NO Conversion Research Articles

High- dose nitric oxide gas inhalation for HIV infection

Therapeutic effect of high-dose nitric oxide gas inhalation (NO concentration was not less than than 1000 ppm) on two patients with HIV infection was shown. Inhaled NO therapy led to a rapid decrease in viral load to an undetectable level which was persistent even after analytical treatment interruption. It is suggested that HIV infection is controlled by nitrosonium (NO+) cations, the oxidized form of neutral NO molecules that enter the blood. Subsequent conversion of NO+ cations into nitrite anions due to a reaction with hydroxyl ions is inhibited by the binding of NO+ cations and chloride anions leading to the formation of nitrosyl chloride in the blood. Further entry of nitrosyl chloride into cells and tissues ensures NO+ transfer to them. Interaction between nitrosyl chloride and thiols requires the appearance of relevant S-nitrosothiols as NO donors in cells and tissues.

Flexible monolithic Pt/CuO-Fe2O3/TiO2 catalysts integrated on Ti mesh for efficient NO removal via CO-SCR reaction

This study reports on the development of highly-efficient Pt/CuO-Fe2O3/TiO2 monolithic catalysts for the low-temperature conversion of NO to N2 via CO-SCR. In this case, ultrathin TiO2 nanosheet arrays are designed to in situ grow on flexible Ti mesh to provide more spaces/areas for the loading of highly-dispersed Fe2O3 and CuO active components. Furthermore, Pt nanoparticles with an average size of 1.30 nm are effectively decorated on the surface of CuO-Fe2O3/TiO2. The H2-TPR and NO-TPD results demonstrate that the excellent synergistic effect between TiO2, CuO, Fe2O3 and trace amounts of Pt is conducive to enhance the adsorption of NO and finally promote the CO-SCR. The obtained Pt/CuO-Fe2O3/TiO2 catalysts exhibit excellent CO-SCR performance with 100 % NO conversion, and 100 % N2 selectivity at 250 °C, showing great potential of de-NOx application by using toxic CO as reductant in industry.

Comparative biotic and abiotic effects on greenhouse gas emissions from agricultural ecosystems: application of straw or biochar?

Farmland has become a significant contributor to greenhouse gas (GHG) emissions, and research has shown that the addition of straw or biochar may be a viable method for mitigating these emissions. However, there is a lack of understanding regarding the comparative biotic and abiotic effects of straw and biochar amendments on GHG emissions. To address this knowledge gap, we conducted a meta-analysis of 100 published papers to quantify the impact of straw and biochar application on GHG emissions. Our findings indicate that straw application significantly increased CO2 and CH4 emissions from agricultural ecosystems by 46.2% and 113.5%, respectively, but did not have a significant effect on N2O emissions. Conversely, biochar amendment significantly reduced CO2, CH4, and N2O emissions by an average of 11.0%, 31.7%, and 22.8%, respectively. We also found that straw and biochar amendments increased soil pH, soil organic carbon (SOC), and C/N ratio, and there were significant differences between them. Moreover, straw application significantly increased the microbial biomass carbon (MBC) content and microbial quotient by 37.1% and 20.1%, respectively, while biochar application increased the MBC content by 25.0% without a significant effect on the microbial quotient. Furthermore, both straw and biochar applications promoted the nitrification process and increased the abundance of ammonia-oxidizing bacteria (AOB) by 50.7% with straw and by 57.5% and 75.1% with biochar for ammonia-oxidizing archaea (AOA) and AOB, respectively. The denitrification process was also stimulated by straw or biochar amendment, resulting in an increase in the abundance of nirK by 22.9% and 16.8%, respectively. Biochar amendment additionally increased the abundance of nosZ by 29.4%, indicating that the main reason for reducing N2O emissions through biochar application is the conversion of NO3--N to N2. Thus, compared to straw application, biochar application is a more effective method for reducing greenhouse gas emissions.

