Stabilities, electronic and magnetic properties of Cu-doped nickel clusters: a DFT investigation

Electronic properties and adsorption mechanism of Ru-doped copper clusters towards CH3OH molecule: A DFT investigation

In this study, we have investigated the stability and electronic properties of the Cu_nRu (n = 2-10) nanoclusters and their interaction with the CH₃OH molecule without and with the presence of O₂ molecule by using DFT calculations with TPSS/SDD/6-311g(d,p) level of theory. Based on the second energy difference (Δ²E), the results reveal that the Cu_nRu (n = 4, 6 and 8) clusters are relatively more stable than their neighboring clusters. The values obtained for the Fukui function (f^-) proves that the Ru atom in the Cu_nRu clusters is an excellent adsorption site for the molecules. The interaction of the Cu_nRu clusters with CH₃OH molecule exhibits that the Ru atom is the preferred adsorption site for the CH₃OH molecule, where the O atom of the CH₃OH molecule is strongly chemisorbed onto the Ru site of the clusters, forming a strong bond between the Ru and O atoms. The copper sites of the clusters were found less preferred for the adsorption of CH₃OH, and the complexes formed between both species are less stable than those obtained from the CH₃OH chemisorption over the Ru site of the clusters. The interaction of CH₃OH with the clusters was also evaluated in an oxidizing environment, and the results obtained reveal that the molecule is greatly chemisorbed over the ruthenium site with adsorption energies which vary from - 1.18 to - 2.05 eV. In the presence of the oxygen, the gap energy of the clusters was sharply changed after their interactions with the CH₃OH molecule, suggesting that these clusters can easily detect the above molecule with great sensitivity. Therefore, the presence of the oxygen not only does not prevent the adsorption process, but it considerably promotes the CH₃OH chemisorption onto the ruthenium site of the clusters and therefore significantly rises their sensitivity performance. In conclusion, the Cu_nRu clusters could be employed as effective nanosensors for the CH₃OH molecule detection.

Dressing of Cu Atom over Nickel Cluster Stimulating the Poisoning-Free CO Oxidation: An Ab Initio Study

In this work using first-principles calculations based on spin-polarized density functional theory (DFT), the role of the Cu atom in degrading the poisoning of carbon monoxide (CO) over Ni_nCu clusters is unveiled. The search has been initiated with the examination of structural, magnetic, and electronic properties of Ni_n+1 and Ni_nCu clusters (1 ≤ n ≤ 12). X-ray absorption near-edge structure (XANES) spectra of Ni K-edge are computed to extract the information on the oxidation states and coordination environment of metal sites of the clusters. This study is operated with the two forms of dispersion corrections, i.e., D2 and D3, with standard DFT (with LDA and GGA functionals) for the consideration of van der Waals interactions during CO adsorption. The PBE and PBE-D3 approaches are found to be capable of yielding the experimentally observed preferential site for CO adsorption. The effect of spin-polarization on the reactivity of transition metals (TMs) toward CO adsorption is crucially assessed by the electronic reactivity descriptors such as d-band center, d-band width, and fractional filling of d-band using a spin-polarized d-band center model. The effective charge transfer from Cu to Ni atoms makes Ni atoms more efficient of charge and is attributed to the degrading adsorption of CO over Ni_nCu clusters. The Ni₁₂Cu cluster stands out with good CO oxidation activity for the Langmuir-Hinshelwood (L-H) reaction pathway.