Synthesis of MMoO4/SiO2 catalysts (M=Ni or Co) by a sol-gel route via silicon alkoxides - Stabilization of beta-NiMoO4 at room temperature

MMoO4/SiO2 composites (M=Ni or Co) were prepared by a sol-gel procedure inv olving Si(OMe)(4), M(NO3)(2) and (NH4)(6)Mo7O24 as Starting materials. The dried gels were treated at increasing temperatures until crystalline grains of MMoO4 highly dispersed in the amorphous silica matrix were formed (675 degrees C). They were evidenced by XRD and TEM measurements. Beside support ing the MMoO4 mixed oxide, the silica xerogel appears to play the important role of stabilizing the beta-phase of nickel molybdate, which otherwise wo uld turn into the a-phase at room temperature. The catalytic activity of th e beta-NiMoO4/SiO2 composite in the oxidative dehydrogenation of isobutane was compared with related systems containing the metastable beta-molybdate. (C) 1999 Elsevier Science B.V. All rights reserved.