Establishing Relationships Between the Geometric Structure and Chemical Reactivity of Alloy Catalysts Based on Their Measured Electronic Structure

Abstract

While it is fairly straightforward to predict the relative chemical reactivity of pure metals, obtaining similar structure-performance relationships for alloys is more challenging. In this contribution we present experimental analysis supported with quantum chemical DFT calculations which allowed us to propose a simple, physically transparent model to predict the impact of alloying on the local electronic structure of different sites in alloys and on the local chemical reactivity. The model was developed through studies of a number of Pt alloys. The central feature of the model is that hybridization of d-orbitals in alloys does not lead to significant charge transfer between the constituent elements in the alloy, and therefore the width of the local density of d-states projected on a site, which is easily calculated from tabulated parameters, is an excellent descriptor of the chemical reactivity of the site.

Effect of Particle Size and Adsorbates on the L3, L2 and L1 X-ray Absorption Near Edge Structure of Supported Pt Nanoparticles

“…Several researchers have drawn parallels between electron energy loss spectroscopy and X-ray absorption near edge spectroscopy [54][55][56]. More recently, Schweitzer et al had found for PtCu, PtRu and Pt 3 Sn alloys that the integrated number of states under the edge did not change significantly, implying that charge transfer is not a dominant effect in these Pt alloy systems in agreement with prior work on Ni alloy systems [10]. Therefore, following a similar procedure, we calculated the density of unoccupied states near the Fermi level to explain the results of our XANES measurements.…”

“…More recently Schweitzer et al have shown that the Pt edge intensity and position changes in Pt alloys and is dependent on the alloying metal [10]. For example, when Pt is alloyed with Sn, Pt L 3 XANES edge broadens and its intensity decreases compared to pure Pt.…”

In situ electron energy loss spectroscopy study of metallic Co and Co oxides

“…Sankar et al utilized the x-ray absorption nearedge structure to characterize the Co oxides and found that the differences between 3d and 4s energy levels of CoO and Co 3 O 4 were 9.5 eV and 11 eV, respectively. Although the shift in the edge is commonly associated with depletion of electron density in the d-band of Co, recent work from Schweitzer et al 44 suggests that the position of the edge is directly related to the density of states at the Fermi level ͑and not due to the charge transfer effects͒. 42,43 Motivated by these results, we performed first-principles modeling of the Co L 3 edge fine-structure for Co 3 O 4 , CoO, and Co ͓Fig.…”

Single-Atom Alloy Pd–Ag Catalyst for Selective Hydrogenation of Acrolein

“…However, there is a trade-off between high selectivity and high activity in that high selectivity to allyl alcohol is a result of the weak binding of acrolein (which is favored over Ag) whereas the efficient dissociation of H 2 takes place over 3 metals such as Pd and Pt which are too reactive for molecular adsorption of acrolein and selectivity shifts towards undesired products. [19][20][21][22] Alloys have been employed previously for the selective hydrogenation of α, β-unsaturated aldehydes. For example, Rh-Cu/SiO 2 alloy catalysts showed both higher selectivity and activity to crotyl alcohol in the selective hydrogenation of crotonaldehyde.…”