Modification of inorganic supports with nickel acetylacetonate: The effect of their surface properties

Abstract

The mesostructured silica SBA-15, γ-Al2O3, and amorphous silica-alumina are modified with Ni(acac)2 in the liquid and gas phases. This process depends crucially on the nature of active sites on the support surface. In the modification of materials containing weakly acidic or weakly basic hydroxyl groups, it is necessary to use low-polarity solvents. The dominant Ni(acac)2 chemisorption sites on amorphous silica-alumina are the acid hydroxyls of ≡Si-OH-Al= bridges. The covalent bonding resulting from the replacement of the acetylacetonate ligand favors the fixation of the adsorbed complex on the support surface. The coordinatively unsaturated sites formed by Al3+ ions play an insignificant role in Ni(acac)2 chemisorption. The degree of dispersion of the oxide phase in the resulting catalysts depends strongly on the strength of the interaction between the modifier molecules and the active sites of the support. This is not the case with the aluminum acetylacetonate complexes that form upon the modification of the Al-containing supports. Gas-phase modification affords finer NiO particles than liquid-phase modification.