Direct Decomposition Of Nitrogen Monoxide Research Articles

Microwave Irradiation Coupled with MeOx/Al2O3 (Me=Cu, Mn, Ce) Catalysts for Nitrogen Monoxide Removal from Flue Gas at Low Temperatures

AbstractThe direct catalytic decomposition of nitrogen monoxide (NO) into nitrogen (N2) and oxygen (O2) with high efficiency remains a significant challenge at low temperatures under excess oxygen conditions. Herein, we report the direct decomposition of NO by microwave‐assisted catalysis over metal oxide catalysts MeOx/Al2O3 (Me=Cu, Mn, Ce) for the first time under these conditions. The CeCuMnOx/Al2O3 catalyst displays an impressively high efficiency with a high NO conversion and N2 selectivity, reaching up to 94.8 % and 98.7 %, respectively, even at a low temperature of 250 °C and oxygen excess of 10 %. Moreover, the cerium‐doped MeOx/Al2O3 (Me=Cu, Mn) catalysts enhance the catalytic performance dramatically, and CeCuMnOx/Al2O3 is more active than CeCuOx/Al2O3 and CeMnOx/Al2O3 under microwave irradiation. Comparatively, these catalysts show extremely low catalytic activity under conventional reaction conditions. Furthermore, the catalytic performance of NO decomposition under microwave irradiation is hardly influenced by the oxygen concentration.

Direct decomposition of nitrogen monoxide over Cu-MFI containing rare-earth elements: Sm and Gd as promoter

The decomposition activities of nitrogen monoxide (NO) were investigated for the copper ion-exchanged ZSM-5 zeolites (Cu-MFI) containing the rare-earth elements: La, Ce, Pr, Nd, Sm, and Gd. It was found that Sm and Gd acted as promoter for NO decomposition over Cu-MFI with 60–70% of the exchange level of copper ion, while the addition of the other rare-earth elements to Cu-MFI showed no positive effect on NO decomposition activity. The introduction of Sm and Gd to Cu-MFI had little influence on the effectiveness of each copper ion for NO adsorption in the MFI zeolite. The presence of Sm and Gd stabilized Cu + as an active center.

Direct decomposition of nitrogen monoxide over a K-deposited Co(0 0 0 1) surface: Comparison to K-doped cobalt oxide catalysts

The influence of deposited potassium on the oxidation and NO reactivity of a Co(0 0 0 1) surface was studied using X-ray photoelectron spectroscopy. The formation of surface CoO was observed when the clean Co(0 0 0 1) surface was exposed to O 2 at 500 K. In contrast, the Co atoms on the K-deposited Co(0 0 0 1) surface remained at a lower oxidation state, CoO x (0 < x < 1). No adsorption or dissociation of NO occurred on the CoO/Co(0 0 0 1) surface at 320 K, whereas a NO 2 − species formed on the oxidized K/Co(0 0 0 1) surface. This species is considered to be an intermediate in NO decomposition. It was concluded that the role of potassium was (i) to form the NO 2 − intermediate, and (ii) to keep the Co surface partially oxidized (CoO x ) as the active site for the dissociation of the NO 2 − species.

Effect of surface structure of supported palladium catalysts on the activity for direct decomposition of nitrogen monoxide

The active sites for direct decomposition of NO on supported palladium catalysts were investigated by a comparative study with single-crystal palladium surfaces. In the study of powder catalysts, the activity of Pd/Al 2O 3 was found to be significantly affected by the type of palladium precursor. Pd/Al 2O 3 catalysts prepared from palladium nitrate showed the highest activity, expressed in terms of turnover frequency (TOF), for NO decomposition to N 2. In studies using single-crystal model catalysts reported previously [I. Nakamura, T. Fujitani, and H. Hamada, Surf. Sci. 514 (2002) 409], the adsorption, dissociation, and desorption behavior of NO was closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. NO adsorption by FT-IR spectroscopy confirmed the presence of the stepped palladium sites on Pd/Al 2O 3 catalysts, and the specific activity (TOF step) for NO decomposition to N 2, calculated on the basis of number of step sites estimated from the amount of chemisorbed NO, was not changed for all the Pd/Al 2O 3 catalysts. These results suggest that direct decomposition of NO mainly proceeds on the step sites of palladium. This is in agreement with the results obtained for single-crystal model catalysts. The present study shows that the activity of powder catalyst can be well interpreted by its surface structure, indicating the usefulness of surface science techniques.

