1. CHEMISTRY 3030: CATALYSIS COURSE, 2011

2. INTRODUCTION WHAT IS THE DEFINITION OF A CATALYST?
Given the following reaction at equilibrium:
A2(g) +2B2(g)  2AB2(g)
Q: What will happen to the equilibrium position in such a reaction, if a small quantity of a catalyst were to be added? A:

3. INTRODUCTION
HENCE: A catalyst is any substance (____________) which, when present in a reaction mixture is directly involved with the reaction sequence (mechanism), and that increases the reaction rate (_________) without altering the position of the thermodynamic equilibrium, but is itself not consumed or altered.
WHAT THEN IS CATALYSIS? A:

4. = uncatalysed reaction
INTRODUCTION
HOW DOES A CATALYST DO THIS?
Reactants
= uncatalysed reaction
Energy
Reaction co-ordinate
Products
Activation Energy
Enthalpy change

5. THREE KEY ISSUES TO CONSIDER WHEN DEVELOPING A CATALYST:
ACTIVITY (A)
This a measure of the _________ at which the catalyst is able to transform reactants into products. This speed is related to the rate constant ‘k’ i.e. Rate = –k [reactants]n
The activity (A) of a catalyst is measured by the SI unit: katal (abbreviated to kat).
If the activity of a catalyst is 1 kat : then it ‘enables’ the reaction rate to be___________

6. CONT.
Often it is necessary to disperse (scatter) the catalyst (or ________) on a solid material which has a high surface area. This material is called a _________. Examples of supports are: Al2O3(s), TiO2(s), CaCO3(s), carbon nanotubes (CNTs), etc.
In these cases, the _________ at which the reactions of supported catalysts are measured, have units of molecules converted/ surface area of exposed active phase (in cm2).
If however the number of exposed catalyst sites have been determined experimentally (for later) then the rate has units of molecules converted/ exposed catalyst sites ____________________.

7. CONT.
SELECTIVITY (S)
Multiple products are often formed in a reaction when a catalyst is added. The catalyst thus has an activity for each reaction that leads to a different product.
The catalyst selectivity is then just a ratio of the activity of one product over another (more about this later). The larger the ratio the higher the catalyst selectivity for that product.
Alternatively selectivity can be viewed as the ability of a catalyst to _____________ the rate of _____________of the thermodynamically feasible reactions more than the others.

8. 1) CO(g) + H2(g) → CH3OH(g) = 1.0 x 10-1 Kat
CONT.
Consider the following reactions and then place them in decreasing order of the catalyst selectivity:
1) CO(g) + H2(g) → CH3OH(g) = 1.0 x 10-1 Kat
2) CO(g) + 2H2(g) → ½C2H5OH(g) = 2.5 x 10-2 Kat
3) CO(g) + 3H2(g) → CH4(g) + H2O(g) = 9.8 x 10-2 Kat
ORDER: _____________
Cu/Zn/Al2O3
Cu/Zn/Al2O3
Cu/Zn/Al2O3

9. CoO nanoparticle Carbon nanotube DEACTIVATION
CONT.
DEACTIVATION
For a variety of reasons catalysts can lose their activity and hence their selectivity ___________.
Some reasons:
1) SINTERING (_______________)
Supported metal catalyst particles are oftentimes more stable when they are ____________or spread out on the support surface.
CoO nanoparticle
Carbon nanotube

10. CONT.
___________ occurs at high temperatures when the supported metal catalyst particles spontaneously migrate on the surface. They combine/coalesce with one another to form bigger particles. Hence the metal catalyst ________________.
A.Binder et al. J. Phys. Chem. C 2010, 114, 7816–7821 (Pd on SiO2 or TiO2)

11. CONT.
2) POISONING
Some elements/ions (e.g. Cl, S, C, etc.), when they build up in concentration, can block active sites on the surface of a catalyst and hence reduce the activity and selectivity of the catalyst.
For example: ___________, in leaded petrol, can deactivate catalytic converters in cars.

12. Q: Which species is the catalyst and which the intermediate?
TYPES OF CATALYSIS
Several types of catalysis:
Homogeneous Catalysis
When the reactants and the catalyst are in the ___________:
e.g. O3(g) + A·(g) → O2(g) + AO(g) ….(1)
AO(g) + O3(g) → A·(g) + O2(g) ….(2)
Q: Which species is the catalyst and which the intermediate?

13. TYPES OF CATALYSIS Heterogeneous Catalysis
When the reactants and the catalyst are in _________________:
For example: The photoreduction of carbon dioxide on titania
Pt/TiO2(s)
CO2(g) CO(g) + O2(g) hν

14. Examples of heterogeneous catalysis:
CO + ½ H2  CO2 (Co, Co-Ni) - Fuel cells. Selec Ox. of CO in H2
CH2CH2 + H2  CH3CH3 (Ni/Pd) Olefin Hydrogenation – Fuel industry. c.a. 119 million tonnes of C2H4 in 2010!)
CHCH + 2H2  CH3CH3 (Pt/Pd) Removal of C2H2 from olefins by hydrogenation)
CO + H2  -CH2n+2- (Fe, Co) Fischer-Tropsch. Fuels, waxes, etc.
N2 + 3H2  2NH3 (Fe, Ru) Haber Process. Fertilizers, explosives..
C6H6 + 3H2  C6H12 (Cu -1925!, Ru,Ni) 90% of cyclohexane used for Nylon 6 and 66.

