Showing papers on "BET theory published in 2001"

Very High Surface Area Microporous Carbon with a Three-Dimensional Nano-Array Structure: Synthesis and Its Molecular Structure

Abstract: By using zeolite Y as a template, a novel microporous carbon with a three-dimensional nano-array structure was prepared. The arrangement and periodicity of this array are identical to those of supercages in zeolite Y crystal. The carbon has a surprisingly high BET surface area (3600 m2/g) with almost no mesoporosity. This carbon may be comprised of very curved graphene sheets whose faceting and curvature are accommodated to the curved inner surface of the zeolite nanochannels.

Activity and Characterization by XPS, HR-TEM, Raman Spectroscopy, and BET Surface Area of CuO/CeO2-TiO2 Catalysts

Abstract: Structural and textural studies of a CuO/TiO2 system modified by cerium oxide were conducted using Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 absorption (BET specific surface area). The introduction of a minor amount of CeO2 (Ce0.09Ti0.82O1.91Cu0.09 sample) resulted in a material with the maximum surface area value. The results of Raman spectroscopy revealed the presence of only two crystalline phases, TiO2 anatase and CeO2 cerianite, with well-dispersed copper species. TEM micrographs showed a trend toward smaller TiO2 crystallites when the cerium oxide content was increased. The XPS analysis indicated the rise of a second peak in Ti 2p spectra with the increasing amount of CeO2 located at higher binding energies than that due to the Ti4+ in a tetragonal symmetry. The CuO/TiO2 system modified by CeO2 displayed a superior performance for methanol dehydrogenation than the copper catalyst supported only on TiO2 or CeO2.

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 ...

Photodegradation of aromatic pollutants in water over TiO2 supported on molecular sieves

Abstract: TiO2 was supported on porous materials, including NaY and Na-mordenite zeolites, as well as mesoporous MCM-41 molecular sieve by using impregnation method with organic solvents. The products were characterized with powder XRD, BET surface area measurement, TEM, IR, Raman and UV–VIS spectroscopies. The supported TiO2 was crystallized in anatase structure and the intensity of its X-ray diffraction peaks increased with TiO2 loading. In contrast, the total surface area of the supported catalyst decreased with TiO2 loading. A blue shift of the absorption edge in the UV–VIS spectra was observed when TiO2 particle size decreased, a phenomenon corresponding to the particle size quantization effect. For photodegradation of aromatic pollutants in water, the activity was found strongly influenced by the chemical nature of the pollutant and the surface property of the support. For volatile pollutants such as benzene and chlorobenzenes, molecular sieve supports facilitated the photodegradation reaction by providing high surface area for adsorption. Moreover, there is an optimal loading of TiO2 to achieve the best photocatalytic activity on various supports. The supports in contrast did not show positive contribution in degradation of hydrophilic pollutants such as phenol.

Heterogeneous Uptake of Sulfur Dioxide On Aluminum and Magnesium Oxide Particles

Abstract: In this study, the heterogeneous uptake of SO2 on α-Al2O3 and MgO particles at 296 K was investigated. Transmission FT-IR experiments reveal that under dry conditions SO2 reacts with α-Al2O3 and MgO to form strongly adsorbed bisulfite, HSO3-(aq), and sulfite, SO32-(aq), on α-Al2O3 and sulfite on MgO. To quantify the uptake of SO2 under dry conditions, heterogeneous uptake coefficients were measured with a Knudsen cell reactor. The Knudsen cell data were modeled to account for gas diffusion in to the underlying layers and surface saturation. The initial uptake coefficient, γo, is calculated using the BET surface area of the powdered samples as diffusion of SO2 into the powder is found to readily occur. Values of γo were determined to be 9.5 ± 0.3 × 10-5 and 2.6 ± 0.2 × 10-4 for SO2 uptake on α-Al2O3 and MgO, respectively, at 296 K under dry conditions at a gas concentration near 1 × 1011 molecules/cm3. Additionally, water uptake on sulfite-coated α-Al2O3 and sulfite-coated MgO particles was investigated wi...

Influence of catalyst pretreatments on volatile organic compounds oxidation over gold/iron oxide

Abstract: This paper reports a study on the influence of calcination pretreatments on the catalytic behaviour of the Au/iron oxide system towards the combustion of some representative volatile organic compounds (2-propanol, ethanol, methanol, acetone and toluene). The catalytic activity of Au/Fe 2 O 3 samples towards the total oxidation to CO 2 has been found to be strongly dependent on the catalyst pretreatment, decreasing on increasing the calcination temperature. On the basis of characterisation data (XPS, FT-IR, XRD, BET surface area) it has been proposed that the catalytic behaviour is related to the gold state and/or the iron oxide phase. It appears plausible to suggest that the gold oxidation state and/or the particle size play a key role in the catalytic combustion of volatile organic compounds.

CeO2–ZrO2 Solid Solution Catalyst for Selective Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide

Abstract: CeO2–ZrO2 solid solution catalysts are very effective for the selective synthesis of dimethyl carbonate from methanol and CO2. The activity was much dependent on the calcination temperature. The higher the calcination temperature, the higher the activity of the catalyst for DMC formation, though the BET surface area is lower on the catalyst calcined at higher temperature.

Cleaner production of carbon adsorbents by utilizing agricultural waste corn cob.

Abstract: In the present study, the porous carbon products from agricultural waste corn cob were manufactured by using the combined activation methods. Under the experimental conditions in the activation temperature ranges of 500‐800°C with less pollution characteristics of potassium hydroxide:potassium carbonate (KOH:K2CO3) as chemical agents and subsequent gasification (i.e. physical activation) at the soaking time of 1 h, the influence of activation temperature on the final products was studied by examining their physical characterizations such as BET surface area, total pore volume and true density. The experimental results show that an elevated temperature is favorable for producing carbon products with high surface area and total pore volume. Also, the values of the true density and the porosity increase with increase in the activation temperature. Comparing the results of physical characterizations of the carbon products with those of commercial activated carbons indicates that the activated carbons prepared from agricultural waste corn cob by using a cleaner process is an available route for the biomass utilization and bioresource recycling. The high-surface-area carbon products thus obtained are very promising adsorbents for pollution control and for other applications. © 2001 Elsevier Science B.V. All rights reserved.

Removal of NO by Reversible Adsorption on Fe−Mn Based Transition Metal Oxides

Abstract: A series of Fe−Mn-based transition metal oxides were prepared and used for NO adsorption at 25 °C in the presence of O2. The sorbents were also characterized by BET surface area, TPD, XRD, and FTIR spectroscopy. Both TGA and chemiluminescent NO/NOx analyzer experiments showed that the mixed oxides were efficient and reversible sorbents for NO removal. The NOx capacity decreased in the order of Fe−Mn−Ti, Fe−Mn−Zr > Fe−Mn−Ce, Fe−Mn−Ni > Fe−Mn−Co > Fe−Mn−Cu, Fe−Mn. The maximum NOx capacity reached 42−45 mg/g of sorbent for the Fe−Mn−Ti and Fe−Mn−Zr oxides. SO2 and CO2 decreased the NOx adsorption amount only slightly. H2O decreased the NOx adsorption significantly, but the inhibition was reversible. TPD profiles indicated that NOx species could desorb at temperatures below 400 °C. The high efficiency for NO removal on these oxides was related to their high activities in NO oxidation to NO2 at 25 °C. FTIR spectra showed that the nitrate was the final species for NO adsorption. NO2 and nitrite were the interme...

XPS and TPD characterization of manganese-substituted iron–potassium oxide catalysts which are selective for dehydrogenation of ethylbenzene into styrene

Abstract: Manganese-substituted (0–100%) iron–potassium oxide (Mn–Fe–K) catalysts which are selective for dehydrogenation of ethylbenzene to styrene were prepared by the alcoxide sol–gel method. They have been characterized by XPS, BET surface area measurement and TPD studies. The differences of surface properties between the Mn–Fe–K catalysts and unsubstituted iron–potassium oxide (Fe–K) catalyst were reasonably reflected in the XPS spectrum of oxygen (O 1s) and potassium (K 2p). The XPS spectra of Mn–Fe–K catalysts based on the binding energy shifts of O 1s and K 2p bands resembled those of KFeO2 as an active phase for the dehydrogenation of ethylbenzene. On the contrary, the unsubstituted Fe–K catalyst showed the XPS spectra including KOH and Fe3O4 as inactive phases. The presence of Mn ions in the catalyst matrix (γ-Fe2O3, MnFe2O4) results in stabilization of the KFeO2 active phase, and did not affect catalytic behavior of the K-promoted iron based oxide. The maximum enhancement of catalytic activity at the optimum 20% Mn-substitution is owing to the large surface area, the minimization of carbonaceous deposition, and the retardation of pyrolysis of KFeO2 to KOH and Fe3O4.

Compositions for producing difficult-to-wet surface

Abstract: The present invention provides a coating composition for producing difficult-to-wet surfaces, comprising i) at least one finely divided powder whose particles have a hydrophobic surface and a porous structure characterized by a BET surface area (determined in accordance with DIN 66131) of at least 1 m 2 /g, and ii) at least one film-forming binder characterized by a surface tension <50 mN/m, the weight ratio of powder to binder being at least 1:4. It also provides a process for producing difficult-to-wet surfaces, and provides for the use of the coating compositions for producing surfaces having a self-cleaning effect and for reducing the flow resistance for liquids in pipes.

Surface properties and catalytic performance for ethane combustion of La1−xKxMnO3+δ perovskites

Abstract: The influence of K substitution in LaMnO3 perovskite on the surface properties and catalytic oxidation of ethane has been studied. La1−xKxMnO3+δ perovskites (x=0.05, 0.10, 0.15, 0.20 and 0.25) with BET surface area of 20–26 m2 g−1 have been prepared by the freeze-drying method and characterized by X-ray diffraction patterns (XRD), TPR, TPD and XPS. The XRD analyses showed the presence of a single crystalline phase (x≤0.15) with the linear increase of the lattice parameter corroborating the incorporation of potassium in the perovskite structure. The XPS studies revealed an enrichment of the perovskite surface with potassium accompanied by an increase in the surface Mn4+/Mn3+ ratio. The TPR and chemical analyses suggested the presence of an oxygen non-stoichiometry (δ) of +0.15 for LaMnO3 which decreases to −0.04 for La0.85K0.15MnO3. Oxygen temperature programmed desorption experiments showed similar results with the amount of β oxygen desorption decreasing in the presence of potassium in the perovskite structure. The catalytic activity for the total oxidation of ethane decreased for K containing perovskite and was closely related to the oxygen non-stoichiometry (δ). The effect of oxygen partial pressure and temperature suggests the predominance of an intrafacial mechanism at higher temperature with a possible contribution of the suprafacial reaction at lower temperatures.

Studies on physico-chemical characterization and catalysis on high surface area titania supported molybdenum hydrotreating catalysts

Abstract: A series of titania supported molybdenum catalysts were prepared by incipient wetness impregnation method and characterized by BET surface area, XRD, TPR, FTIR, ESCA, and low temperature oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating catalytic activities for hydrodesulfurization (HDS), hydrogenation (HYD), and hydrodeoxygenation (HDO) reactions, respectively. XRD results indicate that molybdenum oxide species are dispersed as a monolayer on the support up to 8 wt.% Mo and the formation of crystalline MoO 3 is observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading and polymeric octahedral forms are dominant at higher loading. Both oxygen chemisorption and rates of reaction were found to increase with increasing Mo loading up to 8 wt.% and then decrease with further increase in loading. HDS and HYD activities are more or less same but HDO activity is two times higher than HDS and HYD activities. The results are also interpreted with the help of other parameters, like dispersion, equivalent molybdenum surface area, surface coverage, crystalline size, quasi-turnover frequencies and intrinsic activities. ESCA results suggest that electron transfer is taking place from support to metal.

Catalytic Performance of Rh/CeO2 in the Gasification of Cellulose to Synthesis Gas at Low Temperature

Abstract: The gasification of cellulose has been investigated on Rh catalysts supported on CeO2, ZrO2, Al2O3, TiO2, MgO, and SiO2 at very low temperatures (723−823 K) in a laboratory-scale fluidized-bed reactor using air as a gasifying agent. Of the catalysts, only Rh/CeO2 showed the excellent catalytic performance in the cellulose gasification at above 823 K, resulting in 100% carbon conversion to gas. The details of reaction conditions that affected the performance of the catalyst have been optimized. The best results have been found at above 823 K using the total flow rate of 170 cm3 min-1 of inlet gases. The total carbon conversion was achieved when 50 mg of cellulose was used in a batch. The Rh loading of 1.2 × 10-4 mol (g of catalyst)-1 on CeO2 and W/F of 1.8 gh mol-1 were optima for the total conversion of carbon to gases. Fresh and used catalysts were characterized by a Brunauer−Emmett−Teller (BET) analysis and transmission electron microscopy (TEM). The BET surface area has been decreased from 59 to 24 m2/...