Catalysts For N2O Decomposition Research Articles

Improved activity and significant O2 resistance of Cs doped Co3O4 catalyst for N2O decomposition

Csx-Co3O4 catalysts with excellent low temperature activity and oxygen resistance for N2O decomposition were prepared using a citric acid complexation method. The mechanism of Cs doping on Co3O4 was systematically investigated by characterization techniques such as XRD, Raman, N2 adsorption, HR-TEM, XPS, H2-TPR, O2-TPD, and combined with DFT calculation methods. The results indicated that the presence of Cs inhibited the growth of Co3O4 grains and increased the specific surface area. Cs doping significantly increased the number of exposed oxygen vacancies, which tended to form around CoO4 (Co2+) tetrahedral sites replaced by Cs, following the trend Evac(1 1 1) <Evac(1 1 0) <Evac(1 0 0). Furthermore, the interaction between Cs and Co enhanced the electron donating ability of Co, promoted the reduction of Co3+ to Co2+ and weakened the Co-O bond. Among all the samples, the one with a Cs/Co molar ratio of 0.1 exhibited the highest activity. At 275 °C, the Rs of Cs0.1-Co3O4 was 39.5 times that of pure Co3O4. More importantly, Cs0.1-Co3O4 exhibited excellent oxygen resistance, achieving a high N2O conversion rate of 94 % under conditions of 300 °C and 20 % O2.

First principles energetic span analysis of the activity of transition metal catalysts for N2O decomposition: The reversal of descriptor roles in the presence of NO

The utilization of NH3 combustion faces a significant hurdle in mitigating N2O emissions, a potent greenhouse gas. Current deNOx technologies struggle to effectively decompose N2O, especially under practical conditions due to inhibitory effects from exhaust stream components like O2, NOx, and H2O. This study employs first principles investigations to analyze N2O decomposition activity on precious (Ru, Rh), non-precious (Cu, Ni), and hybrid (Ru/Cu, Rh/Cu, Ru/Ni, Rh/Ni) catalysts. Many new Brønsted-Evans-Polanyi relations are established, enabling mechanistic analysis via the Energetic Span Model. The analyses reveal opportunities for enhancing catalytic activity by exploiting weak correlations between intermediates’ free energies. The model captures the inhibitory effects of surface-adsorbed NO on the N2O decomposition activity, aligning well with experimental observations and catalytic trends. The strong binding energy of adsorbed N2/N2O and O adatom is found to be a key descriptor of activity. It is found to aid the catalytic activity in the presence of NO but becomes limiting in its absence.

The Oscillatory Behaviour of Cu-ZSM-5 Catalysts for N2O Decomposition: Investigation of Cu Species by Complementary Techniques.

Copper-exchanged ZSM-5 (Cu-ZSM-5) is a promising catalyst thanks to the Cu redox pair. A particular feature of this material consists in the presence of spontaneous isothermal oscillations which take place during N2O decomposition reaction, depending on the operating conditions. In the present work, a set of five Cu-ZSM-5 catalysts was synthesised by three procedures and three different copper precursor concentrations: i) wet impregnation, ii) single ion exchange, and iii) double ion exchange. Catalytic tests revealed that the ion-exchanged samples exhibit a low catalytic activity and no oscillatory behaviour, except for the twice-exchanged sample which achieves an average N2O conversion of 26 % at 400 °C. Conversely, the impregnated samples reach higher levels of N2O conversion (66 % for Cu5ZSM5_WI and 72 % for Cu10ZSM5_WI) and demonstrate a similar oscillating pattern. Further investigations disclosed that the most active catalysts, characterised by the presence of oscillatory behaviour, have more abundant and easily reducible copper species (ICP, EDX and H2-TPR) which interact better with the zeolitic support (FT-IR). Catalytic tests under a long time on stream (TOS) suggest that either self-organised patterns or deterministic chaos can be achieved during the reaction, depending on the operating conditions, such as temperature and contact time.

