Carbon monoxide adsorption on platinum-osmium and platinum-ruthenium-osmium mixed nanoparticles

Abstract

Density functional calculations (DFT) on carbon monoxide (CO) adsorbed on platinum, platinum-osmium, and platinum-ruthenium-osmium nanoclusters are used to elucidate changes on the adsorbate internal bond and the carbon-metal bond, as platinum is alloyed with osmium and ruthenium atoms. The relative strengths of the adsorbate internal bond and the carbon-metal bond upon alloying, which are related to the DFT calculated C-O and C-Pt stretching frequencies, respectively, cannot be explained by the traditional 5σ-donation/2π*-back-donation theoretical model. Using a modified π-attraction σ-repulsion mechanism, we ascribe the strength of the CO adsorbate internal bond to changes in the polarization of the adsorbate-substrate hybrid orbitals towards carbon. The strength of the carbon-metal bond is quantitatively related to the CO contribution to the adsorbate-substrate hybrid orbitals and the sp and d populations of adsorbing platinum atom. This work complements prior work on corresponding slabs using periodic DFT. Similarities and differences between cluster and periodic DFT calculations are discussed.

Adsorption of Carbon Monoxide on Platinum–Ruthenium, Platinum–Osmium, Platinum–Ruthenium–Osmium, and Platinum–Ruthenium–Osmium–Iridium Alloys

“…CO Adsorption on PtOs. CO/PtOs has been studied before using cluster 42 and periodic 41 DFT for PtOs alloys with Os atoms located only in the adsorbing substrate layer. In this work, we expand the scope of CO/PtOs, by considering substrate configurations with Os atoms located at any of the three layers, at 8 and 21 Os mole percent (CO/Pt 22 Os 2 and CO/Pt 19 Os 5 , respectively).…”

“…15 Upon adsorption on the Pt, the C−O internal bond weakens and a stable C−M dative bond is formed. Polarization modulated infrared reflection absorption spectroscopy measurements on CO ads on Pt 29−31 and Pt-based alloys (PtRu, PtOs, and PtRuOs) 27,29 showed alloy induced downshift of the CO ads stretching frequency (ν CO ) relative to free CO. Computational simulations for CO ads on Pt-group metals 32−37 and on Pt-based alloys such as PtRu, 38−40 PtOs, and PtRuOs alloys 41,42 verified the ν CO downshift. Several phenomenological models correlate renormalized CO orbitals (i.e., CO adsorbate orbitals) with the strength of the CO ads internal bond and the C−Metal surface bond.…”

“…However, we also examine the effect of the CO coverage for a single PtRu alloy. Consistent with our past reports, − , we choose the (100) as the substrate face for Pt and Pt-based alloys. Moreover, we also performed DFT calculations for CO ads on a two-layer Pt(111) substrate at 1/9 ML CO coverage using the PBE0 functional, , where we found the atop adsorption to be the preferred site (Figure S1).…”

Introductory Chapter: Overview of the Properties and Applications of Noble and Precious Metals

“…use of Ni-Ir and Ni-Os bimetallic NP alloys for hydrogenation reactions [48], Os NPs for CO oxidation [49,50], and Os NP electro-catalysts for PEM fuel cells [51] and direct methanol fuel cells [52].…”

“…Organometallic NPs and carbon-supported NPs containing Ru have been synthesized for application related to solar cells [57] and catalysis [58,59]. There is a wide range of work on Ru in both homogeneous and heterogeneous catalyses and the synthesis of Ru NPs [47,49,50].…”