Ammonia plays a crucial role in agriculture and chemical engineering, and acts as a promising carbon-free transportation fuel. Catalysts design is deemed as a key to solve the restriction of energy-intensive Haber–Bosch process of ammonia production. With the development of computational modeling, computation-aided catalyst design serves as one important driving force for material innovation, saving a lot of experimental efforts based on trial and error. Computational modeling not only provides fundamental mechanistic insights into the reaction with great details regarding adsorbate geometries, electronic structures, and elementary-step energies, but also expedites the material discovery with descriptor-based catalyst design, core of which is the establishment of thermo/kinetic scaling relations. In this review, we present firstly the mechanistic understanding of ammonia synthesis and transition state scaling relations developed on pure transition-metal catalysts. We then summarize catalysts design strategies guided by alloy, size, and magnetic effects with the goal of breaking the limitations set by scaling relations to achieve better catalytic performance. Finally, future opportunities and challenges associated with computation design of optimal catalysts for ammonia synthesis are outlined.

Designing catalyst to achieve ammonia synthesis at mild conditions is a meaningful challenge in catalysis community. Defective g-C₃N₄ nanosheet supported single-cluster ruthenium and iron catalysts were investigated for their ammonia synthesis performance. Based on density functional theory (DFT) calculations and microkinetic simulations, Ru₃ single-cluster anchored on defective g-C₃N₄ nanosheet (Ru₃/N_v-g-C₃N₄) has a turnover frequency (TOF) 5.8 times higher than the Ru(0001) step surface at industrial reaction conditions of 673 K and 100 bar for ammonia synthesis. In other words, similar TOFs could be achieved on Ru₃/N_v-g-C₃N₄ at much milder conditions (623 K, 30 bar) than on Ru(0001) (673 K, 100 bar). Our computations reveal the reaction proceeds parallelly on Ru₃/N_v-g-C₃N₄ through both dissociative and alternative associative mechanisms at typical reaction conditions (600–700 K, 10–100 bar); N–N bond cleavage of *N₂ and *NNH from the two respective pathways controls the reaction collectively. With increasing temperatures or decreasing pressures, the dissociative mechanism gradually prevails and associative mechanism recedes. In comparison, Fe₃/N_v-g-C₃N₄ catalyst shows a much lower catalytic activity than Ru₃/N_v-g-C₃N₄ by two orders of magnitude and the reaction occurs solely through the dissociative pathway. The finding provides a prospective candidate and deepens the mechanistic understanding for ammonia synthesis catalyzed by single-cluster catalysts (SCCs).

Dual-active sites (DASs) catalysts have positive potential applications in broad fields because of their specific active sites and synergistic catalytic effects. Therefore, the controllable synthesis and finely regulating the activity of such catalysts has become a hot research area for now. In this work, we developed a pyrolysis-etching-hydrogen activation strategy to prepare the DASs catalysts involving single-atom Cu and B on N-doped porous carbon material (Cu₁-B/NPC). Numerous systematic characterization and density functional theoretical (DFT) calculation results showed that the Cu and B existed as Cu-N₄ porphyrin-like unit and B-N₃ unit in the obtained catalyst. DFT calculations further revealed that single-atom Cu and B sites were linked by bridging N atoms to form the Cu₁-B-N₆ dual-sites. The Cu₁-B/NPC catalyst was more effective than the single-active site catalysts with B-N₃ sites in NPC (B/NPC) and Cu-N₄ porphyrin-like sites in NPC (Cu₁/NPC), respectively, for the dehydrogenative coupling of dimethylphenylsilane (DiMPSH) with various alcohols, performing the great activity (> 99%) and selectivity (> 99%). The catalytic performances of the Cu₁-B/NPC catalyst remained nearly unchanged after five cycles, also indicating its outstanding recyclability. DFT calculations showed that the Cu₁-B-N₆ dual-sites exhibited the lowest energy profile on the potential energy surface than that of sole B-N₃ and Cu-N₄ porphyrin-like sites. Furthermore, the rate-limiting step of dehydrogenation of DiMPSH on Cu₁-B-N₆ dual-sites also showed a much lower activation energy than the other two single sites. Benefitting from the superiority of the Cu₁-B-N₆ dual-sites, the Cu₁-B/NPC catalyst can also be used for CO₂ electroreduction to produce syngas. Thus, DASs catalysts are promising to achieve multifunctional catalytic properties and have aroused positive attention in the field of catalysis.