Selective Catalytic Reduction Catalyst Research Articles

New Understanding of the Promotional Nature of SO2 on Ce-Based Oxide Catalysts for Selective Catalytic Reduction of NOx with NH3

New Understanding of the Promotional Nature of SO₂ on Ce-Based Oxide Catalysts for Selective Catalytic Reduction of NO_<i>x</i> with NH₃

Influence of different loads on PCDD/F removal by SCR during municipal solid waste incineration

This study was conducted on a full-scale (500 t/d) municipal solid waste incinerator (MSWI), investigating the influence of different loads on the emission of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/Fs) and their removal by selective catalytic reduction (SCR) system. The total concentration of PCDD/Fs at the SCR inlet under 100% load was higher than that under 80% load. The changing loads caused different distribution characteristics of PCDD/Fs at the SCR inlet, and the dominant congeners changed from high-chlorinated PCDDs (80% load) to low-chlorinated PCDFs (100% load). Moreover, the increased load enhanced the removal efficiency of PCDD/Fs by SCR from 17.3% to 64.2%, which was influenced by the inlet PCDD/F distribution and the moisture content. The high-chlorinated PCDD/Fs with the more stable structure were more difficult to be deteriorated and the high moisture content can weaken the catalytic activity of SCR catalysts. Correlation analysis was used to study the relationship between major air pollutants and PCDD/F emissions. The results showed that HCl positively correlated with PCDD/F emission concentrations, while NOx and SO2 negatively correlated. The results of this study can provide a reference for MSWI to operate properly under variable loads.

Hierarchical multi-time-scale predictive thermal management and fuel optimization for heavy-duty compression ignition engines

For heavy-duty diesel engines, NOX emissions reduction is strongly constrained by fuel efficiency. This paper presents a hierarchical model predictive controller (H-MPC) for coordinated control of tailpipe NOX emissions and fuel consumption. The H-MPC uses the separation of slow and fast dynamics that exist in the engine and its aftertreatment system. The controller is synthesized with an architecture in which a high-level MPC uses a longer prediction horizon compared to the low-level predictive controller which tracks the high-level controller command and manages the thermal dynamics of the aftertreatment system. Engine load preview enables the high-level controller to estimate the desired catalyst temperature ahead of time and addresses the selective catalytic reduction (SCR) slow thermal dynamics. Calculated by the high-level controller, the intake manifold pressure, and the start of injection (SOI) crank angle is used as reference trajectories in the low-level controller that regulates fast dynamical behaviors such as engine out NOX emissions. Hardware-in-the-loop (HIL) validation of this integrated H-MPC on a rapid prototype controller shows that when the SCR catalyst temperature is above light-off temperature (warmed-up condition), the engine operation is shifted to operate with the best fuel economy since the warmed-up SCR can efficiently reduce the engine-out NOX emissions. Results indicate that up to 0.8% benefit in cycle averaged BSFC along with a 13% reduction in tailpipe NOX compared to a stock engine calibration can be achieved with the coordinated engine and aftertreatment system through H-MPC.

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.

Selective catalytic reduction (SCR) catalyst market to reach $4.7 bn by 2032

Selective catalytic reduction (SCR) catalyst market to reach $4.7 bn by 2032

Experimental parameters for the preparation of Mn/TiO2 catalysts by ultrasonic spray pyrolysis method for selective catalytic reduction of NOx at low temperature

Mn/TiO2 series selective catalytic reduction (SCR) catalysts with regular spherical shape could be obtained by ultrasonic spray pyrolysis method. The investigation of experimental parameters, such as decomposition temperature and the type and flow rate of carrier gas, showed that a high and stable NOx conversion at 70% could be achieved at 180 °C when the ultrasonic spray pyrolysis temperature was 500 °C and N2 was used as a carrier gas with a flow rate of 2 L/min. The physical and chemical properties of the catalysts were characterized by X-ray diffraction, SEM, and H2-TPR, revealing that a regular spherical structure, a small amount of Mn2O3 crystals, and high redox ability were the important factors affecting the activity of the catalyst. With these properties, Mn(0.5)/TiO2 (500 °C, N2, 2 L/min) exhibited more than 90% conversion at 240 °C with N2 selectivity above 96%.

