Correlation between the surface properties and deNOx activity of ceria-zirconia catalysts

The catalytic activities of ceria-zirconia mixed oxides CexZr1−xO2 (x = 0.17, 0.42, 0.62 and 0.8) are determined by isothermal steady-state experiments using a representative mixture of exhaust gases of coal combustion. Results show that all supports are active in deNOx reaction in the presence of the previous hydrocarbons. However, their catalytic activity varies with the content of cerium and goes through a maximum for x = 0.62, leading to 27% NOx consumption. This activity was correlated with physicochemical properties determined by a linear solvation energy relationship (LSER) approach. Moreover, a mechanism of HC assisted reduction of NO is proposed on ceria-zirconia supported catalysts. This mechanism is divided in three catalytic cycles involving: (i) the oxidation of NO into NO2, (ii) the reaction of NO2 and the hydrocarbons leading to RNOx species and CxHyOz, and finally (iii) the decomposition of NO assisted by these latter CxHyOz species.