Interaction of transition-metal acetylacetonates with γ-Al2O3 surfaces

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).