Search Results (153)

Ammonia-selective catalytic reduction (NH₃-SCR) is a well-established and widely applied technology for the abatement of nitrogen oxides. However, traditional NH₃-SCR catalysts still suffer from a limited effective active temperature window, insufficient hydrothermal stability, and relatively high synthesis costs. In this context, Fe-Cu composite Beta zeolites represent an attractive and economically competitive alternative. In the present work, a one-pot, solvent-free method was developed to synthesize Cu- and Fe-containing Beta zeolites using copper-ammonia complexes and Fe salts as metal precursors. The crystalline structure, morphology, and textural properties of the prepared zeolite samples were examined by X-ray diffraction, scanning electron microscopy, temperature-programmed reduction with H₂ and N₂ sorption isotherms. The obtained product displayed high catalytic activity in the NH₃-SCR reaction together with efficient hydrothermal stability, demonstrating potential for practical applications in nitrogen oxide control. Full article

Accurate single-step prediction of stack NO_x concentration is essential for emission monitoring and ammonia-injection control in cement kiln SNCR–SCR hybrid denitrification systems. However, this task is challenging because industrial kiln data are affected by nonstationary emission fluctuations, nonlinear multivariable coupling, process-dependent time delays, and online deployment constraints. To address these process-specific challenges, this study develops a leakage-free dynamic soft-sensing framework for stack NO_x concentration prediction. In the proposed framework, variational mode decomposition (VMD) is used to characterize the multi-scale nonstationarity of the stack NO_x sequence under a sliding-window protocol. Trend-guided maximal information coefficient (MIC) analysis is then applied for nonlinear feature selection and delay compensation using only the training data, and the identified feature subset and delay parameters are fixed for validation and testing. A TCN-SE-LSTM model is constructed to extract temporal dependencies, recalibrate informative feature channels, and capture long-lag dynamic behavior. In addition, the Dual Adaptive Constrained Ivy Algorithm (DAC-IVY) is used only for offline hyperparameter optimization, so that the online stage requires only the trained prediction model. Experiments using 21,600 raw samples collected from an actual cement kiln Distributed Control System (DCS) show that the proposed framework achieves an RMSE of 0.2084 mg/Nm³ and an $R^2$ of 0.9844 on the test set, outperforming conventional baseline models. These results indicate that the proposed framework can provide an effective soft-sensing basis for subsequent denitrification control and operational optimization. Full article

Ammonia-selective catalytic oxidation (NH₃-SCO) is an effective technology for eliminating NH₃ slip; however, the development of catalysts that simultaneously exhibit excellent low-temperature (<350 °C) activity and high N₂ selectivity remains a significant challenge. A novel structured monolithic mesh-type Fe_x-Mn₂O₃/γ-Al₂O₃/Al catalyst was developed. XPS, H₂-TPR, and O₂-TPD results demonstrate that Fe doping markedly increases the concentration of surface-adsorbed active oxygen species and enhances the redox capability. As a result, the optimally doped Fe_6.61-Mn₂O₃/γ-Al₂O₃/Al catalyst achieved complete NH₃ conversion at 210 °C with a 75% N₂ selectivity, outperforming previously reported Mn-based catalysts. Density functional theory (DFT) calculations further confirm that Fe modification enhances O₂ adsorption energy. In addition, the introduction of Fe significantly improves the catalyst’s resistance to SO₂ and H₂O. In situ FTIR results indicate that the NH₃-SCO reaction over Fe-Mn₂O₃/γ-Al₂O₃/Al proceeds predominantly via an internal selective catalytic reduction (i-SCR) pathway. Full article

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

A novel K-resistant CeSbTi mixed oxide catalyst was prepared by co-precipitation method for ammonia selective catalytic reduction (NH₃-SCR) of NO_x. The experimental results show that the introduction of Sb₂O₅ can significantly improve the catalytic activity of the CeTi catalyst. The modulated CeSbTi catalyst has good resistance to K, and the NO_x conversion rate was as high as 95% after K poisoning. Its superior catalytic activity could be ascribed to the large specific surface area with increased acid sites and more oxygen defects and Ce³⁺ species after the introduction of Sb₂O₅, which prompt NH₃ adsorption and activation. In addition, NH₃-SCR reaction over CeSbTi and K/CeSbTi catalysts follows the E-R mechanism. The introduced Sb-O bond as the base capture site preferentially binds to potassium and releases part of the active Ce sites, thus retaining more acid sites and oxygen defects to a certain extent. Full article

