软模板导向合成多级孔丝光沸石及其苯的苄基化催化性能

doi:10.15541/jim20160151

摘要/Abstract

摘要：

通常认为丝光沸石是具有一维孔道结构的微孔沸石, 在涉及大分子的催化反应中存在较为严重的扩散限制。以双季铵型表面活性剂C₁₈H₃₇N⁺(CH₃)₂C₆H₁₂N⁺(CH₃)₂C₆H₁₃(Br^-)₂(C_18-6-6Br₂)作为软模板, 在水热条件下制备了多级孔丝光沸石分子筛。采用XRD、FT-IR、SEM、TEM、TG-DTG、N₂物理吸附、NH₃-TPD等手段对样品的晶体结构和物化性能进行了表征。结果表明, 加入C_18-6-6Br₂制备了纳米棒定向排列的多级孔丝光沸石, 而且可通过改变合成体系中C_18-6-6Br₂/SiO₂的比值, 对样品的晶粒尺寸、介孔表面积和介孔孔容进行系统调变。在苯与苯甲醇的苄基化反应中, 多级孔样品比传统微孔丝光沸石表现出更好的苄基化反应催化性能和显著提高的反应速率。多级孔丝光沸石优异的催化性能归因于介孔的存在使其具有更多的可接近活性位和更优异的质量传输性质, 这种独特的多级孔丝光沸石在大分子催化转化反应中具有较大的应用潜力。

关键词: 丝光沸石, 多级孔分子筛, 介孔, 模板, 苄基化

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

中图分类号:

Q469

李玉平, 孙翠娟, 贾坤, 张翊, 李晓峰, 窦涛. 软模板导向合成多级孔丝光沸石及其苯的苄基化催化性能[J]. 无机材料学报, 2016, 31(12): 1355-1362.

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.

图/表 13

图1 不同C18-6-6Br2添加量时合成样品的XRD图谱

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

图2 不同C18-6-6Br2添加量时合成样品的FT-IR图谱

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

表1 丝光沸石样品的孔结构参数

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

图3 丝光沸石样品的N2吸附-脱附曲线(a)和相应的孔径分布图(b)

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

图4 不同C18-6-6Br2添加量时合成样品的SEM照片

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

图5 不同C18-6-6Br2添加量时合成样品的TEM照片

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

图6 不同C18-6-6Br2添加量时合成样品的热重(a)和微商热重(b)曲线图

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

图7 合成的丝光沸石样品的NH3-TPD曲线图

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

表2 合成样品的酸性数据

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

图8 不同样品在苯与苯甲醇的苄基化反应中的催化活性

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

图9 不同样品在苯与苯甲醇的苄基化反应的速率常数

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

图 10 HM-0.075样品的催化稳定性

Fig. 10 Catalytic stability of the HM-0.075 sample

表3 不同丝光沸石样品样品的苯与苯甲醇的苄基化反应结果

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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