Showing papers on "BET theory published in 1992"

Structure of poly(vinylpyrrolidone)-silica hybrid

Abstract: This paper is concerned with the solid structure of a new group of transparent glass materials which consist of an organic polymer and a metal oxide, namely a combination of poly(vinylpyrrolidone) and dry silica gel. The structure was analyzed by Atomic Force Microscopy (AFM), BET analysis method, and CP MAS13C-NMR. BET measurement showed that the hybrid material had a quite dense structure which was much less porous than the reference dry silica gel prepared by the conventional sol-gel process. AFM analysis gave the same conclusion, i.e., it showed a granular structure of silica of about 1 nm size. Silica and PVP domains did not show any considerable aggregation. The transparent, homogeneous, and dense structure was attributed to the hydrogen-bond formation between PVP(carbonyl group) and silanol, as demonstrated by CP MAS13C-NMR spectroscopy.

Preparation of hectorite clays utilizing organic and organometallic complexes during hydrothermal crystallization

Abstract: In this paper, a method for incorporating a remarkably diverse variety of intercalants directly during hydrothermal synthesis of hectorite layer-silicate clays is developed. Refluxing a gel of silica sol, magnesium hydroxide sol, and lithium fluoride for just 2 days in the presence of an organic or organometallic intercalant results in crystalline products containing either organic dye molecules such as ethyl violet and methyl green, dye molecules such as alcian blue that are based on a Cu(II) phthalocyanine complex, or transition metal complexes such as Ru(II) phenathroline and Co(III) sepulchrate. The following properties of any intercalant are found to be necessary: water solubility, (ii) positive charge, and (iii) thermal stability under moderately basic (pH 9-10) aqueous reflux conditions. The materials, and ion-exchanged natural hectorites for comparison, are characterized by x-ray powder diffraction, N{sub 2} BET surface area measurements, microanalysis, and thermal gravimetric analysis.

Oxidation catalyst and method of use

Abstract: Oxidation catalyst compositions include a catalytic material having a BET surface area of at least about 10 m2/g and consisting essentially of a combination of bulk ceria and a bulk second metal oxide which may be one or more of titania, zirconia, ceria-zirconia, silica, alumina-silica and α-alumina. The combination may optionally also include activated alumina having a BET surface area of at least about 10 m2/g. The ceria, second metal oxide and optional activated alumina may be mixed together or provided as discrete layers. Optionally, one of platinum or palladium metal may be dispersed on the catalytic material provided that the platinum, when used, is used in limited amounts to preclude excessive oxidation of SO?2? to SO3. The catalyst compositions may be used for oxidation of oxidizable components in a gas-borne stream, e.g., in a method to treat diesel engine exhaust by contacting the hot exhaust with the catalyst composition to promote the oxidation of the volatile organic fraction. The optional inclusion of platinum or palladium promotes the oxidation of gas phase components, e.g., hydrocarbons and carbon monoxide.

Properties of water adsorbed in porous silica aerogels

Abstract: Silica aerogels have been prepared by hydrolysis and condensation of sols of composition TMOS-methanol-H 2 O with molar ratio TMOS:H 2 O=4:1 and volume ratio TMOS:methanol=0.2; 0.3; 0.4 and 0.6. Their true and apparent densities, BET surface area, total pore volume and pore size distribution have been systematically investigated as a function of densification heat treatment. The relaxation properties of water adsorbed on the highly reactive surface have been studied by dielectric and nuclear magnetic resonance techniques as a function of the H 2 O coverage (0<θ H2O <6) and temperature

Controlled architecture of solids with micro- and meso-porosity obtained by pillaring of montmorillonite with an LaNiOx binary oxide

Abstract: High-surface-area solids containing both micropores and mesopores have been synthesized by intercalation of the heterobinuclear cation of the complex NiLa(fsaen)NO3 between the layers of montmorillonite clay and calcination at 500 °C. The adsorption mechanism of the complex follows an exchange reaction involving up to 2 mmol of complex cations per g of clay. Further amounts of complex are adsorbed in sites other than exchange ones as shown by zeta-potential experiments. The IR spectra of the intercalated complex showed no major alterations of the complex during adsorption and a stabilization effect and enhancement of the parallel orientation of the clay plates. X-Ray diffraction (XRD) measurements at low angles showed that the pillared clay possesses an inter-layer distance of 13.4 A at 500 °C. Its BET surface area reaches a maximum of 220 m2 g–1 at this temperature. The as plots showed a maximum microporosity at ⩽2 mmol g–1. Additional loading results in transformation to a mesoporous delaminated structure. X-Ray photoelectron spectra (XPS) of the composite materials showed that the ratios La/Si and Ni/Si are lower than those determined by chemical analysis, owing to the shielded environment of the LaNiOx pillars in the clay. The same method indicated that for a high degree of loading the aggregates seem to be of perovskite origin.

Interaction pathway of chloride ions with γ-Al2O3: surface acidity and thermal stability of the Cl/γ-Al2O3 system

Abstract: The promoting effect of adsorbed chlorine ions (Cl–) on the surface acidity of γ-Al2O3 has been monitored by zero point charge (z.p.c) and catalytic activity measurements in cyclohexene isomerization. A progressive decrease of the z.p.c. values (7.8–4.8) with increasing extent of chloride adsorption (0–1.77 wt. %) has been found. A linear relationship between catalytic activity and z.p.c. is discussed. The thermal stability (300 ⩽T/°C ⩽ 500) of the Cl/γ-Al2O3 system has been investigated by dechlorination tests and surface area measurements. The fundamental role of the surface dehydroxylation in the mechanism of chloride loss and BET surface area decay is pointed out. The kinetics of the chloride loss are well described by a first-order reaction rate (d[Cl]surf/dt=–kT[Cl]surf). Steam markedly enhances the dechlorination rate without altering the activation energy of the process (Ea= 6.2 kcal mol–1).

Molded bodies comprised of macroporous ion exchange resins, and use of said bodies

Abstract: Molded bodies in the form of packing bodies comprising a macroporous strongly acid or basic ion exchange resin having a voids fraction of 5-95 vol % of the macro shape without pores, a BET surface area of 0.1-1,000 sq m/g, and an ion exchange capacity of 0.05-10 meq/g.

Thermally stable chromium-exchanged zeolites and method of making same

Abstract: Thermally stable Cr-zeolites and Cu-Cr-zeolites, and methods of making same are disclosed. The zeolites have a SiO 2 to Al 2 O 3 mole ratio of about 3 to about 200, and an initial alkali content of less than about about 0.5% by weight based on the alkali oxide. Chromium ions are exchanged into the zeolite to produce Cr-zeolite in which the Cr level is greater than about 0.5% by weight. Copper and chromium ions are provided exchanged on a zeolite to produce Cu-Cr-zeolite. The respective Cr-exchanged zeolites are heat-treated to produce the thermally stable zeolites wherein the BET surface area upon exposure to temperatures of up to about 1000° C. is at least about 50% of the BET surface area of the respective thermally stable zeolites at about room temperature, prior to the exposure to temperatures of up to about 1000° C.

Gas-phase adsorption characteristics of high-surface area carbons activated from meso-carbon micro-beads

Abstract: Gas-phase adsorption characteristics of three active carbons, differing in BET surface area, was investigated by measuring the adsorption isotherms of methane, carbon dioxide, and ethane at 273.15, 298.15, and 323.15 K up to 1200 kPa. Among active carbons M-20, M-30, and M-38, having approximately 2000, 3000 and 3800 m2/g BET surface areas respectively, carbon M-30 adsorbs the largest amount of methane and carbon dioxide, while carbon M-38 adsorbs the most ethane at elevated pressure, in a slightly stepwise manner. These adsorption characteristics were explained by the pore-size distribution data (0.4–0.5 nm for M-20 and M-30; 0.5–0.7 nm for M-38) and analysis by use of an isotherm equation. Mixed-gas adsorption data are obtained for two binary gases, methane + ethane and carbon dioxide + ethane, on M-38 at 298.15 K and 500 kPa, which are correlated by the ideal adsorbed solution theory.

Adsorption and reaction of trichlorofluoromethane on various particles

Abstract: As a possible tropospheric sink of trichlorofluoromethane (CCl3F), its adsorption and reaction on solid particles were studied with or without UV light longer than 310 nm. The adsorption and photodesorption occurred for most of the particles examined. The amounts depended not only on the BET surface area but also on the chemical property of the particles. The reaction rates were less than 0.1% h-1. The surface induced degradation of CCl3F in air was confirmed under photoirradiation at room temperature by the detection of Cl- or F- on some metal oxides. When the particles were pretreated with heat and evacuation, the reaction rate became larger and disproportionation of CCl3F took place. The tropospheric lifetime of CCl3F was reevaluated based on a reported model. It is suggested that the heterogeneous reaction of CCl3F on particles may be a possible tropospheric sink.

Method for producing a particulate zeolite and a particulate zeolite produced thereby

Abstract: Finely particulate Zeolites of the ZSM-5 family, exhibiting characteristic peaks in an X-ray powder diffraction pattern, are stably produced by a novel method in which a nucleating slurry containing semicrystalline zeolite having a BET surface area of 100 to less than 250 m²/g is mixed with a raw material mixture of silica, alumina and alkali metal sources to obtain a preliminary slurry, followed by heating to obtain a first precursory slurry mixture containing a precursory zeolite having a BET surface area of 100 to 200 m²/g, and subsequently the first precursory slurry mixture is mixed with a raw material mixture as mentioned above to obtain a second precursory slurry, followed by heating to obtain a product slurry containing a finely particulate zeolite having a BET surface area of at least 250 m²/g. In the method, the first precursory slurry mixture can be advantageously recycled and used as a nucleating slurry. The zeolites are advantageously utilized as catalysts, for example, as a catalyst for hydration of olefins, and also as an adsorbent, a molecular sieve, an agent for soil improvement, a filler for paper and an agent for waste water treatment.

Analysis of the Powder Composite Process by a Mechanical Method

Abstract: Recently, composite particles covered with different kinds of fine particles have been fabricated by several types mechanical methods in a dry phase. However, the quantitative analysis of the composite process has not yet been conducted systematically.In this paper, a mechanical processing method called MECHANOFUSION was used to investigate the composite process with glass beads and titanium dioxide fine particles. As the first trial, the ratio of fine particles fixed onto core particles and the BET surface area of the composite particles obtatined were measured with processing time.As a result, the composite process was described by the following two steps: The first is an adhering step for fine particles onto core particles surface, and the second is a compacting step for fine particle layers.Furthermore, it was found that the BET surface area of the processed powder was correlated with the energy consumption per weight of material in the apparatus.

Photocatalytic Hydrogen Evolution from Aqueous Methanol Solution on Niobic Acid

Abstract: Niobic acid powders, H3NbO4 and H8Nb6O19, obtained by hydrolysis from aqueous potassium niobate (K3NbO4 and K8Nb6O19) solutions with sulfuric acid showed a high photocatalytic activity for hydrogen evolution from an aqueous solution including methanol as a sacrificial reagent without supporting any other materials, such as Pt (quantum yield; ca. 10% at 330 nm). The activity depended on the calcination temperature. H3NbO4 powder dried at 380 K was the most active one. As the calcination temperature was increased, the H3NbO4 photocatalyst was transformed into HNbO3 (or Nb2O5·H2O) and Nb2O5 by dehydration. The BET surface area and the band gap of the powder decreased with the phase transformation. It is concluded that both the surface area and hydrated state strongly affect the activity for sacrificial hydrogen evolution on the niobic acid photocatalysts.

Synthesis and Pyrolysis Chemistry of Polymeric Precursors to SiC and Si3N4

Abstract: A commercial vinylic polysilane has been used to obtain both SiC and Si3N4 by pyrolysis in N2 and NH3 , respectively. The polymer-to-ceramic conversion process was studied by GPC, TGA/DTA, elemental analyses, FTIR, solid state NMR (1H, 13C and 29Si), XRD, BET surface area measurements, and analysis of the gaseous decomposition products, providing a detailed picture of the cross-linking process and the evolution of the ceramic products.

