SO2 Poisoning Research Articles

Redox ability dependent SO2 tolerance for low-temperature NH3-SCR of MnO2@MeOX (Me = Ti, Ce, Cu) catalysts

Elucidating the deposition behavior of sulfates on catalysts of low-temperature ammonia-assisted selective catalytic reduction (NH3-SCR) helps improve their SO2 tolerance and applicability. Therefore, this study aimed to explore the impact of the redox properties of low-temperature NH3-SCR catalysts on their catalytic activity and SO2 tolerance. Oxidizing Mn@Ce, neutral Mn@Ti, and reducing Mn@Cu catalysts were prepared, and their NH3-SCR activities and SO2 tolerances were evaluated. Subsequently, the characteristics of the catalyst poisoned by SO2 over time and the deposition behavior of sulfates on the catalyst were analyzed to determine the reaction pathway between SO2 and the NH3-SCR catalyst. The SO2 tolerance of the catalysts decreased in the following order: oxidizing Mn@Ce > neutral Mn@Ti > reducing Mn@Cu. Combined with the characteristic results, we found that the amount of shell-metal sulfate increased with SO2 poisoning time, indicating it was the dominant factor in catalyst deactivation. Specifically, the amount of shell-metal sulfate followed the order Mn@Cu-S12 (31.4 µmol) > Mn@Ti-S12 (24.9 µmol) > Mn@Ce-S12 (9.5 µmol). Additionally, the increasing SO42− ratio from Mn@Me-S4 to Mn@Me-S12 followed the order Mn@Cu (6.7 %) > Mn@Ti (4.4 %) > Mn@Ce (1.7 %), implying that the reduction of Mn@Cu favors chemical SO2 poisoning pathway and facilitates the deposition of copper sulfate. In contrast, Mn@Ce with its strong oxidation properties, is beneficial for inhibiting the chemical poisoning pathway of SO2 and alleviating the deposition of cerium sulfate. Consequently, this study demonstrates that the redox ability of catalyst regulates the SO2 poisoning pathways, aiding the development of low-temperature NH3-SCR catalysts with high SO2 tolerance.

Enhancing SO2 Resistance of Mn−Ce−Co Loaded Activated Carbon Catalysts for Low‐Temperature NH3‐SCR: Insight into the Effect of Citrate Addition

AbstractThe low‐temperature performance and ability to withstand SO2 poisoning of catalyst are crucial factors in evaluating the NH3‐SCR technology. In this study, honeycomb activated carbon loaded with Mn−Ce−Co catalysts was prepared using the citric acid complex impregnation method, simple impregnation and citric acid pre‐oxidation methods for low‐temperature NH3‐SCR. The synergistic effect of citric acid and ternary metals results in catalysts prepared by the citric acid complex impregnation method exhibiting excellent redox properties and a high abundance of acidic sites. By increasing catalyst acidity and introducing CeO2 sacrificial sites, the catalytic performance was improved, resulting in weaker adsorption capacity of the catalysts for SO2, enhancing SO2 tolerance. The catalyst demonstrated 100 % NOx removal at 160 °C which remained stable even after a 100 ppm SO2 pass for four hours. In addition, the catalyst showed good CO oxidation performance, with 78 % CO removal at 170 °C, which broadened the application scenario of the catalyst. This study highlights the denitrification effect of activated carbon supported Mn−Ce−Co ternary metal oxide catalysts and reveals the potential of multiple coupled approaches in improving the sulfur resistance of the catalysts.

