Abstract
To meet the industrial needs for SSZ-13, variable sizes of SSZ-13 with different Si/Al ratios were firstly obtained by conventional hydrothermal synthesis using the seed method. Using a set of characterizations, like X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM), the physicochemical structure and size distribution could be traced. After the specific Si/Al ratio of SSZ-13 zeolites was optimized, synthesized by changing the amounts of structure-directing agents (SDAs) and NaOH, the obtained SSZ-13 showed a high degree of crystallinity. With the limitation of the pH values, the variation of the alkalinity and water content was not helpful to generate different grain sizes of SSZ-13 materials. With the help of ground seed, the various grain sizes of SSZ-13s from 0.4 to 4 μm had a similar degree of crystallinity and size distribution. Moreover, due to the identical intensity of the Al peak in the NMR results, the different grain sizes of SSZ-13s had the same acidity. Our study revealed that using the seed method was an easy and efficient way to synthesize SSZ-13s with different sizes.
Highlights
Academia and industry have been highly concerned in the last decade with silicoaluminate zeolites of SSZ-13 with the chabzite (CHA) structure, showing the same topological structure as SAPO-34.The SSZ-13 material contains 4, 6, and 8-membered ring (MR) units to form a three-dimensional pore structure with a large 7.3 Å cage and 3.8 Å 8-MR windows [1]
Huang et al [7] found that the small size of SAPO-34 with a low density of surface acidity and the CHA structure was relatively stable after low-temperature hydrothermal aging
It is well known that Na/SSZ-13 materials with a wide range of Si/Al ratios are usually obtained via hydrothermal methods using Al(OH)3 and colloidal silica with TMAda-OH
Summary
Academia and industry have been highly concerned in the last decade with silicoaluminate zeolites of SSZ-13 with the chabzite (CHA) structure, showing the same topological structure as SAPO-34. It is reasonable to believe that the small size of zeolites on a honeycomb carrier may increase the backpressure, and that would hinder the reaction process. Taking all these facts into account, the controllable synthesis of variable sizes of SSZ-13 according to the actual situation is an efficient way to cope with all the possible operating conditions in the real situation. For SSZ-13 zeolites, adding organic compounds into the synthetic precursor solution of SSZ-13 is a common method to generate small-sized SSZ-13 particles. It is important to perform further studies on an easy and efficient method to synthesize different sizes of CHA with a uniform size distribution. In this work, Na/SSZ-13s were firstly synthesized and H/SSZ-13s prepared via ammonia exchange and calcination to probe the above viewpoints
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