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摘要: 采用等体积浸渍法制备了Ni/SiO2及NixZn/SiO2(x代表Ni/Zn原子比)催化剂,在常压固定床反应器上考察了催化剂苯甲醚气相加氢脱氧性能。研究发现,经550 ℃还原后NixZn/SiO2中形成了Ni-Zn合金,当Ni/Zn原子比为30时可获得较小合金晶粒尺寸和较高H2化学吸附量。在苯甲醚加氢脱氧反应中, Ni-Zn合金的形成有利于苯甲醚直接脱氧形成苯,同时抑制了CO甲烷化及C−C键氢解,这是因为形成合金后亲氧性金属Zn对Ni的几何隔离作用。Ni30Zn/SiO2催化剂的活性和苯选择性均高于Ni/SiO2。结果表明,Ni30Zn/SiO2催化剂失活与产物水氧化Ni-Zn 合金表面及积炭有关。Abstract: Herein, SiO2 supported metallic Ni (Ni/SiO2) and bimetallic Ni-Zn (NixZn/SiO2) (x represents the Ni/Zn atomic ratio) catalysts were prepared by the incipient wetness impregnation method and their activities were tested in vapor phase hydrodeoxygenation (HDO) of anisole under 0.1 MPa. The characterization results show that Ni-Zn alloy forms in NixZn/SiO2 after reduction at 550 °C, and a suitable Ni/Zn atomic ratio (30) leads to smaller alloy particle size and consequently more H2 adsorption amount than others. In the HDO reaction, the formation of Ni-Zn alloy facilitates the direct deoxygenation pathway and suppresses CO methanation and C−C bond hydrogenolysis, which is ascribed to the isolation effect of the Ni atoms by the oxophilic Zn ones. Ni30Zn/SiO2 gives not only higher anisole conversion but also higher selectivity to benzene than Ni/SiO2. Therefore, the introduction of a suitable amount of oxophilic Zn in Ni/SiO2 promotes the HDO of anisole to benzene. Finally, we propose that the Ni30Zn/SiO2 deactivation is related to the oxidation of Ni-Zn alloy and carbon deposition on the catalyst surface.
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Key words:
- Ni-Zn alloy /
- hydrodeoxygenation /
- direct deoxygenation /
- methanation /
- C−C bond hydrogenolysis
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Figure 7 Performance of Ni/SiO2, Ni30Zn/SiO2 and Ni10Zn/SiO2 in HDO of anisole
(a): anisole conversion and product selectivity; (b): $n_{{\rm{CH}}_4} $/nΔAnisole, nCO/nΔAnisole and $n_{{\rm{CH}}_3{\rm{OH}}} $/nΔAnisole molar ratios reaction conditions: 300 °C, 0.1 MPa, H2/anisole molar ratio of 25, anisole WHSV of 2 h−1
Figure 10 Effect of reaction temperature on Ni30Zn/SiO2 for HDO of anisole
(a): Anisole conversion and product selectivity; (b): $n_{{\rm{CH}}_4} $/nΔAnisole, nCO/nΔAnisole and $n_{{\rm{CH}}_3{\rm{OH}}} $/nΔAnisole molar ratios reaction conditions: 0.1 MPa, H2/anisole molar ratio of 25, anisole WHSV of 2 h−1
Table 1 Properties of different catalysts
Catalyst SBET/(m2∙g−1) dp/nm vp/(cm3∙g−1) Crystallite
size/nmNi/SiO2 409 5.7 0.78 11.0 Ni30Zn/SiO2 305 5.7 0.65 10.4 Ni10Zn/SiO2 244 5.7 0.51 12.5 Spent-Ni30Zn/SiO2 339 6.6 0.56 8.5 -
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