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In order to meet the increasingly stringent emission regulations for NOx in the exhaust gas of engines, selective catalytic reduction (SCR) technology is extensively studied and practiced. The key to this technology is the catalyst utilized in the chemical reactions of SCR. It is required to develop the SCR catalyst with good low-temperature performance and a wide active temperature window. A series of Cerium-based metal oxides TiCemWrO2−δ synthesized by solution combustion synthesis is studied in this paper. The SCR activity test was used to select the catalyst with the best performance. The NO conversion rate of the best catalyst in our studies reached 80% at 150 °C, kept 100% from 200 °C to 420 °C and the N2 selectivity remained above 95% for 100–500 °C. The SO2 resistance test was carried out at 250 °C and proved that our catalyst had good SO2 resistance. During the test, the NO conversion rate slightly decreased while 100 ppm SO2 was injected, but it remained above 80% for 24 h. The NO conversion rate recovered to the original value when the SO2 supply was cut off. The N2 selectivity remained at 100% throughout the process. Catalysts were characterized using BET, XRD, and SEM methods. In-situ DRIFTS method was used to study the reaction mechanism of the TiCe0.2W0.2O2−δ catalyst. It showed that the NH4+ species absorbed on the Brønsted acid played a dominant role in the SCR reactions. The bridge nitrate resulted from the NO absorption and gas phase NO was involved in the reaction. In conclusion, the mechanism studied included two routes of L-H and E-R. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chlorella@Mn catalyst had excellent resistance to alkali/alkaline earth metal poisoning. • P O Mn site could be used as a sacrificial site to bind to the alkali/alkaline earth metals. • Chlorella@Mn catalyst surface S, P and Si elements were bound to K, Na, Ca and Mg elements. • Poisoning effects of alkali/alkaline earth metals on Chlorella@Mn had been determined. • NH 3 -SCR reaction mechanism in the presence of alkali/alkaline earth metals was determined. In the selective catalytic reduction of NOx by NH 3 (NH 3 -SCR), conventional Mn-based denitration catalysts often suffered from susceptibility to poisoning by alkali and alkaline earth metals, this paper presented an innovative self-protected Chlorella@Mn denitration catalyst. Remarkably, in the presence of high concentrations (2 wt%) of alkali and alkaline earth metal oxides, the Chlorella@Mn catalyst sustained a NOx conversion exceeding 96 % at 175 °C. At an even higher concentration (4 wt%), NOx conversion above 90 % at 175 °C, surface analysis revealed that P O Mn sites acted as sacrificial sites, binding to the alkali and alkaline earth metals, the Chlorella@Mn catalyst surface naturally carried a spectrum of acidic species (such as SO 4 2−, PO 3 −, SiO 3 2−), proficient in capturing alkali/alkaline earth metal effectively, elements such as S, P, and Si formed bonds with K, Na, Ca, and Mg. The synergistic protection of the active sites and the surface elements avoided the deactivation of the catalyst. The detrimental effects of high concentrations of alkali and alkaline earth metals were primarily due to promoting an excessively high valence state of Mn on the catalyst surface and the reduction or loss of NH 3 adsorption and activation at Brønsted acid sites. This research provided valuable insights for advancing the development of low-temperature denitration catalysts with improved resistance to alkali and alkaline earth metal poisoning. [ABSTRACT FROM AUTHOR]

The enhancement effect of Ce modification on V2O5-WO3/TiO2 catalysts at low temperatures was investigated for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR). By adding 9% CeO2 to 0.5%V2O5-3%WO3/TiO2 catalyst, the low-temperature denitrification performance of Ce9V0.5W3Ti catalyst after Ce modification was significantly improved, achieving a NO conversion above 90% within a broad temperature range of 200–350℃, with catalytic activity comparable to that of 3% V2O5-3% WO3/TiO2. The catalysts were characterized by XPS, H2-TPR, NH3, and NO-TPD. The results indicated that the Ce additive could enhance the adsorption of NOx on Ce9V0.5W3Ti catalyst due to the synergetic interaction among the Ce and V, W species. The interaction between V and Ce also promoted the formation of V5+ and Ce3+ on the surface of the catalyst, which was conducive to enhancing the adsorption and oxidation capacity of the catalyst for NO. Additionally, the introduction of Ce led to a substantial deposition of nitrate species on the surface of the catalyst, especially the increase of nitrite species, which was beneficial to the NH3-SCR reaction process, resulting in a significant enhancement of the catalyst's low-temperature catalytic activity. [ABSTRACT FROM AUTHOR]

NH 3 -SCR (SCR: Selective catalytic reduction) is an effective technology for the de-NO x process from both mobile and stationary pollution sources, and the most commonly used catalysts are the vanadia-based catalysts. An innovative V 2 O 5 -CeO 2 /TaTiO x catalyst for NO x removal was prepared in this study. The influences of Ce and Ta in the V 2 O 5 -CeO 2 /TaTiO x catalyst on the SCR performance and physicochemical properties were investigated. The V 2 O 5 -CeO 2 /TaTiO x catalyst not only exhibited excellent SCR activity in a wide temperature window, but also presented strong resistance to H 2 O and SO 2 at 275 ℃. A series of characterization methods was used to study the catalysts, including H 2 -temperature programmed reduction, X-ray photoelectron spectroscopy, NH 3 -temperature programmed desorption, etc. It was discovered that a synergistic effect existed between Ce and Ta species. The introduction of Ce and Ta enlarged the specific surface area, increased the amount of acid sites and the ratio of Ce3+, (V3++V4+) and O α , and strengthened the redox capability which were related to synergistic effect between Ce and Ta species, significantly improving the NH 3 -SCR activity. The synergistic effect between Ce and Ta species enhanced the redox capability and increased the acid sites, which significantly improved the NH 3 -SCR activity. [Display omitted] [ABSTRACT FROM AUTHOR]

With the continuous expansion of industrial activities worldwide, industrial emissions of nitrogen oxides (NOx) pose a serious threat to both ecosystems and human health. Ammonia selective catalytic reduction of NO (NH3‐SCR) technology has emerged as the most effective means to reduce NOx emissions, and the development of catalysts is crucial for the successful implementation of this technology. In gas‐solid multiphase catalytic systems, the performance limitations of conventional catalysts can be effectively overcome by meticulously designing the nanostructures of the catalysts to achieve improved catalytic efficiency. In this review, the unique structural features of core‐shell structures, layered double hydroxide (LDHs), hollow nano spheres and nanotubes, along with their preparation processes, are systematically examined, beginning with the effects of structural changes on catalytic performance. Based on this review, the impact of structural modifications on the catalytic efficiency of the catalysts for the NH3‐SCR reaction and their anti‐poisoning performance were investigated. Ultimately, the influence of catalyst structural changes on the future design of catalysts is anticipated. This provides a robust scientific foundation for the conception of higher performance catalysts, paving the way for technological innovation and advancements in NOx emission reduction practices. [ABSTRACT FROM AUTHOR]

A Fe modified MOF-derived MnOx catalyst has been synthesized and studied for the selective catalytic reduction of NOx with NH3 (NH3-SCR). Compared with pure MnOx, Fe-modified MnOx showed a broader activity temperature window, enhanced N2 selectivity, and improved sulfur tolerance. On one hand, the incorporation of Fe into MnOx increased acidity, thereby facilitating the adsorption of NH3 as well as its activation, which plays a crucial role for the reduction of NOx. On the other hand, the presence of Fe resulted in decreased Mn4+, which contributes to improved N2 selectivity. Over Fe modified MnOx catalyst, the coordinated NH3, NH4+, bridging nitrate and bidentate nitrate are reactive, and participate in the NH3-SCR reaction following both "Eley–Rideal(E-R)" and "Langmuir–Hinshelwood(L–H)" mechanism. The present research provides an idea for broadening the activity temperature window and enhancing the sulfur tolerance of MnOx catalyst for the reduction of NOx, making it more suitable for practical application. [ABSTRACT FROM AUTHOR]

