skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Two-Dimensional Zeolite Materials: Structural and Acidity Properties
Zeolites are generally defined as three-dimensional (3D) crystalline microporous aluminosilicates in which silicon (Si4+) and aluminum (Al3+) are coordinated tetrahedrally with oxygen to form large negative lattices and consequent Brønsted acidity. Two-dimensional (2D) zeolite nanosheets with single-unit-cell or near single-unit-cell thickness (~2–3 nm) represent an emerging type of zeolite material. The extremely thin slices of crystals in 2D zeolites produce high external surface areas (up to 50% of total surface area compared to ~2% in micron-sized 3D zeolite) and expose most of their active sites on external surfaces, enabling beneficial effects for the adsorption and reaction performance for processing bulky molecules. This review summarizes the structural properties of 2D layered precursors and 2D zeolite derivatives, as well as the acidity properties of 2D zeolite derivative structures, especially in connection to their 3D conventional zeolite analogues’ structural and compositional properties. The timeline of the synthesis and recognition of 2D zeolites, as well as the structure and composition properties of each 2D zeolite, are discussed initially. The qualitative and quantitative measurements on the acid site type, strength, and accessibility of 2D zeolites are then presented. Future research and development directions to advance understanding of 2D zeolite materials are also discussed.  more » « less
Award ID(s):
1705284
PAR ID:
10165866
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Materials
Volume:
13
Issue:
8
ISSN:
1996-1944
Page Range / eLocation ID:
1822
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, Cellulose)
    Zeolites (ZSM-5 and Beta) with different SiO2/Al2O3 ratios were synthesized as solid acids for hydrolyzing cellulose in an inorganic ionic liquid system (lithium bromide trihydrate solution, LBTH) under mild conditions. The results indicated that the texture properties of zeolite had little effect on catalytic activity, while acidity of zeolite was crucial to the cellulose hydrolysis. In the LBTH system, H-form zeolites released H+ into the solution from their acid sites via ion-exchange with Li+, which hydrolyzed the cellulose already dissolved. This unique homogeneous hydrolysis mechanism was the primary reason for the excellent performance of the zeolites in catalyzing cellulose hydrolysis in the LBTH system. It was found cellulose could be completely hydrolyzed to glucose and oligoglucan by 2% (w/w on cellulose) zeolite at 140 °C within 3 h with a single-pass glucose yield 61%. The zeolites could be recovered with 50% initial catalytic activity after regeneration and reused with stable catalytic activity. 
    more » « less
  2. ; ; ; (, Catalysis reviews science and engineering)
    Water is ubiquitous in many thermal treatments and reaction conditions involving zeolite catalysts, but the potential impacts are complex. The different types of water interaction with zeolites have profound consequences in the stability, structure/ composition, and reactivity of these important catalysts. This review analyzes the current knowledge about the mechanistic aspects of water adsorption and nucleation on zeolites surfaces and the concomitant role of zeolite defects, cations and extra framework species. Examples of experimental and computational studies of water interaction with zeolites of varying Si/Al ratios, topologies, and level of silanol defects are reviewed and analyzed. The different steps associated with the process of steaming, including the Al-O-Si bond hydrolysis and subsequent structural modifications, such as dealumination, mesopore formation, and amorphization, are evaluated in light of recent DFT calculations, as well as SS NMR and other spectroscopic studies. Differences between the mechanisms of water attack of the zeolite in vapor or liquid phase are highlighted and explained, as well as the effect of hydrophobic/hydrophilic properties of the zeolite walls. In parallel, the various roles of water as modifier of reactivity are reviewed and discussed, both for plain zeolites as well as rare-earth or phosphorous-modified materials. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Materials Chemistry A)