Effects of Zn loading on ZnxCo1−xCo2O4 spinel catalysts for low-temperature catalytic decomposition of N2O in the presence of inhibitors

The recent advancement of NH3-based fuel demands the development of catalysts that can decompose N2O at low temperatures and are stable against various inhibitors. Zn-doped cobalt spinel (ZnxCo1−xCo2O4) catalysts have demonstrated superior activity for N2O decomposition at low temperatures. However, their optimization and deactivation mechanisms with respect to Zn loading when inhibitors are present require further investigation. Herein, we reviewed the effects of Zn loading on catalysts at low temperatures without or with the presence of inhibitors (3 vol% O2, 6 vol% H2O, 200 ppm NO). The results showed that adding an appropriate amount of Zn into Co3O4 spinel catalysts improves their N2O decomposition activity. The Zn-induced enhancement of the catalysts’ redox properties, and reducibility was the underlying mechanism behind the activity promotion. The presence of structural defects created through the addition of Zn enhanced the catalyst’s resistance to O2. The deactivation by H2O and NO upon the addition of Zn could be correlated with the reduced availability of surface Co species and Co2+ as adsorption-active sites and the stronger bond of Co with –NO, respectively. This study underscores the importance of controlling the Zn loading as a bulk redox promoter in ZnxCo1−xCo2O4 spinel catalysts for practical applications.

Facile Synthesis of N-doped Co3O4 Catalyst for Catalytic Decomposition of N2O under Simulated Real Tail Gases

Facile Synthesis of N-doped Co3O4 Catalyst for Catalytic Decomposition of N2O under Simulated Real Tail Gases

A DFT study on Cu-ZSM-5 as a catalyst for NO decomposition: Possible activity of a Cu(I) pair located at the T3 tetrahedral sites

The decomposition of NO catalysed by Cu+ pairs coordinated at the Al-substituted T3 sites of the 10-membered rings of Cu-ZSM-5 was studied by means of DFT/ONIOM calculations. Three mechanisms for NO decomposition were defined on the active site, all based on the formation and further decomposition of an hyponitrite anion, which gives the N2O molecule and a [Cu‒O‒Cu]2+ bridge, where both copper ions are oxidized. N2O can react with the oxidized active site according to two different spin-allowed mechanisms which give immediately the products, N2 + O2. Otherwise, N2O reacts with a new reduced site according to a spin-forbidden mechanism which gives N2 and a second [Cu‒O‒Cu]2+ bridge. When the latter mechanism occurs, reduced sites are restored by further reaction of [Cu‒O‒Cu]2+ with NO and desorption of NO2, which is finally decomposed on a second [Cu‒O‒Cu]2+ site, giving O2 + NO. Turnover frequencies (TOFs) calculated by means of the Energetic Span model showed that one of the spin-allowed mechanisms should be relatively fast, whereas the spin-forbidden one is expected to be extremely slow. Computational results were discussed with reference to experimental data available in the literature.

New insights into the effect of polyvinyl alcohol on Co3O4 spinel oxide catalyst for N2O decomposition

Polyvinyl alcohol (PVA)-assisted precipitation method offered surface modification Co3O4 spinel oxides which were applied to catalytic N2O decomposition. PVA was added in the preparation process and endowed catalysts with changes in surface metal ions valance state properties, i.e. Co2+ ions which served as active centers. Co3O4 adding PVA (Co3O4-P) showed superior performance for catalytic N2O decomposition with a high gas hourly space velocity of 400,000 h−1. Co2+ ion quantities were positively correlated to catalytic performance which was inseparable from PVA superhydrophobicity and reducibility during the preparation process. Moreover, density functional theory (DFT) calculation revealed N2O preferable adsorption on Co2+ sites whether near oxygen vacancies or not, which indirectly affirmed the reason Co3O4-P with superior catalytic N2O decomposition property. Our research gave more evidence to N2O decomposition active sites from atom-scale for Co3O4 spinel oxides and provided a novel pathway for high-performance catalyst preparation.

Boosting N2O Decomposition by Fabricating the Cs-O-Co Structure over Co3O4 with Single-Layer Atoms of Cs.

Developing effective catalysts for N2O decomposition at low temperatures is challenging. Herein, the Cs-O-Co structure, as the active species fabricated by single-layer atoms of Cs over pure Co3O4, originally exhibited great catalytic activity of N2O decomposition in simulated vehicle exhaust and flue gas from nitric acid plants. A similar catalytic performance was also observed for Na, K, and Rb alkali metals over Co3O4 catalysts for N2O decomposition, illustrating the prevalence of alkali-metal-promotion over Co3O4 in practical applications. The catalytic results indicated that the TOF of Co3O4 catalysts loaded by 4 wt% Cs was nearly 2 orders of magnitude higher than that of pure Co3O4 catalysts at 300 °C. Interestingly, the conversions of N2O decomposition over Co3O4 catalysts doped by the same Cs loadings were significantly inhibited. Characterization results indicated that the primary active Cs-O-Co structure was formed by highly orbital hybridization between the Cs 6s and the O 2p orbital over the supported Co3O4 catalysts, where Cs could donate electrons to Co3+ and produce much more Co2+. In contrast, the doped Co3O4 catalysts were dominated by Cs2O2 species; meanwhile, CsOH species was generated by adsorbed water vapor led to a significant decrease in catalytic activity. In situ DRIFTS, rigorous kinetics, and DFT results elaborated the reaction mechanism of N2O decomposition, where the direct decomposition of adsorbed N2O was the kinetically relevant step over supported catalysts in the absence of O2. Meanwhile, the assistance of adsorbed N2O decomposition by activated oxygen was observed as the kinetically relevant step in the presence of O2. The results may pave a promising path toward developing alkali-metal-promotion catalysts for efficient N2O decomposition.

On the optimal Cs/Co ratio responsible for the N2O decomposition activity of the foam supported cobalt oxide catalysts

Structured foam catalysts for N2O decomposition containing Co and Cs were prepared via conventional and organic-assisted impregnation method (acetic acid, citric acid, glycerol, glycine, urea). Organic-assisted impregnation caused higher abundance of smaller particles and different faceting. Glycerol usage leads to increase of specific rate constant for N2O decomposition, urea leads to its decrease. The optimal amount of Cs in Co3O4deposited on the foam was 2–3 times higher than in the bulk Co3O4-Cs due to the dispersion of part of the Cs species over the bare support. The use of glycerol caused a better surface coverage by spinel phase, thus leaving less space for spreading the cesium on the support instead of on the spinel phase. The positive effect of glycerol on the performance of the catalysts with optimized cesium content was attributed to refaceting of the spinal nanocrystals, and greater resistance of the (100) planes to gaseous NO/H2O contaminates.

Waste eggshell to valuable Co3O4/eggshell material as an efficient catalyst for catalytic decomposition of N2O under simulated real tail gases

Co3O4 shows excellent catalytic activity for N2O decomposition, in which it is urgently needed to develop novel efficient catalysts/supports with cheap and environmentally-friendly properties. Herein, Co3O4 nanoparticles decorated eggshell catalysts (Co3O4/eggshell-GR, Co3O4/eggshell-IM, and Co3O4/eggshell-DP) were prepared using simple grinding, impregnation, and deposition-precipitation methods, where waste eggshells were used as an effective support and reaction-promoter. The results indicated that the preparation methods significantly influenced the catalytic activity of Co3O4/eggshell catalysts; the highest activity was obtained over the Co3O4/eggshell-DP. The activity of Co3O4/eggshell-DP was comparable to that of pure Co3O4. More importantly, its specific activity was about 7.3 times that of Co3O4 at 400 °C. The examined Co3O4/eggshell-DP also displayed outstanding stability and anti-poisoning property in NO, O2, and/or H2O-containing atmospheres. It was also verified that the excellent activity of Co3O4/eggshell-DP correlated with the unique structure of the eggshell and the close incorporation between CaCO3 and Co3O4. The Co3O4/eggshell-DP catalyst owned abundant Co3O4 nanoparticles, more Co3+ species, and excellent redox performance, promoting the conversion of N2O at a lower temperature. The presence of abundant surface basic sites and a larger amount of oxygen vacancies also facilitated the catalytic efficiency of Co3O4/eggshell-DP.

