Following the rapid activation, the catalyst test proceeds with three steps designed to generate basic kinetic information: temperature variation (step 1), contact time variation (step 2), and feed variation (step 3), shown in red, grey, and blue, respectively, in Fig. . The feed variation step 3 is further split into three parts in which (a) a reaction intermediate is co-dosed, (b) the alkane/oxygen ratios are varied at a fixed steam concentration, and (c) the water concentration is modified. Based on step 1, a reference temperature ! "#$ is determined for each catalyst and reaction. ! "#$ is the temperature for which 30% alkane conversion is achieved in standard gas composition (see handbook in the SI). If 30% alkane conversion is not achieved, ! "#$ is considered the maximum temperature 450°C. The temperature limit was chosen to minimize contributions from gas phase reactions. Then, steps 2 and 3 are performed at ! "#$ . Catalyst stability during the catalyst test is monitored by measurements under reference conditions (! "#$ and standard gas feed composition) after each step. At each measurement point, a wide range of possible products are quantified (Table ). For instance, 17 molecules are measured in the case of propane oxidation. Moreover, the oxygen conversion is determined. All measurements correspond to steady-state. At the end of the catalyst test, the spent samples are collected for characterization. The detailed description of the catalyst tests is presented in the Supporting Information.