Introducing Catalytic Diversity into Single-Site Chabazite Zeolites of Fixed Composition via Synthetic Control of Active Site Proximity

Abstract

We report a synthesis–structure–function relation describing how different routes to crystallize single tetrahedral-site (T-site) zeolites of fixed composition lead to different arrangements of framework Al atoms and, in turn, of extraframework proton active site ensembles that markedly influence turnover rates of a Bronsted acid-catalyzed reaction. Specifically, synthetic routes are reported that result in systematic changes in the arrangement of aluminum atoms (Al–O(−Si-O)x–Al) in isolated (x > 2) and paired (x = 1, 2) configurations within chabazite (CHA) zeolite frameworks of effectively fixed composition (Si/Al = 14–17). Precursor solutions containing different structure-directing agents and aluminum sources crystallize CHA zeolites with one organic N,N,N-trimethyl-1-adamantylammonium cation occluded per CHA cage, and with amounts of occluded Na+ cations that increase linearly with paired framework Al content (0–44%). Ammonia and divalent cobalt ion titrations are used to quantify total and paired Br...