Preparation and characterization of CeO2 highly dispersed on activated carbon

A new material constituted by cerium dioxide highly dispersed on activated carbon (CeO2/AC) was prepared by an impregnation method using cerium(III) nitrate as CeO2 precursor. In order to evaluate the degree of ceria dispersion on the carbon support, CeO2/AC was characterized by a number of techniques: thermogravimetry coupled with a mass spectrometer (TG-MS), N-2 adsorption at 77 K, temperature-programmed desorption (TPD), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). The analysis of the decomposition process under inert atmosphere indicated that cerium nitrate decomposes at 440-460 K, with the evolution of NO. Furthermore, this process produces an additional oxidation of the carbon surface (with evolution of N2O) and the subsequent onset of new oxygen surface groups, detected by means of temperature-programmed desorption. The ceria deposition process takes place with a decrease in the N-2 adsorption capacity of the starting carbon support, and the analysis of the pore size distribution showed that the majority of ceria particles are situated at the most internal part of the carbon porosity. The temperature-programmed reduction profile of CeO2/AC was very different to that shown by unsupported CeO2, with only one continuous reduction process at low temperatures (800-900 K). Finally, TEM pictures gave direct evidence that ceria is highly dispersed on the carbon surface, with a narrow CeO2 particle distribution centred around 3 nm. (C) 2007 Elsevier Ltd. All rights reserved.