NO Conversion Research Articles

Strong metal oxide-zeolite interactions during selective catalytic reduction of nitrogen oxides

In response to the stricter EU VII emission standards and the "150 ℃ challenge", selective catalytic reduction by ammonia (NH3-SCR) catalysts for motor vehicles are required to achieve high NO conversion below 200 °C. Compounding metal oxides with zeolites is an important strategy to design the low-temperature SCR catalysts. Here, we original prepared Cu-SSZ-13 @ MnGdOx (Cu-Z @ MGO), which achieved over 90% NO conversion and 95% N2 selectivity at 150 ℃. It has been demonstrated that a uniform mesoporous loaded layer of MGO grows on Cu-Z, and a recrystallization zone appears at the MGO-Cu-Z interface. We discover that the excellent low-temperature SCR activity derives from the strong metal oxide-zeolite interaction (SMZI) effects. The SMZI effects cause the anchor and high dispersion of MGO on the surface of Cu-Z. Driven by the SMZI effects, the Mn3+/Mn4+ redox cycle ensures the low and medium temperature-SCR activity and the Cu2+/Cu+ redox cycle guarantees the medium and high temperature-SCR activity. The introduction of MGO improves the reaction activity of -NH2 species adsorbed at Mn sites at 150 ℃, achieving a cycle of reduction and oxidation reactions at low temperatures. This strategy of inducing SMZI effects of metal oxides and zeolites paves a way for development of high-performance catalysts.

W18O49/crystalline g-C3N4 layered heterostructures with full solar energy harvesting towards efficient H2O2 generation and NO conversion

The photocatalytic performance of graphitic carbon nitride (g-C3N4) heterostructures related to the charge carrier separation and transport efficiency is often governed by the interfaces. Herein, in-situ growth of W18O49 nanobelts is attained on amorphous and crystalline g-C3N4 nanosheets to study the effects of the interfaces on photocatalytic oxidation activities. The horizontal growth of W18O49 on g-C3N4 nanosheets is the key in formation of two dimensional (2D)/2D W18O49/g-C3N4 heterostructures. The growth of W18O49 nanobelts on crystalline g-C3N4 nanosheets shows well-developed interfaces (sample W18O49-CCN) in comparison with heterostructures constructed using amorphous g-C3N4 base (sample W18O49-ACN). Characterizations on the structure, components, and properties of the samples demonstrate that these heterostructures reveal extended photo-absorption in visible to near infrared region, with sample W18O49-CCN showing much higher photogenerated charge carrier separation and transport efficiency. A H2O2 evolution rate of 5550 µMg−1h−1 is observed for sample W18O49-CCN under full solar-spectrum illumination (and 398 µMg−1h−1 observed for pristine crystalline g-C3N4), which is ∼ 2.4 times of that of sample W18O49-ACN prepared using amorphous g-C3N4. In addition, a NO removal rate of 72.1% is observed for sample W18O49-CCN with a NO2 selectivity of 6.2%. These results provide inspiration for construction of g-C3N4 homojunctions for practical photo-redox reaction applications.

Numerical investigation of honeycomb channel design: Effect of rounded corners on selective catalytic reduction of NO

In this work, single-channel models are established to investigate the effect of rounded corners on overall performance of honeycomb catalyst with various channel geometries and cell densities (Ncell). As channel shape factor (γ) increases, pressure drops all rise slowly at low γ (0 ∼ 0.5) and increases dramatically when γ > 0.5, aligning with monolith voidage and hydraulic diameter variations. Hexagon-channel catalysts with open corners exhibit the smallest pressure drop increase (17.3 %), while triangle-channel catalysts with acute corners show the highest rise (100.1 %). The increase in Ncell leads to a similar rise (43 %) in pressure drop. NO conversions decrease with γ due to reduced external surface area, with maximum conversions observed for triangle-channels (low γ) and hexagon-channels (high γ). Increasing Ncell enhances NO removal and mitigate rounded-corner effect on conversion (4.5 % to 1.2 % reduction). Based on that, a design strategy suggesting γ = 0.5 is proposed to eliminate ash accumulation and maintain acceptable catalyst performance.

