Recent advances in glycerol valorization via electrooxidation:Catalyst,mechanism and device

甘油电催化氧化的研究进展:催化剂、机理和应用

Glycerol is one of the most important biomass-based platform molecules,massively produced as a by-product in the biodiesel industry.Its high purification cost from the crude glycerol raw material limits its application and demands new strategies for valorization.Compared to the conventional thermocatalytic strategies,the electrocatalytic strategies can not only enable the selective conversion at mild conditions but also pair up the cathodic reactions for the co-production with higher efficiencies.In this review,we summarize the recent advances of catalyst designs and mechanistic understandings for the electrocatalytic glycerol oxidation(GOR),and aim to provide an overview of the GOR process and the intrinsic structural-activity correlation for inspiring future work in this field.The review is dissected into three sections.We will first introduce the recent efforts of designing more efficient and selective catalysts for GOR,especially toward the production of value-added products.Then,we will summarize the current understandings about the reaction network based on the ex-situ and in-situ spectroscopic studies as well as the theoretical works.Lastly,we will select some representative examples of creating real electrochemical devices for the valorization of glycerol.By summarizing these previous efforts,we will provide our vision of future directions in the field of GOR toward real applications.

甘油(丙三醇)是一种重要的生物质基平台分子,也是生物柴油制备过程中产生的副产物.单纯将粗甘油经分离、提纯制取精制甘油存在成本高和用途单一的缺点,开发高效的粗甘油转化方法可以提升其附加值,进而提高资源利用率和延伸生物质基材料产业链.甘油是生物质基平台分子中氢含量最高的分子之一,可通过氧化还原、脱水等过程形成多种含碳短链能源化学品.与传统的热催化相比,电催化不仅能在温和的条件下实现粗甘油的选择性转化,还可使其与阴极发生耦合反应,生成氢气.然而,甘油的电催化氧化微观机制复杂,涉及诸多反应途径及多个电子和质子转移过程,如何合理设计可高选择性地催化生成目标产物的催化剂是实现生物甘油高效转化的关键.本文以甘油电催化氧化产物的选择性调控为核心,总结了甘油电催化氧化(GOR)中催化剂设计和机理研究领域的最新进展,旨在阐述GOR过程及催化剂的构效关系,并为今后设计开发高效GOR催化剂提供参考.首先,结合原位分析和理论计算等领域的研究结果,系统地总结了GOR过程中电位、催化剂结构和组成以及电解质对催化剂性能的影响,阐述了反应过程中的催化机理.针对GOR活性较高时,甘油容易强吸附在催化剂表面形成中间体进而毒化催化剂的现象,介绍了通过金属原子吸附、形成合金或界面修饰等方法在催化剂中引入金属或金属氧化物,并考察催化剂活性中心、甘油吸附构型、电子效应以及电子结构等对产物分布的影响.目前,有关GOR催化剂构效关系的研究主要集中在贵金属催化剂上;为推进生物甘油转化的实际应用,未来应致力于研究如何开发价格低廉的非贵金属催化剂,特别是应用于甘油电重整制氢和甘油燃料电池等领域的催化剂.已报道的非贵金属催化剂虽然有较好的稳定性,但其通常表现出较高的过电位,并且催化甘油生成的主要产物为低价值产物(碳酸盐,草酸盐和甲酸盐等).综上,未来可以利用先进的合成方法、表征技术和理论计算手段,在分子水平充分、深入地认识甘油氧化的途径,进而合理地设计开发出低成本、高性能、抗中毒的电催化剂,为实现粗甘油电催化氧制氢或转化为高附加值化学品的实际应用提供借鉴.