NH3-SCR Process Research Articles

Poisoning mechanism of KCl, K2O and SO2 on Mn-Ce/CuX catalyst for low-temperature SCR of NO with NH3

In this study, a series of K species or/and SO2 poisoned Mn-Ce doped CuX (MCCX) catalysts were prepared from waste blast furnace slag (BFS), and the influence mechanism of K species or/and SO2 poisoning on the catalysts in low-temperature NH3-SCR process was investigated. The results demonstrated that MCCX-KCl catalyst had poorer NO conversion than MCCX-K2O below 200 °C, and the co-existence of K species and SO2 considerably inhibited NO conversion. Aggregation of the Cu active component might also be facilitated by co-poisoning with K species and SO2. Furthermore, K species and SO2 co-poisoned catalysts showed fewer isolated Cu2+ species and Mn4+ species than that of K-poisoned catalysts, indicating a decrease in active sites after the addition of SO2. The co-effect of K2O/KCl and SO2 species impaired the redox capacity and decreased the surface acidity than K-poisoned catalysts to a greater extent. Nevertheless, K-poisoning had little effect on the surface intermediates during SCR reaction process, and K-poisoned catalysts followed both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanism. However, MCCX-KCl-SO2 and MCCX-K2O-SO2 catalysts contained fewer nitrate species, indicating that the co-effect of K species and SO2 impeded the reaction between NO + O2 species and pre-NH3 species, thereby resulting in poor low-temperature NH3-SCR activity.

Comparison of Mn doped CeO2 with different exposed facets for NH3-SCR at low temperature

Herein, the Mn-doped different exposed crystal surfaces of CeO2 were prepared and used for the low-temperature NH3-SCR process. The results showed that Mn/CeO2-NC catalyst possessed the higher catalytic activity than Mn/CeO2-NP and Mn/CeO2-NR catalysts at low temperature, which achieved over 90% NO conversion at 200 °C. XRD and SEM analysis verified that though the grain size was different, the active manganese species still maintained the highly uniform distribution on all catalysts. The excellent low-temperature redox property and strong surface acidity jointly served as the inherent motivations for the superior catalytic performance of Mn/CeO2-NC catalyst. During the transient reaction process, no obvious derivatives transformation behavior was observed on CeO2-NP-based catalyst, while both E-R and L-H reaction mechanisms occurred on both Mn/CeO2-NC and Mn/CeO2-NR catalysts. And the Mn/CeO2-NC catalyst had the greater transient reaction efficiency than Mn/CeO2-NR catalyst at whichever pathways, which might clarify the difference in catalytic activity between Mn/CeO2-NC and Mn/CeO2-NR catalysts. Finally, the possible reaction mechanism model for low-temperature SCR over Mn-modified different exposed crystal surfaces of CeO2 catalysts was proposed.

Catalytic Performance of Bimetallic Systems (Cu-Fe, Cu-Mn, Fe-Mn) Based on Spherical MCM-41 Modified by Template Ion-Exchange in NH3-SCR Process

Mesoporous silica of MCM-41 type with spherical morphology was modified with copper, iron, or manganese as well as pairs of these metals by template ion-exchange (TIE) method. The obtained samples were characterized with respect to their structure (XRD), morphology (SEM-EDS), textural parameters (low-temperature N2 sorption), surface acidity (NH3-TPD), transition metal loadings (ICP-OES), their deposited forms (UV-vis DRS) and reducibility (H2-TPR). The catalytic performance of monometallic and bimetallic samples in the selective catalytic reduction of NO with ammonia (NH3-SCR) was tested. The best catalytic results presented a bimetallic copper-manganese sample, which was significantly more active than the mechanical mixture of monometallic copper and manganese catalysts. The synergistic cooperation of manganese and copper species is possibly related to charge relocation between them, resulting in activation of the catalyst in oxidation of NO to NO2, which is necessary for the fast NH3-SCR reaction.

