SLIDE 1
Mixed Oxides in Selective Mixed Oxides in Selective Mixed Oxides in Selective Mixed Oxides in Selective Oxidation Catalysis: Oxidation Catalysis: Oxidation Catalysis: Oxidation Catalysis: The Role of The Role of The Role of The Role of Disordered Surface Layers Disordered Surface Layers Disordered Surface Layers Disordered Surface Layers
Chris Kiely & Andy Burrows Chris Kiely & Andy Burrows Chris Kiely & Andy Burrows Chris Kiely & Andy Burrows
Center for Advanced Materials and Center for Advanced Materials and Nanotechnology, Lehigh University Nanotechnology, Lehigh University
VPO Au/C Au/C AuPd/Ti AuPd/TiO2
SLIDE 2 Acknowledgements Acknowledgements Acknowledgements Acknowledgements
Graham Hutchings Graham Hutchings, Leverhulme Catalysis Centre, Cardiff University, UK Jos Jose Calvino Calvino, Departmento de Quimica Inorganica, Cadiz University, Spain Jean Claude Volta, Claude Mirodatos, Jean Claude Volta, Claude Mirodatos, Institut de Recherches sur la Catalyse, Lyon, France Jens Perreg Jens Perregaard, Poul ard, Poul Hojlund Hojlund Neilson, Neilson, Haldor Topsoe, Copenhagen, Denmark Rober Robert Schl Schlogl
- gl, Fritz Haber Institute, Berlin, Germany
SLIDE 3
Reaction co-ordinate E Reactants Products A B C D Euncatalysed Ecatalysed ΔHreaction The catalyst tends to provide an alternate reaction pathway with a lower activation energy. A catalyst is a substance that increases the rate at which a chemical system reaches equilibrium without being consumed in the process.
Catalysis 101 Catalysis 101 Catalysis 101 Catalysis 101
Conv Conversion ersion Conv Conversion ersion - the fraction of reactants that are converted to products. Selectivity Selectivity Selectivity Selectivity - the fraction of desired product produced. Lifetime Lifetime Lifetime Lifetime - the time period before a catalyst has to be replaced.
SLIDE 4 Types of Heterogeneous Catalysts Types of Heterogeneous Catalysts Types of Heterogeneous Catalysts Types of Heterogeneous Catalysts
Supported Metals Supported Oxides
e.g. Selective Catalytic Reduction
Nd2O3/MgO WO3/TiO2 Pt-Rh/CeO2
e.g. Automotive CO oxidation catalysts
SLIDE 5 Mixed Oxide Catalysts Mixed Oxide Catalysts Mixed Oxide Catalysts Mixed Oxide Catalysts – – Selective Oxidation Selective Oxidation Selective Oxidation Selective Oxidation
MoBi2O6 butadiene butene Cataly Catalyst st Product Product Reactant Reactant MoBi2O6 acrylonitrile propene FeSbO4 acrolein propene VMgO propene propane VPO maleic anhydride n-butane VPO VPO MoBi2O6
2μm
SLIDE 6 Oxidative Dehydrogenation of Propane (ODHP) Oxidative Dehydrogenation of Propane (ODHP) Oxidative Dehydrogenation of Propane (ODHP) Oxidative Dehydrogenation of Propane (ODHP)
14wt% V in catalyst gives optimum performance V in catalyst gives optimum performance
Propane (C3H8) conversion efficiency – ) conversion efficiency –11% 11%
Propene (C (C3H6) selectivity – ) selectivity – 80% 80%
Desirable Desirable Undesirable Undesirable
Propene Propene (C (C3H6) is an important feedstock chemical for the ) is an important feedstock chemical for the manuf manufacture of isopropanol, acrol cture of isopropanol, acrolei ein, acrylic acid and acrylonitrile. n, acrylic acid and acrylonitrile.
