Carbon Alloys part 16 pdf

Preparation of Metal-loaded Porous Carbons 509 $201 , , , 0 0 5 10 15 20 25 Time [ h ] Fig. 13. Conversion of nitric oxide versus reaction time for reaction-regeneration cycles using carbon monoxide during regeneration of Ni-500-47.0. (S, = 24000 h-') [ll]. when employing this regeneration method. The lifetime of the catalyst after the first regeneration was less than the lifetime of the fresh catalyst. This is because the catalyst was not completely regenerated during the first regeneration. It is necessary and important to find optimum regeneration conditions. Results so far indicate that a reducing regeneration method is effective to utilize the Ni2+ catalyst in practical applications. Next, carbon monoxide was intentionally added in the feed stream during the reaction, because this gas may act as an in situ reducing agent. Figure 14 shows the changes in conversions of nitric oxide, the yields of nitrogen and the concentrations of oxides of carbon in the exit stream for Ni-500-47.0. In the presence of carbon monoxide, nitric oxide was completely removed for more than 20 h without regenera- tion even at 300°C. The concentration of carbon monoxide was smaller than its feed concentration by ca. 500 ppm, and carbon dioxide, which was not detected in the absence of carbon monoxide, was formed in ca. 500 ppm. These results show that amounts of carbon monoxide consumed were almost the same as amounts of carbon dioxide formed or amounts of nitric oxide removed. This means that almost no carbon Reaction time [h] Fig. 14. Conversion of nitric oxide, yield of nitrogen, and concentrations of carbon monoxide and carbon dioxide in the effluent stream for the nitric oxide removal experiment with Ni-500-47.0 in the presence of carbon monoxide at 300°C. (S, = 24000 h-') [ll]. 510 Chapter 31 ,. t-i I , q*' 855 850 865 860 Binding energy [ eV 1 Fig. 15. Comparison of the XPS spectra of fresh catalyst (Ni-500-32.6), deactivated catalyst, and regenerated catalyst and the spectrum of NiO powders [ll]. in the sample was lost during the reaction in the presence of carbon monoxide, maintaining the high catalytic activity for a long time. The yield of nitrogen was kept at more than 90%, indicating that the decomposition of nitric oxide to nitrogen was enhanced in the presence of carbon monoxide. Then, the overall reaction can approximately be written as 2N0 + 2CO 3 N, + 2C0, (2) Thus, it is clear that the Ni2+ catalyst can be utilized for an extended time without loss of carbon when a reducing agent is contained within the feed stream. 5.4 Changes in the Chemical State oflvickel During Reaction XPS studied changes in nickel forms in the Ni-500-32.6 during reactions. Figure 15 compares the XPS spectra of the fresh, deactivated (used for 10 h at 3OO0C), and thermally regenerated samples with the spectrum of NiO powders. The spectra of nickel in the fresh and the regenerated samples were similar to those of nickel, and were of metallic nickel. On the other hand, the nickel in the deactivated sample was NiO. These results indicate that metallic nickel is the active form of the catalyst, and that it is oxidized to NiO through the removal of nitric oxide and accordingly loses its activity. NiO is reduced to nickel by carbon through the thermal regeneration reaction at 500°C as indicated by the formation of oxides of carbon during the regeneration. 5.5 Reaction Mechanisms Non-isothermal experiments, so-called temperature-programmed-reaction (TPR) experiments, were made to examine the mechanisms of the decomposition reaction of nitric oxide. The sample was heated at 5 K mid, from room temperature to 300"C, in Preparation of Metal-loaded Porous Carbons 511 - Y XlOO[ , I I , f -, d < 80t conversion of^^ ,' \/ I /i 50 100 150 200 250 300 Temperature [ 'C ] U Fig. 16. Change of conversion of nitric oxide and yield of nitrogen against the temperature during the TPR experiment for Ni-500-47.0 (S, = 24000 h-') [ll]. a stream of 500 ppm of nitric oxide. Figure 16 shows the concentrations of nitric oxide and nitrogen versus increasing reaction temperature. The concentration of nitric oxide decreased gradually with increasing temperature and fell to -50 pprn even at 200°C. On the other hand, the concentrations of nitrogen was less than 25 pprn at temperatures < 200"C, and then gradually increased to reach about 210 pprn at 300°C. These results indicate that nitric oxide is chemisorbed on the sample and then decomposes to form nitrogen. Based on the above results the following reaction mechanism was proposed for nitric oxide decomposition reaction at 300°C on the Ni-loaded porous carbons in the absence of reducing agents NO + Ni -+ Ni-NO 2Ni-NO + 2Ni0 + N, (3) (4) Nitric oxide is first chemisorbed on nickel (Reaction (3)). The chemisorbed nitric oxide decomposes to form nitrogen and oxidizing nickel to NiO (Reaction (4)). At 300"C, about 20% of the nitric oxide removed remains in the sample. As NiO is not active for the nitric oxide decomposition reaction, the activity gradually decreases with the progress of reaction. However, the initial activity of the catalyst was high because a large amount of metallic nickel (-50 wt%) was highly dispersed within the porous carbon. The regeneration reaction is the reduction of NiO to Ni. Carbon in the sample reduces NiO to Ni forming carbon monoxide at 500°C (Reaction (5)). Carbon monoxide formed through the reduction by carbon also reduces NiO (Reaction (6)). NiO + C -+ Ni + CO (5) NiO + CO + Ni + CO, (6) At 400°C the activity of Ni-500-47.0 remained for more than 40 h without regenera- tion, because the regeneration Reactions (5) and (6) occur simultaneously. 512 Chapter 31 Thus, carbon itself was found to act as a reducing agent when no reducing agents were added meaning that carbon is lost during the reaction and/or during thermal regeneration. The reducing regeneration method and the in situ regeneration method were proposed (Figs. 13 and 14) based on the reaction mechanisms. Both methods used carbon monoxide as a reducing agent which reduced NiO to Ni through Reaction (6). The methods established the regeneration of the Ni2+ catalyst by minimizing loss of carbon. 6 Conclusions A novel method for preparing porous carbons with highly dispersed metals is pre- sented. The method carbonizes ion-exchange resins exchanged by different cations. Of the various carbons prepared, the proposed method uses a nickel-loaded porous carbon which shows high catalytic activity for the decomposition of nitric oxide to nitrogen. The following results were obtained. A nickel-loaded porous carbon, Ni-500-47.0, removed nitric oxide completely for 5 h (S, = 24000 h-') at 300°C without any gaseous reducing reagent. The high activity of Ni-500-47.0 resulted from the large amounts of highly dispersed nickel loaded into the porous carbon. The activity of deactivated sample could be completely recovered by heat treatment at 500°C in a helium atmosphere, but the regeneration method consumed carbon by reducing nickel oxide (NiO) to nickel. To overcome this limitation to thermal regeneration, regeneration using carbon monoxide as a reducing agent was examined. This regeneration method minimized carbon loss suggesting the possibility to use the NiZf catalyst in practical applications. In the presence of the reducing agent carbon monoxide, Ni-500-47.0 com- pletely removed nitric oxide for more than 20 h at 300°C without regeneration. This was because carbon monoxide regenerated nickel oxide (NiO) to nickel during the reaction. This regeneration consumes little carbon and so the supported catalyst can be used for an extended. Nitric oxide is first chemisorbed onto active sites of the metallic nickel, and subsequently decomposes to produce nitrogen and nickel oxide (NiO). The activity is gradually lost with the formation of nickel oxide (NiO) which can be removed by reducing agents such as carbon monoxide or carbon to recover the catalytic activity. References 1. L.R. Radovic and F.R. Reinoso, In: P.A. Thrower (Ed.), Chemistry and Physics of Carbon, Vol. 25, pp. 243-358. Marcel Decker, New York, 1997. 2. F. Nozaki, K. Yamazaki and T. Inomata, Low temperature activity of the copper oxide cat- alyst supported on activated carbon for reduction of nitric oxide with ammonia. Chem. Preparation of Metal-loaded Porous Carbons 513 Lett.: 521-524, 1977. 