Growth Of Carbon Filaments Research Articles

Impact of biogenic impurities on catalytic synthesis of multi-walled carbon nanotubes and hydrogen from polyolefin resins

Biogenic impurities are common contaminants of plastic waste. This study investigated the effects of biogenic impurities on the conversion of a polyolefin mixture (6 wt% low-density polyethylene, 24 wt% high-density polyethylene, and 70 wt% polypropylene) into multi-walled carbon nanotubes (MWCNTs) and hydrogen via pyrolysis-chemical vapor deposition (CVD). Biogenic components from diverse sources were added to the polyolefin mixture, including lignocellulosic materials (pine sawdust, coconut coir pith), biosolids from wastewater treatment (municipal sewage sludge), animal-based waste (crustaceans), and bio-based plastic (polylactic acid). At contamination levels up to 9.1 wt%, 3 out of 5 impurities (coconut coir pith, sewage sludge and crustaceans) caused a decline in the conversion efficiency of feedstock into MWCNTs (33 ± 7% for polyolefins only compared with 20 ± 6%, 16 ± 1% and 16 ± 2% for polyolefins with 9.1 wt% coconut coir pith, sewage sludge and crustaceans, respectively). According to gas analysis, impurities led to a loss of catalyst activity, resulting in a decreased concentration of H2 and increased concentrations of methane and ethylene in the CVD gas. Furthermore, for polyolefins containing 9.1 wt% coconut coir pith, sewage sludge, crustaceans and polylactic acid, microscopy data revealed changes in the growth of filamentous carbon, leading to the appearance of carbon nanofibers in MWCNT samples. On the contrary, biogenic impurities barely changed outer diameters, ID/IG ratios, interlayer spacing, crystallite sizes of graphite-like sites, and the surface chemistry of MWCNT samples. The results suggest the development of quality management system for contaminated plastic feedstock could be advantageous to ensure consistent outcomes of pyrolysis-CVD process.

Waste plastics recycling for producing high-value carbon nanotubes: Investigation of the influence of Manganese content in Fe-based catalysts

Thermo-chemical conversion is a promising technology for the recycle of waste plastics, as it can produce high-value products such as carbon nanotubes (CNTs) and hydrogen. However, the low yield of CNTs is one of the challenges. In this work, the addition of Mn (0 wt.%, 1 wt.%, 5 wt.%, and 10 wt.%) to Fe-based catalyst to improve the production of CNTs has been investigated. Results show that the increase of Mn content from 0 wt.% to 10 wt.% significantly promotes CNTs yield formed on the catalyst from 23.4 wt.% to 32.9 wt.%. The results show that Fe-particles in the fresh catalysts are between 10−25 nm. And the addition of Mn in the Fe-based catalyst enhanced the metal-support interactions and the dispersion of metal particles, thus leading to the improved catalytic performance in relation to filamentous carbon growth. In addition, the graphitization of CNTs is promoted with the increase of Mn content. Overall, in terms of the quantity and quality of the produced CNTs, 5 wt.% of Mn in Fe-based catalyst shows the best catalytic performance, due to the further increase of Mn content from 5 wt.% to 10 wt.% led to a dramatic decrease of purity by 10 wt.%.

Synthesis of nitrogen doped segmented carbon nanofibers via metal dusting of Ni-Pd alloy

A single-phase micro-disperse Ni-Pd (5 wt.%) alloy prepared by coprecipitation technique was studied as a catalyst precursor for the synthesis of the nanostructured carbon product. Catalytic synthesis of N-doped carbon nanofibers was implemented by the joint decomposition of C2H4Cl2 and CH3CN vapors in H2 excess at 600 °C. The in situ kinetic experiments performed in a flow gravimetric setup with McBain balances showed that the carbon deposition process is characterized by an induction period (18−20 min). The intensive metal dusting of the Ni-Pd alloyed precursor in reaction conditions was found to lead to its complete disintegration. The obtained submicron-sized Ni-Pd particles were shown by XRD to have the same composition as the starting Ni-Pd (5%) precursor. The growth of carbon filaments accompanied the rapid disintegration of Ni-Pd alloy. The addition of acetonitrile vapors into the reaction mixture was found to enhance carbon yield from 24 (0%) to 40.5 (5 vol.%) and 50.9 (8 vol.%) grams per 1 g of catalyst for 2 h of reaction. Joint catalytic processing of C2H4Cl2 and CH3CN was shown to be sufficient for the production of carbon nanofibers doped with nitrogen. According to XPS and EDX data, the average amount of nitrogen within the obtained N-CNF was about 1.8 wt.%. It was revealed by microscopic studies (SEM, TEM) that the produced N-doped carbon filaments are characterized with a rather regular segmental structure similar to that observed for a reference sample of N-free CNF. The synthesized N-CNF samples are characterized by ID/IG ∼ 1.3 (Raman spectroscopy) and high textural parameters (SBET ∼ 390−450 m2/g, Vpore ∼ 0.6 cm3/g).

