The selectivity and activity characteristics of the palladium catalysts supported on γ-$Al_2O_3$, activated carbon and titania were investigated for the selective hydrogenation of acetylene in the presence of excess ethylene.
The addition of carbon monoxide which acted as a moderator resulted in slight decrease in the activity but a rather great increase in the selectivity, together with enhanced oligomer (green-oil) formation.
With enough addition of copper (ca. Cu/Pd $\geqq$ 1) the hydrogen spillover was inhibited, and the activity decreased slightly, while the selectivity became much more stable. But in the case of less addition of copper (Cu/Pd=3/7), the tendencies of the activity and the selectivity were reversed against the case of Cu/Pd $\geqq$ 1.
For the palladium catalyst supported on titania the activity had an induction period and then became steady, while the selectivity became much higher and more stable.