The catalytic performance of Ba-Ce-Cu catalysts for N2O decomposition

Series of Ba-Ce-Cu catalysts were prepared by citric acid method and used for N2O decomposition, and the doping effects of Ba and Ce on CuO were studied. It was found that the activity and the tolerance of the catalyst to the impurity gases (NO, O2, H2O) can be effectively modified by the doping components. The Ba0.2Cu displayed much high activity to the reaction due to the significant effect of Ba stabilizing the active Cu+ species in the catalyst, but low tolerance to NO. The Ba0.2Ce0.5Cu catalyst exhibited not only higher catalytic activity compared with the Ba0.2Cu due to the synergistic effect of Ba and Ce, but also strong tolerance to NO, as the CeO2 in the catalyst could remove the adsorbed NOx species from the Cu+ through forming barium nitrate and catalyzing the latter decomposition.

Regulating local coordination environment of rhodium single atoms in Rh/CeO2 catalysts for N2O decomposition

Rh single atom catalysts (SACs) have been insensitively investigated recently due to the maximum utilization efficiency of Rh, one of the most expensive precious metals. Although great efforts have been made in the development and application of Rh SACs, there are few reports on the precise control of the local coordination environment of Rh single sites on CeO2 and their catalytic performance for N2O decomposition. Herein, Rh/CeO2 catalysts with different Rh–O coordination numbers (CNs) were successfully prepared using different CeO2 supports and a simple incipient wetness impregnation (IWI) method. It is observed that the Rh/CeO2 catalyst with slightly higher CN of Rh–O (Rh/CeO2-H) prepared from CeO2 shows much higher N2O decomposition activity than the catalyst with lower CN of Rh–O (Rh/CeO2-L) obtained from Ce(OH)x. The Rh species within Rh/CeO2-H are found to be more reactive than those within Rh/CeO2-L, which can better facilitate the O2 desorption once formed during N2O decomposition. In addition, more surface oxygen vacancies are present on Rh/CeO2-H than on Rh/CeO2-L, well explaining the superior N2O adsorption and activation capability on the former catalyst. It is concluded that more abundant oxygen vacancies and reactive Rh single atom sites with slightly higher CN of Rh–O and significantly higher reducibility altogether contribute to the superior N2O decomposition activity on the Rh/CeO2-H catalyst.

Non-thermal Plasma Synergizes High-Alkalinity Hydroxyapatite Supported RhFe Bimetallic Catalyst for Direct Catalytic Decomposition of N2O at Low Temperature

Non-thermal Plasma Synergizes High-Alkalinity Hydroxyapatite Supported RhFe Bimetallic Catalyst for Direct Catalytic Decomposition of N2O at Low Temperature

Effect of Zinc on the Structure and Activity of the Cobalt Oxide Catalysts for NO Decomposition

Co4−iZniMnAlOx mixed oxides (i = 0, 0.5 and 1) were prepared by coprecipitation, subsequently modified with potassium (2 or 4 wt.% K), and investigated for direct catalytic NO decomposition, one of the most attractive and challenging NOx abatement processes. The catalysts were characterised by atomic absorption spectroscopy, powder X-ray diffraction, Raman and infrared spectroscopy, temperature-programmed reduction by hydrogen, the temperature-programmed desorption of CO2 and NO, X-ray photoelectron spectroscopy, scanning electron microscopy, the work function, and N2 physisorption. The partial substitution of cobalt increased the specific surface area, decreased the pore sizes, influenced the surface composition, and obtained acid-base properties as a result of the higher availability of medium and strong basic sites. No visible changes in the morphology, crystallite size, and work function were observed upon the cobalt substitution. The conversion of NO increased after the Co substitution, however, the increase in the amount of zinc did not affect the catalytic activity, whereas a higher amount of potassium caused a decrease in the NO conversion. The results obtained, which were predominantly the acid-base characteristics of the catalyst, are in direct correlation with the proposed NO decomposition reaction mechanisms with NOx− as the main reaction intermediates.

