Search Results (112)

Effective abatement of nitrogen oxides (NO_x) is achieved by ammonia selective catalytic reduction (NH₃-SCR). In this paper, the effects of single WO₃ doping and WO_x-VO_x co-doping into the MnO_x/TiO₂ catalyst on NH₃-SCR of NO_x removal, sulfur and water resistance, and reaction mechanisms were systematically investigated. The 5MnO_x/TiO₂, WO₃-5MnO_x/TiO₂, and WO₃-V₂O₅-5MnO_x/TiO₂ were prepared using the incipient-wetness impregnation method. Furthermore, the monolithic WO₃-V₂O₅-5MnO_x/TiO₂-CC (cordierite support) catalyst involved a coating process. The WO₃-V₂O₅-5MnO_x/TiO₂ catalyst demonstrated superior NO conversion and maintained over 80% activity following prolonged exposure to SO₂ and H₂O. Characterization results indicated that the introduction of WO₃ regulated Mn valence through the formation of W-O-Mn bonds. The synergistic effect of V₂O₅ and WO₃ further promoted electron transfer, increased surface chemisorbed oxygen and oxygen vacancies, and strengthened reactant adsorption and activation. In situ DRIFTS analysis suggested that WO₃ modulated the reaction pathway, and while 5MnO_x/TiO₂ followed the Langmuir–Hinshelwood (L-H) mechanism, both WO₃-5MnO_x/TiO₂ and WO₃-V₂O₅-5MnO_x/TiO₂ exhibited a combined L-H and Eley–Rideal (E-R) pathway. This study confirmed that WO₃ played a crucial regulatory role in both single-metal and multi-metal systems, and the synergistic interaction between V₂O₅ and WO₃ was the key to achieving superior denitration performance and poisoning resistance. Full article

Nitrogen oxides (NO_x), carbon monoxide (CO), sulfur dioxide (SO₂), and volatile organic compounds (VOCs) in industrial waste gases pose significant threats to environmental quality and human health. Catalytic purification is recognized as a leading abatement technology, crucial for meeting increasingly stringent emission regulations. Rare-earth (RE) catalytic materials, particularly those based on cerium (Ce), lanthanum (La), praseodymium (Pr), and neodymium (Nd) oxides, have attracted intense research due to their unique electronic configurations, high oxygen storage capacity (OSC), facile reversible redox reactions Ce⁴⁺, Ce³⁺, and exceptional thermal stability. This paper provides a comprehensive and methodical overview of RE catalysts used in industrial waste-gas purification. Initially, the physicochemical characteristics of RE elements and their multifaceted roles as active phases, supports, and promoters are explained. Subsequently, the latest developments in RE-based catalysts for NO_x abatement, CO oxidation, VOC degradation, and the removal of sulfur-bearing gas are critically reviewed. The discussion emphasizes structure–activity relationships, reaction mechanisms, and the synergistic interactions between RE elements and transition metals. Comparative analyses are presented through tables focusing on catalyst composition, reaction conditions, performance parameters, and stability. Special attention is given to the enhanced resistance to water vapor and sulfur poisoning afforded by RE materials. Finally, current challenges and future research prospects, including cost reduction, scalability, and long-term durability, are suggested. This review aims to provide practical guidance for the rational design and industrial translation of next-generation RE catalytic materials for air pollution control. Full article

Simultaneous catalytic elimination of nitrogen oxides (NO_x) and volatile organic compounds (VOCs) represents a promising technology for addressing the synergistic pollution of fine particulate matters of <2.5 μm diameter (PM_2.5) and O₃. Nevertheless, it has been maintaining significant challenges in practical implementation, particularly the inherent mismatch in temperature windows between NO_x reduction and VOCs oxidation pathways, coupled with catalyst poisoning and deactivation phenomena. These limitations have hindered the industrial application of bifunctional catalysts for the removal of concurrent pollutant. This review systematically explored the fundamental mechanisms and functional roles of active sites in controlling synchronous catalytic processes. The mechanism of catalyst deactivation caused by multiple toxic substances has been comprehensively analyzed, including sulfur dioxide (SO₂), water vapor (H₂O), chlorine-containing species (Cl*), reaction by-products, and heavy metal contaminants. Furthermore, we critically evaluated the strategies of doping regulation, nanostructure engineering and morphology optimization to enhance the performance and toxicity resistance of catalysts. Meanwhile, emerging regeneration techniques and reactor design optimizations are discussed as potential solutions to improve the durability of catalysts. Based on the above critical aspects, this review aims to provide insights and guidelines for developing robust catalytic systems capable of controlling multi-pollutants in practical applications, and to offer theoretical guidance and technical solutions to bridge the gap between laboratory research and industrial environmental governance applications. Full article

