Preparation, characterization and catalytic properties of Co-Nb2O5-SiO2 catalysts

Co-Nb(2)Q(5)-SiO2 catalysts were prepared using three different sol-gel pro cedures: (i) the colloidal sol-gel method using NbCl5 and SiCl4 as precurso rs; (ii) the polymeric sol-gel method using niobium ethoxide and tetraethyl -orthosilicate (TEOS); (iii) an intermediate procedure between the colloida l and polymeric sol-gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl4. In all procedures, the elimination of the solvent carried out between 80 and 110 degrees C was followed by a reduction in hydrogen flow (30 ml min(-1)) at 7 73 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb2O5) were obtained. The characterization of the catalysts was performed using various techniques: N-2 adsorption and de sorption curves at 77 K, NH3- and H-2-chemisorption, TPO, XPS, XRD, and sol id state H-1 MAS-NMR. Hydrogenolysis of butane was evaluated. The low react ion rates are assigned to the effect of the metal size, whereas the isobuta ne selectivity as well as the relatively high stability is due to the acidi ty of the support. (C)2000 Elsevier Science B.V. All rights reserved.