Experimental and theoretical study of NO decomposition in a catalytic monolith reactor

The objective of this study was to prepare zeolite-based monoliths (Cu/ZSM-5 on cordierite), to test their catalytic activity in the direct decomposition of nitrogen monoxide and to develop mathematical model of the monolith reactor. Reaction of NO decomposition was performed over the monolith catalysts with various thickness of the catalytic washcoat, in temperature range from 573 to 773 K, under atmospheric pressure and at various space times. Two-dimensional heterogeneous model is applied to describe a single channel of the monolith reactor. Langmuir–Hinshelwood type of kinetic model is considered. The influence of both inter- and intraphase diffusion on the performance of the monolith reactor is quantitatively described by means of the governing effectiveness factors. The mean and local gas–solid mass transfer coefficients are derived from the concentration gradients using the proposed model. The proposed model is verified by comparing computer simulation data with experimental laboratory results.

Reaction and mass transfer effects in a catalytic monolith reactor

Zeolite-based monoliths (Cu/ZSM-5 on cordierite) are prepared and used to catalyze direct decomposition of nitrogen monoxide. Two-dimensional heterogeneous model is applied to describe the behavior of the monolith reactor, with the emphasis on the features introduced due to coupling of flow, mass transfer and chemical reaction. The proposed model has been verified by comparing computer simulation data with laboratory experimental data. It is shown that both inter- and intraphase diffusion limitations have to be considered when modeling complex reactor configuration, such as monolith reactors, especially when monolith with thicker catalytic layer are used at higher temperatures.

The role of redox property of La 2− x(Sr,Th) xCuO 4± λ playing in the reaction of NO decomposition and NO reduction by CO

Two systems of mixed oxides, La 2− x Sr x CuO 4± λ (0.0≤ x≤1.0) and La 2− x Th x CuO 4± λ (0.0≤ x≤0.4), with K 2NiF 4 structure were prepared. The average valence of Cu ions and oxygen nonstoichiometry ( λ) were determined by means of chemical analysis. Meanwhile, the adsorption and activation of nitrogen monoxide (NO) and the mixture of NO+CO over the mixed oxide catalysts were studied by means of mass spectrometry temperature-programmed desorption (MS-TPD). The catalytic behaviors in the reactions of direct decomposition of NO and its reduction by CO were investigated, and were discussed in relation with average valence of Cu ions, λ and the activation and adsorption of reactant molecules. It has been proposed that both reactions proceed by the redox mechanism, in which the oxygen vacancies and the lower-valent Cu ions play important roles in the individual step of the redox cycle. Oxygen vacancy is more significant for NO decomposition than for NO+CO reaction. For the NO+CO reaction, the stronger implication of the lower-valent Cu ions or oxygen vacancy depends on reaction temperature and the catalytic systems (Sr- or Th-substituted).

The direct decomposition of nitrogen monoxide

A series of copper-exchanged ZSM-5 samples of various copper contents were prepared. In freshly prepared Cu/ZSM-5, there is surface enrichment in copper, especially for the over-exchanged samples. This enrichment diminishes after heat treatments such as calcination or treatment in an inert gas. The oxidation state of copper can be easily altered. The introduction of nickel into over-exchanged Cu/ZSM-5 did not improve the activity. However, the activity of under-exchanged Cu/ZSM-5 slightly improved in the presence of the second metal.

Decomposition of nitrogen monoxide over NiTa2O6-supported palladium catalysts prepared from amorphous alloy precursors

Active catalysts for the direct decomposition of nitrogen monoxide were prepared from amorphous Ni40TaPd alloys by HF-treatment and subsequent pre-oxidation. The pre-oxidized catalyst consists of NiO, Ta2O5 and PdO, and PdO is decomposed to fcc Pd by heating at temperatures higher than 600°C. At further higher temperatures NiO and Ta2O5 are transformed to a very fine grained double oxide NiTa2O6. The catalysts thus formed consist of three layers and show high catalytic activity for the decomposition of nitrogen monoxide in a wide temperature range from 550 to 850°C. The catalytic behavior is affected by the structural change in the catalyst. With the transformation from NiO and Ta2O5 to NiTa2O6, the catalytic activity and the nitrogen formation selectivity increase significantly. TEM observation of ultramicrotomed cross-sections revealed that finely dispersed palladium supported on very fine-grained NiTa2O6 is formed in the interface between the outer and intermediate layers. High catalytic activities and high nitrogen formation selectivities of the Ni40TaPd alloys are attributable to the formation of the NiTa2O6-supported palladium catalyst.

