Formation Of Carbon Nanofibres Research Articles

CO2 reduction to syngas and carbon nanofibres by plasma-assisted in situ decomposition of water

Simultaneous activation of CO2 and H2O was carried out in a non thermal plasma dielectric barrier discharge reactor operated under ambient conditions. The plasma reactor packed with partially reduced NiO/Al2O3 catalyst showed better CO2 conversion than both the unreduced NiO/Al2O3 and with plasma (no catalyst), whereas, highest syngas selectivity was observed with unreduced NiO/Al2O3. An interesting observation is the formation of carbon nanofibres (CNFs) along with syngas with a reduced NiO catalyst integrated to the plasma, whereas, pure NiO only led to the formation of methane. The reduction of CO2 by in situ formation of hydrogen from water splitting may produce CH4 and plasma-assisted chemical vapour decomposition of CH4 may lead to the formation of CNFs.

Plasma-assisted methane reduction of a NiO catalyst—Low temperature activation of methane and formation of carbon nanofibres

The low temperature reduction of a NiO catalyst by CH4 was performed in a coaxial double dielectric barrier discharge (DBD) reactor for the first time. The reduction involves active surface carbon which is produced via plasma decomposition of CH4. On the reduced Ni catalyst, activation of CH4 and its fragments to form H2 and carbon nanofibres occurred at 330°C. CH4 conversions of 37% were achieved in the plasma-catalytic reaction at atmospheric pressure, with 99% selectivity towards H2 and solid carbon. These results demonstrate a synergistic effect where both the plasma and catalyst are vital for the production of H2 and carbon nanofibres. In the absence of the catalyst stable plasma could not be ignited with a pure CH4 flow and thermal studies showed that in the absence of the plasma CH4 conversion was minimal.

Microwave-assisted pyrolysis of CH 4/N 2 mixtures over activated carbon

The aim of this work was to study the microwave-assisted pyrolysis of CH 4 over an activated carbon, which acted as both microwave receptor and catalyst, and the influence of using different CH 4/N 2 ratios on the conversion of CH 4 to H 2. In order to compare the results obtained in the microwave oven, the pyrolysis was also carried out under conventional heating (electric furnace, EF). The effects of N 2, which enhanced significantly CH 4 conversion, differed depending on the heating device used. Under EF heating, N 2 seemed to have an effect similar to distribute the CH 4 molecules within the activated carbon bed. Under microwave heating (MW), the N 2, as well as distributing the CH 4 molecules, favoured the generation of energetic microplasmas, leading to higher conversions. The prevalence of one role over the other depended on the CH 4/N 2 ratio, the appearance of energetic microplasmas being favoured with high percentages of N 2. Consequently, CH 4 conversion was higher at low CH 4/N 2 ratios. Additionally, the formation of carbon nanofibres in experiments where a combination of N 2 and MW heating was used is also reported.

Microwave-assisted catalytic decomposition of methane over activated carbon for [formula omitted]-free hydrogen production

The aim of this work was to combine microwave heating with the use of low-cost granular activated carbon as a catalyst for the production of CO 2 -free hydrogen by methane decomposition in a fixed bed quartz-tube flow reactor. In order to compare the results achieved, conventional heating was also applied to the catalytic decomposition reaction of methane over the activated carbon. It was found that methane conversions were higher under microwave conditions than with conventional heating when the temperature measured was lower than or equal to 800 ∘ C . However, when the temperature was increased, the difference between the conversions under microwave and conventional heating was reduced. The influence of volumetric hourly space velocity (VHSV) on the conversion tests using both microwave and conventional heating was also studied. In general, there is a substantial initial conversion, which declines sharply during the first stages of the reaction but tends to stabilise with time. An increase in the VHSV has a negative effect on CH 4 conversion, and even more so in the case of microwave heating. Nevertheless, the conversions obtained in the microwave device at the beginning of the experiments are, in general, better than the conversions reported in other works which also use a carbonaceous-based catalyst. Additionally, the formation of carbon nanofibres in one of the microwave experiments is also reported.

Synthesis of carbon nanofibres from a liquid solution containing both catalyst andpolyethylene glycol

Carbon nanofibres (CNFs) exhibiting bamboo-like, hollow fibril morphology were preparedfrom a mixture of polyethylene glycol (PEG) and iron-based compounds such asFe2(SO4)3·nH2O,Fe(NO3)·9H2O or FeO(OH) by a thermal process. These materials were well mixed in distilled water priorto thermal treatment in an air/nitrogen atmosphere. With increasing temperature, themixture underwent solvent removal, dehydrogenation, thermal decomposition,carbonization and catalytic graphitization to form CNFs. Results show that CNFscan be formed with different PEG/catalyst ratios (100/1–1000/1 by weight) at750 °C. The catalyst effect is discussed for the formation of bamboo-like CNFs. Thediameter of the CNFs was about 30–50 nm while the length was a few micrometres.

Immobilization of a layer of carbon nanofibres (CNFs) on Ni foam: A new structured catalyst support

This work describes the preparation of new materials based on immobilizing carbon nanofibres (CNFs) on the surface of Ni foam. CNFs were catalytically synthesized by decomposition of ethene over the Ni foam. The influence of formation conditions on the morphology of the CNFs, on the mechanical stability of the CNFs?Ni-foam composite structures and on the attachment of the CNFs to the Ni foam is discussed. The surface area of the Ni?CNFs-foam composite increased with the loading of CNFs, from less than 1 m2 g?1 to 30 m2 g?1 for 50 wt.% CNFs on the foam. The layer of the CNFs was highly open with a pore volume of 1 cm3 g?1 CNFs. Stable Ni?CNFs-foam composite structures can be obtained under the conditions that the extent of corrosive metal dusting of Ni is limited, via decreasing the temperature and/or the formation time. Some metal dusting is, however, needed to form small Ni particles that allow formation of CNFs. The extent of corrosive metal dusting determines to what extent CNFs are weakly attached. The remaining CNFs, at least 80%, are remarkably strongly attached. Every single CNF is bonded to the Ni structure, probably via penetration of the CNFs into the polycrystalline Ni foam. Controlling the conditions of CNFs formation is vital in order to optimise the mechanical stability of the CNF?Ni-foam composite structures as well as the strong attachment of the CNFs to the surface of the Ni foam.

Growth of carbon nanotubes and nanofibres in porous anodic alumina film

By acetylene pyrolysis at 650 and 550°C, carbon nanotubes were synthesized successfully in porous alumina templates anodized in sulfuric and/or oxalic acid solution. For templates anodized in oxalic acid followed by boiling in distilled water, thermal decomposition of acetylene at 650°C in the pores results in the formation of carbon nanofibres. For templates anodized in sulfuric acid, only carbon nanotubes were formed, even if boiling in water was adopted to process it. This indicates that the modifications of the catalytic effects in acetylene pyrolysis by boiling in water are different for these two types of templates. All the carbon nanotubes and nanofibres have similar lattice structures under HRTEM examination. No carbon nanotubes or nanofibres can be formed when the chemical vapour deposition temperature decreases to 500°C.