Development of - Improved catalysts to be employed within existing production units for existing reactors - Improved catalysts for existing reactors using new procedures calling for new equipment - Integration of catalyst and reactor Heat transfer and mass transport - Integration of catalytic reaction and separation of reactants or reaction products Catalytic distillation as an example : performing a catalytic reaction within a distillation column ......

1. Design and Production
of
Heterogeneous
Catalysts
Gerard B. Hawkins
Managing Director

2. Objectives of
the Design of Solid Catalysts
 Development of
 Improved catalysts to be employed within
existing production units for existing reactors
 Improved catalysts for existing reactors using
new procedures calling for new equipment
 Integration of catalyst and reactor
 Heat transfer and mass transport
 Integration of catalytic reaction and separation of
reactants or reaction products
 Catalytic distillation as an example :
performing a catalytic reaction within a
distillation column

3. Objectives of
the Design of Solid Catalysts
 Most smooth penetration into market for
• Improved catalysts to be employed within existing
production units for existing reactors
• Relatively small rise in conversion and/or selectivity
leads to large increase in profit at low costs of
investment
 Other possibilities are calling for higher costs of
investment and are thus more difficult to get accepted
• Smaller units more easy access to the market; new
concepts to be introduced first in small-scale units

4. Development of Solid Catalysts
 Mechanical strength
 Most important for technical applications
 Size of catalyst bodies
 Determining pressure drop
 Active surface area
 Sufficiently large active surface area per unit volume of
catalyst
 Active surface area stable at temperatures of
pretreatment and catalytic reactions
 Desired structure and chemical composition

5. Development of Solid Catalysts
 Transport of material and thermal energy to
and from the active sites
• Solid catalysts usually highly porous and thus
thermally isolating materials
• Length of pores more important than diameter of
pores (Thiele’s modulus)
 Tri-lobs, quadri-lobs, rings
 Liquid-phase catalysts completely different
constraints than gas-phase catalysts
• Development of gas-phase catalysts much more
advanced

6. Design of Solid Catalysts
 Catalytic activity and selectivity
 Structure and chemical composition of active surface
 Extent of active surface area
 Transport properties
 To catalyst bodies
 Size and shape of catalyst bodies; pressure drop
 Within catalyst bodies
 Size of catalyst bodies
 Pores size distribution

7. Supported Solid Catalysts
Usual separation of functions
 Support
 Size and mechanical strength of catalyst
bodies
 Porous structure
 Active component
 Structure and chemical composition of
catalytically active surface

8. Supported Solid Catalysts
 However, sometimes catalytic function of support
also involved : Bi-functional catalysts
• Acid function of support with precious metal
function in catalytic reforming catalysts
 Support promoting dissociation of carbon monoxide
in some Fischer-Tropsch catalysts
• Different selectivity of titania-supported cobalt
catalysts
Reduced titanium ions at the periphery of the
supported metal particles take up oxygen of
carbon monoxide and thus promote dissociation

9. Unsupported Catalysts
 Reasons to employ unsupported catalysts :
 Active species providing sufficiently large and
thermo stable surface area as well as suitable pore
structure
 Catalytically active species capable of providing
sufficiently strong porous bodies
 Reaction of suitable supports with required
promoters, which prevents promoters to be
effective

10. Unsupported Catalysts
 Examples :
• Pt or Pd gauze for the oxidation of ammonia to
nitrogen oxide in the production of nitric acid and
Pt gauze in Andrussow’s process for the
production of HCN from methane and ammonia
• Silica-alumina cracking catalyst
• Raney metal catalysts
• High-temperature carbon monoxide shift
conversion catalyst : iron oxide-chromium oxide

11. Unsupported Catalysts
 Examples :
• Ethylbenzene dehydrogenation catalyst (iron
oxide promoted with potassium oxide)
 Potassium oxide promoter reacting with the
usual alumina and silica support
• V-P-O catalyst for the selective oxidation of n-
butane to Maleic anhydride
 Alumina support reacts with phosphoric acid
and disturbs vanadium/phosphorous ratio;
vanadium difficult to apply to silica support

12. Catalyst Preparation :
Science or Art
 First example :
Preparation of VPO catalyst for oxidation of n-
butane to Maleic anhydride
 Procedure (1) Centi et al.
 Reduction of 6.7 g of V2O5 for 16 hours in
80 ml of HCl at 100oC
 Addition of 9.3 g 85% H3PO4 and refluxing the
solution for 1 hour
 Evaporate to dryness
 Dry resulting green viscous mass in nitrogen
flow for 10 hours at 125oC

