Selective Reduction Of Nitric Oxide Research Articles

Quantitative evaluation of NO formation and destruction routes during methane MILD combustion using an improved calculation method

Moderate or intense low-oxygen dilution (MILD) combustion has become increasingly attractive because of its ultra-low nitric oxide (NO) emission. Although many efforts have been made to investigate the NO formation and destruction pathways of MILD combustion, their relative contribution still fails to reach an agreement when using previously-developed NO calculation methods. For this reason, these NO calculation methods are first evaluated for methane MILD combustion by the kinetic modeling of a well-stirred reactor (WSR). Then, an improved calculation method for quantifying the contribution of NO sub-routes is proposed, which involves thermal, prompt, N2O-intermediate, NNH, selective non-catalytic reduction of NO, and NO-reburning routes. Also, this improved method allows the application of a more comprehensive mechanism (Progress in Energy and Combustion Science, 2018, 67: 31–68) other than GRI-Mech 2.11. Using the improved method with the more comprehensive mechanism, the NO formation and destruction routes during methane MILD combustion are quantitatively investigated. The results show that in the WSR at 1300 K with 5% O2, the contribution of the N2O-intermediate route accounts for about 80% at an equivalent ratio (Φ) of 0.8, and it gradually decreases as Φ increases. Once Φ is >1.0, the prompt route surpasses the N2O-intermediate route to dominate the NO generation entirely. The NNH mechanism is found to be of little importance at Φ ranging from 0.5 to 1.5. Additionally, the NO-reburning reaction reduces <10% of the total NO production when Φ < 1.0, and its contribution increases abruptly at 1.0 < Φ < 1.1.

A New Robust Ce-Ga/H-Zsm-5 Catalyst for Enhanced Selective Reduction of Nitric Oxide by Methane

A New Robust Ce-Ga/H-Zsm-5 Catalyst for Enhanced Selective Reduction of Nitric Oxide by Methane

Coupling CO2 utilization and NO reduction in chemical looping manner by surface carbon

Carbon deposits typically enforce shutdowns of chemical reactors to periodically regenerate their active materials, a continuous challenge for industry and scientists alike. This downside can however be turned to benefit by utilizing carbon’s reductive power. Here, we integrate dry reforming of methane (DRM) and selective reduction of nitric oxide (SRN) in a novel chemical looping process, coupled by the periodic deposition and removal of surface carbon, which participates in both reactions. Carbon formed on the catalyst during dry reforming is subsequently used as reductant for nitric oxide (NO) conversion into N2, hence not only achieves stable CO2 utilization and NO reduction with cyclic catalyst regeneration, but also reduces the consumption of valuable energy resources demanded by NO removal. In contrast to co-feeding all reactants in a single step, the inherent temporal-spatial separation of reactions in chemical looping allows for complete conversion of carbon and NO, ensuring a higher exergetic efficiency (70 % more efficient). Also, adaptation of the relative duration of the DRM and SRN steps to the conditions of the CO2 and NO industrial point sources allows to account for the differences in supply of carbon and NO, offering an attractive strategy for selective catalytic reduction of NO with greenhouse gases rather than NH3.

Selective Catalytic Reduction of NO by NH3 Using a Combination of Non-Thermal Plasma and Mn-Cu/ZSM5 Catalyst

Dielectric barrier discharge (DBD) could generate non-thermal plasma (NTP) with the advantage of fast reactivity and high energy under atmosphere pressure and low-temperature. The presented work investigated the selective catalytic reduction (SCR) of nitric oxide (NO) using a combination of NTP and an Mn-Cu/ZSM5 catalyst with ammonia (NH3) as a reductant. The experimental results illustrate that the plasma-assisted SCR process enhances the low-temperature catalytic performance of the Mn-Cu/ZSM5 catalyst significantly, and it exhibits an obvious improvement in the NO removal efficiency. The reaction temperature is maintained at 200 °C in order to simulate the exhaust temperature of diesel engine, and the 10% Mn-8% Cu/ZSM5 catalyst shows the highest NO removal performance with about 93.89% at an energy density of 500 J L−1 and the selectivity to N2 is almost 99%. The voltage, frequency and energy density have a positive correlation to NO removal efficiency, which is positively correlated with the power of NTP system. In contrast, the O2 concentration has a negative correlation to the NO removal, and the NO removal efficiency cannot be improved when the NO removal process reaches reaction equilibrium in the NTP system.

Understanding the role of Ru dopant on selective catalytic reduction of NO with NH3 over Ru-doped CeO2 catalyst

Reaction mechanism of the selective catalytic reduction of nitric oxide (NO) by ammonia (NH3-SCR of NO) on the Ru-doped CeO2(111) surface was investigated using density functional theory calculation corrected by on-site Coulomb interactions (DFT + U) to understand the role of Ru dopant toward the catalytic performance of CeO2 based catalysts. The NH3-SCR of NO mechanisms on Ru-CeO2, which consisted of two consecutive NO reduction pathways, were systematically examined. Each NO reduction consists of important elementary steps such as NH3 adsorption/dissociation and water formation/desorption. The calculated results reveal that the Ru dopant substantially affects on the electronic charge property and enhances the Lewis acidity of the CeO2 surface. The NH3 adsorption and dissociation take place at the Lewis acid site of the catalyst. The first NO reduction via the NHNO intermediate is facile when the Ru dopant presents on the catalyst surface. The presence of Brønsted acid on surface catalyst suppresses the NH3 adsorption and dissociation but helps in promoting the water formation, which is the rate-determining step of overall reaction. Thus, the performance of this catalyst can be further enhanced by improving the water formation aspect. The obtained results deepen the fundamental understanding of the role of the different active sites on the crucial steps during the reaction and are useful for guiding the way to develop catalysts used in this application.

Directly catalytic reduction of NO without NH3 by single atom iron catalyst: A DFT calculation

Nitric oxide (NO) has been recognized as a major air pollutant, and the emission of NO has been strictly regulated. The technology of selective catalytic reduction of NO with NH3 injection is mature and efficient, but it still has some obvious drawbacks such as ammonia slipping, secondary fine particulates formation, and equipment corrosion. Therefore, a directly catalytic reduction of NO without ammonia injection by monovacancy graphene-based single atom iron catalyst (Fe/MG) was proposed. The detailed reaction mechanism was investigated through density functional theory calculation. Based on thermodynamic and kinetic analysis, we concluded that Langmuir-Hinshelwood is the dominant reaction mechanism for NO reduction, and the activation energy is 0.81 eV which is lower than char edges. The catalytic reduction reaction of NO is exothermic and thermodynamically favorable. The temperature can accelerate the catalytic reduction of NO. Based on the thermodynamic and kinetic performances of Fe/MG in NO reduction, Fe/MG is suggested to be a novel catalyst for NO reduction without NH3. This theoretical research results can provide a new insight for NO removal and lay some foundations for subsequent experimental research.

Promotional Effect of Cerium and/or Zirconium Doping on Cu/ZSM-5 Catalysts for Selective Catalytic Reduction of NO by NH3

The cerium and/or zirconium-doped Cu/ZSM-5 catalysts (CuCexZr1−xOy/ZSM-5) were prepared by ion exchange and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H2-TPR). Activities of the catalysts obtained on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia were measured using temperature programmed reactions. Among all the catalysts tested, the CuCe0.75Zr0.25Oy/ZSM-5 catalyst presented the highest catalytic activity for the removal of NO, corresponding to the broadest active window of 175–468 °C. The cerium and zirconium addition enhanced the activity of catalysts, and the cerium-rich catalysts exhibited more excellent SCR activities as compared to the zirconium-rich catalysts. XRD and TEM results indicated that zirconium additions improved the copper dispersion and prevented copper crystallization. According to XPS and H2-TPR analysis, copper species were enriched on the ZSM-5 grain surfaces, and part of the copper ions were incorporated into the zirconium and/or cerium lattice. The strong interaction between copper species and cerium/zirconium improved the redox abilities of catalysts. Furthermore, the introduction of zirconium abates N2O formation in the tested temperature range.

Ru-In/H-SSZ-13 for the selective reduction of nitric oxide by methane: Insights from temperature-programmed desorption studies

The selective catalytic reduction of nitric oxide by methane (CH4-SCR) represents the most desirable technique for the post-treatment of nitrogen oxide emissions from gas-fired power plants and the efficient CH4-SCR catalysts are being explored. We herein report the construction of bimetallic Ru-In/H-SSZ-13 catalyst, which exhibited remarkable performance in CH4-SCR under the reaction conditions of a high gas hourly space velocity (GHSV) of 75,000 h−1 and in the presence of 6% H2O. In Ru-In/H-SSZ-13, the close contact between Ru and In species was confirmed by transmission electron microscopy (TEM) analysis, and their electronic interaction was verified by means of X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by hydrogen (H2-TPR). All these features made Ru-In/H-SSZ-13 an elegant example of zeolite-based cooperative catalytic system for CH4-SCR. The surface species formed and their stability on Ru/H-SSZ-13, In/H-SSZ-13 and Ru-In/H-SSZ-13 were investigated by temperature-programmed desorption (TPD) experiments, from which the individual role of H-SSZ-13, Ru and In sites and their cooperation in CH4-SCR were discussed in detail.

