Kevin Brennan

Ammonia plays a central role in global fertilizer production and is increasingly recognized as a versatile energy carrier within emerging sustainable energy systems. The La/Co system is an example of an ammonia production catalyst with efficiency greater than that of current commercial catalysts. A spin-mediated promotion mechanism has been proposed as the mechanism behind the catalytic activity. While the resulting catalytic promotion is clearly observed, the change in spin has not yet been directly demonstrated experimentally. In the present study, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements were performed on a Co(101̅15) crystal and compared with density functional theory (DFT) calculations. The purpose was to obtain an understanding of the properties of the Co(101̅15) crystal surface as a first step to verify the electronic structure changes behind spin promotion. The STM results revealed a stepped surface as expected. A comparison between the STS measurements and DFT calculations indicated that the spin of the Co atoms changes across the surface. This could potentially be caused by adsorbates on the crystal surface or by an interaction between the STM tip and the sample surface.

Asymmetric catalysis underpins pharmaceutical synthesis but is dominated by homogeneousmolecular catalysts that complicate product separation and recycling. Heterogeneousalternatives, including hybrid systems in which molecular catalysts are immobilised on solidsupports, often suffer from diminished activity and poor stability. Here, we use densityfunctional theory and microkinetic modelling to evaluate intrinsically chiral platinum surfacesas a heterogeneous alternative, taking the hydrogenation of hydroxyacetone to 1,2-propanediol (1,2-PD) as a model reaction. On the mirror-image Pt(643)S and Pt(643)ᴿ surfaces,hydroxyacetone chemisorbs at the undercoordinated chiral kink, and the effective transition-state barriers for the two reaction pathways differ by 0.21 eV, favouring S-1,2-PD on Pt(643)S and R-1,2-PD on Pt(643)ᴿ. By contrast, hydroxyacetone is only physisorbed on the achiral Pt(111) terrace and is hydrogenated to a racemic product with a lower effective barrier of 0.75 eV. Microkinetic modelling that accounts for the realistic coexistence of kink and terrace sites identifies an operational window near 500 K and 10⁻² bar in which strong substrate binding at the chiral kink outcompetes the racemic terrace pathway, yielding enantiomeric excesses approaching 99 %. These results establish chiral Pt(643) surfaces as a viable platform for fully heterogeneous asymmetric hydrogenation and motivate experimental verification.

The large-scale production of ammonia via the Haber–Bosch process is an integral part of maintaining global populations, yet it is dependent on the harsh reaction conditions and hydrogen sourced via steam reforming. The electrochemical reduction of hydrogen cyanide (HCNRR), a fixed form of nitrogen, has shown itself to be a promising route for ammonia synthesis at ambient conditions, offering a path to contribute to a circular nitrogen economy. While the HCNRR is still an understudied area of catalysis, few experimental reports have identified nickel as a promising catalyst, outperforming precious metals such as platinum. On a Ni cathode, two sets of HCNRR products have been observed, namely methylamine (major product) and ammonia/methane (minor products). Recent computational studies have rationalized this product distribution with the desorption of methylamine and hinted on the electrolyte playing a role in the selectivity towards ammonia production. Herein, we investigate the HCNRR mechanism on a Ni cathode using different solvation models in a bid to account for the influence of the electrolyte. Our findings reveal that the presence of an explicit solvent environment has indeed a drastic effect on the HCNRR, resulting in different binding modes and an unexpected metastable intermediate which ultimately leads to a different potential limiting step. These results highlight the necessity of including explicit solvent molecules for the effective modelling of physisorbed intermediates in the HCNRR process, although it may also be generalizable to other important electrochemical processes.

The dependence of the global population on ammonia means that the Haber–Bosch process is one of the most studied and optimised processes in chemistry. Despite this focus, the reaction still requires harsh conditions, which has prompted substantial research efforts to enable the electroreduction of N₂ at ambient conditions. The literature regarding this reaction is plagued with reports of competition with the hydrogen evolution reaction and large potentials required for N₂ dissociation. Cyanide, isoelectronic with N₂, has a significantly lower bond dissociation energy which could enable a route to sustainable ammonia production. Herein, we present the first mechanistic study of the cyanide electroreduction on a Ni cathode, experimentally shown to produce methylamine as a major product, and CH₄ and NH₃ as minor products. Theoretical calculations reveal that the dominance of methylamine in the products is due to the weak binding of this species, which desorbs from the surface preventing further hydrogenation. We also present an alternative CNRR pathway which involves the hydrogen atoms comprising the predicted surface coverage at relevant reaction conditions. Interestingly, this new pathway circumvents the formation of methylamine, exclusively producing CH₄ and NH₃, although it is hindered by the presence of a large energy barrier. Strategies to favour this alternative pathway and the prospects of CNRR for the sustainable production of ammonia under ambient conditions are also outlined.