Preparation, characterization and catalytic properties of Co–Nb 2O 5–SiO 2 catalysts

Abstract

Co–Nb 2O 5–SiO 2 catalysts were prepared using three different sol–gel procedures: (i) the colloidal sol–gel method using NbCl 5 and SiCl 4 as precursors; (ii) the polymeric sol–gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol–gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl 4. In all procedures, the elimination of the solvent carried out between 80 and 110°C was followed by a reduction in hydrogen flow (30 ml min −1) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb 2O 5) were obtained. The characterization of the catalysts was performed using various techniques: N 2 adsorption and desorption curves at 77 K, NH 3- and H 2-chemisorption, TPO, XPS, XRD, and solid state 1H MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support.