(377e) Novel Synthesis of Catalytic Active Sites in Flow for on-Demand Hydrogen Production from Ammonia.

In this work, we decouple for the first time, the structural and electronic effects of ruthenium nanoparticles as actives sites for the on-demand production of hydrogen via ammonia decomposition. Long-term storage of renewable energy in the chemical bonds of ammonia can act as a carbon-free energy carrier in a decarbonised society. Ammonia can then be used directly as a fuel or in fuel cells to produce electricity. In both cases, the total or partial decomposition of ammonia to release hydrogen is paramount to avoid the formation of NOx and drive its application.

In this study, ruthenium nanoparticles with controllable sizes were synthesised in a continuous bespoke microreactor without capping ligands through the reduction of ruthenium nitrosyl nitrate with sodium borohydride at ambient temperature. The helical geometry of the reactor is designed to avoid agglomeration of the particles in the absence of catalytically detrimental capping ligands while promoting secondary flows to narrow the time distribution, translating into narrow sizes distributions. The nanoparticles are then supported on a range of supports by electrochemical interaction, maintaining their sizes.

As a result, we reveal unique size-activity relationships for ruthenium nanoparticles associated to their optimum N-adsorption energy¹. We also identify the correlation between sizes and density of ‘B5’ active sites, previously identified using theoretical micro-kinetic studies as the actual active sites for this reaction ³. As a result, we provide unique understanding and guidelines for the development of designer catalysts, moving away from traditional trial-and-error catalyst discovery.

1. A. K. Hill and L. Torrente-Murciano, “In-situ H2 production via low temperature decomposition of ammonia: Insights into the role of cesium as a promoter,” Int. J. Hydrogen Energy, 39 (15), pp. 7646–7654, May 2014.
2. C. J. H. Jacobsen et al., “Structure sensitivity of supported ruthenium catalysts for ammonia synthesis,” J. Mol. Catal. a-Chemical, 163, (1–2), pp. 19–26, 2000.