NO Removal Efficiency Research Articles

An integrated biological system for air pollution control in WtE plants and interaction between NO reduction and toluene oxidation

The abatement of NO and VOCs in the flue gas from WtE plants is of great significance for improving the atmospheric environmental quality at present. In this study, a device of absorption-bioreactor coupling biotrickling-filter (ABR-BTF) was built to realize the simultaneous removal of NO and VOCs, in which the chemical absorption-bioreactor (ABR) was used for reducing NO and the biotrickling-filter (BTF) was employed for eliminating toluene. When the simulated flue gas containing 400 mg m−3 NO and 150 mg m−3 toluene passed through the system for 30 s, the removal efficiency of NO and toluene reached 85% and 90%, respectively. In contrast with the single ABR segment, the loss rate of NO complexing absorber was reduced by 85% in ABR-BTF. Meanwhile, a variety of novel bacterial genera in the field of biological denitrification and VOCs elimination were discovered within the integrated system biome. Thereinto, Candidatus_Cloacamonas and Syntrophomonas produced the hydrogen, which could as electron donors be consumed by the dissolved oxygen species during the process of VOCs degradation, promoting the biological reduction and reducing the loss rate of complexing absorbent in the ABR portion. Meanwhile, Tisierella and Desulfitobacterium could reduce sulfite to S2−, so that part of the complexing absorbent was transformed into FeS and re-entered into the circulation system through the redox reaction with Fe(III). The integrated biological purification system can efficiently remove NO and VOCs simultaneously, and overcome the problems of insufficient microbial reduction rate for poor hydrophobic VOCs, which will provide a fundamental for the optimization and industrial application of the biological technology in WtE plants flue gas treatment.

Experimental and mechanism research on the NOx removal by a novel liquid electrode dielectric barrier discharge reactor

Metal electrode corrosion and poor discharge uniformity are the key factors that restrict the discharge lifetime and de-NOx efficiency of a dielectric barrier discharge (DBD) reactor. In order to solve this problem, a novel DBD reactor with homothermic sodium chloride (NaCl) solution as grounded electrode was designed in this paper. The effects of NaCl solution conductivity on the electrical parameters, the de-NOx performance and the optical emission spectrum characteristics of DBD were studied experimentally. The pathways and mechanism of de-NOx in the whole discharge phase were revealed by numerical simulation, electron impact mechanism and chemical reactions sensitivity analysis. The results showed that the best discharge intensity, uniformity, energy consumption and de-NOx performance were achieved at 32mS/cm of NaCl solution conductivity. The removal efficiency of NO, NO2 and NOx reached close to 100%, 97.4% and 83.9% respectively. The numerical simulation showed that the de-NOx process of DBD could be divided into 3 phases, including the rapid removal phase of NO (0–0.05 s), the removal phase of NO and NO2 (0.05–0.7 s), and the stabilization phase of NOx (0.7–1 s). In terms of de-NOx mechanism, the active particles of N atoms, N(2D) atoms and O atoms dissociated from exhaust gas played key roles in the de-NOx process. The N atoms mainly reduced NO to pure N2, and the selectivity of N2 could reach up to 13.6%. The N(2D) atoms were the only radicals that formed extra NO. The O atoms contributed greatly with NO2 re-conversion to NO. This work is of great significance to promote the removal of NOx from ship exhaust gas by the DBD with liquid electrode.

Insights into samarium doping effects on catalytic activity and SO2 tolerance of MnFeOx catalyst for low-temperature NH3-SCR reaction

The development of catalysts with high NH3-SCR activity in the presence of SO2 was urgent for non-electric industries to control NOx emission at low temperature. Herein, a series of Sm-doping MnFeOx catalysts were synthesized through a typical PEG-assisted co-precipitation method and applied for low-temperature NH3-SCR process. SmMnFe-0.1 catalyst significantly broadened the activation temperature window and yielded almost 100% NO conversion from 75 to 200 °C, simultaneously, the NO removal efficiency still maintained at about 90% in the presence of SO2 and H2O. The characterization results confirmed that Sm could optimize the dispersity of active components and enlarge the surface area of catalyst. Furthermore, strong interaction among active ions facilitated more oxygen vacancies and accelerated NO oxidizing to NO2, further cooperating with abundant adsorbed NH3, leading to cause “Fast SCR” reaction. Both catalysts were dominated by the E-R mechanism despite MnFeOx catalyst also obeyed the L-H pathway. Particularly, the intense redox circles between Sm and Mn inhibited the electron transferring from SO2 to Mn ions, and induced Fe species serving as sacrificial sites along with Sm to preferentially react with SO2, resulting in an excellent SO2 tolerance, and the possible mechanism model was proposed.

