NO Conversion Research Articles

Improving activity and SO2 resistance for NH3-SCR of NOx over V-Ce-Ox catalysts by phosphorylation treatment to regulate both oxidation property and acid sites

SO2 poisoning remains an unresolved issue for NH3-SCR of NOx catalysts, particularly under low temperature conditions. In this study, a phosphorylation approach was used in preparation of V-Ce-Ox (VC) catalysts by regulating both oxidation property and acid sites to improve SO2 tolerance at low temperature in the NH3-SCR process. Among all the as-prepared catalysts, 2.4 wt%P-VC exhibited the widest temperature window (>90 % NO conversion, 240 ∼ 420 °C) and good resistance to SO2. A variety of characterization approaches were used to investigate the effects of the phosphorylation approach on the catalytic activity and microstructure of V-Ce-Ox catalyst. According to the characterization results, the improvement role of 2.4 wt%P-VC is connected to the balance between acidity and oxidation ability. This originates from the largest amount of Brønsted acid sites to adsorb NH3 and surface adsorbed oxygen species. The results also showed that different H3PO4 loading contents can promote or inhibit the NH3-SCR reaction, it is possible that this is because a lower H3PO4 content (≤2.4 wt%) can result in more Brønsted acid sites (P-O-NH4+), whereas the higher H3PO4 content (≥4.2 wt%) can cause a greater reduction in Lewis acid sites and the total surface acidity. Furthermore, the in-situ DRIFTS and SO2-TPD results reveal that the oxidation of SO2 is weakened by the formation of amorphous VOPO4 and CePO4 on xwt%P-VC catalysts, which reduces the formation of VOSO4 and Ce2(SO4)3 by reducing the oxidation of SO2 on the catalyst. This work eventually achieves the highest catalytic performance and the superior SO2 resistance of the V2O5-CeO2-based catalyst by presenting a viable technique for changing the acid and redox sites on the VC catalyst.

High performance of PrMnO3 perovskite catalysts for low-temperature soot oxidation

In the field of heterogeneous catalysis for diesel vehicle exhaust, designing low-cost catalysts with high efficiency and low-temperature catalytic oxidation to reduce the ignition temperature of soot remains a significant challenge. In this study, a series of praseodymium manganese perovskites (PrMnO3) were synthesized using a solution combustion method that regulated the molar ratio of glycine to nitrate (φ). Notably, when φ = 1, the prepared catalyst (PMO-1) exhibited a multistage pore structure and large specific surface area, demonstrating excellent catalytic oxidation performance for soot (T10 = 280 °C, T50 = 377 °C, TOF=16.2 × 10-4 s−1, SCO₂ > 99 %) and NO (maximum NO conversion rate of 80 %). During soot combustion in a NO+O2 reaction atmosphere, the strong NO oxidation capacity of the catalyst provides sufficient NO2 as an oxidant for soot combustion, thereby further enhancing its oxidation performance (T50 = 360 °C). This study concludes that the excellent low-temperature catalytic oxidation performance of the PrMnO3 catalyst is attributed to the large specific surface area provided by its multistage pore structure and the extensive dispersion of active sites, which enhance the contact efficiency between soot particles and active sites. Additionally, based on multiple characterization results such as XPS, TOF calculations, and Soot-TPR, the PMO-1 catalyst exhibits a high content of lattice oxygen and efficient lattice oxygen migration. These properties further supply active oxygen for the NOx-assisted soot oxidation mechanism. This study offers a valuable, simple, and cost-effective strategy for designing perovskite catalysts and efficiently removing PM particles.

Role of Ammonia in Aerosol Liquid Water, pH, and Secondary Inorganic Aerosols Formation at an Ammonia-rich City in Changzhou

Ammonia （NH3） is an important alkaline reactive nitrogen, which, as a precursor of fine particulate matter, raises public health issues. In this study, online NH3, SO2, NO2, PM2.5, and its water-soluble inorganic ions were detected to deduce the influence of NH3 on aerosol liquid water content （AWC） and aerosol pH, including the formation of water-soluble secondary ions in PM2.5 in winter in Changzhou, an ammonia-rich city in the Yangtze River Delta area in winter. The results showed that NH4+ mainly existed in the form of NH4NO3 and （NH4）2SO4, and the remaining NH4+ existed as NH4Cl. Owing to the NH3-NH4+ buffer system, the aerosol pH values were found at 4.2 ± 0.4, which was positively correlated with the NH3 content. The aerosol pH value variation narrowed with the increase in PM2.5 concentration and tended to be between 4 to 5. AWC increased exponentially with the increase in humidity and SNA content, among which NH4NO3, （NH4）2SO4, and NH4Cl contributed 58.5%, 18.4%, and 8.3%, respectively, due to their hygroscopicity. Aerosol pH, AWC, and NH3-NH4+ conversion promoted the gas-to-particle conversion of SO2 and NO2. In Changzhou, rich NH3-NH4+ were found to maintain relatively high pH values, push up AWC, and promote the heterogeneous reaction of SO2, whereas NO3- generation was dominated by a homogeneous reaction, which was accelerated by NH3. According to the simulation results, relatively noticeable changes in aerosol pH and AWC could be found by the reduction of up to 30% of NH3.

Effect of diglyme on diesel engine combustion and un/regulated emission

ABSTRACT The influence of diglyme on diesel engine combustion and emission, including regulated and unregulated emissions, was carried out at various engine modes, in which ultra-low sulfur diesel and diglyme were employed, and diesel-diglyme blends were designed containing specific mass oxygen content varied from 2% to 20% corresponding to 5% to 53% diglyme blended by volume. With the addition of diglyme, actual air/fuel ratio decreased in general, combustion initiated earlier by 5.3% to 14.6% at tested modes but weighted center postponed with short ignition delay and combustion duration, meanwhile maximum in-cylinder combustion temperature reduced by 3 to 30°C, which affected emissions significantly.Consequently, the optimized PM-NOx trade-off was obtained with particulate and NOx decreased simultaneously, but formaldehyde and acetaldehyde increased by the varation from 3% to 190% with the addition of diglyme. Sulfur dioxide emission was much lower with ultra-low sulfur diesel compared that with other fuels including conventional diesel, about one order of magnitude smaller, and diglyme could bring further reduction by maximum of 62.5%. In addition, the oxygen in diglyme promoted CO oxidation and NO2 conversion from NO, leading to an increased NO2/CO ratio by even to 375.9%.

Seasonal variation of water-soluble inorganic ions and carbonaceous components of PM2.5 and PM1 in industrial and residential areas of Suizhou, China

Seasonal variations of fine particulate matter (PM) and its chemical components in Suizhou are investigated by collecting PM2.5 and PM1 samples from industrial and residential areas between March 2017 and February 2018. The findings reveal more severe PM pollution in industrial areas compared to residential areas. Concentrations and percentages of water-soluble inorganic ions (WSII) in PM are higher in spring and winter. Notably, the high levels of SO42− and NO3− in PM1-2.5 indicate that secondary transformation of SO2 and NOx significantly contribute to the rapid increase in PM1-2.5. The conversion of NO2 to NO3− is a key factor in the winter increase of mass concentrations of PM2.5 [ρ(PM2.5)], while photochemical reactions involving NO2 drive the summer increase of ρ(PM2.5). Organic carbon (OC) and elemental carbon (EC) are mainly distributed in PM1, with OC peaking in winter. Chemical fractionation of PM reveals that carbonaceous components have a greater impact on PM1 concentration than WSII, whereas WSII more significantly affects ρ(PM2.5) than carbonaceous components. The OC to EC ratio in industrial areas (2.5 ± 1.4) and residential areas (1.9 ± 0.8) suggests more prominent secondary aerosol pollution in industrial areas. Significant correlations between secondary organic carbon (SOC), SOC conversion rate (ηSOC), and concentrations of O3-8h and NO2 in Suizhou further indicate that O3 and NO2 levels in the atmosphere influence the generation of SOC and ηSOC.

Excellent low-temperature activity and resistance to K-poisoning in NH3-SCR de-NOx reaction over CeSnOx with phosphorylation treatment catalyst

Resistance to alkali metal poisoning remains a challenge for Ce-based denitration (de-NOx) catalysts. In this paper, improved low-temperature performance and resistance to K poisoning were achieved by phosphorylating CeSnOx. The activity tests revealed that the phosphorylated CeSnOx (3 wt%P/CeSn) exhibited over 90 % NO conversion at 190–450 °C and >90 % NO conversion at 240–400 °C even after K poisoning. The mechanism of phosphorylation treatment against K poisoning was investigated by many characterizations and DFT calculation. The results showed that the phosphorylation treatment facilitated the interaction between Ce and Sn, and K interacts more preferentially with PO43- species. This prevents K from destroying the Ce-O-Sn structure to form a Ce-O-K structure, which in turn maintained the catalyst’s redox properties. Moreover, the phosphorylation treatment supplemented the acidity of 3 wt%P/CeSn compared with CeSnOx. This effectively mitigated the reduction of acidity caused by K and ensured the adsorption and activation of NH3 on the catalyst surface.

Facile preparation of Fe-Beta zeolite-supported transition metal oxide catalysts and their catalytic performance for the simultaneous removal of NOx and soot

Diesel engine exhaust comprises nitrogen oxides (NOx) and soot particles, which cause serious air pollution. However, owing to the contradictory nature of NOx reduction and soot oxidation, a trade-off exists in the simultaneous removal of NOx and soot. Consequently, catalytic technology has become a hot research topic. This study prepared MOδ/Fe-Beta (M=Fe, Co, Ni, Mn, Cu) catalysts through incipient wetness impregnation using Fe-Beta as the support and explored the catalytic performance of the above catalysts. The results exhibited the good performance of the prepared catalysts. The introduction of Mn resulted in a lower peak temperature of soot combustion for the catalyst, and slightly decreased deNOx performance of Fe-Beta. The soot combustion temperature was as low as 422 °C, and the temperature window for 80% NO conversion was 164–423 °C. The interaction between MnOδ and zeolite can regulate the acid sites and produce sufficient active oxygen species for the catalyst. The catalytic activity of the MnOδ/Fe-Beta catalyst is due to its strong redox property, appropriate number of acid sites and sufficient number of active oxygen species. In addition, the catalyst had good stability and water and sulfur resistance, therefore it had great potential for future application in simultaneous removal of NOx and soot from diesel engine exhaust.

Influence of bulk-phase acidity, organic fraction, and dissolved oxygen on the photosensitized renoxification of nitrate in NaNO3/humic acid mixtures

Nitrate renoxification significantly influences atmospheric nitrogen cycling and global OH budgets. Although numerous nitrite acid (HONO) formation pathways from nitrate photolysis have been widely reported, the influence of various environmental factors and aerosol properties on reactive nitrogen production remains largely unclear. In this work, we employed NaNO3/humic acid (HA) as a model nitrate photosensitization system to investigate the crucial roles of aerosol acidity, organic fraction, and dissolved oxygen in the production of HONO, NO2, and NO2-. The presence of HA at 10 mg/L resulted in a remarkable increase in HONO production rates by approximately 2–3 times and NO2- concentration by 3–6 times across a pH range of 5.2 to 2.0. Meanwhile, the molar fraction of gaseous HONO in total N(III) production increased from 4 % to 69 % as bulk-phase pH decreased from 5.2 to 2.0. The higher organic fraction (i.e., 20 and 50 mg/L HA concentration) instead inhibited HONO and NO2 release. The presence of dissolved oxygen was found to be adverse for reactive nitrogen production. This suggests that the HA photosensitizer promoted the secondary conversion of NO2 to HONO mainly via reduced ketyl radical intermediates, while superoxide radical formation might exert a negative effect. Our findings provide comprehensive insights into reactive nitrogen production from photosensitized nitrate photolysis mediated by various external and internal factors, potentially accounting for discrepancies between field observations and model simulations.

Synthesis of Co/Ni-Doped mesoporous spinel ferrite microspheres for enhanced Low-Temperature SCR performance

The iron-based catalysts commonly used in the selective catalytic reduction (SCR) process cannot meet the increasingly stringent low-temperature NOx emission targets. In this study, mesoporous microspherical MFe2O4 (M=Co, Ni) spinel ferrite catalysts were synthesized by hydrothermal method and applied to the SCR of ammonia (NH3-SCR) reaction. Compared to Fe3O4, both NiFe2O4 and CoFe2O4 catalysts showed higher SCR catalytic activity at low temperature. The NiFe2O4 catalyst achieved a NO conversion of 95.5 % at 240 °C, while CoFe2O4 exhibited a high NO conversion of 97.6 % at 180 °C and a N2 selectivity of 99.6 %. Various characterization experiments revealed that the introduction of Co and Ni resulted in the formation of a specific mesoporous microsphere morphology in CoFe2O4 and NiFe2O4 catalysts, along with the generation of a large number of oxygen vacancies and acidic sites on the surface. These features facilitate the sequential adsorption and activation of NH3 and NOx species, resulting in excellent catalytic activity at low temperatures. Detailed in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) measurements showed that on NiFe2O4 the reaction follows the Eley–Rideal (E–R) mechanism, whereas it proceeds through the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms on the CoFe2O4 catalyst. This work provides a feasible strategy for enhancing the low-temperature SCR reaction over iron-based catalysts; moreover, the elucidation of the complete reaction mechanism offers a solid foundation for future improvements in denitrification catalysts.

Unraveling the NH3-SCR-DeNOx Mechanism of Cu-SSZ-13 Variants by Spectroscopic and Transient Techniques.

Commercial SSZ-13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post-synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico-chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3-SCR-DeNOx). Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu-containing SSZ-13 materials. The NH3-SCR-DeNOx pathways are verified via in situ DR UV-Vis, in situ FT-IR and EPR, temperature-programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3-SCR-DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu-SSZ-13_6.5 and Cu-SSZ-13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop-flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase.

Synergistic catalysis of NO and chlorobenzene over Mn3O4-CeO2 catalysts: Acid sites, catalytic pathway and mechanism

Catalyst active sites and surface acidity are crucial for the synergistic catalysis of NOx and dioxins, determining the selectivity towards N2 and CO2. This study synthesized Mn3O4-CeO2 catalysts to investigate the influence of these sites on the catalytic performance for NO and chlorobenzene. Mn0.086Ce, made by the redox method, showed the highest Mn-Ce interface, achieving nearly complete conversion of chlorobenzene and NO at 180℃, with CO2 and N2 selectivity reaching about 80 % and 100 %, respectively. EPR, NH3-TPD and Py-IR analyses revealed that the Mn-Ce interface induces the formation of Lewis acid sites and oxygen vacancies, facilitating the adsorption and conversion of chlorobenzene, NH3, and NO. Mn adjacent to Lewis acid sites is the main active site, while Ce acts as an electron transfer agent. Based on the results of in-situ DRIFTS and TOF-SIMS, the possible degradation pathway for chlorobenzene was proposed and as follows: phenol, benzoquinone, maleic anhydride, propionic acid, CO2, and H2O. The NH3-SCR reaction follows the Eley-Rideal mechanism at 150–300℃.

Kinetics and H2O Influence on NOx Trapping and Selective Catalytic Reduction over Ce/Pd Doping Catalyst.

In this paper, the removal effects and activation energy of Ce and Pd doping on pollutants (CO, C3H6, and NO) were comparatively analyzed by using characterization methods and constructed kinetic equations. Furthermore, the problems of the water influence mechanism on the NSR process were also discussed. The results show the following: (1) Pd doping effectively improves the removal of CO (80%) and C3H6 (71%) in the low-temperature section of the catalyst (150-250 °C) compared to Ce doping, while Ce doping exhibits excellent low-temperature conversion of NO. (2) The reaction activation energy of the LaKMnPdO3 catalyst was 9784 kJ/mol, which was significantly lower than that of the LaKMnCeO3 catalyst. (3) The presence of H2O has an important enhancement effect in the storage performance of the LaKMnPdO3 catalyst for NOx but decreases the catalytic reduction of NO. It provides a solution for the effective treatment of the increasing problems of particulate matter and ozone pollution.

A High-Performance Mn/TiO2 Catalyst with a High Solid Content for Selective Catalytic Reduction of NO at Low-Temperatures.

Mn/TiO2 catalysts with varying solid contents were innovatively prepared by the sol-gel method and were used for selective catalytic reduction of NO at low temperatures using NH3 (NH3-SCR) as the reducing agent. Surprisingly, it was found that as the solid content of the sol increased, the catalytic activity of the developed Mn/TiO2 catalyst gradually increased, showing excellent catalytic performance. Notably, the Mn/TiO2 (50%) catalyst demonstrates outstanding denitration performance, achieving a 96% NO conversion rate at 100 °C under a volume hourly space velocity (VHSV) of 24,000 h-1, while maintaining high N2 selectivity and stability. It was discovered that as the solid content increased, the catalyst's specific surface area (SSA), surface Mn4+ concentration, chemisorbed oxygen, chemisorption of NH3, and catalytic reducibility all improved, thereby enhancing the catalytic efficiency of NH3-SCR in degrading NO. Moreover, NH3 at the Lewis acidic sites and NH4+ at the Bronsted acidic sites of the catalyst were capable of reacting with NO. Conversely, NO and NO2 adsorbed on the catalyst, along with bidentate and monodentate nitrates, were unable to react with NH3 at low temperatures. Consequently, the developed catalyst's low-temperature catalytic reaction mechanism aligns with the E-R mechanism.

Zr‐doped β‐MnO2 for Low‐temperature Selective Catalytic Reduction of NO by NH3: Preparation, Characterization and Performance

Nanowire‐MnO2 and a series of Zr‐doped MnO2 catalysts with different Zr/Mn molar ratios were successively prepared by hydrothermal and impregnation methods. The Zr‐doped MnO2 catalyst with Zr/Mn molar ratio of 0.04 and calcination temperature of 400°C, proved to be the optimal that possessed the highest low‐temperature denitration efficiency. It showed the NO conversion of ~92% and N2 selectivity of ~80% at 150°C. Characterization results demonstrated that the main active phase of the catalyst was β‐MnO2, Zr atoms interacted with Mn atoms, and Zr doping increased the structural defects, oxygen vacancies and weak acid sites, which effectively enhanced the low‐temperature denitration activity and N2 selectivity of β‐MnO2, also improved the water and sulphur resistance to some extent.

The effect of SO2 on NH3-SCR reaction synergistic CO oxidation over a Mn-Co-Ti catalyst

Mn–Co–TiO2 prepared using an impregnation method was applied to synergistic NH3-based selective catalytic reduction (NH3-SCR) and CO oxidation in a simulated flue gas. The NO conversion, NO oxidation, and CO oxidation were substantially enhanced after adding 15% Co3O4 to the 20MnTi catalyst. In an NO or NO + NH3 atmosphere, CO oxidation over the Mn–Co–TiO2 catalyst was mainly restrained by the competitive adsorption and formation of sulfate species. In contrast, the NH3-SCR reaction progressed almost unimpeded in a CO atmosphere. A SO2 atmosphere drastically reduced the NO conversion of the catalyst at lower temperatures and almost completely suppressed the oxidation activities toward NO and CO. The amount of remaining NO oxidation (approximately 10%) was primarily contributed by gas-phase oxidation of NO by O2. Next, fresh and SO2-poisoned Mn–Co–TiO2 were characterized using various methods. Results indicated that no conspicuous change occurred in the crystal structure of the samples after SO2 poisoning, but numerous sulfate products were deposited on the catalyst surface. The deposition of sulfate-species byproducts decreased the specific surface area and pore volume of the catalyst and shifted the surface acid sites to a higher temperature range, further reducing the CO oxidation performance. Moreover, the catalytic reaction of CO and NO followed the Eley–Rideal mechanism. Furthermore, the mechanisms through which multicomponent flue gases influence the synergistic NH3-SCR and CO oxidation performance were proposed.

Performance and Mechanism of Co and Mn Loaded on Fe-Metal-Organic Framework Catalysts with Different Morphologies for Simultaneous Degradation of Acetone and NO by Photothermal Coupling.

VOCs can be used instead of ammonia as a reducing agent to remove NO, achieving the effect of removing VOCs and NO simultaneously. Due to the high energy consumption and low photocatalytic efficiency required for conventional thermocatalytic purification, photothermal coupled catalytic purification can integrate the advantages of photocatalysis and thermocatalysis in order to achieve the effect of pollutants being treated efficiently with a low energy consumption. In this study, samples loaded with Co and Mn catalysts were prepared using the hydrothermal method on Fe-MOF with various morphologies. The catalytic performance of each catalyst was analyzed by studying the effects of their physicochemical properties through various characterizations, including XRD, SEM, BET, XPS, H2-TPR, TEM and O2-TPD. The characterization results demonstrated that the specific surface area, pore volume, high valence Co and Mn atoms, surface adsorbed oxygen and the abundance of oxygen lattice defects in the catalysts were the most critical factors affecting the performance of the catalysts. Based on the results of the performance tests, the catalysts prepared with an octahedral-shaped Fe-MOF loaded with Co and Mn showed a better performance than those loaded with Co and Mn on a rod-shaped Fe-MOF. The conversions of acetone and NO reached 50% and 64%, respectively, at 240 °C. The results showed that the catalysts were capable of removing acetone and NO at the same time. Compared with the pure Fe-MOF without Co and Mn, the loaded catalysts showed a significantly higher ability to remove acetone and NO simultaneously under the combination of various factors. The key reaction steps for the catalytic conversion of acetone and NO on the catalyst surface were investigated according to the Mars-van Krevelen (MvK) mechanism, and a possible mechanism was proposed. This study presents a new idea for the simultaneous removal of acetone and NOx by photothermal coupling.

The promotion of rare earth on Pt-SiO2-Al2O3 catalyst for NO oxidation in diesel exhaust

The effective oxidation of NO is the key to the catalytic treatment of diesel vehicle exhaust. Improving the NO oxidation ability is mainly to optimize the chemical state of the active site (Pt), followed by increasing the number of active centers. Considering that the atoms with electronegativity weaker than Pt can provide electrons to change the chemical state of Pt, rare earth elements with weak electronegativity are selected as additives to obtain Pt/M-SiO2-Al2O3 (M = Sc, Y, La, Ce, Pr, Nd, Sm, Eu) catalysts by co-impregnation method. Among them, the Pt/La-SiO2-Al2O3 catalyst has the best NO oxidation performance, compared with the Pt-SiO2-Al2O3, the NO conversion rate increased by 28 %. Due to the special outer electron arrangement of La, its electronegativity is the smallest in rare earth, which makes its outer electrons easy to transfer to Pt atoms, and has the strongest electron interaction. Thus, the highest content of Pt0 was detected in CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS). In addition, CO chemisorption and transmission electron microscopy (TEM) confirmed that the introduction of La in the catalyst can significantly improve the dispersion of precious metals. Notably, this simple approach of affecting electron interaction by introducing weakly electronegative elements provides a reference for the design of noble metal catalysts with different valence states to solve complex problems.

