Insight into Interparticle Hydrogen Spillover Driven by Remote Metal Oxides

Hydrogen spillover is a dynamic phenomenon that involves the generation of atomic hydrogen from H₂ via H-H dissociation at a metal site, followed by rapid diffusion of the H⁺/e^- pairs over the solid support surface. Although intraparticle hydrogen spillover on a single metal oxide support that has metal sites to initiate H₂ dissociation has been extensively investigated, the study of interparticle hydrogen spillover, where atomic hydrogen diffuses to another metal oxide support at the interface, has lagged behind, despite the unique catalytic performance observed. Herein, the interparticle hydrogen spillover phenomenon from a hydrogen donor specimen to a hydrogen acceptor specimen was systematically examined using H₂-temperature-programmed reduction (H₂-TPR), in situ X-ray absorption fine structure (XAFS), and diffuse reflectance infrared Fourier transform (DRIFT). The combination of Ni²⁺/TiO₂ or Ni²⁺/WO₃ with a physically mixed Pt catalyst significantly decreased the reduction temperature of Ni²⁺ ions, which demonstrates the H⁺/e^- pairs generated at the Pt catalyst diffuse to the remote TiO₂ or WO₃ through the oxide particle interface. However, no decrease in the reduction temperature was observed when Ni²⁺/CeO₂ was used as a hydrogen acceptor for any of the hydrogen donors, regardless of the support material. The coupling of benzene with n-heptane catalyzed by aluminum-exchanged montmorillonite (Al-mont) as a solid acid catalyst was also facilitated in the presence of TiO₂-supported Pd, because of the efficient interparticle reverse hydrogen spillover effect. The present work provides not only useful insights into the interparticle hydrogen spillover effect, but also new guidelines for the appropriate design and engineering of catalyst supports.