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.
Highlights
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, their activity and selectivity
Recent works on single-atom catalysis suggest that heteroatoms decorating defect sites play a role similar to ligands in homogeneous catalysis, where the activity of metal centers can be modulated through electron donation and withdrawal[57]
The impact of these electronic effects on metal nanoparticles of 5 nm size, which consist of hundreds of atoms, is negligible: assuming hemispherical nanoparticles with 11% of the Pd atoms at the interface and an oxygen-to-carbon ratio of 0.25, at most ~ 2.75% of the total Pd atoms would be altered through ligand effects
Summary
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, their activity and selectivity. The functionalization of the carbon support with oxygen moieties altered its hydrophilic–hydrophobic character, which in turn modified the reactant’s adsorption mode and the selectivity of the reaction[20] Electronic effects such as charge transfer between the metal and carbon scaffold were not addressed[20,21,22,23], it is well-established that heteroatoms located at defect sites alter the electronic properties of graphene and graphenic carbons[24, 25]. Conventional carbon supports bearing oxygen functionalities may exhibit electronic properties that remain to be harnessed for catalytic applications
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