Equilibrium atomic conformation of Pt 2 Ru 3 nanoparticles under gas atmosphere of CO/H 2 investigated by density functi
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Equilibrium atomic conformation of Pt2Ru3 nanoparticles under gas atmosphere of CO/H2 investigated by density functional theory and Monte Carlo simulation Md Khorshed Alam* and Hiromitsu Takaba, Department of Environmental Chemistry and Chemical Engineering, School of Advanced Engineering, Kogakuin University, 2665-1 Nakano, Hachioji, Tokyo 192-0015, Japan Address all correspondence to Hiromitsu Takaba at [email protected] (Received 1 November 2017; accepted 13 March 2018)
Abstract We have investigated the equilibrium conformation of Pt2Ru3 nanoparticles in the presence of H2 and CO mixture gas using density functional theory (DFT) and Monte Carlo (MC) simulation. A multiple linear regression equation was prepared using DFT results to calculate adsorption energy from the structural descriptors. Using the regression equation, MC simulations were employed to elucidate the equilibrated conformation of Pt2Ru3 particles at a finite temperature of H2/CO where CO concentration in the range 100–500 ppm. MC results indicate that CO/H2 coadsorption induced the rearrangement of alloying atoms and Pt/Ru ratio exposed to the surface decreases with the increase of CO concentration.
Introduction In a polymer electrolyte fuel cells (PEFCs), the existence of tiny volume of CO in H2 feed from the reformer acts to poison Pt anode catalyst.[1,2] The metal surface which binds hydrogen weakly lead high catalytic selectivity; although that metal surfaces usually have high activation barriers for H2 dissociation that bounds the activity of the catalysts.[3,4] Ru addition to Pt helps to hinder CO poisoning of the Pt surface sites that would carry out hydrogen oxidation.[5,6] Ru stimulates oxidation of CO to form CO2 and may diminish the Pt–CO interaction.[7] In such bimetallic alloy, the geometrical layouts of two metals in surfaces are very crucial for their catalytic nature[8–10] because their reactivity and selectivity would be varied by their surface adjustment.[11] The alloying effects of Pt for CO tolerance is likely to be complicated although some facets of it are understood: CO removal is occurred by oxidation to CO2 and the activation barrier for a reaction amid CO and an involved oxidant species on the surface has been found to depend precisely on the adsorption strength of both species.[12–15] Still, this is a very critical issue to speculate the adsorption strengths of the species under complex conditions, such as segregation of mixing elements and coadsorption of other species. Some researchers have also suggested a loosening of the CO bond to the Pt–Ru alloy referring to pure Pt, that established by recent ultrahigh
* Present address: Department of Physics, University of Barisal, Kornokathi, Barisal 8200, Bangladesh.
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vacuum (UHV) studies.[16] For methanol decomposition reaction, Watanabe and co-workers reported that dehydrogenation takes place at Pt sites and CO oxidation takes place at Ru sites with the available formed OH species.[17] Koper and co-workers theoretically investigated adsorption
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