Recent Solutions for Efficient Carbonyl Sulfide Hydrolysis: A Review

Complete solidification of landfill concentrated leachate using a minimal dosage of mayenite and its reutilization for carbonyl sulfide degradation

Landfill concentrated leachate (CL) contains high concentrations of organic pollutants, salts, and heavy metal ions. Treatment methods for CL include recharge, evaporation, and incineration; however, these processes are challenged by high load demands, treatment complexity, and limited potential for resource recovery. Herein, the mayenite-enriched calcium-aluminum oxide (CaxAlyOz) was used to solidify CL. With an optimal dosage of 30 %, the solidified product, marked as CL-CAOSP, was obtained, which not only mitigates the challenges associated with leachate discharge but also enhances the efficiency of water evaporation due to the lower binding energy at the Ca4Al2O6Cl2•10H2O/Al2O3-water interface compared to that of the water-water interface. To dispose of CL-CAOSP, its organic pollutants underwent a high-temperature pyrolysis carbonization process to form porous carbon, which was tightly combined with the alkali and alkaline earth metals-doped Ca12Al14O32Cl2 to create an efficient hydrolysis catalyst for the toxic gas carbonyl sulfide (COS). The calcined CL-CAOSP is also capable of cyclically solidifying CL up to five times, significantly reducing the required dosage of CaxAlyOz and the generation of the terminal solidified product. These results provide novel treatment and resource utilization technologies for CL, serving as valuable guides for the implementation of CL treatment practices.

Reduction of tar, sulfur, chlorine and CO2 in syngas produced by gasification of refuse-derived fuel pellets

Effective waste management is an increasingly urgent global challenge, with gasification emerging as promising alternative to conventional disposal methods. However, the major challenge in thermochemical waste processing is the presence of contaminants in the product streams. Therefore, this study focuses on the experimental gasification of refuse-derived fuel (RDF) pellets, with the aim of characterizing the products, analyzing contaminant distribution, and purifying the syngas from multiple contaminants simultaneously. Gasification experiments were conducted in a two-stage batch reactor, and the produced syngas was purified using two continuous packed absorption columns. Yields of gaseous, liquid, and solid products were 52.5%, 23.5%, and 7.3%, respectively. Resulting char exhibited a lower heating value (LHV) of 18.24 MJ/kg and retained 76.8% of the sulfur and 35.8% of the chlorine from the RDF. Heavy metal concentrations in the char remained below environmental limits. Syngas achieved a maximum LHV of 11.9 MJ/Nm3. Its purification using aqueous solutions of NaOH and methyl-diethanolamine achieved removal efficiencies of 97.77% for H₂S and 43.06% for COS. Efficiency of HCl removal with NaOH solution ranged from 82.15% to 89.27%, also contributing to CO₂ removal. Tar content in the syngas was significantly reduced through catalytic treatment with Ni/activated carbon, achieving a maximum removal efficiency of 85.89%. Concentrations of key contaminants in syngas were reduced to 6.13 ppm for H2S, 41.58 ppm for COS, 19.37 mg/Nm3 for HCl, and 2.11 g/Nm3 for tar. These results demonstrate the feasibility of integrated gasification and multi-contaminant purification for producing cleaner syngas from RDF, advancing sustainable waste-to-energy solutions.

Low-temperature highly efficient catalytic removal of odorous carbonyl sulfide by facile regulating CeO2 morphologies

Unraveling the water activation is essential in the catalytic hydrolysis of organic sulfur compounds, yet its intrinsic mechanism of the water-promoting effect is still unclear. In this work, we describe novel findings of oxygen vacancy (VO) engineering by facile regulating CeO2 nanocatalysts with different shapes (rod, octahedral, sphere, and cube) for COS hydrolysis at lower temperature, aiming at understanding the structural origin of the excellent catalytic hydrolysis activity. Unexpectedly, among CeO2 catalysts with different morphologies, spherical CeO2 (CeO2-S) catalysts can achieve completely conversion of COS at 60 ℃ and maintain 30 hours of non-deactivation, which is a significant improvement in catalytic activity and reaction temperature compared to previously reported catalysts. Through various characterizations and results analysis, it is obvious to see that the more spontaneous formation VO on CeO2-S catalysts synergistically induced the water activation and dissociation thus result in the generation of more surface active hydroxyl groups (-OH), which contributes to the enhanced performance of COS catalytic hydrolysis at lower temperature. The promoting effect of catalyst morphology changes on COS hydrolysis were furthering analyzed using in situ DRIFTS and DFT calculations, and revealed that the exposed (111) crystal plane of CeO2 exhibits the strongest adsorption capacity for COS. Notably, CeO2-S also exhibited good catalytic performance and stability towards to other typical organic sulfur compounds (COS and CS2), which is beneficial for the wide application at complex operating conditions. This study provides new insights for designing OH-rich CeO2 catalysts to remove single as well as multi-component organic sulfur compounds for different applications at lower temperatures.