Efficient visible-light-driven photocatalytic performance for nitrogen oxide abatement application in the air by a typical metal/semiconductor heterojunction

To improve the photocatalytic oxidation activity of SnO2 nanorods, we decorated Ag nanoparticles onto SnO2 nanorods via a photoreduction route at low temperature. The metal/semiconductor heterojunction based on Ag/SnO2 nanorods indicated a high photocatalytic activity towards NO gas removal in visible light region at the air conditions. Detailly, the NO photocatalytic removal performance of Ag/SnO2 heterojunctions are significantly enhanced, achieving 50.6 % after 30 min, approximately 1.9 times higher than that of SnO2 nanorods. In addition, the Ag/SnO2 heterojunctions have a lower NO2 gas conversion efficiency of 1.0 %, while pure SnO2 nanorods have a high NO2 conversion efficiency of 5.2 %. Moreover, photogenerated holes play a crucial role in the photocatalytic activity of NO gas removal.

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.

Experimental study of Fe modified Mn/CeO2 catalyst for simultaneous removal of NO and toluene at low temperature

A series of Mn/CeO2 catalysts modified with different Fe contents were prepared by impregnation method and tested for their low-temperature performance for simultaneous de-nitrification and toluene removal. It was found that the Fe5Mn/CeO2 catalyst showed the best catalytic performance and the conversion efficiency of toluene reached 90% at 175 °C and NO conversion reached 90% at 95−300 °C. The physical and chemical properties of the catalysts were characterized by BET, SEM, XRD, XPS, H2-TPR, NH3-TPD and O2-TPD. XPS results showed that the increased content of Ce3+ and Mn4+ in the Fe5Mn/CeO2 catalyst promoted the formation of oxygen vacancies and unsaturated chemical bonds, providing more active sites, thus facilitating the efficient removal of NO and toluene at low temperatures. Compared with other catalysts, H2-TPR, NH3-TPD and O2-TPD indicate that Fe5Mn/CeO2 catalyst has great redox ability, stronger acidity and better oxygen migration ability. In addition, this paper explores the effects between selective catalytic reduction (NH3-SCR) and catalytic oxidation reaction of toluene over Fe5Mn/CeO2 catalyst. NH3 preferentially reacts with the active site on the catalyst to inhibit the toluene oxidation process, while NO promotes the toluene removal process. Toluene can promote the NH3-SCR process in a certain temperature range. While NO promotes the formation of NO2, NO2 effectively promotes the combination of toluene and active sites, which is conducive to the catalytic oxidation of toluene; The inhibition of toluene on the NH3-SCR process weakens with the increase of temperature. At 100 °C, the inhibition of toluene on the NH3-SCR process disappears. When the temperature exceeds 225 °C, toluene reacts with NO as a reducing agent and promotes the formation of NO2, thus promoting the NH3-SCR reaction.

Intracellular delivery of nitric oxide enhances the therapeutic efficacy of mesenchymal stem cells for myocardial infarction.

Cell therapy by autologous mesenchymal stem cells (MSCs) is a clinically acceptable strategy for treating various diseases. Unfortunately, the therapeutic efficacy is largely affected by the low quality of MSCs collected from patients. Here, we showed that the gene expression of MSCs from patients with diabetes was differentially regulated compared to that of MSCs from healthy controls. Then, MSCs were genetically engineered to catalyze an NO prodrug to release NO intracellularly. Compared to extracellular NO conversion, intracellular NO delivery effectively prolonged survival and enhanced the paracrine function of MSCs, as demonstrated by in vitro and in vivo assays. The enhanced therapeutic efficacy of engineered MSCs combined with intracellular NO delivery was further confirmed in mouse and rat models of myocardial infarction, and a clinically relevant cell administration paradigm through secondary thoracotomy has been attempted.

Low-temperature CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation for selective catalytic reduction of NO using NH3: A structure–activity relationship study

CeCoMnOx spinel-type catalysts for the selective catalytic reduction of NO using NH3 (NH3-SCR) are usually prepared by alkaline co-precipitation. In this paper, a series of CeCoMnOx spinel-type catalysts with different calcination temperatures were prepared by acidic oxalate co-precipitation. The physicochemical structures and NH3-SCR activities of the CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation and conventional ammonia co-precipitation were systematically compared. The results show that the CeCoMnOx spinel-type catalysts prepared by the oxalate precipitation method (CeCoMnOx-C) have larger specific surface area, more mesopores and surface active sites, stronger redox properties and adsorption activation properties than those prepared by the traditional ammonia co-precipitation method at 400 °C (CeCoMnOx-N-400), and thus CeCoMnOx-C have better low-temperature NH3-SCR performance. At the same calcination temperature of 400 °C, the NO conversion of CeCoMnOx-C-400 exceeds 89 % and approaches 100 % within the reaction temperature of 100–125 °C, which is 14.8 %-2.5 % higher than that of CeCoMnOx-N-400 at 100–125 °C. In addition, the enhanced redox and acid cycle matching mechanisms on the CeCoMnOx-C surface, as well as the enhanced monoadsorption Eley-Rideal (E-R) and double adsorption Langmuir-Hinshelwood (L-H) reaction mechanisms, are also derived from XPS and in situ DRIFTS characterization.

Fe Nanoparticles Decorated Pinewood‐Derived Carbon for Highly Efficient Electrocatalytic Conversion of Nitrite to Ammonia

AbstractElectrochemical nitrite (NO2−) reduction reaction (NO2−RR) presents a sustainable approach for the electrochemical synthesis of ammonia (NH3), concurrently facilitating the removal of NO2− contaminants. Developing NO2−RR electrocatalysts with high NH3 selectivity and satisfactory NH3 yield poses a significant challenge. Herein, we present Fe nanoparticles decorated pinewood‐derived carbon (Fe/PC) as a highly proficient electrocatalyst for the conversion of NO2− to NH3. The well‐designed Fe/PC electrocatalyst achieves an impressive NH3 yield of 21924.6 μg h−1 cm−2 and a high Faradic efficiency of 91.5 % under ambient conditions. Notably, the Fe/PC catalyst exhibits robust stability in both prolonged electrolysis and cyclic electrolysis assessments.

Nitrous acid budgets in the coastal atmosphere: potential daytime marine sources

Abstract. Nitrous acid (HONO), a vital precursor of atmospheric hydroxyl radicals (OH), has been extensively investigated to understand its characteristics and formation mechanisms. However, discerning fundamental mechanisms across diverse environments remains challenging. This study utilizes measurements from Mount Lao, a coastal mountain in eastern China, and an observation-based chemical box model (OBM) to examine HONO budgets and their subsequent impacts on atmospheric oxidizing capacity. The model incorporates additional HONO sources, including direct emissions, heterogeneous conversions of NO2 on aerosol and ground surfaces, and particulate nitrate photolysis. The observed mean HONO concentration was 0.46 ± 0.37 ppbv. The updated model reproduced daytime HONO concentrations well during dust and photochemical pollution events. During dust events, daytime HONO formation was dominated by photo-enhanced heterogeneous reactions of NO2 on aerosol surfaces (> 50 %), whereas particulate nitrate photolysis (34 %) prevailed during photochemical pollution events. Nevertheless, the model uncovers a significant unidentified marine HONO source in a “sea case”, with its HONO production rate reaching up to 0.70 ppbv h−1 at noon. Without considering this unidentified source, an extraordinarily high photolysis coefficient of nitrate and/or a heterogeneous uptake coefficient of NO2 would be required to match observed HONO concentrations. This missing marine HONO source affected the peak O3 production rate and OH radical concentration by 36 % and 28 %, respectively, at the observation site. Given the limited HONO observation data in coastal and marine settings, the unidentified HONO source may cause an underestimation of the atmosphere's oxidizing capacity. This study highlights the necessity for further investigation of the role of HONO in atmospheric chemistry in coastal and marine environments.

