The First Systematic Study on the Conditions Affecting the Ionothermal Synthesis of Silicoaluminophosphates

Abstract

The first systematic study on the ionothermal synthesis of silicoaluminophosphates (SAPOs) was performed to study the influence of reaction time, Si/Al or F/Al ratios and changing ionic liquid (cation, anion and alkyl group). The resulting materials were characterised by XRD, liquid ( 1 H) and solid state ( 29 Si) NMR, TPDA, SEM images, Volhard titration, as well as thermogravimetric and nitrogen sorption analyses. 1-Butyl-3methylimidazolium bromide ([C 4 mim]Br) as both solvent and structure-directing agent (SDA) produced the AFI framework. It was found that the resulting Si/Al ratio of SAPO-AFI increases with an increase in initial Si/Al ratio but decreases with F/Al ratio in the reaction mixture. Different ionic liquids giving the same framework type have no effect on the silicon uptake. The formation of Si-islands is favoured at extended reaction times or higher silicon content. The framework type of SAPOs can be changed from AEL to AFI by changing either the alkyl chain from ethyl to butyl, substituting the C2-position of the cation with a methyl moiety, or altering the cation (imidazolium vs. pyridinium). The framework selectivity was altered from AFI to LTA by changing the anion (of [C 4 py]Br to Cl À ), and to CHA by 1-methylimidazole addition. The first successful ionothermal synthesis of the AFI, LTA and CHA framework types of SAPOs is presented, providing a more efficient method than the conventional hydrothermal synthesis.[a] Dr.

Effect of Ionothermal Synthesis on the Acidity and Catalytic Performance of a SAPO‐5 Molecular Sieve

“…The 29 Si NMR show the greatest difference between the two samples. For the E‐SAPO‐5, the 29 Si NMR signals are predominantly centred at −101.4 ppm and −111.8 ppm which nominally correspond Q 3 and Q 4 silicate sites in unreacted colloidal silica or silica islands within the AFI framework . On the other hand, for the SAPO‐5, the 29 Si NMR signal is primarily centred at −90.4 ppm, which is assigned framework Si(OAl) 4 species, with weak signals at −77.0 ppm which are likely Q 0 SiO 4 species.…”

“…ILs have attracted increasing interest in zeolite synthesis because of their thermal stability, negligible vapour pressure and environmental benefits . However, to date only a few literatures reported the ionothermal synthesis of SAPO‐5 molecular sieves, and different solvent and SDA affected the morphology and acidity of SAPO‐5 . In our previous work, hollow AlPO 4 ‐5 zeolite and ZSM‐5/AlPO 4 ‐5 composite zeolite were ionothermally synthesized using tri‐substituted imidazolium bromide ILs as a solvent and template under ambient pressure .…”

“…The total acid, weak acid and strong acid amounts of E‐SAPO‐5 were significantly lower than those of SAPO‐5, because SM2 substitution mechanism for SAPO‐5 led to more acid centers . Furthermore, the presence of [EMMIM]Br IL favored the formation of silica islands, leading to a decrease in the acid amounts of E‐SAPO‐5 …”

“…On the other hand, for the SAPO‐5, the 29 Si NMR signal is primarily centred at −90.4 ppm, which is assigned framework Si(OAl) 4 species, with weak signals at −77.0 ppm which are likely Q 0 SiO 4 species. The results indicated that most of Si species were incorporated by SM3 and SM2 substitution mechanism for E‐SAPO‐5 and SAPO‐5, respectively, which was in agreement to the XRD results . Moreover, (Si/Al) NMR ratios calculated by the formula were 25.0 and 2.0 for E‐SAPO‐5 and SAPO‐5, respectively.…”

“…Moreover, (Si/Al) NMR ratios calculated by the formula were 25.0 and 2.0 for E‐SAPO‐5 and SAPO‐5, respectively. The high (Si/Al) NMR ratio of E‐SAPO‐5 was probably due to the formation of large silica islands via SM3 mechanism …”