Distance Effect of Ni-Pt Dual Sites for Active Hydrogen Transfer in Tandem Reaction

Abstract

Unveiling the distance effect between different sites in multifunctional catalysts remains a major challenge. Herein, we investigate the distance effect by constructing a dual-site distance-controlled tandem catalyst with a five-layered TiO₂/Pt/TiO₂/Ni/TiO₂ tubular nanostructure by template-assisted atomic layer deposition. In this catalyst, the Ni and Pt sites are separated by a porous TiO₂ interlayer, and the distance between them can be precisely controlled on the subnanometer scale by altering the thickness of the interlayer, while the inner and outer porous TiO₂ layers are designed for structural stability. The catalyst exhibits superior performance for the tandem hydrazine hydrate decomposition to hydrogen and subsequent nitrobenzene hydrogenation when the Ni and Pt site distance is on the subnanometer level. The performance increases with the decrease of the distance and is better than the catalyst without the TiO₂ interlayer. Isotopic and kinetic experiments reveal that the distance effect controls the transfer of active hydrogen, which is the rate-determining step of the tandem reaction in a water solvent. Reduced Ti species with oxygen vacancies on the TiO₂ interlayer provide the active sites for hydrogen transfer with -Ti-OH surface intermediates via the continuous chemisorption/desorption of water. A smaller distance induces the generation of more active sites for hydrogen transfer and thus higher efficiency in the synergy of Ni and Pt sites. Our work provides new insight for the distance effect of different active sites and the mechanism of intermediate transfer in tandem reactions.

Keywords: distance effect; dual sites; hydrogen transfer; interlayer; tandem catalyst.