Catalytic performances of Al-ITQ-13 zeolites with different SiO2/Al2O3 ratios in the conversion of methanol to propene
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摘要: 采用晶种法直接合成了硅铝比（SiO2/A12O3物质的量比）为137、224和309的三种Al-ITQ-13分子筛，并采用粉末X射线衍射（XRD）、扫描电镜（SEM）、N2吸附-脱附、固体核磁共振（MAS NMR）和NH3-程序升温脱附（NH3-TPD）等分析方法对不同硅铝比分子筛进行了表征，并在固定床微型反应评价装置上，考察了硅铝比对甲醇转化制丙烯反应性能的影响。结果表明，不同硅铝比Al-ITQ-13分子筛呈现出相似的织构性质，酸量及酸强度随着硅铝比的升高逐渐下降。硅铝比对甲醇转化反应的产物分布存在较大的影响；随着硅铝比的升高，氢转移反应和芳构化反应活性降低，使得乙烯选择性下降，而丙烯和丁烯的选择性升高。硅铝比由137提高到309，丙烯的选择性（质量分数）由46.04%增加到55.52%，而丙烯/乙烯比由3.39提高到6.57。Abstract: Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios were synthesized by using seeds in the gel and characterized by XRD, SEM, N2 physisorption, MAS NMR and NH3-TPD. The effect of SiO2/Al2O3 molar ratio on the catalytic performance of Al-ITQ-13 in the conversion of methanol to propene (MTP) was investigated in a fixed-bed micro-reactor. The results showed that the Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios are similar in their textural properties; however, the amount and strength of acid sites decrease with the increase of SiO2/Al2O3 molar ratio. Moreover, the SiO2/Al2O3 molar ratio has a significant influence on the catalytic behavior of Al-ITQ-13 in MTP. As the hydrogen transfer and aromatization reactions were suppressed over the Al-ITQ-13 zeolite with high SiO2/Al2O3 molar ratio, with the increase of SiO2/Al2O3 molar ratio, the selectivity to propene and butene is increased at the expense of the selectivity to propene; that is, with the increase of SiO2/Al2O3 molar ratio from 137 to 309, the selectivity to propene is increased from 46.04% to 55.52% and meanwhile, the propene/ethene ratio is increased from 3.39 to 6.57.
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Key words:
- methanol to propene (MTP) /
- Al-ITQ-13 zeolite /
- methanol /
- propene /
- SiO2/Al2O3 molar ratio /
- acidity
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图 1 不同硅铝比Al-ITQ-13分子筛的XRD谱图
Figure 1 XRD patterns of as-synthesized Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios
a: 137; b: 224; c: 309
图 2 晶种加入与否对合成Al-ITQ-13分子筛的影响
Figure 2 Effect of seed addition on the synthesis of Al-ITQ-13 zeolites
图 3 不同硅铝比Al-ITQ-13分子筛样品的SEM照片
Figure 3 SEM images of Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios
(a): 137; (b): 224; (c): 309
图 4 不同硅铝比Al-ITQ-13分子筛样品的N2吸附-脱附等温线
■: 137; ●: 224; ▲: 309
Figure 4 Nitrogen adsorption-desorption isotherms of the Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios
图 5 不同硅铝比Al-ITQ-13分子筛样品的27Al MAS NMR谱图
Figure 5 27Al MAS NMR spectrum of the Al-ITQ-13 zeolites with different SiO2/Al2O3 ratios
a: 137; b: 224; c: 309
图 6 不同硅铝比Al-ITQ-13分子筛样品的NH3-TPD谱图
Figure 6 NH3-TPD of the Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios
a: 137; b: 224; c: 309
表 1 不同硅铝比Al-ITQ-13分子筛样品的织构性质
Table 1 Textural properties of various Al-ITQ-13 zeolites
Sample A B C SiO2/Al2O3 in gel 150 250 350 Relatively crystallinity /% 96 93 96 SiO2/Al2O3 in product 137 224 309 ABET /(m2·g-1) 313 310 308 Amicro/(m2·g-1) 290 289 290 vpore /(cm3·g-1) 0.160 0.159 0.159 vmicro /(cm3·g-1) 0.140 0.137 0.137 note: the SiO2/Al2O3 molar ratios in Al-ITQ-13 product were determined by XRF method; BET surface area, micropore surface area and micropore volume were determined by t-plot method; the total pore volume was obtained at p/p0 = 0.99 
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表 2 不同硅铝比Al-ITQ-13分子筛催化剂上MTP反应产物的分布
Table 2 Product distribution for MTP over the Al-ITQ-13 zeolites with different SiO2/Al2O3 molar ratios
Catalyst Conv. x /% Product selectivity w/% C3H6/C2H4 HTC s(C5+)/s(C2=+ C3=) CH4 C2H6 C2H4 C3H8 C3H6 C4H10 C4H8 C5+ C2H4+C3H6 C2H4 +C3H6+C4H8 A 99.9 3.72 0.77 13.60 2.09 46.04 3.44 23.45 6.88 59.64 83.09 3.39 0.03 0.12 B 100 2.29 0.17 10.52 1.10 49.07 2.15 28.50 6.20 59.59 88.09 4.66 0.01 0.10 C 99.9 1.45 0.39 8.44 1.08 55.52 1.35 29.99 1.78 63.96 93.95 6.57 0.01 0.03 note: the reactions were carried out at atmospheric pressure and 450 ℃, with a WHSV of 1.5 h-1, mCH3OH：mH2O=1：1, time on stream (TOS) of 7 h
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