SCR Of NO Research Articles

The influence of the preparation procedures on the catalytic activity of Fe-BEA zeolites in SCR of NO with ammonia and N2O decomposition

Three series of Fe-containing BEA zeolites are prepared by two-step postsynthesis (PS), ion exchange (IE) and conventional wet impregnation (Imp) procedures with various Fe content (1.0–4.0 Fe wt.%). In these series of zeolites iron is mainly present as pseudo-tetrahedral Fe(III) as evidenced by combined used of DR UV–vis, 57Fe Mössbauer and XPS investigations. Two kinds of pseudo-tetrahedral Fe(III) have been distinguished by 57Fe Mössbauer spectroscopy in all Fe-containing BEA zeolites. As evidenced by TPD of NH3, the (Imp)-FexHAlBEA and (IE)-FeHAlBEA have a significantly higher acidity than (PS)-FexSiBEA. This is related to the presence in the former both pseudo-tetrahedral Al(III)–O(H)–Si and Fe(III)–O(H)–Si framework sites and in the latter only pseudo-tetrahedral Fe(III)–O(H)–Si. (PS)-FexSiBEA, (Imp)-FexHAlBEA and (IE)-FeHAlBEA are found to be active and selective catalysts of N2O decomposition, with 100% conversion in the temperature range of 750–800K. Moreover, the samples are active in selective catalytic reduction of NO with ammonia, with selectivity toward N2 exceeding 90% for NO conversions of 80–93% in the temperature range of 550–800K. Isolated pseudo-tetrahedral Fe(III), present in three series of Fe-containing BEA zeolites, seems to be involved in both N2O decomposition and SCR of NO processes. The higher activity of (Imp)-FexHAlBEA and (IE)-FeHAlBEA than (PS)-FexSiBEA in the SCR of NO process suggests that the acidic Al(III)–O(H)–Si framework sites present in the former catalysts play also a significant role in this process.

The enhancement for SCR of NO by NH3 over the H2 or CO pretreated Ag/γ-Al2O3 catalyst

H2 or CO pretreatment had been processed on the Ag/γ-Al2O3 catalyst which significantly enhanced its NH3-SCR activity. The main purpose of this study was to prove that the impacts of pretreatment on silver species caused the enhancement. XRD, UV-vis, XPS, in situ FTIR and NO-TPD results showed the relationship between pretreatment, Ag species, NOX adsorption and NOX conversion. Extra nitrates were adsorbed on the Ag clusters which were produced by the pretreatment, thereby enhancing the activity. The reactivities between NO and NH3 had been studied. The difference between CO-pretreatment and H2-pretreatment had also been discussed. Furthermore, the durability and stability of the pretreated sample were tested. Therefore, a modified Ag2O/Al2O3 catalyst for NH3-SCR was researched.

Novel V2O5/NTiO2–Al2O3 nanostructured catalysts for enhanced catalytic activity in NO reduction by NH3

Nanostructured V2O5/NTiO2–Al2O3 catalysts were prepared by the sol–gel and hydrothermal methods and characterized by XRD, TEM, N2-BET and XPS. The role played by TiO2–Al2O3 as nanostructured support of V2O5 for NO–SCR–NH3 at high temperature was studied. The results show that the V2O5/NTiO2–Al2O3catalyst containing 5wt.% of Al2O3 and 5wt.% of V2O5 featured the highest activity in the 200–500°C temperature interval without NH3 oxidation to NO2.

Study on the Mechanism of SCR NO by Mn-Ce/CNTs Catalyst at Low-Temperature

The prepared Mn-Ce/CNTs catalyst was tested with Temperature-Programmed Desorption (TPD) in this experiment. The adsorption – desorption of NO, NH3, O2on the surface of catalyst were studied and the mechanism of SCR was analyzed. The conclusions were as follows: NH3was easily absorbed on the surface of Mn-Ce/CNTs catalyst for its significant competitive advantage; it can restrain the absorption of NO. The adsorption performance of NH3on catalyst surface was far greater than NO. When NO, O2adsorbed on the catalyst at the same time, the desorption amount of NO from catalyst significantly was less than the NO absorbed only. This shows that the O2can promote the adsorption of NO on the catalyst in SCR system.

