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Electrocatalytic Gas-Phase Conversion of CO2 in Confined Catalysts

Final Report Summary - ELCAT (Electrocatalytic Gas-Phase Conversion of CO2 in Confined Catalysts)

The objective of the ELCAT project was to investigate the feasibility of the electrocatalytic gas-phase conversion of CO2 to liquid fuels (hydrocarbons and alcohols) and more specifically, to investigate two alternative conceptual approaches to reach this objective. The first was based on the gas- phase conversion of CO2 by reaction of protons (diffusing through a proton membrane) and electrons with CO2 on metal nanoparticles located inside nanotubes in order to have a confinement of CO2. The second approach was based on the same type of electrocatalyst, but using oxygen anion (05) conducting membranes to continuously subtract oxygen from the reaction environment and therefore reduce directly CO2 with H2.

The objective of work package (WP) 1 ('Synthesis of material') was the synthesis and base characterisation of the samples to be tested in WP3 ('Reactivity'). The initial activity in WP1 was centred on the synthesis of multi-walled carbon nanotubes (MWNTs) and in particular the preparation of opened nanotubes with a tailored diameter and their functionalisation by (metal) deposition, the preparation of electro-catalysts constituted of copper, nickel and carbon nanofibres on yttrium stabilised zirconium (YSZ), and the preparation of electrocatalysts and assembly of the gas diffusion membrane electrode. A further objective was the analysis of the influence of different characteristics of the NTs on the metal deposition.

The objective of WP2 was the advanced characterisation of materials prepared in WP1 and the analysis of the nanostructure / performance relationship. Several advanced characterisation techniques, from high resolution microscopy to Raman and XPS were used.

The WP3 ('Electrocatalytic and reactivity test') was the core of the project. The original work programme was structured to investigate the two alternative conceptual approaches to convert CO2 described above. Accordingly, this WP had two main tasks, in agreement with the two lines of investigation. A first task was dedicated to the investigation of CO2 reduction using Hi conduction membranes. The second task was dedicated to the investigation of CO2 reduction using O2-conduction membranes. Initial, the focus was on the construction and assembling of the reactor apparatus, the exploratory investigation of NEMCA effect in relation to CO2 hydrogenation, and testing of different reactor configurations. Later, the objective was the analysis of the performances of different kinds of electrocatalysts using different kind of reactor configurations.

WP4 was dedicated to management and coordination.

The main results of the project can be summarised as follows:
- it is possible working in gas phase and using nanoconfined electrocatalysts to form long C-chain hydrocarbons and alcohols at room temperature and atmospheric pressure;
- it is not a FT-distribution, as originally hypothesised;
- limit is the desorption of the products; increasing temperature improve of 1-2 order magnitude productivity, but mainly liquid C3 alcohols are produced;
- use of carbon nanotubes based electrocatalysts instead of other nanostructured carbon-based electrocatalysts allow to maximise the formation of isopropanol from CO2 electrocatalytic reduction;
- working on bimetallic systems it is possible to improve stability which, however, still remains an issue;
- it is still necessary to integrate electrocatalyst with photo catalyst in photoelectrocatalytic (PEC) reactor to make possible to realise an effective conversion of CO2 to liquid fuel in 'artificial tree' systems, but the project made a first relevant step forward in this direction demonstrating that it is possible to convert CO2 to liquid fuels using the proposed approach.

Two are the main problems which should be overcome:
(i) find a more efficient way to improve desorption of the products of reaction from the electrocatalyst;
(ii) avoid transformation of the electrocatalyst during operations.
Progresses have been made during the project, although further studies are necessary.

The project attracted a large public interest, for the need to find innovative solutions to the issue of CO2. In fact, the knowledge-based approach used in the project resulted in a series of advances also for other type of applications. There is a large potential industrial interest on using CO2 as raw material.

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