15. TYPES OF CATALYSIS
Enzyme Catalysis
Enzymes are polymeric molecules which regulate the majority of __________ reactions that take place in living organisms. In the main they are proteins which are made up of amino acid building blocks or ____________.
Enzymes are ___________and have extremely ________________(typically between 10 to 103 molecules converted/enzyme/s).

16. Q: How does an enzyme catalyse a reaction?
CONT.
Q: How does an enzyme catalyse a reaction?
A: The reactant molecules that interact with an enzyme are called ___________.
Each enzyme has a specific site (_________) where only certain shaped substrates can fit into or bind (______________). When the substrate ___________binds to the active site the enzyme changes shape (___________) to form the ___________.
The reaction then takes place, product/s formed and released, enzyme returns to its original shape.

17. CONT.

18. Polymer Supported Catalysis
TYPES OF CATALYSIS
Polymer Supported Catalysis
“These are catalyst systems comprising a polymer support (often based on _________________in the form of ___________to pack in a reactor) in which catalytically active species are ___________through chemical bonds or weaker interactions such as hydrogen bonds or donor–acceptor interactions and can be used repeatedly.”
PAC, 2004, 76, 889 (Definitions of terms relating to reactions of polymers and to functional polymeric materials (IUPAC
Recommendations 2003)) on page 896

19. CONT.
Example: Pd nanoparticles (PdNPs) immobilised on microporous Poly(amidoamine) (PAMAM) dendrimers.
Shin Ogasawara and Shinji Kato J. AM. CHEM. SOC. 2010, 132, 4608–4613

20. Suzuki-Miyaura reaction in water.
CONT.
Suzuki-Miyaura reaction in water.
Advantages:
Water as a solvent for
organic rxn! GREEN rxn!
In bio-active compounds
synthesized the catalyst
is easily retrievable : No
___________ of the
product!
Reduced costs (Pd=$$$);
catalyst ___________
Shin Ogasawara and Shinji Kato * J. AM. CHEM. SOC. 2010, 132, 4608–4613

21. CLASSIFICATION OF HETEROGENEOUS CATALYSTS (BOND pg10)
Catalyst Type:
Examples:
Reactions:
Metals
Ni, Pd, Fe, Pt, Ag
Hydrogenation
Dehydrogenation
Hydrogenolysis
Oxidation
Semiconducting oxides
/sulphides
NiO, ZnO, MnO2, Cr2O3, Bi2O3-MoO3, WS2
Desulphurisation

22. CLASSIFICATION OF HETEROGENEOUS CATALYSTS (BOND pg10)
Catalyst Type:
Examples:
Reactions:
Insulating oxides
Al2O3, SiO2, MgO
Dehydration
Acids
SiO2-Al2O3, Zeolites
Polymerisation, Isomerisation, cracking, alkylation

23. Catalysts and Surfaces
A reactant must react with the surface atoms of a catalyst. Hence the more atoms on the surface, the more reactants can be transformed into products. Thus the expectation that high surface areas lead to ___________.
Surface Areas fall into three categories:
10 m2 g-1  Small (e.g. _______________)
200 m2 g-1  Normal (e.g. _______________)
1200 m2 g-1  Large (e.g. _______________)

24. Catalysts and Surfaces
The rate might be expected to be __________ to the number of surface atoms BUT not all surface atoms are the _______. This gives rise to the concept of an _____________(Taylor 1925).
Q: How then can the surface area be maximized?
A: _______________
For spherical particles on a hemispherical support, the total surface area is give by
SA (in m2)= ____________________
Where M = total mass of catalyst,  = density and
r = average particle radius, Vpart= volume of particle.

25. Catalysts and Surfaces
Q: A batch of hemispherical catalysts (support and active nanoparticles) weighs 1.23 g and has a density of 3.14 g/ml. What is the total surface area of the catalysts if they are loaded with spherical nanoparticles with diameters of 50 nm?
A: SA = _______________

26. Inorganic support Organic support Good _______ OK
Q: How then can the surface area be maximized?
A2: __________
Factor:
Inorganic support
Organic support
Effect of Temperature
Good
_______
Heat transfer
Chemical reactivity OK

27. Q: How then can the surface area be maximized?
Promoters are substances that increase the _______
_______, even though they are not catalysts by themselves. In addition they “allow the active phase to function at its _______________” (Bond pp 76)
e.g. Co or Ni in WS2 catalyst for desulphurisation†
† C. Roukoss et al. / C. R. Chimie 12 (2009)
There are two types of promoters
_________

28. Types of promoters: Structural
A structural promoter ___________by separating the surface ___________.
For e.g. The active phase for the NH3 synthesis catalyst is Fe, but its promoters may include:
_________, ________, _____ and ______*. These inhibit Fe crystallites from coalescing.
*I. Siminiceanu, I. Lazau, Z. Ecsedi, L. Lupa*, C. Burciag.Chem. Bull. "POLITEHNICA" Univ. (Timisoara) Volume 53(67), 1-2, 2008.

