Abstract
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 (Ln3+) increase the overall dispersion of platinum, measured by H2–O2 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 Ln3+, 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 Ln3+ increases the production of heptane isomers, while selectivities to aromatic and terminal hydrogenolysis products significantly decrease.
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