Performance For NO Reduction Research Articles

The Effect of Ligand Field on Enhanced Electrocatalytic Performance of NO Reduction Under Applied Potential

We employed density functional theory to investigate Co-N4/Gra single-atom catalysts, focusing on the modification of axial ligand (X=-F, -CN and -C3H4N2) and examined the influence of ligand field and electric potential on eNORR. Our results demonstrate that Co-N4[X]/Gra exhibit favorable thermodynamic adsorption (ΔG *NO < 0) and remarkable activation activity toward NO molecules. Co-N4/Gra demonstrates a limiting potential of −0.13 V with the potential-determining step (PDS) of *NH3 → * + NH3(g). Notably, under the introduction of ligands, Co-N4[F]/Gra achieves the most favorable overpotential of −0.07 V, superior to most of NORR electrocatalysts, and meanwhile shows an exceptional selectivity of 99.99% for eNORR compared to competitive hydrogen evolution reaction. Under the solvent environment, Co-N4/Gra features the triggering potentials of −0.33 V for a pH of 1, −0.71 V for a pH of 7, and −1.10 V vs RHE for a pH of 13, respectively. Additionally, the potential reduces the desorption energy and adsorption energy of NH3, facilitating the accessibility of the NH3 desorption step (PDS) and promoting NO reduction. Thus, under realistic conditions, the Co ion’s active site displays variable valence electrons and forms a dynamic interplay with the ligand field effect, rendering a crucial effect on the adsorption of reaction species during the eNORR.

Unraveling the morphology and crystal plane dependence of bifunctional MnO2 catalyst for simultaneous removal of NO and CO at low temperature

It is indeed a challenging problem to simultaneously remove NO and CO from the steel sintering flue gas, in which a bifunctional catalyst has proven to be an efficient solution for removing both pollutants at low temperature. In this study, four different crystalline phases of MnO2 (α-, β-, γ-, and δ-) catalysts were synthesized via a facile hydrothermal method, and the effects of their crystal structure, morphology, and physicochemical properties on the catalytic performance for NO reduction and CO oxidation were elucidated. The results indicated that γ-MnO2 catalyst exhibited the best catalytic activity, achieving 90% NO removal efficiency and 82% CO conversion rate at 175 °C. Reaction kinetics confirmed that γ-MnO2 catalyst exhibited a lower Ea for both NO reduction and CO oxidation compared to α-MnO2, β-MnO2 and δ-MnO2 catalysts. Meanwhile, the interaction of between NH3-SCR and CO catalytic oxidation reactions over the catalysts was also studied. Intriguingly, it was found that the presence of CO enhanced the catalytic activity of γ-MnO2 catalyst in the NH3-SCR reaction. The results of NO + O2-TPD and in situ DRIFTS experiments revealed that CO contributed to the adsorption and oxidation of NO, thus promoting the L-H pathway over γ-MnO2 catalyst. Finally, a possible mechanism model for simultaneous removal of NO and CO over γ-MnO2 catalyst was proposed.

Metal-free C2N catalyst with superior H2O/SO2 tolerance for NO reduction with CO during incomplete combustion process

Designing a highly effective catalyst for purification NOx emissions during the incomplete combustion process in coal-fired power plants is a valuable yet challenging task. The presence of H2O and SO2 during the NOx reduction process for flue gas treatment in coal-fired power plants is a major concern because it can lead to catalyst deactivation due to the deposition of ammonium sulfate. In this work, we propose a novel method for removing NO and CO without the traditional NH3 injection (2NO + 2CO = N2 + 2CO2) by utilizing density functional theory (DFT) calculations. Specifically, we designed metal-free single and double atomic catalysts named MFn/C2N and demonstrated that the Si-DAC (Si2/C2N) system has the highest activity for NO reduction, with outstanding resistance to deactivation from H2O and tolerance to SO2. Our findings show that Si-DAC has the best catalytic performance for NO reduction, with an extremely low energy barrier of 0.28 eV, suggesting that Si-DAC is the most effective among the reported computational results for NO removal. Overall, this work could pave the way towards designing catalytic systems with excellent activity and stability for reactions beyond NOx reduction.

Insights into the effect of Cu and Fe dispersion state over Ce0.1Al on the catalytic performance of NO reduction by CO

In this paper, Cu and Fe dispersion states over Ce0.1Al were modified by different doping methods such as impregnation and co-precipitation. Cu and Fe were dispersed on the surface of Ce0.1Al carriers in Cu/Fe/Ce0.1Al sample, while for Cu/FeCe0.1Al catalyst, Fe was doped in the carriers and Cu was uniformly dispersed on the surface. The effects of dispersion states on the catalytic behaviors of NO reduction by CO were investigated. The resistance to O2 and SO2 was also verified. Cu/FeCe0.1Al catalyst owned superior denitrification activity and O2/SO2-tolerance performance than Cu/Fe/Ce0.1Al. For the front one, Fe was introduced by co-precipitation scheme. Small particle size and higher specific surface area was achieved. Thus its redox and adsorption performance were ameliorated. For the latter, more active species were enriched on the surface, which was conductive to the defects formation and the reduction of surface adsorbed oxygen. In combination with microstructure characterizations, the intrinsic mechanism was proposed. In essences, the interaction among Cu, Fe and Ce was modified owing to their different dispersion state of Cu and Fe. As a result, NO+CO reaction followed different mechanism over two catalysts. NO reduction by CO on Cu/Fe/Ce0.1Al catalyst followed E-R mechanism, while L-H mechanism was dominant over Cu/FeCe0.1Al catalyst.

Investigation on the mechanism of Nb and Si co-doping on low SO3 generation from V-based catalyst during NH3-SCR process

Generally, SO3 tends to be formed in the process of selective catalytic reduction (SCR), and SO3 has negative effects on atmospheric environmental production and the safe operation of coal-fired power plants. In this study, a series of Nb and Si codoped V-based catalysts were prepared via the impregnation method, and Nb and Si species were applied to reduce the SO3 generation ratio from the catalyst. Moreover, the controlled condensation method was used to collect the SO3, which formed during the NH3-SCR reaction process. The results indicated that the Nb and Si codoped catalysts exhibited the best NO reduction performance with the lowest SO3 generation ratio. The SO3 generation ratio and the NO conversion ratio for the VW2NbTi-10Si catalyst were 0.39% and 92%, respectively. The physicochemical properties of the catalysts were analysed by a series of characterization techniques. The X-ray diffraction (XRD) results revealed that the Nb and Si species could inhibit the crystallization of TiO2, and the X-ray photoelectron spectroscopy (XPS) results indicated that Nb and Si could decrease the ratio of Oα and V5+ on the surface of the catalyst. From the CO2 and NH3 temperature programmed desorption (CO2 and NH3-TPD) results, the Nb and Si species could reduce the number of alkaline sites on the catalyst surface, and the Si species could significantly enhance the acidity of weak and strong acid sites over the catalyst. Combined with the results of N2-adsorption and desorption, CO2-TPD, H2 temperature programmed reduction (H2-TPR) and XPS experiments, the addition of Nb and Si species was beneficial to inhibiting the adsorption and oxidation of SO2 on the surface of catalysts, resulting in a significant decrease in SO3 emissions. Therefore, in-situ diffuse reflective infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that the Nb and Si species could restrict the reaction between SO2 and V species, decreasing the formation of the intermediate product VOSO4. Furthermore, the enhancement of reaction temperature and NH3 volumetric fraction would significantly promote the formation of SO3. However, the variations in the volumetric fraction of O2 and NO expressed ignorable effects on the SO3 generation ratio.