Decomposition of nitrogen monoxide over NiTa 2O 6-supported palladium catalysts prepared from amorphous alloy precursors

Active catalysts for the direct decomposition of nitrogen monoxide were prepared from amorphous Ni 40Ta Pd alloys by HF-treatment and subsequent pre-oxidation. The pre-oxidized catalyst consists of NiO, Ta 2O 5 and PdO, and PdO is decomposed to fcc Pd by heating at temperatures higher than 600°C. At further higher temperatures NiO and Ta 2O 5 are transformed to a very fine grained double oxide NiTa 2O 6. The catalysts thus formed consist of three layers and show high catalytic activity for the decomposition of nitrogen monoxide in a wide temperature range from 550 to 850°C. The catalytic behavior is affected by the structural change in the catalyst. With the transformation from NiO and Ta 2O 5 to NiTa 2O 6, the catalytic activity and the nitrogen formation selectivity increase significantly. TEM observation of ultramicrotomed cross-sections revealed that finely dispersed palladium supported on very fine-grained NiTa 2O 6 is formed in the interface between the outer and intermediate layers. High catalytic activities and high nitrogen formation selectivities of the Ni 40Ta Pd alloys are attributable to the formation of the NiTa 2O 6-supported palladium catalyst.

Catalytic Decomposition of Nitrogen Monoxide over Valency-Controlled La2CuO4-Based Mixed Oxides

Abstract The direct decomposition of nitrogen monoxide (NO) to N2 and O2 was carried out over valency-controlled La2−xA′xCu1−yB′yO4 (A′ = Sr, Ba, Ca, Ce; B′ = Zr, Al) mixed oxide catalysts with a K2NiF4-type structure. The catalysts were characterized by XRD, XPS, redox titration, and oxygen TPD. It was confirmed by XPS that the surface and bulk compositions generally agreed and by redox titration that the average oxidation number (AON) of copper varied widely from 1.60 to 2.30. XPS showed that the valency of surface copper agreed with AON for AON ≤ 2, while it was in the Cu2+ state for AON &amp;gt; 2.0. The amounts of oxygen desorbed in TPD and the oxygen nonstoichiometry of La2−xSrxCuO4 increased with x in parallel. The catalytic activity for NO decomposition showed a maximum at x = 0.4—0.5, and a good correlation was found between the catalytic activity and AON for all of the catalysts tested. The decomposition of dinitrogen oxide (N2O) was also carried out for La2−xSrxCuO4 for a comparison. Based on the much slower rate of decomposition for NO than that for N2O and the significantly high rate of oxygen TPD, it was concluded that the oxygen desorption was not the rate-determining step in the steady state. The relative activities of the catalysts studied are all well explained by a mechanism in which the active sites for NO decomposition over these catalysts are coordinatively unsaturated Cu 2+ ions on the surface that can be easily oxidized to Cu3+ upon NO adsorption.

ChemInform Abstract: Cocation Effect in Catalytic Property of Copper Ion‐Exchanged ZSM‐5 Zeolites for the Direct Decomposition of Nitrogen Monoxide.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cocation Effect in Catalytic Property of Copper Ion-Exchanged ZSM-5 Zeolites for the Direct Decomposition of Nitrogen Monoxide

Abstract The coexistence of metal cations such as alkaline earth and transition metal cations with Cu ions in ZSM-5 zeolites promoted the catalytic activity of Cu ion for the direct decomposition of nitrogen monoxide at temperatures above 450 °C. The promotion effect was found to depend on the ion exchange mode.

特集 「地球環境および地域環境と化学」 Ｃｕを含むＫ２ＮｉＦ４型複合酸化物Ｌａ２−ｘＡ′ｘＣｕ１−ｙＢ′ｙＯ４触媒による一酸化窒素の直接分解

特集 「地球環境および地域環境と化学」 Ｃｕを含むＫ２ＮｉＦ４型複合酸化物Ｌａ２−ｘＡ′ｘＣｕ１−ｙＢ′ｙＯ４触媒による一酸化窒素の直接分解

Silver-promoted Cobalt Oxide Catalysts for Direct Decomposition of Nitrogen Monoxide

Abstract Silver as a catalyst additive showed an excellent effect to improve the catalytic activity of cobalt oxide for the decomposition of nitrogen monoxide below 773 K. Reaction inhibition by oxygen was very much relieved by using Ag–Co oxide catalysts.

Catalytic Activity of Perovskite-Type Oxides for the Direct Decomposition of Nitrogen Monoxide

Abstract Perovskite-type oxides showed the catalytic activity for NO decomposition above 773 K, which depended largely on constituent metal cations and their composition. Results obtained indicate that perovskite-type oxides such as La0.8Sr0.2CoO3 are a promising NO decomposition catalyst having high activity and thermal stability at elevated temperatures.

Excessively Copper Ion-exchanged ZSM-5 Zeolites as Highly Active Catalysts for Direct Decomposition of Nitrogen Monoxide

Abstract Repeated ion exchange of the ZSM-5 zeolite using aqueous copper(II) acetate solution was found to bring about excess loading of copper ions above 100% of exchange level. The catalytic activities of the resulting Cu-ZSM-5 zeolites for direct decomposition of nitrogen monoxide were very high and increased with increasing exchange level. The activity did not decrease even after 30 h of continuous service.