Abstract
The ambient temperature adsorption of acetonitrile (in its d3 deuterated form, to avoid Fermi resonance band splitting in the analytical νCN spectral region) was studied on pure γ-alumina, γ-alumina doped with two different amounts of sulfates, γ-alumina doped with Ca, and a Ca-doped alumina that was thermally transformed into the δ,θ-alumina form. Acetonitrile adsorption readily reveals the different Lewis acidity due to different surface cationic species (e.g., Al3+ and Ca2+) but is only partly sensitive to the acid strength heterogeneity exhibited by Lewis sites due to the same cationic species (Al3+ ions, in the present case). Acetonitrile uptake perturbs all surface hydroxyl species that are free from H-bonding of the OH···OH type by either ligand insertion (the OH species at ∼3780 cm-1) or by (weak) H-bonding (the OH species at ∼3740 cm-1). When a plain H-bonding is formed, the relevant νCN mode is hardly distinguishable from that of a liquidlike physisorbed phase. The presence of large amounts of s...
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