Abstract
The mechanism and structure requirements of selective and total oxidation of methane in a chemical looping process are both experimentally and theoretically examined on La1–xSrxFeO3−δ (x = 0, 0.2, ...
Highlights
The catalytic redox reaction is playing a pivotal role in numerous industrial, environmental, and energy applications, such as selective oxidation for the production of fine chemicals in the petrochemical industry,[1] total combustion of VOC for environmental protection, total combustion for energy production,[1] oxidative dehydrogenation of alkanes,[2] selective catalytic reduction of NOx,[3] electrochemical water splitting, CO2 reduction,[4] metal air batteries for energy storage,[5] and so forth
We have demonstrated that the oxygen mobility effects on activity and selectivity in methane oxidation could be tuned by the crystal size of the perovskite LaFeO3.27 In the present work, we will investigate the effects of substituting Sr2+ for La3+ in LaFeO3−δ and the substitution of Co3+ for Fe3+ in La0.5Sr0.5FeO3−δ on the oxygen mobility and the activity and selectivity of methane oxidation
The oxygen vacancy formation energy (ΔEf,vac) can be calculated as where Eperfect and Edefective are the total energies of the stoichiometric perovskite structure and its fully relaxed supercell with an oxygen atom removed from the lattice, respectively, and EO2 is the total energy of a free oxygen molecule in its triplet state and has been corrected by fitting the formation energetics of nontransition-metal oxides to available experimental data.[39]
Summary
The catalytic redox reaction is playing a pivotal role in numerous industrial, environmental, and energy applications, such as selective oxidation for the production of fine chemicals in the petrochemical industry,[1] total combustion of VOC for environmental protection, total combustion for energy production,[1] oxidative dehydrogenation of alkanes,[2] selective catalytic reduction of NOx,[3] electrochemical water splitting, CO2 reduction,[4] metal air batteries for energy storage,[5] and so forth. Co or Mn as the B-site cations in ABO3−δ perovskites are suggested to be the most promising materials for complete oxidation of hydrocarbons,[22−25] while Fe is preferential for selective oxidation.[26,27] The La3+ cations are substituted by cations in a lower oxidation state (i.e. Sr2+, Ca2+, or Nd2+), leading either to the partial oxidation of the B cations to a higher oxidation state and/or to the formation of oxygen vacancies, which results in a better catalytic activity.[22,25] By virtue of this flexibility, extensive studies have been carried out on perovskites for searching for the parameters determining their catalytic activity.[28] The eg filling of surface transition-metal cations has been demonstrated as the descriptor of the electrochemical reactions and heterogeneous catalytic reactions.[29] the descriptor above was proposed by only considering a single physicochemical property of the transition-metal cations in perovskites for the activity. The results bridge the C−H activation activity and selectivity with the oxygen mobility of perovskites described by oxygen diffusivity and oxygen vacancy formation energy
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