Catalytic Reduction Of Nitric Oxide Research Articles

MnOx-CeOx Nanoparticles Supported on Graphene Aerogel for Selective Catalytic Reduction of Nitric Oxides

Removal of nitric oxides (NOx) from stationary and transportation sources has been desired for environmental benefits. Selective catalytic reduction (SCR) of NOx by NH3 is attractive for its cost effectiveness and high efficiency but still technically challenging in consideration of operable temperatures. In this research, MnOx-CeOx hybrid nanoparticles supported on graphene aerogel (MnOx-CeOx/GA) are fabricated as the monolithic catalysts for potential applications to low-temperature SCR. The impacts of the particle size along with the amount and valency of catalytic elements in the nanocomposite on the catalytic activities are studied with the help of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalyst crystallites are a few tens of nanometers and uniformly disperse on the surface of three-dimensional (3D) directionally aligned hierarchical porous graphene aerogel (GA) networks. The novel nanocomposite catalysts exhibit over 90% NOx conversion rate in a broad temperature range (200–300°C). Addition of CeOx into the MnOx-GA catalysts significantly reduces the operational temperature at the same conversion rate. In addition to Mn4+ ions in the catalysts, the adsorbed oxygen species which can be increased by the presence of low-valence cerium contribute to high catalytic activities in the MnOx-CeOx/GA catalysts.

Sulfate promotion of selective catalytic reduction of nitric oxide by ammonia on ceria

Selective catalytic reduction of nitric oxide by ammonia (NH3-SCR) is a promising technology for NOx emission control.

Co-treatment of hazardous wastes by the thermal plasma to produce an effective catalyst

In the past two years, a pilot-scale plasma gasification was carried out. With the help of this project, we investigated the possibility to recycle plasma gasification-derived slag as an effective catalyst by adjusting co-treatment ratio between medical waste and fly ash. As a result, when the co-treatment ratio of fly ash increased, the derived slag showed a bigger content of transition metal, together with a higher activity for selective catalytic reduction of nitric oxide. Specifically, the co-treatment slag with a best activity removed 64.4% of nitric oxide (1000 ppm) at 250 °C, 23.5% higher than the slag from single treatment of medical waste. On the other hand, almost all zinc (15.85–16.99 mg/g) and plumbum (0.72–1.16 mg/g) from raw materials were enriched in the secondary fly ash. Hence, if the secondary fly ash was treated by the plasma gasification again, these heavy metals would obtain further enrichments, which transformed the secondary fly ash into a potential resource for metallurgy. The main result of this work indicated a proper co-treatment of hazardous wastes by the plasma gasification produced high-value-added products. The plasma gasification was a “zero discharge” technology for the treatment and recycle of various hazardous wastes.

Low temperature selective catalytic reduction of nitric oxide with urea over activated carbon supported metal oxide catalysts

ABSTRACTSelective catalytic reduction of nitrogen oxides (SCR) with loaded urea is a method for removing NO under oxygen-rich and low-temperature conditions, which can solve the inhibitory effect of oxygen on the catalyst and the slip of ammonia. In present study, a series of activated carbon (wo-AC, co-AC, cs-AC and nu-AC) supported metal (Mn, Fe, Co, Cu and Zn) oxide catalysts with loading urea were prepared by ultrasonic assisted impregnation. The catalysts were used for NO removal at 50–120°C and characterized by XRD, SEM, GFAAS, EDS, XPS, BET and FTIR techniques. The effects of activated carbon type, loaded active element, metal oxides loading, temperature fluctuation on catalytic activity and the catalytic stability were also studied in this paper. The results indicated that nutshell-based activated carbon was more suitable as a carrier than other activated carbons, and urea-10Mn/nu-AC catalyst yielded a higher NO conversion than other catalysts. Besides, for used activated carbons, the larger specific surface area, more micropores distribution and the larger number of hydroxyl group and cyano terminal group are beneficial to the catalytic process. Moreover, the downward trend of NO conversion with increasing temperature suggested the adsorption of reactant gases played a crucial role in the catalytic process of urea-SCR.

Selective catalytic reduction of nitric oxide with ammonia over Fe-Cu modified highly silicated zeolites

In the present study, the solid-state ion exchange method (SSIE) was applied to introduce iron and copper into highly silicate zeolites: beta (BEA, Si/Al = 12.5), ferrierite (FER, Si/Al = 10) and mordenite (MOR, Si/Al = 10). The activity of the prepared samples in the selective catalytic reduction of NO with ammonia (NH3-SCR) was measured. The highest performance was recorded for Cu-Fe-BEA followed by Cu-Fe-MOR while Cu-Fe-FER showed a low catalytic activity over the entire reaction temperature range. It is shown in this study that the zeolite framework is one of the parameters controlling the amount, environment and distribution of metal species formed during the ion exchange process in Cu-Fe-zeolite catalysts.

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.

Bimetallic Cr-In/H-SSZ-13 for selective catalytic reduction of nitric oxide by methane

Bimetallic Cr-In/H-SSZ-13 zeolites were prepared by wet impregnation and investigated for selective catalytic reduction of nitric oxide by methane (CH4-SCR). Reduction-oxidation treatments led to close contact and interaction between Cr and In species in these zeolites, as revealed by transmission electron microscopy and X-ray photoelectron spectroscopy. Compared to monometallic Cr/H-SSZ-13 and In/H-SSZ-13, the bimetallic catalyst system exhibited dramatically enhanced CH4-SCR performance, i.e., NO conversion greater than 90% and N2 selectivity greater than 99% at 550 °C in the presence of 6% H2O under a high gas hourly space velocity of 75 000/h. The bimetallic Cr-In/H-SSZ-13 showed very good stability in CH4-SCR with no significant activity loss for over 160 h. Catalytic data revealed that CH4 and NO were activated on the In and Cr sites of Cr-In/H-SSZ-13, respectively, both in the presence of O2 during CH4-SCR.

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.

A review of carbon-based and non-carbon-based catalyst supports for the selective catalytic reduction of nitric oxide.

Various types of carbon-based and non-carbon-based catalyst supports for nitric oxide (NO) removal through selective catalytic reduction (SCR) with ammonia are examined in this review. A number of carbon-based materials, such as carbon nanotubes (CNTs), activated carbon (AC), and graphene (GR) and non-carbon-based materials, such as Zeolite Socony Mobil–5 (ZSM-5), TiO2, and Al2O3 supported materials, were identified as the most up-to-date and recently used catalysts for the removal of NO gas. The main focus of this review is the study of catalyst preparation methods, as this is highly correlated to the behaviour of NO removal. The general mechanisms involved in the system, the Langmuir–Hinshelwood or Eley–Riedeal mechanism, are also discussed. Characterisation analysis affecting the surface and chemical structure of the catalyst is also detailed in this work. Finally, a few major conclusions are drawn and future directions for work on the advancement of the SCR-NH3 catalyst are suggested.

Novel multi-metal containing MnCr catalyst made from manganese slag and chromium wastewater for effective selective catalytic reduction of nitric oxide at low temperature

Abstract The disposal of manganese slag and chromium electroplating wastewater is a difficult problem worldwide. These wastes contain various transition metals, such as Mn, Cr, Fe, Ni and Cu. Thus, these wastes are also potential resources. In this work, a novel catalyst for selective catalytic reduction of nitric oxide was synthesized with the synergetic utilization of manganese slag and chromium wastewater for the first time. The catalyst was feathered by a multi-metal containing amorphous and crystal MnCr oxides. As a result, the manganese slag after ammonia activation increased the removal of nitric oxide from 25 to 61% at a temperature as low as 150 °C. The nitric oxide removal further increased to 97% after chromium wastewater precipitation. The enhanced efficiency lasted for more than 900 min. The results of X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy revealed that chromium wastewater increased the amount of amorphous Mn4+, which coupled to Cr3+. Moreover, the Ni, Fe and Cu in Mn slag and Cr wastewater were incorporated into the coupling, further enhancing the amount of acid sites and low-temperature activity. This catalyst was even more active than a reagent-synthesized MnCr catalyst. Therefore, the present research developed a new strategy to recycle transition metal-containing wastes and to synthesize catalysts for sustainable development.

Catalytic Reduction of Nitrous Oxide by the Low-Symmetry Pt8 Cluster.

The search for a catalyst for the reduction of nitrous oxide (N2O) is now imperative, as this molecule is a very dangerous pollutant. We found that the low-symmetry Pt8 cluster presents multiple reaction pathways for N2O rupture, which are regioselective. This result was revealed by means of density functional theory calculations within the zero-order-regular approximation, ZORA, explicitly including relativistic effects. It is further proved that Pt8 is a competitive N2O catalyst compared to sub-nanometric rhodium clusters, obtaining similar reaction barriers. The hot adsorption site, a tip atom of Pt8, and the rotation of the N2O molecule over the metallic cluster promote the formation of a frustrated bridge activated transition state, Pt8-N2O. This transition structure yields to spontaneous dissociation of N2O without bridge formation. Along this catalytic process, rearrangements within the metal cluster take place, preserving its stability. Moreover, in addition to being important attributes of the Pt8 particle in the N2O reduction, fluxionality and multiple reaction pathways may also prevent poisoning effects. Overall, this differs from reported results for more symmetric metal particles also used as catalysts.

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.

Synergistic Effect between Surface Anhydride Group and Carbon–Metal Species during Catalytic Reduction of Nitric Oxide

The present work revealed the catalytic reduction of nitric oxide (NO) by synergistic effect of anhydride group and carbon–metal species for the first time. The doping of metal on graphene oxide produced 0.50 mmol/g of carbon–metal species, and increased the amount of anhydride groups from 0.49 to 5.52 mmol/g. The obtained catalyst removed 30% of NO (990 ppm) at 300 °C. However, at the same catalytic conditions, the catalyst showed no activity toward NO reduction if anhydride groups were removed. Similarly, although graphene oxide had anhydride groups, it still exhibited no activity without the help of carbon–metal species. Furthermore, the results of temperature-programmed decomposition indicated that the amounts of anhydride and carbon–metal species were closely related to the total removal amount of NO. At last, transient kinetic and thermogravimetry-mass spectrometry revealed that anhydride group and carbon–metal bonding formed active sites. Then the resulted species reduced NO by a catalytic process ...

Synthesis of a novel catalyst with nano metal core/carbon shell by a facile pre-complexation strategy and its application in enhanced catalytic decomposition of nitric oxide

In this work, a novel and facile pre-complexation strategy was reported for the synthesis of carbon-metal catalyst for the first time. The carbon-metal catalyst (SF250) was obtained by thermal-activating pre-complexation of ferric chloride and sodium salicylate. The HRTEM and XRD showed that SF250 contained nanometer particles with core of FeOOH and shell of carbon species. When SF250 was applied in selective catalytic reduction of nitric oxide (NO), it resulted in outstanding efficiency and long-term stability: the removal of NO was 99.8% with a fluctuation of 0.8%; moreover, the SF250 maintained high efficiency of removal for more than 3000min at 400°C. The analyses of EELS and TG-MS suggested that solid-phase and gas-type carbons both participated in reduction of NO, thus resulting in the excellent activity at low temperature. The solid-phase carbon included the active species with great reducibility distributed on the core-shell interface. The gas-type carbon included CO and benzene radicals. Therefore, our work has suggested a novel method for the synthesis of catalyst with core-shell structure by simple operation and low-cost precursors, together with excellent activity toward catalytic reduction of NO.

Selective catalytic reduction of nitric oxide with carbon monoxide over alumina-pellet-supported catalysts in the presence of excess oxygen

ABSTRACTSelective catalytic reduction of nitrogen oxides with carbon monoxide (CO-SCR) is a promising technology to remove NOx and CO simultaneously from flue gas. The thermodynamic analyses of catalytic process were performed toward four kinds of active metal oxides (CuxOy, CoxOy, MnxOy and CexOy). According to the standard Gibbs free-energy changes calculated, Mn had better resistance to oxygen than Cu, Co and Ce, while Cu and Ce had better resistance to water vapor poisoning, as active metals. Then, a series of binary- and ternary-preformed catalysts with different metal ratios were prepared by the impregnation method using Al2O3 pellets as support and tested in excess oxygen (16 vol%) atmosphere with or without SO2. The results of experiment were analyzed based on thermodynamic analyses. Results indicated that the NO conversions of Cu–Co/Al2O3 catalysts increased with the rise of reaction temperature; however, the tendency changed at 160°C for Cu–Mn/Al2O3. Besides, the NO conversions of Cu–Mn/Al2O3 were better than Cu–Co/Al2O3. The catalysts with the metal ratio of 1.5 had the best denitrification performance. Among various binary catalysts, Cu–Mn/Al2O3 with the metal ratio Cu:Mn of 1.5 showed promising activity for CO-SCR, giving nearly 90% NO conversion. Besides, the doping of Ce could inhibit the sulfur poisoning and promote the oxide of CO under experimental conditions.

Manganese-cerium oxide (MnOx-CeO2) catalysts supported by titanium-bearing blast furnace slag for selective catalytic reduction of nitric oxide with ammonia at low temperature

ABSTRACTA series of manganese-cerium oxide (MnOx-CeO2) catalysts supported by Ti-bearing blast furnace slag were prepared by wet impregnation and used for low-temperature selective catalytic reduction (SCR) of NO with NH3. The slag-based catalyst exhibited high nitrogen oxide removal (deNOx) activity and wide effective temperature range. Under the condition of NO = 500 ppm, NH3 = 500 ppm, O2 = 7–8 vol%, and total flow rate = 1600 mL/min, the Mn-Ce/Slag catalyst exhibited a NO conversion higher than 95% in the range of 180–260 °C. The activity of Mn/Slag catalysts was greatly enhanced with the addition of CeO2. The results indicated that Ti-bearing blast furnace slag had suitable phase composition as good support of SCR catalyst.Implications: Ti-bearing blast furnace slag is a kind of industrial waste in China. Much slag was underused and piling up, which could cause many environmental issues, such as enormous waste of titanium and groundwater and soil contamination by heavy metals in leachates. The utilization of slag as the support of SCR catalyst will not only make use of solid waste but also cut down the NOx emitted from power plant.

Activity of $\gamma $-Al$_{2}$O$_{3}$-based Mn, Cu, and Co oxide nanocatalysts for selective catalytic reduction of nitric oxide with ammonia

Our studies on the selective catalytic reduction of NO (SCR-deNO) properties of M/$\gamma $-Al$_{2}$O$_{3}$ (M = Mn, Co, Cu) nanocatalysts are presented. All catalysts were prepared by homogeneous deposition precipitation using urea as the precursor for the precipitating agent. The SCR activity followed the order Mn/$\gamma $-Al$_{2}$O$_{3} >$ Cu/$\gamma $-Al$_{2}$O$_{3} >$ Co/$\gamma $-Al$_{2}$O$_{3}$. The nanocatalysts were characterized with respect to their texture (N$_{2}$-BET), particle size (TEM), reducibility (H$_{2}$-TPR), and acidity (NH$_{3}$-TPD). The TEM analysis revealed that the metal species have superior dispersion with less agglomeration and sintering on $\gamma $-Al$_{2}$O$_{3}$ support. The H$_{2}$-TPR results confirmed that the Mn/$\gamma $-Al$_{2}$O$_{3}$ nanocatalyst contains various oxidation states of manganese, which is useful for the catalyst to maintain the DeNO activities. The NH$_{3}$-TPD studies indicated that the addition of transition metal can significantly increase the surface acidity and Mn/$\gamma $-Al$_{2}$O$_{3}$ showed the most adsorbed sites of NH$_{3}$. Characterization results indicated that the acidity and the redox properties of the catalyst play important roles in the final catalytic activity in the SCR-NO process.

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts

AbstractThe long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH3) on vanadium‐based catalysts rely on the involvement of Brønsted or Lewis acid sites. This issue has been clearly elucidated using a combination of transient perturbations of the catalyst environment with operando time‐resolved spectroscopy to obtain unique molecular level insights. Nitric oxide reacts predominantly with NH3 coordinated to Lewis sites on vanadia on tungsta–titania (V2O5‐WO3‐TiO2), while Brønsted sites are not involved in the catalytic cycle. The Lewis site is a mono‐oxo vanadyl group that reduces only in the presence of both nitric oxide and NH3. We were also able to verify the formation of the nitrosamide (NH2NO) intermediate, which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach, demonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance.

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium-Based Catalysts.

The long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH3 ) on vanadium-based catalysts rely on the involvement of Brønsted or Lewis acid sites. This issue has been clearly elucidated using a combination of transient perturbations of the catalyst environment with operando time-resolved spectroscopy to obtain unique molecular level insights. Nitric oxide reacts predominantly with NH3 coordinated to Lewis sites on vanadia on tungsta-titania (V2 O5 -WO3 -TiO2 ), while Brønsted sites are not involved in the catalytic cycle. The Lewis site is a mono-oxo vanadyl group that reduces only in the presence of both nitric oxide and NH3 . We were also able to verify the formation of the nitrosamide (NH2 NO) intermediate, which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach, demonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance.