Insights into the Mechanism of Ammonia Decomposition on Molybdenum Nitrides Based on DFT Studies

Abstract

Ammonia can be used to produce carbon-free hydrogen for fuel cells and is considered as a key player in a noncarbon economy. In the present study, we investigated ammonia decomposition on Mo 2 N-( 100) and ( 111) surfaces using density functional theory calculations. The stepwise dissociation of ammonia over the surface Mo atom on Mo 2 N(100) has activation barriers >1.0 eV for all three N−H bonds. In contrast, the activation barriers for dissociating the first and second N−H bond in 3-fold Mo sites on the (111) surface are only 0.64 and 0.22 eV, respectively, whereas the activation barrier for breaking the last N−H bond is 1.12 eV. Coupling of NH x species with intrinsic surface N atoms does not always promote N−H bond activation but the formation of N lat NH x species needs to overcome a high activation barrier. Consequently, N−N coupling is not expected to have significant contributions to overall ammonia dissociation. Our results also showed that recombinative desorption of N atoms involves the formation of highly activated meta-stable dinitrogen species and its subsequent desorption as the N 2 molecule. The overall ammonia decomposition is limited by this recombinative desorption process, with an overall energy cost of ∼2.61 eV on Mo 2 N(100) and ∼1.29 eV on Mo 2 N(111). On both surfaces, the intrinsic surface N atoms of the nitride actively participate in the formation of desorbed nitrogen, making the process follow a Mars−van Krevelen mechanism.

Design of Active Centers in Ammonia Synthesis on Mo-Based Catalysts: A Theoretical Study

“…The site Mo 3 Pt on the plane Mo 3 Pt 3 N(100) reveals the highest TOF due to the successful combination of its local structure and thermodynamics. The calculated Q N in Table 7 give E diff = 129.5 kJ/mol and E des = 258.9 kJ/mol for the dominant M 4 N state on the plane Mo 2 N(100), which is close to the DFT data 125.4 and 258.5 kJ/mol, respectively [55].…”

Simulation of Ammonia Looping Dissociation and Formation for Energy Conversion

“…The results of the two responses can be kept at surrounding or operating temperature. The vitality kept in a thermochemical medium can be stated as [2,17] Q ₌nAΔHr (6) where; nA = number of mole of the reactant A (mol) and ΔHr = enthalpy reaction (kWh/ mol A). The chemical reactions in a TES system are shown in Figure 5.…”

“…Decrease of petroleum products at a fast rate and expanding of value makes essential the development of green power markets. As of now, there is a developing worldwide help for innovative work of sustainable power source advancements, especially for power generation [9][10][11][16][17][18]].…”

Metallic porous nitride single crystals at two-centimeter scale delivering enhanced pseudocapacitance

“…We calculate the unit cell and obtain the lattice parameters of MoN: a = b = 5.73 Å and c = 5.61 Å (a 6 × 6 × 6 k-point grid). A p(2 × 2) superstructure with Mo termination of the [001] surface is used for the slab model 34,53 . In this model, which includes three layers, the atoms in the bottom layers are frozen to its bulk geometry during the optimization and other atoms are fully relaxed.…”