Showing papers on "BET theory published in 2008"

Reporting Physisorption Data for Gas/Solid Systems

Abstract: The sections in this article are Introduction General Definitions and Terminology Methodology Methods for the Determination of Adsorption Isotherms Operational Definitions of Adsorption Experimental Procedures Outgassing the Adsorbent Determination of the Adsorption Isotherm Evaluation of Adsorption Data Presentation of Primary Data Classification of Adsorption Isotherms Adsorption Hysteresis Determination of Surface Area Application of the BET Method Empirical Procedures for Isotherm Analysis Assessment of Mesoporosity Properties of Porous Materials Application of the Kelvin Equation Computation of Mesopore Size Distribution Assessment of Microporosity Terminology Concept of Surface Area Assessment of Micropore Volume General Conclusions and Recommendations Keywords: physisorption data; IUPAC; adsorption isotherms; surface area; BET isotherm

Ordered mesoporous alumina-supported metal oxides

Abstract: The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.

Facile Synthesis of Ordered Mesoporous Carbons with High Thermal Stability by Self-Assembly of Resorcinol−Formaldehyde and Block Copolymers under Highly Acidic Conditions

Abstract: The effect of phenols reactivity with formaldehyde on the formation of ordered mesoporous carbons has been investigated. A strategy to accelerate the polymerization of phenolic resins by using strongly acidic conditions is proposed. The self-assembly of resorcinol-formaldehyde and block copolymers (e.g., F127) under highly acidic concentrations (e.g., 1.5 M HCl) is probably driven by the I+X-S+ mechanism and hydrogen bonding and affords a highly reproducible approach for synthesis of ordered mesoporous carbons. The synthesis can be readily scaled up with no change in sample quality. The carbon material obtained (denoted as C-ORNL-1) exhibits highly ordered hexagonal mesostructure, with a typical BET surface area of approximately 600 m2/g, pore size of 6.3 nm, and pore volume of approximately 0.60 cm3/g. One of the unique structural features of C-ORNL-1 is its high thermal stability; it can be graphitized at 2600 degrees C while considerable mesoporosity is maintained.

Nanocasted Synthesis of Mesoporous LaCoO3 Perovskite with Extremely High Surface Area and Excellent Activity in Methane Combustion

Abstract: Ordered mesoporous LaCoO3 perovskite with high surface area was synthesized via nanocasting strategy by using ordered mesoporous cubic (Ia3d) vinyl silica as the template. The sample, prepared by filling mesopores in silica template with a La−Co citrate complex precursor followed by calcination and silica removal, was characterized by XRD, TEM, and nitrogen sorption techniques, and its catalytic activity was tested for complete methane oxidation. The wide-angle XRD pattern showed LaCoO3 perovskite was formed and no La-oxide/Co-oxide phases were detected in the obtained material. This LaCoO3 perovskite displayed a high BET surface area of 96.7 m2 g−1 from nitrogen sorption analysis and a three-dimensional ordered mesostructure from TEM images, as well as a small-angle XRD pattern. Moreover, this material showed much higher activity in the complete methane oxidation than the conventional bulk LaCoO3 perovskite. The light-off temperature (T10) and the half-conversion temperature (T50) were at 335 and 470 °C,...

Coke study on MgO-promoted Ni/Al2O3 catalyst in combined H2O and CO2 reforming of methane for gas to liquid (GTL) process

Abstract: MgO-promoted Ni/Al2O3 catalysts have been investigated with respect to catalytic activity and coke formation in combined steam and carbon dioxide reforming of methane (CSCRM) to develop a highly active and stable catalyst for gas to liquid (GTL) processes. Ni/Al2O3 catalysts were promoted through varying the MgO content by the incipient wetness method. X-ray diffraction (XRD), BET surface area, H2-temperature programmed reduction (TPR), H2-chemisorption and CO2-temperature programmed desorption (TPD) were used to observe the characteristics of the prepared catalysts. The coke formation and amount in used catalysts were examined by SEM and TGA, respectively. H2/CO ratio of 2 was achieved in CSCRM by controlling the feed H2O/CO2 ratio. The catalysts prepared with 20 wt.% MgO exhibit the highest catalytic performance and have high coke resistance in CSCRM. MgO promotion forms MgAl2O4 spinel phase, which is stable at high temperatures and effectively prevents coke formation by increasing the CO2 adsorption due to the increase in base strength on the surface of catalyst.

