Acidity modifications of nanozeolite-Y for enhanced selectivity to olefins from the steam catalytic cracking of dodecane

Abstract

Nanozeolite-Y was synthesized in the absence of a templating agent with several modification methods. The parent nanozeolite-Y was prepared with different sodium (Na) contents and crystallization conditions. Then, the parent nanozeolite-Y was modified by ion exchange, calcination, and steam treatment. The treatment caused insignificant changes to the ratio of alumina and silica but altered the zeolite acid sites. The Lewis and Brønsted acidity changed after the treatment depending on the modification approach, as indicated by the FTIR spectroscopy of pyridine. The ammonia temperature programmed desorption (NH₃-TPD) confirmed that the acid sites consisted of weak and medium sites, which decreased after modifications. Moreover, the solid-state nuclear magnetic resonance (NMR) spectroscopy revealed that the position of Al shifted from tetrahedral to a combined octahedral and pentahedral framework. The catalytic evaluation for dodecane cracking at 550 °C shows the gas yield as the main product with naphtha as a side product. The gas yield consisted of 50% light olefins from ethylene to butene. However, the process yielded 9% of coke that led to faster catalyst deactivation because of nanozeolite-Y evolution and product transformation.