We now analyze the selectivity of the materials and reaction conditions that present high activity and belong to the identified SG. The evolution of measured S C2H4 values with t OS for the materials in the SG are shown in Fig. and B for T oven 100 and 150 • C, respectively. Some materials such as Pd 1 Ag 9 and Pd 1 Ag 5 present a near-constant S C2H4 for t OS > 30 min. This indicates that for these materials, the steady state is reached in less than 30 min. However, other materials develop an improved selectivity as t OS increases. In particular, the Pd 1 Cu 9 material presents S C2H4 = -1 (total hydrogenation catalyst) at t OS < 30 min, and the S C2H4 value becomes positive (selective catalyst) after ca. 180 min in the case of T oven = 150 • -see Fig. , square brown markers. Thus, for some catalysts, the compound initially placed in the reactor is undergoing significant modifications. The induction period for reaching optimal performance and the steady state is in the range of hours. We stress that all materials shown in Fig. are active towards acetylene conversion (with X C2H2 ≈ 1) since the start of the reaction at t OS = 0. By using only the data points belonging to the SG associated to high acetylene conversion (539 data points), we trained SISSO models for S C2H4 . The mean prediction (test) error evaluated using five-fold nested cross validation is 0.105 for SISSO models with the optimal complexity. Such value is significantly lower than the standard deviation of S C2H4 in the training data set (0.600). This shows that the identified models describe unseen data with good accuracy. The fit of the best SISSO models to the data, shown in Fig. and D for T oven 100 and 150 • C, respectively, indicates that the identified expression (Eq. 6) is able to capture the selectivity trends both across materials and with t OS . In particular, the selectivity shift of the Pd 1 Cu 9 material (Fig. and