CATALYSIS WITH CARBIDES

Recent research in this field has led to very interesting developments in two areas: the use of SIC as a support material and the use of new transition metal carbides as active catalyst phases. The high thermal conductivity of SiC and the fact that it can be formed from carbon th at has any shape or porosity, due to the 'shape memory effect: are str ong positive attributes for future development, The transition metal c arbides that are active catalytic phases, are also showing promise as novel catalytic materials in several reactions, including three-way au to-exhaust catalysts and hydrocarbon selective dehydrogenation or isom erization reactions. Particularly exciting is the discovery that Mo ox ycarbide can selectively isomerize n-heptane with good selectivity, co ntravening existing wisdom that only acidic catalysts can isomerize pe ntane and hexane but not heptane without production of extensive crack ed side products. A new surface phase oxycarbide has been discovered t hat may be described as a carbon stabilized sheer structure of a MoO3 surface plane, That is, the sheer planes contain carbon atoms which st abilize the partially reduced structure of MoO3 and block its reductio n to MoO2.