Catalytic Hybrid Electrocatalytic/Biocatalytic Cascades for Carbon Dioxide Reduction and Valorization

Abstract

Carbon dioxide, as a greenhouse gas, has a critical impact on global climate change. Hence, reducing its emissions and/or transforming it into value-added chemicals is of paramount importance to society. Such a goal can be achieved through the development of electrochemical catalytic processes, which showed initial successes in synthesizing CO and cosynthesis of H 2 (syngas) from CO 2 . However, to further advance the technology toward more complex hydrocarbons (possibly fuels) and more complex organic molecules to be used in industrial chemical synthesis of rubber/resins and plastics or even fine chemical synthesis of pharmaceuticals, catalytic structures have to be designed beyond simple materials. One approach consists of executing the required steps linking CO and small alcohols and the desired products through chemical reactions catalyzed by enzymes or microorganisms, hence combining them with the electrocatalysts used for the initial steps of the CO 2 reduction. Here, we discuss the electrocatalysts, enzymes, and bacteria to be used for those cascade reactions. Inorganic catalysts can be directly utilized for initial steps of CO 2 reduction resulting in formate, carbon monoxide, and methanol, which then can be further reduced by employing enzymatic catalysts such as carbonic anhydrase and formate dehydrogenase, formaldehyde dehydrogenase, and alcohol dehydrogenase. Formate, carbon monoxide, and methanol can also be converted to acetyl-CoA and pyruvate, which are critical intermediates in the production of various chemicals of critical importance. Furthermore, if a chemolithoautotrophic bacteria is employed, the former can be used as a feedstock for biomass. A special emphasis is here given to the compatibility of the different classes of electrocatalysts used in the cascade: heterogeneous electrocatalysts (metals and metal oxides/carbides/nitrites, atomically dispersed transition metal−nitrogen-carbon, etc.), enzymatic catalysts (individually purified enzymes or multienzymatic complexes), bacterial cells (pure or mixed cultures of different classes, planktonic, or biofilm-forming), and their integration in singular bed reactors or multireactors units required for the formation of the products of interest. The electrocatalysts and related cascade reaction pathways are summarized in a descriptive "connectivity map" identifying the most important reaction pathways.

Catalysis for e-Chemistry: Need and Gaps for a Future De-Fossilized Chemical Production, with Focus on the Role of Complex (Direct) Syntheses by Electrocatalysis

“…On the contrary, hybrid electrocatalytic/biocatalytic systems have been more systematically explored. 123 − 125 …”

“…On the contrary, hybrid electrocatalytic/biocatalytic systems have been more systematically explored. [123][124][125] Figure 3 reports a framework scheme of the possibilities derived by developing hybrid electroand biosynthetic catalytic pathways in CO2 conversion. The range of possibilities offered from this symbiosis is evident, further enhanced by considering that enzymes for converting other small molecules (N2, H2O and CH4) are also known.…”

Advances in Palladium-Catalyzed Carboxylation Reactions

“…In fact, it allows converting an important waste (it is well known that carbon dioxide is produced in enormous amounts from the combustion of fossil fuels for the production of energy) into a variety of useful compounds, which can find application as fuels or in the pharmaceutical or material fields. Accordingly, many efforts have been devoted by the scientific community to develop novel efficient and sustainable carboxylation methods, in particular under catalytic conditions, during the last years [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ].…”

Engineering Formaldehyde Dehydrogenase from Pseudomonas putida to Favor Nicotinamide Cytosine Dinucleotide

“…[9] On the other hand, FalDH is essential to construct biocatalytic systems for the conversion of CO 2 into methanol. [10] To expand the capacity for regulation of redox metabolism, efforts have been paid to create redox enzymes depending on non-natural cofactors. [11] In particular, nicotinamide cytosine dinucleotide (NCD, Scheme 1) has been emerged as an effective non-natural cofactor for biocatalysis.…”

“…On one hand, FalDH plays vital roles to develop cell factories to use methanol as carbon source [8] or electron donor [9] . On the other hand, FalDH is essential to construct biocatalytic systems for the conversion of CO 2 into methanol [10] …”