Coaxial 3D Printing of Zeolite-based Core-shell Monolithic Cu-SSZ-13@SiO2 Catalysts for Diesel Exhaust Treatment.

Core-shell catalysts with functional shells could increase the activity and stability of the catalysts in selective catalytic reduction with ammonia (NH3 -SCR) for diesel exhaust NOx treatment. However, the conventional approaches based on the multistep fabrication for core-shell structures encounter persistent restrictions regarding the strict synthesis condition and limited design flexibility. Herein, a facile coaxial 3D printing strategy has been for the first time developed to construct zeolite-based core-shell monolithic catalysts with interconnected honeycomb structures, in which the hydrophilic non-compact silica serves as shell and Cu-SSZ-13 zeolite acts as core. Compared to Cu-SSZ-13 monolith suffered from the interfacial diffusion, the SiO2 shell layer can increase the accessibility of active sites over Cu-SSZ-13@SiO2 , resulting in a 10-20% higher NO conversion at the 200-550 °C under 300,000 cm3 g-1 h-1 . Meanwhile, a thicker SiO2 shell enhances the hydrothermal stability of the aged catalyst by inhibiting the dealumination and the formation of CuOx . Other representative monolithic catalysts with different topological zeolites as shell and diverse metal oxides as core can be also realized by this coaxial 3D printing. This strategy allows multiple porous materials to be directly integrated, which allows for flexible design and fabrication of various core-shell monolithic catalysts with customized functionalities. This article is protected by copyright. All rights reserved.

Low-silica Cu-CHA Zeolite Enriched with Al Pairs Transcribed from Silicoaluminophosphate Seed: Synthesis and Ammonia Selective Catalytic Reduction Performance.

Cu-exchanged low-silica CHA zeolites (Si/Al ≤ 4) synthesized without organic templates are promising candidate catalysts for ammonia selective catalytic reduction of nitrogen oxides (NH3-SCR), but their practical application is restricted due to the low hydrothermal stability. Here, inspired by the transcription from duplex DNA to RNA, we synthesized Al pairs enriched low-silica CHA zeolite (CHA-SPAEI, Si/Al = 3.7) by using silicoaluminophosphate (SAPO) featured by strict alternation of -Al-O-P(Si)-O-Al-O- tetrahedra as seed. The proportion of Al pairs in CHA-SPAEI is 78%, which is much higher than that in the conventional low-silica CHA (CHA-LS, 52%). After hydrothermal ageing at 800 °C for 6 h, Cu-exchanged CHA-SPAEI shows NO conversion above 90% within 225-500 °C under a gas hourly space velocity of 200,000 h-1, which is much better than that of Cu-exchanged CHA-LS. The spatial close proximity of Al pairs in CHA-SPAEI is confirmed by the 27Al double-quantum single-quantum two-dimensional NMR analyses. The strict -P(Si)-O-Al-O-P(Si)-O- sequence in the fragments from the dissolution of SAPO seed promotes the Al pairs with the -Al-O-Si-O-Al-O- sequence via a transcription process. The utilization of aluminophosphate-based zeolites as seeds opens up a new avenue for the regulation of the Al distribution in zeolites.

Low‐silica Cu‐CHA Zeolite Enriched with Al Pairs Transcribed from Silicoaluminophosphate Seed: Synthesis and Ammonia Selective Catalytic Reduction Performance

