Kinetic Characterisation of Zeolite Catalysts Using ... · Kinetic Characterisation of Zeolite...
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Kinetic Characterisation of Zeolite Catalysts Using Cracking, Alkylation and Other Chemical
Reactions
Dmitry B. Lukyanov
Catalysis & Reaction Engineering GroupDepartment of Chemical EngineeringUniversity of Bath, Bath, BA2 7AY, UK
Haldor Topsøe Catalysis ForumMunkerupgaard, 27-28 August 2015
To the Memory of Tanya VazhnovaColleague, Co-Author, Friend and Wife
Contents
Background Objectives Experimental experience Alpha-activity test (protolytic cracking activity) Beta-activity test (hydrogen transfer activity) Alpha-activity and (forgotten) product selectivity Location of acid sites Probing meso-porous zeolites Enhanced activity sites: unexpected(?) results Alkylation of aromatics with alkanes (methane & ethane) Acknowledgements Conclusions
Background
How/Why did I get there?Genes? Destiny?M.I. Temkin, S.L. Kiperman & L.I. Lukyanova. Flow-circulation method for studies of kinetics of heterogeneous catalytic reactions (First paper on gradientless reactor), Doklady Akademii Nauk SSSR, 74 (1950) 763-766.
1978-1995 – Karpov Institute of Physical Chemistry, Moscow1978-1985 – Laboratory of Chemical Reactors1985-1995 – Laboratory of Catalyst Testing
Why zeolite catalysts?
It provides quantitative information about working catalysts (and is really good in doing this) and could ‘see’ some features that are hidden from IR and NMR
Mobil influence?C.D. Chang & A.J. Silvestri. Conversion of methanol and other O-compounds to hydrocarbons over zeolite catalysts, J. Catal. 47 (1977) 249.W.O. Haag & R.M. Dessau. Duality of mechanism of acid-catalyzed paraffin cracking. Proc. 8th ICC, Berlin, 1984, vol. 2, p.305, Dechema, Berlin, 1984.R.M. Lago, W.O. Haag, et al. The nature of the catalytic sites in HZSM-5 – Activity enhancement . Proc. 7th IZC, p.677, Kodansha, Tokyo, 1986.
Why kinetic method?
Objectives of This Talk
To consider Kinetic Method as a tool for characterisation of zeolite catalysts and, hopefully, to demonstrate its (not very well understood) usefulness for catalyst characterisation
To present some interesting data regarding a few catalytic reactions, including cracking, alkylation, MTH
Experimental Experience
Do not get too excited when you see unexpected results – these could lead to a discovery, but more likely something was wrong with your rig
You have to be very careful and follow the procedure exactly (this would not always eliminate all mistakes/errors but, at least, will bring their number down considerably)
Check quantitatively your data against the literature data (have to be careful with the literature source)
Effect of time on stream on the conversion of ethene over H-ZSM-5 in a continuous
flow reactor
Conversion (%)
Time on stream (hours)
10
6
5
00 2 4
Activity of two H-ZSM-5 zeolitesParent Steamed
n-Hexane cracking 1 3.5
Ethene oligomeris. 1 3.6
Toluene alkylationwith methanol 1 3.3
MTH 1 0.5
Note that mild steaming creates Enhanced Activity Sites (Lago, Haag, et al 1986)
Alpha-activity test – Mobil 1965
Has been used for characterisation of catalyst acidity and is used by a few companies nowadays for this and other (?) purposes
n-Hexane cracking in a continuous flow reactor at 1000 F (538oC) and n-hexane concentration of 13 mol% with the measurement of the 1st order rate constant (measure of α-activity)
Haag & Dessau, 1984 Protolytic cracking mechanism Hydrogen transfer mechanism
α-activity test and mechanism of n-hexane cracking
Autocatalysis in n-hexane conversion over H-ZSM-5 at 400 and 500oC.
Experimental data (points) and kinetic modelling curves.
Note: autocatalysis is common for alkane cracking reactions
D.B. Lukyanov, V.I. Shtral & S.N. Khadzhiev, J. Catal., 146 (1994) 87.
Alpha-activity is the measure of the protolytic cracking activity!
First order plots for simulated n-hexane conversion (T = 538oC, Co
C6 = 13 mol%) over Z-240, Z-240(1) and Z-240(2) catalysts.
Points correspond to the kinetic modelling results.
α-activity test – Why 1000 F and what does it measure?
D.B. Lukyanov, V.I. Shtral & S.N. Khadzhiev, J. Catal., 146 (1994) 87.
Beta-activity test – Lukyanov 1994
D.B. Lukyanov, J. Catal., 145 (1994) 54.
Z-34
Z-34ST
Z-240
HY-2
HY-1
Effect of n-hexane conversion on the rate of isobutane formation (A) and on the isobutene concentration (B) over three H-ZSM-5 and two
HY zeolites.
Zeolite HZSM-5 HY
Hydrogen transfer 1 6.1
Protolytic cracking 1 0.4
Alpha-activity and (forgotten) product selectivity
Molar selectivities (%) in n-hexane cracking over different zeolites at 400oC
Zeolite HZSM-5 H100-MOR H45-MOR HY
C6 + Z → C5=Z + C1 4 3 12 11
C6 + Z → C4=Z + C2 27 6 27 28
C6 + Z → C3=Z + C3 49 86 52 53
C6 + Z → C2=Z + C4 20 6 9 8
12MRonly
10MR 12MR& 8MR
12MRonly
Can one use selectivity to probe the location of
active sites?
