Showing papers on "Selective catalytic reduction published in 2014"

Promoting effect of MoO3 on the NOx reduction by NH3 over CeO2/TiO2 catalyst studied with in situ DRIFTS

Abstract: A series of MoO3-doped CeO2/TiO2 catalysts prepared by the impregnation method were investigated for the selective catalytic reduction of NO,c by NH3(NH3-SCR). It was found that CeO2-MoO3/TiO2 catalyst is much more active than CeO2/TiO2 for NH3-SCR and the optimum MoO3 loading is 5%. The mechanistic cause of the promoting effect of MoO3 on the activity of CeO2/TiO2 catalyst for NH3-SCR was studied using in situ diffuse reflectance infrared transform spectroscopy (DRIFTS). The results revealed that the highly dispersed molybdenum on CeO2-MoO3/TiO2 catalyst not only resulted in more Brensted acid sites formed on the catalyst surface, but also reduced the thermal stability of the inactive nitrate specie, leaving more active sites available for the adsorption of NH3, both of which are favorable for the promotion of SCR activity. (C) 2013 Elsevier B.V. All rights reserved.

Novel Mn–Ce–Ti Mixed-Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3

Abstract: Mn-Ce-Ti mixed-oxide catalyst prepared by the hydrothermal method was investigated for the selective catalytic reduction (SCR) of NOx with NH3 in the presence of oxygen. It was found that the environmentally benign Mn-Ce-Ti catalyst exhibited excellent NH3-SCR activity and strong resistance against H2O and SO2 with a broad operation temperature window, which is very competitive for the practical application in controlling the NOx emission from diesel engines. On the basis of the catalyst characterization, the dual redox cycles (Mn4+ + Ce3+ Mn3+ + Ce4+, Mn4+ + Ti3+ Mn3+ + Ti4+) and the amorphous structure play key roles for the high catalytic deNO(x) performance. Diffuse reflectance infrared Fourier transform spectroscopy studies showed that the synergetic effect between Mn and Ce contributes to the formation of reactive intermediate species, thus promoting the NH3-SCR to proceed.

The role of cerium in the improved SO2 tolerance for NO reduction with NH3 over Mn-Ce/TiO2 catalyst at low temperature

Abstract: Manganese-based catalysts have shown excellent low-temperature selective catalytic reduction (SCR) activity for NO x removal. However, they all suffer from the serious SO 2 poisoning effect on activity. Ceria modification has been reported to be able to promote SO 2 tolerance of SCR catalysts probably via the inhibition of surface sulfate species formation. In this study, in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigations were carried out to determine the role of Ceria in the improved resistance for a Ce-modified Mn/TiO 2 catalyst. The results indicated that after the introduction of Ce, SO x ad-species preferentially formed on Ceria as bulk-like sulfate species and lessened the sulfation of the main active phase (MnO x ) during low-temperature SCR processes in the presence of SO 2 . Furthermore, the DRIFT and TG–DSC results also implied that Ce modification could reduce thermal stabilities of the sulfate species covered on catalyst surface, thereby promoting its decomposition. Both of these would be beneficial to the improved SO 2 tolerance of Ce modified catalysts.

Excellent Performance of One-Pot Synthesized Cu-SSZ-13 Catalyst for the Selective Catalytic Reduction of NOx with NH3

Abstract: Cu-SSZ-13 samples prepared by a novel one-pot synthesis method achieved excellent NH3–SCR performance and high N2 selectivity from 150 to 550 °C after ion exchange treatments. The selected Cu3.8-SS...

Ni-Mn bi-metal oxide catalysts for the low temperature SCR removal of NO with NH3

Abstract: A series of nickel–manganese bi-metal oxide catalysts of different Ni/Mn ratios were prepared by a co-precipitation method for the low temperature selective catalytic reduction (SCR) of NO with NH3 in the presence of excess O2. The NO conversion over different catalysts decreased in the following sequence of Ni(0.4)-MnOx > MnOx >> Ni(1)-MnOx > Ni(2.5)-MnOx > NiOx. The Ni(0.4)-MnOx catalyst showed the highest catalytic activity, 85% of NO conversion at 95 °C and 100% from 120 to 240 °C, among the catalysts investigated. The TPR, XPS, NH3-TPD and in situ FTIR results revealed that Mn4+ was the main active species for SCR reaction and the addition of nickel species enhanced the surface concentration and acidity of Lewis acid sites. A possible synergetic catalytic effect was proposed for the low temperature SCR reaction through the electron transfer between Mn and Ni ions.