3. S. Kasaoka, E. Sasaoka and H. Iwasaki, Vanadium oxides (V,O,) catalysts for dry-type and simultaneously removal of sulfur oxides and nitrogen oxides with ammonia at low tempera- ture. Bull Chem. SOC. Jpn., 62 1226-1232, 1989. 4. A. Nishijima, Y. Kiyozumi, A. Ueno, M. Kurita, H. Hagiwara, S. Toshio and N. Todo, Metal halide catalyst for reduction of nitric oxide with ammonia. Bull Chem. SOC. Jpn., 52: 37243727,1979. 5. L. Singoredjo, M. Slagt, J. van Weers, F. Kapteijn and J.A. Moulijn, Selective catalytic re- duction of nitric oxide with ammonia over carbon supported copper catalysts. Catal. Today, 6. D. Mehandjiev and E. Bekyarova, Catalytic neutralization of NO on carbon-supported co- balt oxide catalyst. J. Colloid Interf. Sci., 166: 476480,1994. 7. J. Imai, T. Suzuki and K Kaneko, N2 formation from NO over metal oxide-dispersed microporous carbon fiber. Catal. Lett., 20 133-139, 1993. 8. H. Nakagawa, K. Watanabe, Y. Harada and K. Miura, Control of micropore formation in the carbonized ion-exchange resin by utilizing pillar effect. Carbon, 37: 1455-1461,1999 9. K. Miura, H. Nakagawa and K. Hashimoto, Carbon, 33: 275-282,1995 10. D. Dollimore and G.R. Heal, An improved method for the calculation of pore size distribu- tion from adsorption data. J. Appl. Chem., 56: 109-113, 1964. 11. K Miura, H. Nakagawa, Ryo Kitaura and T. Satoh, Low-temperature conversion of NO to N, by use of a novel Ni loaded porous carbon. Chem. Eng. Sci., 56 1623-1629,2001 12. M. Iwamoto, H. Yahiro, Y. Mine and S. Kagawa, Excessively copper ion-exchanged ZSM-5 zeolites as highly active catalysts for direct decomposition of nitrogen monoxide. Chem. Lett.: 213-216, 1989. 7 157-165,1990. 515 Chapter 32 Formation of a Seaweed Bed Using Carbon Fibers Minoru Shiraishi Tokai University, School of High-technology for Human Welfare, Department of Material Science and Technology, Numam, Shizuoka, 410-0395 Japan Abstract: Micro-organisms rapidly fii onto carbon fiber surfaces when the fibers are placed in the sea. The objective is to create an artificial bed of seaweed so establishing a food chain of bacteria, algae, zoo-plankton, small animals, and fish. Initial studies in fresh water indicated that this approach had considerable potential and should therefore be extended to seawater. Keywords: Carbon fiber, Sea, Seaweed bed, Algae, Micro-organisms. 1 Introduction The fixation of micro-organisms onto carbon fibers has recently been undertaken in freshwater systems, one application being the purification of sewage [1,2]. On the other hand, there is no basic information on the fixation of micro-organisms onto carbon fibers in seawater systems. Therefore, carbon fibers were placed (anchored) in the sea to observe fixation phenomena of marine micro-organisms. Basic data on the utilization of this artificial bed of seaweed, in terms of fish population, were collected [31. 2 Rapid Fixation of Marine Organisms To gain basic information on the fixation of marine organisms, field experiments were undertaken at the Marine Laboratory of Tokai University and also at the seawater intake of the Shinsihmim thermal power station of Chubu Electric Power Co. Inc. in the Shimizu harbor basin, Shizuoka. The Marine Laboratory is in a stagnant location beyond the intake, located at the back in the bay and near to a timber yard. Polyacrylonitrile (PAN)-based carbon fibers with a tensile strength of 3.4 GPa, tensile modulus of 230 GPa, diameter of 7 pm, density of 1.77 g cm-3 and 12,000 filaments per strand were used. A simple apparatus, as shown in Fig. 1, was sunk about 1 m under the surface of the sea and, during the first experiments, was withdrawn from the seawater at intervals of a few days. A plastic float of 30 cm 516 Chapter 32 Fig. 1. Carbon fiber bundles attached to the experimental apparatus. diameter was attached to the upper part of the rope which installs the apparatus, and a 3 kg weight was tied to the lower end of the rope to keep the fibers on the sea floor. Observations were made directly through the naked eye, an underwater camera and an optical microscope. Small organisms (algae) were almost not observed on carbon