AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM7
In-situ Studies of C-C Hydrogenolysis in Cyclopropane on Platinum using a Combination of Soft X-ray Methods

Monday, October 25, 1999, 10:20 am, Room 607

Session: Catalysis on Metals
Presenter: J.L. Gland, University of Michigan
Authors: A.T. Capitano, University of Michigan
A.M. Gabelnick, University of Michigan
D.A. Fischer, National Institute of Standards and Technology
J.L. Gland, University of Michigan
Correspondent: Click to Email
In-situ studies fluorescence soft X-ray studies clearly show that a propyl intermediate plays an important role during cyclopropane hydrogenolysis to form propane over the Pt(111) surface. Through a combination of spectroscopic and in-situ catalytic studies, a complete picture of hydrogen induced C-C bond breaking mechanisms during cyclopropane hydrogenolysis has been developed. Molecular cyclopropane is adsorbed in a tilted configuration and desorbs in the 130 K temperature range. Preadsorbed cyclopropane desorbs before reacting with hydrogen, even for pressures as high as 0.02 torr. When both cyclopropane and hydrogen are present in the gas-phase, propane is formed above 300 K. In this temperature range, in-situ soft X-ray studies of the adsorbed species show that a propyl intermediate is formed. The coverage and stoichiometry of this intermediate has been characterized over a range of temperatures and reactant ratios. For large excesses of hydrogen, the average hydrogen stoichiometry of the adsorbed species increases with increasing temperature while the amount of carbon remains constant. Characterization of the dominant intermediate at 300 K with FY-NEXAFS indicates that the hydrogenated intermediate is an adsorbed propyl species. Detailed isothermal kinetic studies were used to establish both the activation energy and prefactor for hydrogenation of this intermediate. During in-situ catalytic studies, an additional C@sub 3@ adsorbed species is observed in the 150 K temperature range. By using FY-NEXAFS, the structure and bonding of this intermediate has been characterized and is consistent with adsorbed cyclopropyl-like. These exciting results have clearly established for the first time under catalytic conditions that C-C bond breaking in cyclopropane proceeds via sequential hydrogen addition.