Ultra-low temperature selective catalytic reduction of NOx into N2 by micron spherical CeMnOx in high-humidity atmospheres containing SO2

The solvothermal synthesis of optimized micron-sized spherical Ce1Mn7Ox-350 yields remarkable results in ultra-low temperature NH3-SCR of NOx, with over 91 % NOx conversion achieved between 59 and 255 ℃. Notably, under 5 vol% H2O and 50 ppm SO2, the Ce1Mn7Ox maintains NOx conversion >99 % at 127 ℃ for extended periods, surpassing current ultra-low temperature deNOx standards. This superior performance is attributed to the material's unique characteristics: the regular and porous surface morphology enhances exposure to active sites, particularly Mn3O4(112) facets crucial for ultra-low temperature deNOx, while the rough and loose surface and high Mn2O3(222) exposure mitigate water vapor and SO2 poisoning. Furthermore, the thermal storage effect of the Mn2O3/Mn3O4 system within Ce1Mn7Ox facilitates rapid thermal dissipation and ammonium sulfite decomposition. This process is further augmented by the pores, which aid in the confinement of deNOx reaction heat and facilitate the flushing of flowing flue gas, thereby impeding the formation of ammonium bisulfate.

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.

The [(NH3)4Cu2O2]2+‐Peroxo Complex as the Key Intermediate for NH3‐SCR Activity and Deactivation of Cu‐CHA Catalysts.

AbstractIn NH3‐SCR over Cu‐CHA catalysts in the low‐temperature range 150–300 °C, the activation of oxygen occurs via oxidation of a pair of mobile (NH3)2CuI‐complexes located in the cages of the zeolite. In this step, a reactive [(NH3)4Cu2O2]2+‐peroxo complex (μ‐η2,η2‐peroxo diamino dicopper(II)‐complex) is formed. The chemistry of this complex determines several catalytic properties of the Cu‐CHA catalyst. The reaction of NO with the [(NH3)4Cu2O2]2+‐peroxo complex governs the NH3‐SCR activity. A reaction of the [(NH3)4Cu2O2]2+‐peroxo complex with ammonia hinders the reaction of NO with the complex, thus leading to an inhibition of the NH3‐SCR reaction. Finally, the deactivation in presence of SO2 is due to a reaction of SO2 with the [(NH3)4Cu2O2]2+‐peroxo complex, leading to the formation of Cu−S compounds in the catalyst. In this review, the characterization and the reactions of the [(NH3)4Cu2O2]2+‐peroxo complex with NO, NH3, and SO2, and mean‐field kinetic models based on first principles calculations for NH3‐SCR activity and SO2 poisoning are discussed.

Electricity-driven rapid regeneration of ceramic paper-based soot filters with conductive potassium-supported antimony-doped tin oxide catalyst

To address short-term emission of massive particulate matter (PM) from diesel engines, rapid regeneration of catalyzed diesel particulate filters (CDPF) based on soot combustion is a considerable challenge. Herein, we employed an aluminosilicate fiber-weaved ceramic paper (CP) as a filter matrix, on which highly active potassium-supported antimony-doped tin oxides (K/ATO) were coated to fabricate a CDPF. The K/ATO/CP monolith preserves the 3D-network structure of CP while incorporating the mesopores of K/ATO, providing potential for trapping soot particles effectively. Furthermore, electricity pulses are designed to pass through the conductive K/ATO coating on the monolith for CDPF regeneration, achieving nearly complete soot conversion within less than half a minute using 1400 J of energy input. Both the reaction rate and the energy efficiency surpass previously reported those of other methods for soot combustion. Mechanism studies revealed that the electricity pulse can stimulate the release of tremendous lattice oxygen from the catalyst and in turn trigger rapid soot combustion, and boost surface sulfate decomposition to alleviate SO2 poisoning. This work presents an electrification strategy to realize rapid regeneration of CDPF for effective PM elimination utilizing onboard electricity system for hybrid powers.

Formation of Fe2(SO4)3-Fe2O3 interface induced by OCFGs electrostatic anchoring on AC surface: High efficiency NH3-SCR performance at low temperatures

