Supports, Zeolites, Mesoporous Materials - Chapter 9 Krijn P. de Jong Inorganic Chemistry and Catalysis Utrecht University NIOK CAIA Course, Schiermonnikoog, December 4 th, 2009 1
Overview of lecture Introduction Catalysts examples and structure History; market; economic impact Support properties Thermal stability Specific surface area Shaping and mechanical strength Accessibility Summary and conclusions 2
Catalyst examples Catalyst Ni/SiO 2 K 2 O/Al 2 O 3 /Fe Ag/α-Al 2 O 3 CrO x /SiO 2 CoMoS 2 /γ-al 2 O 3 Co/SiO 2 Cu/ZnO/Al 2 O 3 Zeolite Y composite Pt/Mordenite V 2 O 5 /TiO 2 Pt/C Applications Hydrogenation Ammonia synthesis Epoxidation Polymerisation Hydrotreating Fischer Tropsch synthesis Methanol synthesis Catalytic cracking Hydro-isomerization of light alkanes NO x abatement Hydrogenation; fuel cell 3
History of catalyst synthesis Period Material type Key production step Example material and process ~1890 Natural Shaping Bauxite; Claus process ~1930 Natural Shaping Clays; catalytic cracking ~1940 Synthetic Impregnation Pt/Al 2 O 3 ; reforming ~1970 Synthetic Precipitation Cu/ZnO/Al 2 O 3 ; methanol synthesis ~1980 Synthetic Hydrothermal ZSM-5; methanol-to-gasoline >2000 Nanostructured Templating, CVD MCM-41, SBA-15, CNF, CNT From Synthesis of Solid Catalysts (K.P. de Jong, Ed.), Wiley-VCH (2009) 4
Catalysts how do they look like? A note on economics Catalyst sales 2007 18 billion US$ (~80% solid catalysts) Generated margin from their use amounts to >2000 billion US$ (conservative estimate) From Synthesis of Solid Catalysts (K.P. de Jong, Ed.), VCH-Wiley Wiley-VCH (2009) 5
Solid Catalyst Structure Support particles (~20 nm) ~1.5 mm Metal particles (1-10 nm) Porous support body From Synthesis of of Solid Catalysts (K.P. de de Jong, Ed.), Ed.), Wiley-VCH VCH-Wiley (2009) 6
Support requirements (Hydro)thermal stability Specific surface area Mechanical strength & pressure drop Accessibility 7
Thermal stability (1) Δ T Unsupported metal nanoparticles Sintering Δ T Thermostable support prevents sintering Supported metal catalyst 8
Thermal stability (2) Material Melting point, K Tammann temperature, K Au 1336 668 Ag 1234 617 Co 1768 884 SiO 2 (cryst.) 1986 893 TiO 2 2116 1058 α-al 2 O 3 2288 1144 Thermostability oxides >> thermostability metals 9
Support requirements (Hydro)thermal stability Specific surface area Particle sizes needed Nanoparticle synthesis: SiO 2, Al 2 O 3 Mechanical strength & pressure drop Accessibility 10
Specific surface area of supports Particle size, m Surface area, m 2 /g 10-2 0.00026 10-3 (1 mm) 0.0026 10-4 0.026 10-5 0.26 10-6 (1 μm) 2.6 10-7 26 10-8 260 10-9 (1 nm) 2600 10-20 nm particles typical 11
Silica gel synthesis - silicate solution 12
Silicate solution - lowering ph Si-O - + H 3 O + Si-OH + H 2 O Si-O - + HO-Si Si-O-Si + OH - 13
Formation of silica gel 14
Silica-gel support in TEM 15
Pyrogenic silica SiCl 4 + O 2 SiO 2 + 2 Cl 2 Chemically pure - Aerosil (Degussa, Evonik) - Cabosil 16
Alumina preparations Acid route Al-sulphate Base route Na-aluminate Pseudo-boehmite Boehmite Bayerite AlO(OH) AlO(OH) Al(OH) 3 Amorphous γ-al 2 O 3 η-al 2 O 3 Al 2 O 3 α-al 2 O 3 17
γ-alumina - spinel structure 18
Carbon support materials Type Origin Surface area, m 2.g -1 Pores Activated carbon Carbon black pyrolysis of natural materials partial oxidation of hydrocarbons 500-2000 micro, meso, macro 10-400 meso Graphite HT carbon 0.1-300 meso + macro Carbon nanofibers CVD of methane 100-300 meso 19
Carbon nanofiber structure 500 μm 5 nm Van der Lee et al., Carbon 44 (2006) 629-637 20
Selection of supports Criterion/support SiO 2 γ-al 2 O 3 Carbon Thermal stability ++ ++ +++ Steam stability - + - Surface area ++ ++ +* Surface chemistry + ++ ++ Reaction with metal - - - ++ Shaping + ++ - * With activated carbon, micropores often induce diffusion limitation. 21
Support requirements (Hydro)thermal stability Specific surface area Mechanical strength & pressure drop Pressure drop Shaping Accessibility 22
Pressure drop - fixed bed D p [m] ΔP [bar] 10-1 0.04 10-2 0.4 10-3 4.7 10-4 120 10-5 8800 Ergun equation, 1 atm air, 25 ºC, GHSV 2000 Nm 3 /(m 3.h); Reactor: diameter 2 m, height 4 m. Catalyst shape spheres D p = particle size 23