Nitrogen oxides (NO_x) are major atmospheric pollutants, and their escalating emissions, driven by rapid economic development and urbanization, pose a severe threat to both the ecological environment and human health. Conventional denitrification technologies are often hampered by high costs, significant energy consumption, and stringent operational conditions, making them increasingly inadequate in the face of tightening environmental regulations. In this context, photocatalytic technology, particularly systems based on graphitic carbon nitride (g-C₃N₄), has garnered significant research interest for NO_x removal due to its visible-light responsiveness, high stability, and environmental benignity. To advance the performance of g-C₃N₄, numerous modification strategies have been explored, including morphology control, elemental doping, defect engineering, and heterostructure construction. These approaches effectively broaden the light absorption range, enhance the separation efficiency of photogenerated electron-hole pairs, and improve the adsorption and conversion capacities for NO_x. Notably, constructing heterojunctions between g-C₃N₄ and other materials (e.g., metal oxides, noble metals, metal–organic frameworks (MOFs)) has proven highly effective in boosting catalytic activity and stability. Furthermore, the underlying photocatalytic mechanisms, encompassing the generation and migration pathways of charge carriers, the redox reaction pathways of NO_x, and the influence of external factors like light intensity and reaction temperature, have been extensively investigated. From an application perspective, g-C₃N₄-based photocatalysis demonstrates considerable potential in flue gas denitrification, vehicle exhaust purification, and air purification. Despite these advancements, several challenges remain, such as limited solar energy utilization, rapid charge carrier recombination, and insufficient long-term stability, which hinder large-scale implementation. Future research should focus on further optimizing the material structure, developing greener synthesis routes, enhancing catalyst stability and poison resistance, and advancing cost-effective engineering applications to facilitate the practical deployment of g-C₃N₄-based photocatalytic technology in air pollution control. Full article

Nitrogen oxides (NO_x), one of the major air pollutants, not only are key substances in forming acid rain and photochemical smog, but can also enter the stratosphere and damage the ozone layer to some extent. The selective catalytic reduction (NH₃-SCR) technology has been widely utilized in industrial flue gas treatment for its efficient removal of NO_x. In recent years, nitrogen-doped carbon materials (NC) have emerged as a novel type of environmentally friendly catalyst, showing outstanding performance in the low-temperature NH₃-SCR reaction. This paper reviews the application advancements of nitrogen-doped carbon materials in the NH₃-SCR reaction, with a focus on the catalytic mechanisms, modification strategies, and stability issues. This paper analyzes multiple improvement ideas, such as regulating metal types and distributions to achieve synergy effects, optimizing carrier loading, and designing morphology structures, and discusses how these measures jointly act to enhance the overall performance of the catalyst. Finally, solutions to the deactivation problem of NC catalysts are proposed, and the future research directions are explored to meet the increasingly stringent environmental protection requirements and promote the development of related technologies. Full article

The narrow operating temperature window of commercial V-W/TiO₂ catalysts severely limits NO_x removal efficiency, especially during low-load boiler operations. To achieve broad-temperature NO_x abatement, we developed Ce-M/Ti (M = Co, Fe, Mn, Mo) catalysts via a dual-site strategy. The temperatures required for 80% NO conversion (T₈₀) were 302 °C for Ce-Mo/Ti, 372 °C for Ce-Fe/Ti, 393 °C for Ce-Mn/Ti, and 415 °C for Ce-Co/Ti. Among them, Ce-Mo/Ti exhibited the most favorable low-temperature activity, outperforming a commercial catalyst (324 °C). Its turnover frequency (3.12 × 10⁻³ s⁻¹) was 1.29 times higher. Combined physicochemical characterization and density functional theory (DFT) calculations further reveal the mechanism behind the enhanced dual-site synergy in Ce-Mo/Ti. In the Ce-Co, Ce-Fe, and Ce-Mn sites, weak orbital hybridization leads to limited charge transfer. In contrast, Ce-Mo/Ti exhibits stronger hybridization between the Ce 4f/5d and Mo 4d orbitals, which breaks the inherent limitation of the Ce-based (Ce³⁺/Ce⁴⁺) redox capability and enables reverse electron transfer from Mo to Ce. This distinctive electron transfer direction creates a unique electronic environment, activating an efficient redox cycle between Mo⁶⁺/Mo⁵⁺ and Ce⁴⁺/Ce³⁺. This work offers a promising design strategy for dual-site catalysts with high NO_x removal efficiency over a wide temperature range. Full article

