Elucidating Acidic Electro-Oxidation Pathways of Furfural on Platinum
Elucidating Acidic Electro-Oxidation Pathways of Furfural on Platinum
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DOI：
10.1021/acscatal.9b02656
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发表时间：
2019-11-01
期刊：
影响因子：
12.9
通讯作者：
Holewinski, Adam
中科院分区：
文献类型：
--
作者：
Roman, Alex M.;Hasse, Joseph C.;Holewinski, Adam
电催化为生物质衍生的原料的价值化提供了许多可能的优点，最关键的是其在酸性水介质中的直接转化的顺从性。呋喃类生物质衍生物，如糠醛，是通过部分氧化具有许多增值化学品出口的底物，最值得注意的是糠酸（FA），其是2，5-呋喃二甲酸（FDCA）的潜在前体。在电化学电池中将这种部分氧化与H-2析出或其他还原反应（例如CO2）配对提供了在降低的电压下进行电解的机会，同时联产比O-2更有价值的产物。在这里，我们已经利用差分反应器研究与在线电化学质谱（OLEMS），以及原位红外光谱衰减全反射-表面增强红外反射-吸收光谱（ATR-SEIRAS），探测糠醛的氧化反应途径铂催化剂在酸性电解质。我们发现糠醛电氧化的选择性取决于电位，最大的位移对应于Pt的过渡到Pt-氧化物。在1. 2 V-RHE以下，FA和5-羟基糠酸是主要产物。在更高的电位下，选择性主要向5-羟基-呋喃-2（5 H）-酮（HFN）转移，同时也出现马来酸（MA）。ATR-SEIRAS和OLEMS表明，分解和过度氧化为CO2是通过脱羰基或脱羧的环中间体发生的，而MA一旦形成就不太容易被进一步氧化活化。显著的氧化电流仅在表面清除CO的电位下实现，CO来源于糠醛在金属Pt表面上的自发脱羰。随着电势的增加，通过有机中间体的高稳态表面覆盖率促进了相对于CO2的C-4和C-5含氧化合物的选择性，所述有机中间体抑制了从水的排放中快速吸附和添加氧。基于这些发现，我们提出了一个反应途径和方向，设计更积极和选择性的电催化剂。
Electrocatalysis poses a number of possible advantages for the valorization of biomass-derived feedstocks, most critically its amenability to direct conversion in acidic aqueous media. Furanic biomass derivatives, such as furfural, are substrates with a number of value-added chemical outlets via partial oxidation, most notably furoic acid (FA), a potential precursor to 2,5-furandicarboxylic acid (FDCA). Pairing such partial oxidations with H-2 evolution or other reduction reactions (e.g. CO2) in an electrochemical cell presents an opportunity to perform electrolysis at lowered voltages, while coproducing products that are more valuable than O-2. Here, we have utilized differential reactor studies with online electrochemical mass spectrometry (OLEMS), as well as in situ infrared spectroscopy attenuated total reflectance-surface-enhanced infrared reflection-absorption spectroscopy (ATR-SEIRAS), to probe the oxidative reaction pathways of furfural on platinum catalysts in acidic electrolyte. We find furfural electrooxidation selectivity to depend on potential, with the largest shifts corresponding to the transition of Pt to Pt-oxide. Below 1.2 V-RHE, FA and 5-hydroxyfuroic acid are the primary products. At higher potential, selectivity shifts predominantly toward 5-hydroxy-furan-2(5H)-one (HFN), with the appearance of maleic acid (MA) as well. ATR-SEIRAS and OLEMS indicate that decomposition and overoxidation to CO2 occurs via decarbonylated or decarboxylated ring intermediates, while MA is less easily activated toward further oxidation once it is formed. Significant oxidative currents are only achieved at potentials where the surface is cleared of CO, which is derived from spontaneous decarbonylation of furfural on the metallic Pt surface. As potential is increased, selectivity to C-4 and C-5 oxygenates over CO2 is then promoted by a high steady-state surface coverage of organic intermediates that inhibit rapid adsorption and addition of oxygen from the discharge of water. Based on these findings, we propose a reaction pathway and directions for the design of more active and selective electrocatalysts.