Synergistic Mechanisms Underlying Microwave Plasma-Catalytic Degradation of Complex Odorous Mixtures: An In Situ Mass Spectrometry Diagnostic Analysis

Abstract

The fundamental challenge in degrading diverse odorous compounds lies in their low concentration and varied chemical reactivity, which complicates the elucidation of underlying degradation mechanisms. This study investigates the plasma-driven reaction pathways and synergistic effects in a microwave plasma-catalytic system, designed for the degradation of representative odorous compounds including oxygenated volatile organic compounds (OVOCs), benzene derivatives, and sulfur compounds. An end-face enhanced reactor design significantly improved plasma excitation efficiency and stability, enabling effective degradation (> 90%) at low power (50–80 W). Crucially, we report the first mechanistic study on the simultaneous degradation of mixed organic and inorganic sulfur compounds using microwave plasma catalysis. Real-time online monitoring of reaction intermediates and products was achieved via a custom low-pressure assisted microwave plasma time-of-flight mass spectrometry (LAMP-TOFMS) instrument. Target compounds included butanal, ethyl acetate, benzene, toluene, dimethyl sulfide, dimethyl disulfide, methanethiol, and carbon disulfide. The system demonstrated not only high degradation efficiency but also a pronounced control over by-product formation. The introduction of a catalyst was found to critically alter the reaction selectivity, suppressing the formation of undesirable oxygenates (e.g., formic acid) and nitrogen-containing intermediates (e.g., nitromethane), thereby promoting the complete mineralization pathway. This work provides fundamental insights into the plasma-catalytic reaction mechanisms governing the degradation of complex odorant mixtures, offering a novel molecular-level perspective on nonthermal plasma chemistry relevant to environmental remediation.