DRIFT Study of CuO–CeO2–TiO2 Mixed Oxides for NOx Reduction with NH3 at Low Temperatures

Abstract: A CuO–CeO2–TiO2 catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures was prepared by a sol–gel method and characterized by X-ray diffraction, Brunner–Emmett–Teller surface area, ultraviolet–visible spectroscopy, H2 temperature-programmed reduction, scanning electron microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The CuO–CeO2–TiO2 ternary oxide catalyst shows excellent NH3-SCR activity in a low-temperature range of 150–250 °C. Lewis acid sites generated from Cu2+ are the main active sites for ammonia activation at low temperature, which is crucial for low temperature NH3-SCR activity. The introduction of ceria results in increased reducibility of CuO species and strong interactions between CuO particles with the matrix. The interactions between copper, cerium and titanium oxides lead to high dispersion of metal oxides with increased active oxygen and enhanced catalyst acidity. Homogeneously mixed metal oxides facilita...

Novel V2O5–CeO2/TiO2 catalyst with low vanadium loading for the selective catalytic reduction of NOx by NH3

Abstract: The effect of Ce on the activity and alkali resistance of V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NOx by NH3 has been investigated It was found that the addition of Ce not only reduced the vanadium loading of V2O5/TiO2 but also enhanced its activity and alkali resistance The NOx conversion over 05%V2O5-5%CeO2/TiO2 was much higher than that over 1%V2O5/TiO2 catalyst Based on the catalyst characterization, the redox cycle (V4+ + Ce4+ V5+ + Ce3+) can account for the excellent NH3-SCR catalytic performance of 05%V2O5-5%CeO2/TiO2 catalyst In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) measurements revealed that the role of Ce on the V2O5-CeO2/TiO2 catalyst was to contribute to the formation of NO2 and monodentate nitrate species, both of which were reactive intermediates for the NH3-SCR of NOx (C) 2014 Elsevier BV All rights reserved

Mechanism of N2O Formation during the Low-Temperature Selective Catalytic Reduction of NO with NH3 over Mn-Fe Spinel

Abstract: The mechanism of N2O formation during the low-temperature selective catalytic reduction reaction (SCR) over Mn–Fe spinel was studied. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transient reaction studies demonstrated that the Eley–Rideal mechanism (i.e., the reaction of adsorbed NH3 species with gaseous NO) and the Langmuir–Hinshelwood mechanism (i.e., the reaction of adsorbed NH3 species with adsorbed NOx species) both contributed to N2O formation. However, N2O selectivity of NO reduction over Mn–Fe spinel through the Langmuir–Hinshelwood mechanism was much less than that through the Eley–Rideal mechanism. The ratio of NO reduction over Mn–Fe spinel through the Langmuir–Hinshelwood mechanism remarkably increased; therefore, N2O selectivity of NO reduction over Mn–Fe spinel decreased with the decrease of the gas hourly space velocity (GHSV). As the gaseous NH3 concentration increased, N2O selectivity of NO reduction over Mn–Fe spinel increased because of the promo...

Selective catalytic reduction of NO with NH3 over HZSM-5-supported Fe–Cu nanocomposite catalysts: The Fe–Cu bimetallic effect

Abstract: A series of Fe x –Cu 4 /ZSM-5 catalysts with fixed Cu content and variable Fe loading amounts were synthesized by an improved incipient-wetness-impregnation method, and their catalytic performances were tested for selective catalytic reduction (SCR) of NO with ammonia as reductant. The catalysts were characterized by means of XRD, BET, SEM, TEM, FT-IR, UV–vis DRS, UV-Raman, NH 3 -TPD, Py-IR, H 2 -TPR and XPS. The results indicated that the high activities of Fe x –Cu 4 /ZSM-5 could be attributed to the formation of Fe–Cu nanocomposites with high dispersion. The interaction between the iron and copper species in the Fe–Cu nanocomposites leads to the change of electronic properties, the stronger redox ability and more acid sites over catalyst surface for Fe x –Cu 4 /ZSM-5 comparing with Cu 4 /ZSM-5. Thus, the addition of iron to Cu 4 /ZSM-5 catalyst improved its catalytic performance, and Fe 4 –Cu 4 /ZSM-5 catalyst exhibited the high NO conversion (>90%) among the wide temperature range (200–475 °C).