29. Types of promoters: Electronic
Electronic promoters are effective due to their ______________. The most widely used electronic promoters belong to _______, _______ and the _______.
For Groups 1A and 2A, their ability to promote is inversely proportional to their electronegativity. Examples: Cs > K > Na (Group 1A)+
Ba > Ca > Mg (Group 2A)++
+ S. Murata, K. Aika, T. Onishi, Chem. Lett., 1990, p
++ S. R.Tennison, in: J.R. Jennings (Ed.), Catalytic Ammonia Synthesis, Fundamentals and Practice, Plenum
Press, New York, 1991, p. 303.

30. Electronic and structural promoter?
When Cs is added:
No Caesium ruthenates form.
The electronic properties change.
RuO2 clusters reduced to metallic Ru. Increased Activ.
Y.V. Larichev. Effect of Cs+ Promoter in Ru/MgO Catalysts.
J. Phys. Chem. C 2011, 115, 631–635

31. Pauling’s Electronegativity value
Problem
Given the following data for the lanthanides, place them in order of increasing ability to act as electronic promoters:
______________
Element
Pauling’s Electronegativity value
Samarium
1.198
Lutetium
1.201
Lanthanum
1.101

32. Sol-gel process Q: How then can the surface area be maximized?
A3: ______/ _______ maximization
Sol-gel process
TEOS = Tetraethyl orthsilicate
Polymers include: polyvinyl
alcohol and polyethylene glycol with different molec.masses
S SATO, T MURAKATA, T SUZUKI,
T OHGAWARA. JOURNAL OF MATERIALS SCIENCE
25 (1990)

33. Q: How then can the surface area be maximized?
A3: _______/ _______maximization
No polymer
Polymer of low molec. mass
Polymer of higher molec. mass
Mean pore sizes increase from 3 nm to 7 nm
S SATO, T MURAKATA, T SUZUKI,
T OHGAWARA. JOURNAL OF MATERIALS SCIENCE
25 (1990)

34. ATOM SURFACE CONCENTRATION
The atom surface concentration can be determined by the _____________
Assume that the bulk density is 1 g/cm3 then the molecular density will be 5 x 1022 molecules per cm3. The surface concentration (molecules per cm2) is proportional to _______if one assumes cube like packing. This gives a value of _______molecules per cm2.

35. For very small particles D = 1
DISPERSION
The fraction of the atoms on the surface is referred to as _______. Mathematically, dispersion (D) is the ratio of the number of surface atoms (NS) to the TOTAL no. of atoms (NT): i.e. _______
For very small particles D = 1
However, as the particle grows the number of surface atoms will _______.
For a cube of 100 Å, D = 10-3 !!!!

36. DISPERSION
1.0
Total number of atoms
Dispersion (D)

37. Surface Atoms
Consider a cube of metal (or metal oxide). The surface atoms rest on the bulk atoms and so must reflect this situation. Previously you learned about how atoms can pack and the way in which structures were built up. Example: _______
metallic_structures.htm

38. Surface Atoms
Consider a cube of atoms with the _____structure. We can take slices through this structure and this will yield different faces with Miller Indices: (100), (111), (100), etc.
M Bowker, The Basis and Applications of Heterogeneous
Catalysis, Oxford University Press, 1998., pp 12.

39. Surface Atoms
It is quite difficult to get surfaces with only one type of face. Most surfaces have many faces and contain _______, _______, _______ and _______. Thus surfaces are generally not _______. This has implications for the reactant molecules (see example with ammonia synthesis that follows).
Different arrangements of surface atoms have different _______ _______. Generally, surfaces with _______ coordination number have the _______ surface free energy (are the most reactive).

40. Adatom Step Kink edge Terrace
A. N. Chaika, S. I. Bozhko, A. M. Ionov, A. N. Myagkov, and N. V. Abrosimov. Semiconductors, 2007, Vol. 41, No. 4, pp. 431–435

41. Spectroscopy in Catalysis: An Introduction, Third Edition, J. W
Spectroscopy in Catalysis: An Introduction, Third Edition, J. W. Niemantsverdriet
Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, ISBN:

42. Top plane co-ordination Adatom Kink edge 3 Step 4 Terrace 6
Atom type
Top plane co-ordination
Adatom
Kink edge 3
Step 4
Terrace 6
Thus reactivity order is: _______ > _______ > _______ > _______
M Bowker, The Basis and Applications of Heterogeneous Catalysis, Oxford University Press, 1998., pp 13.

