Chemisorption And Reaction Of Small Molecules On A Au(997) Surface

Gold had long been considered catalytically inert until Haruta et al. reported that ultrafine Au nanoparticles supported on transitional metal oxides are very active in catalyzing CO oxidation at low temperatures. Since then, supported Au nanocatalysts have been reported to be active in a wide array of catalytic oxidation reactions. The great progress achieved in Au nanocatalysis has provoked related fundamental studies. Although great strides have been made, controversial issues remain even for the simplest CO oxidation reaction, particularly with respect to the nature of the active site and the reaction mechanism. Surface science studies of model catalysts for supported Au nanocatalysts have also encountered difficulties because of the extremely inertness of extended Au surfaces. For examples, it is still quite difficult to generate chemisorbed oxygen atom on extended Au surfaces.In the present thesis, we reported the investigations of adsorption and reaction of small molecules such as CO, H₂O, NO, NO₂, CO₂ and O₂ on the vicinal Au(997) surface by means of XPS (X-ray photoelectron spetrum) , TPD (Temperature programmed desorption) and LEED (Low energy electron diffraction). CO can chemisorb on Au(997) and repulsive interaction exists among CO(ads). Water adsorbs molecularly with the formation of a nonwetting and three-dimensional (3D) layer on Au(997). NO can chemisorb on Au(997). CO₂ and O₂ does not measurably chemisorb on the surface under our experimental conditions. NO₂ adsorbs on Au(997) and cab generate oxygen adatoms when heated, in which NO+NO3- (a) was found to be an important surface intermediate. Oxygen adstoms on Au(997) can react with H₂O to form hydroxyls on Au(997), can react with NO to form NO₂(a) on Au(997), but do seems not to react with CO. These results shed light on some fundamental issues in Au nanocatalysis.