V2O5-WO3(MoO3)/TiO2 catalysts are widely used in industrial denitrification (deNOx) processes based on the selective catalytic reduction (SCR) technique. To lower their cost and shorten the production cycle, V2O5-MoO3/TiO2 catalysts with and without CeO2 modification were prepared using the ball milling method. This study demonstrates that the CeO2-modified catalyst has high NO conversion and a broader temperature window due to the decreased amount of easily reducible vanadium species and the enhanced property of oxygen species activation in CeO2. Meanwhile, the SO2 resistance of the catalyst is restrained due to the strong adsorption and oxidation of SO2 over CeO2 in the catalyst. [ABSTRACT FROM AUTHOR]

Nitrogen oxides are one of the main atmospheric pollutants and pose a threat to the ecological environment and human health. Selective catalytic reduction (NH3-SCR) is an effective way of removing nitrogen oxides, with the catalyst being the key to this technology. Two-dimensional nanostructured layered double oxide (LDO) has attracted increasing attention due to the controllability of cations in the layers and the exchangeability of anions between layers. As a derivative of layered double hydroxide (LDH), LDO not only inherits the controllability and diversity inherent in the LDH structure but also exhibits excellent performance in the catalytic field. This article contains three main sections. It begins with a brief discussion of the development of LDO catalysts and analyzes the advantages of the LDO structure. The later section introduces the synthesis methods of LDH, clarifies the conversion relationship between LDH and LDO, and summarizes the modification impacts of the properties of LDO catalysts. The application of LDO catalysts used in NH3-SCR under wild temperature conditions is discussed, and the different types, reaction processes, and mechanisms of LDO catalysts are described in the third section. Finally, future research directions and outlooks are also offered to assist the development of LDO catalysts and overcome the difficult points related to NH3-SCR. [ABSTRACT FROM AUTHOR]

Mesoporous silicas of MCM-41 and MCM-48 types were synthesized and modified with copper by template ion-exchange (TIE) technique. A high dispersion of deposited copper species was managed by subsequent treatment of the samples with ammonia, urea, or acetonitrile solution. Copper-modified silicas were analysed in terms of their chemical composition (ICP-OES), ordering of porous structure (XRD), textural parameters (low-temperature N2 sorption), dispersion and form of introduced copper species (UV–vis-DR, XRD, H2-TPR, NH3-TPD). Mesoporous silicas modified with copper exhibited promising catalytic efficiency in selective catalytic reduction of NO with ammonia (NH3-SCR). The samples containing dispersed copper species (predominantly monomeric copper cations) presented enhanced catalytic activity compared to catalysts containing CuO aggregates. On the other hand, CuO aggregates showed greater catalytic activity in the side process of direct ammonia oxidation by oxygen present in the reaction mixture. It was demonstrated that TIE post-treatment of the samples with urea resulted in most effective improving dispersion of deposited copper and is less destructive for ordered porous structures of mesoporous silica comparing to treatment with ammonia solution. [ABSTRACT FROM AUTHOR]

We employ UV/Vis Diffuse Reflectance spectroscopy directly coupled with a packed bed flow reactor to extract quantitative kinetic information. We use as a show‐case the CuII/CuI redox dynamics during the reduction half cycle of the NH3‐Selective Catalytic Reduction (SCR) on Cu‐CHA catalysts. Our measurements enable quantification of the fraction of oxidized Cu, reconstructed by Multivariate Curve Resolution (MCR) together with monitoring of the gas‐phase evolution during the reaction. These data both on the dynamics of the gas‐phase and of the active site oxidation state have been used to assess the reduction half cycle rate equation and estimate the rate constant. Our results in terms of reaction orders and kinetic constant are in line with previous findings in the literature. Overall, our results demonstrate that the combined analysis of the UV spectra and of the gas‐phase dynamics provides converging and unparalleled kinetic insight: this approach effectively resolves ambiguities concerning RHC kinetics and mechanism. More in general, this work provides evidence that operando spectroscopy can be used to extract quantitative kinetic information on catalytic cycles. [ABSTRACT FROM AUTHOR]

Microporous zeolite is commonly employed as the catalyst for selective catalytic reduction of NOx using NH3 as reducing agent (NH3‐SCR) because of its strong acidity and exceptional hydrothermal stability. However, the channel of microporous zeolite limits mass transfer under low temperature. Hierarchical porous molecular sieves can overcome the above imperfections. Hierarchical pore (microporous/mesoporous/macroporous) ZSM‐5 molecular sieves were prepared using polystyrene(PS) microspheres with different particle size as the hard templates and then the ion exchange method was utilized to introduce the active components Ce, Cu, and La. In addition, the effect of PS microspheres with different size and H2O+SO2 on denitrification performance was also investigated. The results exhibited that the specific surface area of the hierarchical pore ZSM‐5 was the smallest when the size of polystyrene microspheres was the largest. The NOx conversion of all supported hierarchical porous catalysts is more than that of supported microporous ZSM‐5 catalyst in the low temperature (200 °C), which was because that the presence of the mesopores favored diffusion‐control in the low temperature, expediting the reactant transport. Furthermore, the supported hierarchical pore ZSM‐5 catalyst exhibited excellent denitrification performance in a wide temperature range of 250–500 °C (the conversion of NOx exceeded 80 % and the N2 selectivity was approaching 100 %). More importantly, the supported hierarchical pore ZSM‐5 catalyst demonstrated notably superior water and SO2 resistance in comparison to the supported micropore ZSM‐5 catalyst. [ABSTRACT FROM AUTHOR]

Fe2O3 supported LaMnO3 is an effective selective catalytic reduction (SCR) denitrification catalyst, but its reaction mechanism has not been reported yet. This article is based on the density functional theory (DFT) method to study the denitrification reaction mechanism of LaMnO3/Fe2O3 catalyst, in order to guide the development and application of denitrification catalysts. The conclusion is as follows: NH3, NO, and O2 molecules can form stable adsorption on the surface of La MnO3/γFe2O3 catalysts, and NH3 molecules are more likely to be adsorbed on Mn ions. Under the oxidation of lattice oxygen, NH3 will gradually dehydrogenate to form NH2, and then will react with NO in the air to form the transitional intermediate NH2NO, to produce N2 and H2O. The mechanisms are same on Mn and Fe sites. The dehydrogenate of NH3 to form NH2 is rate determining step. Compared with pure γFe2O3, the energy barrier decreases to promote the SCR process. [ABSTRACT FROM AUTHOR]

Microporous aluminosilicate zeolites are useful industrial catalysts. However, their hydrothermal synthesis is a multistep process with complicated and unclear reactions, limiting their rational functional design. Herein, we compare the formation pathway and the structural and catalytic properties of several CHA zeolites to obtain fundamental knowledge for intentionally controlling the catalytic function of zeolites. Three CHA zeolites were synthesized using different starting silica/alumina sources in the presence of tetraethylammonium hydroxide as an inexpensive organic structure‐directing agent. FAU zeolite and an amorphous synthesis gel prepared using two different methods were used as starting materials. The obtained CHA zeolites were applied for exhaust gas purification (selective catalytic reduction of NOx with ammonia, NH3‐SCR), and their structural characteristics and formation pathways were investigated using a combination of analytical methods. Stepwise gel preparation (SGP), which divides the compositional control of the amorphous synthesis gel, promotes the decomposition of the initial additive (zeolite seed), resulting in the formation of CHA zeolites with abundant micropores and paired Al sites. This structural feature obtained using the SGP method improves the catalytic durability of the NH3‐SCR reaction. The present relationship, including different crystallization phenomena, structures, and catalytic abilities, provides useful insights into rational zeolite synthesis and its application. [ABSTRACT FROM AUTHOR]

