NO Conversion Research Articles

Modulating the Electrolyte Microenvironment in Electrical Double Layer for Boosting Electrocatalytic Nitrate Reduction to Ammonia.

Electrochemical nitrate reduction reaction (NO3RR) is a promising approach to achieve remediation of nitrate-polluted wastewater and sustainable production of ammonia. However, it is still restricted by the low activity, selectivity and Faraday efficiency for ammonia synthesis. Herein, we propose an effective strategy to modulate the electrolyte microenvironment in electrical double layer (EDL) by mediating alkali metal cations in the electrolyte to enhance the NO3RR performance. Taking bulk Cu as a model catalyst, the experimental study reveals that the NO3 --to-NH3 performance in different electrolytes follows the trend Li+<Cs+<Na+<K+. Theoretical studies illustrate that the proton transport rate in NO3RR and the activity of the rate-determining step (NO3 - to NO2 -) increase in the order Li+<Cs+<Na+<K+. The cation effects are also general for two typical nanostructured catalysts including copper/cuprous oxide and nickel phosphides, achieving near-100 % Faradaic efficiency and over 99 % conversion of NO3 - to NH3. Furthermore, we demonstrate that NO3 - can be converted to high-purity NH4Cl by copper/cuprous oxide catalyst in K+-containing electrolyte.

Modulating the Electrolyte Microenvironment in Electrical Double Layer for Boosting Electrocatalytic Nitrate Reduction to Ammonia

AbstractElectrochemical nitrate reduction reaction (NO3RR) is a promising approach to achieve remediation of nitrate‐polluted wastewater and sustainable production of ammonia. However, it is still restricted by the low activity, selectivity and Faraday efficiency for ammonia synthesis. Herein, we propose an effective strategy to modulate the electrolyte microenvironment in electrical double layer (EDL) by mediating alkali metal cations in the electrolyte to enhance the NO3RR performance. Taking bulk Cu as a model catalyst, the experimental study reveals that the NO3−‐to‐NH3 performance in different electrolytes follows the trend Li+&lt;Cs+&lt;Na+&lt;K+. Theoretical studies illustrate that the proton transport rate in NO3RR and the activity of the rate‐determining step (NO3− to NO2−) increase in the order Li+&lt;Cs+&lt;Na+&lt;K+. The cation effects are also general for two typical nanostructured catalysts including copper/cuprous oxide and nickel phosphides, achieving near‐100 % Faradaic efficiency and over 99 % conversion of NO3− to NH3. Furthermore, we demonstrate that NO3− can be converted to high‐purity NH4Cl by copper/cuprous oxide catalyst in K+‐containing electrolyte.

Cu1-Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate.

The electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3 -) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3 - to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen-containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH-neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3 -. Herein, we constructed a Cu1-Fe dual-site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero-valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3 - removal efficiency of 94.8 % and NH3 selectivity of 99.2 % under neutral pH and nitrate concentration of 50 mg L-1 NO3 --N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3 - adsorption on Fe sites and strengthened water activation on single-atom Cu sites, decreasing the energy barrier for the rate-determining step of *NO-to-*NOH. This work develops a novel strategy of fabricating dual-site catalysts to enhance the electrosynthesis of NH3 from NO3 -, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Cu1−Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate

AbstractThe electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3−) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3− to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen‐containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH‐neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3−. Herein, we constructed a Cu1‐Fe dual‐site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero‐valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3− removal efficiency of 94.8 % and NH3 selectivity of 99.2 % under neutral pH and nitrate concentration of 50 mg L−1 NO3−−N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3− adsorption on Fe sites and strengthened water activation on single‐atom Cu sites, decreasing the energy barrier for the rate‐determining step of *NO‐to‐*NOH. This work develops a novel strategy of fabricating dual‐site catalysts to enhance the electrosynthesis of NH3 from NO3−, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Sustainable nitrogen fixation by novel gliding arc plasma reactor for the production of nitrogen fertilizers

AbstractA novel plasma reactor is being investigated for green NOx production, crucial for nitrate‐based fertilizer manufacturing. Various parameters, including air flow rates, gas ratios, ozone, and catalyst effects are explored for NO → NO2 conversion. NOx concentrations reach ~0.6 vol%, with a total production of ~9.7 gr/h and energy cost of ~3.0 mJ/mol, notably favorable for atmospheric gliding arc plasma. Selectivity (~75%) towards NO2 is achieved with ozone addition or catalytic treatment, pivotal for nitrate fertilizer and HNO3 production.

Organic fertilization reduces nitrous oxide emission by altering nitrogen cycling microbial guilds favouring complete denitrification at soil aggregate scale

Agricultural management practices can induce changes in soil aggregation structure that alter the microbial nitrous oxide (N2O) production and reduction processes occurring at the microscale, leading to large-scale consequences for N2O emissions. However, the mechanistic understanding of how organic fertilization affects these context-dependent small-scale N2O emissions and associated key nitrogen (N) cycling microbial communities is lacking. Here, denitrification gas (N2O, N2) and potential denitrification capacity N2O/(N2O + N2) were assessed by automated gas chromatography in different soil aggregates (>2 mm, 2–0.25 and <0.25 mm), while associated microbial communities were assessed by sequencing and qPCR of N2O-producing (nirK and nirS) and reducing (nosZ clade I and II) genes. The results indicated that organic fertilization reduced N2O emissions by enhancing the conversion of N2O to N2 in all aggregate sizes. Moreover, potential N2O production and reduction hotspots occurred in smaller soil aggregates, with the degree depending on organic fertilizer type and application rate. Further, significantly higher abundance and diversity of nosZ clades relative to nirK and nirS revealed complete denitrification promoted through selection of denitrifying communities at microscales favouring N2O reduction. Communities associated with high and low emission treatments form modules with specific sequence types which may be diagnostic of emission levels. Taken together, these findings suggest that organic fertilizers reduced N2O emissions through influencing soil factors and patterns of niche partitioning between N2O-producing and reducing communities within soil aggregates, and selection for communities that overall are more likely to consume than emit N2O. These findings are helpful in strengthening the ability to predict N2O emissions from agricultural soils under organic fertilization as well as contributing to the development of net-zero carbon strategies for sustainable agriculture.

Reactive oxygen species play key roles in the nitrite formation by the inorganic nitrate photolysis in the presence of urban water-soluble organic carbon

Inorganic nitrates were considered to be a potential source of atmospheric NO2−/HONO during the daytime. To better evaluate the contribution of nitrate photochemistry on NO2−/HONO formation, the photolysis of nitrates in the real atmospheric environment needs to be further explored. Here, the NO2− generation by the photolysis of inorganic nitrates in the presence of total water-soluble organic carbon (WSOC) was quantified. The physicochemical properties of WSOC were measured to understand the underlying mechanism for the photolysis of inorganic nitrates with WSOC. WSOC enhanced or suppressed the photochemical conversion of nitrates to NO2−, with the quantum yield of NO2− (ΦNO2−) varying from (0.07 ± 0.02)% to (3.11 ± 0.04)% that depended on the light absorption properties of WSOC. Reactive oxygen species (ROS) generated from WSOC, including O2−/HO2 and OH, played a dual role in the NO2− formation. Light-absorbing substances in WSOC, such as N-containing and carbonyl aromatics, produced O2−/HO2 that enhanced the secondary conversion of NO2 to NO2−. On the other hand, OH deriving from the WSOC photochemistry inhibited the nitrate photodegradation and the NO2− formation. HONO source strength by the aqueous photolysis of nitrates with WSOC was estimated to be lower than 100 ppt h−1, which may partly contribute to the atmospheric HONO source in some cases.

Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH4-reduced N(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C3N4 photooxidation for NO removal. In this paper, flake graphite-phase g-C3N4 is prepared by thermal polycondensation. Then g–C3N4–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N(ligancy-3)) was prepared by NaBH4 reduction at room temperature. The introduction of N vacancies in g-C3N4 narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C3N4–x shows a superior NO removal performance, especially g–C3N4–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO2, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)2 produced from NO adsorption on the surface of g–C3N4–1.5 is an important intermediate. Additionally, NO2− is observed as an intermediate and a primary product, and NO3− is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N(ligancy-3) vacancy introduces impurity energy levels in g-C3N4 and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C3N4–N(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C3N4 to remediate environmental pollution.

Unraveling the Synergistic Mechanism of Ir Species with Various Electron Densities over an Ir/ZSM-5 Catalyst Enables High-Efficiency NO Reduction by CO.

Selective catalytic reduction using CO as a reducing agent (CO-SCR) has exhibited its application potential in coal-fired, steel, and other industrial sectors. In comparison to NH3-SCR, CO-SCR can achieve synergistic control of CO and NO pollutants, making it a powerful denitrification technology that treats waste with waste. Unfortunately, the competitive adsorption of O2 and NO on CO-SCR catalysts inhibits efficient conversion of NOx under O2-containing conditions. In this work, we obtained two Ir sites with different electron densities, Ir1 single atoms in the oxidized Irδ+ state and Ir0 nanoparticles in the metallic state, by controlled pretreatment of the Ir/ZSM-5 catalyst with H2 at 200 °C. The coexistence of Ir1 single atoms and Ir0 nanoparticles on ZSM-5 creates a synergistic effect, which facilitates the reduction of NO through CO in the presence of O2, following the Langmuir-Hinshelwood mechanism. The ONNO dimer is formed on the Ir1 single atom sites and then spills over to the neighboring Ir0 nanoparticles for subsequent reduction to N2 by CO. Specifically, this tandem reaction enables 83% NO conversion and 100% CO conversion on an Ir-based catalyst at 250 °C under 3% O2.

Observation-Based Diagnostics of Reactive Nitrogen Recycling through HONO Heterogenous Production: Divergent Implications for Ozone Production and Emission Control.

Understanding of nitrous acid (HONO) production is crucial to photochemical studies, especially in polluted environments like eastern China. In-situ measurements of gaseous and particulate compositions were conducted at a rural coastal site during the 2018 spring Ozone Photochemistry and Export from China Experiment (OPECE). This data set was applied to investigate the recycling of reactive nitrogen through daytime heterogeneous HONO production. Although HONO levels increase during agricultural burning, analysis of the observation data does not indicate more efficient HONO production by agricultural burning aerosols than other anthropogenic aerosols. Box and 1-D modeling analyses reveal the intrinsic relationships between nitrogen dioxide (NO2), particulate nitrate (pNO3), and nitric acid (HNO3), resulting in comparable agreement between observed and simulated HONO concentrations with any one of the three heterogeneous HONO production mechanisms, photosensitized NO2 conversion on aerosols, photolysis of pNO3, and conversion from HNO3. This finding underscores the uncertainties in the mechanistic understanding and quantitative parametrizations of daytime heterogeneous HONO production pathways. Furthermore, the implications for reactive nitrogen recycling, ozone (O3) production, and O3 control strategies vary greatly depending on the HONO production mechanism. On a regional scale, the conversion of HONO from pNO3 can drastically enhance O3 production, while the conversion from NO2 can reduce O3 sensitivity to NOx changes in polluted eastern China.

Effect of Nb‐doping on the MnFeOx catalyst for NH3‐SCR reaction at low‐temperature

AbstractBACKGROUNDManganese‐based catalysts were considered the most promising catalysts for low‐temperature selective catalytic reduction (NH3‐SCR) reactions. In this work, a series of Mn3Fe2NbyOx catalysts were synthesized by co‐precipitation method for low‐temperature NH3‐SCR and SO2 tolerance tests.RESULTSThe catalysts were characterized by BET, SEM, XRD, XPS, H2‐TPR, and NH3‐TPD. Mn3Fe2Nb0.01Ox exhibited exceptionally high activity with a conversion of almost 100% from 80°C to 240°C, and a NO conversion of more than 75% at 40°C, while the NO conversion at 140°C in the presence of 100 ppm SO2 remained above 90% for 4 h.CONCLUSIONAccording to the characterization results, Nb modification can expand the specific surface area of the catalyst, improve the structure of the catalyst, and make the active components on the catalyst surface more dispersed. Moreover, the Nb‐modified catalyst reduced the content of Mn2+ on the catalyst surface and strengthened the electronic interactions between elements. The synergistic effects among Mn, Fe, and Nb facilitate the formation of more chemically adsorbed oxygen, which enhances the reduction capacity of the catalyst. This facilitates the adsorption of NH3 by the catalyst at low temperatures and promotes the process of low‐temperature NH3‐SCR reaction. More importantly, the Nb‐modified catalyst possessed more weak acid sites, and the higher surface acidity was conducive to the inhibition of SO3 generation, which enhanced the sulfur poisoning resistance of the catalyst. © 2024 Society of Chemical Industry (SCI).

