Ultra-Low-Temperature CO Oxidation Activity of Octahedral Site Cobalt Species in Co3O4 Based Catalysts: Unravelling the Origin of the Unique Catalytic Property

Baidya, T and Murayama, T and Nellaiappan, S and Katiyar, NK and Bera, Parthasarathi and Safonova, O and Lin, M and Priolkar, KR and Kundu, S and Srinivasa Rao, B and Steiger, P and Sharma, S and Biswas, K. and Pradhan, SK and Lingaiah, N and Malviya, KD and Haruta, M (2019) Ultra-Low-Temperature CO Oxidation Activity of Octahedral Site Cobalt Species in Co3O4 Based Catalysts: Unravelling the Origin of the Unique Catalytic Property. Journal of Physical Chemistry C, 123 (32). pp. 19557-19571. ISSN 19327447

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Abstract

Co3O4 with spinel structure shows CO oxidation activity at very low temperature under dry conditions. This study aims at finding the origin of the unique catalytic activity of Co species in Co3O4 based oxides. Although, octahedral site Co3+ species have been reported to be active in Co3O4 based catalysts, there is no solid explanation as to why Co is so special as compared with other metals like Fe having similar redox states. In this study, mainly, three model spinel catalysts including MnCo2O4, MnFe2O4, and CoCr2O4 have been chosen. A detailed analysis of bulk and crystal surface structure, surface properties of the catalysts, and redox properties of the active metals has been performed to understand the unusual catalytic activity. Low-temperature CO oxidation activity decreases in the following order: MnCo2O4 ≫ MnFe2O4 > CoCr2O4. It indicates that the Co2+ species in a tetrahedral site (in CoCr2O4) remains inactive for low-temperature catalytic activity, while Co3+ in an octahedral site (in MnCo2O4) is active in Co3O4 based catalysts. This result is corroborated with CoFe2O4 which shows a higher activity than CoCr2O4, as it has partial occupation of the octahedral site. Fe, being a weak redox metal, does not show low-temperature activity, although crystallite facets of MnCo2O4 and MnFe2O4 catalysts are predominantly exposed in the (100) and (110) lattice planes, which contain quite similar concentrations of Co3+ and Fe3+ species in both. The intensity of the redox peak for CO oxidation involving a Co3+/Co2+ couple in MnCo2O4 indicates a highly favorable reaction, while a nonresponsive behavior of Co species is observed in CoCr2O4. As expected, MnFe2O4 is proven to be weak, giving a much lower intensity of electrochemical CO oxidation. Both CO- and H2-TPR indicate a much higher reducibility of Co species in MnCo2O4 as compared with Co species in CoCr2O4 or Fe in MnFe2O4.

Item Type:	Article
Subjects:	CHEMISTRY AND MATERIALS > Chemistry and Materials (General) CHEMISTRY AND MATERIALS > Composite Materials CHEMISTRY AND MATERIALS > Inorganic, Organic and Physical Chemistry
Depositing User:	Mrs SK Pratibha
Date Deposited:	23 Nov 2021 11:39
Last Modified:	23 Nov 2021 11:39
URI:	http://nal-ir.nal.res.in/id/eprint/13369

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