Experimental investigation on gas emission characteristics of ammonia/diesel dual-fuel engine equipped with DOC + SCR aftertreatment

After-treatment device diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) were installed in the exhaust system of ammonia/diesel dual-fuel engine to remove harmful pollutants such as hydrocarbon (HC), carbon monoxide (CO), ammonia (NH3), nitrogen oxide (NOx), nitrous oxide (N2O) and other pollutants produced by the dual-fuel combustion mode. The results indicate that the HC, CO and N2O emissions of ammonia/diesel dual-fuel engine increase with the increment of ammonia fraction, whereas NOx emissions decrease. At 50 % load, the CO conversion efficiency of DOC decreases from 100 % at diesel-only mode to 18.9 % at 40 % ammonia fraction, while the HC conversion efficiency is independent of ammonia fraction. NOx can be reduced by NH3 in the exhaust, while NH3 will be oxidized to N2O and NOx in DOC. Moreover, at 50 % load, more NH3 emission is oxidized to N2O compared to 75 % load. After SCR, the NOx, N2O and NH3 emissions in the exhaust are further reduced, but due to the NH3/NOx ratio, there are still a large amount of NOx and NH3 emissions at SCR outlet. The N2O conversion efficiency of SCR is relatively low, with a maximum value of only 47.8 % at 50 % load and 30 % ammonia fraction. Owing to the high N2O emission from dual-fuel engine, the direct introduction of ammonia cannot significantly reduce greenhouse gas (GHG) emissions. Furthermore, the massive amount of unburnt ammonia in the exhaust is oxidized to N2O by DOC, leading to a sharp increase in GHG emissions after DOC + SCR aftertreatment, and the GHG emissions at 50 % load and 40 % ammonia fraction are 6.2 times higher than those before the aftertreatment, and 9.2 times higher than those of diesel-only mode.

Study on CO-SCR performance of Ce modified OMS-2 catalysts

The Ce-modified OMS-2 catalyst (Cex-OMS-2) was synthesized by the hydrothermal synthesis method, after which its catalytic efficacy in the selective reduction of NO by CO was assessed. The experiments showed that Ce0.08-OMS-2 was capable of 100% NO conversion between 175 and 300 °C when 0.05%NO, 0.1%CO, 5%O2 and N2 were used as equilibrium gases, and the N2 selectivity peaked at 93.2% at 175 °C. Additionally, Ce0.08-OMS-2 exhibits good sulfur resistance in the presence of 0.02% SO2 and maintains more than 88% NO conversion at 175–275 °C. By using BET, XPS, H2-TPR, NH3-TPD, and In situ DRIFTS to characterize the catalysts, the effects of doping the active metal Ce on the physicochemical characteristics of OMS-2 catalysts were under investigation. In conclusion, the improvement of the low-temperature activity of the Cex-OMS-2 catalyst is facilitated by lower agglomeration and crystallinity, larger specific surface area, smaller average pore size, enhanced surface oxygen vacancies, increased Mn4+ concentration, and richer Brønsted acid. Reaction gas adsorbed species and intermediates on the catalyst surface were dynamically captured during In situ DRIFTS experiments. The CO-SCR reaction of the catalyst was found to follow the E-R mechanism below 200 ℃ and the L-H mechanism at 200–350 ℃.

Effects of NO and SO2 on the secondary organic aerosol formation from isoprene photooxidation

Investigation of the effects of anthropogenic pollutants on the mass concentrations, particle number concentrations, and chemical compositions of secondary organic aerosol (SOA) formation is essential in understanding the photooxidation mechanism of volatile organic compounds but has been proven to be a very challenging experimental target because of their complex processes. Here, the effects of NO and SO2 on SOA formation from isoprene photooxidation were studied by a number of laboratory studies. The results indicate the accumulated O3 upon the NO conversion triggers the main oxidation reaction, by which the oxidants (i.e., OH and SO4−) are derived. The SOA mass concentrations and particle number concentrations are enhanced by NO under low NO concentrations but suppressed by NO under high NO concentrations, which are consistent with previous studies (Kroll et al., 2005, 2006). This could be rationalized that the large amount of accumulated O3 inhibit the multi-step isoprene oxidation and a large number of less oxidized products (m/z < 130) absorb or condense on the surface of existing particles, which decelerate the SOA nucleation and growth. The presence of SO2 accelerates the conversion of NO and the accumulation of O3, which promotes the main oxidation reaction of isoprene. New compounds are observed at m/z = 134, 137, 150, 152, and 179 measured by threshold photoionization (positive ion mode) with a tunable vacuum ultraviolet free electron laser and are found to be mainly formed from the isoprene oxidization by O3 and OH. The present findings provide both macroscopic and microscopic information to advance understanding of atmospheric components affected by the anthropogenic-biogenic interactions in the neighborhood of emission origins.

Boosting the activity of In-H-SSZ-13 via tuning acid sites for synergistic abatement of NOx and CH4

Selective catalytic reduction of NO by CH4 (CH4-SCR) is a desirable denitration technology for liquefied natural gas (LNG)-powered vehicles and ships, and efficient catalysts have been explored. However, enhancement of the catalytic performance via tuning acid sites of the zeolites is rarely reported. In this work, In-H-SSZ-13 catalysts were prepared via ion exchange method, and the acid sites in the catalysts were adjusted through pre-treatment process of (NH4)2SO4. The activity of the catalyst boosted with improvement of the acid sites in the catalysts, and the activation energy of the reaction decreased from 82.1 to 63.9 kJ/mol over the catalysts. In situ DRIFTS analysis confirmed that more acid sites could facilitate the adsorption and activation of CH4, and R-NCO was a vital intermediate product in the CH4-SCR reaction. The effects of In loading and reaction conditions on the performance of the catalysts were also investigated, and the NO and CH4 conversions reached 75 % and 99 % at 505 °C with a high gas hourly space velocity (GHSV) of 80,000 h−1 over the optimized In-H-SSZ-13 catalyst, respectively.

How do aeration mode and influent carbon/nitrogen ratio affect pollutant removal, gas emission, functional genes and bacterial community in subsurface wastewater infiltration systems?

Abstract This study investigated the influences of aeration mode and influent carbon/nitrogen ratio on matrix oxygen concentration, pollutant removal, greenhouse gas emission, functional gene abundances and bacterial community in subsurface wastewater infiltration systems (SWISs). Intermittent or continuous aeration enhanced oxygen supply at 0.6 m depth in the matrix, which improved organics removal, nitrogen removal, the abundances of bacterial 16S rRNA, amoA, nxrA, narG, napA, nirK, nirS, norB, nosZ genes, bacterial community Alpha diversity, the relative abundances of Actinobacteria at 0.6 m depth, the relative abundances of Chloroflexi, Gemmatimonadetes, Bacteroidetes and Firmicutes at 0.9 and 1.2 m depth and reduced CH4 and N2O conversion efficiencies, the abundance of mcrA gene with carbon/nitrogen ratio of 12 and 16 compared with non-aeration. Increased carbon/nitrogen ratio resulted in higher TN removal efficiencies and lower CH4 and N2O conversion efficiencies in aeration SWISs than those in non-aeration SWIS. Intermittent aeration SWIS obtained high removal efficiencies of 83.2, 85.4 and 90.8% for TN, NH4+ -N and COD and low conversion efficiency of 0.21 and 0.65% for N2O and CH4 with optimal carbon/nitrogen ratio of 12. However, high TN (82.6%), NH4+ -N (84.9%) and COD (92.2%) removal efficiencies and low CH4 (0.67%) and N2O (0.23%) conversion efficiencies were achieved in continuous aeration SWIS with carbon/nitrogen ratio of 16.

