Transesterification of ethylene carbonate with methanol over Zn-La mixed oxide catalysts
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摘要: ZnO、La2O3和Zn-La复合氧化物催化剂用于甲醇与碳酸乙烯酯反应制备碳酸二甲酯和乙二醇。催化剂采用共沉淀法进行制备，并用BET、XRD、TG-DSC、CO2-TPD和Hammett滴定等对催化剂进行表征。考察了Zn-La物质的量比、焙烧温度，反应条件（反应温度、反应时间、催化剂用量等）对催化剂活性的影响。结果表明，ZnLa复合氧化物物质的量比为2：1，焙烧温度为500℃时，催化剂表现了较好的催化效果。催化剂的活性与催化剂表面的碱性强度和碱量有关，碱量越多催化剂的活性越好。Abstract: The transesterification of ethylene carbonate (EC) with methanol to synthesis dimethyl carbonate (DMC) and ethylene glycol (EG) over ZnO, La2O3 and Zn-La mixed oxides were explored. The catalysts were prepared by co-precipitation method and characterized by BET, XRD, TG-DSC, CO2-TPD and Hammett titration. The influence of Zn/La atomic ratio, calcination temperature and reaction parameters (reaction temperature, reaction time, catalyst amount) on the catalytic activity were investigated. The results indicated that the binary Zn-La mixed oxide with Zn/La atomic ratio of 2:1 calcined at 500℃ showed the highest catalytic performance for the title reaction due to its strongest basicity, and the amount of strong basic sites of the catalyst should be responsible for the high transesterification activity.
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Key words:
- transesterification /
- dimethyl carbonate /
- ethylene glycol
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Figure 1 XRD patterns (a) and CO2-TPD (b) profiles of the catalysts with different Zn/La atomic ratios
●:ZnO; ■:La2O3; ∇:La(OH)3
Figure 2 Catalytic performances of ZnO, La2O3 and Zn-La catalysts on the transesterification of EC with methanol reaction conditions:EC 8.0 g, MeOH 23.0 g, catalyst amount 0.62 g, reaction temperature 40 ℃, reaction time 2 h
Figure 3 Dependence of the EC conversion on the total basicity of Zn-La catalysts
(the value of total basicity were obtained from Table 2)
Figure 4 TG-DSC analysis of the ZL-2-uncalcined sample and XRD patterns of ZL-2 catalysts calcined at different temperatures
●:ZnO; ■:La2O3; ∇:La(OH)3; ◇:La2O2CO3
Figure 5 CO2-TPD profiles and catalytic performance of ZL-2 catalysts calcined at different temperatures for the synthesis of DMC reaction conditions:EC 8.0 g, MeOH 23.0 g, catalyst amount 0.62 g, reaction temperature 40 ℃, reaction time 2 h
Figure 6 Effect of reaction temperature (a), reaction time (b) and catalyst amount (c) on the activity of transesterification reaction conditions:EC 8.0 g, MeOH 23.0 g
Table 1 BET specific surface area of various samples
Catalyst ZnO La2O3 ZL-2-700 ZL-4-700 ZL-6-700 ZL-2-500 ZL-2-uncalcined BET area A/(m2·g-1) 1.87 6.67 4.46 3.08 2.14 5.61 5.31 
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Table 2 Base strength (H_) and Basicity obtained from Hammett indicator measurements
Catalyst Base strength Total basicity/(mmol·gcatal.-1) ZL-2-uncalcined 9.3 < H_ < 15 13.3 ZL-2-500 9.3 < H_ < 15 27.6 ZL-2-700 9.3 < H_ < 15 20.7 ZL-4-700 9.3 < H_ < 15 19.3 ZL-6-700 9.3 < H_ < 15 16.2
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