Selective Catalytic Reduction Catalyst Research Articles

Promotion of Cu/Ce supported red mud for NO removal from low and medium temperature flue gas

Red mud is a solid waste in aluminum industry and has been proven to be an efficient alternative to NOx selective catalytic reduction (SCR) catalysts. Acid washing treatment to red mud can improve its alkalinity and surface properties, and increase the conversion rate of NOx. In this paper, Cu, Ce, and Cu/Ce was supported on acid washed red mud and NOx catalytic conversion performance on metal modified red mud catalysts was studied. The research results indicate that Cu+ and Cu2+ in the Cu supported catalyst effectively promote NO conversion rate of red mud in low-temperature (200–300 °C) flue gas, reaching a maximum of 90.7%; Ce3+ and Ce4+ in Ce supported catalysts effectively promote the NO conversion rate of red mud in flue gas at 200–400 °C, reaching a maximum of 94.0%; Cu/Ce supporting exhibits better NO conversion rate than single metal supported catalysts at low-temperatures, the optimal Cu:Ce ratio for supporting is 1:1; and also exhibits better NO conversion rate than Cu supported catalysts at high-temperature (300–400 °C), reaching a maximum of 95.5%. The reason may be that under the synergistic effect of Cu/Ce, ACRM-Cu1Ce1 has stronger low-temperature redox ability, higher weak acidic peaks, higher average oxidation state of Fe ions, and higher Cu+ content.

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.

Enhancing resistance to CaO&PbO poisoning of CeO2/TiO2 NH3-SCR catalyst via hybrid with SO42−/ZrO2: Dual functions of SO42−/ZrO2

Catalyst deactivation caused by the co-poisoning of alkaline earth metals (CaO) and heavy metals (PbO) is still a problem in the NH3 selective catalytic reduction (SCR) of NOx in flue gas. In this work, a hybrid catalyst (Hybrid-CT) was being synthesized by grinding CeO2/TiO2 (CT) catalyst and SO42−/ZrO2 to evaluate the poisoning tolerance. It shown that Hybrid-CT exhibited a higher tolerance against CaO&PbO poisoning compared with CT. Under the co-poisoning of 2.5 wt% CaO and 2.5 wt% PbO, the NOx conversion of Hybrid-CT catalyst could approach to 100 % at 350 °C. Whereas, the NOx conversion of CT was only 66.3 % under the same condition. A series of characterizations suggested that the SO42−/ZrO2 could inhibit the CaO&PbO poisoning. Once the CaO&PbO present on the surface of Hybrid-CT catalyst, SO42− could convert CaO&PbO into CaSO4&PbSO4 with less toxic, which could protect the redox site and acid site of the CeO2/TiO2. Furthermore, the ZrO2 released from SO42−/ZrO2 could serve as a promoter, enhancing the acid performance of CeO2/TiO2 catalysts. Moreover, SO42−/ZrO2 could also reduce the passive effect of CaO&PbO on nitrate oxide. This work provides a simple and novel way to improve the resistance to CaO&PbO of Ce-based SCR catalysts.

A green approach for preparation of MnFeTi Low-temperature NH3-SCR catalysts: utilizing spent V2O5–WO3/TiO2 Catalysts

V2O5–WO3/TiO2 catalysts are commonly used in industry to remove nitrogen oxides. However, spent V2O5–WO3/TiO2 are hazardous solid waste, and their improper disposal can lead to water and soil pollution risks. This study proposes a waste-to-resource approach that promotes the safe disposal of spent catalysts while reducing the production cost of denitrification catalysts. Specifically, vanadium-free low-temperature selective catalytic reduction catalysts are synthesized using spent catalysts. The optimized catalyst, named MnFeTi-22, exhibits a broad temperature activity range, with NO conversion exceeding 96 % from 100 to 300 °C. Even with 5 % H2O, the catalyst maintains a 95 % NO conversion (at approximately 200 °C). Characterization results confirm that the loading of TiO2 recycled from spent catalysts onto MnFe significantly optimizes the distribution of active species. Furthermore, TiO2 can adjust the distribution of acidic sites and the quantity of surface-adsorbed oxygen, promoting electron transfer between Mn4+/Fe2+ and Mn3+/Fe3+.

