Inhibition of NO Decomposition Activity of Perovskite-type Oxides by Coexisting Carbon Dioxide

Catalytic activities for direct NO decomposition were investigated over C-type cubic Y2O3–Tb4O7–ZrO2 prepared by a coprecipitation method. The NO decomposition activity was enhanced by partial substitution of the yttrium sites with terbium in a (Y0.97Zr0.03)2O3.03 catalyst, which shows high NO decomposition activity. Among the catalysts synthesized in this study, the (Y0.67Tb0.30Zr0.03)2O3.33 catalyst exhibited the highest NO decomposition activity; NO conversion to N2 was as high as 67% at 900℃ in the absence of O2 (NO/He atmosphere), and a relatively high conversion ratio was observed even in the presence of O2 or CO2, compared with those obtained over conventional direct NO decomposition catalysts. These results indicate that the C-type cubic Y2O3–Tb4O7–ZrO2 catalyst is a new potential candidate for direct NO decomposition.

Support and particle size effects on direct NO decomposition over platinum

Catalytic activities for direct NO decomposition were investigated on C-type cubic Y2O3–ZrO2 and Y2O3–ZrO2–BaO prepared by coprecipitation. Introduction of excess oxide anions in the Y2O3 lattice was achieved by partial substitution of the Y3+ sites with Zr4+, and high NO decomposition activity was obtained for the (Y0.97Zr0.03)2O3.03 catalyst. In addition, the catalytic activity was further enhanced by partial substitution of the Y3+ sites in the Y2O3–ZrO2 solid solution with Ba2+, and the (Y0.89Zr0.07Ba0.04)2O3.03 catalyst exhibited the highest NO decomposition activity among the samples prepared; NO conversion to N2 reached 90% at 1173 K in the absence of O2 (NO/He atmosphere), and a relatively high conversion ratio was observed even in the presence of O2, H2O, or CO2, compared with the activities of conventional direct NO decomposition catalysts. These results indicate that the C-type cubic Y2O3–ZrO2–BaO catalyst is a new potential candidate for direct NO decomposition.

Direct decomposition of NO into N 2 and O 2 over La(Ba)Mn(In)O 3 perovskite oxide

Comparative study of Nickel-based perovskite-like mixed oxide catalysts for direct decomposition of NO

Direct NO decomposition over conventional and mesoporous Cu-ZSM-5 and Cu-ZSM-11 catalysts: Improved performance with hierarchical zeolites

The catalytic performance of Ba–Y2O3 prepared by a coprecipitation method for the direct decomposition of NO was investigated. Although Y2O3 catalyzed NO decomposition, its activity was increased by addition of Ba. The maximum NO decomposition activity was achieved on Ba–Y2O3 with 5 wt % Ba loading. XRD measurements revealed the formation of a solid solution of Ba and Y2O3 as well as BaCO3 small particles, when Ba loading was increased up to 5 wt %. From the comparison between the amount of CO2 desorption measured by temperature-programmed desorption of CO2 (CO2-TPD) and the NO decomposition activity of Ba–Y2O3, highly dispersed Ba species, which is initially present as BaCO3 small particles, on the catalyst surface act as catalytically active sites for NO decomposition. On the basis of in situ observation of surface species formed during NO decomposition by Fourier transform infrared (FT-IR) spectroscopy, we proposed that highly dispersed Ba species plays a role for the formation and adsorption of nitrite (NO2−) as reactive species for NO decomposition over Ba–Y2O3 catalyst.

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

The direct catalytic decomposition of NO into N2 and O2 with high activity and N2 selectivity at low temperature under excess oxygen is a challenge. Herein, we report a new approach for the direct decomposition of NO into N2 and O2 by microwave catalysis over MeOx‐Cu‐ZSM‐5 (Me=Mn, Ni) under excess oxygen. We observed that the microwave direct catalytic decomposition of NO over MeOx‐Cu‐ZSM‐5 under excess oxygen is highly efficient, and the NO conversions are 94.3 % over MnO2‐Cu‐ZSM‐5 at 300 °C and 92.3 % over Ni2O3‐Cu‐ZSM‐5 at 350 °C. Meanwhile, the N2 selectivity remains more than 98 %. Importantly, the apparent activation energies of MnO2‐Cu‐ZSM‐5 and Ni2O3‐Cu‐ZSM‐5 are as low as 15.5 and 25.7 kJ mol−1, which suggests a significant microwave catalytic effect. Furthermore, microwave irradiation exhibits a microwave selective effect. The oxygen concentration has almost no influence on the activity of catalytic decomposition of NO over MeOx‐Cu‐ZSM‐5 under microwave irradiation.

