An investigation of the surface acidity of mesoporous Al-containing MCM-41 and of the external surface of ferrierite through pivalonitrile adsorption

An investigation of the acid properties of UL-ZSM-5 by FTIR of adsorbed 2,6-ditertbutylpyridine and aromatic transalkylation test reaction

“…These results are confirmed further by TPD of ammonia. In agreement with previous proposals, the Brönsted acidity in amorphous aluminosilicate Al-Meso arises due to the possibility of the oxygen atoms of terminal silanol groups to bridge over a nearest Lewis acidic Al ion [35,38]. The contribution of these sites to the Brönsted acidity of UL-ZSM-5 samples is however not negligible.…”

“…These results show also that for amorphous mesoporous Al-Meso, as in Al-MCM-41 and amorphous silica-aluminas, the only species responsible for the Brönsted acidity are the terminal silanol groups with an absorbance at 3745 cm À1 in the OH stretching vibration region of IR spectrum and whose acidic function arises due to the possibility of their oxygen atoms to bridge over a nearest Lewis acidic Al ion [35,38,41]. Furthermore, the same type of Brönsted acid sites has been identified on the mesopore surface of UL-ZSM-5 and external surface of ZSM-5, respectively.…”

“…In the case of Al-Meso (Fig. 2Aa), a single very intense band is identified at 3745 cm À1 and assigned to terminal silanol groups (and probably of geminal hydroxyls), with a tail at lower frequency which is attributed to H-bonded hydroxyls [35]. The band at 3745 cm À1 is found however in all spectra, but its intensity decreases with the increase in crystallinity.…”

“…1 shows the subtractions of the IR spectra after adsorption and subsequent desorption of pyridine at 200 8C from the spectrum of the same sample only evacuated at 400 8C. Bands at 3745 cm À1 , which are assigned to terminal silanol groups [35], are observed as negative features in all spectra, indicating their perturbation upon adsorption of pyridine. The intensity of the negative band at 3745 cm À1 decreases in the order: Al-Meso > UL-ZSM-5-2-0.1N > UL-ZSM-5-4-0.1N > ZSM-5.…”

Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide

“…The hindered tert-butyl-containing probe pivalonitrile was applied for the first time to the studies of the accessibility of active sites by Trombetta, Busca at al. [38]. Pivalonitrile is not allowed to penetrate micropores of zeolite ZSM-5, therefore it can interact only with the sites situated on the external surface of zeolite crystals, on the surface of mesopores, and in the pore mouths.…”