Abstract:

The adsorption of CO_2 and NO on supported Pd catalysts has been studied by using TPD-MS method and the adsorbed surface species were discussed based on literatures. The amount and intensity of basic sites increase when promoter Li is added, whereas the amount of basic sites decreases when Ce is added. It is found that there are three kinds of basic sites with different intensity on the catalyst surface. On sample Pd/Al_2O_3 and Pd/Al_2O_3-Li_2O, large amount of CO desorption species is detected, this shows some CO_2 on the surface being decomposed. There is no such effect on the sample Pd/Al_2O_3-CeO_2. After analyzing the TPD profiles of NO adsorption on catalysts, it is found that both the NO desorption amount and the shapes of desorption peaks change remarkably when promoter Li or Ce is added. In the case of Li, the γ-peak (nitrate and nitrite species on surface) of NO desorption increases, the intermediate N_2O desorbs at higher temperature. In the case of Ce, the α-peak (species on the Brönstesd acidic sites ) of NO desorption decreases, and N_2O desorbs at lower temperature.

Key words: Temperature programmed desorption, Supported Pd catalyst, NO adsorption, CO₂ adsorption