Enhancing photocatalytic visible-light-driven oxidation of NOx over Mott-Schottky Ag/SnO2 nanorod heterojunctions

Nitrogen oxides (NOx) is formed by primary emission from diesel engine vehicles. In this study, we synthesized and applied the photocatalytic effect over Mott-Schottky Ag/SnO2 nanorod heterojunctions toward NOx removal under visible light. In detail, the presence of Ag NPs in the Ag/SnO2 nanorod heterojunction, the number of electrons participating in the catalysis is enhanced due to the localized surface plasmon resonance (LSPR) of Ag NPs. In addition, the potential of the reducing region of SnO2 is also changed, thereby creating favourable conditions for the photocatalysis. We determined that 1.5% Ag/SnO2 nanorod heterojunction is the best sample with NO (500 ppb) photodegradation efficiency of 50.64% under visible light irradiation. Moreover, Ag/SnO2 nanorod heterojunction has an excellent stability after undergoing five times recycling and is highly applicable in practical applications with a high NO degradation and low NO2 conversion yield. The Mott-Schottky plots, Tauc plots, and trapping tests were used to build the energy scheme of the Ag/SnO2 heterojunction.

Effect of sulfate-modified CeO2 with different morphologies on NH3-SCR

Three CeO2 catalysts with different morphologies (Rod, Spindle and Cube) were modified by SO42− (dented as S–CeO2) and used for NH3-SCR reaction. The results showed that the order of the NO conversion over different catalysts were in the following sequence: S–CeO2-Rod > S–CeO2-Spindle > S–CeO2-Cube (>80 %) at 300–450 °C, the NO conversion of the S–CeO2 catalyst was affected by the morphologies. A series of characterizations (TEM, H2-TPR, NH3-TPD, N2 adsorption-desorption, XPS, Raman and in situ DRIFTS) were used to investigate the physicochemical properties of catalysts with different morphologies. It showed that the active CeO2 (1 1 1) facets was exposed except CeO2-Cube, and the highly active CeO2 (2 0 0) and (2 2 0) facets were shown in CeO2-Cube and CeO2-Rod, respectively. The order of the temperature of H2 reduction peak was in the following sequence: S–CeO2-Rod (544 °C) < S–CeO2-Spindle (576 °C) < S–CeO2-Cube (612 °C). The order of the ratio of ID/IF2g and the amount of total acid of the catalysts were the same as NO conversion, showed the following sequence: S–CeO2-Rod (0.09) > S–CeO2-Spindle (0.05) > S–CeO2-Cube (0.03), S–CeO2-Rod (18.3 μmol/g) > S–CeO2-Spindle (9.69 μmol/g) > S–CeO2-Cube (9.40 μmol/g), respectively. The NH3-SCR reaction over the three S–CeO2 with different morphologies (Rod, Spindle, Cube) followed the Eley-Rideal and Langmuir-Hinshelwood mechanism. The S–CeO2-Rod was more suitable for NH3-SCR reaction.

