Adsorption and Catalysis
Dr. King Lun Yeung
Department of Chemical Engineering
Hong Kong University of Science and Technology
CENG 511
Lecture 3
Physical Adsorption
Texture and morphology
–
–
–
–
–
specific surface area of catalyst
pore size
pore shape
pore-size distribution (same size or various sizes?)
pore volume
Pore Size and Shape
Pore Diameter
– micropores (< 2 nm)
– mesopores (2 – 50 nm)
– macropores (> 50 nm)
Pore Shape
–
–
–
–
cylinder
slit
ink-bottle
wedge
Pore Size and Shape
Pore Structure
Silica
Carbon
Zeolite
Pore Size and Shape
Why is it important?
it dictates the diffusion process through the material.
D (m2/s)
10-4
10-8
Molecular
diffusion
Ea (kJ/mol)
Knudsen
diffusion
100
Surface
migration
10-12
50
10-16
1000
100
10
1
0.1
0
1000
Pore diameter (nm)
100
1
Pore diameter (nm)
Configurational diffusion
Surface migration
10
0.1
Pore Size and Shape
Why is it important?
directly affect the selectivity of the catalytic reaction.
Pore Size and Shape
Measurement Techniques
Hg porosimetry
N2 capillary condensation
Micro
Meso
2
1
Macro
50
10
100
1000
10000
Pore diameter (nm)
N2 Physisorption
Adsorption and Desorption Isotherms
25
n ad (mmol/g) 1
20
Desorption
15
10
Adsorption
5
0
0
0.2
0.4
p/p 0
0.6
0.8
1
N2 Physisorption
Adsorption and Desorption Isotherms
III
nad
nad
II
nad
I
B
p/p0
p/p0
V
VI
B
p/p0
nad
nad
nad
IV
p/p0
p/p0
p/p0
Isotherms
Type I Langmuir Adsorption Isotherm
nad
I
nad
Kp
 nm    nm 
1 K p
p/p0
Assumptions:
• homogeneous surface
(all adsorption sites energetically identical)
• monolayer adsorption (so no multilayer adsorption)
• no interaction between adsorbed molecules
Isotherms
Type II
nad
Multilayer adsorption (starting at B)
Common for pore-free materials
B
p/p0
Type IV
nad
Similar to II at low p
Pore condensation at high p
B
p/p0
Isotherms
Type III
nad
Strong cohesion force between
adsorbed molecules, e.g. when water
adsorbs on hydrophobic activated
carbon
p/p0
Type IV
nad
Similar to III at low p
Pore condensation at high p
p/p0
Physisorption
Surface area measurement
Avogadro’s number
(molecules/mol)
specific surface area
(m2/g)
S = nmAmN
monolayer
capacity (mol/g)
area occupied by one
molecule (m2/molecule)
BET model: SBET
t model: St
Physisorption
Different Adsorbates Used in Physisorption Studies
Boiling Point (K)
Am (nm2/molecule)
N2
77.3
0.162
Ar
87.4
0.142
CO2
194.5
0.17
Kr
120.8
0.152
Adsorbate
N2 Physisorption
Adsorption and Desorption Isotherms
Langmuir Adsorption?
No:
6
a
n ad (mmol/g) 1
5
b
strong adsorption at low p due to
condensation in micropores
4
at higher p saturation due to finite
(micro)pore volume
3
2
1
Zeolite
0
0
0.2
0.4
0.6
p/p
0
0.8
1
BET Isotherm
 Modification of Langmuir isotherm
 Both monolayer and multilayer adsorption
 Layers of adsorbed molecules divided in:
– First layer with heat of adsorption Had,1
– Second and subsequent layers with Had,2 = Hcond
BET isotherm: n
ad
p
1
C 1 p


 0
0
p p
nmC nmC p


 H ad  H cond 
C  exp 

RT


 BET equation does not fit entire adsorption isotherm
– different mechanisms play a role at low and at high p
BET Isotherm
model
reality
5
4

For every layer
Langmuir model
1st
nth
Assume
K1  K1,0 e

K n  K n,0 e
H ads
RT
H
 n
RT
 K n,0 e
H cond

RT
layer
layer
i
3
2
k  pk 
k
n 1
a
n-1
0
nad  nm 0  21  3 2  ...
