出版者・発行元：Chemical Engineering Journal  

Ammonia (NH₃), synthesized from green hydrogen produced via renewable energy sources, is increasingly regarded as a critical carbon-free hydrogen carrier, with significant potential to support the global transition to sustainable energy systems and the achievement of carbon neutrality. To achieve this goal, a novel catalyst that consists of Co, BaO, and MgO has been recently reported, enabling NH<inf>3</inf> synthesis under lower and milder reaction conditions than those for the conventional Haber-Bosch process. In this study, the reaction rates of the Co/BaO/MgO catalyst were experimentally measured over a wide range of pressures (1–7 MPa) and temperatures (305–380 °C), allowing us to assess the influence of the backward reaction. Furthermore, two Langmuir-Hinshelwood (LH) kinetic models, 4-parameter and 8-parameter rate expressions, were developed and implemented in an integral reactor model to describe the ammonia synthesis rate. The results of both LH models showed good agreement with the experimental data within the error of ±20 %, which gives high R² values with a smaller number of parameters compared to the Nielsen rate law. The proposed approach, which utilizes an integral reactor model with LH kinetics, can be a powerful tool for the design of industrial reactors for ammonia synthesis.

DOI： 10.1016/j.cej.2025.168922

Scopus

出版者・発行元：Applied Catalysis B Environmental  

Electrocatalytic upcycling of polyethylene terephthalate (PET) plastic wastes into value-added chemicals is promising to alleviate the environmental and energy crisis. However, the cost effectiveness and long-term stability are still facing great challenges for up-scaling applications. Herein, we developed an efficient and stable metallic Ni bifunctional electrocatalyst for the electrocatalytic upcycling of PET plastic wastes coupled with hydrogen production. The metallic Ni deposited on nickel foam exhibited a current density of 100 mA cm⁻² at 1.4 V<inf>RHE</inf>, and an optimal Faradaic efficiency to formic acid (FE<inf>FA</inf>) of 90 % at 1.5 V<inf>RHE</inf> for the anodic ethylene glycol oxidation reaction (EGOR), while presenting an overpotential of 250 mV at 100 mA cm⁻² and Faradaic efficiency to hydrogen (FE<inf>H2</inf>) close to 100 % for the cathodic hydrogen evolution reaction (HER). Mechanistic studies demonstrated the structural reconstruction of metallic Ni into amorphous nickel (oxy)hydroxides as the reactive sites for the EGOR process. A flow cell reactor was assembled by utilizing the bifunctional electrocatalyst as both anode and cathode. A long-term stability was achieved at a constant current density of 100 mA cm⁻² for 720 h. The superior catalytic performance, long-term stability and economic efficiency of the bifunctional metallic Ni electrocatalyst provide great potential for future scaling up.

DOI： 10.1016/j.apcatb.2025.125211

Web of Science

Scopus

出版者・発行元：Advanced Energy Materials  

Developing non-noble metal catalysts with excellent NH<inf>3</inf> synthesis activity under mild conditions is a long-term goal. The best catalysts reported to date often require laborious fabrication methods and controlled environments to fabricate the catalysts or high temperatures and long times to activate the catalysts. This work introduces a facile one-pot method to fabricate carbon (C)-based, barium (Ba)-promoted cobalt (Co) catalysts via the citric acid sol–gel method with metal nitrates as precursors and water as the solvent. This approach ensures the homogeneous incorporation of metal ions into the carbon framework. The resulting (Ba/Co)<inf>0.3</inf>/C catalyst demonstrates an outstanding NH<inf>3</inf> synthesis activity of 34 mmol g<inf>cat</inf>⁻¹ h⁻¹ (350 °C, 1.0 MPa) with excellent stability. In-depth characterizations reveal that Ba exists as barium oxide (BaO), uniformly distributed on the carbon framework and around the Co nanoparticles. It is uncovered that retarding barium carbonate (BaCO<inf>3</inf>) formation in the fresh catalyst significantly reduces the reduction temperature and time (485 °C/4 h), which is a fundamental advantage of this method. Density functional theory and molecular dynamics simulations indeed support the experimental observations. It is anticipated that this simple and economical strategy will resolve the issues in a broad field of heterogeneous catalyst research.

