Abstract
Ten magnesium oxide supported platinum catalysts, with Pt loadings of 0.5 to 5.9 wt%, sulfur contents of 0.00 to 1.2 wt% and chlorine contents of 0.01 to 6.0 wt%, were characterized by hydrogen chemisorption, wide–angle x-ray diffraction and transmission electron microscopy after various high temperature treatments in oxygen and hydrogen. It is concluded that the H/Pt ratios for Pt/MgO do not, in general, correspond to the Pt dispersion, even for catalysts with very low levels of impurities. Reduction at temperatures ≥400°C (HTR), of sulfur–containing Pt/MgO causes large decreases in hydrogen adsorption, but the hydrogen adsorption capacity can be restored by oxygen treatment at 500 – 550°C followed by reduction in hydrogen at 250 to 300°C (LTR). Treatment of Pt/MgO in oxygen at 550 to 800°C results in decreases in average Pt crystallite size (redispersion); no significant Pt particle growth (sintering) occurs during oxygen treatment at temperatures as high as 800°C. Chlorine increases the rate of Pt redispersion, but chlorine is not required for redispersion of Pt on MgO.
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