SURFACE HETEROGENEITY OF SUPPORTED PALLADIUM CATALYST FOR THE HYDROGENATION OF ACETYLENE-ETHYLENE MIXTURES

The hydrogenation of acetylene-ethylene mixtures over a Pd/alpha-Al2O3 catalyst was studied. Kinetic investigations were carried out in a fl ow system equipped with a gradientless microreactor over a wide range of acetylene and ethylene partial pressures. Three types of active sit es were thus identified: A(1) and A(2) sites which are highly selectiv e in the hydrogenation of acetylene to ethylene via a mechanism involv ing the competitive (A(1)) and noncompetitive (A(2)) adsorption of ace tylene and hydrogen, and E sites which are active only for the hydroge nation of ethylene. E sites are able to adsorb acetylene, an effect wh ich strongly inhibits ethane formation. The above three types of activ e sites are very likely created on the palladium surface by carbonaceo us deposits formed during the stabilization process. The identified si tes determine the selectivity of the catalyst and manifest themselves in kinetic investigations depending on the process conditions.