Unraveling the Synergistic Reaction and the Deactivation Mechanism for the Catalytic Degradation of Double Components of Sulfur-Containing VOCs over ZSM-5-Based Materials

Management of methyl mercaptan contained in waste gases - an overview

Methyl mercaptan is a typical volatile organosulfur pollutant contained in many gases emitted by urban waste treatment, various industries, natural gas handling, refining processes, and energy production. This work is a comprehensive overview of the scientific and practical aspects related to the management of methyl mercaptan pollution. The main techniques, including absorption, adsorption, oxidation, and biological treatments, are examined in detail. For each method, its capability as well as the technical advantages and drawbacks have been highlighted. The emerging methods developed for the removal of methyl mercaptan from natural gas are also reviewed. These methods are based on the catalytic conversion of CH3SH to hydrocarbons and H2S.

Efficient Catalytic Elimination of Toxic Volatile Organic Compounds via Advanced Oxidation Process Wet Scrubbing with Bifunctional Cobalt Sulfide/Activated Carbon Catalysts

Advanced oxidation process (AOP) wet scrubber is a powerful and clean technology for organic pollutant treatment but still presents great challenges in removing the highly toxic and hydrophobic volatile organic compounds (VOCs). Herein, we elaborately designed a bifunctional cobalt sulfide (CoS2)/activated carbon (AC) catalyst to activate peroxymonosulfate (PMS) for efficient toxic VOC removal in an AOP wet scrubber. By combining the excellent VOC adsorption capacity of AC with the highly efficient PMS activation activity of CoS2, CoS2/AC can rapidly capture VOCs from the gas phase to proceed with the SO4•- and HO• radical-induced oxidation reaction. More than 90% of aromatic VOCs were removed over a wide pH range (3-11) with low Co ion leaching (0.19 mg/L). The electron-rich sulfur vacancies and low-valence Co species were the main active sites for PMS activation. SO4•- was mainly responsible for the initial oxidation of VOCs, while HO• and O2 acted in the subsequent ring-opening and mineralization processes of intermediates. No gaseous intermediates from VOC oxidation were detected, and the highly toxic liquid intermediates like benzene were also greatly decreased, thus effectively reducing the health toxicity associated with byproduct emissions. This work provided a comprehensive understanding of the deep oxidation of VOCs via AOP wet scrubber, significantly accelerating its application in environmental remediation.

Portable hydrogel kit driven by bimetallic carbon dots nanozyme for H2O2-self-supplying dual-modal monitoring of atmospheric CH3SH

Due to the typical volatility of gaseous pollutant methyl mercaptan (CH3SH), the development of a facile, reliable, and accurate onsite environmental surveillance of highly toxic CH3SH faces many challenges, but it is critical to environmental atmosphere assessment and safeguarding public health. Here, we prepared a novel bimetallic carbon dots (Fe&Cu@CDs) nanozyme with high peroxidase-mimicking activity to design a portable hydrogel kit for onsite visual H2O2-self-supplying enzymatic cascade catalytic colorimetric and photothermal signal synergistic amplification dual-modal monitoring of CH3SH in atmospheric environment. Assisted by alcohol oxidase (AOX), CH3SH could be specifically converted into H2O2 for oxidizing chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by Fe&Cu@CDs to produce dark blue ox-TMB with absorption at 652 nm and photothermal characters. Consequently, a CH3SH concentration-dependent change both in naked-eye color and photothermal effect-triggered temperature were observed. By hybridizing AOX-assisted Fe&Cu@CDs + TMB with agarose, a H2O2-self-supplying colorimetric and photothermal signal synergistic amplification sensory hydrogel kit integrated with Color Picker APP-installed smartphone and 660 nm laser-equipped handheld thermal imager for CH3SH was proposed with acceptable results in atmospheric environment around wastepile (e.g., solid waste and food waste piles), which exhibited great potentials to further develop commercial onsite monitoring platforms in warning-early abnormal atmospheric CH3SH for safeguarding environmental health.

Mechanism Study of Organic Sulfur Hydrogenation over Pt- and Pd-Loaded Alumina-Based Catalysts

The hydrogenation of organic sulfur (CS2) present in industrial off-gases to produce sulfur-free hydrocarbons and H2S can be achieved by using noble-metal catalysts. However, there has been a lack of comprehensive investigation into the underlying reaction mechanisms associated with this process. In this study, we have conducted an in-depth examination of the activity and selectivity of Pt- and Pd-loaded alumina-based catalysts, revealing significant disparities between them. Notably, Pd/Al2O3 catalysts exhibit an enhanced performance at low temperatures. Furthermore, we have observed that CS2 displays a higher propensity for conversion to methane when employing Pt/Al2O3 catalysts, while Pd/Al2O3 catalysts demonstrate a greater tendency for coke deposition. By combining experimental observations with theoretical calculations, we revealed that the capability of H2 spillover along with the adsorption capacity of CS2, play pivotal roles in determining the observed differences. Moreover, the key intermediate species involved in the methanation and coke pathways were identified. The intermediate CH2S* is found to be crucial in the methanation pathway, while the intermediate CSH* is identified as significant in the coke pathway.

