CARBON NANOFIBRE GROWTH FROM LOW TEMPERATURE METHANE DECOMPOSITION OVER SKELETAL TRANSITION METAL...
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CARBON NANOFIBRE GROWTH FROM LOW TEMPERATURE METHANE DECOMPOSITION OVER SKELETAL TRANSITION METAL CATALYSTS James Highfield 1 , Yook Si Loo 1 , Ziyi Zhong 1 , Ruijiang Li 1 & Benjamin Grushko 2 1 Applied Catalysis Technology, Institute of Chemical & Engineering Sciences, 1 Pesek Road, Jurong Island, SINGAPORE S627833. 2 Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 GERMANY CH 4 C + 2 H 2 H 298 K = + 74.5 kJ mol -1 A. Direct eco-friendly route to “CO-free” H 2 and speciality carbons. B. Single-metal & multinary (alloy ?) skeletal catalysts from quasicrystals (QC) Route: Al 65-75 (TM/Cu) 35-25 arc melt/anneal XRD ideally single-phase QC P N2 T D ual-set point Tem perature C ontroller D ualLock G as valve To vacuum G as cylinder w ith pressure gauge T H eating Block G as D iffuser and Filter T o p lid Pre-calibrated volum e (100 m l) for calculation of gas consum ption Purge line G as cylinder w ith pressure gauge P N 2 O /He 5M NaOH C hem icalLiquid Feed pum p Knock-out pot D rain line P < 5 barg [Selective leach of Al 5 M NaOH under N 2 ] In-situ washed, dried, “passivated” catalyst custom leaching rig characteriza tion TEM XRD XRF BET catalytic testing [TG- FTIR/MS] TEM micrograph of fresh skeletal Co (ex Al 13 Co 4 ) Typical TG curve for CH4 decompositon (skeletal Co) 1. abrupt onset of weight gain (blue curve) above 350 C; 2. rapid establishment of fixed rate (10% per h @ 400 C) 250 C 300 C 350 C 400 C TEM micrographs of carbon nanofibres on skeletal cobalt deposited at 400 C (up to 50 wt. % as carbon) TG% 0.0 1.0 2.0 3. 0 Time/ h 1.0 2. 0 3.0 4.0 on carburization Co “needles” broken into fine “teardrops” metal dusting corrosion ? more proof of irreversible change new activity below 300 C ! 0.00160 0.00165 0.00170 0.00175 0.00180 0.00185 0.00190 0.00195 -4 -2 0 2 Ln rate Linear F itofD ata1_E ln ra te 1/T K M ethane C oking kinetics:250-330 C C o new 2:11/04/05 E app = 129 + /- 6 kJ.m ol -1 330 C 300 C 280 C 250 C Oven T e m p . (C) Rate of wt. gain (%) per hour in CH 4 /H 2 flow ‡ Ni ex A l 2 N i GF Ni 9 Cu ex Al 22 Ni 9 C u Ni/SA (65% Ni) Aldrich Fe 21 Cu 5 ex Al 74 Fe 21 C u 5 Fe ex Al 5 Fe 2 Co 20 Cu 14 ex Al 67 Co 20 Cu 1 4 Co ex Al 13 Co 4 Ru 22 Cu 7 ex Al 71 Ru 22 Cu 7 Ru ex Al 76 Ru 24 250 0.01 0.01 0.03 0.08 -- 0.003 0.0 5 0.005 0.001 280 0.2 8 300 0.06 0.017 0.080 0.35 0.004 0.02 0.8 2 330 1.4 2.5 0 350 0.15 0.030 0.065 zero 0 . 3 5 0.07 0.02 1.7 3.3 0 0.02 TG analysis of CH 4 decomposition: in-situ pre-reduced samples & controls ‡ CH 4 + 2 % H 2 [12 ml/min; 1:1 N 2 ] R ed: start at 400 C, then T [new low-T activity] B lue : as for Red, then switch to CH 4 /N 2 at 250 C & T [dramatic inhibition by H 2 !] Green : mean of increasing rate (Fe-containing samples) [long induction phase?] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 dTG (m g/min) H 2 vol. % Tim e (h) 450 C hold 300 C Stoichiometr y H 2 : C = 2.15 : 1 1.6 ml min -1 H 2 71 mol. min -1 0.40 mg min -1 C or 33 g at. min -1 E app = 129 +/- 6 kJ mol -1 Surface area = 30–160 m 2 g -1 Al = 5-10 wt.% Na < 1 wt.% Amorphous (except Ni) Proof of unimolecular decompn : CH 4 C + 2 H 2 Rate of C deposition vs. H 2 level [T = 450 C; cat. Fe 19 Ni 9 ; CH 4 : 80 ml min -1 ] Summary 1. Skeletal metals made from quasicrystalline precursors are “triggered” into CH 4 conversion at T > 350 C, yielding nanofibrous carbons & H 2 in the ratio C:H 2 = 1:2; 2. Pre-carburization leads to irreversible metal decrepitation, akin to “metal dusting corrosion”, creating particles in the range 20-50 nm well suited for filament growth; 3. 1st-row TMs Co, Ni, Fe, & their combinations most active, while Cu moderates activity; 4. Despite remarkable low-T activity, CH 4 conversion is still quite low (< 2% at 400 C);
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Transcript of CARBON NANOFIBRE GROWTH FROM LOW TEMPERATURE METHANE DECOMPOSITION OVER SKELETAL TRANSITION METAL...
