Effect of the method of addition of Ge on the catalytic properties of Pt-Re/Al2O3 and Pt-Ir/Al2O3 naphtha reforming catalysts

Abstract

Pt-Re/Al2O3 and Pt-Ir/Al2O3 catalysts were modified by addition of an inactive metal, germanium, in order to suppress the strong hydrogenolytic activity of these types of catalysts. The influence of the addition method of germanium over Pt-Re and Pt-Ir catalysts was studied in order to find which one (catalytic reduction, successive impregnations and coimpregnation methods were used) produced the best trimetallic catalysts in terms of activity, selectivity and passivation of the hydrogenolytic activity of the metal function of the parent bimetallic catalyst. Ge addition produces a significant decrease of the activity of the metal function, affecting both non-demanding and demanding reactions and also the methane production during n-heptane reforming. It also produces an inhibition of the acid function but the resulting acid/metal activity ratio is higher than that of the bimetallic parent catalysts. Catalytic reduction was found to be the best method of Ge addition in the case of the Pt-Ir catalyst series, producing the most stable catalysts, with the lowest cracking and the highest toluene yield. The same was true for the Pt-Re catalysts prepared by coimpregnation.