Preparation of core-shell ZSM-5@Beta molecular sieve and catalytic alkylation to 2,6-dimethylnaphthalene
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摘要: 以ZSM-5分子筛为核相,通过聚二烯丙基二甲基氯化铵(PDDA)偶连纳米Beta分子筛晶种,经动态水热合成方法制备了ZSM-5@Beta核壳二元复合分子筛。采用XRD、N2吸附-脱附、SEM、TEM、ICP、NH3-TPD及Py-FTIR等手段对复合分子筛的结构和物性进行了表征,考察了复合分子筛催化2-甲萘(2-MN)与甲醇烷基化合成2,6-二甲基萘(2,6-DMN)的催化性能。结果表明,采用该方法制备出粒径约为500 nm的核壳结构ZSM-5@Beta复合分子筛。与机械混合二元分子筛相比,核壳结构材料具有更高的比表面积和外表面积,并降低了酸强度和强酸中心密度。通过限域催化理念、核壳界面和多级孔道的构建,借助12元环壳相Beta分子筛提高催化活性,利用10元环核相ZSM-5的择形催化作用提高催化选择性。在2-MN与甲醇烷基化反应中提高了2-MN的转化率和2,6-DMN的选择性,产物中2,6-/2,7-DMN比达到1.35,2,6-DMN收率达到4.29%。Abstract: ZSM-5@Beta core-shell molecular sieve was prepared by dynamic hydrothermal synthesis method using ZSM-5 adhered Beta seed crystals as the core phase, and polydiallyl dimethyl ammonium chloride (PDDA) was used as a coupling agent to adhere Beta seed crystals on the surface of ZSM-5. The structure and physical properties of composite molecular sieves were characterized by XRD, N2 adsorption-desorption, SEM, TEM, ICP, NH3-TPD and Py-FTIR. The catalytic performance of composite molecular sieves for alkylation of 2-methylnaphthalene (2-MN) with methanol was investigated. The results showed that ZSM-5@Beta composite molecular sieve prepared by this method had a core-shell structure, and the particle size was about 500 nm. Compared with mechanically mixed binary molecular sieve, core-shell molecular sieve had higher specific surface area and external surface area, lower acid strength and stronger acid center density. Through the construction of core-shell interface and hierarchical porous, the catalytic activity was improved by shell phase Beta molecular sieve with 12-membered ring channel, and the catalytic selectivity was improved by core phase ZSM-5 molecular sieve with 10-membered ring channel in the alkylation reaction of 2-MN with methanol. The 2,6-/2,7-DMN ratio in the products reached 1.35, and the yield of 2,6-DMN reached 4.29%.
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Key words:
- ZSM-5 /
- Beta /
- core-shell structure /
- 2,6-dimethylnaphthalene
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表 1 样品的孔结构参数
Table 1 Pore structure parameter of the samples
Sample ABET/(m2·g−1) Aext/(m2·g−1) vtotal/(cm3·g−1) vmic/(cm3·g−1) vmes/(cm3·g−1) Ratio(Aext/ABET) HBeta 656.40 142.79 0.51 0.21 0.33 0.28 HZSM-5 297.10 16.89 0.19 0.12 0.07 0.06 HZSM-5@Beta-m 449.36 105.88 0.44 0.14 0.31 0.24 HZSM-5@Beta-cs 633.06 169.11 0.45 0.19 0.27 0.27 表 2 元素组成、NH3-TPD和Py-FTIR谱图量化
Table 2 Element composition, the quantitative results of NH3-TPD profile and Py-FTIR spectrum
Sample SiO2/Al2O3 Desorption peak area of NH3-TPD spectruma Acidityb/(μmol∙g−1) Brønsted/Lewis 100−250 ℃ 250−400 ℃ 400−550 ℃ Total Lewis Brønsted HBeta 30 924 1459 342 2725 202 296 1.47 HZSM-5 24.2 1506 617 767 2890 25 100 4.00 HZSM-5@Beta-m 27.5 909 1101 967 2977 77 254 3.30 HZSM-5@Beta-cs 25.8 1018 959 247 2224 133 222 1.67 a: Peak area Gaussian fitting of NH3-TPD spectrum;
b: Quantitative results of Py-FTIR spectrum表 3 2-MN与甲醇烷基化反应的催化性能a
Table 3 Catalytic performance of 2-MN alkylation with methanol over molecular sievesa
Catalyst HBeta HZSM-5 HZSM-5@Beta-m HZSM-5@Beta-cs Conversion x/% 2-MN 90.94 31.34 55.18 61.62 Distributionb s/% NA 1.84 3.95 8.17 4.47 DMNs 44.37 27.44 43.54 47.15 TMNs 45.46 0.00 0.00 15.96 1-MN 8.33 68.61 48.29 32.42 β,β-DMN/DMNs 30.08 52.69 38.57 34.15 2,6-DMN/DMNs 11.73 16.24 16.46 12.85 2,6-/2,7-DMN 0.90 0.68 0.99 0.89 2,6-DMN selectivityc s/% 2.77 4.52 5.52 6.01 2,6-DMN yieldd w/% 2.52 1.42 3.04 3.70 a: t = 400 ℃, WHSV2-MN=1 h−1, n2-MN/nCH3OH/n1,3,5-TMB = 1∶4∶4, p = 0.2 MPa, TOS = 1 h;
b: Mole of 2-MN derivatives in products × 100/mole of 2-MN in raw materials, including NP(Naphthalene), DMNs(Dimethyl naphthalene) TMNs(Trimethyl naphthalene) and 1-MN(1-methylnaphthalene);
c: Mole of 2,6-DMN in products × 100/(mole of 2-MN in raw materials-mole of 2-MN in products);
d: Mole of 2,6-DMN in products×100/mole of 2-MN in raw materials -
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