NO Decomposition Activity Research Articles

N2O catalytic decomposition on electrodeposited Rh-based open-cell metallic foams

The present article reports on Rh-containing hydrotalcite (HT) derived catalysts coated on the surface of open-cell FeCralloy foams. The structured catalysts were prepared by in situ synthesis of Rh/Mg/Al HT precursors through electrodeposition followed by calcination. For comparison purposes, powder catalysts with analogous compositions were obtained by coprecipitation. The catalytic activity in N2O decomposition (deN2O) over structured and pelletized catalysts was investigated in absence and presence of inhibitors (O2 + NO) by keeping similar Rh loading and reaction conditions. Furthermore, stability of the structured catalysts was investigated.A Rh/Mg/Al HT-derived film uniformly coated the surface of the foam. The deN2O performance over both structured and pelletized catalysts was comparable for constant Rh loading in the catalytic bed, though lower activation energy was obtained for the structured catalyst. The coating was stable after a 24 h test at 475 °C in presence of O2 and NO, while rhodium oxide was reduced to Rh0 (2.0 ± 1.1 nm). Due to a low amount of active phase in the thin catalytic coating, the conversion steadily decreased during the first 20 h of time-on-stream from 60 until a constant 51% reaching stable level.

Effects of strain induced by Au dispersion in Ba and Ni doped Y2O3 on direct decomposition of NO

NO direct decomposition on Y2O3 based oxide was studied and it was found that doping Ba and Ni simultaneously in Y2O3 is effective for achieving the high NO decomposition activity. The optimized amount for Ni and Ba doping is 5 and 0.5–1 mol%, respectively and on this Y2O3 based catalyst showed almost 100% N2 yield at 800 °C and high N2 yield was sustained under co-existence of oxygen. Effects of tensile strain caused by Au dispersion was further studied for increasing low temperature NO decomposition activity and it was found that NO decomposition activity around 500 °C was much increased by dispersion of 1 mol% Au which induced a tensile strain.

Direct Decomposition of N2O over C-Type Cubic Yb2O3-Co3O4 Catalysts

Abstract (Yb1−xCox)2O3−δ catalysts with cubic (C-type) rare-earth sesquioxide structure were synthesized by a co-precipitation method. The introduction of Co2+/3+ ions into the Yb2O3 lattice resulted in an improved catalytic activity for N2O decomposition, due to the enhanced redox properties and increased amount of active sites. Among the prepared catalysts, (Yb0.90Co0.10)2O3−δ exhibited the highest activity for the decomposition of N2O, which was completely converted to N2 and O2 at 500 °C. Moreover, (Yb0.90Co0.10)2O3−δ also showed high durability in the presence of H2O, O2, or CO2.

Catalytic decomposition of N2O on supported Rh catalysts

Abstract Numerous Rh catalysts were evaluated for N2O decomposition for automotive applications. Some Rh-containing spinel materials exhibit excellent fresh activities in the absence of H2O but become inactive after hydrothermal aging or when tested in a wet feed. Rh catalysts supported on zeolites can be very active in a dry feed even after aging but are extremely sensitive to H2O. Rh/CeO2 is an exceptional catalyst for this reaction in the presence of both H2O and O2. Hydrothermal aging (750 °C/20 h) significantly increases its activity. A similar activity enhancement was found by calcining the support before Rh impregnation. XPS results show a surface enrichment of Rh species on the aged Rh/CeO2 catalyst relative to the fresh catalyst. Aberration corrected STEM images reveal that Rh is buried in the bulk on the fresh catalyst and pulled out onto the surface of the support after thermal treatments. All catalysts are inhibited by H2O with the zeolite-based Rh catalysts being the worst. The aged Rh/CeO2 catalyst is less sensitive to H2O relative to others. DRIFTS data show that H2O sensitivity is related to catalyst hydrophilicity; a high coverage of OH groups on a catalyst reduces its N2O decomposition activity. H2-TPR results show that a Rh/CeO2 catalyst can be readily reduced at

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.

Atomic-scale insights into zeolite-based catalysis in N2O decomposition

Nitrous oxide (N2O) has been the most serious ozone-depleting species throughout the 21st century. Zeolite-based catalysis is a highly promising method for N2O removal in large-scale industrial applications. However, the exchanged transition metal species in zeolites greatly influence the performance of catalysts. The primary factor governing the catalytic activity is a fiercely debated topic and remains highly uncertain. Here we synthesize a series of transition-metal ion (Fe, Co, Ni, Cu)-exchanged ZSM-5 zeolite catalysts. Both experiments and density functional theory (DFT) calculations demonstrate that the activity for N2O decomposition follows the order Fe ≈ Co > Ni > Cu. Analysis of the electronic structure properties reveals that the catalytic activity of the transition-metal ion-exchanged ZSM-5 zeolites is governed by the local softness of active sites and the composition of their HOMOs. The higher the local softness and the proportion of 4s orbitals in the HOMO, the higher the catalytic activity, which facilitates electron transfer in the redox process and thereby reduces the reaction barriers for N2O decomposition into N2 and O2. Clarification of the nature of catalytic activity advances the understanding of the principles of zeolite-based catalysis, and is helpful for the design of highly efficient zeolite catalysts for pollutant removals.

Tuning the Dissociative Action of Cationic Rh Clusters Toward NO by Substituting a Single Ta Atom

Modification of Rh chemical activity for decomposition of NO by alloying with Ta was studied by vibrational spectroscopy of gas-phase clusters, where one single Rh atom was substituted by Ta, with NO adsorbed. While NO adsorbs molecularly on pure Rh clusters, it was found to adsorb dissociatively on RhnTa+ (n = 2–8) with the O bound to the Ta on-top site. A reaction path for NO decomposition obtained by density functional theory calculations for octahedral Rh5Ta+ and Rh6+ suggests that the Ta oxygen affinity strongly reduces the energy barrier right before bond cleavage, facilitating NO dissociation. The trend is consistent with the Bell–Evans–Polanyi principle. The addition of other less oxophilic dopant atoms could plausibly enhance catalytic reactivity of Rh.

Effect of Cesium Modification on CuO/CeO2 Catalysts for the Catalytic Decomposition of N2O

A series of Cs-modified CuO/CeO2 mixed oxide catalysts was prepared for enhancing the stable activity of N2O decomposition. It was found that Cs modification promoted the catalytic performance of CuO/CeO2 catalysts significantly. The 1%Cs-CuO/CeO2 catalyst exhibited the best activity, and the conversion of N2O reached 100% at 380 °C in the presence of 2% O2. The catalytic behaviors were investigated by means of XRD, N2 adsorption iso-therms, XPS, H2-TPR(TPR: temperature-programmed reduction), CO-IR, O2-TPD(TPD: temperature-programmed desorption) and diffused reflectance infrared Fourier transform spectorscopy(DRIFTs). The results revealed that Cs modification promoted the activity and the oxygen resistance by enhancing the desorption of surface oxygen species and increasing the content of Ce3+. CO-DRIFTs revealed that Ce3+ could efficiently facilitate the regeneration of active Cu+ sites by an oxygen migration step. The possible reaction mechanism was also discussed.

“PdO vs. PtO”—The Influence of PGM Oxide Promotion of Co3O4 Spinel on Direct NO Decomposition Activity

Direct decomposition of NO into N2 and O2 (2NO→N2 + O2) is recognized as the “ideal” reaction for NOx removal because it needs no reductant. It was reported that the spinel Co3O4 is one of the most active single-element oxide catalysts for NO decomposition at higher reaction temperatures, however, activity remains low below 650 °C. The present study aims to investigate new promoters for Co3O4, specifically PdO vs. PtO. Interestingly, the PdO promoter effect on Co3O4 was much greater than the PtO effect, yielding a 4 times higher activity for direct NO decomposition at 650 °C. Also, Co3O4 catalysts with the PdO promoter exhibit higher selectivity to N2 compared to PtO/Co3O4 catalysts. Several characterization measurements, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), and in situ FT-IR, were performed to understand the effect of PdO vs. PtO on the properties of Co3O4. Structural and surface analysis measurements show that impregnation of PdO on Co3O4 leads to a greater ease of reduction of the catalysts and an increased thermal stability of surface adsorbed NOx species, which contribute to promotion of direct NO decomposition activity. In contrast, rather than remaining solely as a surface species, PtO enters the Co3O4 structure, and it promotes neither redox properties nor NO adsorption properties of Co3O4, resulting in a diminished promotional effect compared to PdO.

Probing the existing state of Cu(ii) in a Cu–Al spinel catalyst using N2O decomposition reaction with the aid of conventional characterizations

The spinel and interacting Cu(ii) species have no activity for N2O decomposition, while free Cu(ii) shows activity.

