Leveraging Oxygen Mobility with Zirconia in Low-Temperature Plasma for Enhanced Methane Reforming to Syngas

Abstract

Despite extensive efforts to optimize the single-step production of syngas, hydrocarbons, and oxygenates via plasma catalysis, several challenges remain unresolved. In particular, understanding the various reaction pathways is hindered by the complexity of the reactions and the diverse range of chemical products formed. In this study, we hypothesize that materials capable of mobilizing oxygen could mitigate carbon deposition (coking) and that interaction with atomic oxygen favour syngas production. Our main objective was to evaluate and compare the influence of zirconia on reaction pathways, methane (CH4) and carbon dioxide (CO2) conversions (%), and syngas selectivity (%) relative to the plasma-only route. Experiments were conducted at low Radio-frequency plasma power of 50 Watts without external heating. The results demonstrated significantly enhanced conversions of carbon dioxide and methane when the reaction chamber was packed with zirconia (ZrO2). Methane conversion was observed highest at rich CO2 feed [CO2:CH4 (2:1)], while plasma only revealed conversion of 20.1 % but after packing zirconia the conversion led to 71.2% (3.5 folds increment). On the other hand, carbon dioxide conversions were also observed highest at feed composition of CO2:CH4 (2:1), with plasma only (13.6%) vs. zirconia packed (60.9%) revealing 4.4 folds increase. Interestingly, at the rich CO2 feed composition, the syngas product (CO+ H2) selectivity increased after packing ZrO2 by 1.1 folds for CO and 1.2 folds for H2. Optical emission spectroscopy (OES) analysis revealed an important insight, with signatures of atomic oxygen (O) were the dominant plasma species in the gas phase under plasma-only conditions, while their intensities plummeted when zirconia was introduced, indicating active oxygen diffusion onto the surface of zirconia. These findings provided an integral perspective into the design of catalytic materials that enhance oxygen mobility, enabling low-temperature and energy-efficient dry methane reforming for sustainable future.