Catalytic Reduction Of NO Research Articles

Microstructure and Catalytic Activity of MnSbOx Catalysts for Selective Catalytic Reduction of NO with NH3

AbstractManganese‐antimony composite oxide catalysts were prepared for use in low‐temperature selective catalytic reduction of flue gas, by adopting the strategy of passivation to regulate the valence state of the active component and control catalytic activity. Activity evaluation results found that MnSb0.36Oy delivered 80 % NO conversion in the presence of SO2 at 200 °C, and nearly 90 % conversion at 250 °C. Doping with Sb changed the surface micromorphology, resulting in a perforated porousness layered foam with a porous structure of tens of nanometers, which was conducive to molecular mass transfer of the reaction gas. Doping with Sb regulated the valence state of the active MnOx component, which diminished catalytic oxidation of SO2, thus promoting catalyst stability and limiting the toxic effect of SO2.

Preparation of zeolite type faujasite from glass waste and aluminum scraps for the selective catalytic reduction of NO with NH3

Preparation of zeolite type faujasite from glass waste and aluminum scraps for the selective catalytic reduction of NO with NH3

Reduction of Typical Diesel NOx Emissions by SCR-NH3 Using Metal-Exchanged Natural Zeolite and SBA-15 Catalysts

In this work, the catalytic performance of clinoptilolite (CLIN) and SBA-15 catalysts, doped with Fe and Cu, was evaluated in the selective catalytic reduction of NO using NH3 as a reducing agent (SCR-NH3). Both Cu-CLIN and Fe-CLIN were obtained by ion-exchange using natural clinoptilolite zeolite originating from the Hrabovec deposit (northeast Slovakia region). Cu-SBA-15 and Fe-SBA-15 were prepared by impregnation into SBA-15 mesoporous synthesized silica. Standard catalytic activity tests were carried out on a bench-scale laboratory apparatus using a reaction mixture of a standard test. GHSV of 48,000 h−1 was adopted based on the space velocity of a real NH3-SCR catalyst for diesel vehicles (100–550 °C). All Cu-doped samples showed better NO conversion values than Fe-doped samples. Clinoptilolite catalysts were more active than those based on SBA-15. Maximum NO conversions of about 96% were observed for Cu-CLIN and Fe-CLIN at 350–400 °C, respectively. Moreover, Fe-CLIN also showed higher stability in the presence of SO2 and water steam at 350 °C. These results demonstrate the potential of metal-doped natural clinoptilolite to be used as cost-effective catalysts applied to the abatement of NOx emissions generated in automotive combustion processes.

Essential Features of Gliding Arc Plasma for High-Performance Hydrocarbon Selective Catalytic Reduction of NOxat Low Temperatures

The high removal efficiency of NOx from diesel engine exhaust gas at low temperatures remains challenging due to the poor activity of catalysts under this condition. This work investigated the effectiveness of gliding arc plasma in the NOx removal over the Ag/γ-Al2O3 catalyst with n-heptane as a reducing agent source for NOx reduction. The plasma conjugated with the catalyst was performed like an injection method, i.e., a small part flow (1/26) that consisted of n-heptane was reformed to H2 and oxygenated hydrocarbons (OHCs) by gliding arc plasma before mixing it with the gas containing NOx. Then, the overall gas was passed through the catalyst stage at various temperatures from 127 to 253 °C. The experimental data revealed that NOx removal efficiency significantly increased with plasma treatment. The enhancement by plasma treatment increased with temperature from 127 to 226 °C, but the enhancement reduced at a temperature of 253 °C. The result came from formation of H2 and OHCs in the treated plasma gas, which reactivated NOx removal over the catalyst at low temperatures. Moreover, the enhanced NOx removal efficiency in a wide low-temperature range is obtained due to considerable hydrogen formation by the gliding arc plasma. To sum up, the highest NOx removal efficiency was 68.5% under a temperature of 226 °C and specific energy input of 34.6 J/L, while it was 20.3% for the catalyst alone; in other words, the removal efficiency increased by 48.1% with using plasma under these conditions. Owing to its low energy consumption, high-throughput gas treatment, and effectiveness at low temperatures, the technology is promising in practical applications for refining diesel exhaust gases.

Insight into the Mechanism of Selective Catalytic Reduction of NO by CO over a Bimetallic IrRu/ZSM-5 Catalyst in the Absence/Presence of O2 by Isotopic C13O Tracing Methods.

The development of efficient catalysts for the selective catalytic reduction of NO by CO (CO-SCR) in the presence of O2 is highly desirable for controlling the emission of toxic gases from tailpipes. Here, a bimetallic IrRu/ZSM-5 catalyst was prepared for the selective catalytic reduction of NO by CO in the presence of O2 (5%) for the low-temperature treatment of exhaust gas. IrRu/ZSM-5 afforded 90% NOx conversion in the range of 225-250 °C and maintained 90% NOx conversion after 12 h of reaction. Ru addition inhibited agglomeration of the Ir particles during the reduction process and provided more active sites for NO adsorption. Isotopic C13O tracing and in situ diffuse reflectance infrared Fourier-transform spectroscopy experiments were used to elucidate the CO-SCR mechanism in the absence or presence of O2. NCO could easily form on the surface of catalysts in the absence of O2, whereas NCO formation has been inhibited owing to the quick consumption of CO in the presence of O2. Moreover, some byproducts such as N2O and NO2 are generated in the presence of O2. Finally, a possible mechanism for CO-SCR under different conditions was proposed based on in situ experiments and physicochemical analyses.

Modelling of Selective Catalytic Reduction of NO<sub>x</sub> with NH<sub>3</sub> over the Fe-Cu/ZSM-5 Catalyst

Modelling of Selective Catalytic Reduction of NO<sub>x</sub> with NH<sub>3</sub> over the Fe-Cu/ZSM-5 Catalyst

Catalytic performance of Cu/Hβ catalysts for selective catalytic reduction of NO with NH3

A series of Cu(x)/Hβ catalysts were prepared by the impregnation method and the effect on the performance of the catalysts for the selective catalytic reduction of NO with NH3 (NH3-SCR) was investigated. Characterization techniques such as XRD, N2 adsorption-desorption, NH3-TPD, NO-TPD, H2-TPR, EDS and XPS were used to investigate the physical and chemical properties of the catalysts and the reason of the decrease of catalyst activity in the presence of SO2. It was shown that the catalyst Cu(3)/Hβ, the Cu loading was 3% and Cu(2)/Hβ, the Cu loading was 2%, exhibited the better catalytic activity when the initial reaction material contained no SO2 and SO2, and t95 was 169 and 225 °C, respectively. The analysis results of the catalyst before and after the reaction showed that the main reason for the decrease of catalyst activity in the presence of SO2 was that the ammonium sulfur salt which was formed by the reaction of SO2 and NH3 in the low reaction temperature covers the catalyst active center.

Mechanisms in the Catalytic Reduction of N2O by CO over the M13@Cu42 Clusters of Aromatic-like Inorganic and Metal Compounds.

Metal aromatic substances play a unique and important role in both experimental and theoretical aspects, and they have made tremendous progress in the past few decades. The new aromaticity system has posed a significant challenge and expansion to the concept of aromaticity. From this perspective, based on spin-polarized density functional theory (DFT) calculations, we systematically investigated the doping effects on the reduction reactions of N2O catalyzed by CO for M13@Cu42 (M = Cu, Co, Ni, Zn, Ru, Rh, Pd, Pt) core-shell clusters from aromatic-like inorganic and metal compounds. It was found that compared with the pure Cu55 cluster, the strong M-Cu bonds provide more structural stability for M13@Cu42 clusters. Electrons that transferred from the M13@Cu42 to N2O promoted the activation and dissociation of the N-O bond. Two possible reaction modes of co-adsorption (L-H) and stepwise adsorption (E-R) mechanisms over M13@Cu42 clusters were thoroughly discovered. The results showed that the exothermic phenomenon was accompanied with the decomposition process of N2O via L-H mechanisms for all of the considered M13@Cu42 clusters and via E-R mechanisms for most of the M13@Cu42 clusters. Furthermore, the rate-limiting step of the whole reactions for the M13@Cu42 clusters were examined as the CO oxidation process. Our numerical calculations suggested that the Ni13@Cu42 cluster and Co13@Cu42 clusters exhibited superior potential in the reduction reactions of N2O by CO; especially, Ni13@Cu42 clusters are highly active, with very low free energy barriers of 9.68 kcal/mol under the L-H mechanism. This work demonstrates that the transition metal core encapsulated M13@Cu42 clusters can present superior catalytic activities towards N2O reduction by CO.

Unveiling the Origin of Selectivity in the Selective Catalytic Reduction of NO with NH3 over Oxide Catalysts.

