Research Group – Dr. Arne Wittstock
Liquid phase catalytic application of nanoporous gold (SP 2)
About 9 years ago Raney type npAu was discovered to be an active catalyst for a variety of oxidation reactions (CO, alcohols, aldehydes, and even silanols), and lately even for the first reduction reactions (NO and alkynes). Some of these reactions are best conducted in liquid phase given the low vapour pressure of many organic compounds under desired green and mild chemical conditions (ambient pressure, temperatures below 100 °C).
Besides its stability and selectivity this catalytic system offers unique possibilities to tune the surface chemistry and thus availability of activated oxygen by adding co-metals. This is the very key for eliminating the need, e.g., for additional base, increasing the activity for oxidation of longer chain and aromatic alcohols and various cross coupling reactions, e.g., between an alcohol and amine. A systematic study of the correlation of surface composition and the porous network is critical for lifting the full potential of this catalytic material. The higher density inside the liquid phase results, however, in a higher concentration of reactants and in particular spectator species on the catalyst surface. The solvent such as water might impact the catalytic reaction pathway to the extent that the reactivity is distinctively different from any gas phase catalytic reaction. In this subproject we aim on elucidating (among others) the special role of the solvent and pH on the catalytic cycle.
Samples containing different amounts of ad-metals (Ag, Cu, Al, Pt) are investigated employing a chemical reactor setup (autoclave). Also the role of the solvent is investigated by variation of reaction media (organic vs. water based solvent). Preferably, water will be used as the solvent. Key reactions which will be of interest are (A) the oxidation of primary aliphatic alcohols (in comparison to gas phase and electrocatalytic catalysis, (B) the cross-coupling of alcohols (C) the cross coupling of alcohols and aldehydes (D) the cross coupling of alcohols and amines (acylation) (E) oxidation of secondary aliphatic and also aromatic compounds at low temperatures (benzyl alcohol), and (F) oxidation/epoxidation of styrene and similar compounds.
RESEARCH GROUP - sub project 2: