Soft Template-directed Hierarchical Mordenites and Their Performance in Benzylation of Benzene with Benzyl Alcohol

doi:10.15541/jim20160151

Abstract

Abstract:

Mordenite is generally referred to be a one-dimensional micropore zeolite. The major drawback of this pore structure is severe diffusion limitations, especially for the reactions involving bulky molecules. Herein, hierarchical mordenites were successfully prepared through a soft-templating method using a diquaternary ammonium surfactant [C₁₈H₃₇N⁺(CH₃)₂C₆H₁₂N⁺(CH₃)₂C₆H₁₃(Br^-)₂, C_18-6-6Br₂for short] as mesoporogen. The obtained samples were characterized by XRD, FT-IR, SEM, TEM, TG-DTG, N₂ physical adsorption, and NH₃-TPD techniques. The results show that the hierarchical mordenites with nanorods (20-40 nm in width) oriented-assembled structures are synthesized in the presence of the C_18-6-6Br₂ surfactant. Moreover, the crystal sizes, mesopore surface areas and mesopore volumes of hierarchical mordenites can be systematically tuned by changing the C_18-6-6Br₂/SiO₂ ratios. More importantly, the hierarchical mordenites exhibit much higher catalytic activity and faster reaction rate in the benzylation of benzene with benzyl alcohol than the conventional mordenite. The remarkably enhanced catalytic performance of hierarchical mordenites may be attributable to the more accessible acid sites and much better mass transfer properties with the presence of mesopore. Thus, the special hierarchical mordenites reported here show a great potential for catalytic conversions involving bulky molecules.

Key words: mordenite, hierarchical zeolite, mesopore, template, benzylation

CLC Number:

Q469

LI Yu-Ping, SUN Cui-Juan, JIA Kun, ZHANG Yi, LI Xiao-Feng, DOU Tao. Soft Template-directed Hierarchical Mordenites and Their Performance in Benzylation of Benzene with Benzyl Alcohol[J]. Journal of Inorganic Materials, 2016, 31(12): 1355-1362.

Figures/Tables 13

Fig. 1 XRD patterns of mordenite samples synthesized with different amounts of C18-6-6Br2

Fig. 2 FT-IR spectra of mordenite samples synthesized with different amounts of C18-6-6Br2

Table 1 Pore structure parameters of mordenite samples

Samples	^aSi/Al	^bS_BET/ (m²·g^-1)	S_micro / (m²·g^-1)	^cS_ext / (m²·g^-1)	^dV_total/ (cm³·g^-1)	V_micro/ (cm³·g^-1)	^eV_meso/ (cm³·g^-1)
CM	6.0	318	303	15	0.14	0.12	0.02
HM-0.025	6.2	333	286	47	0.21	0.13	0.09
HM-0.05	6.9	366	291	75	0.26	0.11	0.14
HM-0.075	7.5	362	252	110	0.27	0.09	0.18

Fig. 3 Nitrogen adsorption-desorption isotherms (a) and pore size distributions (b) of mordenite samples

Fig. 4 SEM images of mordenite samples synthesized with different amounts of C18-6-6Br2^(a) CM; (b) HM-0.025; (c) HM-0.05; (d) HM-0.075

Fig. 5 TEM images of mordenite samples synthesized with different amounts of C18-6-6Br2^(a) HM-0.025; (b) HM-0.05; (c) HM-0.075

Fig. 6 Thermogravimetric (TG, a) and derivative thermogravimetric (DTG, b) curves of mordenite samples synthesized with different amounts of C18-6-6Br2

Fig. 7 NH3-TPD profiles of mordenite samples synthesized with different amounts of C18-6-6Br2

Table 2 Acidity data of all mordenite samples

Sample	Acid amount/(mmol·g^-1)			Peak temperature/℃
Sample	Total	Weak	Strong	Weak	Strong
CM	0.855	0.463	0.392	224	528
HM-0.025	1.026	0.499	0.527	219	513
HM-0.05	1.094	0.391	0.703	220	525
HM-0.075	0.952	0.320	0.632	218	519

Fig. 8 Catalytic activities of mordenite samples in the benzylation reaction of benzene with benzyl alcohol

Fig. 9 Rate constant of mordenite samples in the benzylation of benzene with benzyl alcohol

Fig. 10 Catalytic stability of the HM-0.075 sample

Table 3 Benzylation of benzene with benzyl alcohol over mordenite samples a

Catalysts	Conversion of BA/ %	Selectivity/ %		Yield / %		K_a × 10³/ min^-1
Catalysts	Conversion of BA/ %	DPM	DBE	DPM	DBE	K_a × 10³/ min^-1
CMOR	39.06	89.25	10.75	34.86	4.20	3.32
HMOR-0.025	76.84	93.63	6.37	71.95	4.89	8.50
HMOR-0.05	95.08	95.74	4.26	91.03	4.05	19.02
HMOR-0.075	97.33	97.15	2.85	94.56	2.77	22.48

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