The turnover number for benzene hydrogenation over various Pt/alumina catalysts has been found to be constant. It does not depend upon the particle size distribution which varied considerably in the "mitohedral" range (10-50 Å), nor did it vary either with the complex of impregnation (H2PtCl6) or Pt(NO2)2(NH3)2, or with the chlorine content. The value obtained is very close to that obtained by other authors. The results confirm that benzene hydrogenation is a structure-insensitive reaction. Various infrared investigations have explained the "facile" character of the reaction: all the surface platinum atoms are active sites for benzene or hydrogen adsorption. Benzene is adsorbed on a single platinum atom (as for π arene complexes) with a global transfer of electrons toward platinum, and there is no surface steric requirement for adsorption. Hydrogen responsible for the catalytic activity is reversibly and weakly adsorbed.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry