Showing papers on "Selective catalytic reduction published in 2022"
TL;DR: In this article , the progress of research on Mn-based catalysts for selective catalytic reduction of NOx at low temperatures is reviewed, and the prospects and future directions for the development of Mnbased low-temperature selective catalyst reduction catalysts are presented.
56 citations
TL;DR: In this article , an Ag nanoarray using NiO nanosheets array on carbon cloth as support is reported as an efficient electrocatalyst to selectively reduce nitrite to ammonia.
50 citations
TL;DR: In this paper , a novel anti-Pb poisoning Sm and Fe co-doped Mn-Ce/AC catalyst was prepared by impregnation method for low-temperature NH3-SCR of NO reaction.
40 citations
TL;DR: The W modified MnFeW/Ti composite oxide catalyst was proposed and tested for low-temperature SCR of NOx by NH3, which possesses excellent SCR activity, N2 selectivity and SO2 tolerance compared with MnFe/Ti catalyst as discussed by the authors.
34 citations
TL;DR: In this article , several Mn-Ce/AC and xK-Mn−Ce+/Cen+ mixed oxide catalysts were investigated for low-temperature selective catalytic reduction (SCR) of NO with NH3 in the simulated sintering flue gas.
Abstract: To clarify the K modified effects over activated carbon (AC) supported Mn–Ce oxide catalysts, several Mn–Ce/AC and xK–Mn–Ce/AC mixed oxide catalysts prepared via an impregnation method supported on AC were investigated for low-temperature selective catalytic reduction (SCR) of NO with NH3 in the simulated sintering flue gas. The Mn–Ce/AC catalyst with a K loading of 8% showed the highest catalytic activity, corresponding to 92.1% NO conversion and 92.5% N2 selectivity at 225 °C with a space velocity of 12,000 h–1. Furthermore, the 0.08K–Mn–Ce/AC catalyst exhibited better resistance to SO2 and H2O than Mn–Ce/AC, which could convert 72.3% and 74.1% of NO at the presence of 5% SO2 and H2O, respectively. After K modification, the relative ratios of Mn4+/Mnn+ as well as Ce3+/Cen+ and surface adsorbed oxygen increased. Additionally, the reduction performance of the catalyst was improved obviously, and both acid strength and quantity of acid sites increased significantly after the K species were introduced in Mn–Ce/AC. Especially, the NO adsorption capacity of the catalyst was enhanced, which remarkably promoted the denitration efficiency and SO2 resistance. The SCR of NO with NH3 on K–Mn–Ce/AC catalysts followed the L-H mechanism.
34 citations
33 citations
TL;DR: In this article, the effect of the calcination temperature, aging time and space velocity on the de-NOx activities of the 4Ce-10Mn/TiO2 mixed oxides catalysts was investigated.
33 citations
TL;DR: In this paper , the basic perceptions of the green synthesis of metal nanoparticles and their supported-catalyst-based reduction of 4-nitrophenol (4-NP) to 4-aminophenol(4-AP) are discussed.
Abstract: Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research. This review focuses on the basic perceptions of the green synthesis of metal nanoparticles and their supported-catalyst-based reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The mechanisms for the formation of these nanoparticles and the catalytic reduction of 4-NP are discussed. Furthermore, the parameters that need to be considered in the catalytic efficiency calculations and perspectives for future studies are also discussed.
33 citations
TL;DR: In this paper, the influence of Mn doping on FeVO4 in the selective catalytic reduction of NOx with NH3 (NH3-SCR) reaction was in-depth studied.
32 citations
TL;DR: In this paper , the authors summarized the technical characteristics and application problems of marine diesel engine SCR systems in detail, and tracked the development trend of the catalytic reaction mechanism, engine tuning, and control strategy under high sulfur exhaust gas conditions.
