Study on highly efficient hydrogenation of methyl acetate over the lanthanum metal-modified Cu/SiO2 catalyst
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摘要: 采用蒸氨法制备了镧(La)改性的负载型铜硅(Cu/SiO2)催化剂,并研究了其催化乙酸甲酯(MeOAc)气相加氢制乙醇(EtOH)的性能。采用N2吸附-脱附(N2 adsorption–desorption)、X-射线粉末衍射(XRD)、电感耦合等离子体发射光谱(ICP-OES)、氢气程序升温还原(H2-TPR)、傅里叶红外光谱(FT-IR)、高分辨透射电镜(HRTEM)、光电子能谱(XPS)和原子发射光谱仪(AES)等表征手段对催化剂进行了的表征,发现La物种的加入产生了较多的层状硅酸铜,增强了Cu和La物种之间的相互作用。La物种的加入在结构方面提高了催化剂的比表面积,降低了铜物种的粒径,提高了铜物种的分散度;在电子还原调控方面提高了Cu + 的含量,增强了催化剂吸附酰基和甲氧基的能力。与未改性的Cu/SiO2催化剂相比,在相同反应条件下,La掺杂量0.5%的Cu/SiO2催化剂表现出最佳的催化性能,获得了98.5%乙酸甲酯转化率和98.5%乙醇选择性,乙醇的总收率达97.0%。Abstract: The lanthanum (La)-modified Cu/SiO2 catalysts were synthesized by ammonia-evaporation method and applied in the gas-phase hydrogenation of methyl acetate (MeOAc) to produce ethanol (EtOH). These catalysts were characterized by means of the N2 adsorption–desorption, XRD, ICP-OES, H2-TPR, FT-IR, HRTEM, XPS, and AES techniques and so on in detail. Introduction of the La metal results in a strong interplay between the Cu and La, leading to generation of the copper phyllosilicate in a more amount. This increases the specific surface area of the catalyst of which the particle size of the copper metal is thus reduced. Addition of the La also makes the copper species more dispersed over the SiO2 support. Especially, the Cu + contents are increased, as then enhances an electronic absorption of the substrate MeOAc by the acyl and methoxide groups. Compared with the unmodified Cu/SiO2 catalyst, the La-mixed (0.5%) Cu/SiO2 catalyst showed the excellent catalytic property. The conversion of MeOAc by 98.5% was achieved along with the ethanol selectivity of 98.5%. A total yield of 97.0% for ethanol was therefore produced.
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Key words:
- methyl acetate /
- hydrogenation /
- ethanol /
- Cu/SiO2 /
- La modification
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图 7 不同La掺杂量的还原后催化剂的TEM照片和粒径统计分布
Figure 7 The TEM images and the particle size distribution images of the reduced catalysts with different La loadings: (a) 30Cu/SiO2, (b) 30Cu-0.5La/SiO2, (c) 30Cu-1La/SiO2, and (d) 30Cu-2La/SiO2 (The insets are the particle size distribution for the reduced catalysts); (e) HRTEM image of 30Cu-0.5La/SiO2
表 1 30Cu-nLa/SiO2、30Cu/SiO2、2La/SiO2、SiO2催化乙酸甲酯加氢反应制乙醇的结果
Table 1 Catalytic result for hydrogenation of MeOAc to EtOH by using 30Cu-nLa/SiO2 30Cu/SiO2, 2La/SiO2, and SiO2
Catalyst tMeOAc/% sEtOH/% 乙酸乙酯
选择性/%wEtOH/% 30Cu/SiO2 85.6 77.3 22.7 66.2 30Cu-0.5La/SiO2 98.5 98.5 1.5 97.0 30Cu-1La/SiO2 94.8 92.6 7.4 87.8 30Cu-2La/SiO2 81.5 73.4 26.6 59.8 2La/SiO2 1.40 68.7 31.3 1.0 SiO2 0.10 − − − Conditions: t = 230 ℃, p = 2 MPa, LHSV = 2 h−1 and H2/MeOAc = 20. 表 2 不同La掺杂量的催化剂的组织结构特征
Table 2 Structural properties of the catalysts with different La loadings
catalyst wCu/% wLa/% SBETb/(m2·g−1) dporec/(cm3·g−1) vpored/(cm3·g−1) dCue/nm dCuf/nm 30Cu/SiO2 29.6 0.0 295.3 6.0 0.44 5.4 5.4 30Cu-0.5La/SiO2 29.0 0.47 350.4 4.9 0.43 4.8 4.5 30Cu-1La/SiO2 27.9 1.01 336.2 5.4 0.45 5.7 5.5 30Cu-2La/SiO2 28.9 1.91 323.7 5.9 0.49 6.2 5.8 Note: a: Tested by ICP-OES, b: Specific surface area, c: Averaged pore diameter, d: Averaged pore volume at p/p0 = 0.995, e: Calculated from the Debye-Scheerer formula, f: Obtained through the TEM measurement. 表 3 不同La掺杂量的催化剂还原后的XPS和Cu LMM XAES反卷积结果
Table 3 Deconvolution results of XPS and Cu LMM XAES of the reduced catalysts with different La loadings
catalyst XPS binding energy/eV XAES kinetic energy/eV xCu + /% Cu 2p1/2 Cu 2p3/2 Cu + Cu0 30Cu 952.3 932.2 914.0 918.0 38.2 30Cu-0.5La 952.1 932.5 914.0 918.0 49.4 30Cu-1La 952.3 932.6 914.0 918.0 46.7 30Cu-2La 952.8 933.0 914.0 918.0 44.8 -
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