Low Temperature SCR Catalyst Research Articles

Reaction and Characterization of Co and Ce Doped Mn/TiO2 Catalysts for Low-Temperature SCR of NO with NH3

The catalysts of cobalt and cerium doped Mn/TiO2 were tested for low-temperature selective catalytic reduction of NO with NH3, and these samples were characterized by XRD, XPS, Raman, H2-TPR and NH3-TPD methods. The catalytic activity results showed that the NOx conversion was obviously improved by Co and Ce doping. Ternary metal oxide catalyst Mn–Co–Ce/TiO2 exhibited the highest catalytic activity of 99 % at 423 K. The XRD and Raman analysis indicated formation of MnO2 or CoMnO3 phases on Mn/TiO2 and Mn–Co/TiO2. The XPS results demonstrated that the metal cations existed mainly in the form of Mn4+, Co2+ and Ce4+, respectively. XPS and H2-TPR results supported the presence of Mn–Co mixed oxides. Doping of Ce could enhance dispersion of Mn–Co oxides on the surface. Addition of Co and Ce led to higher surface Mn4+/Mn3+ ratio, chemisorbed oxygen, acidity and dispersity, which enhanced NH3 adsorption and oxidation of NO to NO2, subsequently, the NOx reduction was accelerated through the Fast SCR reaction.

MnOx-CeO2 catalysts synthesized by solution combustion synthesis for the low-temperature NH3-SCR

MnOx-CeO2 catalysts with different compositions have been investigated as catalysts for low temperature SCR by preparing a series of samples by the solution combustion synthesis (SCS) method. Variable amounts of two different organic fuels (glycine and citric acid) with respect to the stoichiometry of synthesis were investigated. The samples were characterized by XRD, BET, H2-TPR, XPS, FESEM and their catalytic activity tested for NOx abatement in the range of temperature of interest (120–350°C). By varying the synthesis parameters it was possible to obtain catalysts different in terms of structure, morphology, specific surface area, Mn average oxidation state as well as superficial content of Mn, Ce and O atoms. These features were correlated with the resulting catalytic performances in the SCR reaction and compared to pure MnOx phases obtained through the same synthesis method. All the developed catalysts were considerably active in the temperature range investigated and could be considered suitable for the low-temperature SCR process. The sample with the higher content of manganese oxide obtained with glycine in below-stoichiometric amount showed the best performance in terms of NOx conversion and N2 yield, likely due to the high reducibility as well as the presence of the Mn3O4 phase.

A novel dual layer SCR catalyst with a broad temperature window for the control of NOx emission from diesel bus

In this work, a high temperature SCR catalyst (i.e., Fe–Ti spinel) and a low temperature SCR catalyst (i.e., Mn–Fe spinel) were combined to widen the operating temperature window of the SCR reaction. As the Fe–Ti spinel layer was placed upstream of the Mn–Fe spinel layer, both Fe–Ti spinel and Mn–Fe spinel displayed their strong points at their appropriate temperatures for the SCR reaction. Therefore, the dual layer catalyst showed excellent SCR activity and N2 selectivity at a broad temperature window even in the presence of H2O, which was much better than the performance of other combination modes.

Promoted performance of a MnOx/PG catalyst for low-temperature SCR against SO2poisoning by addition of cerium oxide

Loading of cerium oxide inhibits the formation of manganese sulfates at temperatures higher than 150 °C.

Nanostructured MnOx catalysts for low-temperature NOx SCR

Manganese oxides with different structures and morphologies have been investigated as catalysts for low temperature SCR by preparing a series of samples by both SCS (Solution Combustion Synthesis) and co-precipitation methods. The samples have been characterized by XRD, BET, H2-TPR, NH3-TPD, FESEM and their catalytic activity tested for NOx removal in the range of temperature of interest (120–350°C) both in the presence and in the absence of SO2, and after catalyst regeneration from sulphur deactivation. The different preparation procedures allowed to obtain MnOx systems with variable average oxidation state (measured through H2-TPR) that can be put in correlation with the porosity and the morphology measured by the other techniques, and the resulting catalytic performances in the SCR. The presence of Mn3O4 in the resulting material with low degree of crystallinity seemed to be the key factor to get the best catalyst among those prepared, being this phase not only active, but very selective towards the production of N2. Finally, the presence of a relatively high amount of SO2 among reactants (100ppm) drastically reduces the activity of all samples, but regeneration of catalyst for 2h at 400°C almost completely restores the catalytic performances.

Surface characterization studies on the interaction of V2O5–WO3/TiO2 catalyst for low temperature SCR of NO with NH3

This study aimed at elucidating the surface characterization of V2O5–WO3/TiO2 catalyst to investigate the interaction of V, W and Ti species for the improvement of the catalytic activity in the SCR reaction at low-temperature. Analysis by XRD, UV–vis, PL spectra and DFT theoretical calculations, XPS, EPR and in situ DRIFT showed that WO3 could interact with TiO2 to improve the electrons transfer, and the WO3 hybridization with V2O5 could also improve the reducibility and formation of reduced V2O5 species for the V2O5–WO3/TiO2 catalyst. These aspects resulted in the NO oxidation and NO3− decomposition that were responsible for the high catalytic activity of V2O5–WO3/TiO2 catalyst.

