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摘要: 采用负压沉积沉淀法制备了纳米Au/HZSM-5催化剂前体, 研究了深床焙烧和等离子体焙烧两种方法, 以及焙烧温度和焙烧气氛对催化剂中纳米金粒径和催化性能的影响, 并采用ICP、TEM、XRD、UV-vis、XPS等表征方法对催化剂金粒子进行了物化性能表征, 采用合成气羰基化制乙酸甲酯反应表征催化性能。结果表明, 不同焙烧方法和不同焙烧温度及气氛对负载型纳米Au/HZSM-5催化剂中金粒径、形貌、物化性质和催化性能有明显影响。其中, 以等离子体焙烧方法在500℃氮气气氛下制备的纳米1.86%Au/HZSM-5催化剂中的金粒径最小, 为2-5nm。用于催化合成气羰基化制乙酸甲酯反应, 原料中CO的转化率为67%, 乙酸甲酯选择性可达78%。Abstract: A serial of Au/HZSM-5 samples were prepared by vacuum deposition precipitation, cation exchange and vacuum sulfhydryl protection method. The effect of different preparation method, calcination temperature, calcination atmosphere and addition of potassium on the particle size and distribution of gold was invetigated. Based on the characterization of X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy and transmission electron microscope, it was found that the gold particle size of Au/HZSM-5 was changed greatly with different preparation methods. Gold particle size (about 2-5nm) of Au/HZSM-5 prepared by vacuum sulfhydryl protection was obviously smaller than that of the other preparation methods. Taken Au/HZSM-5 catalyst prepared by vacuum deposition precipitation as an example, low calcination temperature and inert atmosphere (nitrogen and argon) were favorable to the good dispersion of gold particles. The activities and carbonylation selectivities of syngas on Au/HZSM-5 catalysts were evaluated by a micro-fixed pulse reactor. 48% of syngas conversion and 52% of methyl acetate selectivity were obtained at reaction temperature of 350℃ over Au/HZSM-5 catalysts with 1.86% Au loading, calcined in air, while 59% and 70% were obtained over catalyst calcined in argon. By contrast, 67% of syngas conversion and 78% of methyl acetate selectivity were obtained over the catalyst calcined in nitrogen plasma.
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Key words:
- Au/HZSM-5 /
- gold particle /
- calcination temperature /
- calcination atmosphere /
- carbonylation
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图 3 空气气氛下不同焙烧温度纳米Au/HZSM-5沸石催化剂的TEM照片
Figure 3 TEM images of nano-Au/HZSM-5 catalysts after calcination in air
(a, a'): air-80℃ (after drying); (b, b'): air-150℃ (after drying); (c, c'): air-170℃ (after drying); (d, d'): air-180℃ (after drying); (e, e'): air-200℃ (after drying); (f, f'): air-250℃ (after calcination); (g, g'): air-300℃ (after calcination); (h, h'): air-400℃ (after calcination); (i, i'): air-500℃ (after calcination); (j, j'): air-600℃ (after calcination); (k, k'): air-700℃ (after calcination)
表 1 纳米Au/HZSM-5沸石催化剂的ICP数据
Table 1 ICP data of nano-Au/HZSM-5 zeolite
Catalyst Analytical
elementLoadings w/% theoretical value measured value 1 Au 0.30 0.13 2 Au 0.50 0.37 3 Au 1.00 0.79 4 Au 2.00 1.86 5 Au 3.00 2.06 表 2 不同焙烧气氛对Au/HZSM-5催化剂金粒子粒径的影响
Table 2 Effect of calcination atmosphere on gold particle size of Au/HZSM-5 catalysts
Calcination atmosphere Calcination atmosphere (500℃ 4h) Nitrogen plasma (3h) air N2 Ar H2 400℃ 500℃ d/nm 8-25 3-20 5-15 5-30 5-10 2-5 -
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