43. Single crystal faces of Fe for NH3 synthesis
G.A. Somorjai, N. Materer / Surface structures in ammonia synthesis. Topics in Catalysis 1 (1994)

44. Molecular Heterogeneous Catalysis
Metal cluster chemistry can assist as an important model to illustrate the interconnectedness between _______ chemistry and _______ chemistry.
Consider the _____________ reaction of formic acid catalyzed on different metal surfaces:
H-COO-H (aq)  CO2(g) + H2(g)
Metal
Plotting the _______ of each metal surface versus the standard enthalpy of formation (ΔHof) of each metal formate, gives what is called a ‘______________’ :

45. Molecular Heterogeneous Catalysis
_____________ _____________
Speed of
decomposition
of surface
intermediate
is low
_______ ______________Speed of formation of surface intermediate
is low.

46. Molecular Heterogeneous Catalysis
The shape of the ‘_______’ plot is consistent with the notion that surface intermediates closely resemble bulk intermediates (formates in this case).
This is based on the _______ _______. This implies that:
Reaction rate = f(_______, _______).
Thus the optimum catalytic performance does not relate to a specific _______ _______ but to a balance of interaction & desorption. These are the elementary steps in _______ _______.

47. Molecular Heterogeneous Catalysis
Wolfgang Sachtler showed that when reacting molecules _______ onto a surface they form _______ _______. Furthermore, these complexes result in the partial destruction of metal-metal bonds and lead to a ‘______________’ of the surface. This was later termed ‘_______ _______’.
Somorjai & Muetterties showed that the _______ _______ in a catalytic reaction, as well as the surface complexes are similar to homogeneous _______ complexes and reactions.

48. Molecular Heterogeneous Catalysis
Comparison of some Somorjai &Muetterties surface complexes with known organic complexes:

49. ADSORPTION
Molecular and/or atomic species have essentially two ways in which they can attach or adsorb onto a surface: _______ or _______.
Physical Adsorption or ___________
Physisorption often occurs in any liquid/solid or gas/solid system where the molecular/ atomic species attach to the solid surface through _______ _______ _______ (van der Waals forces).
The elementary step in physisorption from a gas phase does not involve an _______ _______.

50. Physisorption (cont.)
The typical binding energy of these physisorbed species on a surface is between ___________. (No chemical specificity).
The process is _______ _______ _______, with little energy. See example of helium gas on metal surfaces afterwards.
The adsorption enthalpy can range between _______ and _______.
For physisorption, under appropriate conditions, gas phase molecules can form _______ adsorption.

51. Example: The physisorption profiles of He on various metal surfaces.
E. Zaremba and W. Kohn (1977). "Theory of helium adsorption on simple and noble-metal surfaces". Phys. Rev. B 15 (4): doi: /PhysRevB  
Retrieved from "

52. Chemical Adsorption or _____________
Chemisorption adsorption occurs when molecular/atomic species chemically attach to a surface through _______ _______. New species are formed. _______ _______ _______ _______
The typical binding energy of chemisorbed species on a surface is between _______. Binding is usually chemically specific.
The process is less easy to reverse and often takes a lot of energy to do so. Sometimes the process is _______ i.e. due to _______ of the species. Example: _______ _______ _______ _______ _______ _______ _______ _______ _______.

53. Chemisorption (cont.)
The elementary step in a chemisorption process from the gas phase often involves an _______ _______. (Recall dissociation of oxygen on metal.)
In chemisorption, because the molecular/atomic species are adsorbed on the surface by covalent bonds, they often only form a single or _______ adsorption.
In chemisorption, the adsorption enthalpy can range between _______ and _______.
Q: Why are the adsorption enthalpies of physisorption and chemisorption negative?

54. ADSORPTION ISOTHERMS
Q: Why is it important to obtain a relationship between the quantity of a substance adsorbed on the surface of a solid and its gas phase pressure?
The _______ of gas coverage on the
surface can be _______ determined.
The _______ of the adsorption of the molecules can be quantitatively determined (i.e. chemi or physisorption).
The _______ _______ of the solid can be quantitatively determined.
The _______ of the catalytic system can be modelled.

55. ADSORPTION ISOTHERMS
Q: What then is an adsorption isotherm?
A: “The relationship between the _______ of gas adsorbed on a surface and the
_______ with which it is in equilibrium, at a _______ _______, is called an adsorption isotherm” (Bond pg 15).
Suppose the maximum surface that could be covered was ____ and that it was covered by an amount __, then the ratio or fraction (___) that the surface is covered is: _______ _______, then an adsorption isotherm, based on various assumptions can be developed.

