${\mathrm{CH}}_3\mathrm{COCl}+{\mathrm{H}}_2\underset{\mathrm{quinoline}}{\overset{\mathrm{Pd}/{\mathrm{BaSO}}_4}{\to }}{\mathrm{CH}}_3{\mathrm{CHO}}_{.}$
Here quinoline acts as

Quinoline acts as a catalytic poison in Rosenmund's reaction as it decreases the rate of the reaction.