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

Abstract

C-type cubic (Y 1Àx Pr x ) 2 O 3+d (0 # x # 0.20) catalysts were prepared for direct NO decomposition. The highest catalytic activity was exhibited

Recent progress in catalytic NO decomposition

“…As given in Fig. 14, the N 2 yield on (Y 0.90 Pr 0.10 ) 2 O 3 þ d was decreased from 80% to 58% by the coexistence of 1% CO 2 under the conditions of NO ¼ 1.0% and W/F ¼ 3.0 g s cm À3 at 900 C. However, further increase in the CO 2 concentration up to 10% did not cause significant decreases in the NO decomposition activity [63]. CO 2 poisoning seems to be much smaller for C-type cubic rare earth oxides than that observed for other conventional catalysts such as perovskite-type oxides.…”

“…Imanaka and co-workers then studied the catalytic performance of C-type cubic rare earth oxides and reported various kinds of effective composite metal oxides with C-type structures such as Gd 2 [63,64] and Ho 2 O 3 eZrO 2 ePr 6 O 11 [65]. As summarized in Table 3, C-type cubic rare earth oxides are highly active catalysts at high temperatures above 800 C. Among the catalysts reported so far, (Y 0.69 Tb 0.30 Ba 0.01 ) 2 O 2.99þd was found to be the best catalyst with 100% NO Fig.…”

“…Effect of partial pressures of O 2 and CO 2 in the feed gas on the conversion of NO over the (Y 0.90 Pr 0.10 ) 2 O 3 þ d catalyst at 900 C[63]. Conditions: NO ¼ 1.0%, O 2 ¼ 0e10%, CO 2 ¼ 0e10%, He balance, and W/F ¼ 3.0 g s cm À3 .…”

Fundamental Aspects of Rare Earth Oxides Affecting Direct NO Decomposition Catalysis

“…The lattice volume of the C-type structure is larger than those of A-type and B-type structures and thus it possesses large interstitial open spaces, which have been found to play an important role during direct NO decomposition in our previous studies. [7][8][9][10] In particular, a C-type cubic (Y 0.69 Tb 0.30 Ba 0.01 ) 2 O 2.99+δ catalyst, in which the Y 3+ sites are partially substituted with Tb 3+/4+ and Ba 2+ , can realize 100 % NO decomposition into N 2 and O 2 at 900°C. [7] To date, however, there have been no systematic studies concerning the fundamental factors associated with pure rare earth oxides (REOs) that exhibit direct NO decomposition activity, and the crucial role of the crystal structure with regard to NO decomposition remains unclear.…”

“…[7][8][9][10] At temperatures below approximately 2000°C, three crystal polymorphs of rare earth sesquioxides are known to exist depending on the ionic size of the respective rare earth elements: A-type hexagonal, B-type monoclinic, and C-type cubic ( Figure 1). [11] Among these, the C-type represents a cubic bixbyite-type structure, which the coordination environments of the rare earth cations within each crystal lattice.…”