Abstract
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.
Highlights
Nitrogen oxides (NOx) are harmful to human beings, but are responsible for photochemical smog and acid rain when present in relatively high levels in the atmosphere
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 ̊C 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
Summary
Nitrogen oxides (NOx) are harmful to human beings, but are responsible for photochemical smog and acid rain when present in relatively high levels in the atmosphere. In our previous works, we found that several C-type cubic rare earth oxide catalysts can exhibit high activities for direct NO decomposition even in the presence of O2 [20,21,22,23,24,25] and that exclusion of alkaline earth ions from the catalyst lattice is significantly effective to induce CO2 tolerance [25,26]. In the present study, (Y0.97–xTbxZr0.03)2O3.03+δ solid solutions (x = 0, 0.10, 0.20, 0.30, and 0.40), which adopt a C-type cubic structure, were designed as novel NO decomposition catalysts In these catalysts, a fraction of the yttrium sites in (Y0.97Zr0.03)2O3.03, which showed the highest NO decomposition activity in (Y1–yZry)2O3+y (0 ≤ y ≤ 0.10) [24], was substituted with terbium to inhibit catalyst poisoning by O2 and CO2, utilizing the redox property of Tb4+/3+ [23,25] for effective direct NO decomposition
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