13. Catalyst Preparation :
Art or Science
 Procedure (2) Katsumoto et al.
 Reduction of 15 g V2O5 at 120oC in 60 ml
1:1 (v/v) i-butanol/cyclohexanol mixture
 Cooling to room temperature and addition of
21 g of o-H3PO4 mixed with 30 ml butanol
 Refluxing for 6 hours leads to blue-green
suspension
 Filtering of suspension and drying in nitrogen
flow for 12 hours at 125oC

14. Catalyst Preparation :
Art or Science
 Reduction of vanadium to mixture of vanadium(IV)
and vanadium(V) by either inorganic (HCl) or organic
reducing agent
 Catalysts produced in either way call for being at
least for 24 h on stream to exhibit a reasonable
selectivity and activity

15. Solid Catalysts
 Usually supported catalysts in view of better control of
properties of catalysts
 Surface area and loading of the support with the active
component as well as the distribution of the active
component over the surface of the support determining
• Extent of catalytically active surface area per unit
volume
• Thermo stability together with the interaction of the
active component with the surface of the support

16. Supported Catalysts
Supported catalyst
ThermostableUnsupported catalyst rapid sintering
Reduction
Supported MetalSupported Metal Oxide

17. Components of Solid Catalysts
 Support
 Shape and size of catalyst bodies
 Porous structure
 Mechanical strength
 Surface area
 Active component
 Size and number (loading) of supported active moieties
 Distribution over surface of support
 Interaction with support

18. Types of Supported Catalysts
 Catalysts containing base metals, base metal oxides or
base metal sulfides
 Active surface area per unit volume decisive
Limiting size of reactor
 Usually high loadings of support with active
component(s)
Loadings of 20 to 50 wt.% usual
 Catalysts containing precious metals
 Active surface area per unit weight of precious
metal decisive
 Low loadings of active component(s)
Less than 1 wt.% usual, sometimes up to about 5
wt.%

19. Production of Finely Divided
Material
Condensation of molecularly dispersed species
Selective removal of some component

20. Preparation Procedures of
Supported Catalysts
 Application of active precursor to separately produced
support
 Application of active precursor into pre-shaped
support bodies
 Application on powdered support and subsequent
shaping
 Selective removal of one or more constituents from
essentially non-porous precursor of support and active
component
 Examples Raney metals; ammonia synthesis
catalyst; methanol and low-temperature carbon
monoxide shift catalyst based on copper/zinc oxide

21. Preparation of Catalysts by
Selective Removal
 Resulting in
 powder, e.g., Raney nickel
 powder to be processed to bodies, e.g.,
methanol synthesis catalyst
 porous solid bodies, e.g., ammonia synthesis
catalyst
Non-porous
Precursof
Powdered catalyst
Porous catalyst body
Shaped
catalyst body

22. Catalyst Preparation: Art or
Science
 Second example :
Ammonia synthesis catalyst
 Trial and error
Iron ore
 About 97% Fe3O4 2% Al2O3 1% K2O
 Double-promoted iron catalyst
 Alumina structural promoter
 Potassium required to maintain activity
at higher pressures

23. Catalyst Preparation: Science
or Art
 Selective removal of oxygen
 Minimum amount of Al2O3 to transport water rapidly
out of porous catalyst bodies
 Al2O3 effectively prevents sintering
 Role of potassium still debated
 Presumably potassium oxide promoting
desorption of ammonia, which is required at
elevated pressures

24. Effect of Structure of Active Surface
 Different surface structures
Different activity
per unit surface area
 Effect of size of active particles
Large active particles
mainly atomically flat
surfaces
Small active particles
penetration of atoms
into surface layer

25. Oxygen on Fe(100)

26. Penetration of Foreign
Atoms into Surface
Extended crystallographic plane
Small crystallographic plane

27. Generally Employed Supports
 By far the most preferred commercial support : Alumina
due to elevated bulk density
• Usually g-alumina, surface area from about 300 to 100
m2/g; most preferable needles from boehmite (AlOOH),
less preferable from gibbsite or bayerite (Al(OH)3)
• a-alumina is support with relatively inert surface and
surface area of usually less than 1 m2/g and
exceptionally 10 m2/g
 When alumina cannot be employed, silica is the second
best

