Adsorption calorimetry in supported catalyst characterization : Adsorption structure sensitivity on Pt/γ-Al2O3

In this study, the structure sensitivity of hydrogen, oxygen and carbon monoxide adsorption was investigated by changing the metal particle size of Pt/Al2O3 catalysts. The 2% Pt/Al2O3 catalysts were prepared by incipient wetness method; the particle size of the catalysts was modified by calcining at different temperatures. The differential heats of adsorption of hydrogen, carbon monoxide and oxygen were measured using a SETARAM C80 Tian-Calvet calorimeter. Hydrogen chemisorption sites with low and intermediate heats were lost when the particle size increased consistent with the previous reports in the literature. No structure dependency was observed for hydrogen, carbon monoxide or oxygen initial heats of adsorption. The adsorbate:total metal stoichiometries at saturation systematically decreased with increasing particle size. While the hydrogen site energy distribution changed with increasing particle size, oxygen and carbon monoxide adsorption site energy distributions did not change appreciably with the metal particle size.