N-doped porous carbon material derived by MOFs calcined in proper oxygen atmosphere as high-performance catalyst for the low-temperature NH3-SCR

Nowadays, with the development of industrial applicability and low energy consumption, a catalyst for implementing the NH3-SCR reaction at low temperature is urgently needed. MOFs derivatives (MD) prepared by calcined of MOFs could reserve many characteristics of MOFs show great potential. And in order to prepare high NO conversion catalysts, the pyrolysis conditions of MOFs draw more attentions in the preparation process. Therefore, in this work, after calcined MOFs precursor at the atmosphere of different oxygen concentration (pure oxygen, air, nitrogen), a series of nanocomposite are obtained. The experimental results reveal that catalyst calcined in the atmosphere of proper oxygen concentration (air) has the best deNOx performance and better resistance of water and sulfur dioxide. Further explorations exhibit that it could be primarily ascribed to the distinctive porous structure which is made up of well-dispersed MnOx-CeOx together with N-doped carbon skeleton. The conductivity can be efficiently increased to hasten the transfer of electrons. In addition, in situ DRIFTS results indicate that the interaction on the surface of catalyst calcined in air is stronger and the mechanism of prepared catalysts is Eley-Rideal (E-R) at low temperature and Langmuir-Hinshelwood (L-H) at high temperature.

Insights into the enhanced activity and SO2 resistance of air oxidation treated Mn-Fe doped biochar catalyst in the low-temperature catalytic reduction of NOx with NH3

In this study, a sustainable two-stage air oxidation (TAO) was employed to prepare Fe modified MnOx-biochar catalyst (C-O2-MF-O2) instead of high temperature treatment and/or chemical activation for selective catalytic reduction of NO with NH3 (NH3-SCR). The collaborative effect of Fe modification and TAO on the physicochemical properties and catalytic performance of catalysts was systematically studied. Compared with counterpart catalysts treated with two-stage N2 (C-N2-MF-N2) or one-stage O2 (C-O2-MF-N2, C-N2-MF-O2), C-O2-MF-O2 showed obvious enhanced physicochemical properties (SBET, pore properties, high-valance metal ratio, chemisorption oxygen (Oα) content), superior catalytic performance, achieving 91.3% NO conversion with nearly 100% N2 selectivity at 150 °C, and much better H2O and SO2 resistance. It is worth noting that TAO facilitated the redox performance of MnOx after Fe modification to generate more dispersed high-valance metal (Mn4+ and Fe3+), thereby favoring the low-temperature SCR activity of the catalyst. Further, the in situ DRIFTS studies revealed TAO produced remarkable effects on the adsorption behaviors of NH3, NO and SO2, and the corresponding mechanisms of catalyst activity enhancement and SO2 resistance were proposed. Generally, TAO could be a favorable avenue to prepare catalysts with binary active metals for improving performance of NH3-SCR.

Investigation of the light-off characteristics and secondary pollutants production mechanism in Pd/Rh catalyst for natural gas engines

To investigate the influence mechanism of the light-off characteristics and secondary pollutants (N2O and NH3) of the Pd/Rh catalytic converter for natural gas engines, a global model of the catalytic converter and a more comprehensive catalytic reaction mechanism were first established. Further, the model and the catalytic reaction mechanism were validated by using experimental data. Then, the effects of exhaust temperature and exhaust composition (H2O, O2, and H2 concentrations) on the catalytic converters were investigated. The results showed that a higher temperature reduced the light-off time t50 of NO and CO. The production of N2O decreased to 0 at high temperatures due to the reduction reactions of R14 (N2O+H2 = H2O+N2) and R16 (N2O+CO = CO2 + N2). NH3 would form at the temperature above 825 K, and the required H2 originated from SR and WGS reactions. Increasing the H2 concentration promoted the conversion of NO and CO. When the temperature exceeds 600 K, increasing the H2 concentration decreases the production of N2O. H2O has the opposite effect on the production of N2O and NH3 at high temperatures. Increasing the content of H2O increased the conversion of NO and inhibited the conversion of CO. O2 concentration at 4000 × 10−6 is beneficial to reduce secondary pollutants of N2O and NH3. At the condition of 730–820 K and 4000 × 10−6 O2, the productions of N2O and NH3 were reduced to 0. This study contributes to the efficient application of Pd/Rh catalytic converters and further enhances the emission reduction of natural gas engines.

