Quantum Effects in the Dissociative Chemisorption of N₂ on Fe(111): Full-Dimensional Quantum Dynamics and Quasi-Classical Trajectory Study

Abstract

The dissociative chemisorption of the N 2 molecule is the rate-limiting step in the ammonia synthesis process. Here, we carried out the full-dimensional quantum dynamics study for the dissociative chemisorption of N 2 on rigid Fe(111) based on a new, accurately fitted potential energy surface (PES). The computed dissociation probabilities reveal significant quantum effects for this heavy-diatomic reaction, as compared with the quasi-classical trajectory (QCT) results. This is due to the deep pretransition state adsorption well for this reaction, which also leads to the strong dynamical steering effects, as confirmed in the QCT calculations. The current magnitude of quantum and quasi-classical dissociation probabilities on a rigid surface agrees much better with the experimental data than the previous theoretical results with approximate surface atom motion treatment at incident energies lower than 4.0 eV. This is also the first time the full-dimensional quantum dynamics study is accomplished for the dissociative chemisorption of a heavy-diatomic molecule.

Dynamics of Dissociative Chemisorption of NH3 on Fe(111) on a Twelve-Dimensional Potential Energy Surface

“…An accurate six-dimensional quantum dynamics study was performed recently by us for the dissociation of N 2 on rigid Fe(111) based on a fundamentalinvariant-neural network (FI-NN) potential energy surface (PES). 23,24 Our results agree much better with the experimental data than the previous theoretical results. It was found that quantum effects are significant for this heavy diatomic molecule−surface reaction.…”

“…The vibrational efficiency of the v 1 state is large at higher total energies. The mode specific reactivity for NH 3 /Fe­(111) is different from those in NH 3 + Ni(111) and NH 3 + Ru(0001) systems. For ammonia dissociation on Ru(0001), increasing the translational energy and vibrational energy have roughly the same effect at both low- and high-energy regions, in which the calculated vibrational efficacies for the first excitation in all vibrational modes are almost equal to 1.…”

“…From the above discussion, we know that there exists a very deep pre-adsorption well at the top site for NH 3 / Fe(111), which is much deeper than for the N 2 /Fe(111) 23 and NH 3 /Ru(0001) 27 systems previously studied. Thus, we are interested in the lifetime of NH 3 in this deep well before dissociation.…”

“…In this process, ammonia is not only the product but also the reactant. The decomposition of ammonia has been considered to be an effective means for hydrogen generation in proton exchange membrane fuel cells, which does not produce CO x byproducts that are toxic to the cathodes. ,− Catalysis on metal surfaces is usually caused by dissociative chemisorption (DC) of gas molecules, which is often the rate-determining step in heterogeneous catalytic processes. − The metal iron is an active good catalyst for ammonia synthesis and decomposition. − …”

Non-linear temperature dependence of nitrogen adsorption and decomposition on Fe(111) surface

“…However, more than 100 years after its discovery, a full understanding of this catalytic process is still lacking. The Fe(111) crystal face is believed to be the most active, and as such it has been thoroughly investigated [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Ertl and coworkers [9,11] have measured the variation of the absorbed N 2 bond vibration frequency.…”