The similarities and differences in structural characteristics and physico-chemical properties of AgAlBEA and AgSiBEA zeolites

AgAlBEA and AgSiBEA zeolites have been prepared by two preparation procedures. The conventional wet impregnation is used to obtain AgAlBEA with silver present mainly in extra-framework position. The two-step postsynthesis procedure which consists of first creating the vacant T-atom sites with associated silanol groups by treatment of TEABEA zeolite with nitric acid and then impregnating of resulting SiBEA zeolite with an aqueous solution of AgNO3 is used to obtain AgSiBEA zeolites with silver present mainly in framework position. The incorporation of Ag ions into the vacant T-atom sites of the framework of SiBEA zeolite as mononuclear Ag(I) has been evidenced by combined use of P-XRD, diffuse reflectance UV–vis, FTIR and XPS. The consumption of OH groups has been monitored by FTIR. The Brønsted and Lewis acidity of AlBEA, AgAlBEA, SiBEA and AgSiBEA has been identified by FTIR spectroscopy of adsorbed pyridine and CO as probe molecules. The catalytic activities of AgAlBEA and AgSiBEA in SCR of NO with ethanol have been investigated. These studies show that silver environment and acid–base properties play a significant role in catalytic activities of these Ag containing BEA zeolites.

Preparation and characterization of Ni-Ti-O mixed oxide for selective catalytic reduction of NO under lean-burn conditions

A novel Ni-Ti-O mixed-oxide catalyst was prepared by a homogeneous coprecipitation method and tested in the selective catalytic reduction of NO by propene (C 3 H 6 -SCR) in the presence of excess O 2 . Catalysts with different molar ratios of Ni-Ti were characterized using X-ray diffraction, N 2 adsorption-desorption, pyridine adsorption, temperature-programmed desorption, and in-situ Fourier-transform infrared spectroscopy. The Ni 1 Ti 1 catalyst showed good activity in C 3 H 6 -SCR at 430 °C and the NO x conversion achieved 68%. This catalyst displayed an anatase structure and had a high surface area (149 m 2 /g), which is helpful to enhance the catalyst activity. Lewis acid sites were beneficial for adsorbing nitrate, which was the main intermediate produced during the SCR of NO by C 3 H 6 . A novel Ni-Ti-O mixed-oxide catalyst was used in the selective catalytic reduction of NO by C 3 H 6 under lean-burn conditions; the catalyst demonstrated good activity at 430 °C.

Efficient One‐Pot Preparation of Cu‐SSZ‐13 Materials using Cooperative OSDAs for their Catalytic Application in the SCR of NOx

AbstractThe cooperative use of the Cu‐tetraethylenepentamine complex and N,N,N‐trimethyl‐1‐adamantammonium as organic structure‐directing agents (OSDAs) enabled the rationalized “one‐pot” preparation of Cu‐containing SSZ‐13 zeolites. A detailed study of different synthetic variables permitted the control of the Si/Al and Cu/(Si+Al) ratios in the final solids. Cu‐SSZ‐13 molecular sieves synthesized in alkaline media demonstrate excellent catalytic activities and good hydrothermal stabilities for the selective catalytic reduction of NOx. Finally, the effect of synthesis media on the catalytic active sites is also demonstrated and a remarkable activity loss for samples synthesized in fluoride media is observed.

Remarkable activity of Ag/Al2O3/cordierite catalysts in SCR of NO with ethanol and butanol

Structured silver–alumina catalysts were prepared by the one-step deposition of Al2O3 directly on the surface of cordierite block matrices with subsequent incipient wetness impregnation of Al2O3/cordierite with an AgNO3 aqueous solution. The catalysts were characterized by BET, XRD, XPS and FTIR spectroscopy with CO and pyridine as molecule probe, diffuse reflectance UV–vis, TEM and SEM. The Ag/Al2O3/cordierite catalysts are highly active in SCR of NO with ethanol and butanol and very selective toward N2. The conversion of NO over 0.6%Ag/45%Al2O3/cordierite catalyst reaches the high values of 95–99% already at 250°C and remains at this high level up to 430°C. The optimal silver loading in the silver–alumina catalysts is differing for C2 and C4 alcohols. It is shown that the role of silver in the Ag/Al2O3/cordierite catalyst consists in the modification of both redox and acid–base properties of the catalyst surface. Isolated cations (Ag+) and/or silver nanoclusters (Agnδ+) contain adsorbed oxygen in quantities sufficient only for the partial oxidation of alcohols toward oxygenated compounds, which then reduce NO.

