Carbon Nanotubes Roles in Enhancing the Catalytic ehavior of α-Fe2O3 Nanowires for Green Ammonia...

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Copyright American Scientific Publishers

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Copyright copy 2014 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofSurfaces and Interfaces of Materials

Vol 2 94ndash101 2014

Carbon Nanotubes Roles in Enhancing the CatalyticBehavior of -Fe2O3 Nanowires for Green Ammonia

Production Using the Magnetic Induction Method (MIM)

Noorhana Yahya1lowast Krzysztof Koziol2 Gregory Kozlowski3 Jeefferie Abd Razak4Poppy Puspitasari5 and Tshai Kim Hoe5

1Department of Fundamental and Applied Sciences Universiti Teknologi PETRONAS Bandar Seri Iskandar31750 Tronoh Perak Darul Ridzuan Malaysia

2Department of Materials Science and Metallurgy University of Cambridge Pembroke Street Cambridge CB2 3QZ United Kingdom3Department of Physics Wright State University Dayton OH 45435 United States of America4Department of Chemical Engineering Universiti Teknologi PETRONAS Bandar Seri Iskandar

31750 Tronoh Perak Darul Ridzuan Malaysia5Electrical and Electronics Engineering Department Universiti Teknologi PETRONAS BandarSeri Iskandar

31750 Tronoh Perak Darul Ridzuan Malaysia

Small surface area of catalyst and high energy consumptions environmental condition for currentindustrial ammonia production are not environmental friendly and sustainable A novel ammoniasynthesis strategy by using -Fe2O3 nanowires-CNT supported nanocatalyst was developed in thisresearch -Fe2O3 nanorods structure provides a new cutting edge in novel materials research forcatalyst application of green chemical reaction Further investigation of -Fe2O3 nanorods should becarried out to comprehend the underlying scientific fundamentals of this new generation catalyst formany valuable chemicals synthesis The preliminary works on the spontaneous growth of -Fe2O3

nanorods through thermal oxidation method and the effects of substrate surface modification by theacid treatment to the catalytic activity of -Fe2O3 nanorods supported by the CNTs are reportedand evaluated further in this paper The trial-run experimental study utilizing an appropriate designof experiment is also reported Ammonia synthesis was conducted at 25 C in ambient pressureand 02T magnetic field The highest reaction rate was 253 moleg middoth by using the hybrid cata-lyst system of treated iron nanowires with the presence of CNT nanocatalyst This method is thepromising new route for green ammonia production at room temperature and ambient pressure

Keywords -Fe2O3 Nanorods Magnetic Induction Method Inhomegeneity

1 INTRODUCTIONAmmonia is a chemical substance which has been usedas an additive in various applications such as explo-sives detergent and about 76 from the total productionof ammonia has been applied in the fertilizer industryRegrettably the current production is only capable to gen-erate 10ndash20 of ammonia yields with capital and energyintensive production environment In order to overcomethese drawbacks nanotechnology is seen as an excellentsolution By introducing -Fe2O3 nanowires and hybridnanocatalyst (iron nanowires-CNT) nanocatalyst with thenew concept of magnetic induction method the catalyticactivity can be induced and the yield can be enhanced Theobjective of this preliminary work focuses on vigorous and

lowastAuthor to whom correspondence should be addressed

systematic investigation on the -Fe2O3 nanowire-CNTnanocatalyst in promoting the yield of ammonia (NH3)under the magnetic induction method (MIM) at ambientreaction conditions with different catalyst substrate modifi-cation The role of CNTs in enhancing the catalytic behav-ior of -Fe2O3 nanorods are emphasized in this workHematite (-Fe2O3) is the most common form of crys-

talline iron oxide with the referred growth direction alongthe [110] planes and typically red in colour1 Hematiteis thermodynamically stable at ambient environment andsignificant scientific and technological importance due toits excellent properties like a small band gap (21 eV)an n-type semiconductor high resistivity to corrosion andlow cost as well as environmental friendly properties1ndash5

In terms of crystal system -Fe2O3 typical unit cell isbased on hexagonal close packing of anion O2minus with dense

94 J Surf Interfac Mater 2014 Vol 2 No 2 2164-754220142094008 doi101166jsim20141046



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Yahya et al CNTs Roles in Enhancing the Catalytic Behavior of -Fe2O3 Nanowires for Green Ammonia Production

arrangement of iron (Fe3+) occupying two third of theoctahedral sites (FeO6) that share a face with another in thelayer above or below2 The crystallographic arrangement issimilar to corundum structure which is trigonal-hexagonalscalenohedral class 32m of space group=R3c-167 neutralstructure with no charge excess or deficit with the latticeconstant of ao = 05034 nm and co = 1375 nm135 Con-sidering all the benefits and robust characteristic of thismaterial it is suggested to be used as a catalyst for chem-ical reaction by modifying the morphologies of the oxidesusing the thermal oxidation method and substrate modi-fication with acid treatment for development of -Fe2O3

nanorods growth with the assistance of very small additionof carbon nanotubes

Carbon nanotubes have metallic or semiconductionproperties due to their fiber geometry and the curvatureof graphitic planes6 It has small dimension and excellentmechanical electrical thermal and chemical properties7

CNTs are available in two forms multi-walled carbonnanotubes (MWCNTs) and the second type is singlewalled carbon nanotubes (SWCNTs)8ndash10 SWCNTs can beconsidered as a single graphene sheet which is a mono-layer of sp2 bonded carbon atoms that rolled into a seam-less cylinder MWCNTs are close to hollow graphite fibersbut have a much higher degree of structural perfectionThey are made of concentric cylinders placed around acommon central hollow911 Nano-dimensions provide alarge surface area which could be useful in mechanicaland chemical applications The physico-mechanical prop-erties of CNTs are dependent upon their size dimensionshelicity or chirality810 CNTs are chemically inert sincethe only exposed surface in nanotubes is the unreactivebasal graphite plane812 As a result of it the CNTs aresubject to the rules of carbon chemistry which means thatthey can be covalently functionalized12 The MWCNTsused in this study were synthesized by using the method offloating catalyst chemical vapor deposition (FC-CVD)13

Since the reactions are carried out at lower temperatures(700 to 1500 C) than those of the carbon arc the CNTsproduced by CVD are not straight but curved and entan-gled in a conglomeration containing also catalyst particlesand other carbonaceous products likes soot and fibers89

CNTs made from CVD method generally have very largequantities of defects Their physical properties suffer dueto the presence of defects with thermal electronic andmechanical properties deviating significantly from thoseexpected for pristine CNTs

Carbon nanotubes supported catalyst is a novel sup-ported catalyst instead of the conventional alumina orsilicon For carbon nanotubes (CNTs) the exceptionalphysical properties such as large specific surface areasexcellent electron conductivity incorporated with the goodchemical inertness and relatively high oxidation stabilitymakes it a promising support material for heterogeneouscatalysis14

2 EXPERIMENTAL METHODS ANDCHARACTERIZATION

21 CNTs and -Fe2O3 Nanorods Synthesis andCharacterization

CNTs were grown by the FC-CVD method Synthesisparameters were fixed based on the best condition param-eters obtained by previous researchers131516 Synthesisparameters employed in this study were 50 minutes forthe reaction period at 850 C 350 mlmin for the hydrogenflow rate and 200 mg for the amount of ferrocene catalystMicroscopy observation through the Scanning ElectronMicroscope (SEM) were performed on a Philips XL30(Holland) Environmental Scanning Electron Microscope(ESEM) operated at 250 kV of the accelerating volt-ages Microscopy observations through the TransmissionElectron Microscope (TEM) were performed on a PhilipsTEM-400 High resolution transmission electron micro-scope (HRTEM) model Philips Technai 20 with an accel-eration voltage of 200 kV was employed for the CNTsstructural characterization-Fe2O3 nanorods were grown on pure Fe wire sub-

strate (1 mm diameter) in the ambient air furnace condi-tion at various oxidation temperatures (350ndash950 C) within75 minutes Further substrate surface modification usingacid treatment at 18M of H2SO4 molarity concentrationwas conducted followed by thermal oxidation at 750 C