28. Support for Precious Metals
 Precious metals used in liquid-phase processes :
 Activated carbon attractive support
• Carbon is not attacked by acids and alkaline liquids
• Carbon bodies of about 50 mm therefore often used
suspended in liquids
• To reclaim the precious metal a carbon support can
be removed by simple combustion

29. Activated Carbon Supports
 Since activated carbon is produced from peat or wood,
it is a natural product and therefore difficult to
reproduce accurately
 Mechanical strength of carbon supports is often
problematic
 (Carbon supports cannot be calcined in air)
 Apparent surface area of activated carbon about 1200
m2/g
• Activated carbon contains many micropores
• Besides very small particles also stacking of
graphite layers present

30. Commercial
Pre-Shaped Support Bodies
 Main deficiency of alumina and silica supports : not
compatible with alkaline promoter species
 Silica is volatile with steam at high pressure and/or high
temperatures
 Other supports, such as, zirconia or titania more difficult to
process to mechanically strong bodies of an elevated
surface area; supports are much more expensive
• Zirconia and titania compatible with alkaline materials
• Alternative supports much more expensive
 Important producer of alternative supports : HAISO

31. Preparation Procedures of
Supported Catalysts
 Application of active precursor onto
separately produced support
• Application of active precursor into pre-
shaped support bodies
• Application on powdered support and
subsequent shaping
 Employing commercial pre-shaped support
bodies most obvious
• Wide range of different shapes and sizes of
alumina and silica available

32. Preparation of Supported
Precious Metal Catalysts
 Most obvious procedure
Pore-volume impregnation and drying of pre-shaped support bodies
 Actually adsorption of active precursor on surface of support
Alumina impregnation with acid, negatively charged precursors
Silica impregnation with positively charged ammonia complexes
 With alumina neutralization of acid components of
impregnating liquid often important
 No risk of loss of precious metal with, e.g., waste water
 Selection of size, shape, pore structure, and mechanical strength of
support bodies viable from large range of commercial support
bodies

33. Pore Volume Impregnation
Incipient Wetness
Impregnation
Also known as
“dry impregnation”

34. Preparation of Supported
Precious Metal Catalysts
 Precious metal precursor often adsorbing on surface
support
 At the usual low loadings of precious metals
adsorption brings about inhomogeneous distribution
of the precious metal over the support bodies
 Chromatographic effect

35. Distribution of
Active Precious Metal Particles
Uniform distribution
of precious metal particles
Usually desired when
transport limitations are
not expected
Egg-shell distribution
of precious metal particles
Resulting from adsorption from
the impregnating liquid
Only desired with transport limitations

36. Preparation of Supported
Precious Metal Catalysts
 Alternative industrial procedure to arrive at egg-shell
distribution of precious metal particles :
Spraying of solution of dissolved precious metal
precursor onto agitated volume of support bodies
 To limit penetration of solution of active precursor into
pores of support, support is often pre-heated
 Egg-shell distribution of active precious metal particles
on support bodies often desired with catalysts intended
for liquid-phase processes

37. Preparation of Supported
Precious Metal Catalysts
 Establishment of an egg-shell distribution of precious
metal particles on alumina support bodies
 Fill pore volume of pre-shaped support bodies
completely with water
 Pass acid solution of precious metal along water-filled
support bodies
• Neutralization of acid solution at external surface of
alumina support and consequent deposition of
palladium compound
• Slow transport of dissolved precious metal species
through water present within pore system of support

38. Preparation of Supported
Precious Metal Catalysts
 Soaking of alumina support in solution of precious
metal or recirculation of solution of precious
metal for long periods of time leads to uniform
distribution and high loading

39. Preparation of Supported
Precious Metal Catalysts
 Uniform distribution of precious metal(s) can be
achieved more readily by employing less strongly
adsorbing species
• With alumina supports change H2PtCl6 for K2PtCl6
Generation of adsorbing Al+ sites by reaction of
proton with surface OH- groups of alumina
Reportedly PtCl6
2- generating protons by exchange
with water and dissociation of water, which
proceeds slowly
•
PtCl6
2- + H2O = PtCl5(H2O)- + Cl-
PtCl5(H2O)- + H2O = PtCl5(OH)- + H3O+

40. Preparation of Supported
Precious Metal Catalysts
 Control of location of active component within
support bodies
 Competitive adsorption with dibasic organic acids,
e.g., oxalic acid, tartaric acid, citric acid or
aromatic acids with hydroxyl group besides
carboxyl group, as, e.g., salicylic acid
Homogeneously applied Egg-shell Egg-white