AbstractCu‐exchanged low‐silica CHA zeolites (Si/Al≤4) synthesized without organic templates are promising candidate catalysts for ammonia selective catalytic reduction of nitrogen oxides (NH3‐SCR), but their practical application is restricted due to the low hydrothermal stability. Here, inspired by the transcription from duplex DNA to RNA, we synthesized Al pairs enriched low‐silica CHA zeolite (CHA‐SPAEI, Si/Al=3.7) by using silicoaluminophosphate (SAPO) featured by strict alternation of −Al−O−P(Si)−O−Al−O− tetrahedra as seed. The proportion of Al pairs in CHA−SPAEI is 78 %, which is much higher than that in the conventional low‐silica CHA (CHA‐LS, 52 %). After hydrothermal ageing at 800 °C for 6 h, Cu‐exchanged CHA‐SPAEI shows NO conversion above 90 % within 225–500 °C under a gas hourly space velocity of 200,000 h−1, which is much better than that of Cu‐exchanged CHA‐LS. The spatial close proximity of Al pairs in CHA‐SPAEI is confirmed by the 27Al double‐quantum single‐quantum two‐dimensional NMR analyses. The strict −P(Si)−O−Al−O−P(Si)−O‐ sequence in the fragments from the dissolution of SAPO seed promotes the Al pairs with the −Al−O−Si−O−Al−O− sequence via a transcription process. The utilization of aluminophosphate‐based zeolites as seeds opens up a new avenue for the regulation of the Al distribution in zeolites.

Unveiling the temperature-dependent effect of Zn on phosphotungstic acid-modified MnOx catalyst for selective catalytic reduction of NOx: A poison at < 180 °C or a promoter at > 180 °C

MnOx-based catalysts are highly efficient for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures, but Zn contained in industrial flue gas may poison conventional SCR catalysts, and MnOx-based catalysts usually have low Zn tolerance. Herein, phosphotungstic acid-modified MnOx (denoted as Mn-HPW) was prepared to study the Zn tolerance. It was found that the deposition of Zn on Mn-HPW decreases the SCR activity at < 180 °C, but both NOx conversion and N2 selectivity are enhanced at 180–300 °C, and > 95% NOx conversion can be achieved on Zn/Mn-HPW. Relevant catalysts were characterized and the results reveal that the decline in the activity at < 180 °C is related to the decrease in the quantities of Mn4+, Mn3+, and chemisorbed oxygen as well as the decreased capacities for adsorbing and activating NH3 and NOx. The unusual improvement of SCR performance on Zn/Mn-HPW at 180–300 °C is mainly attributed to two aspects: (i) HPW can protect effectively the surface acid sites from Zn poisoning; (ii) The decrease in oxidation properties alleviates the over-oxidation of NH3, promoting the participation of more NH3 in SCR.

Simulation study of De-NO x and ammonia slip with two-stage selective catalytic reduction for diesel engine

ABSTRACT Selective catalytic reduction (SCR) technology has several benefits for reducing NO x . It offers significant NO x removal efficiency, often greater than 90%. Due to increasingly strict pollution rules, SCR catalysts have lately been installed in diesel engines all over the world. The dynamics and economy of the original diesel engine are examined in this work concerning the addition of various SCR catalyst after-treatment methods, including a one-stage vanadium-based SCR catalyst (V-I), a two-stage vanadium-based SCR catalyst (V/V-II), and a two-stage vanadium-based-copper-based SCR catalyst (V/Cu-II). A complete engine model of a marine diesel engine is built on this model. The findings indicate that each of the three layouts decreases diesel engine power and raises fuel consumption rates. The V/Cu-II is the best configuration for this kind of marine machine because the V-I satisfies the most recent Tier III NO x emission limits only at 100% load, the V/V-II satisfies them at 75% to 100% load, and the V/Cu-II satisfies them at 50% to 100% load. For all three arrangements, ammonia slip reduces with increasing load, with the V/Cu-II having the lowest ammonia slip. In the end, it was determined for the V/Cu-II how different ammonia-to-nitrogen ratios affected ammonia slip and NO x conversion. The results revealed that with an ammonia-to-nitrogen ratio of 0.7, both the ammonia slip and NO x emission limits could be reached at 50% to 100% load, saving urea expenditures.

Synthesis and Characterization of V2O5 Supported on TiO2 Selective Catalytic Reduction (SCR) Catalyst for De-NOX Application

Synthesis and Characterization of V2O5 Supported on TiO2 Selective Catalytic Reduction (SCR) Catalyst for De-NOX Application

Revealing the Dynamic Behavior of Active Sites on Acid-Functionalized CeO2 Catalysts for NOx Reduction.