TiO2 recovered from spent selective catalytic reduction catalysts as anode material for lithium-ion batteries

Environmental protection and sustainable development are among the most severe problems in the world today. Spent selective catalytic reduction (SCR) catalysts are recognized as hazardous waste. Here, the TiO2, which accounts for nearly 80% of spent SCR catalysts, is recovered by the alkaline leaching method, and performed higher electrochemical performances than commercial TiO2 products for anode materials of Lithium-ion batteries. W, V, Si, and Al leaching rates are 40.04%, 89.59%, 61.64%, and 11.57%, respectively. A combination of density functional theory (DFT)--based calculations and experiments revealed that trace doping of Al is beneficial to the electrochemical performance of the cell, which helps us tune the Al content in the obtained materials. On this basis, the regenerated TiO2 anode materials with graphene (GR) materials are synthesized to improve the electrochemical performance, and the specific capacity of the recycled TiO2 is 188.5 mAh·g−1 after 500 cycles, and that of the regenerated TiO2/GR is the highest at 275.2 mAh·g−1. Finally, an environmental assessment of this recycling process is also carried out, human toxicity potential, CO2 gas emissions, NMVOC gas emissions, and SO2 gas emissions in this work are reduced by nearly 86.9%, 87.0%, 92.5%, and 87.0% compared with commercial sol-gel synthetic method. This work highlights the significance of recovery for preparing new energy storage materials from secondary resources.

Low-cost Co–Al spinel and M–Co–Al (M = Fe and Ce) catalysts for selective catalytic reduction of NOx with NH3

Low-cost Co–Al spinel and M–Co–Al (M = Fe and Ce) catalysts for selective catalytic reduction of NOx with NH3

Stability challenges and prospects for the industrial application of non‐noble catalysts for selective catalytic reduction of NOx by CO (CO‐SCR)

AbstractThe selective catalytic reduction of NOx by CO (CO‐SCR) holds considerable promise as a simple and cost‐effective technology capable of concurrently removing CO and NOx from mobile and stationary sources. This is especially pertinent for industry sectors with high CO emissions, such as the iron and steel industry, making CO‐SCR an attractive solution with significant industrial applicability. However, despite the promising industrial potential of CO‐SCR technology, its widespread adoption is hindered by several factors, most notably the impacts of SO2, H2O, and O2 on catalyst performance and stability. Current research on these limiting factors is not exhaustive, posing challenges for the comprehensive industrial implementation of CO‐SCR technology. Therefore, this review paper focuses on the variables impeding the industrial utilization of CO‐SCR, summarizing existing bottlenecks and emphasizing the urgent need to address the inhibitory effects of O2 on the CO‐SCR reaction, a critical issue in contemporary research. This review aims to clearly articulate the key challenges of CO‐SCR technology and provide direction for future research.

Designing a Ce/In-CHA OXZEO catalyst for high-efficient selective catalytic reduction of nitrogen oxide with methane

Selective catalytic reduction of nitrogen oxides with methane (CH4-SCR) has emerged as a promising technology for mitigating exhaust emissions from natural gas vehicles, while its insufficient catalytic activity and durability are key barriers to application. In this study, novel Ce/In-CHA OXZEO catalysts were prepared, demonstrating exceptional catalytic performance and stability in the CH4-SCR reaction. Over these OXZEO catalysts, indium species predominantly existed in the form of InO+ and InxOy within the CHA zeolite framework, while CeO2 nanoparticles primarily resided as an external layer. During the CH4-SCR reaction, NO oxidation to form NO2 and nitrate species was triggered by CeO2, which further enhanced the activation of CH4 on InO+ sites, thus boosting the low-temperature CH4-SCR process by facilitating the formation of the key intermediate CH3NO2. The synergy between InO+ and CeO2 underscores the exceptional performance and stability of the Ce/In-CHA with a low SiO2/Al2O3 ratio in reducing NOx and CH4 emissions.

