Unraveling the Principles of Lattice Disorder Degree of Bi₂B₂O₇ (B = Sn, Ti, Zr) Compounds on Activating Gas Phase O₂ for Soot Combustion

Abstract

With the combination of experimental methods and DFT calculations, the influence of lattice disorder degree on the catalytic property of Bi2B2O7 compounds with different B-site cations (B = Sn, Ti, Zr) has been elucidated in this work. The crystal structures of the samples vary from a well-ordered pyrochlore (Bi2Sn2O7) to a less-ordered pyrochlore (Bi2Ti2O7), and eventually to a disordered defect fluorite (Bi2Zr2O7) phase, hence the lattice disorder degree increases. DFT calculation and oxygen ion conductivity results have testified that the surface oxygen vacancy formation energies (E O‑f) of the catalysts decrease with the increase of the disorder degree, accompanying the improvement of the lattice ion mobility and the formation of more surface oxygen vacancies. Isotopic 18O2 tracing experiments have demonstrated that the adsorbing and activating of gas phase O2 molecules mainly follow an R2 mechanism requiring two adjacent surface vacancies. With the synergistic actions of surface oxygen vacancies and lattice O2– anions, both active O2 – and O2 2– sites contributing vitally to soot combustion can be formed. Therefore, the abundance of surface oxygen vacancies is of great importance for this process, which is intimately related to the lattice disorder degree of the compounds. From this point of view, it is concluded that the lattice disorder degree is the inherent factor to determine the redox property and reaction performance of Bi2B2O7 compounds for soot combustion.

Elucidating Ru Distribution State of Ru‐Promoted Pr2Sn2O7 Pyrochlore and its Effect on the Catalytic Performance for Toluene Deep Oxidation

“…In addition, pure Pr 2 Sn 2 O 7 has much a higher activation energy than the Ru‐modified catalysts, which implies that the properties of the active sites have been changed. Former studies have proved that Pr 2 Sn 2 O 7 , as a pyrochlore compound, possesses inherent oxygen vacancies, which can induce the generation of active surface electrophilic oxygen sites [8b,10] . On pure Pr 2 Sn 2 O 7 , these surface active oxygen sites might play as the major role for toluene oxidation.…”

“…For instance, we have discovered that the surface property as well as the reactivity of pyrochlores can be significantly affected by the crystal structures. A pyrochlore compounds with a higher lattice disorder degree generally possesses better redox property, hence improving the reaction performance of those reactions involving oxidizing process [10] . However, up to date, A 2 B 2 O 7 compounds have been rarely used to support noble metals for VOCs combustion.…”

“…A pyrochlore compounds with a higher lattice disorder degree generally possesses better redox property, hence improving the reaction performance of those reactions involving oxidizing process. [10] However, up to date, A 2 B 2 O 7 compounds have been rarely used to support noble metals for VOCs combustion. Our former studies have demonstrated that Pd supported on a high surface area La 2 Sn 2 O 7 pyrochlore synthesized with a hydrothermal method shows favorable activity for carbon monoxide oxidation, because of the high dispersion of Pd species and the formation of a larger quantity of active surface oxygen sites.…”

Reactive oxygen species on transition metal-based catalysts for sustainable environmental applications

“…The MvK mechanism of O L -mediating oxidation is well supported by isotope labelling, as using 18 O 2 as the stoichiometric oxidant will install 18 O in the lattice of the metal oxides. 102 Heating is generally required to activate O L and regenerate O L from O 2 , which can increase cost and make the reaction procedure tedious. The reactivity and regeneration of O L can be tuned by regulating the strength of the M-O bond (M: metal) and the chemical states of the metal, to enable stronger oxidation performance at a lower temperature.…”

“…13c). 102 3.5 Tailoring the reactive oxygen species generation PMS, PDS and H 2 O 2 are strong oxidants but normally have low reaction rates with most organic pollutants. Catalysts bearing transition metal ions (e.g., Fe, Mn, Co, Ni, V, Ce, etc.)…”