Effect of calcination temperature on MgAlOx mixed oxides for converting formaldehyde and acetaldehyde to propanal
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摘要: 采用共沉淀法制备了镁铝水滑石前驱体,通过在不同温度下焙烧得到系列MgAlOx复合氧化物催化剂,采用XRD、TG、N2吸附-脱附、NH3-TPD和CO2-TPD等技术对催化剂的物理和化学性质进行了表征,采用甲醛和乙醛缩合反应对催化剂反应性能进行了评价。结果表明,随着焙烧温度的提高,乙醛转化率以及正丙醛时空收率先增加后减少,C-550催化剂最大,分别达到39.22%和103.86 g/(kg·h),这与催化剂中强碱和强碱数目变化趋势一致。此外,提高催化剂中强碱和强碱数目还会促进副产物甲醇和CO2的生成。
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关键词:
- 甲醛和乙醛 /
- 正丙醛 /
- MgAlOx复合氧化物 /
- 焙烧温度
Abstract: A series of MgAlOx mixed oxides were prepared by calcination of hydrotalcite materials at various temperatures ranging from 400 to 700℃. The physical and chemical properties of the catalysts were characterized by XRD, TG, N2 adsorption/desorption, NH3-TPD, and CO2-TPD techniques. The catalytic activity was evaluated by the condensation of formaldehyde and acetaldehyde. The results show that as the calcination temperatures increase, both the conversion of acetaldehyde and the space time yield of propanal first increase and then decrease, which shows the same trend with the amount of moderate basic sites, and the C-550 catalyst has the maximum of 39.22% and 103.86 g/(kg·h), respectively. Moreover, the yields of by-products including methanol and CO2 are also significantly related to the moderate and strong basic sites.-
Key words:
- formaldehyde and acetaldehyde /
- propanal /
- MgAlOx mixed oxides /
- calcination temperature
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表 1 催化剂的织构参数以及表面酸碱分布
Table 1 Textural properties, acidity, and alkalinity of the samples
Sample ABET /(m2·g-1) vp /(cm·g-1) dp /nm Amount of acid sites /(μmol·g-1)a Amount of basic sites /(μmol·g-1)b total weak moderate total weak moderate strong HT 116.2 0.67 10.86 - - - - - - - C-400 208.6 0.34 6.71 105.68 38.12 67.56 198.76 24.91 141.53 32.32 C-500 226.7 0.49 7.57 171.54 51.69 119.85 267.29 23.69 176.26 67.35 C-550 249.2 0.48 6.53 115.23 38.47 76.76 276.30 6.14 182.93 87.22 C-600 223.8 0.55 8.30 175.43 46.36 129.07 242.11 19.46 162.65 60.00 C-700 165.2 0.13 6.62 135.07 39.65 95.42 213.40 28.35 148.60 36.45 ABET: BET surface area; vp: BJH pore volume; dp: average pore diameter; a: calculated from NH3-TPD; b: calculated from CO2-TPD 表 2 催化剂催化甲醛和乙醛反应的评价
Table 2 Catalytic performance of the catalysts in condensation of formaldehyde and acetaldehyde
Catalyst x/% s/% STY/(g·kg-1·h-1) propanal methanol CO2 isobutanal 1-propanol MF ethanol propanal methanol CO2 C-400 22.12 77.54 9.01 9.60 1.72 0.45 0.75 0.93 60.42 11.61 17.00 C-500 35.69 60.17 18.35 16.32 2.35 0.92 1.05 0.84 95.19 48.04 58.70 C-550 39.22 56.59 19.17 17.80 2.68 1.05 1.98 0.73 103.86 58.23 74.28 C-600 29.27 62.18 15.11 17.11 2.73 0.99 0.87 1.01 77.55 31.19 48.52 C-700 24.21 69.09 13.40 13.00 1.86 0.67 1.06 0.92 65.54 21.04 28.03 reaction conditions: t=260 ℃, p=0.1 MPa, reaction time=5 h, formaldehyde/acetaldehyde (molar ratio)=4, GHSV=1000 h-1, LHSV=2.0 h-1; x: acetaldehyde conversion, s: selectivity, STY: space time yield, MF: methyl formate -
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