Synthesis, characterization and catalytic properties of a LEV type silicoaluminophosphate molecular sieve, SAPO-35 from aqueous media using aluminium isopropoxide and hexamethyleneimine template

Investigation of the Crystallization Process of SAPO-35 and Si Distribution in the Crystals

“…A crystalline material with layered phase and AlPO compositions appears after heating the gel for 1.25 h. SAPO-35 is observed in Figure 9. 29 Si, 27 Al, 31 P NMR, and XRF imply that Si directly participates in the formation of the framework of SAPO-35 since the initial crystallization. Si substitutes for P first to generate the Si(OAl) 4 environment (SM II), and then a combination of SM II and SM III (2Si for the pairs of P and Al) mechanisms leads to the formation of Si islands in SAPO-35 crystals.…”

“…37 ppm arising from SAPO-35 is observed in the spectrum of the 25.25 h sample together with a weak signal at 9.1 ppm. This weak signal The 29 Si MAS NMR spectra of selected samples are obtained to follow the Si incorporation during the crystallization ( Figure 7). One broad resonance centered at −111.3 ppm is observed in the spectrum of the unwashed 0.95 h sample, which can be assigned to amorphous Si with Si(OSi) 4 environments.…”

“…The resonance frequencies were 156.4, 242.9, and 119.2 MHz for 27 Al,31 P, and 29 Si, respectively. 27 Al and 31 P MAS NMR experiments were performed on a 4 mm MAS probe with a spinning rate of 13 kHz.…”

“…Chemical shifts were referenced to 85% H 3 PO 4 at 0 ppm. 29 Si MAS NMR spectra were recorded with a 7 mm MAS probe with a spinning rate of 5 kHz using high-power proton decoupling. 5000−6000 scans were accumulated with a π/4…”

Effect of framework topology of SAPO catalysts on selectivity and deactivation profile in the methanol-to-olefins reaction

“…Prior to catalyst testing and characterization, the organic template and the water trapped within the micropores of the as-synthesized solids were removed by calcination at 823 K. Silicoaluminophosphate SAPO-35 was prepared from a synthesis gel in which the reactants were combined in the proportions detailed in Table 2. According to the procedure followed [46][47][48], aluminum hydroxide hydrate (Sigma-Aldrich) was dispersed in deionized water (33% of the total weight of water required) in a beaker, and a 34 wt% aqueous solution of orthophosphoric acid (Sigma-Aldrich, 85%) was added slowly to the suspension. The mixture was stirred for two hours before adding the fumed silica (Aerosil 200, Degussa) and the remaining amount of water.…”