Key Takeaways & Executive Findings
- •• • Mixed thiol systems (e.g., CH3SH + C2H5SH) exhibit faster catalyst deactivation than single-component systems, with stability differences attributed to 'molecular size–active site matching' and site competition, as demonstrated by La/ZSM-5 maintaining 100% activity for 30 h at 450 °C in mixed thiol streams. • • Catalytic oxidation/decomposition can achieve >95% degradation of S-VOCs at low temperatures (25–450 °C) with high space velocities (up to 1,800,000 mL·h−1·g−1), but stability varies: Co@NCNT retained 95.6% activity after 1 h and declined slightly over 60 h, while Fe2-N-C showed 79.6% activity at room temperature with slight decline over 200 h at 60% RH. • • Catalyst design strategies such as single-atom Fe-N4/CMK-3 achieve 90% CH3SH conversion at 25 °C but drop to 80% after 8 h, highlighting the trade-off between low-temperature activity and sulfur poisoning resistance. • • The review emphasizes that industrial S-VOC emissions are multi-component, and ignoring synergistic effects leads to inaccurate predictions; future models must incorporate temperature, humidity, and concentration variables to guide rational design of sulfur-resistant catalysts.
Abstract
The efficient treatment of sulfur-containing volatile organic compounds (S-VOCs) has become a critical task for air pollution control and green low-carbon transition under China's 14th Five-Year Plan. Industrial emissions often contain multiple S-VOC species, whose interactions can complicate degradation pathways, generate uncontrollable byproducts, and deactivate catalysts, limiting practical application. This review systematically summarizes the past decade of research on catalytic degradation of thiols and thioethers in multi-pollutant systems, focusing on competitive adsorption mechanisms, interfacial reaction pathways, and environmental factor regulation. Performance differences and reaction mechanisms across various catalyst systems under coexisting S-VOCs and inorganic sulfur are compared. Key findings indicate that mixed thiol systems exhibit faster deactivation than single-component systems due to temperature-dependent competitive adsorption and pathway switching, governed by molecular size–active site matching. Strategies such as metal–support strong interactions, zeolite confinement, nanocluster effects, and single-atom catalysts have improved activity and stability. However, dynamic competition mechanisms at active sites remain unresolved. Future research should develop atomic/molecular-level characterization techniques and multi-variable kinetic models, and shift from end-of-pipe purification to resource recovery, e.g., converting H2S and thiols into high-value chemicals like methanethiol, achieving dual goals of pollution control and sulfur resource recycling.
1. Introduction
Industrial off-gas streams from coal clean utilization, coke oven gas, petroleum refining, and chemical/pharmaceutical sectors rarely contain a single sulfur-containing volatile organic compound (S-VOC). Instead, thiols (e.g., methanethiol, ethanethiol) and thioethers (e.g., dimethyl sulfide) coexist with inorganic sulfur species such as H2S, at concentrations ranging from mg·m−3 to g·m−3. Conventional catalytic oxidation and decomposition technologies, while effective for single-component S-VOCs at 200–400 °C, suffer from severe performance degradation when exposed to multi-component mixtures. The strong adsorption of sulfur molecules onto active sites induces irreversible sulfation, shortening catalyst lifespan and causing uncontrolled byproduct formation. This mismatch between laboratory studies and real-world complexity has stalled the deployment of robust catalytic solutions for S-VOC abatement.
This review addresses the bottleneck by systematically analyzing the competitive adsorption and synergistic conversion mechanisms in binary S-VOC systems. It synthesizes recent progress on catalyst systems—including metal oxides, zeolites, and single-atom catalysts—that have been engineered to resist sulfur poisoning and steer reaction pathways toward valuable products like H2S and CH4. By identifying the molecular descriptors that govern site competition and pathway switching, this work provides a rational basis for designing catalysts that maintain high activity and stability under realistic multi-pollutant conditions, ultimately advancing the transition from end-of-pipe treatment to sulfur resource recovery.
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FENG Yu, FANG Jian, XU Zhizhi, LAI Junyu, LU Jichang, LUO Yongming (2026). Catalytic Conversion Behavior and Degradation Mechanisms of Sulfur-Containing Multi-Pollutants such as Thiols and Thioethers: A Review. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202510044
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Frequently Asked Questions
What are the primary deactivation mechanisms when multiple S-VOCs coexist, and how do they differ from single-component feeds?
In mixed thiol systems, deactivation is accelerated due to competitive adsorption on active sites, where larger molecules block access to smaller ones, and temperature-dependent pathway switching leads to deposition of sulfur or carbonaceous species. For example, La/ZSM-5 maintained 100% activity for 30 h at 450 °C in a mixed CH3SH/C2H5SH stream, but without such site matching, rapid deactivation occurs.
Can catalytic oxidation achieve both high activity and long-term stability at near-ambient temperatures?
Near-ambient operation is possible with advanced catalysts like Fe2-N-C, which achieved 79.6% CH3SH conversion at room temperature and 60% RH, with only slight decline over 200 h. However, stability is compromised at higher conversions or in the presence of moisture; for instance, Fe-N4/CMK-3 dropped from 90% to 80% after 8 h at 25 °C.
What are the key performance indicators for evaluating catalysts in multi-pollutant S-VOC degradation?
Key metrics include conversion efficiency (e.g., >95% for Co@NCNT), stability over time (e.g., 60 h with slight decline), operating temperature window (25–450 °C), space velocity (up to 1,800,000 mL·h−1·g−1), and selectivity to valuable products like H2S or CH4. Resistance to sulfur poisoning is quantified by the duration of sustained activity.
How does the 'molecular size–active site matching' concept guide catalyst design?
This concept implies that catalysts should have pore sizes and active site geometries that accommodate the largest S-VOC molecules in the mixture to prevent blockage. For example, zeolites with tuned pore structures (e.g., ZSM-5) can selectively adsorb and convert thiols of varying chain lengths, as demonstrated by La/ZSM-5's 30-h stability in mixed thiol streams.
What are the scalability challenges for translating these catalytic systems from laboratory to industrial applications?
Scalability issues include maintaining uniform catalyst dispersion at large scales, managing exothermic reactions to avoid hot spots, and ensuring long-term stability under fluctuating feed compositions and flow rates. The review notes that current studies often use idealized conditions; industrial streams may contain particulates and other poisons, necessitating robust reactor designs and catalyst regeneration strategies.
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