James Highfield 1 , Yook Si Loo 1 , Ziyi Zhong 1 , Ruijiang Li 1 & Benjamin Grushko 2
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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);
description
James Highfield 1 , Yook Si Loo 1 , Ziyi Zhong 1 , Ruijiang Li 1 & Benjamin Grushko 2 - PowerPoint PPT Presentation
Transcript of James Highfield 1 , Yook Si Loo 1 , Ziyi Zhong 1 , Ruijiang Li 1 & Benjamin Grushko 2
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.
