Synergistic non-thermal plasma-catalytic reforming of toluene over hierarchical Ni/mHZSM-5 catalysts for efficient syngas production

Abstract

Biomass tar reforming is generally constrained by the high energy demand of conventional thermal processes because of the chemical stability of aromatic compounds. In this work, dielectric barrier discharge plasma was coupled with hierarchical Ni/mHZSM-5 catalysts for the steam reforming of toluene as a representative biomass tar compound. The effects of Ni loading, reaction temperature, and discharge power on toluene conversion, syngas formation, carbon recovery, and energy efficiency were systematically investigated. Among the catalysts, 15 wt% Ni/mHZSM-5 exhibited the best performance because of its favorable Ni dispersion, high proportion of surface chemisorbed oxygen, enhanced reducibility, and balanced acidity distribution. Among the operating conditions investigated, the best overall reforming performance was obtained at 75 W and 525 °C, achieving a toluene conversion of 99.2%, an H 2 yield of 48.3%, a CO selectivity of 36.0%, and a gaseous carbon balance of 60.1%. In comparison, conventional catalytic reforming required substantially higher temperatures to achieve lower conversion and syngas production, demonstrating the promotional effect of plasma excitation on aromatic activation and subsequent surface reforming. The highest toluene conversion energy efficiency of 6.5 g·kWh −1 was obtained at 30 W, indicating a trade-off between conversion performance and energy input. The catalyst also maintained high activity during a 48 h stability test, although gradual deactivation occurred because of carbon deposition. Identification of reactive species and by-products suggests the involvement of plasma-generated species in toluene and steam transformation, while Ni-containing sites may contribute to the subsequent conversion of intermediates toward H 2 and CO. These results demonstrate that hierarchical Ni/mHZSM-5 is a promising catalyst for energy-efficient plasma-assisted biomass tar upgrading.