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.