Promotional role of Nb modification on CuCeOx catalyst for low temperature selective catalytic reduction of NO with NH3: A mechanism investigation

CuCeOx and CuCeNbOx-k with different Nb doping ratios were obtained by the citric acid method and applied in NH3-SCR process. The activity test results elucidated that the addition of Nb effectively ameliorated the low-temperature SCR performance. Among them, CuCeNbOx-0.4 catalyst had the finest SCR activity (more than 90% in 185–370 °C), highest N2 selectivity, excellent SO2&H2O resistance and thermal stability. Numerous characterization analysis demonstrated that CuCeNbOx-0.4 had the largest specific surface area, the strongest surface acidity and the most excellent redox properties. The conclusions of in situ DRIFT manifested the Nb modification generated more activated species, enhanced the reactivity of ad-NH3 and ad-NOx species, and the SCR reaction on CuCeNbOx-0.4 mainly followed the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Furthermore, the Nb doping also formed the dual redox cycle (Cu2+ + Nb4+ ↔ Cu+ + Nb5+, Cu2+ + Ce3+ ↔ Cu+ + Ce4+), which facilitated the low-temperature SCR reaction.

Calcium poisoning mechanism on the selective catalytic reduction of NOx by ammonia over the γ-Fe2O3 (001) surface.

γ-Fe2O3 has an excellent low-temperature selective catalytic reduction (SCR) deNOx performance, but its resistance to alkaline earth metal calcium (Ca) is poor. In particular, the detailed mechanism of Ca poisoning on the γ-Fe2O3 catalyst at the atomic level is not clear. Hence, the density functional theory method was used in this research to investigate the influence mechanism of Ca poisoning on the NH3-SCR over the γ-Fe2O3 catalyst surface. The findings reveal that NH3, NO, and O2 molecules can bind to the γ-Fe2O3 (001) surface to generate coordinated ammonia, monodentate nitroso, and adsorption oxygen species, respectively. The main active site is Fe1-top. For the γ-Fe2O3 with Ca poisoning, the Ca atom has a high adsorption energy on the surface of γ-Fe2O3 (001), which covers the catalyst surface and reduces the active sites. The presence of Ca atom decreases the adsorption performance of NH3, while slightly improving the NO and O2 adsorption. In particular, the Ca atom restrains the NH3 activation and NH2 formation, which is detrimental to the NH3-SCR process.

Multiple pollutants control of NO, benzene and toluene from coal-fired plant by Mo/Ni impregnated TiO2-based NH3-SCR catalyst: A DFT supported experimental study

There was a dearth of understanding regarding the mechanism of MPC catalyst activity and the creation of effective MPC catalysts for industrial low oxygen and high SO2 concentration environments. Herein, Mo/Ni was utilized to modify the commonly used WVTiOX catalyst to investigate the role and reaction mechanism of Mo/Ni in the MPC process. Mo/Ni doping greatly improved the MPC performance of the WVTiOX catalyst, increased the number of Brønsted and Lewis acid sites on the surface, promoted surface active oxygen Oα ratio, and intensified metal oxide synergy. The TiO2 (001) models of WVTiOX and NiWVTiOX catalysts were built, and the adsorption energies of NH3, O2, NO, C6H6, and C7H8 gaseous molecules on the surfaces of the two catalysts were calculated by density functional theory (DFT). The DFT and in situ DRIFTS results proved that NH3-SCR process of the catalyst was mainly governed by the L-H mechanism, while the E-R mechanism also worked to a certain extent. The following are possible benzene and toluene oxidation pathways on NiWVTiOX: C6H6 → C6H4O2 → C4H2O3 → CO2 + H2O and C7H8 → C6H5CH2OH → C6H5CHO → C6H5COOH → C4H2O3 → CO2 + H2O.

