Structural and Textural Properties of Pyrolytic Carbon Formed within a Microporous Zeolite Template

A new class of pyrolytic carbon materials has been prepared by chemical vapor infiltration of a microporous zeolite powder followed by removal of the zeolitic substrate. A wide-pore Y zeolite was used as the substrate 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 N₂ at 77 K and CO₂ at 273 K. Carbon reactivity studies were performed by both nonisothermal and isothermal thermogravimetric analysis. Under the present conditions of chemical vapor infiltration (800-850°C, 2.5 vol % C₃H₆, 1 atm of N₂), 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 with increasing propylene pyrolysis temperature. The morphology of the carbons was very similar to that of the zeolite template. Their O₂-reactivity profiles exhibited a two-stage behavior, with the inflection point between the two stages occurring at different conversion levels depending on the deposition temperature. Such oxidation behavior suggests 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 second stage. These carbons do not exhibit molecular sieving properties for small adsorbate/reactant species.