Low-temperature activity and SO2 poisoning were the key factors limiting the application of NH3-SCR catalysts. In this study, Fe2(SO4)3/AC and Fe2(SO4)3/OAC catalysts were prepared by oxidation function modification and incipient wetness impregnation. In the temperature range of 100–250 ℃, the catalytic performance and SO2 resistance of Fe2(SO4)3/AC and Fe2(SO4)3/OAC catalysts were investigated, the denitrification efficiency increased from 28 % (Fe2(SO4)3/AC) to 80 % at 100 °C and reached 100 % at 170 °C, and 100 ppm SO2 was introduced at 250 ℃ for 24 h, the denitrification efficiency remains 100 % unchanged. The mechanism of activity enhancement was further explored by BET, XRD, ICP, TG, XPS, FT-IR, H2-TPR and NH3-TPD. The results showed that (NH4)2S2O8 modification enhanced the surface acidity, and the increase of surface oxygen-containing functional groups improved the redox performance. At the same time, due to electrostatic anchoring effects of oxygen-containing functional groups, Fe3+ and SO42- were adsorbed at different sites and promoted the binding of S to the carbon skeleton to form −C-S-C-. Thus, the interaction between OAC and Fe2(SO4)3 caused part of Fe2(SO4)3 to decompose into Fe2O3, and the formation of Fe2(SO4)3-Fe2O3 interface further enhanced the acidity and redox properties. More importantly, the decomposition temperature of NH4HSO4 was lower and the decomposition was more thorough on the Fe2(SO4)3/OAC than that of Fe2(SO4)3/AC. Finally, the possible mechanism of (NH4)2S2O8-modified Fe2(SO4)3/OAC catalyst to improve NH3-SCR performance was proposed, which is of great significance for the development of NH3-SCR catalyst with sulfur resistance at low temperatures.

Crystalline phase-modulated PtOx nanoparticles exhibit superior methane combustion performance and sulfur poisoning resistance: Multi-interaction regulation

Up to now, methane combustion catalysts generally suffer from issues such as poor reaction stability and susceptibility to sulfur poisoning, which have become the key factors restricting their application, so it is necessary to construct catalysts with excellent chemical stability of the active center and strong sulfur resistance. Here, we showed the crystal phase-modulated state of PtOx nanoparticles (PtOx NPs) on TiO2 and investigated their effects on the reactivity of methane catalytic combustion and anti-SO2 poisoning properties. It was found that Pt/r-TiO2 showed superior activity, stability, and resistance to SO2 poisoning. Transmission electron microscope (TEM) images showed that the PtOx NPs on the surface of r-TiO2 were much more stable than a-TiO2 for the reason that the Ostwald ripening of PtOx NPs on a-TiO2 was facilitated due to the strong metal-support interaction (MSI) between PtOx NPs and TiO2 and the low migration energy of the PtOx NPs on TiO2, while they were moderate of Pt/r-TiO2, and then the active sites were stabilized during methane combustion. The activity was controlled by the size and electronic structure of PtOx NPs, which were stable on the surface of r-TiO2 with a higher Pt4+ content, and the density functional theory (DFT) calculations further revealed the role of r-TiO2 in increasing the quantities of surface oxygen vacancies. Moreover, the SO2 tolerance of Pt/r-TiO2 was also the best among all kinds of Pt-based catalysts prepared, which was attributed to the minimal adsorption energy (Ead) of SO2 on r-TiO2, and the absence of sulfate and sulfite deposition on the Pt/r-TiO2 catalyst confirmed by TGA and in-situ DRIFTS studies on SO2 adsorption. In this research, the anti-SO2 poisoning and reaction stability were realized by adjusting the interaction between SO2, active components, and supports, which provided a new insight for the design of stable Pt-based SO2-resistant catalysts.

Exploring the joint influence of SO2 and alkali metal on FeW mixed oxides catalyst for NOx elimination

The coexistence of multiple substances in the flue gas, such as alkali metal and SO2, results in the NH3-SCR catalysts suffering from serious deactivation. Therefore, we systematically studied the effects of coexisting SO2 and Na on the FeW oxides for NOx elimination. This study elucidates that the joint influence mechanism of these substances on SCR activity was regulated by reaction temperatures. When the temperature was below 300 °C, the catalyst suffered a double whammy. The addition of SO2 in process of NH3-SCR resulted in a decrease in the activity of Na-poisoned FeW catalyst. It was largely due to the formation of inorganic SO42-, which not only consumed the NH3 but also blocked active sites. With the increase of reaction temperatures above 300 °C, the SO2 could interact with Na2O to construct a ternary electron interaction of SO42--Na+-FeW, contributing to the improvement of alkali metal resistance. This sulfate adjusted the D-band center energy of the catalyst closer to the Fermi level, thereby boosting the adsorption energies of NH3 and NO, increasing their adsorption abilities. Furthermore, sulfate binding broke the Na-O-Fe and Na-O-W bonds, resulting in the restoration of Fe-O-W and Fe-O-Fe active sites and accumulation of Na+ species. Precise characterizations and theoretical calculations shed light on the joint mechanism of SO2 and alkali metals which provide guidance to the design SCR catalyst with excellent resistance to SO2 and alkali metal poisoning.

High-temperature selective reduction of NOx into N2 catalyzed by different ion-doped titania

The active titanium-based composite oxide carrier with strong thermal stability and surface acidity is the key to ensure the steady operation of high-temperature deNOx catalyst for gas-fired exhaust. In this paper, W6+, Zr4+, Mo6+, Al3+, Si4+, Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides were synthesized by sol–gel method. The effects of ion species, doping amount, calcination temperature on NH3-SCR deNOx efficiency and resistance to water vapor and SO2 poisoning were investigated. Results showed that the Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides calcined at 630 °C had negligible deNOx activity, while the doping of W6+, Zr4+, Mo6+, Al3+ and Si4+ improved the NH3-SCR activity and anti-water vapor and SO2 poisoning of titanium-based composite oxide. The deNOx efficiency of the best compatibility of the five ions doping was TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 ≈ TiSi0.04Ox-582, which was consistent with the order of total acid amount. The order of resistance to water vapor and SO2 poisoning and resistance to high temperature thermal shock was TiW0.1Ox-630 ≈ TiMo0.12Ox-630 > TiSi0.04Ox-582 > TiZr0.06Ox-538 > TiAl0.11Ox-487. Doping of five ions inhibited the transformation of anatase TiO2 to rutile TiO2 in different degrees. Among them, W6+ doping had the best inhibitory effect and the exposure ratio of TiO2 (101) crystal plane in TiW0.1Ox-630 was the highest, which was beneficial to NH3-SCR of NOx. Furthermore, the concentration of chemisorbed oxygen Oα was in the order of TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 > TiSi0.04Ox-582. The higher the concentration of Oα is, the more conducive to the oxidation of NO to NO2 and the promotion of NH3 adsorption and dehydrogenation oxidation.

SO2-resistant hollow carbon spheres encapsulated Pt nanoparticles for benzene oxidation

In the catalytic combustion of volatile organic compounds (VOCs) using noble metal catalysts, resistance to SO2 poisoning poses a significant challenge. To tackle this problem, Pt nanoparticle catalysts encapsulated in hollow carbon spheres (Pt@HCS catalysts) are synthesized. The Pt@HCS catalyst exhibits excellent benzene conversion, achieving 100 % conversion at 165 °C under an air velocity of 20,000 mL/(g h). Compared to the conventional supported Pt/HCS catalyst, the Pt@HCS catalyst demonstrates a significantly improved resistance to SO2 poisoning. In the presence of 25 ppm SO2, the Pt@HCS catalyst is capable of maintaining a 100 % benzene conversion rate within 24 h, whereas the conversion rate of Pt/HCS drops substantially to approximately 52 %. It is confirmed that the hollow porous structure provided a larger specific surface area and more adsorption sites, thereby facilitating benzene oxidation. More importantly, in situ DRIFTS reveals that the adsorption and desorption processes of SO2, along with the generation of substances like SO32−, are strictly limited to the surface of the carbon shell, thereby preserving the integrity of the internal reaction environment. Multiple characterizations combined with density functional theory (DFT) have demonstrated a unique separation effect over Pt@HCS, whereby the hydroxyl groups on the carbon shell preferentially capture SO2 while allowing benzene molecules to enter the cavities of the catalyst. In this way, any internal ingress of SO2 and competition with benzene for Pt adsorption is effectively avoided. This study offers a potential solution to enhance the performance of noble metal catalysts in the presence of sulfur compounds.

Experimental and theoretical study on recovered nano amorphous selenium as efficient adsorbents for mercury capture from flue gas

The cost-effective removal of gaseous elemental mercury from coal-fired flue gas is crucial for environmental protection. In this study, nano amorphous selenium (nano-a-Se) adsorbent was recovered from desulfurization wastewater to remove Hg0 in flue gas. The results indicate that nano-a-Se has a high efficiency in the amorphous form with a saturated adsorption capacity of 2034.32 mg g−1. The Se utilization ratio of nano-a-Se reached 80% of the theoretical limit. Meanwhile, nano-a-Se exhibited high resistance to NO and SO2 poisoning. Moreover, the Hg0 removal mechanism of nano-a-Se was analyzed by experimental analysis and density functional theory (DFT) calculations. The results demonstrate that nano-a-Se can convert Hg0 into stable mercury selenide, a high-value by-product with little risk of mercury re-release. Therefore, nano-a-Se is expected to be a novel adsorbent with high efficiency in capturing Hg0, which can help realize the resource utilization of toxic elements from the environment.

Deciphering SO2 poisoning mechanisms for passive NOx adsorption: A kinetic modeling approach and development of a high-resistance catalyst

Passive NOx adsorption (PNA) is a promising technology aimed at reducing NOx emissions from vehicles during the cold start phase of the engine. This work investigated the SO2 poisoning mechanism of PNA through a combination of experimental research and kinetic modeling, leading to the development of a novel PNA sample with high resistance to SO2 poisoning. Pd/SSZ-13 samples were synthesized using different drying conditions, revealing that samples dried at room temperature showed lower degradation (10 %) compared to those dried at 80 °C (26 %). Investigation into the degradation revealed that ion-exchanged Pd sites with a hydroxyl group were more resistant to SO2 poisoning than other Pd sites. It is also found that SO2 aids in NOx storage on Pd sites, enhancing the PNA performance. A kinetic model was developed to describe the SO2 poisoning behavior and its influence on NOx storage. The model, which was verified under various conditions, effectively simulated the PNA behavior and SO2 poisoning of Pd/SSZ-13.

New insight into the intrinsic effect of sulfur dioxide on Hg0 oxidation in the absence/presence of SCR atmosphere

Collaborative control of Hg0 in selective catalytic reduction (SCR) device is considered to be feasible and cost-effective, whereas the negative impact of SO2 remains a thorny issue for industrial applications. Herein, the intrinsic effect mechanism of SO2 on Hg0 oxidation in the absence/presence of SCR atmosphere over the hollow nanotube CoMnTiOx was systematically investigated. It was demonstrated that SO2 possessed a bidirectional effect on Hg0 oxidation, the facilitating effect was attributed to the production of HgSO4 and the inhibiting effect was due to the formation of metal sulfate, which was exactly equilibrated when the deposition of sulfate on the catalyst reached 3.88 %. Interestingly, the presence of SCR atmosphere enhanced the suppression of SO2 on Hg0 oxidation, which was caused by the fact that SO2 + O2 consumed partial Hg0 to form HgSO4, upsetting the reaction equilibrium of HgO reduction induced by SCR atmosphere and ultimately aggravating the reduction process of the already generated HgO. This work provides a new and comprehensive insight into the effect of SO2 on Hg0 oxidation during the synergistic removal of Hg0 in SCR device, which is instructive in exploring strategies to mitigate the SO2 poisoning.

Constructing Heterointerfaces in Dual-Phase High-Entropy Oxides to Boost O2 Activation and SO2 Resistance for Mercury Removal in Flue Gas.

