Abstract
The effects of thermal treatments in oxygen (300 to 600 °C) and hydrogen (500 to 800 °C) on the metal dispersions of 1% Pt, 1% Ir, and 1% Pt-1% Ir catalysts were studied. Treatment in oxygen at 400 to 600 °C resulted in increases in dispersion for the Pt catalyst. Small increases in dispersion for the Ir catalysts were observed after treatment in oxygen at 300 °C; at higher temperatures the Ir dispersion decreased significantly. Segregation of the metals occurred in the bimetallic PtIr catalysts during treatment in oxygen. The largest decreases in dispersion due to treatment in hydrogen were observed for the Pt catalyst. Surprisingly, hydrogen treatment of the Ir and PtIr catalysts resulted in essentially the same relative decreases in metal dispersions.
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