Synthesis and characterization of GaZSM-5 with different Si/Ga molar ratio and its catalytic performance in the MTH reaction
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摘要: 通过水热合成法制得不同硅镓比的GaZSM-5分子筛，经酸交换后压片成型，得到甲醇转化制烃类的GaZSM-5催化剂。采用XRD、SEM、FT-IR、XPS、ICP、低温氮气吸附-脱附、NH3-TPD和Py-FTIR技术对其进行了表征，并在连续流动固定床反应器上进行MTH反应性能评价。结果表明，分子筛中Ga物种主要以骨架Ga和骨架外表面游离态的Ga2O3两种状态存在。凝胶SiO2/Ga2O3配比为60合成所得GaZSM-5分子筛催化剂酸性适中，酸量为0.62 mmol NH3/g，B酸和L酸比值为4.88，形成较大的晶间介孔孔容，达到0.51 cm3/g；具有高的MTH活性稳定性，在相同评价条件下，催化剂寿命最高可达到456 h。与AlZSM-5相比，GaZSM-5的酸性弱，能够抑制积炭生成；纳米GaZSM-5的晶间介孔改善了扩散性能，进一步提高反应活性稳定性，催化剂寿命延长120 h。Abstract: GaZSM-5 molecular sieve catalysts with different Si/Ga molar ratios were prepared with hydrothermal synthesis method followed by acid exchange and pelletization. The catalyst samples were characterized using XRD, SEM, FT-IR, XPS, ICP, low temperature N2 physical adsorption and desorption, NH3-TPD and Py-FTIR. The catalytic performance in the reaction of methanol to hydrocarbons was evaluated in a fixed bed reactor system. The results indicated that there were two kinds of gallium species, i. e. Ga in the framework Ga and Ga2O3 species on the crystal surface. The catalysts synthesized from SiO2/Ga2O3 (60/1) gel with modest acidity (0.62 mmol NH3/g and the ratio of B/L 4.88) and large mesopore volume of 0.51 cm3/g had the best catalytic stability. Under the same reaction conditions, the lifetime of GaZSM-5 catalyst was 456 h. The acid strength of GaZSM-5 was weaker than that of AlZSM-5, which could inhibit the coke formation. The intercrystalline mesopores of the nano GaZSM-5 crystal improved the diffusion property as well the catalyst stability. The GaZSM-5 lifetime was prolonged by 120 h.
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Key words:
- Si/Ga molar ratio /
- ZSM-5 /
- acid catalysis /
- methanol /
- hydrocarbon
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图 1 不同硅镓物质的量比HGaZSM-5催化剂的XRD谱图
Figure 1 XRD patterns of the HGaZSM-5 catalysts with different Si/Ga molar ratios
图 2 不同硅镓比HGaZSM-5催化剂的SEM照片
Figure 2 SEM imagines of the HGaZSM-5 catalyst with different Si/Ga ratios
图 3 不同硅镓物质的量比HGaZSM-5催化剂的FT-IR谱图
Figure 3 FT-IR spectra of the HGaZSM-5 catalysts with different Si/Ga molar ratios
图 4 不同硅镓物质的量比HGaZSM-5催化剂中Ga 2p的XPS谱图
Figure 4 Ga 2p XPS spectra of the HGaZSM-5 catalysts with different Si/Ga molar ratios
图 5 不同硅镓物质的量比HGaZSM-5催化剂的NH3-TPD谱图
Figure 5 NH3-TPD spectra of the HGaZSM-5 catalysts with different Si/Ga molar ratios
图 6 不同硅镓物质的量比HGaZSM-5催化剂的Py-FTIR谱图
Figure 6 Py-FTIR spectra of the HGaZSM-5 catalysts with different Si/Ga molar ratios
图 7 不同硅镓物质的量比HGaZSM-5催化剂的低温氮气吸附-脱附等温线
Figure 7 Low temperature N2 adsorption and desorption of the HGaZSM-5 catalysts with different Si/Ga molar ratios
表 1 不同硅镓比HGaZSM-5催化剂ICP、NH3-TPD和Py-FTIR表征
Table 1 ICP, NH3-TPD and Py-IR results of the HGaZSM-5 catalysts with different Si/Ga ratios
Sample Na contenta w/% Ga contenta w/% Si contenta w/% Si/Gaa
(molar ratio)Total acidb/
(mmol(NH)3·g-1)B/Lc G-1 0.0069 3.34 41.20 30.71 0.95 3.73 G-2 0.0074 2.78 42.00 37.62 0.85 4.59 G-3 0.0058 2.47 43.44 43.79 0.62 4.88 G-4 0.0049 1.54 42.50 68.71 0.53 4.91 G-5 0.0081 1.38 43.01 77.60 0.25 5.99 G-6 0.0073 1.11 42.60 95.56 0.26 6.36 a: determined from ICP; b: density of acid sites, determined from NH3-TPD of the catalyst; c: determined from 300 ℃ Py-FTIR spectrum 
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表 2 不同硅镓物质的量比HGaZSM-5催化剂的低温氮气吸附-脱附表征
Table 2 Low temperature N2 adsorption and desorption results of the HGaZSM-5 catalysts with different Si/Ga molar ratios
Sample ABET/
(m2·g-1)Amicroa/
(m2·g-1)Aexta/
(m2·g-1)vtotalb
/(cm3·g-1)vmicroc/
(cm3·g-1)vmesod/
(cm3·g-1)Pore widthe
d/nmG-1 430.76 368.84 61.92 0.56 0.16 0.40 5.24 G-2 425.06 353.47 71.59 0.60 0.16 0.44 5.64 G-3 450.81 370.70 80.11 0.67 0.16 0.51 5.93 G-4 412.76 359.65 53.11 0.57 0.16 0.41 5.50 G-5 398.61 344.10 54.51 0.46 0.15 0.31 4.60 G-6 403.74 361.56 42.17 0.48 0.16 0.32 4.72 a: external surface area, from t-plot; b: single point adsorption total pore volume of pores; c: micropore volume, from t-plot;
d: mesopore volume, from BJH method; e: pore width, from t-plot
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表 3 不同硅镓物质的量比HGaZSM-5催化剂上甲醇转化制烃产物分布
Table 3 Product distribution of MTH over the HGaZSM-5 catalysts with different Si/Ga molar ratios
Sample Life time t/h Product distributiona w/% C1，2 LPG C5+ othersb aromatic G-1 336 6.01 34.37 58.11 1.51 33.86 G-2 360 6.09 36.13 56.14 1.64 32.23 G-3 456 5.80 32.01 60.41 1.78 35.57 G-4 384 5.86 37.10 55.22 1.82 28.79 G-5 312 7.18 38.12 53.03 1.67 21.87 G-6 288 7.32 37.86 52.89 1.93 21.46 a：reaction conditions: 380 ℃，0.1 MPa，WHSV=2 h-1; b：oxygenates including CO and CO2
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