Enhanced adsorption of NO onto activated carbon by gas pre-magnetization

The NO removal efficiency was relatively low in the traditional activated carbon adsorption process. In this work, a gas pre-magnetization and activated carbon adsorption process was developed to enhance the adsorption of NO onto activated carbon. In this innovative and green process, the mixed gas was magnetized in the external magnetic field and then absorbed by activated carbon. The results indicated that the maximal removal rate of NO could be increased from 75.0% to 89.5%, and the NO adsorption capacity of commercial activated carbon in one hour elevated from 2.28 to 2.60 mg/g when the magnetic induction intensity of external magnetic field increased from 0 T to 2 T. The strengthening mechanism of the gas pre-magnetization was investigated. It was found that magnetic field could elevate the oxidation rate of NO by 11.4% and thus promote the physical adsorption of NO onto activated carbon. External magnetic field could increase the reaction activity of NO and promote the chemical reaction between NO and some functional groups (CO, CO and COOH) on the activated carbon and thus promote the chemisorption process of NO.

A novel double metal ions-double oxidants coactivation system for NO and SO2 simultaneous removal

• Novel NO/SO 2 removal technique by a dual ions-dual oxidants system was proposed. • Dual ions-dual oxidants system displays higher free radical yield and removal efficiency. • Oxidation via OH and SO 4 − plays a key role in the pollutant removal. • No by-products are produced in pollutant removal process using this new technique. A novel simultaneous removal technique of NO and SO 2 from simulated flue gas using a double metal ions-double oxidants coactivation system (Cu 2+ /Fe 2+ /Oxone/H 2 O 2 coactivation system) was proposed. Process parameters optimization, products, free radicals and mechanisms of pollutant removal were studied. Results demonstrate that the double metal ions-double oxidants coactivation system achieves far higher free radical yield and pollutant removal efficiency relative to other contrasting systems, which are associated with the redox cycling by double metal ions and the free radical capture intermediate formed between double oxidants. NO removal efficiency is increased with higher concentrations of Oxone and Cu 2+ , and is reduced with increasing inlet contents of NO and SO 2 . Changing operating temperature, reagent pH value or concentrations of Fe 2+ and H 2 O 2 have dual influence on the NO removal efficiency. SO 2 is 100% removed within all studied process parameters. The products of NO and SO 2 removals mainly contain recyclable nitric acid and sulphuric acid after the reaction, and no by-products are found. Oxidation by OH and SO 4 - possesses a crucial role for removing NO, which is the primary pathway of the NO removal.

Integrated on-site collection and off-site analysis of airborne molecular contamination in cleanrooms for integrated circuit manufacturing processes

Both long-term on-site collection and off-site analysis methods were conducted to investigate airborne molecular contaminants (AMCs) in a semiconductor wafer cleanroom. The removal efficiency of SO2 and NO2 for chemical filters on a make-up air unit (MAU) in the cleanroom is approximately 50%, though this value does not meet the removal efficiency mentioned in the GB 36306 standard. The removal efficiencies of SO2, H2S, NO, NO2, NH3, and TVOC were approximately 76.5%, 50.9%, 83.5%, 99.3%, 94.8%, and 97.1% after the fan filter unit (FFU) was equipped with a chemical filter. AMCs mainly include benzene, toluene, ethylbenzene, xylene (BTEX), alkanes and alkenes, though BTEX accounts for 77% of the total. VOC concentrations in cleanrooms fitted with FFU chemical filters and where the process equipment was not in operation were found to be lower than those at domestic residences and slightly higher than those found in commercial aircraft cabin air. The daily average TVOC concentrations were negatively correlated with temperature (R2 = 0.46, p < 0.01) and positively correlated with humidity (R2 = 0.26, p < 0.01). The daily average NH3 concentrations were negatively correlated with T (R2 = 0.19, p < 0.05) and positively correlated with RH (R2 = 0.18, p < 0.01). Dibutyl phthalate (DBP) and dioctyl phthalate/diethylhexyl phthalate (DOP/DEHP) were detected in the new sealing joint strips in the HEPA filters. Phthalates and organophosphates were not detected in the new filter papers.

