Preparation of supported silver catalysts

Abstract

In this thesis, the preparation of supported silver catalysts is described. We used model support materials to simplify the system and to make advanced characterization methods more powerful. One of the used support materials is macroporous α-alumina with ordered spherical pores. Important aspects of this material are the high specific surface area and the fact that it has the α-structure. We managed to improve the stability of the porous structure during preparation, leading to a more regular structure with high specific surface area. The stability of silver particles was studied by supporting them on, among others, the macroporous α-alumina. We identified which factors were of importance for particle growth and concluded that growth mainly took place via Ostwald ripening. This knowledge is important to design and to prepare catalysts with longer life-times. A different support material, i.e. silica with ordered cylindrical pores was used for exploring two alternative catalyst preparation methods. In one method, catalysts with high silver contents were prepared by introducing a silver salt into the pores of the silica via melt infiltration, followed by decomposition of the salt to form either silver nanowires or silver nanoparticles. For the other method, we let the silver salt react with the silica to form silver silicate. This proved an excellent method for the preparation of tiny silver particles. The performance of the catalysts was studied for the oxidation of carbon monoxide, the hydrogenation of cinnamaldehyde and the epoxidation of ethylene.