Impact of oxygen and nitrogen-containing species on performance of NO removal by coal pyrolysis gas

Coal pyrolysis gas is considered a promising reburn fuel with excellent NO reduction performance because of the present of nitrogen-containing species (HCN and NH3) in the pyrolysis gas. In this study, we explored the effects of oxygen and nitrogen-containing species on NO removal performance with HCN and NH3 by reactive force field (ReaxFF) molecular dynamics (MD) simulations. Results indicate that appropriately reducing O2 concentrations and increasing the amount of nitrogen-containing species can benefit the NO reduction performance by coal pyrolysis gas. In addition, the effects of oxygen and nitrogen-containing species content on the NO removal and mechanisms of NO consumption and N2 formation are illustrated during NO reduction with HCN and NH3, respectively. Finally, based on the simulations results, practical operating strategies are proposed to optimize the NO reduction efficiency. In summary, this study provides new insights into NO reduction performance, which may contribute to optimizing the operating parameters to decrease NOx emissions during coal combustion.

Insights into the promotional effect of alkaline earth metals in Pt-based three-way catalysts for NO reduction

Enhancing NO reduction efficiency of Pt-based three-way catalysts (TWCs) is very challenging due to poor NO activation ability. In this work, NO reduction performance was improved by introducing alkaline earth metals to adjust the electron environment of Pt, while the promoting effect was systematically studied. Structure-activity relationship indicated that NO reduction activity over the Pt-M/LA catalysts (M = Mg, Ca, Sr or Ba, LA = La-Al2O3) increases as the electronegativity of M decreases, and the TOF of Pt-Ba/LA is about 3 times more active than that of Pt/LA, which is attributed to more Pt0 species resulting from Pt-Ba interaction. Moreover, kinetic studies revealed that alkaline earth metals weaken the poisoning effect of CO and improve promoting effect of HCs, leading to an improved NO adsorption and an increased reaction rate of NO with CO and HCs. This study provides an insightful understanding for the promotional effect of alkaline earth metals on NO reduction over Pt-based TWCs.

Effects of nitrogen-free species on NO removal performance by coal pyrolysis gas via reactive molecular dynamics simulations

Coal splitting and reburning is a promising technology to control NO emissions during coal combustion. During this process, coal pyrolysis gas is used as reburn fuel to convert NO to N2. Nitrogen-containing compounds (HCN and NH3) play dominant roles in the NO reduction performance. In this study, we investigated the influence of nitrogen-free species (CH4, CO and H2) in coal pyrolysis gas on the NO reduction by HCN and NH3 via reactive force field (ReaxFF) molecular dynamics (MD) simulations. The nitrogen distribution in products is determined and monitored during the process of NO removal by HCN and NH3 under different additives. In addition, mechanisms of NO reduction by HCN and NH3 are revealed, accounting for the changes of nitrogen distribution in the products at the atomic level. The present research provides new insights into the influence of CH4, CO and H2 on the NO reduction by HCN and NH3, which may be helpful to reduce the NOx emissions during coal combustion by optimising the nitrogen-free components of coal pyrolysis gas.

A reactive molecular dynamics study of NO removal by nitrogen-containing species in coal pyrolysis gas

Coal splitting and staging is a promising technology to reduce nitrogen oxides (NOx) emissions from coal combustion through transforming nitrogenous pollutants into environmentally friendly gasses such as nitrogen (N2). During this process, the nitrogenous species in pyrolysis gas play a dominant role in NOx reduction. In this research, a series of reactive force field (ReaxFF) molecular dynamics (MD) simulations are conducted to investigate the fundamental reaction mechanisms of NO removal by nitrogen-containing species (HCN and NH3) in coal pyrolysis gas under various temperatures. The effects of temperature on the process and mechanisms of NO consumption and N2 formation are illustrated during NO reduction with HCN and NH3, respectively. Additionally, we compare the performance of NO reduction by HCN and NH3 and propose control strategies for the pyrolysis and reburn processes. The study provides new insights into the mechanisms of the NO reduction with nitrogen-containing species in coal pyrolysis gas, which may help optimize the operating parameters of the splitting and staging processes to decrease NOx emissions during coal combustion.

