RESEARCH GROUP - PROF. MARCUS BÄUMER

Nanoporous gold (npAu) is an active catalyst for a variety of catalytic applications in liquid and in gas phase (oxidation of CO, benzaldehyde, glucose, and methanol and many more). The finding that npAu can be highly active for oxidation reactions using molecular oxygen was a surprise within the field as gold based catalysts are usually comprised of oxide-supported nanoparticles in the range of a few nanometers – one order of magnitude smaller than the ligaments of npAu. The amount of Ag, for example, was already shown to be critical for the catalytic performance – pointing towards a bifunctional catalyst. How will the presence of other metals, such as Cu and Pt, impact the catalytic performance of npAu? We seek to get insight into options to control activity and selectivity as well as to improve long-term stability, using the oxidation of alcohols as a relevant reaction. As far as structural features are concerned, the pore and ligament sizes will not only influence the number of lowcoordinated sites but also mass transport within the material.

The catalytic performance of differently prepared npAu catalysts is investigated under ambient pressure conditions using a laboratory scale flow through reactor. Alcohol oxidation will be studied in the absence and presence of co-reactants such as H2O or H2 which were shown to modify the catalytic cycle. By dealloying master alloys containing for example Ag or Cu as the less noble constituent and ternary alloys containing we will generate npAu containing different types of ad-metals. By employing different preparation routes we want to achieve a deeper insight into the interplay of fundamental materials characteristics (composition and structural size) for example in the context of the activation of molecular oxygen. The mass transport (diffusion) of reactants out and into the porous network is obviously a function of the aspect ratio of the pores (ratio between length and diameter).

Monolithic pieces of npAu with varying thickness (e.g. 100 to 300 micrometer) will be prepared, the ligament as well as the pore diameter of such samples will be tailored between about 20 nm up to 1 micrometer by annealing at suitable temperatures (aspect ratio of the pores 10,000 down to 100). By independently varying the structural size and composition of the material we seek to understand the interplay between surface reaction and mass transport on the catalytic performance.