Plasma – Catalyst Synergy Unlocked to Reduce Methane Emissions

As part of the CANMILK project, a collaborative research visit by VTT to Maastricht University has produced promising results by successfully combining microwave (MW) plasma with catalytic materials to achieve complete oxidation of methane.

Between August 4 and 23, 2025, Abhinash Kumar Singh (VTT) partnered with Stijn Helsloot (Maastricht University) to integrate palladium-based monolith catalysts, prepared and provided by Vladimir Demidyuk (Johnson Matthey), into a MW plasma reactor. The primary objective was to demonstrate plasma – catalyst synergy for efficient conversion of methane into carbon dioxide (CO2).

Challenges in plasma – catalyst integration

The integration of catalysts with MW plasma has been constrained by two major challenges. First, the plasma and afterglow regions reach extremely high temperatures, often exceeding 1000 K during start-up. At such conditions, catalysts are prone to rapid deactivation and degradation, making it unsuitable to place them too close to the discharge. Second, for true plasma – catalyst synergy, the reactive species generated in the plasma are to interact with the catalyst surface. These species are highly reactive but short – lived due to quick recombination into stable molecules. Therefore, the catalyst may not be placed too far downstream else the reactive species will not reach the catalyst. As a result, the plasma is only used as a heat source that drives further thermal catalysis downstream, limiting true plasma – catalyst synergy. Therefore, careful placement of the catalyst is essential to maintain its activity while enabling efficient interaction with plasma – generated species.

Key findings

  • Methane conversion was primarily driven by MW plasma. Above 99% methane conversion was achieved above 700 W.
  • The main products were carbon monoxide (CO) and CO2. The CO2 selectivity increased with increase in plasma power.
  • Catalyst placement played a significant role: when placed closer to the downstream region and plasma zone, the CO2 selectivity increased immediately to above 87%, whereas more distant placement did not demonstrate plasma – catalyst synergy (Figure 1).
  • The Pd/Al2O3 monolith catalyst enhanced methane conversion slightly only, however, the catalyst was able to enhance CO2 selectivity significantly (Figure 1). The key role of Pd/Al2O3 monolith catalyst was the oxidation of CO into CO2 demonstrating plasma – catalyst synergy.
  • Overall, plasma drives conversion, while the catalyst primarily enhanced product selectivity.

Potential applications

This study demonstrates the potential for MW plasma and catalysts to operate synergistically, paving the way for more effective methane abatement technologies. Future optimization of palladium loading, catalyst configuration, and catalyst placement may further improve efficiency and selectivity. These findings form part of the CANMILK project and contribute to the development of a proof-of-concept unit designed to explore scalable solutions for reducing methane emissions coming from dairy barn and cattle farms.

Figure 1. Effect of plasma power and different monolith catalysts on (a) Methane conversion (b) CO2 selectivity and (c) Temperature of the catalyst/monolith bed.
Figure 2. The position of catalyst where catalyst – plasma synergy was observed.