Truth is, we all are transients: A perspective on the time-dependent nature of reactions and those who study them

Understanding and mastery of Transient Kinetics in the context of multi-scale transport-reaction systems employed in catalysis is one of the ultimate frontiers in chemical science and engineering. In this perspective, we will highlight key results enabled by experiments in the Temporal Analysis of Products (TAP) Reactor Systems spanning several decades of research, several length-scales of space and time, as well as several ensembles of individual (re)actors, ranging from a single 350 µm-sized catalytic particle to a bed fully packed with them. Conclusions are drawn and new horizons are discerned.