Supports, Zeolites, Mesoporous Materials - Chapter 9

Transcription

1 Supports, Zeolites, Mesoporous Materials - Chapter 9 Krijn P. de Jong Inorganic Chemistry and Catalysis Utrecht University NIOK CAIA Course, Schiermonnikoog, December 4 th,

2 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

3 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

4 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

5 Catalysts how do they look like? A note on economics Catalyst sales 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

6 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

7 Support requirements (Hydro)thermal stability Specific surface area Mechanical strength & pressure drop Accessibility 7

8 Thermal stability (1) Δ T Unsupported metal nanoparticles Sintering Δ T Thermostable support prevents sintering Supported metal catalyst 8

9 Thermal stability (2) Material Melting point, K Tammann temperature, K Au Ag Co SiO 2 (cryst.) TiO α-al 2 O Thermostability oxides >> thermostability metals 9

10 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

11 Specific surface area of supports Particle size, m Surface area, m 2 /g (1 mm) (1 μm) (1 nm) nm particles typical 11

12 Silica gel synthesis - silicate solution 12

13 Silicate solution - lowering ph Si-O - + H 3 O + Si-OH + H 2 O Si-O - + HO-Si Si-O-Si + OH - 13

14 Formation of silica gel 14

15 Silica-gel support in TEM 15

16 Pyrogenic silica SiCl 4 + O 2 SiO Cl 2 Chemically pure - Aerosil (Degussa, Evonik) - Cabosil 16

17 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

18 γ-alumina - spinel structure 18

19 Carbon support materials Type Origin Surface area, m 2.g -1 Pores Activated carbon Carbon black pyrolysis of natural materials partial oxidation of hydrocarbons micro, meso, macro meso Graphite HT carbon meso + macro Carbon nanofibers CVD of methane meso 19

20 Carbon nanofiber structure 500 μm 5 nm Van der Lee et al., Carbon 44 (2006)

21 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

22 Support requirements (Hydro)thermal stability Specific surface area Mechanical strength & pressure drop Pressure drop Shaping Accessibility 22

23 Pressure drop - fixed bed D p [m] ΔP [bar] 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

24 Techniques for shaping Spray drying for 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

25 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

26 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

27 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 27

28 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)

29 Mesopores in USY ~ 500 nm crystal Janssen et al., Angew. Chem. Int. Ed. 40 (2001)

30 USY-steamed + acid leached 2D-TEM Slice from 3D-TEM Janssen et al., Angew. Chem. Int. Ed. 40 (2001)

31 Synthesis Ordered Mesoporous Materials H 2 O Silica OH - calcination 31

32 Ordered Mesoporous Materials, MCM-41 32

33 SBA-15 in 3D: Tilt series 100 nm A.H. Janssen et al., Chem. Comm. (2002)

34 Shape of pores in 3D A.H. Janssen et al., Chem. Comm. (2002)

35 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

36 Supports, Zeolites, Mesoporous Materials - Chapter 9 Krijn P. de Jong Inorganic Chemistry and Catalysis Utrecht University NIOK CAIA Course, Schiermonnikoog, December 4 th, 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

37 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

38 Catalysts how do they look like? A note on economics Catalyst sales 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

39 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

40 Thermal stability (2) Material Au Ag Co SiO 2 (cryst.) TiO 2 α-al 2 O 3 Melting point, K Tammann temperature, K 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

41 Specific surface area of supports Particle size, m Surface area, m 2 /g (1 mm) (1 μm) (1 nm) nm particles typical 11 Silica gel synthesis - silicate solution 12 6

42 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

43 Silica-gel support in TEM 15 Pyrogenic silica SiCl 4 + O 2 SiO Cl 2 Chemically pure - Aerosil (Degussa, Evonik) - Cabosil 16 8

44 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

45 Carbon support materials Type Origin Surface area, m 2.g -1 Pores Activated carbon Carbon black pyrolysis of natural materials partial oxidation of hydrocarbons micro, meso, macro meso Graphite HT carbon meso + macro Carbon nanofibers CVD of methane meso 19 Carbon nanofiber structure 500 μm 5 nm Van der Lee et al., Carbon 44 (2006)

46 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

47 Pressure drop - fixed bed D p [m] ΔP [bar] 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 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

48 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

49 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 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)

50 Mesopores in USY ~ 500 nm crystal Janssen et al., Angew. Chem. Int. Ed. 40 (2001) USY-steamed + acid leached 2D-TEM Slice from 3D-TEM Janssen et al., Angew. Chem. Int. Ed. 40 (2001)

51 Synthesis Ordered Mesoporous Materials H 2 O Silica OH - calcination 31 Ordered Mesoporous Materials, MCM

52 SBA-15 in 3D: Tilt series 100 nm A.H. Janssen et al., Chem. Comm. (2002) Shape of pores in 3D A.H. Janssen et al., Chem. Comm. (2002)

53 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