TY - JOUR

T1 - The thermal activation of MnOx-Al2O3 catalysts: Effect of gallium doping

AU - Bulavchenko, O. A.

AU - Afonasenko, T. N.

AU - Vinokurov, Z. S.

AU - Pochtar, A. A.

AU - Rogov, V. A.

AU - Tsybulya, S. V.

N1 - Funding Information: This work was supported by the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15-2022-263 ). The experiments were performed using large-scale research facilities "EXAFS spectroscopy beamline". Publisher Copyright: © 2022 Elsevier B.V.

PY - 2022/11/15

Y1 - 2022/11/15

N2 - In this study, the effect produced by the gallium oxides intercalation into MnOx-Al2O3 catalysts on their catalytic properties and structural aspects of the active component formation was investigated. Three series of the catalysts, Mn–Al, Mn–Ga, and Mn–Al-Ga, having a similar Mn content but different Al/Ga ratio, were synthesized by coprecipitation and subsequent calcination at temperatures from 600 to 1200°С°. The catalysts were tested in CO oxidation. For the Mn–Al series of catalysts, a thermal activation effect is observed, defined as an increase in catalytic activity after high-temperature treatment at 900-1000°С. The increase in the activity after calcination is related to the formation of the Mn3-xAlxO4 solid solution at the synthesis temperature and its segregation upon cooling. Segregation of the solid solution leads to the formation of the Mn3O4+δ defect oxide and an amorphous aluminum-containing component. The addition of 5%Ga to the Mn–Al catalyst changes the phase transformation route during thermal activation. The in situ XRD data has showed that at 1000°С the high-temperature solid solution (MnGaAl)3O4 with the cubic spinel structure is formed; however, its further segregation upon cooling is hindered. The introduction of gallium stabilizes the structure of the (MnGaAl)3O4 mixed oxide, the parent oxide is partially decomposed after cooling with Mn3O4 nanoparticles formation. However the amount of produced active Mn3O4 particles and/or weakly bound oxygen is much lower, which in turn adversely affects the catalytic properties.

AB - In this study, the effect produced by the gallium oxides intercalation into MnOx-Al2O3 catalysts on their catalytic properties and structural aspects of the active component formation was investigated. Three series of the catalysts, Mn–Al, Mn–Ga, and Mn–Al-Ga, having a similar Mn content but different Al/Ga ratio, were synthesized by coprecipitation and subsequent calcination at temperatures from 600 to 1200°С°. The catalysts were tested in CO oxidation. For the Mn–Al series of catalysts, a thermal activation effect is observed, defined as an increase in catalytic activity after high-temperature treatment at 900-1000°С. The increase in the activity after calcination is related to the formation of the Mn3-xAlxO4 solid solution at the synthesis temperature and its segregation upon cooling. Segregation of the solid solution leads to the formation of the Mn3O4+δ defect oxide and an amorphous aluminum-containing component. The addition of 5%Ga to the Mn–Al catalyst changes the phase transformation route during thermal activation. The in situ XRD data has showed that at 1000°С the high-temperature solid solution (MnGaAl)3O4 with the cubic spinel structure is formed; however, its further segregation upon cooling is hindered. The introduction of gallium stabilizes the structure of the (MnGaAl)3O4 mixed oxide, the parent oxide is partially decomposed after cooling with Mn3O4 nanoparticles formation. However the amount of produced active Mn3O4 particles and/or weakly bound oxygen is much lower, which in turn adversely affects the catalytic properties.

KW - Catalyst

KW - Decomposition

KW - In situ

KW - Solid solution

KW - Spinel

UR - http://www.scopus.com/inward/record.url?scp=85137618744&partnerID=8YFLogxK

U2 - 10.1016/j.matchemphys.2022.126715

DO - 10.1016/j.matchemphys.2022.126715

M3 - Article

AN - SCOPUS:85137618744

VL - 291

JO - Materials Chemistry and Physics

JF - Materials Chemistry and Physics

SN - 0254-0584

M1 - 126715

ER -