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A Comparative Study of the Catalytic Efficiency of Au, Ag, Pd and Pt Based Mono- and Bimetallic Trimers for the CO Oxidation ReactionAuthor: Saumya Gurtu Date: 2020-06-12 Report no: IIIT/TH/2020/57 Advisor:Deva U Priyakumar AbstractMetal nanoparticles have shown exceptional catalytic properties with relatively high chemical activity and specificity of the interaction. The chemical reactivity of metal nanoparticles is intimately linked to their elementary composition, atomic arrangement, shape, and size, a variety of features whose role is often intertwined. Understanding synergistic effects by studying the electronic structure and interaction of molecules in a reaction is essential to fine-tune the catalytic properties of bimetallic nano-alloy clusters which might be used in designing novel efficient catalysts. Density functional theory PBE0 calculations were performed to examine the structure and energetics of various intermediates involved in the CO oxidation reaction catalyzed by Au3−xYx (x = 0-3 and Y denotes Ag or, Pt or, Pd) trimer clusters through two possible pathways: Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms. The results of this investigation show that the catalytic behavior of the nano-cluster highly depends on its composition and the reaction site taken into consideration. It is observed that with a lower dopant percentage in the cluster composition, the barrier heights for a bimetallic trimer varies highly over different reaction sites. Thus, the reaction site becomes an important aspect of catalysis with clusters having a low dopant percentage. The gold-silver clusters and AuPt2 prefer ER mechanism due to low barrier height and higher extent of O–O bond activation for respective ER transition states whereas, gold-palladium and Au2Pt selectively favor LH mechanism due to low barrier height and more charge transfer from the corresponding cluster. The most active reaction centres found for gold-silver, gold-palladium, gold-platinum clusters are gold, palladium and platinum atoms respectively which, is also supported by the barrier height analysis, charge transfer analysis, and adsorption energetics. Our results show that the bimetallic clusters, in general, are more catalytically efficient in comparison to their pristine mono-metallic counterparts, owing to the strong synergistic effects. They efficiently activate the O–O bond in the oxidation reaction and have relatively easy CO2 dissociation. Positive linear correlations between transition state energies, ETS (ER) and ETS (LH), and the binding energies, ECO + EO2 and ECO-ADSORPTION, are found for the bimetallic clusters with Pearson correlation coefficient of 0.92 and 0.86, respectively. A correlation between ECO-ADSORPTION and ECO + EO2 is also found to be positive linear with a 0.92 Pearson correlation coefficient. Overall results of this investigation indicate that the alloyed clusters could potentially have better catalytic activity as compared to pure gold clusters for CO oxidation at low temperatures. Full thesis: pdf Centre for Computational Natural Sciences and Bioinformatics |
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