70.
Several Pt/L‐zeolite catalysts were prepared by the impregnation method from L‐zeolite samples previously exchanged with Ba
2+, La
3+, Pr
3+, Nd
3+ and Sm
3+. 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, Ba
2+ 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.
This revised version was published online in July 2006 with corrections to the Cover Date.
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