41. Preparation of Supported
Precious Metal Catalysts
 Adsorption of precious metal on activated carbon
• Freshly produced activated carbon hydrophobic
• Storage without exposure to atmospheric air
maintains hydrophobicity
• Usual activated carbon hydrophilic due to surface
oxidation leading to carboxylic acid groups
• Oxidation, e.g., by hydrogen peroxide, nitric acid
(cautious for explosions) or ozone can increase
number of carboxylic acid sites and thus raises
hydrophilicity

42. Adsorption of Precious
Metals on Activated Carbon
 Limited adsorption of positively charged complexes of
precious metals, such as, ammonia complexes
 More extensive loading from strongly acid solutions of
precious metals
• Reason not completely clear
 Adsorption on positively charged carboxyl acids
due to uptake of additional proton
 More likely good wetting of carbon by acidic
solution and deposition by evaporation of liquid as
species badly crystallizing from acid film on carbon
surface

43. Preparation of Supported
Precious Metal Catalysts
 With pre-shaped silica supports preferably impregnation
with positively charged precious metal complexes
• Ammonia complexes attractive
• Organic nitrogen complexes may lead to reduction of
precious metals at slightly elevated temperatures
 At pH levels above about 2 silica increasingly negatively
charged due to dissociation of surface hydroxyl groups;
only at pH levels above about 6 sufficient reactivity of silica
 At more elevated pH levels dissolution of finely divided
silica to be considered

44. Impregnation of Pre-Shaped
Support Bodies and Drying
 Impregnating with active precursor solution not (strongly)
adsorbing on surface of support
 Most rapid procedure to arrive at industrial catalysts
 Selection of appropriate support from wide range of
commercial supports
 Pore volume and solubility of active precursor determine
maximum loading
 Difficult to achieve uniformly distributed active
component(s)
 Often concentration of active component at external
edge of support bodies

45. Production of Supported
Catalysts by Impregnation and
Drying
 Impregnation with solutions of species not
strongly adsorbing on surface of support
 Higher loadings can be achieved than with
adsorbing species
 Difficult to achieve :
Uniform distribution within support body

46. Production of Supported
Catalysts by Impregnation and
Drying
 Impregnation and drying of pre-shaped support bodies
 Evacuation of pre-shaped support bodies
• Laboratory-scale catalyst preparation : employ vapor
• Addition of volume of impregnating solution equal to
pore-volume to evacuated support
 Dry (under vacuum) at room temperature and
subsequently at increasingly higher temperatures up to
about 120 to 150oC
 Subsequent calcination at about 350 to 500oC

47. Production of Supported
Catalysts by Impregnation and
Drying
 Impregnation of porous support bodies filled with air
may lead to fracture of bodies when the amount of
liquid is larger than the pore volume
• Experiments on sol-gel silica spheres produced by
GBHE upon immersion in water
 With pore volume impregnation some volume
elements may not be penetrated by impregnating
liquid
• Volume elements not containing active components

48. Impregnation and Drying of
Pre-Shaped Support Bodies
 Often Active Precursor selectively Deposited on
External Edge of Support Bodies
With Supports of Wide Pores to be Expected
With all Hydrophilic Supports Migration of Liquid
to External Edge

49. Support Bodies having Wide
Pores
 Incipient wetness impregnation and drying
 Deposition of active precursor at external edge
 Result : Eggshell catalyst

50. Shape of Drop dried on Glass
Drop of solution of copper(II) nitrate dried on microscope glass slide
Note preferential build up of crystallites at the rim of the drop

51. Shape of Drop dried on Glass
Drop of solution of copper(II) citrate dried on microscope glass slide
Note absence of large crystallites

52. Preparation of Supported Catalysts
by Impregnation and Drying
 Also with supports having fairly narrow pores
deposition of active precursor at external edge of bodies
 Evaporation of liquid at external edge and transport of
liquid to external edge
 Achieve uniform distribution throughout support bodies
by using solutions of badly crystallizing active
precursors the viscosity of which raises when the
solvent is removed by volatilization
 Citric acid complexes
 EDTA complexes
 Addition of, e.g., sugar (prevent explosive
decomposition)

53. Preparation of Supported Catalysts
by Impregnation and Drying
 Upon suitable impregnation pores of support are
uniformly filled with solution of active precursor,
provided no substantial adsorption on the surface of the
support proceeds
 Accumulation of active species at external edge of
support bodies is established during drying
• During the main part of the drying process the
evaporation of solvent takes place exclusively at the
external edge of the support bodies
• Transport of water vapor within porous structure
proceeds too slowly to lead to significant gradients in
partial pressure

