Showing papers on "BET theory published in 1997"
TL;DR: In this article, an exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction.
Abstract: Titanium(IV) oxide (TiO2) powders of various amorphous−anatase compositions were prepared by heat treatment (573−1073 K) of amorphous TiO2 in air and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and BET surface area measurements. An exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction of amorphous phase. The fraction of anatase crystallites (f(anatase)) was calculated as the remainder after the amorphous phase and contaminated water or organic residue. The XRD data showed that the size of anatase crystallites was slightly decreased but almost constant along with the increase in f(anatase), being consistent with the small change in the BET surface area. These results suggest that each amorphous particle transforms into an anatase crystallite of similar size without sintering or crystal growth. The particles of mixture of amorphous and anatase were ...
782 citations
TL;DR: In this article, a high surface area (over 3000 m 2 g −1 ) active carbon (MAXSORB) was developed from a mixture of petroleum coke and an excess amount of potassium hydroxide.
342 citations
TL;DR: The mesopore distribution remains within the low-size range even at high impregnation ratios (up to 2.3), where the highest contribution of mesoporosity was observed as discussed by the authors.
Abstract: Chemical activation of kraft lignin with ZnCl2 allows one to obtain high surface area activated carbons with a predominantly microporous structure. Most of porosity develops within the thermal range of 400−500 °C, where an increase of temperature leads to increasing micropore volume values (up to ≈1 cm3/g) and a wider distribution of micropore size. An increasing mesoporositiy is also observed. Increasing the impregnation ratio (ZnCl2/lignin, wt) has a similar effect on the evolution of the porous structure. The mesopore distribution remains within the low-size range even at high impregnation ratios (up to 2.3). At 500 °C and an impregnation ratio of 2.3, where the highest contribution of mesoporosity was observed, the mesopore volume reached a value of 0.59 cm3/g. These conditions allowed us to obtain a BET surface area of 1800 m2/g, including the external or non-microporous surface of 200 m2/g. The porous structure developed suggests a fairly homogeneous distribution of the activating agent favored by t...
143 citations
TL;DR: In this article, the feasibility of producing activated carbons from agricultural waste corn cobs was investigated by using zinc chloride (ZnCl 2 ) as a chemical activation with zinc chloride.
137 citations
TL;DR: In this article, a high surface area titania−silica binary oxide support was prepared according to the homogeneous precipitation method and was coated with a monolayer of vanadium oxide.
Abstract: A high surface area titania−silica binary oxide support was prepared according to the homogeneous precipitation method and was coated with a monolayer of vanadium oxide. The TiO2−SiO2 support and the V2O5/TiO2−SiO2 catalyst were then subjected to thermal treatments from 773 to 1073 K. The influence of heat treatments on the dispersion and thermal stability was investigated by X-ray diffraction, FT infrared, X-ray photoelectron spectroscopy, oxygen uptake, and BET surface area methods. The results suggest that TiO2−SiO2 is quite thermally stable even up to 1073 K calcination temperature. However, the V2O5/TiO2−SiO2 catalyst is stable, in terms of dispersion and surface area, only up to a calcination temperature of 873 K. Thermal treatments beyond this temperature transformed vanadia and titania into crystalline phases and then titania anatase into rutile phase.
127 citations
TL;DR: In this paper, the thermal and hydrothermal stability of MCM-41 with a Si/M molar ratio of 40 (M = Al, Ti) was assessed, and the pore structure of Si-MCM-1 and Al-MCm1 collapsed at a calcination temperature of above 800°C.
123 citations
TL;DR: In this article, it was shown that carbon aerogels derived from these RF-aerogels have a small mesopore surface area, however an especially large micropore area.
