Catalytic N2 Research Articles

Taming the acidity and redox property of phosphorylated Ca doped LaMnO3 for catalytic n-butylamine elimination: Breaking the see-saw effect of activity and N2 selectivity

The see-saw effect of catalytic activity and N2 selectivity is a long-stand challenge towards industrial nitrogen-containing volatile organic compounds (NVOCs) deep degradation. Herein, a series of Ca doped LaMnO3 perovskite catalysts with varied acidity were engineered by a H3PO4 post-modification strategy, which remarkably improve the catalytic activity and N2 selectivity in n-butylamine purification. Amongst, Ca-1-P20 exhibits superior activity (T90 at 156 °C), high N2 selectivity (98 % at 200 °C), and satisfactory stability under dry/humid conditions. Surface La(PO)4 species weaken the Mn-O bonds and result in the generation of oxygen vacancy and adsorbed oxygen species, accelerating the cleavage of C-C and C-N bonds of n-butylamine and intermediates as amide and alcohols. H3PO4 post-modification-induced acidity facilitates the adsorption of n-butylamine and provides plenty of NH2* species, further promoting the internal SCR process and ultimately enhancing the N2 selectivity. Nevertheless, excessive acid sites can strongly absorb amide species and reduce the catalytic activity.

Production of γ-valerolactone from furfural by core-shell ZSM-5 supporting Ru-Zr bimetals through enhanced cascade reaction

In this study, a catalyst comprising Ru-Zr bimetals supported on core-shell ZSM-5 zeolite is tailored for catalytic conversion of furfural to yield γ-valerolactone via promoted two-step cascade reaction. ZrO2 encapsulated within hierarchical ZSM-5 zeolite is synthesized via a one-pot hydrothermal method, followed by sequential treatment with NaOH to yield Zr@ZSM-OH. Subsequently, the RuO2 component is introduced through impregnation, followed by calcination to obtain Ru-Zr@ZSM-OH. In conversion of furfural, the synergistic effect of highly dispersed ZrO2 acting as Lewis acid sites, combined with Brønsted acid sites provided by zeolite, facilitates the production of isopropyl levulinate via catalytic hydrogenation transfer, under either H2 or N2 atmosphere. In the secondary step, the introduced RuO2 promotes the adsorption and spillover of active H2, thereby accelerating the conversion of isopropyl levulinate to γ-valerolactone. The as-synthesized Ru-Zr@ZSM-OH catalyst achieves an impressive yield of 92.6 wt% of γ-valerolactone after just a 2 h reaction at 175 °C.

The interface electric field accelerated charge transfer kinetics of 1D/0D TiO2/Bi2Sn2O7 Z-scheme heterojunction with close contact interface significantly improves photothermal catalytic N2 reduction

The slow kinetics of charge transfer and weak redox ability hindered the practical application of photocatalytic N2 reduction. Therefore, in this article, Bi2Sn2O7 nanoparticles were grown in situ on the surface of TiO2 nanorods using a solvothermal method to form a 1D/0D TiO2/Bi2Sn2O7 (TBSO-15) Z-scheme heterojunction with a tight contact interface. The results of density functional theory calculations (DFT) and Kelvin probe force microscopy (KPFM) indicated that the difference in Fermi levels led to spontaneous rearrangement of charges at the heterojunction interface and the formation of a strong interfacial electric field (IEF). IEF provided a powerful driving force for the spatial separation of photogenerated charges, accelerating charge transfer dynamics. Secondly, the Z-scheme migration pathway of photo-generated charges between TiO2 and Bi2Sn2O7 enhanced the redox ability of TBSO-15 and formed a spatially separated redox center. In addition, molecular dynamics simulations (MD) showed that the photothermal effect significantly promoted the dynamic diffusion of N2 and H2O, accelerating the chemical reaction kinetics. Therefore, the synergistic effect of the two significantly improved the performance of Photothermal catalytic N2 reduction (PTC-NRR). After simulating solar irradiation for 2 h, the PTC-NRR performance of TBSO-15 achieved 327.25 μmoL·g−1 in pure water, which was 19.7 times that of TiO2 and 4.2 times that of Bi2Sn2O7, respectively. This study provides a reference for the synergistic effect of charge space transfer dynamics and photothermal effect to promote PTC-NRR.

