Coexisting Gas-resistant C-type Cubic Yb2O3–Tb4O7 Catalysts for Direct NO Decomposition

Abstract

C-type cubic (Yb1−xTbx)2O3±δ (0 ≤ x ≤ 0.62) catalysts were synthesized by coprecipitation. Among the samples prepared, (Yb0.50Tb0.50)2O3±δ showed the highest catalytic activity and high tolerability for O2 or CO2 coexistence was recognized. In particular, the negative effect of CO2 on the NO decomposition activity is significantly reduced compared to those of conventional catalysts, and N2 yield as high as 33% was obtained even in the presence of 5 vol % CO2.

Direct Decomposition of NO into N<sub>2</sub> and O<sub>2</sub> Over C-type Cubic Y<sub>2</sub>O<sub>3</sub>-Tb<sub>4</sub>O<sub>7</sub>-ZrO<sub>2</sub>

“…As a result, NO decomposition activity as high as 47% was maintained, even in the presence of 5 vol% O 2 , and the activity did not deteriorate during the 10-h catalytic test. This conversion ratio in the presence of 5 vol% O 2 (47%) was higher than that for C-type cubic (Yb 0.50 Tb 0.50 ) 2 O 3±δ (35%) [25]. In contrast, the effect of CO 2 on the NO decomposition activity was relatively larger than that for O 2 , but the decreasing tendency of the N 2 yield with the increase in the partial pressure of CO 2 was similar to that observed for O 2 .…”

“…Since CO 2 is acidic, adsorption of CO 2 on the basic sites of the catalyst surface will inhibit NO adsorption on the open space sites of the catalyst. However, for the (Y 0.67 Tb 0.30 Zr 0.03 ) 2 O 3.33 catalyst, a high N 2 yield of 36% was maintained even in the presence of 5 vol% CO 2 , which is higher than those for the (Yb 0.50 Tb 0.50 ) 2 O 3±δ (34%) [25], Ba 0.8 La 0.2 Mn 0.8 Mg 0.2 O 3 (20% at 850˚C) [12], and La 0.8 Sr 0.2 CoO 3 (10% at 800˚C) catalysts [15].…”

“…It has been generally accepted that large open spaces in a catalyst play an important role in direct NO decomposition, and for this reason the C-type cubic rare earth oxide is suitable as a direct NO removal catalyst. Furthermore, 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 O 2 [20][21][22][23][24][25] and that exclusion of alkaline earth ions from the catalyst lattice is significantly effective to induce CO 2 tolerance [25,26].…”

“…In the present study, (Y 0.97-x Tb x Zr 0.03 ) 2 O 3.03+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 (Y 0.97 Zr 0.03 ) 2 O 3.03 , which showed the highest NO decomposition activity in (Y 1-y Zr y ) 2 O 3+y (0 ≤ y ≤ 0.10) [24], was substituted with terbium to inhibit catalyst poisoning by O 2 and CO 2 , utilizing the redox property of Tb 4+/3+ [23,25] for effective direct NO decomposition.…”

Direct decomposition of nitrogen monoxide over C-type cubic Y2O3–Pr6O11solid solutions

“…These catalysts are composed almost entirely of heavier rare earth ions, purposely excluding alkaline earth ions such as Ba 2+ and Sr 2+ from the catalyst lattice. 10,14 In these catalysts, the redox properties of rare earth ions, which can exist in multivalent states, contribute to the NO decomposition activity, since desorption of O 2 and CO 2 from the catalyst surface is facilitated by their presence and leads to the regeneration of active sites for NO decomposition. 13 The NO decomposition activities of these catalysts, however, were found to be insufficient, with (Y 0.67 Tb 0.30 Zr 0.03 ) 2 O 3.33 and (Yb 0.50 Tb 0.50 ) 2 O 3AEd exhibiting conversions of only 36% (ref.…”