Chemical Imaging of Hierarchical Porosity Formation within a Zeolite Crystal Visualized by Small‐Angle X‐Ray Scattering and In‐Situ Fluorescence Microscopy

Abstract

Introducing hierarchical porosity to zeolites is vital for providing molecular access to microporous domains. Yet, the dynamics of meso-and macropore formation has remained elusive and pore space ill-characterized by a lack of (in situ) microscopic tools sensitive to nanoporosity. Here, we probe hierarchical porosity formation within a zeolite ZSM-5 crystal in real-time by in situ fluorescence microscopy during desilication. In addition, we introduce small-angle X-ray scattering microscopy as novel characterization tool to map intracrystal meso-and macropore properties. It is shown that hierarchical porosity formation initiates at the crystal surface and propagates to the crystal core via a pore front with decreasing rate. Also, hierarchical porosity only establishes in specific (segments of) subunits which constitute ZSM-5. Such spacedependent meso-and macroporosity implies local discrepancies in diffusion, performance and deactivation behaviors even within a zeolite crystal.Zeolite catalysts are microporous crystalline aluminosilicates, displaying unique shape selectivity through their steric pore space. [1,2] However, such selectivity requires molecu-

Construction of Single‐Crystalline Hierarchical ZSM‐5 with Open Nanoarchitectures via Anisotropic‐Kinetics Transformation for the Methanol‐to‐Hydrocarbons Reaction

“…The ZSM-5 nanocages also exhibit excellent hydrothermal stability. There is no obvious change in 27 Al MAS NMR spectrum and XRD pattern after being treated by 10 % water steaming at 600 27 Al MAS NMR spectra, c) 29 Si MAS NMR spectra, d) NH 3 -TPD curves, e) N 2 adsorption/desorption isotherms, and f) pore size distributions of silicalite-1 nanocrystals and ZSM-5 nanocages.…”

“…The Si/ Al molar ratio of the resultant ZSM-5 nanocages is � 62. The 27 Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of ZSM-5 nanocages consists of one peak at � 56 ppm (Figure 2b), implying most Al is incorporated as tetrahedral AlO 4À into the MFI framework. The peak at � À 106 ppm shown in the 29 Si MAS NMR spectra is attributed to the corresponding [Si(OSi) 3 (OAl)] moieties in the ZSM-5 framework (Figure 2c).…”

“…The XRD patterns show that all the nanostructures exhibit characteristic peaks of MFI framework (Figure S14, Supporting Information). 27 Al MAS NMR spectra of the ZSM-5 nanostructures show that most Al is incorporated as tetrahedral AlO 4À in the MFI framework (Figure S15, Supporting Information). The Si/Al molar ratios of the resultant ZSM-5 samples decrease gradually with the increasing of TPAOH concentration in the synthetic system.…”

“…The obtained product shows a cage‐like nanostructure with a hollow interior and six openings in each nanoshell (Figure 3a, b and Figure S6, Supporting Information), among which four openings along [101] direction are marked by red squares and two openings along a ‐axis direction are marked by orange squares. The density of defects might be high in region that is etched fast in alkaline solution [27] . Second, we investigate the recrystallization process by the epitaxial growth of the small nanocrystalline precursors on silicalite‐1 templates by addition of TPAOH and silica source under hydrothermal condition.…”

“…Figure 2. a) XRD patterns, b)27 Al MAS NMR spectra, c)29 Si MAS NMR spectra, d) NH 3 -TPD curves, e) N 2 adsorption/desorption isotherms, and f) pore size distributions of silicalite-1 nanocrystals and ZSM-5 nanocages.…”