Reactivity of Surface Nitrates in H2-Assisted SCR of NO x Over Ag/Al2O3 Catalyst

The role of nitrate ad-species in H2-assisted SCR over Ag/Al2O3 was compared in NH3-SCR and n-C6H14-SCR processes. It was found that nitrates could be reduced by NH3 or n-C6H14 at similar rates with H2 co-feeding which indicates a common rate-limiting step. However, contributions of surface nitrate reduction to the overall NH3-SCR or n-C6H14-SCR are different as revealed by comparing the rates of nitrate reduction with the rates of steady-state processes. The rate of the steady-state n-C6H14-SCR is virtually identical to the rate of surface nitrate reduction suggesting a significant contribution of the surface nitrates reduction to the overall n-C6H14-SCR process. On the other hand, the steady-state rate of NH3-SCR is by ~15 times higher, which indicates that the reduction of surface nitrates plays a marginal role in the overall NH3-SCR.

Selective catalytic reduction of NO with NH3 over Cr-ZSM-5 catalysts: General characterization and catalysts screening

Cr exchanged ZSM-5 catalysts (Cr/Al=1) prepared by solid-state ion exchange were tested in SCR of NO with ammonia. Since CrCl3 precursor sublimates during the solid-state reaction, chromate species were stabilized in the exchange sites of H+-ZSM-5 (Si/Al=15) and Cr2O3 formation is, therefore, limited. However, using Cr nitrate and NH4+-ZSM-5 (Si/Al=26) zeolite, massive particles of α-Cr2O3 occupied the catalyst surface. At the contrary, well-dispersed particles of Cr2O3 were detected with H+-ZSM-5 and Cr nitrate precursor. Starting from Cr acetate precursor, agglomerates of amorphous oxide were detected with H+-ZSM-5 like support. In the temperature range 50–300°C, Cr chloride and Cr nitrate precursors and H+-ZSM-5 led to highly active catalysts, while Cr nitrate and NH4+-ZSM-5 led to a poorly active catalyst. However, catalysts issued from Cr acetate are promising in SCR but inefficient agglomerates of oxide (amorphous or crystalline chromia) could be avoided with NH4+-ZSM-5 like support.

Microwave Plasma Treatment for Catalyst Preparation: Application to Alumina Supported Silver Catalysts for SCR NO<sub>x</sub> by Ethanol

Thermal treatment either in the presence of oxygen (calcination) or of a reducing agent (reduction) result is all the time a key issue within the preparation of a catalyst. In this work, a microwave plasma treatment was chosen as an alternative to typical calcinations, because it is a more energy efficient process. Thus, a Microwave Fluidized Bed Plasma reactor (MFBP) was employed in catalyst synthesis process under different gas compositions, such as argon and argon/oxygen mixtures over g-alumina supported silver catalysts, which are generally used for selective reduction of NOx by ethanol. After the first catalytic tests performed in the presence of plasma treated catalyst, it can be concluded that plasma treatment process represents an interesting alternative to conventional calcination during catalyst synthesis, resulting in a more sustainable process, moreover in view of its industrial application. In order to understand the particular effect of plasma treatment, the catalysts submitted to this treatment were carefully characterized by means of thermo gravimetric analysis (TGA), differential thermal analysis (DTA) and UV-VIS-NIR.

Effect of nitrogen doping on oxygen vacancies of titanium dioxide supported vanadium pentoxide for ammonia-SCR reaction at low temperature

A V2O5/N-doped TiO2 catalyst has been developed by partly substituting the lattice oxygen of TiO2 support with nitrogen, which showed a remarkable increase in activity for the reduction of NO with NH3 at low temperature. The catalyst was characterized by Brunauer–Emmett–Teller (BET), transmission electron microscope (TEM), photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The results demonstrated that N doping cannot noticeably change the microscopic features but dramatically enhanced the formation of surface oxygen vacancies, which can play a vital role in the formation of superoxide ions to improve the SCR activity. The catalyst with [N]/[Ti]=1.0×10−2 showed the highest NO removal efficiency in the SCR reaction at low temperature. Furthermore, the V1TiN1.0 catalyst showed better resistance to SO2 and H2O during the SCR of NO.

Regulation of the copper-oxide cluster structure and DeNOx activity of Cu-ZSM-5 catalysts by variation of OH/Cu2+

