Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO_3−δ and Sr₃Fe₂O_7−δ Perovskites

Abstract

The Ruddlesden–Popper (RP)-type layered perovskite is a candidate material for a new nitrogen oxide (NO x ) storage catalyst. Here, we investigate the adsorption and oxidation of NO x on the (001) surfaces of RP-type oxide Sr3Fe2O7−δ for all of the terminations by comparing to those of simple perovskite SrFeO3−δ by the density functional theory (DFT) calculations. The possible (001) cleavages of Sr3Fe2O7 generate two FeO2- and three SrO-terminated surfaces, and the calculated surface energies indicated that the SrO-terminated surface generated by the cleavage at the rock salt layer is the most stable one. The oxygen of the FeO2-terminated surfaces could be removed with significantly low energy because the process involves the favorable reduction of the Fe4+ site. Consequently, the surface oxygen at the FeO2 site could easily oxidize adsorbed NO to NO2 by the Mars–van Krevelen mechanism. The resulting oxygen vacancy in the surface would be filled easily with lattice oxygen in bulk. The oxidation of NO with adsorbed molecular O2 was unfavorable by both the Langmuir–Hinshelwood and Eley–Rideal mechanisms because this process does not involve the reduction of the Fe4+ site. The oxygen of the SrO-terminated surfaces was tightly bound and acted as the adsorption site of NO and NO2. An electron transfer strengthened the NO x binding to the surface by forming nitrite (NO2 –) or nitrate (NO3 –) species. The DFT calculations revealed that the RP-type structure promoted NO x oxidation and storage properties by forming active oxygen due to the Jahn–Teller distortion and by exposing SrO-terminated surfaces due to the cleavage at the rock salt layer.

Raspberry-like TiO2 hollow spheres consisting of small nanocrystals towards efficient NO removal

“…73 The absorption peak at 1304 cm −1 was attributed to HNO 3 . 70 The above results were consistent with formulas (1)- (8).…”

“…NO + ˙OH → HNO 2 (7) NO 2 + ˙OH → HNO 3 (8) Weak photocatalytic activity always induces the generation of NO 2 , which is due to the incomplete oxidation of NO. Since NO 2 is more toxic than NO and leads to greater damage to the environment, the production of NO 2 should be minimized when NO is oxidized to NO x .…”

“…They are also important substances leading to acid rain and photochemical smog. [6][7][8] NO accounts for more than 90% of nitrogen oxides, but the direct treatment of NO is very difficult. 9,10 The usual treatment is to reduce NO emission or to convert NO into other easily treated nitrogen oxides.…”

NOx Storage Performance at Low Temperature over Platinum Group Metal-Free SrTiO3-Based Material

“…The disappearance of the IR absorptions at approximately 473 K indicated that the large desorption peak at low temperatures observed in the NO x desorption profile of the Mn-doped catalyst (Figure ) was from the bridging nitrate and nitro species. Generally, basic sites such as the Ba sites in Pt/Ba/Al 2 O 3 and Sr sites in Sr–Fe perovskites can easily adsorb NO x species. ,, Both bidentate nitrate and free surface nitrite ions were observed on all the examined catalysts, suggesting that these species must be adsorbed on the Sr sites. However, bridging nitrate and nitro species at 1623 and 1393 cm –1 , respectively, were observed in the Mn-doped catalysts and SrTiO 3 in the DRIFT spectra of the NO x species adsorbed on SrTi 1– x Mn x O 3 (Figure S7), suggesting that the Mn or Ti sites act as the adsorption sites.…”

Coupling of LaFeO3–Plasma Catalysis and Cu+/Cu0 Electrocatalysis for Direct Ammonia Synthesis from Air

“…29 Generally, the efficiency of N 2 fixation in the NTP can be improved by using a catalyst. 30−32 Perovskites are used in various reactions, 33−36 especially for oxidation reactions such as the oxidation of nitrogen oxide 35,37,38 and carbon monoxide, 39,40 because of their excellent thermal stability, electronic structure, ionic conductivity, electron mobility, and redox behavior.…”