According to the United Nations and the European Union, any discarded material or object that is being disposed of or recovered (OECD definition) is classified as “waste” as they can no longer be re-used. Some catalysts are able to be used several times, but after a while they reach a point where they are beyond re-use. At this point they become a waste and are therefore subject to international waste laws. Even if some wastes have a very high value (such as certain spent catalysts) they are still wastes, which also usually possess hazardous characteristics.