The Preparation and Current Situation of Ce and Mn Catalyst

NOx is the main air pollutant of coal-fired power plants, which is one of the important reasons to cause pollution such as acid rain, photochemical smog and so on. Selective catalytic reduction process is the major technology for reducing NOx emissions from coal-fired power plants. However, the commercial vanaidia-based catalyst is active within a narrow temperature window of 300-400°C, easily to be deacticed by SO2 in the flue gas. And the formation of N2O and toxicity of vanaidia cause secondary pollution. Therefore, it is of more importance to develop a new environmental-friendly catalyst for low temperature SCR with high activity.

Mechanism study of the promotional effect of O2 on low-temperature SCR reaction on Fe–Mn/TiO2 by DRIFT

In this manuscript, the low-temperature SCR catalyst Fe–Mn/TiO2 was prepared by sol–gel method, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) was used for revealing the mechanism of the promotional effect of O2 on low-temperature SCR reaction on Fe–Mn/TiO2. The experiments showed that surface OH species were consumed during NO adsorption, indicating that O2 could promote the dehydration reaction of the manganese oxides to produce active oxygen, and greatly enhance the amount of NO complexes on the catalyst. NO removal was influenced by O2 through two reaction ways. In the first reaction way, with the active oxygen obtained, coordinated NH3 was easier to be activated. Active oxygen could abstract H from coordinated NH3, giving amide species to react with NO. In the second reaction way, with the active oxygen, much more bidentate nitrate could be formed from nitrosyl, and transformed to monodentate nitrate, producing new Brønsted acid sites to form NH4+. With more NO2 obtained from the decomposition of monodentate nitrate in the presence of O2, NO could be removed effectively by the reaction between NH4+ and NO2.

High-surface-area zinc aluminate supported silver catalysts for low-temperature SCR of NO with ethanol

The NOx selective catalytic reduction of ethanol (EtOH-SCR) was studied using a complex gas mixture representative of a diesel exhaust, over zinc alumina mixed oxide supported silver catalysts (2wt.% Ag/Znx-Al2O3, with x=10–20–33at.%). The supports were obtained using a template assisted sol–gel route in order to achieve high surface areas. For the higher Zn loading (33%), the calcination temperature has been raised from 600°C to 800°C then 1000°C in order to evaluate thermal stability of these materials. Addition of zinc in alumina network leads to the formation of the spinel-type zinc aluminate structure. Chemical and physical characterizations of the catalysts have been confronted with the EtOH-SCR results, in order to understand the respective influence of the metal and support in nitrogen formation. This study shows that addition of zinc and modification of the support calcination temperature both play upon the Lewis acidic sites (LAS) concentration and density, determined by pyridine adsorption monitored by FTIR spectroscopy. This parameter is shown to be related with ammonia emission at T≥350°C. Besides, formation of nitrogen at T≤350°C is shown to be dependent on (i) the rate of acetaldehyde formation and (ii) the reactivity of acetaldehyde in SCR of NO reaction. Modification of the alumina support directly impacts these parameters. Finally, it is demonstrated that Zn is a hopeful candidate to increase the EtOH-SCR activity at low temperature (T≤300°C).

Mn–Fe/ZSM5 as a low-temperature SCR catalyst to remove NOx from diesel engine exhaust

A Mn–Fe/ZSM5 catalyst has been developed for removing NOx from diesel engine exhausts and its excellent low-temperature SCR activity and N2 selectivity demonstrated in comparison with other representative SCR catalysts including CuZSM5 and a Cu-based commercial catalyst (COM). The well-dispersed MnO2 and the high NH3 adsorption capacity of the Mn–Fe/ZSM5 catalyst have been identified as the primary sources for its high deNOx activity for NH3/SCR. Hydrothermal stability and durability of the Mn–Fe/ZSM5 catalyst have been examined and compared to those of the CuZSM5 and COM catalysts. The hydrothermal stability of the catalyst improved upon the increase of Mn content and/or the addition of Er, the latter of which helps to stabilize the dispersion of MnOx on the catalyst surface during hydrothermal aging. The deNOx activity of the Mn–Fe/ZSM5 and its Er-promoted counterpart was less affected by HC poisoning, C3H6 poisoning in particular, compared to the CuZSM5 and COM catalysts, mainly due to the excellent C3H6 oxidation activity of MnO2. No poisoning of the Mn-based ZSM5 and CuZSM5 catalysts has been observed upon the addition of 2wt.% of K+ and Ca2+ to their surface, primarily due to the high NH3 adsorption capacity of the ZSM5 support, whereas the COM catalyst has been severely deactivated by the deposition of K+ and Ca2+. The deNOx activity of the Mn-based ZSM5 catalyst, particularly the Er-promoted one, was less affected by SO2 compared to the CuZSM5 and COM catalysts, although it was hardly regenerated at 500°C. Formation of MnSO4 on the catalytic surface appears to be the primary cause for the deactivation of the Mn-based ZSM5 catalysts in the presence of SO2 in the feed gas stream.

