Thermocatalytic reactors are a proposed atmospheric methane removal technology that use heat to activate a catalyst that oxidizes methane. This takes place inside an engineered system with high airflow. One type of thermocatalyst, zeolites—porous, crystalline materials that can be doped with metal ions—are able to oxidize low concentrations of methane at moderate temperatures (2 ppm CH₄ at 300°C). Laboratory research is underway to improve the performance of these zeolites at lower temperatures and to structure them to be able to tolerate high airflows. Air must be moved through the localized reactor, either through active methods such as fans, or passive methods such as solar updraft chimneys that use convective heat transfer to move air.

For thermocatalytic reactors to be a feasible atmospheric methane removal approach there would have to be a dramatic decrease in operating temperature (from 300°C today to under 6°C), as well as extremely low energy, essentially free, airflow. The required airflow to achieve large-scale atmospheric methane removal would be tremendous, far beyond planned carbon dioxide direct air capture capacity in the next decade.

Using thermocatalytic reactors to remove atmospheric methane would require energy to heat the catalyst and to transport large volumes of air. Both are currently energy-intensive, and therefore costly and carbon-intensive. In order to work at low atmospheric concentrations, major improvements would be necessary. Either energy costs of air-handling and heat generation would have to come down by orders of magnitude, or passive sources of heat and airflow would have to be incorporated into the reactor design.

Forthcoming research estimates that thermocatalytic reactors operating above 300°C (as currently known approaches would) are climate detrimental for atmospheric methane removal due to the heating requirements alone, even when clean energy sources and highly efficient heat recovery systems are used. The energy cost of operating thermocatalytic reactors is expected to exceed the social cost of methane by orders of magnitude, likely making them cost-implausible. Achieving cost effectiveness of thermocatalytic flow reactors to remove atmospheric methane, if at all possible, would likely require catalyst innovation to bring down the required temperature to below 6°C, or using waste heat to heat the catalyst.

Cost and climate impacts are also driven by the energy requirements to move air through the reactor. This could be negligible for passive air flow, but must be considered for active methods. Energy costs of active air flow methods could be lowered by co-locating the system with existing air movement systems, such as cooling towers, heat exchangers, or direct air capture facilities.

The potential scale thermocatalytic converters could reach is limited by their energy requirements, high cost, and lack of net climate benefit. Given the low atmospheric concentration of methane, any flow through system would have to process massive amounts of air to oxidize 10 million metric tons of methane per year. For example, if you add methane oxidizing catalysts to every carbon dioxide direct air capture system that is supposed to be installed by 2030 (60 Mt CO₂/yr or around 5 billion cubic feet per minute), only around 0.1 Mt/yr of methane could be removed.

Even if thermocatalytic reactors are made feasible, it will be extremely challenging and resource intensive to reach meaningful scale, as the amount of methane addressed will be directly related to the number and scale of the reactors built. Thus an approach of this sort would be expected to take decades to scale after feasibility and cost-effectiveness were established.

Compared to the feasibility and scalability concerns outlined above, the side effects of thermocatalytic reactors are relatively minor.

Preliminary research suggests that apart from oxidizing methane or other gasses, thermocatalysis has minimal negative side effects. In a closed reactor system, byproducts could be measured in situ and potentially be selectively removed, reducing the uncertainty as to what gasses would be produced and emitted.