N2O decomposition has also been investigated on a 4.9% Cu=ת ─ Al2O3 catalyst in which, after a pretreatment in H2 at 573 K, the Cu was highly dispersed and present almost completely as zero-valent Cu at the surface [56]. These small Cu crystallites exhibited significant deactivation, which was attributed to strong oxygen adsorption at the Cu surface, except at high temperatures above 823 K. Additional studies indeed showed that rapid O2 desorption required much higher temperatures than with the Cu/ZSM-5 catalysts; therefore, O2 adsorption/desorption was assumed to be reversible, rather than quasi-equilibrated, and no RDS existed, as shown in the sequence of steps proposed below, where * represents an active site: