Search Results (13)

Advancing catalysts for low-temperature NH₃-SCR enhances their viability as a terminal flue gas denitration solution across diverse operating regimes. A high-performance, hydrothermally stable catalyst for low-temperature SCR was synthesized by depositing MnO_x onto MgAlO_x composite oxide supports. These supports, featuring varied Mg/Al ratios, originated from layered double hydroxide (LDH) precursors. The obtained catalyst with the Mg/Al ratio of 2 (Mn/Mg₂AlO_x) possesses relatively high concentrations of active oxygen species (O_α) and Mn⁴⁺ and exhibits remarkable catalytic performance. The Mn/Mg₂AlO_x catalyst exhibits a wide operating temperature range (100–300 °C) for denitration, achieving over 80% NO_x conversion, along with robust water resistance. The temperature-programed surface reactions and NO oxidation reactions are performed to elucidate the promoting effect of water on N₂ selectivity, which is not only due to inhibition of catalyst oxidation capacity at high temperature but also is related to the competing adsorption of water and NH₃. In situ DRIFTS analysis confirmed that the NH₃-SCR mechanism over Mn/Mg₂AlO_x adheres to the Eley–Rideal (E–R) pathway. These findings highlight the significant promise of Mn/MgAlO_x catalysts for deployment as downstream denitration units within exhaust treatment systems. Full article

Mn/TiO₂ catalysts with varying solid contents were innovatively prepared by the sol–gel method and were used for selective catalytic reduction of NO at low temperatures using NH₃ (NH₃-SCR) as the reducing agent. Surprisingly, it was found that as the solid content of the sol increased, the catalytic activity of the developed Mn/TiO₂ catalyst gradually increased, showing excellent catalytic performance. Notably, the Mn/TiO₂ (50%) catalyst demonstrates outstanding denitration performance, achieving a 96% NO conversion rate at 100 °C under a volume hourly space velocity (VHSV) of 24,000 h⁻¹, while maintaining high N₂ selectivity and stability. It was discovered that as the solid content increased, the catalyst’s specific surface area (SSA), surface Mn⁴⁺ concentration, chemisorbed oxygen, chemisorption of NH₃, and catalytic reducibility all improved, thereby enhancing the catalytic efficiency of NH₃-SCR in degrading NO. Moreover, NH₃ at the Lewis acidic sites and NH⁴⁺ at the Bronsted acidic sites of the catalyst were capable of reacting with NO. Conversely, NO and NO₂ adsorbed on the catalyst, along with bidentate and monodentate nitrates, were unable to react with NH₃ at low temperatures. Consequently, the developed catalyst’s low-temperature catalytic reaction mechanism aligns with the E-R mechanism. Full article

In order to realize the full-time denitration of a boiler, high-temperature flue gas needs to be introduced when SCR is conducted during the boiler start-up stage, and there is a fire risk due to the presence of combustible fly ash at this time. Therefore, research on reburning and the explosion risk of tail flue gas encountering high-temperature flue gas during start-up and shutdown was carried out. A small testbed was designed to record the temperature of the flue gas and the composition of the flue gas before and after the test, and the ignition characteristics of combustible fly ash in the flue gas were systematically studied. The ignition temperature of combustible fly ash in various conditions was obtained, the ignition characteristics of combustible fly ash in the airflow were analyzed, and the effects of combustible gas, high-temperature flue gas temperature, and fly ash composition on ignition were also analyzed. The results show that the flue gas temperature in the test section was about 400 °C, the low-temperature flue gas temperature increased from 650 °C to 813 °C, and the combustible fly ash did not ignite regardless of whether alcohol was added as a combustible gas component. When the volatile content of combustible fly ash was 10~26.7%, the ignition temperature was 660~760 °C. The lower the volatile content of combustible fly ash was, the higher the ignition point was. When alcohol was added as a combustible component of gas, the ignition point decreased by about 50 °C. The critical ignition temperature of combustible fly ash in this test was lower than that under actual power plant operation conditions. Full article

Herein, two CeO₂ samples dominantly decorated with surface and bulk sulfates were constructed and their distinct effects on high-temperature NH₃-SCR were investigated by strictly controlling the sulfate content at a comparable level. The obtainment of surface and bulk sulfates was revealed using a designed leaching experiment, and further evidenced by the characterization results from XPS and H₂-TPR. In comparison with CeO₂ modified with bulk sulfates (B-CeS), sufficient acid sites with strong intensity were generated on CeO₂ modified with surface sulfates (S-CeS). In addition, due to electron-withdrawing effect from S=O in sulfate species, NH₃ oxidation over S-CeS was greatly suppressed, providing an additional contribution to enhanced performance in high-temperature NH₃-SCR. Full article

Selective catalytic reduction (SCR) of NO_x with NH₃ as the reductant has been proven an efficient and cost-effective technology to remove NO_x pollutants in industries. Traditional SCR catalysts usually operate above 300 °C and suffer from intoxication and limited lifetime. Nano-catalysts are attractive for their high catalytic activities at reduced operating temperatures. We have recently developed a series of nitrogen-doped graphene-supported Mn-Ce oxides (MnCeO_x/NG). The influences of reaction temperature, space velocity, mole ratio of NH₃/NO and O₂ concentration on SCR de-nitration activity were assessed. The novel catalyst with optimal Mn/Ce ratio, at appropriate processing conditions, can achieve a NO conversion efficiency of 99.5% at a temperature of 180 °C, and 93.5% at 150 °C. The kinetics of the SCR reaction on this novel catalyst were also established, exhibiting first-order with respect to NO, zero-order to NH₃, and nearly 0.5-order to O₂ at low temperatures. In the presence of sufficient O₂ content, the apparent activation energy of the NH₃-SCR on MnCeO_x/NG is 37.6 kJ/mol, which is promising for low-temperature applications. Full article

Iron-based particles loaded on porous carbon materials have attracted extensive attention as catalysts for denitration and desulfurization reactions. However, the carbon support of a high-temperature denitration catalyst is inevitably oxidized in the presence of H₂O and O₂. The mechanism of denitration catalyst oxidation and its influence on the catalytic reaction remain to be further explored. Fe₂O₃-loaded graphene models with carbon vacancy (G_def), hydroxyl (HyG), and carboxyl (CyG) were constructed to investigate the effects of hydroxylation and carboxylation on the catalytic activity of Fe₂O₃/graphene for oxidative desulfurization and denitration by using density functional theory (DFT) calculations. According to the analysis of structural properties and adsorption energy, the adsorption process of Fe₂O₃ on HyG and CyG was observed to have proceeded more favorably than that on G_def. The density-of-states (DOS) results also affirmed that HyG and CyG promote the electron delocalization of Fe₂O₃ around the Fermi level, enhancing the chemical activity of Fe₂O₃. Moreover, adsorption energy analysis indicates that hydroxylation and carboxylation enhanced the adsorption of SO₂ and H₂O₂ on Fe₂O₃/graphene while also maintaining preferable adsorption stability of NO. Furthermore, mechanistic research explains that adsorbed H₂O₂ on HyG and CyG directly oxidizes NO and SO₂ into HNO₂ and H₂SO₄ following a one-step reaction. The results provide a fundamental understanding of the oxidized catalyst on catalytic denitration and desulfurization reactions. Full article

Aiming at NO_x (NO 90%, NO₂ 10%) and SO₂ in simulated vessel emissions, denitration and desulfurization were studied through ozone oxidation combined with seawater as absorbent. Specifically, the different influencing factors of denitration and desulfurization were analyzed. The results indicated that the oxidation efficiency of NO can reach over 90% when the molar ratio of O₃/NO is 1.2. Ozone oxidation and seawater washing in the same unit can decrease the temperature of ozone oxidation of NO, avoid high temperature ozone decomposition, and enhance the oxidation efficiency of NO. When NO inlet initial concentration is lower than 800 ppm, the NO_x removal efficiency can be improved by increasing NO inlet concentration, and when NO inlet initial concentration is greater than 800 ppm, increasing the concentration of NO would decrease the NO_x removal efficiency. Increasing the inlet concentration of SO₂ has minor effect on desulfurization, but slightly reduces the absorption efficiency of NO_x due to the competition of SO₂ and NO_x in the absorption solution. Besides, final products (${\mathrm{NO}}_2^{-}$, ${\mathrm{NO}}_3^{-}$, ${\mathrm{SO}}_3^{2-}$, and ${\mathrm{SO}}_4^{2-}$) were analyzed by the ion chromatography. Full article

Biochar materials are good reducers of nitrogen oxides. The composition and structure of biochar affect significantly its ability to reduce C–NO. In order to study the denitration of flue gases by biochar at high temperature, three kinds of biochar (bamboo charcoal (BC), rice husk ash (RHA), and straw charcoal (SC)) were mixed with cement raw meal in a fixed-bed quartz reactor at the temperature of 800–900 °C and O₂ concentration of 0.5%–2%. The results showed that the initial denitration rate of BC was higher than that of RHA, and that of SC was the lowest. RHA had the largest specific surface area, and BC the smallest. The elements C, N, and O and the functional groups of the three types of biochar had a greater influence on the denitration rate than their structures. The denitration rate decreased faster as the O/C ratio increased, and the increase in the relative content of the N element induced the formation of nitrogen-containing functional groups catalyzing C–NO reduction. The content of the C–C bond affected directly the rate of denitration, and both (NCO)_x and C–O bonds had a positive effect on the reduction capability of biochar. It can be concluded that the composition of biochar has an important effect on the reduction of C–NO. Full article

Vanadium-based catalysts are mainly used for marine diesel exhaust denitration. However, their poor catalytic ability at low temperature and poor sulfur tolerance, as well as high toxicity and cost, are big turnoffs. AC (Activated carbon) exhibits good adsorption capacity and catalytic ability in denitration because of its high specific surface area and chemical activity. In this paper, coal-based AC was used for simulating diesel exhaust denitration in different conditions. The results show that the NO removal ability of AC is poor in an NO/N₂ system. The NO₂ removal ability is excellent in an NO₂/N₂ system, where NO is desorbed. The NOx removal efficiency is 95% when the temperature is higher than 200 °C in an NO₂/NH₃/N₂ system. When the temperature is lower than 100 °C, AC can catalytically oxidize NO to NO₂ in an NO₂/O₂/N₂ system. The near-stable catalytic efficiencies of AC for a slow SCR (Selective Catalytic Reduction) reaction, a standard SCR reaction, and a fast SCR reaction at 300 °C are 12.1%, 31.6%, and 70.8%, respectively. When ships use a high-sulfur fuel, AC can be used after wet scrubber desulfurization to catalytically oxidize NO to NO₂ at a low temperature. When ships use a low-sulfur fuel, AC can be used as a denitration catalyst at high temperatures. Full article

A series of NiFe mixed oxide catalysts were prepared via calcining hydrotalcite-like precursors for the selective catalytic reduction of nitrogen oxides (NO_x) with NH₃ (NH₃-SCR). Multiple characterizations revealed that catalytic performance was highly dependent on the phase composition, which was vulnerable to the calcination temperature. The MO_x phase (M = Ni or Fe) formed at a lower calcination temperature would induce more favorable contents of Fe²⁺ and Ni³⁺ and as a result contribute to the better redox capacity and low-temperature activity. In comparison, NiFe₂O₄ phase emerged at a higher calcination temperature, which was expected to generate more Fe species on the surface and lead to a stable structure, better high-temperature activity, preferable SO₂ resistance, and catalytic stability. The optimum NiFe-500 catalyst incorporated the above virtues and afforded excellent denitration (DeNO_x) activity (over 85% NO_x conversion with nearly 98% N₂ selectivity in the region of 210–360 °C), superior SO₂ resistance, and catalytic stability. Full article