Low Temperature NO and CO Conversion with a Mechanistic Approach on Ru-Composed Cerium Oxide.

Catalytic reduction of NO with CO at a lower temperature is an extremely challenging task, thus requiring conceivable surfaces to overcome such issues. Ru-substituted CeO2 catalysts prepared via the solution combustion method were employed in CO oxidation and NO-CO conversion studies. The characterization for material formation and surface structure was carried out through XRD, SEM, TEM, and BET surface area. The catalytic study revealed the promising behavior of 5% Ru in CeO2 for the 100% conversion of NO-CO at 150 °C, proving it to be an excellent exhaust material. These observed results are also supported by temperature-programmed studies, i.e. TPD of NO and CO in addition to NH3-TPD and H2-TPR for their convincible surface interaction that is inclined toward a significant change in the conversion path. Additionally, the proposed mechanism, based on the experimental evidence, sheds light on the NO-CO redox reaction, directing the reaction pathway toward the Langmuir-Hinshelwood and Mars-Van Krevelen-type route. Moreover, the exceptional performance can be attributed to the strategic incorporation of Ru in CeO2, where the strong interaction of Ru-Ce is able to gain a high synergy for NO and CO conversion.

Post-Synthetically Treated ERI and SSZ-13 Zeolites Modified with Copper as Catalysts for NH3-SCR-DeNOx

ERI and SSZ-13 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results in terms of NH3-SCR-DeNOx show that the applied treatments improved the catalytic activity of the Cu-containing ERI-based materials; however, the NO conversion did not vary for the different materials treated with NaOH or NaOH/HNO3. For the micro-/mesoporous Cu-containing SSZ-13, a lower NO conversion in NH3-SCR-DeNOx was observed. Thus, our findings challenge the current paradigm of enhanced activity of micro-/mesoporous catalysts in NH3-SCR-DeNOx. The modification of the supports results in the presence of different amounts and kinds of copper species (especially isolated Cu2+ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The present copper species further differentiate the formation of reactive reaction intermediates. Our studies show that besides the μ-η2,η2-peroxo dicopper(II) complexes (verified by in situ DR UV-Vis spectroscopy), copper nitrates (evidenced by in situ FT-IR spectroscopy) also act as reactive intermediates in these catalytic systems.

An effective cascade strategy over a Sn-enriched phosphate material: Upcycling a reductive adsorbent into an environmental catalyst

A calcium phosphate-based material enriched with Sn (8.3 at.%, as revealed by X-ray photoelectron spectroscopy) was successfully used in the reductive adsorption of Cr(VI) to Cr(III) for water remediation and, after use, repurposed into a catalyst for NO oxidation into NO2.The use of multiple characterization techniques (Mӧssbauer spectroscopy, synchrotron X-ray diffraction, TEM, and HAADF-STEM/EDS) provided information on Sn-speciation (Sn(II)/Sn(IV) = 1.2), structural composition, and morphological features. Cassiterite (rutile-type SnO2) and hydroromarchite (tin oxide-hydroxide Sn6O4(OH)4) crystalline phases characterized the material, along with the presence of an amorphous Ca3(PO4)2 phase.Notably, about 15 mgCr(VI)∙g−1 could be effectively reduced over a broad pH range (2–11), even in the simultaneous presence of various anions and cations, with concurrent adsorption of the resulting Cr(III), thanks to the adsorption properties of the phosphate phase. The kinetic constant of Cr(VI) removal was as high as 0.0058 g∙mg−1∙min−1 and increased in the presence of a pool of cations (0.0147 g∙mg−1∙min−1). The catalytic performances of the adsorbent after use in Cr(VI) reductive adsorption were studied in the 150–450 °C interval at 15,000–80,000 h−1 space velocity. About 90 % of NO conversion at 350 °C was observed.This study highlights the adaptability and efficiency of the developed material across different environmental remediation processes.