Integrating Materials in Non-Thermal Plasma Reactors: Challenges and Opportunities

Abstract

Electricity-driven chemical processes play a crucial role in mitigating the CO₂ footprint of the process industry. Non-thermal plasmas (NTP) hold significant potential for electrifying the chemical industry by activating molecules through electron-based mechanisms in the absence of thermal equilibrium. However, the broad application of NTPs is hampered by their general inability to direct energy toward a specific chemical pathway, limiting their effectiveness as a selective and scalable technology. Therefore, the integration of NTPs with catalytic materials in a single reactor assembly is being considered more and more to overcome this limitation. Recently, two multifunctional plasma concepts have emerged, demonstrated at small scales. The first concept is in-plasma catalysis (IPC), where a solid catalyst is directly exposed to the plasma discharge. The second concept is post-plasma catalysis (PPC), involving a conventional heterogeneous catalytic step following the plasma activation. Another option explores the combination of non-catalytic materials with plasma, leveraging their distinct physiochemical affinities with molecules for improved selectivity (e.g., membranes and adsorbents), through either in-plasma or post-plasma adoption. Despite these possibilities, the limited understanding of interactions between plasma and surface-adsorbed/permeated species, coupled with discharge-related catalysts and material deactivation, often restricts the design choice to post-plasma catalysis. To harness synergies, energy-efficient NTP technologies are essential. In this context, nanosecond-pulsed discharges (NPDs, also known as nanosecond repetitively pulsed, NRP) emerge as potentially disruptive solutions due to their activation of both electronic and thermal channels. This results in high energy efficiency, facilitating applications such as cleavage of C–C, C–O, and N–N bonds and providing sufficiently high temperatures for thermal integration with post-plasma materials. This integration can be tailored to the NPD product distribution, creating a synergy with conventional materials unique to NTPs and enhancing the overall process throughput.

While promising, further advancements in materials science are necessary to maximize the interplay between high-energy bond breakage in plasma and the selectivity enhancement of integrated materials. Our research group has dedicated extensive efforts to the development of multifunctional two-step plasma reactors, with a particular focus on NPD. This has led to remarkable energy efficiency in non-oxidative coupling of methane (NOCM) and CO₂ splitting. Key applications involved a 3D-printed triply periodic minimal surface (TPMS) copper support with a Pd/Al₂O₃ catalytic layer and a looping process with a CeO₂/Fe₂O₃ nanostructured scavenger. The potential of such reactors is vast, given the various applications for which conversion and selectivity currently pose limitations. As current designs are mostly heuristic and the literature on the topic is limited, our ultimate goal is to establish a systematic in silico design and optimization procedure for both the geometrical and chemical features of plasma-coupled materials, with special focus on post-plasma NPD applications.