Barium hydride activates Ni for ammonia synthesis catalysis

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Abstract

Barium hydride activates Ni for ammonia synthesis catalysis showing an activity that is comparable to that of the Cs promoted MgO supported Ru catalyst.

Abstract

Nickel (Ni) metal has long been considered to be far less active for catalytic ammonia synthesis as compared to iron, cobalt, and ruthenium. Herein, we show that Ni metal synergized with barium hydride (BaH ₂) can catalyse ammonia synthesis with an activity comparable to that of an active Cs–Ru/MgO catalyst typically below 300 °C. Kinetic analyses show that the addition of BaH ₂ makes the apparent activation energy for the Ni catalyst decrease dramatically from 150 kJ mol ⁻¹ to 87 kJ mol ⁻¹. This result together with N ₂-TPR experiments suggests a strong synergistic effect between Ni and BaH ₂ for promoting N ₂ activation and hydrogenation to NH ₃. It is suggested that an intermediate [N–H] species is generated upon N ₂ fixation and then is hydrogenated to NH ₃ with the regeneration of hydride species, forming a catalytic cycle.

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Beyond fossil fuel–driven nitrogen transformations

Sergei V Lymar, Jingguang G Chen, Richard M Crooks … (2018)

Nitrogen is fundamental to all of life and to many industrial processes. Nitrogen in its various oxidation states comprises the global nitrogen cycle, with the change between forms being redox reactions involving electrons and protons. The interchange of nitrogen oxidation states constitutes some of the most important industrial processes, with the energy for these processes being provided largely by fossil fuel. A key goal of research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, or biological catalysts, or by inventing new energy-efficient processes that rely on catalysts. These approaches, as well as the challenges involved, are discussed in this review. This review article reports on the current state of the field of nitrogen activation chemistry and discusses future directions.

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A Roadmap to the Ammonia Economy

Douglas MacFarlane, Pavel Cherepanov, Jaecheol Choi … (2020)

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Is Open Access

Current and future role of Haber–Bosch ammonia in a carbon-free energy landscape

Collin S. Smith, Alfred K. Hill, Laura Torrente-Murciano (2020)

The future of green ammonia as long-term energy storage relies on the replacement of the conventional CO 2 intensive methane-fed Haber–Bosch process by distributed and agile ones aligned to the geographically isolated and intermittent renewable energy. The future of a carbon-free society relies on the alignment of the intermittent production of renewable energy with our continuous and increasing energy demands. Long-term energy storage in molecules with high energy content and density such as ammonia can act as a buffer versus short-term storage ( e.g. batteries). In this paper, we demonstrate that the Haber–Bosch ammonia synthesis loop can indeed enable a second ammonia revolution as energy vector by replacing the CO 2 intensive methane-fed process with hydrogen produced by water splitting using renewable electricity. These modifications demand a redefinition of the conventional Haber–Bosch process with a new optimisation beyond the current one which was driven by cheap and abundant natural gas and relaxed environmental concerns during the last century. Indeed, the switch to electrical energy as fuel and feedstock to replace fossil fuels ( e.g. methane) will lead to dramatic energy efficiency improvements through the use of high efficiency electrical motors and complete elimination of direct CO 2 emissions. Despite the technical feasibility of the electrically-driven Haber–Bosch ammonia, the question still remains whether such revolution will take place. We reveal that its success relies on two factors: increased energy efficiency and the development of small-scale, distributed and agile processes that can align to the geographically isolated and intermittent renewable energy sources. The former requires not only higher electrolyser efficiencies for hydrogen production but also a holistic approach to the ammonia synthesis loop with the replacement of the condensation separation step by alternative technologies such as absorption and catalysis development. Such innovations will open the door to moderate pressure systems, the development and deployment of novel ammonia synthesis catalysts, and even more importantly, the opportunity for integration of reaction and separation steps to overcome equilibrium limitations. When realised, green ammonia will reshape the current energy landscape by directly replacing fossil fuels in transportation, heating, electricity, etc. , and as done in the last century, food.