A facile organic-free synthesis of high silica zeolite Y with small crystal in the presence of Co2+

The direct synthesis of zeolite Y with high SiO2/Al2O3 (SAR > 6.0) and small crystal size is a great challenge. The conventional production of high silica Y usually involves organic template into the synthesis system, which takes high cost. Here, zeolite Y with SAR of 6.15 and small crystal size via introducing Co2+ in a facile one-step hydrothermal method without organic template was achieved. The SAR increased from 5.2 to 6.15 compared to normal NaY, and the crystal size decreased to 50%. The introduction of Co2+ in synthesis system affects the formation of 5-coordination intermediate (M-O-Si)* around Co2+ during crystallization process which is the critical factor to nucleation. The stability of (Co–O–Si)* is weaker than that of (Al–O–Si)*, which leads to the increase of SAR around Co2+. The microcrystals of Co(OH)2 provide adhesive surface for the amorphous material and promote nucleation. The zeolite Y shows good performance in the cracking of 1,3,5-triisopropylbenzene because of larger surface area and more active sites being exposed. This is a new strategy for industrial synthesis of high SiO2/Al2O3 and small crystal size zeolite Y.