近临界水中Ce-Zr复合金属氧化物催化丙酸液相酮基化反应的研究

Liquid phase ketonization of propanoic acid over Ce-Zr composite metal oxides in near-critical water

酮基化反应是生物质基有机酸高值化利用的途径之一,能同时实现碳链增长和脱氧。针对生物质基有机酸很多情况下与水共存的现状,本研究提出了近临界水中有机酸直接液相酮基化制备长链酮的思路。以丙酸为模型物质,开展了铈(Ce)、锆(Zr)、锰(Mn)复合氧化物的筛选,得到了近临界水中丙酸液相酮基化较佳的复合金属催化剂Ce_(2)ZrO_(x)。在340℃、Ce_(2)ZrO_(x)催化下丙酸水溶液酮基化反应30 h,丙酸转化率为85%、3-戊酮收率达81.6%,而且该复合金属氧化物具有良好的重复使用性能。对部分Ce-Zr复合金属氧化物开展了X射线衍射仪(XRD)、红外光谱仪(FT-IR)、透射电子显微镜(TEM)、比表面积及微介孔分析仪(BET)、X射线光电子能谱(XPS)、化学吸附仪(CO_(2)-TPD)等表征,阐明了Ce_(2)ZrO_(x)具有较高酮基化催化活性和水热稳定性的原因是形成了Ce-O-Zr固溶体结构、较高的氧空位浓度、较大的比表面积和较多数量的碱性位。此外,还开展了酮基化动力学研究,得到丙酸转化反应活化能为98.9 kJ·mol^(-1)、3-戊酮生成活化能为90.0 kJ·mol^(-1)、其他副产物生成活化能为105.7 kJ·mol^(-1)。研究工作可为高效、耐水性酮基化催化剂的研发提供借鉴。

Ketonization is one of the pathways for high-value utilization of bio-based organic acids,which can increase carbon chain length and deoxygenate at the same time.Because bio-based organic acids often co-exist with water,liquid phase ketonization of organic acids to long-chain ketones in near-critical water was proposed.With propanoic acid as the model organic acid,the catalysis of Ce-Zr-Mn composite oxides were studied and Ce_(2)ZrO_(x) was found to have the highest catalytic activity for liquid phase ketonization in near-critical water.The conversion of propanoic acid reached 85% and the yield of 3-pentanone was 81.6% with Ce_(2)ZrO_(x) at 340℃ for 30 h,and the catalyst had good reusability.Some Ce-Zr composite metal oxides were characterized by the techniques of XRD,FT-IR,TEM,BET,XPS and CO_(2)-TPD.It was clarified that the reasons for the higher ketonization activity and higher hydrothermal stability of Ce_(2)ZrO_(x) were the formation of Ce-O-Zr solid solution,higher oxygen vacancy concentration,larger surface area and more basic sites.According to the first-order ketonization kinetics,the activation energies of propanoic acid degradation,3-pentanone and by-side products formation were 98.9,90.0 and 105.7 kJ·mol^(-1),respectively.The results provide a reference for the development of efficient and water-resistant ketonization catalysts.