Nitrogen oxides (NO_x) emissions pose environmental and health risks. Selective catalytic reduction (SCR) is effective for NO_x removal, and using CO as a reductant can eliminate both NO_x and CO. This study explores CuCe catalysts on SiO₂, Al₂O₃, and TiO₂ for CO-SCR. Results show catalytic activity relates to the synergy between lattice oxygen and CuCe species. TiO₂ enhances this interaction, promoting Cu⁺ and lattice oxygen for NO adsorption and dissociation. The CuCe/TiO₂ catalyst achieves 100% NO conversion at 300 °C and 40.2% at 100 °C, indicating excellent low-temperature performance. These findings are valuable for developing efficient SCR catalysts. Full article

In wet flue gas desulfurization and denitrification processes, nitrite accumulation inhibits denitrification efficiency and induces secondary pollution due to its acidic disproportionation. This study developed a Mn-modified ZSM-5 zeolite catalyst, achieving efficient resource conversion of nitrite in nitrogen-containing wastewater through an O₃ + Mn/ZSM-5 catalytic system. Mn/ZSM-5 catalysts with varying SiO₂/Al₂O₃ ratios (prepared by wet impregnation) were characterized by BET, XRD, and XPS. Experimental results demonstrated that Mn/ZSM-5 (SiO₂/Al₂O₃ = 400) exhibited a larger specific surface area, enhanced adsorption capacity, abundant surface Mn³⁺/Mn⁴⁺ species, hydroxyl oxygen species, and chemisorbed oxygen, leading to superior oxidation capability and catalytic activity. Under the optimized conditions of reaction temperature = 40 °C, initial pH = 4, Mn/ZSM-5 dosage = 1 g/L, and O₃ concentration = 100 ppm, the $\mathrm{N}{\mathrm{O}}_2^{-}$ oxidation efficiency reached 94.33%. Repeated tests confirmed that the Mn/ZSM-5 catalyst exhibited excellent stability and wide operational adaptability. The synergistic effect between Mn species and the zeolite support significantly improved ozone utilization efficiency. The O₃ + Mn/ZSM-5 system required less ozone while maintaining high oxidation efficiency, demonstrating better cost-effectiveness. Mechanism studies revealed that the conversion pathway of $\mathrm{N}{\mathrm{O}}_2^{-}$ followed a dual-path catalytic mechanism combining direct ozonation and free radical chain reactions. Practical spray tests confirmed that coupling the Mn/ZSM-5 system with ozone oxidation flue gas denitrification achieved over 95% removal of liquid-phase $\mathrm{N}{\mathrm{O}}_2^{-}$ byproducts without compromising the synergistic removal efficiency of NO_x/SO₂. This study provided an efficient catalytic solution for industrial wastewater treatment and the resource utilization of flue gas denitrification byproducts. Full article

