Abstract
Two kinds of hexagonal boron nitride (h-BN), with different crystallinities, were selected as supports of oxidation catalysts and compared with alumina accordingly. Platinum catalysts were prepared by the incipient wetness method with the precursor H 2PtCl 6·6H 2O. Catalysts were treated at various temperatures in air or hydrogen. TEM micrographs indicate that migration of Pt particles occurred on the highly crystalline face of h-BN due to the weaker bonding between the crystalline face and Pt particles than between Pt and Pt. The grain boundary of the h-BN support with lower crystallinity strengthened bonding to Pt particles, causing the Pt particles to be well dispersed. The Pt particles dispersed on the support yielding low Pt bonding strength, such as h-BN and especially highly crystallized h-BN, were less easily oxidized. UV absorption spectra of Pt also revealed that the h-BN support can eliminate the influence of chloride from Pt particles at low temperature. Pt/h-BN is more active than Pt/γ-Al 2O 3 in benzene deep oxidation. This finding is believed to follow from Pt in the reduced state supplying more active adsorbed oxygen atoms and the lower effect of chlorine on the support. The h-BN support with low crystallinity, appropriate specific surface areas, and chemical anchoring sites is recommended as the preferred support to maintain the dispersion and activity of Pt particles.
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