AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM9
Studies of the Oxidation Reactions of Methanol on a Heated Silver Membrane

Tuesday, October 26, 1999, 11:00 am, Room 607

Session: Model Catalysts
Presenter: R.J. Beuhler, Brookhaven National Laboratory
Authors: R.J. Beuhler, Brookhaven National Laboratory
R.M. Rao, Brookhaven National Laboratory
M.G. White, Brookhaven National Laboratory
Correspondent: Click to Email
A polycrystalline Ag-membrane is being used as a model substrate for investigating the kinetics and dynamics of Ag-catalyzed oxidation reactions, such as the epoxidation (EO) of ethylene and the partial oxidation of methanol. These Ag-catalyzed reactions are carried out on a large-scale commercially, and despite considerable effort to understand the reaction mechanisms, much still remains uncertain. We have been attempting to study these oxidation reactions under collision free conditions (pressures less than 10@super -5@ torr), allowing both electron impact mass spectroscopy and state-selective laser ionization techniques to be used for product analysis. The main advantage of the membrane is that high surface coverages of adsorbed O@sub (a)@ can be prepared by diffusion of oxygen atoms produced by dissociative adsorption at the high pressure side of the heated Ag foil. The oxygenated Ag-foil is found to be very active in promoting the partial oxidation of methanol to formaldehyde. At a methanol pressure of 10@super -6@ torr, the reaction rate is on the order of 10@super 15@ molecules/cm sec@super 2@, with a measurable lower limit of about 5 x 10@super 13@ molecules/cm sec@super 2@. During the initial heating of the foil, activation of the surface is observed. In complementary studies, O 1s XPS measurements have been performed on the Ag-foil surface to identify the chemical state of the adsorbed oxygen, and (2+1) REMPI laser spectroscopy has been used to extract ro-vibronic and velocity distributions for desorbed molecular oxygen formed by the recombination reaction O@sub (a)@ + O@sub (a)@ = O@sub 2(g)@.