A Density Functional Theory Study on Carbon Monoxide Adsorption on Platinum–Osmium and Platinum–Ruthenium–Osmium Alloys

Abstract

Periodic density functional theory calculations on carbon monoxide (CO) adsorbed atop on platinum−osmium binary alloys (PtOs 2 and PtOs 4 ) and the platinum−ruthenium−osmium tertiary alloy (PtRu 2 Os 2 ) are used to elucidate the changes in the C−O and C−Pt bonds upon alloying Pt with Ru/ Os atoms. As Pt is alloyed with Ru/Os atoms, the adsorbate internal bond (C−O bond) and the adsorbate−metal bond (C−Pt bond) strengthen following the substrate trends of PtOs 4 > Pt > PtOs 2 > PtRu 2 Os 2 and Pt > PtOs 4 > PtOs 2 > PtRu 2 Os 2 , respectively. These trends are manifested by the corresponding C−O and C−Pt stretching frequencies and the CO adsorption energy variations. Here, we establish a theoretical framework based on the π-attraction σ-repulsion mechanism to explain the above results. This model correlates the charges, polarizations, and electron densities of the adsorbate CO orbitals, and the sp/d populations of the adsorbing Pt atom. For the systems studied here, the traditional theoretical model of 5σ-donation/2π*-back-donation with the metal substrate bands is not always sufficient to explain the relative C−O and C−Pt bonds strengths.

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

“…This work complements our prior work on CO ads on binary PtOs 2 and PtOs 4 alloys and on the PtRu 2 Os 2 tertiary alloy using periodic DFT, 35 where the variations on the CO ads and C-Pt bonds were correlated with changes in the populations of the carbon 2s and p xy atomic orbitals, as well as the s, p, and d orbitals of the adsorbing Pt atom (Pt c ). Here, we study the validity of our last model by examining the CO adsorption on Pt 26 , Pt 24 Os 2 , Pt 22 Os 4 , and Pt 22 Ru 2 Os 2 nanoclusters, where the nanocluster structure mostly corresponds to the slab structure priory explored by periodic DFT.…”

“…Density functional theory (DFT) on small Pt and PtOs nanoparticles was used by Ishikawa et al 20 to observe ν CO , C-Pt stretching frequency (ν CPt ), and CO ads enthalpy of adsorption (E ads ) reductions upon Pt alloying with Os. Recently, Dimakis et al 35 using periodic DFT for CO ads on PtOs 2 and PtOs 4 binary alloys and the on the tertiary PtRu 2 Os 2 alloy observed CO ads internal bond and adsorbatemetal bond (C-Pt bond) strengthening following the substrate trends of PtOs 4 > Pt > PtOs 2 > PtRu 2 Os 2 and Pt > PtOs 4 > PtOs 2 > PtRu 2 Os 2 , respectively. However, the importance of the work of Dimakis et al 35 was the theoretical interpretation of the above trends using charges and polarizations of adsorbate-substrate hybrid orbitals.…”

“…Recently, Dimakis et al 35 using periodic DFT for CO ads on PtOs 2 and PtOs 4 binary alloys and the on the tertiary PtRu 2 Os 2 alloy observed CO ads internal bond and adsorbatemetal bond (C-Pt bond) strengthening following the substrate trends of PtOs 4 > Pt > PtOs 2 > PtRu 2 Os 2 and Pt > PtOs 4 > PtOs 2 > PtRu 2 Os 2 , respectively. However, the importance of the work of Dimakis et al 35 was the theoretical interpretation of the above trends using charges and polarizations of adsorbate-substrate hybrid orbitals. Their work was based on a modified π -attraction σ -repulsion mechanism, with the inclusion of the σ -attractive part via charge donation to the substrate (vide infra).…”

Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state

“…[1][2][3][4][5], and theoretically, e.g., refs. [6][7][8][9][10][11][12][13][14][15][16]. The bonding is popularly described in terms of σ-donation and π* back-donation in a frontier orbital scheme, but detailed experimental measurements using x-ray emission spectroscopy (XES) in combination with density functional theory (DFT) spectrum simulations have revealed a different picture.…”

Orbital mechanism of upright CO activation on Fe(100)

“…We have seen any sigma or pi system lacking in CO-metal bonding in general. Recent investigations by [34][35][36][37] suggest that the σ system is not completely repulsive and that it contains both attractive and repulsive components. This extended model actually represents a real step forward toward revealing the fundamental nature of orbital roles in CO-metal interactions.…”