Abstract: Due to their large specific surface area and their high electrical conductivity carbon aerogels are promising materials for electrodes in electrochemical double-layer capacitors (“supercapacitor”). The carbon aerogels were made via pyrolysis of resorcinol formaldehyde aerogels. The latter were prepared by supercritical and subcritical drying as well. The important findings of our investigation were, that the highest capacities of 46 F/cm3 were measured for samples with a density of about 800 kg/m3 pyrolyzed at 800°C. Also it was shown that RF-gels with molar resorcinol/catalyst ratios ≥1000 or higher can be dried subcritically without cracking or significant shrinkage. Carbon aerogels derived from these RF-aerogels have a small mesopore surface area, however an especially large micropore area. They provide electrical capacities which are most suitable for their use in supercapacitors.
118 citations
TL;DR: In this article, a Pd{sub 25}Zr{sub 75} glassy metal alloy has been activated by controlled oxidation in air, resulting in highly active catalysts for the catalytic, combustion of methane.
104 citations
TL;DR: In this article, a sonochemical reduction of an aqueous solution containing ammonium dichromate [(NH4)2Cr2O7] and potassium permanganate (KMnO4), respectively, was used to obtain nanosized ultrafine powders of manganese oxide and chromium oxide.
Abstract: Ultrafine powders of chromium oxide (Cr2O3) and manganese oxide (Mn2O3) have been prepared at room temperature by the sonochemical reduction of an aqueous solution containing ammonium dichromate [(NH4)2Cr2O7] and potassium permanganate (KMnO4), respectively. The yield of the sonochemical reduction has been enhanced by raising the reaction temperature or by using an aqueous solution of ethanol (0.1 M). The solid oxide residue formed on insonation has been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), differential scanning calorimetry (DSC), elemental analysis, electron microscopy (TEM, SEM/EDX), powder density, particle size (adsorption and microscopy), and BET surface area measurements. The powders are nanosized (50−200 nm), and the surface area varies from 35 to 48 m2/g. The as-formed X-ray amorphous Mn2O3 and Cr2O3 powders were converted into crystalline form by heating them at 600 and 900 K, for 4 h, respectively.
86 citations
Patent•
25 Apr 1997
TL;DR: In this paper, a process for sizing (i.e., comminuting) a tantalum powder including agglomerates of smaller particles is described, which yields tantalum powders having an as-comminuted agglerate size distribution with the product of the Volume Mean Diameter, MV (in microns as measured by light scattering techniques such as Microtrac analysis), times specific surface area, being less than about 25.
Abstract: A process for sizing (i.e., comminuting) a tantalum powder including agglomerates of smaller particles, which process yields a tantalum powder having an as-comminuted agglomerate size distribution with the product of the Volume Mean Diameter, MV (in microns as measured by light scattering techniques such as Microtrac analysis), times specific surface area BET (m2/g), being less than about 25. These powders after sizing typically have ratios of Scott Bulk Density: BET Surface Area in the range from about 20 to about 35. Also provided are powders having a substantially unimodal and narrow agglomerate size distribution in all stages of production, namely after sizing (i.e., deagglomeration by comminution), thermal agglomeration (i.e., heat treatment), and deoxidation. These resultant powders have high surface area and good flowability properties and, upon sintering, exhibit controlled shrinkage with high porosity. Further provided are sized heat treated tantalum powders having agglomerate particle sizes wherein the product of the Volume Mean Diameter, MV, times the specific surface area, BET, is in the range from about 90 to about 250. Sized and agglomerated powders which are deoxidized are also provided wherein the product of the Volume Mean Diameter, MV, times the specific surface area, BET, is in the range from about 90 to about 250.
86 citations
TL;DR: In this article, the performance of activated carbon fibers (ACF) was characterized by scanning electronic microscopy and the surface areas and pore volumes were determined, showing that ACF is significantly higher than granular activated carbon (GAC) in terms of adsorption velocity and selectivity for micropollutants.
