Organic-free,Ultrafast Synthesis of K-CHA Nano-aggregates with Various Morphologies and Their Adsorption Performances

K-Chabazite(K-CHA)zeolites were synthesized with an ultrafast procedure through an eco-friendly and cost-effective“one-pot”method.By solely employing colloidal silica and aluminum hydroxide in the K^(+)/Sr^(2+)system without the assistance of seeds,fluorides or organic structure as directing agents,the K-CHA nano-aggregates were successfully synthesized in a few hours.The crystallization behavior of the gels with different SiO_(2)/Al_(2)O_(3) molar ratios(SARs)was investigated using X-ray diffraction(XRD);scanning electron microscope(SEM);X-ray fluorescence(XRF);27Al and 29Si magic angle spinning nuclear magnetic resonance(MAS NMR);Fourier-transform infrared spectra(FTIR);UV-Raman characterizations.As the nucleation rates were changed with the SARs,three kinds of K-CHA nano-aggregates,namely,hamburger-,disk-and walnut-shaped,were obtained.A possible formation mechanism of the K-CHA nano-aggregates was proposed.Additionally,the walnut-shaped sample with an SAR of 7 possessed the largest pore volume and specific surface area,resulting in the highest methane adsorption capacity.Furthermore,it exhibited a CH_(4)/N_(2) selectivity of more than 3 under relative pressures ranging from 0 to 0.6.This work offers guidance for modifying the stacking modes of other nano-sized zeolites.

Synthesis of LSX Using Seed-iteration Approach with High N_(2) Adsorption Capacity for Air Separation

A series of low silica X zeolites (LSX) was synthesized through a seed-iteration approach,based on the seed addition strategy,and then loaded with lithium ions by an ion exchanging method to obtain high N_(2) adsorption capacity.These zeolites were characterized by X-ray diffraction (XRD);scanning electron microscopy (SEM);Fourier transform infrared spectra (FTIR);thermogravimetric analysis (TGA);N_(2) adsorption-desorption,and the adsorption capacity of N2 and O_(2) was evaluated by the vacuum pressure swing adsorption (VPSA) operation.The results showed that the nucleation period of the synthetic process could be effectively shortened by adding seed;as the seed iterations increased,the specific surface area and pore volume of the zeolites increased;the higher specific surface area and the pore volume,the higher the extent of the N2 adsorption capacity,with the maximum reaching 28.05 cm^(3)/g.However,there were no significant differences in the adsorbed capacity of O_(2) by each sample.Therefore,the N2/O_(2) separation factor also increased gradually with iterations,with the maximum up to 6.61.