A series of highly dispersed Nia-xMnxAlOy catalysts derived from layered double hydroxides (LDHs) were prepared for selective catalytic reduction of NOx with ammonia (NH3-SCR) at low temperature. The physicochemical and catalytic performance of the prepared catalysts with different M2+/M3+molar ratios were systematically investigated by XRD, BET, XPS, TPX (i.e. TPD and TPR) and in situ DRIFTs. Fortunately, Ni4-xMnxAlOy as the optimal catalyst exhibited prominent NH3-SCR performance with NOx conversion greater than 90% at low temperature range of 120~210 °C. Especially, the influence of H2O and SO2 revealed that the catalyst activity could be miraculously promoted by H2O, while deactivated by SO2. The proper M2+/M3+molar ratios not only provided the surface acidic sites, the high Mn4+ content ratio and the adsorbed oxygen of Nia-xMnxAlOy catalysts, but also promoted the transformation of NOx intermediate species to more stable bidentate nitrates. Results of the in situ DRIFTs illustrated that the SCR reaction path of Nia-xMnxAlOy catalysts followed both E-R and L-H mechanisms, and the former played the dominant role. [ABSTRACT FROM AUTHOR]

The reduction of nitrogen oxides (NOx), critical pollutants from stationary to mobile sources, mainly relies on the selective catalytic reduction (NH3-SCR) method, employing ammonia to reduce NOx into nitrogen and water. However, conventional catalysts, while effective, pose both environmental and operational challenges. This study investigates ceria-zirconia-supported molybdenum-based catalysts, exploring the effects of zirconium doping and different catalyst synthesis techniques, i.e., co-precipitation and impregnation. The catalytic performance of the differently prepared samples was significantly influenced by the molybdenum incorporation method and the zirconium content within the ceria-zirconia support. Co-precipitation at higher temperatures resulted in catalysts with better structural attributes but slightly lower catalytic activity compared to those prepared via impregnation. Optimal NOx reduction (close to 100%) was observed at a 15 mol% zirconium doping level when using the impregnation method. [ABSTRACT FROM AUTHOR]

A series of rare-earth (Ce, La, Nd, and Y) oxides doped Mn/Al2O3 catalysts were prepared by the impregnation method and used for the selective catalytic reduction (SCR) of NOx with NH3. The additions of rare-earth oxides greatly enhance the SCR catalytic activity of Mn/Al2O3, and the highest activity was obtained over CeMn/Al2O3 with a NOx conversion higher than 85% at 125–300 °C. The results of characterization show that the rare-earth oxides additives except for Y2O3 promote the surface distribution of Mn element and enhance the ratio of chemisorbed oxygen and Mn4+ on the surface of Mn/Al2O3. Moreover, with the introduction of rare-earth oxides, the reducibility of MnO2 species is improved and a larger amount of the weak acid sites are obtained. The increase in the ratio of Mn4+ and the enhancement in the reducibility of MnO2 are the main reasons for the elevation in SCR activity of the rare-earth oxides modified Mn/Al2O3 catalysts. This study sheds light on the promotional effect of rare-earth oxides over the Mn-based catalysts for SCR reaction. Rare-earth oxides greatly enhance the SCR catalytic activity of Mn/Al2O3, and the highest activity was obtained over CeMn/Al2O3 with a NOx conversion higher than 85% at 125–300 °C. [ABSTRACT FROM AUTHOR]

In this paper, the CoxMn1Cey composite oxide catalyst was synthesized by the co-precipitation method. The structure–activity relationship of the catalyst was analyzed by characterization methods such as XRD, Raman, H2-TPR, NH3/NOx-TPD, XPS, and in situ DRIFTS. The results showed that the Co3Mn1Ce1 catalyst resisted high space velocity, water, and sulfur. In addition, Ce doping could effectively increase the specific surface area of the catalyst. In a sulfur-containing atmosphere, Ce could preferentially react with SO2 and act as a sacrifice site to protect the active components from toxicity. Co-doping greatly enhanced the redox capacity of the catalyst and increased the chemisorbed oxygen (OS) content on the surface of catalysts. Co-presence of Co and Ce increased the content of surface-active Mn species, which further effectively improved the adsorption capacity of the catalyst for NH3 and NO reactants. In situ DRIFTS results showed that the reaction on the Co3Mn1Ce1 catalyst followed both the Langmuir–Hinshelwood and Eley–Rideal mechanisms. [ABSTRACT FROM AUTHOR]

Cu/SSZ-13 is considered to be a promising material for NH3-SCR catalysts. However, in practical applications, Cu/SSZ-13 is inevitably exposed to alkali metal deposition. In this paper, Cu/SSZ-13 molecular sieve catalysts were prepared by the ion exchange method, catalysts with different degrees of alkali metal K/Na poisoning were prepared by the wet-impregnation method, and the SCR activity and N2 selectivity of fresh and poisoned catalysts were compared. The effects of alkali ion (Na+ and K+) poisoning on the comprehensive properties of Cu/SSZ-13 were studied. The distribution and quantity of Cu2+ active components in the catalyst before and after poisoning and the change of acidic sites were explored using NH3-TPO, NH3-TPD, H2-TPR, BET, and XRD. The characteristics of crystal structure, specific surface area, and pore structure revealed the influence of the loading of alkali metal K/Na on the adsorption performance, weakened redox characteristics, and a certain degree of structural damage of Cu/SSZ-13 molecular sieve catalyst. It explains that the reason for the decline in catalyst performance after poisoning is due to the decrease in the number of active sites caused by the ion-exchange between alkali metal ions and Cu2+ and H+, the increase of CuxOy species, the decrease of acidic sites, and pore blockage. This provides data support and theoretical basis for the design of highly resistant Cu/SSZ-13 catalysts. [ABSTRACT FROM AUTHOR]

In this paper, the CoxMn1Cey composite oxide catalyst was synthesized by the co-precipitation method. The structure–activity relationship of the catalyst was analyzed by characterization methods such as XRD, Raman, H2-TPR, NH3/NOx-TPD, XPS, and in situ DRIFTS. The results showed that the Co3Mn1Ce1 catalyst resisted high space velocity, water, and sulfur. In addition, Ce doping could effectively increase the specific surface area of the catalyst. In a sulfur-containing atmosphere, Ce could preferentially react with SO2 and act as a sacrifice site to protect the active components from toxicity. Co-doping greatly enhanced the redox capacity of the catalyst and increased the chemisorbed oxygen (OS) content on the surface of catalysts. Co-presence of Co and Ce increased the content of surface-active Mn species, which further effectively improved the adsorption capacity of the catalyst for NH3 and NO reactants. In situ DRIFTS results showed that the reaction on the Co3Mn1Ce1 catalyst followed both the Langmuir–Hinshelwood and Eley–Rideal mechanisms. [ABSTRACT FROM AUTHOR]

