Sol–gel prepared Co–Mg–O oxide systems: redox behavior, thermal stability and catalytic performance in CO oxidation

Cobalt–Magnesium Oxide Catalysts for Deep Oxidation of Hydrocarbons

“…JCPDS 45-946 [27], and CoO, JCPDS 48-1719 [24]) or their solid solution were observed in the diffraction patterns of the Co-Mg samples. Cobalt oxide Co3O4 is a standard normal spinel A 2+ B2 3+ O4, with tetrahedral vacancies occupied by Co 2+ cations, and octahedral vacancies by Co 3+ (Co 2+ [Co 3+ O4]) [35].…”

“…It is known from the literature that the reduction in Co3O4 occurs in two temperature regions: in the first region, Co 3+ is reduced to Co 2+ , and in the second, Co 2+ is reduced to Co 0 [9,[25][26][27]42]. The stoichiometric ratio of oxygen in the first and second regions is 1:3.…”

“…Cobalt oxide Co3O4 is a standard normal spinel A 2+ B2 3+ O4, with tetrahedral vacancies occupied by Co 2+ cations, and octahedral vacancies by Co 3+ (Co 2+ [Co 3+ O4]) [35]. In addition to normal spinels, inverse spinels B 3+ [A 2+ B 3+ O4] are known, in which divalent cations occupy an octahedral position, while half of the trivalent cations occupy a tetrahedral [8,27,33], JCPDS 81-671 [34]) and the cubic oxide phases (MgO, JCPDS 45-946 [27], and CoO, JCPDS 48-1719 [24]) or their solid solution were observed in the diffraction patterns of the Co-Mg samples. [35].…”

“…Other studies note the high thermal stability of CoO-MgO solid solutions and their low tendency to coking, which determines their high potential in the dry reforming of methane [12]. Recently, the number of studies on MgCo 2 O 4 spinel has increased in connection with the search for active components and supports for catalysts [24][25][26][27], as well as nanostructured compositions for electrocatalysis [28], thermochemical energy storage cycles [29], and electrodes for Li-ion batteries and supercapacitors [30,31]. However, studies examining the genesis of the Co-Mg oxide system during its heat treatment with the transition of the spinel into the solid solution are few and contradictory [12,31,32].…”

“…The deep oxidation of methane and other hydrocarbons occurs at high temperatures (550-800 • C) [1,4,6], with the temperature range of the catalyst operation partially coinciding with the region of phase transition, which determines the influence of mutual transformations between the spinel and the solid solution phases on the catalyst efficiency. Most importantly, reversible phase transitions of this type ensure the ability of the catalyst to regenerate after deactivation during thermal shocks or local overheating [12,27]. In this regard, establishing the patterns of formation of the CoO x -MgO oxide system as heat treatment proceeds and its effect on the catalytic activity using the example of the methane oxidation reaction is of particular relevance.…”