In the general framework of studies on nanomaterials for micro-sensors, cerium dioxide nanopowders (CeO2-z) and nanocomposites systems of copper doped ceria (CuOx-CeO2-z) were prepared and characterized. The aim of this specific study is to try to connect catalytic activity of such nanopowders with microstructure, additional phases and/or doping effect. The nanopowders of pure and doped cerium oxide were elaborated from various “Sol-Gel” chemical routes. Microstructural analysis was first carried out by X-ray diffraction (XRD). The specific areas were determined from BET adsorption techniques and the results were correlated to the size determinations obtained from XRD. The catalytic activity of such nanopowders in presence of methane gas CH4 was analyzed making use of FTIR spectrometry and a homemade device. For a better understanding of such catalytic responses, we proposed a modeling approach of solid gas interactions that takes into account a typical temperature dependent Avrami's model.