Catalysts For N2O Decomposition Research Articles

Carbonaceous materials are not suitable catalysts for direct NO decomposition in exhaust aftertreatment

New approaches for direct NO decomposition catalysis are urgently needed, but using carbonaceous supports appears not to be the way to go.

A Review on the Catalytic Decomposition of NO by Perovskite-Type Oxides

Direct catalytic decomposition of NO has the advantages of being a simple process, producing no secondary pollution, and being good for the economy, which has attracted extensive research in recent years. Perovskite-type mixed oxides, with an ABO3 or A2BO4 structure, are promising materials as catalysts for NO decomposition due to their low cost, high thermal stability, and, of course, their good catalytic performances. In this review, the influence factors, such as A-site substitution, B-site substitution and reaction conditions on the catalytic performance of catalysts have been expounded. The reaction mechanisms of direct NO decomposition are also discussed. Finally, major conclusions are drawn and some research challenges are highlighted.

Cu, Fe and Mn oxides intercalated SiO2 pillared magadiite and ilerite catalysts for NO decomposition

Synthesized magadiite and ilerite samples were pillared with SiO2 and then intercalated with Cu, Fe and Mn oxides to utilize for direct NO decomposition between 400 and 600 °C. Cu-SiO2-pil-ile and Cu-SiO2-pil-mag catalysts exhibited high NO decomposition activity compared to Fe and Mn oxide intercalated catalysts. Remarkably, Cu-SiO2-pil-ile offered 90 % NO conversion and 83 % N2 selectivity at 600 °C. Elemental analysis, XRD, FESEM, DR UV-vis, Raman spectroscopy, N2-adsorption, H2-TPR, O2-TPD and XPS were utilized to study physicochemical characteristics of the materials. The results from XRD and N2 adsorption demonstrated that the samples possessed different pore structures from SiO2-pillared silicates, due to different nature of metal oxides. The Cu-SiO2-pil-ile and Cu-SiO2-pil-mag samples possess a smaller number of Lewis and Brønsted acid sites compared with Fe and Mn oxide intercalated samples. Presence of Cu2+/Cu+ and Fe3+/Fe2+, and synergism between redox centers are major reason for superior performance in NO decomposition. Therefore, the impact of redox properties and NO adsorption on the surface of the catalyst are significant.

Investigation of Different Apatites-Supported Co3O4 as Catalysts for N2O Decomposition

Two types of apatite supports including hydroxyapatite (HAP) and fluorapatite (FAP) were prepared by the co-precipitation method. Supported Co catalysts with the above carriers were synthesized from Co(NO3)2·6H2O via the impregnation method. The catalytic activity for N2O decomposition was investigated using a continuous flowing microreactor system. The catalytic results demonstrated that the Co/HAP exhibited more excellent catalytic activity as well as the impurity gas (H2O, O2, and NO) resistance capability than the Co/FAP in the temperature range of 300–600 °C. Furthermore, the physicochemical properties of Co/HAP and Co/FAP were determined by several relevant characterization methods. The obtained experimental results revealed that Co/HAP possessed larger specific surface area, more ion-exchanged Co2+ and stronger oxygen desorption capacity than Co/FAP, which are the key factors for high N2O decomposition activity. Moreover, compared with Co/FAP, Co/HAP has not only more basic content, but also higher basic site density, which may be also conducive to enhance the electron donating ability of Co2+, thereby promoting the N2O catalytic decomposition.

