The much debated challenge is describing these formation rates in terms of the current reaction conditions. This functional dependency is referred to as the reaction kinetics. However, it is often not trivially accessible, how many reaction steps make up a seemingly simple reaction. This matter is further complicated by the fact that heterogeneously catalyzed reactions only take place at a phase boundary where interactions between bulk phase and catalytic phase (and oftentimes even supposedly inert phases like catalyst support ) occur. This results in the fact that the unknown number of reaction steps might be (and more often than not is) interconnected in an unknown way by an unknown number of intermediate species at the phase boundary.