C3H8 + 5O + 5O2 3CO 3CO2 + 4H + 4H2O + + H + H2O
SLIDE 7 Catalyst Preparation Procedure Catalyst Preparation Procedure Catalyst Preparation Procedure Catalyst Preparation Procedure
Mg(OH)2 precipitated from magnesium nitrate solution precipitated from magnesium nitrate solution using KOH using KOH
- Precipitate filtered off,
Precipitate filtered off, purif purified and crushed ed and crushed
Mg(OH)2 added to hot ammonium metavanadate added to hot ammonium metavanadate (NH (NH4VO VO3)
- Suspension evaporated to dryness leaving VMgO
Suspension evaporated to dryness leaving VMgO catalyst catalyst
Calcined in O in O2 at 550 at 550oC (6h) and then at 800 C (6h) and then at 800oC (6h) C (6h)
Reaction Conditions Reaction Conditions Reaction Conditions Reaction Conditions
Fixed bed reactor: 500-550 Fixed bed reactor: 500-550oC : atmospheric pressure C : atmospheric pressure C3H8 / O / O2 / He : 1.0 / 0.1 / 98.9 / He : 1.0 / 0.1 / 98.9
SLIDE 8 Mixed Mixed Mixed Mixed VMgO VMgO VMgO VMgO (V (V (V (V5+
5+ 5+ 5+) Phases
) Phases ) Phases ) Phases
Mg Mg3V2O8 Ortho- Ortho-vanadate vanadate Cmca Cmca (64) (64) Orthorhombi Orthorhombic (mmm) c (mmm) Mg Mg2V2O7 Pyro- Pyro-vanadate vanadate P21/c (14) P21/c (14) Monoclinic (2/m) Monoclinic (2/m) MgV MgV2O6 Meta- Meta-vanadate vanadate C2/m (12) C2/m (12) Monoclinic (2/m) Monoclinic (2/m)
In isolation, none none of the pure VMgO phases is particularly active
- r selective for the oxidative dehydrogenation of propane.
SLIDE 9 XRD of the 14V/VMgO Catalyst XRD of the 14V/VMgO Catalyst XRD of the 14V/VMgO Catalyst XRD of the 14V/VMgO Catalyst
- To study the interactions between the constituent phases
To study the interactions between the constituent phases
- f the VMgO
- f the VMgO catalyst
catalyst
To follow any structural change llow any structural changes that occur under typical s that occur under typical reaction conditions reaction conditions
SLIDE 10 Mg3V2O8 MgO
Microstructure of the 14V/VMgO Catalyst Microstructure of the 14V/VMgO Catalyst Microstructure of the 14V/VMgO Catalyst Microstructure of the 14V/VMgO Catalyst
Mg3V2O8 Mg2V2O7 Trace phase Trace phase Minority phase Minority phase
[100] [100] [121] [121]
SLIDE 11
MgO MgO MgO MgO Component of the 14V/VMgO Catalyst Component of the 14V/VMgO Catalyst Component of the 14V/VMgO Catalyst Component of the 14V/VMgO Catalyst
5nm 5nm 5nm 5nm 50nm 50nm 50nm 50nm [111] [111] [111] [111] [111] [111] [111] [111] [200] [200] [200] [200] MgO MgO MgO MgO [011] 011] [011] 011]
SLIDE 12 MgO MgO MgO MgO Facet Structure Facet Structure Facet Structure Facet Structure
{100} neutral {100} neutral {100} neutral {100} neutral facets facets facets facets {111} polar {111} polar {111} polar {111} polar facet facet facet facet 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm
14V/VMgO 14V/VMgO 14V/VMgO 14V/VMgO
SLIDE 13 Brucite Brucite Brucite Brucite – – Mg(OH) Mg(OH) Mg(OH) Mg(OH)2
2
Magnesia Magnesia Magnesia Magnesia -
MgO MgO MgO
Hexagonal Hexagonal Hexagonal Hexagonal a=0.314n a=0.314nm a=0.314n a=0.314nm c=0.476n c=0.476nm c=0.476n c=0.476nm Cubic Cubic Cubic Cubic a=0.423n a=0.423nm a=0.423n a=0.423nm
SLIDE 14 Brucite Brucite Brucite Brucite to Magnesia Transformation to Magnesia Transformation to Magnesia Transformation to Magnesia Transformation
Br Bruci ucite Br Bruci ucite 300 300 300 300o
C 800 800 800 800o
C 500 500 500 500o
C 10nm 10nm 10nm 10nm 15nm 15nm 15nm 15nm 15nm 15nm 15nm 15nm 15nm 15nm 15nm 15nm Magnesia Magnesia Magnesia Magnesia
SLIDE 15 Thermogravimetric Thermogravimetric Thermogravimetric Thermogravimetric an analysis of alysis of an analysis of alysis of brucite brucite brucite brucite decomposition decomposition decomposition decomposition
