A unique "nano-reactor" concept was presented for producing nano-sized materials that cannot be produced in a macro-reactor. The concept utilizes nano-space of porous materials such as activated carbon and activated alumina as a kind of "nano-reactor". The reactant adsorbed in the nano-space was subjected to reaction in such a manner that most of reaction will be completed in the nano-space. The validity of this concept was examined by utilizing two pyrolysis reactions forming carbon and TiO2 from volatile compounds. The rapid heating as large as 3000 K/s and a high pressure of 2 MPa were employed as the means to complete the pyrolysis reaction within the nano-space. The carbon yield reached as high as 0.89 when anthracene adsorbed on an activated carbon was pyrolyzed, and the TiO2 yield reached a value as high as 0.60 when tetraisopropoxide (TTIP) adsorbed on the activated carbon was pyrolyzed. The carbon produced by this nano-reactor was a nano-graphite consisting of 2-3 graphene layers of less than 2 nm in diameter, and TiO2 produced were fine particles of 5-8 nm in diameter. Such products were significantly different from those that are obtained when the same reactions were carried out in the bulk phase. Thus the "nano-reactor" concept was validated. (c) 2007 Elsevier Ltd. All rights reserved.