Highly Efficient Synthesis of LTA-type Aluminophosphate Molecular Sieve by Improved Ionothermal Method with Low Dosage of Structure-directing Agent

doi:10.15541/jim20160062

Abstract

Abstract:

Aluminophosphate molecular sieve with LTA topology was efficiently synthesized by seed-assisted and improved ionothermal method with low dosages of organic amines and ionic liquids (ILs). The influences of organic amine type, crystallization temperature, amount of organic species, and seed crystals on the synthesis of LTA-type material were investigated, to refine the synthetic conditions. The results indicate that LTA-type molecular sieve is synthesized even by adding small amount of seed crystal into initial gels, of which both molar ratios of ILs/Al₂O₃ and Amine/Al₂O₃ are decreased to 0.67. Utilization rate of inorganic raw materials during as-synthesis is up to 86% under optimal conditions. Structure and morphology of the products, together with organic species occluded in cavities were fully analyzed by XRD, SEM, N₂ physisorption, TG-DTA, CHN elemental analysis, and liquid ¹³C NMR. The results show that the resultant LTA molecular sieve is a hierarchically porous material with both micropores and mesopores inside. It is the cooperative structure-directing effect between morpholine and 1-ethyl-3-methylimidazolium cations that guides the formation of LTA molecular sieve.

Key words: ionothermal synthesis, seed crystals, solvent-free synthesis, LTA zeolite, hierarchical porous

CLC Number:

O614

ZHAO Xin-Hong, GAO Xiang-Ping, ZHAO Jiang-Bo, ZHANG Xiao-Xiao, HAO Zhi-Xin. Highly Efficient Synthesis of LTA-type Aluminophosphate Molecular Sieve by Improved Ionothermal Method with Low Dosage of Structure-directing Agent[J]. Journal of Inorganic Materials, 2016, 31(11): 1212-1218.

Figures/Tables 9

Table 1 Conditions and corresponding synthetic products

Sample	Al₂O₃:P₂O₅:HF:Amine :ILs (molar ratio)	Temper- ature/℃	Product phases
A1	1:1:1:1:2	150	LTA
A2	1:1:1:1^a:2	150	LTA+Impurities
A3	1:1:1:1^b:2	150	LTA+Impurities
A4	1:1:1:1^c:2	150	Amorphous
B1	1:1:1:1:2	170	LTA
B2	1:1:1:1:2	190	CHA
C1	1:1:1:0.33:0.67	150	CHA+Berlinite
C2	1:1:1:0.67:0.67	150	CHA+Berlinite
C3	1:1:1:0.5:1	150	CHA+Berlinite
C4	1:1:1:1:1	150	LTA+Impurities
D1	1:1:1:0.67:0.67^d	150	LTA+Amorphous
D2	1:1:1:0.5:1^d	150	CHA+Berlinite
D3	1:1:1:1:1^d	150	LTA+Impurities

Fig. 1 XRD patterns of the products synthesized from [emim]Br adding with different amines

Fig. 2 SEM images of the as-synthesized samples (a) A1; (b) A3; (c) B1; (d) B2; (e) C1; (f) C2; (g) C3; (h) C4; (i) D1; (j) D2; (k) D3. Bars are 10 μm

Fig. 3 XRD patterns of the products synthesized at different crystallization temperatures

Fig. 4 XRD patterns of the products synthesized with low dosages of morpholine and ionic liquid

Fig. 5 Solution 13C NMR and TG-DTA profiles of the as- synthesized LTA-type aluminophosphate molecular sieve (sample B1)

Fig. 6 XRD patterns of the products synthesized in the presence of seed crystals

Fig. 7 N2 adsorption/desorption isotherms of the calcined samples A1, B1, C4, D1, and D3

Table 2 Nitrogen physisorption data of the representative samples

Samples	S_BET /(m²·g^-1)	S_Ext /(m²·g^-1)	V_Micropore /(m³·g^-1)^a	V_Mesopore /(m³·g^-1)^b
A1	692	89	0.281	0.089
B1	729	111	0.287	0.112
C4	566	65	0.233	0.083
D1	299	100	0.092	0.400
D3	654	111	0.252	0.159

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