    The synthesis of hierarchical lamellar zeolites with a controlled meso-/microporous morphology and acidity is an expanding area of research interest for a wide range of applications. Here, we report a one-step synthesis of a hierarchical meso-/microporous lamellar MFI–Sn/Al zeolite ( i.e. , containing both Lewis acidic Sn- and Al-sites and a Brønsted acidic Al–O(H)–Si site) and its catalytic application for the conversion of glucose into 5-(ethoxymethyl)furfural (EMF). The MFI–Sn/Al zeolite was prepared with the assistance of a diquaternary ammonium ([C 22 H 45 –N + (CH 3 ) 2 –C 6 H 12 –N + (CH 3 ) 2 –C 6 H 13 ]Br 2− , C 22-6-6 ) template in a composition of 100SiO 2 /5C 22-6-6 /18.5Na 2 O/ x Al 2 O 3 / y SnO 2 /2957H 2 O ( x = 0.5, 1, and 2; y = 1 and 2, respectively). The MFI–Sn/Al zeolites innovatively feature dual meso-/microporosity and dual Lewis and Brønsted acidity, which enabled a three-step reaction cascade for EMF synthesis from glucose in ethanol solvent. The reaction proceeded via the isomerization of glucose to fructose over Lewis acidic Sn sites and the dehydration of fructose to 5-hydroxymethylfurfural (HMF) and then the etherification of HMF and ethanol to EMF over the Brønsted acidic Al–O(H)–Si sites. The co-existence of multiple acidities in a single zeolite catalyst enabled one-pot cascade reactions for carbohydrate upgrading. The dual meso-/microporosity in the MFI–Sn/Al zeolites facilitated mass transport in processing of bulky biomass molecules. The balance of both types of acidity and meso-/microporosity realized an EMF yield as high as 44% from the glucose reactant. 
    more » « less
  4. ; ; ; ; ; ; ; (, Dalton Transactions)
    We report a scalable delamination procedure for a SSZ-70-framework layered-zeolite precursor, which for the first time does not involve either sonication or long-chain surfactants. Our approach instead relies on the mild heating of layered zeolite precursor B-SSZ-70(P) in an aqueous solution containing Zn(NO 3 ) 2 and tetrabutylammonium fluoride. Powder X-ray diffraction data are consistent with a loss of long-range order along the z -direction, while 29 Si MAS NMR spectroscopy demonstrates preservation of the zeolite framework crystallinity during delamination. The resulting delaminated material, DZ-2, possesses 1.4-fold higher external surface area relative to the nondelaminated three-dimensional zeolite B-SSZ-70, based on N 2 physisorption data at 77 K. DZ-2 was functionalized with cationic Ti heteroatoms to synthesize Ti-DZ-2 via exchange with framework B. Ti-DZ-2 contains isolated titanium centers in its crystalline framework, as shown by UV-Vis spectroscopy. The generality of the synthetic delamination approach and catalyst synthesis is demonstrated with the synthesis of delaminated material DZ-3, which is derived from layered zeolite precursor ERB-1(P) with MWW framework topology. Upon catalytic testing for the epoxidation of 1-octene with ethylbenzene hydroperoxide as oxidant, under harsh tail-end conditions that deactivate amorphous Ti-silica-based catalysts, Ti-DZ-2 exhibits the highest per-Ti-site activity, selectivity, and stability for 1-octene epoxidation of all catalysts investigated. This testing includes the prior benchmark delaminated zeolite catalyst in this area, Ti-UCB-4, which possesses similar external surface area to Ti-DZ-2 but requires sonication and long-chain surfactants for its synthesis. The synthesis of DZ-2 is the first example of an economical delamination of layered zeolite precursor SSZ-70(P) and opens up new doors to the development of delaminated zeolites as commercial catalysts. 
    more » « less
  5. ; ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Zeolite reactivity depends on the solvating environments of their micropores and the proximity of their Brønsted acid sites. Turnover rates (per H+) for methanol and ethanol dehydration increase with the fraction of H+sites sharing six‐membered rings of chabazite (CHA) zeolites. Density functional theory (DFT) shows that activation barriers vary widely with the number and arrangement of Al (1–5 per 36 T‐site unit cell), but cannot be described solely by Al–Al distance or density. Certain Al distributions yield rigid arrangements of anionic charge that stabilize cationic intermediates and transition states via H‐bonding to decrease barriers. This is a key feature of acid catalysis in zeolite solvents, which lack the isotropy of liquid solvents. The sensitivity of polar transition states to specific arrangements of charge in their solvating environments and the ability to position such charges in zeolite lattices with increasing precision herald rich catalytic diversity among zeolites of varying Al arrangement. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email