Selective Catalytic Reduction Performance Research Articles

One-pot synthesis of FeCu-SSZ-13 zeolite with superior performance in selective catalytic reduction of NO by NH3 from natural aluminosilicates

Heterobimetallic zeolites have been considered as highly efficient catalysts to reduce nitrogen oxide emissions, but economic and sustainable preparation methods have been lacking. This paper presents an economic and sustainable one-pot synthesis strategy to prepare the heterobimetallic FeCu-SSZ-13 zeolite (FeCu-SSZ-13M) with high crystallinity via the mesoscale depolymerization-reorganization of natural aluminosilicate minerals without the use of any synthetic silicon-, aluminum-, and iron-containing chemicals. Systematic characterization results reveal that the resultant FeCu-SSZ-13M sample has smaller crystallize size, larger specific surface area and pore volume (especially external specific surface area and mesopore volume), lower acid strength and more isolated Cu2+ and framework Fe3+ ions when compared with Cu-SSZ-13C and FeCu-SSZ-13C prepared from conventional precursors. Therefore, it exhibits outstanding catalytic performance (such as super-wide reaction temperature window, excellent hydrothermal stability, high H2O and SO2 tolerance, and good gaseous hourly space velocity flexibility) in the selective catalytic reduction of NO by NH3. Our research contributes to the design and synthesis of an efficient environmental protection catalyst in an economic and sustainable manner.

The promoting effect of palygorskite on CeO2-WO3-TiO2 catalyst for the selective catalytic reduction of NOx with NH3

A series of CeO2-WO3-Pal/TiO2 catalysts were prepared by doping with different contents of palygorskite (Pal). More importantly, the CeO2-WO3–20%Pal/TiO2 catalyst prepared by impregnation method showed excellent performance for selective catalytic reduction (SCR) NOx with NH3. In more detail, the NO conversion could reach to 82% at 240 °C and keep above 92% in the range of 280–400 °C. According to the NH3-TPD tests, the surface acidity of the CeO2-WO3–20%Pal/TiO2 catalyst was increased obviously, which is beneficial to the NH3 adsorption in the SCR reaction. Besides, through XRD, XPS, Raman spectra and TEM characterizations, it suggested that the active species cerium and tungsten were uniformly dispersed on the surface of Pal, and it is very important for the improvement of SCR performance. In a word, the optimum Pal proportion was helpful to improve the catalyst catalytic performance, so it was more widely used in the SCR process.

Synthesis of SSZ-13 Zeolite in the Presence of N,N,N-Dimethylethylcyclohexyl Ammonium for Selective Catalytic Reduction of NOx

Abstract: Since NOx emission requirements from stationary and mobile sources are more strictly regulated in the United States, Europe, and other countries; researchers have conducted many studies to improve the performance of selective catalytic reduction (SCR) catalysts to meet more and more stringent emission standards. Herein, we reported the synthesis of small pore zeolite (Cu)-SSZ-13 using N,N,N-dimethylethylcyclohexylammonium as the structure directing agent. The catalytic activity of the fresh and hydrothermal aged copper exchanged supported on SSZ-13 catalyst was investigated in the SCR of NOx using NH3 as a reductant. Cu-SSZ-13 possessing a high SCR performance (NOx conversion reached approximately 100% at 250oC), and high hydrothermal stability in combination with an easy synthesis route is considered to be a potential catalyst for SCR application.
 Keywords: Zeolite, SSZ-13, synthesis, SCR, NOx.