The low O2 activation ability at low temperatures and SO2 poisoning are challenges for metal oxide catalysts in the application of Hg0 removal in flue gas. A novel high-entropy fluorite oxide (MgAlMnCo)CeO2 (Co-HEO) with the second phase of spinel is synthesized by the microwave hydrothermal method for the first time. A high efficiency of Hg0 removal (close to 100%) is achieved by Co-HEO catalytic oxidation at temperatures as low as 100 °C and in the atmosphere of 145 μg m-3 Hg0 at a high GHSV (gas hourly space velocity) of 95,000 h-1. According to O2-TPD and in situ FT-IR, this extremely superior catalytic oxidation performance at low temperatures originates from the activation ability of Co-HEO to transform O2 into superoxide and peroxide, which is promoted by point defects induced from the spinel/fluorite heterointerfaces. Meanwhile, SO2 resistance of Co-HEO for Hg0 removal is also improved up to 2000 ppm due to the high-entropy-stabilized structure, construction of heterointerfaces, and synergistic effect of the multicomponents for inhibiting the oxidation of SO2 to surface sulfate. The design strategy of the dual-phase high-entropy material launches a new route for metal oxides in the application of catalytic oxidation and SO2 resistance.

Significant enhanced SO2 resistance of Ce-doped OMS-2 catalyst by building the CeO2 shell for the low-temperature SCR of NO with NH3

Developing highly SO2-resistance catalysts for the NOx reduction at low temperatures is a significant challenge. In this study, we fabricate a catalyst of Ce-doped manganese oxide octahedral molecular sieve by building the CeO2 shell (Ce-OMS-2@CeO2) to solve this problem. This catalyst showed high selective catalytic reduction with NH3 (NH3-SCR) activity and enhanced resistance to SO2-induced deactivation. Ce-OMS-2@CeO2 exhibited outstanding NH3-SCR activity and anti-sulfur performance at 200 °C. The mesoporous CeO2 shells exerted no influence on the transport of reactants to catalytic active sites. The NH3-SCR on Ce-OMS-2@CeO2 catalyst occurred via the Langmuir-Hinshelwood mechanism with adsorption of NH3 and NO on different sites, thus preventing competing adsorption. The CeO2 shell bound SO2 strongly in priority, thus protecting the Ce-OMS-2 core from SO2 poisoning. Moreover, a dynamic balance was established between NH4HSO4 formation and decomposition over our Ce-OMS-2@CeO2 catalyst at low temperatures, which also hindered the SO2 poisoning in NH3-SCR reaction.

Influence of Particle Size of CeO2 Nanospheres Encapsulated in SBA-15 Mesopores on SO2 Tolerance during NH3-SCR Reaction

Ce-based selective catalytic reductions with an NH3 (NH3-SCR) catalyst have emerged as a focal point in denitrification catalyst research. However, the correlation between the structural characteristics of Ce-based catalysts and the influence of CeO2 nanoparticle size on SO2 resistance remains unclear. CeO2 nanospheres with different sizes of less than 10 nm were synthesized, and a series of supported CeO2/SBA-15 catalysts were prepared according to the 10 nm pore size of SBA-15. These catalysts were used to explore the influence of the size of the CeO2 nanospheres on these catalysts, specifically on their SO2 resistance in NH3-SCR reactions. With the increase in size, their SO2 resistance became stronger. The results of NH3-TPD, H2-TPR, and XPS indicated that the catalyst with the largest particle size had the lowest adsorption of SO2, which was attributed to more acid sites and a mutual effect between Si and Ce, resulting in the best SO2 resistance. It was also observed that there was less sulfate deposition on the catalyst by thermogravimetric analysis. In situ DRIFTs revealed that after SO2 poisoning, the NH3-SCR reaction on the catalyst predominantly follows the E-R mechanism. This study offers recommendations for the development of Ce-based SO2-resistant NH3-SCR catalysts, specifically focusing on the synthesis and interaction of nanomaterials.

