Low-temperature synthesis of Mg(x)Co(1-x)Co2O4 spinel catalysts for N2O decomposition

Abstract

Low-temperature synthesis of spinels Mg(x)Co(1-x)Co2O4 (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 Mg(x)Co(1-x)Co2O4 (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 Mg(x)Co(1-x)Co2O4 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.