Catalytic characteristics of specialty (color and conductive) carbon blacks (CBs) for methane decomposition were investigated and compared with those of rubber blacks. The catalytic characteristics of the color blacks were more similar to those of the rubber blacks, in such that both blacks exhibited very stable activity, a positive correlation of the activity with increasing specific surface area, and higher activation energies. However, the conductive blacks showed quasi-stable behavior, leveling-off of the activity at a somewhat higher value despite their specific surface areas being several times higher than the most active color black, and significantly lower activation energies. These differences were attributed to their morphology differences: the color and rubber blacks were nonporous, whereas the conductive blacks were highly porous. Particularly, the conductive blacks had many dented corners at the pore wall with a highly active armchair structure, resulting in the lower activation energies. Meanwhile, the reaction orders over all the specialty and rubber blacks lay between ca. 0.7 and 1, but no obvious trend in the reaction order was discernible with respect to the surface area or type of CBs. 相似文献
The energetic surface heterogeneity of various carbon blacks has been investigated by means of volumetric gas adsorption techniques. From the adsorption isotherms of ethene at a coverage of about 0.001 up to 1 monolayer the energy distribution functions of adsorption sites are evaluated. Four discrete species of energetic adsorption sites are identified on all carbon black surfaces irrespective of morphology. The fraction of the different adsorption sites is found to depend significantly on the microstructure and primary particle size and on manufacturing conditions as well. 相似文献
Catalytic characteristics of carbon black for methane decomposition at high temperatures were investigated. A fixed bed reactor was made of carbon steel with 28 mm I.D and 450 mm height. The reaction was carried out under atmospheric pressure at temperature of 1,293–1,443 K. The objective was to investigate the catalytic activity of carbon black at high temperature, similar to the manufacturing process of carbon black. Almost 100% methane conversion was observed at 1,443 K, and the activation energy of the catalytic reaction over carbon black was 198 kJ/mol. The specific surface area decreased as the amount of deposited carbon increased. Since a large amount of the produced carbon was deposited on the surface, the increase of aggregates size and protrusions size of deposited carbon was larger than in the results of previous work. 相似文献
A wide variety of carbon materials (ordered mesoporous carbons, carbon blacks, activated carbon, carbon nanotubes, coke and graphite) have been investigated as catalysts for hydrogen production by methane decomposition, with the aims of identifying the carbon properties which control in a greater extension the catalytic activity and determine the nature of the active sites involved in the reaction.The catalytic activity of the different carbon materials was determined and compared using temperature-programmed experiments in a thermobalance. The initial activity was followed through the threshold temperature, defined as the temperature at which hydrogen production starts being detected, whereas the average reaction rate was also calculated and compared. The lowest threshold temperature was observed with ordered mesoporous carbons (CMK materials), followed by activated carbon and carbon blacks. On the other hand, at long reaction times activated carbon was quickly deactivated yielding a relatively low average reaction rate. The deactivation process seems to be greatly linked to the presence of micropores while the long-term activity is retained in those materials with ordered mesoporosity (CMKs) or formed by nanoparticles (carbon blacks), which make them more resistant to deactivation by the formation of carbonaceous deposits.Whereas no clear dependence is observed between the threshold temperature and the surface area neither with the presence of polar groups in the carbon catalysts, characterization of these materials by XPS shows that a direct relationship exists with the amount of defects present on the graphene layers. This fact strongly supports that these defects are the main active sites for methane decomposition over carbon catalysts. 相似文献
The variation in the catalytic activity of carbon black (CB) during methane decomposition was investigated by considering
the number of active sites of CB. We demonstrated that the activity variation could be well estimated by assuming the edge
length of graphitic sheets evolving from the CB surface. The results suggested that the activity variation originated from
surface structural changes due to carbon deposition. 相似文献
The surface activity of commercial and experimental carbon blacks varying in particle size and primary aggregate structure was investigated with regard to surface roughness and energetic surface structure of primary particles. The energetic surface structure was described by the site energy distribution function f(Q), which was determined mainly from the gas adsorption isotherms of ethene. It was found that the surface of carbon black was energetically very heterogeneous. It consisted of at least four different adsorption sites (I: Q ≈ 16 kJ · mol?1; II: Q ≈ 20 kJ · mol?1; III: Q ≈ 25 kJ · mol?1; IV: Q ≈ 30 kJ · mol?1). The fraction of the sites I–IV depended on the production process of the carbon black grades and the particle size. For the furnace blacks, the fraction of high‐energy sites decreased significantly with particle size and disappeared almost completely during graphitisation. This indicates that the reinforcing potential of carbon black is closely related to the amount of highly energetic sites that can be well quantified by the applied gas adsorption technique. The surface roughness was characterised by the surface fractal dimension, Ds, which was determined by two different techniques: the yardstick‐method and the extended Frenkel‐Halsey‐Hill‐theory (fractal FHH‐theory). It is found that the furnace blacks have an almost equal roughness with a surface fractal dimension of Ds ≈ 2.6 beyond a length scale z ≈ 6 nm. This result is shown to be in fair agreement with analytical models and computer simulations of surface growth of carbon black in a furnace reactor.
