In this work, we have studied various aspects of catalysts and catalytic processes at the solid-liquid interface, e.g. the reduction of supported PdO, the formation of Pd hydrides, their quantification, the their reactivity in a transient in time-resolved manner, Ru and P-modified Ru based catalysts and zeolites. In order to provide structural information mainly X-ray absorption spectroscopy, infrared spectroscopy and X-ray diffraction were used, while the measurements were made possible by the realization of a dedicated setup including reactor cells. The cells are designed to allow for monitoring structural changes of oxidation state and nature of adsorbates in a time-resolved manner. This is of particular interest to study the reactivity of species, such as the Pd hydrides, formed on the catalyst in the liquid environment exploiting tools that are already widely applied to study gas phase reactions.