Probing Surface Chemistry with Ion Imaging

Chemical reactions at surfaces are of paramount importance to chemical and energy industries. Most large-scale chemical processes rely on heterogeneous catalysis, where reactants and catalysts are separated in different phases and the reaction takes place at the phase boundary. As computing power continues to increase exponentially, this holy grail of predicting reactivity seems to be within our grasp. Chemical kinetics and dynamics at surfaces can now be simulated with more detail and accuracy than ever, and thus require top-notch experimental results for comparison. The goal of researchers should thus be to design experiments which can be easily compared to theoretical calculations. This requires clear assignment of the observed processes, ideally elementary step processes, and the related rate coefficients and dynamical information. In order to correctly assign the observed processes, the experiment must thus be carried out for the simplest possible system. As inorganic catalysts possess different sites with distinct activity, such as closed-packed terraces, step edges or defect sites, reactions often take place at different sites. As the discrimination between the different pathways is extraordinarily difficult, most experiments measure a combination of reactions taking place at different active sites. Unless the reaction at other sites can be suppressed, this limits mechanistic understanding and makes meaningful comparison to theory impossible.