Electrochemical reduction selectivity of crotonaldehyde on copper

Abstract Lignocellulosic waste is a potential feedstock for the generation of fuels and commodity chemicals, but existing conversion methods are too cost-intensive to be viable long-term solutions. Electrochemical reductions are promising for decentralized biomass valorization due to their modular scaling and capacity to run intermittently and without high temperatures or pressures. Using crotonaldehyde as a multi-functional model compound for the many partially unsaturated oxygenates found in processed biomass, we here demonstrate the production of butanal, butanol, butene, and butane (variously useful as commodity chemicals and major components of liquified petroleum gas) under ambient conditions by reductive bulk electrolysis with a copper mesh working electrode. We identify an optimum potential for reduced organic production under the reaction conditions and compare product distributions from reductions of intermediate species to further propose branching reaction pathways. Though butanal is typically the most abundant product from crotonaldehyde reduction, most of the butene and butane appear to result from a pathway involving initial reduction of the aldehyde group. We discuss evidence that selectivity is driven by interplay between crotonaldehyde reduction, local pH shifts due to the hydrogen evolution reaction, and changes in site reactivity and availability due to electrode fouling. This demonstration of model electrochemical biomass valorization also serves to inform further exploration into reduction of multi-functional molecules and electrochemical biomass processing in general. Graphic Abstract

摘要：木质纤维素废弃物是生产燃料和商品化学品的潜在原料，但现有的转化方法成本过高，无法成为可行的长期解决方案。电化学还原由于其模块化的规模以及能够间歇性运行且无需高温或高压的能力，在分散式生物质增值方面很有前景。以巴豆醛作为加工生物质中许多部分不饱和含氧化合物的多功能模型化合物，我们在此展示了在环境条件下，通过使用铜网工作电极进行还原整体电解来生产丁醛、丁醇、丁烯和丁烷（它们分别可用作商品化学品以及液化石油气的主要成分）。我们确定了在反应条件下有机产物还原的最佳电位，并比较了中间物种还原的产物分布，以进一步提出分支反应途径。尽管丁醛通常是巴豆醛还原最主要的产物，但大部分丁烯和丁烷似乎是由涉及醛基初始还原的途径产生的。我们讨论了选择性是由巴豆醛还原、析氢反应导致的局部pH变化以及电极污染引起的位点反应性和可用性变化之间的相互作用所驱动的证据。这种模型电化学生物质增值的演示也有助于为进一步探索多功能分子的还原以及一般的电化学生物质处理提供信息。图形摘要