First-Principles Insights into the Thermodynamics of Variable-Temperature Ammonia Synthesis on Transition-Metal-Doped Cu (100) and (111)

Ammonia (NH₃) is one of the most produced chemicals worldwide. NH₃ synthesis predominantly utilizes the Haber-Bosch (HB) process, requiring high temperatures and pressures. Despite significant process advances, ample opportunity remains for improving the rate, selectivity, catalyst stability, and energy efficiency. Inspired by a recently developed programmable heating and quenching (PHQ) technique, here we present a first-principles screening of candidate single-atom alloy catalysts generated from doping (111) and (100) surfaces of copper (Cu), an ineffective HB catalyst in its pure form. We predict the thermodynamics of two rate-limiting reactions, N₂ dissociative adsorption and the final hydrogenation step leading up to NH₃ release, at 400 and 900 K. Thermodynamically, the former reaction is favored at low temperatures, while the latter is favored at high temperatures. Vanadium-, chromium-, and molybdenum-doped Cu surfaces, due to intermediate M-N covalent bonding character, emerge as appealing candidate catalysts for PHQ NH₃ synthesis, as they balance the thermodynamics of the above-mentioned reaction steps at their respective optimal temperatures.