Effect of (M = Co, Cu, Cr, and Mo) M/CeO2-MgO catalysts in selective catalytic reduction of NOx with hydrogen under excess oxygen condition

Efficient NOx removal is an important for controlling air pollution, and developing effective catalysts is a significant challenge. In this study, (M = Co, Cu, Cr, and Mo) M/CeO2-MgO catalysts were prepared by the co-precipitation method followed by the wet-impregnation method for NO removal by H2-SCR technology. The catalysts were characterized by BET, XRD, XPS, TEM, and H2-TPR. The CeO2-MgO showed the BET surface area of 78 m2/g, which is slightly decreased after the impregnation of Cu, Co, Cr, and Mo metals. X-ray diffraction showed the presence of cubic phase by CeO2 and MgO. The Cu/CeO2-MgO catalyst shows the highest lattice strain, Ce3+ content, and adsorbed oxygen with values of 0.66%, 30.54%, and 74.12%. A maximum NOx conversion of 78% was achieved over the Cu/CeO2-MgO catalyst with a slightly large temperature window (100–250 ℃) among all the catalysts. The catalyst’s sequence of NOx conversion was as follows: Cu/CeO2-MgO > Mo/CeO2-MgO > Co/CeO2-MgO > Cr/CeO2-MgO > CeO2-MgO. The N2 selectivity followed the same order as NO conversion except for the Cr catalyst, which performed better than the Co impregnated catalyst.

A stable spherical MOF-derived Mnx-Fe2O3/C catalysts for low-temperature CO-SCR

A series of spherical Mnx-Fe2O3/C catalysts derived from MnFe-MOF-74 were fabricated via a sacrificing template method and applied for CO-SCR. Among the tested catalysts, Mn0.5-Fe2O3/C catalysts achieved a maximum NO conversion of 100 % in a broad temperature range between 225 and 500 °C, significantly higher than monometallic Fe2O3/C. Based on TPR, BET and XPS results, a redox reaction Fe3+ + Mn2+ ↔ Fe2+ + Mn3+ over Fe-O-Mn sites was constructed, which greatly facilitated the adsorption and activation of NO molecules. DFT calculations revealed that the incorporation of Mn obviously increased the local electron density of Fe-Mn sites not only resulting in a strong C-Fe/Mn and N-Fe/Mn bonding, but also effectively weaken the N-O bond. And the NO adsorption energy of Fe-O-Mn site over Mn doped α-Fe2O3 is −0.87 eV which indicates the stability of the adsorption configuration. Combined with the in situ FT-IR results, important intermediates Fe2+-(NO)22– and N2O were identified respectively at 1261 and 1358 cm−1, which were promoted by the synergistic interaction of Mn and Fe. This Mn-Fe synergistic interaction could contribute to lowering reaction barrier and boosting CO-SCR performance.

Improving low-temperature NH3-SCR denitration activity and resistance to H2O and SO2 over Nb-modified NbaSn0.3CeOx catalysts by enhancing acidity to compensate for its weak oxidation ability

In this paper, a series of Nb-modified NbaSn0.3CeOx (a = 0.2, 0.4, 0.5) catalysts for denitrification were prepared using a facile co-precipitation method. In order to explore the various individual properties of the samples, the catalysts were characterized by XRD, Raman, N2 adsorption and desorption, TEM, NH3-TPD, H2-TPR, XPS and in-situ DRIFTS tests to understand the influences of the Nb introduction on the NH3-SCR reaction. Among these catalysts, the Nb0.4Sn0.3CeOx catalyst exhibit excellent NH3-SCR performance in the temperature range of 155–450 °C with more than 90 % NO conversion, 100 % N2 selectivity, and possess good resistance to H2O and SO2. Compared with the Sn0.3CeOx catalyst, we believe that the improvement of the low-temperature NH3-SCR performance of the Nb0.4Sn0.3CeOx catalysts is mainly due to the change in the amount of acid, special for the increase in B acid content, which compensates for the effect of the weaken oxidizing ability on the low-temperature activity. Beyond that, the good H2O and SO2 resistance at low temperature after the introduction of Nb into Nb0.4Sn0.3CeOx catalysts was analyzed by using in-situ DRIFTS characterization in detail, and the results indicate that the incorporation of Nb can inhibit the oxidation of SO2 to form sulfate on the catalysts, and prevent the competing adsorption of H2O and NOx, but the adsorption of NH3 is not affected. This work proves that the acidity regulation can improve low-temperature SCR activity by the synergistic effect between oxidation capacity and acidity.

