Abstract
A series of sulfated zirconia (SZ) catalysts were synthesized by immersion of amorphous zirconium hydroxide in sulfuric acid of various concentrations (1–5N). These samples were fully characterized by X-ray diffraction (XRD), thermogravimetric analysis and mass spectrometry (TGA-MS), and aqueous sulfuric acid immersion and high temperature oxide melt solution calorimetry. We investigated the enthalpies of the complex interactions between sulfur species and the zirconia surface (ΔHSZ) for the sulfated zirconia precursor (SZP), ranging from −109.46±7.33 (1N) to −42.50±0.89 (4N) kJ/mol S. ΔHSZ appears to be a roughly exponential function of sulfuric acid concentration. On the other hand, the enthalpy of SZ formation (ΔHf), becomes more exothermic linearly as sulfur surface coverage increases, from −147.90±4.16 (2.14nm−2) to −317.03±4.20 (2.29nm−2) kJ/mol S, indicating formation of energetically more stable polysulfate species.
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