Unraveling the dynamics of the active sites upon CeO2-based catalysts in selective catalytic reduction of nitrogen oxides by ammonia (NH3-SCR) is challenging. In this work, we prepared tungsten-acidified and sulfated CeO2 catalysts and used operando spectroscopy to reveal the dynamics of acid sites and redox sites on catalysts during NH3-SCR reaction. We found that both Lewis and Brønsted acid sites are needed to participate in the catalytic reaction. Notably, Brønsted acid sites are the main active sites after a tungsten-acidified or sulfated treatment, and the change of Brønsted acid sites significantly affects the NOx removal. Moreover, acid functionalization promotes the cerium species cycle between Ce4+ and Ce3+ for the NOx reduction. This work is critical to deeply understanding the natural properties of active sites, and it also provides new insights into the mechanism for NH3-SCR over CeO2-based catalysts.

Water-tolerant and anti-dust CeCo-MnO2 membrane catalysts for low temperature selective catalytic reduction of nitrogen oxides

The present work successfully proposes a domain knowledge–guided Machine Learning (ML) strategy, which successes the development of a water-tolerant anti-dust catalyst for Low-Temperature (LT) Selective Catalytic Reduction (SCR) of nitrogen oxides (NOx) from catalyst discovery to industrial deployment. The discovered catalyst is able to convert 99 % of NOx at 150 °C in the standard waste gas, even in the waste gas containing 7 vol% of water vapors, the efficiency is still retained at 97 %. The superior LT activity and water-tolerance are attributed to abundant surface-active oxygen, Brønsted acid and microcellular structure. The SCR reaction mainly follows the Eley-Rideal (E-R) pathway driven by Brønsted acid and the Langmuir-Hinshelwood (L-H) pathway maintained by abundant reactive oxygen species in moisture waste gases. And then, catalyst is synthesized on a polyphenylene sulfide filter to render the membrane configuration in order to have the anti-dust ability. The final membrane catalyst has the capacity of converting 95 % NOx in the waste gas containing 7 vol% of moisture at 150 °C and the dedusting, and denitrification ability. The domain knowledge–guided Machine Learning (ML) strategy paves a wide avenue for the whole chain development from the data-driven discovery to the industrial deployment associated with mechanism exploration.

Preparation of coal fly ash supported high-temperature SCR catalyst by a novel alkali-acid combined activation

Coal fly ash (CFA) is an alternative carrier of selective catalytic reduction (SCR) catalyst, but its reactivity is usually poor. Herein, the alkali-acid combined activation was proposed to prepare the CFA-supported high-temperature SCR catalyst. The results revealed that 1.2 g/gCFA of NaOH and 0.6 g/gCFA of H2SO4 was the optimal CFA activation condition. The NaOH first destroyed the quartz crystal over the CFA, generating the Si-OH groups. Subsequently, H2SO4 enhanced the extraction of aluminates and enriched the acid sites, which promoted the standard SCR. Besides, the generated porous fragments facilitated the dispersion of Fe3+ species and improved the fast SCR.

Promotional Effects of FeOx on the Commercial SCR Catalyst for the Synergistic Removal of NO and Dioxins from Municipal Solid Waste Incineration Flue Gas

In view of the atmospheric pollutants in flue gas raised by municipal solid waste (MSW) incineration, simultaneous abatement of nitric oxide and dioxins is the keystone to alleviate the existing environmental issues. By using the commercial selective catalytic reduction (SCR) catalyst, nitric oxide and dioxins can be directly removed in separate temperature windows, while the catalytic performances still remain unsatisfactory. Herein, a collection of commercial V2O5–MoO3/TiO2 (VMT) catalysts modified with transition metal oxides were prepared in this study, and their synergistic removal activities for NO and dioxins were systematically investigated. Catalyst performance tests indicated that the loading of FeOx demonstrated considerable promotional effects. To further elucidate the enhancing mechanism of FeOx doping on the physical and chemical properties of the catalyst, a series of characterizations were conducted. The results indicated that FeOx increased the specific surface area and pore volume of the catalyst, which was more conducive to the dispersion of vanadium species. The modification with FeOx also enriched surface acid centers, as well as the V5+ species on the catalyst surface, so that the adsorption and destruction efficiencies of both nitric oxide and dioxins were further increased. Furthermore, the abundant chemisorbed oxygen species and the redox capacity of the catalyst were intensified, owing to the newly formed Fe3+–V4+/Fe2+–V5+ catalytic redox cycle.

