In spite of the growth of various renewable energy sources in the last few decades, carbon-rich fossil fuels continue to be the most dominant source of energy globally. This situation coupled with the ever-increasing global energy requirements has led to an alarming increase in the atmospheric levels of CO₂, which is a major greenhouse gas. Three main solutions to this perennial challenge include: (i) reduction in the amount of CO₂ produced by a paradigm shift from fossil fuels to renewable energies, (ii) CO₂ capture at its source followed by sequestration in the geological subsurface (iii) conversion of CO₂ into fuels and chemicals such as methane, methanol, ethanol or dimethyl ether. So far, CO₂ methanation (reaction between CO₂ and H₂ producing CH₄) has been unanimously agreed upon as a major pathway of CO₂ recycling/valorisation. For the first time we studied Fe impregnated Ce_xZr_1-xO₂ supports for CO₂ methanation at 300, 400 and 500degC under pressures 1 bar to 30 bars using a H₂/CO₂ (4:1 v/v) mixture. The highest CH₄ yield was 25% with 10%Fe-Ce_0.1Zr_0.9O₂ at 500degC and 30 bar. This composition was also found to be highly stable over a continuous testing period of 100 h at 500degC and 20 bars. In-situ DRIFTS studies indicated the possibility of a formate-assisted pathway of CH₄ formation on Fe-Ce_xZr_1-xO₂. In the next phase, 10%Fe-Ce_0.1Zr_0.9O₂was loaded on 3D-printed metal monoliths and investigated between 300 to 500degC under 1 bar and 20 bar pressure. Methane selectivity of 95.2% was obtained at 400degC and 20 bars pressure. This is the highest methane selectivity recorded in the literature for CO₂ methanation using an iron catalyst. The catalyst loaded monoliths were stable over a continuous operation of 100 h at 500degC and 20 bar. Such increased methane selectivity and yield combined with a long duration stability as well as cheaper and easier synthesis process vouches for the great potential of catalyst loaded 3D monoliths for industrial application.

Sankar Bhattacharya

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