Studies in heterogeneous catalysis and x-ray spectroscopy of water
The research of the group is focused on fundamental problems in heterogeneous and electrochemical catalysis and the determination of the structure and origin of the anomalous properties of liquid water. We have developed a new picture of ambient water based on fluctuations between two types of local structures connected to the anomalous properties of water. These become enhanced upon supercooling where thermodynamic response functions seem to diverge at a temperature of 228 K, i.e. below the temperature of homogeneous nucleation. We perform MD simulations in the supercooled regime to analyze the origin of the enhanced fluctuations. We will apply computed x-ray absorption (XAS) and emission (XES) spectra in conjunction with a fit to the O-O radial distribution function to determine structures that reproduce these data sets. We will then perform an extensive simulation of XES on water based on the determined structures. This will contribute strongly to finally determine the elusive structure of water. These techniques will also be used to investigate structure models from newly developed force-field descriptions of water where we are also actively developing the SCME-GAP force-field model. We will study the dynamics in the liquid through the van Hove intermediate scattering function at ambient and supercooled conditions. In heterogeneous catalysis we exploit new opportunities created by the ultrashort pulses from the LCLS free-electron x-ray laser which enable following chemical reactions in real time. We compute structures, barriers and spectra to assist in the analysis of the experiments which have included CO desorption and oxidation on Ru(0001), as well as hydrogenation of CO on the way to synthetic fuels. We will continue by studying associative desorption of C+O as CO, N2 dissociation and the Haber-Bosch process to make ammonia as well as CO2 reduction both heterogeneously and electrocatalytically. The electrocatalytic CO2 reduction reaction shows high selectivity for ethylene when using specially prepared Cu nanocubes reduced from Cu2O. The origin of this selectivity and enhanced reactivity is still unknown. We will continue our studies in sulfide mineral chemistry related to acid mine drainage by investigating band offsets of mixed sulfide minerals and also the effects of dopants on dissolution rates where we can also compare to experimental XAS to validate our models.