Alumina- and titania- supported palladium catalysts were prepared and their catalytic behaviors for the selective hydrogenation of acetylene were investigated in the presence of excess ethylene.
The activity and selectivity were widely affected by the reaction temperature, $C_2H_2$ concentration, $H_2/C_2H_2$ ratio, CO as a moderating component, and copper as an additive metal.
For alumina- supported palladium catalyst, the addition of carbon monoxide resulted in a slight decrease in activity but an increase in selectivity together with enhanced rate of oligomer formation, while the addition of copper improved the activity and selectivity significantly and inhibited the rate of oligomer formation. Enhancement in the selectivity of ethylene was found at lower ranges of reaction temperatures and $H_2/C_2H_2$ ratios and at higher $C_2H_2$ concentrations.
For titania- supported palladium catalyst, however, the selectivity was influenced only slightly by reaction conditions. The selectivity remained stable during the reaction and was much higher than that on alumina- supported catalyst.
Copper decreased both the activity and selectivity, while the rate of oligomer formation was greatly increased due to the presence of copper. The rate of oligomer formation on alumina- supported catalyst was always higher than that on titania- supported one irrespective of reaction conditions.
