Selective Catalytic Reduction Of NO Research Articles

Significantly Improving N2 Selectivity and H2O Resistance by Confining Mn into TiO2 Nanotubes for Low-Temperature Selective Catalytic Reduction of NO with NH3

Significantly Improving N₂ Selectivity and H₂O Resistance by Confining Mn into TiO₂ Nanotubes for Low-Temperature Selective Catalytic Reduction of NO with NH₃

Tailoring Iridium Valence States on ZSM-5 for Enhanced Catalytic Performance in CO Selective Catalytic Reduction of NO under Oxygen-Enriched Environments.

Barium and iridium supported on Zeolite Socony Mobil-5 (ZSM-5) are efficient catalysts for the selective catalytic reduction of nitric oxide by carbon monoxide (CO-SCR), with enhanced cyclic stability. The introduction of Ba hindered the oxidation of metallic Ir active species and enabled Ir to maintain an active metallic state, thereby preventing a decrease in catalytic activity in the CO-SCR reaction. Moreover, the Ba modification increased the NO adsorption of the catalyst, further improving the catalytic activity. Owing to the better anti-oxidation ability of Ir0 in IrBa0.2/ZSM-5(27) than in Ir/ZSM-5(27), IrBa0.2/ZSM-5(27) showed better stability than Ir/ZSM-5(27). Considering that all samples in the present study were tested to simulate actual flue gases (such as sintering flue gas and coke oven flue gas), NH3 was introduced into the reaction system to serve as an extra reductant for NOx. The NOx conversion to N2 (77.1%) was substantially improved using the NH3-CO-SCR system. The proposed catalysts and reaction systems are promising alternatives for treating flue gas, which contains considerable amounts of NOx and CO in oxygen-enriched environments.

Combined Experimental and Density Functional Theory Study on the Mechanism of the Selective Catalytic Reduction of NO with NH3 over Metal-Free Carbon-Based Catalysts.

Metal-free carbon-based catalysts are attracting much attention in the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR). However, the mechanism of the NH3-SCR reaction on carbon-based catalysts is still controversial, which severely limits the development of carbon-based SCR catalysts. Herein, we successfully reconstructed carbon-based catalysts through oxidation treatment with nitric acid, thereby enhancing their low-temperature activity in NH3-SCR. Combining experimental results and density functional theory (DFT) calculations, we proposed a previously unreported NH3-SCR reaction mechanism over carbon-based catalysts. We demonstrated that C-OH and C-O-C groups not only effectively activate NH3 but also remarkedly promote the decomposition of intermediate NH2NO. This study enhances the understanding of the NH3-SCR mechanism on carbon-based catalysts and paves the way to develop low-temperature metal-free SCR catalysts.

Selective catalytic reduction of NO with NH3 over copper-manganese spinel oxides at low temperature: effects of calcination temperature and dispersant

Selective catalytic reduction of NO with NH3 over copper-manganese spinel oxides at low temperature: effects of calcination temperature and dispersant

The reduction of copper in LaFeO3, La2CuO4 and CuO three-phase system improves the efficiency of NO removal: Experimental and density functional theory calculation

Hollow spherical LaCu0.5Fe0.5O3 (LCF) and La0.8Ce0.1Cu0.5Fe0.5O3 (LCCF) catalysts are synthesized by solvothermal method, and CuO is reduced in two samples, so that the two corresponding multiphase catalysts (R-LCF and R-LCCF) were prepared and used for the selective catalytic reduction of NO with CO (CO-SCR). The results show that the balance of Ce3++Cu2+↔Cu++Ce4+ between Ce and Cu ions promotes the reduction of CuO in the Ce-doped LCCF catalyst more obviously. In addition, the reduction of Ce and Cu in R-LCCF generates more oxygen vacancies, which leads to more surface adsorbed oxygen species, thus facilitating the conversion of more NO to NOx species. Besides, the presence of reduced Cu is highly active and can inhibit the production of carbonates occupying the active site. The ability to activate both CO and NO after the evolution of Cu0 to the key species Cu+ leads to a rapid reaction between Cu+-CO and NOx species. These are the key factors for the significant increase in catalytic activity at low temperatures. It is worth noting that the CO-SCR reaction on the R-LCCF catalyst corresponds to the Langmuir-Hinshlwood (L-H) and Eley-Rideal (E-R) mechanisms at different temperature windows, respectively.

Al-rich Cu-SSZ-13 zeolite synthesized by interconversion from Y: Crystallization process resolution and application in the selective catalytic reduction of NO with NH3

Cu-SSZ-13 zeolite is a promising catalyst in the selective catalytic reduction (SCR) of NOx with NH3 and the interzeolite conversion is considered as a convenient method with relatively low cost to get the Al-rich SSZ-13 zeolite with great hydrothermal stability. However, the crystallization process of interzeolite conversion and its relation to the catalytic performance of Cu-SSZ-13 in the NH3-SCR of NOx are still poorly understood. Herein, the interzeolite conversion process of Y to SSZ-13 was well resolved and the effect of major synthesis factors on the hydrothermal stability and catalytic performance of Cu-SSZ-13 in the NH3-SCR of NOx was investigated. The results indicate that highly crystalline SSZ-13 can be synthesized by the interzeolite conversion from Y, using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as the structure-directing agent (SDA) and with a SDA/Si molar ratio of 0.06–0.2. The Y zeolite of FAU framework is first degraded and decomposed into the oligomeric aluminosilicate fragments quickly in the alkaline circumstance; thereafter, the oligomeric fragments develop into the crystal nuclei that arouse the rapid crystallization of the SSZ-13 zeolite of CHA framework with the help of SDA and solid Al(OH)3, during which the Al(OH)3 source is dissolved and restructured to tetrahedral Al species and incorporated into the CHA framework. The synthesized Cu-SSZ-13 zeolite exhibits excellent catalytic performance in the NH3-SCR of NO, achieving an NO conversion of nearly 90% at a rather low temperature of 150 °C and a gaseous hourly space velocity (GHSV) of 100,000 h−1. Moreover, the Cu-SSZ-13 catalyst displays great hydrothermal stability and remains highly active even after aging at 800 °C. These results help to clarify the mechanism of interzeolite conversion and provide an effective method to synthesize highly crystalline Al-rich SSZ-13 zeolite with great potential for application in the NH3-SCR of NOx.

Promotional effect of aluminum doping on the sulfated Fe2O3 catalyst in selective catalytic reduction of NO with NH3

Promotional effect of aluminum doping on the sulfated Fe2O3 catalyst in selective catalytic reduction of NO with NH3

Insight into the Alkali Resistance Mechanism of FeMoTiOx Catalysts for NH3 Selective Catalytic Reduction of NO: Self-Defense Effects of MoOx for Alkali Capture.

The deactivation of selective catalytic reduction (SCR) catalysts caused by alkali metal poisoning remains an insurmountable challenge. In this study, we examined the impact of Na poisoning on the performance of Fe and Mo co-doped TiO2 (FeaMobTiOx) catalysts in the SCR reaction and revealed the related alkali resistance mechanism. On the obtained Fe1Mo2.6TiOx catalyst, the synergistic catalytic effect of uniformly dispersed FeOx and MoOx species leads to remarkable catalytic activity, with over 90% NO conversion achieved in a wide temperature range of 210-410 °C. During the Na poisoning process, Na ions predominantly adsorb on the MoOx species, which exhibit stronger alkali resistance, effectively safeguarding the FeOx species. This preferential adsorption minimizes the negative effect of Na poisoning on Fe1Mo2.6TiOx. Moreover, Na poisoning has little influence on the Eley-Rideal reaction pathway involving adsorbed NHx reacting with gaseous NOx. After Na poisoning, the Lewis acid sites were deteriorated, while the abundant Brønsted acid sites ensured sufficient NHx adsorption. As a benefit from the self-defense effects of active MoOx species for alkali capture, FeaMobTiOx exhibits exceptional alkali resistance in the SCR reaction. This research provides valuable insights for the design of highly efficient and alkali-resistant SCR catalysts.

Copper-based catalysts supported on novel Metal-Organic Framework MIL-125(Ti) for selective catalytic reduction of NO with CO

A type of novel copper-based catalysts supported on MIL-125(Ti), a kind of metal–organic frameworks (MOFs), noted as Cu-MIL-125(Ti), was synthesized for the selective catalytic reduction (SCR) of NO with CO. The reactivity of Cu-MIL-125 catalysts for selective catalytic reduction of NO by CO (SCR-CO) was evaluated in a fixed bed reactor. A number of characterization techniques were used to explore the basic physical–chemical properties and the reaction mechanism. The results showed that the large specific surface area and micro-mesopores of the MIL-125 carrier promoted the high dispersion of Cu species, leading to the outstanding SCR-CO performance. Among the results, 90 % NO conversion and 92 % N2 selectivity were proved for the 6.2Cu-MIL-125 catalyst at 325 °C in oxygen-rich environment. XRD results showed that the metal organic frame structure and TiO2 structure coexisted in the catalysts, which was the major factor to influence the NO reduction efficiency. XPS characterization and H2-TPR reduction results showed that the catalytic performance of the catalyst was mainly determined by the path of Cu2+ reduction to Cu+ and then Cu+ to Cu0. Lewis acid on the catalyst surface played an important role in the CO-SCR reaction. In situ DRIFTS study proved that NO was first adsorbed on the surface of the catalyst to form different nitrate, NCO and isocyanate species. Then the adsorbed NO and the intermediates reacted with gaseous CO, which is a typical interaction between adsorbed molecules and gas molecules. Oxygen vacancies on the catalyst surface was involved in the reaction of CO to CO2. The whole reaction follows the M–K mechanism and the E-R mechanism. A preliminary reaction pathway was proposed based on the in situ DRIFTS results.

