Catalytic decomposition of N2O over some calcined products of hydrotalcite-like compounds containing Co,Cu and Ni

Sonic hydrotalcite-like (HTL) compounds, M/Mg-Al-HTL (M = Co, Cu, Ni), were prepared, and their calcination products were applied to the decomposition of N2O. The decomposition reactivity of N2O over Co/Mg-Al-HTL is much higher than that over Cu/Mg-Al-HTL or Ni/Mg-Al-HTL. Keeping Al content unchanged, the catalytic activity of Co/Mg-Al-HTL increases with the increase of Co content but decreases with the increase of Mg content. The catalytic activity of these compounds are in the following order: Co/Al-HTL> Co/Mg-Al-HTL>Cu/Mg-Al-HTL>NI/Mg-Al-HTL. The effect of Co/Al ratio in Co/Mg-Al-HTL on the catalyst activity was studied. The HTL Compounds containing Co (Co/Al-HTL and Co/Mg-Al-HTL) and their calcination products were characterized by means of XRF, XRD and N2O-TPD techniques. The results showed that Co/Al-HTL and Co/Mg-Al-HTL have typical hydrotalcite structure and their calcination products possess spinel phase, the Co-O-Al active centers in the spinel phase are responsible for the high decomposition activity of N2O. The spinel structure in the calcination product of Co/Al-HTL becomes more apparent when Co/Al ratio increases, therefore the Co-O-Al active centers increase, leading to the increase of the catalyst activity. The active center Co-O-Al can adsorb N2O very fast and then the adsorbed N2O can react easily with the oxygen ion of Co-O-Al in spinel to produce 0(2) and cause decomposition of N2O. However, the oxygen ion of M-O is not easy to react with the adsorbed N2O resulting in that the catalytic activity of the calcined Co/Mg-Al-HTL is lower than that of Co/Al-HTL. The calcined Co/Al-HTL can completely decompose N2O at 350 degreesC, but the calcined Co/Mg-Al-HTL (n(Co): n(Mg): n(Al) = 3:1:1)can completely decompose N2O at 400 degreesC. When n(Co)/n(Al) of Co-Al-HTL is up to 7, the calcined Co-Al-HTL can completely decompose N2O only at 320 degreesC.