22 2-Level Factorial Design of Experiment2-level factorial design of experiment has been used forthe preliminary study of the effect of magnetic induc-tion strength quantity of Helmholtz coils frequency ofHelmholtz coils and N2 flow rate on the ammonia syn-thesis at normal pressure and at room temperature The-Fe2O3 nanocatalyst which was annealed at 750 C wasused in both reactor and Helmholtz coils system to lowerthe reaction energyThe Helmholtz coils were located before the reactor and

connected to an AC circuit where the frequency can beadjusted up to 80 MHz A total of 36 runs of experi-ment were conducted with factors 2 replicates and 4 cen-ter points The experimental parameters are tabulated asshown in Table IDuring the experiments N2 gas was set as an excess

reactant which will react with H2 to produce NH3 N2

and H2 gases were flowed continuously for 30 min intothe reactor and the product was further collected or dis-solved by 25 mL acid hydrochloric (HCl) for ammoniaquantification by using the Kjeldahl method

Table I Design of experiment of MIM trial-run

Factor Units Low level High level

Qty of helmholtz coils No of coils (pair) 1 3Freq of helmholtz coils MHz 30 80N2 flow rate mLmin 50 100Magnetic induction strength Tesla 0 02

J Surf Interfac Mater 2 94ndash101 2014 95



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CNTs Roles in Enhancing the Catalytic Behavior of -Fe2O3 Nanowires for Green Ammonia Production Yahya et al

Fig 1 Magnetic induction reaction zone

23 Kjeldahl Method for Ammonia QuantificationKjeldahl method is a method to quantify the amount ofnitrogen in chemical substance9 A titration process wasdone to trace the amount of produced ammonia10

HClreacted+NH3g rarrNH4Cl

NaOH+HClexcess rarrNaCl+H2O

HCltotal = HClreacted+HClexcess

Amount of HClreacted = Amount of NH3

Amount of HClexcess = Amount of NaOH

Ammonia detection was done by dissolving the gas in25 ml of 001 M HCI (in excess) to produce NH4Cl Theamount of excess HCl was determined by titration with001M NaOH(aq) The amount of NH3 produced is equalto the amount of HCl reacted

24 CNTs--Fe2O3 Nanorods Hybrid Nanocatalystfor Ammonia Synthesis

For this part CNTs were added in small amount(03 grams) to the existing -Fe2O3 nanorods on themetal substrate (13 g) to evaluate its role in enhanc-ing the catalytic activity of the -Fe2O3 nanorods forammonia production The reaction period of 30 min inthe semi-continuous tabular flow reactor (Fig 1) wasapplied The experimental strategies are tabulated in thefollowing Table II Similar ammonia (NH3) quantificationmethod utilizing the Kjeldahl method is applied for thispart

Table II CNTs--Fe2O3

Type of nanocatalyst and treatment (18M H2SO4)

None (blank reactorndashcontrol)Untreated -Fe2O3 without CNTTreated -Fe2O3 without CNTUntreated -Fe2O3 with CNTTreated -Fe2O3 with CNT

3 DISCUSSION31 -Fe2O3 Nanorods CharacterizationFigure 2 clearly depicts the formation of -Fe2O3

nanorods at temperature of 600 C and 750 C At 350 Cthe morphology of sharp nanoflakes of -Fe2O3 has beendetected whereas at 950 C the Fe substrate experi-enced over oxidation and oxide layer cracked Dimensionalobservation on each nanorods found that the optimumdiameter of rods ranges between 20ndash29 nm for 600 C and80ndash120 nm for 750 C of oxidation temperature -Fe2O3