Reactivity of Ni-modified MIL-100(Fe) catalysts for C3H6-SCR and reaction mechanism

Metal-organic frameworks (MOFs)-based carrier, MIL-100(Fe), was synthesized by hydrothermal method and Ni was supported on the MIL-100(Fe) by wet impregnation method to prepare the catalysts for selective catalytic reduction of NO with C3H6 (C3H6-SCR). The addition of Ni significantly improved the reactivity of C3H6-SCR. At 275 °C, the NO conversion of MIL-100(Fe) was 74.5%, whereas the NO conversion of 5.8%Ni/MIL-100(Fe) with 100% N2 selectivity was 100%. The in-situ DRIFTS prove that the interaction between NO2−/NO3− and CxHyOz substances generated intermediate isocyanates (R-NCO), and the reaction pathway was proposed based on the DRIFTS results to understand the mechanism.

Deactivation of the Ce/TiO2 Catalyst by POx for Selective Catalytic Reduction of NO with NH3: An Undergraduate Laboratory Experiment

Deactivation of the Ce/TiO₂ Catalyst by POx for Selective Catalytic Reduction of NO with NH₃: An Undergraduate Laboratory Experiment

Hollow Mn-doped CeO2@Co3O4 catalyst for NO reduction by CO

Selective catalytic reduction of NO using CO (CO-SCR) is a promising technology for the purification of NO in the flue gas. However, the presence of O2 significantly inhibits the activity of the CO-SCR catalyst. Herein, we synthesize a hollow Mn-doped CeO2@Co3O4 catalyst (Mn-CeO2@Co3O4), which achieved 82% NO conversion, 100% CO conversion, and 78% N2 selectivity under 5 vol% O2 at 200 °C, superior to those of CeO2@Co3O4 and Co3O4@CeO2 catalysts. The characterization results indicate that the strong electronic interaction at the heterointerfaces between Co3O4 and CeO2 plays a crucial role in promoting selective adsorption of NO. Furthermore, the Mn doping into the Co3O4 lattice of the catalyst facilitates the conversion of N2O intermediates, thereby enhancing the overall activity. This research provides a new strategy for the design and synthesis of CO-SCR catalysts.

Dy-Modified Mn/TiO2 Catalyst Used for the Selective Catalytic Reduction of NO in Ammonia at Low Temperatures.

A novel Mn/TiO2 catalyst, prepared through modification with the rare-earth metal Dy, has been employed for low-temperature selective catalytic reduction (SCR) denitrification. Anatase TiO2, with its large specific surface area, serves as the carrier. The active component MnOx on the TiO2 carrier is modified using Dy. DyxMn/TiO2, prepared via the impregnation method, exhibited remarkable catalytic performance in the SCR of NO with NH3 as the reducing agent at low temperatures. Experiments and characterization revealed that the introduction of a suitable amount of the rare-earth metal Dy can effectively enhance the catalyst's specific surface area and the gas-solid contact area in catalytic reactions. It also significantly increases the concentration of Mn4+, chemisorbed oxygen, and weak acid sites on the catalyst surface. This leads to a notable improvement in the reduction performance of the DyMn/TiO2 catalyst, ultimately contributing to the improvement of the NH3-SCR denitrification performance at low temperatures. At 100 °C and a space velocity of 24,000 h-1, the Dy0.1Mn/TiO2 catalyst can achieve a 98% conversion rate of NOx. Furthermore, its active temperature point decreases by 60 °C after the modification, highlighting exceptional catalytic efficacy at low temperatures. By doubling the space velocity, the NOx conversion rate of the catalyst can still reach 96% at 130 °C, indicating significant operational flexibility. The selectivity of N2 remained stable at over 95% before reaching 240 °C.

Selective catalytic reduction of NOx with NH3 over copper-based catalysts: recent advances and future prospects

This review presents the important progress of Cu-based catalysts for the NH3-SCR reaction. Special attention is given to elucidating the design of high-performance catalysts, as well as anti-inactivation measures in industrial applications.

Phosphorus poisoning and regeneration of the Cu-LTA catalyst for the selective catalytic reduction of NOx with NH3

In this study, the phosphorus poisoning and regeneration of the Cu-LTA catalyst for the selective catalytic reduction of NOx with NH3 (NH3-SCR) were investigated.

