AN INFRARED STUDY OF CO ADSORBED ON SURFACES OF ZINC OXIDE. INFLUENCE OF PRE-OXIDATION AND DOPING,

The adsorption of CO on pure as well as Li2O- and Ga2O3-doped zinc oxides was studied at 30C following various oxidative and reductive pre-treatments. The use of a null-reading quartz spring microbalance in combination with an infrared grating spectrometer permitted the simultaneous measurement of amounts adsorbed and infrared transmission. Integrated band intensities thus obtainable for weakly adsorbed CO species were consistent with the proposed dipolar nature of the interaction both frequencies and intensities varied with pretreatment, but were uniquely dependent on each other irrespective of substrate. A slow oxidation process on pure zinc oxide surfaces resulting in electron donation to the solid was followed by means of the infrared absorption of the free carriers the oxidation was thought to lead to a surface donor complex of the metal carbonato type, with weakly adsorbed CO molecules playing the part of a reaction intermediate in its formation. The complex itself must be regarded as a possible precursor in the formation of CO2. Author