Privileged structures is a term that is used in drug design to indicate a fragment that is popular in the population of drugs or drug candidates that are in the application or investigation phases, respectively. Privileged structures are popular motifs because they generate efficient drugs. Similarly, some elements appear to be more efficient and more popular in catalyst design and development. To indicate this fact, we use here a term privileged metal combination. In particular, Ru-based catalysts have paved a bumpy road in a variety of commercial applications from ammonia synthesis to carbon (di)oxide methanation. Here, we review Ru/Ni combinations in order to specifically find applications in environmental nanocatalysis and more specifically in carbon (di)oxide methanation. Synergy, ensemble and the ligand effect are theoretical foundations that are used to explain the advantages of multicomponent catalysis. The economic effect is another important issue in blending metal combinations. Low temperature and photocatalytic processes can be indicated as new tendencies in carbon (di)oxide methanation. However, due to economics, future industrial developments of this reaction are still questionable.