Enhanced SO2 Resistance of Cs-Modified Fe-HZSM-5 for NO Decomposition

Direct decomposition of NO into N2 and O2 is an ideal technology for NOx removal. Catalyst deactivation by sulfur poisoning is the major obstacle for practical application. This paper focuses on strengthening the SO2 resistance of metal-exchanged HZSM-5 catalysts, by investigating the metals, promoters, preparation methods, metal-to-promoter molar ratios, Si/Al ratios and metal loadings. The results show that in the presence of SO2 (500 ppm), Fe is the best compared with Co, Ni and Cu. Cs, Ba and K modification enhanced the low-temperature activity of the Fe-HZSM-5 catalyst for NO decomposition, which can be further improved by increasing the exchanged-solution concentration and Fe/Cs molar ratio or decreasing the Si/Al molar ratio. Interestingly, Cs-doped Fe-HZSM-5 exhibited a high NO conversion and low NO2 selectivity but a high SO2 conversion within 10 h of continuous operation. This indicates that Cs-Fe-HZSM-5 has a relatively high SO2 resistance. Combining the characterization results, including N2 physisorption, XRD, ICP, XRF, UV–Vis, XPS, NO/SO2-TPD, H2-TPR and HAADF-STEM, SO42− was found to be the major sulfur species deposited on the catalyst’s surface. Cs doping inhibited the SO2 adsorption on Fe-HZSM-5, enhanced the Fe dispersion and increased the isolated Fe and Fe-O-Fe species. These findings could be the primary reasons for the high activity and SO2 resistance of Cs-Fe-HZSM-5.

Strong Electronic Orbit Coupling between Cobalt and Single-Atom Praseodymium for Boosted Nitrous Oxide Decomposition on Co3O4 Catalyst.

Nitrous oxide (N2O) has gained increasing attention as an important noncarbon dioxide greenhouse gas, and catalytic decomposition is an effective method of reducing its emissions. Here, Co3O4 was synthesized by the sol-gel method and single-atom Pr was confined in its matrix to improve the N2O decomposition performance. It was observed that the reaction rate varied in a volcano-like pattern with the amount of doped Pr. A N2O decomposition reaction rate 5-7.5 times greater than that of pure Co3O4 is achieved on the catalyst with a Pr/Co molar ratio of 0.06:1, and further Pr doping reduced the activity due to PrOx cluster formation. Combined with X-ray photoelectron spectroscopy, X-ray absorption fine structure, density functional theory and in situ near-ambient pressure X-ray photoelectron spectroscopy, it was demonstrated that the single-atom doped Pr in Co3O4 generates the "Pr 4f-O 2p-Co 3d" network, which redistributes the electrons in Co3O4 lattice and increases the t2g electrons at the tetracoordinated Co2+ sites. This coupling between the Pr 4f orbit and Co2+ 3d orbit triggers the formation of a 4f-3d electronic ladder, which accelerates the electron transfer from Co2+ to the 3π* antibonding orbital of N2O, thus contributing to the N-O bond cleavage. Moreover, the energy barrier for each elementary reaction in the decomposition process of N2O is reduced, especially for O2 desorption. Our work provides a theoretical grounding and reference for designing atomically modified catalysts for N2O decomposition.

Washcoated open-cell foam cobalt spinel catalysts for N2O decomposition

The Co3O4 modified with 1 wt.% Cs was deposited on α-Al2O3 open-cell foam covered with different washcoats (MgO, MnO2, SiO2, TiO2), investigated by XRD, Raman microspectroscopy, nitrogen physisorption, XPS, SEM and TPR-H2 in order to elucidate interactions between Cs-Co3O4 and the washcoat and their effect on surface area, reducibility, dispersion, and low temperature decomposition of N2O. The samples with SiO2 and TiO2 washcoats had the largest surface areas. Only SiO2 did not interact with the active phase and did not change the reducibility of the catalyst. Although the same Cs concentration was adjusted during preparation of all catalysts, differences in the Cs/Co surface molar ratio were observed due to a different level of Co3O4 particles aggregation and cesium dispersion. Catalytic activity correlated with the surface Cs/Co molar ratio closely interconnected with the surface Co3+/Co2+ molar ratio while there were no direct relationships to the redox properties and surface area. The highest activity was achieved for the MgO washcoat prepared from carbonate with the highest Co3+/Co2+ molar ratio corresponding to the optimal Cs/Co surface molar ratio around 0.1.

