Preparation of BN catalyst supports from molecular precursors.: Influence of the precursor on the properties of the BN ceramic

Thin powders and foams of boron nitride have been prepared from various molecular precursors in order to be used as noble metal supports in the catalytic conversion of methane. Different kinds of precursors have been studied issued from borazines bearing different substituents. To get boron nitride presenting the required porosity and specific areas, thermal or chemical treatments have been performed to favour these properties. The best results were obtained using a molecular precursor derived from trichloroborazine (TCB) which, after reaction with ammonia at room temperature and then thermolysis up to 1800degreesC, led to BN powders with a specific area of more than 300 m(2).g(-1). rable results were obtained using polyborazylene thermolysed under ammonia. Surprisingly, the aminoborazine-derived precursors did not yield such high surface areas when thermolysed, but the BN texture was more expanded and looked like a foam. Attempts have been made to incorporate directly a molecular precursor of a noble metal into the BN precursor before the thermal treatment. Good results have been obtained for the incorporation of the metal up to 1100degreesC, but the high temperature required to stabilise the BN powder has limited the choice of metal to platinum, whose presence has been characterised on the BN support. This new catalyst is currently being tested.