Abstract: Processes and apparatus are disclosed for the catalytic purification of styrene monomer by hydrogenating the phenylacetylene contaminant therein to styrene in a catalytic bed using multiple hydrogen injection; dilution of the hydrogen by a diluent such as nitrogen; mixing the hydrogen with a catalyst-selectivity improver such as carbon monoxide; using ethylbenzene dehydrogenation ventgas to supply hydrogen; and, using a multiple-catalyst-bed-reactor, or multiple reactors, each with a single catalyst bed. One preferred phenylacetylene reduction catalyst used is palladium on an alumina carrier.