Recent Developments in Catalytic Carbonyl Sulfur Hydrolysis

Carbonyl sulfide (COS) is the most abundant and longest-lasting organic reduced sulfur compound in the atmosphere. Removing it is a critical and challenging aspect in desulfurization technology in order to comply with global restrictions on harmful emissions. Catalytic hydrolysis refers to the process whereby COS reacts with water under the influence of a catalyst to generate carbon dioxide and hydrogen sulfide. Due to its high conversion rate, minimal side reactions, no hydrogen consumption, and mature technology, it has emerged as the most crucial COS removal method at present. Since its inception in the 1940s, research on the catalytic hydrolysis of COS has witnessed encouraging progress over the past several decades. This review summarizes recent advancements in this field. In this review, the evaluation metrics, influencing factors, and reaction mechanism for the COS hydrolysis reaction are briefly introduced. The recent advancements in COS hydrolysis catalysts in recent years are emphasized. Additionally, the existing challenges and potential solutions in this field are also proposed. Finally, the future development directions for this research area are envisioned. The purpose of this review is to offer a reference for the subsequent design and research of high-activity and high-stability hydrolysis catalysts.

Influence of Surface Basic Sites and Oxygen Vacancies on the Performance of Metal-Modified Rod-Like Ceria Catalysts for Low-Temperature Hydrolysis of Carbonyl Sulfide

This study utilized a hydrothermal method to synthesize various metal-modified rod-like ceria catalysts (Fe, Co, Cu, Ni, La), achieving efficient COS removal at low temperatures. The research identified surface oxygen vacancies and basic sites as critical factors that influence the catalytic performance of COS hydrolysis. The addition of different metals to pristine ceria rods increased the specific surface area, oxygen vacancy content (Ov), and basicity, which enhanced the catalysts' sulfur resistance and stability. Among all the catalysts tested, 10La-CeO2 demonstrated the highest COS removal rate. This is because La doping significantly augmented Ov, providing more H2O adsorption and activation sites. Furthermore, 10La-CeO2 showed enhanced Lewis basicity, making it easier for COS to adsorb and promote hydrolysis. The in situ DRIFTS results confirmed that appropriate oxygen vacancies and basic sites favored the formation of intermediates such as HCO3 - and HSCO2 -, promoting the decomposition of COS into H2S and CO2.

Synthesis of Asymmetric Urea Derivatives from COS and Amines: Substrate Selection, Scope Studies, and Mechanism Investigation

A series of asymmetric ureas were synthesized by a one-pot reaction of amines and carbonyl sulfide (COS) under catalyst-free conditions. The highly selective synthesis of asymmetric urea was successfully achieved by the use of weakly nucleophilic aromatic amines and highly nucleophilic secondary aliphatic amines. Moreover, a reaction mechanism was proposed based on the detailed NMR and FTIR study. This efficient synthetic methodology provides a mild and selective method for synthesizing asymmetric urea derivatives.

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.

Carbonyl sulfur removal from blast furnace gas: Recent progress, application status and future development

Carbonyl sulfide (COS), a poisonous and harmful gas, is found in industrial gas products from various coal-firing processes. The emission of COS into the atmosphere contributes to aerosol particles that affect the global climate, posing a risk to climate change and population health. In recent years, the total amount of anthropogenic COS emissions has increased significantly, resulting in the prominent COS pollution problem and becoming a vital environmental issue. This review summarizes the research progress of removing COS from industrial gases. According to the characteristics of different industrial gas products, the COS removal mechanism and influence factors, as well as the advantages and disadvantages for various methods, are discussed, including oxidation, absorption/adsorption, hydrogenation, and hydrolysis. Although COS emission control technologies have attracted widespread attention, the progress of application in blast furnace gas purification has been extremely slow, insufficient and sporadic. To fill the gap, this work provides a timely review on blast furnace gas characteristics and application process of various methods for removing COS from blast furnace gas with varying compositions, and their challenges and future development. This work aims to provide guidance on how effective processes and techniques for removal of COS from blast furnace gas can be developed. This review emphasizes the desirability of direct COS removal from blast furnace gas compared to expensive terminal desulfurization technologies. Furthermore, the development of a new process for low-temperature COS removal from blast furnace gas based on a dual-functional catalyst of hydrolysis/adsorption is advocated.