F-doped V2O5-WO3/TiO2 catalyst has been confirmed to have excellent denitration activity at low temperatures. Since the V2O5-WO3/TiO2 catalyst is a structure-sensitive catalyst, the loading order of V2O5 and WO3 may affect its denitration performance. In this paper, a series of F-doped V2O5-WO3/TiO2 catalysts with different V2O5 and WO3 loading orders were synthesized to investigate the effect of denitration performance at low temperatures. It was found that the loading orders led to significant gaps in denitration performance in the range of 120–240 °C. The results indicated loading WO3 first better utilized the oxygen vacancies on the TiF carrier promoting the generation of reduced vanadium species. In addition, loading WO3 first facilitated the dispersion of V2O5 thus enhanced the NH3 adsorption capacity of VWTiF. In situ DRIFT verified the rapid reaction between NO2, nitrate, and nitrite species and adsorbed NH3 over the VWTiF, confirming that the NH3 selective catalytic reduction (NH3-SCR) reaction over VWTiF at 240 °C proceeded by the Langmuir-Hinshelwood (L-H) mechanism. This research established the constitutive relationship between the loading order of V2O5 and WO3 and the denitration performance of the F-doped VWTi catalyst providing insights into the catalyst design process. [ABSTRACT FROM AUTHOR]

Mesoporous/hierarchical zeolites (HZs) are a relatively new group of materials, and interest in their application in catalysis is continuously growing. This paper presents recent achievements in the application of mesoporous zeolites in catalytic reactions of nitrogen pollutant conversion. The analysis presented includes processes such as selective catalytic reduction of NOx with ammonia (NH3-SCR, DeNOx), selective catalytic oxidation of ammonia (NH3-SCO, AMOx), and catalytic decomposition of N2O. Different zeolite topologies and methods of their modification focused on mesoporosity generation (e.g., desilication, dealumination, steaming, self-assembly techniques, and application of hard and soft templates) are reviewed and compared with respect to catalytic processes. Special attention is paid to the role of porous structure and acidity, as well as the form of deposited transition metals, in the catalytic activation of modified zeolites in the elimination of nitrogen pollutants from flue gases. [ABSTRACT FROM AUTHOR]

• A Ce-Nb/SnO2 catalyst with excellent NH3-SCR activity and hydrothermal stability was synthetized by simple impregnation method. • The impregnation sequence can affect the activity and hydrothermal stability of the catalyst. • The developed Ce-Nb/SnO2 catalyst can be used for the NOx removal from diesel and hydrogen-fueled engines. Hydrothermal stability is crucial for the practical application of deNO x catalyst on diesel vehicles, for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). SnO 2 -based materials possess superior hydrothermal stability, which is attractive for the development of NH 3 -SCR catalyst. In this work, a series of Ce-Nb/SnO 2 catalysts, with Ce and Nb loading on SnO 2 support, were prepared by impregnation method. It was found that, the NH 3 -SCR activities and hydrothermal stabilities of the Ce-Nb/SnO 2 catalysts significantly varied with the impregnation sequences, and the Ce-Nb(f)/SnO 2 catalyst that firstly impregnated Nb and then impregnated Ce exhibited the best performance. The characterization results revealed that Ce-Nb(f)/SnO 2 possessed appropriate acidity and redox capability. Furthermore, the strong synergistic effect between Nb and Sn species stabilized the structure and maintained the dispersion of acid sites. This study may provide a new understanding for the effect of impregnation sequence on activity and hydrothermal stability and a new environmental-friendly NH 3 -SCR catalyst with potential applications for NO x removal from diesel and hydrogen-fueled engines. [Display omitted] [ABSTRACT FROM AUTHOR]

The synthesis process of conventional Mn-based denitrification catalysts is relatively complex and expensive. In this paper, a resource application of chlorella was proposed, and a Chlorella@Mn composite denitrification catalyst was innovatively synthesized by electrostatic interaction. The Chlorella@Mn composite denitrification catalyst prepared under the optimal conditions (0.54 g/L Mn2+ concentration, 20 million chlorellas/mL concentration, 450°C calcination temperature) exhibited a well-developed pore structure and large specific surface area (122 m2/g). Compared with MnOx alone, the Chlorella@Mn composite catalyst achieved superior performance, with ∼100% NH 3 selective catalytic reduction (NH 3 -SCR) denitrification activity at 100-225°C. The results of NH 3 temperature-programmed desorption (NH 3 -TPD) and H 2 temperature-programmed reduction (H 2 -TPR) showed that the catalyst had strong acid sites and good redox properties. Zeta potential testing showed that the electronegativity of the chlorella cell surface could be used to enrich with Mn2+. X-ray photoelectron spectroscopy (XPS) confirmed that Chlorella@Mn had a high content of Mn3+ and surface chemisorbed oxygen. In-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) experimental results showed that both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms play a role in the denitrification process on the surface of the Chlorella@Mn catalyst, where the main intermediate nitrate species is monodentate nitrite. The presence of SO 2 promoted the generation and strengthening of Brønsted acid sites, but also generated more sulfate species on the surface, thereby reducing the denitrification activity of the Chlorella@Mn catalyst. The Chlorella@Mn composite catalyst had the characteristics of short preparation time, simple process and low cost, making it promising for industrial application. [Display omitted] Schematic diagram of NH 3 -SCR performance of Chlorella@Mn composite denitrification catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CeCoMnO x spinel-type catalyst prepared using oxalic acid precipitant has a more favorable physicochemical structure for NO conversion than that prepared using alkaline precipitant. • 400 °C is the optimum calcination temperature for oxalic acid precipitated CeCoMnO x spinel for NH 3 -SCR reaction. • The oxalic acid precipitated CeCoMnO x calcined at 400 °C has nearly 100 % NO conversion at 100–200 °C at GHSV = 15,000 mL·g−1·h−1. • An interface-enhanced redox macrocycle mechanism incorporating acid cycling is proposed for oxalic acid precipitated CeCoMnO x catalysts. CeCoMnO x spinel-type catalysts for the selective catalytic reduction of NO using NH 3 (NH 3 -SCR) are usually prepared by alkaline co-precipitation. In this paper, a series of CeCoMnO x spinel-type catalysts with different calcination temperatures were prepared by acidic oxalate co-precipitation. The physicochemical structures and NH 3 -SCR activities of the CeCoMnO x spinel-type catalysts prepared by oxalate co-precipitation and conventional ammonia co-precipitation were systematically compared. The results show that the CeCoMnO x spinel-type catalysts prepared by the oxalate precipitation method (CeCoMnO x -C) have larger specific surface area, more mesopores and surface active sites, stronger redox properties and adsorption activation properties than those prepared by the traditional ammonia co-precipitation method at 400 °C (CeCoMnO x -N-400), and thus CeCoMnO x -C have better low-temperature NH 3 -SCR performance. At the same calcination temperature of 400 °C, the NO conversion of CeCoMnO x -C-400 exceeds 89 % and approaches 100 % within the reaction temperature of 100–125 °C, which is 14.8 %-2.5 % higher than that of CeCoMnO x -N-400 at 100–125 °C. In addition, the enhanced redox and acid cycle matching mechanisms on the CeCoMnO x -C surface, as well as the enhanced monoadsorption Eley-Rideal (E-R) and double adsorption Langmuir-Hinshelwood (L-H) reaction mechanisms, are also derived from XPS and in situ DRIFTS characterization. [ABSTRACT FROM AUTHOR]

