Optimization of nitrogen-doped sludge char preparation and mechanism study for catalytic oxidation of NO at room temperature

Catalytic oxidation of NO at room temperature was carried out over nitrogen (N)-doped sludge char (SC) prepared from pyrolysis of municipal sewage sludge, and urea was adopted as nitrogen source. The effects of different N-doping methods (one-step and two-step method), dried sludge (DS)/urea mass ratios (5:1, 4:1, 3:1, 2:1, and 1:1), SC preparation procedures (pyrolysis only, pyrolysis with acid washing, and pyrolysis with KOH activation and acid washing), and different pyrolysis temperatures (500, 600, 700, and 800°C) on the catalytic oxidation of NO were compared to optimize the procedure for SC preparation. The results indicated that N-doping could obviously promote the catalytic performance of SC. The one-step method with simultaneous sludge pyrolysis (at 700°C), KOH activation, and N-doping (DS/urea of 3:1) was the optimal procedure for preparing the N-doped SC with the NO conversion rate of 54.7%, whereas the optimal NO conversion rate of SC without N-doping was only 47.3%. Urea worked both as carbon and nitrogen source, which could increase about 2.9%-16.5% of carbon and 24.8%-42.7% of nitrogen content in SC pyrolyzed at 700°C. N-doping significantly promoted microporosity of SC. The optimal N-doped SC showed specific surface areas of 571.38 m2/g, much higher than 374.34 m2/g of the optimal SC without N-doping. In addition, N-doping also increased amorphousness and surface basicity of SC through the formation of N-containing groups. Finally, three reaction paths, i.e. microporous reactor, active sites, and basic site control path, were proposed to explain the mechanism of N-doping on promoting the catalytic performance of NO.

Confining Bismuth-Halide Perovskite in Mesochannels of Silica Nanomembranes for Exceptional Photocatalytic Abatement of Air Pollutants

Spatially confined photocatalysis has emerged as a viable strategy for the intensification of various redox reactions, but the influence of confined structure on reaction behavior is always overlooked in gas-solid reactions. Herein, we report a nanomembrane with confining Cs3 Bi2 Br9 nanocrystals inside vertical channels of porous insulated silica thin sheets (CBB@SBA(⊥)) for photocatalytic nitric oxide (NO) abatement. The ordered one-dimensional (1D) pore channels with mere 70 nm channel length provide a highly accessible confined space for catalytic reactions. A record-breaking NO conversion efficiency of 98.2 % under a weight hourly space velocity (WHSV) of 3.0×106  mL g-1  h-1 , as well as exceptionally high stability over 14 h and durability over a wide humidity range (RH=15-90 %) was realized over SBA(⊥) confined Cs3 Bi2 Br9 , well beyond its nonconfined analogue and the Cs3 Bi2 Br9 confine in Santa Barbara Amorphous (SBA-15). Mechanism studies suggested that the insulated pore channels of SBA(⊥) in CBB@SBA(⊥) endow concentrated electron field and enhanced mass transfer that render high exposure of reactive species and lower reaction barrier needs for ⋅O2 - formation and NO oxidation, as well as prevents structural degradation of Cs3 Bi2 Br9 . This work expands an innovative strategy for designing efficient photocatalysts for air pollution remediation.

Understanding the effects of A-site Ag-doping on LaCoO3 perovskite for NO oxidation: Structural and magnetic properties

The partial substitution of A-site in perovskites is a major strategy to enhance the catalytic oxidation activity. This study explores the use of silver (Ag) to partially replace the lanthanum (La) ion at the A-site in LaCoO3 perovskite, investigating the role of Ag in the ABO3 perovskite structure, elucidating the nitric oxide (NO) oxidation mechanism over La1-xAgxCoO3 (x = 0.1-0.5) perovskites. La0.7Ag0.3CoO3 with an Ag-doping amount of 0.3, exhibited the highest NO oxidation activity of 88.5% at 275 °C. Characterization results indicated that Ag substitution enhanced the perovskite, maintaining its original phase structure, existing in the form of a mixture of Ag0 and Ag+ in the La1-xAgxCoO3 (x = 0.1-0.5) perovskites. Notably, Ag substitution improved the specific surface area, reduction performance, Co3+, and surface adsorption oxygen content. Additionally, the study investigated the relationship between magnetism and NO oxidation from a magnetism perspective. Ag-doping strengthened the magnetism of La-Ag perovskite, resulting in stronger adsorption of paramagnetic NO. This study elucidated the NO oxidation mechanism over La-Ag perovskite, considering structural and magnetic properties, providing valuable insights for the subsequent development and industrial application of high oxidation ability perovskite catalysts.

Strategy and Technical Progress of Recycling of Spent Vanadium-Titanium-Based Selective Catalytic Reduction Catalysts

Selective catalytic reduction denitration technology, abbreviated as SCR, is essential for the removal of nitrogen oxide from the flue gas of coal-fired power stations and has been widely used. Due to the strong demand for energy and the requirements for environmental protection, a large amount of SCR catalyst waste is produced. The spent SCR catalyst contains high-grade valuable metals, and proper disposal or treatment of the SCR catalyst can protect the environment and realize resource recycling. This review focuses on the two main routes of regeneration and recycling of spent vanadium-titanium SCR catalysts that are currently most widely commercially used and summarizes in detail the technologies of recycling, high-efficiency recycling, and recycling of valuable components of spent vanadium-titanium SCR catalysts. This review also discusses in depth the future development direction of recycling spent vanadium-titanium SCR catalysts. It provides a reference for promoting recycling, which is crucial for resource recovery and green and low-carbon development.

