Modification of the properties of γ-alumina as a support for nickel and molybdate catalysts by addition of silica

Commercial pure γ-Al2O3 and SiO2 (1−30 wt.%) doped γ-Al2O3 were characterized as acid catalysts in ethanol conversion and used as supports for NiO and MoO3. Supported catalysts were prepared by incipient wetness impregnation. All catalytic materials were characterized by BET, XRD, FE-SEM microscopy, UV–vis and IR spectroscopies. Pure and silica-doped NiO/Al2O3 materials were used as precursors of metal catalysts for CO2 hydrogenation. Pure and silica-doped MoO3/Al2O3 materials were used as catalysts for ethanol oxidative dehydrogenation to acetaldehyde. These data show that the addition of silica in moderate amounts selectively influences a part of the alumina surface and strongly modifies the dispersing properties of alumina support. In particular, silica preferentially bonds over the strongest Lewis acid-base sites of γ-Al2O3, where also Ni2+ and molybdate species tend to interact. Being the SiO2-Al2O3 interaction stronger than the NiO-Al2O3 interaction and the MoO3-Al2O3 interaction, silica displaces nickel and molybdate species to less preferential sites where their interaction with exposed alumina is weaker. This results in more easily reducible Ni2+ species and larger Ni metal particles for silica doped Ni/Al2O3, and more monomeric and less polymeric molybdate species for silica doped MoO3/Al2O3.