Catalytic formation of carbon-carbon bonds in ultrahigh vacuum: Cyclotrimerization of alkynes on reduced TiO2 surfaces
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The steady-state reaction of a molecular beam of methylacetylene impinging on a reduced TiO2(001) crystal was examined under UHV (10-9to 10-8mbar) conditions. Cyclotrimerization to form trimethylbenzene took place at steady-state. The reaction is truly catalytic; more than 20 turnovers could be obtained without deactivation of the single crystal catalyst. Experiments examining the cyclotrimerization rate as a function of pressure showed that, in the region from 3.0 × 10-9to 2.4 × 10-8mbar, the reaction was approximately first order in alkyne partial pressure. Temperature variation experiments showed a small decrease in rate as temperature was increased, indicating a slightly negative overall activation energy between 400 K and 535 K. A four-step kinetic model of the cyclotrimerization reaction was constructed using information derived from TPD experiments. These results demonstrate that steady-state catalytic studies of carbon-carbon bond forming reactions, characterized by an overall decrease in number of moles, can be performed on single crystal metal oxides under UHV conditions. © 1996 Elsevier Science B.V. All rights reserved.
author list (cited authors)
Pierce, K. G., Lusvardi, V. S., & Barteau, M. A.