Firstly, deactivation may be induced by temperature, due to thermal degradation (e.g. sintering) of the catalyst. The respective kinetic models depend on a kinetic constant, 𝑘 , the current catalyst activity, 𝑎 , and a persistent activity, 𝑎 . Coming back to the example, the deactivation will level off for large catalytically active nanoparticles, which are immune to sintering. The corresponding temporal change in activity can be expressed by Eq. ( ).