Techniques for shaping Spray drying for 10-100 µm particles Granulation for 2-30 mm particles Pelletization for low-cost particles Extrusion for different particle shapes Oil drop / sol-gel method for mechanically strong, spherical particles 24
Shaping technique - extrusion DIE PLATE -Peptizing agent added to support powder -Wet paste fed to screw transport system -Paste pressed through holes of the die plate 25
Support requirements (Hydro)thermal stability oxides Specific surface area Mechanical strength & pressure drop Accessibility Ordered support materials Zeolites (microporous) Mesoporous zeolites (micro + meso) Ordered mesoporous materials 26
Zeolites microporous solid acids Si Al O H 8 MR side pockets 2.6 x 5.7 Å 12 MR channels 6.7 x 7.0 Å Zeolite Mordenite http://www.iza-structure.org/databases/ 27
Mesopores in zeolites Processes with key role for mesopores: Fluid Catalytic Cracking Hydrocracking Xylene isomerisation Hexane isomerisation k 1 φ = L. D e φ = Thiele modulus L = diffusion path length mesopores reduce L Van Donk et al., Catal. Rev. 45 (2003) 207-319 28
Mesopores in USY ~ 500 nm crystal Janssen et al., Angew. Chem. Int. Ed. 40 (2001) 1102 29
USY-steamed + acid leached 2D-TEM Slice from 3D-TEM Janssen et al., Angew. Chem. Int. Ed. 40 (2001) 1102 30
Synthesis Ordered Mesoporous Materials H 2 O Silica OH - calcination 31
Ordered Mesoporous Materials, MCM-41 32
SBA-15 in 3D: Tilt series 100 nm A.H. Janssen et al., Chem. Comm. (2002) 1632-1633 33
Shape of pores in 3D A.H. Janssen et al., Chem. Comm. (2002) 1632-1633 34
Summary of lecture Key support properties Thermal stability oxides often preferred Specific surface area nanoparticles Macroscopic particle size & mechanical strength shaping of nanoparticles to form mm-sized bodies Porosity, tortuosity and accessibility limitation of diffusion path length Nanostructured supports & catalysts Zeolites (established) Carbon nanotubes, nanofibers Ordered mesoporous materials Hierarchical pore systems needed 35
Supports, Zeolites, Mesoporous Materials - Chapter 9 Krijn P. de Jong Inorganic Chemistry and Catalysis Utrecht University NIOK CAIA Course, Schiermonnikoog, December 4 th, 2009 1 Overview of lecture Introduction Catalysts examples and structure History; market; economic impact Support properties Thermal stability Specific surface area Shaping and mechanical strength Accessibility Summary and conclusions 2 1
Catalyst examples Catalyst Ni/SiO 2 K 2 O/Al 2 O 3 /Fe Ag/α-Al 2 O 3 CrO x /SiO 2 CoMoS 2 /γ-al 2 O 3 Co/SiO 2 Cu/ZnO/Al 2 O 3 Zeolite Y composite Pt/Mordenite V 2 O 5 /TiO 2 Pt/C Applications Hydrogenation Ammonia synthesis Epoxidation Polymerisation Hydrotreating Fischer Tropsch synthesis Methanol synthesis Catalytic cracking Hydro-isomerization of light alkanes NO x abatement Hydrogenation; fuel cell 3 History of catalyst synthesis Period Material type Key production step Example material and process ~1890 Natural Shaping Bauxite; Claus process ~1930 Natural Shaping Clays; catalytic cracking ~1940 Synthetic Impregnation Pt/Al 2 O 3 ; reforming ~1970 Synthetic Precipitation Cu/ZnO/Al 2 O 3 ; methanol synthesis ~1980 Synthetic Hydrothermal ZSM-5; methanol-to-gasoline >2000 Nanostructured Templating, CVD MCM-41, SBA-15, CNF, CNT From Synthesis of Solid Catalysts (K.P. de Jong, Ed.), Wiley-VCH (2009) 4 2
Catalysts how do they look like? A note on economics Catalyst sales 2007 18 billion US$ (~80% solid catalysts) Generated margin from their use amounts to >2000 billion US$ (conservative estimate) From Synthesis of Solid Catalysts (K.P. de Jong, Ed.), VCH-Wiley Wiley-VCH (2009) 5 Solid Catalyst Structure Support particles (~20 nm) ~1.5 mm Metal particles (1-10 nm) Porous support body From Synthesis of of Solid Catalysts (K.P. de de Jong, Ed.), Ed.), Wiley-VCH VCH-Wiley (2009) 6 3
Support requirements (Hydro)thermal stability Specific surface area Mechanical strength & pressure drop Accessibility 7 Thermal stability (1) Δ T Unsupported metal nanoparticles Sintering Δ T Thermostable support prevents sintering Supported metal catalyst 8 4