Hard templating synthesis of mesoporous and nanowire SnO2 lithium battery anode materials

Abstract: Mesoporous and nanowire SnO2 anode materials for lithium batteries were prepared using KIT-6 and SBA-15 SiO2 templates, and their electrochemical properties were compared at different current rates. The as-prepared SnO2nanowires had a diameter of 6 nm and a length of >3 μm and Brunauer–Emmett–Teller (BET) surface area of 80 m2 g−1 while mesoporous SnO2 showed a pore size of 3.8 nm and a BET surface area of 160 m2 g−1. The charge capacities of these two anodes were similar to each other at 800 mAh g−1, but mesoporous SnO2 showed much improved cycle life performance and rate capabilities because of its higher surface area than nanowire SnO2. Especially, the capacity retention of the mesoporous SnO2 was 98%, compared with 31% for the SnO2nanowires at a 10 C rate (= 4000 mA g−1). The improved electrochemical performance of the mesoporous SnO2 was related to the regular porosity which permitted thorough flooding of the electrolyte between the particles, and the mesopores which acted as a buffer zone during the volume contraction and expansion of Sn.

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)

Structure-activity Relation of Fe2O3–CeO2 Composite Catalysts in CO Oxidation

Abstract: A series of Fe2O3–CeO2 composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), BET surface area measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their catalytic activities in CO oxidation were also tested. The Fe2O3–CeO2 composites with an Fe molar percentage below 0.3 form solid solutions with the CeO2 cubic fluorite structure, in which the doped Fe3+ initially substitutes Ce4+ in fluorite cubic CeO2, but then mostly locate in the interstitial sites after a critical concentration of doped Fe3+. With an Fe molar percentage between 0.3 and 0.95, the Fe2O3–CeO2 composites are mixed oxides of the cubic fluorite CeO2 solid solution and the hematite Fe2O3. XPS results indicate that CeO2 is enriched in the surface region of Fe2O3–CeO2 composites. The Fe2O3–CeO2 composites have much higher catalytic activities in CO oxidation than the individual pure CeO2 and Fe2O3, and the Fe0.1Ce0.9 composite shows the best catalytic performance. The structure-activity relation of the Fe2O3–CeO2 composites in CO oxidation is discussed in terms of the formation of solid solution and surface oxygen vacancies. Our results demonstrate a proportional relation between the catalytic activity of cubic CeO2-like solid solutions and their density of oxygen vacancies, which directly proves the formation of oxygen vacancies as the key step in CO oxidation over oxide catalysts.

Hybrid surfactant-templated mesoporous silica formed in ethanol and its application for heavy metal removal.

Abstract: This paper presents the physico-chemical characteristics of coconut-based activated carbon of commercial grade (ACC) and the sorption behaviour and kinetics of adsorption of toxic metal ions onto ACC. The proximate and CHN analysis of the ACC showed the presence of ∼41% carbon, ∼16% hydrogen and ∼2% nitrogen in ACC. Bulk density and heating value of ACC were found to be 599.32 kg/m 3 and 18.81 MJ/kg, respectively. The BET surface area was 171.05 m 2 /g whereas the BET average pore diameter was 31.03 A. The meso-porous surface area was found to be 76% and the micro-porous surface area was 24% of the total pore surface area. The polar groups present on the ACC surface impart considerable cation exchange capacity to it. ACC worked as a very good adsorbent at an optimum initial pH (pH 0 ) of 6.0 and at a dose of 20 g/dm 3 for the adsorption of cadmium (Cd(II)), nickel (Ni(II)) and zinc (Zn(II)) metal ions at a concentration of 100 mg/dm 3 . The adsorption of metal ions onto ACC was found to be a gradual process and the quasi-equilibrium condition reached in 5 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient was of the order of 10 −12 m 2 /s.