A 660 MW coal-fired unit was investigated to clarify the combustion behavior over a wide load range and the effects of static mixers on selective catalytic reduction (SCR) performance. A full-process CFD model covering the furnace, rear pass duct, and SCR system was established, and the combustion characteristics, NO_x formation, and SCR performance were analyzed over a boiler load range of 25–100%. The results showed that, as the boiler load decreased, the furnace heat release weakened, the high-temperature zone contracted, and the flame center shifted downward, with more pronounced flame maldistribution at 25% load. The average NO_x concentration at the SCR inlet first decreased and then increased with decreasing boiler load, reaching a minimum at 75% load. Without a static mixer, the NO_x concentration at the SCR inlet increased from 238 mg/Nm³ at 100% load to 312 mg/Nm³ at 25% load. After a static mixer was installed, the distance required for NH₃ homogenization downstream of the ammonia injection grid was markedly shortened, and the uniformity of the velocity, NH₃ concentration, and temperature fields at the SCR catalyst inlet was improved. In particular, the coefficient of variation in NH₃ concentration decreased from about 4–5% to about 2–3%, while the denitrification efficiency increased by about 1–5 percentage points compared with the case without a static mixer. The variation in denitrification efficiency among different boiler loads was also significantly reduced, indicating improved adaptability of the SCR system to wide-load operation. Among the tested configurations, the static mixer with small blades and a larger blade angle relative to the vertical plane showed the best overall performance. These results provide useful guidance for SCR system improvement in coal-fired units operating over a wide load range. Full article

The emission of hydrogen cyanide (HCN) from formaldehyde (CH₂O) during ammonia-assisted selective catalytic reduction (NH₃-SCR) remains a critical challenge for aftertreatment of bio-hybrid fuel combustion exhaust. The mechanistic details of HCN formation are still poorly understood, especially on widely deployed commercial catalysts like Cu-SSZ-13. In this work, we employed density functional theory calculations in combination with the Energetic Span Model to elucidate HCN formation pathways from CH₂O in the presence of NO₂ and H₂O over Cu-SSZ-13. The results revealed the HCN formation pathway with intermediate methylene imine as the dominant one under typical reaction conditions. These findings resonate very well with reports of hexamethylenetetramine (HMT) formation during NH₃-SCR with CH₂O, for which methylene imine is a critical intermediate. Turnover frequency (TOF) estimations highlighted the strong influence of NO₂ and H₂O: higher NO₂ concentrations promoted CO selectivity and suppressed HCN by oxidizing CH₂O to HCOOH, while lower H₂O enhanced HCN formation. These findings establish a detailed mechanistic framework for HCN emission on Cu-SSZ-13 and suggest that controlling NO₂/NO_x ratios and water content can mitigate HCN formation during NH₃-SCR. Full article

The common root characteristic of CO₂ and air pollutants in the power industry, both derived from fossil fuel combustion, provides a natural basis for their synergistic emission reduction. However, existing studies suffer from the lack of a multi-pollutant synergistic evaluation system and an imperfect emission reduction technology database, which hinder their ability to support low-cost and high-efficiency emission reduction practices in the industry. Targeting the minimization of synergistic emission reduction costs and the maximization of emission reduction effects, this study integrated the process and economic parameters of 11 power generation technologies and 55 pollutant control technologies to establish a full-chain energy conservation and emission reduction technology database for the power industry, through literature research, industry surveys, and data mining. Based on the definition of pollution equivalent in the Environmental Protection Tax Law, we innovatively developed an air pollutant equivalent normalization evaluation method and constructed a two-dimensional coordinate system comprehensive evaluation system for CO₂ and air pollutants, enabling quantitative analysis and visual evaluation of the synergistic emission reduction effects of various technologies. The results show that new energy power generation technologies such as nuclear power and wind power, as well as O₂/CO₂ cycle combustion, ammonia-based desulfurization, and SNCR-SCR combined reduction technologies, exhibit excellent synergistic emission reduction performance for CO₂ and multiple pollutants. In contrast, some conventional pollutant control technologies, such as the limestone-gypsum method and traditional electrostatic precipitation, have significant CO₂ emission increase antagonistic effects. This study also completed the two-dimensional classification of 66 emission reduction technologies based on “emission reduction efficiency-economic cost”, identified application scenarios for different types of technologies, and proposed optimized paths for synergistic emission reduction adapted to the development of the power industry. The research findings fill the gap in quantitative standards for multi-pollutant synergistic emission reduction, provide theoretical support and detailed technical references for emission reduction technology selection and environmental policy formulation in the power industry, and help the industry achieve the dual development requirements of the “double carbon” goal and air quality improvement. Full article

