The lewis acidity of sulfate-doped ZrO₂: FTIR and microcalorimetric study of CO uptake at ∼ 300 K on low S-loaded specimens

When loading sulfates on a microcrystalline ZrO₂, using H₂SO₄, the first sulfate groups form on crystal defects, then on regular crystal planes, and eventually complex sulfates (e.g., pyrosulfates) are formed. CO uptake at ∼ 300 K onto SO₄/ZrO₂ decreases fast with increasing sulfate loading, while the Lewis acidity of the residual sites is variably enhanced by the presence of the various types of sulfates, as shown by the spectral features of the σ-coordinated CO complexes and by the relevant adsorption heats.