Role of Sulfite Oxidation in NO2 Absorption in a pH-Neutral Scrubber Solution

Nitrogen dioxide (NO2) absorption in aqueous sulfite solutions has recently gained more attention to reduce NOx emissions. The NO2 removal efficiency is strongly influenced by the competing reactions of NO2 absorption and sulfite oxidation. The present study investigates the role of sulfite oxidation in NO2 absorption at neutral pH. The effects of sulfite concentration, thiosulfate, pH, NO2 inlet concentration, oxygen concentration on NO2 absorption efficiency, and sulfite oxidation rates were investigated under well-controlled conditions at 25 °C in a laboratory-scale wet scrubbing system. NO2 absorption rates showed a strong dependence on the sulfite concentration and increased linearly with increasing NO2 inlet concentrations between 25 and 150 ppm. At the highest investigated sulfite concentration, 20 mM, the NO2 removal efficiency was around 80%. Oxidation rates of sulfite during NO2 absorption in the presence of 5 vol % O2 increased with increasing sulfite concentrations in the scrubbing solution and ranged from 20 mg·L–1·min–1 with 1 mM sulfite to 200 mg·L–1·min–1 with 20 mM sulfite. The oxidation rate decreased significantly when thiosulfate was added, while the oxidation rates were independent of the oxygen concentration between 2–10 vol % O2. The NO2 absorption rate decreased with decreasing pH between pH 6 and 8 proportionally to the sulfite concentration as predicted by the sulfite–bisulfite equilibrium. The implication from these results is that significantly less sulfite feeding is needed in industrial NO2 absorption if the pH can be maintained at neutral pH, instead of lower pH such as in simultaneous SO2 and NO2 scrubbing.

Oxygen vacancies-modified S-scheme Bi2Ti2O7/CaTiO3 heterojunction for highly efficient photocatalytic NO removal under visible light

Photocatalytic NO removal is limited by many factors, such as high recombination rate of photogenerated charge carriers and secondary pollution caused by incomplete oxidation. Here, S-scheme Bi2Ti2O7/CaTiO3 heterojunction composites with oxygen vacancies were prepared by solvothermal synthesis in conjunction with calcination. After Bi2Ti2O7/CaTiO3 calcined at 600 °C, the photocatalytic NO removal efficiency increases from 58% to 78% under visible light with the lowest production of intermediate NO2, where the initial concentration of NO was diluted to ca. 600 ppb by air stream and the flow rate was controlled at 1 L·min−1. The enhanced photocatalytic performance is attributed to the synergistic effect of S-scheme heterojunction structure and oxygen vacancy as evinced by ESR and XPS analysis. Active species trapping experiments suggest that photogenerated electrons, superoxide ions and holes are the main active species in the photocatalytic NO conversion. This study provides a reference for the design of highly efficient visible-light responsive photocatalyst by construction of S-scheme heterojunction and oxygen vacancy simultaneously.

Nitrogen removal of mine-influenced water in a hybrid bioreactor with floating hook-moss (Warnstorfia fluitans) in cold climate conditions

To remove nitrogen in cold conditions, we studied new nature-based treatment solutions using six pilot-scale reactors. The pilots were woodchip bioreactor (WBR), aquatic floating hook-moss (Warnstorfia fluitans) (MBR), and a combined woodchip and floating hook-moss hybrid unit (HBR) with an improved hydraulic design. The experiment was run in a climate room at temperatures of 10 °C and 5 °C and using mine water from two sites located in northern Finland. Unlike traditional horizontal flow woodchip bioreactors, in this study the hydraulic efficiency was improved from poor (λ = 0.06) in the woodchip bioreactor to satisfactory (λ = 0.51) in the hybrid unit by inserting two inner plates along the water flow and adding floating hook-moss. The hybrid bioreactor revealed the highest capability of nitrogen removal in all inorganic forms at T ≤ 10 °C with a mean HRT of 70.5 h. On average, 30–78 % of dissolved inorganic nitrogen was removed in the hybrid unit, which was 2 and 3 times more than in units consisting only of woodchip or floating hook-moss. The hybrid bioreactor revealed a maximum NO−3-N removal rate of 1.0–5.2 g m−3 d−1 and a 21.8–99.7 % removal efficiency for an average incoming NO−3-N load of 40 g d−1. The maximum NH+4-N removal efficiency of 75.6 and 53 % took place in HBR and MBR, respectively, when the incoming NH+4-N load was 23.6 ± 0.7 g d−1 at 10 °C. Over the 154 days of the experiment, the hybrid unit removed a total of 2.95 kg DIN-N, which was 0.8 kg higher than the sum of the DIN-N mass removed in the individual woodchip (1.7 kg) and moss units (0.55 kg). The nitrogen content of the aquatic moss was higher in the hybrid unit compared to the moss unit, showing a higher contribution of N plant uptake. Overall, our results suggest that combining woodchips and aquatic moss in a hybrid unit with improved hydraulic efficiency using inner walls may enhance nitrogen removal in cold climate conditions.