Simultaneous removal of NO and Hg0 using Fe and Co co-doped Mn-Ce/TiO2 catalysts

Fe and Co co-doped Mn-Ce/TiO2 (MCT) catalysts were investigated for the simultaneous removal of nitric oxide (NO) and elemental mercury (Hg0) at reaction temperature lower than 200 °C. The catalysts were characterized by Brunauer–Emmett–Teller (BET), temperature program reduction (TPR), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The experimental results showed that the co-doped 2Fe4Co-MCT catalyst exhibited better performance for the simultaneous removal of NO and Hg0 compared to Fe or Co doped catalysts. This could be due to higher BET surface area and better redox property of 2Fe4Co-MCT catalyst. In addition, we propose that chemisorbed O2 played a dominant role in selective catalytic reduction (SCR) of NO while lattice O2 played a key role in Hg0 oxidation. The results also indicate that the introduction of Fe species enhanced the activity of SCR, whereas the introduction of Co species enhanced the oxidation of Hg0. The synergistic effect of Fe and Co species in the 2Fe4Co-MCT catalyst are also suggested to be an important mechanism for simultaneously removing NO and Hg0.

Highly active copper-based Ce@TiO2 core-shell catalysts for the selective reduction of nitric oxide with carbon monoxide in the presence of oxygen

A novel core-shell K/Cu/SmCe@TiO2 catalyst is here reported being highly active on the selective reduction of nitric oxide with carbon monoxide under oxidizing conditions. It was found that the reaction proceeds with the generation of nitrates and nitrites adsorbed on the support and ionic nitrates adsorbed on alkaline sites. Full conversion of CO was achieved from 255°C and 97% NO conversion was reached at 330°C.

Catalytic performance of highly dispersed WO3 loaded on CeO2 in the selective catalytic reduction of NO by NH3

AbstractThe influence of tungsten trioxide (WO3) loading on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia (NH3) over WO3/cerium dioxide (CeO2) was investigated. The NO conversion first rose and then declined with increasing WO3 loading. It was found that the crystalline WO3 in the 1.6WO3/CeO2 sample could be removed in 25 wt% ammonium hydroxide at 70 °C, which improved the catalytic activity of the sample. The obtained samples were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, hydrogen (H2) temperature programmed reduction, NH3 temperature programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The results revealed that the dispersed WO3 promoted the catalytic activity of WO3/CeO2 while the crystalline WO3 inhibited catalytic activity. The oxygen activation of CeO2 was inhibited by the coverage of WO3, which weakened NO oxidation and adsorption of nitrate species over WO3/CeO2. In addition, the NH3 adsorption performance on CeO2 was improved by modification with WO3. NH3 was the most stable adsorbed species under NH3 SCR reaction conditions. In situ DRIFT spectra suggested that the NH3 SCR reaction proceeded via the Eley-Rideal mechanism over WO3/CeO2. Thus, when the loading of WO3 was close to the dispersion capacity, the effects of NH3 adsorption and activation were maximized to promote the reaction via the Eley-Rideal route.

Octahedral Ni-nanocluster (Ni85) for Efficient and Selective Reduction of Nitric Oxide (NO) to Nitrogen (N2)

Nitric oxide (NO) reduction pathways are systematically studied on a (111) facet of the octahedral nickel (Ni85) nanocluster in the presence/absence of hydrogen. Thermodynamic (reaction free energies) and kinetic (free energy barriers, and temperature dependent reaction rates) parameters are investigated to find out the most favoured reduction pathway for NO reduction. The catalytic activity of the Ni-nanocluster is investigated in greater detail toward the product selectivity (N2 vs. N2O vs. NH3). The previous theoretical (catalyzed by Pt, Pd, Rh and Ir) and experimental reports (catalyzed by Pt, Ag, Pd) show that direct N-O bond dissociation is very much unlikely due to the high-energy barrier but our study shows that the reaction is thermodynamically and kinetically favourable when catalysed by the octahedral Ni-nanocluster. The catalytic activity of the Ni-nanocluster toward NO reduction reaction is very much efficient and selective toward N2 formation even in the presence of hydrogen. However, N2O (one of the major by-products) formation is very much unlikely due to the high activation barrier. Our microkinetic analysis shows that even at high hydrogen partial pressures, the catalyst is very much selective toward N2 formation over NH3.