1
0
a 0
1
1
d 1
 pk 
n
d n
p
p0
nad
C

nm 
p 
p 
1  0  1  C  1 0 
p 
p 

k a0
1  1 p 0  K1p 0
kd
k a0
n  1 p n-1  K n p n-1
kd
with C  e
H ads  H cond
RT
BET Isotherm
Nonporous Silica and Alumina
Low p/p0:
(B)
nad/nm
BET equation
(A)
• filling of micropores
• favoured adsorption at most
reactive sites (heterogeneity)
High p/p0:
• capillary condensation
p/p0
Range 0.05 < p/p0 < 0.3 is
used to determine SBET
Pore Size and Surface Area
Mean dp (nm)
SBET (m2/g)
10
200
6
400
4
800
10
150
5
500
Zeolite
0.6-2
400-800
Activated carbon
2
700-1200
TiO2
400-800
2-50
Aerosil SiO2
-
50-200
MeOH synthesis (Cu/ZnO/Al2O3)
20
80
NH3 synthesis (Fe/Al2O3/K2O)
100
10
Reforming (Pt/Re/Al2O3)
5
250
Epoxidation (Ag/-Al2O3)
200
0.5
Material
Catalyst supports
Silica gel
-Al2O3
Catalysts
Pore Size Distribution
Kelvin Equation
Pore Size Distribution
Kelvin Equation
t
Cylindrical pore
dm
dp
Adsorbed layer
Ink-bottle pore
Pore with shape of interstice
between close-packed particles
Kelvin Equation
p
2VL 1
ln 0  
p
RT rm
VL = 34.6810-6 m3/mol
 = 8.88 mN/m
Relative pressure p/p0
1
0.8
0.6
0.4
0.2
0
0.1
1
10
100
dm (nm)
micro
meso
macro
1000
10000
Kelvin Equation
Pore filling Model
Cylindrical Pore Channel
Hysteresis Loop
p/p0
nad
H3
nad
H2
nad
HI
p/p0
Information on pore shape
p/p0
Pore Size Distribution
t-Method
t
nad
 0.354 nm
nm
nad
Proportional to St
t
St  nm  Am  N
nad
 0.354  10 9  Am  N
t
 6 nad
 St  5.73  10 
t
 St 
Note:
nad is experimental result
t is calculated from
correlation t versus p
Kelvin Equation
t-Method
 BET
– only valid in small pressure interval
– interpretation not very easy
 thickness (t) of adsorbed layer can be calculated
0.354 nm
 plot of t versus p for non-porous materials is the same (has been
checked experimentally)
 t-plot helps in interpretation
Kelvin Equation
Shape of t-plots
Adsorption isotherm
nad
n
t  ad  0.354 nm
nm
p
t = f(p)
Non-porous
nad
Micro- and
mesoporous
Microporous
nad
nad
Smesopores
St
t
t
t
Kelvin Equation
Interpretation of t-Plot
-alumina
10
St = 200 m2/g
n ad (mmol/g)
8
macropores
6
4
mesopores
SS
= 0 m2/g 2
t,micro
t,micro = 0 m /g
V t,micro = 0 ml/g
2
Vt,micro = 0 ml/g
0
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
Kelvin Equation
Pore Size Distribution
-alumina
0.5
r = t + 2sV
RTIn P0
dV/dd (ml/g/nm)
0.4
P
0.3
0.2
0.1
0.0
1
100
10
dp (nm)
1000
Mercury Porosimetry
Pore Size Distribution
 Hg does not wet surfaces; pressure is needed to force intrusion
 From a force balance:
14860
dp 
p
(d in nm, p in bar)
 Convenient method for determining pore volume versus pore
size
Mercury Porosimetry
Pore Size Distribution
-alumina
1.2
V (ml/g)
1.0
0.8
0.6
0.4
0.2
0.0
0.1
1
10
p (MPa)
100
1000
N2 Physisorption versus Hg Porosimetry
• Hg cannot penetrate small (micro)pores, N2 can
• Uncertainty of contact angle and surface tension values
• Cracking or deforming of samples
SHg
SBET

m2/g
m2/g
deg
Iron Oxide
14.3
13.3
130
Tungsten Oxide
0.11
0.10
130
Anatase
15.1
10.3
130
Hydroxy Apatite
55.2
55.0
130
Carbon Black (Spheron-6)
107.8
110.0
130
0.5 % Ru/-Al2O3
237.0
229.0
140
0.5 % Pd/-Al2O3
115.0
112.0
140
TiO2 Powder
31.0
25.0
140
Sintered Silica Pellets
20.5
5.0
140
Zeolite H-ZSM-5
39.0
375.0
140
Norit Active Carbon R1 Extra
112.0
915.0
140
Adsorbent
Texture Data on Common Catalysts
N2-physisorption
Hg-porosimetry
SBET
St
Vp
dp
SHg
Vp
dp
m2/g
m2/g
ml/g
nm
m2/g
ml/g
nm
Wide Pore Silica
78
52
0.91
47
80
0.92
54
-Alumina
196
202
0.49
10
163
0.49
10
-Alumina
9
8
0.12
112
12
0.48
150
1057a
28
0.51
2
0.6
0.46
106
Raney Ni
76
-
0.14
5.80
-
-
-
ZSM-5
345
344
0.19
0.58
11
1.1
820b
Active Carbon
a
p/p0 range of 0.01-0.1 was used in the calculation.
