Periodic Reporting for period 1 - CATALYSTNH3SYNTHESIS (Synthetically Tuned Atomic Ordering and Electronic Properties of Nano-Intermetallic Compounds for the Ammonia Synthesis.)
Reporting period: 2019-09-01 to 2021-08-31
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 This is a major reason why Fe-based catalysts used in HBP has not been replaced by Ru catalyst in addition to the cost associated with it.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.
Work Package 1: According to work package1, we calculated the N2 adsorption energy and N2 dissociation barrier for some of the IMCs based on the modeling. The first milestone to find the appropriate IMCs was successfully completed. Some of the IMCs exhibited high adsorption energy of N2 with a low dissociation barrier. For the rest of the work, IMCs were predicted based on the literature and scientific knowledge available in the field of N2 activation. Work Package 2: Synthesis of IMCs by different routes was carried out based on the Theoretical Calculation (WP1) and based on the literature survey. One milestone “Reliable and reproducible synthesis of IMCs” has been successfully passed. Several IMCs were synthesized by different routes. Work Package 3: Characterization of IMCs included some routine analyses of IMCs as well as advanced and original characterization experiments (especially surface characterization). It also encompassed the training on analytical techniques, which were new for the researcher: XPS, CO, and H2 chemisorptions, TPR_H2, and TPD of NH3/CO2. A manuscript comparing the impact of IMCs on NH3 synthesis - was prepared on the basis of results obtained mainly in WP2-Synthesis and WP3-Characterization and is currently under review. Work Package 4: Catalytic testing was completed first by setting up the catalytic reactor and learning how to set the correct parameters for catalytic reactions. Several IMCs exhibited markedly improved ammonia synthesis rate and low activation energy. We continued with catalytic testing on our IMCs in NH3 synthesis, ran the analytical tools, analyzed the data, and elucidated which characteristics were crucial for obtaining active catalysts. Based on these data one another manuscript can be prepared but still needs some more theoretical calculations and characterization, which are under progress. Finally, Work Package 4: Management & Dissemination took place during the whole project duration. The researcher and the supervisor worked for hand in hand at the dissemination tasks. In addition to the already described preparation of manuscripts and conference presentations, w engaged in public dissemination (social media and Twitter).
1. Novel IMC catalysts for NH3 were synthesized, fully characterized and their effect on the N2 activation was understood. 2. Despite the low number of surface-active sites, IMCs derived catalysts provide new and exciting perspectives to attain further exploration of different wide varieties of IMCs as catalyst precursors. 3. Catalytic activity, stability, and mechanism were studied. IMCs displayed very low activation energy suggesting a new catalytic mechanism for the activation of N2. 4. Consequently, the catalytic activity in NH3 synthesis was fully governed by the number of basic sites, metallic sites, strong metal support interactions (electronic) and, IMC structure. (geometrical) . All these results are very important for the understanding of emerging materials for NH3 synthesis. This result will help the Fertilizer industries to further develop and broaden the idea of implementing these materials in the field for NH3 synthesis.