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03269 Mechanism of the carbon catalysed reduction of nitrobenzene by hydrazine
04 By-products related to fuels Intercalation of Ni atoms under a two-dimensional graphene film (ZDGF) on (111) Ir was studied in ultra high vacuum using high-resolution Auger spectroscopy. Ni atoms were shown to be intercalated effectively at 900 to 1500 K, and a polylayer nickel film was shown to grow under the 2DGF. A relationship between a proportion n of Ni atoms intercalated under 2DGF and temperature, was determined and it was shown that ti decreases from -30% at 900 K to ~3% at 1500 K.
possible to determine the probable identity of the acid sites present on a given carbon. Collective consideration of the data from all techniques suggests that ammonia pretreatments create a surface whose chemistry is completely different from that of the original carbon. Not only are new acidic sites created, but a high concentration of basic sites are introduced as well. Thus, the final surface is clearly amphoteric, to an extent which is largely dictated by the pretreament temperature.
Investigation of bond strength and failure mode 00103268 between Sic-coated mesophase ribbon fiber and an epoxy matrix Harwell, M. G. er al. Carbon, 2000, 38, (8), 1111~1121. The use of mesophase pitch-based carbon fibres in composite materials has been limited by their poor oxidation resistance at high temperatures. Ribbon-shaped mesophase fibres with excellent axial thermal conductivity were spun at Clemson University and coated with SIC at the University of Erlangen-Niirnberg using chemical vapour deposition (CVD) in an effort to protect them from high-temperature oxidation. Using the microbond technique with a newly developed microfixture to apply an axisymmetric load to each specimen, the failure modes and interfacial shear stress (IFSS) were investigated for untreated ribbon fibres and ribbon fibres with 0.75 pm and 1.2 pm thick SIC coatings. For microbond testing, an Epon” 828-based epoxy was used as a model thermoset matrix material. The three distinct failure modes found for Sic-coated fibres included microdrop debonding, fibre breakage, and coating failure. The uncoated fibres exhibited the debonding failure mode for approximately 90% of the samples. However, the fibres with a 0.75 pm thick coating exhibited all three failure modes with uniform frequency, while the fibres with a 1.2 pm thick coating exhibited coating failure for 70% of the samples. The SIC coating was found to increase the IFSS by approximately 40%. However, the coating thickness had no effect on the increase of the IFSS.
00103272 Modeling of nitrogen oxide release in coal combustion Repic, B. S. er ul. J. Eng. P/r,r.~. Thermophys., 1999, 72, (I), 18-23. A calculation model for the chemical thermodynamic equilibrium of compounds and elements contained in coal and in the air required for combustion is described. The results can be used in coal combustion to evaluate the possibihty of decreasing the NO, release in the process., release, release from coal combustion
Mechanism of the carbon catalysed reduction of 00103269 nitrobenzene by hydrazine Larsen, J. W. et al. Carbon, 2000, 38, (5), 6555661. The reduction of nitroaromatics to anilines by hydrazine is catalysed by carbons. The carbon serves as an adsorbent and electrical conductor to enable the reaction to occur. Hydrazine is a two-electron reducing agent as shown by trapping the diimide intermediate with norbornene. The nitrobenzene reduction is a four-electron process proceeding first to phenylhydroxylamine, which was observed in low concentrations in the reacting system by NMR. Phenylhydroxylamine is reduced to aniline in a second step. The two-electron intermediate, nitrosobenzene, gave different products than nitrobenzene under the reaction conditions and could not be trapped, supporting the expected four-electron pathway. By serving as an adsorbent and collecting hydrazine on their surfaces, carbons make it possible to execute a four-electron reduction using a two-electron reducing agent. This role of carbon was confirmed by successfully operating an emf cell using graphite or carbon paste electrodes immersed in solutions of hydrazine and nitrobenzene. The initial rates of reduction of substituted nitrobenzenes showed only a tiny substituent effect and proceed at nearly the same rate as the carbon-catalysed decomposition of hydrazine leading to the conclusion that hydrazine reaction at the carbon surface is the rate determining step.groups 00/03270 Metalloporphyrin-derived carbons: models for investigating NO, release from coal char combustion Jones, J. M. e/ crl. Carbon, 1999, 37, (7), 1123-1131. In order to study NO, release during coal char combustion, nitrogencontaining carbons prepared by the co-carbonization of tetraphenylporphine and acenaphthylene have been used as models. In addition, carbons prepared from metalloporphyrins have been studied in an attempt to examine the role of well-dispersed metal catalysts on nitrogen release during combustion. The nitrogen functionality in some of the carbons was investigated by nitrogen X-ray absorption near-edge structure spectroscopy (XANES), and thermogravimetric analysis-mass spectrometry was used as a means of studying the combustion properties. The nitrogen species present in the carbon are similar to those observed in coals and carbons, and there is some indication of a portion of chelated metal still being present for a lower (873 K) heat-treated carbon prepared from tetraphenylporphine cobalt (II). Even so, the effect of nitrogen functionality on NO emission is secondary to the effect of carbon structure on NO reduction. A model is presented which discusses NO emission in terms of the steady-state surface oxygen concentration on the carbon. In the case of catalysed carbon combustion, the NO reduction reaction is also catalysed. Carbons prepared from these types of metal-containing precursors show larger catalytic effects in combustion than transition metal-impregnated carbons. Microcalorimetric study of acid sites on ammonia00/03271 and acid-pretreated activated carbon Xie, F. e! al. Carbon, 2000, 38, (5) 691-700. This study was designed to determine the value of microcalorimetry as a probe of acidibase sites on carbon surfaces. Calorimetric studies of ammonia adsorption on acid and ammonia pretreated activated carbon (BDH) samples demonstrated that the technique does tttrate acid sites (at equilibrium) according to their relative strengths. However, only in conjunction with other techniques, including Boehm titration, point of zero charge (PZC) and temperature programmed desorption (TPD) is it
368
Fuel and Energy Abstracts
November 2000
00/03273 Nz and COz adsorption on activated carbon fibres prepared from Nomex chars Blanco, M. C. Curbon, 2000, 38, (X), 1177-l 182. Activated carbon fibres were obtained by pyrolysis followed by CO1 activation of Nomex (poly(m-phenylene isophtalamide)] polymeric libres in their crystalline form. The materials obtained were characterized by Nz adsorption (77 K), CO* adsorption (273 K) and XRD. They show BET surface areas up to 1200 m* g , and they are essentially microporous. The pore size distribution is narrower than using Kevlar as precursor. This feature can be related with the degree of crystallinity obtained with the corresponding chars. 00103274 On surface of micropores and fractal dimension of activated carbon determined on the basis of adsorption and SAXS investigations Diduszko, R. Curhon, 2000, 38. (8) 1153-l 162. Granulated commercial activated carbon obtained from hard coal was separated for fractions, by elutriation, in an air stream of constant flow-rate. Three samples of different fall down distances from the outlet tube were demineralized. Benzene adsorption isotherms were determined at 293 K and SAXS measurements were performed for each one. The Dubininlzotova and Dubinin-Stoeckli equations were used for evaluation of micropore structural parameters of examined carbon samples. On the basis of these equations different methods of calculation of geometric surface area were discussed. Obtained results were compared with values evaluated by using the method proposed here. This method comprises results of SAXS and adsorption measurements. Changes of geometric surface area were confirmed by analysis of surface roughness measured by fractal dimension. The values of fractal dimension were obtained by method of calculation on the basis of adsorption data proposed previously by Ehrburger-Dolle and were compared with modification proposed here. This modification is based on well known correlation given by McEnaney. Obtained values of fractal dimension were compared with values determined on the basis of SAXS data. On the characteristics of tar from gasification of 00103275 energy crops Yu, Q. er al. Sum. Comhust. Rrs. Sled., Proc. List Parlicipants, 1999, l81185. Edited by Olsson E. One important parameter for bringing the gasification of biomass for energy generation to commercial viability is the level and composition of the generated tar by-products. This is because condensible tars may cause plugging problems in lines and downstream equipments and also impact the environment. Three kinds of energy crops (reed canary grass; Miscanthus; Salix) were gasified in a pressurized fluidized-bed at 900°C and 0.4 MPa and the tar evolution was monitored. Tar sampling for light compounds were performed using a solid-phase adsorption method (SPA) recently developed in the laboratory. The samples were subsequently analysed by capillary gas chromatography (CCC) with flame ionization detection (FID). Heavy tars were collected by a conventional cold-trapping method (CT) and then determined by gravimetry. The analysis results were compared with those from gasification of birch and coal obtained under similar conditions. Benzene, toluene, naphthalene, acenaphthylene and phenanthrene were the principal constituents of the tar samples that differ mainly in their component distribution and total amount of tar. The total amount of light tar decreased in the following order: Birch > Salix > Reed canary grass > coal > Miscanthus. In contrast, the highest yield of heavy tar components from the three energy crops was obtained from Miscanthus. The new sampling method (SPA) used for light compounds is a key factor for successful tar monitoring since the sampling time has been reduced from one hour for conventional methods based on cold trapping to about one minute. 00103276 Palladium catalysts on activated carbon supports. Influence of reduction temperature, origin of the support and pretreatments of the carbon surface Gurrath, M. et al. Carbon. 2000, 38, (8), 1241-1255. A number of activated carbons produced from peat, coconut shell, and by pyrolysis of hydrocarbons have been subjected to treatment with oxygen, chlorine, hydrogen or ammonia at elevated temperatures to get a representative series of catalyst supports differing in porous structure and surface chemistry (characterized by nitrogen adsorption and selective
possible to determine the probable identity of the acid sites present on a given carbon. Collective consideration of the data from all techniques suggests that ammonia pretreatments create a surface whose chemistry is completely different from that of the original carbon. Not only are new acidic sites created, but a high concentration of basic sites are introduced as well. Thus, the final surface is clearly amphoteric, to an extent which is largely dictated by the pretreament temperature.