Nitric Oxide Decomposition via Selective Catalytic Reduction by Ammonia on a Transition-Metal Cluster of W2TcO6

Decomposition of nitric oxide (NO) gas on a reactive transition-metal cluster of W2TcO6 has been examined and investigated via selective catalytic reduction by ammonia (NH3-SCR) using the M06-L density functional method. The transition-metal cluster of W2TcO6 can be employed to transform NO to N2 gas efficiently over an active site of tungsten (W). A reaction mechanism of NO conversion based on the NH3-SCR process has been elucidated by a potential energy surface along the reaction pathways. The reaction pathways of this NH3-SCR process begin with adsorption of NH3, adsorption of NO to the cluster, formation of nitrosamine (NH2NO) and NHNO/NHNOH intermediates, and rearrangement of NHNO/NHNOH to obtain N2 and H2O, respectively. Notably, a significant NH2NO as a key intermediate, namely, "nitrosamine", must be formed before further steps can take place in the generation of N2 from NO, followed by the involvement of the NHNO or NHNOH intermediate. From our calculated results, the NHNO intermediate via TS3a is found in pathway a, while NHNOH is found in pathway b via TS3b. Pathway b has a lower energy barrier of 35.1 kcal/mol than pathway a with an energy barrier of 41.8 kcal/mol, indicating that pathway b should be more energetically favorable. The step for NHNO intermediate rearrangement is a rate-determining step for the reaction occurring through pathway a, which is found to be more difficult in accordance with a difficult N-H bond cleavage to form the NNOH intermediate before N2 formation. The overall reaction is an exothermic process with thermodynamic and kinetic favors. Thus, this bimetallic W2TcO6 cluster could be used as a promising and active catalyst for NO decomposition via the NH3-SCR process to an eco-friendly gas, that is, N2.

Insights into samarium doping effects on catalytic activity and SO2 tolerance of MnFeOx catalyst for low-temperature NH3-SCR reaction

The development of catalysts with high NH3-SCR activity in the presence of SO2 was urgent for non-electric industries to control NOx emission at low temperature. Herein, a series of Sm-doping MnFeOx catalysts were synthesized through a typical PEG-assisted co-precipitation method and applied for low-temperature NH3-SCR process. SmMnFe-0.1 catalyst significantly broadened the activation temperature window and yielded almost 100% NO conversion from 75 to 200 °C, simultaneously, the NO removal efficiency still maintained at about 90% in the presence of SO2 and H2O. The characterization results confirmed that Sm could optimize the dispersity of active components and enlarge the surface area of catalyst. Furthermore, strong interaction among active ions facilitated more oxygen vacancies and accelerated NO oxidizing to NO2, further cooperating with abundant adsorbed NH3, leading to cause “Fast SCR” reaction. Both catalysts were dominated by the E-R mechanism despite MnFeOx catalyst also obeyed the L-H pathway. Particularly, the intense redox circles between Sm and Mn inhibited the electron transferring from SO2 to Mn ions, and induced Fe species serving as sacrificial sites along with Sm to preferentially react with SO2, resulting in an excellent SO2 tolerance, and the possible mechanism model was proposed.

Effects of Chlorine Addition on Nitrogen Oxide Reduction and Mercury Oxidation over Selective Catalytic Reduction Catalysts.