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M - C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Alkali metal doped crystalline g-C3N4 with an enriched cyano group for visible-light photocatalytic degradation of methylamine

In this study, alkali-metal-doped crystalline g-C3N4 with an enriched cyano group was synthesized using the molten salt method and used for the visible-light photocatalytic degradation of methylamine (MA), a common organic amine compound with a low odor threshold. Different types and proportions of melting salts (Li, K, and Na) were added during secondary calcination to regulate the morphology, crystallinity, and surface defects of graphitic carbon nitride (g-C3N4). With molten salt treatment matched the melting point of the binary salt system, a cyano group and alkali metal co-doped crystalline g-C3N4 with a high surface area and good crystallinity were prepared. Co-decorating the alkali metal and cyano groups on crystalline g-C3N4 facilitated the adsorption of MA, realized an excellent photo-charge transfer efficiency, and generated more superoxide radicals. Compared with pristine g-C3N4 (PCN), the apparent rate constant of LiK15 : 5-CCN for the degradation of MA increased by 10.2 times and the degradation efficiency of 1000 ppm MA gas was 93.1% after 90 min of irradiation with visible light, whereas the degradation efficiency of PCN was 19.2%.

Influence of Carbonization Conditions on Structural and Surface Properties of K-Doped Mo2C Catalysts for the Synthesis of Methyl Mercaptan from CO/H2/H2S

The cooperative transition of sulfur-containing pollutants of H2S/CO/H2 to the high-value chemical methyl mercaptan (CH3SH) is catalyzed by Mo-based catalysts and has good application prospects. Herein, a series of Al2O3-supported molybdenum carbide catalysts with K doping (denoted herein as K-Mo2C/Al2O3) are fabricated by the impregnation method, with the carbonization process occurring under different atmospheres and different temperatures between 400 and 600 °C. The CH4-K-Mo2C/Al2O3 catalyst carbonized by CH4/H2 at 500 °C displays unprecedented performance in the synthesis of CH3SH from CO/H2S/H2, with 66.1% selectivity and a 0.2990 g·gcat-1·h-1 formation rate of CH3SH at 325 °C. H2 temperature-programmed reduction, temperature-programmed desorption, X-ray diffraction and Raman and BET analyses reveal that the CH4-K-Mo2C/Al2O3 catalyst contains more Mo coordinatively unsaturated surface sites that are responsible for promoting the adsorption of reactants and the desorption of intermediate products, thereby improving the selectivity towards and production of CH3SH. This study systematically investigates the effects of catalyst carbonization and passivation conditions on catalyst activity, conclusively demonstrating that Mo2C-based catalyst systems can be highly selective for producing CH3SH from CO/H2S/H2.

Accelerated Catalytic Ozonation in a Mesoporous Carbon-Supported Atomic Fe-N4 Sites Nanoreactor: Confinement Effect and Resistance to Poisoning

The design of a micro-/nanoreactor is of great significance for catalytic ozonation, which can achieve effective mass transfer and expose powerful reaction species. Herein, the mesoporous carbon with atomic Fe-N4 sites embedded in the ordered carbon nanochannels (Fe-N4/CMK-3) was synthesized by the hard-template method. Fe-N4/CMK-3 can be employed as nanoreactors with preferred electronic and geometric catalytic microenvironments for the internal catalytic ozonation of CH3SH. During the CH3SH oxidation process, the mass transfer coefficient of the Fe-N4/CMK-3 confined system with sufficient O3 transfer featured a level of at least 1.87 × 10-5, which is 34.6 times that of the Fe-N4/C-Si unconfined system. Detailed experimental studies and theoretical calculations demonstrated that the anchored atomic Fe-N4 sites and nanoconfinement effects regulated the local electronic structure of the catalyst and promoted the activation of O3 molecules to produce atomic oxygen species (AOS) and reactive oxygen species (ROS), eventually achieving efficient oxidation of CH3SH into CO2/SO42-. Benefiting from the high diffusion rate and the augmentation of AOS/ROS, Fe-N4/CMK-3 exhibited an excellent poisoning tolerance, along with high catalytic durability. This contribution provides the proof-of-concept strategy for accelerating catalytic ozonation of sulfur-containing volatile organic compounds (VOCs) by combining confined catalysis and atomic catalysts and can be extended to the purification of other gaseous pollutants.

Functional materials contributing to the removal of chlorinated hydrocarbons from soil and groundwater: Classification and intrinsic chemical-biological removal mechanisms

Chlorinated hydrocarbons (CHs) are the main contaminants in soil and groundwater and have posed great challenge on the remediation of soil and ground water. Different remediation materials have been developed to deal with the environmental problems caused by CHs. Remediation materials can be classified into three main categories according to the corresponding technologies: adsorption materials, chemical reduction materials and bioaugmentation materials. In this paper, the classification and preparation of the three materials are briefly described in terms of synthesis and properties according to the different types. Then, a detailed review of the remediation mechanisms and applications of the different materials in soil and groundwater remediation is presented in relation to the various properties of the materials and the different challenges encountered in laboratory research or in the environmental application. The removal trends in different environments were found to be largely similar, which means that composite materials tend to be more effective in removing CHs in actual remediation. For instance, adsorbents were found to be effective when combined with other materials, due to the ability to take advantage of the respective strengths of both materials. The rapid removal of CHs while minimizing the impact of CHs on another material and the material itself on the environment. Finally, suggestions for the next research directions are given in conjunction with this paper.