Abstract: In recent years, the International Maritime Organization (IMO), Europe, and the United States and other countries have set up different emission control areas (ECA) for ship exhaust pollutants to enforce more stringent pollutant emission regulations. In order to meet the current IMO Tier III emission regulations, an after-treatment device must be installed in the exhaust system of the ship power plant to reduce the ship NOx emissions. At present, selective catalytic reduction technology (SCR) is one of the main technical routes to resolve excess NOx emissions of marine diesel engines, and is the only NOx emission reduction technology recognized by the IMO that can be used for various ship engines. Compared with the conventional low-pressure SCR system, the high-pressure SCR system can be applied to low-speed marine diesel engines that burn inferior fuels, but its working conditions are relatively harsh, and it can be susceptible to operational problems such as sulfuric acid corrosion, salt blockage, and switching delay during the actual ship tests and ship applications. Therefore, it is necessary to improve the design method and matching strategy of the high-pressure SCR system to achieve a more efficient and reliable operation. This article summarizes the technical characteristics and application problems of marine diesel engine SCR systems in detail, tracks the development trend of the catalytic reaction mechanism, engine tuning, and control strategy under high sulfur exhaust gas conditions. Results showed that low temperature is an important reason for the formation of ammonium nitrate, ammonium sulfate, and other deposits. Additionally, the formed deposits will directly affect the working performance of the SCR systems. The development of SCR technology for marine low-speed engines should be the compromise solution under the requirements of high sulfur fuel, high thermal efficiency, and low pollution emissions. Under the dual restrictions of high sulfur fuel and low exhaust temperature, the low-speed diesel engine SCR systems will inevitably sacrifice part of the engine economy to obtain higher denitrification efficiency and operational reliability.
31 citations
TL;DR: In this paper , the structure of surface iron sulfate and subsurface ceria was successfully constructed on CeO2/TiO2 catalysts, which delivered improved SO2 resistance for NOx reduction at 250 °C.
Abstract: Currently, SO2-induced catalyst deactivation from the sulfation of active sites turns to be an intractable issue for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. Herein, SO2-tolerant NOx reduction has been originally demonstrated via tailoring the electron transfer between surface iron sulfate and subsurface ceria. Engineered from the atomic layer deposition followed by the pre-sulfation method, the structure of surface iron sulfate and subsurface ceria was successfully constructed on CeO2/TiO2 catalysts, which delivered improved SO2 resistance for NOx reduction at 250 °C. It was demonstrated that the surface iron sulfate inhibited the sulfation of subsurface Ce species, while the electron transfer from the surface Fe species to the subsurface Ce species was well retained. Such an innovative structure of surface iron sulfate and subsurface ceria notably improved the reactivity of NHx species, thus endowing the catalysts with a high NOx reaction efficiency in the presence of SO2. This work unraveled the specific structure effect of surface iron sulfate and subsurface ceria on SO2-toleant NOx reduction and supplied a new point to design SO2-tolerant catalysts by modulating the unique electron transfer between surface sulfate species and subsurface oxides.
TL;DR: In this article , an efficient Nb2O5/CuO/CeO2 (NbCuCe) oxide catalyst for the selective catalytic reduction (SCR) of NOx, showing much higher DeNOx activity below 200 °C, superior sulfur resistance, faster response, and much less NH3 slip than the state-of-the-art Cu-CHA zeolite catalyst.
Abstract: To reduce nitrogen oxide (NOx) emission from diesel engines in the cold-start process benefitting the atmospheric environment, catalysts with superior low-temperature NOx removal efficiency are highly demanded. Herein, we report an efficient Nb2O5/CuO/CeO2 (NbCuCe) oxide catalyst for the selective catalytic reduction (SCR) of NOx, showing much higher DeNOx activity below 200 °C, superior sulfur resistance, faster response, and much less NH3 slip than the state-of-the-art Cu-CHA zeolite catalyst. Atomically dispersed Cu species facilitate the strong interaction between Cu and the Nb/Ce base catalyst, which significantly improves the low-temperature redox properties at Cu–O–Ce sites and NH3 adsorption/activation at Nb–O–Cu sites, thus contributing to the superior SCR performance of NbCuCe at low temperatures. The developed NbCuCe catalyst is highly promising for efficient DeNOx from cold-start diesel engines and can be coupled with Cu-CHA to achieve a broad operation temperature window.
TL;DR: In this paper , the W modified MnFeW/Ti composite oxide catalyst was proposed and tested for low-temperature SCR of NOx by NH3, which possesses excellent SCR activity, N2 selectivity and SO2 tolerance compared with MnFe/Ti catalyst.
