On the role of additives to platinum catalysts for reforming reactions

The effect of various additives to platinum catalysts has been compared under standard reaction conditions at which aromatization of n-hexane occurs. With the same catalysts, (Pt/SiO2, Pt-K+/SiO2, Pt-Mg2+/SiO2, Pt-KL zeolite, Pt-Mg2+-KL-zeolite, Pt/Al2O3, Pt-K+/Al2O3) dehydrogenation of cyclohexane to benzene has also been monitored. It has been established that the presence of K+- or Mg2+- additives can enhance the aromatization activity, but the condition is that the additive-free catalyst is monofunctional. A discussion of the data presented together with the relevant pieces of information from the literature leads to a conclusion that the effect of K+ or Mg2+ is of electrostatic nature, influencing the ring-closure.