Thermal stability (2) Material Au Ag Co SiO 2 (cryst.) TiO 2 α-al 2 O 3 Melting point, K 1336 1234 1768 1986 2116 2288 Tammann temperature, K 668 617 884 893 1058 1144 Thermostability oxides >> thermostability metals 9 Support requirements (Hydro)thermal stability Specific surface area Particle sizes needed Nanoparticle synthesis: SiO 2, Al 2 O 3 Mechanical strength & pressure drop Accessibility 10 5
Specific surface area of supports Particle size, m Surface area, m 2 /g 10-2 0.00026 10-3 (1 mm) 0.0026 10-4 0.026 10-5 0.26 10-6 (1 μm) 2.6 10-7 26 10-8 260 10-9 (1 nm) 2600 10-20 nm particles typical 11 Silica gel synthesis - silicate solution 12 6
Silicate solution - lowering ph Si-O - + H 3 O + Si-OH + H 2 O Si-O - + HO-Si Si-O-Si + OH - 13 Formation of silica gel 14 7
Silica-gel support in TEM 15 Pyrogenic silica SiCl 4 + O 2 SiO 2 + 2 Cl 2 Chemically pure - Aerosil (Degussa, Evonik) - Cabosil 16 8
Alumina preparations Acid route Al-sulphate Base route Na-aluminate Pseudo-boehmite Boehmite Bayerite AlO(OH) AlO(OH) Al(OH) 3 Amorphous γ-al 2 O 3 η-al 2 O 3 Al 2 O 3 α-al 2 O 3 17 γ-alumina - spinel structure 18 9
Carbon support materials Type Origin Surface area, m 2.g -1 Pores Activated carbon Carbon black pyrolysis of natural materials partial oxidation of hydrocarbons 500-2000 10-400 micro, meso, macro meso Graphite HT carbon 0.1-300 meso + macro Carbon nanofibers CVD of methane 100-300 meso 19 Carbon nanofiber structure 500 μm 5 nm Van der Lee et al., Carbon 44 (2006) 629-637 20 10
Selection of supports Criterion/support SiO 2 γ-al 2 O 3 Carbon Thermal stability ++ ++ +++ Steam stability - + - Surface area ++ ++ +* Surface chemistry + ++ ++ Reaction with metal - - - ++ Shaping + ++ - * With activated carbon, micropores often induce diffusion limitation. 21 Support requirements (Hydro)thermal stability Specific surface area Mechanical strength & pressure drop Pressure drop Shaping Accessibility 22 11
Pressure drop - fixed bed D p [m] ΔP [bar] 10-1 0.04 10-2 0.4 10-3 4.7 10-4 120 10-5 8800 Ergun equation, 1 atm air, 25 ºC, GHSV 2000 Nm 3 /(m 3.h); Reactor: diameter 2 m, height 4 m. Catalyst shape spheres D p = particle size 23 Techniques for shaping Spray drying for 10-100 µm particles Granulation for 2-30 mm particles Pelletization for low-cost particles Extrusion for different particle shapes Oil drop / sol-gel method for mechanically strong, spherical particles 24 12
Shaping technique - extrusion DIE PLATE -Peptizing agent added to support powder -Wet paste fed to screw transport system -Paste pressed through holes of the die plate 25 Support requirements (Hydro)thermal stability oxides Specific surface area Mechanical strength & pressure drop Accessibility Ordered support materials Zeolites (microporous) Mesoporous zeolites (micro + meso) Ordered mesoporous materials 26 13
Zeolites microporous solid acids Si O H Al 8 MR side pockets 2.6 x 5.7 Å 12 MR channels 6.7 x 7.0 Å Zeolite Mordenite http://www.iza-structure.org/databases/ 27 Mesopores in zeolites Processes with key role for mesopores: Fluid Catalytic Cracking Hydrocracking Xylene isomerisation Hexane isomerisation =. k 1 φ L D e φ = Thiele modulus L = diffusion path length mesopores reduce L Van Donk et al., Catal. Rev. 45 (2003) 207-319 28 14
Mesopores in USY ~ 500 nm crystal Janssen et al., Angew. Chem. Int. Ed. 40 (2001) 1102 29 USY-steamed + acid leached 2D-TEM Slice from 3D-TEM Janssen et al., Angew. Chem. Int. Ed. 40 (2001) 1102 30 15
Synthesis Ordered Mesoporous Materials H 2 O Silica OH - calcination 31 Ordered Mesoporous Materials, MCM-41 32 16
SBA-15 in 3D: Tilt series 100 nm A.H. Janssen et al., Chem. Comm. (2002) 1632-1633 33 Shape of pores in 3D A.H. Janssen et al., Chem. Comm. (2002) 1632-1633 34 17
Summary of lecture Key support properties Thermal stability oxides often preferred Specific surface area nanoparticles Macroscopic particle size & mechanical strength shaping of nanoparticles to form mm-sized bodies Porosity, tortuosity and accessibility limitation of diffusion path length Nanostructured supports & catalysts Zeolites (established) Carbon nanotubes, nanofibers Ordered mesoporous materials Hierarchical pore systems needed 35 18