The Partial Benzene/Butane Maleic Anhydride …The Detailed Kinetics of the Partial Oxidation...
Transcript of The Partial Benzene/Butane Maleic Anhydride …The Detailed Kinetics of the Partial Oxidation...
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The Detailed Kinetics of the Partial Oxidation Reactions:
Benzene/Butane to Maleic Anhydride
Ethylene to Ethylene Oxide
Ken Waugh
Emeritus Professor of Physical Chemistry
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ICI Central Instruments Research LabBozedown House Berkshire
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The Oxidation of Benzene to Maleic Anhydride Over Vanadium Pentoxide D(V‐O) = 600 kJmol‐1
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D A Dowden mechanism of benzene oxidation to MA using molecularly adsorbed O2
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Maleic anhydride temperature programmed desorption spectra from V2O5: adsorption temperature (a) 135, (b) 150, (c) 160, (d) 170, (e)
180, (f) 190, (g) 200 C
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Benzene temperature programmed desorption spectra: curve (a) benzene, curve (b) maleic anhydride
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Desorption spectra following the adsorption of benzene at (a) 75, (b) 90 and (c) 100 C. Curves 1and 2 are benzene; curve (c) is maleic anhydride
Activation Energy 31 kJmol‐1
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The Oxidation of n‐butane to Maleic Anhydride
• Anaerobic Selectivity 80%
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The (100) face of (VO)2P2O7 – the active face
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Recirculating Solids Reactor forn‐butane Oxidation to Maleic Anhydride ‐ DuPont
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Schematic Representation of the Mars and van Krevelen Mechanism
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Oxygen desorption from (VO)2P2O7
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Anaerobic Temperature Programmed Oxidation of n‐butane over the (VO)2P2O7 Catalyst
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Anaerobic Temperature Programmed Oxidation of but‐1‐ene over the (VO)2P2O7 Catalyst
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Anaerobic Temperature Programmed Oxidation of but‐1,3‐diene over the (VO)2P2O7 Catalyst
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Side View of n‐butane Adsorbed End‐on
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Identification of the Origins of Selectivity in Ethylene Epoxidation on Promoted and
Unpromoted Ag/α‐Al2O3 Catalysts: a detailed kinetic, mechanistic and
adsorptive study
Matt Hague, Ken Waugh
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The Reaction
CH2 = CH2 + 1/2O2
Ag/Al2O3
CH2Cl CH2ClCH2 CH2
OComposition (CH2 = CH2) 12 bar (CH2Cl CH2Cl) ppm
O2 3 bar
Temperature 500K Pressure 15 atmospheres
The Catalyst Ag/Cs/Al2O3
Ag area 2.0 m2g-1 Ag particle size 280 nm
The Problem:• Reaction mechanism• Role of Cl• Role of Cs
Ag loading 10% w/wCs loading 0.1% w/w
+ CO2
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Oxygen desorption spectra from the Ag/α‐Al2O3 catalyst Tm=250°C(523K), the α1‐state;
Tm = 300°C(573 K), the α2‐stateDose: O2, 1 atmosphere, 25 cm3/min, 240ºC
0
1x10-10
2x10-10
3x10-10
4x10-10
373 473 573 673 773
1st Oxygen TPD2 d O y en T
Temperature / K
Massspecresponse/arb.units
Mas
s sp
ec re
spon
se /
arb
units 1st Oxygen TPD
2nd Oxygen TPD
Temperature / C
0.4
0.3
0.2
0.1
100 200 300 4000
1x10-10
2x10-10
3x10-10
4x10-10
373 473 573 673 773
1st Oxygen TPD2 d O y en T
Temperature / K
Massspecresponse/arb.units
Mas
s sp
ec re
spon
se /
arb
units 1st Oxygen TPD
2nd Oxygen TPD
Temperature / C
0.4
0.3
0.2
0.1
100 200 300 400100 200 300 400
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Temperature programmed reaction of ethylene with the α1‐ and α2‐O species adsorbed on the Ag/α‐Al2O3 catalyst
m/z = 29 is EO, m/z = 44 is CO2
0
1x10-1
2x10-1
3x10-1
4x10-1
5x10-1
-100 0 100 200 300
0.5
0.4
0.3
0.2
0.1Mas
s sp
ec re
spon
se /
arb
units
Temperature / °C
-100 0 100 200 300
Mass 44Mass 29
0
1x10-1
2x10-1
3x10-1
4x10-1
5x10-1
-100 0 100 200 300
0.5
0.4
0.3
0.2
0.1Mas
s sp
ec re
spon
se /
arb
units
Temperature / °C
-100 0 100 200 300
Mass 44Mass 29
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EO and CO2 Formed SimultaneouslyThey therefore originate in a common intermediate
