Effect of heat treatment time on the performance of CuZnAl catalysts in the synthesis of higher alcohols from syngas
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摘要: 采用完全液相法在不同热处理时间下制备了CuZnAl催化剂，利用X射线光电子能谱（XPS）、X射线衍射（XRD）、H2程序升温还原（H2-TPR）、NH3吸附-脱附（NH3-TPD-MS）和N2物理吸附-脱附等方法对其结构进行了表征分析，并在浆态床反应器上对其催化合成气制C2+OH的性能进行了研究。研究发现，延长热处理时间增强了催化剂中Cu和Al物种之间的相互作用力，改变了其中Cu+的量，从而影响Cu+-Cu0活性位的协同作用。同时，热处理时间的延长减少了催化剂的表面酸量，增大了孔容和孔径；催化剂表面较少的弱酸位及较大孔容和孔径均有利于C2+OH的生成。热处理时间为7 h时所制备的CuZnAl催化剂表现出了优良的低碳醇合成催化活性，CO转化率和总醇中C2+OH的质量分数分别达到了38.1%和65.9%。Abstract: A series of CuZnAl catalysts were prepared by the complete liquid-phase method with different heat treatment times and characterized by XPS, XRD, H2-TPR, NH3-TPD-MS and N2 adsorption-desorption; their catalytic performances in the synthesis of higher alcohols from syngas were investigated in a slurry bed reactor. The results indicate that an increase in the heat treatment time can enhance the interaction between the Cu and Al species and alter the amount of Cu+ species over the CuZnAl catalysts, influencing the synergistic effect of Cu+-Cu0 sites. In addition, with the increase of heat treatment time, the surface acidity of CuZnAl catalyst decreases, accompanying with an increase in the pore volume and pore size; small amount of surface weak acid sites, large pore volume and large pore size are beneficial to the formation of higher alcohols. The CuZnAl catalyst obtained by heat-treating for 7 h exhibits excellent performance in the synthesis of higher alcohols, with a CO conversion of 38.1% and a higher alcohols mass fraction of 65.9% in the total alcohols.
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Key words:
- complete liquid-phase method /
- CuZnAl catalyst /
- heat treatment time /
- higher alcohols /
- Cu+-Cu0
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图 1 CuZnAl催化剂在不同热处理时间下的催化性能
Figure 1 Performance of CuZnAl catalysts prepared with different heat treatment times in the synthesis of higher alcohols from syngas
(a): CO conversion as a function of reaction time;
(b): higher alcohols mass fraction in total alcohols as a function of reaction time reaction conditions: 280 ℃, 4.0 MPa, V(H2)/V(CO) = 2, feed flow rate = 150 mL/min
图 2 CuZnAl催化剂在不同热处理时间下产物的碳数分布
Figure 2 Products carbon number distribution for higher alcohols synthesis over various CuZnAl catalysts prepared with different heat treatment times
(a): alcohols; (b): hydrocarbons
图 3 CuZnAl催化剂在不同热处理时间下的Cu 2p XPS谱图
Figure 3 Cu 2p XPS spectra of CuZnAl catalysts prepared with different heat treatment times
图 4 CuZnAl催化剂在不同热处理时间下的XRD谱图
Figure 4 XRD patterns of the CuZnAl catalysts prepared with different heat treatment times
图 5 CuZnAl催化剂在不同热处理时间下的H2-TPR谱图
Figure 5 H2-TPR profiles of CuZnAl catalysts prepared with different heat treatment times
(a): fresh ones before reaction; (b): spent ones after reaction
图 6 CuZnAl催化剂在不同热处理时间下的NH3-TPD-MS谱图
Figure 6 NH3-TPD-MS profiles of the CuZnAl catalysts prepared with different heat treatment times
表 1 CuZnAl催化剂在不同热处理时间下的表面元素组成
Table 1 Surface compositions of the CuZnAl catalysts prepared with different heat treatment times
Catalyst Atom/% Molar ratio C O Cu Zn Al Cu/Zn Cu/Al Zn/Al Cat-3.5 38.3 37.5 1.1 4.5 18.6 0.24 0.06 0.24 Cat-7 22.3 48.7 1.3 4.4 23.4 0.30 0.06 0.19 Cat-10.5 10.5 55.3 1.4 5.5 27.3 0.25 0.05 0.20 
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表 2 CuZnAl催化剂在不同热处理时间下的织构参数
Table 2 Textural properties of the CuZnAl catalysts with different heat treatment times
Catalyst ABET/(m2·g-1) vBJH/(cm3·g-1) d/nm before reaction after reaction before reaction after reaction before reaction after reaction Cat-3.5 175.4 186.1 0.41 0.44 9.4 10.0 Cat-7 168.9 139.2 0.52 0.43 12.6 15.5 Cat-10.5 155.9 129.3 0.54 0.41 15.0 14.1 notes: ABET: BET surface area; vBJH: pore volume; d: average pore diameter
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