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Influence of hierarchization on electron transfers in structured MFI-type zeolites

Abstract

H-ZSM-5 zeolite (Si/Al = 19.3) was hydrothermally synthesized. Alkaline and/or acid post-synthesis treatments were carried out to give rise to an interconnected mesoporous volume. The desilication treatment parameters have been tuned (temperature, organic base addition) to obtain a series of samples with increasing mesoporous volume and a constant number of acid sites. The physico-chemical properties of the resulting materials were fully characterized by many techniques (NMR, BET, PXRD, pyridine thermal desorption followed by infrared spectroscopy). To assess the effect of post-treatments on sample reactivity, the charge separation processes between the zeolite framework and adsorbed trans-stilbene (t-St) molecule were investigated by UV-visible diffuse reflectance. The spectra obtained after t-St adsorption show clear difference depending on the applied post-treatments. It appears that the desilication treatments performed without acidic washing highly stabilize the radical cation resulting from the t-St spontaneous ionization. In contrast, by applying an acidic washing after desilication, the ionization process becomes significantly weaker. The results show that the proportion of Strong Lewis acid sites in vicinity of Brønsted sites named Brønsted Strong Lewis Pair (BSLP), are responsible for the amount of radical cation observed in the different samples. More precisely, it exists an optimal proportion of BSLP to achieve high ionization rate. These pairs mostly result from a reorganization of framework aluminum distribution after alkaline treatments.

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Publication details

The article was received on 01 Jun 2018, accepted on 03 Oct 2018 and first published on 04 Oct 2018


Article type: Paper
DOI: 10.1039/C8CP03485K
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Influence of hierarchization on electron transfers in structured MFI-type zeolites

    T. Crémoux, I. Gener-Batonneau, A. Moissette, J. Paillaud, M. Hureau, E. Ligner, C. Morais, S. Laforge, C. Marichal and H. Nouali, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP03485K

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