Adsorption of toxic metal ions onto activated carbon Study of sorption behaviour through characterization and kinetics

Abstract: This paper presents the physico-chemical characteristics of coconut-based activated carbon of commercial grade (ACC) and the sorption behaviour and kinetics of adsorption of toxic metal ions onto ACC. The proximate and CHN analysis of the ACC showed the presence of ∼41% carbon, ∼16% hydrogen and ∼2% nitrogen in ACC. Bulk density and heating value of ACC were found to be 599.32 kg/m 3 and 18.81 MJ/kg, respectively. The BET surface area was 171.05 m 2 /g whereas the BET average pore diameter was 31.03 A. The meso-porous surface area was found to be 76% and the micro-porous surface area was 24% of the total pore surface area. The polar groups present on the ACC surface impart considerable cation exchange capacity to it. ACC worked as a very good adsorbent at an optimum initial pH (pH 0 ) of 6.0 and at a dose of 20 g/dm 3 for the adsorption of cadmium (Cd(II)), nickel (Ni(II)) and zinc (Zn(II)) metal ions at a concentration of 100 mg/dm 3 . The adsorption of metal ions onto ACC was found to be a gradual process and the quasi-equilibrium condition reached in 5 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient was of the order of 10 −12 m 2 /s.

Calcination temperature and CuO loading dependence on CuO-CeO2 catalyst activity for water-gas shift reaction

Abstract: In this work we investigated the influence of CuO loading and catalyst pretreatment procedure to derive an optimal CuO-CeO2 catalyst for water-gas shift (WGS) reaction, and to study in detail structure–activity relationships. Nanostructured catalyst samples prepared by co-precipitation and a 10, 15 and 20 mol% CuO content were examined by XRD, BET and TPR/TPD analyses and subjected to pulse WGS activity tests in the temperature range of 180–400 °C. As evaluated by TPR/TPD and N2O chemisorption analyses, with increasing CuO loading the portion of finely dispersed CuO nanoparticles decreases on behalf of larger CuO aggregates. Strong surface structure–activity dependence in WGS reaction was observed for all catalyst samples. It was established that increasing CuO content results in higher extent of CeO2 reduction, which has a positive effect on H2 production during the WGS reaction. Increasing calcination temperature on the other hand reduces BET surface area, induced by CuO sintering and agglomeration of CeO2 particles resulting in a negative effect on H2 production. Distinctive WGS activity dependence on surface acidity of examined solids was observed for all CuO loadings.

Preparation, characterization, and photocatalytic activity of sulfate-modified titania for degradation of methyl orange under visible light.

Abstract: Hydrated titania was prepared by a sol–gel method, taking tetraisopropyl orthotitanate as starting material, and then promoted with different weight percentages of sulfate by an incipient wetness impregnation method The materials were characterized by various advanced techniques such as PXRD, BET surface area, N2 adsorption–desorption measurements, FTIR, and SEM Analytical results demonstrated that TiO2 is mesoporous in nature, and sulfate modification could inhibit the phase transformation and enhance the thermal stability of TiO2 It was also found that sulfate modification could reduce the crystallite size and increase the specific surface area of the catalysts The degradation of methyl orange under solar radiation was investigated to evaluate the photocatalytic activity of these materials Effects of different parameters such as pH of the solution, amount of catalyst, additives, and kinetics were investigated At 25 wt% sulfate loading, the average percentage of degradation of methyl orange was nearly two times than that of neat TiO2 The photocatalytic degradation followed first-order kinetics

Mesoporous H3PW12O40-silica composite: Efficient and reusable solid acid catalyst for the synthesis of diphenolic acid from levulinic acid

Abstract: Mesoporous H 3 PW 12 O 40 -silica composite catalysts with controllable H 3 PW 12 O 40 loadings (40–651%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials With H 3 PW 12 O 40 loading lower than 20%, the materials exhibit larger BET surface area (6045–7530 m 2 g −1 ), larger and well-distributed pore size (61–86 nm), larger pore volume (075–12 cm 3 g −1 ), and highly dispersed Keggin unit throughout the materials Raman scattering spectroscopy studies confirm that the primary Keggin structure remained intact after formation of the composites As a novel kind of reusable solid acid catalyst, as-prepared H 3 PW 12 O 40 -silica composite was applied for the synthesis of diphenolic acid (DPA) from biomass platform molecule, levulinic acid (LA), under solvent-free condition, and remarkably high catalytic activity and stability were observed