Modification of Pd and Pt by Thiophene and Carbon Tetrachloride During Hydrogenation and Isomerization of (+)-Apopinene

The effects of poisons (thiophene and carbon tetrachloride) on the rates of hydrogenation and isomerization of (+)-apopinene on Pt and Pd catalysts were studied. Neither of these poisons completely eliminates hydrogenation activity, but a new phenomenon is observed. A minimum occurs in the plot of the ratio k1/ka (isomerization to addition) vs. the amount of poison on Pd. This minimum may be explained by the different effects of the poisons on the adsorption of apopinene and hydrogen.