Fabrication of an FAPbBr3/g-C3N4 heterojunction to enhance NO removal efficiency under visible-light irradiation

The FAPbBr 3 /g-C 3 N 4 heterostructures show excellent photocatalytic activity for NO reduction under visible light irradiation. • An FAPbBr 3 /g-C 3 N 4 heterojunction is a new type of photocatalytic composite. • FAPbBr 3 /g-C 3 N 4 composites show excellent NO removal efficiency under irradiation. • The best removal rate is 58%, which is much higher than that of FAPbBr 3 and g-C 3 N 4 . • The photocatalytic mechanism of Type-II heterojunction for NO removal is discussed. Previously, many methods have been used to reduce NOx pollution. Semiconductor photocatalytic oxidation technology has been widely used among those methods because of its environmental friendliness, high efficiency, and simple implementation. Hybrid halide perovskites with exceptional optical properties prove to be promising photocatalysis material; however, their high surface energy, unpaired bonds, and instability are obstacles to large-scale application. In this work, FAPbBr 3 /g-C 3 N 4 heterostructures were successfully synthesized by growing FAPbBr 3 nanocrystals on 2D g-C 3 N 4 nanosheets. Compared with the pristine elements, FAPbBr 3 /g-C 3 N 4 composites show significant NO removal efficiencies under 600 ppb concentration at room temperature. The high performance could be attributed to the formation of a type-II heterojunction and accelerated the separation and transfer of electrons and holes. Furthermore, cycling experiments and XRD results verify that the FAPbBr 3 /g-C 3 N 4 heterojunction owns good stability. Thus, this work not only shows the great potential prospect of halide perovskite for the photocatalysis field, but also demonstrate its promise in solving energy issues and environment science.

Mechanism of Fuel Gas Denitration on the KOH-Activated Biochar Surface.

Previous experimental studies have found that biochar after KOH activation can significantly improve the efficiency of NO removal, but its mechanism is still unclear. To investigate the reaction mechanism of this denitration reaction, in this study, the aromatic benzene ring structure was used to simulate the surface of biochar, and the reaction process was calculated by density functional theory (DFT). The reaction process on the pristine biochar was simulated for comparison. The results indicated that there were two potential mechanisms for NO removal and had the identical rate-determining step, with an activation energy of 161.5 kJ/mol. Second, the influence by K coadsorbates on the NO reduction mechanism was studied. The adsorption by K atoms does not alter the last reaction step, but it was found to reduce the activation energy of this rate-determining step (to 129.3 kJ/mol). A third type of reaction mechanism was theoretically studied for the situation with both K and OH coadsorbates on the biochar surface. The reaction mechanism changed with an increase in the overall reaction rate by increasing the pre-exponential factor. In summary, the rate-determining activation energy for the heterogeneous NO reduction was found to decrease in the following order: 161.5 kJ/mol (pristine biochar) → 129.3 kJ/mol (activation by K adsorbates) → 125.8 kJ/mol (activation by both K and OH adsorbates); the pre-exponential factor was found to change in the following order: 6.23 × 1014 s-1 (pristine biochar) → 4.86 × 1014 s-1 (activation by K adsorbates) → 8.89 × 1014 s-1 (activation by K and OH adsorbates). Hence, the role by K adsorbates is primarily to reduce the rate-determining activation energy, while the OH group adsorbate increases the number of active sites on the surface of biochar.

