High activity and stability of the Rh-free Co-based ex-hydrotalcite containing Pd in the catalytic decomposition of N2O

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has bee n studied over calcined hydrotalcite-like compounds containing different co mbinations of bivalent (Co, Pd, Mg) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co-precipit ation 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. The presence of Rh, La, or Pd in the Co-based HTlc's improves considerably the catalytic activity. Co-Rh,Al- HTlc (Co/Rh/Al=3/0.02/1) proved to be a very active catalyst, although the presence of the noble metal Pd in this catalyst ex-Co,Pd-La,Al-HT (Co/Pd/La /Al=3/1/1/1) produces a similar catalytic activity to that of Rh-containing catalyst, both in a N2O-containing stream and in one containing also SO2 a nd O-2, but with a better performance in stability tests. PdO phase has bee n identified by XRD as being responsible for the considerable improvement i n the activity. The presence of Mg as spinel structure exerts a stabilizing effect in the more active catalysts when mixtures of SO2 and O-2 are consi dered.