Low-Temperature Synthesis of Mg<i>_x</i>Co₁_-<i>_x</i>Co₂O₄ Spinel Catalysts for N₂O Decomposition

Abstract

Low-temperature synthesis of spinels MgxCo1-xCo2O4 (x = 0.0−0.9) has been investigated with two important synthetic parameters and XRD/FTIR/DSC/BET/ICP/CHN methods. It is found that with an increase in hydrothermal treatment temperature, precursor compounds change from the hydrotalcite-like to brucite-like and then to cubic spinel phase when the initial metal concentration ratio [Mg2+]:[Co2+] ≥ 1, while from the turbostratic to hydrotalcite-like and then to cubic spinel phase when the [Mg2+]:[Co2+] < 1. The MgxCo1-xCo2O4 (x ≤ 1/3) spinels were formed at temperatures as low as 50−100 °C. In the postsynthesis thermal treatment, various thermal events have been observed, and in all cases the spinel phase can be prepared at temperatures below 300 °C. On the basis of FTIR results, a topotactic mechanism for the formation of the spinel phase has been confirmed. Specific surface area as high as 210 m2/g has been attained in 400 °C calcined MgxCo1-xCo2O4 with x = 0.9. Causes for the formation of the spinel phase at low temperatures have been addressed. Excellent catalytic activity for N2O decomposition (30.6−38.9 mmol (N2O)/g·h at GHSV = 21200 h-1 and 380−400 °C; N2O = 10 mol % balanced with He) has been observed and discussed for these Mg−Co spinels.