Low-Temperature Synthesis of Mg_xCo_1-xCo₂O₄ Spinel Catalysts for N₂O Decomposition

Low-temperature synthesis of spinels Mg x Co 1 - x Co 2 O 4 ( 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 [Mg 2+ ]:[Co 2+ ] ≥ 1, while from the turbostratic to hydrotalcite-like and then to cubic spinel phase when the [Mg 2+ ]:[Co 2+ ] < 1. The Mg x Co 1 - x Co 2 O 4 ( 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 m 2 /g has been attained in 400 °C calcined Mg x Co 1 - x Co 2 O 4 with x = 0.9. Causes for the formation of the spinel phase at low temperatures have been addressed. Excellent catalytic activity for N 2 O decomposition (30.6−38.9 mmol (N 2 O)/g·h at GHSV = 21200 h - 1 and 380−400 °C; N 2 O = 10 mol % balanced with He) has been observed and discussed for these Mg−Co spinels.