The effect of chlorine on mercury oxidation and nitrogen oxides (NOx) reduction over selective catalytic reduction (SCR) catalysts was investigated in this study. Commercial SCR catalysts achieved a high Hg0 oxidation efficiency when Cl2 was sprayed into the flue gas. Results indicated that an appropriate concentration of Cl2 was found to promote NOx reduction and Hg0 oxidation significantly. An optimal concentration of Cl2 (25 ppm) was found to significantly promote NOx reduction and Hg0 oxidation. Moreover, we studied the effects of Cl2 on NOx reduction and Hg0 oxidation over SCR catalysts under different concentrations of SO2. The SO2 poisoning effect was decreased by Cl2 when the SO2 concentration was low (below 1500 ppm). However, sulfate gradually covered the catalyst surface over time during the reaction, which limited the impact of Cl2. Finally, different sulfur-poisoned catalysts were examined in the presence of Cl2. The NOx reduction and Hg0 oxidation performances of sulfate-poisoned catalysts improved when Cl2 was added to the flue gas. Mechanisms for NOx reduction and Hg0 oxidation over fresh catalysts and sulfate-poisoned catalysts in the presence of Cl2 were proposed in this study. The mechanism of Cl2-influenced NOx reduction was similar to that for the NH3-SCR process. With Cl2 in the flue gas, the number of Brønsted active sites increased, which improved catalytic activity. Furthermore, Cl2 reoxidized V4+–OH to V5+=O and caused the NH3-SCR process to operate continuously. The Langmuir–Hinshelwood mechanism was followed for Hg0 oxidation by SCR catalysts when Cl2 was in the flue gas. Cl2 increased the number of Lewis active sites, and catalytic activity increased. Hg0 adsorbed on the surface of the catalysts and was then oxidized to HgCl2. Adding Cl2 to the flue gas increased the strength and number of acid sites on sulfate-poisoned catalysts.

Constructing TiO2@CeMnOx nanocages by self-sacrificial hydrolytic etching MIL-125 for efficient wide-temperature selective catalytic reduction of nitrogen oxides

A nanocage-confined composite catalyst TiO2@CeMnOx-NC was carefully designed and fabricated by directional hydrolytic etching of MIL-125. With the directional protection of tannic acid and PVP used as stabilizer agents, MIL-125(Ti) was controllably etched from its inside out by self-hydrolysis. Notably, MnOx was encapsulated into the cavity of the TiO2 nanocage, and CeO2 was mainly anchored on its outside surface. With the help of related characterization methods, it was found that amorphous TiO2 formed after annealing, and fluorite cubic structured CeO2 inhibited the crystallization of MnOx clusters. Thanks to this unique structure, strong metal-support interactions occurred between Ce/Mn oxides and TiO2, which dramatically enhanced its surface acidity and adsorption ability. Besides, the redox capacity has also been significantly affected. Consequently, the carefully designed composite confined TiO2@CeMnOx-NC with a nanocage structure showed excellent NH3-SCR catalytic performance over a wide working temperature window. In addition, benefiting from the double protection of TiO2 nanocages and CeO2 on the outer surface, the MnOx encapsulated in the cavity could be effectively protected from the influence of water vapor in the flue gas, thus exhibiting good water resistance. In situ DRIFTs analysis revealed that the NH3-SCR process on TiO2@CeMnOx-NC mainly followed the Eley-Rideal (E-R) reaction mechanism. Comparing with nanosheets TiO2@CeMnOx-NS and nanoparticles TiO2@CeMnOx-NP, the nanocages TiO2@CeMnOx-NC have more promising prospects in NH3-SCR applications.

Structure–activity relationship and the inhibitory effect of sulfur dioxide and water on nitrous oxide formation in selective catalytic reduction of nitrogen oxides by ammonia over hollow Co3O4@CoMn2O4 catalyst

Hollow structures have attracted great interest in many areas for their diverse applications. In this work, a new catalyst with an open and hollow structure (Co3O4@CoMn2O4) is designed for selective catalytic reduction of nitrogen oxides by ammonia (NH3-SCR). The as-prepared hollow-structured catalyst provides a high surface area and has thin shells. Owing to its structural benefits, this catalyst exhibited enhanced nitrogen oxides (NOx) removal activity and better resistance to water and sulfur dioxide than cobalt manganate nanoparticles. It also has proved that both the Eley-Rideal and Langmuir-Hinshelwood mechanisms are present in the NH3-SCR process in this catalyst. The improved nitrogen selectivity after the addition of water and sulfur dioxide occurs owing to the inhibition of nitrous oxide formation through the Eley-Rideal and Langmuir-Hinshelwood mechanisms. The deep insight into the structure–activity relationship and the influence of water and sulfur dioxide on nitrogen selectivity provide a new perspective for constructing high-performance de-NOx catalysts.

