Multipotent Atomic Palladium Species Pd¹⁺, Pd²⁺–O₂^–, and Pd³⁺ Formed at the Interface of Pd/TiO₂ Nanoparticles: Electron Paramagnetic Resonance Study

Abstract

Atomic palladium states formed on Pd nanoparticles are recognized as key components for many catalytic processes. Herein, we have generated a library of atomic Pd states (Pd 1+ , Pd 2+ −O 2 − , and Pd 3+ ) stabilized on TiO 2 support using flame spray pyrolysis. Using electron paramagnetic resonance (EPR) spectroscopy, we have identified the g-tensors and molecular orbital configuration of these Pd 1+ , {Pd 2+ -O 2 − }, and Pd 3+ states formed at the Pd/TiO 2 interface. Their evolution was studied under conditions pertinent to a wide range of catalytic processes, that is, such as H 2 , BH 4 treatment, solar-light irradiation, or catalytic HCOOH dehydrogenation. Under these conditions, the Pd 1+ and Pd 3+ states can act as electron acceptors and hydride acceptors. The unconventional {Pd 2+ −O 2 − } state is formed as a transient intermediate from a Pd 1+ precursor. Our data reveal a dynamic landscape regarding these multipotent Pd n+ states formed at the interface of Pd nanoparticles with TiO 2 , in relation to catalytic processes.