The present work studies RedOx properties and reactivity in N2O decomposition and selective catalytic reduction of NO (NO-SCR) by propane of Cu-modified ZSM-5 catalysts prepared by hydrolytic polycondensation (HPC). Their characteristics are compared with properties of Cu-ZSM-5 samples having the same copper content (1wt.%) and produced by ion exchange (IEX) with water–ammonia solutions of copper chloride at NH4OH/Cu2+ equal to 6–30.The HPC method consists in the treatment of the copper-impregnated zeolite by water–ammonia solution for polycondensation of hydrolyzed copper ions in the zeolite pores. It is shown that varying the NH4OH/Cu2+ ratio allows a regulation of the size and structure of copper active complexes. The copper-impregnated zeolite contains copper as CuO-like particles after calcination. At NH4OH/Cu2+ equal to 1–3, active sites in dried samples are disordered polynuclear copper-hydroxo complexes, which are characterized by symmetric ESR signal with g0=2.18. Increase of NH4OH/Cu2+ to 6–30 lead to the orbital ordering of Cu2+ ions in the copper–ammoniate complexes, observed as the rhombic ESR signals (gzex,1=2.18, gyex,1=2.08, gxex,1=2.03 and g∥ex,2=2.24, g⊥ex,2=2.03), and to dispersion of CuO-like particles during following thermal treatment at 500°C. The dried 1%Cu(30)ZSM-5-HPC sample prepared at NH4OH/Cu2+=30 has a higher amount of isolated tetraammine–copper complex and a lower number of weak associates of Cu2+ ions among samples.The addition of ammonia solution to the copper-impregnated zeolite for hydrolytic polycondensation has a favorable impact on the Cu-ZSM-5 activity in DeNOx processes. In N2O decomposition, the ion-exchanged CuZSM-5 catalysts were more reactive in the low-temperature region, while the ex-polycondensation catalysts provided a high N2O conversion at high temperatures. In NO-SCR by propane, the more reactive were the ion-exchanged catalysts, and NO reduction rate increased with NH4OH/Cu2+ grew for 10. It is suggested that the ordered associated Cu2+ ions of ex-polycondensation and ion-exchanged catalysts have higher reactivity and selectivity in both DeNOx processes as compared to the isolated copper ions.

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).

Further insights on the physico-chemical aspects of PdIn-Hmordenite catalysts for the NOx-SCR with CH4

The addition of Pd improves the catalytic performance of InH mordenite for the SCR of NO with methane, but this effect depends on the In/Al ratio. We studied two PdInMordenite samples, one with In/Al=1/3 (PdInHM(1/3)) and the other with In/Al=1/6 (PdInHM(1/6)). While in the former the presence of Pd in the InHM(1/3) catalyst increased the activity, in the sample with lower In content this effect was not observed. In order to explain these observations, the catalysts were characterized with several techniques. TPR results showed that the presence of palladium shifted the reduction peak of the solid PdInHM(1/3) towards higher temperatures, while on solid PdInHM(1/6), the shift was negligible. This effect could be ascribed to a higher Pd-In interaction in the PdInHM(1/3) catalyst. FTIR of CO adsorbed showed the presence of Pd2+, Pd+ and Pd0 adsorption sites in the calcined PdInHM(1/3). However, in the case of PdInHM(1/6), there was no evidence of Pd2+ species. The TEM images of used PdInHM(1/3) catalysts suggested the mobilization of indium to inner positions into the matrix, thus increasing the interactions with Pd. In the fresh PdInHM(1/6) the indium particles could not be detected but after reaction some agglomeration of particles could be observed, which is in agreement with CO-FTIR and XPS results. In brief, the results indicate that in the PdInHM(1/3) catalyst, Pd and In interact closely, giving place to a promotional effect of Pd, which prevents the agglomeration of In species.

Effect of Sn on MnO –CeO2 catalyst for SCR of NO by ammonia: Enhancement of activity and remarkable resistance to SO2

Abstract SnO 2 –MnO x –CeO 2 catalysts prepared by a co-precipitation method have been investigated for NH 3 -SCR reaction. The catalyst with a molar ratio of Sn / (Sn + Mn + Ce) = 0.1 showed complete conversion of NO in a temperature range of 80–230 °C. A remarkably high activity, N 2 selectivity and SO 2 resistance was obtained at 200–500 °C, attributed to the significantly enhanced Lewis acid sites that are created by surface sulfation during SO 2 -containing SCR reaction.

MnOx supported on carbon nanotubes by different methods for the SCR of NO with NH3

In order to modify the catalytic properties of MnOx via confinement within the channels of carbon nanotubes (CNTs), a series of MnOx catalysts supported by CNTs were prepared by different methods, in which MnOx was introduced on the outside surface only or on the inside and outside surface of CNTs. The catalysts showed different activity in SCR of NOx with NH3 in the temperature range of 80–300°C. The catalyst in which some MnOx was introduced into CNT channels exhibited higher NOx conversion than that in which all the MnOx was on the outside surface of CNTs. From the result of the activity test, it was indicated that the internal diffusion of molecules may not be the key influencing factor on the catalytic activity when the particle diameter was very smaller comparing with the tubes. In addition, the result of characterization showed that MnOx confined in the channels had better abilities of supplying oxygen and adsorbing NO which played an important role in the NH3-SCR, and it can partially be attributed to the electronic interaction between MnOx and the inner surface of nanotubes.

