Effect of Ce introduced Rh-UiO-66-Zr catalyst in syngas converting to ethanol
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摘要: 在合成气直接合成乙醇过程中，Rh基催化剂对乙醇等C2含氧化合物具有良好的选择性而持续成为研究热点。本工作利用UiO-66作为载体，将金属Ce4 +引入UiO-66-Zr的[Zr6O4(OH)4]金属节点替换部分金属Zr4 +形成[Zr6−xCexO4(OH)4]金属节点，从而较为精确地对合成气制备乙醇活性位点问题进行研究。XRD、TG、Raman、BET、H2-TPR、XPS和in-situ DRIFTS等表征结果显示，随着UiO-66[Zr6O4(OH)4]节点上金属Ce4 +的引入，催化剂上形成了-(Zr-O)-Rh-(O-Ce-位点，而在Rh/UiO-66-Zr催化剂上形成的-(Zr-O)-Rh-(O-Zr)-位点，结合催化反应评价结果发现，乙醇活性位点数量显著提升。由于Rh物种与-(O-Zr)-物种的相互作用较强，Rh与-(O-Ce)-位点的相互作用较弱，这种相互作用的势差有利于电子的高效率传输。另一方面，-(Zr-O)-Rh-(O-Ce)-可以稳定合成气制备乙醇的关键中间体，从而促进乙醇的形成。Abstract: In the process of direct synthesis of ethanol from syngas, rhodium-based catalysts continue becoming a hot topic because of their high selectivity for C2 oxygen-containing compounds such as ethanol. In this work, UiO-66 was used as a support to introduce the metal Ce4 + species into the [Zr6O4(OH)4] metal node of UiO-66-Zr to replace some of the metal Zr4 + species formation [Zr6−xCexO4(OH)4] metal nodes, so as to accurately study the problem of ethanol activity sites for the preparation of syngas. The characterization results of XRD, TG, Raman, BET, H2-TPR, XPS, and in-situ DRIFTS showed that with the introduction of metal Ce4 + species at the UiO-66 [Zr6O4(OH)4] node, -(Zr-O)-Rh-(O-Ce)-sites were formed on the catalyst, and -(Zr-O)-Rh-(O-Zr)-sites were formed on the Rh/UiO-66-Zr catalyst. Combined with the evaluation results of the catalytic reaction, the number of ethanol active sites was significantly increased. Because of the interaction between Rh species and -(O-Zr)-species is stronger than Rh species with -(O-Ce)- sites, the potential difference of this interaction favors the efficient transport of electrons. On the other hand, -(Zr-O)-Rh-(O-Ce)- can stabilize the key intermediates for the preparation of ethanol from syngas, which can promote the formation of ethanol.
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图 2 不同催化剂在300 ℃煅烧后的XRD谱图
Figure 2 XRD patterns of different catalysts after calcination at 300 ℃
图 3 不同催化剂的N2吸附-脱附等温线
Figure 3 N2 adsorption and desorption isotherms of different catalysts
图 6 催化剂在300 ℃煅烧后的TEM照片
Figure 6 TEM images of the catalyst after calcination at 300 ℃
(a): Rh/UiO-66-Ce; (b): Rh/UiO-66-Zr; (c): Rh/UiO-66-ZrCe; (d): EDS spectra of the catalyst Rh/UiO-66-ZrCe
图 8 不同催化剂的CO转化率和各含氧化合物在所有含氧化合物中的选择性
Figure 8 CO conversion of different catalysts and the selectivity of each carbohydrate in all carbon oxides of different catalysts
图 10 不同催化剂的XPS光谱谱图
Figure 10 XPS spectra of the catalysts
(a): Rh/UiO-66-Zr (Rh 3d region); (b): Rh/UiO-66-ZrCe (Rh 3d region); (c): Rh/UiO-66-Zr (O 1s region); (d): Rh/UiO-66-ZrCe (O 1s region); (e): XPS spectra of the catalyst Rh/UiO-66-Zr (Zr 3d region); (f): Rh/UiO-66-ZrCe (Zr 3d region)
图 11 三种催化剂在250 ℃、1.2 MPa、原料气H2∶CO∶Ar为16∶8∶1的条件下的原位红外光谱谱图
Figure 11 In-situ DRIFITS spectra of three catalysts under the conditions of 250 ℃ 1.2 MPa and the H2∶CO∶Ar ratio is 16∶8∶1
表 1 不同催化剂的结构参数
Table 1 Properties of different catalysts
Sample SBET/
(m2·g−1)Pore volume/
(cm3·g−1)Average pore
diameter /nmRh/UiO-66-Ce 45.9 0.043 5.59 Rh/UiO-66-Zr 274 0.183 7.14 Rh/UiO-66-ZrCe 253 0.160 6.90 
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表 2 催化剂Rh/UiO-66-ZrCe中的相对元素含量
Table 2 Relative element content in the catalyst Rh/UiO-66-ZrCe
Element Atomic
fraction / %Atomic
error / %Mass
fraction / %Mass
error / %C 46.41 6.65 22.45 1.92 O 39.59 9.70 25.51 5.52 Zr 12.92 2.45 47.47 7.14 Rh 1.04 0.19 4.31 0.63 Ce 0.05 0.01 0.26 0.04
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表 5 Rh基催化剂的XPS定量
Table 5 XPS quantitative results of Rh-based catalysts
Sample Atomic /% Rh Ce Zr O C Rh/UiO-66-Ce 0.46 9.23 0.12 35.40 54.79 Rh/UiO-66-Zr 0.40 0.12 8.44 39.07 51.98 Rh/UiO-66-ZrCe 0.32 0.16 8.44 39.30 51.79
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表 3 催化剂Rh/UiO-66-Zr和Rh/UiO-66-ZrCe上Rh 3d的XPS谱图拟合
Table 3 XPS spectrogram fitting results of Rh 3d on Rh/UiO-66-Zr and Rh/UiO-66-ZrCe
Sample Position /eV Chemical specie Relative content /% Rh/UiO-66-Zr 307.00/311.70 Rh0 42.71 308.60/313.30 RhV + 57.29 Rh/UiO-66-ZrCe 307.00/311.70 Rh0 66.60 308.60/313.30 RhV + 33.40
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表 4 催化剂上O 1s的XPS谱图拟合
Table 4 XPS spectrogram fitting results of O 1s on Rh/UiO-66-Zr and Rh/UiO-66-ZrCe
Sample Oα Oβ EB /eV area /% EB /eV area /% Rh/UiO-66-Zr 530.16 24.75 531.79 75.25 Rh/UiO-66-ZrCe 530.14 25.90 531.81 74.10
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