Nonstoichiometric oxygen in Mn–Ga–O spinels: reduction features of the oxides and their catalytic activity

Abstract

The hydrogen reduction of Mn1.7Ga1.3O4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn1.7Ga1.3O4+δ → Mn1.7Ga1.3O4. In the second step, Mn3+ cations are reduced to Mn2+ in the spinel structure and formation of MnO, Mn1.7Ga1.3O4 → Mn2Ga1O4 + MnO.

High-Temperature Thermal Cycling Effect on the Irreversible Responses of Lattice Structure, Magnetic Properties, and Electrical Conductivity in Co2.75Fe0.25O4+δ Spinel Oxide

“…This property is highly sensitive to the surface response along the (111) direction in the spinel structure 26 and structural changes in the defective spinels during heating cycles. 38 The structure of the Co 3 O 4 spinel oxide along the (111) direction has been modeled as a sequence of Co 3+ /Co 2+ layers separated by layers of O ions. The surface can by either be A-terminated (by Co 2+ and Co 3+ ions) or B-terminated (by Co 3+ ions) or oxidized on the A (AO) or B (BO) surfaces.…”

“…The cations (Fe and Co ions) occupy A and B sites, and anions (O ions) occupy the 32e positions. Nonstoichiometry of the metal/ oxygen ratio incorporates cationic vacancies in the spinel structure (A 1x1 B 2x2 [] y O 4 ) to preserve the closest oxygen packing or the chemical formula unit can be written as AB 2 O 4+ to incorporate the excess oxygen [25,42]. We show that lattice deformation at higher temperatures plays an important role in modifying magnetic and electrical properties.…”

“…In the W2C2 cycle, activation energy decreased to 0.679 eV and 0.617 eV during warming and cooling modes, respectively. Stabilization of the activation energy both in warming and cooling modes of the W2C2 cycle can be attributed to microstructural changes in the system, where absorbing and releasing capacity of oxygen atoms is decreased during repeated heating cycles [42]. The activation energy of the (high temperature annealed) CF_90 sample in W2C2 cycle was found 0.99 eV and 0.67 eV during warming and cooling modes, respectively.…”

Electrospun Ternary Composite Metal Oxide Fibers as an Anode for Lithium-Ion Batteries

“…As for Mn 2p core level, the difference in binding energy between (ix-xi)/(ix'-xi) are 12.1/10.9 eV. Peaks (ix') and 11) can be assigned to Mn 4+ oxidation state, where the deconvoluted peak (ix) can be attributed to Mn 3+ oxidation state (Bulavchenko et al, 2018). The reduction of Mn 4+ to Mn 3+ could be the stabilizing act to neutralize charge changes when both Ni 2+ and Co 2+ were oxidized to Ni 3+ and Co 3+ (He et al, 2020;Wangda Li et al, 2020).…”

The Reasons for Nonlinear Phenomena in Oxidation of Methane over Nickel

“…To find out the reasons for the oscillatory behavior, we carried out an operandо study using X-ray diffraction (XRD) and mass spectrometry. It should be noted that, unlike XPS, which makes it possible to determine the chemical composition of the surface of the functioning catalyst at a pressure below 10 mbar [17], XRD can be used in in situ study at atmospheric pressure [18,19]. The use of laboratory sources of X-ray radia-tion does not allow one to carry out studies with a high temporal resolution.…”