Interaction of transition-metal acetylacetonates with γ-Al2O3 surfaces

Abstract

Virtually all acetylacetonate (acac) complexes [the only exceptions known so far are Ru(acac)₃ and Rh(acac)₃] react with coordinatively unsaturated (c.u.s.) Al³⁺ sites of γ-alumina surfaces. As far as the surface OH groups are concerned, there appears to be a correlation between the acid/base sensitivity of an acac complex and its reactivity towards these groups, i.e acac complexes which are unstable in the presence of OH^– react with the basic OH groups, and those which are sensitive to H⁺ react (to a certain extent) with the acidic ones. High metal loadings cannot be achieved through controlled adsorption at room temperature, however; the reactivity of acidic OH groups is very low, and neutral OH groups are not involved at all. On the other hand, the M(acac)_n/Al₂O₃ interactions are sufficiently well behaved (i) to enable the quantitative determination of c.u.s. Al³⁺ sites and basic OH groups and (ii) to follow surface modifications as a result of pretreatments(s).