TL;DR: In this paper , the electronic structure tailoring of the applied catalyst was an efficient pathway for balancing the catalytic behaviors in the NH3-SCR of NO and chlorobenzene catalytic oxidation (CBCO).
Abstract: Balancing the NH3 selective catalytic reduction (NH3-SCR) and catalytic oxidation performance is difficult but necessary for the synergistic elimination of NOx and chlorine-containing volatile organic compounds (CVOCs). We herein unveiled that electronic structure tailoring of the applied catalyst was an efficient pathway for balancing the catalytic behaviors in the NH3-SCR of NO and chlorobenzene catalytic oxidation (CBCO). Specifically, environmentally friendly CeO2 substituted by low valent Al3+ exhibited better NH3-SCR of NO and CBCO activity in comparison with the CeO2 sample without doping. Detailed characterizations and theoretical simulations revealed that the strong dopant-oxide pairs in the CeO2 with Al3+ doping significantly tailored the electronic structure of O 2p states, enhancing the amount of Lewis acid sites and promoting the ability of lattice oxygen to act as an oxidizing agent, thereby leading to superior performance for the synergistic elimination of NO/CB. The counterpart with substitution of high valent Ta5+ showed an opposite trend, due to that Ta5+ donated more electrons to the coordination oxygen than Ce4+ inhibiting lattice oxygen separating from the surface of the catalyst, and Lewis base sites were formed.
TL;DR: In this paper , the influence of Mn doping on FeVO4 in the selective catalytic reduction of NOx with NH3 (NH3-SCR) reaction was in-depth studied.
TL;DR: In this article , the low-temperature NH3-SCR performance of Mn-Ce/zeolite catalysts and specific promotion influence between MnCe active components and zeolite supports was investigated.
Abstract: To clarify the low-temperature NH3-SCR performance of Mn-Ce/zeolite catalysts and the specific promotion influence between Mn-Ce active components and zeolite supports, Mn-Ce/zeolite catalysts were synthesized using Mn-Ce mix oxides loading on several kinds of zeolites (ZSM-5 zeolite, Beta zeolite, X zeolite and Y zeolite) by impregnation method. The results indicated that Mn-Ce/X catalyst had high NO conversion of nearly 100% at 150 °C and the excellent SO2 resistance at different temperature. The Mn-Ce/ZSM-5 and Mn-Ce/Beta catalysts had NO conversion of about 100% at 275 °C while the Mn-Ce/Y catalyst had the lowest NO conversion. Additionally, Mn-Ce/X catalyst had higher relative ratio of Mn4+ and Ce3+ species, more Brønsted acid sites and better reducibility than that of other three catalysts, which could promote NH3-SCR activity. Moreover, the Brønsted acid sites and the Lewis acid sites on Mn-Ce/X catalyst were more stable at low-temperature. Besides, the SCR reaction of Mn-Ce/ZSM-5, Mn-Ce/Beta and Mn-Ce/X catalysts mainly followed Langmuir-Hinshelwood (L-H) mechanism at lower temperature and Eley-Rideal (E-R) mechanism at higher temperature. Furthermore, Mn-Ce/X catalyst had better adsorption ability of nitrate and nitrite species as well, which could enhance NH3-SCR reaction process
TL;DR: In this article , the deactivation mechanisms of SO2, H2O, alkali/alkaline earth metals (K, Na, Ca), and heavy metals (As, Pb, etc.) over Mn-based catalysts are discussed in detail.
TL;DR: In this article , a series of titania-carbon nanotubes (CNTs) supported MnOx-CuO catalysts were prepared and investigated for NH 3 -SCR of NO at low temperature.
TL;DR: In this paper , the authors investigated the effects of using an integrated system (DOC + DPF/POC + SCR + ASC) on non-road diesel engine emissions under steady-state and transient operating conditions, respectively.
TL;DR: In this paper , a core-shell catalyst with confinement of titania nanotubes (TNTs) was applied to the selective catalytic reduction of NOx with ammonia.
TL;DR: A series of titania-carbon nanotubes (TiO2-CNTs) supported MnOx-CuO catalysts were prepared and investigated for NH3-SCR of NO at low temperature as discussed by the authors.
