Palladium on barium sulfate is a supported heterogeneous catalyst widely used in organic synthesis for selective hydrogenation reactions. It is particularly renowned for the Rosenmund reduction, converting acid chlorides to aldehydes without over-reduction to primary alcohols, often with the addition of poisons like quinoline or sulfur to enhance selectivity. The barium sulfate support moderates the palladium's reactivity, making it less active than unsupported or carbon-supported palladium, which allows for precise control in complex transformations. It is commonly employed in the pharmaceutical industry for synthesizing fine chemicals and intermediates, as well as in the production of flavors, fragrances, and specialty polymers where controlled hydrogenation of functional groups such as alkynes, alkenes, or nitro compounds is essential.