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Issue 19, 2012
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Styrene oligomerization as a molecular probe reaction for Brønsted acidity at the nanoscale

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Abstract

The Brønsted acid-catalyzed oligomerization of 4-fluorostyrene has been studied on a series of H-ZSM-5 zeolite powders, steamed under different conditions, with a combination of UV-Vis micro-spectroscopy and Scanning Transmission X-ray Microscopy (STXM). UV-Vis micro-spectroscopy and STXM have been used to monitor the relative formation of cyclic and linear dimeric carbocations as a function of the steaming post-treatment (i.e., parent vs. steaming at 600, 700 and 800 °C). It was found that the UV-Vis band intensity ratios of linear to cyclic dimeric species increase from 0.79 (parent H-ZSM-5) over 1.41 (H-ZSM-5 steamed at 600 °C) and 1.88 (H-ZSM-5 steamed at 700 °C) to 2.33 (H-ZSM-5 steamed at 800 °C). STXM confirms this trend in reaction product selectivity, as the relative intensities of the transitions attributed to the presence of the cyclic dimer in the carbon K-edge spectra decrease with increasing severity of the steaming post-treatment. Furthermore, STXM reveals spatial heterogeneities in reaction product formation within the H-ZSM-5 zeolite powders at the nanoscale. More specifically, a shrinking carbon core–shell distribution was detected within the zeolite aggregates, in which the relative amount of cyclic dimeric species is higher in the core relative to the shell of the zeolite aggregate and the relative amount of cyclic dimeric species in the zeolite core gradually decreases with increasing severity of the steaming post-treatment. These differences are rationalized in terms of spatial differences in Brønsted acidity within H-ZSM-5 zeolite powders as well as by changes in the formation process of linear and dimeric carbocations within H-ZSM-5 micro- and mesopores.

Graphical abstract: Styrene oligomerization as a molecular probe reaction for Brønsted acidity at the nanoscale

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Supplementary files

Article information


Submitted
07 Sep 2011
Accepted
19 Dec 2011
First published
25 Jan 2012

Phys. Chem. Chem. Phys., 2012,14, 6967-6973
Article type
Paper

Styrene oligomerization as a molecular probe reaction for Brønsted acidity at the nanoscale

L. R. Aramburo, S. Wirick, P. S. Miedema, I. L. C. Buurmans, F. M. F. de Groot and B. M. Weckhuysen, Phys. Chem. Chem. Phys., 2012, 14, 6967
DOI: 10.1039/C2CP22848C

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