Increasing demands in green and sustainable production of chemicals and energy require new approaches, materials and technologies in catalysis, energy storage, and energy harvesting. Lately, highly porous bulk-nanostructured metals became popular in this context. Among which nanoporous gold (npAu) emerged as the prime representative with many promising perspectives in the mentioned applications. The vision of this research unit is that by bringing together groups from chemistry, physics, and materials science critical progress on this topic can be achieved. The mission of this unit is to develop this material as a prototype for a rational design of catalysts by studying the interplay between composition and structural parameters and the catalytic properties of npAu.
This is, the correlation between:
•the composition of the surface (bimetallic effects and later metal-oxide deposit) and the catalytic performance (activity, selectivity, stability)
•mass transport of reactants and the observable kinetics, as to create a bridge between macro- and microscopic kinetics
•the structure, specifically the ligament size and its curvature and the chemical reactivity
•performance the surface stress and strain of the material and the chemical reactivity of the surface
Pivotal characteristics of the material can be changed or added independently:
a) Variation of structure:
A number of different options exist to change the structure of npAu or to apply it in different forms for catalytic reactions. The ligament size and thus the porosity can be altered by controlled annealing. This will change the number of low-coordinated sites but will also have a large impact on the diffusion of reactants in the pores, i.e. the transport properties. The various subprojects of the research unit will deal with these topics by studying the transport within the material and the dependence of catalytic properties on the ligament size. This information is essential to determine the optimal ligament and pore size.
b) Variation of composition:
As demonstrated by preliminary work, the catalytic potential of npAu is influenced to a large degree by a second metal remaining from the dealloying or deposited deliberately in a subsequent step. Depending on the type of metal (Cu, Ag, Pt), the concentration and segregation tendency and the distribution (single atoms, islands, patches), specific reactivities evolve. These foreign metals can be changed by changing the master alloys or by techniques, such as UPD. The research unit will deal with the question of the specific catalytic activity and selectivity as a function of theses parameters.
c) Variation of catalytic reactions:
Previous work has clearly demonstrated the potential of npAu for selective oxidation reactions. Therefore, the study of alcohol oxidations and coupling of alcohols is a very good platform to start with. The formation of active oxygen species from molecular oxygen on the catalyst surface and the influence of water in the feed will be foci of the research in the various groups. The insight gained will be used as a platform to proceed to other coupling reactions and partial oxidation reactions.