Hydrogen-Assisted 1,2-Dichloroethane Dechlorination Catalyzed by Pt-Cu/SiO2: Insights into the Nature of Ethylene-Selective Active Sites
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URI (for links/citations):
https://elib.sfu-kras.ru/handle/2311/903Author:
Kazachkin, Dmitry V.
Luebke, David R.
Kovalchuk, Vladimir I.
d’Itri, Julie L.
(Dmitry V. Kazachkin, David R. Luebke,
Vladimir I. Kovalchuk and Julie L. d’Itri: Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, e-mail: vkovalchuk@mckasd.net)
Date:
2008-12Abstract:
Differently pretreated silica-supported Pt, Cu, and Pt-Cu catalysts with Cu to Pt atomic ratio of 1 to 6
have been investigated by a combination of reaction kinetics and FTIR spectroscopic studies in order
to understand the factors that control the selectivity toward ethylene and ethane in the CH2ClCH2Cl+H2
reaction. Carbon monoxide adsorption was used to probe the electronic modification of Pt and Cu as
well as the nature of ethylene-selective active sites. It was shown that there is a very limited, if any,
electronic interaction between Pt and Cu in the bimetallic catalysts reduced at 493 K. However, the
Pt-Cu catalysts, for which no dipole-dipole coupling shift was observed in the IR spectra of adsorbed
CO suggesting extremely small Pt ensembles on the catalyst surface, demonstrated high ethylene
selectivity in the 1,2-dichloroethane dechlorination. Electronic interactions between Pt and Cu have
been discovered for the Pt-Cu/SiO2 catalysts reduced at 773 K. The interactions manifested themselves
by a higher stability of Cu0-CO adsorption complexes in vacuum and by an increase in intensity of the
Pt-CO band in the FTIR spectra upon evacuation of CO from the gas phase suggesting the formation
of Pt-Cu solid solutions. The higher temperature reduction resulted in the dipole-dipole coupling shift
of 6 to 19 cm-1 in the FTIR spectra of adsorbed CO. The initial ethylene selectivity of the catalysts was
inversely proportional to the dipole-dipole coupling shift. The observations are consistent with the
idea that the nature of the Pt-Cu species, viz., alloy particles as opposed to Cu/Pt overlayers, does
not control the reaction selectivity, which is a function of the Pt ensemble size on the surface of Pt-Cu
moieties.