CeO2–MnOx mixed oxides supported on different carriers (ZSM-5, TiO2, and SAPO-34) were prepared by the sol-gel combustion method and evaluated for the selective catalytic reduction of NO with NH3. The physicochemical properties of the samples were determined by using XRD, TEM, N2 adsorption (BET method), H2-TPR, and NH3-TPD. The Ce–Mn/TiO2 exhibited a higher NO conversion than Ce–Mn/ZSM-5 in the 100-200°C temperature range, but the NO conversion of Ce–Mn/ZSM-5 increases with reaction temperature (being the N2 selectivity close to 100%) whereas, for Ce–Mn/TiO2, the N2 selectivity extremely decreases. The reducibility and surface acidity of samples seems to explain the catalytic performance. Thus, although the reducibility of Ce–Mn/ZSM-5 and Ce–Mn/TiO2 was similar, the large number of surface acid sites of Ce–Mn/ZSM-5 could be a plausible reason for its excellent SCR activity. In fact, the superior SCR activity of Ce–Mn/ZSM-5 (94% NO conversion and 95% N2 selectivity at 300°C) is related to the presence of well-dispersed Ce–Mn mixed oxide nanoparticles, high reducibility, and a large number of surface acid sites. [ABSTRACT FROM AUTHOR]

Ce-based selective catalytic reductions with an NH3 (NH3-SCR) catalyst have emerged as a focal point in denitrification catalyst research. However, the correlation between the structural characteristics of Ce-based catalysts and the influence of CeO2 nanoparticle size on SO2 resistance remains unclear. CeO2 nanospheres with different sizes of less than 10 nm were synthesized, and a series of supported CeO2/SBA-15 catalysts were prepared according to the 10 nm pore size of SBA-15. These catalysts were used to explore the influence of the size of the CeO2 nanospheres on these catalysts, specifically on their SO2 resistance in NH3-SCR reactions. With the increase in size, their SO2 resistance became stronger. The results of NH3-TPD, H2-TPR, and XPS indicated that the catalyst with the largest particle size had the lowest adsorption of SO2, which was attributed to more acid sites and a mutual effect between Si and Ce, resulting in the best SO2 resistance. It was also observed that there was less sulfate deposition on the catalyst by thermogravimetric analysis. In situ DRIFTs revealed that after SO2 poisoning, the NH3-SCR reaction on the catalyst predominantly follows the E-R mechanism. This study offers recommendations for the development of Ce-based SO2-resistant NH3-SCR catalysts, specifically focusing on the synthesis and interaction of nanomaterials. [ABSTRACT FROM AUTHOR]

• P modified Cu-SAPO-34 were prepared using bulk CuO particles as Cu2+ precursor. • The high-temperature hydrothermal aging significantly enhanced de-NO x performance. • The amount of active sites-isolated Cu2+ and Brønsted acid sites was greatly enhanced. • Phosphate ions also contributed to the catalysis performance of the aged samples. Phosphate ions promoted Cu-SAPO-34 (P-Cu-SAPO-34) were prepared using bulk CuO particles as Cu2+ precursor by a solid-state ion exchange technique for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). The effects of high temperature (H-T) hydrothermal aging on the NO x removal (de-NO x) performance of Cu-SAPO-34 with and without phosphate ions were systematically investigated at atomic level. The results displayed that both Cu-SAPO-34 and P-Cu-SAPO-34 presented relatively poor NO x removal activity with a low conversion (< 30%) at 250-500°C. However, after H-T hydrothermal treatment (800°C for 10 hr at 10% H 2 O), these two samples showed significantly satisfied NO x elimination performance with a quite high conversion (70%-90%) at 250-500°C. Additionally, phosphate ions decoration can further enhance the catalytic performance of Cu-SAPO-34 after hydrothermal treatment (Cu-SAPO-34H). The textural properties, morphologies, structural feature, acidity, redox characteristic, and surface-active species of the fresh and hydrothermally aged samples were analyzed using various characterization methods. The systematical characterization results revealed that increases of 28% of the isolated Cu2+ active species (Cu2+-2Z, Cu (OH)+-Z) mainly from bulk CuO and 50% of the Brønsted acid sites, the high dispersion of isolated Cu2+ active component as well as the Brønsted acid sites were mainly responsible for the accepted catalytic activity of these two hydrothermally aged samples, especially for P-Cu-SAPO-34H. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel low-temperature mineral-based Mn X Fe 3−X O 4 spinel NH 3 -SCR catalysts were synthesized from natural ferromanganese minerals. • The X value of 1.5 is the best X value of Mn X Fe 3−X O 4 (Fe based) for NH 3 -SCR reaction (with H 2 O (g)). • Mn 1.5 Fe 1.5 O 4 nano-particles (201 nm) have nearly 100 % NO conversion (with H 2 O (g)) at 125–300 °C. • The increase of X value activates the dehydrogenation catalytic process of key intermediates NHNO-Fe and NH 2 NO-Mn on the (3 1 1) plane of Mn X Fe 3-X O 4. The process of smelting and purifying the catalyst precursor salt from minerals is extremely complex, which directly leads to high catalyst costs and serious secondary pollution. In order to achieve energy saving and emission reduction in the catalyst preparation process, in-situ synthesis of catalyst materials from natural minerals is a new research direction. In this study, we firstly explored the optimal X value of Mn X Fe 3-X O 4 for the NH 3 selective catalytic reduction of NO (NH 3 -SCR) reaction, i.e., the Mn, Fe ratio, and then prepared a novel highly active mineral-based pure phase Mn X Fe 3-X O 4 spinel NH 3 -SCR catalyst by natural ferromanganese ore fines with iron-red fines (Fe 2 O 3) allotment through in situ solid-phase synthesis and magnetic separation methods according to this ratio. The results show that the X value of 1.5 (Mn 1.5 Fe 1.5 O 4) is the best for NH 3 -SCR reaction. Mn 1.5 Fe 1.5 O 4 nano-particles (201 nm) has nearly 100 % NO conversion (with 5 % H 2 O (g)) at 125–300 °C. The combination of characterizations and density functional theory (DFT) calculation shows that the catalytic process of Eley-Rideal (E-R) dehydrogenation is enhanced at both the active site Mn site and Fe site, which is a key factor in the acceleration of the NH 3 -SCR reaction with increasing X value at the Mn X Fe 3-X O 4 surface. [ABSTRACT FROM AUTHOR]

5Cu-USY and Ce-doped 5Cu8Ce-USY zeolite catalysts were prepared by the conventional impregnation method. The obtained catalysts were subjected to the hydrothermal ageing process. The catalytic performance of the selective catalytic reduction of NOx with NH3 (NH3-SCR) was evaluated on both fresh and aged catalysts. Physical/chemical characterizations such as X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were performed, along with detailed in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) experiments including CO adsorption, NH3 adsorption, and NO + O2 reactions. Results showed that, for the 5Cu-USY catalyst, hydrothermal ageing treatment could somehow improve the low-temperature SCR activity, but it also led to significant formation of unfavorable byproducts NO2 and N2O. Such an activity change can be attributed to hydrothermal ageing inducing the migration of isolated Cu+ species in the sodalite cavities towards the super cages of the USY zeolites. The increased content of Cu+ species in the super cages was beneficial for the low-temperature activity improvement, but, at the same time, it also facilitated ammonia oxidation at high temperatures. Ce doping after hydrothermal ageing has a "double-edged sword" effect on the catalytic performance. First of all, Ce doping can inhibit Cu species migration by self-occupying the internal cage sites; thus, the catalytic performance of 5Cu8Ce-USY-700H remains stable after ageing. Secondly, Ce doping introduces a CuOx–CeO2 strong interaction, which facilitates lattice oxygen mobility by forming more oxygen vacancies so as to increase the concentration of surface active oxygen. These changes, on the one hand, could help to promote further oxidative decomposition of nitrate/nitrite intermediates and improve the catalytic performance. But, on the other hand, it also causes the byproduct generation to become more severe. [ABSTRACT FROM AUTHOR]