In-situ DRIFTS study of CeO2 supported Rh catalysts for N2O decomposition

Ceria supported Rh catalysts exhibit superior activities for the decomposition of N2O in the presence of water and excess O2 comparing with other oxides supported Rh catalysts. In contrast to Rh/γ-Al2O, hydrothermal aging (750 °C for 20 h with 10% H2O in air) significantly enhances the catalytic activity of Rh/CeO2 for the decomposition of N2O. The presence of H2O, on the other hand, inhibits the reaction rate on all Rh catalysts, but this inhibition effect is less on the aged Rh/CeO2 than on its fresh state. The focus of this work is to explore the nature of this activity enhancement on the aged Rh/CeO2 catalyst and the effect of water. Ceria and alumina supported Rh catalysts were characterized by in-situ DRIFTS with CO and N2O as probe molecules to investigate the synergism between Rh species and ceria support and the interaction between water molecules and the Rh/CeO2 catalysts. The results suggest that Rh supported on ceria has more CO adsorption sites and better hydrothermal stability than that on alumina. On Rh/CeO2 catalysts, the surface Rh species was found to facilitate the reduction of Ce4+ ions to Ce3+ at the interfacial area and as a result increased the concentration of Ce3+ species relative to the CeO2 support after a reduction treatment. Ce3+ ions at the interface between Rh and CeO2 support can be easily oxidized to Ce4+ by N2O at room temperature and played an important role in the disassociation of N2O. After a hydrothermal aging treatment on Rh/CeO2, more surface Rh sites were found that can adsorb CO and N2O. In addition, on the aged Rh/CeO2 catalyst, a different type of Rh species was found to be situated in a more electron-rich environment. These combined factors may be responsible for its enhanced N2O decomposition activity on the aged Rh/CeO2 catalyst. DRITFS were also collected on fresh and aged Rh/CeO2 catalysts with different degrees of sample hydration. The intensity of the OH group at 3658 cm−1 over an aged catalyst was found to decrease with increasing temperature at a faster rate than that on the fresh catalyst. This finding may explain their difference in H2O sensitivity for the N2O decomposition reaction.

Effect of alkaline earth metal doping on the catalytic performance of cobalt-based spinel composite metal oxides in N2O decomposition

A series of cobalt-based spinel composite metal oxides doped with alkaline earth metals, viz., MxCo3-xO4 (M = Mg, Ca, Sr and Ba; x = 0, 0.1, 0.3, 0.5, 0.7 and 0.9), were prepared by the coprecipitation method and characterized by XRD, SEM, nitrogen sorption, H2-TPR, O2-TPD-MS and XPS; the effect of alkaline earth metal doping on the catalytic performance of MxCo3-xO4 composites in N2O decomposition was investigated in a fixed bed micro-reactor. The results showed that after doping with the alkaline earth metals, the particle size of MxCo3-xO4 catalysts is decreased, accompanying with an increase in the specific surface area and the amount of surface adsorbed oxygen and Co2+ species. Meanwhile, the redox performance and catalytic activity of MxCo3-xO4 in N2O decomposition are also greatly enhanced. Under the conditions of 0.68% N2O, 3% O2 and Ar as balance gas, the Sr0.7Co2.3O4 catalyst doped with Sr (x = 0.7) exhibits highest activity in N2O decomposition; the reaction temperatures where the N2O conversion reaches 10% and 95% are as low as 312 and 451°C, respectively.

Direct N2O decomposition over iron-substituted small-pore zeolites with different pore topologies

Four cage-based, small-pore zeolites with similar framework Fe contents (0.7-0.9 wt%) but different framework structures (i.e., Fe-PST-7, Fe-LTA, Fe-SSZ-13, and Fe-RTH) have been synthesized and employed as direct N2O decomposition catalysts. When steam-activated, the light-off temperatures (770 K) for Fe-PST-7 and Fe-LTA were found to be about 40 K lower under wet feed conditions than that (810 K) for Fe-ZSM-5, the most widely studied catalyst for this reaction. Furthermore, their light-off temperatures were found to be even lower than the temperature (780 K) for Fe-FER, the best direct N2O decomposition catalyst. The overall characterization results of our study strongly suggest that the presence of strong Brønsted acid sites in zeolites, as well as the zeolite framework topology, has a profound effect on the type and distribution of extraframework Fe species, and therefore the N2O decomposition activity of supported Fe catalysts.