At present, the most commonly used denitration process is the selective catalytic reduction (SCR) method. However, in the SCR method, the service life of the catalyst is short, and the industrial operation cost is high. The selective catalytic oxidation absorption (SCO) method can be used in a low temperature environment, which greatly reduces energy consumption and cost. The C/N ratio of the sludge produced in the wastewater treatment process of the soybean oil plant used in this paper is 9.64, while the C/N ratio of the sludge produced by an urban sewage treatment plant is 10–20. This study shows that the smaller the C/N ratio, the better the denitration efficiency of the catalyst. Therefore, dried oil sludge is used as a catalyst carrier. The influence of different activation times, and LiOH concentrations, on catalyst activity were investigated in this paper. The denitration performance of catalysts prepared by different activation sequences was compared. The catalyst was characterized by Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The experimental results showed that: (1) When the concentration of the LiOH solution used for activation is 15%, and the activation time is four hours, the denitration effect of the catalyst is the best; (2) the catalyst prepared by activation before plasma roasting has the best catalytic activity. Full article

Bayer red mud was selected, and the NH₃-SCR activity was tested in a fixed bed in which the typical flue gas atmosphere was simulated. Combined with XRF, XRD, BET, SEM, TG and NH₃-Temperature Programmed Desorption (TPD) characterization, the denitration characteristics of Ce-doped red mud catalysts were studied on the basis of alkali-removed red mud. The results showed that typical red mud was a feasible material for denitration catalyst. Acid washing and calcining comprised the best treatment process for raw red mud, which reduced the content of alkaline substances, cleared the catalyst pore and optimized the particle morphology with dispersion. In the temperature range of 300–400 °C, the denitrification efficiency of calcined acid washing of red mud catalyst (ARM) was more than 70%. The doping of Ce significantly enhanced NH₃ adsorption from weak, medium and strong acid sites, reduced the crystallinity of α-Fe₂O₃ in ARM, optimized the specific surface area and broadened the active temperature window, which increased the NO_x conversion rate by an average of nearly 20% points from 250–350 °C. The denitration efficiency of Ce_0.3/ARM at 300 °C was as high as 88%. The optimum conditions for the denitration reaction of the Ce_0.3/ARM catalyst were controlled as follows: Gas Hourly Space Velocity (GHSV) of 30,000 h⁻¹, O₂ volume fraction of 3.5–4% and the NH₃/NO molar ratio ([NH₃/NO]) of 1.0. The presence of SO₂ in the feed had an irreversible negative effect on the activity of the Ce_0.3/ARM catalyst. Full article

From the viewpoints of securing a stable supply of energy and protecting our global environment in the future, the integrated gasification combined cycle (IGCC) power generation of various gasifying methods has been introduced in the world. Gasified fuels are chiefly characterized by the gasifying agents and the synthetic gas cleanup methods and can be divided into four types. The calorific value of the gasified fuel varies according to the gasifying agents and feedstocks of various resources, and ammonia originating from nitrogenous compounds in the feedstocks depends on the synthetic gas clean-up methods. In particular, air-blown gasified fuels provide low calorific fuel of 4 MJ/m³ and it is necessary to stabilize combustion. In contrast, the flame temperature of oxygen-blown gasified fuel of medium calorie between approximately 9–13 MJ/m³ is much higher, so control of thermal-NOx emissions is necessary. Moreover, to improve the thermal efficiency of IGCC, hot/dry type synthetic gas clean-up is needed. However, ammonia in the fuel is not removed and is supplied into the gas turbine where fuel-NOx is formed in the combustor. For these reasons, suitable combustion technology for each gasified fuel is important. This paper outlines combustion technologies and combustor designs of the high temperature gas turbine for various IGCCs. Additionally, this paper confirms that further decreases in fuel-NOx emissions can be achieved by removing ammonia from gasified fuels through the application of selective, non-catalytic denitration. From these basic considerations, the performance of specifically designed combustors for each IGCC proved the proposed methods to be sufficiently effective. The combustors were able to achieve strong results, decreasing thermal-NOx emissions to 10 ppm (corrected at 16% oxygen) or less, and fuel-NOx emissions by 60% or more, under conditions where ammonia concentration per fuel heating value in unit volume was 2.4 × 10² ppm/(MJ/m³) or higher. Consequently, principle techniques for combustor design for each IGCC were established by the present analytical and experimental research. Also, this paper contains some findings of the author’s previously published own works and engages in wide-ranging discussion into the future development of gasification technologies. Full article