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The catalytic hydrogenation of aromatic molecules, such as tetralin, on platinum supported on amorphous silica−alumina is significantly reduced by the presence of quinoline and/or dibenzothiophene compared with the reactions with pure tetralin. Quinoline neutralizes acid sites and weakens the positive effect of the acidic carrier on platinum, whereas dibenzothiophene and sulfur, resulting from dibenzothiophene hydrogenolysis, poisons selectively the metal sites. In the latter case, acid sites at the perimeter of the supported metal particles serve to bind the substrates more efficiently than Lewis acid sites and are crucial for maintaining catalytic activity. The presence of both poisons drastically reduces this pathway, lowering the catalytic activity far beyond the additive behavior.