b
intraparticle voids.
NN
Isotherms
&&Pore
Volume
Distributions
2 Adsorption
Adsorption
Isotherms
Pore
Volume
Distributions
2
-alumina
25
25
20
20
n ad (mmol/g) 1
n ad (mmol/g) 1
wide-pore silica
15
10
10
5
5
0
0
0
0.2
0.4
p/p 0
0.6
0.8
0
1
0.10
0.5
0.08
0.4
0.2
0.4
p/p 0
0.6
0.8
1
dV /dd (ml/g/nm)
dV /dd (ml/g/nm)
15
0.06
0.3
0.04
0.2
0.02
0.1
0.00
0.0
1
10
d pore (nm)
100
1000
1
10
d pore (nm)
100
1000
N2 Adsorption Isotherms & Pore Volume Distributions
activated carbon
25
25
20
20
n ad (mmol/g) 1
n ad (mmol/g) 1
-alumina
15
10
15
10
5
5
0
0
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.010
0.5
0.008
0.4
dV /dd (ml/g/nm)
dV /dd (ml/g/nm)
0.6
0.8
1
p/p 0
p/p 0
0.006
0.004
0.002
0.3
} Tensile strength effect
0.2
0.1
0.000
0.0
1
10
100
d pore (nm)
1000
1
10
d pore (nm)
100
1000
N2 Adsorption Isotherms & Pore Volume Distributions
ZSM-5
25
25
20
20
n ad (mmol/g) 1
n ad (mmol/g) 1
Raney Ni
15
10
10
5
5
0
0
0
0.2
0.4
p/p
0
0.6
0.8
0
1
0.10
0.2
0.4
p/p 0
0.6
0.8
1
10
0.08
8
dV /dd (ml/g/nm)
dV /dd (ml/g/nm)
15
0.06
0.04
6
4
2
0.02
0
0.00
1
10
d pore (nm)
100
1000
0.0
0.5
1.0
d pore (nm)
1.5
2.0
Hg Intrusion Curves & Pore Volume Distributions
-alumina
1.0
1.0
0.8
0.8
V (ml/g)
1.2
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
0.1
1
10
p (MPa)
100
0.1
1000
0.08
1
10
p (MPa)
100
1000
1000
10000
0.5
0.4
0.06
dV /dd (ml/g/nm)
dV /dd (ml/g/nm)
V (ml/g)
wide-pore silica
1.2
0.04
0.02
0.3
0.2
0.1
0
1
10
100
d pore (nm)
1000
10000
0.0
1
10
100
d pore (nm)
Hg Intrusion Curves & Pore Volume Distributions
activated carbon
1.2
1.2
1.0
1.0
0.8
0.8
V (ml/g)
V (ml/g)
-alumina
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
0.1
1
10
p (MPa)
100
0.1
1000
0.010
10
p (MPa)
100
1000
1000
10000
dV /dd (ml/g/nm)
0.005
0.008
dV /dd (ml/g/nm)
1
0.006
0.004
0.003
0.004
0.002
0.002
0.001
0.000
0.000
1
10
100
d pore (nm)
1000
10000
1
10
100
d pore (nm)
Hg Intrusion Curves & Pore Volume Distributions
ZSM-5
1.2
1.2
1.0
1.0
0.8
0.8
V (ml/g)
V (ml/g)
Raney Ni
0.6
0.4
0.6
0.4
0.2
0.2
0.0
0.1
1
10
100
0.0
1000
0.1
1
p (MPa)
0.10
100
1000
dV /dd (ml/g/nm)
0.005
0.08
dV /dd (ml/g/nm)
10
p (MPa)
0.06
0.04
0.004
0.003
0.002
0.02
0.001
0.00
1
10
100
1000
10000
0
1
d pore (nm)
10
100
1000
d pore (nm)
10000
100000
BET- & t-plots
