Departmental Papers (CBE)

Document Type

Journal Article

Date of this Version

August 2002

Abstract

The adsorption and reaction properties of an Al-free H-[Fe]ZSM-5 were examined and compared to an H-[Al]ZSM-5 sample with the same site density. H-[Fe]ZSM-5 was shown to have Brønsted-acid sites in a concentration equal to the framework Fe concentration. Differential heats of adsorption for ammonia and pyridine were shown to be identical to that obtained in H-[Al]ZSM-5, with differential heats of ~150 kJ/mol for ammonia and 200 kJ/mol for pyridine. For H-[Al]ZSM-5, adsorption of either propylene or 1-butene at room temperature results in rapid oligomerization. TPD-TGA measurements of the oligomers in H-[Al]ZSM-5 show evidence for hydride-transfer reactions, in addition to simple oligomer cracking. By contrast, it is necessary to heat H-[Fe]ZSM-5 to 370 K for rapid oligomerization of propylene and oligomerization of 1-butene occurs only slowly at 295 K. TPD-TGA measurements of the oligomers in H-[Fe]ZSM-5 show no evidence for hydride-transfer reactions and H-[Fe]ZSM-5 forms much less coke than H-[Al]ZSM-5 during steady-state reaction in 1-butene at 573 K. Adsorption measurements of 1-butene on D-[Fe]ZSM-5 suggest that the protonated complexes of 1-butene are formed but that these are relatively stable towards reaction, implying that the carbocation transition states are relatively unstable.

Comments

Postprint version. Published in Journal of Catalysis, Volume 210, Issue 1, 15 August 2002, pages 106-115.
Publisher URL: http://dx.doi.org/10.1006/jcat.2002.3657

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Figures 1, 4, 6-9, 11

Figures_2_10.ppt (1095 kB)
Figures 2, 10

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Figures 3, 5

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Date Posted: 06 February 2006

This document has been peer reviewed.