The Study of C3H6 Impact on Selective Catalytic Reduction by Ammonia (NH3-SCR) Performance over Cu-SAPO-34 Catalysts

In present work, the catalytic performance of Cu-SAPO-34 catalysts with or without propylene during the NH3-SCR process was conducted, and it was found that the de-NOx activity decreased during low temperature ranges (<350 °C), but obviously improved within the range of high temperatures (>350 °C) in the presence of propylene. The XRD, BET, TG, NH3-TPD, NOx-TPD, in situ DRIFTS and gas-switch experiments were performed to explore the propylene effect on the structure and performance of Cu-SAPO-34 catalysts. The bulk characterization and TG results revealed that neither coke deposition nor the variation of structure and physical properties of catalysts were observed after C3H6 treatment. Generally speaking, at the low temperatures (<350 °C), active Cu2+ species could be occupied by propylene, which inhibited the adsorption and oxidation of NOx species, confining the SCR reaction rate and causing the deactivation of Cu-SAPO-34 catalysts. However, with the increase of reaction temperatures, the occupied Cu2+ sites would be recovered and sequentially participate into the NH3-SCR reaction. Additionally, C3H6-SCR reaction also showed the synergetic contribution to the improvement of NOx conversion at high temperature (>350 °C).

Confinement of MnOx@Fe2O3 core-shell catalyst with titania nanotubes: Enhanced N2 selectivity and SO2 tolerance in NH3- SCR process

Surface interface regulation is an important research content in the field of heterogeneous catalysis. To improve the interface interaction between the active component and matrix, tremendous efforts have been dedicated to tailoring the morphology, size, and structure of composite catalysts. In this work, we report a confinement strategy to synthesize a series of core-shell catalysts loaded with metal oxides on titania nanotubes (TNTs), which were applied to the selective catalytic reduction of NOx with ammonia. Interestingly, the core-shell catalyst with confinement of TNTs exhibited the remarkable activity at low temperature region, N2 selectivity and sulfur tolerance. Benefiting from the superior interfacial confinement characteristic of TNTs and Fe2O3, strong component interactions, the surface acid sites and strong oxidizability of MnOx were properly regulated, thus obtained the outstanding activity, N2 selectivity and provide chemical protection to effectively prevent SO2 poisoning. As far as the reaction mechanism, we found that the adsorption and reactivity of Lewis acid sites were the dominant factors affecting the activity in the NH3-SCR process by in situ DRIFT spectra. In general, our work provides an innovative strategy for constructing an TNTs-enwrapped nanocomposite with nano-confinement and core-shell structure to improve the low temperature SCR process.

Mesoporous silicas of MCM-41 type modified with iron species by template ion-exchange method as catalysts for the high-temperature NH3-SCR process – Role of iron species aggregation, silica morphology and associated reactions

Mesoporous silica of MCM-41 type with cylindrical and spherical morphology was synthesized and modified with iron species by template ion-exchange (TIE) method. Methanol solutions of FeCl2 and [Fe3(OCOCH3)7·OH·2 H2O]NO3, used as iron precursors, resulted in deposition of this metal in highly dispersed and aggregated forms, respectively. The obtained samples were characterized with respect to chemical composition - iron loading and surfactant content in non-calcined silicas (ICP-OES, TG-DSC), texture (low-temperature N2 sorption, XRD), morphology (SEM-EDS), form and aggregation of deposited iron species (UV–vis DRS, XRD, SEM-EDS), surface acidity (NH3-TPD) and reducibility of deposited iron species (H2-TPR). Iron modified silicas presented a very good catalytic performance in the high-temperature NH3-SCR process (effective operation in the range of 350–475 °C), however the specific catalytic activity depends on the morphology of the silica samples as well as the form and aggregation of deposited iron species. Moreover, the reactions associated with the NH3-SCR process, such as NO to NO2 oxidation and direct ammonia oxidation were studied.

