Synthesis of SiGeAl-ITQ-13 and SiAl(B)-ITQ-13 and their catalytic performance in the conversion of methanol to hydrocarbons
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摘要: 采用直接水热合成和后合成两种方法制备Al-ITQ-13分子筛，用于催化甲醇转化制备烃类化合物。采用XRD、27Al MAS NMR、NH3-TPD、Py-FTIR和SEM等技术对所合成样品进行了表征。结果表明，两种方法制备的Al-ITQ-13结晶度都较高，且晶体形貌为薄片。与ZSM-5相比，Al-ITQ-13在甲醇转化反应中显示出较高的丙烯选择性、较高的丙烯/乙烯产物比以及较好的催化稳定性。同时，由于后合成所得到的SiAl（B）-ITQ-13强酸量减少，其催化性能优于直接合成的SiGeAl-ITQ-13。Abstract: Al-ITQ-13 molecular sieves, viz., SiGeAl-ITQ-13 and SiAl(B)-ITQ-13, were prepared by the direct hydrothermal synthesis and post-synthesis methods and characterized by XRD, 27Al MAS NMR, NH3-TPD, Py-FTIR and SEM; their catalytic performance in the conversion of methanol to hydrocarbons (MTH) was investigated. The results indicated that two Al-ITQ-13 samples have high crystallinity with a slice-like morphology. In comparison with ZSM-5, Al-ITQ-13 as a catalyst in MTH exhibits higher selectivity to propene, higher propene/ethene (P/E) ratio and longer catalytic lifetime. Moreover, as the amount of strong acid sites on SiAl(B)-ITQ-13 is decreased by post-synthesis, SiAl(B)-ITQ-13 exhibits better catalytic performance in MTH, in comparison with SiGeAl-ITQ-13 obtained by direct hydrothermal synthesis.
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Key words:
- Al-ITQ-13 /
- methanol to hydrocarbons /
- direct hydrothermal synthesis /
- post-synthesis
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Figure 1 27Al MAS NMR spectra of calcined SiAl(B)-ITQ-13 zeolites exchanged in different concentrations of Al(NO3)3 solution
Figure 3 SEM images of the as-synthesized SiGeAl-ITQ-13, SiAl(B)-ITQ-13 and ZSM-5 zeolites
(a): SiGeAl-ITQ-13; (b): SiAl(B)-ITQ-13; (c): ZSM-5
Figure 4 27Al MAS NMR spectra of the calcined SiGeAl-ITQ-13, SiAl(B)-ITQ-13 and ZSM-5 zeolites
Figure 5 NH3-TPD profiles of the as-synthesized SiGeAl-ITQ-13, SiAl(B)-ITQ-13 and ZSM-5 zeolites
Figure 6 Methanol conversions along with the time on stream in MTH over the SiGeAl-ITQ-13, SiAl(B)-ITQ-13 and ZSM-5 zeolites
Table 1 Chemical compositions and textural properties of the as-synthesized zeolites
Zeolite Molar ratio SBET/(m2·g-1) vmicro /(cm3·g-1) gel product SiGeAl-ITQ-13 Si/Ge=30(Si+Ge)/Al=100 Si/Ge=31(Si+Ge)/Al=87 416 0.13 SiAl(B)-ITQ-13a Si/B=60 Si/Al=95 429 0.14 ZSM-5 Si/Al=100 Si/Al=90 425 0.17 a: SiAl(B)-ITQ-13 is obtained by a post-synthesis through ion exchange from a starting ITQ-13 sample of Si/B=74 
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Table 2 Acidity of SiGeAl-ITQ-13 and SiAl(B)-ITQ-13 determined by Py-FTIR
Zeolite Brφnsted acidity c /(μmol·g-1) Lewis acidity c /(μmol·g-1) 150℃ 250℃ 350℃ 150℃ 250℃ 350℃ SiGeAl-ITQ-13 25.9 19.8 12.0 7.6 5.1 3.9 SiAl(B)-ITQ-13 12.8 10.3 8.2 12.2 7.0 6.9
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Table 3 Product distribution for MTH over various as-synthesized catalysts a
Zeolite Product selectivity s/% C3=/C2= C1 C2 C3 C4 C2= C3= C4= C5+b aromatics SiGeAl-ITQ-13 0.7 0.1 1.8 3.1 7.9 40.7 23.7 17.1 4.9 5.2 SiAl(B)-ITQ-13 0.6 0.1 1.0 2.7 5.5 43.2 23.8 19.8 3.2 7.9 ZSM-5 1.2 0.2 3.4 10.4 12.2 27.0 15.9 16.2 13.6 2.2 a: reaction conditions: 450℃, WHSV=1.0h-1, CH3OH/N2=1/4;
b: for C5 and higher hydrocarbons, aromatics are excluded
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