Synthesis of Filamentous Carbon Material via Decomposition of CF<sub>2</sub>Cl<sub>2</sub> over Self-Organizing Ni-Cr Catalyst

The way to produce the nanostructured carbon filaments via H2-assisted catalytic decomposition of CF2Cl2 over self-organizing Ni-based catalyst has been reported. The self-organizing 6%Ni/CNM catalyst, where CNM is a carbon nanomaterial, resulted from carbon erosion of bulk Ni-Cr alloy (nichrome) in C2H4Cl2 vapors was also shown to be effective for catalytic chemical vapor deposition of CF2Cl2 with formation of bimodal carbon structures. It was demonstrated that interaction of nichrome with CF2Cl2/H2 reaction mixture at 600 °C leads to its rapid disintegration caused by carbon erosion to form disperse active Ni-particles catalyzing the growth of carbon filaments. The resulted filamentous carbon material is characterized with high textural parameters.

CO2 reforming of methane over supported LaNiO3 perovskite-type oxides

This work investigated the performance of supported LaNiO3 perovskite-type oxides for the CO2 reforming of methane. The methane and CO2 conversion increased at the beginning of reaction for LaNiO3 and LaNiO3/Al2O3 catalysts. On the other hand, conversion remained quite constant for LaNiO3/CeSiO2. in situ XPS experiments under reaction conditions revealed that the metallic Ni particles were oxidized by CO2 from the feed for LaNiO3 and LaNiO3/Al2O3 catalysts. Ceria support was preferentially oxidized, limiting the oxidation of the metallic phase. Raman spectroscopy and thermogravimetric analysis showed that carbon was formed mainly over LaNiO3 and LaNiO3/Al2O3 catalysts. Supporting LaNiO3 over CeSiO2 almost completely suppressed carbon deposition. in situ XPS experiments showed a continuous change of ceria oxidation states between Ce4+ and Ce3+ under reaction conditions. This result in a high oxygen mobility of ceria support that reacts with carbon, inhibiting the formation of nickel carbide and consequently the nucleation and growth of carbon filaments.

Highly dispersed Ni nanoparticles on 3D-mesoporous KIT-6 for CO methanation: Effect of promoter species on catalytic performance

Promoter-modified Ni-based catalysts were synthesized by an incipient-wetness impregnation method using 3D-mesoporous KIT-6 as a support modified by ethylene glycol, and evaluated for the catalytic production of synthetic natural gas (SNG) from CO methanation. Characterization results suggested that the addition of promoter species could remarkably improve the low-temperature catalytic activity for CO methanation, which was due to a large dispersion of Ni nanoparticles, an enhanced interaction between metal and support as well as a confinement effect of 3D-mesopores. Among all catalysts, Ni-V/KIT-6 possessed the best catalytic performance, which was ascribed to the largest H 2 uptake of 177.6 μmol/g and Ni dispersion of 26.5%, an intimate interaction with the support from the formation of Si–O–V linkage and an enhanced confinement effect of 3D-mesopores to effectively prevent the growth of Ni nanoparticles and carbon filaments. In consequence, Ni-V/KIT-6 displayed excellent catalytic performance as well as high catalytic stability, which can be regarded as a promising candidate for CO methanation. The addition of promoter species can improve the catalytic performance at the low-temperature, and the Ni-V/KIT-6 exhibited the best catalytic performance for CO methanation due to higher dispersion of Ni nanoparticles on 3D-mesoporous KIT-6.

Synthesis of bimodal carbon structures via metal dusting of Ni-based alloys

A prospect of using metal dusting as an approach to synthesize self-organizing Ni-based catalysts for production of bimodal carbon materials has been discussed. Forced metal dusting of bulk Ni-M alloys driven by decomposition of chlorinated hydrocarbons led to a rapid and full disintegration of alloyed Ni-M precursors with spontaneous formation of active catalytic particles responsible for the growth of carbon filaments. Self-organizing catalysts were shown to be effective for utilization of organochlorine waste, processing of freons and various hydrocarbons into carbon nanomaterials. Secondary disintegration of metal particles resulted in the appearance of bimodal structures. The structural and morphological peculiarities of carbon nanomaterials obtained have been described.