fiber surfaces after the first day of the experiment. However, a weak adhesive property appeared on the fiber surfaces to provide an adhesive membrane and so the fiber surfaces adopted a membrane-like feature, as shown in Fig. 2. This phenomenon was observed in the sea at the two locations throughout the year. To facilitate access to the interior fibers of the strand for this membrane formation, it was found necessary to separate the strands into filaments. A colony grew homogeneously from these fibers on the agar medium in one or two days. There are differences between the colonies proliferated by carbon fibers picked up and the seawater without carbon fibers from the same place. The results indicate that the adhesive material was preferentially fixed to carbon fibers in the sea and was made up of micro-organisms such as Bacillus carboniphilus, discovered by Matsuhashi [4]. Fig. 2. Adhesive material spread to the membrane on carbon fiber surface. Formation of a Seaweed Bed Using Carbon Fibers 517 Fig. 3. Minute algae (Navicula) fixed on carbon fibers. -v- i u Fig. 4. Diatoms grown on the periphery of carbon fiber bundles. Within a week after dipping, the carbon fibers had adopted the appearance of brown bio-mud, as observed macroscopically or through the camera. Minute algae, as shown in Fig. 3, were fixed to the carbon fibers as observed by optical microscopy. These algae were diatoms to be seen in seawater at depths of about 2 m. These algae were initially attached to the outside of the carbon fiber bundle, and then penetrated gradually to the inside of bundle. They grew as a slender string as shown in Fig. 4 at the Table 1 Changes with dipping time of varieties marine organisms fixed or living on carbon fibers in the sea After dipping Marine organism ~- 1 day adhesive material 5 day diatom, zooplankton I day 14 day 1 month 2 month 3 month diatom, zooplankton, Caprella, small shrimp (Maera serratipalma etc.) small shrimp (Maera serratipalma etc.), Protohydroides elegans, Caprella, ascidian small shrimp (Maera serratipalma etc), ascidian, Protohydroides elegans, Hydrozoa small shrimp (Maera serratipalma etc.), Hydrozoa, barnacle, fish small shrimp (Maera serratipalma etc.), barnacle, sponges, fish 518 Chapter 32 Fig. 5. Small shrimp (Maera seratipalma) observed in carbon fiber bundles. periphery of the fiber bundle. Also, organisms of a size larger then several centimeters soon became associated with the bundles as well as zooplankton, as seen by optical microscopy. Small animals, several millimeters in size, seen after 10 days and shown in Fig. 5, were confirmed as small shrimp (Maera serratipalma and Photis reinhardi). The development and growth rates of these animals were more rapid in the summer than in the winter. Large colonies of Maera serratipalma and Prehotis reinhardi, etc. lived in the apparatus in the sea during an autumn and winter. 3 Food Chain Through a Carbon Fiber Seaweed Bed The carbon fibers were pulled out of the sea and sampled to measure the population of algae using the microscope. The results show the growth rate of these minute algae with increasing number of days in the seawater (Fig. 6). A maximum number of algae appeared after about 30 days. It is suggested that the zooplankton and small animals grow in numbers during this 30-day period and feed off these algae. Other fish, such as filefish (Stephanolepis cirrhifer) and globefish (Ostracion immaculatus) which swim h +brine Laboratry X €+Searater Intake - loot d -i_ -1 7 $ Ob 20 40 60 80 100 n Dipping Time (days) Fig. 6. Variation of quantities of algae with time of dipping (submergence). [...]