54. Preparation of Supported Catalysts
by Impregnation and Drying
 Hydrostatic pressure of liquid within porous system of
support bodies determined by capillary forces
ΔP = 2γ/r
• ΔP pressure difference between air pressure outside
pore system and hydrostatic pressure within system
having pores of radius r at the external edge
• g surface energy of the liquid/gas boundary;
water 72.88 dyne/cm 20oC 71.40 dyne/cm 30oC
• Since r the radius of curvature of the meniscus is
negative, the hydrostatic pressure in the liquid is
lower than the air pressure

55. Stages during Evaporation of
Solvent
Initial stage
Second stage
Formation of
menisci at the
liquid-gas interface
Radii of menisci
between different
particles equal
Four stages during the evaporation of the solvent of an impregnated
support body
Third stage
Haines jump
by emptying
of volume V1
Fourth stage
Transport through
adsorbed liquid
film to external
surface within
funicular region

56. Haines Jump
Filling of
smaller pockets
upon emptying
of larger pockets

57. Evaporation of Solvent from
Impregnated Support Bodies
 Transport of liquid also as a liquid film over the
surface of the support much more rapid than transport
of vapor through emptied pores of support
• Evident from the fact that the rate of evaporation is
constant during a large fraction of the drying
process
• In the last stage of the drying process the liquid film
has disappeared from a significant fraction of the
volume of the support body, this is stage is known
as the pendular state

58. Formation of Bubbles within
Impregnated Support Bodies

59. Formation of Bubbles within Liquid
present in Impregnated Support Bodies
Formation of bubbles of
vapor of solvent during
evaporation of solvent
from impregnated support
bodies
Bubbles can only arise within
pores of a diameter larger
than the diameter of the
necks between the elementary
particles at the external edge

60. Rate of Drying of Porous Bodies
Impregnated with Water
GBHE A2ST a-alumina ring extrudates 0.27m2/g, 0.40 ml/g, void fraction 0.62
GBHE A2ST silica spheres 70 m2/g, 0.85 ml/g, void fraction 0.66
GBHE A2ST

61. Rate of Drying of Porous Bodies
Impregnated with Water
GBHE A2ST silica spheres 70 m2/g, 0.85 ml/g, void fraction 0.66
GBHE A2ST a-alumina cyl. Tablets 1.0 m2/g, 0.20 ml/g, void fraction 0.45
GBHE A2ST

62. Impregnation and Drying of
Support Bodies
 Apparently transport of liquid either through filled pores or
as a liquid film on the surface of the support to the external
edge of the support bodies
 With the liquid the dissolved species is migrating, which
leads to deposition of the active precursor at the external
edge of the support body
 Important parameters : viscosity of the liquid, especially as
a function of the concentration, and the interaction of the
liquid with the surface of the support

63. Impregnation and Drying of
Support Bodies
 Impregnation with different dissolved iron(III)
species
 Evaluation of the distribution obtained after drying
and calcination by X-ray diffraction
• Finally divided material evident from absence of
sharp X-ray diffraction profiles

64. Impregnation of Silica with
Different Iron Precursors
Support : Silica extrudates 2.1 mm diameter
Prepared from Ox 50 Degussa
Surface area 44 m2/g; pore volume 0.8 ml/g
void fraction 0.65
Fe EDTA pH 8.5
Fe EDTA pH 10.1
Fe gluconate
NH4 Fe citrate
Fe(NH4)2(SO4)2.6H2O
Fe2(SO4)3.5H2O)
FeCl3.6H2O
Fe(NO3)3.9H20

65. Impregnation of Silica with
Different Iron Precursors
 Simple, well soluble salts of iron(III) lead to deposition of relatively
large crystallites, mainly at the external edge of the support bodies
 Complexes of iron with organic ligands or the presence of
dissolved organic species containing hydroxyl groups or other
hydrophilic groups substantially improves the distribution of the
iron species over the support
 Interesting is the effect of the pH value of the impregnating liquid
with the iron(III) EDTA complexes

66. Impregnation and Drying of
Support Bodies
 Employing a liquid the viscosity of which rises when
the solvent is evaporating suppresses motion of the
liquid as an adsorbed film to the external edge of the
support bodies
 Interesting to establish the viscosity of the
impregnating liquid as a function of the
concentration taking into account that evaporation
of the solvent leads to an increase in concentration