Mesoporous carbons (MCs) were directly prepared from direct coal liquefaction residue (CLR) by KOH activation, and used as catalysts for methane decomposition. The results indicated that the prepared MCs were of a narrow pore size distribution centered at about 3.5 nm. The mineral matters in the CLR and their salts formed during KOH activation process served as templates for mesopore formation, through washing off the mineral matters and the salts occupied in the inner space of the carbon. The resultant MCs showed higher and more stable activity in methane decomposition reaction than commercial coal-based activated carbon and carbon black catalysts. 相似文献
The adsorption of butadiene on carbon black is a function of surface properties, high reinforcing, high surface area carbon black adsorbs more butadiene than low reinforcing big particle size carbon black. It is found that the functional groups on modified carbon blacks, oxidized or sulfur modified carbon blacks significantly reduces the butadiene concentration in headspace. Chemisorption of butadiene on the carbon black surface strongly holds butadiene on the surface, which prevents desorption of butadiene from the carbon black surface. These modified carbon blacks result in a very low concentration of butadiene in the headspace, usually 50-100 times lower than unmodified carbon black. 相似文献
The catalytic activities of rubber, color and conductive carbon black catalysts for decomposition of ethane were investigated in the temperature range from 973 to 1173 K. Significantly higher ethane conversion and lower ethylene selectivity were obtained in the presence of carbon black catalysts compared with non-catalytic decomposition, resulting in much higher hydrogen yields. This indicates that carbon black catalysts are effective catalysts for dehydrogenation of ethane to hydrogen and ethylene, as well as for the subsequent decomposition of ethylene to hydrogen and solid carbon. However, more methane was produced in the presence of carbon black catalysts than in non-catalytic decomposition. A reaction mechanism was proposed for the catalytic decomposition of ethane. The hydrogen yield increased with an increase in the specific surface area of the nonporous rubber and color carbon black catalysts with a surface area of up to approximately 100 m2/g. However, the hydrogen yield over the carbon black catalysts with higher surface areas, including the conductive carbon black catalysts with very high surface areas, did not increase significantly. The carbon black catalysts exhibited stable activity for ethane decomposition and hydrogen production for 36 h despite carbon deposition. 相似文献
The thermo-catalytic decomposition of waste lubricating oil over a carbon catalyst was investigated in an I.D. of 14.5mm and length of 640mm quartz tube reactor. The carbon catalysts were activated carbon and rubber grade carbon blacks. The decomposition products of waste lubricating oil were hydrogen, methane, and ethylene in a gas phase, carbon in a solid phase and naphthalene in a liquid phase occurring within the temperature ranges of 700 °C-850 °C. The thermo-catalytic decomposition showed higher hydrogen yield and lower methane yield than that of a non-catalytic decomposition. The carbon black catalyst showed higher hydrogen yield than the activated carbon catalyst and maintained constant catalytic activity for hydrogen production, while activated carbon catalyst showed a deactivation in catalytic activity for hydrogen production. As the operating temperature increased from 700 °C to 800 °C, the hydrogen yield increased and was particularly higher with carbon black catalyst than activated carbon. As a result, carbon black catalyst was found to be an effective catalyst for the decomposition of waste lubricating oil into valuable chemicals such as hydrogen and methane. 相似文献