Synthesis of MMoO4/SiO2 catalysts (M=Ni or Co) by a sol–gel route via silicon alkoxides: Stabilization of β-NiMoO4 at room temperature Original Research Article

MMoO4/SiO2 composites (M=Ni or Co) were prepared by a sol–gel procedure involving Si(OMe)4, M(NO3)2 and (NH4)6Mo7O24 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°C). They were evidenced by XRD and TEM measurements. Beside supporting the MMoO4 mixed oxide, the silica xerogel appears to play the important role of stabilizing the β-phase of nickel molybdate, which otherwise would turn into the α-phase at room temperature. The catalytic activity of the β-NiMoO4/SiO2 composite in the oxidative dehydrogenation of isobutane was compared with related systems containing the metastable β-molybdate.