NO2 emissions from oil refineries in the Mississippi Delta

Of the >17,943 thousand barrels per calendar day (bbl/d) of oil refining capacity located in the US, the Petroleum Administration for Defense District 3 (PADD-3) region has the largest number of refineries and accounts for >53 % (or 9607 tbbl/d) of all US oil refining capacity. Processing facilities in this area are mainly located on the Gulf of Mexico coast in Texas and Louisiana. This study selected a sub-region for analysis within the Mississippi River delta in the state of Louisiana between the cities of New Orleans and Baton Rouge. This region is characterized by intensive industrial activity connected with oil refining and related activities. The TROPOspheric Monitoring Instrument (TROPOMI) detected highly localized NO2 vertical column densities (VCDs) over the two largest US refineries in Baton Rouge (503,000 bbl/d) and Garyville (578,000 bbl/d). TROPOMI NO2 VCD over these stations were 100 μmol/m2 and 80 μmol/m2, respectively. A high correlation coefficient (r = 0.65, p < 0.05) was also found between TROPOMI NO2 and population density. Data from the National Emissions Inventory (NEI) showed high NOx emissions from refineries and other industries including coal-fired power generation, chemical, and aluminum processing plants. The results of the NO2 analysis are of practical interest for a comparative assessment of air pollution, as well as for the exchange of best practices in the field of low-waste fuel combustion technologies.

Effects of Nickel Impregnation on the Catalytic Removal of Nitric Oxide by Polyimide-Based Activated Carbon Fibers

Activated carbon fibers (ACFs) are beneficial for adsorbing harmful gases because of the well-developed micropores on their surface. Usually, the physical adsorption of harmful gases by ACFs is limited by their textural properties. In this study, the effect of nickel particle catalyst impregnation on the physicochemical removal of nitric oxide (NO) by polyimide (PI)-based ACFs (PI-ACFs) was investigated. Ni(NO3)2 was used as the precursor of nickel particle catalysts and impregnated on ACFs as a function of concentrations. The Ni(NO3)2/ACFs were then thermally reduced in an argon atmosphere containing 4% hydrogen (400 °C, 1 h). The gases generated during heat treatment were verified using Fourier transform infrared spectroscopy, and the impregnation amount of metallic nickel was also calculated based on the gas amount generated. The specific surface areas of the ACF and Ni-ACFs were determined to be 1010-1180 m2/g, while the nickel impregnation amount was 0.85-5.28 mg/g. The NO removal capacity of the Ni-ACF was found to be enhanced with the addition of Ni catalysts. In addition, metallic nickel particles on the ACFs maintained their chemical molecular structures before and after the NO removal tests.a.

Understanding structure-performance relationships of CoOx/CeO2 catalysts for NO catalytic oxidation: Facet tailoring and bimetallic interface designing

Crystalline structure and bimetallic interaction of metal oxides are essential factors to determine the catalytic activity. Herein, three different CoO_x/CeO₂ catalysts, employing CeO₂ nanorods (predominately exposed {110 facet), CeO₂ nanopolyhedra ({111} facet) and CeO₂ nanocubes ({100} facet) as the supports, are successfully prepared for investigating the effect of exposed crystal facets and bimetallic interface interaction on NO oxidation. In comparison with the {111} and {100} facets, the exposed crystal facet {110} exists the best superiority to anchor and stabilize Co species. Moreover, ultra-small CoO_x clusters composed of strong Co-O coordination shells with minor Co-O-Ce interaction are formed and uniformly dispersed on the CeO₂ nanorods. Structural characterizations reveal that the active exposed crystal facet {110} and the strong bimetallic interface interaction in CoO_x/CeO₂-nanorods (R-CC) result in more structural defect, endowing it with abundant oxygen vacancies, excellent reducibility and strong adsorption capacity. The DRIFTs spectra further indicate that the exposed crystal facet {110} has a significant promoting effect on the strength of nitrates compared with {111} and {100} facets. The bimetallic interface interaction not only significantly facilitates the formation of nitrate species at lower temperature, but also effectively suppresses the generation of sulfate and lower the sulphation rate. Therefore, R-CC catalyst exhibits the maximum NO oxidation activity with the conversion of 86.4 % at 300 °C and still sustains its high activity under cyclic condition or 50 ppm SO₂. The provided crystalline structure and interaction-enhanced strategy sheds light on the design of high-activity NO oxidation catalysts.

NO Selective Catalytic Reduction over Atom-Pair Active Sites Accelerated via In Situ NO Oxidation

Selective catalytic reduction (SCR) of NO_x with NH₃ is the most efficient technology for NO_x emissions control, but the activity of catalysts decreases exponentially with the decrease in reaction temperature, hindering the application of the technology in low-temperature SCR to treat industrial stack gases. Here, we present an industrially practicable technology to significantly enhance the SCR activity at low temperatures (<250 °C). By introducing an appropriate amount of O₃ into the simulated stack gas, we find that O₃ can stoichiometrically oxidize NO to generate NO₂, which enables NO reduction to follow the fast SCR mechanism so as to accelerate SCR at low temperatures, and, in particular, an increase in SCR rate by more than four times is observed over atom-pair V₁-W₁ active sites supported on TiO₂(001) at 200 °C. Using operando SCR tests and in situ diffuse reflectance infrared Fourier transform spectra, we reveal that the introduction of O₃ allows SCR to proceed along a NH₄NO₃-mediated Langmuir-Hinshelwood model, in which the adsorbed nitrate species speed up the re-oxidation of the catalytic sites that is the rate-limiting step of SCR, thus leading to the enhancement of activity at low temperatures. This technology could be applicable in the real stack gas conditions because O₃ exclusively oxidizes NO even in the co-presence of SO₂ and H₂O, which provides a general strategy to improve low-temperature SCR efficacy from another perspective beyond designing catalysts.

Removal of NO at low concentrations from polluted air in semi-closed environments by activated biochars from renewables feedstocks

Efficient measures are urgently required in large cities for nitric oxide (NO) elimination from air in urban semi-closed environments (parking lots and tunnels), characterized by low NO concentrations (<10 ppmv) and temperatures. One of the most promising abatement alternatives is the NO oxidation to NO₂, which can be further easily captured in an alkali solution or over a porous solid. However, most of the research devoted to this topic is focused on the elimination of NO from fuel exhaust gases, with high NO concentrations (400-2000 ppmv). In this work, sustainable and low-cost activated biochars of different origin and having very different ash contents were employed in NO removal at very low concentrations. Thus, low ash content forestry (oak woodchips, OAK) and high ash content from agriculture (oilseed rape straw, OSR) biochars were subjected to physical activation with CO₂ at 900 °C (OAK550-A900CO₂ and OSR700-A900CO₂, respectively). The NO removal performance tests of such activated carbons were carried out at different experimental conditions: i.e., temperature, relative humidity (0-50 vol% RH), NO-containing gas (N₂ or air), amount of activated carbon, and NO concentration, to assess how the activated biochar properties influence their NO removal capacity. The sample OSR700-A900CO₂ contained a higher population of oxygen surface functionalities, which might play an important role in the NO removal efficiency in dry conditions since they could assist NO oxidation on carbon active sites when used above room temperature (50-75 °C). However, at room temperature (25 °C), the presence of narrow micropore size distribution at 6 Å became a more relevant property, since it facilitates an intimate contact between NO and O₂. Accordingly, the activated biochar from OAK was much more efficient, achieving complete removal of NO from air flow (dry or with 50 vol% RH) at 25 °C during 400 min of testing, making it an ideal candidate as biofilter for purifying air streams of semi-closed spaces contaminated with low concentrations of NO.

Investigation on low energy-consumed embedded selective catalytic reduction technology for pelletizing flue gas and the CO2 emission reduction assessment

Based on the unique technique property of grate-kiln pellet production process and its demand of ultra-low emission of NO_x, a low energy-consumed embedded selective catalytic reduction (SCR) denitration technology was proposed. The temperature of the NO_x-containing tributary flue gas was 350-500 °C, which basically accorded with the temperature range of SCR by V₂O₅-based catalyst. Considering the potential inhibition effect of high SO₂ concentration (8000-10000 mg/m³) and metal-containing dust in the pelletizing flue gas, the catalyst compositions were optimized to V₂O₅ (0.5%) and WO₃ (5%), giving NO conversion over 90% with low yield of N₂O by-product. Compared with the low-medium temperature SCR technology, it was no longer necessary to reheat the flue gas, showing a remarkable CO₂ emission reduction effect. The CO₂ emission reduction ratios were 94% and 66% contributed by the decrease of fuel and electricity consumption for the embedded SCR technology, respectively. The operating cost was also greatly reduced from 11.4 CNY/t-pellet to 3.1 CNY/t-pellet (Chinese Yuan).

Single Ru(II) Ions on Ceria as a Highly Active Catalyst for Abatement of NO

Atom trapping leads to catalysts with atomically dispersed Ru₁O₅ sites on (100) facets of ceria, as identified by spectroscopy and DFT calculations. This is a new class of ceria-based materials with Ru properties drastically different from the known M/ceria materials. They show excellent activity in catalytic NO oxidation, a critical step that requires use of large loadings of expensive noble metals in diesel aftertreatment systems. Ru₁/CeO₂ is stable during continuous cycling, ramping, and cooling as well as the presence of moisture. Furthermore, Ru₁/CeO₂ shows very high NO_x storage properties due to formation of stable Ru-NO complexes as well as a high spill-over rate of NO_x onto CeO₂. Only ∼0.05 wt % of Ru is required for excellent NO_x storage. Ru₁O₅ sites exhibit much higher stability during calcination in air/steam up to 750 °C in contrast to RuO₂ nanoparticles. We clarify the location of Ru(II) ions on the ceria surface and experimentally identify the mechanism of NO storage and oxidation using DFT calculations and in situ DRIFTS/mass spectroscopy. Moreover, we show excellent reactivity of Ru₁/CeO₂ for NO reduction by CO at low temperatures: only 0.1-0.5 wt % of Ru is sufficient to achieve high activity. Modulation-excitation in situ infrared and XPS measurements reveal the individual elementary steps of NO reduction by CO on an atomically dispersed Ru ceria catalyst, highlighting unique properties of Ru₁/CeO₂ and its propensity to form oxygen vacancies/Ce⁺³ sites that are critical for NO reduction, even at low Ru loadings. Our study highlights the applicability of novel ceria-based single-atom catalysts to NO and CO abatement.

Supported Mn2O3-based catalysts for NO-SCO: an experimental study

In this paper, the NO-SCO (the selective catalytic oxidation of NO) experiments of single-phase Mn₂O₃, supported Mn₂O₃/Al₂O₃, and the Ce-doped Mn_xCe_y/Al catalyst system were carried out. The physical and chemical properties of the catalysts were analyzed by XRD, BET, XPS, SEM, O₂-TPD, and H₂-TPR. The effects of loading and Ce doping on catalyst activity were studied. The results show that the Mn₂O₃ catalyst exhibited the best activity at 300 ℃, and the NO conversion rate of Mn₂O₃ was 78.2%. The relative content of O_α adsorbed on the surface of the Mn_x/Al catalyst decreased obviously by loading Mn₂O₃ on γ-Al₂O₃, which led to the decrease in catalyst activity. And the temperature window moved to the high-temperature region. After doping Ce, the dispersion of Mn enhanced, and the relative content of oxygen O_α adsorbed on the surface increased. The low-temperature activity and fluidity of oxygen in catalysts were improved. Among them, the Mn_0.2Ce_0.08/Al catalyst obtained a high specific surface area, good pore structure, large oxygen storage capacity, and excellent surface oxygen species. The corresponding NO conversion rate reached 83.5% at 290 ℃. Then, the effects of operating parameters such as space velocity, NO concentration, and O₂ content on the catalytic activity of Mn_0.2Ce_0.08/Al were discussed. The experimental results show that the NO conversion rate of Mn_0.2Ce_0.08/Al decreased with increasing NO concentration and space velocity. The O₂ content had a positive effect on the catalytic activity of the catalyst. However, the NO conversion rate tended to be stable due to the saturation of oxygen adsorbed on the catalyst. Through cycling experiments, we found that Mn₂O₃, Mn_0.2/Al, and Mn_0.2Ce_0.08/Al catalysts showed good oxidation stabilities for NO oxidation. The evaluation of the water and sulfur resistance of the catalyst shows that the toxicity of SO₂ was reduced by the aqueous atmosphere to a certain extent. Through the structural optimization of the basic model and the calculation of the NO-SCO reaction path, the results show that the NO-SCO reaction on the Mn₂O₃ (110) face followed the ER mechanism more. For the Mn₂O₃/Al₂O₃ (110) surface, the LH-MvK hybrid mechanism can greatly reduce the desorption energy barrier of the reaction intermediates, which is more favorable for the NO-SCO reaction. The catalytic mechanisms of the Mn_xCe_y/Al catalysts require further in-depth research.

Nitrogen atom coordination tuned transition metal catalysts for NO oxidation and reduction

Developing an efficient catalyst for NO oxidation and reduction at ambient temperature is a significant challenge. Recent studies have suggested that the N-coordinated transition metal (TM) single atom catalysts (SACs) have high catalytic activity and stability. Herein, we report the activation potential of a series of 3d TM atoms supported on N coordination-tuned graphene (GR) for NO oxidation and reduction. The results show that the N coordination pattern can greatly alter the catalytic reactivity of TM on the catalysts, and the TM atom on the catalysts with three-coordinated pyridinic nitrogen TM-N₃@GR exhibit the strongest chemical activity. Among the TM-N₃@GR catalysts, Ti-N₃@GR is the most promising candidate. The rate constants and equilibrium constants were calculated to evaluate the kinetic and thermodynamic feasibility of the catalytic reaction, respectively. Our results demonstrate that the reduction of NO to N₂ on Ti-N₃@GR can occur at ambient temperature with a large exotherm of 6.99 eV, and the oxidation of NO to NO₂ on Ti-N₃@GR can easily proceed when the temperature reaches 360 K with a large equilibrium constant. Our studies are of great significance for understanding the performance of N coordination-tuned catalysts and designing Ti-based catalysts for NO oxidation and reduction.

Recent Advances in Vehicle Exhaust Treatment with Photocatalytic Technology

Vehicle exhaust has been acknowledged as an essential factor affecting human health due to the extensive use of cars. Its main components include volatile organic compounds (VOCs) and nitrogen oxides (NOx), which can cause acute irritation and chronic diseases, and significant research on the treatment of vehicle exhaust has received increasing attention in recent decades. Recently, photocatalytic technology has been considered a practical approach for eliminating vehicle emissions. This review highlights the crucial role of photocatalytic technology in eliminating vehicle emissions using semiconductor catalysts. A particular emphasis has been placed on various photocatalytic materials, such as TiO2-based materials, Bi-based materials, and Metal–Organic Frameworks (MOFs), and their recent advances in the performance of VOC and NOx photodegradation. In addition, the applications of photocatalytic technology for the elimination of vehicle exhaust are presented (including photocatalysts combined with pavement surfaces, making photocatalysts into architectural coatings and photoreactors), which will offer a promising strategy for photocatalytic technology to remove vehicle exhaust.

Interactions of Nitric Oxide Molecules with Pure and Oxidized Silver ClustersAgn{plus minus}/AgnO{plus minus} (n=11-13). A Computational Study

In this work we studied, within DFT, the interaction of NO with pure and oxidized Agn, both anionic and cationic, composed from11 to 13 Ag atoms. In that size interval, shell closing effects are not expected, and structural and electronic odd-even effects will determine the strength of interaction. We obtained that species Agn{plus minus} and AgnO{plus minus} with odd number of electrons (n=12) adsorb NO with higher energy than their neighbours. This result agrees with the facts observed in recent mass spectroscopy measurements, which were performed at finite temperature. The adsorption energy is about twice for oxidized clusters compared to pure ones, and higher for anions than for cations. The adsorption of another NO molecule on AgnNO{plus minus} forms Agn(NO)2{plus minus}, with the dimer (NO)2 in cis configuration, and binding the two N atoms with two neigbour Ag atoms. The n=12 show the higher adsorption energy again. In absence of reaction barriers, Agn(NO)2{plus minus} dissociate spontaneously into AgnO{plus minus} and N2O, except the n= 12 anion. The máximum high barrier along the dissociation path of Ag13(NO)2- is about 0.7 eV. Further analysis of PDOS for Ag11-13 (NO)x{plus minus} (x=0,1,2) molecules shows that bonding between NO and Agn mainly occurs in the range between -3.0 eV and 3.0 eV. The overlap between 4 d of Ag and 2 p of N and O is larger for Ag12(NO)2{plus minus} than for neighbour sizes. For n=12, the d bands are close to the (NO)2 2π orbital, leading to extra back-donation charge from the 4 d of Ag to the closer 2π orbital of (NO)2.

Advances in Designing Efficient La-Based Perovskites for the NOx Storage and Reduction Process

To overcome the inherent challenge of NOx reduction in the net oxidizing environment of diesel engine exhaust, the NOx storage and reduction (NSR) concept was proposed in 1995, soon developed and commercialized as a promising DeNOx technique over the past two decades. Years of practice suggest that it is a tailor-made technique for light-duty diesel vehicles, with the advantage of being space saving, cost effective, and efficient in NOx abatement; however, the over-reliance of NSR catalysts on high loadings of Pt has always been the bottleneck for its wide application. There remains fervent interest in searching for efficient, economical, and durable alternatives. To date, La-based perovskites are the most explored promising candidate, showing prominent structural and thermal stability and redox property. The perovskite-type oxide structure enables the coupling of redox and storage centers with homogeneous distribution, which maximizes the contact area for NOx spillover and contributes to efficient NOx storage and reduction. Moreover, the wide range of possible cationic substitutions in perovskite generates great flexibility, yielding various formulations with interesting features desirable for the NSR process. Herein, this review provides an overview of the features and performances of La-based perovskite in NO oxidation, NOx storage, and NOx reduction, and in this way comprehensively evaluates its potential to substitute Pt and further improve the DeNOx efficiency of the current NSR catalyst. The fundamental structure–property relationships are summarized and highlighted to instruct rational catalyst design. The critical research needs and essential aspects in catalyst design, including poisoner resistance and catalyst sustainability, are finally addressed to inspire the future development of perovskite material for practical application.

Reducibility Studies of Ceria, Ce0.85Zr0.15O2 (CZ) and Au/CZ Catalysts after Alkali Ion Doping: Impact on Activity in Oxidation of NO and CO

The aim of these studies was to perform thorough research on the influence of alkali metal ions (Li, Na, K and Cs) on the properties of nanogold catalysts supported on ceria–zirconia. The addition of alkali metal ions onto CeO2 further affected the reducibility, which was not noted for the Zr-doped support (Ce0.85Zr0.15O2). Despite the substantial impact of alkali metal ions on the reducibility of ceria, the activity in CO oxidation did not change much. In contrast, they do not have a large effect on the reducibility of Au/CZ but suppressed the activity of this system in CO oxidation. The results show that for CO oxidation, the negative effect of potassium ions is greater than that of sodium, which corresponds to the shift in the Tmax of the reduction peak towards higher temperatures. The negative effect of Li+ and Cs+ spans 50% CO conversion. The negative effect was visible for CO oxidation in both the model stream and the complex stream, which also contained hydrocarbons and NO. In the case of NO oxidation to NO2, two temperature regimes were observed for Au + 0.3 at% K/CZ, namely in the temperature range below 350 °C; the effect of potassium ions was beneficial for NO oxidation, whereas at higher temperatures, the undoped gold catalyst produced more NO2.

A Sulfur-Tolerant MOF-Based Single-Atom Fe Catalyst for Efficient Oxidation of NO and Hg0

Catalytic oxidation of NO and Hg⁰ is a crucial step to eliminate multiple pollutants from emissions from coal-fired power plants. However, traditional catalysts exhibit low catalytic activity and poor sulfur resistance due to low activation ability and poor adsorption selectivity. Herein, a single-atom Fe decorated N-doped carbon catalyst (Fe₁ -N₄ -C), with abundant Fe₁ -N₄ sites, based on a Fe-doped metal-organic framework is developed to oxidize NO and Hg⁰ . The results demonstrate that the Fe₁ -N₄ -C has ultrahigh catalytic activity for oxidizing NO and Hg⁰ at low and room temperature. More importantly, Fe₁ -N₄ -C exhibits robust sulfur resistance as it preferably adsorbs reactants over sulfur oxides, which has never been achieved before with traditional catalysts. Furthermore, SO₂ boosts the catalytic oxidation of NO over Fe₁ -N₄ -C through accelerating the circulation of active sites. Density functional theory calculations reveal that the Fe₁ -N₄ active sites result in a low energy barrier and high adsorption selectivity, providing detailed molecular-level understanding for its excellent catalytic performance. This is the first report on NO and Hg⁰ oxidation over single-atom catalysts with strong sulfur tolerance. The outcomes demonstrate that single-atom catalysts are promising candidates for catalytic oxidation of NO and Hg⁰ enabling cleaner coal-fired power plant operations.

Dopant-driven tuning of toluene oxidation and sulfur resistance at the B-site of LaCo1−xMxO3 (M = Fe, Cr, Cu) perovskites

The optimization effect of Fe dopant on toluene oxidation and sulfur resistance is better than that of Cr and Cu dopants.

Structure Sensitivity and Hydration Effects in Pt/TiO2 and Pt/TiO2–SiO2 Catalysts for NO and Propane Oxidation

The NO and propane oxidation activities of a series of 1%Pt/TiO2–SiO2 catalysts show different underlying trends as the support composition changes. Surface characterisation of the catalysts indicates that the trend for NO conversion is consistent with the oxidation rate being dependent on the degree of metallic character of the Pt nanoparticles, rather than their morphology. Although a similar correlation is expected for the total oxidation of propane, it is masked by the effects of adventitious ions originating during manufacture of the support materials. When residual chloride is present in the support, most of the exposed Pt is stabilised in its low-activity ionic form; while support materials containing W or oxidised-S ions give rise to catalysts with much higher activity than expected from their measured Pt0 content. When a Cl-containing, but SiO2-free, TiO2 support material is pre-treated hydrothermally, the propane-oxidation activity of the resultant Pt/TiO2 catalyst is substantially improved, so that it matches the performance of highly-metallic Pt supported on TiO2 containing 16 wt% SiO2. The hydrothermal pre-treatment removes residual chloride from the support material, but it also leaves the catalyst in a hydrated state. We show that, by controlling the metallic content of Pt nanoparticles, understanding the promoting and inhibiting effects of adventitious ions, and optimising the degree of catalyst hydration, the activity of 1%Pt/TiO2–SiO2 catalysts can be made to exceed that of a benchmark 2%Pt/γ-Al2O3 formulation for both NO and propane oxidation.

Biological nitrogen removal from stormwater in bioretention cells: a critical review

Excess nitrogen in stormwater degrades surface water quality via eutrophication and related processes. Bioretention has been recognized as a highly effective low-impact development (LID) technology for the management of high runoff volumes and reduction of nitrogen (N) pollutants through various mechanisms. This paper provides a comprehensive and critical review of recent developments on the biological N removal processes occurring in bioretention systems. The key plant- and microbe-mediated N transformation processes include assimilation (N uptake by plants and microbes), nitrification, denitrification, and anammox (anaerobic ammonia oxidation), but denitrification is the major pathway of permanent N removal. Overall, both laboratory- and field-scale bioretention systems have demonstrated promising N removal performance (TN: >70%). The phyla Bacteroidetes and Proteobacteria are the most abundant microbial communities found to be enriched in biofilter media. Furthermore, the denitrifying communities contain several functional genes (e.g., nirK/nirS, and nosZ), and their concentrations increase near the surface of media depth. The N removal effectiveness of bioretention systems is largely impacted by the hydraulics and environmental factors. When a bioretention system operates at: low hydraulic/N loading rate, containing a saturation zone, vegetated with native plants, having deeper and multilayer biofilter media with warm climate temperature and wet storm events periods, the N removal efficiency can be high. This review highlights shortcomings and current knowledge gaps in the area of total nitrogen removal using bioretention systems, as well as identifies future research directions on this topic.

Cometabolism of 17α-ethynylestradiol by nitrifying bacteria depends on reducing power availability and leads to elevated nitric oxide formation

17α-ethynylestradiol (EE2) is a priority emerging contaminant (EC) in diverse environments that can be cometabolized by ammonia oxidizing bacteria (AOB). However, its transformation kinetics and the underlying molecular mechanism are unclear. In this study, kinetic parameters, including maximum specific EE2 transformation rate, EE2 half-saturation coefficient, and EE2transformation capacity of AOBwere obtained by using the model AOB strain, Nitrosomonas europaea 19718. The relationship between EE2 cometabolism and ammonia oxidation was divided into three phases according to reducing power availability, namely "activation", "coupling", and "saturation". Specifically, there was a universal lag of EE2 transformation after ammonia oxidation was initiated, suggesting that sufficient reducing power (approximately 0.95 ± 0.06 mol NADH/L) was required to activate EE2 cometabolism. Interestingly, nitric oxide emission increased by 12 ± 2% during EE2 cometabolism, along with significantly upregulated nirK cluster genes. The findings are of importance to understanding the cometabolic behavior and mechanism of EE2 in natural and engineered environments. Maintaining relatively high and stable reducing power supply from ammonia oxidation can potentially improve the cometabolic removal of EE2 and other ECs during wastewater nitrification processes.

Life Cycle Assessment of Nitrogen Circular Economy-Based NOx Treatment Technology

Humans are significantly perturbing the global nitrogen cycle, leading to excess reactive nitrogen in the environment. Nitrogen oxides as a key reactive nitrogen species are mainly controlled by selective non-catalytic reduction and selective catalytic reduction. Converting nitrogen oxides to ammonia, defined as ReNOx, emerges as an alternative method under a disparate design concept. However, little is known about its overall environmental performance. In this study, we conducted for the first time a life cycle assessment of ReNOx. Compared with the eco-index in the condition of 200 °C with a conversion rate of 95%, it would increase substantially in the condition of 160 °C with a conversion rate of 80% and in the case without a sound NH3 treatment. Feedstock format change, adsorption material performance deterioration, and recovery rate decline would increase the eco-index by 8%, 12%, and 18%, respectively. The eco-index was decreased by 31% in the optimized scenario with a renewable energy source and an increased conversion rate. The environmental impacts were compared with traditional methods at impact, damage, and eco-index levels. Finally, the implications on process arrangement in the flue gas system, the externality for power generation, and the contribution to the nitrogen circular economy were examined. The results can serve as a reference for its developers to improve the technology from the environmental perspective.