Investigation of the structure, acidity, and catalytic performance of CuO/Ti0.95Ce0.05O2 catalyst for the selective catalytic reduction of NO by NH3 at low temperature

Abstract: Anatase TiO2, Ti0.95Ce0.05O2 solid solution, and CeO2 were synthesized by inverse co-precipitation method, and then used as supports to prepare CuO/TiO2, CuO/Ti0.95Ce0.05O2, and CuO/CeO2 catalysts through incipient-wetness impregnation method. The obtained samples were investigated in detail by means of N2-physisorption, XRD, LRS, H2-TPR, XPS, NH3-TPD, and in situ DRIFTS technologies. Furthermore, NH3-SCR of NO in the presence of excess oxygen was chosen as a model reaction to evaluate the catalytic performances of these samples. The obtained results indicate that the incorporation of Ce4+ into the lattice of anatase TiO2 leads to the formation of unstable distorted octahedral coordination structure of Cu2+ in CuO/Ti0.95Ce0.05O2 catalyst and the enhancement of the electron interaction between copper oxide species and Ti0.95Ce0.05O2 support through the redox cycles of Cu2+ + Ce3+ ↔ Cu+ + Ce4+ and Cu2+ + Ti3+ ↔ Cu+ + Ti4+, which are beneficial to the formation of more Lewis acid sites on the surface of CuO/Ti0.95Ce0.05O2 catalyst and the activation of reactant molecules to generate more NH4NO2 species, all of these may promote the enhancement of catalytic performance for NH3-SCR of NO in the presence of excess oxygen. Finally, a possible reaction mechanism (schematic diagram) is tentatively proposed to further understand this model reaction.

Determining the storage, availability and reactivity of NH3 within Cu-Chabazite-based Ammonia Selective Catalytic Reduction systems.

Abstract: Three different types of NH3 species can be simultaneously present on Cu(2+)-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4(+)), formed on the Bronsted acid sites, [Cu(NH3)4](2+) complexes, resulting from NH3 coordination with the Cu(2+) Lewis sites, and NH3 adsorbed on extra-framework Al (EFAl) species, in contrast to the only two reacting NH3 species recently reported on Cu-SSZ-13 zeolite. The NH4(+) ions react very slowly in comparison to NH3 coordinated to Cu(2+) ions and are likely to contribute little to the standard NH3-SCR process, with the Bronsted groups acting primarily as NH3 storage sites. The availability/reactivity of NH4(+) ions can be however, notably improved by submitting the zeolite to repeated exchanges with Cu(2+), accompanied by a remarkable enhancement in the low temperature activity. Moreover, the presence of EFAl species could also have a positive influence on the reaction rate of the available NH4(+) ions. These results have important implications for NH3 storage and availability in Cu-Chabazite-based NH3-SCR systems.

Economical way to synthesize SSZ-13 with abundant ion-exchanged Cu+ for an extraordinary performance in selective catalytic reduction (SCR) of NOx by ammonia.

Abstract: In this study, an economical way for SSZ-13 preparation with the essentially cheap choline chloride as template has been attempted. The as-synthesized SSZ-13 zeolite after ion exchange by copper nitrate solution exhibited a superior SCR performance (over 95% NOx conversion across a broad range from 150 to 400 °C) to the traditional zeolite-based catalysts of Cu-Beta and Cu-ZSM-5. Furthermore, the opportune size of pore opening (∼3.8 A) made Cu-SSZ-13 exhibiting the best selectivity to N2 as well as satisfactory tolerance toward SO2 and C3H6 poisonings. The characterization (XRD, XPS, XRF, and H2-TPR) of samples confirmed that Cu-SSZ-13 possessed the most abundant Cu cations among three investigated Cu-zeolites; furthermore, either on the surface or in the bulk the ratio of Cu+/Cu2+ ions for Cu-SSZ-13 is also the highest. New finding was announced that CHA-type topology is in favor of the formation of copper cations, especially generating much more Cu+ ions than the others, rather than CuO. The activity te...

