Synthesis and Characterization of Intergrowth Structured SAPO-18/SAPO-34†

doi:10.7503/cjcu20150527

Abstract

Abstract:

SAPO-18(AEI structure) and SAPO-34(CHA structure) intergrowth structured silicoaluminophosphate molecular sieves were synthesized hydrothermally with trimethylamine(TEA) and N,N-diisopropylethylamine(DIEA) as double templates. Influencing factors, such as DIEA content, SiO₂/Al₂O₃ molar ratio and crystallization time were investigated in detail. The crystalline phase, morphology and acidic property of the products were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and temperature-programmed desorption of ammonia(NH₃-TPD), respectively. The results showed that well crystallized, morphology uniformed AEI/CHA intergrowth structured silicoaluminophosphate molecular sieves with AEI/CHA=74/26 could be synthesized under the following synthesis conditions: n(DIEA)/n(AEI)=0.2, n(SiO₂)/n(Al₂O₃)=0.6 and the crystallization time 96 h. The extending of crystallization time resulted in the disappearance of SAPO-5 and the gradual increase of AEI/CHA proportion. It is therefore concluded that the thermodynamic stability of SAPO-5, SAPO-34, SAPO-18 increased in this order. Dimethylether-to-olefins(DTO) reaction was chosen to test the catalytic performance of the prepared catalysts. The prepared catalyst using TEA-DIEA as double templates exhibited excellent catalytic performance in DTO(dimethyl ether to olefins) process. The conversion of dimethylether and selectivity of ethylene and propylene are up to 100% and 84.29%, respectively.

Key words: Intergrowth structured AEI/CHA, Triethylamine, N,N-diisopropylethylamine, Double templates

CLC Number:

O643
O613

TrendMD:

ZHAO Dongpu, ZHAO Quansheng, ZHANG Yan, SHI Tuo, YAO Hengguo, YU Jianqiang. Synthesis and Characterization of Intergrowth Structured SAPO-18/SAPO-34^†[J]. Chem. J. Chinese Universities, 2016, 37(2): 342.

Figures/Tables 14

Table 1 Composition of synthesis gels for samples using various DIEA content*

Sample	Gel composition(molar ratio)
Sample	Template	Al₂O₃	SiO₂	P₂O₅	H₂O
a	1.8TEA	1.0	0.6	0.9	50
b	1.6TEA+0.2DIEA	1.0	0.6	0.9	50
c	1.6TEA+0.4DIEA	1.0	0.6	0.9	50
d	1.6TEA+0.6DIEA	1.0	0.6	0.9	50

Table 2 Intensity and relative intensity of peaks near 16.2°(sign: A in Fig.1) and 17.0°(sign: B in Fig.1) in different samples

Sample	Intensity, I_A	Intensity, I_B	Relative intensity, I_B/I_A
a	437	117	0.27
b	422	306	0.72
c	353	295	0.83
d	361	323	0.89

Fig.1 XRD patterns of samples synthesized at various contents of DIEA a. 1.8TEA; b. 1.6TEA+0.2DIEA; c. 1.6TEA+0.4DIEA; d. 1.6TEA+0.6DIEA; e. CHA; f. AEI.

Fig.2 XRD patterns of intergrowth structured AEI/CHA(a), physical mixture of AEI/CHA(b), CHA(c) and AEI(d) AEI/CHA ratio: 74/26.

Fig.3 SEM images of samples synthesized at various DIEA contents (A) 1.8DIEA; (B) 1.6TEA+0.2DIEA; (C) 1.6TEA+0.4DIEA; (D) 1.6TEA+0.6DIEA;(E) physical mixture of SAPO-18/SAPO-34=74/26; (F) pure SAPO-18.

Fig.4 NH3-TPD curves of samples synthesized at various DIEA contents a. 1.8DIEA; b. 1.6TEA+0.2DIEA; c. 1.6TEA+0.4DIEA; d. 1.6TEA+0.6DIEA.

Table 3 Catalytic performance and products distribution of different catalysts

Sample	Conversion(%)	Selectivity(%)					Coke/(g· $g cat - 1$ )
Sample	Conversion(%)	$C 2 =$	$C 3 =$	$C 4 =$	$C 2 = + C 3 =$	$C 2 = + C 3 = + C 4 =$	Coke/(g· $g cat - 1$ )
a	100	44.62	35.65	8.88	80.27	89.15	5.6
b	100	48.80	35.49	4.66	84.29	88.95	4.5
SAPO-18	100	35.88	37.82	12.3	73.70	86.03	4.2

Table 3 Catalytic performance and products distribution of different catalysts

Sample	Conversion(%)	Selectivity(%)					Coke/(g· $g cat - 1$ )
Sample	Conversion(%)	$C 2 =$	$C 3 =$	$C 4 =$	$C 2 = + C 3 =$	$C 2 = + C 3 = + C 4 =$	Coke/(g· $g cat - 1$ )
a	100	44.62	35.65	8.88	80.27	89.15	5.6
b	100	48.80	35.49	4.66	84.29	88.95	4.5
SAPO-18	100	35.88	37.82	12.3	73.70	86.03	4.2

Table 4 Intensity and relative intensity of peaks near 16.2°(sign: A in Fig.5) and 17.0°(sign: B in Fig.5) in different samples

Sample	2θ_A/(°)	Intensity, I_A	2θ_B/(°)	Intensity, I_B	Relative intensity, I_B/I_A
a	16.15	174	17.05	185	1.06
b	16.05	422	16.90	306	0.72
c	16.05	420	16.85	236	0.56

Fig.5 XRD patterns of samples synthesized with various SiO2/Al2O3 molar ratios Molar ratio of SiO2/Al2O3: a. 0.4; b. 0.6; c. 0.8; d. CHA; e. AEI.

Fig.6 NH3-TPD curves of samples synthesized at various SiO2/Al2O3 molar ratios Molar ratio of SiO2/Al2O3: a. 0.4; b. 0.6; c. 0.8.

Fig.7 XRD patterns of samples synthesized at various crystallization time a. 48 h; b. 96 h; c. 144 h; d. CHA; e. AEI.

Table 5 Intensity and relative intensity of peaks near 16.2°(sign: A in Fig.7) and 17.0°(sign: B in Fig.7) in different samples

Sample	2θ_A/(°)	Intensity, I_A	2θ_B/(°)	Intensity, I_B	Relative intensity, I_B/I_A
b	16.05	422	16.90	306	0.72
c	16.10	156	17.00	172	1.10

Fig.8 SEM images of samples synthesized at crystallization time of 48 h(A), 96 h(B) and 144 h(C)

Fig.9 NH3-TPD curves of samples synthesized at crystallization time of 48 h(a), 96 h(b) and 144 h(c)

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