Al-free Fe-beta as a robust catalyst for selective reduction of nitric oxide by ammonia

Al-free Fe-beta prepared via a post-synthesis solid-state metallation route is established as an active and durable catalyst for NH3-SCR.

MnO2catalysts uniformly decorated on polyphenylene sulfide filter felt by a polypyrrole-assisted method for use in the selective catalytic reduction of NO with NH3

A manganese dioxide (MnO2)/polypyrrole (PPy) nanocoating was uniformly decorated on the surface of polyphenylene sulfide (PPS) filter felt via an in situ synthesis method to fabricate a catalytic filter material. The pyrrole functioned as a dispersant for the MnO2 catalysts and the PPy generated acted as a binder to adhere the MnO2 catalysts and filter felt together. The catalytic filter material obtained, had a high adhesive strength between that of the MnO2/PPy nanocoating and the PPS filter felt, and was used for the selective catalytic reduction of nitric oxide (NO) with ammonia under model conditions without any sulfur dioxide or water vapor in the gas. More than 70% conversion of NO was achieved at 160–180 °C at a high space velocity of 38 000 h−1.

Structure–Activity Relationships of NiO on CeO2 Nanorods for the Selective Catalytic Reduction of NO with NH3: Experimental and DFT Studies

CeO2 nanorods impregnated with 2.5 atom % of NiO (NiO/CeO2 nanorods) were successfully synthesized and examined as catalysts for the NH3-selective catalytic reduction (NH3-SCR) of nitric oxide (NO). The catalytic activity of NiO/CeO2 nanorods resulted in up to ∼90% NO conversion at 250 °C, which is superior to that of pure CeO2 nanorods or NiO nanoparticles. Subsequently, extensive studies of the NiO/CeO2-catalyzed reduction of NO were conducted using X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed desorption, and density functional theory periodic calculations. Compared to that of the pure CeO2 nanorods, the results demonstrated that the NiO/CeO2 nanorods resulted in (i) a higher concentration of Ce3+ chemical species, (ii) a larger amount of active Oα, (iii) lower temperature reducibility, (iv) a lower amount of energy required for oxygen vacancy distortion, and (v) a significant adsorption of and strong interaction between NO and NH3 molecules. Our findings therefore elucidated considerable details of the structural properties of the NiO/CeO2 nanorods that were decisive for achieving a highly efficient conversion of NO by the NH3-SCR process at low temperatures.

A Novel Catalyst Ag/MgO-CeO2-Al2O3 for the Low-temperature Ethanol- SCR of NO under lean de-NOx Conditions

The present work reports data on a novel catalyst having excellent activity, selectivity and stability for the selective reduction of nitric oxide to nitrogen in the presence of ethanol or ethanol/hydrogen mixture as reducing agent, in the low temperature range of 150-300°C and in the presence of excess oxygen, H2O and SO2 in the feed. The novelty of the present catalyst compared to other patented ones, for the reaction at hand, lies upon the simplicity and the remarkably low Ag loading (wt&percnt;) used, characteristics that are required for a practical application. In addition, the latter catalyst shows significant activity (rate of NO reduction) at much lower temperatures (below 300°C) compared to other already patented catalysts. The present inventive catalyst consists of silver crystals that are in contact with a mixed oxide support comprised of MgO, CeO2 and Al2O3 in 1:1:2 wt&percnt; ratio. This novel catalyst presents high activity in terms of NO conversion (XNO = 60-90&percnt;) and high selectivities towards N2 (SN2 = 92-95&percnt;) and CO2 (SCO2 > 97&percnt;) in the range of 150-400°C, at a GHSV of 40,000 h-1 and using a feed stream of 0.05vol&percnt; NO, 0.1vol&percnt; EtOH, 5vol&percnt; O2 and 5vol&percnt; H2O. To our knowledge, this is the highest selectivity towards N2 and CO2 ever reported. In addition, the current catalyst shows remarkable stability with time on stream and in the presence of 5 vol&percnt; H2O and 50 ppm SO2 in the feed stream. After 48 h on stream the patented catalyst retains its stability expressed in high activity (XNO > 80&percnt;) and selectivities to N2 (SN2 > 95&percnt;) and CO2 (SCO2 > 97&percnt;). Keywords: Ethanol-SCR, HC-SCR, Lean de-NOx, NO reduction, supported-Ag.