nanorods grown at 750 C produces inhomogeneity inlength and tip size which is good to create high den-sity electron environment that is required for promotingthe chemical reaction through the physics route Forma-tion of -Fe2O3 nanorods is confirmed through the pointand mapping EDX spectroscopy technique whereby therelative concentration of Fe to O is approximately 4060or 23 for FeO (mapped along the tip to the base ofnanorods) The effect of acid treatment with different con-centration on -Fe2O3 nanorods growth at 750 C is pre-sented in Figure 3 It is obviously found that the acidtreatment caused the dimension increase by increasingthe acid molarities during the treatment Acid treatmentincreased the density of -Fe2O3 nanorods with certaindegree of inhomegeneity random growth of nanorodsor nanowires However the nanorods experienced severestructural imperfection and the tip breakage due to acidtreatmentThe -Fe2O3 nanorods morphologies has been viewed

and observed by using the High Resolution Transmis-sion Electron Microscope (HRTEM) The HRTEM imagesconfirmed the nanorods produced is a single crystallineof -Fe2O3 (Fig 4) Selected area electron diffraction(SAED) pattern revealed that the nanorods preferentialgrowth direction is [110] and the interplanar spacingof 02213 nm agrees well with the fringe spacing of-Fe2O3 nanostructure The SAED pattern reveals that thecrystal structure of the -Fe2O3 nanorods is rhombohe-dral The schematic of growth mechanism is adapted17

and is depicted as in Figure 4(b) where Fe is sup-plied from the substrate and O2 from the surround-ing Insets show rhombohedral tip and amorphous edgeof the rods which provide some hints on the growthmechanism11

32 CNTs Support CharacterizationThe bulk morphology of the long CNTs is ldquospaghettirdquolike randomly oriented and some of them are entangledIt is interesting to note that the ldquoforestrdquo of CNTs wasclearly viewed at 5000times of magnification power CNTsproduced were in the bundles of long layered structuremuch like grass and not well aligned to the certain direc-tion of orientation (Fig 5) In addition the presences ofbright spots indicate the presence of ferrocene catalyst par-ticle in the sample30 By increasing the magnification of

96 J Surf Interfac Mater 2 94ndash101 2014



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(a) Pure Fe (Control) (c) 600 degC(b) 350 degC

(d) 750 degC (e) 950 degC

Fig 2 The morphologies of oxide formation at various oxidation temperatures (a) Pure Fe (b) 350 C (c) 600 C (d) 750 C (e) 950 C

SEM to 40000times (Fig 5) it was clearly observed that theCNTs produced were open-ended type

Each individual tube has ID and OD values more or lessthe same with their diameter of up to 1 m and 500 nmrespectively In addition it can be clearly seen that the wallof CNTs is made up of a series of lines or fringes wherein the graphitic layers are well separated and aligned

As can be seen in Figure 6 the metal catalysts werestuck inside the middle part of the tubes Basically duringthe growth process of CNTs in the FC-CVD process thecatalysts particles can either stay at the tips of the grow-ing nanotubes or remain at the nanotubes base dependingon the adhesion between the catalyst particle and the sub-strate Since the process of CNTs growth does not involveany substrate thus floating growth mechanism allowedthe metallocene catalysts to initiate the growing processin the bi-directional way or so-called double tip growthmechanism During the tip growth the end of nanotubesremained stuck to the surface and the catalyst particleshoots into the air at the opposite end of the extruding

(a) Untreated at 750 ordmC (b) 1M H2SO4 at 750 ordmC (c) 18M H2SO4 at 750 ordmC

Fig 3 The effect of acid concentration on -Fe2O3 nanorods growth at 750 C with (a) untreated (b) 1 M H2SO4 (c) 18 M H2SO4 at 750 C

nanotubes Thus it can be seen that most of the catalystis prone to be trapped at the middle of the tubes Thismechanism of CNTs growth can be called as the gas phasegrowth whereby the formation of nanotubes occurred lit-erally in the mid-air18 The diameters of the nanotubes thatare to be grown are also related to the size of the cata-lysts particles This can be validated from the presence oftrapped catalysts particle inside the tube Different diame-ter of trapped catalysts created different internal diameterfor the CNTs grown

