Study on aldol condensation of acetic acid with formaldehyde to acrylic acid over TiO2 modified VPO
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摘要: 采用有机溶剂热法制备了系列TiO2改性的钒磷氧催化剂,利用TEM、XRD、XPS、NH3-TPD及CO2-TPD对催化剂结构及表面物化性质进行了表征,以醋酸甲醛合成丙烯酸为探针反应对催化剂的反应性能进行了评价。结果表明,与未改性的钒磷氧催化剂相比,TiO2的加入显著改变钒磷氧催化剂的(
${I_{{{\rm{V}}^{{\rm{5 + }}}}/{{\rm{V}}^{{\rm{4 + }}}}}} $ )/IV比值,当TiO2的前驱体为金红石相并且Ti/V物质的量比为2.0时,(${I_{{{\rm{V}}^{{\rm{5 + }}}}/{{\rm{V}}^{{\rm{4 + }}}}}} $ )/IV比值达到最高,因此,该催化剂具有最高的丙烯酸收率(18.0%)和丙烯酸生成速率(6.61 mmol/(g·h)),表明对于TiO2改性的钒磷氧催化剂,V5+与V4+的氧化还原循环在催化醋酸甲醛制丙烯酸反应过程中起主要作用。-
关键词:
- TiO2改性钒磷氧催化剂 /
- 羟醛缩合 /
- 丙烯酸
Abstract: A class of TiO2 modified VPO catalysts were prepared by organic solvent-heating method in the present work. The catalysts were characterized by TEM, XRD, XPS, NH3-TPD and CO2-TPD techniques. The catalytic performances were evaluated in the aldol condensation of acetate acid and formaldehyde to acrylic acid in a fixed-bed reactor. The results show that the addition of TiO2 significantly changes the proportion of V content forming V5+ and V4+ ion pair to total V with the unmodified VPO catalyst. As the precursor of TiO2 is rutile phase and Ti/V molar ratio is 2.0, the proportion of V content forming V5+ and V4+ ion pair to total V reaches the maximum, resulting in the best acrylic acid yield (18.0%) and acrylic acid space-time yield (6.61 mmol/(g·h)). It indicates that for the VPO catalyst modified by TiO2, the redox cycle of V5+ and V4+ ion pair plays a major role in the catalytic reaction of formaldehyde and acetate acid to acrylic acid.-
Key words:
- TiO2 modified VPO catalysts /
- aldol condensation /
- acrylic acid
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图 9 催化剂(
${I_{{{\rm{V}}^{{\rm{5 + }}}}/{{\rm{V}}^{{\rm{4 + }}}}}} $ )/IV比值与其催化性能的关系Figure 9 Relationship between proportion of V content forming V5+ and V4+ ion pair to total V on the catalyst surface and the reaction performances
(a): VPO catalysts with different TiO2 content; (b): VPO catalysts with different TiO2 precursors
表 1 催化剂的表面组成
Table 1 Surface composition of catalysts
Sample Relative amount / % P/V (mole ratio) Ti/V (mole ratio) (${I_{{{\rm{V}}^{{\rm{5 + }}}}/{{\rm{V}}^{{\rm{4 + }}}}}} $)/IV Binding energy/eV P V5+ V4+ Ti O P V5+ V4+ VPO 17.4 1.7 3.4 0 77.5 3.4 0 66.8% 134.9 518.5 517.5 VPO-Rut-1 14.1 1.6 2.1 3.1 79.0 3.7 0.81 85.3% 133.9 518.3 516.9 VPO-Rut-2 10.9 1.3 1.5 4.4 82.0 3.9 1.5 90.3% 134.2 518.4 517.0 VPO-Rut-4 10.4 1.0 1.3 10.2 77.2 4.6 4.5 85.8% 133.8 517.6 516.6 VPO-Rut-6 5.2 0.8 1.0 10.0 82.9 2.7 5.3 86.2% 133.7 517.4 516.4 VPO-Rut-12 2.4 2.4 0.6 12.3 82.2 0.78 4.0 41.6% 133.5 517.1 516.1 VPO-TBOT-2 15.8 0.8 1.5 5..8 76.0 6.5 2.4 75.6% 134.3 518.4 517.1 VPO-Ana-2 15.0 0.7 1.0 6.8 76.5 8.6 3.9 82.6% 134.3 518.5 517.1 (${I_{{{\rm{V}}^{{\rm{5 + }}}}/{{\rm{V}}^{{\rm{4 + }}}}}} $)/IV: Proportion of V content forming V5+ and V4+ ion pair to total V 表 2 催化剂的表面酸碱性
Table 2 Surface acidity and basicity of catalysts
Sample NH3-TPD Total acid quantities /
(μmol·g−1)CO2-TPD Total basic
quantities /
(μmol·g−1)weak acid
quantities /
(μmol·g−1)intermediate
acid quantities /
(μmol·g−1)weak basic
quantities /
(μmol·g−1)intermediate basic
quantities /
(μmol·g−1)VPO 7.9 10.3 18.2 10.8 12.1 22.9 VPO-Rut-1 42.1 630.6 672.6 49.3 37.8 87.1 VPO-Rut-2 102.4 1910.9 2013.3 60.2 56.5 116.7 VPO-Rut-4 98.5 478.5 576.9 46.4 72.0 118.4 VPO-Rut-6 150.2 204.9 355.2 132.3 105.3 237.6 VPO-Rut-12 172.5 110.3 282.8 159.4 129.8 289.2 表 3 催化剂的反应性能
Table 3 Reaction performances of catalysts
Sample Conv. of HAc /% Selec. of AA /% Yield of AA /% STY /(mmol·g−1·min−1 ) VPO 15.1 83.0 12.5 4.62 VPO-Rut-1 19.5 83.0 16.2 5.95 VPO-Rut-2 21.1 85.4 18.0 6.61 VPO-Rut-4 21.0 82.1 17.3 6.34 VPO-Rut-6 20.6 84.6 17.4 6.39 VPO-Rut-12 11.8 65.1 7.7 2.81 VPO-TBOT-2 18.6 79.7 14.8 5.43 VPO-Ana-2 20.1 83.8 16.9 6.24 the reaction condition: amount of catalysts 6 g; HAc/HCHO = 3/1; volume of feedstock 0.25 mL/min; LHSV is 2.5 h−1 ; reaction temperature 365 ℃ (HAc, acetic acid; AA, acrylic acid ) 表 4 温度对催化剂反应性能的影响
Table 4 Effect of reaction temperature on the catalytic performance
Temp. /℃ Conv. of HAc /% Selec. of AA /% Yield of AA /% STY /
(mmol·g−1·min−1 )320 17.2 81.4 14.0 5.14 350 20.9 84.1 17.5 6.44 365 21.1 85.4 18.0 6.61 380 15.8 80.5 12.7 4.65 reaction condition: amount of catalysts 6 g; HAc/HCHO = 3∶1; volume of feedstock 0.25 mL/min; LHSV is 2.5 h−1; (HAc, acetic acid; AA, acrylic acid ) 表 5 液空对催化剂的反应性能的影响
Table 5 Effect of LHSV on the catalytic performance
LHSV /h−1 Conv. of HAc /% Selec. of AA /% Yield of AA /% STY / (mmol·g−1·min−1 ) 1.0 25.7 80.9 20.8 3.04 2.5 21.1 85.4 18.0 6.61 4.0 14.7 72.3 10.7 6.26 reaction condition: amount of catalysts 6 g; HAc/HCHO = 3∶1; reaction temperature 365 ℃ (HAc, acetic acid; AA, acrylic acid) -
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