TY - JOUR
T1 - Ultra-Low Temperature CO Oxidation Activity of Octahedral Site Cobalt Species in Co3O4 Based Catalysts: Unravelling the Origin of Unique Catalytic Property
AU - Kumar, Nirmal
PY - 2019/8/15
Y1 - 2019/8/15
N2 - 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.
AB - 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.
U2 - 10.1021/acs.jpcc.9b04136
DO - 10.1021/acs.jpcc.9b04136
M3 - Article
SN - 1932-7447
JO - The Journal of Physical Chemistry C
JF - The Journal of Physical Chemistry C
ER -