Computational Evaluation of Potential Molecular Catalysts for Nitrous Oxide Decomposition.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with limited use as a mild anesthetic and underdeveloped reactivity. Nitrous oxide splitting (decomposition) is critical to its mitigation as a GHG. Although heterogeneous catalysts for N2O decomposition have been developed, highly efficient, long-lived solid catalysts are still needed, and the details of the catalytic pathways are not well understood. Reported herein is a computational evaluation of three potential molecular (homogeneous) catalysts for N2O splitting, which could aid in the development of more active and robust catalysts and provide deeper mechanistic insights: one Cu(I)-based, [(CF3O)4Al]Cu (A-1), and two Ru(III)-based, Cl(POR)Ru (B-1) and (NTA)Ru (C-1) (POR = porphyrin, NTA = nitrilotriacetate). The structures and energetic viability of potential intermediates and key transition states are evaluated according to a two-stage reaction pathway: (A) deoxygenation (DO), during which a metal-N2O complex undergoes N-O bond cleavage to produce N2 and a metal-oxo species and (B) (di)oxygen evolution (OER), in which the metal-oxo species dimerizes to a dimetal-peroxo complex, followed by conversion to a metal-dioxygen species from which dioxygen dissociates. For the (F-L)Cu(I) activator (A-1), deoxygenation of N2O is facilitated by an O-bound (F-L)Cu-O-N2 or better by a bimetallic N,O-bonded, (F-L)Cu-NNO-Cu(F-L) complex; the resulting copper-oxyl (F-L)Cu-O is converted exergonically to (F-L)Cu-(η2,η2-O2)-Cu(F-L), which leads to dioxygen species (F-L)Cu(η2-O2), that favorably dissociates O2. Key features of the DO/OER process for (POR)ClRu (B-1) include endergonic N2O coordination, facile N2 evolution from LR'u-N2O-RuL to Cl(POR)RuO, moderate barrier coupling of Cl(POR)RuO to peroxo Cl(POR)Ru(O2)Ru(POR)Cl, and eventual O2 dissociation from Cl(POR)Ru(η1-O2), which is nearly thermoneutral. N2O decomposition promoted by (NTA)Ru(III) (C-1) can proceed with exergonic N2O coordination, facile N2 dissociation from (NTA)Ru-ON2 or (NTA)Ru-N2O-Ru(NTA) to form (NTA)Ru-O; dimerization of the (NTA)Ru-oxo species is facile to produce (NTA)Ru-O-O-Ru(NTA), and subsequent OE from the peroxo species is moderately endergonic. Considering the overall energetics, (F-L)Cu and Cl(POR)Ru derivatives are deemed the best candidates for promoting facile N2O decomposition.

Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors.

Nitrous oxide (N2 O) is a potent greenhouse and ozone-reactive gas for which emissions are growing rapidly due to increasingly intensive agriculture. Synthetic catalysts for N2 O decomposition typically contain precious metals and/or operate at elevated temperatures driving a desire for more sustainable alternatives. Here we demonstrate self-assembly of liposomal microreactors enabling catalytic reduction of N2 O to the climate neutral product N2 . Photoexcitation of graphitic N-doped carbon dots delivers electrons to encapsulated N2 O Reductase enzymes via a lipid-soluble biomolecular wire provided by the MtrCAB protein complex. Within the microreactor, electron transfer from MtrCAB to N2 O Reductase is facilitated by the general redox mediator methyl viologen. The liposomal microreactors use only earth-abundant elements to catalyze N2 O removal in ambient, aqueous conditions.

Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors.

Nitrous oxide (N2O) is a potent greenhouse and ozone-reactive gas for which emissions are growing rapidly due to increasingly intensive agriculture. Synthetic catalysts for N2O decomposition typically contain precious metals and/or operate at elevated temperatures driving a desire for more sustainable alternatives. Here we demonstrate self-assembly of liposomal microreactors enabling catalytic reduction of N2O to the climate neutral product N2. Photoexcitation of graphitic N-doped carbon dots delivers electrons to encapsulated N2O Reductase enzymes via a lipid-soluble biomolecular wire provided by the MtrCAB protein complex. Within the microreactor, electron transfer from MtrCAB to N2O Reductase is facilitated by the general redox mediator methyl viologen. The liposomal microreactors use only earth-abundant elements to catalyze N2O removal in ambient, aqueous conditions.