in heterogenous catalysis
The time on stream during which the rate constant
for the catalytic reaction, ,
falls to a specified fraction of its original value, often 0.5.
PAC, 1976, 46, 71
(Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix
II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II:
on page 83