Issue 11, 1993

Acetylene, methylacetylene and ethylacetylene polymerization on H-ZSM5: a spectroscopic study

Abstract

Acetylene, methylacetylene and ethylacetylene interact with the Brønsted acid sites of H-ZSM5 with the formation of hydrogen-bonded (precursor) species characterized by well defined IR properties. These precursors are then protonated to give intensely coloured carbocationic species. The speed of protonation is in the order: C2H5—C[triple bond, length as m-dash]CH > CH3—C[triple bond, length as m-dash]CH > HC[triple bond, length as m-dash]CH. Insertion of the monomer into the first protonation product, leads to an oligomeric species with carbocationic character. The IR and UV–VIS spectra of the carbocationic species are discussed in detail and found to correspond to those of analogous species generated in the homogeneous phase. The π-delocalization of the positive charge on the backbone is responsible for the peculiar and intense spectroscopic manifestations both in the IR and UV–VIS. The positive charge in the carbocationic species can be captured by bases (NH3, pyridine) and subtracted to π-delocalization. This is accompanied by the disappearance of the spectroscopic manifestations associated with the positive charge and by the appearance of new absorptions associated with neutral oligomeric chains. The process can be fully reversed.

The dimensions and shape of the oligomers are discussed in terms of the steric constraints imposed by the zeolitic framework, by means of computer graphics and molecular mechanics modelling.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans., 1993,89, 1843-1855

Acetylene, methylacetylene and ethylacetylene polymerization on H-ZSM5: a spectroscopic study

S. Bordiga, G. Ricchiardi, G. Spoto, D. Scarano, L. Carnelli, A. Zecchina and C. O. Areán, J. Chem. Soc., Faraday Trans., 1993, 89, 1843 DOI: 10.1039/FT9938901843

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements