A key step for preparing highly active Mg–Co composite oxide catalysts for N2O decomposition

Abstract

The catalytic decomposition of N₂O was investigated over Mg–Co composite oxide catalysts. It was found that the activities of the catalysts could be significantly enhanced by hydrothermally treating the precipitate coming from the co-deposition of Mg²⁺ and Co²⁺ using Na₂CO₃ as a precipitant. By correlating the physical and chemical characterization results with the activities for the catalyst samples prepared with and without the hydrothermal treatment, a mechanism accounting for the increased activity due to the hydrothermal treatment was discussed. It was demonstrated that the substitution extent of Co^T (tetrahedral cobalt of the spinel) by Mg is the key factor that determines the activity of the composite catalysts, and hydrothermal treatment is highly favorable for the ions' replacement during the preparation procedure. The formation of the coordinatively unsaturated octahedral cobalt (Co^O) on the spinel surface is therefore remarkably accelerated under the reaction conditions, since the Co^O–O bond is significantly weakened by the substitution, which explains why the hydrothermal treatment gave the resulting catalyst with a much higher activity compared with that without the treatment.