Conversion of NO to NH3 with C3H6 Over TiO2-Supported Ag Catalysts in the Presence of a Large Excess of Oxygen and Water Vapor: Turning a Hazardous Waste into a Resource

Conversion of NO to NH3 with C3H6 Over TiO2-Supported Ag Catalysts in the Presence of a Large Excess of Oxygen and Water Vapor: Turning a Hazardous Waste into a Resource

The promotion effect of Pr doping on the catalytic performance of MnCeOx catalysts for low-temperature NH3-SCR

Using a one-step impregnation method, a series of Pr-modified MnCeOx catalysts with different Pr molar ratios were created to manufacture an efficient and effective catalyst for low-temperature NH3-SCR. It was demonstrated that the Pr modification could extensively boost the MnCeOx catalysts’ de-NOx activity and SO2 resistance and led to the formation of a unique broom-like morphology, especially when the molar ratio of Pr/Mn = 0.3, the MnCePrOx-0.3 exhibited above 90 % NO conversion at 250 °C with the existence of 100 ppm SO2. According to the characterization results, the enhancement of Pr doping for MnCeOx catalysts was mainly manifested by the expanded specific surface area, the improved dispersion of active components, the enhanced surface acidity and redox ability, and the generated more chemisorbed oxygen (Oads) species. All these characteristics allowed the NH3-SCR reaction over MnCePrOx-0.3 catalysts to proceed through the both Eley-Rideal (E-R) and Langmuir-hinshelwood (L-H) mechanism.

Glass-fiber catalysts for selective catalytic reduction of nitrogen oxides by CO and hydrocarbons

Glass-fiber catalysts (GFCs) are investigated in the process of the catalytic reduction of nitrogen oxides by hydrocarbons and carbon monoxide contained in waste and flue gases. Studies show that the platinum-based GFCs prepared by surface high-temperature synthesis approach demonstrates higher activity in the reactions of NOx reduction and CO and CxHy oxidation, in comparison with conventional GFCs and catalytic systems based on oxides of MnCe and FeV. Structured cartridges with a corrugated and flat metal mesh with longitudinal flow direction and satin type GFC were found to provide the highest apparent catalyst activity. The kinetic model for Pt/GFC was proposed based on the experimental data. The best kinetic description is provided under account of formation of nitrite-nitrate surface compounds resulting from NO chemisorption and further interaction of these compounds with CO, as well as under account of simultaneous catalytic and non-catalytic oxidation of propane by oxygen both to CO and CO2. The proposed model may adequately reproduce the non-trivial experimental regularities, such as CO and NO conversion decrease at high temperatures and synergetic effect of oxygen on the rate of NO reduction by CO.

Effects of different soil water holding capacities on vegetable residue return and its microbiological mechanism.

With the gradual expansion of the protected vegetable planting area, dense planting stubbles and increasing labor cost, the treatment of vegetable residues has become an urgent problem to be solved. Soil bacterial community structure plays an important role in vegetable residue return and is susceptible to environmental changes. Therefore, understanding the influences of different soil water holding capacities on plant residue decomposition and soil bacterial communities is important for biodegradation. During the whole incubation period, the weight loss ratio of plant residue with 100% water holding capacity was 69.60 to 75.27%, which was significantly higher than that with 60% water holding capacity in clay and sandy soil, indicating that high water holding capacity promoted the decomposition of plant residue. The degradation of lignin and cellulose was also promoted within 14 days. Furthermore, with the increase in soil water holding capacity, the contents of NH4+ increased to 5.36 and 4.54 times the initial value in the clay and sandy soil, respectively. The increase in napA and nrfA resulted in the conversion of NO3- into NH4+. The increase in water holding capacity made the bacterial network structure more compact and changed the keystone bacteria. The increase in water holding capacity also increased the relative abundance of Firmicutes at the phylum level and Symbiobacterium, Clostridium at the genus level, which are all involved in lignin and cellulose degradation and might promote their degradation. Overall, these findings provide new insight into the effects of different soil water holding capacities on the degradation of plant residues in situ and the corresponding bacterial mechanisms.

