Abstract:

The fossil fuel depletion and environmental pollution have made the search for sustainable and renewable energy sources (e.g. biofuels) become a world focus. In this paper, 3D flower-spherical Bi₂SiO₅ was prepared via a simple hydrothermal method and used for the photocatalytic esterification of oleic acid with methanol under simulated sunlight irradiation. To understand the physical, chemical and optical properties of Bi₂SiO₅ catalyst, the as-prepared samples were characterized by XRD, XPS, SEM, HRTEM, NH₃-TPD and UV-vis DRS, and the compositions of reaction products were analyzed by FTIR. The yield of methyl oleate as the esterification product was quantified by ¹H NMR, due to the simple calculation and accurate and reliable results. Under simulated sunlight irradiation, the optimum reaction conditions were 12:1 alcohol to oil ratio, 5% catalyst, 70℃ and 6h, under which the yield of methyl oleate was 28.8%. The ¹H NMR analysis showed that the selectivity of methyl oleate was as high as 100% and the yield of methyl oleate was still 26.8% after three recycles of catalyst. ESR tests confirmed the existence of hydroxyl radical (·OH) and superoxide radical (·O{}_{\mathrm{2}}^{-}) in the reaction. As the first application of Bi₂SiO₅ in photocatalytic esterification, a possible reaction mechanism was proposed to explain the relative catalytic activity.

Key words: oleic acid, methyl oleate, photocatalytic esterification reaction, reaction mechanism, ¹H nuclear magnetic resonance spectra (¹H NMR)

摘要：

化石燃料资源的枯竭和环境污染等问题，使寻找生物燃料等可持续、可再生能源成为世界关注的焦点。本文通过简单水热法制备3D花球状Bi₂SiO₅，并用于在模拟太阳光照射下油酸与甲醇的光催化酯化反应。为了解Bi₂SiO₅催化剂的物理、化学和光学性质，采用X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）、高分辨率透射电子显微镜（HRTEM）、氨-程序升温脱附（NH₃-TPD）和紫外-可见漫反射光谱（UV-vis DRS）对其进行表征，且通过傅里叶变换红外光谱（FTIR）分析反应产物成分组成。酯化反应产物油酸甲酯的产率通过¹H NMR进行定量分析，计算过程简单、结果精确可靠。在模拟太阳光照射下，最优反应条件为：醇油比为12∶1、催化剂用量为5%（质量分数）、反应温度为70℃、光照反应时间为6h，油酸甲酯产率为28.8%。核磁共振氢谱（¹H NMR）分析结果显示油酸甲酯选择性高达100%，且催化剂循环3次后油酸甲酯产率仍可达26.8%，稳定性强。电子自旋共振（ESR）测试表明，Bi₂SiO₅光催化酯化反应过程中存在羟基自由基（·OH）和超氧基自由基（·O{}_{\mathrm{2}}^{-}）。基于Bi₂SiO₅首次用于光催化酯化反应，为解释其具有催化活性的原因，提出了其光催化酯化反应机理。

关键词: 油酸, 油酸甲酯, 光催化酯化反应, 反应机理, 氢核磁共振