GRAPHITE-SUPPORTED PLATINUM CATALYSTS - EFFECTS OF GAS AND AQUEOUS-PHASE TREATMENTS

The effects on the platinum particle diameter and the available platin um surface area of a graphite-supported platinum catalyst resulting fr om pretreatments and from performing a selective oxidation reaction ar e investigated. In the gas phase considerable catalyst sintering occur s only in the presence of oxygen at 773 K due to extensive carbon burn -off, whereas in an aqueous phase platinum particle growth is limited upon oxidative treatment. A hydrogen treatment in aqueous phase at 363 K causes platinum particle growth, aggregate formation, and covering of metal sites. These phenomena become more important with increasing pH. Platinum particle growth and aggregate formation are attributed to platinum particle rather than platinum adatom mobility and is caused by the destruction of the oxygen-containing surface groups on the grap hite support, which serve as anchorage sites for the platinum particle s. Site covering is caused by products originating from the graphite s upport, which are formed as a result of the reductive treatments. When performing the aqueous phase oxidation of methyl alpha-D-glucopyranos ide at 323 K and a pH of 9, catalyst modifications are small under oxi dative conditions. Exposure of the catalyst for several hours to methy l alpha-D-glucopyranoside under the same conditions but in the absence of oxygen causes site covering. (C) 1997 Academic Press.