SO2 poisoning impact on the NH3-SCR reaction over a commercial Cu-SAPO-34 SCR catalyst

Abstract: Sulfur poisoning is a durability issue for Cu/SAPO-34 selective catalytic reduction (SCR) catalysts. In this study, the impact of SO2 on the SCR performance, and the sulfur poisoning mechanism itself, was investigated. SO2 inhibited SCR activity at low temperature (

Highly efficient reusable catalyst based on silicon nanowire arrays decorated with copper nanoparticles

Abstract: Non-noble metal copper (Cu) nanoparticles (NPs) with controlled size and surface coverage are decorated on silicon nanowire arrays (SiNWAs) by a simple galvanic displacement reaction. Using the combined efforts of all these approaches, SiNWAs-supported Cu NPs (SiNWAs–Cu) exhibit excellent and stable activity for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH4) in an aqueous solution, which can be recycled for five successive cycles of the reaction with a conversion efficiency of more than 95%. This novel catalyst also shows excellent catalytic performance for the degradation of other organic dyes, such as methylene blue (MB) and rhodamine B (RhB). Additionally, we demonstrate that the catalytic activity of SiNWAs–Cu is comparable to other SiNWAs-supported noble metal NPs (i.e., Ag and Au). Furthermore, SiNWAs as powerful substrates can be reused for decorating with Cu NPs after dilute HNO3 treatment. SiNWAs–Cu is particularly attractive as a catalyst, although Cu is orders of magnitude cheaper than any noble metals, its catalytic performance is comparable to other noble metals. So SiNWAs–Cu is thus expected to have the potential as a highly efficient, cost-effective and eco-friendly reusable catalyst to replace noble metals for certain catalytic applications.

Structure–activity relationship of VOx/CeO2 nanorod for NO removal with ammonia

Abstract: A series of vanadia supported on ceria nanorods are prepared by impregnation method for selective catalytic reduction (SCR) of NO with ammonia. Two kinds of vanadia species (VOx) (oligomeric and polymeric VOx) and CeVO4 are dispersed on the ceria surface according to the vanadium surface density. These species slightly suppress the catalyst reducibility and concentration of surface oxygen defects rather than distort the ceria cubic lattice or enlarge the BET surface areas. Polymeric VOx and CeO2 create the Lewis acid sites and CeVO4 could be served as the Bronsted acid sites. Polymeric VOx provide new active sites compared with pure CeO2 for the SCR reaction and CeVO4 enhance the number of active sites. Moreover, part of the Lewis acid sites might be converted into the Bronsted acid sites at high temperature under the SCR gas flow. According to the investigations of the reaction mechanism, both Lewis and Bronsted acid sites are reactive with gaseous NO. At low temperature, cis-N2O22− and dimer (NO)2 are active, while surface nitrite or nitrate species are active at high temperature.

Low-Temperature Selective Catalytic Reduction of NOx with NH3 over Novel Mn−Zr Mixed Oxide Catalysts

Abstract: Novel Mn–Zr mixed oxide catalysts have been prepared by the citric acid method for the low-temperature selective catalytic reduction (SCR) of NOx with ammonia in the presence of excess oxygen. They have been characterized by a series of techniques, specifically N2 adsorption–desorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). It was found that an Mn(0.5)–ZrOx-450 (Mn/(Mn + Zr) mole ratio of 0.5) catalyst showed the highest activity, giving 100% NOx conversion at 100 °C with a space velocity of 30 000 h–1. XRD results suggested that an Mn–Zr solid solution was formed in the Mn(0.5)–ZrOx-450 catalyst, with highly dispersed MnOx. TPR data indicated a strong interaction between the zirconium oxide and manganese oxide, which improved the reduction ability of the MnOx. The TPD results indicated that an appropriate NH3 adsorption ability was beneficial for the low-temperature SCR. The catalyst showed a c...

Chemical deactivation of Cu-SSZ-13 ammonia selective catalytic reduction (NH3-SCR) systems

Abstract: The chemical deactivation of Cu-SSZ-13 Ammonia Selective Catalytic Reduction (NH3-SCR) catalysts by Pt, Zn, Ca and P has been systematically investigated using a range of analytical techniques in order to study the influence on both the zeolitic framework and the active Cu2+ ions. The results obtained demonstrate a crucial impact of P, completely suppressing the catalytic activity as a result of different deactivation mechanisms (i.e. site blocking, disruption of the zeolite framework, CuO formation and else reduction in the number of isolated Cu2+ ions). A less pronounced drop in activity is found with Ca and Zn introduction, without an appreciable adverse effect on N2 selectivity, since the catalytic deactivation is mainly brought about through a pore blocking/filling mechanism. Additionally, a drop in the amount of Cu2+ ions with the formation of CuO species also takes place, observed to be most important for the Zn-deactivated materials. Deactivation by Pt strongly affects N2 selectivity, but without a significant influence on the active sites or the zeolitic structure, basically due to the high oxidation activity of the Pt species, which highly promote N2O and NO2 formation.