Metal Active Sites and Their Catalytic Functions in Zeolites: Insights from Solid-State NMR Spectroscopy

• DOI: 10.1021/acs.accounts.9b00125
• Publication Date: 2019-05-07T22:21:54Z
• Authors: Jun Xu; Qiang Wang; Feng Deng
• Keywords: Petrochemical; Characterization; Fluid catalytic cracking

Zeolites are important heterogeneous catalysts widely used in the modern chemical and petrochemical industries. Metal-containing zeolites show distinct performance catalytic processes such as fluid cracking, activation conversion of light alkanes, methanol-to-aromatics conversion, biomass transformation, so on. The metal speciation, distribution, interactions on have enormous impact their property performance. Significant efforts been devoted to synthesis more active selective by engineering sites. However, nature species role reactions still poorly understood, which makes it difficult establish structure-activity relationship toward rational design application zeolites. For example, synergic sites often present metal-containing zeolites, but structure, quantification remain be resolved. Solid-state NMR is a powerful tool for characterization providing information about both molecular structure dynamics. heterogeneity low concentration usually leads great challenge characterization. In this Account, we will describe our effort study sites, host-guest interactions, reaction intermediates using solid-state spectroscopy, with aim highlight recent advances techniques probing well relevant mechanisms. Using sensitivity-enhanced methods 67Zn, 71Ga, 119Sn, enables identification speciation constituted (as Lewis acid sites) acidic protons Brønsted that amount only small fraction whole system can directly probed quantified advanced 1H-67Zn or 1H-71Ga double-resonance NMR. We developed observing spatial interaction/proximity between aluminum (associated zeolite host carbon atoms organic molecule guest formed during reaction, formation supramolecular centers methanol-to-olefins reaction. mechanisms underlying metal-modified revealed key situ 13C MAS spectroscopy. Our discussion based representative examples shows how serving significantly affect activity related pathways. structural obtained state-of-the-art provides new insights into catalysis, should beneficial highly efficient catalysts.