CARBON NANOFIBRE GROWTH FROM LOW TEMPERATURE METHANE DECOMPOSITION
OVER SKELETAL TRANSITION METAL CATALYSTSJames Highfield1, Yook Si Loo1, Ziyi Zhong1, Ruijiang Li1 & Benjamin Grushko2
1 Applied Catalysis Technology, Institute of Chemical & Engineering Sciences, 1 Pesek Road, Jurong Island, SINGAPORE S627833. 2 Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 GERMANY
CH4 C + 2 H2 H298 K = + 74.5 kJ mol-1
A. Direct eco-friendly route to “CO-free” H2 and speciality carbons.
B. Single-metal & multinary (alloy ?) skeletal catalysts from quasicrystals (QC)
Route: Al65-75(TM/Cu)35-25 arc melt/anneal XRD ideally single-phase QC
P
N2
T
Dual-set pointTemperature
Controller
Dual Lock Gas valve
To vacuum
Gas cylinder with pressure gauge
T
Heating Block
Gas Diffuser and Filter
Top lid
Pre-calibrated volume (100 ml) for calculation of gas consumption
Purge line
Gas cylinder with pressure gauge
P
N2O
/He
5M NaOH Chemical Liquid Feed pump
Knock-out pot
Drain line
P
< 5 barg
[Selective leach of Al 5 M NaOH under N2]
In-situ washed, dried, “passivated” catalyst
custom leaching rig
characterization
TEMXRD
XRFBET
catalytic testing [TG-FTIR/MS]
TEM micrograph of fresh skeletal Co (ex Al13Co4) Typical TG curve for CH4 decompositon (skeletal Co)
1. abrupt onset of weight gain (blue curve) above 350 C;
2. rapid establishment of fixed rate (10% per h @ 400 C)
250 C
300 C
350 C
400 C
TEM micrographs of carbon nanofibres on skeletal cobalt deposited at 400 C (up to 50 wt. % as carbon)
TG%
0.0
1.0
2.0
3.0
Time/h 1.0 2.0 3.0 4.0
on carburization Co “needles” broken into fine “teardrops”
metal dusting corrosion?
more proof of irreversible change
new activity below 300 C !
0.00160 0.00165 0.00170 0.00175 0.00180 0.00185 0.00190 0.00195-4
-2
0
2 Ln rate Linear Fit of Data1_E
ln r
ate
1/T K
Methane Coking kinetics: 250-330 C Co new2: 11/04/05
Eapp
= 129 +/- 6 kJ.mol-1330 C
300 C
280 C
250 C
Oven Temp.
(C)
Rate of wt. gain (%) per hour in CH4/H2 flow‡
Ni ex Al2Ni
GF
Ni9Cu
ex
Al22Ni9Cu
Ni/SA(65% Ni)
Aldrich
Fe21Cu5
ex
Al74Fe21Cu5
Feex
Al5Fe2
Co20Cu14
ex
Al67Co20Cu14
Coex
Al13Co4
Ru22Cu7
ex
Al71Ru22Cu7
Ruex
Al76Ru24
250 0.01 0.01 0.03 0.08 -- 0.003 0.05 0.005 0.001
280 0.28
300 0.06 0.017 0.080 0.35 0.004 0.02 0.82
330 1.4 2.50
350 0.15 0.030 0.065 zero 0.35 0.07 0.02 1.7 3.30 0.02
360 2.6 -
380 5.3 -
400 8.80 2.20 0.001 1.5 4.4 0.57 8.1 10.6 11.25 0.80 0.07
TG analysis of CH4 decomposition: in-situ pre-reduced samples & controls
‡ CH4 + 2 % H2 [12 ml/min; 1:1 N2]
Red: start at 400 C, then T [new low-T activity]
Blue: as for Red, then switch to CH4/N2 at 250 C & T [dramatic inhibition by H2!]
Green: mean of increasing rate (Fe-containing samples) [long induction phase?]
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.00.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
dTG
(m
g/m
in)
H2 v
ol.
%
Time (h)
450 C hold
300 C
StoichiometryH2 : C = 2.15 : 1
1.6 ml min-1 H2 71 mol. min-1
0.40 mg min-1 C or 33 g at. min-1
Eapp = 129 +/- 6 kJ mol-1
Surface area = 30–160 m2 g-1
Al = 5-10 wt.%Na < 1 wt.%
Amorphous (except Ni)
Proof of unimolecular decompn: CH4 C + 2 H2
Rate of C deposition vs. H2 level [T = 450 C; cat. Fe19Ni9; CH4: 80 ml min-1]
Summary
1. Skeletal metals made from quasicrystalline precursors are “triggered” into CH4 conversion at T > 350 C, yielding nanofibrous carbons & H2 in the ratio C:H2 = 1:2;
2. Pre-carburization leads to irreversible metal decrepitation, akin to “metal dusting corrosion”, creating particles in the range 20-50 nm well suited for filament growth;
3. 1st-row TMs Co, Ni, Fe, & their combinations most active, while Cu moderates activity;
4. Despite remarkable low-T activity, CH4 conversion is still quite low (< 2% at 400 C);
5. Process operation would need high recycle ratios and rapid (in-situ?) removal of product H2, a powerful inhibitor.