Raspberry-like TiO2 hollow spheres consisting of small nanocrystals towards efficient NO removal

Raspberry-like hollow spheres consisting of small TiO2 nanocrystals exhibited excellent photocatalytic activity for the removal of nitrogen oxides.

Study on Air-Purifying Performance of Semi-Flexible Asphalt Samples Coated with Titanium Dioxide Using Different Methods

Titanium dioxide (TiO2) was recently employed to apply onto road surfaces to degrade the harmful compounds from vehicle emissions. However, it remains a challenging task to find a highly compatible pavement type for TiO2 application to achieve durable and efficient air-purifying performance. This study proposed to coat TiO2 particles onto semi-flexible pavement surface and tried to investigate an optimum coating method. Three coating methods, including direct mixing TiO2 (MT) with asphalt mixture, spraying dry TiO2 (ST) coating and water-solution-based TiO2 (WT) coating on semi-flexible pavement surface. To achieve this objective, semi-flexible samples were prepared to evaluate and compare the performances of three coating methods by employing resistance to wearing, NO removal efficiency tests and residual texture depth tests. It was found that the ST method not only provided better NO degrading efficiency but also improved the resistance to wearing than the other two methods.

High-efficiency adsorption of elemental mercury from flue gas by K-intercalated 1T&2H MoS2

Alkali metal K is widely present in the earth's crust (the seventh abundant element), which can improve the activity and stability of the adsorbent. This study explored a simple calcination method, using the intercalation of K ions, successfully partially transformed commercial molybdenum disulfide (2H-MoS2) into 1T-MoS2, and used it for the adsorption of Hg0 in the flue gas. The experimental results showed that when the K ratio was 2:1(MK-3), the removal rate of Hg0 can reach 90.5 in a wide temperature range. Compared with 2H-MoS2, the mercury removal efficiency of MK-3 was increased by about 40%. After long-term and cycles experiments, the mercury removal efficiency of the MK-3 remained largely unchanged. In the simulated flue gas experiment, HCl could promote the mercury removal efficiency of sample MK-3, SO2 had no obvious effect on the mercury removal efficiency of sample MK-3, while SO2 and low concentration NO have no obvious effect on the mercury removal efficiency of the sample. It was found that during the intercalation of K ions, the interlayer spacing of MK-3 increased, and holes and cracks appeared on the base surface, which made it possible for Hg0 to enter the MoS2 interlayer and adsorb, thereby expanded the adsorption space of Hg0. DFT simulations showed that 1T-MoS2 significantly improves the surface activity of the adsorbent, thereby enhancing the stability of the sample to adsorb Hg0. Therefore, K intercalated in MoS2 can provide a promising method to capture Hg0 in coal-fired flue gas.

Enhanced performance and SO2 tolerance of Ce modified TiO2 supported Mn[sbnd]Sm catalyst for synergetic removal of Hg0 and NO from flue gas

By adjusting the redox property and surface acidity/basicity, the Ce modified TiO2 supported MnSm catalyst with high activity and good anti‑sulfur ability was developed for synergetic removal of Hg0 and NO. MnSm/TiCe achieved a simultaneous removal efficiency of NO and Hg0 of 98.7%, 90.4% and 83.7%, 76.8% (with presence of 200 ppm SO2 and 3% H2O) at 200 °C in simulated flue gas, respectively. Characterization results indicated that MnSm/TiCe possessed well-dispersed active components, increased Mn4+concentration and Lewis acid sites and enhanced reducibility and oxygen storage capacity, which were in favor of the catalyst performance. Abundant active nitrogenous species derived from adsorbed NO contributed to Hg0 oxidation. The in-situ DRIFTS experiments manifested that the reaction of gaseous NO with NH2 on Lewis acid sites via Eley-Rideal mechanism was the main route for NH3-SCR. Due to strong basicity, Sm species served as a SO2 trap agent, which protected the Mn active sites against SO2 poisoning and inhibited the formation of sulfates, thus strengthening the SO2 tolerance of catalyst. Regeneration and stability evaluation tests indicated that MnSm/TiCe might be a promising catalyst that can be applied to the simultaneous removal of Hg0 and NO.

