BET theory

About: BET theory is a research topic. Over the lifetime, 9046 publications have been published within this topic receiving 286142 citations.

Template-Free Synthesis, Controlled Conversion, and CO Oxidation Properties of CeO2 Nanorods, Nanotubes, Nanowires, and Nanocubes

Abstract: A general large-scale synthesis of single-crystalline and uniform CeO2 nanorods was first realized without templates by a precipitation method at room temperature and pressure. Such nanorods have an aspect ratio of ca. 3 nm with a diameter of ca. 8 nm and a large BET specific area of 128.2 m2/g. On the basis of this, the controlled conversion of the as-prepared nanorods into nanotubes, nanowires, and nanocubes through hydrothermal reactions has been realized. Further experimental results show that the growth of nanorods is a function of the base concentration, temperature, and time. In addition, particle size measurements demonstrate that the primary nanorods grow by Ostwald ripening. It is found that CeO2 growth is faster at higher base concentration and temperature due to the accelerated ripening. During the synthesis, the formation of Ce(OH)3 intermediate species and their transformation into CeO2 have been dynamically demonstrated and are regarded as the key factors responsible for the evolution of shape. The CO oxidation properties of CeO2 nanorods, nanowires, nanotubes, and nanocubes were investigated, and CeO2 nanotubes have the best performance due to the large BET surface area and the novel inner surface. In addition, CeO2 nanorods aged for 9 d also have an excellent catalytic performance for CO oxidation due to the exposed crystal surface (110) of CeO2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Preparation Characterization and Photocatalytic Activity of Polycrystalline ZnO/TiO2 Systems. 1. Surface and Bulk Characterization

Abstract: Polycrystalline ZnO/TiO2 solids have been prepared with four different methods using home prepared TiO2 (anatase) or TiO2 (rutile) as supports and Zn(NO3)2·6H2O or Zn(CH3COO)2·2H2O as precursors for ZnO. The bulk and surface properties of the samples were investigated by means of TG-DTA, XRD, TEM, SEM-EDAX, XPS, BET surface area determination, and porosity measurements. XRD and TEM results indicate that no significant defect structures exist in any of the samples. The ZnO crystallinity and its enrichment on the surface of TiO2 particles were dependent on the preparation method. The surface areas generally decrease by increasing the amount of ZnO except when ZnO from Zn(CH3COO)2·2H2O was supported on TiO2 (rutile). The samples prepared from Zn(CH3COO)2·2H2O were more porous than those prepared from Zn(NO3)2·6H2O. This was confirmed by BET surface area determinations and SEM observations. XPS spectra indicate that the atomic ratio between OH- and O2- on the particles surface is similar for samples with the ...

New Heterogeneous Polyoxometalate Based Mesoporous Catalysts for Hydrogen Peroxide Mediated Oxidation Reactions

Abstract: Inorganic−organic hybrid mesoporous materials were prepared by cocrystallization of a “sandwich” type polyoxometalate, [ZnWZn2(H2O)2(ZnW9O34)2]12-, and branched tripodal organic polyammonium salts, tris[2-(trimethylammonium)ethyl]-1,3,5-benzenetricarboxylate or 1,3,5-tris[4-(N,N,N-trimethylammoniumethylcarboxyl)phenyl]benzene trications. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed formation of three-dimensional perforated coral-shaped amorphous materials with the organic cations surrounding polyoxometalate anions. N2 sorption analysis showed that the hybrid materials have a BET surface area of ∼30−50 m2 g-1 and an average pore diameter of 36 A leading to the classification of these materials as mesoporous materials with moderate surface areas. These hybrid materials behaved as very effective and selective heterogeneous catalysts for the epoxidation of allylic alcohols and oxidation of secondary alcohols to ketones with hydrogen peroxide as oxidant. The activity and...