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The Detailed Kinetics of the Partial Oxidation Reactions: Benzene/Butane to Maleic Anhydride Ethylene to Ethylene Oxide

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The Detailed Kinetics of the Partial Oxidation Reactions: Benzene/Butane to Maleic Anhydride Ethylene to Ethylene Oxide 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 Lab Bozedown 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 for n‐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 Ag/Al2O3 CH2 = CH2 + 1/2O2 CH2 CH2 + CO2 CH Cl CH Cl 2 2 O Composition (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 Ag loading 10% w/w Cs loading 0.1% w/w The Problem: • Reaction mechanism • Role of Cl • Role of Cs Oxygen desorption spectra from the Ag/α‐Al2O3 catalyst Tm =250°C(523K), the α1‐state; Tm = 300°C(573 K), the α2‐state 3 Dose: O2, 1 atmosphere, 25 cm /min, 240ºC 0.44x10-10 1st Oxygen TPD 2dOyenT 1st Oxygen TPD 0.33x10-10 s it un b. ar nd / 2 Oxygen TPD se on p 0.22x10-10 es cr pe s s Ma 0.11x10-10 Mass spec response / / arb arb response response spec spec Mass Mass units units 0 100373 473200 300573 673400 773 TemperatureTemperature / K / C 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 5x100.5-1 4x100.4-1 -1 3x100.3 Mass 44 Mass 29 2x100.2-1 -1 Mass spec response / / arb arb response response spec spec Mass Mass units units 1x100.1 0 -100-100 00 100100 200200 300300 Temperature / °C EO and CO2 Formed Simultaneously They 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 -10 2.0x100.2 -10 s 1.5x10 it un b. ar e/ ns o -10 p 1.0x100.1 es .r ec sp s as m -10 0.5x10 MassMassMass spec spec spec response response response / arb / arb / arb units units units 0 0 100373 200473 300573 400673 500773 Temp / K 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) 0.55x10-10 4x100.4-10 -10 3x100.3 -10 2x100.2 Mass 44 Mass 29 1x100.1-10 MassMassMass spec spec spec response response response / / / arb arb arb units units units 0 -100173 27300 100373100 200200473 300573300 Temperature / °C 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 2.0x100.2-10 α atomic surface β subsurface oxygen Atomic surface oxygen 813 K oxygen 753 K s -10 it 1.5x10 693 K un 633 K Subsu b. ar e/ ns o -10 sp 1.0x100.1 Re ec Sp s 540°C Ma 0.5x10-10 480°C 420°C Mass spec specMass Mass response response / / arb arb units units 360°C 0 200473 400673 600873 file g25-28 TemperatureTemperature // °C K Temperature programmed reaction of ethylene with an oxidised Ag/α‐Al2O3 catalyst containing both surface and 2.3 ML of subsurface O atoms -10 6x100.6 Mass 29 Mass 18 (Water) Mass 44 s nit u b. Mass 18 ar / e 4x100.4-10 ns o p Mass 44 es r ec p s s as M 2x100.2-10 Mass 29 Mass spec responseMass spec responseMass spec response / arb / arb / arb units units units 0 100373 150 673400300 450 973700600 750 Temp / K Temperature / °C .
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