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Staining of Fluid‐Catalytic‐Cracking Catalysts: Localising Brønsted Acidity within a Single Catalyst Particle
Author(s) -
Buurmans Inge L. C.,
RuizMartínez Javier,
van Leeuwen Sanne L.,
van der Beek David,
Bergwerff Jaap A.,
Knowles William V.,
Vogt Eelco T. C.,
Weckhuysen Bert M.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102949
Subject(s) - catalysis , zeolite , reactivity (psychology) , brønsted–lowry acid–base theory , fluid catalytic cracking , chemistry , particle (ecology) , fluorescence , desorption , particle size , inorganic chemistry , analytical chemistry (journal) , photochemistry , adsorption , organic chemistry , optics , medicine , oceanography , alternative medicine , physics , pathology , geology
A time‐resolved in situ micro‐spectroscopic approach has been used to investigate the Brønsted acidic properties of fluid‐catalytic‐cracking (FCC) catalysts at the single particle level by applying the acid‐catalysed styrene oligomerisation probe reaction. The reactivity of individual FCC components (zeolite, clay, alumina and silica) was monitored by UV/Vis micro‐spectroscopy and showed that only clay and zeolites (Y and ZSM‐5) contain Brønsted acid sites that are strong enough to catalyse the conversion of 4‐fluorostyrene into carbocationic species. By applying the same approach to complete FCC catalyst particles, it has been found that the fingerprint of the zeolitic UV/Vis spectra is clearly recognisable. This almost exclusive zeolitic activity is confirmed by the fact that hardly any reactivity is observed for FCC particles that contain no zeolite. Confocal fluorescence microscopy images of FCC catalyst particles reveal inhomogeneously distributed micron‐sized zeolite domains with a highly fluorescent signal upon reaction. By examining laboratory deactivated FCC catalyst particles in a statistical approach, a clear trend of decreasing fluorescence intensity, and thus Brønsted acidity, of the zeolite domains is observed with increasing severity of the deactivation method. By comparing the average fluorescence intensities obtained with two styrenes that differ in reactivity, it has been found that the Brønsted acid site strength within FCC catalyst particles containing ZSM‐5 is more uniform than within those containing zeolite Y, as confirmed with temperature‐programmed desorption of ammonia.