ISSN 2070-0504, Catalysis in Industry, 2013, Vol. 5, No. 4, pp. 350–357. © Pleiades Publishing, Ltd., 2013. Original Russian Text © Yu.V. Larichev, P.M. Eletskii, F.V. Tuzikov, V.A. Yakovlev, 2013, published in Kataliz v Promyshlennosti. 350 INTRODUCTION Rice husks are an abundant agricultural waste. The amount of rice husks wasted in the world is about 80 million tons per year [1, 2], including Russia’s 100000–150000 t/year. Because of their insufficient caloricity, rice husks are difficult to recycle. In view of this, researchers seek efficient methods for its conver- sion into highly marketable products. Rice husks s are a promising renewable raw material for manufacturing a wide variety of organics (bio-oil [3, 4], bioethanol [5], cellulose [6], and others [2, 7–9]) and inorganic products, including silicon- and carbon-containing materials (SiO 2 [1, 2, 10–12], SiC, Si 3 N 4 , etc.) [13–20] and porous carbon-containing composites and carbon materials [1, 2, 21–26]. The possibility of producing this diversity of products is due to the specific compo- sition of the raw material. According to the literature, rice husks contain 50–60% cellulose and hemicellu- lose, 15–25% lignin, and 13–29% SiO 2 [27]. The total amount of other elements and compounds does not exceed 1–3%, so rice husks can be considered as a nat- ural composite consisting of a biopolymer matrix and a reinforcing silica phase. Porous carbon materials are commonly derived from rice husks by carbonizing them in an inert medium followed by chemical activation of the prod- uct [21, 23–25]. The carbonization of rice husks in a fluidized-bed catalytic reactor at 450–600°C in flow- ing air to obtain carbon–silicon composites [22] and their subsequent activation with KOH afford microporous carbon materials with a specific surface area close to its maximum possible value (>3000 m 2 /g as determined by the BET method and up to 2700 m 2 /g according to NLDFT) and a pore volume of up to 3.0 cm 3 /g [25, 28]. Use of sodium or potas- sium carbonate in place of the alkali in the heat treat- ment procedure makes it possible to obtain carbon materials with a mesopore-dominated texture [26]. In this case, the particle size of the template silica phase (i.e., the phase serving as the template for the porous structure of the carbon material forming from tem- plate-containing composite) is among the crucial fac- tors in the porosity of the resulting carbon materials, particularly in the porosity of mesoporous ones. The conventional methods of producing carbon materials with a developed porous structure—steam– gas and chemical activation of low-ash carbon-con- taining precursors from vegetable raw materials (saw- dust, nutshells, pits, etc.)—typically yield micropore- dominated materials whose BET surface area can be up to 1500 m 2 /g in the case of steam–gas activation and over 3000 m 2 /g in the case of chemical activation [29–35]. However, these methods include heat treat- ment at 600–950°C, which needs appropriate equip- Porous Carbon–Silica Composites and Carbon Materials from Rice Husk: Production Technology, Texture, and Dispersity Yu. V. Larichev, P. M. Eletskii, F. V. Tuzikov, and V. A. Yakovlev Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia e-mail: ylarichev@gmail.com; yeletsky@catalysis.ru; tuzikov@catalysis.ru; yakovlev@catalysis.ru Received November 21, 2012 Abstract—A method based on carbonization in a fluidized-bed catalytic reactor is suggested for utilization of rice husks, which are hard-to-recycle waste from paddy production. The bottom ash resulting from car- bonization at 465–600°C is a carbon–silica nanocomposite (C/SiO 2 ) with a SiO 2 content of 58.7–81.8 wt % and a specific surface area of S BET = 152–232 m 2 /g. Leaching of SiO 2 with hydrofluoric acid yields porous carbon materials with a specific surface area of 165–494 m 2 /g and a SiO 2 content of <1%. These materials have been characterized by small-angle X-ray scattering (SAXS), transmission electron microscopy, and X-ray diffraction. Particle size data for SiO 2 in the carbon–silica nanocomposite have been obtained for the first time. As the carbonization temperature is raised from 465 to 600°C, the average particle size of silica increases from 5.5 to 8.1 nm. Development of the SAXS procedure for determining the size of silica particles in the carbon matrix would provide a promising tool for knowingly designing porous carbon materials with preset properties. The carbonization of rice husks in a fluidized catalyst bed is among the most promising methods of their conversion into C/SiO 2 nanocomposites and porous carbon materials with the use of tem- plate synthesis approaches. Keywords: SAXS, rice husks, fluidized bed, carbon materials, carbon–mineral composites DOI: 10.1134/S2070050413040065 BIOCATALYSIS