Theoretical Analysis of Energy Efficiency of Plasma-Assisted Heterogeneous Activation of Nitrogen for Ammonia Synthesis

Availability and reactivity of N2(v) for NH3 synthesis by plasma catalysis

“…In addition to dissociative adsorption reactions that are proposed to be responsible for NH 3 formation from N 2 (v), N 2 (v) can quench in gas-phase collisions and in collisions with surfaces that do not contribute to NH 3 formation. Through ab initio molecular dynamics, Kedalo et al [18] demonstrate that N 2 (v) adsorbed on Ru undergoes vibrational relaxation on sub-ns timescales, and as a result, only higher vibrational levels of N 2 (v) undergo dissociative adsorption faster than vibrational relaxation. Vibrational relaxation of N 2 (v) on surfaces has also been experimentally measured by Black et al [19] using Raman scattering and by Marinov et al [20] using quantum cascade laser absorption spectroscopy, where they show that N 2 (v = 1) has a relaxation probability of ∼10 −3 for every collision with a surface, irrespective of whether the surface is SiO 2 , Al 2 O 3 , TiO 2 , stainless steel, Al, Cu, or Teflon.…”

Applicability of the Fridman–Macheret α-Model to Heterogeneous Processes in the Case of Dissociative Adsorption of N2 on the Ru Surface

“…We note that unlike α V FM , α V discussed in present work includes entropy effects and cannot be estimated solely by eq . However, for the microkinetic simulation of NH 3 synthesis − the F–M model reasonably approximates the vibrational efficacy of highly excited molecules with v ≥ 7 which play a crucial role when the vibrational–vibrational exchange collisions prevail in nonequilibrium plasma, and the vibrational distribution is assumed to have a Treanor shape. , One should mention that applicability of the F–M model to other catalytic systems is a subject for further investigation. We also performed an analysis of the angular distribution of dissociated N 2 molecules on Ru(113) and observed that the polar angle distribution for Ru(113) is notably more smeared compared to Ru(0001), while the highest peak of the azimuth angle distribution corresponds to the direction parallel to the step, whereas the molecules with direction perpendicular to the step are known to have a lowered dissociation barrier …”

“…Training data were obtained using DFT calculations with the PBE functional, as implemented in the Vienna Ab initio Simulation Package (VASP), 3 × 3 × 1 Monkhorst–Pack Γ-centered mesh of k -points, plane wave cutoff E cut = 400 eV, and pseudopotential in the form of projector augmented waves (PAW) . It should be noted that the RPBE functional appears to be a more precise functional for the N 2 + Ru system. , Nevertheless, calculated values of minimum energy barriers with PBE are 1.9 eV for flat Ru(0001) and 1.0 eV for stepped Ru(113), which are in reasonable agreement with the ones obtained using the RPBE functional. , …”

“…30,31 Nevertheless, calculated values of minimum energy barriers with PBE are 1.9 eV for flat Ru(0001) and 1.0 eV for stepped Ru(113), which are in reasonable agreement with the ones obtained using the RPBE functional. 5,32 The simulation was performed on both flat Ru(0001) and stepped Ru(113) surfaces. The view of the Ru(113) surface is shown in Figure 1.…”

“…Moreover, it was shown by molecular beam experiments that vibrational excitation of a nitrogen molecule can promote its dissociation process on a catalyst’s surface . Therefore, several works − investigated the possibility of vibrational excitation in plasma systems to increase the performance of a synthesis and reduce the process temperature. However, in these works it was assumed that the effectiveness of vibrational excitation for dissociation process on a surface can be described by the Fridman–Macheret (F–M) α-model, though it was initially developed for gas phase processes of small molecules.…”