Nelly M. Rodriguez

The effect of copper on the structural characteristics of carbon filaments produced from iron catalyzed decomposition of ethylene

Abstract Carbon filaments were produced by the decomposition of ethylene over unsupported iron-copper powders in the presence of varying amounts of hydrogen at temperatures ranging from 500°C to 800°C. The structure and properties of the carbon filaments were found to be dependent on a number of parameters including the composition of the catalyst, the temperature and the percent of hydrogen in the reactant gas mixture. Temperature programmed oxidation in CO 2 of demineralized samples of carbon filaments indicated that the most stable structures were those produced from a bimetallic catalyst containing a large fraction of iron. The addition of hydrogen to the system also caused changes in the structure of the carbon filaments and this aspect was manifested by variations in the graphitic nature of the material. High resolution transmission electron microscopy examination indicated the presence of two distinct morphologies: one in which the filaments appeared to have smooth surfaces and where the graphite platelets were preferentially oriented at an angle with respect to the fiber axis; and a second type consisting of a tubular structure in which the graphite platelets were aligned in a direction parallel to the axis of the fiber. Surface areas of the carbon filaments, as determined by nitrogen adsorption at −196°C, were also found to be dependent on the catalyst composition, the reaction temperature and the fraction of hydrogen in the feed gas.

Carbon deposition on iron-nickel alloy particles

Abstract A combination of flow reactor studies and electron microscopy techniques have been used to investigate the manner by which the composition of iron-nickel alloy particles influence the growth characteristics of carbon deposits formed during the decomposition of ethane at temperatures over the range 815 to 865°C. Major differences in the selectivity patterns of alloys were evident with the amount of catalytically produced solid carbon being significantly higher on a Fe-Ni (5:5) powder than on a Fe-Ni (8:2) sample. Examination of the deposit revealed the existence of two types of structures, carbon nanofibers and a graphite shell-like material, both of which contained associated metal particles. The latter structures appeared to predominate at the higher temperature and were most abundant on the Fe-Ni (5:5) particles. A dramatic change in catalyst activity and selectivity was found when 50 ppm H 2 S was added to the ethane feed. Analysis of the gas phase product distribution showed that the behavior of the two alloy powders was almost identical. On the other hand, the yields of solid carbon were generally higher on the iron-rich sample and tended to consist of the shell-like form on both alloys when sulfur species were present in the reactant.

Carbon Nanofibers as a Novel Catalyst Support

Catalytically grown carbon nanofibers have been prepared by the thermal decomposition of carbon containing gases over copper-nickel and iron surfaces. This material is found to be highly graphitic in nature when prepared from certain catalysts and gaseous reactants. In the as-grown state, carbon nanofibers have surface areas in the range 200 to 300 m 2 /g, and by following careful activation procedures this value can readily be increased to ˜700 m 2 /g. Electrical measurements indicate that the material has a conductivity approaching that of single crystal graphite. This material combines the attributes of active carbon and graphite and in addition, the physical form of carbon nanofibers offers some interesting opportunities for the design of unique catalyst systems.

Catalytic Materials: Nanofibers—From Research to Manufacture

Graphene nanofibers are materials that display extraordinary properties suitable for a number of advanced energy storage devices as well as chemical processes. These solids offer the most direct route for the manufacture of bulk quantities of high quality graphene . The cost of producing these materials on a commercial scale presents a major challenge, which we have sought to overcome via the use of natural gas as a source of carbon. The key breakthrough in the process has been the design of a catalyst system that is capable of generating high purity graphene nanofibers and hydrogen in a very efficient manner.