CeO2–nanorod support was synthesized by hydrothermal method and different manganese oxides (MnO, MnO2, and Mn2O3) were impregnated over support by the wet‐impregnation forming MnO/CeO2‐NR, MnO2/CeO2‐NRm and Mn2O3/CeO2‐NR. The physico‐chemical properties of the as‐prepared catalysts were analyzed using x‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, x‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscope–energy‐dispersive x‐ray spectroscopy (SEM–EDX), hydrogen‐temperature‐programmed reduction (H2‐TPR), and Raman spectroscopy. These catalysts were further analyzed for NO reduction using NH3 as a reducing gas in the temperature range of 50 to 450°C. The results confirmed that MnO2/CeO2‐NR gave the maximum NO conversion (65%) and N2 selectivity (89%) among all catalysts. Further, MnO2/CeO2‐NR catalyst was studied for the effect of MnO2 loading and more than 90% NO conversion and N2 selectivity were obtained in the temperature range of 250 to 300°C. [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NOx) are very common air pollutants that are harmful to the environment and human bodies. Selective catalytic reduction with ammonia (NH3-SCR) is considered an effective means to remove NOx emissions due to its good environmental adaptability, high catalytic activity, and remarkable selectivity. In this paper, the preparation methods, types, advantages, and challenges of ZSM-5 catalysts are reviewed. Special attention is paid to the catalytic properties and influence factors of ZSM-5 catalysts for NH3-SCR. The SCR performances of ZSM-5 catalysts doped with single or multiple metal ions are also reviewed. In addition, the environmental adaptabilities (sulfur resistance, alkali resistance, water resistance, and hydrothermal stability) of ZSM-5 catalysts are discussed, and the development of ZSM-5 catalysts in denitrification is summarized. [ABSTRACT FROM AUTHOR]

BACKGROUND: Selective catalytic reduction of NOx with NH3 (NH3‐SCR) technology is effective for NOx removal. Acidity and redox ability are two significant characteristics for NH3‐SCR catalysts. This study investigated the effects of N2 calcination on the NH3‐SCR performance of FeCeOx, inspired by the promotion of active oxygen species with inert atmosphere calcination. The structure‐activity relationship and reaction mechanism of the two catalysts (Fe9CeOx‐N2 and Fe9CeOx‐air) were concluded based on the results of characterization. RESULTS: Fe9CeOx‐N2 showed better NOx conversion and SO2 resistance than Fe9CeOx‐air, especially in low and medium temperature range. For fresh catalysts, a higher amount of Oα, Fe3+ and Ce3+ promoted the redox ability of Fe9CeOx‐N2, and further improved the NOx adsorption and activation. Additionally, the greater number of acid sites of Fe9CeOx‐N2 was another reason for its competitive performance. For SO2‐poisoned catalysts, the primary reaction pathway was the reaction between pre‐adsorbed NH3 species and NOx. The higher amount of acidity from metal sulfate contributed to its better SO2 tolerance of Fe9CeOx‐N2. CONCLUSION: Higher redox ability and acidity led to better NH3‐SCR activity and SO2 tolerance of Fe9CeOx‐N2. This study provides a feasible preparation method for enhancing the NOx conversion and SO2 tolerance of NH3‐SCR catalysts. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Mn/TiO2, Mn-Ce/TiO2, and Sb-modified Mn-Ce-Sbx/TiO2 catalysts were prepared by the impregnation method. The catalysts were characterized by BET, XRD, XPS, SEM, NH3-TPD, FTIR, TG-DSC, H2-TPR, and the SCR (Selective Catalytic Reduction) activity, and investigated by SO2, and H2O resistance between 90 °C and 220 °C. Results showed that the molar ratio of Sb/Mn is 0.2, the catalytic activity of Mn-Ce-Sb0.2/TiO2 can reach 94% of NO conversion rate at 120 °C. Meanwhile, Mn-Ce-Sb0.2/TiO2 has the best SO2 and H2O resistance. Characterization results demonstrated that the modification of Sb can decrease the crystallinity of the Mn element, while Sb can inhibit the formation of sulfate and reduce the poisonous effect of SO2 on the catalyst. [ABSTRACT FROM AUTHOR]

The doping of different elements will make the Fe2O3 catalyst show different catalytic characteristics and improve the activity of the Fe2O3 catalyst in selective catalytic reduction (SCR), mainly by increasing the types of reactive oxygen species and the specific surface area of the catalyst. In this paper, density functional theory (DFT) was used to reveal the reaction path and adsorption behaviour of the Mg‐doped γ‐Fe2O3 catalyst. The results show that the doping of Mg ions can contribute electrons and lead to electron migration on the catalyst surface, which changes the acidity of some sites on the catalyst surface. The adsorption energy of NH3 is related to the binding sites of N atoms on the catalyst surface, and different adsorption sites will be enhanced or weakened due to Mg doping. NH2 reacts with NO to form N2 and H2O, so the dehydrogenation of NH3 to the NH2 radical is a key step in SCR. With doping, this process becomes more likely to occur. In addition, the activation energy barrier of NH2 formation in the aerobic environment is lower than that in the anaerobic condition, which contributes to NH3 dehydrogenation. Therefore, doping Mg on the surface of γ‐Fe2O3 catalyst can improve the catalytic activity of NO removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • The intrinsic De-NO x characteristic of CuO and Cu 2 O was revealed. • Strong dehydrogenation capacity of Cu2+ and adsorption ability of Cu+ were proved. • The synergistic promote effect of Cu2+ and Cu+ over NH 3 -SCR was confirmed. • The denitration mechanism over CuO and Cu 2 O at different temperatures was identified. Understanding the effect of CuO x valence state specifically is significant for constructing high-performance Cu based oxide catalyst for low-temperature selective catalytic reduction of NO with NH 3 (NH 3 -SCR). In this work, CuO x with different valence state including Cu 2 O, Cu 2 O-CuO and CuO particles are synthetized as model catalysts, which present same variation laws in catalytic performance at 180 ℃, 210 ℃ and 240 ℃. NH 3 -SCR catalytic performance of Cu 2 O-CuO heterojunction is the best, CuO exhibits good catalytic activity, while Cu 2 O possesses excellent N 2 selectivity. Experimental results combined with density functional theory (DFT) calculations reveal that Cu2+ favor to form monodentate nitrate and possess strong ability of activation and dehydrogenation of NH 3. The energy barrier for the form of NH 2 * is 79.5 kJ/mol, which is much lower than that for Cu+. While Cu+ is beneficial to NH 3 and NO x adsorption and the form of bidentate nitrate, which have a positive impact on improving the selectivity of N 2. Moreover, the collaboration of Cu2+ and Cu+ facilitates the redox capability and the form of surface adsorbed oxygen species, thus the reaction progress is further promoted. The SCR reaction catalyzed by three samples are dominated mainly by Langmuir-Hinshelwood (L-H) mechanism at 180 ℃. While at 240 ℃, the reaction over Cu 2 O follows Eley-Rideal (E-R) mechanism, during which the rate-limiting step is the internal hydrogen transfer procedure (NH 2 NO*→NHNOH*). Over CuO, the reaction follows L-H mechanism, the process of atomic isomerism (NHNOH*+ *→N 2 *+H 2 O*) is the rate-determining step. The energy barriers are 136 and 146 kJ/mol, respectively. This work may supply important theoretical support for the preparation of high-performance Cu-based oxide catalysts. [ABSTRACT FROM AUTHOR]