Pulsed Laser in Liquids Made Nanomaterials for Catalysis

Catalysis is essential to modern life and has a huge economic impact. The development of new catalysts critically depends on synthetic methods that enable the preparation of tailored nanomaterials. Pulsed laser in liquids synthesis can produce uniform, multicomponent, nonequilibrium nanomaterials with independently and precisely controlled properties, such as size, composition, morphology, defect density, and atomistic structure within the nanoparticle and at its surface. We cover the fundamentals, unique advantages, challenges, and experimental solutions of this powerful technique and review the state-of-the-art of laser-made electrocatalysts for water oxidation, oxygen reduction, hydrogen evolution, nitrogen reduction, carbon dioxide reduction, and organic oxidations, followed by laser-made nanomaterials for light-driven catalytic processes and heterogeneous catalysis of thermochemical processes. We also highlight laser-synthesized nanomaterials for which proposed catalytic applications exist. This review provides a practical guide to how the catalysis community can capitalize on pulsed laser in liquids synthesis to advance catalyst development, by leveraging the synergies of two fields of intensive research.

Review on the NO removal from flue gas by oxidation methods

Due to the increasingly strict emission standards of NOx on various industries, many traditional flue gas treatment methods have been gradually improved. Except for selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) methods to remove NOx from flue gas, theoxidation method is paying more attention to NOx removal now because of the potential to simultaneously remove multiple pollutants from flue gas. This paper summarizes the efficiency, reaction conditions, effect factors, and reaction mechanism of NO oxidation from the aspects of liquid-phase oxidation, gas-phase oxidation, plasma technology, and catalytic oxidation. The effects of free radicals and active components of catalysts on NO oxidation and the combination of various oxidation methods are discussed in detail. The advantages and disadvantages of different oxidation methods are summarized, and the suggestions for future research on NO oxidation are put forward at the end. The review on the NO removal by oxidation methods can provide new ideas for future studies on the NO removal from flue gas.

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO3-δ and Sr3Fe2O7-δ Perovskites

The Ruddlesden-Popper (RP)-type layered perovskite is a candidate material for a new nitrogen oxide (NO_x) storage catalyst. Here, we investigate the adsorption and oxidation of NO_x on the (001) surfaces of RP-type oxide Sr₃Fe₂O_7-δ for all of the terminations by comparing to those of simple perovskite SrFeO_3-δ by the density functional theory (DFT) calculations. The possible (001) cleavages of Sr₃Fe₂O₇ generate two FeO₂- and three SrO-terminated surfaces, and the calculated surface energies indicated that the SrO-terminated surface generated by the cleavage at the rock salt layer is the most stable one. The oxygen of the FeO₂-terminated surfaces could be removed with significantly low energy because the process involves the favorable reduction of the Fe⁴⁺ site. Consequently, the surface oxygen at the FeO₂ site could easily oxidize adsorbed NO to NO₂ by the Mars-van Krevelen mechanism. The resulting oxygen vacancy in the surface would be filled easily with lattice oxygen in bulk. The oxidation of NO with adsorbed molecular O₂ was unfavorable by both the Langmuir-Hinshelwood and Eley-Rideal mechanisms because this process does not involve the reduction of the Fe⁴⁺ site. The oxygen of the SrO-terminated surfaces was tightly bound and acted as the adsorption site of NO and NO₂. An electron transfer strengthened the NO_x binding to the surface by forming nitrite (NO₂^-) or nitrate (NO₃^-) species. The DFT calculations revealed that the RP-type structure promoted NO_x oxidation and storage properties by forming active oxygen due to the Jahn-Teller distortion and by exposing SrO-terminated surfaces due to the cleavage at the rock salt layer.

Recent advances in selective catalytic oxidation of nitric oxide (NO-SCO) in emissions with excess oxygen: a review on catalysts and mechanisms

Nitric oxides (NO_x, which mainly include more than 90% NO) are one of the major air pollutants leading to a series of environmental problems, such as acid rain, haze, photochemical smog, etc. The selective catalytic oxidation of NO to NO₂ (NO-SCO) is regarded as a key process for the development of selective catalytic reduction of NO_x by ammonia (via fast selective catalytic reduction reaction) and also the simultaneous removal of multipollutant (pre-oxidation and post-absorption). Until now, scholars have developed various types of NO-SCO catalysts, dividing the main groups into noble metals (Pt, Pd, Ru, etc.), metal oxides (Mn-, Co-, Cr-, Ce-based, etc.), perovskite-type oxides (LaMnO₃, LaCoO₃, LaCeCoO₃, etc.), carbon materials (activated carbon, carbon fiber, carbon nanotube, graphene, etc.), and zeolites (ion-exchanged ZSM-5, CHA, SAPO, MCM-41, etc.) in this review. This paper summarizes the recent progress of the above typical catalysts and mostly analyzes the catalytic performance for NO oxidation in terms of the H₂O and/or SO₂ resistances and also the influencing factors, and their reaction mechanisms are described in detail. Finally, this review points out the key problems and possible solutions of the current researches and presents the application prospects and future development directions of NO-SCO technology using the above typical catalysts.

Efficient Conversion of NO to NO2 on SO2-Aged MgO under Atmospheric Conditions

The NO-NO₂ cycle determines the formation of O₃ and hence plays a critical role in the oxidizing capacity of troposphere. Traditional view concluded that the heterogeneous oxidation of NO to NO₂ was negligible due to the weak reactivity of NO on aerosols, compared to the homogeneous oxidation process. However, the results here reported for the first time that SO₂ can greatly promote the heterogeneous transformation of NO into NO₂ and HONO on MgO particles under ambient conditions. The uptake coefficients of NO were increased by 2-3 orders of magnitudes on SO₂-aged MgO, compared to the fresh sample. Based on spectroscopic characterization and density functional theory (DFT) calculations, the active sites for the adsorption and oxidation of NO were determined to be sulfates, where an intermediate [SO₄-NO] complex was formed during the adsorption. The decomposition of this species led to the formation of NO₂ and the change of sulfate configuration. The formed NO₂ could further react with surface sulfite to form HONO and sulfate. The conversion of NO to NO₂ and HONO on the SO₂-aged MgO surface under ambient conditions contributes a new formation pathway of NO₂ and HONO and could be quite helpful for understanding the source of atmospheric oxidizing capacity as well as the formation of air pollution complexes in polluted regions such as the northern China.

