The Synthesis And Catalyze Performance Of Metal Cluster-Polyoxometalate Composite

The advent of nano-size gold cluster over high surface area support has exhibited high activity as a heterogeneous catalyst in both gas and liquid phases.Gold in the nanocrystalline state is an amazingly active redox catalyst.It can activate carbon monoxide and dioxygen at temperature as low as 197 K to form carbon dioxide Polyoxometalate chemistry is an old field with rapidly emerging horizons in several disciplines,such as bioinorganic chemistry,medicine,electrochemistry, photochemistry,surface chemistry,and catalysis.Among numerous dapplications of polyoxometalates,catalysis has been widely recognized as one of the most important and promising research areas,because of their unique advantages:multifunctionality and structure mobility.They can be used as Brφnsted acidic catalysts,oxidation catalysts,or bifunctional catalysts and their catalytic reactions can be carried out in some polar solvents as well as in heterogeneous systems.Most highly efficient polyoxometalate catalysts were applied in homogeneous systems, but the recovery and recycle of the catalyst remain problematic in the practical use.In this work,polyoxometlate anions were used to stabilize gold cluster complexes and series of novel redox catalysts were prepared. Utlize polyoxometlate to stabilize gold via a special ligand,4-dimethylaminopyridine, because of the ligand could be removed easily;a new kind of gold cluster-polyoxometalate composite will be obtained.A series of Gold Cluster- PW11MOx composite,such as Au-N-PW₁₁FeO_x,Au-N-PW₁₁CuO_x,Au-N-PW₁₁MnO_x,Au-N-PW₁₁Co_x,A series of Gold Cluster-PW11MOx composite,such as Au-N-WO_x,Au-N-MoO_x,Au-N-VO_x and a series of Au-WO_x,Au-MoO_x are prepared with characterizing by XPS,IR and TEM.Catalytic cyclohexene epoxidation was applied as a model reaction to investigate the catalytic performance of three series as-synthesized catalysts.The catalytic reactions proceed at room temperature(25℃)and show high activity and the selectivity to valuable products is above 80%.The catalyst without stabilizing ligand show higher activity,but more substrate is over-oxidized.