Excellent Activity of Nb in Promoting Performance of ZSM-5–USY for the Catalytic Cracking of n-Hexane to Light Olefins

To improve the catalytic activity of zeolites in cracking of petroleum components for the production of light olefins, ZSM-5–USY composite catalysts modified with transition metals (e.g. Nb, Ni, or W) have been synthesized by an impregnation method. The catalytic performance of the obtained catalysts in the cracking of n-hexane as a model compound of petroleum for the production of light olefins has been evaluated using a fix-bed reactor. The Nb-modified composite zeolite has shown an excellent catalytic activity. The optimal Nb loading for the composite catalyst is 1.5% (1.5% Nb/Z–Y) that provides the highest amount of acid sites. The yield up to 50% and the selectivity up to 68% of the C2–C4 olefins have been achieved at 650°C. The kinetic study of the catalytic n-hexane cracking on 1.5% Nb/ZSM-5–USY has characterized it as the first-order reaction with the apparent activation energy of 115.16 kJ/mol.