Characterization studies of plasma-sprayed cobalt and iron catalysts

Abstract: Tube-wall reactor surfaces were prepared by plasma-spraying five catalysts, namely, Fe, 75Fe/25Co, 50Fe/50Co, 25Fe /75Co, and Co (weight percent basis), and the catalyst surface was characterized for the first time by using BET surface area measurements, chemisorption measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). It was interesting to observe that despite the low BET surface areas for plasma-sprayed catalysts, the hydrogen and carbon monoxide uptakes were found to be quite high. XRD studies showed that the various catalyst phases present on the surface were stable up to 350°C and also that the surface consists of three types of particles, namely Fe and Co oxides and cemented particles of CoO.Fe 2 O 3 . The SEM studies confirmed that these particles were uniformly distributed throughout the catalyst layer. The crystallite sizes determined from hydrogen chemisorption measurements are fairly close to those obtained from X-ray line-broadening experiments. EPMA measurements show that, usually, the plasma-sprayed-catalyst surface possessed a higher concentration of iron particles than cobalt particles, suggesting that iron tends to migrate to the surface at the expense of cobalt

Indium oxide powder and production of ito sintered body

Abstract: PURPOSE: To obtain indium oxide powder from which the high-density ITO sintered body is obtainable by atm. sintering by forming this powder into a fine and highly dispersed state specified in BET surface area, ratio between a BET diameter and a crystallite diameter and a primary particle size. CONSTITUTION: The acicular indium hydroxide obtd. by adjusting the pH of a liquid mixture composed of an aq. In salt soln. and an aq. alkaline soln. to ≥7, then subjecting the mixture to maturing, filtering and drying treatments is calcined. The indium oxide powder product having 15 to 30m 2 /g BET surface area (A), ≤2 ratio (R) between the BET diameter and the crystallite diameter and ≤0.1μm average particle size (D) of the primary particle determined from a grain size distribution is obtd. The particles aggregate at area A 30m 2 /g. Either case, the high-density ITO sintered body is not yielded. The cohesion of the primary particles is strong, sintering activity degrades and the high-density sintered body is hardly yielded at ratio R>2. The primary particles aggregate and the high-density sintered body is hardly yielded at 0.1μm diameter D. COPYRIGHT: (C)1993,JPO&Japio

Relation Between the Conditions of Preparation and the Polarization Characteristics of Spongy Raney Nickel Electrodes Used as Anodes for Fuel Cells

Abstract: This paper reports on Spongy Raney nickel electrodes that were prepared from substrates of spongy nickel plate coated with aluminum. Influences of the temperature for alloying and the weight ratio of aluminum to nickel (Al/Ni) in the substrate on polarization characteristics were studied in connection with the alloy compositions formed, and the surface microstructure of the catalysts. For this, the ratio Al/Ni in the substrate was varied ranging from 0.1 to 2.5. Electrode performance was improved, with increases in both the temperature for alloying and the Al/Ni ratio of the substrates. However, the higher the temperature used for alloying, the lower were the effects of the Al/Ni ratio. The activated Raney nickel was prepared from an alloy whose components were NiAl{sub 3} and/or Ni{sub 2}Al{sub 3}. It was also shown that a good polarization performance resulted from the increase in activated nickel grains, which were observed by scanning electron microscopy, and in increase in the Brunauer, Emmett, and Teller (BET) surface area of the electrode-catalyst. The broad peaks observed in x-ray diffraction of Raney nickel catalysts implied crystal distortions, which should be closely related to an increase in the BET surface area.

Combustion Synthesis of Sr-Substituted LaCo0.4Fe0.6O3 Powders

Abstract: Sr-substituted perovskite LaCo0.4Fe0.6O3 is known to have excellent mixed ionic and electronic conductivity and increased O2 sorption characteristics. These perovskites are usually prepared by lengthy solid-state reactions of the component oxides at temperatures near 1150°C, and often produce inhomogeneous, multi-phase powders. Presently, it has been prepared by the calcination of combustion-derived fine mixed oxides at 850°C in 6 hrs. Combustion reactions are carried out using precursor solutions containing the corresponding metal nitrates (oxidizers) and glycine (fuel) at 250°C. The metal oxides produced by this process and subsequent calcination were characterized by XRD, TEM and BET surface area analysis.