Promotional effect for SCR of NO with CO over MnO -doped Fe3O4 nanoparticles derived from metal-organic frameworks

Abstract MnOx-Fe3O4 nanomaterials were fabricated by using the innovative scheme of pyrolyzing manganese-doped iron-based metal organic framework in inert atmosphere and exhibited extraordinary performance of NO reduction by CO (CO-SCR). Multi-technology characterizations were conducted to ascertain the properties of fabricated materials (e.g., TGA, XRD, SEM, FT-IR, XPS, BET, H2-TPR and O2-TPD). Moreover, the interaction between reactants and catalysts was ascertained by in situ FT-IR. Experimental results demonstrated that Mn was an ideal promoter for iron oxides, resulting in decrease of crystallite size, improve reducibility property, enhance the mobility and the amount of lattice O2– species, as well as strength the adsorption ability of active NO and CO to form multiple species (e.g., nitrate and carbonate). The unprecedented enhancement of CO-SCR activity over Mn-Fe nanomaterials follows the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction pathway.

An ammonia-free denitration method: Direct reduction of NOx over activated carbon promoted by Cu-K bimetals

As ammonia slip becomes more serious with the traditional deNOx application, ammonia-free technologies have received more and more attention recently. Cu-K bimetal loaded activated carbon catalysts were prepared by equivalent-volume impregnation method for the direct reduction of NO and showed good NO reduction performance in a wide temperature range under temperature-programmed surface reactions (TPSRs) conditions in aerobic and anaerobic environments. The catalysts were characterized by BET, SEM, XRD, XPS, H2-TPR, Raman and FT-IR techniques and the NO reduction mechanism was analyzed. Experimental results show that the active functional groups formed on the surface of activated carbon are the important intermediate products and play a key role in the reduction reaction. The presence of O2 greatly promotes the formation of the intermediate, C(O) (Oxygen-containing functional groups on the carbon surface), leading to the increase reduction rate of NO. The bimetallic oxides catalysts are obviously effective to directly reduce NO. When the ratio of copper: potassium is 2:1, the NO reduction efficiency is about 90% at 300 °C. The catalytic activity mainly depends on the redox cycle of CuO/Cu2O, and the potassium inhibits the agglomeration of copper on the surface of carbon materials and enhances the catalytic reactivity of Cu.

Unravelling the functional complexity of oxygen-containing groups on carbon for the reduction of NO with NH3

BackgroundOxygen-containing groups on carbon materials play a crucial role in thermocatalytic and electrocatalytic reactions. A series of carbon-based catalysts with various oxygen-containing groups were synthesized by hydrogen peroxide oxidation for selective catalytic reduction (SCR) of NO with NH3. MethodsThe textural properties and oxygen-containing groups types were measured by N2 adsorption-desorption and spectroscopic characterization, respectively. Denitrification experiment results show the denitrification efficiency is correlated with the oxygen contents. The density functional theory (DFT) calculations demonstrate that oxygen-containing groups can promote the chemisorption for NO and NH3, thus resulting in high performance for NO reduction. Significant findingsThe carboxyl and phenol groups on carbon materials facilitate the catalytic performance of denitrification. Furthermore, based on mechanism analysis that the formation of CO (NH4) and C(NO) on surface oxides is considered significant steps for NO reduction with NH3. Our finding paves a new strategy for the design and synthesis of SCR catalysts with excellent activity for oxygen-containing carbon material at a relatively low temperature.

Green and Moderate Activation of Coal Fly Ash and Its Application in Selective Catalytic Reduction of NO with NH3.