33 2-Level Factorial Design of ExperimentThe normal plot of residuals (Fig 7) is in a straight lineThis indicates that there are no abnormalities during theexperiment19 Hence the experimental results can be usedfor further analysisAccording to the user guide of Design-Expert where

the Probgt F value of less than 005 is an indication thatthe model terms are significant Table III shows that the




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(a) (b)

Fig 4 TEM images of -Fe2O3 nanorods (750 C treated with 18M H2SO4) and schematic of growth mechanism

analysis model is statistically significant and the valuescan be fitted into the model (the Probgt F value for Lackof Fit is not significant) The Anova summary table alsoshows that the frequency that was applied to the HelmholtzCoils is a significant factor that will alter the ammo-nia synthesis reaction Besides it has interaction effect inbetween quantity of Helmholz Coils and magnetic induc-tion strength frequency of Helmholz Coils and magneticinduction strength N2 flow rate and magnetic inductionstrengthFigure 8 shows that better yield of ammonia synthesis

can be obtained by setting the magnetic induction strengthto high level under the high frequency condition This maybe at high frequency more fluctuation of electrons couldhappen and weakening the bond and tend to help on bonddissociation2024

As shown in Figure 9 the ammonia synthesis yield canbe improved by decreasing the N2 flow rate (still main-taining the N2 gas as excess gas)

Fig 5 SEM observation of other carbonaceous product obtained by FC-CVD process (20000times of magnification) Open-ended structure of theas-produced CNTs observed at 40000times of magnification power

The ammonia synthesis yield can be predicted by usingthe equation

NH3Yield = +21976181minus603125lowastAminus00225lowastBminus004lowastCminus399375lowastD+004625lowastAC+209375lowastAD+08625lowastBDminus063750lowastCD

WhereA= Qty of Helmholtz CoilsB = Freq of Helmholtz CoilsC = N2 flow rateD =Magnetic induction strengthThis can be shown in Figure 10 Referring to the 3D

plots of interaction the highest yield of ammonia synthesiscan be achieved by going to large number of HelmholtzCoils high frequency of Helmholtz Coils low flow rate ofN2 and high magnetic induction strength




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(a) (b)

Fig 6 Micrographs of trapped catalyst particles and its dimensional analysis

Fig 7 Normal plot of residuals

34 CNTs--Fe2O3 Nanorods Hybrid Nanocatalystfor Ammonia Synthesis-Conversion Results

The ammonia synthesis was conducted at room tem-perature and ambient pressure using -Fe2O3 nanowires

Table III Annova summary

Source Sum of squares Df Mean square F value p-value probgt F

Model 50475 8 6309 58 00003A-QTY of Helmholtz coils 703 1 703 065 04286B-frequency of helmholtz coils 8128 1 8128 747 00111C-N2 flow rate 253 1 253 023 06335D-magnetic induction strength 078 1 078 0072 07908AC 4278 1 4278 393 0058AD 14028 1 14028 129 00013BD 14878 1 14878 1368 0001CD 8128 1 8128 747 00111Curvature 6142 1 6142 565 00251Residual 28272 26 1087Lake of fit 9847 7 1407 145 02435Pure error 18425 19 97Core total 84889 35

and -Fe2O3 nanowires-CNT as nanocatalysts The reac-tant gases (hydrogen and nitrogen) were reacted withthe nanocatalyst under 02T magnetic induction method(MIM) for 30 minutes duration The yield of ammoniasynthesis is shown in Table IVFrom the result in Table IV the treated -Fe2O3 with

CNT shows the highest yield at 253 ppm This resultshows the increase of ammonia conversion of 2 com-pared to the untreated -Fe2O3 with CNT27 It reveals thatthe strength of the hydrogen bond inside the carbon nano-tube will become weaker if there is a larger intramolecularelectron-density transfer from the electron rich region ofthe hydrogen atom donor to the antibonding orbital of theXndashH bond It also involved in the formation of the hydro-gen bond and will become stronger if there is a largerintermolecular electron-density transfer from the electron-rich region of the hydrogen atom acceptor to the antibond-ing orbital of the XndashH bond21 It is well known that CNTcontains an effective catalyst for oxygen reduction andwith the iron-carbon centers it forms the catalytic activesite2226