Flue gas denitrification represents an environmentally friendly and economically viable strategy for alleviating energy crises and advancing carbon neutrality goals. Although traditional selective catalytic reduction (SCR) catalysts demonstrate excellent denitrification efficiency and catalytic stability, they still face significant challenges, including high cost and ammonia slip. In this study, the high-entropy oxide (HEO) NiCoZnVCrO_x was synthesized via the sol–gel method and evaluated for the reduction of NO to N₂. The effects of varying reaction conditions on the NO reduction performance of this material were systematically investigated alongside the underlying reaction mechanism. The results reveal that the reduced oxygen carrier (OC) achieves optimal performance at an oxidation temperature of 800 °C, oxidizing gas flow rate of 200 mL/min and reduction time of 60 min, yielding the highest NO conversion and N₂ selectivity while simultaneously minimizing NO₂ selectivity. The reaction mechanism was further elucidated through a series of characterization techniques, including DRIFTS. Overall, this HEO demonstrates significant potential as a candidate OC for flue gas denitrification. Full article

A series of novel Ce-modified MnCoAl layered double oxides (Ce/MCA LDOs) were prepared using solvothermal and impregnation methods for NH₃-SCR denitration. Various characterizations, such as X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and H₂ temperature-programmed reduction (H₂-TPR) were used to investigate their structural properties and the mechanism of ammonia selective catalytic reduction (NH₃-SCR). The incorporation of Ce was found to effectively integrate into the LDO framework and enhance the catalytic activity over a wide temperature window. Moreover, the thermal stability and resistance of H₂O and SO₂ were evaluated. In situ DRIFTS studies revealed that the reaction follows both the “Langmuir–Hinshelwood” (L–H) and “Eley–Rideal” (E–R) mechanisms. This work provides systematic insights into the design of LDO-based catalysts, demonstrating their potential for practical application in denitration. Full article

Underground mining environments present elevated occupational health risks, primarily due to substantial exposure to diesel exhaust emissions within confined and poorly ventilated spaces. This study assesses the real-world performance of two advanced retrofit emission control systems—Proventia NOxBuster and Purifilter—installed on underground mining trucks operating in a Spanish mine. Emissions of carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxide (NO₂) were quantified using a Testo 350 multigas analyser, while ultrafine particle (UFP) concentrations were measured with an Engine Exhaust Particle Sizer (EEPS-3090) equipped with a thermodiluter. Controlled tests under both idling and acceleration conditions revealed substantial reductions in pollutant emissions: CO decreased by 60–98%, NO by 51–92%, and NO₂ by 20–87%, depending on the system and operational phase. UFP concentrations during idling dropped by approximately 90%, from 542,000 particles/cm³ in untreated trucks to below 50,000 particles/cm³ in retrofitted vehicles. Under acceleration, the Proventia NOxBuster achieved reductions exceeding 95%. Conversely, Purifilter-equipped trucks exhibited a counterintuitive increase in UFPs within the 5.6–40 nm range, potentially due to ammonia slip events during selective catalytic reduction (SCR). Despite these discrepancies, both systems demonstrated considerable mitigation potential, albeit highly dependent on exhaust temperature (optimal: 200–450 °C), urea dosing precision, and maintenance protocols. This work underscores the necessity of in situ performance verification, regulatory vigilance, and targeted intervention strategies to protect underground workers effectively. Further investigation is warranted into the long-term health benefits, system durability, and nanoparticle emission dynamics under variable load conditions. Full article