A comparison of bifunctional MnOx catalysts prepared via different precipitants for simultaneous removal NO and CO

In this work, ammonium carbonate, sodium hydroxide, and ammonium hydroxide were selected as the precipitants to prepare bifunctional MnOx catalysts via the PEG-assisted co-precipitation method. SEM analysis revealed that MnOx catalysts prepared with ammonium carbonate (AC) displayed a spherical morphology with relatively large size, whereas the catalysts synthesized with sodium hydroxide (SH) and ammonium hydroxide (AH) exhibited polyhedron shapes with smaller size. The results demonstrated that Mn-AC catalyst presented superior catalytic activity for both NO reduction and CO oxidation, achieving 89% NO conversion at 100 ºC and over 80% CO conversion at 200 ºC, outperforming Mn-SH and Mn-AH catalysts. Mn-AC catalyst possessed more abundant Mn4+ species and surface chemisorbed oxygen than Mn-AH and Mn-SH catalysts, which served as a significant motivation for the difference in catalytic activity. Additionally, Mn-AC catalyst exhibited stronger surface acidity, which facilitated the adsorption and activation of ammonia species in the NH3-SCR reaction. Furthermore, in situ DRIFTS experiment suggested that the pre-desorption of CO promoted the adsorption and activation of NO. On this basis, the possible mechanism model of three precipitants on bifunctional MnOx catalysts was proposed.

Insights into Nb doping effects on the catalytic activity and SO2 tolerance of Mn–Cu/BCN catalyst for low-temperature NH3-SCR reaction

Biochar-based supported denitration catalysts have shown tremendous potential in reducing NOx, while improving low-temperature NH3-SCR catalytic activity and SO2 tolerance still faces great challenges. In this work, Mn7–Cu3/BCN and Mn7–Cu3-Nbx/BCN catalysts were prepared by one-step wet impregnation. The enhanced effect of Nb doping on the catalytic performance and SO2 tolerance over the Mn7–Cu3/BCN catalyst was evaluated in the temperature range of 75–275 °C. The denitrification activity test showed that the introduction of an appropriate amount of Nb increased the catalytic activity and N2 selectivity of the catalyst. The NO conversion of Mn7–Cu3–Nb0.05/BCN with an optimum doping ratio of 0.05 wt% Nb was higher than 94% at 150–275 °C. The characterization results indicated that the introduction of Nb enhanced the interaction between the active components MnOx and CuOx, accelerated the electron transfer between elements, and thus improved the Mn4+/Mnn+ and Oα/(Oα+Oβ+Oγ) proportions and redox performance. On the other hand, Nb modification increased the number of weakly acidic sites, which was beneficial for the adsorption and activation of the reducing agent NH3 under low-temperature conditions. Meanwhile, Nb could significantly improve the SO2 poisoning resistance of the Mn7–Cu3/BCN–S catalyst when SO2 was added to the reaction system. The NO conversion of Mn7–Cu3–Nb0.05/BCN remained above 75% after a 13.5 h reaction under 100 ppm SO2 and 5 vol% H2O at 225 °C. By combining experimental characterization results with DFT calculation results, we effectively confirmed that Mn7–Cu3–Nb0.05/BCN had good sulfur resistance, mainly because Nb could effectively inhibit the formation of manganese sulfate and promote the decomposition of ammonium bisulfate.