Promoting effect of Ce and Mn addition on Cu-SSZ-39 zeolites for NH3-SCR reaction: Activity, hydrothermal stability, and mechanism study

Abstract In this work, Ce and Mn were added to Cu-SSZ-39 zeolites by ion-exchange process, and their activity performance for selective catalytic reduction of NOx with ammonia (NH3-SCR), especially hydrothermal stability (hydrothermal aging at 750, 800, 850 °C) was investigated systematically. It is found that the addition of Ce and Mn, Mn more evidently, both can greatly improve the activity of Cu-SSZ-39 catalyst. Moreover, MnCu-SSZ-39 catalyst have shown superior hydrothermal stability compared with Cu-SSZ-39 catalyst, and outstandingly its activity is not only not decreased significantly like Cu-SSZ-39 but improved obviously after hydrothermal aging at as high as 850 °C. The high and improved activity of Ce and Mn added Cu-SSZ-39 is ascribed to more active CuO crystallites formation in the inner channel and higher acidity strength. The superior hydrothermal stability of MnCu-SSZ-39 may be due to its well-preserved structure and acid density even after hydrothermal aging at as high as 850 °C. Moreover, during the hydrothermal aging process, not only Cu oxides aggregation is inhibited, but also more Cu2+ ion species are induced to ion exchange sites in MnCu-SSZ-39, which may account for its excellent hydrothermal stability (even higher than the activity of fresh samples). The mechanism analysis has shown NH3-SCR reaction over Cu-SSZ-39 and CeCu-SSZ-39 samples follow the “Langmuir–Hinshelwood” (L-H) mechanism, while on MnCu-SSZ-39, it follows both “L–H” and “Eley–Rideal” (E–R) mechanisms, which may also be another reason for its excellent activity and hydrothermal stability. Moreover, “Fast SCR” mechanisms also occur and contribute over hydrothermal aged A-MnCu-SSZ-39 sample, in addition to “L-H” and “E-R” mechanisms. Thus, the easily prepared MnCu-SSZ-39 catalyst has shown the excellent activity and super hydrothermal stability, with 90% NO conversion at 245 °C and broader temperature window of 245 °C to 550 °C, even after hydrothermal aging at 850 °C, therefore indicate great potential for future application in NOx purifying from diesel engine exhaust.

Response of a direct-drive large marine two-stroke engine coupled to a selective catalytic reduction exhaust aftertreatment system when operating in waves

Large two-stroke marine diesel engines are used as the prime mover in the majority of ocean going commercial vessels and are currently facing new stringent NOx emission reductions. Selective catalytic reduction is an aftertreatment technology which is able to reduce emitted NOx at allowable levels. In most marine applications, the selective catalytic reduction system is placed on the high pressure side of the turbine, due to limitations at the exhaust gas temperature at the inlet of selective catalytic reduction system. In this article, the operation of a large two-stroke marine diesel with a selective catalytic reduction aftertreatment system, is investigated in heavy weather conditions. Operation of a vessel in heavy weather results in increased ship resistance, wave-induced ship motions, and a highly varying flow field in the propeller due to ship motions. This results in a fluctuation of propeller demanded torque and hence a fluctuation in engine load and exhaust gas temperature which may affect engine and selective catalytic reduction performance significantly. To investigate this phenomenon and taking into account the engine–propeller interaction, the entire propulsion system was modeled, namely the propulsion engine, the high pressure selective catalytic reduction system, the directly driven propeller, and the ship’s hull. A propeller model was employed to simulate the transient propeller torque demand and torque fluctuations due to ship motions. A three-dimensional six degrees of freedom panel code was used to calculate ship motions and wave added resistance in regular waves. The coupled model of the marine propulsion plant was validated against available measured data from a ship-board propulsion system on good weather conditions. The model was then used to simulate the behavior of the system during transient loading conditions in the presence of regular waves.