(Invited) Evolution of Catalyst Role in Single Wall Carbon Nanotube Growth

Undoubtedly, the catalyst plays a key role in the nucleation and growth of various carbon filaments, as evidenced by the large number of studies for more than 40 years that focus on catalyst preparation methods, composition, morphology and size. Variation of catalyst compositions have led to morphological control of grown carbon filaments such as vermicular, twisted, platelet, tubular and conical. Reduction of the catalyst nanoparticle size to the 1–5 nm range resulted in the formation of new allotrope, carbon nanotubes, with unique properties that depend on their structure. It is commonly accepted that a careful designed catalyst could control the structure of grown single walled carbon nanotubes and thereby their properties. However, a catalyst a few nanometers in diameter introduces peculiarities for classical understanding of the features e.g., melting temperature, binary/ternary phase diagrams with carbon and other metals, equilibrium shape (Wulff construction), crystallographic structure, impact of the substrate, etc. Current state of the art of thermodynamics and kinetics of nanoparticles for controllable growth of carbon nanotubes and challenges will be presented and discussed.

Catalytic conversion of 1,2-dichloroethane over Ni-Pd system into filamentous carbon material

The alloyed Ni-Pd system with Pd content of 3wt.% was prepared by coprecipitation method followed by reduction in hydrogen atmosphere at 800°C. The formation of single-phase solid solution with unit cell parameter a=3.532(1) Å (determined by (331) reflex at 2θ ≈ 145°) corresponding to NiPd alloy with weight ratio 97:3 was confirmed by XRD analysis. Kinetic studies on catalytic conversion of 1,2-dichloroethane (DCE) over NiPd alloy into carbon nanomaterial (CNM) were performed in a flow reactor equipped with McBain balances in a temperature range of 580–700°C. It was shown that interaction of DCE with NiPd system results in a fast disintegration of pristine alloy with formation of submicron (0.2-0.9μm) particles, which efficiently catalyze the growth of segmented carbon filaments. According to Raman spectroscopy and transmission electron microscopy data, hydrogen concentration in reaction mixture strongly affects the structural features and density of segmented filaments. The average values of inter-segmental distance calculated from TEM micrographs of carbon filaments were found to be 96, 46, 16nm for hydrogen concentration of 23, 36 and 47 vol.%, respectively. Strongly chemisorbed chlorine species were suggested to be responsible for the cyclic perturbations in carbon transfer and deposition. Obtained carbon nanomaterials were characterized with comparatively high specific surface area (300–400m2/g) and extremely low bulk density (<0.03g/ml).

Ni/CeO2–Al2O3 catalysts for methane thermo-catalytic decomposition to COx-free H2 production

The effect of ceria addition to alumina on the catalytic performance of the active NiO particle has been investigated during methane decomposition to CO/CO2 free H2 production. The CeO2-Al2O3 supports with different CeO2 loading were prepared by co-precipitation and loaded with 50 wt% Ni by incipit wetness impregnation method. The catalysts were characterized by XRD, HRTEM, BET, TPR and Raman spectroscopy. The results revealed that the catalytic activity was strongly depended on the ceria content in the catalyst. The highest methane decomposition to H2 was achieved over the Ni/Ce25-Al75 catalyst. TEM images illustrated that, various kinds of carbon nano-structured materials were obtained on the catalyst surface according to the Ce content. Carbon nanofiber (CNF) and graphene films (GF) were formed on the surface of Al2O3, Ni/Ce25-Al75, Ce50-Al50 and Ce75-Al25 supported Ni catalysts. While only multi-walled carbon nanotubes (MWCNT) was obtained on Ni/Ce catalyst. The formation of Ni-O-Ce solid solution induced highly dispersed Ni particles with relatively small sizes, leading to the growth of filamentous carbon.

Distinct carbon growth mechanisms on the components of Ni/YSZ materials

Using pure YSZ and Ni-doped YSZ materials we provide a direct comparison of the morphology and specific growth mechanisms of carbon deposits following treatment in CO as the common component of reformate gas fuels at temperatures up to 1273 K. Under these experimental conditions, carbon is deposited on both constituents following distinctly different pathways: metallic Ni particles are both encapsulated and subsequently act as catalysts for growth of carbon filaments – leading to chemically and electronically altered Ni particles. In contrast to that, also pure YSZ oxide particles are without exception only encapsulated by distorted graphitic layers of up to 2–3 individual layers. This carbon layer is not formed by carbon spillover from the Ni particle, but directly deposited on the oxide grains by CO dissociation. While the pathway over the metallic component is dominant at high Ni loadings, the oxide especially at lower loadings can contribute directly to the structural and chemical alterations of the electrode material by changing the physico-chemical properties, e.g. by altering the conductivity via C-deposition at the intergrain regions or may also serve as additional carbon supply for re-distributed and dispersed “dusted” Ni particles attached to the carbon-covered YSZ grains.

