Phase transformation in the cupric magnesium oxide system

Ketchik, S. V.; Plyasova, L. M.; Chigrina, V. A.; Minyukova, T. P.; Yurieva, T. M.

doi:10.1007/bf02061277

Cited by 13 publications

(5 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The proximity of the lattice parameter values of the samples of different compositions at low temperatures is probably explained by the fact that under these conditions the rocksalt phase is predominantly comprised of magnesia, which is saturated with Co 2+ only during the thermal decomposition of the spinel, forming a solid solution with a composition corresponding to the initial cobalt loading. The higher value of the lattice parameter of low-temperature MgO relative to the theoretical value (4.2112 Å) is confirmed in [35] and is explained by the paracrystalline structure of anion-modified low-temperature oxide systems [36]; this phenomenon can also be explained by the presence of microstresses and strain in the structure [28,29]. The characteristic decrease of the lattice parameter values of both the spinel phase in the 400-750 °C range and the rocksalt phase formed during spinel thermal decomposition in the 900-1100 °C range is presumably explained by the stress relaxation together with decomposition of anionic residues in the phase structure.…”

Section: Phase Composition and Structure Of Samplessupporting

confidence: 53%

Patterns of Formation of Binary Cobalt-Magnesia Oxide Combustion Catalysts of Various Composition

Khussain,

Sass,

Brodskiy

et al. 2024

Preprint

View full text Add to dashboard Cite

In order to establish the formation patterns of the Co–Mg oxide system, samples with different Co:Mg ratios and heat treatment temperatures were synthesized and studied. Study of the sam-ples confirmed the phase transition of MgxCo2–xO4 spinels into corresponding solid solutions at 800–900 °C. The similarity of formation patterns for different compositions is shown. The rock-salt oxide in low-temperature samples is an anion-modified paracrystalline phase that forms a “true” solid solution only upon spinel decomposition. TPR profiles of decomposed Co3O4 spinel show surface Co3O4 peaks and a wide peak corresponding to well-crystallized CoO, while par-tial Co3O4 TPR up to 380 °C results in dispersed and amorphous CoO. High-temperature non-stoichiometric samples are poorly reduced, indicating their low oxygen reactivity. Spinel reoxidation after heat treatment to 1100 °C by calcination at 750 °C showed complete regenera-tion for MgCo2O4–Co3O4 samples and its absence in case of an excess of MgO relative to stoi-chiometry. Based on the data obtained, it can be concluded that the processes governing the formation of Co–Mg oxide systems are determined by both Co:Mg ratio and the heat treatment conditions, potentially providing the possibility of fine tuning for specific catalytic processes.

show abstract

Section: Phase Composition and Structure Of Samplessupporting

confidence: 53%

Patterns of Formation of Binary Cobalt-Magnesia Oxide Combustion Catalysts of Various Composition

Khussain,

Sass,

Brodskiy

et al. 2024

Preprint

View full text Add to dashboard Cite

show abstract

“…This may indicate the presence of additional ruthenium valence states in spectrum. This could be RuO 2 or Ru 3+ and Ru 4+ ions dissolved in the MgO lattice . However, the Ru3d spectra are fairly symmetric and can be described well by a single peak.…”

Section: Resultsmentioning

confidence: 98%

“…This could be RuO 2 or Ru 3+ and Ru 4+ ions dissolved in the MgO lattice. 20 However, the Ru3d spectra are fairly symmetric and can be described well by a single peak. So, it is impossible to make an unambiguous conclusion on the presence or absence of additional ruthenium states different from Ru 0 based only on these data.…”

Section: Resultsmentioning

confidence: 99%

Valence State Study of Supported Ruthenium Ru/MgO Catalysts

Larichev

2008

J. Phys. Chem. C

View full text Add to dashboard Cite

Ru/MgO catalysts have been studied by X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction. Significant part (up to 75%) of supported metal was found to exist in an X-ray amorphous state with the particle size smaller than 3 nm. The analysis of the spectra belonging to the core levels and the valence zone showed that the X-ray amorphous part of ruthenium may exist in the forms of both metal and oxide clusters and nanoparticles depending on the ruthenium precursor.

show abstract

“…The red brick color of the sample after this treatment allows supposing Cu 2 O phase formation and XRD proves decomposition of Cu-Mg oxide solid solution and formation of two individual oxide phases-Cu 2 O and MgO. One should note that the decomposition of Cu 0.15 Mg 0.85 O in air wasn't observed even at significantly higher temperature (up to 1,100°C) in [11]. The lower temperature of decomposition in the inert gas flow (i.e.…”

Section: Resultsmentioning

confidence: 94%

“…In earlier publications (see e.g. [11]), it was shown that the binary hydroxide system of Cu(OH) 2 and Mg(OH) 2 has limited solubility range. According to our data, the solubility limit of Cu 2?…”

Section: Resultsmentioning

confidence: 98%

Effect of anionic admixtures on the copper–magnesium mixed oxide reduction

Khassin

Filonenko

Minyukova

et al. 2010

Reac Kinet Mech Cat

View full text Add to dashboard Cite

The anionic composition, structural parameters, optical properties and reduction behavior of Cu-MgO solid solution in hydrogen dramatically change after exposure to air. The air-exposed Cu-Mg oxide contains a lot of CO 3 2-and OHanions. Its reduction proceeds via two stages: (1) diffusion of Cu 2? to the surface and (2) chemical interaction of Cu 2? with hydrogen. The effective activation energy gradually increases from that of the chemical step (65 kJ/mol) to that of the transport step of Cu 2? diffusion (130 kJ/mol). This behavior follows the ''compensation effect'', which is close to those reported earlier for CuO reduction. On the contrary, reduction of Cu 2? from the Cu-Mg oxide sample, which was not exposed to air after thermal pretreatment in the inert gas, proceeds in one step at 120-160°C with the effective activation energy of 19 kJ/mol, which is manifold less than the reported effective activation energies for various Cu-oxide systems. Water molecules eliminate from the sample slowly along with further heating up to 450°C.

show abstract

Phase transformation in the cupric magnesium oxide system

Cited by 13 publications

References 1 publication

Patterns of Formation of Binary Cobalt-Magnesia Oxide Combustion Catalysts of Various Composition

Patterns of Formation of Binary Cobalt-Magnesia Oxide Combustion Catalysts of Various Composition

Valence State Study of Supported Ruthenium Ru/MgO Catalysts

Effect of anionic admixtures on the copper–magnesium mixed oxide reduction

Contact Info

Product

Resources

About