Low-temperature NO oxidation using lattice oxygen in Fe-site substituted SrFeO3-δ

Improvement of the low-temperature activity for NO oxidation catalysts is a crucial issue to improve the NO_x storage performance in automotive catalysts. We have recently reported that the lattice oxygen species in SrFeO_3-δ (SFO) are reactive in the oxidation of NO to NO₂ at low temperatures. The oxidation of NO using lattice oxygen species is a powerful means to oxidize NO in such kinetically restricted temperature regions. This paper shows that Fe-site substitution of SFO with Mn or Co improves the properties of lattice oxygen such as the temperature and amount of oxygen release/storage, resulting in the enhancement of the activity for NO oxidation in a low-temperature range. In particular, NO oxidation on SrFe_0.8Mn_0.2O_3-δ is found to proceed even at extremely low temperatures <423 K. From oxygen release/storage profiles obtained by temperature-programmed reactions, Co doping into SFO increases the amount of released oxygen owing to the reducibility of the Co species and promotes the phase transformation to the brownmillerite phase. On the other hand, Mn doping does not increase the oxygen release amount and suppresses the phase transformation. However, it significantly decreases the oxygen migration barrier of SFO. Substitution with Mn renders the structure of SFO more robust and maintains the perovskite structure after the release of oxygen. Thus, the oxygen release properties are strongly dependent on the crystal structure change before and after oxygen release from the perovskite structure, which has a significant effect on NO oxidation and the NO_x storage performance.

Sensing Behavior of Two Dimensional Al- and P-Doped WS2 Toward NO, NO2, and SO2: an Ab Initio Study

Two-dimensional transition metal dichalcogenides (2D TMDs), such as WS2, are considered to have the potential for high-performance gas sensors. It is a pity that the interaction between gases and pristine 2D WS2 as the sensitive element is too weak so that the sensor response is difficult to detect. Herein, the sensing capabilities of Al- and P-doped WS2 to NO, NO2, and SO2 were evaluated. Especially, we considered selectivity to target gases and dopant concentration. Molecular models of the adsorption systems were constructed, and density functional theory (DFT) was used to explore the adsorption behaviors of these gases from the perspective of binding energy, band structure, and density of states (DOS). The results suggested that doping atoms could increase the adsorption strength between gas molecules and substrate. Besides, the sensitivity of P-doped WS2 to NO and NO2 was hardly affected by CO2 or H2O. The sensitivity of Al-doped WS2 to NO2 and SO2 was also hard to be affected by CO2 or H2O. For NO detection, the WS2 with 7.4% dopant concentration had better sensitive properties than that with a 3.7% dopant concentration. While for SO2, the result was just the opposite. This work provided a comprehensive reference for choosing appropriate dopants (concentration) into 2D materials for sensing noxious gases.

Heterologous expression and functional study of nitric oxide reductase catalytic reduction peptide from Achromobacter denitrificans strain TB

Biological denitrification is a promising and green technology for air pollution control. To investigate the nitric oxide reductase (NOR) that dominates NO reduction efficiency in biological purification, the heterologous prokaryotic expression system of the norB gene, which encodes the core peptide of the catalytic reduction structure in the NOR from Achromobacter denitrificans strain TB, was constructed in Escherichia coli BL21 (DE3). Results showed that the 1218 bp-long norB gene was expressed at the highest level under 1.0 mM IPTG for 5 h at 30 °C, and the relative expression abundance of norB in recombinant E. coli was increased by 16.6 times compared with that of the wild-type TB. However, the NO reduction efficiency and NOR activity of strain TB was 2.7 and 1.83 times higher than those of recombinant E. coli, respectively. On the basis of genomic reassembly and protein structure modeling, the core peptide of the NOR catalytic reduction structure from Achromobacter sp. TB can independently exert NO reduction. The low NO degradation efficiency of recombinant E. coli may be due to the lack of a NorC-like structure that increases the enzyme activity of the NorB protein. The results of this study can be used as basis for further research on the structure and function of NOR.

Inorganic acids – technology background and future perspectives

The presented chapter deals with technological aspects concerning industrial production of major inorganic chemicals such as sulfuric, nitric and phosphorous acids. The idea was to highlight the main assumptions related to their fabrication as well as to point out novel aspects and perspectives concerning their industry. The main attention will be paid to raw materials and their transformation in order to obtain indirect precursors of inorganic acids – acid anhydrides. Characteristics of the individual stages of synthesis, with a special regard to the process conditions will be also of key importance. The environmental impact of this particular technology will be raised and discussed. Finally, the review over recently published scientific papers, concerning innovative solutions in inorganic acids production, will be performed.

Perovskite-Based Catalysts as Efficient, Durable, and Economical NOx Storage and Reduction Systems

Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO2 emissions than stoichiometric gasoline engines. However, NOx reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NOx storage and reduction (NSR), also known as lean NOx trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NOx emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NOx removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO3) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NOx from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO2 conversion, NOx storage capacity, and NOx reduction efficiency is addressed. Furthermore, the NOx removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al2O3) in the absence and presence of SO2 and H2O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted.