Carbon dioxide/methanol conversion cycle based on cascade enzymatic reactions supported on superparamagnetic nanoparticles

ABSTRACT The conversion of carbon dioxide into important industrial feedstock is a subject of growing interest in modern society. A possible way to achieve this goal is by carrying out the CO2/methanol cascade reaction, allowing the recycle of CO2 using either chemical catalysts or enzymes. Efficient and selective reactions can be performed by enzymes; however, due to their low stability, immobilization protocols are required to improve their performance. The cascade reaction to reduce carbon dioxide into methanol has been explored by the authors, using, sequentially, alcohol dehydrogenase (ADH), formaldehyde dehydrogenase (FalDH), and formate dehydrogenase (FDH), powered by NAD+/NADH and glutamate dehydrogenase (GDH) as the co-enzyme regenerating system. All the enzymes have been immobilized on functionalized magnetite nanoparticles, and their reactions investigated separately in order to establish the best performance conditions. Although the stepwise scheme led to only 2.3% yield of methanol per NADH; in a batch system under CO2 pressure, the combination of the four immobilized enzymes increased the methanol yield by 64 fold. The studies indicated a successful regeneration of NADH in situ, envisaging a real possibility of using immobilized enzymes to perform the cascade CO2-methanol reaction.

摘要 将二氧化碳转化为重要工业原料是当今社会日益受到关注的研究课题。实现这一目标的可行途径之一是开展CO₂/甲醇级联反应，通过化学催化剂或酶实现二氧化碳的循环利用。酶可催化高效且高选择性的反应，但由于其稳定性较差，需采用固定化工艺以优化其催化性能。本文作者已对将二氧化碳还原为甲醇的级联反应进行了探索，依次采用乙醇脱氢酶（alcohol dehydrogenase, ADH）、甲醛脱氢酶（formaldehyde dehydrogenase, FalDH）和甲酸脱氢酶（formate dehydrogenase, FDH），以NAD⁺/NADH作为反应辅酶，谷氨酸脱氢酶（glutamate dehydrogenase, GDH）作为辅酶再生体系。所有酶均被固定于功能化四氧化三铁纳米颗粒表面，并分别对各酶的催化反应进行了研究，以确定最优反应条件。尽管分步反应策略下每分子NADH对应的甲醇产率仅为2.3%；但在施加二氧化碳压力的分批式反应体系中，四种固定化酶的组合使甲醇产率提升了64倍。研究表明NADH可实现成功的原位再生，为使用固定化酶开展CO₂-甲醇级联反应提供了切实可行的应用前景。