Ceria supported gold-platinum catalysts for the selective oxidation of alkyl ethoxylates

摘要

This work covers the development of a ceria based AuPt catalyst for the selective aerobic oxidation of alkyl ethoxylates to their corresponding carboxylic acids. By optimizing metal loading and the Au to Pt ratio the activity of the catalyst could be increased significantly, while maintaining total selectivity. Although the choice of ceria as a support helped to suppress intermediate metal leaching, the catalyst still showed poor long-term stability in repeated batches. The cause for deactivation could finally be identified by TPR studies as over-oxidation. These suspicions were confirmed by a long-term stability study in continuous-mode. It proved to be possible to deactivate the catalyst on purpose by employing unfavourable oxidising reaction conditions, i.e. low substrate concentrations and excess oxygen. By avoiding such unfavourable conditions either in continuous-flow mode or in repeated batches, the long-term stability of the catalyst increased tremendously. A substrate screening of various ethoxylates showed that the catalyst was very well-suited to selectively oxidize a wide range of alkyl ethoxylates.