Effect of Y doping on oxygen vacancies of TiO2 supported MnOX for selective catalytic reduction of NO with NH3 at low temperature

A Y-doped TiO 2 -supported MnO X has been developed by partly substituting the Ti 4+ of the catalyst with Y 3+ to promote oxygen vacancies for charge compensation. The aim of this study was to improve the activity of low-temperature SCR of NO with NH 3 in the presence of excess oxygen by means of increasing the amount of oxygen vacancies. Analysis by PL spectra, XPS and EPR showed that Y doping increased the amount of oxygen vacancies and superoxide ions. The catalytic activity of NO removal was promoted by Y doping. ► NO removal is enhanced on the Y-doped MnO X /TiO 2 catalysts for low-temperature SCR. ► Y doping can increase oxygen vacancies for charge compensation on the catalysts. ► Oxygen vacancies by Y doping are responsible for the high catalytic activity.

Original carbon-based honeycomb monoliths as support of Cu or Mn catalysts for low-temperature SCR of NO: Effects of preparation variables

Abstract A series of catalysts consisting in Cu or Mn supported on lab-scale carbon-based honeycomb monoliths, which have been previously prepared following an original methodology, have been investigated in the low-temperature selective catalytic reduction of NO with NH 3 . Special attention has been paid to the effect of changing different preparative variables for the incorporation of the active phase: way of introducing the metal, concentration of the precursor solution and time of contact with the monoliths in the case of impregnation, use or not of a chemical pre-treatment of the support, and the final drying procedure. Complementary techniques employed for the chemical, textural and structural characterisation have revealed significant differences between the catalysts depending on their preparative procedure.

Effect of transition metals addition on the catalyst of manganese/titania for low-temperature selective catalytic reduction of nitric oxide with ammonia

To retard the sintering, a series of transition metals were added to the low-temperature SCR catalysts based on Mn/TiO2, and activity of these catalysts was investigated. It was found that the transition metal had significant effects on the catalytic activity. With the addition of transition metals, more NO could be removed at lower temperature. The temperature of 90% NO conversion could decrease to 361K by using Fe(0.1)–Mn(0.4)/TiO2. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction spectra (EDS) indicated that manganese oxides and titania could be better dispersed in the catalyst, and higher catalytic activity was obtained. From X-ray photoelectron spectrum (XPS) it could be known that solid solution was formed among the transition metal, manganese oxides and titania. With the formation of this solid solution, the Brunauer–Emmett–Teller (BET) area and pore volume increased. Furthermore, the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) results showed that by using these catalysts, more NO could be oxidized to NO2 and nitrate, and then reacted with NH3. Therefore, the catalytic activity was greatly improved by the addition of transition metals.

Identification of Surface Species on Titania-Supported Manganese, Chromium, and Copper Oxide Low-Temperature SCR Catalysts

TiO2-supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH3 have been synthesized by wet impregnation. The adsorption and coadsorption of NH3, NO, and O2, in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K. While Cr was the only transition metal that generated significant amounts of Bronsted acidity, strong Lewis acid sites were present over all of the materials. The peak strength corresponding to the δs(NH3) coordinated to Lewis acid sites decreased in the following order: Ti > Mn > Cr ∼ Cu. Similarly, the peak strength corresponding to the δas(NH3) coordinated to Lewis acid sites decreased as follows: Mn > Cr ∼ Cu. Exposing the catalysts to oxygen before the introduction of NO did not impact the adsorption of NO as nitrates on the catalysts, suggesting that labile lattice oxygen plays an important role in the formation of nitrates. Three types of nitrates were observed after the adsorption of ...

Kinetics of the Low-Temperature Selective Catalytic Reduction of NO with NH3 Over Activated Carbon Fiber Composite-Supported Iron Oxides

A kinetic analysis in a variety of conditions (gas composition and temperature) has been conducted on catalysts of iron oxides supported on activated carbon fiber composites (ACFC). Additionally, experiments of temperature-programmed desorption (TPD) of NO were conducted on the catalysts in order to reveal mechanistic features of the low-temperature SCR reaction. In the light of current SCR literature and previous work, a qualitative picture of the catalytic behavior of low-temperature SCR catalysts is offered. Apparently, the strength of adsorption of NO during the low-temperature SCR reaction is responsible for the governing reaction mechanism. Thus, highly stable nitrates formed on the surface provoke catalyst deactivation and reaction through an ER mechanism, with NO reacting from the gas phase, whereas the absence of these nitrates permits reaction of less stable nitrites from the catalyst surface, following an LH-type mechanism. This is the case for the ACFC-supported iron oxide catalyst analyzed in this work.