Coal fly ash (CFA) is an ideal source for the preparation of heterogeneous catalysts due to its abundant silicon and aluminum oxides, but its activity needs to be improved. In this study, a green and moderate approach for CFA activation was proposed, and a series of CFA-based catalysts were prepared for NO selective catalytic reduction (SCR). The results indicated that CFA could be well activated via mechanochemical activation with 3 h of milling duration in 1 mol/L of acetic acid, and 90% of NO removal was achieved over the CFA-based catalyst in 250 to 375 °C. Two activating mechanisms, i.e., the enhanced CFA fragmentation and the motivated Al dissolution, were revealed during the mechanochemical activation. The former facilitated the formation of mesopores and the exposure of Fe components in CFA fragments, which enhanced the capacity of oxygen storage over the as-activated catalyst. The latter motivated the formation of Si-OH groups, which promoted the migration of electrons and the dispersion of V species, thereby increasing the capacity of NH3 adsorption over the as-obtained catalyst. Therefore, the performance of NO reduction was improved. The proposed activating approach could be a promising integration for CFA disposal and NO removal from inside coal-fired power plants.

Thermodynamic and kinetic study of NO reduction by pyridine/pyrrole during biomass tar reburning: the quantum chemical method approach

NOx emission is a serious problem during fossil fuel combustion. Novel reburning fuels, namely, nitrogen-containing tar compounds, including pyridine and pyrrole were taken into consideration for NO reduction and investigated by quantum chemical method. Theoretical calculation results show that pyridine could first decompose into small species, such as CN and hydrocarbon radicals, then reduce NO to N2. The decomposition of pyridine should overcome quite high energy barrier and adsorb a large amount of heat. This pathway may occur at high temperature zone, such as core flame zone of pulverized coal fired boiler. As soon as pyridine decomposes, the active intermediates (CN radical, etc.) could reduce NO very quickly. The direct reduction of NO by pyridine molecule should overcome lower energy barrier, which could occur at wider temperature range. Pyrrole is less thermostable than pyridine; the energy barriers of pyrrole cracking and direct reduction of NO stay at same level. Therefore, the reburning efficiency of pyrrole may be better at lower temperature than pyridine. Theoretical calculations indicate that nitrogen-containing tar compounds produced during biomass pyrolysis/gasification could have good performance for NO reduction in pulverized coal fired boiler as well as biomass or MSW furnace.

A study of ageing effect: Migration of rhodium under air atmosphere

Rh is the most important element for the current TWC technology. However, the deterioration of Rh is occurred during the high-temperature ageing under an air condition, leading to Rh migration. From the EPMA results, the migration of Rh was found to really take place, resulting in the formation of new Rh – support interaction. This was also supported by the formation of RhAlOx on the catalyst surface, which was confirmed by XPS, in the aged “Rh/CZ + Al” sample. Although Rh/CZ showed higher NO reduction than Rh/Al under dynamic conditions, “Rh/CZ + Al” and “Rh/Al + CZ” after high-temperature ageing showed similar NO reduction performance, which seems to be a sum of the activity of Rh/CZ and Rh/Al. This was explained by the Rh migration. The results of H2-TPR and FT-IR spectroscopy following CO adsorption revealed that many of Rh particles are still present on CZ even after the high-temperature ageing because of Rh – CZ interaction.

Experimental combustion characteristics and NOx emissions at 50% of the full load for a 600-MWe utility boiler: Effects of the coal feed rate for various mills

For realizing higher boiler efficiency and lower NOx emissions at a half load of a 600-MWe utility boiler, a novel approach is proposed for various coal feed rates. In this study, at 50% of the full load, industrial-size experiments were conducted at various coal feed rates with measurements of local gas temperatures and species concentrations (in the burner region and near-wall region, respectively), the carbon content of the fly ash, the carbon content of the slag, and the NOx emissions. The pulverized-coal ignition positions of two burners at low loads were at 0.2–0.3 m from the burner nozzle outlet; hence, satisfactory ignition performance was realized. At larger coal feed rates of mill A, both the ignition performance and the NO reduction performance improved. The unburnt carbon in the fly ash decreased monotonically and the carbon in the slag increased monotonically, with settings from 50%:50%–36%:64% (namely, changing the coal-feed rate pair of the middle and bottom mills from 50%:50%–43%:57%–36%:64%).

