With the increase in demand for renewable energy, understanding chemical processes is essential for improving the design of catalysts in order to achieve better performance. This thesis summarises the experimental investigation of three types of catalytic gold materials: gold oxide formed from gold films, oxide-derived gold (OD-Au) produced from gold films, and gold nanoparticles supported on metal oxides. Different spectroscopic techniques were employed, such as operando sum frequency generation (SFG) and in situ and ex situ X-ray spectroscopies. These methods allowed the probing of the electronic and chemical states of gold after oxidising electrochemical treatments. The results indicate the presence of subsurface gold oxide remnants after formation of OD-Au, which may help explain its improved catalytic properties with respect to pure gold. In addition, a mathematical model to couple the early stages of gold oxide formation with the nonlinear optical response of gold during this process is presented. This model suggests that the growth proceeds from small oxide islands to 3D oxide growth, while SFG oxidation variation is due to the suppression of the free electron density by negatively-charged adsorbing oxygen atoms. Gold oxide was also studied with both in situ and operando X-ray spectroscopies, showing the importance of a continuous electrochemical treatment during measurements to avoid beam induced effects. Furthermore, gold nanoparticles supported on metal oxides (TiO₂ and γ-Fe₂O₃) were investigated mainly with mass spectrometry. The results indicate two different reaction pathways for oxidation of CO to CO₂ depending on the type of metal oxide support. These findings could be used to help design future gold-based catalysts.