‐ TS1 (or the oxametallacycle)
• SELECTIVITY = EO formed/Ethylene Converted
• SELECTIVITY of 100°C(373K) Peak = 57%: the selective and unselective reactions have nearly the same energetics
• SELECTIVITY of 200°C(473K) Peak = 33%: the unselective pathway is 2 times more likely than the selective one
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Oxygen desorption spectrum from the Ag/α‐Al2O3 catalyst after having desorbed the low temperature oxygen peak (the α1‐state) by heating
in He to 503 K for 10 min
0
0.5x10-10
1.0x10-10
1.5x10-10
2.0x10-10
373 473 573 673 773
Temp/ K
massspec.response/arb.units
Mas
s sp
ec re
spon
se /
arb
units
0.2
0.1
0 100 200 300 400 500
Temperature / °C
0
0.5x10-10
1.0x10-10
1.5x10-10
2.0x10-10
373 473 573 673 773
Temp/ K
massspec.response/arb.units
Mas
s sp
ec re
spon
se /
arb
units
Temp/ K
massspec.response/arb.units
Mas
s sp
ec re
spon
se /
arb
units
0.2
0.1
0 100 200 300 400 500
Temperature / °C
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Temperature programmed reaction of ethylene with the oxidised Ag/α‐Al2O3 catalyst having desorbed 80% of the α1‐O state (m/z = 29 is
EO, m/z = 44 is CO2)
0
1x10-10
2x10-10
3x10-10
4x10-10
5x10-10
-100 0 100 200 300173 273 373 473 5730
1x10-10
2x10-10
3x10-10
4x10-10
5x10-10
-100 0 100 200 300173 273 373 473 573
0.2
0.4
0.3
0.5
0.1
-100 0 100 200 300
Mas
s sp
ec re
spon
se /
arb
units
Temperature / °C
Mass 44Mass 29
0
1x10-10
2x10-10
3x10-10
4x10-10
5x10-10
-100 0 100 200 300173 273 373 473 5730
1x10-10
2x10-10
3x10-10
4x10-10
5x10-10
-100 0 100 200 300173 273 373 473 573
0.2
0.4
0.3
0.5
0.1
-100 0 100 200 300
Mas
s sp
ec re
spon
se /
arb
units
Temperature / °C
0
1x10-10
2x10-10
3x10-10
4x10-10
5x10-10
-100 0 100 200 300173 273 373 473 5730
1x10-10
2x10-10
3x10-10
4x10-10
5x10-10
-100 0 100 200 300173 273 373 473 573
0.2
0.4
0.3
0.5
0.1
-100 0 100 200 300
Mas
s sp
ec re
spon
se /
arb
units
Temperature / °C
Mass 44Mass 29
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The coverage of the α1‐O state is only 20% of saturation
• The selectivity of the low coverage α1‐O state is 75% compared with a value of 57% for saturation coverage. This is an important observation
• The selectivity of the α2‐O state remains unchanged at 34%. The two surfaces react independently.
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O atom adlayer on the Ag(110)
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The stronger the Ag‐O bond is, the less likely it is to stretch and cyclise to EO
The stronger the Ag‐O is, the more likely it is to abstract H atoms from the adsorbate
Both result in its being less selective
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The role of subsurface O atoms: TPD spectra of an oxidised, sintered Ag/α‐Al2O3 catalyst containing 1.6, 2.0, 2.3 and 2.8 ML of subsurface O atoms produced by dosing O2(1 bar) for 1 h at the temperatures indicated
0
0.5x10-10
1.0x10-10
1.5x10-10
2.0x10-10
473 673 873
813 K753 K693 K633 K Subsu
Atomic surface oxygen
file g25-28Temperature / K
MassSpecResponse/arb.units
Mas
s sp
ec re
spon
se /
arb
units
540°C480°C420°C360°C
α atomic surface oxygen β subsurface
oxygen
0.2
0.1
200 400 600
Temperature / °C
0
0.5x10-10
1.0x10-10
1.5x10-10
2.0x10-10
473 673 873
813 K753 K693 K633 K Subsu
Atomic surface oxygen
file g25-28Temperature / K
MassSpecResponse/arb.units
Mas
s sp
ec re
spon
se /
arb
units
540°C480°C420°C360°C
α atomic surface oxygen β subsurface
oxygen
0.2
0.1
200 400 600
Temperature / °C
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Temperature programmed reaction of ethylene with an oxidised Ag/α‐Al2O3
catalyst containing both surface and 2.3 ML of subsurface O atoms
0
2x10-10
4x10-10
6x10-10
150 300 450 600 750
Mass 29Mass 18 (Water)Mass 44
Temp / K
Massspecresponse/arb.units
373 673 973
Mas
s sp
ec re
spon
se /
arb
units 0.6
0.4
0.2
100 400 700
Temperature / °C
Mass 18
Mass 44
Mass 29
0
2x10-10
4x10-10
6x10-10
150 300 450 600 750
Mass 29Mass 18 (Water)Mass 44
Temp / K
Massspecresponse/arb.units
373 673 973
Mas
s sp
ec re
spon
se /
arb
units 0.6
0.4
0.2
100 400 700
Temperature / °C
0
2x10-10
4x10-10
6x10-10
150 300 450 600 750
Mass 29Mass 18 (Water)Mass 44
Temp / K
Massspecresponse/arb.units
373 673 973
Mas
s sp
ec re
spon
se /
arb
units 0.6
0.4
0.2
100 400 700
Temperature / °C
Mass 18
Mass 44
Mass 29
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