Ammonia and sulfur poisoning effects on hydrogenation of phenylacetylene over Pd supported catalysts

The effect of palladium dispersion, on the selectivity for phenylacetylene hydrogenation was studied. Low dispersed palladium catalysts showed to be more selective to partial hydrogenation than high dispersed ones. The initial selectivity to styrene is increased with time on stream. Carbonaceous deposits were assumed to be responsible for this phenomenon. Selectivity was also modified by ammonia and sulfur addition: ammonia increased the styrene selectivity while sulfur had a negative effect. The poisoning effects were explained through an electronic effect. Ammonia is an electron donor modifier whereas sulfur is an electron acceptor modifier.