Co/CNF catalysts tailored by controlling the deposition of metal colloids onto CNFs: Preparation and catalytic properties

Carbon nanofiber-supported Co nanocomposites were prepared by means of a modified ethylene glycol (EG) process, in which the Co salts are reduced in EG and are subsequently deposited onto carbon nanofibers (CNFs). It has been found that the deposition of cobalt colloids onto CNFs can be tailored by simply adjusting the pH of the EG and by heating the mixture of CNFs and colloidal solution at 100 degrees C for some time. The pH value (< 7) and the temperature (at least 100 degrees C) for heating the mixture of CNFs and colloidal solution are found to be the key factors for depositing Co particles onto CNFs. The obtained Co/CNFs have a high and homogeneous dispersion of spherical Co metal particles with a narrow size distribution of 10-15 nm with a peak around 13.5 nm; this result is consistent, to a certain degree, with the value of 12.8 nm obtained from the XRD study. The different states of the stabilizer including carboxylates (pH > 7) and carboxylic acids (pH < 7) as well as the decomposition of carboxylic acids during heat treatment were monitored by using FTIR and UV-visible spectroscopy. On the basis of experimental results, the mechanism of depositing cobalt colloids onto CNFs is also addressed. ne as-synthesized Co/CNF catalysts show excellent activity and regioselectivity for the 1-octene hydroformylation.