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Fig 8 Interaction in between magnetic induction strength and fre-quency of Helmholtz coil

Fig 9 Interaction in between magnetic induction strength and N2 flowrate

Higher ammonia yield can be resulted from the ortho-para hydrogen interconversion under the influence ofapplied magnetic field23 The interconversion ortho-parahydrogen depends on the relative realignment of the twoproton spins in the molecule The ortho-para interconver-sion work should come from the inhomogeneous magneticfields which can interchange singlet and triplet electronspin phasing well as the nuclear spins This interconversionwill then affect the chemical reaction A singlet-phasedpair of spins can be induced to switch into a triplet if theirindividual precession frequencies differ25 The quantitativeof the discussion can be written by using Hamiltonianequation as follows28

H = fA middotSA+ fB middotSB = 12fA+ fB middot SA+SB

+ 12fAminus fB middot SAminusSB (1)

This formula is the antisymmetric in the spins and con-tributes to matrix elements T H S Because the singletis antisymmetric in the spins the triplet is symmetric and

Fig 10 3D plots of interactions of magnetic induction and frequencyof Hemholtz

Table IV Ammonia conversion obtained by MIM method

Type of nanocatalyst Ammonia conversionNo and treatment (ppm)

1 None 2372 Untreated -Fe2O3 without CNT 2403 Treated -Fe2O3 without CNT 2454 Untreated -Fe2O3 with CNT 2485 Treated -Fe2O3 with CNT 253

the whole matrix element must be symmetric if it is notto be zero The term sAndashsB will be vanished if fA = fBand this is the reason why the Larmor precession frequen-cies must be differ if singlet-triplet interconversion are tooccur29

4 CONCLUSIONSIt can be concluded that the -Fe2O3 nanorods has beensuccessfully grown by using the simple method of thermaloxidation in normal air condition The preliminary stud-ies on the effect of acid treatment have been conductedand several related and reliable characterization has beenmade Treatment at 750 C with 18 M H2SO4 yields inhomogeneous growth of nanorods From the preliminarydesign of experiment studied it is found that the ammo-nia synthesis yield is affected by adjusting the magneticinduction strength quantity of Helmholtz Coils frequencyof Helmholtz Coils and N2 flow rate Furthermore addi-tion of the very small quantity of CNTs (sim03 grams)helps to maximize the conversion of ammonia catalyzedby -Fe2O3 nanorods catalyst up to 253 ppm

Acknowledgments The authors express a specialthanks to Ministry of Higher Education (MOHE) Malaysiafor the Long Term Research Grant (LRGS) under theProject title ldquoGreen Ammonia Synthesisrdquo and Cost center0153AB-C71 and Universiti Teknologi PETRONAS forfinancial assistance

References and Notes1 D Chen S Xiong S Ran B Liu L M Wang and G Z Shen

Sci China Phys Mech Astron 7 1190 (2011)2 J R Morber Understanding Growth and Properties as Steps toward

Biomedical and Electrical Application [PhD dissertation] GeorgiaInst of Tech (2008)

3 V B Trindade R Borin B Z Hanjari S Yang U Krupp andH-J Christ High Materials Research 8 365 (2005)

4 Y Fu J Chen and H Zhang Chem Phys Lett 350 491 (2001)5 Q Han Y Y Fu H Zhang R M Wang T M Wang and Z Y

Chen Chem Phys Lett 431 100 (2006)6 Y Cai J D Lin H B Chen H B Zhang G D Lin and D W

Liao Chin Chem Lett 11 373 (2000)7 S G Kim S Y Kim and H W Lee Trans Nonferrous Met Soc

China 21 130 (2011)8 P M Ajayan Chem Rev 99 1787 (1999)9 G O Shonaike and S G Advani Advanced Polymeric Materials

Structure Property Relationships CRC Press (2003)




