Reliable Element-Specific d-Band Analysis of Transition Metal Nanoparticles Using X-ray Absorption Spectroscopy

Metallic nanoparticles (NPs) have been extensively studied as improved catalysts due to their unique atomic structures and electronic properties. A reliable strategy to characterize the electronic properties, specifically the d-band structure, of metal NPs is challenging. In this work, we present a general strategy for fitting the X-ray absorption near-edge spectroscopy (XANES) spectrum to accurately determine the electronic properties in metal NPs and deduce d-band parameters such as the d-band width and d-band center position. In conjunction with valence-band X-ray photoelectron spectroscopy (VBXPS), our fitting analysis reliably calibrates the XANES spectrum such that effects of instrumental and core-hole broadening are minimized and the d-band structure can be accurately determined. For a series of palladium (Pd) NPs, we use our XANES fitting analysis approach to characterize the Pd d-band and identify trends in the electronic properties consistent with prior literature reports. In closing, we propose a mechanism in which the Pd d-band changes due to size and surface effects based on our element-specific XANES fitting analysis within the framework of the popular Nørskov d-band model of transition metal surfaces. We anticipate that this experimental d-band analysis methodology will be useful for studying structure–property relationships and catalysis on monometallic and multimetallic NPs.