Enhanced NOx reduction through reburning of potassium chloride doped biomass at intermediate temperature in oxy-biomass combustion

The challenge of achieving low nitrogen oxide (NOx) emissions in carbon-negative oxy-biomass combustion remains significant. This study focuses on enhancing NOx reduction by doping washed biomass with varying ratios of potassium chloride (KCl) to determine the optimal quantity for maximum NOx reduction. Unlike the traditional high-temperature reburning method used in PC furnaces (above 1000 °C), this study explores reburning at intermediate temperatures (550–850 °C) to assess its feasibility in fluidized bed or grate fired furnaces. Flue gas analysis is performed using an FTIR gas analyzer (Gasmet DX-4000, Finland), while solid residue analysis utilizes SEM-EDS, XRD, XRF, and TGA techniques. Results demonstrate that the highest NO reduction efficiency, up to 80 %, is achieved at a stoichiometric ratio of 0.6, a temperature of 700 °C, and 1.5 % KCl doping in an oxygen-rich environment. These findings highlight the effectiveness of a small amount of KCl doping (1.5 %) in catalyzing heterogeneous NO reduction reactions for enhanced NO reduction. Furthermore, this same KCl doping quantity (1.5 %) effectively suppresses the formation of harmful substances such as HCN and N2O, thus improving the conversion of NO to N2. Overall, this study provides valuable insights for the development of NOx control methods in intermediate temperature oxy-biomass combustion systems.

Ni-modified MIL-100(Fe) catalysts for CO-SCR of NO and reaction mechanism

To promote the activation of the catalysts in the presence of oxygen and at lower temperatures for the selective catalytic reduction of NO with CO (CO-SCR), iron-based metal-organic frameworks (MOFs) catalysts, called MIL-100 (Fe), were prepared by hydrothermal synthesis and further modified with Ni by wet impregnation method. The CO-SCR of NO was evaluated in a fixed-bed reactor. Results proved that the NO conversion over MIL-100(Fe) and 5.8 %Ni-modified catalysts under oxygen-free conditions was 96.6 % and 100 % at 325 °C, respectively. When 2 vol% oxygen was present, the NO conversions over MIL-100(Fe) and 5.8 %Ni modified catalysts at 250 °C were 37.2 % and 96.6 %, respectively, demonstrating that the Ni-modified MIL-100(Fe) catalyst obviously improved the CO-SCR reactivity under O2 atmosphere. UV–vis DRS, HRTEM, FTIR, TGA, etc., and in situ DRIFTS techniques were used to characterize the physical and chemical properties of the catalysts and study the reaction mechanism. The outcomes demonstrated that the incorporated Ni engaged in interactions with Fe the CO-SCR reaction, resulting in the formation of additional surface or surface synergistic oxygen vacancies (SOV and SSOV), thus improving the redox performance of catalysts. Additionally, the Ni-modified catalyst had better redox performance, which was beneficial to converting the adsorbed NOx substances into active substances. The adsorption behavior of NO, CO, and the reaction intermediates were investigated by in situ DRIFTS and a preliminary reaction path was proposed.

Experimental investigation of NO reduction by H2 on Pd using planar laser-induced fluorescence

This study investigates the NO reduction by H2 on a Pd/Al2O3 catalyst in a temperature range of 100–300 °C and NO/H2 ratios from 0.5–2, aiming to gain a deeper understanding of the reaction kinetics and its interaction with mass transfer. Planar laser-induced fluorescence (PLIF) is used to visualize the NO distributions over the catalyst, supplemented by end-of-pipe gas analysis of other components. The reduced Pd-based catalyst undergoes a slow deactivation after exposure to the reactive flow, leading to reduced overall NO conversion and decreased selectivity towards N2. The NO-PLIF measurements are only conducted on the reduced catalyst without considering the temporal evolutions. Despite the overall NO conversion varying only around 50%–65% across all the investigated conditions, the spatially resolved NO distributions reveal three distinct regimes that limit the overall NO conversion: the regime governed by intrinsic reaction rates, the regime constrained by H2 availability, and the regime restricted by NO diffusion. These findings, demonstrating the interaction between reaction kinetics and mass transfer over a heterogeneous catalyst, highlight the significance of analyzing spatially resolved concentration distributions obtained through PLIF measurements. This approach complements the conventional end-of-pipe analysis, offering a more comprehensive understanding of the underlying processes.