A Nanocrystalline ZSM‐5 for the Catalytic Cracking of Waste Cooking Oil

Abstract

AbstractA series of hierarchical ZSM‐5 nanocrystalline aggregates (HNZ‐5) was synthesized using a hydrothermal method with tetrapropylammonium hydroxide as a structural guide. The HNZ‐5 samples having different Si/Al molar ratios all showed suitable hierarchical architectures and the maximum surface area was found to be 329 m2/g. The SEM image displayed the width of the individual crystal particles was ~100 nm, and its nanocrystalline clusters generated intercrystalline pores. Temperature‐programmed desorption with NH3 indicated that the total acidity of this material increased with increases in the Al3+ content to a maximum of 0.47 mmol/g at a Si/Al ratio of 15. In addition, 27Al magic angle spinning nuclear magnetic resonance spectra showed that the acid sites were associated with tetrahedral and octahedral Al sites. This HNZ‐5 was applied to the catalytic cracking of waste cooking oil model compound and gave a light olefin yield as high as 43.9 % at 550 °C. Extending the reaction time to 6000 min provided a yield of light olefins in excess of 30 %, which was higher than that achieved using traditional ZSM‐5. These data confirmed that the hierarchical pore structure of HNZ‐5 resulting from the self‐assembly of nanocrystals, together with exposed acidic sites, promoted the catalytic conversion of large molecules.