Refinery off-gas often contains important amounts of ethylene and nowadays is burned as fuel gas. A simple way to valorize this wasted ethylene is to convert it into more easily transportable liquid products, like oligomers C4+. This is the study focusing on the oligomerization of diluted ethylene, conducted at moderate pressure and temperature. The first objective was to provide new efficient heterogeneous catalysts and a process able to convert diluted ethylene into heavier olefins. Thus, two catalysts, Ni-AlSiO2 and NiAlSBA-15, were prepared, characterized, and evaluated in the oligomerization process at 250 degrees C and 15 bar. The second aim was to evaluate the effect/role on the catalysts of some potential contaminants, such as H2O, CO, and H-2, which are usually present in the refinery off-gas.