56. LANGMUIR ISOTHERM
Suppose that a solid surface has a gas (of a certain pressure) _______ _______ on its surface and at dynamic equilibrium then: 1 2 3 1 2 3 

57. If the ratio or fraction that the surface is
If the ratio or fraction that the surface is covered is θ, then Langmuir made the following assumptions:
Adsorption isotherms do not exceed a _______ _______. Thus molecular/ atomic species can only maximally fill the surface, then no further adsorption occurs i.e. _______ _______ _______
All sites on the surface are _______ and
_______. This implies that the surface is _______ _______ and that the _______ _______ would be equivalent throughout the surface.

58. When molecules adsorb onto a surface,
When molecules adsorb onto a surface, they _______ _______ or _______ one another or incoming molecules that will adsorb. i.e. molecules will adsorb onto a site ___________ from whether or not a site next to them is _______ or _______.
In the light of what you have already learned, take some time to critically analyze Langmuir’s assumptions.

59. DERRIVATION OF LANGMUIR ISOTHERM
1) Mono/single site adsorption
Consider a gas A that can reversibly _______
and ______ on an active site *, then:
Where kA = ________________________
Where kD = ________________________
the number of molecules colliding with the
surface in unit time is proportional to the
____________of gas A i.e. ____________

60. Suppose the surface has a total of _____
________and at some time the ________
________ is , then:
Fraction of unoccupied sites = ________
Number of unoccupied sites = ________
Rate of adsorption  PA
But:
Rate of adsorption  no of unoccupied sites
 ________
So:
Rate of adsorption  PA × N(1-)
Rate of adsorption = _____________,
(where kA = _____________________)

61. But, the rate of desorption  amount of adsorbed gas
 ________
Rate of desorption = ________
(where kD = _____________________)
At equilibrium:
Rate ___________ = Rate ___________
thus: kA× PA × N(1-) = kD × N
Where___ and ___ are the equilibrium values
of pressure and surface coverage.

62. Cancelling like terms and rearranging gives:
(kA× PA ) – ( × kA× PA ) = kD × 
So:  = (kA× PA ) (kD + kA× PA )
Then let _______ or the ______________
_________ then you obtain the following:
L ___
This is the ______________for _____ site
adsorption.

63. Langmuir adsorption isotherm
Thus:
________
Recall:
b = kA/kD

64. If V = volume actually covered
And Vm = monolayer coverage then:
θ = ________ then since
___
Then rearranging and substituting gives:
This is in the form Y= mX + C , where Y = ____
m = ____ , X = __ C = ____.This is allows the
monolayer coverage to be calculated

65. Since ________
and kA = AA×e–{EA/RT} with kD = AD×e–{ED/RT}
____
Where ________
Thus b is a function of ________ and
________ at temperature ________.
When b is ________ then ________ is _______
bonded, conversely when b is ________ it is
________ bonded.

66. 2) Dual site adsorption
Consider a gas A that must strike the surface
at a location where there are _____ adjacent
active sites *, then:
Up to fairly high fractional coverage () it can
be assumed that the adsorption of _____
_________ will depend on the fraction of
vacant sites or ____, and that the adsorption
of the other fragment will also depend on
this ____________.

67. 2) Dual site adsorption (cont.)
Then: Rate of adsorption = _____________
Rate of desorption = ________
At equilibrium: Rate of ads= Rate of desorp,
So: k’APA[N(1 - )]2 = k’D(N)2
If b = k’A/k’D, Then by subsitution and
Rearrangement:  = (bPA)½ /(1 + (bPA)½ )
For the monolayer coverage (Vm), again, let
 = V/Vm, then
This is in the form Y= mX + C , where
Y =______, m = ____ , X = ___ C = _______.
Thus a plot of _______ against ___ will give a
straight line.

68. Measured amounts adsorbed of the pure gases CH4 ( ),
CO2 ( ), and N2 ( ) on AC Norit R1 at T D 298 K. Simultaneous
fit of all data with the generalized dual-site Langmuir isotherm (—)
F. DREISBACH, R. STAUDT AND J.U. KELLER Adsorption 5, 215–227 (1999)

69. 3) Non-competitive adsorption
It is possible that ___________(gas A, and
gas B), may be in the same container and
will adsorb on different sites. The adsorption
is _________________.
Then the isotherm for each gas is simply a
Langmuir isotherm for ________ gas. i.e.
 = bPA/(1 + bPA) for gas A, and
 = bPB/(1 + bPB) for gas B

70. 4) Adsorption of more than one species on the
same surface
Consider the reaction of _______ gases on a surface (i.e. the adsorption is ____________).
with rate constants ka(A) and kd(A)
with rate constants ka(B) and kd(B)
Then A = bAPA/(1 + bAPA + bBPB)
And B = bBPB/(1 + bAPA + bBPB)

71. Other Non-Langmuir Isotherms
5) The General expression
We can work with 1,2,3,4, ….. up to i gases.
Each gas can be expressed by a Langmuir Isotherm:
A = bAPA/(1 +biPi)
Other Non-Langmuir Isotherms
i) ____________ Isotherm
This assumes that a __________ decrease of the enthalpy of ____________ occurs with fractional coverage. ( = kP1/n where k and n are constants with n > 1)

72. L Zhang, S Hong, J He, F Gan, Y-S Ho
L Zhang, S Hong, J He, F Gan, Y-S Ho. Clean – Soil, Air, Water 2010, 38 (9), 831–836.
Freundlich isotherms obtained using linear and nonlinear regression methods for the adsorption of phosphorus onto Al2O3 at temperature of 308 K.