Testing and Correlation of 8mm Pitch Honeycomb & Plate Type Module Performance in a 20 Litres SCR Test Facility

The main aim of this experiment is to reduce the concentration of NOx in the exhaust gas below 100ppm with the most effective technique named selective catalytic reduction (SCR) with ammonia over to evaluate the performance of honeycomb and plate type catalyst in NOx reduction by varying the performance parameters such as flue gas temperature, space velocity, NH3 /NO molar ratio, etc., and to find the optimum values of the above parameters under which we get the maximum efficiency of NOx conversion at which air is not polluted and we have the sustained and eco-friendly environment. The effect of various performance parameters on the SCR process is also evaluated and the optimum values of performance parameters are also found to get the maximum efficiency of NOx conversion. SCR performance is substantially under the effects of reactant (ammonia) concentration and operating temperature, so that the concentration of untreated ammonia emitted from reactor discharge (ammonia slip) increases significantly at NH3 /NO ratios of more than 1.14 and operating temperatures less than 360 ºC and 300 ºC, respectively, in the catalytic filter medium and honeycomb reactor. low level of ammonia slip can be achieved at the NH3 /NO ratio of 1 and temperature range of 300–350 ºC in both reactors.The temperature of SCR is varied between 300OC to 350OC ,with a fixed space velocity of exhaust gas and a fixed value of NH3/NO ratio of 1.

Nanosized V-Ce Oxides Supported on TiO2 as a Superior Catalyst for the Selective Catalytic Reduction of NO

Nanosized V-Ce oxides supported on TiO2 (VCT) were prepared and utilized in the low-temperature selective catalytic reduction (SCR) of NO with NH3. Compared with the other V-Ce oxides-based catalysts supported on Al2O3, ZrO2, and ZSM-5, VCT showed the best SCR activity in a low-temperature range. The NOx conversion of 90% could be achieved at 220 °C. Characterizations including X-ray diffraction (XRD), scanning election micrograph (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption with NH3 (NH3-TPD), and temperature-programmed reduction with H2 (H2-TPR) showed that V1.05Ce1/TiO2 exhibited a good dispersion of V2O5, enrichment of surface Ce3+ and chemical-absorbed oxygen, and excellent redox capacity and acidity, which resulted in the best SCR performance at low temperature.

Preparation of the Coupling Co-Precipitation and Impregnation Catalyst Ag/Al₂O₃ with High Catalytic Performance in Selective Catalytic Reduction of NO with C₃H6.

This brief paper reported an Ag/Al₂O₃ catalyst of high catalytic performance in C₃H6-SCR (selective catalytic reduction with C₃H6 as the reducer), and demonstrated a new strategy for the preparation of high active Ag/Al₂O₃ catalyst by the coupling co-precipitation and impregnation method. The results show that the coupling co-precipitation and impregnation catalyst was higher active than the usual impregnated catalyst in C₃H6-SCR of NO with broad active temperature window (420-600 °C), and the highest conversions of NO achieved 91% over the coupling co-precipitation and impregnation catalyst at 500 °C. The porous structure parameter, crystal phase structure, surface acidity property and particle morphology of the Ag/Al₂O₃ catalyst were characterized by the Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectra and temperature programmed desorption of ammonia (NH₃-TPD), respectively. Based on the characterization, it is found that the catalyst prepared by the coupling co-precipitation and impregnation method has smaller particles and better dispersion than the usual impregnated catalyst, and so the catalyst exhibited excellent catalytic activity. NH₃-TPD results illustrate that the weak and medium-strong acid sites is conducive to the reactivity of catalyst.

The positive effect of siderite-derived α-Fe2O3 during coaling on the NO behavior in the presence of NH3

