Building Zeolites from Precrystallized Units: Nanoscale Architecture

Abstract

Since the early reports by Barrer in the 1940s on converting natural minerals into synthetic zeolites, the use of precrystallized zeolites as crucial inorganic directing agents to synthesize other crystalline zeolites with improved physicochemical properties has become a very important research field, allowing the design, particularly in recent years, of new industrial catalysts. This Review highlights how the presence of some crystalline fragments in the synthesis media, such as small secondary building units (SBUs) or layered substructures, not only favors the crystallization of other zeolites with similar SBUs or layers, but also permits control over important parameters affecting their catalytic activity (chemical composition, crystal size, or porosity, etc.). Recent advances in the preparation of 3D and 2D zeolites through seeding and zeolite-to-zeolite transformation processes will be discussed extensively in this Review, including their preparation in the presence or absence of organic structure-directing agents (OSDAs). The aim is to introduce general guidelines for more efficient approaches for target zeolites.

Synthesis of reaction‐adapted zeolites as methanol-to-olefins catalysts with mimics of reaction intermediates as organic structure‐directing agents

“…The use of different sources of Si, Al, or P has been proposed, including pre-crystallized zeolites, which can favor the rearrangement and crystallization of other structures sharing similar secondary building units (SBUs) in their structures. 34,35 Interestingly, the silicoaluminate form of the CHA zeolite, SSZ-13, was obtained using OSDA1a and OSDA1b (see Supplementary Figure 6 and 7). In the case of OSDA1a, the SSZ-13 material was crystallized only under very specific synthesis conditions (Si/Al=6, see SSZ-13 in Supplementary Figure 6).…”

Organic‐Free Interzeolite Transformation in the Absence of Common Building Units

“…One method of minimizing or eliminating OSDAs in zeolite synthesis is the use of a parent crystal that undergoes an interzeolite transformation to a desired (daughter) structure . This approach has been demonstrated for a range of metastable zeolites, such as faujasite (FAU) and beta (*BEA) .…”

“…In a majority of OSDA‐free interzeolite transformations, the parent and daughter crystals exhibit some degree of structural similarity. Several groups have hypothesized that OSDA‐free interzeolite transformations only occur when both parent and daughter share at least one common composite building unit (CBU) . Examples include (but are not limited to) the transformation of LEV to CHA (common CBU: d6r ) and *BEA to MFI (common CBU: mor ) .…”

“…Herein, we demonstrate the direct transformation of USY (FAU) to ZSM‐5 in the absence of organics and without the use of ZSM‐5 seeds. This specific transformation involving two zeolites lacking a common CBU was previously deemed improbable . The FAU‐to‐MFI interzeolite transformation is accomplished using a growth medium that favors OSDA‐free ZSM‐5 crystallization.…”

Highly efficient crystallization of AlPO4-5 accelerated by a rotating hydrothermal synthesis route

“…Zeolites and molecular sieves, an important class of microporous crystal materials, have wide applications in chemical industry as the most important sorbent and separator, ion exchanger, catalyst, and functional materials. [1][2][3][4][5][6] Various methods have been developed to synthesize zeolites with novel structure, tunable composition, and unique morphology based on different applications.…”