High-performing and durable MgO/Ni catalysts via atomic layer deposition for CO2 reforming of methane (CRM)

MgO-coated Ni catalysts with two different shell thicknesses were prepared using atomic layer deposition (ALD) and their catalytic activities for the CO2 reforming of CH4 (CRM) were compared with that of bare Ni catalyst. Conversion of CO2 and CH4 in the CRM reaction at 800°C was enhanced with increasing thickness of the ALD-deposited MgO shells. In particular, the catalytic activity of MgO/Ni catalyst prepared using 200 ALD MgO deposition cycles was fairly durable, with negligible deactivation during a 72h CRM reaction. We suggest that the MgO shell, which is highly basic and has high affinity to CO2, likely, accelerated the reverse CO disproportionation, thereby reducing the poisoning of Ni active sites during the CRM reaction. Furthermore, the 200-cycled MgO shell destroyed ensemble of Ni catalysts surface, allowing preservation of Ni active sites with preferential growth of filamentous carbon to layered graphitic ones. We suggest that the preparation of core–shell structures using ALD can be a promising strategy for fabricating highly active and durable catalysts that are operable at relatively high temperatures.

Dry reforming of methane with carbon dioxide over NiO–MgO–ZrO2

NiO–MgO–ZrO2 catalysts were synthesized via a melt impregnation technique on a zirconia support with equimolar amounts of Ni and Mg in the range of 2–35mol%. The catalysts were characterized by TPDA, TPR, PXRD, TEM and EDX. The catalysts are basic in nature and contain both tetragonal and monoclinic zirconia. After impregnation, Ni and Mg are homogeneously distributed over the zirconia support in oxidic form. After reduction of the composite system, metallic Ni is highly dispersed on the support together with a solid solution of NiO–MgO present. The prepared NiO–MgO–ZrO2 catalysts show a high activity in the dry reforming of methane at 1123K and atmospheric pressure. At high Ni and Mg contents, the catalysts are subject to severe coking leading to pronounced deactivation. From TEM investigations, a coking mechanism is proposed including the growth of filamentous carbon followed by formation of graphitic carbon, partly encapsulating metallic Ni particles. An optimum stability can be achieved in a small compositional corridor with Ni and Mg contents of 8–20mol%. In this composition range, the presence of MgO leads to a suppression of carbon formation, especially when compared to Ni supported on Mg-free zirconia. According to their activity and stability depending on the Ni- and Mg-contents, the catalysts were assigned to three categories: (I) low activity and high stability, (II) high activity and some stability and (III) high activity, but low stability.

Thermal Decomposition of Methane for Production of CO&lt;sub&gt;x&lt;/sub&gt; Free Hydrogen over Ni-Supported Y Zeolite Based Catalysts

The thermo-catalytic decomposition (TCD) of methane has attracted the attention of numerous researchers’ around the world as an ideal approach for hydrogen production, which in turns, can be used as an appropriate feeding gas in fuel cells operating at low temperatures. The TCD of methane is capable to produce a valuable by–product, pure carbon, which can excessively alleviate the total cost of the process. In this study, we report TCD of methane over 30% Ni supported Y zeolite catalyst at 550 and 600 °C was conducted in a fixed bed reactor and the yield of hydrogen from the reactor was analyzed by GC. As can be observed that, the TCD of methane over Ni-supported Y zeolite showed maximum conversion (31 and 15.90 % at 600 and 550 °C, respectively) at the initial stages and on stream of reaction time, it decreased gradually; and ultimately, deactivated the catalyst completely. The cause for this is the formation of encapsulating carbon on Ni active sites which deactivates the catalyst over the course of reaction time. Hydrogen production rate, carbon accumulation (CA) and carbon formation rate (CFR) were investigated at three representative times for both temperatures. The CFR analysis showed that the growth of filamentous carbon was steady-state at the first stage and then reduced to a relic activity and it remains constant during the rest of the reaction. The descriptive dissemination of methane TCD over Ni-supported Y zeolite has been speculated in this paper.