73. ii) __________ Isotherm
Assumption here is that the ________ heat of adsorption falls off _________ with coverage:
θ= k’ln(k”bPA)
where b and PA have been defined previously.

74. SUMMARY OF LANGMUIR ISOTHERMS

75. POROUS MATERIALS
Many materials are _______. Information about the pore ______, pore ________, pore ________ as well as the _________ can be obtained from two different types of adsorption experiments:
1) Multilayer gas adsorption
Here we use an _________ _________ or _______e.g. N2, Ar, Kr to physisorb onto the material.
2) Mercury Porosimetry
Liquid mercury is forced _______ into the pores of the material (e.g. _______ gives information on ______pore radius)

76. Uniform/cylindrical Blind pore Through pore Funnel shaped
PORE SHAPES/TYPES
Uniform/cylindrical
Blind pore
Through pore
Funnel shaped
Porous network
Ink bottle shaped
Closed pore

77. Pores are classified according to size _________ < 2 nm
POROUS MATERIALS
Pore Size
Pores are classified according to size
_________ < 2 nm
_________ 2 nm < x < 20 nm
_________ > 20 nm
Yun Wu, Xianfeng Du, Honghua Ge and Zhen Lv Starch/
Stärke 2011, 00, 1–9 DOI /star
Microprous starch

78. IUPAC Classification of porous solids
There are _________ of adsorption isotherms that have been observed. Each gives information about the types of pores contained in a solid as well as the capacity of the solid to adsorb a gas.

79. IUPAC Classification of porous solidsII
III IV V VI

80. IUPAC Classification of porous solids (Cont.)
In the previous figures the _________ of the curve gives information about the solid – its _________. Let us examine these a bit closer:
Microporous solids (see I)
At ______pressure: adsorption in _________ first
At _________ pressure: then coverage of _________ surface takes place.
Mesoporous solids (see IV)
At _____ pressure: ________coverage (plateaus)
At _________ pressure: adsorption in _________. After the pores are filled adsorption occurs on the external surface.

81. Macroporous solids (see II) At _____ pressure: __________ coverage
At _______ pressure: _______ coverage until condensation occurs. There tends to be overlap between the 2 regions
Uniform ultra-microporous solids (see VI)
If all sites the same: _________ coverage
If not: _________ isotherm for _________
Example: Zeolites
Range of pore sizes
Zeolite (small size
range)

82. HYSTERESIS LOOPS
Evaporation from a pore takes place at a _________ than condensation thus the path of _________ differs from _________. Four types of Hystereses have been identified and classified (IUPAC)
P/P*
Adsorbed volume
The four _________ shapes of adsorption isotherms typically associated with N2 adsorption
Type H1
Type H2
Type H3
Type H4

83. HYSTERESIS LOOPS (cont.)
H1/H2 TYPE
Particles with _________ or aggregates of _________ particles
H1: uniform size/shape
H2: non-uniform size/shape i.e. different size pore mouth and pore body e.g. ink bottle type pores
H3/H4 TYPE
Aggregates with _________ pores
H4: uniform size/shape
H3: non-uniform size/shape
e.g. zeolites, carbons

84. KELVIN EQUATION
Lord Kelvin noted that the evaporation of condensed gas molecules from a surface with very fine pores is more difficult than their condensation. This is because there is a greater probability, as compared to a _________ _________, that the molecules which evaporate from a ____________ meniscus will _________.
Using the Kelvin equation, it is possible to measure a pore radius at a given P/P*:
_________ _________, where
V = molar volume of liquid,  = surface tension
r = pore radius,  = contact angle (usually = zero)
R=gas constant, T = temperature

85. PROBLEM
P/P*
Adsorbed volume ml/mol
Consider a zeolite material onto which nitrogen was adsorbed and desorbed.
If the P/P* was 0.25 at –183.15oC and the surface tension of nitrogen was
1.0 x 10-1 Nm-1 (and the contact angle was zero), then use the graph to calculate what the pore radius of the zeolite was.

