CATALYSTNH3SYNTHESIS · Synthetically Tuned Atomic Ordering and Electronic Properties of Nano-Intermetallic Compounds for the Ammonia Synthesis.

Synthetically Tuned Atomic Ordering and Electronic Properties of Nano-Intermetallic Compounds for the Ammonia Synthesis.

Ammonia (NH3) is a crucial agricultural feedstock along with industrial, household chemicals, and a precursor for hydrogen storage with upcoming alternative fuel. The significant use of NH3 is in the production of synthetic fertilizers, which assist in the high yield of nutrients crops. Therefore, demand for NH3 production continues to increase to support the growing global population with affordable food supply and as carbon-neutral fuel. Despite shortcomings, such as high-energy use (28–166 GJ per ton NH3), process complexity, CO2 gas emission (1.87 ton per ton NH3), there remains no alternative to the Haber-Bosh process (HBP). In HBP, a mixture of N2 and H2 passes over a Fe-based catalyst promoted with K2O and Al2O3 at high temperatures (400–600°C) and pressures (20–40 MPa), consuming more than 1% of the world’s power production. Therefore, the reduction of N2 to NH3 under mild conditions is one of the most challenging topics in catalysis. Cleavage of stable N≡N bond (945 kJ/mol) is a significant step in NH3 synthesis and demands high-energy input. Even after 100 years of discovery, the same old high energy-consuming Fe-based catalytic process is still operating commercially. The substitute to HBP through dynamic heterogeneous catalyst development remained a Never-Ending Story. The absence of significant success towards further development of Fe-based catalysts stipulates looking at alternative completely different catalysts. In this regard, Ruthenium (Ru) based catalysts supported on carbon emerged as second-generation catalysts for the NH3 synthesis at the end of 20th century. The special type of B5 sites in Ru nanoparticles is the active centers for N2 cleavage at low temperatures. However, NH3 synthesis commensurates with an increase in pressure is not expected in conventional Ru-based catalysts because of severe hydrogen poisoning on Ru surfaces. This is a major reason why Fe-based catalysts used in HBP has not been replaced by Ru catalyst in addition to the cost associated with it. As a counterpart, there have been limited intermetallic compounds (IMCs) that have been studied as catalysts for ammonia synthesis long back in the 19th century. Intermetallic compounds (IMCs) exhibit unique structural features accompanied by appropriate changes in the electronic properties making that they have been explored in catalysis. A decade later, few promising efforts on LaCoSi, LaRuSi, and Ru2Y IMCs in NH3 synthesis, open up new study directions and innovative ideas with several possibilities for catalytic development. The study of these compounds further strengthens the thoughtful scientific exploration for ammonia synthesis. In this project, we proposed to explore and evaluate new IMC catalysts to tackle these challenges, thereby supporting the efficiency and competitiveness of N2 activation at lower temperatures. The main objective of our research project was to take advantage of the structural and electronic properties of the intermetallic compounds (IMCs) as catalysts for the activation of N2 in the NH3 synthesis reaction. The main work was focused on the preparation, characterization of IMCs and their catalytic performance in gas phase NH3 synthesis reaction. In terms of catalyst synthesis, we (i) studied different IMCs synthesized by layered double hydroxide route, arc melting, annealing, and solution phase. (ii) We tried to synthesize the pure phase of the binary and ternary IMCs using appropriate synthesis conditions. These IMCs were characterized by an array of advanced physio-chemical tools to evaluate the effects of preparation parameters on the phase purity, surface area, and texture. The materials were evaluated as heterogeneous catalysts in an NH3 synthesis reaction.

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