Boosted photocatalytic NO removal performance by S-scheme hierarchical composites WO3/Bi4O5Br2 prepared through a facile ball-milling protocol

• Composites WO 3 /Bi 4 O 5 Br 2 were constructed via a facile ball-milling protocol. • The structure-effect relationship was successfully established. • These binary composites showed enhanced photocatalytic NO removal efficiencies. • A plausible S-scheme model was speculated in photocatalysis mechanism. It is crucial to develop an efficient system of high photocatalytic capability over NO removal and simultaneous avoidance of toxic NO 2 formation. In this study a serious of hierarchical composites WO 3 /Bi 4 O 5 Br 2 (WB) were successfully fabricated by a facile ball-milling protocol and systematically characterized by various analytical techniques. Both expected ingredients were realized and coexisted in composites to generate heterojunction structures by microstructural analyses. Under visible light irradiation, these samples were exposed to photocatalytic removal of NO measurements, where aforementioned binary hierarchical WB composites showed reinforced NO removal efficiency with the high selectivity for NO 3 – /NO 2 – species in comparison to bare WO 3 and Bi 4 O 5 Br 2 , mainly associating to the efficient migration and spatial segregation of charge carries through heterojunction domains with suitable phase composition instead of the slightly varied visible light absorption and specific surface area. In addition, a possible photocatalysis mechanism was deduced in a S-scheme model by active species determination and band structures estimation of these robust catalysts. This investigation shed light on the facile fabrication of hierarchical composites via the ball-milling treatment with enhanced photocatalytic removal of low concentration NO in ppb level under visible light.

Acid treatment of ZrO2-supported CeO2 catalysts for NH3-SCR of NO: Influence on surface acidity and reaction mechanism

BackgroundDue to excellent oxygen storage capacity and redox ability, Ce-based catalysts are usually considered as one of the promising candidates of traditional V-based catalysts for NH3-SCR of NO. However, surface acidity of Ce-based catalysts is often insufficient which restrains their SCR performance to some extent. MethodsHerein, ZrO2-supported CeO2 catalysts were prepared by precipitation and wet impregnation methods. Aiming to promote catalyst surface acidity, a novel method was proposed to pre-treat ZrO2 support with various acids (HCl, HNO3, H3PO4 and H2SO4) via impregnation process. and the effects of acid treatment on SCR performance of CeO2/ZrO2 catalysts had been investigated. Significant findingsIt was worthy to note that H2SO4-treated CeO2/ZrO2 catalyst exhibited a superior NO removal efficiency which was higher than 94% in a wide temperature range of 248–500 °C. NH3-TPD results revealed that the surface acidities acidity of CeO2/ZrO2 catalysts had been obviously enhanced after acid treatment with HNO3, H3PO4 and H2SO4, except for HCl. According to in-situ DRIFRS results, one could infer that SCR reactions occurred over CeO2/ZrO2 catalyst without acid treatment might proceed only in E-R mechanism. But for acid-treated CeO2/ZrO2 catalysts, both E-R and L-H mechanisms were might be followed in SCR reaction process.

Homogeneous Ni(I)tetra Sulfonated Phthalocyanine Electrocatalyst Generated at Low Overpotential Clubbed with a Wet‐Scrubbing Column for High Efficiency NO Reduction to NH3

AbstractAlthough the degradation of NO gas to a less toxic form is a promising strategy to help solve atmospheric health and ozone depletion problems, conversion to a useful gas is a recent strategy. The generation of NH3 from NO with high efficiency per catalyst area or weight is in the early stages. In this investigation, a tetra sulfonated phthalocyanine with a Ni(II) (Ni(II)TSPc) complex was used to produce a low valent homogenous electrocatalyst Ni(I)TSPc in an alkaline medium at a lower overpotential. Ni(I)TSPc formation at a lower overpotential was demonstrated by the initial change in oxidation/reduction potential from 25 mV to −360 mV during electrolysis, peak potential change in cyclic voltammetry, and UV‐Vis spectral analysis. A potentiometric titration method used to quantify the electrogenerated Ni(I)TSPc revealed 90 % efficiency in 1 h. The decrease of Ni(I)TSPc concentration when contacting NO gas at the wet scrubber column showed that the NO removal process followed a Ni(I)TSPc (Ni(I)) mediation or mediated electrocatalytic reduction (MER) process. The NO removal efficiency reached almost 100 % at a 0.2 L/min gas flow rate of 20 ppm. The selective formation of NH3 with a maximum of 1492 μmol/g Ni(I) was achieved for the first time in the homogeneous electrocatalytic reduction process. The developed process generated NH3 from NO gas and has the potential for scale‐up.

