Dendrimer-mediated formation of Cu-CuO_x nanoparticles on silica and their physical and catalytic characterization

Copper-silica catalysts were synthesized by impregnation of sol-gel derived silicas containing entrapped DAB-Am-64 dendrimer as both chelating and pore-templating agent, with methanolic copper nitrate solutions. Basic materials characterization included X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption. The metallic and monovalent copper contents were determined by N₂O decomposition and CO adsorption, respectively. The N₂O decomposition reaction and CO adsorption were followed by mass spectrometry (MS) and thermogravimetry in an oscillating balance reactor (OBR). Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was used to monitor the modes of co-adsorption of N ₂O and CO as a function of temperature. The N₂O + CO temperature-programmed reaction indicates that the copper oxidation state changes under reaction, and as a consequence a transition in reaction regime occurs as temperature increases. Control of the ultimate particle size of Cu species, while heavily influenced by the dendrimer especially at lower Cu:dendrimer ratios, is not exact. Factors such as calcination and reduction temperatures needed to be investigated in order to maximize the impact of dendrimer complexation on the final state of the catalyst.