Insights into the role of surface functional species in Cu-Mn-O thin film catalysts for N2O decomposition

Efficient N2O decomposition using catalytic materials has been gaining attention for long time. Catalytic materials based on noble metals have proved good feasibility; however, their applications are restricted because of the high cost and limited resources. Herein, low-cost catalysts based on copper manganese oxides were synthesized by chemical vapor deposition technique for N2O decomposition. The obtained catalysts were characterized to identify the structure, morphology, composition and arrangement of formed species. The results showed that the particles are getting agglomerated when increasing Mn content, which could be due to the difference in growth and crystallization rates of Cu and Mn. XPS analysis exhibited the existence of several active species such as, Cu and Mn cations, hydroxides and metal carbonates. The ratio of Cu/Mn in bulk is found to be in correlation with the catalytic activity. The catalytic tests of N2O decomposition revealed good activity of all catalysts, and the quality and quantity of the formed surface species have dramatic effect on the activity of the catalysts. When doping by Mn to promote the catalytic activity, formed Cu(OH)2 species at catalysts’ surface appeared to be good promoters in the studied reaction of N2O decomposition by C3H6. However, the existence of Cu metal, as more reduced Cu state, at the surface of catalysts is appeared to decrease the catalytic activity, which may play an inhibitor role in this studied reaction. In addition, Cu auger peak identification revealed the existence of Cu cations with varied oxidation states, leading to establish a correlated sequence of Cu1+>Cu2+>Cu0 with the catalytic activity. This approach of fine-tuning the surface formed species could lead to enhance the performance of other catalysts in different applications.

Nature of active Fe species and reaction mechanism over high-efficiency Fe/CHA catalysts in catalytic decomposition of N2O

Fe/CHA catalysts for N2O decomposition with various Fe loadings (Fe/SAPO-34 and Fe/SSZ-13) were synthesized by a solid-state ion exchange method. Under the same reaction conditions, obviously superior activities of Fe/CHA catalysts were observed in comparison with the current state-of-the-art Fe/zeolite, i.e., Fe/FER. Meanwhile, Fe/CHA catalysts exhibited a robust high-temperature hydrothermal stability. The characterization results and density functional theory (DFT) calculations indicated that the dispersion of Fe species over Fe/CHA catalysts was strongly influenced by the nature of the support, although SAPO-34 and SSZ-13 have similar morphology. Combined with the catalytic performance, dinuclear [HO–Fe–O–Fe–OH]2+ species were identified as the most active Fe species for Fe/CHA catalysts in the N2O decomposition reaction. Furthermore, the dimeric Fe species in SSZ-13 were more active than those in SAPO-34, due to lower Fe–O binding energies. Finally, DFT calculations provided a comprehensive understanding of the N2O decomposition mechanism over Fe/CHA catalysts.

Graphitic carbon nitride-supported cobalt oxides as a potential catalyst for decomposition of N2O

A material of graphitic carbon nitride-supported cobalt oxides (Co3O4/g-CN) was synthesized via a facile and cost-effective impregnation route as a high-performance catalyst for decomposition of N2O. For comparison, bare Co3O4 and other Co3O4 catalysts supported on activated carbon (AC) and γ-Al2O3 (Co3O4-A, Co3O4/AC, and Co3O4/γ-Al2O3, respectively) were also prepared. While g-CN was found to be active in the decomposition of N2O, AC and γ-Al2O3 were inert to this reaction. Co3O4/g-CN showed superior catalytic activity than the other catalysts, and concurrently exhibited much higher specific activity compared to Co3O4-A. The experimental results revealed that all examined catalysts had the spinel structure. The Co species could incorporate into the g-CN matrix/layers and bond to the g-CN matrix through Co-N coordination bonds. The excellent performance of Co3O4/g-CN was attributed to the high surface Co2+ content, massive surface oxygen species, facile electrons transfer from the catalyst to N2O domains, and the synergistic coupling effects among active species such as Co3+/Co2+ redox couple, Co-N, and nitrogen sites. The active Co3O4/g-CN catalyst additional activity tests were conducted with N2O gas contaminated with H2O, O2, or NO.

Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition

Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), X-ray powder diffraction (XRD), N2 physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity.