Effect of CO&lt;sub&gt;2&lt;/sub&gt; Pretreatment Operation Conditions on the Catalytic Performance and Structure of Ni-Co Bimetallic Catalyst

The performance of the Ni-Co bimetallic catalyst was significantly improved by a novel H2 and CO2 (HCD) pretreatment in the dry reforming of methane compared with traditional H2 pretreatment. The effects of the HCD pretreatment operating conditions, such as pretreatment time, temperature, gas feeding ratio, and gas flow rate, on the catalytic performance of Ni-Co bimetallic catalyst were investigated. The optimal pretreatment time, temperature, gas feeding ratio (CH4/CO2), and gas flow rate were 0.5-1 h, 780800 °C, 0:10, and 175-200 mL∙min-1, respectively. Biogas was simulated with CH4 and CO2 in a volume ratio of 1 and without any other diluted gas. The catalyst was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry (TG) coupled to differential scanning calorimetry (DSC). In a 511 h stability test under the optimized operating conditions, the catalyst pretreated with both H2 and CO2 exhibited excellent stability. The average conversions of CH4 and CO2, selectivities for H2 and CO, and volume ratio of H2/CO were 96%, 97%, 98%, 99%, and 0.98, respectively. The average carbon deposition rate over the Ni-Co bimetallic catalyst was only about 0.2 mg∙g-1∙h-1. The characterization results revealed that the sintering speed of the metal greatly decreased with testing time, and the metal particle will not greatly sinter with further testing time. The amount of deposited carbon on the catalyst gradually decreased and growth of filamentous carbon over the surface of the catalyst could be inhibited. 1325 Acta Phys. -Chim. Sin. 2014 Vol.30

Metal Dusting Corrosion Initiation in Conversion of Natural Gas to Synthesis Gas

Ni-based industrial alloy samples (INCONEL® 601) were subjected to oxidizing conditions, followed by exposure to a high carbon activity gaseous mixture containing 10% CO in Ar at 550°C in order to reveal factors critical to the initial carbon-formation. Fresh and treated samples were studied via optical-microscopy, SEM, Auger depth-profile analysis, TEM and EPMA. The results show that the extent of carbon formation is dependent on the oxidation parameters, since these affect both the composition and the structure of the 20-60nm thick oxide layer formed. A high oxygen partial pressure during oxidation appears to promote inclusion of Ni or Fe species in the oxide, which subsequently reduce and catalyse the growth of carbon filaments. Surface pre-treatment (i.e. polishing before oxidation) is also found to affect the carbon formation.

Effect of Ag on the control of Ni-catalyzed carbon formation: A density functional theory study

First-principles calculations have been performed to examine the effect of doped Ag on the kinetics of Ni-catalyzed methane dissociation and coke formation. The close-packed Ag/Ni(111) and stepped Ag/Ni(211) surfaces as well as the defect facets with step sites blocked by Ag or C atoms are constructed to investigate the role of the coordinatively unsaturated sites in the catalytic performance of Ni nanoparticles. The most stable CHx (x=0–4) adsorption configurations and transition states for methane dissociation have been identified on both Ni and Ag/Ni surfaces. The calculated results indicate that the activation energy for methane dissociation is increased with the Ag coverage on Ni(111), and the C atoms deposited on the catalyst surface can be readily separated into small islands by Ag. On Ni(211) Ag atoms are predicted to bind preferentially to the middle-step sites which act as the nucleation center for the growth of filamentous carbon and therefore have the potential to prevent catalyst particles from being destroyed. Meanwhile, as the energy barrier for methane dissociation on the Ag-blocked Ni(211) surface is even higher than that on pure Ni(111), the active center is transferred from the stepped surface to the close-packed surface. These findings provide a rational interpretation of the experimental observations that Ag/Ni catalyst exhibits lower catalytic activity towards steam methane reforming but high resistance to coke deposition.

Effect of precursors on the growth of carbon filaments onto clay surface

The successful growth of carbon filaments on two different precursors, i.e., the pristine sodium-montmorillonite (Na +MMT), which undergoes reflux at 100 °C ( r-MMT), and the Na +MMT exchanged with Fe 3+ ions (MMT(Fe)), was attained through chemical vapor deposition (CVD). The products obtained were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy, and transmission electron microscopy. Refluxing can make the Fe 3+ ions in the octahedral layer of Na +MMT migrate to the interlayer and exchange with Na + ions. Furthermore, through calcination at 500 °C, the Fe 3+ ions migrate again to the surface of the clay layer and form iron oxides, which can serve as precursors for the deposition of carbon. Although r-MMT contained less iron than the MMT(Fe), the ultimate yield of carbon components grown was almost the same, indicating that the iron species in r-MMT possess higher catalytic activity. However, on the surface of r-MMT, CVD hardly generated carbon nanotubes with a clear hollow structure but that those with a carbon fiber structure instead.