67. Course of Viscosity of Liquid
during Drying

68. Impregnation and Drying of
Support Bodies
 Effect of interaction of the species of the active
precursor deposited from the solution with the surface of
the support
• An effect of interaction with the support indicated by
the effect of the pH of the impregnating solution with
the iron(III) EDTA complexes
 Experiments with silicon wafers covered by a thin silica
layer upon exposure to atmospheric air
• Application of thin layer of solution by spin coating
• Evaluation of the deposition by AFM (Atomic Force
Microscopy)

69. Deposition of Copper Oxide
on Silicon Wafers
Deposition of clusters of copper(II) oxide particles from a solution of
Cu(NO3)2 in cyclohexane on “natural” oxide layer present on silicon
wafers
When some small particles
have been deposited, the
remaining solution
is taken up within
the pores in between the
particles due to capillary
forces
Note high magnification

70. Deposition of Copper Oxide
on Silicon Wafers
Silica layer on silicon wafers hydrophobic, treatment with ammonia and H2O2
required to produce a hydrophilic silica layer.
On the hydrophilic
silica surface, much more
interaction with the
solution, which leads to
deposition of well
distributed small copper
oxide particles

71. Deposition of Iron Oxide on
Silica Extrudates
 Confirming effect of interaction with surface of support
by experiments with silica extrudates
• Impregnation with a solution of Fe(NO3)3 and
subsequent drying
Calcined at 750oC Fresh Treated at 100oC
with NH3/H2O2/H2O)

72. Impregnation and Drying of
Support Bodies
 Interaction of the species to be deposited with the
surface of the support certainly important as evident
from the effect of pretreatment of silica surfaces
 Effect of organic species only rise in viscosity or is
organic species also enhancing the interaction with the
surface of the support ?

73. Elution Experiments with Different
Iron Species adsorbed on Silicagel
 Solutions of different iron compounds brought on silica
gel column
 Subsequently eluted with water of the same pH as the
initial iron solution
 Elution volumes reflecting interaction with silica surface
 Precursor salt Elution volume (ml)
 (NH4)2Fe(SO4)2 6.2
 FeCl3 6.3
 Fe(NO3)3 7.7
 NH4 Fe citrate 5.6

74. Elution Experiments with Different
Iron Species adsorbed on Silica gel
 Apparently interaction of dissolved species behaving
completely differently during drying after impregnation
not significantly different
 Spin-coating experiments with silicon wafers
pretreated with ammonia and hydrogen peroxide

75. Deposition of Iron Oxide on Silicon
Wafers by Spincoating
Before investigation in the AFM the wafers have been calcined
(NH4)2Fe(II)(SO4)2 FeCl3
Fe(NO3)2
NH4 Fe citrate
Wafer surfaces pre-treated with NH4/H2)2/H20

76. Deposition of Iron Oxide on
Silicon Wafers by Spin coating
 Apparently at room temperature interaction of support
(silica) surface with dissolved species containing organic
molecules not substantially different
 At more elevated temperatures interaction much more
stronger leading to tenaciously adhering film to surface of
the support
 Due to elevated viscosity growth of crystal nuclei
impeded within the film layer
 Other organic molecules containing hydroxy groups, such
as, sugar or HEC exhibit same effect

77. Impregnation of a-Alumina with
Different K3Fe(CN)6 Precursors
No HEC 1 wt.% HEC 2 wt.% HEC
HEC = hydroxy ethyl cellulose

78. Extrudates impregnated with
Different Iron Precursors

79. Conclusions about
Impregnation and Drying
 Impregnation and drying of pre-shaped support bodies
excellent and rapid procedure to produce supported
catalysts
• No waste water; no loss of active species
• Scale up can be performed readily
 At low loadings of active species adsorption on the
surface of the support can allow one to control the range
within the support body where the active precursor will
be deposited

80. Conclusions about
Impregnation and Drying
 To achieve higher loadings adsorption of active
precursors on the surface of the support can not
effectively be employed
 Bad distributions of the active precursors within the
support bodies is due to migration of liquid elements
during evaporation of the solvent at the external edge
of the support bodies

81. Conclusions about
Impregnation and Drying
 Impregnation with solutions the viscosity of which
increases during evaporation of the liquid is very
effective in establishing a uniform distribution of the
active species throughout the support bodies
 The agent raising the viscosity generally also increases
the interaction with the surface of the support, but as
required only at elevated temperatures when the
solvent has largely evaporated