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

Abstract

Pt-based catalysts are commonly employed as NO x -trapping catalysts for automobiles, while perovskite oxides have received attention as Pt-free NO x -trapping catalysts. However, the NO x storage performance of perovskite catalysts is significantly inferior at low temperatures and with coexisting gases such as H2O, CO2, and SO2. This study demonstrates that NO x storage reactions proceed over redox site (Mn, Fe, and Co)-doped SrTiO3 perovskites. Among the examined catalysts, Mn-doped SrTiO3 exhibited the highest NO x storage capacity (NSC) and showed a high NSC even at a low temperature of 323 K. Moreover, the high NO x storage performance of Mn-doped SrTiO3 was retained in the presence of poisoning gases (H2O, CO2, and SO2). NO oxidation experiments revealed that the NSC of Co-doped SrTiO3 was dependent on the NO oxidation activity from NO to NO2 via lattice oxygen, which resulted in an inferior NSC at low temperatures. On the other hand, Mn-doped SrTiO3 successfully adsorbed NO molecules onto its surface at 323 K without the NO oxidation process using lattice oxygens. This unique adsorption behavior of Mn-doped SrTiO3 was concluded to be responsible for the high NSC in the presence of poisoning gases.

Oxygen Storage Capacity of Co-Doped SrTiO3 with High Redox Performance

“…SrTi 1– x Co x O 3−δ ( x = 0, 0.2, 0.4, 0.6, and 0.8) and Ce 0.5 Zr 0.5 O 2 (CZ), a benchmark OSM, were synthesized by the Pechini method. , Citric acid (400 mmol, 98.0%) was dissolved in deionized water (180 mL), and starting materials were added to a citric acid solution. The starting materials were used as follows: SrCO 3 (20 mmol, 99.0%), titanium­(IV) tetraisopropoxide (20­(1 – x ) mmol, 95.0%), Co­(NO 3 ) 2 ·6H 2 O (20 x mmol, 98.0%), Ce­(NO 3 ) 3 ·6H 2 O (10 mmol, 98.0%), and ZrO­(NO 3 ) 2 ·2H 2 O (10 mmol, 97.0%).…”

“…Then, we investigated the chemical stability of Sr–Fe materials and found that Ti doping into Fe sites in SrFeO 3−δ dramatically suppressed SrCO 3 formation and improved the oxygen storage rate . Furthermore, in the context of the NO oxidation activity over SrTi 0.8 B 0.2 O 3 (B = Mn, Fe, and Co), the lattice oxygen in Co-doped SrTiO 3 materials has recently been shown to have extremely high reactivity with NO, compared to that of Mn- or Fe-doped materials …”

“…32 Furthermore, in the context of the NO oxidation activity over SrTi 0.8 B 0.2 O 3 (B = Mn, Fe, and Co), the lattice oxygen in Co-doped SrTiO 3 materials has recently been shown to have extremely high reactivity with NO, compared to that of Mn-or Fe-doped materials. 33 In this study, we investigated the redox mechanism of Codoped SrTiO 3 and its functionality as a catalyst material for purifying exhaust gases. The Co-doped SrTiO 3 materials were determined to release/store oxide ions via topotactic transformation, and doping Co into the SrTiO 3 framework induced the high redox activity of the Co species.…”

Exceptionally high and reversible NOx uptake by hollow Mn–Fe composite nanocubes derived from Prussian blue analogues

“…A similar finding has also been reported about Mn-doped SrTiO 3 showing higher NO x storage capacity than SrTiO 3 . 46…”

“…A similar finding has also been reported about Mn-doped SrTiO 3 showing higher NO x storage capacity than SrTiO 3 . 46 To further understand the NO x adsorption mechanism, the in situ DRIFTS of NO + O 2 on Mn 1 Fe 2 -450 was performed, and the results are shown in Fig. 9.…”