Nitrogen oxides emitted from diesel vehicle exhaust seriously endanger the atmospheric environment and human health, which have attracted people's attention. Among numerous nitrogen oxide (NOx) removal technologies, photocatalytic removal of NOx and SCR have received widespread attention. The photocatalytic treatment of NOx technology is a good choice due to its mild reaction conditions and low costs. Moreover, NH3-SCR has been widely used in denitration technology and plays an important role in controlling NOx emissions. In NH3-SCR technology, the development of high-efficiency catalysts is an important part. This paper summarizes the research progress of metal oxide catalysts for NH3-SCR reactions, including V-based catalysts, Mn-based catalysts, Fe-based catalysts, Ce-based catalysts, and Cu-based catalysts. Meanwhile, the detailed process of the NH3-SCR reaction was also introduced. In addition, this paper also describes a possible SO2 poisoning mechanism and the stability of the catalysts. Finally, the problems and prospects of metal oxide catalysts for NOx removal were also proposed. [ABSTRACT FROM AUTHOR]

A series of Mn/γ-Al2O3, Mn–Cu/γ-Al2O3, Mn–Ce/γ-Al2O3 and Mn–Ce–Cu/γ-Al2O3 catalysts were prepared by equal volume impregnation. The denitrification effects of the different catalysts were studied by activity measurement, X-ray diffraction, Brunauer, Emmett, and Teller surface area tests, Scanning electron microscopy, H2-temperature programmed reduction and Fourier-transform infrared spectroscopy. The experimental results show that Ce and Cu are added to a Mn/γ-Al2O3 catalyst as bimetallic additives, which weakens the interaction between Mn and the carrier, improves the dispersion of MnOx on the surface of the carrier, improves the specific surface area of the catalyst, and improves the reducibility. Mn–Ce–Cu/γ-Al2O3 catalyst reaches a maximum conversion of 92% at 202 °C. Also, the addition of the auxiliary metals promotes the reaction mechanism to a certain extent, and the addition of Ce especially promotes the conversion of NO–NO2, which is conducive to the production of intermediate products that promote the NH3-SCR reaction. [ABSTRACT FROM AUTHOR]

Mn/TiO2 catalysts 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/TiO2 catalyst was employed to evaluate its SCR activity with and without the presence of KNO3 at 100–300 °C. The influence of various parameters such as KNO3 loading amount, calcination time, temperature and catalyst deactivation was investigated. The characterization results indicated that the doping of potassium on Mn/TiO2 surface obviously resulted in a great decrease of reducibility, surface acidity and NH3 adsorption 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/TiO2 catalyst after calcining treatment, which may lead to a poorer performance of SCR catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu-SAPO-34 with P/Al ratio of 1.2 showed good hydrothermal stability. • The grain size of Cu-SAPO-34 increased with the increase of P/Al ratio. • Large grain size promoted transformation of CuO to Cu2+ after hydrothermal aging. • Large grain size limited aggregation of Cu2+ after hydrothermal aging. Cu-SAPO-34 is a promising catalyst for abatement of NO via selective catalytic reduction with NH 3 (NH 3 -SCR), but its hydrothermal stability needs to be enhanced. In this work, the Cu-SAPO-34 catalysts with different P/Al ratios of 0.8, 1.0 and 1.2 were prepared, and the temperature window with NO conversion >90% (T 90) for all catalysts were similar (160–570 °C). The T 90 of Cu-SAPO-34 with P/Al of 0.8 dramatically decreased (220–470 °C) after hydrothermal treatment, and interestingly, the catalysts with high P/Al ratios (1.0 and 1.2) remained high activity. The T 90 of the aged catalysts with P/Al of 1.2 was 155–525 °C. The characterizations showed that the increase of P/Al ratio not only enhanced the crystallinity but also enlarged the grain size of catalysts, which were conducive to the zeolite framework stability. Moreover, the Cu-SAPO-34 with large grain size facilitated the conversion of CuO to isolated Cu2+ ions as well as inhibited the aggregation of Cu species. Furthermore, the large grain sized catalysts provided more acid sites, and thus, the catalysts presented excellent hydrothermal stability. In situ DRIFTS analysis confirmed the existence of both Langmuir-Hinshelwood and Eley-Rideal pathway over the catalyst with a P/Al ratio of 1.2. This work provided a facile method to promote the hydrothermal stability of Cu-based zeolite catalysts. [ABSTRACT FROM AUTHOR]

A series of X%Cu/SAPO-34 (X = 1.0, 2.0, 4.0 and 6.0) catalysts were prepared by ultrasonic impregnation method for selective catalytic reduction (SCR) of NOx with ammonia. The effect of different Cu loadings on the selective catalytic reduction of NO by molecular sieve catalysts was examined on a fixed-bed reactor. Catalyst physicochemical properties were characterized and analyzed using XRD, TEM, NH3-TPD, H2-TPR, and in situ DRIFTS. Catalysts were used in reaction kinetics studies from the perspective of transient and steady-state kinetics. Cu/SAPO-34 catalyst with 4% Cu loading had the best denitrification efficiency and wide activity window. Copper species were highly dispersed on the catalyst surface. Cu/SAPO-34 catalyst with 4% Cu loading had rich acidic sites and excellent redox performance. Cu/SAPO-34 catalysts with 4% Cu loading possess minimal activation energy and were lower than commercial catalysts. According to the results of in situ IR, transient and steady-state analysis, the Cu/SAPO-34 catalyst with 4% Cu loading in the NH3-SCR reaction process was mainly E-R mechanism, and there was L–H mechanism. [ABSTRACT FROM AUTHOR]

V-modified phosphomolybdic acid catalysts (V-HPMo/TiO2) supported on TiO2 were developed for selective catalytic reduction of NOx with NH3 (NH3-SCR). The V-doping could promote the catalytic activity of HPMo catalysts. When the V/Mo molar ratio is 1, the NOx conversion of V-HPMo/TiO2 can reach over 99% and N2 selectivity is close to 100% in the temperature range of 200–350 °C. After introducing 200 ppm SO2 and 4 vol.% H2O in the feed gas, the catalytic activity decreased by 15% and recovered within 2 h after cutting off SO2 and H2O. V-HPMo/TiO2 catalysts exhibit outstanding redox property and resistance to SO2&H2O. V-doping can also increase the Lewis acid sites and N2 selectivity of HPMo/TiO2 catalysts. The in-situ DRIFTS results show that NH3-SCR reaction over V-HPMo/TiO2 catalysts follows L–H mechanism at low temperature (< 150 °C) and both E-R and L–H mechanisms at high temperature (> 150 °C). [ABSTRACT FROM AUTHOR]

Fe-doped CoCr oxide catalysts are prepared by solid-phase mixing method, coprecipitation method, mechanical mixing method, and citric acid method, respectively, and their catalytic activity in the selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) is tested. The Fe0.5CoCrOx catalysts prepared by all preparation methods have good water resistance and sulfur resistance when the calcination temperature is 400 °C. Fe0.5CoCrOx prepared by coprecipitation method by calcination at 400 °C (CP-400) is shown to have the optimum catalyst activity. In addition, the catalysts are characterized by a series of characterizations. The characterization results show that CP-400 has the largest specific surface area, which makes the active and acidic sites highly dispersed on the surface of CP-400, resulting in stronger redox and acidity and improved SCR activity. The removal of NO by NH3-SCR over CP-400 at 150 °C follows the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. [ABSTRACT FROM AUTHOR]

Cobalt‐chromium oxide catalyst and cerium‐doped cobalt‐chromium oxide catalyst were prepared by the coprecipitation method. The doping effect of Ce on the catalyst for selective catalytic reduction of NO with NH3 was investigated. Compared to Cobalt‐chromium oxide catalyst, the doping of Ce improved the catalytic activity and water and sulfur resistance of the catalyst. The doping of Ce significantly changed the surface morphology, reduced the crystallinity and increased the specific surface area of the catalyst. The large specific surface area of the catalyst facilitated the high dispersion of the acidic sites and promoted the adsorption and desorption of NH3. The doping of Ce increased the chemisorbed oxygen content and the number of acidic sites, enhancing the SCR activity of the catalyst. In addition, the doping of Ce increased the percentage of Co3+ and changed the ionic state of Cr, promoting the interaction between metal ions. [ABSTRACT FROM AUTHOR]

