Effect of Ba and rare earths cations on the properties and dehydrocyclization activity of Pt/K-LTL catalysts

Several Pt/L-zeolite catalysts were prepared by the impregnation method from L-zeolite samples previously exchanged with Ba2+, La3+ Pr3+, Nd3+ and Sm3+. Lanthanides (Ln(3+)) increase the overall dispersion of platinum, measured by H-2-O-2 titration. TPR and CO/FTIR measurements indicate that these ions modify the distribution of Pt in the zeolite lattice, increasing the fraction of metal on the external surface. Additionally, both CO/FTIR and competitive hydrogenation of toluene-benzene mixtures indicate that in the presence of Ln(3+), the electron density of the platinum decreases in comparison with Pt/KL-zeolite. On the other hand, Ba2+ does not substantially modify neither the distribution nor the electronic state of Pt. The reactivity measurements in the hydroconversion of n-heptane show that Pt/BaKL and Pt/KL exhibit similar catalytic behaviour with a high dehydrocyclization activity. However, the exchange of K+ by Ln(3+) increases the production of heptane isomers, while selectivities to aromatic and terminal hydrogenolysis products significantly decrease.