In-situ generation of maximum trivalent cobalt in synthesis of hydrotalcite-like compounds (MgxCo1-x-yCoyIII)-Co-II(OH)(2)(NO3)(y)center dot nH(2)O

In-situ generation of trivalent cobalt cations has been investigated for th e hydrotalcite-like compounds (MgxCo1-x-yCoyIII)-Co-II(OH)(2)(NO3)(y). nH(2 )O at 25-40 degrees C under oxygen-containing atmospheres. It is noted that with more involvement of Mg2+ in the compounds, less Co2+ cations are need ed to maintain the hydrotalcite-like structure. Because of the presence of the Mg2+, more Co2+ can be oxidized under the current experimental conditio ns and the highest mole ratios of Co3+ to total cobalt cations (Co3+:Co) ob served in this work is 57%. The mole ratio of Co3+ to total metal cations ( Co3+:(Mg+Co)) achieved in this work is 31% after 4 days of oxidation reacti on, which is close to its upper charge limit to produce a single-phase hydr otalcite-like structure (33%). Two major thermal events are observed when t he compounds are heated. The first one at 113-134 degrees C is attributed t o the removal of interlayer water molecules while the second at 274-333 deg rees C to the dehydroxylation and decomposition of intercalated anions. Hig her catalytic activity for nitrous oxide (N2O) decomposition is observed fo r the Mg-Co oxides with the same cobalt content but lower mole ratios of Co 3+:Co in their hydrotalcite-like precursors. The reason for this activity v ariation has also been addressed.