86. SURFACE AREA Porous Materials I) Internal surface area
If the pores are _______, _________ uniform cylinders then:
r = radius of pore, S = internal surface area
II) Total Surface Area
This is given by: S = nmLm, where:
nm = moles gas adsorbed in __________
m = area of ________ adsorbed molecule
L (or N) = Avagadro constant
S = 2Vp/r
Vp =pore volume

87. SURFACE AREA X Slope Y The Brunauer, Emmett and Teller (BET) Method
(Used on type II adsorption curves for multiple layer physisorption - see IUPAC classification of porous solids)
Here:
Which can be rearranged to give the ____________:
Vm = volume of gas, monolayer coverage,
C = _________ _________ constant
V = θ = CP
Vm (P* –P) (C–1)P P* X
P P
P* = (C-1) P*
Vm 1 – P C.Vm C. Vm P* Y
Y – intercept. Thus calculate Vm
Slope

88. _________ _________ _________
P/P*
P/P* / 10-1 cm-3
Vm (1-P/P*)

89. BET SURFACE AREA (cont).
Single point method
This is a _________ method. It arises because the slope > intercept (which tends to zero when P/P* is in the 0.2 to 0.3 region see (type II)).
Hence assume the BET plot passes through the origin. i.e. assume Y-intercept at the origin.
Then slope = (C-1)/C.Vm and thus Vm can be calculated.
An error bar of 5% is acceptable in these experiments.

90. V P/P* Single point method (cont.)
Alternatively, if a simple extrapolation is made from the _________ of a set of data, then the molar volume can be obtained. This method delivers a rough estimate of the molar volume of within 10% (Bowker pp 57).
P/P* V

91. BET SURFACE AREA (cont).
The constant C in the BET equation is related to the following equation:
C = e[(Ha – H1)]/RT, where Ha = enthalpy of _________ of the _________ and H1 = enthalpy liberated from the second and subsequent layers (similar to the _________ of the gas). Thus C helps give an estimate of ΔHads and it influences the ______ of the adsorption isotherm:
C=10 000 V 1
P/P*
C=10
C=2
C=1

92. SURFACE AREA Gases used for analyses:
Gas Area/10-20m2 Saturation P (torr)
N at 77K
Ar at 77K
O at 77 K
There is a limit on using nitrogen: _______ pore corresponds to 5 molecule width. Hence we use
Ar or Kr for low surface area measurements (_________ ). 

93. KINETICS
Kinetic measurements and the interpretation of the kinetic data lies at the heart of catalysis. Kinetic analysis allows for:
Reactor design
Correlating and rationalising catalytic activity
Mechanism determination
Rates of reaction, Order, Effect of Temperature
Consider the reaction
__A + __B  __C
Rate (r) given by (rate of form = rate of consump):
r = – (1/__)dA/dt = – (1/__)dB/dt = +(1/__)dC/dt
Units of r = _________

94. KINETICS
In a heterogeneous reaction the rate will depend on the _____________area available to the reactants. This is expressed as the ____________ (TOF). TOF = no of molecules converted per unit of time _______________ .
Gas Phase Reaction (Homogeneous reactions)
We know that the reaction rate can be expressed in terms of _________ _________ .
Reaction : aA + bB  cC
Rate = k(PA)a(PB)b(PC)c ….This is referred to as a ________________

95. Given: Rate = k(PA)a(PB)b(PC)c ,
a,b,c = orders of the reactants (don’t have to =
integers).
k = rate constant
Rate can be expressed per _________ :
r = mrm, where m = mass of catalyst OR
If the total surface area (S) of the catalyst has
been determined, then rate can be expressed
______________ : r = Srs
Recall the Arrhenius equation:
k = Acatexp(–Ecat/RT)
Where Ecat = Activation Energy
And Acat = pre-exponential factor

96. ADSORPTION MECHANISMS
We will now look at two different mechanisms proposed for adsorption:
(A) Langmuir-Hinshelwood
(B) Eley-Rideal

97. Two types to consider: LANGMUIR-HINSHELWOOD (L-H) MODEL
Three general assumptions to this model:
Adsorption is _____ and _________from the gas phase
The reaction of the adsorbed molecules is the rate determining step (RDS) i.e. the surface chemical reaction = RDS i.e. k very small
The _________ of an _________ species is determined by the appropriate Langmuir Isotherm.
Two types to consider:

98. (A) L-H model for unimolecular reactions
Example: E(g)  E (Ads) → C(g) θE
fast
Surface rxn
=RDS
Molecule E
at PE
Product
Molecule C E C
If bE or PE are _______, then: Rate= k bE PE …i.e. __________
If bE or PE are _______, then: Rate → k …..i.e. ____________

99. Things to note about L-H model for unimolecular reactions
This type of kinetics is not specific to catalysis
Mainly applies in:
3 step reactions
Pre-equilibrium systems
e.g. Michaelis Menton equation for enzymatic catalysis in Biochemistry

100. (B) L-H model for bimolecular reactions
A(g)  A (Ads)
B(g)  B (Ads)
And
Surface rxn
=RDS
Fast
A(Ads) + B(Ads) → AB(Ads) → AB(g)
Two extra assumptions to this model:
Molecules A and B are adsorbed on _______ sites with _____________
Product molecule AB is very ___________and comes off the surface fast.