Understanding the origins of N2O decomposition activity in Mn(Fe)CoAlOx hydrotalcite derived mixed metal oxides

The catalytic decomposition of N2O was studied over a series of calcined Mn(Fe)CoAl hydrotalcite-like compounds. The precursors were prepared by coprecipitation and characterized by XRD and TGA. The mixed metal oxides derived after calcination at 600 °C were characterized by XRD, N2 adsorption, H2-TPR and XPS. Moreover, in situ XAFS measurements over selected mixed metal oxides were performed. Such investigations under relevant reaction conditions are rare, while a comprehensive understanding of the involved active species may facilitate a knowledge-based catalyst optimization. The activity of the CoAlOx (Co/Al = 3/1, mol.%) catalyst varied depending on the loading of Mn or Fe (0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%). In the investigated series, Mn0.1725Co3AlOx reached the highest activity with T50 of about 305 and 376 °C under N2O/N2 and N2O,NO,O2/N2 feed, respectively. In situ X-ray absorption experiments over Mn0.1725Co3AlOx suggested that MnxCoyO4 spinels undergo reduction to CoO and MnO upon heating up to 600 °C in He. Under N2O/He conditions, initial reoxidation of cobalt species began at 350 °C. The lower activity obtained for Fe0.1725Co3AlOx is explained by the fact that the majority of Fe was not incorporated into the Co3O4 structure but instead formed less reactive iron oxide clusters.

The core-shell type Co0.24Ba catalyst with high activity for N2O decomposition

Core-shell type Co0.24Ba (CS) catalyst was prepared by adsorption-deposition method, in which cobalt oxide with small amount of Ba incorporation mainly exists in the porous shell over the BaCO3 support core. This structure of the catalyst not only endues the active component Co a high accessibility to the reactant, but also made the active component promoted by barium better. Due the special structure, the catalyst is much more active in N2O decomposition compared with the catalysts with traditional structure. Over the Co0.24Ba (CS) catalyst that containing only 8.91 wt.% of Co3O4, N2O in feed gas 2000 ppmv N2O/Ar with 20,000 h-1 was 100% decomposed at 400 °C.

N2O decomposition and reduction on Co-MOR, Fe-MOR and Ni-MOR catalysts: in situ UV–vis DRS and operando FTIR investigation. An insight on the reaction pathways

Co-, Fe- or Ni-exchanged Na-MOR (Si/Al = 9.2) were prepared by ion-exchange method. The catalytic activity for N2O decomposition in the absence or in the presence of NO and for N2O reduction with CH4 in the absence of O2(CRN2O), or in the presence of O2(SCRN2O) was investigated. The catalytic measurements were performed in a flow apparatus with GC analysis of reactants and products. On Fe-MOR, in situ FTIR and UV–vis characterization evidenced coordinatively unsaturated sites (c.u.s.) Fe2+ arising from two families of Fe3+ dimers with different reducibility. Characterization and catalytic results combined with operando FTIR experiments gave an insight into the transition metal ion (tmi) species working during N2O abatement and into the reaction pathways.For N2O decomposition the activity order was Co-MOR > Fe-MOR in the absence of NO and Fe-MOR ≥ Co-MOR in the presence of NO, whereas Ni-MOR was always inactive. The decomposition occurred via redox mechanism passing through the formation of activated surface oxygen species, Oads*. The quasi-oxidic character of this activated oxygen in the Fe3+-O(1+δ)−---Fe(2+δ)+ intermediates with respect to the oxyl character of that in Co3+O‒ intermediates accounted for the lower activity and for the activity enhancement by NO addition to the feed of Fe-MOR with respect to Co-MOR. In Ni-MOR, both isolated or dimeric Ni2+ species were unable to be oxidized by N2O yielding Oads*.For N2O reduction, (CRN2O) and (SCRN2O), the activity order was Fe-MOR > Ni-MOR > Co-MOR. On all catalysts operando FTIR experiments revealed CHxOy intermediates (methoxy, formaldehyde and two types of formate species). The investigation of surface species changing the addition order of the reactants evidenced that the formation of CHxOy intermediates was favored on Co-MOR by pre-saturation with N2O, that yielded Co3+O− able to activate CH4, whereas on Ni-MOR by pre-saturation with CH4, that reduced Ni2+ dimers to Ni+ dimers, able to activate N2O. On Fe-MOR, the Fe2+ dimers formed during activation behaved as Co2+, whereas the Fe2+ dimers formed by reduction with CH4 behaved as Ni+ dimers.The formation and the stability of Oads* surface species were key factors for N2O decomposition and reduction pathways. These factors were affected by the mobility of the tmi electrons, that depends on the oxidation state, nuclearity and location in MOR framework of tmi.