-alumina
wide-pore silica
0.5
0.4
0.3
0.2
2
S BET = 78 m /g
0.1
C = 146
0.0
0.00
0.05
0.10
0.15
p/p 0
0.20
0.25
0.4
0.3
0.2
0.1
0.30
2.5
10
2.0
8
1.5
1.0
S t,micro=28 m2/g
0.5
2
S BET = 196 m /g
C
0.0
0.00
n ad (mmol/g)
n ad (mmol/g)
p /[n ad (p 0-p )] (g/mmol)
p /[n ad (p 0-p )] (g/mmol)
0.5
0.05
0.10
0.15
p/p 0
0.25
0.30
6
4
S t,micro= 0 m2/g
V t,micro = 0 ml/g
2
V t,micro = 0.013 ml/g
0.20
= 97
0
0.0
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
BET- & t-plots
-alumina
activated carbon
0.5
p /[n ad (p -p )] (g/mmol)
0.4
0.3
0
0
p /[n ad (p -p )] (g/mmol)
0.5
0.2
S BET = 9.3 m2/g
0.1
0.4
S BET = 1057 m2/g
C = 1057
p/p 0 = 0.01 - 0.1
0.3
0.2
0.1
C = 142
0.0
0.00
0.0
0.00
0.05
0.10
0.15
0
p/p
0.20
0.25
0.30
0.05
0.10
0.15
p/p
0.20
0.25
0.30
0
15
0.25
n ad (mmol/g)
n ad (mmol/g)
0.20
0.15
0.10
0.05
10
5
S t, micro= 1.4 m2/g
S t,micro = 856 m2/g
V t,mcro = 0.001 ml/g
V t,micro = 0.42 ml/g
0.00
0
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
BET- & t-plots
Raney Ni
ZSM-5
0.5
p /[n ad (p -p )] (g/mmol)
0.4
0.3
0.2
0
p /[n ad (p 0-p )] (g/mmol)
0.5
2
S BET = 76 m /g
0.1
0.0
0.00
C = 46
0.05
0.10
0.15
p/p 0
0.20
0.25
0.4
0.3
C
0.2
= -245
0
p/p : 0.01 -0.1
0.1
0.0
0.00
0.30
S BET = 345 m2/g
0.05
0.10
0.15
0
p/p
0.20
0.25
0.30
6
5
nad (mmol/g)
nad (mmol/g)
4
3
2
St,micro = 0 m2/g
1
4
2
St,micro = 344 m2 /g
Vt,micro = 0 ml/g
Vt,micro = 0.18 ml/g
0
0
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
0.0
0.2
0.4
0.6
t ( nm)
0.8
1.0
1.2
Chemisorption
Surface Characterization
•
•
•
•
•
Specific surface area of phases
Types of active sites
Number of active sites
Reactivity of active sites
Stability of active sites
Chemisorption
Metal Dispersion
nS
D
nT
 Dispersion:
ns = number of surface atoms
nT = total number of atoms
 Chemisorption: titration of surface sites
number of moles in monolayer
nads
Stoichiometry ??
p
ns
Adsorption Mode
O
C
a.
O
O
O
O
C
C
C
C
b.
c.
d.
C
O
e.
a. linear or terminal (X = 1)
b. bridged (X = 0.5)
c. bridged (X = 0.67)
d. valley or triple (X = 0.33)
e. dissociative adsorption (X = 0.5)
X = average number of
adsorbed molecules per
active site
Adsorption Stoichiometry
Metal
N2O/Me
Pt
H/Me
CO/Me
1
1
Cu
0.5
poor H2 dissociation
catalyst
1
Ni
0.67
1
carbonyl formation!
