Catalytic synthesis of anisole over LDHs with different Mg/Al ratios
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摘要: 采用共沉淀法合成了一系列不同镁铝比的类水滑型层状金属氢氧化物(LDHs),通过XRD、SEM、FT-IR、NH3-TPD、CO2-TPD、TG和ICP-OES方法对MgAl-LDHs和焙烧产物进行表征,并用于催化苯酚与碳酸二甲酯(DMC)气相合成苯甲醚。结果表明,共沉淀法合成的MgAl-LDHs在Mg/Al比为2~4时具有良好的类水滑石结构,主要以球形层片聚集体的形态存在,其层间距、平均孔径和碱酸比在Mg/Al比为2~4之间逐渐增加;所制备的MgAl-LDHs样品均显示出良好的反应活性,并发现苯甲醚的选择性随催化剂酸碱比先增加后减小,当镁铝比为4时,其酸碱比为0.32,此时苯甲醚选择性最高为88.93 %。此外,还考察了反应温度和质量空速对苯甲醚催化效果的影响。Abstract: A series of layered hydroxides(LDHs)with different Mg/Al ratios were synthesized by coprecipitation method.MgAl LDHs and their calcined products were characterized by XRD, SEM, FT-IR, NH3-TPD, CO2- TPD, TG and ICP-OES, and were used to catalyze the vapor phase synthesis of anisole from phenol and dimethyl carbonate(DMC).The results show that MgAl LDHs synthesized by coprecipitation method have good hydrotalcite like structure when Mg/Al ratio is 2 to 4, mainly in the form of spherical lamellar aggregates.The interlayer spacing, average pore size and alkali acid ratio increase gradually when Mg/Al ratio is from 2 to 4.It is found that the selectivity of anisole first increases and then decreases with the acid-base ratio of the catalyst.The highest anisole selectivity of 88.93 % is achieved when the Mg/Al ratio is 4 and the acid/base ratio is 0.32.In addition, the effect of reaction temperature and mass space velocity on the catalytic performance are also investigated.
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Key words:
- hydrotalcite /
- phenol /
- anisole /
- coprecipitation method /
- Mg/Al ratio
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表 1 不同镁铝比焙烧水滑石的元素组成
Table 1. Elementary composition of calcined hydrotalcite with different Mg/Al ratios
样品 mMg/(mol·kg-1) mAl/(mol·kg-1) nMg/nAl Mg2Al-LDO 0.364 0.195 1.87 Mg3Al-LDO 0.289 0.130 2.22 Mg4Al-LDO 0.307 0.084 3.65 Mg5Al-LDO 0.306 0.067 4.57 Mg10Al-LDO 0.344 0.038 9.05 表 2 MgAl-LDHs的XRD分析结果
Table 2. XRD analysis of MgAl-LDHs
晶面 参数 Mg2Al-LDH Mg3Al-LDH Mg4Al-LDH 003 2θ/(°) 11.82 11.42 11.30 d/nm 0.748 1 0.774 2 0.782 4 FWHM 0.826 0.814 0.775 006 2θ/(°) 23.52 22.92 22.66 d/nm 0.377 9 0.387 7 0.392 1 FWHM 0.942 0.936 0.852 009 2θ/(°) 34.96 34.62 34.54 d/nm 0.256 4 0.258 9 0.259 5 FWHM 0.897 0.922 0.766 110 2θ/(°) 61.12 60.50 60.32 d/nm 0.151 5 0.152 9 0.153 3 FWHM 0.617 0.691 0.723 表 3 不同镁铝比焙烧水滑石的孔结构参数
Table 3. Pore structure of calcined hydrotalcite with different Mg/Al ratios
样品 比表面积/(m2·g-1) 孔容/(cm3·g-1) 平均孔径/nm Mg2Al-LDO 268.00 0.77 13.94 Mg3Al-LDO 202.73 0.68 16.86 Mg4Al-LDO 230.66 0.95 19.70 Mg5Al-LDO 252.05 0.85 17.51 Mg10Al-LDO 169.47 0.96 27.31 表 4 不同镁铝比焙烧水滑石的酸碱量
Table 4. Acid and base amount of calcined hydrotalcite with different Mg/Al ratios
样品 总碱/(mol·kg-1) 总酸(mol·kg-1) 总酸/总碱 Mg2Al-LDO 0.491 0.218 0.44 Mg3Al-LDO 0.500 0.184 0.37 Mg4Al-LDO 0.549 0.176 0.32 Mg5Al-LDO 0.549 0.145 0.26 Mg10Al-LDO 0.397 0.201 0.51 表 5 不同镁铝比水滑石对苯甲醚合成反应的性能
Table 5. Performance of MgAl-LDOs with different Mg/Al ratios for anisole synthesis
转化率/% 选择性/% 收率/% Mg2Al-LDO 99.25 88.04 87.38 Mg3Al-LDO 97.63 87.71 85.63 Mg4Al-LDO 98.87 88.93 87.92 Mg5Al-LDO 99.67 80.51 80.24 Mg10Al-LDO 99.75 85.78 85.57 反应条件:催化剂0.1 g,苯酚、DMC摩尔比为1∶3,进料量0.2 mL/h,时间150 min,温度380 ℃,常压。 -
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