Adaptive time-step unscented kalman filtering (ATS-UKF) based observer design for urea selective catalytic reduction (SCR) performance of diesel engines

To reduce the number of sensors in the SCR catalyst, state feedback and fault diagnosis information are provided. Firstly, a model based on the coupling of flow, heat transfer, and gas-solid phase catalytic reaction in the SCR system is investigated in this paper. The parabolic partial differential equations are simplified by the variable substitution method and the method of lines approach (MOL). The simplified system of equations is solved by backward differentiation formulas (BDF) with adaptive adjustment time step strategy. Meanwhile, the chemical reaction parameters are accurately calibrated per second using the Levenberg-Marquardt method. Secondly, the ATS-UKF is designed in this paper, and to ensure the synchronisation between the ATS-UKF and the SCR model calculations, the time step of solving the BDF by the SCR model is taken as the time step of propagating the sigma points. Two observation scenarios are assumed: (1) no downstream NH3 concentration sensor, ammonia coverage and downstream NH3 concentration are observed by ATS-UKF; (2) no downstream NOx sensor, ammonia coverage and downstream NOx concentration are observed by ATS-UKF. Finally, the paper carries out bench tests. In the first case, the ammonia coverage obtained by the ATS-UKF reached 0.99 with respect to the model-calculated value R². The mean absolute error (MAE) between the observed and experimental values of the ATS-UKF for the downstream NH3 concentration was 2.76 ppm. In the second case, the ammonia coverage obtained by the ATS-UKF reached 0.99 with respect to the model-calculated value R², and the MAE between the observed and experimental values of the ATS-UKF for the downstream NOx concentration was 1.53 ppm. Environmental ImplicationThe Adaptive Time-Step Unscented Kalman Filtering (ATS-UKF) enhances urea Selective Catalytic Reduction (SCR) in diesel engines, improving environmental outcomes. This method minimizes sensor dependence, enabling more precise SCR system management and effective emission reduction. By advancing emission control technologies, ATS-UKF contributes to global air pollution mitigation efforts, supporting cleaner air and environmental sustainability. Its innovative approach in monitoring and predicting SCR performance marks a significant step towards eco-friendly diesel engine operation.

Unexpected Promotion Effect of H2O on the Selective Catalytic Reduction of NOx with NH3 over Cu-SSZ-39 Catalysts.

Water molecules commonly inhibit the selective catalytic reduction (SCR) of NOx with NH3 on most catalysts, and water resistance is a long-standing challenge for SCR technology. Herein, by combining experimental measurements and density functional theory (DFT) calculations, we found that water molecules do not inhibit and even promote the NOx conversion to some extent over the Cu-SSZ-39 zeolites, a promising SCR catalyst. Water acting as a ligand on active Cu sites and as a reactant in the SCR reaction significantly improves the O2 activation performance and reduces the overall energy barrier of the catalytic cycle. This work unveils the mechanism of the unexpected promotion effect of water on the NH3-SCR reaction over Cu-SSZ-39 and provides fundamental insight into the development of zeolite-based SCR catalysts with excellent activity and water resistance.

The effect of hydrothermal aging on Mn2O3/Cu-SSZ-39 composite catalysts for selective catalytic reduction of NOx by NH3

The latest generation of fuel-efficient engines produces exhaust at cooler temperatures, highlighting a need for enhancement in the low-temperature effectiveness of Cu-zeolite catalysts. The metal oxide/Cu-zeolite composite catalysts have demonstrated superior deNOx performance at lower temperatures compared to Cu-zeolite alone. However, the hydrothermal stability of these composite catalysts remains unexplored. In this study, we focus on the Mn2O3/Cu-SSZ-39 catalyst, chosen for its exceptional activity at low temperatures. The synergy between the nitrate groups on Mn2O3 and NH4+ ions on the Brønsted acid sites of Cu-SSZ-39 enhances NOx conversion efficiency. Nonetheless, the efficiency of Mn2O3/Cu-SSZ-39 diminishes following exposure to hydrothermal conditions at various temperatures (700 °C, 750 °C, and 800 °C), with the degradation degree intensifying at higher temperatures. Characterization studies revealed that hydrothermal treatment leads to the recrystallization of Mn2O3 particles, which reduces the content of active adsorbed oxygen. This reduction impedes the formation of active bridged nitrates in the aged catalysts and disrupts the SCR pathway through the interaction between bridged nitrates and NH4+ on the composite catalysts. Despite these challenges, some adsorbed oxygen remains on the Mn2O3/Cu-SSZ-39 after aging, ensuring that the aged composite catalyst still exhibits higher activity than the fresh Cu-SSZ-39 catalyst. This observation suggests that there is potential for the application of Mn2O3/Cu-SSZ-39 in practical scenarios.

Strategy and Technical Progress of Recycling of Spent Vanadium-Titanium-Based Selective Catalytic Reduction Catalysts.

Selective catalytic reduction denitration technology, abbreviated as SCR, is essential for the removal of nitrogen oxide from the flue gas of coal-fired power stations and has been widely used. Due to the strong demand for energy and the requirements for environmental protection, a large amount of SCR catalyst waste is produced. The spent SCR catalyst contains high-grade valuable metals, and proper disposal or treatment of the SCR catalyst can protect the environment and realize resource recycling. This review focuses on the two main routes of regeneration and recycling of spent vanadium-titanium SCR catalysts that are currently most widely commercially used and summarizes in detail the technologies of recycling, high-efficiency recycling, and recycling of valuable components of spent vanadium-titanium SCR catalysts. This review also discusses in depth the future development direction of recycling spent vanadium-titanium SCR catalysts. It provides a reference for promoting recycling, which is crucial for resource recovery and green and low-carbon development.

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.

Research on structural strengthening technology for regenerative denitration catalysts.

The cost of replacing failed selective catalytic reduction (SCR) catalysts and their disposal as hazardous solid waste is high. If failed catalysts are recovered and regenerated into new SCR denitration catalysts, the cost of flue gas denitration can be effectively reduced. However, regenerated SCR catalysts have relatively low structural strength and activity and cannot yet form an effective replacement. In this study, aluminum dihydrogen phosphate, aluminum nitrate, and aluminum sulfate were used as structural strengthening agents in the regeneration of SCR catalysts, and over-impregnation, drumming-assisted impregnation, and ultrasonic-assisted preparation techniques were compared. The corresponding regenerated SCR catalysts were then prepared and analyzed for compressive strength, wear strength, H2-TPR, NH3-TPD, and in situ IR. Factors influencing the structural strength, physical properties, and catalytic activity of the regenerated catalysts were investigated. The best results were obtained as follows: compressive strength of 4.57 MPa, wear rate of 0.088% kg-1, and denitration of 58% after 10 min of drumming-assisted impregnation in an aluminum sulfate solution with a concentration of 16%. Based on this, a synergistic method for catalyst activity and structural strengthening was explored to support the design of better SCR catalysts for regeneration.

Theoretical insight into H2O impact on V2O5/TiO2 catalysts for selective catalytic reduction of NOx.

