X‐ray Excited Optical Fluorescence and Diffraction Imaging of Reactivity and Crystallinity in a Zeolite Crystal: Crystallography and Molecular Spectroscopy in One

Abstract

Structure–activity relationships in heterogeneous catalysis are challenging to be measured on a single‐particle level. For the first time, one X‐ray beam is used to determine the crystallographic structure and reactivity of a single zeolite crystal. The method generates μm‐resolved X‐ray diffraction (μ‐XRD) and X‐ray excited optical fluorescence (μ‐XEOF) maps of the crystallinity and Brønsted reactivity of a zeolite crystal previously reacted with a styrene probe molecule. The local gradients in chemical reactivity (derived from μ‐XEOF) were correlated with local crystallinity and framework Al content, determined by μ‐XRD. Two distinctly different types of fluorescent species formed selectively, depending on the local zeolite crystallinity. The results illustrate the potential of this approach to resolve the crystallographic structure of a porous material and its reactivity in one experiment via X‐ray induced fluorescence of organic molecules formed at the reactive centers.

3D Raman Spectroscopy of Large Zeolite ZSM‐5 Crystals

“…These differences can be explained by the effect of the steaming procedure on the structural integrity of the zeolite ZSM‐5. The presence of water at elevated temperatures, in addition to thermal effects, causes the hydrolytic splitting of the Si‐O‐Al‐bonds . The Al species, leaving the zeolite framework, can migrate towards the formed mesopores to create either framework species (Brønsted acid sites) or non‐framework species .…”

“…The formation of non‐framework Al due to steam treatment was shown previously by our group to occur mainly in the Al‐rich domains, rather than Al‐poor regions, by 2D μXRD measurements on single zeolite ZSM‐5 crystals …”

Probing Zeolite Crystal Architecture and Structural Imperfections using Differently Sized Fluorescent Organic Probe Molecules

“…The zeolite MFI crystals were provided by ExxonMobil and have a Si/Al ratio of 17. Details on these crystals have been reported in previous work from our group . The synthesis gel had a molar composition of 6.65 (NH 4 ) 2 O/0.67 TPA 2 O/0.025 Al 2 O 3 /10 SiO 2 /121 H 2 O.…”

“…Studying the accessibility and reactivity of small molecules can provide a wealth of information on the pore network of zeolites and their active sites . Well‐known examples include probing the accessibility of zeolites using gases and the study of zeolite acidity by oligomerization of styrene derivatives, thiophene derivatives, or furfuryl alcohol . The regular pore system of zeolite crystals can be exploited in polarization dependent measurements in which the alignment of probe reaction products within the pore system can be used to gain more insight in the location and orientation of these molecules in porous catalytic solids …”

Nickel Poisoning of a Cracking Catalyst Unravelled by Single‐Particle X‐ray Fluorescence‐Diffraction‐Absorption Tomography

“…Despite the similar RDA average ring‐like distribution of Ni and Fe in ECAT1‐F1, we observed for the first time the presence of Ni hotspots in high correlation with the γ‐Al 2 O 3 matrix through the whole particle (Figure b, c). Principal components analysis (PCA) and k‐means/Gaussian mixture model (GMM) cluster analysis (CA) on γ‐Al 2 O 3 [400] reflection helped us to rationalize this evidence and compare matrix distribution in presence or absence of Ni (Figure a, details in Supporting Information Section S.3.E), while having approximately the same Fe concentration in both particles . While Ni‐rich ECAT1‐F1 sample formed these γ‐Al 2 O 3 hotspots, having high spatial correlation with Ni and Fe regions (particularly on the surface), Ni‐lean ECAT2 preserved a more uniform matrix distribution, with few γ‐Al 2 O 3 hotspots and a surface ring mostly correlated with Fe.…”