Effect of preparation conditions on the morphology of Cu-SSZ-13 zeolites and their performance in the selective catalytic reduction of NOx by NH3
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摘要: 采用传统水热法合成SSZ-13分子筛,铜离子交换法制备Cu-SSZ-13分子筛催化剂,用于氨选择性催化还原(NH3-SCR)脱硝,研究了有机模板剂(OSDA)用量、硅源、铝源、水硅比、硅铝比以及老化时间等制备参数对Cu-SSZ-13分子筛形貌、晶粒大小、酸性、Cu2+位点以及NH3-SCR催化性能的影响。结果表明,在一定范围内,SSZ-13分子筛的硅铝比越高,其晶粒越大,所负载的活性铜含量越低,NH3-SCR催化活性也越差。以硅溶胶为硅源、硫酸铝为铝源所合成的SSZ-13分子筛晶粒较小,结晶度最高,所得到的Cu-SSZ-13催化剂的NH3-SCR活性也最好。较高的水硅比所合成的分子筛晶粒较大,而增加模板剂的用量有利于提高SSZ-13分子筛的结晶度,降低其晶粒尺寸。适当延长老化时间,能降低SSZ-13分子筛晶粒尺寸,提升Cu-SSZ-13的NH3-SCR催化活性。其中,Si/Al比为10、硅溶胶为硅源、硫酸铝为铝源、OSDA/Si比为0.4、水硅比为88、老化2 h得到的Cu-SZ-A10催化剂最优,在240000 h−1的高空速下,200 ℃时NO转化率达60%,且在中高温区NO转化率保持为100%。该工作对SSZ-13分子筛形貌的调控以及高性能NH3-SCR脱硝催化剂的制备具有重要的参考价值。Abstract: SSZ-13 zeolites were synthesized by conventional hydrothermal method and the Cu-SSZ-13 zeolite catalysts were then prepared by Cu ion-exchange and used in the selective catalytic reduction of NOx with NH3 (NH3-SCR); the effect of various preparation parameters including the organic template agent (OSDA) dosage, silicon source, aluminum source, H2O/Si ratio, Si/Al ratio and aging time on the morphology, crystal size, acidity, state of Cu2+ sites and the catalytic performance of Cu-SSZ-13 in NH3-SCR were investigated. The results indicate that silica sol (JN25) and Al2(SO4)3 are appropriate as the silicon and aluminum sources, respectively, to prepare SSZ-13 zeolites with small crystals, high crystallinity and high activity in NH3-SCR. With the increase of Si/Al ratio, the crystal size of SSZ-13 increases and the copper content loaded on Cu-SSZ-13 decreases, leading to the degradation of NH3-SCR activity. A high H2O/Si ratio of 88 is conducive to forming larger SSZ-13 crystals, whilst increasing the OSDA dosage is beneficial to improving the crystallinity, reducing the crystal size, and accordingly enhancing the catalytic activity of Cu-SSZ-13 in NH3-SCR. In addition, a relatively longer aging time can also reduce the crystal size and raise the catalytic activity of Cu-SSZ-13. In particular, the Cu-SZ13-A10 zeolite catalyst synthesized with a Si/Al ratio of 10 (with the gel composition of 1SiO2 : 0.01Al2(SO4)3 : 0.3NaOH : 0.4SDA : 88H2O; JN25 as silicon source and aging for 2 h) exhibits high activity in NH3-SCR; under a high GHSV of 240000 h−1, the NO conversion reaches 60% at 200 ℃ and keeps at 100% in the moderate-high temperature range. These results should be useful for the regulation of SSZ-13 zeolite morphology and the preparation of high efficient Cu-SSZ-13 catalysts for NH3-SCR.
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Key words:
- SSZ-13 zeolite /
- hydrothermal synthesis /
- crystal size /
- morphology /
- Cu-SSZ-13 /
- NH3-SCR
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表 1 不同SSZ-13分子筛的化学组成及织构性质
Table 1 Compositional and textural properties of various SSZ-13 zeolites
Sample Si/Algel Si
sourceAl
sourceSDA/Si H2O/Si taging/
hF/Si Si/Al Cryst./
%dave/
μmCu/Al LCu/
%SBET/
(m2·g−1)SZ13-A-5 5 JN25 Al2(SO4)3 0.4 88 2 0 <10 SZ13-A-10 10 JN25 Al2(SO4)3 0.4 88 2 0 10 94 0.7 0.19 1.8 563 SZ13-A-20 20 JN25 Al2(SO4)3 0.4 88 2 0 18 88 0.8 0.31 1.7 519 SZ13-A-40 40 JN25 Al2(SO4)3 0.4 88 2 0 27 82 5.4 0.35 1.2 506 SZ13-A-100 100 JN25 Al2(SO4)3 0.4 88 2 0 40 100 8.6 0.22 0.6 458 SZ13-A-200 200 JN25 Al2(SO4)3 0.4 88 2 0 52 93 7.1 0.15 0.4 447 SZ13-A-inf ∞ JN25 Al2(SO4)3 0.4 88 2 0 <5 SZ13-B-TS 10 TEOS Al2(SO4)3 0.4 88 2 0 9 59 1.2 0.11 1 477 SZ13-B-FS 10 Fume
silicaAl2(SO4)3 0.4 88 2 0 8 88 0.7 0.17 1.6 487 SZ13-C-AlCl3 10 JN25 AlCl3 0.4 88 2 0 11 89 14.3 0.29 1.4 470 SZ13-C-Al(OH)3 10 JN25 Al(OH)3 0.4 88 2 0 18 87 0.9 0.18 1.6 480 SZ13-D-0 10 JN25 Al2(SO4)3 0 88 2 0 −0 SZ13-D-0.1 10 JN25 Al2(SO4)3 0.1 88 2 0 10 49 2.1 0.14 1.4 512 SZ13-D-0.2 10 JN25 Al2(SO4)3 0.2 88 2 0 9 61 0.9 0.16 1.6 527 SZ13-D-0.3 10 JN25 Al2(SO4)3 0.3 88 2 0 9 73 0.8 0.19 1.8 577 SZ13-E-44 10 JN25 Al2(SO4)3 0.4 44 2 0 10 74 0.4 0.18 1.7 571 SZ13-E-66 10 JN25 Al2(SO4)3 0.4 66 2 0 10 81 0.5 0.19 1.8 552 SZ13-F-24h 20 JN25 Al2(SO4)3 0.4 88 24 0 16 94 0.4 0.24 1.6 589 SZ13-G-0.2 20 JN25 Al2(SO4)3 0.4 88 2 0.2 20 83 1.1 0.25 1.3 547 SZ13-G-0.15 20 JN25 Al2(SO4)3 0.4 88 2 0.15 20 71 2.1 0.24 1.3 512 SZ13-G-0.1 20 JN25 Al2(SO4)3 0.4 88 2 0.1 19 77 4.8 0.27 1.5 533 Notes: The relative crystallinity (cryst.) was estimated by comparing the intensity of peaks at 9.6°, 20.6° and 30.6° in the XRD patterns of each zeolite sample to that of SZ13-A-100. The BET surface area (SBET) was determined from nitrogen sorption isotherms. The Si/Al and Cu/Al ratios and Cu loadings (LCu) were measured by ICP-AES. The average crystal size (dave) was estimated from the SEM images -
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