Abstract
It is known that Pt clusters on the surface of chlorinated alumina are highly stable against sintering in reducing or inert environments and easily disintegrate into single atoms upon heat treatments under O2. However, this study reveals that partially oxidized nanoclusters tend to grow in size and reconstruct upon further annealing in an inert gas (conventionally prepared 0.25 ÷ 1 %Pt/γ-Al2O3-Cl samples). Even more surprisingly, the sintering takes place at rather mild conditions (He/Ar, 400–500 °C) but stops soon after it commences (within minutes). The lower the temperature of O2-pretreatment (500 → 20 °C), the sharper the further drop in metal dispersion, and one to a few cycles of the consecutive treatments could be sufficient for the unique properties of Pt clusters to be lost. Possible reasons, contributing factors, and implications of the results for different catalytic systems are discussed.
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