1
2
1
Rh d > 2 nm
Rh d < 2 nm
Particle Size and Dispersion
15
dVS
VA 1
 6 
SA D
nS
D
nT
dVS
(nm)
10
Pt
5
Ni
0
0.0
0.5
1.0
D
D
most fundamental parameter
dVS
most convenient for measuring directly (XRD, EM)
Supported Metal Particles
a.
b.
Spherical
Hemispherical
c.
Crystallite
poisoned part of
surface
d.
Complete wetting
Number of Surface Atoms
part. size ca 5 nm
33% (111) plane
33% (100) plane
33% (110) plane
(atoms.nm-2)
part. size ca 15 nm
70% (111) plane
25% (100) plane
5% (110) plane
(atoms.nm-2)
Co
15.1
-
Ni
15.4
17.5
Pt
12.5
14.2
Pd
12.7
14.5
Ru
16.3
-
Rh
13.3
15.5
Cu
14.7
16.7
Metal
Pulse Chemisorption
Catalyst
Detector
CO
Pulse
Response
Example: Ptsurface + CO
Pt-CO
Difference in total peak area
nsurface
Pulse Chemisorption
On-line Thermoconductivity Detector
CO chemisorption on reduced 5wt% Pt/Al2O3
CO chemisorption on reduced 5wt% Pt/Al2O3
TCD signals after CO pulses
Cumulative amount of chemisorbed CO
0.08
n ad (mmol/g)
Detector signal
1.0
0.06
2 2
SPt
=3
S Pt
= 3mm/g/g
0.04
DPt
24 %
D=
Pt = 24 %
0.02
0.00
0.0
0
Time of analysis
1
0
0.5
1
Pulsed volume (ml)
Monolayer capacity:
0.06 mmol / g Pt
1.5
Step Chemisorption
On-line Mass Spectrometer
Example:
2 Cu(s) + N2O
Catalyst
Cu2O(s) + N2
Mass
Spectrometer
N2O
N2O
N2
t
Step
Response
Temperature Programmed Desorption
Adsorption Site Differentiation
NH3 desorption from HZSM-5
Weak acid sites
Strong acid sites
Temperature Programmed Desorption
Adsorption Energetics
After ammonia saturation the sample is degassed at 120 °C for 60 minutes
Heating Rate of 5, 10, 15 and 20 °C/min
235289
300
219621
400
205024
Signal (mV/g)
200
100
200
0
0
50
100
Time ( min )
0
150
Temperature ( °C )
240866
600
Temperature Programmed Desorption
Adsorption Energetics
Beta (K/min) Tp °C Tp K
5
266 539
10
311 584
15
356 629
20
382 655
2
Tp
290521
341056
395641
429025
2
1/Tp K
Ln(Tp /beta)
0.0018552
10.9699
0.0017123
10.4372
0.0015898
10.1802
0.0015267
9.9735
Slope
2948.07
Intercept
5.4639
Ed (kJ/mole)
24.51
A factor
12.49
Desorption Energy Calculation
11.2
Beta = heating rate [K / min]
Tp = maximum desorption peak
temperature
Ed = Desorption energy [Kj / mole]
A = Arrhenius factor
R = 8.314451 [J / mol K]
11
Ln(Tp2/beta)
10.8
10.6
10.4
10.2
10
9.8
0.0015
0.00155
0.0016
0.00165
0.0017
1/Tp (K)
0.00175
0.0018
0.00185
0.0019
Temperature Programmed Reduction
– characterisation of oxidic catalysts and other reducible
catalysts
– qualitative information on oxidation state
– quantitative kinetic data
– optimisation of catalyst pretreatment
Reduction of oxidic species:
MO + H2
M + H2O
Study of coke deposits:
coke + H2
Reduction of sulphides:
hydrocarbons + H2O
Temperature Programmed Reduction
Fe2O3
H2/Ar saturated
with 3% H2O
7.0 mg
d
dry H2/Ar
15.9 mg
c
8.2 mg
b
3.6 mg
a
500
600
700
Temperature (K)
Temperature Programmed Reduction
