Acid-activated vermiculites and phlogophites as catalysts for the DeNOx process

Vermiculite and phlogopite were reacted with nitric acid under controlled conditions. The products were characterized by the composition (XRF), structure (XRD, FTIR, UV–vis–DRS), texture (BET); morphology (SEM) and surface acidity (NH3-TPD). Acid-activation increased the specific surface area and porosity and led to partial leaching of iron, aluminium and magnesium from the octahedral sheets. The acid-activated vermiculites and phlogopites were active and selective catalysts of the DeNOx process (4 NO + 4 NH3 + O2 = 4 N2 + 6 H2O). The best catalytic results were obtained for vermiculite activated with nitric acid (0.8 M) at 95 °C for 24 h. The modified phlogopites were less active. The best catalytic results were also obtained after reaction with HNO3 for 24 h.