Field-emission studies on nickel. Part 2.—Adsorption of acetylene and ethane

Abstract

The adsorption of acetylene and ethane on clean nickel surfaces was studied by field-emission microscopy (FEM). Acetylene initially increased the work function ϕ, but finally Δϕ was about –0.8 eV. The FEM patterns showed features which were also characteristic of ethylene adsorption (i.e., the development of bright(112) regions and crystallite formation on heating to 350–370°C) but in addition acetylene appeared to adsorb on planes such as (102) and (203). Differences between ethylene and acetylene adsorption are discussed in terms of bonding possibilities with available surface orbitals, and the possible significance of these differences for catalysis is indicated. FEM observations on acetylene adsorption were extremely sensitive to the “history” of the nickel emitter. Ethane at 10 ^–8 Torr adsorbed on nickel emitters at 20°C; its behaviour contrasted with the unsaturated hydrocarbons, ethylene and acetylene, with respect both to pattern and ϕ variation.