The trade-off between activity and selectivity is a century-old puzzle in catalysis. In the selective catalytic reduction of NO with NH3 (NH3-SCR), various typical oxide catalysts exhibit distinct characteristics of activity and selectivity: Mn-based catalysts show outstanding low-temperature activity and poor N2 selectivity, mainly caused by N2O formation, while Fe- and V-based catalysts possess inverse characteristics. The underlying mechanism, however, has remained elusive. In this study, by combining experimental measurements and density functional theory calculations, we demonstrate that the distinct difference in the selectivity of oxide catalysts is determined by the gap in the energy barriers between N2 formation and N2O formation from the consumption of the key intermediate NH2NO. The gaps in the energy barriers follow the order of α-MnO2 < α-Fe2O3 < V2O5/TiO2, in correspondence with the order of N2 selectivity of the catalysts. This work discloses the intrinsic link between the target reaction and side reactions in the selective catalytic reduction of NO, providing fundamental insights into the origin of selectivity.

Co Single Atoms and CoOx Nanoclusters Anchored on Ce0.75Zr0.25O2 Synergistically Boosts the NO Reduction by CO

AbstractAchieving high NO conversion and N2 selectivity in selective catalytic reduction of NO by CO (CO‐SCR) in a wide operating temperature window, particularly in the presence of high O2 concentration, remains a big challenge. Herein, guided by density functional theory (DFT) calculations, a catalyst is rationally developed with dual active centers consisting of both Co single‐atoms (SAs) and CoOx nanoclusters (NCs) co‐anchored on Ce0.75Zr0.25O2 support (CZO), which show above 99.7% NO conversion and 100% N2 selectivity at 250–400 °C under 5 vol% O2. DFT calculation and experimental results confirm a strong interaction among Co SAs, CoOx NCs, and CZO support. Co SAs enhance CO adsorption and accompany the oxygen vacancies (OVs) formation in CZO, while the CoOx NCs promote both NO conversion to nitrate intermediate and the breakage of the NO bond at OVs, thus synergistically boosting the N2 formation.

Influence of Y Doping on Catalytic Activity of CeO2, MnOx, and CeMnOx Catalysts for Selective Catalytic Reduction of NO by NH3

Novel yttrium-doped CeO2, MnOx, and CeMnOx composites are investigated as catalysts for low-temperature NH3-SCR. The study involves the preparation of unmodified oxide supports using a citrate method followed by modification with Y (2 wt.%) using two approaches, including the one-pot citrate method and incipient wetness impregnation of undoped oxides. The NH3-SCR reaction is studied in a fixed-bed quartz reactor to test the ability of the prepared catalysts in NO reduction. The gas reaction mixture consists of 800 ppm NO, 800 ppm NH3, 10 vol.% O2, and He as a balance gas at a WHSV of 25,000 mL g−1 h−1. The results indicate that undoped CeMnOx mixed oxide exhibits significantly higher deNOx performance compared with undoped and Y-doped MnOx and CeO2 catalysts. Indeed, yttrium presence in CeMnOx promotes the competitive NH3-SCO reaction, reducing the amount of NH3 available for NO reduction and lowering the catalyst activity. Furthermore, the physical-chemical properties of the prepared catalysts are studied using nitrogen adsorption/desorption, XRD, Raman spectroscopy, temperature-programmed reduction with hydrogen, and temperature-programmed desorption of ammonia. This study presents a promising approach to enhancing the performance of NH3-SCR catalysts at low temperatures that can have significant implications for reducing NO emissions.

Reaction mechanism of selective catalytic reduction of NO with NH3 on Fe3O4 (1 1 1) surface: Experimental and DFT studies

Iron-based catalysts have vast potential for application prospect in selective catalytic reduction of NOx with NH3 (NH3-SCR). These catalysts offer excellent SCR activity at medium and high temperatures, N2 selectivity and environmental performance. Among these catalysts, Fe3O4 catalyst is highly active and significant in the denitration reaction due to the presence of both ferrous and ferric ions. This study utilized density functional theory (DFT) in combination with experimental measurements to investigate the reaction pathway of NH3-SCR on the Fe3O4(111) surface. The research found that the surface was favorable for the adsorption of NO molecules and followed the NO activation mechanism. Upon activation of NO at the Feoct site, it reacted with NH3 to form NH2NO, This compound then underwent decomposition into N2 and H2O. The presence of O2 on the catalyst facilitated the surface dehydrogenation reaction and completed the SCR cycle reaction. Based on the DFT results, the formation of NH2NO intermediate was the rate-determining step of SCR reaction. The Fe3O4(111) surface followed the L-H mechanism, which was in line with the experimental results. This study provided novel insights into the SCR reaction process and can be useful in developing new iron-based SCR catalysts.

