Catalytic Study of Hexadecane Cracking over Novel and Efficient HY/AI-HMS/K10 Hybrid Catalysts

The aim of this study is to provide a new and high-performance catalytic system for the cracking process by combining HY-zeolite, Al-hexagonal mesoporous molecular sieves (HMS) as a new matrix, and montmorillonite K10 as filler components. The Al-HMS molecular sieve was synthesized with different Si/Al molar ratios in the range of 2.5-35 and assembled with various amounts of HY-zeolite and montmorillonite K10 to prepare two- and three-component catalysts. After calcination, their catalytic activities were investigated in a cracking reaction of n-hexadecane at 500 degrees C and atmospheric pressure as a model reactant. The structure and surface properties of the synthesized catalysts were characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller, temperature-programmed desorption of NH3, and pyridine-IR techniques. Results indicated that the desired hybrid catalysts were successfully synthesized with the micro-mesoporous structures, high surface area, and suitable pore volume, and their performance was directly related to the strength of Lewis and Bronsted acid sites as well as the ratio of microporous mesoporous structures. The optimized ZAK(35) catalyst (containing 35 wt % NH4Y, 50 wt % K10, 15 wt % Al-HMS(5), and Si/Al molar ratio of 5 in matrix) with proper textural properties, appropriate ratio of mesopore to microspore structure, suitable thermal stability to about 750 degrees C, and a higher Bronsted/Lewis acid sites ratio exhibited an excellent ability in the cracking of n-hexadecane. In optimum condition over the ZAK(35) catalyst, n-hexadecane conversion of 69% was achieved, and the selectivity values of gasoline, liquefied petroleum gas, and dry gas were 71, 20, and 4.5%, respectively.