TL;DR: In this paper , the authors proposed a distinct pathway for promoting the combination of chlorobenzene catalytic oxidation and NH3-SCR, and is expected to provide a novel strategy for synergistic catalytic elimination of NOx and chlorinated volatile organic compounds.
Abstract: The synergistic catalytic removal of NOx and chlorinated volatile organic compounds under low temperatures is still a big challenge. Generally, degradation of chlorinated organics demands sufficient redox ability, which leads to low N2 selectivity in the selective catalytic reduction of NOx by NH3 (NH3-SCR). Herein, mediating acid sites via introducing the CePO4 component into MnO2/TiO2 NH3-SCR catalysts was found to be an effective approach for promoting chlorobenzene degradation. The observation of in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) and Raman spectra reflected that the Lewis acid sites over CePO4 promoted the nucleophilic substitution process of chlorobenzene over MnO2 by weakening the bond between Cl and benzene ring. Meanwhile, MnO2 provided adequate Brønsted acid sites and redox sites. Under the cooperation of Lewis and Brønsted acid sites, relying on the rational redox ability, chlorobenzene degradation was promoted with synergistically improved NH3-SCR activity and selectivity. This work offers a distinct pathway for promoting the combination of chlorobenzene catalytic oxidation and NH3-SCR, and is expected to provide a novel strategy for synergistic catalytic elimination of NOx and chlorinated volatile organic compounds.
TL;DR: In this paper , a new strategy for SO2 and H2O-tolerant catalytic reduction of NOx at a low temperature has been originally demonstrated via engineering polymeric VOx species by CeO2.
Abstract: Selective catalytic reduction (SCR) of NOx over V2O5-based oxide catalysts has been widely used, but it is still a challenge to efficiently reduce NOx at low temperatures under SO2 and H2O co-existence. Herein, SO2- and H2O-tolerant catalytic reduction of NOx at a low temperature has been originally demonstrated via engineering polymeric VOx species by CeO2. The polymeric VOx species were tactfully engineered on Ce-V2O5 composite active sites via the surface occupation effect of Ce, and the obtained catalysts exhibited remarkable low-temperature activity and strong SO2 and H2O tolerance at 250 °C. The strong interaction between Ce and V species induced the electron transfer from V to Ce and tuned the SCR reaction via the E-R pathway between the NH4+/NH3 species and gaseous NO. In the presence of SO2 and H2O, the polymeric VOx species had not been hardly influenced, while the formation of sulfate species on Ce sites not only promoted the adsorption of NH4+ species and the reaction between gaseous NO and NH4+ but also facilitated the decomposition of ammonium bisulfate through weakening the strong bond between HSO4- and NH4+. This work provided a new strategy for SO2- and H2O-tolerant catalytic reduction of NOx at a low temperature.
TL;DR: In this paper , a large number of catalysts were systematically investigated and it was shown that, at low-temperature, the intrinsic SCR activity of the Mn active sites is not positively affected by Ce species in intimate contact.
Abstract: Mn-based oxides are promising for the selective catalytic reduction (SCR) of NOx with NH3 at temperatures below 200 °C. There is a general agreement that combining Mn with another metal oxide, such as CeOx improves catalytic activity. However, to date, there is an unsettling debate on the effect of Ce. To solve this, here we have systematically investigated a large number of catalysts. Our results show that, at low-temperature, the intrinsic SCR activity of the Mn active sites is not positively affected by Ce species in intimate contact. To confirm our findings, activities reported in literature were surface-area normalized and the analysis do not support an increase in activity by Ce addition. Therefore, we can unequivocally conclude that the beneficial effect of Ce is textural. Besides, addition of Ce suppresses second-step oxidation reactions and thus N2O formation by structurally diluting MnOx. Therefore, Ce is still an interesting catalyst additive.
TL;DR: In this paper , a single-atom Ce-modified α-Fe2O3 catalyst (Fe0.93Ce0.07Ox) was synthesized by a citric acid-assisted sol-gel method, which exhibited excellent performance for selective catalytic reduction of NOx with NH3 (NH3-SCR) over a wide operating temperature window.