... performance carbon fibers to develop high performance carbonharbon composites The term carbon fibers’ includes carbon fibers, carbon nanotubes and micro -carbon coils Carbon matrices can contain fullerenes such as CH,, graphite, and composites of carbon with metals Selected combinationsof carbon fibers with carbon matrices produce high performance carbordcarbon composites Reviews and books on carbon/ carbon... electro-magnetic wave absorption Keywords :Carbon fiber, Carbon matrix, Interface, Composite, Microstructure, Properties 1 Introduction Carbon/ carbon composites, carbon fiber-reinforced carbon matrix composites,under the Carbon Alloys project have been investigated to develop new starting (parent) materials and new functionalities Carbon/ carbon composites consist of carbon fibers and carbon matrices However, despite... Achievements of research into carbodcarbon composites are described Novel carbon materials, carbon fibers, carbon matrices, high quality carbon alloys and new material evaluation methods were developed within this project New processing methods for carbon/ carbon composites and carbon related composites were explored Improvements to the following properties of carbon/ carbon composites were made: oxidation... Alloys project has changed ways of thinking about how to improve properties of carbon/ carbon composites A carbon/ carbon composite material that consists of carbon nanotubes and C,, is a new composite material developed in the Carbon Alloys project Progress in the production technology of carbon fibers, carbon nanotubes, carbon coils and fullerenes, including control of their microstructures, is expected... of interfaces between carbon fibers and carbon matrices In order to do this it is necessary to control microstructures at the interface The Carbon Alloys project has supported research into the microstructures of CarbonlCarbon Composites and Their Properties 543 Fig 22.Reaction process between titanium particle and graphite at 1200°C [24] interfaces The concept of the Carbon Alloys project has changed... added carbon particles increased with increase in their particle size More significant changes to the crystallinity of microstructures in particle composite materials were brought about by additions of the larger carbon particles (Fig 8) The curvature of the interface was important for 0 50 100 150 200 Mean particle size of the additives [pm] Fig 8 Crystallite size along c-axis as a function of mean particle... on carbon fibers with high compressive strengths Carbon coils with new functions have been developed with applications to carbonkarbon composites being investigated Novel composites containing carbon Chapter 33 524 nanotubes instead of carbon fibers with the C,,, fullerene as carbon matrix have been developed and their properties examined The mechanical properties and oxidation resistance of carbon/ carbon... carbon fiber and carbon matrix have received attention The additions of copper and small amounts of titanium to carbodcarbon composites are effective in increasing thermal conductivities compared with conventional carbon/ carbon composites Fracture mechanisms in carbon/ carbon composites have been examined theoretically making use of various material parameters Microstructures of interfaces between carbon. .. nanotube 3.2 Control o Microstructures in CarbonlCarbon Composites f Yasuda et al [12] attempted to control the microstructures of interfaces between carbon fiber and matrix for carbon/ carbon composites Thermosetting resin (furan resin) and a thermoplastic coal-tar pitch (C!")were selected as carbon matrix precursors In the furan resins, stress-induced graphitization of carbon was observed The effects of... durability of carbon fibers Accumulation of silicon was observed on the surface of carbon fibers in some places when the carbon fibers had been in the sea for a while, and the carbon fibers may become brittle Also, the quantity of the carbon fibers Formation of a Seaweed Bed Using Carbon Fibers 521 considerably decreased in about three months after the dipping Fish appear to tear the carbon fibers . Keywords: Carbon fiber, Carbon matrix, Interface, Composite, Microstructure, Properties. 1 Introduction Carbon/ carbon composites, carbon fiber-reinforced carbon matrix composites, under the Carbon. high performance carbon fibers to develop high performance carbonharbon composites. The term carbon fibers’ includes carbon fibers, carbon nanotubes and micro -carbon coils. Carbon matrices. micro-structures. Achievements of research into carbodcarbon composites are described. Novel carbon materials, carbon fibers, carbon matrices, high quality carbon alloys and new material evaluation methods