Investigation of the selective catalytic reduction of nitric oxide with ammonia over Mn/TiO2 catalysts through transient isotopic labeling and in situ FT-IR studies

The transient isotopic labeling studies were performed under steady state conditions by using 15N (15NO and 15NH3) and 18O (18O2) containing species to investigate the reaction mechanism of the low-temperature SCR of NO over Mn/TiO2. Our investigation has suggested that the nitric oxide forms neither nitrous oxide nor it is oxidized to nitrogen dioxide with the gas phase oxygen. The results acquired with the time resolution illustrated that the reaction of ammonia with lattice oxygen was practically instantaneous. The formation of labeled N218O, N18O, and H218O species is evident through the NH3 contact with catalyst surface lattice oxygen but not direct contact with the gas phase oxygen. This is consistent with the view that the lattice oxygen of Mn/TiO2 catalyst has direct effect on the reaction mechanism rather than gas phase oxygen. Our labeling experiments suggest that the SCR reaction rate is very small in the absence of gas phase oxygen and enhanced distinctly by the addition of excess oxygen. The cross-labeled 15N14N is the dominant form of nitrogen during the NH3 labeling studies. The increase in the SCR reaction temperature monotonically enhanced the ammonia oxidation. The evolution of 15N14N, 15N14NO, and 15NO species from the labeled ammonia (15NH3) and unlabeled nitric oxide (14NO) revealed the occurrence of ammonia oxidation. The results obtained in these experiments were combined with oxygen exchange experiments to arrive at conclusions regarding the plausible mechanism of the SCR reaction. The oxygen exchange between nitric oxide and the catalyst lattice oxygen established in the catalytic reduction of NO reaction. The effect of oxygen on activity and selectivity is noteworthy in both SCR and ammonia oxidation reactions over Mn/TiO2. The role of ammonia oxidation has been quantified for the overall SCR reaction network at low-temperatures. The role of ammonia oxidation and surface oxygen species has been addressed to substantiate the conclusions drawn.

Activity of yFe-10Cu/H-Sep and xCu/H-Sep for the Selective Catalytic Reduction of NO with Propylene

Cu supported on acid-treated sepiolite catalysts (xCu/H-Sep, x = 0  20.0 wt%) or Cu-Fe mixed supported on acid-treated sepiolite catalysts (yFe-10Cu/H-Sep, y = 0  20.0 wt%) were prepared by the incipient wetness impregnation method. The xCu/H-Sep and yFe-10Cu/H-Sep catalysts were characterized by means of XRD, BET, XRF, XPS, and H2-TPR techniques, and their catalytic activities were evaluated for the SCR of NO with propylene. XPS and XRD results indicate that there was the co-presence of Cu+-Cu2+ and Fe2+-Fe3+ over the surfaces of yFe-10Cu/H-Sep catalysts, and there was a strong interaction between Cu, Fe and sepiolite. High promotional effect of iron additive on the catalytic performance of Cu/H-Sep catalyst were found in C3H6-SCR of NO reaction. The highest activity of 65% NO conversion was obtained over 15Fe-10Cu/H-Sep catalyst at 280 oC under the condition of 1000 ppm NO, 1000 ppm C3H6, and 5% O2. The high catalytic activity of 15Fe-10Cu/H-Sep catalyst for NO reduction was due to its high reducibility to activate C3H6 to selectively reduce NO in the presence of excess O2. The high dispersion of copper oxides and strong metal-support interaction over 15Fe-10Cu/H-Sep catalyst also improve its catalytic performance.

Acid-activated vermiculites as catalysts of the DeNOx process

Vermiculite was treated with 0.8M solutions of hydrochloric and sulphuric acids for 2, 8, and 24h. The obtained materials were characterized with respect to their composition (XRF), structure (XRD, FTIR, UV–vis-DRS), texture (BET), surface acidity (NH3-TPD) and catalytic properties. Modification of vermiculite with acids significantly increased its surface area and pore volume and led to partial leaching of iron, aluminium and magnesium ions from its octahedral sheets. Efficiency of the leaching process depended on its duration and the nature of acid used. Acid treatment strongly modified the vermiculite structure leading to a distinct increase of its catalytic activity in the selective catalytic reduction of nitric oxide (SCR NO) process. In a series of the studied samples the best catalytic performance was found for vermiculite treated with sulphuric acid for 8h.