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

Abstract

The direct synthesis of zeolite Y with high SiO 2 /Al 2 O 3 (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 Co 2+ 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 Co 2+ in synthesis system affects the formation of 5-coordination intermediate ( M-O -Si )* around Co 2+ 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 Co 2+ . 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 SiO 2 /Al 2 O 3 and small crystal size zeolite Y. • Zeolite Y with SiO 2 /Al 2 O 3 of 6.15 and small crystal size was achieved by introducing Co 2+ in a facile hydrothermal method. • The nucleation free energy was reduced by the microcrystalline Co(OH) 2 species via adhering to the amorphous materials. • The ΔG of (Co-O-Si)* is higher than that of (Al-O-Si)*, Si species combine with (Al-O-Si)* to increase the SiO 2 /Al 2 O 3 .