Characteristic behavior of chemisorbed oxygen on silver in the reaction with carbon monoxide

When chemisorbed oxygen on silver at full coverage was exposed to carbon mo noxide at 273 K, a small amount of the chemisorbed oxygen reacted readily w ith carbon monoxide, but the rest of the oxygen remained inert. However, wh en some oxygen gas was added to the ambient carbon monoxide, the reaction t o form carbon dioxide proceeded at a remarkable rate. The rate of the react ion in the presence of both oxygen and carbon monoxide in the ambient gas w as first order with respect to carbon monoxide, and zero order with respect to oxygen gas. Such behavior suggests that the reaction between oxygen and carbon monoxide takes place in a very limited part of the silver surface, all the rest part remaining unreactive, and both active and unreactive regi ons being fully covered by oxygen during the reaction. A method to identify the limited number of active sites on the surface is suggested using scann ing tunneling microscopy (STM) at nanoscale resolution. It is in conjunctio n with the isotope jump method at condition where all the surface species a re immobile except those on the limited active part of the surface during t he reaction. (C) 2000 Published by Elsevier Science B.V.