Influence of sulfation on CeO 2 -ZrO 2 catalysts for NO reduction with NH 3

CeO 2 -ZrO 2 (CeZr) and sulfated CeO 2 -ZrO 2 (S-CeZr) catalysts were prepared for the selective catalytic reduction of NO with NH 3 . The CeZr catalysts exhibited higher activity at low temperatures ( 200℃) than the S-CeZr catalysts. The sulfation of CeZr was studied in terms of surface acidity, redox properties and NO adsorption-desorption by temperature-dependent experiments and in situ infrared spectroscopy. S-CeZr displayed high con-centrations of acidic sites and increased surface acidities, but poor reducibility compared with CeZr. The high acidity of S-CeZr was attributed to the presence of Bronsted acid sites, arising mainly from the surface sulfates. Because the surface was covered with sulfate species, S-CeZr showed lower NO adsorption and weaker oxidation ability than CeZr. The adsorption of NH 3 on the Bronsted acid sites restricted the reaction with NO at low temperatures, but the selective catalytic reduction cycle oc-curred easily at relatively low temperatures (150℃), and the weakly bound nitrite was partially activated on the S-CeZr catalyst at relatively high temperatures (300℃). The catalytic mechanisms for the CeZr and S-CeZr catalysts at 150 and 300℃ were also studied.