The Research On The Preparations And N₂O Catalytic Decomposition Of Ca And Sr Modified Co₃O₄ Catalysts

Nitrous oxide （N₂O） is regarded as a major environmental pollutant since it could largely contribute to the greenhouse effect and the stratospheric ozone destruction. N₂O is regard as the third most important greenhouse gas after CO₂ and CH₄. Direct catalytic decomposition of N₂O to nitrogen and oxygen is considered as one of the most economical and effective method. Therefore, investigating the catalysts with excellent low-temperature activity has become an important topic of the researchers in this field.Transition metal oxides exhibited high N₂O catalytic decomposition activity, especially the Co-based oxide showed excellent low-temperature activity. The addition of alkaline earth metals in Co₃O₄ can weaken Co-O bond on the surface of the catalyst and promote desorption of surface oxygen, thereby increasing N₂O decomposition activity and stabilityof the catalyst.Co₃O₄ was prepared by precipitation of cobalt nitrate in aqueous solutions using vari-ous precipitation agents （K₂CO₃, Na₂CO₃, NaOH, NaHCO₃）. Especially the catalysts prepared by K₂CO₃ showed high catalytic activity in N₂O decomposition.The Co₃O₄- K₂CO₃ sample possessed the largest BET surface area and highest reducibility of Co³⁺to Co²⁺ among studied materials.The performance of N₂O catalytic decomposition was obviously enhanced by the addition of Ca into the Co₃O₄ catalyst. The Ca modified Co₃O₄ catalyst with Ca/Co molar ratio of 1:2 exhibited the highest catalytic performance and almost 100% N₂O conversion was achieved at 400℃. The addition of Ca into the Co₃O₄ catalyst could suppress the crystal growth of Co₃O₄, increase the BET surface area and pore volume, promote the reduction of Co²⁺to Co, which can benefit the N₂O decomposition. Moreover, the Co₃O₄ doped with Ca species presented smaller particle diameter and provided higher amount of surface oxygen. The kinetics studies revealed that the N₂O catalytic decomposition reaction was first-order for the CaCoOx catalysts. The activation energy for CalCo2 catalyst （Ea=17.84 kJ/mol） was lower than the pure Co₃O₄ （Ea=43.21 kJ/mol）, suggesting that the addition of Ca enhanced the catalytic decomposition of N₂O.The Co₃O₄ catalyst modified by Sr exhibited high activity for N₂O decomposition. The Sr modified Co₃O₄ catalyst with Sr/Co molar ratio of 1:4 exhibited the highest catalytic performance and almost 90% N₂O conversion was achieved at 375℃. The addition of Sr into the Co₃O₄ catalyst made the particle diameter decreased and the BET surface area incressed. It is indicated that the addition of Sr species in Co₃O₄ catalyst promoted the reduction of Co³⁺to Co²⁺ and thus enhanced the catalytic activity for N₂O decomposition. Furthermore, the SrxCoy catalyst presented higer atomic ratio of Oads/（Oads+Olat）, which can facilitate O₂ desorption from thecatalys surface, thereby enhancing the catalytic activity of N₂O decomposition.