Effect of Mn-doped CaO on NO removal by CO in carbonation of calcium looping for CO2 capture in a fluidized bed reactor

By utilizing CO as NO reductant and CaO as the catalyst, NO removal by CO can be realized in the carbonation stage of calcium looping for CO2 capture, but the carbonation of CaO decreases the catalytic effect on NO removal. To realize efficient and stable NO removal in the carbonation stage, CaO was modified by Mn in this work. NO removal performance of CO in the carbonation stage of Mn-doped CaO in the calcium looping process was investigated in a bubbling fluidized bed reactor. In the carbonation stage, NO removal efficiency sharply increases from 0% to 99% and CO2 capture efficiency increases from 73% to 88% due to the presence of Mn. Compared with CaO, Mn-doped CaO possesses a stronger catalysis on NO removal by CO and higher CO2 capture capacity. MnO in Mn-doped CaO is an excellent and stable catalyst for NO removal by CO, which greatly mitigates the negative effect of the carbonation and the sintering of CaO on NO removal. The molar ratio of Mn/Ca = 3.5:100 is recommended. To achieve efficient NO removal and CO2 capture in the carbonation stage of Mn-doped CaO, CO concentration in the range of 3000–4000 ppm and carbonation temperature of 650 °C are recommended. Under severe calcination conditions (950 °C and 80% CO2), CO2 capture and NO removal efficiencies reach 85% and 99% in 10 cycles, respectively. The periodic density functional theory calculations show that the catalytic active sites for NO removal by CO are changed from O-tops to Mn-tops in Mn-doped CaO, so the adsorptions of NO and CO2 are greatly enhanced, promoting the subsequent simultaneous NO removal and CO2 capture. Thus, Mn is a bi-functional additive to promote CO2 capture by CaO and catalyze NO removal by CO. Mn-doped CaO seems promising for efficient simultaneous NO removal and CO2 capture in the carbonation stage of the calcium looping process.

Effect of preparation method on the performance of Fe-Ag/Al2O3 catalyst in the selective catalytic reduction of NO with propene

Previous works demonstrated that the Fe-Ag/Al2O3 catalyst could efficiently reduce NO into N2 by propene with a good resistance towards H2O and SO2. In this work, the effect of preparation method on the performance of Fe-Ag/Al2O3 catalyst in the selective catalytic reduction (SCR) of NO with propene was investigated. Three typical methods, viz., physical grinding (PG), direct impregnation (DI) and sol-gel-impregnation (SGI), were comparatively used to load the active components onto the supports. The results indicate that all the catalysts prepared by these three methods display good tolerance towards water vapor and SO2. However, they are rather different in the denitration efficiency; the maximum NO removal efficiency of the catalysts prepared by three methods follows the order of SGI (100%) > PG (62%) > DI (58%). Various characterization results reveal that the catalytic performance of Fe-Ag/Al2O3/CM was mainly related to the porous surface and Fe-Ag interaction. By using the SGI approach, the primary support of cordierite and the secondary support of Al2O3 work together to achieve a large surface area and an intense interaction between Fe and Ag on the resultant DP-Fe/Ag/Al2O3/CM catalyst, forming the bimetal AgFeO2 oxide and displaying the best reducibility. In terms of the PG method, the prepared GR-Fe/Ag/Al2O3 catalyst is powdery and shows the largest surface area; however, without cordierite serving as the monolithic support, Ag2O and Fe3O4 exist as separate oxides together with a hint of elemental Ag. As a result, the GR-Fe/Ag/Al2O3 catalyst shows poor reducibility due to the lack of porous surface to facilitate the Fe-Ag interaction. In contrast, the DP-Fe/Ag/CM catalyst prepared using the DI method shows rather poor dispersion of Fe and Ag due to the absence of the secondary support of Al2O3; in fact, individual Ag2O and Fe3O4 agglomerate on the catalyst surface and no AgFeO2 species is detected. Therefore, the DP-Fe/Ag/CM catalyst, with the surface area of only 1/4 of that for Fe-Ag/Al2O3/CM-SGI, exhibits the poorest activity in the SCR of NO by propene.