Bimetallic Fe, Co-Modified TiO2 Derived from NH2-MIL-125(Ti) as an Efficient Photocatalyst for N2 Fixation

The conversion of nitrogen (N2) and water (H2O) into NH3 by photocatalysis under ambient conditions has been considered an environmentally friendly strategy. However, developing effective catalysts for N2 fixation is still challenging. Herein, we report a bimetallic JH Fe, Co/TiO2 derived from NH2-MIL-125(Ti) by the fast Joule heating (FJH) method for visible–light–driven catalytic N2 fixation. It was found that the photocatalytic N2 reduction efficiency of bimetallic FC@TiO2-JH was improved, enabling an NH3 yield rate of 110.14 µmol g−1 h−1 without any sacrificial agents. Furthermore, the rate was higher than those of Fe@TiO2-JH and Co@TiO2-JH, suggesting that the synergistic effect between Fe and Co broke the electronic equilibrium and increased the center of its d-band, enhancing electronic feedback to the antibonding π* orbitals of N2 while weakening the bonding energy of N≡N. Meanwhile, the rate was about 2.75 times higher than that of FC@TiO2-TF, which was calcined in a tube furnace. It is assumed that FJH might lead to the formation of lattice defects, leading to localized charge deficiency, enhanced carrier separation, and transport. Thus, doping of Fe and Co synergistically interacted with the defects produced from FJH, facilitating the photocatalytic reduction process. As detected, it had a greater ability to separate hole–electron pairs and transferred electrons to adsorbed N2 at faster rates. Our work demonstrates a prospective strategy for designing bimetallic catalysts derived from NH2-MIL-125(Ti) for N2 fixation.

Copper-perovskite interfacial engineering to boost deNOx activity

By adjusting the Cu doping level and calcination temperature during synthesis of a series of noble metal-free lanthanum copper manganite perovskites LaCuxMn1-xO3, we show the importance of tuning the redox chemistry for optimum steering of the catalytic activity and N2 selectivity in the catalytic reduction of NO by CO. A prerequisite is the in situ formation of an extended copper-perovskite phase boundary. The associated improvement of redox and surface properties by Cu addition leads to an optimized balance of the reduction of the catalyst in the NO+CO reaction mixture. The creation of oxygen vacancies improves the reaction kinetics and initiates the NO dissociation. Strongly dependent on the calcination temperature, the Cu/Mn ratio, the reducing agent, as well as the reaction temperature as parameters for Cu-perovskite interfacial control, surface reduction can induce partial copper exsolution, significant perovskite reduction, agglomeration of exsolved Cu particles and eventual decomposition of the catalyst structure. We show that increasing the amount of initial copper incorporated into the perovskite structure can beneficially extend the phase boundary, but exceeding the amount of copper leads to increased sintering of the copper particles at the expense of catalyst activity, especially in repeated catalytic cycles. Increasing the calcination temperature, in addition to the initial sintering of the catalyst and shifting the reaction onset temperature to higher temperatures in the first cycle, improves the reduction resistance of the catalyst. Consequently, in order to form a higher amount of phase boundary-bound active sites, stronger reducing conditions than provided by the NO+CO reaction mixture are needed. This effect can be counterbalanced by using stronger reduction agents prior to performing subsequent catalytic cycles by inducing the exsolution process.

Radiocatalytic ammonia synthesis from nitrogen and water.

The development of alternative methods to the Haber-Bosch process for ammonia (NH3) synthesis is a pressing and formidable challenge. Nuclear energy represents a low-carbon, efficient and stable source of power. The harnessing of nuclear energy to drive nitrogen (N2) reduction not only allows 'green' NH3 synthesis, but also offers the potential for the storage of nuclear energy as a readily transportable zero-carbon fuel. Herein, we explore radiocatalytic N2 fixation to NH3 induced by γ-ray radiation. Hydrated electrons (e- aq) that are generated from water radiolysis enable N2 reduction to produce NH3. Ru-based catalysts synthesized by using γ-ray radiation with excellent radiation stability substantially improve NH3 production in which the B5 sites of Ru particles may play an important role in the activation of N2. By benefitting from the remarkable penetrating power of γ-ray radiation, radiocatalytic NH3 synthesis can proceed in an autoclave under appropriate pressure conditions, resulting in an NH3 concentration of ≤5.1mM. The energy conversion efficiency of the reaction is as high as 563.7mgNH3·MJ-1. This radiocatalytic chemistry broadens the research scope of catalytic N2 fixation while offering promising opportunities for converting nuclear energy into chemical energy.

