ON THE RELATION BETWEEN CATALYTIC PERFORMANCE AND MICROSTRUCTURE OF POLYCRYSTALLINE SILVER IN THE PARTIAL OXIDATION OF METHANOL

Electrolytic silver was investigated as partial oxidation catalyst for the conversion of methanol to formaldehyde. Using the mass spectromet ric technique as on-line detector the relation between feed compositio n and temperature was determined allowing us to conclude that two simu ltaneous reaction pathways operate under steady state conditions. The microstructure was analysed by XRD and STM. A pronounced restructuring of the surface on the mesoscopic scale was detected. The atomic struc ture of the gamma oxygen phase was determined on the (111) face of fac ets grown during reaction. The two reaction pathways find their counte rparts in two distinctly different surface microstructures providing d ifferent geometries for the respective active sites. After prolonged t ime on stream the high surface mobility of the silver atoms removes al l mesoscopic restructuring without changing the conversion characteris tics. The observed restructuring is thus considered as a frozen large scale image of the continuously changing surface under reaction condit ions.