Effect of Cu substitution on the structure and reactivity of CuxCo3-xO4 spinel catalysts for direct NOx decomposition

A Cu-substituted, Co-based spinel catalyst (CuxCo3-xO4) is introduced for direct NO decomposition to N2 and O2. A series of CuxCo3-xO4 catalysts with varying Cu content (0 ≤ × ≤ 1) were synthesized via a co-precipitation method. Reactivity for direct NO decomposition was measured at 450 °C, with the maximum activity of 2.8 × 10−2 [(μmol NO to N2) g-1 s-1] and selectivity to N2 of 61 % occurring over the Cu0.4Co2.6O4 (x = 0.4) catalyst. Additionally, the CuxCo3-xO4 catalysts demonstrated the ability to mitigate N2O formation as all traces of this greenhouse gas were decomposed regardless of Cu content. Characterization by X-ray diffraction and X-ray absorption spectroscopy revealed the effects of Cu substitution on the occupancies and valencies of the Co and Cu ions in the spinel structure. Activity was shown to correlate with increasing incorporation of Cu2+ into the tetrahedral sites of the normal spinel structure; however, significant formation of a segregated CuO phase caused the activity to decrease when x ≥ 0.4. The bulk structure-activity relationships we elucidate are expected to provide a guide for the design of improved direct NO decomposition catalysts and other bulk oxide catalyst systems based on careful design of the cation arrangements in oxides.

Effect of Water Molecule on Photo-Assisted Nitrous Oxide Decomposition over Oxotitanium Porphyrin: A Theoretical Study

Water vapor has generally been recognized as an inhibitor of catalysts in nitrous oxide (N2O) decomposition because it limits the lifetime of catalytic reactors. Oxygen produced in reactions also deactivates the catalytic performance of bulk surface catalysts. Herein, we propose a potential catalyst that is tolerant of water and oxygen in the process of N2O decomposition. By applying density functional theory calculations, we investigated the reaction mechanism of N2O decomposition into N2 and O2 catalyzed by oxotitanium(IV) porphyrin (TiO-por) with interfacially bonded water. The activation energies of reaction Path A and B are compared under thermal and photo-assisted conditions. The obtained calculation results show that the photo-assisted reaction in Path B is highly exothermic and proceeds smoothly with the low activation barrier of 27.57 kcal/mol at the rate determining step. The produced O2 is easily desorbed from the surface of the catalyst, requiring only 4.96 kcal/mol, indicating the suppression of catalyst deactivation. Therefore, TiO-por is theoretically proved to have the potential to be a desirable catalyst for N2O decomposition with photo-irradiation because of its low activation barrier, water resistance, and ease of regeneration.

Potassium promoted Y2O3-Co3O4 catalysts for N2O decomposition

A Y2O3-Co3O4 catalyst was prepared by an innovative co-precipitation method at the solution boiling temperature, and tested for the N2O decomposition reaction. The catalyst exhibited a higher catalytic activity than that prepared by the common co-precipitation method at 90 °C. In addition, the catalytic performance of the Y2O3-Co3O4 catalyst was further enhanced by K-promoter, which might be related to the weakening of CoO bond and higher concentration of adsorbed oxygen (Oα) on the catalyst surface. Even under the co-presence of oxygen and steam in the feed stream, the K/Y2O3-Co3O4 catalyst showed good catalytic stability and maintained 100% conversion of N2O after a continuous reaction at 400 °C for 30 h.

Preparation and evaluation of iron nanoparticles embedded CNTs grown on ZSM-5 as catalysts for NO decomposition

Due to their high activity and selectivity, single-atoms based catalysts for oxygen removal and wastewater treatment have received enormous attentions in academia and industry. The present work sought to extend the single-atom catalyst concept to NO decomposition. A series of catalysts with highly dispersed iron nanoparticles embedded in carbon nanotubes grown on a ZSM-5 zeolite were prepared using an induced growth method, by pyrolysing melamine and ferric nitrate precursors impregnated on ZSM-5 at 900 °C. The catalysts were then tested for their catalytic activity in NO decomposition using a fixed-bed reactor operating at 300 °C and were shown to be able to completely decompose NO under the test conditions. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), BET, Raman and temperature-programmed oxidation (TPO) were used to study the effects of molar ratio of ferric nitrate to melamine on the active species, sample structures and NO decomposition mechanism. An increase in the molar ratio of melamine to iron nitrate led to an improvement to the dispersibility of iron nanoparticles and enhancement of NO decomposition. The use of ZSM-5 increased the dispersion of iron, thus enhancing the catalytic decomposition of NO. The characterisation of the used catalysts revealed that it was possible to regenerate the catalytic activity by doping and pyrolysing the deactivated catalysts with melamine, with no significant difference to that of the fresh catalysts.

