Microstructure evolution and impact of mechanics for catalysis

点击翻译按钮获取中文摘要

Processes at materials surfaces in heterogeneous catalysis depend on the state of the surface through local chemical composition, density of defects such as step edges or kinks, and the presence of stable adsorbed species such as oxygen. Chemical composition is a particularly important issue, since previous work on the catalysis of nanoporous gold made by alloy corrosion has emphasized the impact of the re-sidual content of the sacrificial element in the corrosion process, Ag, for catalysis. The first of the two superordinate aims of this project in the ongoing first funding period is to synthesize and characterize nanoporous metal samples in which variations in composition, adsorbate coverage, and structure size are explored. These samples are being supplied to all experimental subprojects (SPs) for studies of catalytic activity (SP1–SP4) and for characterization of surface composition (SP4) and structure (SP6). In the requested second funding period we propose to continue preparing samples via the established protocols as benchmarks for the established sample quality. The research focus in SP3 will shift to investi-gating the microstructure evolution during dealloying and during annealing (a key step for tuning the lig-ament size) as well as in operando during catalysis. This investigation will be based on atomistic computer simulation studies, conducted so as to account for the environmental variables such as time-temperature profiles and the chemical environment at the surface. To this end we shall use a Kinetic Monte Carlo computer code that is already established in our team. The simulation will use materials parameters from DFT (SP7, SP8, SP8(new)) and will be matched to experimental studies of surface composition by x-ray photoelectron spectroscopy (SP4) and of solute distribution by transmission electron microscopy (SP6).Recent theory and experiment advertise a decisive role of elastic strain for heterogeneous catalysis. Na-noporous metals are inherently strained. Exploring and understanding the relevance of mechanics for the catalytic performance of nanoporous gold is the second superordinate aim of this project. The lattice strain is being experimentally quantified for all sample qualities under study, partly in cooperation with SP6. Reference measurements on planar electrodes explore modulated electrocatalytic reaction rates during fast cyclic straining of planar electrode surfaces. The observations will be connected to the exper-imental studies of catalytic or electro-catalytic activity (in SP1–SP4) and of atomic-scale structure (in SP6), and they will be conducted in close feedback with the theory projects supplying in data for adsorption enthalpies (SP7) and surface composition profiles (SP8).