Siderite is a naturally occurring mineral that can be found extensively in coal. The structural evolution of siderite in the process of coaling and its performance in the transformation of NO in the presence of NH3 were investigated in this work. In addition, the effects of the coexisting component, including vapor, SO2, and the alkali metal K, were also discussed. Heat treatment was performed at 450, 500, 550, 600, and 700°C to obtain siderite-derived α-Fe2O3, which was then evaluated in de-NOx via the selective catalytic reduction (SCR) of NO with NH3 in a fixed bed. The X-ray diffraction (XRD), the X-ray fluorescence spectrometer (XRF), N2 adsorption-desorption (BET), the X-ray photoelectron spectrometer (XPS), the scanning electron microscope (SEM), and the transmission electron microscope (TEM) were used to investigate the variations in the morphology and structure of the thermally treated siderite. The results showed that siderite was gradually oxidized and decomposed into α-Fe2O3 with a nanoporous structure and large surface area of 27.27m2g-1 after calcination under an air atmosphere. The α-Fe2O3 derived from siderite at 500°C (H500) exhibited an excellent SCR performance, where the NO conversion rate was great than 90% between 250 and 300°C due to the pore structure and high specific surface area, additional adsorbed oxygen states, abundant oligomeric Fe oxide clusters, and large amount of acid sites. Regardless of the vapor content, SO2 concentration, and reaction temperature, the α-Fe2O3 derived from siderite at 500°C (H500) still favored the conversion of NO. When the reaction temperature was lower than 350°C, H500 favored the conversion of NO even in the presence of an alkali metal (K). The experimental data demonstrated the positive effect of siderite-derived α-Fe2O3 in SCR technology and provided insight into NO behavior in coaling flue gas after NH3 injection.

The role of the Cu dopant on a Mn3O4 spinel SCR catalyst: Improvement of low-temperature activity and sulfur resistance

Mn-based oxides are regarded as one of the most promising catalysts for selective catalytic reduction (SCR) of NOx by NH3 at low temperatures, but their applications are extremely restricted by the irreversible poisoning of SO2. Improving the SO2 tolerance of Mn-based catalyst has longtime received the most attentions from both academia and industry. In this work, a series of Cu-modified Mn3O4 spinels were synthesized, and the roles of the Cu dopant were investigated. The (Cu1.0Mn2.0)1–δO4 spinel showed both excellent SCR performance and SO2 resistance at low temperature. Cu doping improved the BET surface area, the quantities of active Mn4+ and the acid sites of Mn3O4 spinels, all of which contributed to the increase in low-temperature SCR activity. The formation of MnSO4 was mainly responsible for the irreversible deactivation of the Mn3O4 spinel upon exposure to SO2. DFT calculations suggested that SO2 was more likely to be adsorbed as “–Mn–O–S–O–Mn–” on Mn3O4 and (Cu1.0Mn2.0)1–δO4 spinels. Therefore, the formation of MnSO4 on the (Cu1.0Mn2.0)1–δO4 spinel was significantly mitigated by Cu doping, mainly due to reduced amounts of adjacent Mn. Moreover, resulting from the electronic transfer between copper and manganese cations within the spinel lattice (Cu2+ + Mn3+ ⇄ Mn4++ Cu+), the (Cu1.0Mn2.0)1–δO4 spinel retained a high surface ratio of Mn4+/Mntotal, which maintained an excellent low-temperature SCR activity under the SO2-containing condition. This work shows that doping with the low–valence dopant of Cu can significantly improve the low-temperature SCR activity and SO2 tolerance of the Mn3O4 spinel, which could be a strategy for the further design of Mn-based SCR catalysts.

Effect of SO2 treatment in the presence and absence of O2 over ceria–titania oxides for selective catalytic reduction

The performance of selective catalytic reduction of NO over ceria–titania (Ce–TiOx)-based materials after aging in SO2 atmosphere in the presence and absence of O2 was investigated, showing that O2 gave acceleration on the deactivation of the samples for the enhanced SO2 adsorption and sulfation over ceria-based materials. FT-IR and TPD–MS over samples with 10wt%, 50wt% and 90wt% of CeO2 were carried out. The results indicated the poisoning effect of SO2 over Ce–TiOx catalyst for SCR is in accordance with the amount of sulfite or sulfate over Ce–TiOx with a certain percentage of CeO2.

Dual-template assembled hierarchical Cu-SSZ-13: morphology evolution, crystal growth and stable high-temperature selective catalytic reduction performance

Assembled hierarchical Cu-SSZ-13 zeolites maintained excellent high-temperature activity due to mesoporous inhibition of ammonia oxidation.

