Inorganic synthesis for the stabilization of nanoparticles:: Application to Cu/Al2O3 nanocomposite materials

A series of copper/aluminium nanocomposites with different mixing homogeneities and different texture features were prepared via various inorganic synthesis methods including coprecipitation, gelation, and stepwise thermal modification. Nitrogen sorption measurements and X-ray diffraction were used for textural and structural analysis, respectively. Solid-solid reaction analysis and differential scanning calorimetry (DSC) analysis were developed for the determination of the mixing homogeneities of copper-based nanocomposite materials. A sintering experiment at 250-600 degrees C for 350 h under methanol-steam reforming conditions was carried out to compare the stability of supported Cu-0 nanoparticles. Although a large initial size of supported nanoparticles is not favorable, those supported nanoparticles with a small initial size cannot ensure good thermal stability. The mixing homogeneities of CuO/Al2O3 mixed metal oxide (MMO) nanocomposites significantly affected the thermal stability of their reduced Cu-0 crystallites. Besides homogeneity control, creation of narrow distributions of pore sizes with small major pore diameters (e.g., around 3.5 nm) can also be used for the stabilization of supported Cu-0 nanoparticles. We found that mixing homogeneity of a nanocomposite is likely the major factor in the stabilization of nanoparticles, whereas a narrow distribution of pore sizes might confine the growth of nanoparticles, possibly via space limitations. Field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and convergent beam electron diffraction (CBED) were used for the observation or structure determination of the copper/aluminum nanocomposites. This paper also provides information on the deactivation of copper catalysts via thermal sintering under methanol-steam reforming conditions.