Abstract: The adsorption of polluted waters is performed by activated carbon fibers (ACF). This new material is characterized by scanning electronic microscopy. BET surface areas and pore volumes are determined. Adsorption of natural organics (humic substances) and micropollutants (aromatic compounds such as benzene and toluene) is carried out in a batch or dynamic reactor. Classical models are applied and kinetic constants calculated. The results show that the performance of ACF is significantly higher than that of granular activated carbon (GAC) in terms of adsorption velocity and selectivity for micropollutants. These higher performances are due to some ACF physical properties, such as their high BET surface area and micropore volume. Moreover, the micropores are directly connected on the external surface area of fibers, which allows smaller mass transfer resistance. In a dynamic reactor, the breakthrough curves obtained with ACF beds are particularly steep, suggesting a smaller mass transfer resistance than tha...
TL;DR: In this article, an amorphous carbon-activated palladium metallic clusters have been prepared at room temperature by ultrasound irradiation of an organometallic precursor, tris-μ-[dibenzylideneacetone]dipalladium [(φ-CHCH−CO−CHCH-φ)3Pd2] in mesitylene.
Abstract: Nanostructured particles of amorphous carbon-activated palladium metallic clusters have been prepared (in situ) at room temperature by ultrasound irradiation of an organometallic precursor, tris-μ-[dibenzylideneacetone]dipalladium [(φ-CHCH−CO−CHCH-φ)3Pd2] in mesitylene. Characterization by elemental analysis, transmission electron microscopy, differential scanning calorimetry, X-ray diffraction, X-ray photoelectron spectroscopy, and BET surface area measurements shows that the product powder consists of nanosize particles, agglomerated in clusters of approximately 800 A. Each particle is found to have a metallic core, covered by a carbonic shell that plays an important role in the stability of the nanoparticles. The catalytic activity in a Heck reaction, in the absence of phosphine ligands, has been demonstrated.
TL;DR: In this paper, surface data for the Cu system suggest the presence of CuCO3 and Cu(OH)2 on the surface whereas Mo is deposited throughout the bulk of the Mo-loaded activated carbon systems.
Abstract: Diffuse reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning Auger microscopy, elemental analyses, BET surface area, and thermogravimetric analyses have been used to study metals and adsorbed organics on the surface of metal-loaded activated carbon materials. Metals such as copper, zinc, and molybdenum have been deposited on activated carbon via incipient wetness methods. Studies of ground and unground samples show that the organic functional groups such as OH, CH2, CH3, CO, C−O, C−O−C, and CH are exclusively found on the exterior of the metal loaded samples and not in the bulk. Surface studies show that Cu and Zn deposits are on the surface whereas Mo is deposited throughout the bulk of the Mo-loaded activated carbon systems. Surface data for the Cu system suggest the presence of CuCO3 and Cu(OH)2. The Zn species appears to be Zn2+ on the basis of XPS and SAM data. Mo appears to be oxidized, but a specific oxidation state and the oxidic species are not yet able ...
TL;DR: In this article, the pyrolysis of siloxane polymers at a maximum temperature of 1000 °C was used to prepare silicon oxycarbides, which contained some graphene sheets.
Abstract: We have prepared silicon oxycarbides by the pyrolysis of siloxane polymers at a maximum temperature of 1000 °C. The resulting silicon oxycarbides are networked glasses which we believe also contain some graphene sheets. After washing in a dilute solution of hydrofluoric acid for times between 2 min and 24 h, these materials lost, at most, 40% of their mass. Powder X-ray diffraction (XRD), small-angle scattering (SAX), BET surface area measurements, elemental analysis, and silicon K-edge X-ray absorption spectroscopy (XAS) were used to determine the physical structure of the bulk material and the local chemical environments of the Si atoms. It was found that a microscopic pore network was created in the material upon HF washing. The number of pores, but not their size, increased with HF washing time. The HF etching revealed a passivating layer, which we believe consists mainly of silicon and carbon, that prevented further etching of the material. The electrochemical behavior of these materials in Li batter...