Ammonia (NH₃) is a promising carbon-free fuel for internal combustion engines, but its low reactivity and poor ignition properties present significant challenges for stable operation. This study presents the development and experimental validation of a spark-ignited combustion process that enables stable engine operation using 100% liquid NH₃ as a single fuel. A modified single cylinder research engine, equipped with NH₃ port fuel injection and a high-energy capacitive ignition system was used to investigate combustion behavior under various load conditions. The results show that stable, knock-free combustion with pure NH₃ is feasible at every operating point without any ignition aids like diesel fuel or hydrogen (H₂). The full load conditions of a diesel engine can be represented with an indicated efficiency of 50% using this combustion process. The emission measurements show nitrogen oxides (NO_x) and NH₃ emissions in a 1:1 ratio, which is advantageous for a passive SCR system. Increased nitrous oxides (N₂O) formation occurs at low loads and cold combustion chamber temperatures. This work demonstrates the technical viability of carbon-free NH₃ combustion in spark-ignited (SI) engines and represents a promising step towards net-zero combustion. Full article

The emissions from biomass combustion systems have recently been the subject of increased attention. In addition to elevated concentrations of particulate matter and hydrocarbons (HCs) in the flue gas, significant levels of NO_x emissions occur depending on the used fuel, such as biogenic residues. In response to legal requirements, owners of medium-sized plants (≈100 kW) are now also forced to minimize these emissions by means of selective catalytic reduction systems (SCR). The implementation of a selective sensor is essential for the efficient dosing of the reducing agent, which is converted to ammonia (NH₃) in the flue gas. Preliminary laboratory investigations on a capacitive NH₃ sensor based on a zeolite functional film have demonstrated a high sensitivity to ammonia with minimal cross-influences from H₂O and NO_x. Further investigations concern the application of this sensor in the real flue gas of an ordinary wood-burning stove and of combustion plants for biogenic residues with an ammonia dosage. The findings demonstrate a high degree of agreement between the NH₃ concentration measured by the sensor and an FTIR spectrometer. Furthermore, the investigation of the long-term stability of the sensor and the poisoning effects of SO₂ and HCl are of particular relevance to the laboratory measurements in this study, which show promising results. Full article

The pathways and mechanistic aspects of H₂-SCR over precious metal-based catalysts is still under debate. This study focusses on low loaded platinum-based catalysts (0.07–0.3%) in a large temperature range (50–500 °C), with special focus on (i) the role of NH₃ as a possible intermediate species, (ii) the origin of the undesired N₂O emission and (iii) the platinum sites involved in the H₂-SCR deNO_X reactions. Up to 60 °C, the N₂O selectivity was close to 100%, with no influence of the presence of oxygen in the 50–100 °C temperature range. Ammonia formation was observed at relatively low temperatures (from 60 °C), but its reactivity was then limited. All these low temperature reactions were associated with the same platinum sites, probably a mix of edge and face sites. The maximum outlet NH₃ was observed around 100 °C and the role of the NH₃-SCR in the whole H₂-SCR process appeared very limited. On the contrary, the ammonia oxidation by O₂, which started near 120 °C, significantly contributed to the H₂-SCR process and appeared responsible for the second N₂O emission peak (150–500 °C). This reaction did not imply the same platinum sites and appears mainly dependant on the platinum particle size. Full article

This research considers a preliminary comparative technical evaluation of two micro-gas turbine (MGT) systems in combined heat and power (CHP) mode (100 kWe), aimed at supplying heat to a residential community of 15 average-sized buildings located in Central Europe over a year. Two systems were modelled in Ebsilon 15 software: a natural gas case (benchmark) and an ammonia-fueled case, both based on the same on-design parameters. Off-design simulations evaluated performance over variable ambient temperatures and loads. Idealized, unrecuperated cycles were adopted to isolate the thermodynamic impact of the fuel switch under complete combustion assumption. Under these assumptions, the study shows that the ammonia system produces more electrical energy and less excess heat, yielding marginally higher electrical efficiency and EUF (26.05% and 77.63%) than the natural gas system (24.59% and 77.55%), highlighting ammonia’s utilization potential in such a context. Future research should target validating ammonia combustion and emission profiles across the turbine load range, and updating the thermodynamic model with a recuperator and SCR accounting for realistic pressure losses. Full article