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

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CO₂程序升温脱附（CO₂-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）CsNO₃/SiO₂为催化剂，在反应温度为300 ℃条件下，2, 3-戊二酮的收率达54.1%。

Comparative Study on Catalytic Performance of the Production of 2, 3-Pentanedione from Lactic Acid Condensation over SiO2-Supported Alkali Metal Nitrates

The production of 2, 3-pentanedione from lactic acid over SiO₂-supported alkali metal nitrates under various conditions was investigated. Using nitrate (NO₃^-) 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 ℃.