Hydrodechlorination over zeolite supported catalysts - Clarifi cation of reaction mechanism -

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Abstract

Chlorinated compounds emitted into the atmosphere are responsible for the current thinning and shrinking of the ozone layer in the stratosphere. The performances of halogenated compounds over the zeolites and the noble metal-containing zeolite catalysts were characterized by different spectroscopic methods to clarify the reaction mechanism of hydrodechlorination over the catalysts. Hydrodechlorination of CCl4 was applied as a model reaction for testing Pt- and Pd-containing zeolites. The Pt-containing zeolite catalyst was more active in this reaction than the Pd-containing catalyst. Methane and HCl as the main products were formed, with chloroform as intermediate product. The bond strength between fragments of CCl4 was stronger over Pd centers than on Pt sites. The main product was methane on Pt-containing material, and ethane on palladium. When noble metal-containing zeolites were prepared by ion exchange and reduced in hydrogen, Brønsted acid sites were formed as well as the metal centers. The transformation mechanisms of the chlorinated hydrocarbons over this type of zeolite were very complex. When the adsorption took place on the Brønsted acid sites, decomposition of the chlorinated molecules might take place and the product of this reaction was oxygen-containing compound (phosgene). The presence of oxygenate indicated the partial decomposition of the zeolite framework by the formation of lattice vacancies with increasing concentrations. The acid resistance of the zeolites in the hydrodechlorination reaction increased with the Si/Al ratio.

Original languageEnglish
Pages (from-to)105-113
Number of pages9
JournalJournal of the Japan Petroleum Institute
Volume49
Issue number3
DOIs
Publication statusPublished - Jul 24 2006

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Keywords

  • Acidity
  • Dealumination
  • Hydrodechlorination
  • IR spectroscopy
  • Noble metal
  • Zeolite

ASJC Scopus subject areas

  • Fuel Technology
  • Energy Engineering and Power Technology

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