Fe2O3
500
600
700
Temperature (K)
f
10.0 K/min
0.08 mg
e
5.0 K/min
0.19 mg
d
2.0 K/min
0.91 mg
c
1.0 K/min
1.8 mg
b
0.5 K/min
2.8 mg
a
0.2 K/min
3.6 mg
Dry H2/Ar
Temperature Programmed Reduction
Fe2O3
500
600
700
Temperature (K)
800
f
10.0 K/min
0.17 mg
e
5.0 K/min
0.33 mg
d
2.0 K/min
0.90 mg
c
1.0 K/min
1.5 mg
b
0.5 K/min
2.6 mg
a
0.2 K/min
7.0 mg
Wet H2/Ar
(3% H2O)
Temperature Programmed Reduction
Fe2O3
 β 
ln 2  (K-1 s-1)
 Tmax 
b
c
a
-15
-16
dry series
main peak
-17
Ea = 111 kJ/mol
wet series
low T peak
wet series
main peak
-18
-19
12
13
14
15
16
1
Tmax
(10-4 K-1)
17
18
Kinetic Models for Reduction
Model
nth Order
f()
(1-)n
g()
(1-(1-)1-n)/(1-n)
Random nucleation
Unimolecular decay law
(1-)
-ln(1-)
Phase boundary controlled reaction
(contracting area)
(1-)1/2
2(1-(1-)1/2)
Phase boundary controlled reaction
(controlled volume)
(1-)2/3
3(1-(1-)1/3)
Two dimensional growth of nuclei 2(1-)[-ln(1-)]1/2
(Avrami-Erofeev)
[-ln(1-)]1/2
Three dimensional growth of nuclei 3(1-)[-ln(1-)]2/3
(Avrami-Erofeev)
[-ln(1-)]1/3
One dimensional diffusion
Parabolic law
1/2
2
-1/ln(1-)
(1-)ln(1-) + 
Three dimensional diffusion
(Jander)
[3(1-)2/3]/ [2(1-(1-)1/3)]
[1-(1-)1/3]2
Three dimensional diffusion
(Ginstling-Brounshtein)
3/[2((1-)-1/3 -1)]
1-2/3 - (1-)2/3
Two dimensional diffusion
Infrared Spectroscopy
Applications:
 Catalyst characterisation
– direct measurement of catalyst IR spectrum
– measurement of interaction with “probe” molecules:
• NH3, pyridine: acidity
• CO, NO: nature of active sites (e.g. Pt on alumina)
 Mechanistic studies
– adsorbed reaction intermediates
– deactivation by strongly adsorbing species
 Analysis of reactants and products (in situ reaction
monitoring
Electromagnetic Spectrum
UV
Visible
IR
4000 - 400 cm-1
Infrared Spectroscopy
Reactor Cell
Transmittance
DRIFTS
Analysis of Catalyst Preparation
Surface Hydroxyl Groups
NH4ReO4
Alumina
H
O
Neutral
OH
Acidic
Al
Al
Basic
Al
Al
Dry
impregnation
Re2O7
loading
0%
Calcination
323 K, 2 h
Re-loading
increases
Absorbance
Drying 383
K, 16 h
3%
6%
12%
Re2O7/
Alumina
18%
3900
3800
3700
3600
3500
Intensity
decreases
Analysis of Catalyst Preparation
O
OH
O
Re
O
Al3+
a
ReO4 on Lewis
site
not active
O
O
O
Re –
O
O
Re +
O
Al
O
O
Al
Al
Basicb-OH
substituted by ReO4
Acidicc -OH
substituted by ReO4
slightly active
active
 Alumina contains Lewis and Brönsted sites
 OH-spectrum
different acid sites
 Impregnation
– OH + HOReO3
-OReO3 + H2O
– Al3+ + HOReO3
coordination complex
 Low-loading Re/Al not effective
 IRS gives detailed picture of surface
IR Probe Molecule
Acidity Measurement
Pyridine adsorbs on acid sites
Spectrum changes
N
N
N
Lewis acid
Brönsted acid
Different IR Spectra
IR Probe Molecule
Acidity Measurement
F/Al2O3 very active in acid-catalysed reactions
Al2O3
HF
F-salt
F/Al2O3
F/Al2O3
Structure of F/Al2O3 ???