Abstract: A single-atom Ce-modified α-Fe2O3 catalyst (Fe0.93Ce0.07Ox catalyst with 7% atomic percentage of Ce) was synthesized by a citric acid-assisted sol-gel method, which exhibited excellent performance for selective catalytic reduction of NOx with NH3 (NH3-SCR) over a wide operating temperature window. Remarkably, it maintained ∼93% NO conversion efficiency for 168 h in the presence of 200 ppm SO2 and 5 vol % H2O at 250 °C. The structural characterizations suggested that the introduction of Ce leads to the generation of local Fe-O-Ce sites in the FeOx matrix. Furthermore, it is critical to maintain the atomic dispersion of the Ce species to maximize the amounts of Fe-O-Ce sites in the Ce-doped FeOx catalyst. The formation of CeO2 nanoparticles due to a high doping amount of Ce species leads to a decline in catalytic performance, indicating a size-dependent catalytic behavior. Density functional theory (DFT) calculation results indicate that the formation of oxygen vacancies in the Fe-O-Ce sites is more favorable than that in the Fe-O-Fe sites in the Ce-free α-Fe2O3 catalyst. The Fe-O-Ce sites can promote the oxidation of NO to NO2 on the Fe0.93Ce0.07Ox catalyst and further facilitate the reduction of NOx by NH3. In addition, the decomposition of NH4HSO4 can occur at lower temperatures on the Fe0.93Ce0.07Ox catalyst containing atomically dispersed Ce species than on the α-Fe2O3 reference catalyst, resulting in the good SO2/H2O resistance ability in the NH3-SCR reaction.
TL;DR: In this paper, the surface acidity instead of redox capacity was the main limiting factor for SCR activity of CeO2 and MoO3-CeO2-Fe2O3.
TL;DR: In this article , a hydrothermal synthesis method was used to prepare porous denitration catalysts with polycarboxyl organic isomers (trimellitic acid, phthalic acid, and benzoic acid).
TL;DR: In this article , the self-defense effects of Ti-modified attapulgite (ATP) for NOx catalytic reduction have been clarified, which provided new inspiration for the development of novel and efficient selective NOx with NH3-SCR catalysts with high alkali resistance.
Abstract: Nowadays, the serious deactivation of deNOx catalysts caused by alkali metal poisoning was still a huge bottleneck in the practical application of selective catalytic reduction of NOx with NH3. Herein, alkali-resistant NOx catalytic reduction over metal oxide catalysts using Ti-modified attapulgite (ATP) as supports has been originally demonstrated. The self-defense effects of Ti-modified ATP for alkali-resistant NOx catalytic reduction have been clarified. Ti-modified ATP with self-defense ability was obtained by removing alkaline metal cation impurities in the natural ATP materials without destroying its initial layered-chain structure through the ion-exchange procedure, accompanied with an obvious enrichment of Brønsted acid and Lewis acid sites. The self-defense effects embodied that both ion-exchanged Ti octahedral centers and abundant Si-OH sites in the Ti-ion-exchange-modified ATP could effectively anchor alkali metals via coordinate bonding or ion-exchange process, which induced alkali metals to be immobilized by the Ti-ion-exchange-modified ATP carrier rather than impair active species. Under this special protection of self-defense effects, Ti-ion-exchange-modified ATP supported catalysts still retained plentiful acidic sites and superior redox ability even after alkali metal poisoning, giving rise to the maintenance of sufficient NHx and NOx adsorption and the subsequent efficient reaction, which in turn resulted in high NOx catalytic reduction capacity of the catalyst. The strategy provided new inspiration for the development of novel and efficient selective catalytic reduction of NOx with NH3 (NH3-SCR) catalysts with high alkali resistance.
TL;DR: CeO2-TiO2 catalysts with four different morphologies were successfully synthesized by a hydrothermal method and tested for selective catalytic reduction of NOx with NH3 (NH3-SCR) as mentioned in this paper .
TL;DR: In this paper , a self-supported Cu foam with enriched oxygen vacancies was developed to enable selective NO2-reduction to NH3, exhibiting a maximum NH3 yield rate of 7510.73 μg h-1 cm-2 and high faradaic efficiency of 94.21% at -0.6 V in 0.1 M PBS containing 0.5 M NaNO2.