DEUTERIUM TRACER STUDY ON THE EFFECT OF CO ON THE SELECTIVE HYDROGENATION OF ACETYLENE OVER PD/AL2O3

The effect of carbon monoxide on the selectivity to ethylene during the selective hydrogenation of acetylene over Pd/Al2O3 has been studied by isotopic tracer techniques. CO enhanced the total amount of deuterium exchange during acetylene deuteration while reducing the hydrogenation rate and increasing the selectivity to ethylene. For ethylene deuteration, CO suppressed the deuterium exchange reaction without affecting the reaction rate. Acetylene results are consistant with the mechanistic argument that the probability of hydrogenating adsorbed vinyl decreases when CO is added, which is caused by the displacement of surface hydrogen. However, for ethylene hydrogenation, CO increases the probabilities of ethylene desorption and adsorbed ethyl hydrogenation, which is consistant with the interpretation that CO displaces ethylene. For industrial processes for removal of trace acetylene from ethylene, it is suggested that the selectivity increase induced by CO is largely due to CO displacement of ethylene.