TL;DR: In this article, the effect of process parameters such as reaction time, fluidizing velocity, particle size, static bed height, temperature of activation, fluidization medium, and solid raw material on activation is studied.
Abstract: Activated carbon is produced from coconut shell char using steam or carbon dioxide as the reacting gas in a 100 mm diameter fluidized bed reactor. The effect of process parameters such as reaction time, fluidizing velocity, particle size, static bed height, temperature of activation, fluidizing medium, and solid raw material on activation is studied. The product is characterized by determination of iodine number and BET surface area. The product obtained in the fluidized bed reactor is much superior in quality to the activated carbons produced by conventional processes. Based on the experimental observations, the optimum values of process parameters are identified.
TL;DR: It was found that polycondensation sets on immediately after mixing the reagents, with a continuous increase of the fraction of 4-connected silicate tetrahedra (Q4) at the expense of Q1 and Q2.
TL;DR: In this paper, the authors showed that the titania phase is responsible for the increase in surface area of the oxide coating, and demonstrated a novel preparation method using titanium bis-ammonium lactato dihydroxide (TALH), a water soluble precursor.
Abstract: Control of the hydrolysis and condensation of soluble precursors of titanium is shown to yield oxide coatings of well-defined morphology A ``smooth'' coating, consisting of patches of titania on silica, causes only a small increase in the surface area, from 130 m2/g for the uncoated silica gel to 154 m2/g On the other hand, the ``rough'' coating, which consists of 3 nm diameter titania particles dispersed over the silica surface, results in an increase in the BET surface area to 350 m2/g The specific titania surface area was determined via isopropanol dehydration activity and was found to be comparable to the BET surface area indicating that the titania phase is responsible for the increase in surface area Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) provide definitive evidence for the coating morphology while X-ray photoelectron spectroscopy (XPS) was used to determine the dispersion of the titania The supported titania maintains its surface area upon calcination at temperatures up to 873 K while unsupported titania looses much of its surface area Also demonstrated in this work is a novel preparation method using titanium bis-ammonium lactato dihydroxide (TALH), a water soluble precursor
TL;DR: A series of V-doped titania-pillared clay catalysts, characterized by ICP-AES chemical analysis, X-ray diffraction, BET surface area measurement, and ESR spectroscopy, have been tested in the selective catalytic reduction of NO by NH 3.
Abstract: A series of V-doped titania-pillared clay catalysts, characterized by ICP-AES chemical analysis, X-ray diffraction, BET surface area measurement, and ESR spectroscopy, have been tested in the selective catalytic reduction of NO by NH 3 . An ESR analysis shows that V dopant is anchored to the titania pillars. Vanadyl species with differing degrees of in-plane V-O pi -covalent bonding are produced depending on the method of sample preparation. Polymeric V species appear as the V content is increased. Catalytic performance of these systems depends on the method of preparation and on the V content. The best catalyst, converting 90-100% NO in the temperature range 523-623 K, is obtained by exchange of pillared montmorillonite with vanadyl ions, at an extent of exchange below the level where significant amounts of polymeric V species appear. The co-pillared catalyst, containing vanadyl centres characterized by a higher degree of in-plane pi -covalent bonding (according to ESR), is less selective than the exchanged samples.
TL;DR: In this article, the SO2 adsorption behaviors of activated carbons produced from Illinois coal and of commercially prepared activated carbon fibers (ACFs) were compared, and it was shown that higher surface area ACFs had wider pores and adsorbed less SO2.
