrocatalytic performance for hydrogen evolution and other electrocatalytic organic synthesis. Different from hydrogen spillover for thermocatalysis under high H2 pressure, hydrogen spillover for electrocatalysis involves the migration of active hydrogen species (H*) from metals with strong hydrogen adsorption to supports with weak hydrogen adsorption, thereby suffering from a thermodynamically unfavorable process accompanied by a high kinetic barrier. Thus, the occurrence of hydrogen spillover at the electrocatalytic interface is not easy, and successful cases are rare. Understanding the underlying nature of hydrogen spillover at the electrocatalytic interface of metal-supported catalysts is critical to the rational design of advanced electrocatalysts.In this Account, we provide in-depth insights into recent advances in hydrogen spillover at the electrocatalytic interface for a significantly enhanced hydrogen evolution performance. Electron accumulation at the metal-support interface induces severe interfacial H* trapping and is recognized as the main factor in the failed hydrogen spillover. Given this, we developed two novel strategies to promote the occurrence of hydrogen spillover at the electrocatalytic interface. These strategies include (i) the introduction of ligand environments to enrich the local hydrogen coverage on metals and lower the barrier for interfacial hydrogen spillover and (ii) the minimization of work function difference between metals and supports (ΔΦ) to relieve electron accumulation and lower the kinetic barrier for hydrogen spillover. Also, we summarize the previously reported strategy of shortening the metal-support interface distance to lower the kinetic barrier for interfacial hydrogen spillover. Afterward, some criteria and methodologies are proposed to identify the hydrogen spillover phenomenon at the electrocatalytic interface. Finally, the remaining challenges and future perspectives are also discussed. Based on this Account, we aim to provide new insights into electrocatalysis, particularly the targeted control of hydrogen spillover at the electrocatalytic interface, and then to offer guidelines for the rational design of advanced electrocatalysts.

Manganese-Catalyzed Mono-N-Methylation of Aliphatic Primary Amines without the Requirement of External High-Hydrogen Pressure.

The synthesis of mono-N-methylated aliphatic primary amines has traditionally been challenging, requiring noble metal catalysts and high-pressure H2 for achieving satisfactory yields and selectivity. Herein, we developed an approach for the selective coupling of methanol and aliphatic primary amines, without high-pressure hydrogen, using a manganese-based catalyst. Remarkably, up to 98 % yields with broad substrate scope were achieved at low catalyst loadings. Notably, due to the weak base-catalyzed alcoholysis of formamide intermediates, our novel protocol not only obviates the addition of high-pressure H2 but also prevents side secondary N-methylation, supported by control experiments and density functional theory calculations.