Reductive hydrodechlorination of trichloroethylene by palladium-on-alumina catalyst: 13C solid-state NMR study of surface reaction precursors

Langmuir : the ACS Journal of Surfaces and Colloids
Watanee SriwatanapongseChristopher A Klug

Abstract

Adsorption of trichloroethylene (TCE) on alumina-supported palladium catalysts (Pd/Al2O3) was studied in the presence and absence of hydrogen using 13C-solid state NMR. Carbon-13 NMR spectra indicate that at low coverage strongly adsorbed species are formed while at high coverage additional physisorbed species are present. Carbon-13 spin-echo amplitude data measured as a function of pulse separation, tau, was used to determine the 13C-13C intramolecular dipolar coupling and the carbon-carbon bond length of adsorbed species. Results indicate that a substantial fraction of the chemisorbed carbon species had undergone carbon-carbon bond scission forming single-carbon fragments, suggesting that the activation energy for carbon-carbon bond scission is comparable to the heat of adsorption. For the remaining surface species, the double bond is elongated to 1.46 +/- 0.03 A and is suspected to be chemically bonded ethynyl. At room temperature, adding an excess of hydrogen to catalyst that is covered to saturation with TCE precursors produces only in a small amount of ethane, indicating the fraction of surface species that are hydrodehalogenation precursors is small.

References

Oct 15, 1995·Physical Review. B, Condensed Matter·L R BecerraJ H Sinfelt
Jan 7, 1985·Physical Review Letters·S L RudazJ H Sinfelt

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Citations

Mar 1, 2012·Environmental Science & Technology·Brian P ChaplinCharles J Werth
Feb 1, 2012·Dalton Transactions : an International Journal of Inorganic Chemistry·Hai-Qun WangJie-Sheng Chen
Aug 23, 2008·Angewandte Chemie·Zhaorong Zhang, Thomas J Pinnavaia
Dec 22, 2006·Environmental Science & Technology·Matthew G DavieJohn R Shapley

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