Boron nitride, mesoporous

Because of the uniquely ordered structure of template-synthesized porous carbons, they themselves can be used as templates to replicate other materials with an ordered porous structure that is difficult to make using traditional methods [121,338-348], Thus, CMK-3 carbon was first demonstrated as a template to prepare mesoporous silica [121,338]. An OMC prepared from an MCM-48 template was used to prepare nanostructured silica [339]. Nanocasting of CMK-3 using ZSM-5 crystals yielded a mesoporous zeolite with both mesopores and micropores [340]. More recently, the preparation of a novel class of mesoporous aluminosilicate molecular sieves was described [341]. The preparation of mesoporous boron nitride (MBN) and mesoporous carbon nitride (MBCN) with very high surface area and pore volume was recently realized using a well-ordered hexagonal mesoporous carbon as a template and boron trioxide as a boron source [342]. Nonspherical silica nanocases with a hollow core and mesoporous shell were also produced [343]. 

FIGURE 20. Syntheses of mesoporous carbon, mesoporous carbon nitride, mesoporous boron nitride, and mesoporous boron carbon nitride. 

In the present work, porous boron nitride samples have been prepared from different molecular precursors. The nature and the pretreatment of the precursors have been investigated in order to determine accurately the optimal conditions leading to high surface area porous boron nitride materials suitable to be used as catalysts supports. The best results led to BN powders presenting surface areas of about 250 to 300 m. g. The porosity resulted from the presence of two kind of pores mesopores down to 2 nm, and a microporosity corresponding to pores from 0.5 to 1 nm. Attempts were made to incorporate directly a noble metal precursor into the BN precursor. Up to 1100°C, Pd or Pt were kept in the porous structure, but the very high temperature required to stabilise BN powders lowered drastically the metal concentration on the catalyst As a consequence, only the platinum sample could be obtained and characterized this catalyst is currently being tested. 

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