Theoretical Modeling of Addition Reactions of an H2 Molecule to Mg17L Magnesium Clusters Doped with 3d Metals

Density Functional Theory Modeling of Reactions of Addition of H2 Molecules to Magnesium Clusters Mg17M Doped with Atoms M of Transition 3d Elements

“…As it can be seen from Table S1, the high-multiplicity states are preferable for the Mg 17 M clusters with early 3d metal dopants with two, three, and four parallel spins for Ti, V, and Cr. In contrast, for clusters with later 3d metal dopants, the medium- and low-spin terms with three, two, and one spin for Mn, Fe, and Co and the zerovalent state of Ni are preferred. The calculated spin densities ρ­(M) on the dopant atoms correlate well with the number of their spins.…”

“…Transition states F and H correspond to activation barriers separating the local minima E , G , and I . The second (postsorption) stage between structures E , F , G , H , and I has been entitled , as a stage of “dopant cleaning from hydrogen atoms” in the structure I of which the dopant is liberated from Mg–H bonds and, if it remains at an open surface position in I , is potentially prepared to interact with a following molecule H 2 and to start the next cycle. The third stage between I and J corresponds to migration of H atoms from I to more distant surface sites at the “lower” hemisphere of the backbone (opposite to dopant).…”

“…The third stage between I and J corresponds to migration of H atoms from I to more distant surface sites at the “lower” hemisphere of the backbone (opposite to dopant). The last segment between J and K should be taken in account if the dopant is not retained at an open surface position in I and J , but in parallel with H atom displacements, shifts into the internal cavity of the cage and becomes sterically screened by neighboring surface Mg atoms (see refs and and the present section for more detail).…”

“…In section 5 we discuss a modified pathway of hydrogenation In addition to calculations of structural, energetic, and spectroscopic properties of the intermediates and transition states, our aim was to determine the "limiting" stages of the reactions, to evaluate the energies and activation barriers at the The catalytic cycle of elementary hydrogenation reactions, which had been addressed earlier, 33,36,37 together with the key structures of stationary points of the PES, corresponding to intermediates and transitional states along the MEP, are presented in Figure 1. The structures A, B, C, D, and E correspond to the sorption stage: A, infinitely distant reagents Mg 17 Ni + H 2 (∞), whose energy is taken as the reference on the energy scale; B, transition state on the way from A to a weakly bonded physisorbed complex C (hereafter, μ-H 2 complex); D, transition state of transformation of the μ-H 2 into a chemisorbed complex Mg 17 NiH 2 with the structure E containing both H atoms in bridging positions over the edges or faces of the Mg 17 backbone.…”