Synthesis of loosely aggregating polycrystalline ZSM-5 with luxuriant mesopore structure and its hierarchically cracking for bulky reactants.

ZSM-5 zeolite with different morphologies from compact large single crystals, to loose polycrystalline aggregates, and to monodispersed nanocrystals were finely tailored without adding any secondary templates by only changing the TPAOH/SiO 2 ratio in the gel precursors. The factors affecting the morphologies of the crystals in the synthesized samples were investigated in details. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N 2 adsorption-desorption isotherm, thermogravimetric (TG) analysis, in situ infrared (IR) spectrometry of pyridine, and temperature-programmed desorption of ammonia (NH 3 -TPD). The effect of affluent mesopore structure resulted from loosely aggregating primary nanosized crystals on the as-prepared catalysts was investigated during catalytic cracking of 1,3,5-triisopropylbenzene (TIPB), and the result shows that the catalysts have excellent catalytic performances with enhanced conversions as compared with a commercial ZSM-5 catalyst. The remarkable increased catalytic activity is mainly ascribed to the increased external surface area, which contributes to offering highly effective and accessible acid sites for the bulky molecules reactants. Image 1 • Hierarchical ZSM-5 were synthesized without a secondary template. • Different morphologies from dense to loose structure were tailored by changing TPAOH/Si ratios. • Increased external surfaces offer more effective acid sites for cracking bulky reactants. • Hierarchically cracking contributes to solving challenge for larger and larger heavy oil molecules. [ABSTRACT FROM AUTHOR]