30wt% weight loss at ~420oC as water of hydration is lost
Relative stability of Relative stability of Relative stability of Relative stability of hydroxylated hydroxylated hydroxylated hydroxylated MgO MgO MgO MgO surfaces surfaces surfaces surfaces
De Leeuw et al. J.Phys.Chem, 99 99, (1995), 17219
Polar surface stabilized a adsorbed –OH groups
SLIDE 16
XRD comparison of the 14V/VMgO catalyst in the XRD comparison of the 14V/VMgO catalyst in the XRD comparison of the 14V/VMgO catalyst in the XRD comparison of the 14V/VMgO catalyst in the unused and used state unused and used state unused and used state unused and used state
SLIDE 17 In In In In-
- situ XRD analysis of the 14V/VMgO catalyst under
situ XRD analysis of the 14V/VMgO catalyst under situ XRD analysis of the 14V/VMgO catalyst under situ XRD analysis of the 14V/VMgO catalyst under redox redox redox redox cycling cycling cycling cycling
Is a spinel-type phase form Is a spinel-type phase formed on ed on reduction? reduction? MgV MgV2O4
4 a=0.843nm
a=0.843nm
SLIDE 18 EXAFS of standard phases EXAFS of standard phases EXAFS of standard phases EXAFS of standard phases XANES of the V K XANES of the V K XANES of the V K XANES of the V K-
edge edge edge
V2O3 (V3+) V2O4 (V4+) V2O5 (V5+) Pure Mg3V2O8 Looks like V5+ in the unused and used state
SLIDE 19 In In In In-
- situ EXAFS of the 14V/VMgO catalyst
situ EXAFS of the 14V/VMgO catalyst situ EXAFS of the 14V/VMgO catalyst situ EXAFS of the 14V/VMgO catalyst XANES of the V K XANES of the V K XANES of the V K XANES of the V K-
edge edge edge
14V/VMgO in reaction mixture @ 500oC Resembles V3+ in the used state 14V/VMgO in air @ 500oC Resembles V5+ in the unused state
SLIDE 20 In In In In-
- situ electrical conductivity measurements on the
situ electrical conductivity measurements on the situ electrical conductivity measurements on the situ electrical conductivity measurements on the 14V/VMgO catalyst 14V/VMgO catalyst 14V/VMgO catalyst 14V/VMgO catalyst
Increased n-type conductivity observed on reduction
SLIDE 21 Ex Ex Ex Ex-
- situ gas reaction cell for JEOL 2000EX HREM
situ gas reaction cell for JEOL 2000EX HREM situ gas reaction cell for JEOL 2000EX HREM situ gas reaction cell for JEOL 2000EX HREM
SLIDE 22 Reminder : 14V/VMgO catalyst microstructure Reminder : 14V/VMgO catalyst microstructure Reminder : 14V/VMgO catalyst microstructure Reminder : 14V/VMgO catalyst microstructure
~10 ~10 ~10 ~10 vol vol vol vol% of catalyst % of catalyst % of catalyst % of catalyst consists of Mg consists of Mg consists of Mg consists of Mg3
3V
V2
2O
O8
8
XEDS analysis XEDS analysis XEDS analysis XEDS analysis Mg : V Mg : V Mg : V Mg : V 3 : 2 3 : 2 3 : 2 3 : 2 ~90 ~90 ~90 ~90 vol vol vol vol% of catalyst % of catalyst % of catalyst % of catalyst consists of consists of consists of consists of MgO MgO MgO MgO XEDS analysis XEDS analysis XEDS analysis XEDS analysis Mg : V Mg : V Mg : V Mg : V 45 : 1 45 : 1 45 : 1 45 : 1
SLIDE 23 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm 10nm Air Air Air Air Air Air Air Air Rea Reaction mixture
Reaction mixture Reaction mixture Rea Reaction mixture
Rea Reaction mixture
Component 1 Component 1 Component 1 Component 1 -
MgO MgO MgO under oxidation/reduction cycling under oxidation/reduction cycling under oxidation/reduction cycling under oxidation/reduction cycling
SLIDE 24 a b c x y z
14V/VMgO 14V/VMgO 14V/VMgO 14V/VMgO – – reduction in pure propane reduction in pure propane reduction in pure propane reduction in pure propane
V3+
3+ spi
spinel el ph phase ase MgV MgV2O4 a=0.843nm a=0.843nm Ordered overlayer is seen both in plan view (X) and in profile (Y) Y Y X X 5nm 5nm 5nm 5nm
