CoOx/CeO2 nanocomposite powders: Synthesis, characterization, and reactivity

CoOx/CeO2 nanocomposite materials with increasing Co/Ce atomic ratio were prepared by wet impregnation and characterized by means of X-ray photoelectron, diffuse reflectance infrared Fourier transform, and inductively coupled plasma atomic emission spectroscopic techniques, by BET and by thermal analysis. CoO is prevalent in the samples with lower cobalt content, whereas Co3O4 is the main presence at high Co/Ce atomic ratios. CeO2 is slightly reduced: Ce(III) is evident at the interface supported/ supporting oxide. X-ray diffraction and transmission electron microscopy allowed us to obtain interesting information concerning particle dimensions and growing morphology. The acidic/basic properties of the catalysts surfaces were investigated by studying the interaction of CoOx/CeO2 powder samples with pyridine and CO2. New acidic/basic sites are evident on the surface of the nanocomposites; this is particularly evident in the samples with lower cobalt content. The interaction with methanol was also investigated. Methanol chemisorbs molecularly and dissociatively on the CoOx/CeO2 samples; dissociation is prevalent in the sample characterized by a lower content of cobalt oxide. The oxidation of methanol is evident at rather low temperatures. When water is added to methanol, the oxidation temperature decreases (373 K instead of 433 K) and the formation of carbon monoxide is not observed.