Experimental and numerical study of the effect of H2O and CO2 dilution on NH3/CH4 co-oxidation characteristics in a jet-stirred reactor

This work reports an experimental and kinetic modeling study of NH3/CH4 co-oxidation in O2/N2 in a jet-stirred reactor (JSR) covering a reaction temperature of 900–1450 K, equivalence ratio of 0.5–2.0, and dilution degree of 0%–30% with H2O and CO2, respectively. Experimental results show that CO formation is inhibited by H2O dilution while enhanced by CO2 dilution. NO formation is suppressed by either H2O or CO2 dilution under lean condition, however these two diluents generally would accelerate NO formation under stoichiometric and rich conditions. Dong2022 mechanism is selected for further kinetic analysis for NO conversion under stoichiometric condition. It shows that N2H2 plays a more significant role in NO generation in N2/CO2 atmosphere. The reactions of NH + OH ↔ HNO + H and NH2 + O ↔ HNO + H contribute the most for boosting NO formation under both H2O and CO2 dilution conditions.

Depth investigation of the regulation mechanism of SiO2 on the denitrification performance and sulfur resistance of MnCe/Ti SCR catalyst

The “deep peaking” of coal-fired units presents great challenges for SCR catalysts’ de-NOx activity at wide temperatures. Mn-based catalysts have good de-NOx activity at low temperatures, but their poor sulfur resistance is one of the key issues affecting industrial applications. In this study, the effects of SiO2 doping on the denitrification, sulfur resistance, and physicochemical performance of the MnCe/Ti catalyst were investigated. The results showed that SiO2 improved the de-NOx activity of catalysts at high temperatures and enhanced SO2/H2O resistance at wide temperatures. Under short reaction time conditions, the MnCe/Ti0.9Si0.1 catalyst exhibited the highest NO conversion rate at 400 °C, which was 33% higher than that of the MnCe/Ti catalyst. The NO conversion rates of Si-doped MnCe/Ti catalysts increased rapidly to over 85% (65% of the MnCe/Ti catalyst) as the reaction temperature increased from 200 °C to 250 °C under SO2-containing atmosphere due to the promoting effects of SiO2 on the decomposition of ammonium bisulfate. MnCe/Ti0.7Si0.3 catalyst exhibited the optimal sulfur and H2O resistance, with NO conversion rate higher than 85% with 600 min under SO2/H2O-containing atmospheres. SiO2 inhibited the crystallization of anatase TiO2, and increased the specific surface area to 306.60 m2/g. Additionally, the ratios of Mn4+/Mnn+ and Ce3+/Cem+, and the surface adsorbed oxygen and weak-medium acid amount also increased due to the multiple interactions between the TiO2-SiO2 and Mn/Ce, resulting in the higher de-NOx activity. Compared with the MnCe/Ti catalyst, Si-doped MnCe/Ti catalysts have lower SO2(g) adsorption amount and the sulfation of Mn, and higher SO3(a) desorption performance, resulting in better sulfur resistance at wide temperatures.

Highly efficient MnOx catalysts supported on Mg-Al spinel for low temperature NH3-SCR

Selective catalytic reduction (SCR) has been extensively employed in industries for the removal of NOx while it is still a challenge to develop novel low-temperature catalysts. The redox and acid sites on the catalyst are often preconditions that cooperate in the SCR reaction. In this study, a series of MnOx supported on MgAl2O4 spinel catalysts (denoted as Mn/MAS) were successfully prepared by incipient wetness impregnation method for low-temperature SCR of NOx with ammonia. The effects of the calcination temperature of MAS support and Mn loading on catalyst structure and performance were examined. The Mn0.12/MAS-700 catalyst showed the best low-temperature denitrification performance, with more than 80% conversion of NO at 150–300 °C and higher than 60% N2 selectivity. Moreover, the denitrification efficiency remained at nearly 90% in the presence of H2O. The physicochemical properties of the catalysts were determined using various characterization methods, and the corresponding results found that the higher concentration of Mn4+ and surface chemisorption oxygen enhanced the low-temperature activity of the catalysts. The addition of Mn species increased the surface acidity of weak acid centers which promoted the catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) revealed that the Eley-Rideal mechanism was introduced mainly at 100 °C on the Mn0.12/MAS-700 catalyst. This work provides new inspiration into the effect of Mn species, and the synergistic role of active components Mn and MAS support in the SCR reaction.