The catalytic deoxygenation reaction temperature and N2 gas flow rate influence the conversion of soybean fatty acids into Green Diesel

BackgroundGreen diesel is a promising alternative as a petroleum replacement given the worldwide demand for petroleum fuel. Environmental issues have drawn public attention and concerns towards advancing renewable energy development. A catalytic deoxygenation (deCOx) was carried out to produce green diesel from soybean oil (SO) using a low-cost NiO-doped calcined dolomite (NiOCD) catalyst. MethodThe structure, chemical composition and morphology of NiOCD were comprehensively characterized by XRF, BET, TPD-CO2, SEM and TEM. In this study, the effect of two operating parameters, reaction temperature and flow rate of nitrogen, was discovered using a one-factor-at-a-time (OFAT) optimisation study. In addition, the life cycle cost analysis (LCCA) of stepwise catalyst preparation and green diesel production has been performed. Significant findingsAn optimal reaction temperature of 420 °C was found to provide the highest yield of green diesel (47.13 wt.%) with an 83.51% hydrocarbon composition. The ideal nitrogen flow rate, however, was found to be 50 cm3/min, which produced 41.80 wt.% of green diesel with an 88.63% hydrocarbon composition. The deoxygenation reaction was significantly impacted by both reaction temperature and nitrogen flow rate. According to LCCA, NiOCD catalyst has potential to lower the overall cost of producing green diesel compared to commercial zeolite catalysts.

Promoting photothermal catalytic N2 reduction through dynamic mass transfer and accelerated charge transfer dynamics

The effective adsorption and mass transfer of N2 at the catalytic active site, along with efficient photogenerated charge transfer at the interface are the prerequisites for the photothermal catalysis N2 reduction. Here, the hydrophobic-hydrophilic biphasic heterojunction Bi2WO6/ Bi2Sn2O7 (BWSO-20) was prepared by solvothermal method, and a strong interfacial internal electric field (IEF) was formed. The effects of N2 dynamic mass transfer and interface charge transfer kinetics on the performance of photothermal catalytic N2 reduction (PTC-NRR) was investigated. The results from in-suit DRIFTS, DFT, and molecular dynamics simulations (MD) indicated that a biphasic structure enhanced the dynamic mass transfer of N2 in the hydrophobic phase (BSO) and H2O in the hydrophilic phase (BWO) simultaneously. Additionally, the IEF that accelerates the transfer kinetics of photo-generated charges. Therefore, more photo-generated electrons and holes could transfer to the surface of the hydrophobic/hydrophilic phase catalyst and undergo redox semi-reactions with N2 and H2O. The PTC-NRR reached 366.1 μmoL·g−1 when using BWSO-20 without adding sacrificial agent. This work provides a new way to achieve efficient photothermal N2 reduction based on the interfacial charge transfer kinetics accelerated by the interfacial internal electric field and the dynamic mass transfer enhanced by hydrophobic – hydrophilic two-phase heterojunction.

Catalytic performance and mechanism of PtxVW catalyst for selective catalytic oxidation of high-concentration NH3

It is foreseeable that a high-concentration NH3 may exist in exhaust gas of NH3-fuel engines, which may result in some negative damages to ecological environment. Herein, a series of PtxVW catalysts with extremely low Pt doping amounts were synthesized with the aim to remove high-concentration NH3 efficiently via selective catalytic oxidation (SCO) method. The results showed that, Pt0.04VW catalyst (0.04 wt% Pt) achieved a complete NH3 conversion at 250 ºC. Both catalytic activity and N2 selectivity of Pt0.04VW catalyst were much superior over Pt/Al2O3 catalyst (1 wt% Pt) in a wide temperature range of 250–450 ºC. XPS, Raman and H2-TPR results indicated that Pt existed in the lattice of VOx and formed Pt-V bimetallic oxides. The interaction between Pt and V played a key role in the NH3-SCO reactions. DFT calculation demonstrated that dual electron transfer pathways between Pt and V atoms in PtxVW catalysts were beneficial for NH3 coordination on Lewis acid sites, then enhancing NH3-SCO reactions. In-situ DRIFTS and NH3-TPD product analysis suggested that NH3-SCO reactions on Pt0.04VW catalyst surface abide by internal selective catalytic reduction (i-SCR) and hydrazine mechanisms. Moreover, coordinated NH3 species on Lewis acid sites, bidentate nitrate species were the main intermediates in NH3-SCO reactions over Pt0.04VW catalyst.