Enhanced activity and water resistance of hierarchical flower-like Mn-Co binary oxides for ammonia-SCR reaction at low temperature

Manganese-based catalysts applied for selective catalytic reduction of NOx with ammonia (NH3-SCR) still exist certain drawbacks, including narrow operating window, weak water resistance and low selectivity. A number of novel Mn-Co binary oxides with hierarchical flower morphology are synthesized through solvothermal to boost the catalytic performance and H2O tolerance. The formation of the hierarchical flower morphology with high specific surface area could provide short diffusion channels and accessible adsorption sites for NH3 and NO species. Moreover, strong interaction between Mn and Co oxides endows the catalyst with enhanced Lewis acid sites, which could preferentially adsorb NH3 species than H2O. Therefore, the catalyst Mn-Co-F (1:1) presents superior activity with NOx conversion and N2 selectivity > 80% within 60–320 °C, together with remarkable water resistance of 99% NOx conversion under the condition of 15 vol% H2O. The reaction process over Mn-Co-F catalyst follows Langmuir-Hinshelwood mechanism below 200 °C and Eley-Rideal mechanism above 200 °C, respectively. This study creates a unique route for designing high-efficiency Mn-based catalysts used for the NH3-SCR process.

Hybrid Cu-Fe/ZSM-5 Catalyst Prepared by Liquid Ion-Exchange for NOx Removal by NH3-SCR Process

A series of Cu/ZSM-5, Fe/ZSM-5, and Cu-Fe/ZSM-5 catalysts (Si/Al in ZSM-5 = 25) were prepared by different metal loadings using the liquid ion-exchange method. Several characterization methods were conducted to explore the effects of metals on the physical and chemical properties of catalysts. Meanwhile, the electron paramagnetic resonance method is also used to assess the copper and/or iron elements’ coordination and valence state at intersections or in channels of ZSM-5. The metal-loading effects of all catalysts on the catalytic activities were studied for the removal of NOx in a fixed-bed flow reactor using selective catalytic reduction with ammonia (NH3-SCR). The results showed that the iron’s addition could markedly broaden the operation temperature range of the Cu/ZSM-5 catalyst for NH3-SCR between 200 and 550°C due to the presence of more isolated Cu2+ ions as well as additional oligomeric Fe3+ active sites and FexOy oligomeric species. This paper gives a facile and straightforward way to synthesize the practical-promising catalyst applied in NH3-SCR technology to control NOx emissions.

Comparison of sulfur poisoning resistance of Ce/Mn doped γ-Fe2O3 (0 0 1) surface in NH3-SCR reaction with DFT method

The catalyst is the core of the NH3-SCR NOx removal process, and sulfur resistance is important performance to ensure its stability and efficiency. The γ-Fe2O3 catalyst has great NOx removal efficiency but its sulfur resistance need to be enhanced to meet the needs of development of Fe based catalyst. In this paper, the sulfur resistance of γ-Fe2O3 and Ce/Mn doped catalyst was studied by quantum chemistry and DFT, and this study can reveal the adsorption process of sulfur oxides on the catalyst surface and the decomposition of surface sulfate. The result shows that the SO2 and SO3 prefer to be adsorbed on the Ce sites and let more Fe active sites exposed to participate NH3-SCR process, but the Mn doping hardly works on improving adsorption. Moreover, Ce doping can effectively decrease the activation energy of the decomposition of ammonium sulfate and promote its decomposition on the catalyst surface, but Mn doping almost cannot improve the decomposition of ammonium sulfate on the catalyst surface. Therefore, doping Ce on γ-Fe2O3 catalyst can effectively improve the sulfur resistance of the catalyst, while Mn has little effect.