Alkali-resistant NOx reduction over FeVO4/TiO2 catalysts via regulating the electron transfer between Fe and V

The presence of alkali metals in exhaust gas from stationary resources causes a grand challenge for the practical application of selective catalytic reduction (SCR) of NOx with NH3. Here, alkali-resistant NOx reduction has been successfully implemented via tailoring the electron transfer over Fe and V species on FeVO4/TiO2 catalysts. The strong interaction between Fe and V induced electron transfer from V to Fe and strengthened the adsorption and activation of NH3 and NO over active VOx sites. In the presence of K2O, the strong electron withdrawing effect of Fe offset the electron donating effect of K on the VOx species, thus protecting the active species VOx to maintain the NOx reduction ability. The enhanced adsorption and activation of NH3 allowed SCR reaction to proceed via E-R mechanism even after K2O poisoning. This work elucidated the electronic effects on the alkali metals resistance of traditional ferric vanadate SCR catalysts and provided a promising strategy to design SCR catalysts with superior alkali resistance.

Boosting Water-Resistance Ability on a PTFE Modified Ti-OMS-2 Catalyst for Low-Temperature NH3-SCR Reaction

Manganese-based catalysts are considered as ideal alternative catalysts for NH3 selective catalytic reduction of NOx due to their excellent denitrification performance, but their weak water resistance limits industrial applications. To improve the water resistance of low-temperature Mn-based catalysts in the NH3-SCR reaction, a Ti-OMS-2 (titanium-manganese oxide octahedral molecular sieve) catalyst was prepared by the hydrothermal method, and polytetrafluoroethylene (PTFE) powder was methodically introduced on the catalyst surface by the impregnation method. Importantly, the introduction of PTFE on the Ti-OMS-2 catalyst surface could effectively inhibit the adsorption of water molecules and reduce the probability of active species being consumed. Thus, it showed better catalytic activity and water resistance. The activity of the Ti-OMS-2-20%-PTFE catalyst could reach more than 80% when water vapor was introduced at 180 °C. More importantly, the Ti-OMS-2-20%-PTFE catalyst did not readily bind the active species (Mn4+ and Oads) and maintained the adsorption and activation of NH3 species. Moreover, it was easy for PTFE to form a weak surface hydrophobic layer on the Ti-OMS-2 catalyst surface that could effectively inhibit water toxicity. Therefore, this work provided a reasonable idea and experimental accumulation for the industrial application of Mn-based catalysts.

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.

Potassium Poisoning Effects on Sol‐gel Mn/TiO2Catalyst for Selective Catalytic Reduction (SCR) of NOx with NH3at Low Temperature

AbstractMn/TiO2catalysts exhibited more excellent activity and higher selectivity in low‐temperature SCR of NOx with NH3. Alkali metal, particularly potassium presented in the ash, could severely deactivate SCR catalyst and then reduce its lifetime. In this study, sol‐gel Mn/TiO2catalyst was employed to evaluate its SCR activity with and without the presence of KNO3at 100–300 °C. The influence of various parameters such as KNO3loading amount, calcination time, temperature and catalyst deactivation was investigated. The characterization results indicated that the doping of potassium on Mn/TiO2surface obviously resulted in a great decrease of reducibility, surface acidity and NH3adsorption capacity. XPS spectra revealed the decrease of Mn4+atomic concentration and chemisorbed oxygen species caused by potassium doping. In addition, obvious variation of potassium states (K1.04Ti8O16) was detected for K−Mn/TiO2catalyst after calcining treatment, which may lead to a poorer performance of SCR catalyst.