The efficient simultaneous removal of NO_x and CO from sintering flue gas under low-temperature conditions (110–180 °C) in iron and steel enterprises remains a significant challenge in the field of environmental catalysis. In this study, we present an innovative strategy to enhance the performance of CuSmTi catalysts through silver modification, yielding a bifunctional system capable of oxygen structure regulation and demonstrating superior activity for the combined NH₃-SCR and CO oxidation reactions under low-temperature, oxygen-rich conditions. The modified AgCuSmTi catalyst achieves complete NO conversion at 150 °C, representing a 50 °C reduction compared to the unmodified CuSmTi catalyst (T_100% = 200 °C). Moreover, the catalyst exhibits over 90% N₂ selectivity across a broad temperature range of 150–300 °C, while achieving full CO oxidation at 175 °C. A series of characterization techniques, including XRD, Raman spectroscopy, N₂ adsorption, XPS, and O₂-TPD, were employed to elucidate the Ag-Cu interaction. These modifications effectively optimize the surface physical structure, modulate the distribution of acid sites, increase the proportion of Lewis acid sites, and enhance the activity of lattice oxygen species. As a result, they effectively promote the adsorption and activation of reactants, as well as electron transfer between active species, thereby significantly enhancing the low-temperature performance of the catalyst. Furthermore, in situ DRIFTS investigations reveal the reaction mechanisms involved in NH₃-SCR and CO oxidation over the Ag-modified CuSmTi catalyst. The NH₃-SCR process predominantly follows the L-H mechanism, with partial contribution from the E-R mechanism, whereas CO oxidation proceeds via the MvK mechanism. This work demonstrates that Ag modification is an effective approach for enhancing the low-temperature performance of CuSmTi-based catalysts, offering a promising technical solution for the simultaneous control of NO_x and CO emissions in industrial flue gases. Full article

Metal–organic frameworks (MOFs) are a novel type of porous crystalline materials assembled from metal ions and organic linkers. Their derivatives can inherit characteristics such as high specific surface area, tunable porosity, and unique topological structures, which make MOF-derived metal oxides ideal catalysts for the selective catalytic reduction (SCR) of NO_x. This review focuses on the synthetic strategies of MOF-derived metal oxides and the latest progress of oxides derived from various typical MOFs materials (including MILs, ZIFs, UiO, BTC series, MOF-74, MOF-5, and Prussian blue analogs, etc.) in the catalytic reduction in NO_x, and analyzes the mechanisms for the enhanced catalytic performance. In addition, the challenges and prospects of MOF derivatives in catalytic applications are discussed. It is hoped that this review will help researchers understand the latest research progress of MOF-derived metal oxide materials in the catalytic removal of NO_x pollution. Full article

Mesoporous silicas of MCM-41 and MCM-48 types were synthesized and modified with copper using the ammonia-driven deposition precipitation (ADP) method, resulting in highly dispersed copper species. Samples with varying copper loadings were thoroughly characterized in terms of their porous structure, metal content, copper species’ aggregation, and the stability of deposited forms under reaction conditions. Copper-modified mesoporous silicas exhibited excellent catalytic performance in the low-temperature NH₃-SCR process. Their activity in NO to NO₂ oxidation suggests that the fast-SCR pathway plays a significant role in NO_x conversion at low temperatures. However, direct ammonia oxidation limited SCR efficiency at higher temperatures. These findings demonstrate the potential of ADP-modified copper–silica catalysts for effective and selective NO_x removal under low-temperature conditions. Full article

In pursuing sustainable environmental solutions, the concept of ‘waste to treasure’ has emerged as a promising approach. In this study, a new process is proposed to combine solid copper slag with hydrogen peroxide (H₂O₂) to remove nitrogen oxides (NOx) from acidic exhaust gases, thus effectively utilizing waste materials. Firstly, different smelting slags were screened to determine the catalytic potential of copper slag for hydrogen peroxide. Subsequently, the catalytic activity of the copper slags at various stages of the copper smelting process was thoroughly evaluated and optimized. In addition, a multifactorial evaluation of slow-cooled copper slag catalysts for removing NOx was carried out. Preliminary indications are that the iron phase in the copper slag is identified as the main source of catalytic activity sites. The results suggest that Fe²⁺/Fe³⁺ sites on the surface of the Fe phase in the slow-cooled copper slag may be crucial in improving the NOx removal efficiency. The main reactive oxygen species detected in the system were ·OH, ·O₂⁻, and ¹O₂. In addition, the transformation products, formation pathways, and reaction mechanisms of NO in the liquid phase were initially investigated and determined. This study provides a green and sustainable path for the utilization of solid waste and management of atmospheric fumes in the non-ferrous metal industry and offers new perspectives to address environmental challenges in industrial processes. Full article