SLIDE 25 Model A Model A Model A Model A – – Spinel Spinel Spinel Spinel layer layer layer layer MgV MgV MgV MgV2
2O
O4
4/MgO
/MgO /MgO /MgO Model B Model B Model B Model B – – Ortho layer Ortho layer Ortho layer Ortho layer Mg Mg Mg Mg3
3V
V2
2O
O8
8/MgO
/MgO /MgO /MgO
MgO[100]//MgV2O4[100] MgO[011]//MgV2O4[011] MgO[100]//Mg3V2O8[001] MgO[011]//Mg3V2O8[100]
SLIDE 26 Comparing experimental HREM images with Comparing experimental HREM images with Comparing experimental HREM images with Comparing experimental HREM images with simulations from theoretical models simulations from theoretical models simulations from theoretical models simulations from theoretical models
Exp Experimental rimental Exp Experimental rimental Spinel/MgO Spinel/MgO Spinel/MgO Spinel/MgO Mg Mg Mg Mg3
3V
V2
2O
O8
8/MgO
/MgO /MgO /MgO
SLIDE 27 Component 1: Vanadium containing surface layer Component 1: Vanadium containing surface layer Component 1: Vanadium containing surface layer Component 1: Vanadium containing surface layer
MgO MgO MgO
SLIDE 28 Component 2 Component 2 Component 2 Component 2 -
Mg Mg Mg3
3V
V2
2O
O8
8 under reaction conditions
under reaction conditions under reaction conditions under reaction conditions
10nm 10nm 10nm 10nm
MgO MgO MgO MgO
MgO crystallites on surface MgV2O4 sub-surface layer Disordered interior
Mg Mg Mg Mg3
3V
V2
2O
O8
8
2MgO + MgV 2MgO + MgV2O4
4 + 2O
+ 2O
Reaction Reaction Reaction Reaction catalysed catalysed catalysed catalysed by lattice O atoms which are replenished from by lattice O atoms which are replenished from by lattice O atoms which are replenished from by lattice O atoms which are replenished from atmospheric oxygen atmospheric oxygen atmospheric oxygen atmospheric oxygen (Mars van (Mars van (Mars van (Mars van Krev Krevelen elen Krev Krevelen elen mechanism) mechanism) mechanism) mechanism) MgV MgV MgV MgV2
2O
O4
4
Disordered layer Disordered layer Disordered layer Disordered layer
SLIDE 29 14V/VMgO Catalyst 14V/VMgO Catalyst 14V/VMgO Catalyst 14V/VMgO Catalyst
Component 1 Component 1 Component 1 Component 1 – – film supported on film supported on film supported on film supported on MgO MgO MgO MgO {111} platelets {111} platelets {111} platelets {111} platelets Component 2 Component 2 Component 2 Component 2 – – bulk bulk bulk bulk VMgO VMgO VMgO VMgO mixed oxide mixed oxide mixed oxide mixed oxide
Disordered Partially ordered Disordered Partially ordered Disordered Partially ordered Disordered Partially ordered MgV MgV MgV MgV2
2O
O4
4/MgO
/MgO /MgO /MgO
erlayer
erlayer
erlayer
erlayer epitaxial epitaxial epitaxial epitaxial ov
erlayer
erlayer V V5+
5+ 5+ 5+ / V
/ V / V / V 4+
4+ 4+ 4+
V V3+
3+ 3+ 3+
V V3+
3+ 3+ 3+
Crystalline MgO/MgV Crystalline MgO/MgV Crystalline MgO/MgV Crystalline MgO/MgV2
2O
O4
4 on Crystalline
- n Crystalline
- n Crystalline
- n Crystalline
Mg Mg Mg Mg3
3V
V2
2O
O8
8 8 8 disordered interior MgV
disordered interior MgV disordered interior MgV disordered interior MgV2
2O
O4
4
V V5+
5+ 5+ 5+ V
V3+
3+ 3+ 3+/V
/V /V /V5+
5+ 5+ 5+
V V3+
3+ 3+ 3+
Oxidizing Oxidizing Oxidizing Oxidizing Partially Partially Partially Partially Reduced Reduced Reduced Reduced Fully Fully Fully Fully Reduced Reduced Reduced Reduced
SLIDE 30 a b c
a b c
Vanadium Phosphorus Oxide (VPO) Vanadium Phosphorus Oxide (VPO) Vanadium Phosphorus Oxide (VPO) Vanadium Phosphorus Oxide (VPO)
n-butane maleic anhydride Vanadyl phosphate hemihydrate VOHPO4 .0.5H2O Vanadyl pyrophospate (VO)2P2O7 1.5% n-butane in air 400oC, 50h
SLIDE 31 Does the VPO catalyst have a disordered surface layer? Does the VPO catalyst have a disordered surface layer? Does the VPO catalyst have a disordered surface layer? Does the VPO catalyst have a disordered surface layer?