Unexpected increase in low-temperature NH3-SCR catalytic activity over Cu-SSZ-39 after hydrothermal aging

The control of nitrogen oxides (NOx) from heavy-duty diesel vehicles is becoming increasingly urgent due to its detrimental effects on the environment. Cu-SSZ-39, with its exceptional NH3-SCR activity and hydrothermal stability, has attracted more and more attention in the field of diesel vehicle emission control. In this work, an unexpected phenomenon was observed for Cu-SSZ-39 after hydrothermal aging. Generally, the hydrothermal aging process causes deterioration of the catalytic performance of catalysts. However, a remarkable increase in low-temperature NH3-SCR catalytic activity was observed in Cu-SSZ-39 after it was exposed to 850 ℃ hydrothermal aging conditions for 16 h. EPR, DRIFTS, H2-TPR, UV–vis and XANES were utilized to detect the changes in Cu species. It was determined that a portion of the Cu2+ ions near double six-membered rings (d6r) transformed into CuxOy species after hydrothermal treatment. These CuxOy species facilitated the production of nitrate species which were critical intermediates in the NH3-SCR process, resulting in an increase in low-temperature catalytic activity.

A strategy for constructing highly efficient yolk-shell Ce@Mn@TiOx catalyst with dual active sites for low-temperature selective catalytic reduction of NO with NH3

In this work, Ce@MnOx catalysts with core-shell structure were obtained via simple hydrothermal treatment, and the redox capacity can be effectively improved through co-existence of Ce and Mn. Since the strong oxidation capacity of MnOx can lead to the peroxidation of ammonia, the redox capacity can be suppressed with the decrease of manganese content. However, in the case of low manganese content, it is discovered that the surface acidity is very weak and the ammonia adsorption behavior on the catalyst is limited, which is detrimental to the NH3-SCR process. To solve this problem, a series of yolk-shell structured Ce@Mn@TiOx were accordingly constructed, where the TiO2 shell can provide more surface acid sites to promote the adsorption and activation of ammonia. As expected, the Ce@Mn@TiOx exhibits excellent catalytic performance for NH3-SCR at low temperature and possesses a relatively wide working temperature window. More importantly, the TiO2 shell could protect the active sites from water vapor competitive adsorption as well as sulfur attack. Thus, the Ce@Mn@TiOx-10% catalyst exhibited satisfied water vapor resistance in the SCR process, and its sulfur tolerance was also improved to a certain extent. In situ DRIFTs analysis demonstrated that the Ce@Mn@TiOx-10% catalyst mainly follows the L-H reaction mechanism. Consequently, the separation of acid and redox sites has been successfully accomplished by the construction of Ce@Mn@TiOx with yolk-shell structure, where the outer shell (TiO2) mainly enhanced the adsorption capacity of ammonia and protected active centers from attacking by moisture and even sulfur species, while the MnOx interlayer enhanced the interfacial electronic interaction of Ce/Mn and ensured efficient redox cycle during the NH3-SCR process.

Spherical Al-MCM-41 Doped with Copper by Modified TIE Method as Effective Catalyst for Low-Temperature NH3-SCR.

Aluminum containing silica spherical MCM-41 was synthesized and modified with copper by the template ion-exchange method (TIE) and its modified version, including treatment of the samples with ammonia solution directly after template ion-exchange (TIE-NH3). The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low temperature N2 sorption), morphology (SEM-EDS), form and aggregation of deposited copper species (UV-vis DRS), reducibility of copper species (H2-TPR), and surface acidity (NH3-TPD). The deposition of copper by the TIE-NH3 method resulted in much better dispersion of this metal on the MCM-41 surface comparing to copper introduced by TIE method. It was shown that such highly dispersed copper species, mainly monomeric Cu2+ cations, deposited on aluminum containing silica spheres of MCM-41, are significantly more catalytically effective in the NH3-SCR process than analogous catalysts containing aggregated copper oxide species. The catalysts obtained by the TIE-NH3 method effectively operated in much broader temperature and were less active in the side process of direct ammonia oxidation by oxygen.