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Establishing structure-activity relationships in complex, hierarchically structured nanomaterials, such as fluid catalytic cracking (FCC) catalysts, requires characterization with complementary, correlated analysis techniques. An integrated setup has been developed to perform transmission electron microscopy (TEM) and single-molecule fluorescence (SMF) microscopy on such nanostructured samples. Correlated structure-reactivity information was obtained for 100 nm thin, microtomed sections of a single FCC catalyst particle using this novel SMF-TEM high-resolution combination. High reactivity in a thiophene oligomerization probe reaction correlated well with TEM-derived zeolite locations, while matrix components, such as clay and amorphous binder material, were found not to display activity. Differences in fluorescence intensity were also observed within and between distinct zeolite aggregate domains, indicating that not all zeolite domains are equally active. [ABSTRACT FROM AUTHOR]

We used single-molecule fluorescence microscopy to study self-diffusion of a feedstock-like probe molecule with nanometer accuracy in the macropores of a micrometer-sized, real-life fluid catalytic cracking (FCC) particle. Movies of single fluorescent molecules allowed their movement through the pore network to be reconstructed. The observed tracks were classified into three different states by machine learning and all found to be distributed homogeneously over the particle. Most probe molecules (88%) were immobile, with the molecule most likely being physisorbed or trapped; the remainder was either mobile (8%), with the molecule moving inside the macropores, or showed hybrid behavior (4%). Mobile tracks had an average diffusion coefficient of D = 8 x 10-14 ± 1 x 10-13 m² s-1, with the standard deviation thought to be related to the large range of pore sizes found in FCC particles. The developed methodology can be used to evaluate, quantify and map heterogeneities in diffusional properties within complex hierarchically porous materials. [ABSTRACT FROM AUTHOR]

A micro-spectroscopic method has been developed to probe the accessibility of zeolite crystals using a series of fluorescent 4-(4-diethylaminostyryl)-1-methylpyridinium iodide (DAMPI) probes of increasing molecular size. Staining large zeolite crystals with MFI (ZSM-5) topology and subsequent mapping of the resulting fluorescence using confocal fluorescence microscopy reveal differences in structural integrity: the 90° intergrowth sections of MFI crystals are prone to develop structural imperfections, which act as entrance routes for the probes into the zeolite crystal. Polarization-dependent measurements provide evidence for the probe molecule's alignment within the MFI zeolite pore system. The developed method was extended to BEA (Beta) crystals, showing that the previously observed hourglass pattern is a general feature of BEA crystals with this morphology. Furthermore, the probes can accurately identify at which crystal faces of BEA straight or sinusoidal pores open to the surface. The results show this method can spatially resolve the architecture-dependent internal pore structure of microporous materials, which is difficult to assess using other characterization techniques such as X-ray diffraction. [ABSTRACT FROM AUTHOR]

Fluid catalytic cracking (FCC) is a major process in oil refineries to produce gasoline and base chemicals from crude oil fractions. The spatial distribution and acidity of zeolite aggregates embedded within the 50-150 μm-sized FCC spheres heavily influence their catalytic performance. Single-molecule fluorescence-based imaging methods, namely nanometer accuracy by stochastic chemical reactions (NASCA) and super-resolution optical fluctuation imaging (SOFI) were used to study the catalytic activity of sub-micrometer zeolite ZSM-5 domains within real-life FCC catalyst particles. The formation of fluorescent product molecules taking place at Brønsted acid sites was monitored with single turnover sensitivity and high spatiotemporal resolution, providing detailed insight in dispersion and catalytic activity of zeolite ZSM-5 aggregates. The results point towards substantial differences in turnover frequencies between the zeolite aggregates, revealing significant intraparticle heterogeneities in Brønsted reactivity. [ABSTRACT FROM AUTHOR]

This road is limited to molecules with a width of 6 Å or less! One of the goals of microscopy is to enlarge our view of functional materials in such a way that we can see what is really going on, as if it were an everyday object you can hold in your hand or walk around. The cover depicts a zeolite scientist's utopia: using model zeolite crystals so large that you can walk around inside. In this work, we learn more about the accessibility of zeolite materials by using fluorescence microscopy in combination with molecules differing in their size. More information can be found in the Full Paper by B. M. Weckhuysen, et al. on page 6305 ff. [ABSTRACT FROM AUTHOR]