Interzeolite transformation through cross-nucleation: A molecular mechanism for seed-assisted synthesis

Polymorph selection and efficient crystallization are cen-tral goals in zeolite synthesis. Crystalline seeds are used for both purposes. While it has been proposed that zeolite seeds induce interzeolite transformation by dissolving into structural units that promote nucleation of the daugh-ter crystal, the seed's structural elements do not always match those of the target zeolite. This discrepancy raises the question of how the seed promotes the daughter phase. Here, we present the first molecularly resolved investigation of seed-assisted zeolite synthesis. Using molecular simulations, we demonstrate that a parent zeo-lite can promote nucleation of a daughter zeolite even when they lack common composite building units (CBUs) or crystal planes. Modeling the seed-assisted synthesis of an AFI-type zeolite using zeolite CHA, our simulations indicate that stand-alone CBUs from the parent seed do not facilitate daughter crystal formation. However, in-troducing the intact seed significantly reduces synthesis time, supporting that seed integrity is key to increased efficiency. This reduction arises from cross-nucleation of the AFI-type zeolite on the CHA (001) face. We find that parent and daughter zeolites are connected by an inter-facial transition layer with order distinct from both zeo-lites. Simulations reveal that cross-nucleation occurs over a broad range of synthesis conditions. Based on nuclea-tion theory, we argue that if cross-nucleation occurs be-tween frameworks without common planes, as in our study, it could be even more favorable for zeolite pairs that share crystalline planes, such as those forming inter-growths.