The Detailed Kinetics of the Partial Oxidation Reactions:
Benzene/Butane to Maleic Anhydride
Ethylene to Ethylene Oxide
Ken Waugh
Emeritus Professor of Physical Chemistry
ICI Central Instruments Research LabBozedown House Berkshire
The Oxidation of Benzene to Maleic Anhydride Over Vanadium Pentoxide D(V‐O) = 600 kJmol‐1
D A Dowden mechanism of benzene oxidation to MA using molecularly adsorbed O2
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
Benzene temperature programmed desorption spectra: curve (a) benzene, curve (b) maleic anhydride
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
The Oxidation of n‐butane to Maleic Anhydride
• Anaerobic Selectivity 80%
The (100) face of (VO)2P2O7 – the active face
Recirculating Solids Reactor forn‐butane Oxidation to Maleic Anhydride ‐ DuPont
Schematic Representation of the Mars and van Krevelen Mechanism
Oxygen desorption from (VO)2P2O7
Anaerobic Temperature Programmed Oxidation of n‐butane over the (VO)2P2O7 Catalyst
Anaerobic Temperature Programmed Oxidation of but‐1‐ene over the (VO)2P2O7 Catalyst
Anaerobic Temperature Programmed Oxidation of but‐1,3‐diene over the (VO)2P2O7 Catalyst
Side View of n‐butane Adsorbed End‐on
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
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
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
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
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
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
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
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.
O atom adlayer on the Ag(110)
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
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
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