Growth of oriented vapor grown carbon fibers on pyrolytic carbon films without catalyst

Vapor-grown carbon fibers (VGCFs) have been of great interest to scientific and industrial communities for many years due to their unique crystalline structure as well as excellent physical and chemical properties [1–3]. They have potential applications as fillers in composites, superhigh hydrogen storage materials, and good electrode materials [4–8]. VGCFs are usually prepared by the decomposition of hydrocarbons, such as benzene and methane, using ultra-fine transition metal particles or their alloys as a catalyst at a growth temperature of 600–1300 C [9–11]. However, these methods sustain the disadvantage of introducing catalyst particles, which can make the synthesis process more complex, and the existence of catalyst must influence the properties of the products. Moreover, the mesoporous template or the d.c. bias was generally needed to enhance the growth of the oriented carbon nanotubes and carbon nanofibers [12, 13]. Recently, Lin et al. [14] prepared multi-walled carbon nanotubes on a porous carbon surface using carbon black as a substrate by the decomposition of diluted ethylene. Rantonen et al. [15] synthesized needle-shaped carbon filaments at low temperature by ultraviolet laser irradiation under nearand supercritical conditions without catalyst. These reports showed that the growth of carbon filaments without the aid of catalysts is possible. In this paper, microwave-assisted CVD method was used to prepare oriented VGCFs on pyrolitic carbon films by direct pyrolysis of methane without the use of any catalysts. The influence of reaction time (2, 10, 25, and 30 min) on the morphologies and structures of products at 1100 C was also discussed. The experiments were carried out in a vertical quartz tube heated in a home-made microwave furnace. The schematic of the experimental device is shown in Fig. 1. Carbon source gas is introduced into the gap between quartz tube and microwave absorbing materials, and then conducted out of microwave furnace via gas outlet. The silver-gray pyrolytic carbon films were deposited on the inner wall of quartz tube with a gas residence time of 0.1 s at 1000 C for 60 min by the microwave chemical vapor infiltration technique, and then used as the substrate. The reaction was conducted at 1100 C with the flow of mixture gas CH4/N2 (1:1 vol), for 2, 10, 25, and 30 min, respectively. After the reaction, the furnace was cooled down to room temperature in the atmosphere of N2. A layer of black filament-like substance deposited on the surfaces of the substrate was collected for analysis. The morphology and structure of products were characterized by field emission scanning electron microscopy (FESEM, Hitachi S-4700), and Raman spectroscopy (Renishaw Invia Reflex). The elemental composition of the materials was analyzed by an energy-dispersive X-ray (EDX) analysis technique attached to the scanning electron microscopy. Figure 2 shows typical FESEM images of oriented VGCFs with a uniform diameter of about 50 lm when the reaction time is 30 min. Figure 2a shows a side view of VGCFs formed on pyrolytic carbon film. It shows that the D. Fu F. Deng H. Sheng School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, Shannxi 710072, China

Effect of support and cobalt precursors on the activity of Co/AlPO 4 catalysts in Fischer–Tropsch synthesis

Cobalt supported on amorphous aluminum phosphate (Co/AlPO 4) catalysts were prepared by the impregnation method using three different cobalt precursors such as cobalt nitrate, acetate and chloride to elucidate the activity of Fischer–Tropsch synthesis. The use of AlPO 4 as a support for cobalt-based catalysts exhibits better catalytic performance during FTS reaction than the corresponding Co/Al 2O 3 catalyst. TPR results also suggest that the reducibility of the catalysts varies with the nature of cobalt precursors employed during the impregnation on AlPO 4 support. The Co/AlPO 4 catalyst prepared from cobalt nitrate shows higher CO conversion and C 8+ selectivity than the others due to the facile formation of homogeneous cobalt particles with proper electronic characters and high reducibility. Interestingly, all Co/AlPO 4 showed a growth of filamentous carbon initiated from the large mobile cobalt particles during the reaction. The differences in catalytic properties of Co/AlPO 4 are mainly attributed to the cobalt particle size, reducibility with different electronic states of metallic cobalt, pore diameter of AlPO 4 and formation of filamentous carbon.