Ammonia has attracted much interest as a potential green and renewable hydrogen carrier or energy vector. Compared to hydrogen, ammonia offers several advantages. For example, ammonia has a significantly higher energy density and can be liquefied at room temperature at a moderate pressure of 8 bars. While ammonia can be cracked to supply hydrogen, it is also possible to convert it directly into high-temperature solid oxide fuel cells (SOFCs) to generate electricity. The Ship-FC project aims to install an ammonia-fed 2MW SOFC system on board the vessel Viking energy to demonstrate the feasibility of zero CO₂ emission shipping. For this NH₃ SOFC system, a catalytic afterburner is required to remove the hydrogen and ammonia present in the SOFC off-gas and to recover heat. The current study analysed the effects of different catalyst supports, with a focus on NO_X formation through the combustion of an SOFC off-gas surrogate. The study investigated the performance of catalysts based on the active metals, platinum and iridium, as well as the catalyst supports, Al₂O₃, SiO₂, and TiO₂. The results were correlated with catalyst characterisation data and ammonia TPD results. The investigations showed that the formation of NO_X was clearly affected by the nature of the catalyst support. The highest selectivity towards NO_X was observed for Al₂O₃, followed by SiO₂, and the lowest selectivity was observed for TiO₂. This trend was evident for the supported platinum and iridium catalysts and for the samples exclusively containing the support. The trend for N₂O formation was opposite to that of NO_X formation (TiO₂ > SiO₂ > Al₂O₃) in both the presence and absence of platinum or iridium. Full article

The alumina, in the form of α-Al₂O₃ tabular balls, considered in this study is a high-purity form of aluminum oxide that has been fired at high temperatures (well above 1900 °C), virtually removing porosity. However, the purity and inertness of the surface of the Al₂O₃ tabular balls minimize the catalytic activity, which is why lithium doping was tried. Thus, the target of this study was the effect of doping with lithium ions in some tabular balls of Al₂O₃ (the crystalline structure is corundum) on the improvement of the catalytic properties of alumina. This study examined the impact of a lithium catalyst on the combustion of various fuels within a porous inert medium (PIM) burner. This study specifically compared low calorific gaseous fuel (e.g., biogas) combustion in a PIM burner with and without the lithium catalyst. The experimental setup comprised a gas preparation unit for mixing CNG and CO₂ to simulate biogas and a PIM burner. The PIM burner comprised Al₂O₃ spheres (13 mm diameter, 45% porosity) in a random packing configuration. Three fuels, varying in composition and lower heating value (LHV ranging from 20.771 to 27.695 MJ/m³), were combusted at air ratios ranging from 1.67 to 1.79. The results indicated that the catalyst increased peak combustion temperatures by 23.2 °C to 51.4 °C, depending on the fuel type and air ratio. Significantly higher carbon monoxide (CO) concentrations were observed without the catalyst, particularly with fuel type F1, while nitrous oxide (NOx) levels remained consistently low. Upstream flame propagation was observed in the presence of the catalyst. These findings demonstrate the potential of lithium catalysts to enhance combustion stability and reduce emissions in porous media combustion burners. Following these studies, it can be stated that Li(I) has the role of promoter of the catalytic process. Full article

Nitrogen oxides (NOx) and chlorinated volatile organic compounds (CVOCs) are major environmental pollutants, posing severe risks to human health and ecosystems. Traditional single-component catalysts often fail to remove both pollutants efficiently, making synergistic catalytic technologies a critical research focus. In this study, a mesoporous HPW-CS-Ce-Ti oxide catalyst, modified with H₃PW₁₂O₄₀ (HPW) and chitosan (CS), was synthesized via self-assembly. The optimized 10HPW-CS-Ce_0.3-Ti catalyst achieved nearly 100% NO conversion at 167–288 °C and a T₉₀ of 291 °C for CVOC conversion, demonstrating superior dual-pollutant removal. HPW and chitosan facilitated mesoporous structure formation, enhancing mass transfer and active site availability. HPW doping also modulated the Ce⁴⁺/Ce³⁺ ratio, boosting redox capacity and surface-active oxygen species, while increasing acidity to promote NH₃ and CVOC adsorption. This study presents a novel catalyst and synthesis method with significant potential for environmental protection and human health. Full article