101. θB θA B A Product molecule BA Molecule B at PB Molecule A at PA fast
RDS
Molecule A
at PA
Product molecule BA θB B A
.. Langmuir-Hinshelwood
Equation

102. Things to note about L-H model for bimolecular reactions
If molecules A and B are _______ adsorbed, bA and bB are _______ , then:
Rate = k’ PAPB ….i.e. _______, (Where k’= kbA bB)
If molecule ____is _______ adsorbed and molecule B is strongly adsorbed i.e. _____________then: Rate = k’’ PA/ PB , (Where k’’= kbA/bB). This is an indication that B poisons the surface.
Similarly the rate is affected if the _______ _______of molecule A and B are varied:

103. θB>>θA θA >> θB B B
The effect of surface concentration on the rate in bimolecular reactions PA
rate
For constant PB
Rate limited
by surface
Concentration
of A
θB>>θA A B
Rate limited by
surface concentration
of B
θA >> θB A B

104. II) Eley-Rideal (E-R) model for bimolecular reactions
Unlike the L-H model, in the E-R model it is proposed that an adsorbed molecule may react _______with an _______ gas molecule by a collisional mechanism. The surface reaction is still the RDS i.e. PA
fast
RDS PB A B θA

105. Eley-Rideal bimolecular surface reactions
Note: For constant PA, the rate is always first order wrt PB
θA = 1 PA
Rate
For constant PB
_________
bAPA >> 1
_________
Thus:
Rate = k PB …zero
order
in A
bAPA << 1
Thus:
Rate = k bA PA PB …….. first order in A
_____
_____

106. How can the two bimolecular reaction models be distinguished from one another?
Experimentally if the reaction rate is measured as a function of the surface coverage of A i.e. θA, then the rate will initially increase for both mechanisms at ___________________. There will be slight to no difference between the two proposed models observed. BUT:
If the reaction proceeds by the model proposed by Eley-Rideal then at ___________________(i.e. θA  1) the _________________until the surface is covered by A.
If the reaction proceeds by the model proposed by Langmuir-Hinshelwood then the ______________
________________and then gradually decreases to zero as θA  1.

107. Q: Will the rate of E-L model increase ad infinitum?
The effect of surface coverage on rate for the Eley-Rideal and Langmuir-Hinshelwood models θA
Rate 1
Eley-Rideal model
Langmuir-Hinshelwood
Q: Will the rate of E-L model increase ad infinitum?

108. CURVATURE IN ARRHENIUS PLOTS
THE EFFECT OF TEMPERATURE ON KINETICS:
CURVATURE IN ARRHENIUS PLOTS
In heterogeneous systems we will still assume for the
reaction: A  C
Rate = –dPA/dt = kA = kbAPA.
BUT in this equation BOTH ___ and _____ are functions of temperature. For instance:
If bA is ________ and _____ is ________, then k will be the only variable that is a function of T. i.e. k = A·exp(-Etrue/RT)
If bA is small then  tends to _____, then from the van’t Hoff Isochore we have:
(dlnbA)/dT = HθA/RT2 , then ∫(dlnbA) = ∫ (HθA/RT2) dT

109. Thus:
lnbA = –HθA /RT + C OR bA = C·exp(–HθA/RT)
(where C = integration constant & –HθA is the standard
molar enthalpy of adsorption of reactant A)
Now we have rate = kA and A = bAPA
We can substitute into the equation for both k and bA
i.e. Rate = –dPA/dt = kA = kbAPA = k[C·exp(–HθA/RT)](PA)
= A·exp(–Etrue/RT)[C·exp(–HθA/RT)](PA)
Re-writing this out: = PA·A·C·exp(–Etrue–HθA)/RT
= PA·A·C·exp(–Eapp)/RT
Where: (–Eapp) = (–Etrue–HθA), hence Etrue = Eapp–Hθa
and since HθA is always negative, then Etrue > Eapp

110. Arrhenius plot for a catalysed reaction over a range of temperatures gives:
III II I
Log 10 Rate
1/T I II
III
Surface coverage 1
1>>0
~ 0
Order,n
1>n>0
Slope x 2.3R
Etrue
----
Eapp

111. THE EFFECT OF DIFFUSION ON KINETICS
Diffusion or mass-transport limited reactions are those in which the transport of the ________ /or ____________ the catalyst influence the rate:
Rate  [catalyst]n and n< 1 vs ______________
Rate  stirring rate vs ____________________
Eact about 10 – 15 kJ mol–1 vs ______________
Rate  (temperature)1/2 vs _________________
An Arrhenius plot showing the onset of
diffusion limitation can be drawn:

112. R Q’ Q R’
Log 10 Rate
1/T
A’A: Surface reaction is
rate-limiting
B’B: Reaction
is diffusion
limited A
____________ for diffusion limited reactions the RAQ’ curve
(purple curve) is detected, because the slower of the two
processes controls the rate.