(VO)2P2O7 platelets often show disordered surface layer –is this a real effect or an artifact of beam damage? XPS shows good catalysts to have:-
- a P/V ratio of 1.1 instead of 1.0 indicating a surface
enrichment in P
- a mixture of V5+ and V4+ cations instead of only V4+
SLIDE 32 Amorphous Vanadium Phosphate Catalysts from Amorphous Vanadium Phosphate Catalysts from Amorphous Vanadium Phosphate Catalysts from Amorphous Vanadium Phosphate Catalysts from Supercritical CO Supercritical CO Supercritical CO Supercritical CO2
2 Antisolvent
Antisolvent Antisolvent Antisolvent Precipitation Precipitation Precipitation Precipitation
SLIDE 33 2.20 x 10 2.20 x 10-5
6 48 48 24 24 VPO VPOSC
SCC
1.19 x 10 1.19 x 10-5
43 43 64 64 62 62 VPD VPD 1.35 x 10 1.35 x 10-5
14 14 52 52 27 27 VPO VPO Specific Activity Specific Activity (Mol MA m (Mol MA m-2
Surface Surface Area Area (m (m2g-1
Selectivity Selectivity (%) (%) Conversion Conversion (%) (%) Preparation Preparation Route Route
VPO VPO VPO VPO – – comparison of catalytic comparison of catalytic comparison of catalytic comparison of catalytic activities activities activities activities
SLIDE 34 MoBi MoBi MoBi MoBi2
2O
O6
6 –
– surface disordered layers surface disordered layers surface disordered layers surface disordered layers
1 1-
2nm thick disordered layer cont ered layer containing (by EELS) Mo, Bi and O aining (by EELS) Mo, Bi and O 2nm thick disord 2nm thick disordered layer cont ered layer containing (by EELS) Mo, Bi and O aining (by EELS) Mo, Bi and O
important catalyst for important catalyst for important catalyst for acrylonitrile acrylonitrile acrylonitrile acrylonitrile and butadiene formation and butadiene formation and butadiene formation and butadiene formation
SLIDE 35 Conclusion Conclusion Conclusion Conclusion
MoBi2O6 butadiene butene Cataly Catalyst st Product Product Reactant Reactant MoBi2O6 acrylonitrile propene FeSbO4 acrolein propene VMgO propene propane VPO maleic anhydride n-butane
2μm
It appears that a disordered It appears that a disordered surface layer is the active surface layer is the active It appears that a disordered It appears that a disordered surface layer is the active surface layer is the active layer in these mixed oxide selective oxidation catalysts. layer in these mixed oxide selective oxidation catalysts. layer i layer in these mixed oxi these mixed oxide e selective oxidation catalysts. selective oxidation catalysts.
SLIDE 36
Zeolitic Zeolitic Zeolitic Zeolitic Nanofish Nanofish Nanofish Nanofish
Courtesy Robert Courtesy Robert Courtesy Robert Courtesy Robert Schlogl Schlogl Schlogl Schlogl – – FHI, Berlin FHI, Berlin FHI, Berlin FHI, Berlin SBA15 SBA15 SBA15 SBA15 zeolite zeolite zeolite zeolite