Insight into the low-temperature DeNOx performance of copper-based oxides: Perspective from the valence state distribution

Understanding the effect of CuOx valence state specifically is significant for constructing high-performance Cu based oxide catalyst for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR). In this work, CuOx with different valence state including Cu2O, Cu2O-CuO and CuO particles are synthetized as model catalysts, which present same variation laws in catalytic performance at 180 ℃, 210 ℃ and 240 ℃. NH3-SCR catalytic performance of Cu2O-CuO heterojunction is the best, CuO exhibits good catalytic activity, while Cu2O possesses excellent N2 selectivity. Experimental results combined with density functional theory (DFT) calculations reveal that Cu2+ favor to form monodentate nitrate and possess strong ability of activation and dehydrogenation of NH3. The energy barrier for the form of NH2* is 79.5 kJ/mol, which is much lower than that for Cu+. While Cu+ is beneficial to NH3 and NOx adsorption and the form of bidentate nitrate, which have a positive impact on improving the selectivity of N2. Moreover, the collaboration of Cu2+ and Cu+ facilitates the redox capability and the form of surface adsorbed oxygen species, thus the reaction progress is further promoted. The SCR reaction catalyzed by three samples are dominated mainly by Langmuir-Hinshelwood (L-H) mechanism at 180 ℃. While at 240 ℃, the reaction over Cu2O follows Eley-Rideal (E-R) mechanism, during which the rate-limiting step is the internal hydrogen transfer procedure (NH2NO*→NHNOH*). Over CuO, the reaction follows L-H mechanism, the process of atomic isomerism (NHNOH*+ *→N2*+H2O*) is the rate-determining step. The energy barriers are 136 and 146 kJ/mol, respectively. This work may supply important theoretical support for the preparation of high-performance Cu-based oxide catalysts.

Selective catalytic reduction of NO by CO over MOF-based CuOx@ZIF-67 catalysts and reaction mechanism

The selective catalytic reduction of NOx using CO as a reduction gas (CO-SCR) is a promising method to eliminate NO and CO simultaneously and attracted much of the attention recently. Currently, the majority of CO-SCR catalysts tested showed high activity in the absence of oxygen, but their performance was poor when oxygen was present. As a result, it is important to explore an effective catalyst under aerobic conditions. This work proposed a new catalysts for CO-SCR based on metal organic framework (MOF) material, specially, ZIF-67. A series ofx%CuOx@ZIF-67 catalysts were successfully prepared and the CO-SCR reactivity was evaluated in a fixed-bed micro reactor with simulated flue gas in the presence of O2, containing 500 ppm NO, 1000 ppm CO, 0–10% O2 balanced by N2 at a temperature range of 200–375 °C. The catalysts were characterized by SEM, XRD, TGA, NH3-TPD, XPS, BET, H2-TPR, and in situ DRIFTS to investigate the influence of microstructure, texture, and chemical properties of the catalyst on the SCR performance. The result demonstrates that the CuOx@ZIF-67 catalysts were effective for CO-SCR performance and NO conversion was 100% at 300 °C for 8.0 %CuOx@ZIF-67 catalyst. Cu improved the surface oxygen vacancies and the reduction ability of the catalyst. The synergy effect of Cu on Co can increase the acid sites and the amount of Lewis acid on the catalyst surface. The primary intermediate species, according to in situ DRIFTS analysis, were Cu+–CO, bidentate nitrate, and bridging nitrate. The reaction path of CO-SCR on CuOx@ZIF-67 was proposed based on the in situ DRIFTS analysis.

Catalytic NO Reduction by Noble-Metal-Free Vanadium-Aluminum Oxide Cluster Anions.

By using state-of-the-art mass spectrometry and guided by the newly discovered single-electron mechanism (SEM; e.g., Ti3+ + 2NO → Ti4+-O•- + N2O), we determined experimentally that the vanadium-aluminum oxide clusters V4-xAlxO10-x- (x = 1-3) can catalyze the reduction of NO by CO and substantiated theoretically that the SEM still prevails in driving the catalysis. This finding marks an important step in cluster science in which a noble metal had been demonstrated to be indispensable in NO activation mediated by heteronuclear metal clusters. The results provide new insights into the SEM in which active V-Al cooperative communication favors the transfer of an unpaired electron from the V atom to NO attached to the Al atom on which the reduction reaction actually takes place. This study provides a clear picture for improving our understanding of related heterogeneous catalysis, and the electron hopping behavior induced by NO adsorption could be a fundamental chemistry for driving NO reduction.