Location of acid sites
FTIR spectroscopy, for a change…
IR spectra (left) and FSD traces of four MOR zeolites
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
3450 3500 3550 3600 3650 3700 3750 3800 Wavenumbers (cm-1)
Abso
rban
ce
3745
3610
H45Na55-MOR
H63Na37-MOR
H82Na18-MOR
H-MOR
0
1
2
3
4
5
6
7
8
9
3540 3560 3580 3600 36203640 3660 3680
Abso
rban
ce
Wavenumbers (cm-1)
3625
3617
3609
3599
3590
3581
H45Na55-MOR
H63Na37-MOR
H82Na18-MOR
H-MOR
T. Vazhnova & D.B. Lukyanov, Anal. Chem., 85 (2013) 11291.
D.B. Lukyanov, T. Vazhnova, etc., J. Phys. Chem. C, 118 (2014) 23918.
Location of acid sites
Structure of MOR zeolite with three ion-exchange positions (I, IV and VI)Six IR bands have been assigned to specific oxygen atoms.
T atoms Oxygen atoms
T4 T3
T1
T2
O7O3
O9
O1
O5O2O6
O4
O8
O10IIV
VI
D.B. Lukyanov, T. Vazhnova, etc., J. Phys. Chem. C, 118 (2014) 23918.
Probing meso-porous zeolites
A B CokeD
CH3OH Alkenes Coke
CH3OCH3 AromaticsAlkanes
0 2 4 6 8 10 120
20
40
60
80
Con
vers
ion
(%)
Time on stream (h)
Steamed HZSM-5Micro- & Meso-pores
Parent HZSM-5Micro-pores
Steamed HZSM-5Micro- & Meso-poresConversion of methanol into
hydrocarbons over parent and two steamed zeolites
D.B. Lukyanov, 2015, in preparation.
Hierarchical zeolite catalysts – Stability enhancement
Probing meso-porous zeolites
Hierarchical zeolite catalysts – Selectivity enhancement
CH3OH Alkenes Coke
CH3OCH3 AromaticsAlkanes
Parent HZSM-5 27
Steamed HZSM-5-2h 36
Steamed HZSM-5-4h 37
Catalyst Maximum yieldof alkenes (%)
D.B. Lukyanov, 2015, in preparation.
Probing meso-porous zeolites
Schematics of bulk modification, i.e. external surface is not shown.
Microporous Zeolite MMP Zeolite 1 MMP Zeolite 2
Cracking (activity & selectivity) and FSD-FTIR?
Enhanced activity sites: unexpected(?) results
Mildly steamed H-ZSM-5
Parent H-ZSM-5
D.B. Lukyanov, Zeolites, 13 (1993) 64.
Activity of two H-ZSM-5 zeolitesParent Steamed
n-Hexane cracking 1 3.5
Ethene oligomeris. 1 3.6
Toluene alkylationwith methanol 1 3.3
MTH 1 0.5
There is principal difference between hydrocarbon
reactions and formation of C–C bond from methanol!
Alkylation of aromatics with alkanes (ethane)
In principle, direct alkylation of benzene with ethane into ethylbenzene (EB) can be carried out over a bifunctional catalyst by coupling two reactions:
C2H5C2H4+
C2H6 C2H4 + H2
H+
Me
T. Vazhnova & D.B.Lukyanov, J. Mol. Catal., 279 (2008) 128.
T. Vazhnova & D.B.Lukyanov, J. Catal., 257 (2008) 382.
Alkylation of aromatics with alkanes (ethane)
Effect of TOS on benzene conversionat different contact times.
0 10 20 30 40 500
5
10
15
20
25
Ben
zene
con
vers
ion
(%)
Time on stream (h)
Contact time(WHSV-1)() = 0.32 h
() = 0.081 h() = 0.024 h
Alkylation of aromatics with alkanes (ethane)
Effect of TOS on EB selectivity in aromatic products at different benzene conversions.
0 10 20 30 40 5020
40
60
80
100E
B s
elec
tivity
in a
rom
atic
prod
ucts
(mol
.%)
Time on stream (h)
Initial benzene conversion() X = 8%() X = 12.5%
() X = 20%
Alkylation of aromatics with alkanes (methane)
PtH-MFI catalyst at 370oC.
Methane to benzene molar ratio in the feed was 9:1.
Benzene and Methane Conversions vs. Time on Stream
0 4 8 12 16 20 240
2
4
6
8C
onve
rsio
n (%
)
0 4 8 12 16 20 240.0
0.2
0.4
0.6
0.8
Con
vers
ion
(%)
Time on stream (h)
Benzene
Methane
T. Vazhnova & D.B.Lukyanov, J. Mol. Catal. (2009).
Alkylation of aromatics with alkanes (methane)
Benzene and Methane Conversions vs. Time on Stream
Selectivities to all carbon containing products observed over PtH-MFI catalyst at 370oC and TOS of 4 hours
Catalyst PtH-MFI
Methane conversion (%) 0.53Benzene conversion (%) 4.5Selectivity (mol.%)Ethane 2.7Toluene 96.1Ethylbenzene 0.15Xylenes 1.05
Organisations
Karpov Institute of Physical Chemistry, Moscow
University of Bath
EPSRC, BP Chemicals, ICI (different divisions), Johnson Matthey
Haldor Topsøe
Acknowledgements
People
Tanya VazhnovaVsevolod TimoshenkoJohn Dwyer
Conclusions
Hopefully, we can draw some conclusions during this session!