Experimental and Kinetic Study of Low Temperature Selective Catalytic Reduction of NO with NH3 over the V2O5/AC Catalyst

Selective catalytic reduction (SCR) of NO (nitric oxide) by NH3 (ammonia) at temperatures of 393−523 K over AC (activated carbon) supported V2O5 (vanadium pentoxide) was investigated in this work. The V2O5/AC catalyst was prepared by the pore volume impregnation method. The intrinsic kinetics for this catalyst was first measured in the absence of internal and external diffusions in a fixed-bed microreactor. Then, five intrinsic kinetic models, i.e. the Eley−Rideal model, the Langmuir−Hinshelwood model, the Mars-van Krevelen model, the first-order model, and the power-rate law model, were applied to correlate the experimental data. Among them, the Eley−Rideal model is the most accurate, and the Langmuir−Hinshelwood model is unfeasible for describing SCR of NO by NH3 over the V2O5/AC catalyst. Therefore, the SCR of NO with NH3 over V2O5/AC is likely to follow the Eley−Rideal mechanism in light of intrinsic kinetic measurements. Finally, the kinetic equations were incorporated into a 3D mathematical model fo...

ChemInform Abstract: Selective Reduction of Nitric Oxide over Cu-ZSM-5 Zeolite by Water- Soluble Oxygen-Containing Organic Compounds.

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ChemInform Abstract: Vanadium Oxide Catalysts Supported on Laser-Synthesized Titania Powders: Characterization and Catalytic Activity in the Selective Reduction of Nitric Oxide.

Abstract Laser-activated pyrolysis was applied to the synthesis of ultrafine TiO2, producing a non porous monocrystalline material in anatase phase with high specific surface area and uniform particle size. This powder was used as support for the preparation of vanadia catalysts with different compositions by wet impregnation. The pure TiO2 and the vanadia catalysts were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform IR, X-ray photoelectron spectroscopy, ammonia temperature-programmed desorption and were tested in the reaction of nitric oxide reduction by ammonia. It has been proposed that two different VOx species formed in the submonolayer region: a VIV containing species which prevails up to 6 wt.-% V2O5 and a VV containing species which develops from 6 wt.-% V2O5 up to monolayer completion. The structure of these species has been hypothesized. A reaction scheme has been proposed to interpret the catalytic activity for the selective catalytic reduction (SCR) of NOx. The selectivity of catalysts for nitrogen is related to the prevalence of the VIV containing species.

ChemInform Abstract: Selective Catalytic Reduction of Nitric Oxide with Ethane and Methane on Some Metal Exchanged ZSM-5 Zeolites.

Abstract The selective reduction of nitric oxide by methane or ethane, in the presence and in the absence of a large excess of oxygen, has been investigated on Cu/ZSM-5, Co/ZSM-5, Rh/ZSM-5 and Pt/ZSM-5 catalysts over a wide range of temperatures. It has been found that the maximum nitric oxide conversion is higher with ethane than with methane and the temperature of this maximum is lower with ethane. In the absence of oxygen the order of activity is Rh/ZSM-5>Pt/ZSM-5>Co/ZSM-5 > Cu/ZSM-5 with the Cu/ZSM-5 being essentially inactive, while in the presence of oxygen the order is: Rh/ZSM-5>Co/ZSM-5>Cu/ZSM-5 > Pt/ZSM-5 when ethane is used as reductant and: Rh/ZSM-5>Co/ZSM-5 > Cu/ZSM-5>Pt/ZSM-5 when methane is used. The effect of the oxygen content has been investigated for the Co/ZSM-5 catalyst. It has been found that with a small quantity of oxygen the catalytic activity decreases markedly; with higher oxygen content the activity of the catalyst rises again. It appears that two different reaction schemes may be operative, one in the absence of oxygen the other in the presence of oxygen. It is concluded that neither carbonaceous deposits, nor nitrogen dioxide formation in the gas phase are important in the reaction mechanism on metal-containing zeolites. It is proposed that the reaction is essentially a redox process in which decomposition of nitric oxide occurs on reduced metallic or metal ion sites (the relative activity of each of these depending on the choice of metal), leading to the formation of gaseous nitrogen and adsorbed oxygen, followed by the removal of the adsorbed oxygen by the hydrocarbon, thus recreating the active centres.