Performance of Mn-Ce-Fe/FA Catalysts on Selective Catalytic Reduction of NOX with CO under Different Atmospheres

Gas turbines produce a large amount of NOx and CO due to high temperatures and insufficient combustion. Through the selective catalytic reduction of NO with CO (CO-SCR) in a gas turbine, the activities of the Mn-Fe-Ce/FA catalyst using fly ash (FA) as a carrier under different atmospheres were studied. The catalysts prepared by calcining different active materials under different atmospheres were used to analyze their denitrification abilities and resistance to water vapor. The denitrification performance of the catalyst prepared under reducing atmosphere is about 30 percent higher than that of the catalyst prepared under air atmosphere, and the decarburization performance is about 40 percent higher. In the presence of oxygen, the denitrification rate and decarburization rate of the 1:1 ratio of the Mn-Ce catalyst reach 67.16% and 59.57%, respectively. In an oxygen-containing atmosphere, the catalyst prepared by replacing Ce with Fe shows better denitrification and decarburization performances, which are 78.56% and 78.39%, respectively. When the flue gas space velocity is 4000 h−1 and the carbon-nitrogen ratio is 1.6, the catalyst shows better performance. After the water vapor is introduced, the denitrification and decarbonization rates of the catalyst decrease by about 10% and 9%, respectively. After ceasing water vapor, it rebounds by about 8%, and the activity could not be fully restored. However, the catalyst still shows strong water resistance in general.

Low-Temperature Selective Catalytic Reduction of NO with NH3 over a Biochar-Supported Perovskite Oxide Catalyst

Low-Temperature Selective Catalytic Reduction of NO with NH₃ over a Biochar-Supported Perovskite Oxide Catalyst

Investigation of catalytic reduction of NO by CO over A- and B- site substituted La(Sr)Fe(Co)O3 perovskites

In this study, La1−xSrxFeO3 and LaFe1−xCoxO3 perovskites with different La/Sr and Fe/Co ratios have been synthesized via auto combustion method using glycine as fuel. After complete characterization, the catalytic activity of the perovskites was evaluated in the nitrogen monoxide reduction by carbon monoxide, in a lab-scale plug flow reactor. The most active catalysts were La0.75Sr0.25FeO3 and LaFe0.25Co0.75O3. Substitution in different sites of perovskite structure influences differently the catalytic activity and selectivity. The A-site substitution of La by Sr resulted in decrease of activity due to the presence of strontium carbonate, formed by strong adsorption of the produced carbon dioxide on the catalyst surface while selectivity of the reaction is correlated with the oxygen reverse uptake. The B-site substitution of Fe by Co increases the activity due to the partial -reduction of the classic ABO3 phase to A2BO4 Ruddlesden-Popper perovskite phase La2CoO4.

Synergistic effect between the acidity and redox performance of the SO42−-CeO2 catalysts for NO reduction

Herein, a series of SO42−-CeO2 catalysts were synthesized by a sol-gel method for the selective catalytic reduction of NO by NH3 (NH3-SCR). The introduction of SO42− endowed composite catalyst with higher catalytic activity than pure CeO2. In particular, 3% SC with 3% SO42− showed over 90% NO removal between 247 and 450 °C. SO42− promoted the increase of Ce3+ content, adsorbed oxygen, and surface acidity of the composites. Furthermore, the interaction between SO42− and cerium oxide induced the synergistic effect between acidic sites and redox sites in the NH3-SCR reaction. The introduction of SO42− significantly supported the increase of B-acid and the enhancement of l-acid sites, and promoted the NH3-SCR reaction to follow both Eley-Rideal and Langmuir-Hinshelwood mechanisms.

Effect of Cu loading on the performance and kinetics of Cu/SAPO-34 catalysts for selective catalytic reduction with NH3

A series of X%Cu/SAPO-34 (X = 1.0, 2.0, 4.0 and 6.0) catalysts were prepared by ultrasonic impregnation method for selective catalytic reduction (SCR) of NOx with ammonia. The effect of different Cu loadings on the selective catalytic reduction of NO by molecular sieve catalysts was examined on a fixed-bed reactor. Catalyst physicochemical properties were characterized and analyzed using XRD, TEM, NH3-TPD, H2-TPR, and in situ DRIFTS. Catalysts were used in reaction kinetics studies from the perspective of transient and steady-state kinetics. Cu/SAPO-34 catalyst with 4% Cu loading had the best denitrification efficiency and wide activity window. Copper species were highly dispersed on the catalyst surface. Cu/SAPO-34 catalyst with 4% Cu loading had rich acidic sites and excellent redox performance. Cu/SAPO-34 catalysts with 4% Cu loading possess minimal activation energy and were lower than commercial catalysts. According to the results of in situ IR, transient and steady-state analysis, the Cu/SAPO-34 catalyst with 4% Cu loading in the NH3-SCR reaction process was mainly E-R mechanism, and there was L-H mechanism.