Interfacial charge distributions in carbon-supported palladium catalysts

Abstract

Controlling the charge transfer between a semiconducting catalyst carrier and the supported transition metal active phase represents an elite strategy for fine turning the electronic structure of the catalytic centers, hence their activity and selectivity. These phenomena have been theoretically and experimentally elucidated for oxide supports but remain poorly understood for carbons due to their complex nanoscale structure. Here, we combine advanced spectroscopy and microscopy on model Pd/C samples to decouple the electronic and surface chemistry effects on catalytic performance. Our investigations reveal trends between the charge distribution at the palladium–carbon interface and the metal’s selectivity for hydrogenation of multifunctional chemicals. These electronic effects are strong enough to affect the performance of large (~5 nm) Pd particles. Our results also demonstrate how simple thermal treatments can be used to tune the interfacial charge distribution, hereby providing a strategy to rationally design carbon-supported catalysts.

Understanding Heteroatom-Mediated Metal–Support Interactions in Functionalized Carbons: A Perspective Review

“…Electron micrographs (Figure 8) unveiled the drastic difference between the intimate contact at the interface of Pd particles on defective carbon surfaces, including heteroatom and topological defects, and the undamaged grain boundary of Pd NP supported on an undoped graphitic surface [69]. Besides TEM, other imaging techniques have been successfully used to characterize supported metal nanoparticles.…”

“…The simultaneous analysis of N 1s signals allowed unraveling a prevalent interaction of Pd species with pyridinic and pyrrolic nitrogen [68]. This interaction leads to a charge transfer between the metal and the carbon support, resulting in the stabilization of electron-depleted palladium atoms (Pd δ+ ), whose signal has been detected in XPS spectra [67,69]. In some cases, a very strong bond between Pd 2+ precursor ions and pyridinic nitrogen is created before and during the synthesis, resulting in the low reducibility of palladium species, and thus in the stabilization of isolated Pd 2+ ions in the final catalyst [63].…”

“…This highlights the central role of heteroatoms in activating the carbon atom of the support and mediating the interaction with the metal clusters. QUAMBO (QUAsi-atomic Minimal Basis set Orbitals) charge analysis can be alternatively used to gain theoretical evidence for charge transfer [69]. Rao et al applied periodic DFT and QUAMBO charge analysis to explore the interactions at the metal-support interface in the case of Pd nanoclusters varied in size and deposited onto carbon nanofibers with different graphitization degrees and O-functionality content.…”

Nanopolyaniline Coupled with an Anticorrosive Graphene as a 3D Film Electrocatalyst for Efficient Oxidation of Toluene Methyl C−H Bonds and Hydrogen Production at Low Voltage

“…After being used as the anode, however, the peak intensity of S increased clearly (Figure S10 b in the Supporting Information), which resulted from in situ sulfuric acid doping of PANI during the electrochemical reaction. In particular, the inclusion of sulfur produces electronic perturbations that significantly enhance the electrocatalytic activity of the inert carbon as a result of doping . Doped PANI is the most promising and only electroconducting form of PANI …”

Toward an Understanding of Capping Molecules on Pt Nanoparticles for Hydrogenation: the Key Role of Hydroxyl Groups

“…pointed out that increasing d ‐orbital vacancies and static density around Fermi energy band of Pt could enhance its catalytic activity. In homogenous catalysts, ligand can serve as electric‐withdrawing to reduce the electron density of metal to adjust the property of metal . Li et al .…”