Efficient Conversion of CO₂ to Methanol Catalyzed by Three Dehydrogenases Co-encapsulated in an Alginate−Silica (ALG−SiO₂) Hybrid Gel

Abstract

In this study, the conversion of carbon dioxide to methanol was realized through a novel biochemical approach that was catalyzed by three dehydrogenases: formate dehydrogenase (FateDH), formaldehyde dehydrogenase (FaldDH), and alcohol dehydrogenase (ADH). The dehydrogenases were encapsulated in an alginate−silica (ALG−SiO2) hybrid gel, which was prepared through in situ growth of the silica precursor within an alginate solution, which was followed by Ca2+ cross-linking. Methanol yields that were catalyzed by free dehydrogenases, and by dehydrogenases immobilized in pure alginate (ALG) gel and in ALG−SiO2 hybrid gel, were 98.8%, 71.3%, and 98.1%, respectively. Furthermore, methanol yield that was catalyzed by dehydrogenases in an ALG−SiO2 composite could be retained as high as 76.2% after 60 days storage and as high as 78.5% after 10 times recycling. The significantly improved catalytic properties of the dehydrogenases in the ALG−SiO2 composite were attributed to the creation of the appropriate immobilizing microenvironment: high hydrophilicity, moderate rigidity and flexibility, ideal diffusion characteristics, and optimized cage confinement effect.

Regeneration of the NADH Cofactor by a Rhodium Complex Immobilized on Multi-Walled Carbon Nanotubes

“…[2][3][4][5] In this enzyme cascade, one molecule of methanol is produced at the cost of three equivalents of NADH. It is environmentally beneficial to convert CO 2 into useful biofuel by enzymatic reactions, but the high cost of stoichiometric NADH consumption makes this process impractical.…”

“…1 It was reported that the combination of three NAD + -dependent dehydrogenases (formate dehydrogenase, formaldehyde dehydrogenase and alcohol dehydrogenase) is capable of generating methanol from CO 2 by reversing the original enzymatic reaction direction. [2][3][4][5] In this enzyme cascade, one molecule of methanol is produced at the cost of three equivalents of NADH. It is environmentally beneficial to convert CO 2 into useful biofuel by enzymatic reactions, but the high cost of stoichiometric NADH consumption makes this process impractical.…”

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

“…In addition, different immobilization strategies have also been described in the literature, such as enzyme encapsulation (Xu et al 2006), but showing lower yields in comparison with our methodology. Encapsulation of dehydrogenase enzymes in silica matrix exhibited methanol yields between 16.8% and 43.8%.…”

Recent Progress and Novel Applications in Enzymatic Conversion of Carbon Dioxide

“…To overcome these problems, several modifications to the sol-gel technique were proposed to improve the stability of the biological activity [36][37][38][39][40]. The dehydrogenases encapsulated in the alginate-silicate composite showed high initial enzyme activity retention, and significantly improved stability during storage and reuse [36]. These enzymes can be also immobilized in flat-sheet polymeric membranes simultaneously or separately by simple pressure-driven filtration (i.e., by directing membrane fouling formation), without any addition of organic solvent [41].…”

“…To provide the possibility for practical application, a hybrid enzymatic/photocatalytic approach for efficient converting CO2 into methanol was recently proposed [35]. The proposed approach includes two processes: the enzymatic transformation of CO2 to However, this process still has several problems such as cosolvents and catalysts are in the sol-gel process due to low water solubility and reactivity of the silica precursor, and the alcohol liberated from hydrolysis, cosolvents, and catalysts are deleterious to bioactivity [36]. To overcome these problems, several modifications to the sol-gel technique were proposed to improve the stability of the biological activity [36][37][38][39][40].…”