Search

Single-unit-cell Sn-MFI, with the detectable Sn uniformly distributed and exclusively located at framework sites, is reported for the first time. The direct, single-step, synthesis is based on repetitive branching caused by rotational intergrowths of single-unit-cell lamellae. The self-pillared, meso- and microporous zeolite is an active and selective catalyst for sugar isomerization. High yields for the conversion of glucose into fructose and lactose to lactulose are demonstrated., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Commonly used methods to assess crystallinity, micro-/mesoporosity, Brønsted acid site density and distribution (in micro- vs. mesopores), and catalytic activity suggest nearly invariant structure and function for aluminosilicate zeolite MFI two-dimensional nanosheets before and after superheated steam treatment. Yet, pronounced reaction rate decrease for benzyl alcohol alkylation with mesitylene, a reaction that cannot take place in the zeolite micropores, is observed. Transmission electron microscopy images reveal pronounced changes in nanosheet thickness, aspect ratio and roughness indicating that nanosheet coarsening and the associated changes in the external (mesoporous) surface structure are responsible for the changes in the external surface catalytic activity. Superheated steam treatment of hierarchical zeolites can be used to alter nanosheet morphology and regulate external surface catalytic activity while preserving micro- and mesoporosity, and micropore reaction rates.

Micro/meso/macroporous (hierarchical) zeolites show remarkable catalytic performance for reactions involving bulky reactants. However, quantitative assessment of the microstructural characteristics contributing to the observed performance remains elusive. Here, structure–activity relationships are established for a set of micro/mesoporous self‐pillared pentasil (SPP) zeolites using two parallel liquid‐phase reactions (benzyl alcohol alkylation and self‐etherification) based on analysis of mass transport and reaction kinetics. A reaction–diffusion mathematical model is developed that quantitatively assigns the catalytic contributions of the external surface and micropores of SPP zeolites for these reactions. In addition, the effect of the zeolite external surface structure on the corresponding catalytic activity is quantitatively assessed by comparing SPP zeolites (with MFI structure) with MCM‐22 (with MWW structure). This work demonstrates that reaction–diffusion modeling allows quantitative description of the catalytic performance of hierarchical zeolites and provides a model reaction to assess nm‐sized characteristic diffusion lengths in MFI. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1067–1075, 2019 [ABSTRACT FROM AUTHOR]

Nanoscale crystal growth control is crucial for tailoring two-dimensional (2D) zeolites (crystallites with thickness less than two unit cells) and thicker zeolite nanosheets for applications in separation membranes and as hierarchical catalysts. However, methods to control zeolite crystal growth with nanometer precision are still in their infancy. Herein, we report solution-based growth conditions leading to anisotropic epitaxial growth of 2D zeolites with rates as low as few nanometers per day. Contributions from misoriented surface nucleation and rotational intergrowths are eliminated. Growth monitoring at the single-unit-cell level reveals novel nanoscale crystal-growth phenomena associated with the lateral size and surface curvature of 2D zeolites. [ABSTRACT FROM AUTHOR]

Pillared Sn-MWW (Sn-MWW(SP)-SSE) was prepared through a solid-state-exchange (SSE) route. The pillared structure was inherited from pillared B-MWW, and Sn was inserted in the framework by boron leaching and solid-state-exchange with tin tetrachloride pentahydrate. The Sn-MWW(SP)-SSE with framework Sn sites exhibits Lewis acidity and good catalytic performance for the Baeyer--Villiger oxidation, and mono- and disaccharide isomerizations. [ABSTRACT FROM AUTHOR]

Single-unit-cell Sn-MFI, with the detectable Sn uniformly distributed and exclusively located at framework sites, is reported for the first time. The direct, single-step, synthesis is based on repetitive branching caused by rotational intergrowths of single-unit-cell lamellae. The self-pillared, meso- and microporous zeolite is an active and selective catalyst for sugar isomerization. High yields for the conversion of glucose into fructose and lactose to lactulose are demonstrated. [ABSTRACT FROM AUTHOR]

The preparation of hierarchical zeolites usually involves hard or soft templates and multiple synthesis steps, which often prohibit their industrial uses. One way to overcome these issues is to build hierarchical zeolites using repetitive branching, where the intrinsic growth patterns of zeolites, instead of porogenic templates, are utilized. This paper expands on an earlier report to unravel the sequence of events leading to this repetitive branching process for the framework type MFI zeolite structure using small‐angle X‐ray scattering and transmission electron microscopy. Moreover, adsorption and transport properties of the hierarchical zeolite are probed using 2,2‐dimethylbutane, n‐hexane, and n‐nonane. [ABSTRACT FROM AUTHOR]

Berichtigung: Steam-Induced Coarsening of Single-Unit-Cell MFI Zeolite Nanosheets and Its Effect on External Surface Brønsted Acid Catalysis The authors of this Research Article became aware that the reported mass-normalized rates (column 3 of Table 1 in the manuscript) and the corresponding turnover frequencies (column 2 of Table S3 in the Supporting Information) for diethyl ether formation during ethanol dehydration were multiplied by a fixed factor of 7. HT