H2O in flue gas causes the deactivation of V2O5/TiO2 catalysts for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. Developing water resistance requires understanding the theoretical mechanism of H2O impact on the catalysts. The aim of this work was to clarify the adsorption process of H2O and the deactivation mechanism induced by H2O through density functional theory (DFT). The process of H2O adsorption was studied based on a modeled V2O5/TiO2 catalyst surface. It was found that H2O had a strong interaction with exposed titanium atoms. Water adsorption on the catalyst surface significantly alters the electronic structure of VOx sites, transforming Lewis acid sites into Brønsted acid sites. Exposed titanium sites contribute to the decrease of Lewis acidity via adsorbed water. Ab initio thermodynamic calculations show that H2O adsorption on V2O5/TiO2 is stable at low coverage but less favorable at high coverage. Adsorption of NH3 is the most critical step for the SCR of NOx, and the adsorption of H2O can hinder this process. The H2O coverage below 15% of adsorption sites could enhance the NH3 adsorption rate and have a limited effect on the acidity, while higher coverage impeded the adsorption ability of VOx sites. This work provided electron-scale insight into the adsorption impact of H2O on the surface of V2O5/TiO2 catalysts, presented thermodynamic analysis of the adsorption of H2O and NH3, paving the way for the exploration of V2O5/TiO2 catalysts with improved water resistance.

Heteropoly acid-grafted iron oxide catalysts for efficient selective catalytic reduction of NOx with NH3

A series of heteropoly acid-grafted Fe2O3 catalysts (i.e., HPA/Fe2O3) for selective catalytic reduction of NOx with NH3 (NH3-SCR) were investigated.

Superior low temperature activity over α-MnO2/β-MnOOH catalyst for selective catalytic reduction of NO x with ammonia.

Manganese octahedral molecular sieves with an α-MnO2 crystal structure (OMS-2) and their related materials have attracted significant attention for the selective catalytic reduction of NO x using NH3 (NH3-SCR) at low temperatures. Further lowering their operating temperature should be an effective method to develop an environmentally friendly de-NO x system; however, their catalytic activity at low temperatures, especially below 100 °C, remains poor. This study describes a post-synthetic approach to develop Mn-based catalysts superior to those in the literature that operate at ultralow temperatures. Post-synthetic planetary ball milling for OMS-2 caused the partial conversion of OMS-2 into β-MnOOH. The obtained nanocomposite catalysts possessed abundant surface oxygen vacancies and strong surface acidity, allowing the milled catalyst to exhibit higher NO conversion at 90 °C (91%) than that in freshly prepared OMS-2 without planetary ball milling (29%). Lowering the operation temperature of OMS-2 catalysts contributed to the suppression of N2O evolution during NH3-SCR over manganese-based catalysts, resulting in high N2 selectivity over the milled OMS-2 catalyst (93%).

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.

An Investigation of Selective Catalytic Reduction Catalyst SO2/SO3 Conversion in Coal-fired Power Plants

An Investigation of Selective Catalytic Reduction Catalyst SO2/SO3 Conversion in Coal-fired Power Plants

Sustainable solution to the recycling of spent SCR catalyst and its prospective gas sensor application

Nitrogen oxides (NOX) are often produced in industrial combustion processes and are among the most harmful air contaminants. Selective catalytic reduction (SCR) is currently the most effective technology for reducing effluents. Due to increasingly strict environmental regulations, the demand for SCR catalysts has increased, and inevitably, the need to dispose of the spent catalysts has increased and produced an environmental burden. The necessity for disposal while finding secondary sources for the vanadium, tungsten and titanium present in the catalyst makes recycling of spent SCR catalysts a pressing issue. During this investigation, two tertiary amines were compared to determine their effectiveness in extracting vanadium and tungsten from a spent SCR catalyst. The enrichment process was optimized, and the loaded organic solution (9-fold increased concentration) was further stripped to prepare a mixed metal oxide (MMO) based active sensing material for use in H2S gas detection. The H2S gas sensing characteristics of the MMO material were studied systematically. The MMO sensor showed an excellent sensing response to H2S gas with a high sensitivity of 12.73 % for 100 ppm and quick response/recovery times (tr = 101 s/tf = 133 s) at a low operating temperature of 130 °C. In addition, the sensor exhibited enhanced selectivity, long-term stability, and a detection limit of ∼47 ppb to H2S gas. The experimental findings of this work suggest that the recycled materials from spent SCR catalysts could have sustainable potential in reproducing the active sensing catalyst materials for the practical applications in the field of environmental protection.