Barium Oxide Encapsulating Cobalt Nanoparticles Supported on Magnesium Oxide: Active Non-noble Metal Catalyst for Ammonia Synthesis under Mild Reaction Condition

To realize a sustainable, carbon-free society, catalysts for the synthesis of ammonia using renewable energy under mild reaction conditions (<400 °C, <10 MPa) are needed. Ru-based catalysts are currently the most promising candidates; however, Ru is expensive and of low abundance. Here, we discovered that encapsulation of Co nanoparticles with BaO enhanced the ammonia synthesis activity of the Co, and that a simple Ba-doped Co/MgO catalyst pre-reduced at an unusually high temperature of 700 °C (Co@BaO/MgO-700red) showed outstanding ammonia synthesis activity. <a>The ammonia synthesis rate (24.6 mmol gcat</a>−1 h−1) and turnover frequency (0.255 s−1) of the catalyst at 350 °C and 1.0 MPa were 22 and 64 times higher, respectively, than those of the non-doped parent catalyst. At the same temperature but higher pressure (3.0 MPa), the ammonia synthesis rate was increased to 48.4 mmol gcat−1 h−1, which is higher than that of active Ru-based catalysts. Scanning transmission electron microscopy and energy dispersive X-ray spectrometry investigations revealed that after reduction at 700 °C the Co nanoparticles had become encapsulated by a nano-fraction of BaO. The mechanism underlying the formation of this unique structure was considered to comprise reduction of oxidic Co to metallic Co, decomposition of BaCO3 to BaO, and migration of BaO to the Co nanoparticle surface. Spectroscopic and density-functional theory investigations revealed that adsorption of N2 on the Co atoms at the catalyst surface weakened the N2 triple bond to the strength of a double bond due to electron donation from the Ba atom of BaO via adjacent Co atoms; this weakening accelerated cleavage of the triple bond, which is the rate-determining step for ammonia synthesis.

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Co/Ba/La2O3 catalyst for ammonia synthesis under mild reaction conditions

10.26434/chemrxiv-2021-1qb7z ◽

2021 ◽

Author(s):

Katsutoshi Nagaoka ◽

Shin-ichiro Miyahara ◽

Katsutoshi Sato ◽

Yuta Ogura ◽

Kotoko Tsujimaru ◽

...

Keyword(s):

Ammonia Synthesis ◽

Nickel Catalysts ◽

Ruthenium Catalysts ◽

Synthesis Rate ◽

Turnover Frequency ◽

Reaction Conditions ◽

Synthesis Activity ◽

Co Nanoparticles ◽

Ammonia Poisoning ◽

Nanoparticle Catalyst

Ruthenium catalysts may allow realization of renewable energy–based ammonia synthesis processes using mild reaction conditions (<400 °C, <10 MPa). However, ruthenium is relatively rare and therefore expensive. Here, we report a Co nanoparticle catalyst loaded on a basic Ba/La2O3 support and pre-reduced at 700 °C (Co/Ba/La2O3_700red) that showed higher ammonia synthesis activity at 350 °C and 1.0–3.0 MPa than two benchmark Ru catalysts, Cs+/Ru/MgO and Ru/CeO2. The synthesis rate of the catalyst at 350 °C and 1.0 MPa (19.3 mmol h−1g−1) was 8.0 times that of Co/Ba/La2O3_500red and 6.9 times that of Co/La2O3_700red. The catalyst showed activity at temperatures down to 200 °C. High-temperature reduction induced formation of a BaO-La2O3 nano-fraction around the Co nanoparticles, which increased turnover frequency, inhibited Co nanoparticle sintering, and suppressed ammonia poisoning. These strategies may also be appliable to nickel catalysts.

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Homogeneous cobalt-catalyzed reductive amination for synthesis of functionalized primary amines

Nature Communications ◽

10.1038/s41467-019-13351-7 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 8

Author(s):

Kathiravan Murugesan ◽

Zhihong Wei ◽

Vishwas G. Chandrashekhar ◽

Helfried Neumann ◽

Anke Spannenberg ◽

...

Keyword(s):

Density Functional ◽

Reductive Amination ◽

Primary Amines ◽

Metal Catalyst ◽

Gaseous Ammonia ◽

Free Energy Surface ◽

Chemical Research ◽

Rate Determining Step ◽

Earth Abundant ◽

Density Functional Theory Computation

AbstractThe development of earth abundant 3d metal-based catalysts continues to be an important goal of chemical research. In particular, the design of base metal complexes for reductive amination to produce primary amines remains as challenging. Here, we report the combination of cobalt and linear-triphos (bis(2-diphenylphosphinoethyl)phenylphosphine) as the molecularly-defined non-noble metal catalyst for the synthesis of linear and branched benzylic, heterocyclic and aliphatic primary amines from carbonyl compounds, gaseous ammonia and hydrogen in good to excellent yields. Noteworthy, this cobalt catalyst exhibits high selectivity and as a result the -NH2 moiety is introduced in functionalized and structurally diverse molecules. An inner-sphere mechanism on the basis of the mono-cationic [triphos-CoH]+ complex as active catalyst is proposed and supported with density functional theory computation on the doublet state potential free energy surface and H2 metathesis is found as the rate-determining step.

