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Authors: Hussain, Riaz
Keywords: Natural Sciences
Applied chemistry
Issue Date: Apr-2017
Publisher: Government College University, Faisalabad, Pakistan
Abstract: Metal clusters play key role in chemical industry, nanotechnology and cellular biology. Chemical industry depends on the selection, development and application of catalysts. The most valuable catalysts used in these modern chemical industries consist of metal clusters. Introduction of a dopant atom in a metal cluster significantly enhances the catalytic activity. Moreover, in heterogeneous catalysis, the ability of metal cluster to react chemically with different molecular species totally depends on the size of the clusters. Bimetallic nano clusters have gained significant interest due to their specific and matchless structural, optical, electronic, and magnetic properties and their significance in nano technology and catalysis. Full range of bimetallic silver-yttrium AgnYm cluster of low nuclearity (n + m = 2-10) are studied using the density functional theory (DFT) at TPSSTPSS method with a Lanl2dz pseudopotential. The results for various properties including structural, ionization potential adiabetic, electron affinity, binding energy, HOMO-LUMO gap, average bond length, total energy, bond dissociation energy and 2nd order difference energy are evaluated as function of (n+m) size of the system. Moreover, the results for these bimetallic clusters are compared with pure silver and yttrium clusters. Different spin multiplicities of each cluster are also studied to locate the low energy structures. Cluster with higher nuclearity (n + m ≥7) favors three dimensional structure where clusters with low nuclearity (m + n ≤6) except (n + m = 5) favor two dimensional structure. Ag6 cluster also preferred planar 2D configuration. All pure silver clusters are more stable in low spin multiplicity, while pure yttrium clusters are more stable in higher spin multiplicity. Multiple bimetallic silver yttrium clusters have stability at varying spin state. Based on binding energy values the pure yttrium clusters are more stable than pure silver and bimetallic clusters. Density functional theory calculations have also been performed on pure silver (Agn), yttrium (Ym) and bimetallic silver yttrium clusters AgnYm (n+m = 2-10) for reactivity descriptors in order to find active sites for electrophilic and nucleophilic attack. The results illustrates that atoms in a stable ground state in a geometry can be categorized into different types of reactive sites. The reactivity of numerous sites as a function of cluster size and shape was thus investigated. The investigation reveals that the sizes and shapes of the pure silver, yttrium and bimetallic silver yttrium cluster (n = 2-10) influence the number and position of active sites for an electrophilic and/or nucleophilic attack. Doping of pure clusters with the other elements also influences the hardness, softness and chemical reactivity of the clusters. The softness increases as we increase the number of silver atoms in the cluster, whereas the hardness decreases. The chemical reactivity increases with silver doping whereas it decreases by yttrium doping. Silver atoms are nucleophilic in small clusters whereas, in large clusters, silver atoms are electrophilic in nature. The research here is designed at the investigation of new bimetallic clusters with distinctive electronic properties. These distinctive electronic properties comfort in finding new applications in electronic devices. Furthermore, these silver yttrium bimetallic clusters are expected to have improved catalytic activity which will assist industrial processes.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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