1. Loss of Activity: A decrease in the rate of reaction indicates that the catalyst is losing its activity. 2. Selectivity Changes: A shift in product distribution suggests that the catalyst is no longer selective. 3. Increased Pressure Drop: In heterogeneous catalysis, fouling can cause a pressure drop across the reactor. 4. Visual Changes: Physical changes in the catalyst, such as color change or pellet breakage, can indicate degradation.