Abstract: The SO2 adsorption behaviors of activated carbons produced from Illinois coal and of commercially prepared activated carbon fibers (ACFs) were compared. There was no relation between surface area of coal-based carbons and SO2 adsorption, whereas adsorption of SO2 on the series of ACFs was inversely proportional to N2 BET surface area. Higher surface area ACFs had wider pores and adsorbed less SO2; thus, pore size distribution is thought to play a significant role in SO2 adsorption for these materials. Oxidation with HNO3 and/or H2SO4, followed by heat treatment at 700−925 °C to remove carbon−oxygen complexes, resulted in increased SO2 adsorption for both coal chars and ACFs. This behavior was explained by an increase in the available number of free sites, previously occupied by oxygen and now available for SO2 adsorption. The use of nitrogen-containing functional groups on ACFs of proper pore size shows promise for further increasing SO2 adsorption capacities. Knowledge of the relationship among the numbe...
TL;DR: In this article, an Illinois Basin bituminous coal (IBC-106) was produced by a three-step process: oxidation of the coal in air at 150-250 °C for 2-40 hours, devolatilization of these oxidized coals in nitrogen at 500-730 °C, and activation (gasification) of the chars in 45% steam, 4% oxygen in nitrogen, at 730-880 °C.
TL;DR: In this paper, heat treatment of chromia-pillared clay under the conditions applied did not drastically change the pore structure or the chromium oxidation state and the distribution of pillars, but strongly influenced its aggregate morphology.
Journal Article•
TL;DR: In this article, a two-stage transferred-arc plasma reactor using NH 3 and Al vapor as reactants was used to synthesize nanosize aluminum nitride particles, which were quantitatively analyzed using X-ray diffraction analysis.
Abstract: Nanosize aluminum nitride particles were synthesized from the vapor phase in a two-stage transferred-arc plasma reactor using NH 3 and Al vapor as reactants. The powders were quantitatively analyzed using X-ray diffraction analysis. Samples for which complete conversion was achieved were characterized by dynamic light scattering (particle size and size distribution), BET analysis for specific surface area, scanning electron microscope, atomic force microscope (morphology), X-ray diffraction (crystal structure and particle size), and Fourier transform infrared (chemical bonds). White aluminum nitride powder with spheroidal shape and with hexagonal crystal structure was produced. The mean particle size was approximately 20 nm. The specific surface area varied from 80 to 100 m 2 /g. FTIR analysis indicated the presence of O-H bonds.
TL;DR: In this article, a two-stage method used a stirred tank reactor followed by a recirculating flow fixed-bed reactor was developed to coat anthracite and sand filter media with synthetic manganese oxides.
Abstract: A method was developed to coat anthracite and sand filter media with synthetic manganese oxides. The two-stage method used a stirred tank reactor followed by a recirculating flow fixed-bed reactor. Treated anthracite developed encapsulating coatings of manganese oxides up to 30-μm thick, at loadings over 4 mg/g−1 extractable Mn2+. Media were characterized by BET surface area analysis and electron microscopy. Laboratory-scale column tests confirmed the efficient Mn-removal capability of the synthetically coated media in adsorption and oxidation modes. This method may help improve the removal of Mn2+ from drinking water and hazardous effluents by filtration with oxide-coated media.
TL;DR: In this article, the influence of calcination and reduction conditions, the metal-incorporation technique, and metal loading on the hydroisomerization of n-butane over bifunctional Pt/HZSM-5 catalysts was studied.
Abstract: The influence of calcination and reduction conditions, the metal-incorporation technique, and metal loading on the hydroisomerization of n-butane over bifunctional Pt/HZSM-5 catalysts was studied. Temperature-programmed desorption of ammonia (TPDA), atomic absorption spectroscopy (AA), BET surface area/pore size distributions, chemisorption measurements, temperature-programmed reduction (TPR), and transmission electron microscopy (TEM) techniques were used to characterize the catalysts. The calcination conditions have a significative influence on ion-exchanged catalysts, as they control the final metal distribution. The reduction conditions and the method used for platinum incorporation were found to be important factors that affected both the activity and selectivity of the catalysts. Thus, the highest selectivity to isobutane was achieved over an ion-exchanged catalyst.
TL;DR: In this article, the characteristics and structure of several silica-supported nickel systems, prepared by impregnation and precipitation-deposition and in a wide range of nickel contents (from 0.58 up to 69 wt% Ni), have been studied.