Investigation of bond strength and failure mode 00103268 between Sic-coated mesophase ribbon fiber and an epoxy matrix Harwell, M. G. er al. Carbon, 2000, 38, (8), 1111~1121. The use of mesophase pitch-based carbon fibres in composite materials has been limited by their poor oxidation resistance at high temperatures. Ribbon-shaped mesophase fibres with excellent axial thermal conductivity were spun at Clemson University and coated with SIC at the University of Erlangen-Niirnberg using chemical vapour deposition (CVD) in an effort to protect them from high-temperature oxidation. Using the microbond technique with a newly developed microfixture to apply an axisymmetric load to each specimen, the failure modes and interfacial shear stress (IFSS) were investigated for untreated ribbon fibres and ribbon fibres with 0.75 pm and 1.2 pm thick SIC coatings. For microbond testing, an Epon” 828-based epoxy was used as a model thermoset matrix material. The three distinct failure modes found for Sic-coated fibres included microdrop debonding, fibre breakage, and coating failure. The uncoated fibres exhibited the debonding failure mode for approximately 90% of the samples. However, the fibres with a 0.75 pm thick coating exhibited all three failure modes with uniform frequency, while the fibres with a 1.2 pm thick coating exhibited coating failure for 70% of the samples. The SIC coating was found to increase the IFSS by approximately 40%. However, the coating thickness had no effect on the increase of the IFSS.
00103272 Modeling of nitrogen oxide release in coal combustion Repic, B. S. er ul. J. Eng. P/r,r.~. Thermophys., 1999, 72, (I), 18-23. A calculation model for the chemical thermodynamic equilibrium of compounds and elements contained in coal and in the air required for combustion is described. The results can be used in coal combustion to evaluate the possibihty of decreasing the NO, release in the process., release, release from coal combustion
Mechanism of the carbon catalysed reduction of 00103269 nitrobenzene by hydrazine Larsen, J. W. et al. Carbon, 2000, 38, (5), 6555661. The reduction of nitroaromatics to anilines by hydrazine is catalysed by carbons. The carbon serves as an adsorbent and electrical conductor to enable the reaction to occur. Hydrazine is a two-electron reducing agent as shown by trapping the diimide intermediate with norbornene. The nitrobenzene reduction is a four-electron process proceeding first to phenylhydroxylamine, which was observed in low concentrations in the reacting system by NMR. Phenylhydroxylamine is reduced to aniline in a second step. The two-electron intermediate, nitrosobenzene, gave different products than nitrobenzene under the reaction conditions and could not be trapped, supporting the expected four-electron pathway. By serving as an adsorbent and collecting hydrazine on their surfaces, carbons make it possible to execute a four-electron reduction using a two-electron reducing agent. This role of carbon was confirmed by successfully operating an emf cell using graphite or carbon paste electrodes immersed in solutions of hydrazine and nitrobenzene. The initial rates of reduction of substituted nitrobenzenes showed only a tiny substituent effect and proceed at nearly the same rate as the carbon-catalysed decomposition of hydrazine leading to the conclusion that hydrazine reaction at the carbon surface is the rate determining step.groups 00/03270 Metalloporphyrin-derived carbons: models for investigating NO, release from coal char combustion Jones, J. M. e/ crl. Carbon, 1999, 37, (7), 1123-1131. In order to study NO, release during coal char combustion, nitrogencontaining carbons prepared by the co-carbonization of tetraphenylporphine and acenaphthylene have been used as models. In addition, carbons prepared from metalloporphyrins have been studied in an attempt to examine the role of well-dispersed metal catalysts on nitrogen release during combustion. The nitrogen functionality in some of the carbons was investigated by nitrogen X-ray absorption near-edge structure spectroscopy (XANES), and thermogravimetric analysis-mass spectrometry was used as a means of studying the combustion properties. The nitrogen species present in the carbon are similar to those observed in coals and carbons, and there is some indication of a portion of chelated metal still being present for a lower (873 K) heat-treated carbon prepared from tetraphenylporphine cobalt (II). Even so, the effect of nitrogen functionality on NO emission is secondary to the effect of carbon structure on NO reduction. A model is presented which discusses NO emission in terms of the steady-state surface oxygen concentration on the carbon. In the case of catalysed carbon combustion, the NO reduction reaction is also catalysed. Carbons prepared from these types of metal-containing precursors show larger catalytic effects in combustion than transition metal-impregnated carbons. Microcalorimetric study of acid sites on ammonia00/03271 and acid-pretreated activated carbon Xie, F. e! al. Carbon, 2000, 38, (5) 691-700. This study was designed to determine the value of microcalorimetry as a probe of acidibase sites on carbon surfaces. Calorimetric studies of ammonia adsorption on acid and ammonia pretreated activated carbon (BDH) samples demonstrated that the technique does tttrate acid sites (at equilibrium) according to their relative strengths. However, only in conjunction with other techniques, including Boehm titration, point of zero charge (PZC) and temperature programmed desorption (TPD) is it
