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Dalton Trans ; 49(19): 6407-6417, 2020 May 19.
Artigo em Inglês | MEDLINE | ID: mdl-32352455


Nickel nanoclusters are very promising for catalysis-related applications, especially involving chemical reactions with polluting molecules, such as carbon, nitrogen, and sulfur monoxides, which are directly or indirectly involved in serious environmental pollution problems. Therefore, it is of utmost importance to improve the understanding of the interaction between Ni nanoclusters and diatomic molecules, such as CO, NO, and SO, to provide insights into real subnano catalysts. Thus, here, we report an ab initio investigation based on density functional theory calculations within van der Waals D3 corrections to investigate the adsorption properties of CO, NO, and SO on Ni nanoclusters. From energetic and electronic criteria applied to Nin nanoclusters (n = 2-15), we selected Ni6 (octahedron) and Ni10 (triangular pyramid) nanoclusters as supports. According to our analyses, the molecular adsorption increases the stability of Ni nanoclusters, especially for Ni6 systems. The interaction intensity is larger for SO than for NO and CO in adsorbed systems, and the strong OS-Ni interaction is responsible for the well-known sulfur poisoning on transition-metal systems. The lowest energy adsorption sites are onefold for CO/Ni6, NO/Ni6, and CO/Ni10; twofold for NO/Ni10; and threefold for SO/Ni6 and CO/Ni10, where CO and NO molecules sustain linear and perpendicular geometries, while SO geometry changes to a bent configuration resulting from a sideways adsorption. The equilibrium bond lengths of the molecules expand upon adsorption, from 0.9% (NO/Ni6/10) to 11.3% (SO/Ni6/10), consequently, the internal molecular bond strengths decrease, since there is a reduction in the molecular stretching frequencies. This result occurs most strongly for SO followed by NO and CO systems, which was confirmed by an estimation of the energetic contribution of the distortion after the adsorption process. Thus, the strong S-Ni interaction, given by SO chemisorption on hollow sites with a sideways interaction, implies an energetic decrease and, consequently, a part of the energy gained from the SO-Ni interaction is from the SO and nanocluster distortions. Ultimately, using the energy decomposition analysis (from SAPT0) for XO/Ni6 systems, we improved the understanding of the CO and NO (SO) singlet (doublet) spin multiplicities' interaction with Ni6 nanoclusters.

J Chem Inf Model ; 60(2): 537-545, 2020 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-31917570


In this work, we report an ab initio investigation based on density functional theory calculations within van der Waals D3 corrections to investigate the adsorption properties and activation of CO2 on transition-metal (TM) 13-atom clusters (TM = Ru, Rh, Pd, Ag), which is a key step for the development of subnano catalysts for the conversion of CO2 to high-value products. From our analyses, which include calculations of several properties and the Spearman correlation analysis, we found that CO2 adopts two distinct structures on the selected TM13 clusters, namely, a bent CO2 configuration in which the OCO angle is about 125 to 150° (chemisorption), which is the lowest energy CO2/TM13 configuration for TM = Ru, Rh, Pd. As in the gas phase, the linear CO2 structure yields the lowest energy for CO2/Ag13 and several higher energy configurations for TM = Ru, Rh, Pd. The bent CO2 (activated) is driven by a chemisorption CO2-TM13 interaction due to the charge transfer from the TM13 clusters toward CO2, while a weak physisorption interaction is obtained for the linear CO2 on the TM13 clusters. Thus, the CO2 activation occurs only in the first case and it is driven by charge transfer from the TM13 clusters to the CO2 molecule (i.e., CO2-δ), which is confirmed by our Bader charge analysis and vibrational frequencies.

J Chem Phys ; 144(5): 054310, 2016 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-26851924


Several studies have found that the Pt55 nanocluster adopts a distorted reduced core structure, DRC55, in which there are 8-11 atoms in the core and 47-44 atoms in the surface, instead of the compact and high-symmetry icosahedron structure, ICO55, with 13 and 42 atoms in the core and surface, respectively. The DRC structure has also been obtained as the putative global minimum configuration (GMC) for the Zn55 (3d), Cd55 (4d), and Au55 (5d) systems. Thus, the DRC55 structure has been reported only for systems with a large occupation of the d-states, where the effects of the occupation of the valence anti-bonding d-states might play an important role. Can we observe the DRC structure for 55-atom transition-metal systems with non-occupation of the anti-bonding d-states? To address this question, we performed a theoretical investigation of the Y 55, Zr55, Nb55, Mo55, Tc55, and Pt55 nanoclusters, employing density functional theory calculations. For the putative GMCs, we found that the Y 55 adopts the ICO55 structure, while Nb55 and Mo55 adopt a bulk-like fragment based on the hexagonal close-packed structure and Tc55 adopts a face-centered cubic fragment; however, Zr55 adopts a DRC55 structure, like Zn55, Cd55, Pt55, and Au55. Thus we can conclude that the preference for DRC55 structure is not related to the occupation of the anti-bonding d-states, but to a different effect, in fact, a combination of structural and electronic effects. Furthermore, we obtained that the binding energy per atom follows the occupation of the bonding and anti-bonding model, i.e., the stability of the studied systems increases from Y to Tc with a small oscillation for Mo, which also explains the equilibrium bond lengths. We obtained a larger magnetic moment for Y 55 (31 µB) which can be explained by the localization of the d-states in Y at nanoscale, which is not observed for the remaining systems (0-1 µB).