Synthesis of High Performance ZSM-5-L Composite Zeolite and Its Catalytic Properities for n-Pentane Aromatization†

doi:10.7503/cjcu20140274

Abstract

Abstract:

Nano-sized L zeolite was synthesized via an improved hydrothermal synthesis method. On this basis, efficiently ZSM-5-L molecular sieves with micro-mesoporous hierarchically structure were obtained through the way of hydrothermal treatment incorporated with in situ recrystallization. X-Ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR) were applied to characterize the effect of pH value and recrystallize temperature on the manufacture of the composite ZSM-5-L molecular sieves, and optimum synthesis conditions(pH=10.5—11.5, crystallization temperature 170 ℃, crystallization time 24 h) were confirmed. The structure of the as-synthesized composite ZSM-5-L molecular sieves was micro-mesoporous hierarchically, which was different from that of pure L zeolite, ZSM-5 zeolite and their mechanical mixture zeolite. The light hydrocarbon aromatization properties of the composite ZSM-5-L molecular sieves were evaluated via a n-pentane probe reaction. Compared with the properties of L zeolite, ZSM-5 zeolite and their mechanical mixture zeolite catalyst, the composite ZSM-5-L molecular sieves show superior catalytic performances in aromatization, and exhibit potentially applications as a catalyst in light hydrocarbon aromatization field.

Key words: Hydrothermal crystallization, L zeolite, ZSM-5 zeolite, Composite zeolite, Aromatization

TrendMD:

WAN Hai, ZHANG Xiaoyu, ZHANG Ruojie, ZHANG Xiaotong, SONG Lijuan. Synthesis of High Performance ZSM-5-L Composite Zeolite and Its Catalytic Properities for n-Pentane Aromatization^†[J]. Chem. J. Chinese Universities, 2014, 35(10): 2220.

Figures/Tables 11

Fig.1 XRD patterns of zeolite L products for different aging time Aging time/h: a.0; b.1; c.2; d.6; e.12.

Fig.2 SEM image of zeolite L

Fig.3 XRD patterns of ZSM-5-L composite zeolite under different pH pH: a. 9; b. 10.5; c. 11.5; d. 12.5.

Fig.4 XRD patterns of the samples with different crystal temperatures Crystal temperature/℃: a. 90; b.130; c.150; d.170; e.190.

Fig.5 FTIR spectra of ZSM-5(a), L(b),ZSM-5+L(c) and ZSM-5-L(d)

Fig.6 SEM images of ZSM-5(A) and ZSM-5-L(B) composite zeolite

Fig.7 TEM images of grain boundary(A) and texture(B) of ZSM-5-L composite zeolite

Fig.8 NH3-TPD profiles of ZSM-5(a), ZSM-5+L(b), ZSM-5-L(c) and L zeolite(d)

Fig.9 N2 adsorption-desorption isotherms and pore size distributions(inset) of ZSM-5-L(a) and ZSM-5+L(b)

Table 1 Structural parameters of ZSM-5-L composite zeolite and mechanical mixture of L and ZSM-5 zeolites

Sample	Specific surface area/(m²·g^-1)			Pore diameter/nm	Pore volume/(cm³·g^-1)
Sample	S_BET		S_micro	S_ext	V_total	V_micro	V_meso
ZSM-5+L	289	240	49	1.63	0.17	0.12	0.05
ZSM-5-L	292	248	44	1.71	0.22	0.13	0.09

Table 2 Reaction results of n-pentane over different catalysts

Catalyst	Conversion(%)	YLP^a(%)	Distribution of aromatics(mass fraction, %)
Catalyst	Conversion(%)	YLP^a(%)	B^b	T^c	EBZ^d	PX^e	MX^f	OX^g	$C 9 +$
ZSM-5	93.4	62.7	12.3	39.6	3.1	7.0	15.9	7.2	14.9
L zeolite	89.5	68.8	12.5	41.9	4.3	6.9	16.6	7.9	9.9
ZSM-5+L	92.7	65.6	11.8	40.5	4.1	7.3	15.6	7.4	13.3
ZSM-5-L	95.7	70.9	13.9	38.5	2.8	9.2	14.7	8.3	12.6

Table 2 Reaction results of n-pentane over different catalysts

Catalyst	Conversion(%)	YLP^a(%)	Distribution of aromatics(mass fraction, %)
Catalyst	Conversion(%)	YLP^a(%)	B^b	T^c	EBZ^d	PX^e	MX^f	OX^g	$C 9 +$
ZSM-5	93.4	62.7	12.3	39.6	3.1	7.0	15.9	7.2	14.9
L zeolite	89.5	68.8	12.5	41.9	4.3	6.9	16.6	7.9	9.9
ZSM-5+L	92.7	65.6	11.8	40.5	4.1	7.3	15.6	7.4	13.3
ZSM-5-L	95.7	70.9	13.9	38.5	2.8	9.2	14.7	8.3	12.6

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