Heterogeneous metal catalysts are amongst the most important industrial catalysts. During catalyst preparation it is of high interest to yield a stable and highly dispersed active metal phase. Reduction of catalyst precursors is a vital step in catalyst preparation as it determines the dispersion and thereby activity. There has been a wealth of investigations on the reduction mechanism, however, most studies were performed either ex-situ or with model systems. This project focuses on gaining insights into the reduction mechanisms of nickel catalysts, which proved to be very complex as it involves transformation of various Ni –species, formed during preparation of industrial Ni-catalyst (e.g. Ni(OH)2, NiCO3, Ni(OH)x(CO3)y), into the active metal phase. Therefore, it is vital to understand the evolution of the active phase with a combination of complementary techniques. Finally, the project aims at improving the manufacturing process by adjusting the reduction conditions, and ultimately designing improved Ni-catalysts.