NOx Reactivity on Microporous Metal-Aluminophosphates. A Combined Spectroscopic and Catalytic Studies

A combined spectroscopic and catalytic study of the NOx reactivity on microporous aluminophosphates and silico-aluminophosphates containing Co and Cu ions in AlPO4-34, -5 and -11 type structures, is reported. CoAPO-34 is very efficient catalyst in the NO oxidation to NO2 reaching the equilibrium conversion value at 350°C, whereas is inactive in the NO reduction by CO, a reaction which, on the contrary, proceeds efficiently on Cu-based catalysts. In particular, catalytic tests in the NO reduction by CO on CuAPO-34 suggested that this catalyst is a very active and selective in the 300-550°C range. N2O decomposition and NO oxidation to NO2 are also effective on Cu-containing catalysts, and followed the sequence of activity: Cu- SAPO-34 ≥ CuAPSO-34 > CuAPO-34 > CuAPO-5 ≈ CuAPO-11. NO adsorption on the most active catalysts was investigated by FTIR and this showed that Cu2+ and Cu+ mononitrosyl complexes were formed in larger amount on the silicon-containing (CuAPSO-34 and Cu- SAPO-34 in comparison with CuAPO-34). The reactivity of the CuAPSO-34 catalysts towards NO adsorption was proved by the fact that a large fraction of Cu+ ions were oxidised to Cu2+ and N2O and NO2 adsorbed species were formed.