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10 X L Xie Y-W Mai and X-P Zhou Materials Science and Engi-neering R 49 89 (2005)

11 M Moniruzzaman and K I Winey Macromolecules 39 5194(2006)

12 M D Ventra S Evoy and J R Heflin Jr Introduction toNanoscale Science and Nanotechnology 88 (2004)

13 N Girun A Fakhrul-Razi A R Suraya and M A AtiehFullerenes Nanotubes and Carbon Nanostructures 15 207 (2007)

14 M S Dresselhaus G Dresselhaus and P Avouris SpringerNew York (2001)

15 R N Izawati MSc Thesis Universiti Putra Malaysia (2007)16 M A Atieh N Girun E-S Mahdi H Tahir C T Guan M F

Alkhatib A Fakhru-Razi and D R Baik Fullerenes Nanotubesand Carbon Nanostructures 14 641 (2006)

17 P Hiralal H E Unalan K G U Wijayantha A KursumovicD Jefferson J L MacManus-Driscoll and G A J AmaratungaNanotechnology 19 1 (2008)

18 C Vargis MSc Thesis Universiti Putra Malaysia (2007)19 Design-Expert 6 Userrsquos Guide Stat-Ease (2000)

20 T Christopher Rodgers Pure Appl Chem 81 19 (2010)21 W Wang D Wang Y Zhang B Ji and A Tian J Chem Phys

134 (2011)22 K Gong Science 323 760 (2009)23 P W Atkins and T P Lambert The effect of a Magnetic Field on

Chemical Reactions Available httppubsrscorg24 F Garbassi G Fagherazzi and M Calcaterra J Catal 26 338

(1972)25 J Pernicone F Ferrero Z Rosetti L Forni P Canton P Rinello G

Fagherazzi M Signorot and J Pinna Appl Catal 251 121 (2003)26 Y Ando X Zhao H Shimoyama G Sakai and K Kaneto Int J

Inorg Mater 1 77 (1999)27 A A Tsyganenko D V Fozdnyakov and V N Filimonov J Mol

Struct 29 299 (1975)28 Teacher guide Infrared Spectroscopy Genesis 129 J Y Park and D E Woon The Astrophysical Journal 648 1285

(2006)30 R Loos J Wollgast T Huber and G Hanke Analytical Bioanual

Chemistry 387 1869 (2007)

Received 15 August 2014 Accepted 9 September 2014




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arrangement of iron (Fe3+) occupying two third of theoctahedral sites (FeO6) that share a face with another in thelayer above or below2 The crystallographic arrangement issimilar to corundum structure which is trigonal-hexagonalscalenohedral class 32m of space group=R3c-167 neutralstructure with no charge excess or deficit with the latticeconstant of ao = 05034 nm and co = 1375 nm135 Con-sidering all the benefits and robust characteristic of thismaterial it is suggested to be used as a catalyst for chem-ical reaction by modifying the morphologies of the oxidesusing the thermal oxidation method and substrate modi-fication with acid treatment for development of -Fe2O3

nanorods growth with the assistance of very small additionof carbon nanotubes

Carbon nanotubes have metallic or semiconductionproperties due to their fiber geometry and the curvatureof graphitic planes6 It has small dimension and excellentmechanical electrical thermal and chemical properties7

CNTs are available in two forms multi-walled carbonnanotubes (MWCNTs) and the second type is singlewalled carbon nanotubes (SWCNTs)8ndash10 SWCNTs can beconsidered as a single graphene sheet which is a mono-layer of sp2 bonded carbon atoms that rolled into a seam-less cylinder MWCNTs are close to hollow graphite fibersbut have a much higher degree of structural perfectionThey are made of concentric cylinders placed around acommon central hollow911 Nano-dimensions provide alarge surface area which could be useful in mechanicaland chemical applications The physico-mechanical prop-erties of CNTs are dependent upon their size dimensionshelicity or chirality810 CNTs are chemically inert sincethe only exposed surface in nanotubes is the unreactivebasal graphite plane812 As a result of it the CNTs aresubject to the rules of carbon chemistry which means thatthey can be covalently functionalized12 The MWCNTsused in this study were synthesized by using the method offloating catalyst chemical vapor deposition (FC-CVD)13

