二氧化硅负载的不同碱金属硝酸盐催化乳酸缩合反应制备2,3-戊二酮的催化性能比较研究（英文）

Comparative Study on Catalytic Performance of the Production of 2,3-Pentanedione from Lactic Acid Condensation over SiO_2-Supported Alkali Metal Nitrates

考察了二氧化硅负载的不同碱金属硝酸盐催化乳酸缩合制备2,3-戊二酮的催化性能。在考察的碱金属硝酸盐如硝酸锂、硝酸钠、硝酸钾和硝酸铯作为催化剂的前驱体中,重点关注的是碱金属阳离子对乳酸缩合反应的影响。通过对这些硝酸盐前驱体在反应中的作用研究,发现硝酸铯的催化性能最佳。为了探究影响催化剂性能的原因,对新鲜催化剂和用过的催化剂采用X射线衍射(XRD)、傅里叶变换红外(FT-IR)光谱进行表征,发现所有的硝酸盐在反应过程中快速地转变为乳酸盐,并认为乳酸盐才是催化活性物种。随后,又借助CO_2程序升温脱附(CO_2-TPD)表征手段对用过的催化剂的碱性进行表征,发现二氧化硅负载的硝酸铯具有最强的碱性。乳酸缩合反应制备2,3-戊二酮被广泛认为是碱催化反应,因此,二氧化硅负载的硝酸铯展示了最佳的催化性能。此外,本文还讨论了反应温度、硝酸盐的负载量等工艺条件对反应的影响。以4.4%(x,摩尔分数)CsNO_3/SiO_2为催化剂,在反应温度为300°C条件下,2,3-戊二酮的收率达54.1%。

The production of 2,3-pentanedione from lactic acid over SiO2-supported alkali metal nitrates under various conditions was investigated. Using nitrate （NO;） as the anion, the effect of alkali metal cations on Claisen condensation of lactic acid into 2,3-pentanedione was focused on. Among precursors such as LiNO3, NaNO3, KNO3, and CsNO3, CsNO3 displayed the best catalytic performance. Characterization of the fresh and used catalysts by X-ray diffraction （XRD） and Fourier transform infrared （FT-IR） spectroscopy revealed that all MNO3 （M = Li, Na, K, Cs） salts were transformed into alkali metal lactates during the reaction. Alkali metal lactates were identified as active species for catalytic Claisen condensation of lactic acid into 2,3-pentanedione. CO2 temperature-programmed desorption （TPD） results of the used catalysts showed that the CsNO3/SiO2 catalyst was the most alkaline. For that reason, the CsNO3/SiO2 catalyst displayed the highest catalytic performance of those examined. The effects of reaction temperature and loading amount of CsNO3 on reaction performance were also discussed. Over the 4.4% （x, molar fraction） CsNO3/SiO2 catalyst, a 54.1% yield of 2,3-pentanedione was achieved at 300 ℃.