Molecular-Level Proximity of Metal and Acid Sites in Zeolite-Encapsulated Pt Nanoparticles for Selective Multistep Tandem Catalysis

摘要

The proximity of different catalytic sites is key to selective catalysis; however, the controlled placement of multiple types of active sites is synthetically challenging. In this work, we show that the framework Al atoms are enriched around intracrystalline mesopores that encapsulate Pt nanoparticles in H-ZSM-S, referred to as the "halo effect". The molecular level proximity between Bronsted acid and Pt sites is demonstrated by quantitative Fourier-transform infrared spectroscopy and transmission electron microscopy. The halo effect enables the selective conversion of furfural to valeric acid and ethyl valerate (VA/EV) via a 5-step tandem reaction in one pot with an 86% yield. In contrast, control experiments show that catalysts with identical metal and acid site densities but without the halo effect produce only a 5% yield of VA/EV under identical conditions. The ready access of intermediates to the active sites in the subsequent reaction enabled by the halo effect is key to the enhanced performance in tandem catalysis and reduced catalyst deactivation.