Understanding Oxygen Release from Nanoporous Perovskite Oxides and Its Effect on the Catalytic Oxidation of CH₄ and CO

Abstract

The design of nanoporous perovskite oxides is considered an efficient strategy to develop performing, sustainable catalysts for the conversion of methane. The dependency of nanoporosity on the oxygen defect chemistry and the catalytic activity of perovskite oxides towards CH 4 and CO oxidation was here studied. A novel colloidal synthesis route for nanoporous, high-temperature stable SrTi 0.65 Fe 0.35 O 3-δ with specific surface area (SSA) ranging from 45 to 80 m 2 /g and pores from 10 to 100 nm was developed. High-temperature investigations by in situ synchrotron XRD and TG-MS combined with H 2 -TPR and Mössbauer spectroscopy showed that the porosity improved the release of surface oxygen and the oxygen diffusion, whereas the release of lattice oxygen depended more on the state of the iron species and strain effects in the materials. Regarding catalysis, light-off tests showed that low-temperature CO oxidation significantly benefitted from the enhancement of the SSA, whereas high-temperature CH 4 oxidation is influenced more from the dioxygen release. During isothermal long-term catalysis tests however the continuous oxygen release from large SSA materials promoted both CO and CH 4 conversion. Hence, if SSA maximization turned out to efficiently improve low-temperature and long-term catalysis applications, the role of both reducible metal center concentration and crystal structure cannot be completely ignored, as they also contribute to the perovskite oxygen release properties. TOC GraphicsScheme 1: Graphical representation of the synthesis of the SrTi 0.65 Fe 0.35 O 3-δ perovskites showing the dependency of the materials porosity and crystallite size from the type of polyol (ethylene glycol, glycerol, and 1,6 hexandiol) used

Brownmillerites CaFeO2.5 and SrFeO2.5 as Catalyst Support for CO Oxidation

“…Pt/SFO_eaf remains rather stable during the three runs (T20 = 238 °C). These values are well above the CO oxidation performance of other well-known Pt catalysts tested, such as Pt/CeO2 [14], but similar to perovskites of similar composition, e.g., Pt/SrTi0.65Fe0.35O3−δ [15]. The deactivation observed in particular for Pt/SFO_cp could be due to platinum nanoparticle growth, or changes in the support, as already noted after the ILPOR experiment (vide sopra).…”

High-Surface-Area Synthesis of Iron-Doped CaTiO3 at Low Temperatures: New Insights into Oxygen Activation, Iron States, and the Impact on Methane Oxidation

“…Here, we optimized the synthesis protocol with respect to the polyol/citric acid:cation ratio and the calcination protocol to limit the generation of undesired species during the decomposition of the precursors and the crystallization step. By lowering the amount of polyol and citric acid as compared to literature protocols, 26 the formation of crystalline carbonates can be suppressed. We figured that an optimum is reached with a polyol/citric acid:cation A molar ratio of 15:7.5:1 (cation A refers to the A site in the perovskite ABO 3 ).…”

“…For x = 0.4, the Fe 4+ content increases to 19%, and the Fe 3+ -4CN content also increases at the cost of pentacoordinated iron, which is not present in CTF40-Gly, in accordance with the results from Figueiredo et al 1 Also, such a relatively high amount of Fe 4+ in iron-doped perovskites has been recently reported for SrTi 0.65 Fe 0.35 O 3−δ. 26 For CTF40-Gly, the best fit is obtained for a partially ordered structure in which Fe is distributed over one 4CN site and two 6CN sites, denoted as Fe 3+ -6CN and Fe 3+ -6CN′, respectively. Despite this increase in Fe 4+ , the amount of oxygen ion vacancies expressed as δ in CaTi 1−x Fe 0x O 3−δ increases with increasing Fe doping on the B site (Figure 5b).…”

Deep Insight into the Mechanism of Catalytic Combustion of CO and CH4 over SrTi1–xBxO3 (B = Co, Fe, Mn, Ni, and Cu) Perovskite via Flame Spray Pyrolysis

“…The emission of these hazardous gases into the atmosphere threatens both the ecological environment and human health. 1 Therefore, highly efficient ways for the removal of lean combustible gases are urgently desired. Catalytic combustion is a promising way to convert a low concentration of CO/CH 4 into CO 2 and/or H 2 O.…”

“…The diluted combustible gases, including CO and CH 4 , released from various industrial sectors through human activities are serious issues. The emission of these hazardous gases into the atmosphere threatens both the ecological environment and human health . Therefore, highly efficient ways for the removal of lean combustible gases are urgently desired.…”