TY - JOUR

T1 - In Situ Study of Reduction of Mn xCo3- xO4Mixed Oxides: The Role of Manganese Content

AU - Bulavchenko, Olga A.

AU - Afonasenko, Tatyana N.

AU - Ivanchikova, Anastasya V.

AU - Murzin, Vadim Yu

AU - Kremneva, Anna M.

AU - Saraev, Andrey A.

AU - Kaichev, Vasily V.

AU - Tsybulya, Sergey V.

N1 - Funding Information: The authors are grateful to the Ministry of Science and Higher Education of the Russian Federation (Project AAAA-A21-121011390011-4). O.A.B. acknowledges support from the Russian Foundation for Basic Research (Project No. 18-33-00542). The authors acknowledge PETRA III, DESY on the P65 Beamline (in-house research, proposal # I-20180720) and Dr. V.A. Rogov for the TPR-H measurements. The XPS experiments were performed using the facilities of the shared research center “National Center of Investigation of Catalysts” at the Boreskov Institute of Catalysis. 2 Publisher Copyright: © 2021 American Chemical Society.

PY - 2021/11/1

Y1 - 2021/11/1

N2 - A series of Mn-Co mixed oxides with a gradual variation of the Mn/Co molar ratio were prepared by coprecipitation of cobalt and manganese nitrates. The structure, chemistry, and reducibility of the oxides were studied by X-ray diffraction (XRD), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). It was found that at concentrations of Mn below 37 atom %, a solid solution with a cubic spinel structure is formed. At concentrations above 63 atom %, a solid solution is formed on the basis of a tetragonal spinel, while at concentrations in a range of 37-63 atom %, a two-phase system, which contains tetragonal and cubic oxides, is formed. To elucidate the reduction route of mixed oxides, two approaches were used. The first was based on a gradual change in the chemical composition of Mn-Co oxides, illustrating slow changes in the TPR profiles. The second approach consisted in a combination of in situ XRD and pseudo-in situ XPS techniques, which made it possible to directly determine the structure and chemistry of the oxides under reductive conditions. It was shown that the reduction of Mn-Co mixed oxides proceeds via two stages. During the first stage, (Mn, Co)3O4 is reduced to (Mn, Co)O. During the second stage, the solid solution (Mn, Co)O is transformed into metallic cobalt and MnO. The introduction of manganese cations into the structure of cobalt oxide leads to a decrease in the rate of both reduction stages. However, the influence of additional cations on the second reduction stage is more noticeable. This is due to crystallographic peculiarities of the compounds: the conversion from the initial oxide (Mn, Co)3O4 into the intermediate oxide (Mn, Co)O requires only a small displacement of cations, whereas the formation of metallic cobalt from (Mn, Co)O requires a rearrangement of the entire structure.

AB - A series of Mn-Co mixed oxides with a gradual variation of the Mn/Co molar ratio were prepared by coprecipitation of cobalt and manganese nitrates. The structure, chemistry, and reducibility of the oxides were studied by X-ray diffraction (XRD), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). It was found that at concentrations of Mn below 37 atom %, a solid solution with a cubic spinel structure is formed. At concentrations above 63 atom %, a solid solution is formed on the basis of a tetragonal spinel, while at concentrations in a range of 37-63 atom %, a two-phase system, which contains tetragonal and cubic oxides, is formed. To elucidate the reduction route of mixed oxides, two approaches were used. The first was based on a gradual change in the chemical composition of Mn-Co oxides, illustrating slow changes in the TPR profiles. The second approach consisted in a combination of in situ XRD and pseudo-in situ XPS techniques, which made it possible to directly determine the structure and chemistry of the oxides under reductive conditions. It was shown that the reduction of Mn-Co mixed oxides proceeds via two stages. During the first stage, (Mn, Co)3O4 is reduced to (Mn, Co)O. During the second stage, the solid solution (Mn, Co)O is transformed into metallic cobalt and MnO. The introduction of manganese cations into the structure of cobalt oxide leads to a decrease in the rate of both reduction stages. However, the influence of additional cations on the second reduction stage is more noticeable. This is due to crystallographic peculiarities of the compounds: the conversion from the initial oxide (Mn, Co)3O4 into the intermediate oxide (Mn, Co)O requires only a small displacement of cations, whereas the formation of metallic cobalt from (Mn, Co)O requires a rearrangement of the entire structure.

UR - http://www.scopus.com/inward/record.url?scp=85118276489&partnerID=8YFLogxK

U2 - 10.1021/acs.inorgchem.1c02379

DO - 10.1021/acs.inorgchem.1c02379

M3 - Article

C2 - 34648258

AN - SCOPUS:85118276489

VL - 60

SP - 16518

EP - 16528

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

IS - 21

ER -