Selective catalytic reduction of NO with hydrocarbon on Cu 2+-exchanged pillared clay: An IR study of the NO decomposition mechanism

Effect of Mn content on physical properties of CeO x–MnO y support and BaO–CeO x–MnO y catalysts for direct NO decomposition

Co1.5M1.5/Al1−xTix hydrotalcite-like compounds (where M = Co, Ca and x = 0, 0.1) were synthesized by a constant-pH coprecipitation. The derived oxides from hydrotalcites upon calcination at 800 °C for 4 h were all of spinel phase without crystalline TiO2 phase being detected. Substitution of partial Al for Ti significantly enhanced NO direct decomposition activity of these catalysts. In particular, catalyst Co3.0/Al0.9Ti0.1O (CATO) showed the highest NO direct decomposition percentage, up to 86% at 300 °C with GHSV of 30 000 h−1 (800 ppm of NO and 8% O2 in N2 stream). CATO also showed the highest resistance to SO2 poisoning to NO direct decomposition, with the activity being only reduced by 16% in the presence of 64 ppm of SO2 in the mixed gas stream at 300 °C. The in-situ FT-IR spectra indicate different adsorption species over the catalysts, revealing NO surface storage/decomposition involves different adsorption reactions that determine the NO decomposition activity and resistance to SO2 poisoning.

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.

C-type cubic Y2O3, (Y0.70Tb0.30)2O3+δ, and (Y0.99−xTbxBa0.01)2O2.99+δ (x = 0, 0.10, 0.20, 0.30, and 0.40) were prepared to investigate their catalytic performance for NO decomposition. In the direct NO decomposition process, NO is adsorbed on basic sites of the catalyst surface to form adsorbed nitrosyl, and the number of basic sites affects the NO decomposition activity. In particular, the negative effect of CO2 presence on the catalytic activity is related to the number of the surface basic sites. Furthermore, it was evidenced from temperature programmed desorption (TPD) of NO and IR measurements that adsorbed nitrosyl reacts with gas-phase NO and decomposes to N2. The effects of Ba2+ and Tb3+/4+ introduction on the activity of the catalyst are discussed based on this NO reaction mechanism. It is concluded that the principal effects of Ba2+ doping are an increase in the number of basic sites and the generation of oxide anion vacancies in the lattice. In addition, we demonstrate that Tb3+/4+ ions in the lattice facilitate O2 desorption and act as NO adsorption sites, so that the catalytic activity is significantly enhanced by Tb3+/4+ introduction, despite the small number of basic sites on the catalyst surface.

NO direct decomposition on doped SrFeO3 perovskite oxide was investigated. The ability of SrFeO3 for direct decomposition of NO is strongly affected by the dopant in Fe sites. Among the examined dopants and compositions, the highest yield of N2 was achieved on SrFe0.7Mg0.3O3. When SrFe0.7Mg0.3O3 was loaded with Pt, the N2 yield further improved, and the light-off temperature fell by 100 K. On this catalyst, the yields of N2 and O2 were 56 and 35%, respectively, at 1123 K. On the Pt-loaded SrFe0.7Mg0.3O3 catalyst, the NO decomposition rate increased with increase in the NO partial pressure with PNO1.31. The presence of oxygen slightly decreased the N2 yield with PO2−0.12. Therefore, the effect of oxygen poisoning on NO decomposition upon Pt-loaded SrFe0.7Mg0.3O3 is small. From the result of O2-TPD, Pt loading possibly weakens the adsorption strength of surface oxygen and enhances NO adsorption. In summary, this study shows that the substitution of Fe with lower valence cation in SrFeO3 and also loading a small amount of Pt are highly effective for increasing the NO decomposition activity.