Modification of Co3O4 by Al2O3: Influence on the Reducibility | Sciact - CRIS-система Института катализа

Modification of Co3O4 by Al2O3: Influence on the Reducibility Научная публикация

Журнал

Journal of Solid State Chemistry
ISSN: 0022-4596 , E-ISSN: 1095-726X

Вых. Данные

Год: 2024, Том: 340, Номер статьи : 125012, Страниц : 11 DOI: 10.1016/j.jssc.2024.125012

Ключевые слова

In situ XRD; Al3+-modified Co3O4; (Co,Al)3O4 solid solution; Reduction

Авторы

Cherepanova Svetlana V. ^1,2 , Koemets Egor G. ¹ , Gerasimov Evgeny Yu. ^1,2 , Simentsova Irina I. ¹ , Bulavchenko Olga A. ^1,2

Организации

1	Boreskov Institute of Catalysis SB RAS, Lavrentiev Ave., 5, Novosibirsk, 630090, Russia
2	Department of Physics, Novosibirsk State University, Pirogova, 2, Novosibirsk, 630090, Russia

Информация о финансировании (1)

Министерство науки и высшего образования Российской Федерации (с 15 мая 2018)

075-15-2022-263

In this study, we used a coprecipitation method followed by calcination at 500 °C to synthesize undoped and Al3+-doped Co3O4 nanoparticles with different aluminum fractions (x = Al/(Co + Al) = 1/60, 1/30, 1/15, 1/75, 1/6 and 1/5). An addition of Al3+ ions led to a decrease in the average crystallite size from 29 to 11 nm, and growth of the specific surface area from 28 to 91 m2/g. TEM images indicated round and platelet shapes of the nanoparticles. According to HAADF-STEM combined with EDS elemental mapping, the platelet shape particles are Al3+-enriched, while the round shape particles are Al3+-depleted. The origin of Al3+ distribution over the oxide volume is conditioned by the state of the hydroxide precursor. It was shown by XRD that the coprecipitation yielded homogeneous hydroxides only for Al fractions x = 0 and x = 1/5. For the intermediate compositions, the precursors represent a mixture of Co6(CO3)2(OH)8*H2O and Co0.8Al0.2(OH)2(CO3)0.1*nH2O. On the TPR-H2 profiles, reduction peaks for three (Co,Al)3O4 oxides differing in the Al3+ concentration (y) can be found. Two of these oxides with y = 0 and y = 0.2 are formed from different hydroxides, and third one with y ∼0.05 is the result of their mutual interaction. In situ XRD allowed us to interpret the TPR peaks correctly and showed that the reduction of all the oxides occurs in two steps. In the first step, Co3+ → Co2+, and (Co1-yAly)3O4 oxides transform to (Co,Al)O. In the second step, Co2+ → Co0, and (Co,Al)O is reduced into metallic cobalt. In undoped Co3O4, Co3+ → Co2+ and Co2+ → Co0 reduction steps occur at T1 = 280 and T2 = 325 °C, respectively. For Al-depleted (Co1-yAly)3O4 (y ∼ 0.05 in the interior of particles), both reduction steps shift toward higher temperatures T1 = 305 and T2 = 405 °C, respectively. The reduction of Al-enriched (Co0.8Al0.2)3O4 is more difficult; first and second reduction steps occur at T1 = 345 and T2 = 610−690 °C. Therefore, Al3+ ions have a little effect on the first step and very significantly influence the second one. Additionally, it was shown by TEM that after the reduction at 700 °C metallic cobalt particles were surrounded by the Al-enriched oxide shell. Apparently, that is why the addition of even a small amount of Al3+ ions prevents a quick sintering of metallic cobalt observed for pure Co3O4.

Cherepanova S.V. , Koemets E.G. , Gerasimov E.Y. , Simentsova I.I. , Bulavchenko O.A.
Modification of Co3O4 by Al2O3: Influence on the Reducibility
Journal of Solid State Chemistry. 2024. V.340. 125012 :1-11. DOI: 10.1016/j.jssc.2024.125012 WOS Scopus CAPlus OpenAlex

Поступила в редакцию:	5 июн. 2024 г.
Принята к публикации:	11 сент. 2024 г.
Опубликована online:	12 сент. 2024 г.
Опубликована в печати:	1 дек. 2024 г.

Web of science:	WOS:001317418400001
Scopus:	2-s2.0-85203645940
Chemical Abstracts:	2024:1989304
OpenAlex:	W4402533160

Пока нет цитирований