Search Results (144)

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

In response to increasingly stringent emission regulations, low-carbon fuels have received significant attention as sustainable energy sources for internal combustion engines. This study investigates four representative low-carbon fuels, methane, methanol, hydrogen, and ammonia, by systematically summarizing their combustion characteristics and emission profiles, along with a review of existing after-treatment technologies tailored to each fuel type. For methane engines, unburned hydrocarbon (UHC) produced during low-temperature combustion exhibits poor oxidation reactivity, necessitating integration of oxidation strategies such as diesel oxidation catalyst (DOC), particulate oxidation catalyst (POC), ozone-assisted oxidation, and zoned catalyst coatings to improve purification efficiency. Methanol combustion under low-temperature conditions tends to produce formaldehyde and other UHCs. Due to the lack of dedicated after-treatment systems, pollutant control currently relies on general-purpose catalysts such as three-way catalyst (TWC), DOC, and POC. Although hydrogen combustion is carbon-free, its high combustion temperature often leads to elevated nitrogen oxide (NO_x) emissions, requiring a combination of optimized hydrogen supply strategies and selective catalytic reduction (SCR)-based denitrification systems. Similarly, while ammonia offers carbon-free combustion and benefits from easier storage and transportation, its practical application is hindered by several challenges, including low ignitability, high toxicity, and notable NO_x emissions compared to conventional fuels. Current exhaust treatment for ammonia-fueled engines primarily depends on SCR, selective catalytic reduction-coated diesel particulate filter (SDPF). Emerging NO_x purification technologies, such as integrated NO_x reduction via hydrogen or ammonia fuel utilization, still face challenges of stability and narrow effective temperatures. Full article

The combustion of biomass fuels releases alkali metals, which induce severe catalyst deactivation due to alkali metal (K) poisoning in low-temperature ammonia selective catalytic reduction (NH₃-SCR) systems. To address this issue, this study developed a series of heteropoly acid (HPA)-modified Ce/AC catalysts prepared via incipient wetness impregnation. The low-temperature NH₃-SCR performance (80–200 °C) of these catalysts was systematically evaluated, with particular emphasis on their denitrification activity and K-poisoning resistance. The silicotungstic-acid (TSiA)-modified Ce/Ac (TSiA-Ce/AC) catalyst showed an improvement (>20%) in NO conversion activity under the K poisoning condition. The superior K-poisoning resistance of the TSiA-Ce/AC catalyst was attributed to the high density of Brønsted acidic sites and the strong K binding affinity of TSiA, which together protected active sites and preserved the standard SCR reaction pathway under K contaminations. This study proposes a novel strategy for enhancing catalyst K resistance in low-temperature NH₃-SCR systems. Full article

There is a lack of research on screening new strains of high-efficiency ammonia nitrogen degrading bacteria and treating high-concentration ammonia nitrogen aquaculture wastewater using immobilized composite bacteria. In this study, two strains capable of degrading ammonia nitrogen and nitrite were isolated from surface water. The species of the strains were accurately identified using ITS sequencing technology. Scp1 was identified as Pseudomonas and Scr1 as Rhodococcus erythropolis. Both strains were preserved. When the initial concentration of ammonia nitrogen was 1.50 mg/L, the degradation efficiency of ammonia nitrogen after 4 days of inoculation with Scp1, Scr1, and a combination of Scp1 and Scr1 was 90%, 93.3%, and 99.99%, respectively. Similarly, when the initial concentration of nitrite was 0.25 mg/L, the degradation efficiency after 4 days of inoculation with Scp1, Scr1, and a combination of Scp1 and Scr1 was 60%, 82%, and 97.2%, respectively. In addition, when the initial concentration of COD was 20 mg/L, the degradation efficiency after 6 days of inoculation with Scp1, Scr1, and a combination of Scp1 and Scr1 was 59%, 59.4%, and 93.75%, respectively. The results demonstrated that the combined bacteria, Scp1 and Scr1, had a better degradation effect on ammonia nitrogen, nitrite, and COD. Furthermore, a degradation test was conducted in a Penaeus vannamei breeding base, which showed good degradation effects. These findings provide theoretical support for the treatment of high ammonia nitrogen wastewater in aquaculture and have important practical applications. Full article

This study proposes a data-driven optimization framework to enhance emission control performance in diesel engine selective catalytic reduction (SCR) systems under transient operating conditions. A one-dimensional SCR model was constructed in GT-Power, and simulation datasets were generated using experimentally measured inputs from the World Harmonized Transient Cycle (WHTC), with representative emission responses obtained by varying fixed ammonia-to-NOx (A/N) ratios. Building on these datasets, a hybrid prediction model combining Long Short-Term Memory (LSTM) networks and multi-head attention mechanisms was developed to accurately forecast SCR outlet NH₃ leakage and NOx emissions. The model exhibited high predictive accuracy, achieving R² values exceeding 0.977 and low RMSE across training, validation, and test sets. Based on the model predictions, a constrained dynamic multi-objective optimization strategy was implemented to adaptively adjust ammonia dosing, aiming to simultaneously minimize NH₃ leakage and NOx emissions. The optimized NH₃ injection profiles were validated through reapplication in the GT-Power simulation environment. Compared to the baseline fixed-ratio control strategy, the proposed approach reduced NH₃ leakage and NOx emissions by 34.40% and 11.15%, respectively, as determined for the transient segment of the WHTC cycle. These results demonstrate the effectiveness of integrating physics-based simulation, deep learning prediction, and dynamic optimization for improving aftertreatment adaptability and emission compliance in real-world diesel engine applications. All reported values are based on a single simulated WHTC cycle without statistical uncertainty analysis. Full article