Highly active and stable VOx/TiO2 nanosheets for low-temperature NH3-SCR of NO: Structure-directing role of support

Low-temperature NH3-SCR over conventional catalysts based on V2O5/TiO2 is significantly limited by the narrow range of operating temperatures and poor activity at low temperatures. Herein, a novel catalyst consisting of defective TiO2 nanosheets supported vanadia (V/TNS) is successfully developed for the low-temperature NH3-SCR of NO. The V/TNS catalyst demonstrated excellent SCR performance, achieving over 95 % conversion with high N2 selectivity (>90 %) over a wide temperature range of 140–380 °C. Importantly, V/TNS was highly resistant to H2O and SO2 poisoning during 30 h of continuous operation, maintaining an NO conversion efficiency that exceeded 92 % at 180 °C. In contrast, a high-surface-area anatase TiO2 particle-supported catalyst (V/TiO2(A)) suffered from catalytic deactivation. Detailed characterization revealed that the TNS support, with its abundant surface defects and high surface area, improved vanadia dispersion and facilitated the formation of surface V4+ species and oxygen vacancies. These factors synergistically enhanced the adsorption and activation of NH3 and NOx, boosting catalytic performance. Moreover, the presence of SO2 had a notable inhibitory effect on the adsorption and activation of NH3 and NOx and their reactions on V/TiO2(A), while these detrimental effects were considerably mitigated on V/TNS.

Unraveling the multi-pollutant removal using M-MoWTi (M = Fe, Mn, Cr) catalyst: experiment and mechanistic study of competition for active sites.

Multi-pollutant removal (MPR) of NO and VOCs simultaneously is efficient of flue gas treatment in coal-fired power plants. But reducing the competition for active sites between NH3, NO, C6H6, and C7H8 remains challenging. Herein, Cr, Mn, and Fe were respectively doped to MoWTi catalyst via wet impregnation. The Fe3+ + Mo5+ ↔ Fe2+ + Mo6+ redox cycle led to an increased proportion of low valence ions (Mo5+ and W5+) and facilitated the creation of active oxygen vacancies with several active sites. It also possessed plentiful mild to strong acid sites with ideal ratio. These factors enhanced catalytic activity of Fe-MoWTi. Remarkable MPR efficiencies of NO, C6H6, and C7H8 were achieved under industrial SCR condition, characterized by low oxygen but high SO2 levels at 340 °C, with removal rates reaching 89.85%, 97.57%, and 86.30% respectively. Theory calculations further revealed that Fe-MoWTi favor NH3 and O2 adsorptions. NO elimination was found to follow both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) processes, supported by in situ DRIFTS analysis. The reactions involving NO/NO2/nitrite/nitrate occurred with NH3(ads)/ NH4+(ads)/NH2 (ads). C6H6 and C7H8 underwent gradual oxidation, formatting alcohols, aldehydes, acids, and maleic acids, before eventually being mineralized to gaseous CO2 and H2O. Findings hold significant potential for application, providing guidance for the development of catalysts with improved resistance against SO2 poisoning and enhanced MPR capabilities.

An entropy engineering strategy to design sulfur-resistant catalysts for dry reforming of methane

The real-world conditions for dry reforming of methane (DRM) inevitably involve the presence of sulfur-containing compounds. Therefore, a general principle for designing sulfur-resistant catalysts is highly desired for the DRM process. In this work, driven by lower Gibbs free energy via entropy engineering, the high-entropy NiAl2O4-type catalyst {(Ni3MoCoZn)Al15Ox} is synthesized by a mechanochemical ball milling process. The DRM performance of the high-entropy catalyst was tested before and after being sulfided by SO2, and compared with those of the control catalysts. Various techniques such as XPS, HAADF-STEM, SO2-TPD, TGA-DSC, FTIR, and DFT theoretical calculations are utilized to reveal the mechanism of sulfur resistance in the high-entropy catalyst. The results indicate that the formation of crystalline high-entropy oxides in the (Ni3MoCoZn)Al15Ox, with its relatively higher configurational entropy, protects itself from SO2 poisoning. This contributes to superior SO2 tolerance compared to the control (Ni3)Al18Ox, and thus offers better DRM stability than the control binary, ternary, or quaternary catalysts after pre-sulfurization. The key essence of sulfur resistance lies in the lower adsorption energy of SO2 on the high-entropy catalyst. This high-entropy stabilization towards an anti-sulfur strategy may inspire the design and development of sulfur-resistant catalysts for catalytic applications in the near future.