STRUCTURAL AND TEXTURAL PROPERTIES OF PYROLYTIC CARBON FORMED WITHIN A MICROPOROUS ZEOLITE TEMPLATE

A new class of pyrolytic carbon materials has been prepared by chemica l vapor infiltration of a microporous zeolite powder followed by remov al of the zeolitic substrate: A wide-pore Y zeolite was used as the su bstrate for the pyrolytic carbon, and propylene was used as the carbon precursor. The structure and porous texture of the resulting carbons were examined by X-ray diffraction, scanning and transmission electron microscopy, and by adsorption of N-2 at 77 K and CO2 at 273 K. Carbon reactivity studies were performed by both nonisothermal and isotherma l thermogravimetric analysis. Under the present conditions of chemical vapor infiltration (800-850 degrees C, 2.5 vol % C3H6, 1 atm of N-2), high-surface-area microporous carbons, with wide microporosity, well- developed mesoporosity and high adsorption capacity were obtained. The carbon yield and the apparent surface area of the carbon increased wi th increasing propylene pyrolysis temperature. The morphology of the c arbons was very similar to that of the zeolite template. Their O-2-rea ctivity profiles exhibited a two-stage behavior, with the inflection p oint between the two stages occurring at different conversion levels d epending on the deposition temperature. Such oxidation behavior sugges ts that the carbons consist of two different structures with different reactivities, the oxidation of the more reactive carbon taking place first and the remaining more ordered carbon being consumed in the seco nd stage. These carbons do not exhibit molecular sieving properties fo r small adsorbate/reactant species.