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.