Effect of Si content on the performance of direct synthesis of dimethyl ether over slurry CuZnAl catalyst prepared by complete liquid phase technology
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摘要: 在完全液相法制备工艺中，考察不同Si含量对浆状CuZnAl催化剂上合成气直接制备二甲醚性能的影响。其中，SA0.5催化剂（Si/Al=0.5）显示了最优异的催化性能，CO转化率为63.31%，二甲醚选择性为72.96%，在反应480 h过程中催化剂催化性能稳定。通过X射线衍射（XRD）、透射电子显微镜（TEM）和氮气吸附-脱附表征发现，Si的引入促进了催化剂Cu物种颗粒的分散及比表面积的增大，提高了CO转化率。此外，氢气程序升温还原（H2-TPR）和X射线光电子能谱（XPS）表征揭示了Cu物种与催化剂其他组分（Si物种）之间存在电子相互作用，抑制了Cu物种还原，催化剂表面富集更多Cu+物种，有利于甲醇合成，同时有效地抑制了水煤气副反应产物CO2的生成。再者，SA0.5催化剂表面富集了大量的Al物种（AlOOH），有利于甲醇脱水，促进二甲醚的生成。总之，浆状CuZnAlSi体系中Cu+和AlOOH协同催化作用，提高了催化剂活性及二甲醚选择性。
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关键词:
- Si含量 /
- Cu+-AlOOH协同催化 /
- 二甲醚 /
- 完全液相法 /
- 合成气
Abstract: The effect of Si content on the performance of slurry CuZnAl catalyst prepared by complete liquid phase technology for direct synthesis of dimethyl ether from syngas was investigated. Among them, catalyst with Si/Al ratio of 0.5 showed the best catalytic performance with the CO conversion of 63.31% and the dimethyl ether selectivity of 72.96%. The catalyst was stable after 480 h reaction. As revealed by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption and desorption characterizations, the introduction of Si promoted the dispersion of Cu species nanoparticles and led to increased specific surface area, which was beneficial for improving the CO conversion. Besides, temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) characterizations showed that an electronic interaction between Cu species and other components of the catalyst (especially, Si species) could inhibit the reduction of Cu species, resulting in the abundant Cu+ species on the catalyst surface. This was conducive to the synthesis of methanol and could effectively inhibit the formation of CO2, which was a by-product of the water-gas shift reaction. Moreover, a large amount of Al species (AlOOH) was enriched on the SA0.5 catalyst surface, which might contribute to the dehydration of methanol to produce dimethyl ether. In conclusion, the synergetic catalysis of Cu+ and AlOOH in slurry CuZnAlSi system improved the catalytic activity and dimethyl ether selectivity. -
图 1 （a）不同催化剂的反应性能数据和（b）SA0.5催化剂在反应480 h过程中稳定性测试
Figure 1 (a) Catalytic performance of different catalysts and (b) CO conversion and selectivity of DME for SA0.5 catalyst with reaction time on stream
图 3 （a）SA0、（b）SA0.5催化剂反应前TEM照片; （c） SA0.5催化剂反应前HRTEM照片及相应傅里叶变换光谱谱图
Figure 3 TEM images of fresh (a) SA0 and (b) SA0.5 catalyst; (c) the HRTEM image of fresh SA0.5 catalyst and its corresponding FFT
图 5 不同催化剂反应前（a）N2吸附-脱附等温曲线和（b）孔径分布
Figure 5 (a) N2 adsorption-desorption isotherms and (b) pore size distribution curves of the fresh catalysts
表 1 不同催化剂试样比表面积及孔结构参数
Table 1 Specific surface area and pore structure parameters of different catalysts
Sample BET surface area A/(m2·g−1) Pore volume v/(cm3·g−1) Average pore diameter d/nm SA0 128.0 0.29 9.2 SA0.25 133.5 0.24 6.8 SA0.5 162.7 0.22 5.8 SA1 151.4 0.23 6.1 
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表 2 不同催化剂反应前Cu物种结合能及俄歇动能数据
Table 2 Binding energy (BE) and Kinetic energy (KE) of Cu species over fresh catalysts
Catalyst BE/eV KE/eV α′Cu SA0 932.5 916.3 1848.8 SA0.25 932.4 916.5 1848.9 SA0.5 932.2 916.4 1849.0 SA1.0 932.0 916.8 1848.8
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表 3 不同催化剂反应前表面元素物质的量比
Table 3 Molar ratios between relevant elements on fresh catalysts
Catalyst Si/Al Cu/Zn Zn/Al Al/(Cu+Zn) SA0.25 0.32 0.58 0.13 4.86 SA0.5 0.24 0.67 0.11 5.27 SA1.0 0.50 0.36 0.17 4.46
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