| Popis: |
A new principle of preparing catalysts on alumosiiicate carriers is described. The carriers are loaded by impregnation out of solution or suspension with planar or nearly planar complexes of transition metals, e.g., Cu, Mn, VO, Fe. The complexes are decomposed and oxidized; meanwhile, additional ligands are present in the oxidizing gas mixture. The products, though showing the overall composition of the respective metal oxide, exhibit fundamental differences with respect to structure and catalytic activity as well. The essential feature of the formation of the active catalysts is found to be the incorporation of part of the central metal into the alumosiiicate surface immediately at the start of the oxidative decomposition of the adsorbed planar complexes. Those metal atoms merged into the surface of the alumosiiicate structure are centres for the further growth of the active compound at the surface in the course of the oxidative degradation of further complex molecules. At the start of the oxidative degradation it is the planar shape of the precursor complexes adsorbed on the alumosiiicate surface that keeps the metal atoms at long distance. Once the metal atoms are anchored and merged into the alumosiiicate surface they act as centres for degradation of further precursor complexes. This fact, as well as the temporary binding of the transient ligands offered in the gas phase during degradation, prevent the final formation of an ordered oxide structure. Instead, a highly disordered material with many centres of stressed ligand fields is generated granting high activity and selectivity at low temperatures. |
