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!