Abstract A study was made of the effects of metal acetate salts on the ability of a commercial silica-alumina catalyst to promote the conversion of cumene to benzene and propylene. The typical effect of the salts was to reduce the conversion. The extent of this reduction was determined by the amount, size, valence, and chemical type of the poisoning cation. Graphs of percent conversion versus the area (or volume) of catalyst surface actually covered by poisoning metal ions showed three distinct activity curves with the alkali metala exhibiting greatest, the alkali earth metals poorest, and zinc and cadmium an intermediate poisoning ability. Very small amounts of divalent metal cations showed a small promoting action. Acetic acid had no effect on conversion. The results suggest that cracking occurred on acid sites present in clusters on the catalyst surface and that site blocking and chemical neutralization both contributed to the poisoning of the catalyst.