Structure-sensitivity of alumina supported palladium catalysts for N2O decomposition

The catalytic activity of Pd/γAl2O3 for N2O decomposition was found to be highly dependent on the preparation methodology and the number of reaction cycles. Chloride species on the surface of a 2.6 wt. % Pd-Al2O3 catalyst prepared by wet impregnation were identified as inhibiting the activity. Multiple reaction cycles were shown to remove these species, and a subsequent increase in activity was observed; 10.3 molN2O h−1 kgcat−1 in the first use, increased to 28.7 molN2O h−1 kgcat−1 on the fourth use both at 550 °C. Additionally, removal of physisorbed water from the support prior to metal deposition increased the thermal stability of Pd nanoparticles and increased the catalyst activity. Catalysts were subsequently prepared using a deposition technique with an increased concentration of Cl- ions resulted in increased Pd-Cl species in the final catalyst and the catalytic activity was consequently increased due to the improved control of Pd particle size.

Preparation of LaNiO3 perovskite by oxalate and carbonate precursor method for utilization as catalyst for high-temperature decomposition of N2O

The mixed oxide LaNiO3 with perovskite structure was prepared by two relatively new and unconventional methods including preparation and thermal decomposition of mixed metal oxalate or carbonate precursors. The intermediates were prepared by reaction in a highly concentrated suspension (paste). The thermal decomposition conditions of these intermediates were described, and the final calcination temperatures were determined, which were done using thermal analysis methods and X-ray diffraction. During the decomposition of mixed carbonates, one-phase LaNiO3 is produced directly, and in case of decomposition of oxalates, a mixture of LaNiO3 and La2O3 is produced due to the formation of La2O2CO3 during the heating. Catalytic decomposition of nitrous oxide at high temperature (650–930 °C) and high loading (GHSV = 350,000 h−1) has shown high LaNiO3 activity, even at lower temperatures. The results were compared with the same compound obtained by co-precipitation and by solid-state reaction. Methods of preparation based on decomposition of oxalate and carbonate intermediates lead to the preparation of materials with appropriate composition, morphology, specific surface and high catalytic activity.

Highly Efficient NO Decomposition via Dual-Functional Catalytic Perovskite Hollow Fiber Membrane Reactor Coupled with Partial Oxidation of Methane at Medium-Low Temperature.

A novel dual-functional catalytic perovskite hollow fiber membrane reactor was fabricated by integrating BaBi0.05Co0.8Nb0.15O3-δ (BBCN) perovskite hollow fiber membrane with Ni-phyllosilicate hollow sphere catalysts for simultaneous NO decomposition and partial oxidation of methane (POM) reaction. With this novel catalytic membrane reactor, NO could be completely converted to N2 at a medium-low temperature (675 °C) owing to instantaneous oxygen removal from the NO decomposition reaction system. Coupled POM reaction on the other side of BBCN hollow fiber membrane not only increased the driving force for oxygen permeation but also produced valuable products (syngas). This novel membrane reactor showed high NO removal capacity at comparatively low temperatures (675-700 °C), which is 100-200 °C lower than those of other membrane reactors reported in literature. In addition, even with the presence of a 2-5% oxygen concentration in NO stream, NO could still be completely decomposed to N2 via this catalytic BBCN membrane reactor. Evidently, the application of this novel catalytic membrane reactor could overcome the inhibition of oxygen present atmosphere for NO decomposition and achieve a remarkably high efficiency for NO removal.

