Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d-Band Energies of Metals for Catalytic Applications

Abstract

The valence band structures (VBS) of eight transition metals (Fe, Co, Ni, Cu, Pd, Ag, Pt, Au) were investigated by photoelectron spectroscopy (PES) using He I, He II, and monochromatized Al Kα excitation. The influence of final states, photoionization cross-section, and adsorption of residual gas molecules in an ultrahigh vacuum environment are discussed in terms of their impact on the VBS. We find that VBSs recorded with monochromatized Al Kα radiation are most closely comparable to the ground state density of states (DOS) derived from quantum mechanics calculations. We use the Al Kα-excited PES measurements to correct the energy scale of the calculated ground-state DOS to approximate the "true" ground-state d-band structure. Finally, we use this data to test the d-band center model commonly used to predict the electronicproperty/catalytic-activity relationship of metals. We find that a simple continuous dependence of activity on d-band center position is not supported by our results (both experimentally and computationally).

Explaining the Size Dependence in Platinum‐Nanoparticle‐Catalyzed Hydrogenation Reactions

“…Therefore,ad ecrease of crystallinity and am etal-oxide transition were observed with the decreasing size of the PtNPs.T ofurther reveal their interaction with hydrogen and quinoline molecules,t he d-band electron structures of the PtNPs were characterized by high-resolution valence-band (VB) XPS spectra (Figure 2e), which are proportional to the density of states (DOS), and directly related to the strength of interaction between the PtNPs and guest molecules. [5,42,43] The spectra were recorded in an ultra-high vacuum (UHV), so could be different from those taken under ambient reaction conditions.T herefore,t his analysis provides ag eneral, qualitative trend of the d-band structure of the PtNPs varying with their sizes.A ccording to the d-band center theory,w hen aguest molecule is adsorbed on ametal surface,hybridization between the metal d-band and an induced state by the guest molecule occurs to form fully filled bonding DOS and partially filled antibonding DOS states.T he bond strength is determined by the filling degree of the antibonding states, which can be described by the position of the d-band center. [44][45][46] Because the antibonding states lie directly above the de lectron band, [44] we chose the VBM as ar eference for the d-band center.…”

Fast Prediction of Adsorption Properties for Platinum Nanocatalysts with Generalized Coordination Numbers

“…The trends in the adsorption energies of small oxygen-and hydrogen-containing adsorbates on Pt nanoparticles of various sizes and on extended surfaces were analyzed through DFT calculations by making use of the generalized coordination numbers of the surface sites. [5] Moreover, theoretical chemistry nowadays encounters the need for more realistic descriptions of catalytic nanoparticles. It generates linear adsorption-energy trends, captures finite-size effects, and provides more accurate descriptions than d-band centers and usual coordination numbers.…”

“…[2] The costs are lowered by using nanoparticles, as their high surface area to volume ratio reduces catalyst loadings. [5] Moreover, theoretical chemistry nowadays encounters the need for more realistic descriptions of catalytic nanoparticles. Experimentally, this requires facile synthesis methods that permit the preferential formation of active sites with the highest turnover frequencies.…”

Electronic-structure-based material descriptors: (in)dependence on self-interaction and Hartree–Fock exchange

“…11,12 This descriptor has been tremendously successful in predicting adsorptive and reactive properties as a function of structural saturation, strain, and alloy composition, 6,13 including surface and subsurface alloys. 14-17 However, the d-band center descriptor has been found to be inadequate for a few cases, 18,19 and to loose accuracy on late transition metals, 20 for instance.Recent studies addressed the improvement of the first-order d-band center descriptor. In particular, the poorer alignment of late transition metals has been attributed to the proportionality deviations of d-band width W, 21 mainly affecting late transition metals.…”