Effect of the zeolite crystal size on the structure and properties of carbon replicas made by a nanocasting process

Zeolite Beta particles with size of 0.1, 0.5 and 1 mu m were employed as molds for the synthesis of microporous carbon. After infiltration and pyrolysis of propylene at 800 degrees C for 2 h, zeolite/carbon composites were obtained and further subjected to acid extraction of the zeolite precursor. The initial zeolite samples, zeolite/carbon composites and carbon replicas were studied by XRD, TG analysis, SEM/TEM, DLS, N-2 adsorption measurements and chemical analysis. The experimental data revealed that the carbon replicas faithfully replicate the zeolite morphology and possess higher micropore volume than that of the parent zeolite molds. The use of zeolite molds of different sizes resulted in carbons with fairly different pore structure. Thus, larger (0.5 and 1 mu m) zeolite crystals provided replicas wit a pore structure possessing mainly micropores, whereas the carbon replication of 0.1 mu m zeolite aggregates built of much smaller crystallites resulted in a material with lower micropore volume and substantial contribution of mesopores to the total pore volume. The different pore structure of the latter carbon was found to be a result of the larger external surface area of the nanosized mold, loss of crystallinity during the preparation procedure and the presence of interparticles porosity. (C) 2008 Elsevier Ltd. All rights reserved.