Enhancement of the activity and stability of Au/TS-1 catalyst in the gas-phase epoxidation of propene through alkali carbonate modification
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摘要: 制备了不同碱金属碳酸盐(Na2CO3、K2CO3、Rb2CO3和Cs2CO3)超声浸渍改性的Au/TS-1催化剂,采用XRD、ICP、XPS、UV-vis、NH3-TPD、FT-IR和HAADF-STEM等手段对催化剂结构性质进行了表征,研究了碱金属碳酸盐改性对Au/TS-1催化剂的丙烯气相环氧化活性和稳定性的影响。结果表明,碱金属碳酸盐改性可以降低Au/TS-1催化剂的表面酸性,减缓环氧丙烷(PO)在催化剂表面吸附引起的积炭失活,抑制金颗粒粒径的增大;此外,Cs2CO3和Rb2CO3改性还可减少Au/TS-1催化剂上的骨架外Ti含量。碱金属碳酸盐改性后的Au/TS-1的催化活性和稳定性都得到明显的改善,其中,Cs2CO3改性的Au/TS-1表现出最佳的催化活性,丙烯转化率为6.2%,环氧丙烷选择性为86.2%,氢气利用效率为26.2%。相关研究为提高Au/TS-1催化剂的丙烯气相环氧化活性和稳定性提供了新的思路。
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关键词:
- 碱金属碳酸盐 /
- Au/TS-1催化剂 /
- 丙烯环氧化 /
- 超声浸渍 /
- 活性和稳定性
Abstract: A serious of robust Au/TS-1 catalysts were prepared by modifying with various alkali carbonates including Na2CO3, K2CO3, Rb2CO3 and Cs2CO3 via the ultrasonic impregnation. The alkali carbonate-modified Au/TS-1 catalysts were characterized by XRD, ICP, XPS, UV-vis, FT-IR, NH3-TPD and HAADF-STEM and their catalytic activity and stability in the gas-phase epoxidation of propene were investigated in a fixed-bed reactor in the presence of H2 and O2. The results indicate that the modification with alkali carbonates can decrease the surface acidity and inhibit the aggregation of Au particles; moreover, Rb2CO3 and Cs2CO3 can even reduce the content of extra-framework Ti in Rb-Au/TS-1 and Ce-Au/TS-1. The catalytic activity and stability of Au/TS-1 in the gas-phase epoxidation of propene are significantly improved after the modification with alkali carbonates. In particular, Cs2CO3-modified Cs-Au/TS-1 catalyst exhibits the best performance, with a propene conversion of 6.2%, selectivity of 86.2% to propene oxide (PO) and H2 utilization efficiency of 26.2%. The results suggest that alkali carbonate modification could be a novel strategy to enhance the catalytic activity and stability of Au/TS-1 in propene epoxidation.-
Key words:
- alkali carbonate /
- Au/TS-1 /
- propene epoxidation /
- ultrasonic impregnation /
- activity and stability
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图 3 Au/TS-1和x-Au/TS-1催化丙烯气相环氧化的PO时空产率(a)及丙烯转化率、PO选择性及氢效(b)
Figure 3 Space-time yield of PO via the time on stream (a) and propene conversion, selectivity to PO and H2 efficiency (b) for the gas phase propene epoxidation over the pristine Au/TS-1 and alkali carbonate-modified x-Au/TS-1 catalysts H2, O2, C3H6 and N2 were fed into the reactor (0.15 g catalyst) with the flow rate of 3.5, 3.5, 3.5 and 24.5 mL/min, respectively, with a space velocity of 14000 h-1
表 1 催化剂的结构性质
Table 1 Textural properties of the fresh Au/TS-1 and x-Au/TS-1 catalysts as well as the spent ones after reaction for 20 h and those treated in oxygen atmosphere at 250℃
Catalyst Au
loading w/ %Si/ Ti Fresh catalyst Spend for 20 h Treatment at 250℃ ABET
/(m2·g-1)vtotal
/(mL·g-1)ABET
/(m2·g-1)vtotal
/(mL·g-1)ABET
/(m2·g-1)vtotal
/(mL·g-1)Au/TS-1 0.14 78 374 0.36 117 0.14 375 0.35 Na-Au/TS-1 0.14 78 348 0.30 233 0.21 347 0.31 K-Au/TS-1 0.14 78 352 0.30 257 0.26 355 0.32 Rb-Au/TS-1 0.14 78 355 0.35 273 0.30 360 0.34 Cs-Au/TS-1 0.14 78 356 0.34 278 0.17 350 0.35 A: specific surface area; v: volume -
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