Synthesis of nano-sized LTL zeolite by addition of a Ba precursor with superior n-octane aromatization performance

摘要

A nano-sized LTL-type zeolite was successfully synthesized using a facile and commercially viable hydrothermal method by the addition of a small amount of Ba precursor to the conventional synthesis mixture regardless of the types of Ba precursors used. The results showed that the Ba added can be used to finely tune LTL particle sizes in the range of 0.1-1 m and shorten the synthesis time, indicating that Ba had a significant effect on the crystallization process of LTL-type zeolite. By comprehensively tracing the evolution of two systems, namely KL and BaKL, it was found that the crystallization of KL zeolite took place by a chain of processes including the appearance of worm-like particles (WLPs), their random aggregation/coalescence and crystallization of these aggregates. On the other hand, the Ba added can accelerate the coordination between monosilicate and alumina species. Therefore, LTL zeolites with small crystal sizes were quickly produced by rapid crystallization of the amorphous phase to the final products. The Pt/LTL catalysts were obtained by impregnating the obtained zeolites with Pt and then evaluated in n-octane aromatization reactions. Compared with conventional LTL zeolite, the nano-sized LTL zeolite-supported Pt catalyst exhibited superior catalytic performance with an about 3-fold prolonged catalytic lifetime and higher selectivity for aromatics due to the shorter diffusion path of the primary aromatic products in nano-sized zeolites, which inhibited the secondary undesirable reactions (coke formation and hydrogenolysis).