Acid sites? Bronsted, Lewis???, How many??
Kelvin Equation
Pore Size Distribution
no reaction
with HCl
1438 vs
1487 vs
1482 m
1536 s
1585 vs
1610 m
1601 m
1636 m
vs: very strong; s: strong; m: medium
with BH3
1458 s
1488 s
1587 m
1621 vs
L
L
B
B
N
N
H+ Cl-
B
1700
1600
1500Cl
s (cm-1)
1400
Cl
Cl
Kelvin Equation
Pore Size Distribution
Lewis site
H2O
L
1452
Brönsted site
L
1619
Transmission
B
1490
L
1497
After adsorption of pyridine at 330 Kb
After addition of H2O at 330 K
and evacuation at 330 K
Background spectrum F/Al2O3
L
1579
B
1542
B
1639
c
a
1300
1500
Wavenumber
1700
(cm-1)
In-Situ Reaction Study
1263
UV / min
3105
950
1568
1602
850
TCE Photocatalytic Oxidation
2345
2365
0
26
66
1649
1747
1787
1589
1234
1413
46
86
3751 3868
106
126
146
166
1610
1415
186
3452
UVair 60
3298
2978
800
1200
1600
2000
2400
2400
2800
-1
Wavenumber / (cm )
3200
3600
-1
Wavenumber / (cm )
Figure 2a TCE on P-11t on 21/3/01
4000
In-Situ Reaction Study
PCO of Ethylene
1
Fig. 6a
Fig. 6c
Fig. 6c
P-11t
P-11h(new)
P-11h(old)
CO2
H2 O
I950(=C-H)
0.75
H2 O
CO2
0.5
HCHO
0.25
0
0
50
100
150
Irradiation time / (min)
200
0
50
100
150
Irradiation time / (min)
200
0
50
100
150
200
Irradiation time / (min)
In-Situ Reaction Study
PCO of 1,1-DCE
1
Fig. 4b
Fig. 4a
Fig. 4c
P-11t
P-11h
I1095 (-CCl)
0.8
H2 O
Cl2 COO
H2 O
CO2
0.6
0.4
CO2
HCHO
0.2
Cl2 COO
HCHO
0
0
50
100
150
Irradiation time/ (min)
200
0
50
100
150
Irradiation time / (min)
200 0
50
100
150
Irradiation time / (min)
200
In-Situ Reaction Study
PCO of cis-1,2-DCE
1
Fig. 2b
P-11t
I 864(ClC-H)
Fig. 2a
Fig. 2c
P-11h
0.8
H2 O
HCHO
0.6
CO2
Cl2 CCO
H2 O
HCHO
CO2
Cl2 CCOO
0.4
0.2
0
0
50
100
150
Irradiation time / (min)
200
0
50
100
150
Irradiaition time /(min)
200 0
50
100
150
Irradiation time / (min)
200
In-Situ Reaction Study
PCO of trans-1,2-DCE
1
Fig. 3b
Fig. 3a
Fig. 3c
I898(ClC-H)
0.75
0.5
CO2
Cl2 COO
HCHO
H2 O
0.25
Cl2 COO
CO2
HH
2O
2O
HCH
O
HCHO
0
0
50
100
150
200
Irradiation time / (min)
0
50
100
150
200
Irradiation time / (min)
0
50
100
150
200
Irradiaiton time / (min)
In-Situ Reaction Study
PCO of TCE
1
Fig. 1a
Fig. 1c
Fig. 1b
P-11t
CO2
Cl2 CCOO
P-11h
CO2
H2 O
I947(ClC-H)
0.75
0.5
HCHO
H2 O
HCHO
Cl2 COO
0.25
0
0
50
100
150
Irradiation time / (min)
200
0
50
100
150
Irradiation time / (min)
200
0
50
100
150
Irradiation time / (min)
200
In-Situ Reaction Study
PCO of Tetrachloroethylene
1
Fig. 5a
P-11t
P-11h
Fig. 5c
Fig. 4b
I921?(H-CCl)
0.8
CO2
H2 O
0.6
0.4
CO2
HCHO
HCHO
0.2
H 2O
0
0
0
50
100
150
Irradiation time / (min)
50
100
150
200
200
0
Irradiation time / (min)
50
100
150
Irradiation time / (min)
200