Abstract: The characteristics and structure of several silica-supported nickel systems, prepared by impregnation and precipitation-deposition and in a wide range of nickel contents (from 0.58 up to 69 wt% Ni), have been studied. Using mainly conventional sorption techniques the textural properties - BET surface area, pore volume, average pore radius, pore size distribution - and surface chemical distribution - nickel surface area, reduction degree, dispersion, crystallite particle diameter - of the samples have been determined. All these characteristics have been related to each other and globally analyzed to advance in the understanding of the final structure of the catalysts and its relationship with support structure, preparation procedure and nickel content.
TL;DR: In this paper, a carbon fiber-based adsorbent material has been used for the separation of CO 2 from a model gas and enhanced desorption is achieved using an electrical current passed through the material at low voltage.
TL;DR: In this article, the pore size distributions referred to volume, surface and number of bulk pores, along with the internal surface area and the size parameters of surface pores are determined for two polyethersulphonic microporous composite membranes of nominal MWCO of 4000 and 30 000 Da.
TL;DR: In this paper, a Pd/titania catalyst was used for NO reduction using CH4 as a reducing agent and the results obtained from the reaction experiments, together with the findings from the characterization studies, are used to explain the mechanistic aspects of this reaction.
TL;DR: In this article, a linear correlation was found between specific surface area (SA) and catalytic activity derived from literature cumene cracking data, and a close interrelation was revealed between SA, the average crystallite size (Dav), and the sulfate level (e.g., wt % SO4) by applying a simple geometric model.
Abstract: Sulfated metal oxides (SMO's) were prepared by thermal decomposition of metal sulfate salts at various temperatures in an attempt to relate their physicochemical properties with the decomposition temperature and the resultant catalytic activity. Work centered on SMO's of Ti, Zr, Fe, Sn, and Al, which have been claimed in the literature to possess superacidity. In all cases, the BET surface area (SA) passed through a maximum as a function of sulfate decomposition temperature. Up to that maximum, a linear correlation was found in the case of Ti and Zr between SA and catalytic activity derived from literature cumene cracking data. Above the maximum, a close interrelation was revealed between SA, the average crystallite size (Dav), and the sulfate level (e.g., wt % SO4) by applying a simple, straightforward geometric model. From the specific surface area (SSA), i.e., surface area occupied by a single sulfate species, two saturated surface states of the sulfate have been found: a dilute state corresponding to...
TL;DR: In this paper, the deoiled clays were regenerated by acid and heat treatments and the surface areas and pore volumes increased after heat treatment, which indicated an increase in mesopores with radii of between 25 and 100 A.
Abstract: Samples of spent bleaching clay were deoiled by hexane, methanol, hexane-methanol, and supercritical CO2 extractions. The deoiled clays were regenerated by acid and heat treatments. Nitrogen adsorption isotherms for these samples are type IV with hysteresis loops corresponding to type H3, indicating slit-shaped pores. Used deoiled and dried samples have smaller surface areas and pore volumes than unused clay. The surface areas and pore volumes increased after heat treatment. Acidified heat-treated deoiled samples have smaller surface areas and greater pore volumes than unused clay, except for the methanol-deoiled sample. Thus, heat and acid treatments removed substances adsorbed in the pores that were not removed by solvents or CO2 extraction. This was confirmed from the ratios of the cumulative surface area/BET surface area, as well as analysis of the pore size distributions, which indicated an increase in mesopores with radii of between 25 and 100 A. The t-plots showed that smaller pores with sizes between 7 and 25 A, present originally in the unused clays, were closed by heat treatment. These pores were absent in the deoiled and the heat-treated samples except for the heat-treated sample that was deoiled by hexane followed by methanol. Smaller pores, accompanied by an increase in surface area, were also observed for all deoiled samples after acid and heat treatments.