Low-temperature NO reduction performance of peanut shell-derived few-layer graphene loaded CeCoxMn1-xO3 catalyst

The catalysts were prepared by the hydrothermal method using agricultural waste biomass peanut shell-derived few-layer graphene (PS-FLG) as the support. The NO reduction performance test of NH3-SCR and various characterization means were employed to preliminarily explore the mechanism of Co-doping activity at the B site. The results showed that the conversion rate of NOx of the three catalysts reached 99.1% and remained stable in the range of 250 ∼ 400 °C. The order of activity at low temperature was 5% CeCo0.5Mn0.5O3 > 5% CeMnO3 > 5% CeCoO3. Partial doping of Co could inhibit the aggregation of active components, increase the percentage of high valence ions, improve the migration of lattice oxygen (Oβ) to the adsorbed oxygen (Oα), and enhance the redox performance. CeCo0.5Mn0.5O3 exhibited better low-temperature activity, and the conversion rate of NOx reached 97.0% at 200 °C, and had excellent SO2 resistance.

The influence of support composition on the activity of Cu:Ce catalysts for selective catalytic reduction of NO by CO in the presence of excess oxygen

Excellent catalytic performance for NO reduction by CO in the presence of 5% O2over Cu1:Ce3/Al2O3.

Oxygen Vacancy-rich Porous Co3O4 Nanosheets toward Boosted NO Reduction by CO and CO Oxidation: Insights into the Structure-Activity Relationship and Performance Enhancement Mechanism.

Oxygen vacancy-rich porous Co3O4 nanosheets (OV-Co3O4) with diverse surface oxygen vacancy contents were synthesized via facile surface reduction and applied to NO reduction by CO and CO oxidation. The structure-activity relationship between surface oxygen vacancies and catalytic performance was systematically investigated. By combining Raman, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and O2-temperature programmed desorption, it was found that the efficient surface reduction leads to the presence of more surface oxygen vacancies and thus distinctly enhance the surface oxygen amount and mobility of OV-Co3O4. The electron transfer towards Co sites was promoted by surface oxygen vacancies with higher content. Compared with the pristine porous Co3O4 nanosheets, the presence of more surface oxygen vacancies is beneficial for the catalytic performance enhancement for NO reduction by CO and CO oxidation. The OV-Co3O4 obtained in 0.05 mol L-1 NaBH4 solution (Co3O4-0.05) exhibited the best catalytic activity, achieving 100% NO conversion at 175 °C in NO reduction by CO and 100% CO conversion at 100 °C in CO oxidation, respectively. Co3O4-0.05 exhibited outstanding catalytic stability and resistance to high gas hour space velocity in both reactions. Combining in situ DRIFTS results, the enhanced performance of OV-Co3O4 for NO reduction by CO should be attributed to the promoted formation and transformation of dinitrosyl species and -NCO species at lower and higher temperatures. The enhanced performance of OV-Co3O4 for CO oxidation is due to the promotion of oxygen activation ability, surface oxygen mobility, as well as the enhanced CO2 desorption ability. The results indicate that the direct regulation of surface oxygen vacancies could be an efficient way to evidently enhance the catalytic performance for NO reduction by CO and CO oxidation.

Sb modified Fe–Mn/TiO2 catalyst for the reduction of NO x with NH3 at low temperatures

Manganese-based catalysts have attracted much attention due to their excellent performance for NO reduction with NH3 (NH3-SCR) at low temperatures. In the current study, the novel metal Sb was modified into Mn/TiO2 and Fe–Mn/TiO2, and the NO x conversion was compared with those of Mn/TiO2 and Fe–Mn/TiO2 catalysts to investigate the effect of the Sb. The NO x reduction activities of the catalysts were evaluated in the temperature range of 100–250 °C at a space velocity of 60,000 h−1. The physicochemical properties of all the catalysts were characterized by Brunauer–Emmett–Teller surface area, temperature-programmed desorption of ammonia, temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Interestingly, the Sb-promoted Mn-based catalysts showed significantly higher NO x conversion than the other catalysts with or without 6 vol% of H2O. The high performance of the Sb-modified catalysts could be related to the increase of acid sites and redox properties.