Long-term behaviour of Pd-Ag/Al2O3 catalyst was evaluated experimentally and mathematically for tail-end acetylene selective hydrogenation process. It was observed that a kinetic model based on first order for C2H2 and H2 for main reaction and first order independent decay law for catalyst deactivation can investigate catalyst performance in an acceptable manner. Moreover, a two-stage deactivation was observed for catalyst which is a result of coke deposits that had dual role on catalyst behaviour according to its type and amount. TG and FT-IR analyses confirmed that these carbonaceous deposits are of soft ones for 100 h on stream operation.