Lomonosov Vladimir, Asselin Jérémie, Ringe Emilie
Department of Materials Science and Metallurgy, University of Cambridge 27 Charles Babbage Road Cambridge CB3 0FS UK
Department of Earth Sciences, University of Cambridge Downing Street Cambridge CB2 3EQ UK.
React Chem Eng. 2022 Apr 29;7(8):1728-1741. doi: 10.1039/d2re00044j. eCollection 2022 Jul 26.
The reduction of 4-nitrophenol (4-NiP) to 4-aminophenol (4-AP) with an excess of sodium borohydride is commonly used as a model reaction to assess the catalytic activity of metallic nanoparticles. This reaction is considered both a potentially important step in industrial water treatment and an attractive, commercially relevant synthetic pathway. Surprisingly, an important factor, the role of the reaction medium on the reduction performance, has so far been overlooked. Here, we report a pronounced effect of the solvent on the reaction kinetics in the presence of silver and gold nanoparticles. We demonstrate that the addition of methanol, ethanol, or isopropanol to the reaction mixture leads to a dramatic decrease in the reaction rate. For typical concentrations of reactants, the reduction is completely suppressed in the presence of 50 vol% alcohols. 4-NiP reduction rate in aqueous alcohol mixtures can, however, be improved noticeably by increasing the borohydride concentration or the reaction temperature. The analysis of various factors responsible for solvent effects reveals that the decrease in the reduction rate in the presence of alcohols is related, amongst others, to a substantially higher oxygen solubility in alcohols compared to water. The results of this work show that the effects of solvent properties on reaction kinetics must be considered for unambiguous comparison and optimization of the catalytic performance of metallic nanoparticles in the liquid phase 4-NiP reduction.
用过量硼氢化钠将4-硝基苯酚（4-NiP）还原为4-氨基苯酚（4-AP）通常用作评估金属纳米颗粒催化活性的模型反应。该反应被认为既是工业水处理中潜在的重要步骤，也是一条有吸引力的、与商业相关的合成途径。令人惊讶的是，一个重要因素，即反应介质对还原性能的作用，迄今为止一直被忽视。在此，我们报道了在银和金纳米颗粒存在下，溶剂对反应动力学有显著影响。我们证明，向反应混合物中添加甲醇、乙醇或异丙醇会导致反应速率急剧下降。对于典型的反应物浓度，在存在50体积%醇的情况下，还原反应完全被抑制。然而，通过提高硼氢化钠浓度或反应温度，可以显著提高水醇混合物中4-NiP的还原速率。对导致溶剂效应的各种因素的分析表明，在醇存在下还原速率降低与醇中氧的溶解度比水高得多等因素有关。这项工作的结果表明，在液相4-NiP还原中，为了明确比较和优化金属纳米颗粒的催化性能，必须考虑溶剂性质对反应动力学的影响。