DOI： 10.1002/aenm.202404030

Open Access

Web of Science

Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Sustainable Energy and Fuels  

To realize a carbon-neutral society, developing highly active and inexpensive catalysts for ammonia (NH<inf>3</inf>) production working under moderate conditions (<400 °C, <10 MPa) using hydrogen fabricated from the electrolysis of water is demanded. Current industrial fused iron (Fe) catalysts show deficient activity under such conditions. Although Ru-based catalysts have been introduced as highly efficient catalysts working under desired conditions, they are scarce and consequently expensive. This work introduces Fe/Ba/MgO (reduced at 700 °C) as an active catalyst with a high ammonia production rate working at mild temperature and pressure (350 °C, 1.0 MPa). Ba doping to Fe nanoparticles supported on MgO and pre-reduction at high temperatures dramatically ameliorated the NH<inf>3</inf> production rate. Due to the absence of hydrogen poisoning, the catalytic activity of the Fe/Ba/MgO increased gradually by raising the pressure from 0.1 to 3.0 MPa. The activity of this catalyst at 3.0 MPa was higher than that of two benchmark Ru catalysts. After pre-reduction at high temperature, electrons are donated from the BaO encapsulating the Fe⁰ nanoparticles to the N<inf>2</inf> molecule, which promotes the rate-determining step of ammonia synthesis. We anticipate that these findings will contribute to developing inexpensive Fe catalysts for decarbonizing the ammonia synthesis process to achieve a carbon-neutral society.

DOI： 10.1039/d4se00411f

Open Access

Web of Science

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemsuschem  

An important part of realizing a carbon-neutral society using ammonia will be the development of an inexpensive yet efficient catalyst for ammonia synthesis under mild reaction conditions (<400 °C, <10 MPa). Here, we report Fe/K(3)/MgO, fabricated via an impregnation method, as a highly active catalyst for ammonia synthesis under mild reaction conditions (350 °C, 1.0 MPa). At the mentioned conditions, the activity of Fe/K(3)/MgO (17.5 mmol h⁻¹ g<inf>cat</inf>⁻¹) was greater than that of a commercial fused iron catalyst (8.6 mmol h⁻¹ g<inf>cat</inf>⁻¹) currently used in the Haber-Bosch process. K doping was found to increase the ratio of Fe⁰ on the surface and turnover frequency of Fe in our Fe/K(3)/MgO catalyst. In addition, increasing the pressure to 3.0 MPa at the same temperature led to a significant improvement of the ammonia synthesis rate to 29.6 mmol h⁻¹ g<inf>cat</inf>⁻¹, which was higher than that of two more expensive, benchmark Ru-based catalysts, which are also potential alternative catalysts. A kinetics analysis revealed that the addition of K enhanced the ammonia synthesis activity at ≥300 °C by changing the main adsorbed species from NH to N which can accelerate dissociative adsorption of nitrogen as the rate limiting step in ammonia synthesis.

DOI： 10.1002/cssc.202300942

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PubMed

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開催年月日： 2022年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：富山大学  

開催年月日： 2022年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：富山大学  

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開催年月日： 2020年6月

記述言語：英語   会議種別：ポスター発表  

開催地：San DIego, California   国名：アメリカ合衆国  

開催年月日： 2016年3月

記述言語：日本語   会議種別：口頭発表（一般）  

記述言語：日本語   会議種別：口頭発表（一般）  

出願人：東京大学

出願番号：特願2021-195780  出願日：2021年12月

出願人：東京大学

出願番号：特願2021-165732  出願日：2021年10月

出願人：東京大学

出願番号：特願2020-012202  出願日：2020年1月

公開番号：特開2021-116468  公開日：2021年8月