Structural promotion and stabilizing effect of Mg in the catalytic decomposition of nitrous oxide over calcined hydrotalcite-like compounds

Abstract

Catalytic decomposition of nitrous oxide to nitrogen and oxygen has been carried out on in-situ generated calcined hydrotalcite-like compounds containing different combinations of bivalent (Mg, Co, Ni) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co-precipitation under low supersaturation conditions and characterized by XRD and TG/DSC. The mixed oxides derived after calcination at 723 K were characterized by XRD, N 2 adsorption at 77 K, and XRF. These catalysts show high activity on a mass basis in comparison with the active catalyst Co-ZSM-5 under similar experimental conditions. The presence of Mg in the catalysts exerts an important influence on the catalytic behaviour, increasing the surface area of the calcined materials, acting as a stabilizing agent against SO 2 inhibition at low temperature and eliminating the initial deactivation, but decreasing the specific activity. Addition of Rh or La to the cobalt-based catalyst improves the catalytic activity considerably. Ex-Co-Rh,Al-HTlc (Co/Al = 3/1 and 0.7 wt.% Rh), with and without Mg, proved to be the most active catalyst, followed by ex-Co-La,Al-HTlc (Co/La/Al = 3/1/1).