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

Caterina G.C Marques Netto,Leandro H Andrade,Henrique E Toma

doi:10.1590/0001-3765201720170330

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.

Highlights

CARBON DIOXIDE-METHANOL CYCLEBiological evolution required the use of carbon dioxide as a carbon source to construct important natural building blocks, compelling the employment of natural catalysts, the enzymes (Emsley 2011, Smith and Morowitz 2016)
In this review article we focused on enzymatic immobilization to perform the conversion of carbon dioxide to methanol by using a sequential reduction catalysis involving formate dehydrogenase (FDH), formaldehyde dehydrogenase (FalDH) and alcohol dehydrogenase (ADH) enzymes immobilized on magnetic nanoparticles, and glutamate dehydrogenase (GDH) as the enzyme responsible for accomplishing the NAD+/NADH cycle
As a matter of fact, in our system, if only FDH, FalDH and ADH were taken into consideration, the FDH reaction would be the rate determining step, since as soon as formic acid was formed, formaldehyde and methanol were produced (Figure 5b)

Summary

Introduction

CARBON DIOXIDE-METHANOL CYCLEBiological evolution required the use of carbon dioxide as a carbon source to construct important natural building blocks, compelling the employment of natural catalysts,- the enzymes (Emsley 2011, Smith and Morowitz 2016). In this review article we focused on enzymatic immobilization to perform the conversion of carbon dioxide to methanol by using a sequential reduction catalysis involving FDH, FalDH and ADH enzymes immobilized on magnetic nanoparticles, and GDH as the enzyme responsible for accomplishing the NAD+/NADH cycle. The systems have been evaluated in terms of activity/stability for each support, in comparison with the free enzyme, by applying an external magnetic field, either to analyze the solution content or to remove the product and add new reactants in a recycle study.

Results

Conclusion