Transition metal single-atom supported on W2N3 as efficient electrocatalysts for the nitrogen reduction reaction: A DFT study

The problems of poor Faraday efficiency and high overpotential usually limit electrochemical nitrogen reduction (NRR) catalysts. In this paper, 28 different transition metal single-atoms (TM-SAs) supported on W2N3 (TM@W2N3) were designed by density functional theory (DFT) for catalytic N2 reduction. The stability, N2 activation capacity, selectivity and NRR mechanism of TM@W2N3 were analyzed. Following the screening process, only 9 TM@W2N3 (TM=Sc, Ti, V, Co, Cu, Y, Mo, Ag, W) structures were identified as exhibiting high stability, strong activation capacity and high NRR selectivity. And then N2 activation mechanism of V@W2N3, Mo@W2N3 and W@W2N3, as well as the Gibbs free energies of its four NRR reaction pathways were further discussed. The overpotentials (η) of Mo@W2N3 and V@W2N3 to NRR are 0.129 V and 0.470 V, respectively. The overpotential (η) of W@W2N3 is the lowest at 0.059 V, while its catalytic activity is the highest. V@W2N3 and W@W2N3 are more likely to follow the distal pathway for NRR, while Mo@W2N3 is more likely to follow the enzymatic pathway. This study offers some theoretical foundation and reference for the design of new and efficient electrocatalytic NRR catalysts.

Engineering single-atom catalysts on triazine-based covalent organic frameworks for enhanced photocatalytic performance in N2 reduction

The solar conversion of nitrogen to ammonia is a green, sustainable, and promising way to fix nitrogen. However, designing a photocatalyst with high activity, selectivity, and stability for the N2 reduction reaction (NRR) is challenging because of the slow inert activation of N2 and competitive hydrogen evolution reaction (HER). Herein, a single metal site anchored to a triazine-based covalent organic framework (Tr-COF) backbone (named TM@Tr-COF; TM = Fe, Co and Ni) is fabricated for high-performance catalytic N2 reduction. Density functional theory calculations show that the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF can effectively activate N2 and reduce it to NH3 via the electron “acceptance–donation” process. Meanwhile, the NRR occurs via the enzymatic pathway on the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF with a limiting potential of 0.38 V, 0.58 V and 0.54 V, respectively. Furthermore, the anchoring of Fe/Co/Ni on the Tr-COF allows the Tr-COF to be adjusted to the appropriate edge position and visible light-absorption region, indicating that the system may be a promising and efficient photocatalyst. Compared with other competitive reactions, the system exhibits high selectivity for NH3 production and inhibits competitive HERs. These findings have considerable implications for innovatively designing highly active single-atom catalysts supported by COFs.

Construction and Function of Thiolate-Bridged Diiron NxHy Nitrogenase Model Complexes.

ConspectusBiological nitrogen fixation mediated by nitrogenases has garnered significant research interest due to its critical importance to the development of efficient catalysts for mild ammonia synthesis. Although the active center of the most studied FeMo-nitrogenases has been determined to be a complicated [Fe7S9MoC] hetero-multinuclear metal-sulfur cluster known as the FeMo-cofactor, the exact binding site and reduction pathway of N2 remain a subject of debate. Over the past decades, the majority of studies have focused on mononuclear molybdenum or iron centers as potential reaction sites. In stark contrast, cooperative activation of N2 through bi- or multimetallic centers has been largely overlooked and underexplored, despite the renewed interest sparked by recent biochemical and computational studies. Consequently, constructing bioinspired bi- or multinuclear metallic model complexes presents an intriguing yet challenging prospect. In this Account, we detail our long-standing research on the design and synthesis of novel thiolate-bridged diiron complexes as nitrogenase models and their application to chemical simulations of potential biological N2 reduction pathways.Inspired by the structural and electronic features of the potential diiron active center in the belt region of the FeMo-cofactor, we have designed and synthesized a series of new thiolate-bridged diiron nitrogenase model complexes, wherein iron centers with +2 or +3 oxidation states are coordinated by Cp* as carbon-based donors and thiolate ligands as sulfur donors. Through the synergistic interaction between the two iron centers, unstable diazene (NH═NH) species can be trapped to generate the first example of a [Fe2S2]-type complex bearing a cis-μ-η1:η1-NH═NH subunit. Significantly, this species can not only catalyze the reductive N-N bond cleavage of hydrazine to ammonia but also trigger a stepwise reduction sequence NH═NH → [NH2-NH]- → [NH]2-(+NH3) → [NH2]- → NH3. Furthermore, an unprecedented thiolate-bridged diiron μ-nitride featuring a bent Fe-N-Fe moiety was successfully isolated and structurally characterized. Importantly, this diiron μ-nitride can undergo successive proton-coupled electron transfer processes to efficiently release ammonia in the presence of separate protons and electrons and can even be directly hydrogenated using H2 as a combination of protons and electrons for high-yield ammonia formation. Based on combined experimental and computational studies, we proposed two distinct reductive transformation sequences on the diiron centers, which involve a series of crucial NxHy intermediates. Moreover, we also achieved catalytic N2 reduction to silylamines with [Fe2S2]-type complexes by ligand modulation.Our bioinspired diiron cooperative scaffold may provide a suitable model for probing the potential N2 stepwise reduction pathways from the molecular level. Different from the traditional alternating and distal pathways dominated by mononuclear iron or molybdenum complexes, our proposed alternating transformation route based on the diiron centers may not involve the N2H4 intermediate, and the convergence point of the alternating and terminal pathways is imide, not amide. Our research strategy could inform the design and development of new types of bioinspired catalysts for mild and efficient nitrogen reduction in the future.

Active learning driven discovery of novel alloyed catalysts for selective ammonia oxidation

Alloy catalysts design faces the contradiction of small sample and huge screen space, especially in rational design with multi-objective and multi-constraints. Here, we conduct the active learning enabled innovative catalyst screening in alloy space composed of transition metal elements. First, the small dataset and large search space are constructed based on knowledge informed feature group. Then, the surrogate model based on Gaussian process regression are trained for predicting catalytic activity and N2 selectivity descriptors for selective catalytic oxidation of ammonia (NH3-SCO) process, merely based on the small dataset. Furthermore, coupling pareto solution and Bayesian optimization, the active learning driven material searching are performed in the huge alloy spaces with more than 1000 configurations. After 3 iterations with high throughput calculation on 30 alloyed configurations and further theoretical validation based on microkinetic and stability analysis, 9 ensemble configurations are considered as innovative alloy catalysts of NH3-SCO with reactivity and selectivity trade-off. Our study provides the reliable framework for catalyst design with multi-objective and multi-constraints when facing with small sample data and huge searching space and gives the specific guidance for rational design of NH3−SCO alloy catalysts.

Bimetallic NH2-MIL-101(Fe, Co) as highly efficient photocatalyst for nitrogen fixation

Developing effective catalysts for N2 photofixation at ambient conditions is highly desirable but still challenging. Herein, we reported a novel Co-doped NH2-MIL-101(Fe) (NM-Fe) bimetallic organic framework (BMOF) for visible-light-driven catalytic N2 fixation. It was found that the doping of Co ions could effectively enhance light-harvesting, reduce the conduction band potential, suppress the recombination of photogenerated carriers, and promote the activation of N2. Consequently, the photocatalytic N2 reduction efficiency of bimetallic NH2-MIL-101(Fe, Co) (NM-Fe-Co) was obviously boosted. The sample with the optical Co/Fe molar ratio of 0.15, namely NM-Fe-0.15Co, enabled an ammonia evolution rate up to 335.7 µmol g−1 h−1 without the aid of any sacrificial agents, a 4.4-fold increase over the monometallic NM-Fe baseline. Additionally, the bimetallic NM-Fe-Co displayed excellent stability. The possible reaction mechanism of nitrogen fixation over NM-Fe-Co was proposed based on in-situ infrared analysis. Our study demonstrates a promising strategy for designing potent MOF-based catalysts for N2 photofixation.

O defect anchored Ru on BiOBr with nanoconfined structure for catalytic N2 fixation

Photocatalytic N2 reduction using H2O to produce NH3 offers a promising alternative to the energy-intensive Haber-Bosch process. Nevertheless, its efficiency is hampered by the low solubility of N2 in water, the high stability of NN and the competing H2 evolution reaction (HER). In this study, we present a highly efficient nanohybrid system employing BiOBr nanoflowers with O defect as a platform for anchoring Ru. The designed nanohybrids exhibit a significantly higher NH3 generation rate of 121.97 μmol g−1 h−1, which is 6.1 and 2.8 times higher than that of pristine BiOBr-NS and Ru modified BiOBr without O defect, respectively. Experimental analyses and theoretical calculations reveal that the nanoflower structure with confined nano-space promotes the enrichment of N2 on the catalyst, the synergistic O defects and Ru facilitate the selective adsorption and activation of N2 and lower the energy barriers of the rate-determining *N-N to *N-NH step.

Efficient Cu-Co Dual-Site promotes selective catalytic oxidation of ammonia over cobalt based catalysts

Selective catalytic oxidation of NH3 (NH3-SCO) into N2 and H2O is an efficient method to eliminate excessive NH3 emission from stock farming, agriculture, industrial sectors and NH3 slip in coal-fired power plants and diesel vehicles. However, it is a great challenge to develop the Co3O4 catalyst with high activity and high N2 selectivity at low temperature. Herein, a series of Cu doped Co3O4 catalysts is designed and synthesized, with discovering the role of Co-O bond strength by copper regulation in modulating oxygen vacancies and lattice oxygen to enhance the intrinsic activity and N2 selectivity of NH3-SCO. The Cu1Co2O4 catalyst (93 % NH3 conversion and 80 % N2 selectivity at 160 °C) achieves a higher catalytic performance compared with Co3O4 (78 % NH3 conversion and 50 % N2 selectivity at 160 °C). In addition, the N2 generation rate by normalizing over specific surface area for Cu1Co2O4 (13.1 μmol m-2h−1) is 1.7 times to that of Co3O4 (8.0 μmol m-2h−1), and the apparent activation energy of Cu1Co2O4 (36.7 kJ mol−1) is lower compared to that of Co3O4 (59.8 kJ mol−1). Reactive oxygen species and enhanced electron transfer promote the oxidation of NH3 to nitrate species, which can be further converted to N2 rather than N2O by remaining NH3 on the Cu site. The Cu-Co dual sites significantly contribute to the catalytic activity and N2 selectivity. This doping strategy is beneficial for the development of Co-O bond strength modulation in spinel catalyst and also provides a new idea for improving the NH3-SCO activity and N2 selectivity of Co-based spinel.

Single-atom catalytic N2 fixation with integrated descriptors on a novel π-π conjugated graphitic carbon nitride (g-C13N15) platform obtained by self-doping design: Prediction of ultrahigh activity and desirable selectivity

Great enthusiasm in nitrogen reduction reaction (NRR) towards the robust design of efficient catalysts is being stimulated by a promising active moiety featured by metal-Nx, yet tackling the activity and selectivity dilemmas remains one of the most urgent and challenging tasks. Herein, based on a self-doping strategy and first-principles calculations, an emerging and stable graphitic carbon nitride, g-C13N15, is rationally proposed for the first time, and TM@g-C13N15 (TM = from Ti to Au) single-atom catalysts benefiting from delocalized π−π conjugated interactions between substituted C3N3 rings toward NRR are constructed. High-throughput “Four-Step” screening strategy helps Re@g-C13N15 stand out from 23 TM-centers quickly since the binding strength of the target *N2H and *NH2 adsorbates can be manipulated by Re to compromise. First-principles calculations reveal that Re@g-C13N15 possesses satisfactory selectivity and impressively, miserly energy consumption with a low limiting potential of −0.20/-0.31 V for side-on/end-on N2-adsorption. Also, good thermodynamic stability, large Re-diffusion barrier, outstanding electrochemical durability, and facile synthesis for Re@g-C13N15 ensure its implementations in ambient conditions. Particularly, good linear relationships between descriptors (ICOHP, Bader charge, bond length, d-band center, and spin moment) are established to describe/explain intrinsic activity trends/mechanism, bridging the relation between the intrinsic property and activity.

