Anaerobic bacteria named as acetogens have been shown to ferment gases such as CO and CO₂ plus H₂ into chemicals (acetate, ethanol, lactate, 2,3-BDO, etc.) through the acetyl-CoA pathway. Depending on the composition of the C1 gases and particularly depending of the CO content of syngas, some bacteria can be more efficient to produce acetate. In this context, metabolic engineering and synthetic biology are powerful tools to increase the acetate production and reduce the spectrum of unwanted by-products.
CO2SMOS proposes two routes to optimize the productivity of the CO₂ to C2-C4 compounds:

• Tech 1.1: Biotransformation of CO₂ into acetate
• Tech 1.2: Biotransformation of CO₂ derived syngas into C2 (acetate) and C4 (2,3 BDO) compounds

The electrochemical conversion of CO₂ to syngas must compete with syngas from fossil sources, which is yet abundant and can be converted using highly optimised industrial processes. Thus, it is critical to achieve high efficiencies in the electrochemical route. CO2SMOS proposes:

• Tech 2.1: Electrocatalytic reactor for direct syngas production from CO₂ and H₂O
• Tech 2.2: PCEC for simultaneous polyols oxidation and CO₂/H₂O conversion into syngas and HCAs

The proposed technology based on heterogeneous and reusable organic catalysts will lead to 100% bio-based cyclic carbonates, serving as potential building blocks in the synthesis of bio-based polycarbonates. Potentially, CO₂ can be used as an interesting bio-based building block in preparing aliphatic polycarbonates, which has good biodegradability and biocompatibility, with low carbon footprints. CO2SMOS will combine different bio-based epoxides derived from terpenes or fatty acid esters coming from biomass with metals to provide heterogeneous catalysts with different structures, tuned functionalities and pore diameters. These developed reusable organic catalysts will be tested in the thermocatalytic conversion using CO₂ as reagent, leading to the synthesis of new bio-polymers.

The CO₂-derived bio-acetate produced in the first stage (Tech1) can be used as carbon source by many microorganisms and compete with traditional carbon sources (glucose, sucrose, starch) for industrial fermentations. CO2SMOS proposes the use of CO₂-derived acetate as a key-starting material to be transformed in a second stage by means of aerobic liquid-phase fermentations into high added-value chemicals. Further assistance by synthetic biology tools will enable increasing the efficiency of acetate transformation by modifying wild type strains. Mcl-PHA and PHB will be produced by genetically engineered P. putida and C. necator, respectively. LcDCAs will be generated by recombinant Y. lipolytica and 2,3-BDO will be produced by recombinant E. coli. After completing each of the different fermentation processes, it will be necessary to carry out the DSP to obtain high purity added-value chemicals for further transformation.

Direct conversion of syngas to BTEX and PX will be conducted in a CMR combining catalytic conversion of syngas to BTEX with a ceramic membrane-based separation. The reaction will take place in presence of a tandem catalyst combining metallic oxides to produce specific intermediates from syngas with a zeolite to in-situ transform, via acid catalysis, the intermediates into aromatics. Over the metallic sites, CO and H₂ will form methoxy intermediates that diffuse to the acid sites within the pores of the zeolite. Inside this pore system, these intermediates will first form olefins. The zeolite composition, topology and surface chemistry will be adjusted to drive the product distribution towards the aimed aromatics, while minimising undesired methanation and coking. As a result of the CO reduction, lots of water will form in the reactor. By means of a SEOS, the formed water will split into H₂ and oxide ions (O^2-), and the latter will be extracted. Extraction of O^2- will have a double effect: (i) the subtraction of a reaction product shifts the equilibrium favouring the formation of more product, and (ii) the H₂ formed by water deoxygenation is a reaction substrate, that will push the reduction of CO. The SEOS will be a dense ceramic solid-oxide electrolyte able to pump oxide ions from one side to the other when a current is applied. The inner surface of the electrolyte will promote water splitting and avoid coking or methanation, providing protection against reduction.