Facile Fabrication of Ce/V-Modified Multi-Channel TiO2 Nanotubes and Their Enhanced Selective Catalytic Reduction Performance.

To optimize one-dimensional (1D) TiO2 nanofibers, tailor-made multi-channel TiO2 nanotubes have been successfully fabricated by electrospinning technology. After loading with Ce and V, the CeVTi-tube catalyst exhibited a broad working temperature window and acceptable resistance to H2 O and SO2 for elimination of NOx . The corresponding analysis revealed that the multi-channel structure provided more surface adsorbed oxygen species and that the wall of nanotubes anchored active components efficiently, which was beneficial to improve the stability as well as dispersion of the active components. Besides, a synergistic effect between Ce and V easily occurred at the CeVTi-tube catalyst, and its reducibility was significantly improved since the electron transformation between Ce and V was dramatically enhanced. Consequently, the tailor-made multi-channel CeVTi-tube catalyst exhibited satisfied de-NOx efficiency at the temperature range of 220-460 °C. It seemed that the multi-channel TiO2 nanotubes hold great potential as an excellent carrier for SCR catalysts.

Precursor and dispersion effects of active species on the activity of Mn-Ce-Ti catalysts for NO abatement

Mn-Ce-Ti catalysts were prepared by different precursors (including manganese nitrate, manganese acetate, and manganese chloride) and used for selective catalytic reduction (SCR) of NO with ammonia. The relationships among the structure, physicochemical properties, and catalytic activity were explored by N2 adsorption/desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), scanning electron microprobe (SEM) and energy dispersive spectroscopy (EDS) techniques. The results show that the different Mn precursors play important roles in the catalytic activity. The Mn-Ce-Ti(N) catalyst synthesized by manganese nitrate precursor exhibits the best catalytic activity, while the Mn-Ce-Ti(C) and Mn-Ce-Ti(Cl) catalyst prepared by manganese acetate and manganese chloride, respectively, exhibit relatively low catalytic activity. The manganese nitrate precursor could promote the specific surface area and redox ability, enhance the amounts of Bronsted and Lewis acid sites, and enrich the surface active species such as Mn4+, Ce3+ and surface chemisorbed oxygen of the catalyst, all of which will contribute to the SCR performance. Moreover, the Mn-Ce-Ti(N) catalyst possesses highly dispersed and uniform surface active species, which will result in the optimal physicochemical properties and superior catalytic performance.

Low-Temperature Selective Catalytic Reduction of NO with NH3 over Natural Iron Ore Catalyst

The selective catalytic reduction of NO with NH3 at low temperatures has been investigated with natural iron ore catalysts. Four iron ore raw materials from different locations were taken and processed to be used as catalysts. The methods of X-ray diffraction (XRD), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were used to characterize the materials. The results showed that the sample A (comprised mainly of α-Fe2O3 and γ-Fe2O3), calcined at 250 °C, achieved excellent selective catalytic reduction (SCR) activity (above 80% at 170–350 °C) and N2 selectivity (above 90% up to 250 °C) at low temperatures. Suitable calcination temperature, large surface area, high concentration of surface-adsorbed oxygen, good reducibility, lots of acid sites and adsorption of the reactants were responsible for the excellent SCR performance of the iron ore. However, the addition of H2O and SO2 in the feed gas showed some adverse effects on the SCR activity. The FT-IR analysis indicated the formation of sulfate salts on the surface of the catalyst during the SCR reaction in the presence of SO2, which could cause pore plugging and result in the suppression of the catalytic activity.

Modeling the Effect of Nonuniformities from Urea Injection on SCR Performance Using CFD

A computational fluid dynamics model, consisting of a mixing chamber coupled with a catalytic converter, is developed for the selective catalytic reduction (SCR) of NOx using urea. The NH3 required...