368
Fuel and Energy Abstracts
November 2000
00/03273 Nz and COz adsorption on activated carbon fibres prepared from Nomex chars Blanco, M. C. Curbon, 2000, 38, (X), 1177-l 182. Activated carbon fibres were obtained by pyrolysis followed by CO1 activation of Nomex (poly(m-phenylene isophtalamide)] polymeric libres in their crystalline form. The materials obtained were characterized by Nz adsorption (77 K), CO* adsorption (273 K) and XRD. They show BET surface areas up to 1200 m* g , and they are essentially microporous. The pore size distribution is narrower than using Kevlar as precursor. This feature can be related with the degree of crystallinity obtained with the corresponding chars. 00103274 On surface of micropores and fractal dimension of activated carbon determined on the basis of adsorption and SAXS investigations Diduszko, R. Curhon, 2000, 38. (8) 1153-l 162. Granulated commercial activated carbon obtained from hard coal was separated for fractions, by elutriation, in an air stream of constant flow-rate. Three samples of different fall down distances from the outlet tube were demineralized. Benzene adsorption isotherms were determined at 293 K and SAXS measurements were performed for each one. The Dubininlzotova and Dubinin-Stoeckli equations were used for evaluation of micropore structural parameters of examined carbon samples. On the basis of these equations different methods of calculation of geometric surface area were discussed. Obtained results were compared with values evaluated by using the method proposed here. This method comprises results of SAXS and adsorption measurements. Changes of geometric surface area were confirmed by analysis of surface roughness measured by fractal dimension. The values of fractal dimension were obtained by method of calculation on the basis of adsorption data proposed previously by Ehrburger-Dolle and were compared with modification proposed here. This modification is based on well known correlation given by McEnaney. Obtained values of fractal dimension were compared with values determined on the basis of SAXS data. On the characteristics of tar from gasification of 00103275 energy crops Yu, Q. er al. Sum. Comhust. Rrs. Sled., Proc. List Parlicipants, 1999, l81185. Edited by Olsson E. One important parameter for bringing the gasification of biomass for energy generation to commercial viability is the level and composition of the generated tar by-products. This is because condensible tars may cause plugging problems in lines and downstream equipments and also impact the environment. Three kinds of energy crops (reed canary grass; Miscanthus; Salix) were gasified in a pressurized fluidized-bed at 900°C and 0.4 MPa and the tar evolution was monitored. Tar sampling for light compounds were performed using a solid-phase adsorption method (SPA) recently developed in the laboratory. The samples were subsequently analysed by capillary gas chromatography (CCC) with flame ionization detection (FID). Heavy tars were collected by a conventional cold-trapping method (CT) and then determined by gravimetry. The analysis results were compared with those from gasification of birch and coal obtained under similar conditions. Benzene, toluene, naphthalene, acenaphthylene and phenanthrene were the principal constituents of the tar samples that differ mainly in their component distribution and total amount of tar. The total amount of light tar decreased in the following order: Birch > Salix > Reed canary grass > coal > Miscanthus. In contrast, the highest yield of heavy tar components from the three energy crops was obtained from Miscanthus. The new sampling method (SPA) used for light compounds is a key factor for successful tar monitoring since the sampling time has been reduced from one hour for conventional methods based on cold trapping to about one minute. 00103276 Palladium catalysts on activated carbon supports. Influence of reduction temperature, origin of the support and pretreatments of the carbon surface Gurrath, M. et al. Carbon. 2000, 38, (8), 1241-1255. A number of activated carbons produced from peat, coconut shell, and by pyrolysis of hydrocarbons have been subjected to treatment with oxygen, chlorine, hydrogen or ammonia at elevated temperatures to get a representative series of catalyst supports differing in porous structure and surface chemistry (characterized by nitrogen adsorption and selective