Effect of La2O3 addition on the catalytic performance of Rh/SiO2 for CO hydrogenation
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摘要: 采用溶胶凝胶法制备了SiO2和La2O3-SiO2载体，再通过浸渍法分别引入Rh-La和Rh组分，研究考察了La引入方式对Rh/SiO2催化CO加氢反应性能的影响。结果表明，La的添加有利于提高Rh的分散度，促进Rh+中心数的增加，有效地抑制产物中CO2的生成，提高含氧化合物选择性。此外，La的引入方式会影响La与Rh间的相互作用强弱，Rh和La共浸渍制得的2Rh-5La2O3/SiO2催化剂中Rh-La相互作用较强，削弱的Rh-CO键有利于反应过程中CO的插入反应，使得产物以C2+含氧化合物为主。而La以助剂形式掺入SiO2制得的2Rh/5La2O3-SiO2催化剂具有较弱的La-Rh相互作用，其产物则以甲醇、乙醇等低碳醇为主。
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关键词:
- La2O3助剂 /
- Rh/SiO2催化剂 /
- CO加氢 /
- C2含氧化合物
Abstract: SiO2 and La2O3-SiO2 were synthesized via sol-gel method and used as support to prepared Rh-La or Rh doped catalysts by iso-volumic impregnation. Effects of doping mode of La on the catalytic performance of Rh/SiO2 for CO hydrogenation are investigated detailedly. The results reveal that the addition of La can improve the dispersion of Rh and increase Rh+ centers, which can effectively inhibit the formation of CO2 and improve the selectivity of oxygenates. Furthermore, the doping mode of La can affect the interaction between La and Rh. A strong La-Rh interaction is achieved over the 2Rh-5La2O3/SiO2 catalyst prepared by co-impregnation of Rh and La with SiO2 support. The strong interaction between La and Rh can efficiently weaken the Rh-CO bonds and enhance the CO insertion reaction in the reaction process, which makes the product dominated by C2+ oxygenates. The 2Rh/5La2O3-SiO2 catalyst prepared via La2O3-SiO2 composite support exhibits a weak La-Rh interaction, and methanol, ethanol and other low-carbon alcohols are obtained as the main products.-
Key words:
- La2O3 addition /
- Rh/SiO2 catalyst /
- CO hydrogenation /
- C2 oxygenates
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图 1 2Rh/5La2O3-SiO2催化剂的稳定性
Figure 1 Catalytic performance vs. time-on-stream for the 2Rh/5La2O3-SiO2 catalyst
图 2 催化材料的XRD(a)和H2-TPD(b)谱图
Figure 2 XRD patterns (a) and H2-TPD profiles (b) of the catalysts
图 4 30 ℃(a)和300 ℃(b)时流动的CO/N2混合气中吸附CO的红外光谱谱图
Figure 4 Infrared spectra of the adsorbed CO in CO/N2 flow at (a) 30 ℃ and (b) 300 ℃
图 5 在300 ℃流动状态下CO吸附及CO与H2反应的红外光谱谱图
Figure 5 Infrared spectra of the adsorbed CO in CO/N2 flow and CO hydrogenation at 300 ℃ for 30 min
(a): 2Rh/SiO2; (b): 2Rh/5La2O3-SiO2; (c): 2Rh-5La2O3/SiO2
表 1 La引入方式对Rh/SiO2催化性能的影响
Table 1 Effects of La doping mode on the catalytic porformance of the Rh/SiO2 catalysts
Catalyst CO conv. xC/% Selectivity of products sC/% STY(C2+Oxy) /(g·kg-1·h-1) CO2 CH4 MeOH AcH EtOH C2+Oxy a C2+HC b 2Rh/SiO2 3.0 21.0 11.3 9.0 5.5 11.2 18.4 40.3 18.6 2Rh/5La2O3-SiO2 2.8 7.2 6.6 40.5 6.9 21.5 37.6 8.1 32.6 2Rh-5La2O3/SiO2 2.1 8.3 11.9 17.9 12.0 19.5 42.7 19.2 25.3 reaction conditions: 300 ℃, 3 MPa, S.V.=10000 mL/(g·h), V(CO)/V(H2)=1:2, data collected after 15 h when the steady state reached; a: C2+Oxy denotes oxygenates containing two and more carbon atoms as well as acetic acid and ethyl acetat; b: C2+HC denotes hydrocarbons containing two and more carbon atoms 
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表 2 催化材料的比表面积、孔容、孔径及其氢气化学吸附
Table 2 Specific surface areas, pore volume and pore diameter from N2 adsorption and H2 chemisorption
Catalyst ABET/ (m2·g-1) vp / (cm3·g-1) dp /nm H2 chemisorption H2，ads/(μmol·g-1) dispersion /% particle size d/nm 2Rh/SiO2 228 0.156 2.7 38.4 51.8 2.3 2Rh-5La2O3/SiO2 235 0.112 2.1 42.3 57.8 2.0 2Rh/5La2O3-SiO2 416 0.276 4.3 54.6 73.4 1.4
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