Revisiting effects of alkali metal and alkaline earth co-cation additives to Cu/SSZ-13 selective catalytic reduction catalysts

Cu,M/SSZ-13 (M = Na+, K+ and Ca2+) selective catalytic reduction (SCR) catalysts with Si/Al = 6 and M/Cu ratios varying from 0.1 to 1.0 are prepared by solution ion exchange, followed by slurry drying and hydrothermal aging at 800 °C. The catalysts are characterized with X-ray diffraction and N2 adsorption isotherms to probe their textural properties; 27Al and 29Si nuclear magnetic resonance and NH3 temperature-programmed desorption to probe their acidity properties and levels of dealumination; and electron paramagnetic resonance and H2 temperature-programmed reduction to quantitatively explore the nature of Cu moieties in the catalysts. These studies are followed by density functional theory calculations to elucidate Cu and co-cation interactions at an atomic level and SCR reaction tests to reveal correlations between the chemical and physical properties of the catalysts and their SCR performance. Through these comprehensive investigations, it is discovered that alkali metal co-cation addition can be used for the synthesis of highly stable, and highly active and selective Cu/SSZ-13 catalysts with relatively high Al content. In catalysts with optimal alkali incorporation, dealumination of the SSZ-13 substrate is largely inhibited, allowing high concentrations of SCR-active isolated Cu ions. At the same time, repulsive interactions between Cu ions and alkali metal co-cations preclude excessively high isolated Cu-ion loadings. Interplay between and optimization of these two factors is considered the underlying origin for this successful catalyst synthesis strategy. On the other hand, the alkaline earth co-cation Ca2+ fails to demonstrate any beneficial effects, since it destabilizes isolated Cu ions via site competition.

Effect of Hydrocarbon on DeNOx Performance of Selective Catalytic Reduction by a Combined Reductant over Cu-Containing Zeolite Catalysts

The effects of hydrocarbons (HCs) on a combined selective catalytic reduction (SCR) system by NH3 and mixed HCs for simulated exhaust over five different types of Cu2+-exchanged zeolite catalysts h...

Constructing hollow silkworm structure in MnOx–TiO2 catalysts for improving the performance in selective catalytic reduction of NO by NH3

A novel MnOx–TiO2 catalyst with hollow silkworm structure was synthesized successfully via an ethanol-thermal strategy by using activated carbon fiber felt as template for the first time. The silkworm-like MnOx–TiO2 catalyst (MnTi) exhibited higher NOx conversion in the whole experimental temperature region (90–330 °C) under a high space velocity of 36,000 h−1 in comparison with the common MnOx–TiO2 catalyst without hollow silkworm structure (MnTi-B). The excellent catalytic performance of MnTi can be attributed to its high specific surface area, large content of active surface oxygen species (OS), and more surface acid sites. In addition, the MnTi catalyst also exhibited excellent resistance to water or SO2 poisoning.

The superior performance of CoMnOx catalyst with ball-flowerlike structure for low-temperature selective catalytic reduction of NOx by NH3

A novel ball-flowerlike catalyst (CoMnOx-BF) was developed by hydrothermal method for the selective catalytic reduction (SCR) of NOx by NH3. Besides, a counterpart sample (CoMnOx) was prepared by coprecipitation way for comparison. The activity test results demonstrated that CoMnOx-BF catalyst exhibited admirable SCR performance and N2 selectivity in a broad temperature range of 150–350 °C, along with an excellent resistance to SO2 and high durability. Based on characterization experiments, it could be found that the superior surface area resulted from suppressed crystallization, the enrichment of surface labile oxygen and Mn4+, the stronger surface acidity and redox ability were all beneficial to the NH3-SCR performance of CoMnOx-BF catalyst. Additionally, the enhanced NO oxidation and more activated ad-reactants on catalyst surface could also conduce to the outstanding SCR activity of CoMnOx-BF at low temperature.