Low-temperature CO selective catalytic reduction denitrification and sulfuric acid regeneration mechanism of Cu-Ce/AC catalyst poisoned with zinc salt

To explore Cu–Ce/activated carbon (AC) catalyst poisoned of with zinc salt and its mechanism of low-temperature CO selective catalytic reduction (CO-SCR) denitrification following sulfuric acid regeneration, this paper uses ZnCl2 and ZnSO4 to poison Cu–Ce/AC catalyst and H2SO4 pickling to regenerate the poisoned catalyst. Not only the catalyst denitrification activity was investigated but also the surface morphology, pore structure, variation of active component phases and elemental valence, surface functional groups, reduction characteristics and adsorption mechanism of catalyst before and after regeneration were systematically characterized. The low-temperature CO-SCR denitrification mechanism of the poisoned Cu–Ce/AC catalyst was revealed. After being poisoned with zinc salt, the oxide on the catalyst surface aggregated, causing the blockage of the pore, thereby inhibiting the adsorption capacity of the reaction gas and the synergistic reaction between Cu-Ce. Moreover, zinc salt not only occupies the active site, but also destroys the -C=O and –OH oxygen-containing functional groups. This not only reduces the chemically adsorbed oxygen (Oβ) and oxygen vacancy but also leads to the reduction of Cu+–CO species, the reduction of catalyst redox capacity, and the reduction of NO conversion rate. The regeneration mechanism of the sulfuric acid method was as follows. First, the solid particles deposited on the catalyst surface are removed, thereby restoring its specific surface area and pore structure, and increasing the adsorption area of reaction gas. Additionally, the content of Cu and Ce active components was increased, which promoted the synergistic reaction, and the content of Cu+–CO species, oxygen vacancy, and Oβ was increased, resulting in enhanced redox capacity. Finally, sulfuric acid impregnation generated S2O82− groups, which sulfated the surface of the catalyst, and its S=O reacted with Zn to form S–O–S, which prevented zinc salt from destroying the oxygen-containing functional groups and improved the reducing capacity and CO adsorption capacity of the catalyst, thereby restoring the denitrification activity of the catalyst.

Insights Into NOx and HONO Chemistry in the Tropical Marine Boundary Layer at Cape Verde During the MarParCloud Campaign

AbstractChemical processing of reactive nitrogen species, especially of NOx (= NO + NO2) and nitrous acid (HONO), determines the photochemical ozone production and oxidation capacity in the troposphere. However, sources of HONO and NOx in the remote marine atmosphere are still poorly understood. In this work, the multiphase chemistry mechanism CAPRAM in the model framework SPACCIM was used to study HONO formation at Cape Verde (CVAO) in October 2017, adopted with the input of current parameterizations for various HONO sources. Three simulations were performed that adequately reproduced ambient HONO levels and its diurnal pattern. The model performance for NOx and O3 improves significantly when considering dust‐surface‐photocatalytic conversions of reactive nitrogen compounds with high correlation coefficients up to 0.93, 0.56, and 0.89 for NO, NO2, and O3, respectively. Photocatalytic conversion of the adsorbed HNO3 on dust is modeled to be the predominant contributor for daytime HONO at CVAO, that is, accounting for about 62% of the chemical formation rate at noontime. In contrast, the ocean‐surface‐mediated conversion of NO2 to HONO and other discussed pathways are less important. The average OH levels at midday (9:00–16:00) modeled for cluster trajectory 1, 2, and 3 are 5.2, 5.1, and 5.2 × 106 molecules cm−3, respectively. Main OH formation is driven by O3 photolysis with a contribution of 74.6% to the total source rate, while HONO photolysis is negligible (∼1.8%). In summary, this study highlights the key role of dust aerosols for HONO formation and NOx cycling at CVAO and possibly in other dust‐affected regions, urgently calling for further investigations using field and model studies.