Effect of Ce modification on the performance of CuLDH catalyst for CO2 hydrogenation to methanol
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摘要: 通过向CuMgAl水滑石(CuLDH)催化剂中添加不同量的Ce,合成了一系列Ce改性的CuLDH-Cex催化剂。采用X射线衍射(XRD),N2吸附-脱附(BET),透射电子显微镜(TEM),X射线光电子能谱(XPS)等分析手段对催化剂的理化性质进行表征。结果表明,添加Ce会改变Cu-LDH催化剂的水滑石结构,适量的Ce会增加催化剂的比表面积,改善了Cu颗粒的分散度。同时,适量的Ce有利于增加催化剂表面强碱性位点的密度和氧空位的数量,促进了CO2的吸附和转化。Ce有利于调变催化剂表面的Cu + /Cu0比例,较高的Cu + /Cu0比例有利于甲醇的生成。当Ce/Cu比例为0.3时,在空速为9000 mL/(g·h),温度为240 ℃,压力为2.5 MPa的条件下,催化剂的CO2的转化率为7.5%,甲醇选择性为78.4%,甲醇的时空收率最高可达362.8 g/(kg·h)。通过原位红外(in situ DRIFTS)证明CuLDH-Ce0.3催化剂在CO2加氢合成甲醇过程中遵循HCOO*反应路径。Abstract: A series of Ce modified CuLDH-Cex catalysts were synthesized by adding different amounts of Ce to CuMgAl hydrotalcite (CuLDH) catalysts. The physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), N2 adsorption desorption (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. The results showed that the addition of Ce changed the hydrotalcite structure of CuLDH catalyst, and an appropriate amount of Ce increased the surface area of the catalyst and improved the dispersion of Cu particles. At the same time, an appropriate amount of Ce was beneficial for increasing the density of strong alkaline sites and the number of oxygen vacancies on the catalyst surface, promoting the adsorption and conversion of CO2. Ce was beneficial for adjusting the Cu + /Cu0 ratio on the catalyst surface, and a higher Cu + /Cu0 ratio ratio was conducive to the formation of methanol. When the Ce/Cu ratio was 0.3, the catalyst exhibited higher activity with 7.5% CO2 conversion, 78.4% methanol selectivity and 362.8 g/(kg·h) spatiotemporal yield at 240 ℃ under 2.5 MPa with GHSV = 9000 mL/(g·h). It has been proved by in situ DRIFTS that CuLDH-Ce0.3 catalyst followed HCOO* reaction path during CO2 hydrogenation for methanol.
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Key words:
- Ce /
- hydrotalcite /
- CO2 hydrogenation /
- alkaline sites /
- oxygen vacancies /
- methanol
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表 1 CuLDH-Cex催化剂的物理化学性质
Table 1 Physical and chemical properties of CuLDH-Cex catalysts
Catalyst Molar ratio Cu/Mg/Al/Cea SBETb/
(m2·g−1)vpb/
(cm3·g−1)dpb/
nmdCu c/
nmdCud /
%SCud/
(m2·g−1)CuLDH-Ce0 9.9/29.7/10.4/0 199.5 0.41 6.2 4.9 23.5 32.1 CuLDH-Ce0.1 10.2./29.9/9.8/1.1 208.4 0.47 7.3 3.7 26.3 35.4 CuLDH-Ce0.3 10.1/30.3/9.7/2.9 205.6 0.43 6.5 4.5 24.2 33.2 CuLDH-Ce0.5 9.8/29.8/10.2/5.2 194.9 0.35 5.3 5.2 20.4 29.6 CuLDO-Ce0.7 10.3/29.7/9.9/7.1 182.3 0.31 4.4 7.2 18.1 25.3 a−Measured by ICP; b−Calculated by BET and BJH equations; c−Measured by TEM; d−Measured by N2O titration. 表 2 CuLDH-Cex催化剂碱性位点密度
Table 2 The basic sites density of CuLDH-Cex catalysts
Catalyst Total basic
sites /
(μmol·g−1)Weakly basic
sites /
(μmol·g−1)Moderately basic
sites /
(μmol·g−1)Density of moderately
basic site /
(μmol·m2)CuLDH-Ce0 232.8 55.7 177.1 0.89 CuLDH-Ce0.1 256.5 23.2 233.3 1.12 CuLDH-Ce0.3 297.2 34.5 262.7 1.28 CuLDH-Ce0.5 210.3 48.8 161.5 0.83 CuLDO-Ce0.7 198.6 64.3 134.3 0.74 -
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