In-situ generation of maximum trivalent cobalt in synthesis of hydrotalcite-like compounds MgxCoII1-x-yCoIIIy(OH)2(NO3)y.nH2O

In-situ generation of trivalent cobalt cations has been investigated for the hydrotalcite-like compounds Mg x Co II 1-x-y Co III y (OH) 2 (NO 3 ) y .nH 2 O at 25-40 °C under oxygen-containing atmospheres. It is noted that with more involvement of Mg 2+ in the compounds, less Co 2+ cations are needed to maintain the hydrotalcite-like structure. Because of the presence of the Mg 2+ , more Co 2+ can be oxidized under the current experimental conditions and the highest mole ratios of Co 3+ to total cobalt cations (Co 3+ :Co) observed in this work is 57%. The mole ratio of Co 3+ to total metal cations (Co 3+ :(Mg+Co)) achieved in this work is 31% after 4 days of oxidation reaction, which is close to its upper charge limit to produce a single-phase hydrotalcite-like structure (33%). Two major thermal events are observed when the compounds are heated. The first one at 113-134 °C is attributed to the removal of interlayer water molecules while the second at 274-333 °C to the dehydroxylation and decomposition of intercalated anions. Higher catalytic activity for nitrous oxide (N 2 O) decomposition is observed for 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 variation has also been addressed.