Ortho-xylene isomerisation on H-MFI zeolite at temperatures between 393 and
573 K was studied in an infrared reactor-cell. 2D correlation analysis of
the spectra recorded during the experiment allowed the detection of traces
of coke on the catalyst, and the determination of the OH groups specificall
y perturbed by the coke molecules. Adsorption of collidine and pyridine on
fresh and coked samples was used to determine the location of these OH grou
ps in the microporous structure. It appears that coke is not perturbing Bro
nsted acidity (bridged OH) under these conditions on the MFI zeolite. It is
mainly located on silanol groups; these silanols are not located on the ex
ternal surface of the crystallites, but at defects located inside the pore
system. (C) 2001 Elsevier Science B.V. All rights reserved.