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Altering the rate-determining step over cobalt single clusters leading to highly efficient ammonia synthesis

National Science Review ◽

10.1093/nsr/nwaa136 ◽

2020 ◽

Cited By ~ 1

Author(s):

Sisi Liu ◽

Mengfan Wang ◽

Haoqing Ji ◽

Xiaowei Shen ◽

Chenglin Yan ◽

...

Keyword(s):

Active Sites ◽

Density Functional ◽

Ammonia Synthesis ◽

Density Functional Theory Calculations ◽

High Energy ◽

Ambient Conditions ◽

Property A ◽

Strong Electron ◽

Faradaic Efficiency ◽

Rate Determining Step

Abstract Activation of high-energy triple-bonds of N2 is the most significant bottleneck of ammonia synthesis under ambient conditions. Here, by importing cobalt single clusters as strong electron-donating promoter into the catalyst, the rate-determining step of ammonia synthesis is altered to the subsequent proton addition so that the barrier of N2 dissociation can be successfully overcome. As revealed by density functional theory calculations, the N2 dissociation becomes exothermic over the cobalt single cluster upon the strong electron backdonation from metal to the N2 antibonding orbitals. The energy barrier of the positively shifted rate-determining step is also greatly reduced. At the same time, advanced sampling molecular dynamics simulations indicate a barrier-less process of the N2 approaching the active sites that greatly facilitates the mass transfer. With suitable thermodynamic and dynamic property, a high ammonia yield rate of 76.2 μg h–1 mg$^{-1 }_{\rm cat.}$ and superior Faradaic efficiency of 52.9% were simultaneously achieved.

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Achieving industrial ammonia synthesis rates at near-ambient conditions through modified scaling relations on a confined dual site

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2106527118 ◽

2021 ◽

Vol 118 (30) ◽

pp. e2106527118

Author(s):

Tao Wang ◽

Frank Abild-Pedersen

Keyword(s):

Density Functional ◽

Ammonia Synthesis ◽

Synthesis Rate ◽

Ambient Conditions ◽

Functional Theory ◽

Ru Catalyst ◽

Bosch Process ◽

Energy Scaling ◽

Industrial Solutions ◽

Dual Site

The production of ammonia through the Haber–Bosch process is regarded as one of the most important inventions of the 20th century. Despite significant efforts in optimizing the process, it still consumes 1 to 2% of the worldwide annual energy for the high working temperatures and pressures. The design of a catalyst with a high activity at milder conditions represents another challenge for this reaction. Herein, we combine density functional theory and microkinetic modeling to illustrate a strategy to facilitate low-temperature and -pressure ammonia synthesis through modified energy-scaling relationships using a confined dual site. Our results suggest that an ammonia synthesis rate two to three orders of magnitude higher than the commercial Ru catalyst can be achieved under the same reaction conditions with the introduction of confinement. Such strategies will open pathways for the development of catalysts for the Haber–Bosch process that can operate at milder conditions and present more economically viable alternatives to current industrial solutions.

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Computationally-Guided Investigation of Dual Amine/pi Lewis Acid Catalysts for Direct Additions of Aldehydes and Ketones to Unactivated Alkenes and Alkynes

10.26434/chemrxiv.7538114.v2 ◽

2020 ◽

Author(s):

Eric Greve ◽

Jacob D. Porter ◽

Chris Dockendorff

Keyword(s):

Lewis Acid ◽

Density Functional ◽

Acid Catalyst ◽

Metal Catalyst ◽

Catalyst Poisoning ◽

Lewis Acid Catalysts ◽

Metal Ligands ◽

Aldehydes And Ketones ◽

Lewis Acid Catalyst ◽

Catalyst Systems

Dual amine/pi Lewis acid catalyst systems have been reported for intramolecular direct additions of aldehydes/ketones to unactivated alkynes and occasionally alkenes, but related intermolecular reactions are rare and not presently of significant synthetic utility, likely due to undesired coordination of enamine intermediates to the metal catalyst. We reasoned that bulky metal ligands and bulky amine catalysts could minimize catalyst poisoning and could facilitate certain examples of direct intermolecular additions of aldehyde/ketones to alkenes/alkynes. Density Functional Theory (DFT) calculations were performed that suggested that PyBOX-Pt(II) catalysts for alkene/alkyne activation could be combined with MacMillan’s imidazolidinone organocatalyst for aldehyde/ketone activation to facilitate desirable C-C bond formations, and certain reactions were calculated to be more exergonic than catalyst poisoning pathways. As calculated, preformed enamines generated from the MacMillan imidazolidinone did not displace ethylene from a biscationic (t-Bu)PyBOX-Pt2+complex, but neither were the desired C-C bond formations observed under several different conditions.

