Efficient catalytic degradation of VOCs using Mn-based hydrotalcite-like compounds coupled with non-thermal plasma

Aiming to discover a novel catalyst that exhibits a high synergistic effect with plasma technology for the degradation of volatile organic compounds (VOCs), we employed manganese-based layered double hydroxides (LDHs), which are referred to as MMn-LDHs (M=Ni, Co, Fe). Comprehensive physicochemical characterization via catalyst characterization techniques such as XRD, SEM, XPS, BET, confirmed the successful synthesis of the catalysts. These analyses revealed excellent crystallinity, distinctive lamellar structure, and remarkable thermal stability for three synthesized catalysts. The experimental results demonstrate that post non-thermal plasma (post-NTP) catalytic system has significantly improved the degradation efficiency, CO2 selectivity, and carbon balance for toluene, while notably suppressing the formation of by-products (e.g., NOx and O3) compared to the NTP alone system. Among the three MMn-LDHs, NiMn-LDHs exhibited the best performance in the post-NTP-catalytic system, achieving a toluene degradation rate of 95.87%, a CO2 selectivity of 57.41%, a carbon balance of 79.86%, and an energy efficiency of 3.19 g·kWh−1 at a specific energy density (SED) of 930.45 J/L. The catalytic degradation mechanism of toluene was proposed based on a combination of catalyst characterization techniques, plasma emission spectroscopy, and gas chromatography-mass spectrometry (GC-MS). The findings revealed that plasma discharge generated a substantial amount of free radicals and active species, thereby promoting the decomposition of toluene. Subsequently, the residual toluene and intermediate products were adsorbed onto the catalysts, where they underwent further reacted with the abundant hydroxyl radicals and activate metal species on the catalyst surface, ultimately decomposing into CO2 and H2O. Additionally, the interaction of ozone with LDHs facilitated the generation of reactive oxygen species, consequently accelerating the decomposition of organic intermediates, formation of CO2, and the enhancement of toluene mineralization. The finding in this work offer valuable theoretical support for the plasma-catalytic degradation of VOCs.