Oxidative coupling of methane over Ba-doped Y2O3 catalyst—Similarity with active site for direct decomposition of NO

A similarity of catalytically active sites for oxidative coupling of methane (OCM) and NO decomposition was investigated. Y2O3 prepared by different methods showed the activity for both reactions. However, no good correlation between the C2 (C2H6 and C2H4) yield for the OCM reaction and the NO decomposition activity was observed. Since the disagreement of the catalytic activity for both reactions was suspected to be due to the non-uniform surface morphological properties of Y2O3, detail experiments were performed for Ba-doped Y2O3 catalysts. It was noteworthy that the addition of Ba into Y2O3 prepared by precipitation method caused a significant increase in not only the C2 yield for the OCM reaction but also the NO decomposition activity. The order of the C2 yield for the OCM reaction over Ba/Y2O3 with different Ba loading was in good agreement with that for the NO decomposition, suggesting the similarity of the active sites for the OCM and NO decomposition reactions. XRD, FT-IR spectroscopy following methanol adsorption and 16O/18O isotopic exchange reaction revealed that the oxygen-deficient Y3+ sites interacting strongly with Ba play a beneficial role in O2 activation, leading to the activation of CH4 and NO molecules to form intermediate in the OCM and NO decomposition reactions.

Superior performance of iridium supported on rutile titania for the catalytic decomposition of N2O propellants

AbstractN2O is a promising green propellant and exhibits great potential for satellite propulsion systems. It is difficult for catalytic decomposition, which is an important way to initiate the propulsion process, to occur at temperatures below 600 °C due to the high activation energy of N2O. In this work, we report an Ir supported on rutile TiO2 (Ir/r-TiO2) catalyst which exhibits a fairly high activity for high-concentration N2O decomposition. HAADF-STEM, H2-TPR, and XPS results indicate that highly dispersed Ir particles and improved oxygen mobility on the Ir/r-TiO2 could facilitate the decomposition of N2O and desorption of the adsorbed oxygen. Bridge-bonded peroxide intermediates were observed with in-situ DRIFT and herein, a detailed decomposition route is proposed.

Effect of preparation parameters on the catalytic performance of hydrothermally synthesized Co3O4 in the decomposition of N2O

With hexadecyl trimethyl ammonium bromide (CTAB) as the template, cobaltosic oxide precursors were hydrothermally synthesized. Co3O4 catalysts were then prepared by calcining the cobaltosic oxide precursors, which was further modified by impregnation with K2CO3 solution and used in the decomposition of N2O. The catalysts were characterized by means of X-ray diffraction (XRD), nitrogen physisorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), and oxygen temperature-programmed desorption (O2-TPD); the effect of CTAB concentration, CTAB/cobalt molar ratio and urea/cobalt molar ratio on the catalytic activity of Co3O4 was investigated. The results indicated that the Co3O4 catalyst prepared by using 0.05 mol/L CTAB solution, with a CTAB to cobalt molar ratio of 1 and a urea to cobalt molar ratio of 4, exhibits high activity in N2O decomposition. The catalytic performance of Co3O4 can be further enhanced by modifying with K. Over the 0.02K/Co3O4 catalyst, the N2O conversion remains over 91% at 400°C after conducting the N2O decomposition reaction for 50 h in the presence of oxygen and steam.

The promotion effect of nickel and lanthanum on Cu-ZSM-5 catalyst in NO direct decomposition

A number of M-Cu-ZSM-5 (M = La, Ni, La-Ni) samples were prepared via an aqueous solution ion-exchange method. The co-doping with Ni and La into a Cu-ZSM-5 catalyst enhanced the NO decomposition activity in a temperature range 350–550 °C. The characterization results indicate that doping with La effectively improved the dispersion of the Cu species forming more Cu2+ ions in the sample, while the effect of Ni is likely to facilitate the implantation of Cu2+ to form (Cu2+-O2–-Cu2+)2+ dimers. The synergistic effect of La and Ni contributes to the increased (Cu2+-O2−-Cu2+)2+ content in the co-doped sample, thus enhancing the NO decomposition activity.