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Computationally-Guided Investigation of Dual Amine/pi Lewis Acid Catalysts for Direct Additions of Aldehydes and Ketones to Unactivated Alkenes and Alkynes

10.26434/chemrxiv.7538114 ◽

2020 ◽

Author(s):

Eric Greve ◽

Jacob D. Porter ◽

Chris Dockendorff

Keyword(s):

Lewis Acid ◽

Density Functional ◽

Acid Catalyst ◽

Metal Catalyst ◽

Catalyst Poisoning ◽

Lewis Acid Catalysts ◽

Metal Ligands ◽

Aldehydes And Ketones ◽

Lewis Acid Catalyst ◽

Catalyst Systems

Dual amine/pi Lewis acid catalyst systems have been reported for intramolecular direct additions of aldehydes/ketones to unactivated alkynes and occasionally alkenes, but related intermolecular reactions are rare and not presently of significant synthetic utility, likely due to undesired coordination of enamine intermediates to the metal catalyst. We reasoned that bulky metal ligands and bulky amine catalysts could minimize catalyst poisoning and could facilitate certain examples of direct intermolecular additions of aldehyde/ketones to alkenes/alkynes. Density Functional Theory (DFT) calculations were performed that suggested that PyBOX-Pt(II) catalysts for alkene/alkyne activation could be combined with MacMillan’s imidazolidinone organocatalyst for aldehyde/ketone activation to facilitate desirable C-C bond formations, and certain reactions were calculated to be more exergonic than catalyst poisoning pathways. As calculated, preformed enamines generated from the MacMillan imidazolidinone did not displace ethylene from a biscationic (t-Bu)PyBOX-Pt2+complex, but neither were the desired C-C bond formations observed under several different conditions.

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On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

10.26434/chemrxiv.7851848.v3 ◽

2019 ◽

Author(s):

Hassan Harb ◽

Lee Thompson ◽

Hrant Hratchian

Keyword(s):

Triple Bond ◽

Density Functional ◽

Valence Electron ◽

Density Functional Theory Calculations ◽

Electron Configuration ◽

Functional Theory ◽

Key Species ◽

Pi Orbitals ◽

Lanthanide Hydroxide ◽

Linear Geometry

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.

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On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

10.26434/chemrxiv.7851848 ◽

2019 ◽

Author(s):

Hassan Harb ◽

Lee Thompson ◽

Hrant Hratchian

Keyword(s):

Triple Bond ◽

Density Functional ◽

Valence Electron ◽

Density Functional Theory Calculations ◽

Electron Configuration ◽

Functional Theory ◽

Key Species ◽

Pi Orbitals ◽

Lanthanide Hydroxide ◽

Linear Geometry

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.

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Electron Donation by Low-Crystalline Ba-La-Ce Oxygen-Deficient Composite Oxide Accumulating on Ru Nanoparticles for Ammonia Synthesis under Mild Conditions

10.26434/chemrxiv.7763657.v1 ◽

2019 ◽

Author(s):

Katsutoshi Sato ◽

Shin-ichiro Miyahara ◽

Yuta Ogura ◽

Kotoko Tsujimaru ◽

Yuichiro Wada ◽

...

Keyword(s):

Ammonia Synthesis ◽

Bond Cleavage ◽

Synthesis Process ◽

Strong Electron ◽

Mild Conditions ◽

Ru Nanoparticles ◽

Rate Determining Step ◽

Highly Active ◽

Composite Oxides ◽

Low Crystalline

To mitigate global problems related to energy and global warming, it is helpful to develop an ammonia synthesis process using catalysts that are highly active under mild conditions. Here we show that the ammonia synthesis activity of Ru/Ba/LaCeOx pre-reduced at 700 °C is the highest reported among oxide-supported Ru catalysts. Our results indicate that low crystalline oxygen-deficient composite oxides, which include Ba2+, Ce3+ and La3+, with strong electron-donating ability, accumulate on Ru particles and thus promote N≡N bond cleavage, which is the rate determining step for ammonia synthesis.

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