Since the reactions are carried out at lower temperatures(700 to 1500 C) than those of the carbon arc the CNTsproduced by CVD are not straight but curved and entan-gled in a conglomeration containing also catalyst particlesand other carbonaceous products likes soot and fibers89

CNTs made from CVD method generally have very largequantities of defects Their physical properties suffer dueto the presence of defects with thermal electronic andmechanical properties deviating significantly from thoseexpected for pristine CNTs

Carbon nanotubes supported catalyst is a novel sup-ported catalyst instead of the conventional alumina orsilicon For carbon nanotubes (CNTs) the exceptionalphysical properties such as large specific surface areasexcellent electron conductivity incorporated with the goodchemical inertness and relatively high oxidation stabilitymakes it a promising support material for heterogeneouscatalysis14

2 EXPERIMENTAL METHODS ANDCHARACTERIZATION

21 CNTs and -Fe2O3 Nanorods Synthesis andCharacterization

CNTs were grown by the FC-CVD method Synthesisparameters were fixed based on the best condition param-eters obtained by previous researchers131516 Synthesisparameters employed in this study were 50 minutes forthe reaction period at 850 C 350 mlmin for the hydrogenflow rate and 200 mg for the amount of ferrocene catalystMicroscopy observation through the Scanning ElectronMicroscope (SEM) were performed on a Philips XL30(Holland) Environmental Scanning Electron Microscope(ESEM) operated at 250 kV of the accelerating volt-ages Microscopy observations through the TransmissionElectron Microscope (TEM) were performed on a PhilipsTEM-400 High resolution transmission electron micro-scope (HRTEM) model Philips Technai 20 with an accel-eration voltage of 200 kV was employed for the CNTsstructural characterization-Fe2O3 nanorods were grown on pure Fe wire sub-

strate (1 mm diameter) in the ambient air furnace condi-tion at various oxidation temperatures (350ndash950 C) within75 minutes Further substrate surface modification usingacid treatment at 18M of H2SO4 molarity concentrationwas conducted followed by thermal oxidation at 750 C

22 2-Level Factorial Design of Experiment2-level factorial design of experiment has been used forthe preliminary study of the effect of magnetic induc-tion strength quantity of Helmholtz coils frequency ofHelmholtz coils and N2 flow rate on the ammonia syn-thesis at normal pressure and at room temperature The-Fe2O3 nanocatalyst which was annealed at 750 C wasused in both reactor and Helmholtz coils system to lowerthe reaction energyThe Helmholtz coils were located before the reactor and

connected to an AC circuit where the frequency can beadjusted up to 80 MHz A total of 36 runs of experi-ment were conducted with factors 2 replicates and 4 cen-ter points The experimental parameters are tabulated asshown in Table IDuring the experiments N2 gas was set as an excess

reactant which will react with H2 to produce NH3 N2

and H2 gases were flowed continuously for 30 min intothe reactor and the product was further collected or dis-solved by 25 mL acid hydrochloric (HCl) for ammoniaquantification by using the Kjeldahl method

Table I Design of experiment of MIM trial-run

Factor Units Low level High level

Qty of helmholtz coils No of coils (pair) 1 3Freq of helmholtz coils MHz 30 80N2 flow rate mLmin 50 100Magnetic induction strength Tesla 0 02




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Chemistry 387 1869 (2007)





RESEARCH

ARTIC

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RESEARCH

ARTIC

LE



















Chemistry 387 1869 (2007)





RESEARCH

ARTIC

LE



















Chemistry 387 1869 (2007)



Carbon Nanotubes Roles in Enhancing the Catalytic ehavior of α-Fe2O3 Nanowires for Green Ammonia...

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Transcript of Carbon Nanotubes Roles in Enhancing the Catalytic ehavior of α-Fe2O3 Nanowires for Green Ammonia...