Cobalt‐chromium oxide catalyst and cerium‐doped cobalt‐chromium oxide catalyst were prepared by the coprecipitation method. The doping effect of Ce on the catalyst for selective catalytic reduction of NO with NH3 was investigated. Compared to Cobalt‐chromium oxide catalyst, the doping of Ce improved the catalytic activity and water and sulfur resistance of the catalyst. The doping of Ce significantly changed the surface morphology, reduced the crystallinity and increased the specific surface area of the catalyst. The large specific surface area of the catalyst facilitated the high dispersion of the acidic sites and promoted the adsorption and desorption of NH3. The doping of Ce increased the chemisorbed oxygen content and the number of acidic sites, enhancing the SCR activity of the catalyst. In addition, the doping of Ce increased the percentage of Co3+ and changed the ionic state of Cr, promoting the interaction between metal ions. [ABSTRACT FROM AUTHOR]

TS-1 zeolite with desirable pore structure, an abundance of acidic sites, and good thermal stability promising as a support for the selective catalytic reduction of NO with NH3 (NH3-SCR). Herein, a series of Mn–Fe/TS-1 catalysts have been synthesized, adopting tetraethylenepentamine (TEPA) as a metal complexing agent using the one-pot hydrothermal method. The introduced TEPA can not only increase the loading of active components but also prompts the formation of a hierarchical structure through decreasing the size of TS-1 nanocrystals to produce intercrystalline mesopores during the hydrothermal crystallization process. The optimized Mn–Fe/TS-1(R-2) catalyst shows remarkable NH3-SCR performance. Moreover, it exhibits excellent resistance to H2O and SO2 at low temperatures. The characterization results indicate that Mn–Fe/TS-1(R-2) possesses abundant surface Mn4+ and Fe2+ and chemisorbed oxygen, strong reducibility, and a high Brønsted acid amount. For comparison, Mn–Fe/TiO2 displays a narrower active temperature window due to its poor thermostability. [ABSTRACT FROM AUTHOR]

Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method. The obtained catalysts were subjected to selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) performance evaluation, structural/chemical characterizations such as X-ray diffraction (XRD), N 2 adsorption/desorption, H 2 temperature-programmed reduction (H 2 -TPR), NH 3 temperature-programmed desorption (NH 3 -TPD) as well as detailed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments including CO adsorption, NH 3 adsorption and NO+O 2 in situ reactions. Results show that Cu-USY with proper Cu loading (in this work 5Cu-USY with 5 wt.% Cu) could be promising candidates with highly efficient NH 3 -SCR catalytic performance, relatively low byproduct formation and excellent hydrothermal stability, although its SO 2 poisoning tolerability needs alleviation. Further characterizations reveal that such catalytic advantages can be attributed to both active cu species and surface acid centers evolution modulated by Cu loading. On one hand, Cu species in the super cages of zeolites increases with higher Cu content and being more conducive for NH 3 -SCR reactivity. On the other hand, higher Cu loading leads to depletion of Brønsted acid centers and simultaneous formation of abundant Lewis acid centers, which facilitates NH 4 NO 3 reduction via NH 3 adsorbed on Lewis acid centers, thus improving SCR reactivity. However, Cu over-introduction leads to formation of surface highly dispersed CuO x , causing unfavorable NH 3 oxidation and inferior N 2 selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Pore confined Pore-CeW/OMT and framework confined FW-CeW/OMT catalysts with ordered mesoporous structure were successfully designed for NH 3 -SCR process. Framework confined structure could effectively prevent the migration and aggregation of highly dispersed nanoparticles on catalyst. Citric acid pretreatment has a significant activation effect on the catalyst by enhancing surface acidity and redox ability. The FW-CeW/OMT exhibited wide operating temperature window, good thermal stability, as well as strong sulfur resistance in NH 3 -SCR process. [Display omitted] • Ordered mesoporous structured TiO 2 (OMT) was successfully fabricated. • Pore confined and framework confined CeW/OMT catalysts were constructed. • Confinement effect of different active site position on NH 3 -SCR was revealed. • Citric acid pretreatment was essential for confined catalyst activation. In heterogeneous catalysis, the migration and aggregation of active nanoparticles has always been a challenging problem in catalyst design. Two types of confined catalysts, including the pore confined Pore-CeW/OMT and framework confined FW-CeW/OMT were successfully designed for NH 3 -SCR process in this work. Experimental results revealed that the framework confined structure could effectively prevent the migration and aggregation of highly dispersed nanoparticles on catalyst. Benefiting from the structural advantages of ordered mesopores TiO 2 (OMT), large specific surface area as well as abundant active sites could be supplied for catalytic reaction. It should be noted that citric acid pretreatment was essential for confined catalyst activation. The activation treatment could dramatically enhance catalyst surface acidity, especially a large number of strong acid sites were supplemented, resulting in significantly enhancement of catalytic activity at high temperature. Furthermore, it could also accelerate reduction of Ce4+ to Ce3+ and generate more active oxygen species, which resulted in a significant improvement in its low-temperature catalytic activity. Owning with strong surface acidity as well as framework confinement effect, the unique ordered mesoporous TiO 2 framework could inhibit SO 2 adsorption and protect active sites from SO 2 attacking. Thus, the framework confined FW-CeW/OMT exhibited wide operating temperature window, good thermal stability, as well as strong sulfur resistance in NH 3 -SCR process. [ABSTRACT FROM AUTHOR]

This paper explores the effects of concentration of acid activation on the properties of rare earth tailings catalyst. The results show that the denitration activity of rare earth tailings catalyst is enhanced by acid activation. The best denitration activity of catalyst, activated by sulfuric acid of 8 mol/L, is 86%. [ABSTRACT FROM AUTHOR]

This paper explores the effects of concentration of acid activation on the properties of rare earth tailings catalyst. The results show that the denitration activity of rare earth tailings catalyst is enhanced by acid activation. The best denitration activity of catalyst, activated by sulfuric acid of 8 mol/L, is 86%. [ABSTRACT FROM AUTHOR]

Lead (Pb) is a heavy metal commonly found in industrial exhaust gases, which can reduce catalytic activity of a catalyst for the NH3‐SCR reaction. In this study, 4.0 wt% Mn‐loaded Fe‐pillared interlayer clay (4Mn/Fe‐PILC) and its Co‐modified catalyst (2Co‐4Mn/Fe‐PILC) were prepared, in the meanwhile the 4Mn/Fe‐PILC‐Pb and 2Co‐4Mn/Fe‐PILC‐Pb samples were also obtained using the impregnation method with a Pb(CH3COO)2 aqueous solution. It was found that the addition of 2.0 wt% cobalt could significantly enhance Pb resistance of the 4Mn/Fe‐PILC catalyst. The characterization results revealed that the doping of Co to Mn/Fe‐PILC increased the surface Mn4+ species concentration, reducibility, and acid site amount, thereby improving Pb resistance of the catalyst. Furthermore, the in situ DRIFTS results demonstrated that Co modification enhanced the adsorption capacity of NH3 or NO, especially influenced formation of the NH3 intermediates and bridging nitrate species, which were also conducive to the improvement in Pb resistance of the catalyst. [ABSTRACT FROM AUTHOR]