34th International Field Emission Symposium / 34ème Symposium International d'Emission de Champ

J. Phys. Colloques 48 (1987) C6-493-C6-498
DOI: 10.1051/jphyscol:1987681

ELECTROSTATIC FIELD EFFECTS ON INTERMEDIATES OF CATALYTIC SURFACE REACTIONS

G.-K. Chuah¹, N. Kruse², J.H. Block³ et G. Abend<sup>3

1</sup>  Texas A&M University, Dept. of Chemistry, College Station, Texas 77843, U.S.A.
²  Lab. de Microscopie et Diffractions Electroniques, Faculté des Sciences & Techniques de Saint-Jéromè, Rue Henri Poincaré, 13397 Marseille Cedex 13, France
³  Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-1000 Berlin 33, F.R.G.

Abstract
Pulsed Field Desorption Mass Spectrometry (PFDMS) has been applied to investigate reaction intermediates and products of "field sensitive" catalytic surface reactions. During the reaction of methanol with single crystal planes of Ru and Rh (T= 300 ... 700 K, p ? 1.3.10^-5Pa) field desorption mass spectra contain the parent ion, CH₃OH⁺ and productions, CO⁺, H⁺, H⁺₂ as well as reaction intermediates COH_x⁺ (x = 1, 2, 3). The initial dissociation of CH₃OH on Ru and Rh forms adsorbed CH₃O-species. The electrostatic field stabilizes COH_x-structures (x = 1 ... 3), decelerating the catalytic surface decomposition to final products. The interaction of NO with Pt(111)-planes normally leads to a non-dissociative chemisorption structure which can be reversibly desorbed. Electrostatic fields, F_R > 4 V/nm, cause field induced surface dissociation. The products N₂O⁺, N₂⁺ and O⁺ are observed. Similarities with the behaviour of K-covered Pt(111)-planes are thus observed.