The selective catalytic reduction (SCR) of NO_x emissions by hydrocarbons (HCs) using a silver (Ag)-based catalyst offers significant advantages over conventional SCR systems that rely on ammonia reductants and vanadium-based catalysts. However, the conversion rate of SCR is influenced by several factors, among which catalyst poisoning is a major concern. Toxic metals such as sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) can degrade catalyst activity and lead to deactivation. Poisoned catalysts suffer from reduced conversion rates and premature deactivation before reaching their intended operational lifespan. In particular, calcium poisoning results in the formation of CaO (calcium oxide), which reacts to produce a CaWO₄ compound that severely impairs SCR performance. This study investigates the role of antimony (Sb) in mitigating Ca-induced deactivation in HC-SCR of NO_x. Five catalysts with varying Sb loadings were prepared and tested to evaluate Sb’s effect on NO_x conversion rate at a space velocity of 30,000 h⁻¹. The results demonstrate that Sb effectively suppresses Ca deactivation, enhancing the conversion rate across all engine test conditions. The highest NO_x conversion rate (95.88%) was achieved using a catalyst with 3% Sb. 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

Platinum- and/or palladium-containing silica-based supports were applied for the selective catalytic reduction of NO_x with hydrogen (H₂-SCR-DeNO_x). To obtain enhanced activity and N₂ selectivity below 150 °C, we varied the type and loading of noble metals (Pt and Pd both individually and paired, 0.1–1.0 wt.-%), silica-containing supports (ZrO₂/SiO₂, ZrO₂/SiO₂/Al₂O₃, Al₂O₃/SiO₂/TiO₂), as well as the H₂ concentration in the feed (2000–4000 ppm). All of these contributed to enhancing N₂ selectivity during H₂-SCR-DeNO_x over the (0.5 wt.-%)Pt/Pd/ZrO₂/SiO₂ catalyst in the presence of 10 vol.-% of O₂. H₂ was completely consumed at 150 °C. A comparison of the catalytic results obtained during H₂-SCR-DeNO_x,(H₂-)NH₃-SCR-DeNO_x, as well as stop-flow H₂-SCR-DeNO_x and temperature-programmed studies, revealed that in the temperature range between 150 and 250 °C, the continuously coupled or overlaying mechanism of NO reduction by hydrogen and ammonia based on NH₃ formation at lower temperatures, which is temporarily stored at the acid sites of the support and desorbed in this temperature range, could be postulated. Full article

In the presented work, titanosilicate with the MWW structure (Ti-MWW) was hydrothermally synthesized using boron and titanium precursors, with piperidine as a structure-directing agent. The resulting layered zeolite precursor, with a Si/Ti molar ratio of 50, was treated in an HNO₃ solution to remove extraframework Ti and B species. The acid-modified zeolite was functionalized with transition metal cations (Cu²⁺, Fe²⁺, Mn²⁺) and trinuclear oligocations (Fe(3) and Mn(3)). The application of this catalytic system is supported by the presence of titanium in the catalytic support structure—similar to a commercial system, V₂O₅–TiO₂. The obtained samples were characterized with respect to their structure (P-XRD, DRIFT), textural parameters (low-temperature N₂ sorption), surface acidity (NH₃-TPD), transition metal content (ICP-OES) and form (UV–vis DRS) as well as catalyst’s reducibility (H₂-TPR). Ti-MWW zeolite samples modified with transition metals were evaluated as catalysts for the selective catalytic reduction of NO with ammonia (NH₃-SCR). The effective temperature range for the NO conversion varied depending on the type of active phase used to functionalize the porous support. The catalytic performance was influenced by transition metal content, its form, and accessibility for reactants as well as interactions between the active phase and titanium-containing support. Among the catalysts tested, the copper-modified Ti-MWW zeolite showed the most promising results, maintaining 90% NO conversion rates across a relatively broad temperature range from 200 to 325 °C. This catalyst meets the requirements of modern NH₃-SCR installations, which aim to operate in the low-temperature region, below 250 °C. Full article

Perovskite materials in the CaTiO₃-SrTiO₃ system doped with different amounts of iron (1, 2 and 5 mol.%) and various Ca/Sr ratios were prepared by the modified citrate method. Additionally, the materials with 0.05 deficiency in strontium/calcium sublattice and 5 mol.% of Fe were also synthesised. The materials were subjected to structural (XRD, XANES) and microstructural (SEM) characterisation, as well as the analysis of susceptibility to reduction/oxidation processes. The structural analysis indicates a lack of iron-containing phases; thus, an incorporation of Fe into the perovskite structure was postulated. Additionally, the oxidation state of iron in the perovskite structure changes with the dopant amount. The temperature-programmed reduction measurements showed partial reversibility of the reduction processes. For the materials with the highest iron amount, the catalytic tests in NH₃-SCO and NH₃-SCR reactions were carried out. The materials showed high catalytic activity and high selectivity to N₂ in the NH₃-SCR process; however, they were inactive in NH₃-SCO. Full article