The Oscillatory Behaviour of Cu-ZSM-5 Catalysts for N2O Decomposition: Investigation of Cu Species by Complementary Techniques.

Copper-exchanged ZSM-5 (Cu-ZSM-5) is a promising catalyst thanks to the Cu redox pair. A particular feature of this material consists in the presence of spontaneous isothermal oscillations which take place during N2O decomposition reaction, depending on the operating conditions. In the present work, a set of five Cu-ZSM-5 catalysts was synthesised by three procedures and three different copper precursor concentrations: i) wet impregnation, ii) single ion exchange, and iii) double ion exchange. Catalytic tests revealed that the ion-exchanged samples exhibit a low catalytic activity and no oscillatory behaviour, except for the twice-exchanged sample which achieves an average N2O conversion of 26 % at 400 °C. Conversely, the impregnated samples reach higher levels of N2O conversion (66 % for Cu5ZSM5_WI and 72 % for Cu10ZSM5_WI) and demonstrate a similar oscillating pattern. Further investigations disclosed that the most active catalysts, characterised by the presence of oscillatory behaviour, have more abundant and easily reducible copper species (ICP, EDX and H2-TPR) which interact better with the zeolitic support (FT-IR). Catalytic tests under a long time on stream (TOS) suggest that either self-organised patterns or deterministic chaos can be achieved during the reaction, depending on the operating conditions, such as temperature and contact time.

The intense charge migration and efficient photocatalytic NO removal of the S-scheme heterojunction composites Bi7O9I3-BiOBr

For purpose of efficient photocatalytic removal of NO molecules, both components of bismuth-rich Bi7O9I3 and BiOBr were typically selected to create binary heterojunction composites Bi7O9I3-BiOBr (BI-BBX) through a facile in-situ synthetic protocol. These composites underwent thorough characterization using a range of analytical methods and were subjected to photocatalytic removal of NO at ppb level under visible light for the first time. These produced composites showed enhanced photocatalytic behavior and the best candidate BI-BB0.2 demonstrated the highest removal efficiency among all tested samples. Density-functional theory (DFT) calculations revealed the intense charge migration at the interface. In addition, the composites surface exhibited a propensity to adsorb and activate O2, H2O, and NO molecules, thus promoting the catalytic conversion of NO to NO2– and further NO3– species. Entrapping experiments and electron spin resonance (ESR) results demonstrated the increased generation of oxygen-containing species O2–, 1O2, and ·OH, which was attributed to the rational creation of heterojunctions with similar crystal structures and efficient migration and separation of generated charge carriers in an S-scheme model. This study provides insight into the design and development of Bi7O9I3-based composites for effective dislodge of NO upon the visible-light irradiation.

Fine tuning dual active sites in modulating cascade electrocatalytic nitrate reduction over covalent organic framework

Conversion of NO3− to NH3 proceeds stepwise in natural system under two different enzymes involving intermediate NO2−. Artificial electro-driven NO3− reduction also faces the obstacle of low faradaic efficiency due to insufficient utilization of this intermediate. Herein, we demonstrate a bimetallic COF-based electrocatalyst for the cascade catalysis of NO3−-to-NO2−-to-NH3 for the first time. TpBpy-Cu2Co4 exhibits a significantly improved performance, with an enhancement factor of 1.4–2 compared to monometallic TpBpy-M. The NH3 yield rate achieves 25.6 mg h−1 mgcat.−1 at −0.55 V vs RHE over TpBpy-Cu2Co4, together with excellent faradaic efficiency (93.4 %). This achievement demonstrates cascade catalysis between Co and Cu units, and their distinct roles are investigated through electrochemical experiments and theory calculations. In electrocatalytic process, Cu site facilities *NO3-to-*NO3H step, while the Co site significantly decreases the energy barrier of *NHOH-to-*NH. The present work provides a valuable inspiration in designing efficient catalysts for cascade reaction.

M-MnCeOX derived from MOF for low temperature selective catalytic reduction of NOX by NH3: Experiments and mechanisms

A series of M-MnCeOX catalysts using MOF (Metal-organic Framework) were prepared to apply for NH3-SCR (Selective Catalytic Reduction) of NOX. The effects of Mn/Ce molar ratio, calcination temperature and its activity including catalytic activity, H2O/SO2 resistance and stability were systematically investigated. The results showed that under the Mn/Ce molar ratio of 1 and calcination temperature of 400 ℃, the catalyst exhibited excellent catalytic activity, H2O/SO2 resistance, and stability. When the concentration of NO was 500 ppm, the gas spatiotemporal velocity (GHSV) was 36,000 h−1, and the reaction temperature was 100 ℃, the NO conversion efficiency of M-MnCeOX exceeded 90.0 %. Added 200 ppm SO2 and 3 vol% H2O simultaneously, the NO conversion efficiency was close to 80.0 %. By analyzing the physicochemical properties of the catalyst, M-MnCeOX had a large specific surface area, numerous acidic sites, and excellent redox properties. According to density functional theory (DFT), the NH3/NO adsorption energy of M-MnCeOX were −2.35 and −2.40 eV, exhibiting lower than a single MOF-derivative, promoting the adsorption of NH3 or NO. The reaction mechanism on the M-MnCeOX catalyst followed the E-R and L-H mechanisms by In situ DRIFTS.

Nitrate reduction to nitrogen in wastewater using mesoporous carbon encapsulated Pd–Cu nanoparticles combined with in-situ electrochemical hydrogen evolution

The conversion of NO3−-N to N2 is of great significance for zero discharge of industrial wastewater. Pd–Cu hydrogenation catalysis has high application prospects for the reduction of NO3−-N to N2, but the existing form of Pd–Cu, the Pd–Cu mass ratio and the H2 evolution rate can affect the coverage of active hydrogen (*H) on the surface of Pd, thereby affecting N2 selectivity. In this work, mesoporous carbon (MC) is used as support to disperse Pd–Cu catalyst and is applied in an in-situ electrocatalytic H2 evolution system for NO3−-N removal. The Pd–Cu particles with the average size of 6 nm are uniformly encapsulated in the mesopores of MC. Electrochemical in-situ H2 evolution can not only reduce the amount of H2 used, but the H2 bubbles can also be efficiently dispersed when PPy coated nickel foam (PPy/NF) is used as cathode. Moreover, the mesoporous structure of MC can further split H2 bubbles, reducing the coverage of *H on Pd. The highest 77% N2 selectivity and a relatively faster NO3−-N removal rate constant (0.10362 min−1) can be achieved under the optimal conditions, which is superior to most reported Pd–Cu catalytic systems. The prepared catalyst is further applied to the denitrification of actual deplating wastewater. NO3−-N with the initial concentration of 650 mg L−1 can be completely removed after 180 min of treatment, and the TN removal can be maintained at 72%.

Amorphous Ce-Ti composite as an efficient bifunctional catalyst for deep oxidation of volatile organic compounds and selective catalytic reduction of NO

In this work, a series of Ce-Ti composite oxides with different Ti/Ce molar ratios was prepared by co-precipitation method, and investigated for the catalytic degradation of toluene and selective catalytic reduction of NO. The phase transition process between Ce species and Ti species is limited by modulating the interaction between Ce4+ and Ti4+, while a completely amorphous composite is generated with an appropriate molar ratio of Ti/Ce (1.5/1). The catalyst CeTi1.5Ox exhibits the best catalytic performance, where the values of T90 and T50 for deep degradation of toluene are 297 and 330 °C respectively at high weight hours space velocity (WHSV=120000 mL/(g⋅h)). Compared with CeO2, T90 and T50 decrease by 48 and 34 °C respectively while declining by 67 and 70 °C compared to TiO2. For the SCR reaction, CeTi1.5Ox reaches 100% NO conversion at 250 °C with WHSV=60000 mL/(g⋅h), reduced by 50 °C compared to pure CeO2. The amorphous nanostructure with highly dispersed Ce and Ti species was confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations. The X-ray photoelectron spectroscopy (XPS) and Raman analyses show that a large number of active Ce-O-Ti species and surface oxygen vacancies are generated due to the strong interaction between Ti4+ and Ce4+ in CeTi1.5Ox. Additionally, H2-TPR and O2-TPD further confirm that the interaction promotes the low-temperature reducibility and mobility of surface-active oxygen species. Meanwhile, in-situ DRIFTS study reveals that CeTi1.5Ox with amorphous nanostructure can dramatically enhance the dissociative and complete oxidation capacity for toluene.

Selective catalytic reduction of NO by CO over spinel CuFe2O4 catalyst: The vital role of oxygen vacancies

Oxygen vacancies are widely employed to augment the catalytic reactivity in the selective catalytic reduction of NO by CO (CO-SCR) process. Herein, the specific promotion mechanism of oxygen vacancies was intensively explored through a series of CuFe2O4 catalysts via experiments and density functional theory (DFT) simulations. After the modification of oxygen vacancies, NO conversion was enhanced by 20 %-32 % and N2 selectivity was improved. Characterizations revealed that the redox performance, NO adsorption and activation capacity, active centers, and acidic sites of CuFe2O4 can be improved by enriched oxygen vacancies, contributing to the superior CO-SCR performance. DFT results identified that the adsorption energies of reactants were elevated and the intermediate reaction energy barriers were decreased with more oxygen vacancies. Furthermore, the CO-SCR reaction pathways with CuFe2O4 catalyst were proposed according to in-situ test results: it follows the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms in the low-temperature range (50–250 ℃) and the Marse-van-Krevelen (Mvk) mechanism in the high-temperature range (≥250 ℃). Overall, this work highlights the bright prospects of oxygen vacancies on the modification of CO-SCR catalysts.

Simultaneous removal of naphthalene and NOx over V-Ce/Ti catalyst: Design of separated active sites for naphthalene degradation and SCR reaction

V-Ce/Ti catalysts were prepared for the removal of naphthalene and NOx in the flue gas. The adverse effects of NH3 and NO on the naphthalene degradation were weakened on V-Ce/Ti, resulting in a decrease of only 2.5 % in COx selectivity. The formation of high molecular weight byproducts was also reduced. Besides the acid sites on the catalysts, Ce introduced new Brønsted basic sites, which could also adsorb and degrade naphthalene into naphthol effectively. With the separated active sites for naphthalene degradation and NO removal, the reaction between NH3 and the intermediates during the naphthalene degradation was also inhibited, decreasing the formation and accumulation of phthalimide. The oxidation of the intermediates was promoted by active V5+ introduced by Ce, inhibiting the transformation of the intermediates to higher molecular weight byproducts. Nearly 100 % conversion of naphthalene and NO, as well as 40.1 % of the COx selectivity were obtained on V-Ce/Ti.

Enhanced low-temperature activity of Mn-based catalysts for NH3 selective catalytic reduction of NO through Ce-modulated redox and TiO2 shell construction

Manganese-based catalysts presented great challenges for the wide operating window in the selective catalytic reduction of NOx with NH3 (NH3-SCR). Aiming at enhancement of the SCR performance, a series of MnCeOx (MnyCe1) and Mn1Ce1@TiO2 catalysts were prepared. Impressively, the Mn1Ce1 catalyst exhibited excellent low-temperature activity, achieving over 80 % conversion of NO within the temperature range of 85–350 °C, but the N2 selectivity decreased with the increasing temperature. Upon coating a TiO2 shell, the temperature window with N2 selectivity exceeding 80 % was significantly widened to 85–350 °C since the weak redox ability limited the NH3 oxidation to undesired N2O. High surface area, together with abundant acid sites and chemical adsorbed oxygen that formed via the interaction between Mn4+/Mn3+, Ce4+/Ce3+ and Ti4+/Ti3+, contributed to the superior catalytic performance of Mn1Ce1@TiO2. In addition, through in situ DRIFTS analysis, both Eley-Rideal and Langmuir-Hinshelwood reaction routes were observed. This work would provide an efficient and low-cost strategy for preparing Mn-based catalysts with excellent low-temperature activity for NOx removal.