Enhanced activity and SO2 tolerance in low-temperature NH3-SCR of NOx over MnCr catalyst by hetero-oxide modification

Developing NH3-SCR catalysts with high humid-SO2 resistance is of great significance for NOx emission control of the two-stroke low-speed ship. For further optimizing the catalytic performance and SO2 tolerance of Mn-Cr catalyst, Al2O3, CeO2 and Nb2O5 were doped by coprecipitation. Through structural analyses, it was determined that the incorporation of Al and Ce effectively increased the surface area of the catalysts and promoted the dispersion of various components throughout them. Moreover, the introduction of Nb led to the formation of secondary particle aggregates, ultimately strengthening the structural stability of the catalysts. The catalytic performance, N2 selectivity and SO2 tolerance of the co-doped catalyst containing Al2O3, CeO2 and Nb2O5 showed remarkable improvement. The NOx conversion of MnCrCeAlNb was exceeding 90% and N2 selectivity above 97% at 175–300 °C and remained around 88% after 10 h reaction under 150 ppm SO2 and 10 vol% H2O at 225 °C. Co-doping Al2O3, CeO2 and Nb2O5 greatly improved the reducibility and significantly increased the number of surface acid sites. And the XPS results demonstrated that the addition of niobium enhanced the redox properties and adsorbed oxygen through the electron transfer between Mn4+ and Cr3+, resulting in a significant promotion in the NH3-SCR performance and humid-SO2 tolerance. In particular, the cause of the excellent humid-SO2 tolerance of the MnCrCeAlNb was investigated by TG and FT-IR, demonstrating that the Nb addition significantly reduce the formation of (NH4)2SO4, NH4HSO4 and sulfate on the surface of MnCr catalyst. These results suggested that the doping of Hetero-oxide greatly enhanced the low-temperature NH3-SCR and SO2 tolerance of Mn-Cr based catalysts.

Effect of Sn(II)/Sn(IV) additive on the catalytic combustion of diethylamine and N2 selectivity over CeZrOx catalyst

The synthesis of CeZrSnOx by co-precipitation with different valence-state of Sn for diethylamine combustion is novel and intriguing. In this research, the Sn(II)/Sn(IV)-doped CeZrOx catalysts (CeZr(Sn)Ox-(Sn2+) and CeZr(Sn)Ox-(Sn4+)) were facilely prepared using the co-precipitation method, and their catalytic activities on destruction of diethylamine were evaluated. Detailed characterizations of the catalysts were conducted using X-ray photoelectron spectrometer (XPS), X-ray powder diffraction (XRD), hydrogen-temperature programmed reduction (H2-TPR), temperature programmed ammonia desorption (NH3-TPD) and so on. For diethylamine combustion, CeZr(Sn)Ox-(Sn2+) showed higher activity and nitrogen selectivity than other catalysts, and a high conversion of diethylamine (>90 %) at 250 °C was obtained. After hydrothermal aging treatment, a high conversion (>90 %) and high N2 selectivity maintained over CeZr(Sn)Ox-(Sn2+)-H at 280 °C, indicating high hydrothermal stability of CeZr(Sn)Ox-Sn2+. Owe to the large specific surface area (SSA), high oxygen mobility and strong redox performance, and the synergy between metal elements in CeZr(Sn)Ox-Sn2+ catalysts, the catalytic properties were enhanced. Moreover, Sn2+/Sn4+ ratio in the catalyst and strong acidic sites on the surface of the catalyst both had significant impacts on the catalytic activity and N2 selectivity of the catalyst. Finally, the mechanism of diethylamine combustion over CeZr(Sn)Ox-Sn2+ was obtained by analyzing the reaction through in-situ diffuse reflection infrared Fourier-transform spectrum (in situ DRIFTS) test.

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.