Co-Mn-Al Mixed Oxides Promoted by K for Direct NO Decomposition: Effect of Preparation Parameters

Fundamental research on direct NO decomposition is still needed for the design of a sufficiently active, stable and selective catalyst. Co-based mixed oxides promoted by alkali metals are promising catalysts for direct NO decomposition, but which parameters play the key role in NO decomposition over mixed oxide catalysts? How do applied preparation conditions affect the obtained catalyst’s properties?

Effect of Fe precursors on the catalytic activity of Fe/SAPO-34 catalysts for N2O decomposition

Different Fe/SAPO-34 catalysts were prepared by a solid-state ion exchange method and used to catalyze N2O decomposition. The catalytic performance of these catalysts was strongly related to their Fe precursors. Relevant characterization was carried out using X-ray diffraction, N2 adsorption-desorption, UV–vis spectroscopy, electron paramagnetic resonance, and H2 temperature-programmed reduction. The data indicated that the nature and distribution of Fe species in the catalysts changed with different Fe precursors used. Furthermore, monomeric Fe3+ ions and small oligomeric FexOy were the active Fe species for the Fe/SAPO-34 catalysts. Finally, it is reasonable to speculate that such a Fe source effect could be explored for other reactions.

Room‐Temperature Photocatalytic Decomposition of N2O over Nanobelt‐Like Bi2MoO6

AbstractA series of nanobelt‐like Bi2MoO6 photocatalysts were design and controllably constructed via a simple hydrothermal approach, and their catalytic performances were investigated for photocatalytic decomposition of N2O for the first time. It was found that Bi2MoO6 synthesized at 170 °C (BM‐170) exhibits the highest photocatalytic activity with 21.7% N2O conversion at 25 °C under UVA irradiation (λ=365 nm) for 12 h, and that the excellent activity should be attributed to its highest content of Oads, strongest absorption capacity for visible light, lowest recombination rate of photo‐generated electron‐hole pairs, and highest separation efficiency for photogenerated charge carriers. Therefore, this study shed new light on the understanding and application of Bi2MoO6 catalysts for photocatalytic decomposition of N2O.

Y2O3 promoted Co3O4 catalyst for catalytic decomposition of N2O

Co3O4 and the Y2O3-Co3O4 catalysts were synthesized via the precipitation method and the co-precipitation method. Y2O3-Co3O4 exhibits excellent activity and stability for catalytic decomposition of N2O in comparison with Co3O4. The characterization results show that Y2O3-Co3O4 catalyst possesses larger SBET, smaller particle size and the enhanced surface basic property than Co3O4 resulting from the interactions between Y and Co oxides. Furthermore, the promoted electron-donating ability of Co2+ and the facilitated O2 desorption capacity endow the Y2O3-Co3O4 catalyst a lower activation energy for N2O decomposition. Moreover, the Y2O3-Co3O4 catalyst shows better catalytic performance in the presence of O2 or H2O than Co3O4.

Experimental and DFT insights of BiVO4 as an effective photocatalytic catalyst for N2O decomposition

A series of BiVO4 semiconductor photocatalysts with different crystallographic forms and crystallite sizes are designed and controllably constructed by a facile hydrothermal method, and their photocatalytic activities are examined for N2O decomposition. It is found that monoclinic BiVO4 prepared at 150 °C shows the highest activity because of its strongest adsorption ability for visible light and highest separation efficiency for photogenerated charge carriers, which achieves 26.7% N2O conversion at 25 °C after 12 h of irradiation. Oxygen vacancy significantly influences the photocatalytic performance of N2O decomposition, which can not only promote the formation of excess electrons but also reduce the activation energy barrier. Moreover, DFT + U calculation is employed to explore the electronic properties of the catalyst at the microscopic level, as well as the reaction pathway of N2O decomposition over these photocatalysts, is illustrated.