Copper-exchanged SUZ-4 zeolite catalysts for selective catalytic reduction of NOx

The copper-exchanged SUZ-4 zeolite with optimal compositions exhibits comparable catalytic properties to commercial Cu-SSZ-13 for the selective catalytic reduction reaction.

Simultaneously accomplishing selective catalytic reduction of NO and catalytic oxidation of CO in a catalyst coupling system

Considering that nitrogen oxides (NOx) and carbon monoxide (CO) usually meantime exist in industrial flue gas, it is meaningful to develop a collaborative control technology for the simultaneous purification of NOx and CO. In this work, the catalysts xCu-1V-5W/Ti were evaluated in the simultaneously selective catalytic reduction by NH3 (NH3-SCR) and CO oxidation. The introduction of CuO provided the active sites for the oxidation of CO, while inhibited the NH3-SCR process and facilitated the generation of N2O by-product at high temperature. Accordingly, a catalyst coupling system was designed by employing 1V-5W/Ti and 2Cu-1V-5W/Ti catalysts in one reactor, and high NO conversion (>90 %) and CO removal efficiency (>80 %) could be simultaneously realized within 350–500 °C. This work would provide valuable insights for achieving simultaneous removal of NOx and CO using the catalyst coupling method.

Orchestrating dual adsorption sites and unravelling Ce-Mn interaction and reaction mechanisms for efficient NH3-SCR

Mechanism insight is suggested to be one of the most challenging issues in selective catalytic reduction of NO with NH3 (NH3-SCR), and the development of efficient NH3-SCR catalysts for industrial application needs a deep understanding of the catalytically active sites, reaction pathways and rate-determining steps. Herein, we study the NH3-SCR reaction mechanism on CeMn oxide catalyst. Mn3+ ions enter the CeO2 lattice to generate a Mn-O-Ce structure with a strong interaction, and Ce can synergize Mn species to orchestrate co-adsorption and accelerate the reaction rate. Theoretical studies verify that Ce and Mn sites act as double adsorption sites for NH3 and NOx, respectively. The proposed two reaction pathways including NH3 with NO and NH3 with NO2 may occur simultaneously owing to the same rate-determining step and the similar energy barriers. More interesting, the simulation results suggest that oxygen vacancies can automatically generate and supplement during the NH3-SCR reaction. This present work highlights the importance of elaborately modulating the double adsorption sites for NH3 and NOx and proposes the possible reaction mechanisms.

Insight into the SO2 poisoning of heterobimetallic FeCu‐SSZ‐13 zeolite in NH3‐SCR reaction

AbstractThe SO2 poisoning of a heterobimetallic FeCu‐SSZ‐13 in selective catalytic reduction of NO with NH3 (NH3‐SCR) was systematically investigated in this study. It was shown that when SO2 is involved in the feeding flue gas, the losses in the redox ability of active metals (primary contributor to deactivation) and in the number of Brønsted acid sites both inhibit the formation of NH4NO2 intermediate, resulting in the rapid deactivation of FeCu‐SSZ‐13. The SO2 poisoning of FeCu‐SSZ‐13 at low temperature is more serious than at high temperature, because of the more severe loss of redox ability of active metals. Unlike that of monometallic Cu‐/Fe‐CHA, the SO2 poisoning of the bimetallic one is saliently featured by that partial SO2 is oxidized to SO3 and partial Brønsted acid sites are destroyed due to the formation of H2SO4. This work may provide a fundamental understanding on the SO2 poisoning of heterobimetallic zeolite‐based NH3‐SCR catalysts.

Numerical investigation of honeycomb channel design: Effect of rounded corners on selective catalytic reduction of NO

In this work, single-channel models are established to investigate the effect of rounded corners on overall performance of honeycomb catalyst with various channel geometries and cell densities (Ncell). As channel shape factor (γ) increases, pressure drops all rise slowly at low γ (0 ∼ 0.5) and increases dramatically when γ > 0.5, aligning with monolith voidage and hydraulic diameter variations. Hexagon-channel catalysts with open corners exhibit the smallest pressure drop increase (17.3 %), while triangle-channel catalysts with acute corners show the highest rise (100.1 %). The increase in Ncell leads to a similar rise (43 %) in pressure drop. NO conversions decrease with γ due to reduced external surface area, with maximum conversions observed for triangle-channels (low γ) and hexagon-channels (high γ). Increasing Ncell enhances NO removal and mitigate rounded-corner effect on conversion (4.5 % to 1.2 % reduction). Based on that, a design strategy suggesting γ = 0.5 is proposed to eliminate ash accumulation and maintain acceptable catalyst performance.