Progress in Seed-assisted Synthesis of (Silico)Aluminophosphate Molecular Sieves

Regulation of the Si/Al ratios and Al distributions of zeolites and their impact on properties

“…Compared to AAS, ICP-AES is especially suitable for refractory elements, such as Si and Al, which perform poorly by flame AAS. 52,112,164 However, analysis of Si and Al by AAS and ICP-AES requires the complete dissolution of zeolite samples into solution, which usually involves toxic hydrofluoric acid. This is the disadvantage of the AAS and ICP-AES.…”

“…[104][105][106][107][108][109] In the dealumination of Beta zeolites, the Si/Al ratio was increased to over 200 if the starting Si/Al ratio was greater than 12, while the framework collapsed if the starting Si/Al ratio was less than 12. 105 Besides nitric acid, many other acids and chelates can also be used in the dealumination of zeolites, such as oxalic acid, [109][110][111][112] ethylene diamine tetraacetic acid (EDTA), 103,107,113 and hydrochloric acid. 103,107 For example, Valtchev and co-workers recently reported the mild dealumination of zeolites with chromic acid.…”

Small pore SAPO-14-based zeolites with improved propylene selectivity in the methanol to olefins process

“…Among these samples, the S-34 sample has a high BET surface area ( S BET ) of about 682.5 m 2 g −1 , but a small external surface area ( S ext ), indicating a typically microporous zeolite. 33 The S BET value of sample S-14 is 194.9 m 2 g −1 , much smaller than that of S-34. This is because the pore size of AFN is much smaller than those of other 8-ring zeolites.…”

“…The difference may be caused by the different silicon contents in these two zeolites. 32,33 As for the S-1 sample, the obtained crystals have irregular morphologies, but the particle size decreases significantly compared with S-14 and S-34. The result is consistent with the effect of seed addition on the crystal size of zeolites.…”

“…The result is consistent with the effect of seed addition on the crystal size of zeolites. 32,33 This indicates that the SAPO-34 seeds added in the synthesis not only can introduce the CHA structure in the final product, but also can adjust the particle size of the product. With an increase of the added SAPO-34 seeds, the large rectangular plate appears in the S-2 sample, which may be due to the incomplete transformation of SAPO-34 seeds.…”