The effect of type of acid sites in molecular sieves on activity and selectivity in acylation reactions

Article abstract of DOI:10.1135/cccc20070728

The role of the type of acid site (Broensted vs. Lewis) on the activity and selectivity of molecular sieve catalysts was investigated in ferrocene and toluene acylation. H-, Zn-, Fe-, Aland La-forms of zeolite Beta, USY and mesoporous molecular sieves (A1

Full text of DOI:10.1135/cccc20070728

7
28
Bejblová, Vlk, Procházková, Šiklová, Čejka:
THE EFFECT OF TYPE OF ACID SITES IN MOLECULAR SIEVES ON
ACTIVITY AND SELECTIVITY IN ACYLATION REACTIONS
1
,
2
3
4
Martina BEJBLOVÁ *, Josef VLK , Dana PROCHÁZKOVÁ , Helena ŠIKLOVÁ and
Jiří ČEJKA5
J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i.,
1
Dolejškova 3, CZ-182 23, Prague 8, Czech Republic; e-mail: martina.bejblova@jh-inst.cas.cz,
2
3
4
5
josef.vlk@vscht.cz, prochazkova@jh-inst.cas.cz, siklova@jh-inst.cas.cz, cejka@jh-inst.cas.cz
Received February 1, 2007
Accepted April 2, 2007
Dedicated to Dr Karel Mach on the occasion of his 70th birthday.
Th e role of th e type of acid site (Broen sted vs. Lewis) on th e activity an d selectivity of m o-
lecular sieve catalysts was in vestigated in ferrocen e an d toluen e acylation . H-, Zn -, Fe-, Al-
an d La-form s of zeolite Beta, USY an d m esoporous m olecular sieves (Al)MCM-41, (Al)SBA-15
were tested. It was observed th at addition of m etal cation s actin g as Lewis acid sites can in -
crease th e acidity of various m olecular sieve catalysts. No gen eral relation sh ip between th e
type of cation an d con version of in dividual substrate was foun d. Wh ile th e h igh est activity
in ferrocen e acylation was observed after addition of Zn , in th e case of toluen e acylation
Al-form s of catalysts were th e m ost active. Th e results in dicate th at th e acid stren gth of
cation ic Lewis sites con trols th eir activity in acylation reaction s.
Keyw ord s: Molecular sieves; Zeolites; Acylation s; Ferrocen e; Toluen e.
1
2
Zeolites are widely used in organ ic syn th esis , petroch em ical processes an d
3
in th e syn th esis of fin e ch em icals . Th e key properties in th e use of zeolites
as acid catalysts are tun ed acidity, con trolled site den sity, h igh th erm al an d
h ydroth erm al stability, an d sh ape selectivity towards reactan ts, products,
4
,5
an d tran sition states . Friedel–Crafts acylation s are reaction s, in wh ich
zeolites are th e m ost prom isin g group of catalysts. Th ey could replace tradi-
tion al catalysts (AlCl , FeCl , BF , TiCl , Zn Cl or ph osph oric acid), th e ap-
3
3
3
4
2
plication of wh ich brin gs ecological an d tech n ical problem s. In addition ,
Lewis acids form stable com plexes with products, wh ich h ave to be decom -
posed with water.
Successful application of zeolite catalysts in th e Friedel–Crafts acylation
of arom atics h as been described in literature. Atten tion h as been especially
paid to acylation reactions producing arom atic ketones, which can be used in
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746
©
2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20070728

The Effect of Type of Acid Sites in Molecular Sieves
729
fine chem ical industries. Naphthalene , toluene7,8, 2-m ethoxynaphthalene9,10,
6
1
1,12
13,14
15,16
an d isobutylben zen e17 belon g to th e
ph en ol
, an isole
, veratrole
m ost frequen tly in vestigated substrates. Zeolite Beta was distin guish ed as a
h igh ly active an d selective catalyst in acylation of bulkier substrates. Vari-
ous acyl h alides, acid an h ydrides or carboxylic acids were used as acylatin g
agen ts in th ese reaction s.
Th e con ven tion al h om ogen eous catalysts in acylation reaction s are of
both Broen sted an d Lewis acid types. With regard to th at, zeolite acidity
can be varied in a sign ifican t ran ge as for as th e type an d con cen tration of
acid sites are con cern ed. Th e objective of th is con tribution is to evaluate
th e effect of th e acid site type on th e activity of zeolites USY an d Beta an d
m esoporous m olecular sieves (Al)MCM-41 an d (Al)SBA-15 in acylation of
ferrocen e an d toluen e.
Acylation of ferrocen e leads to th e form ation of acylferrocen es, wh ich are
used as in term ediates in th e production of fun ction al m aterials like fun c-
tion al polym ers, ch iral catalysts, com bustion catalysts for propellan ts, ph ar-
1
8
m aceuticals, etc. .
Acylation of toluen e with derivatives of isobutyric acid is th e m odel reac-
tion of th e first reaction step in th e syn th esis of Ibuprofen . In our previous
paper, we h ave sh own th at toluen e (as a less toxic substrate com pared with
ben zen e) can be easily acylated usin g acid form s of large-pore zeolites, such
8
as ultrastable zeolite Y an d Beta .
EXPERIMENTAL
Catalysts
Zeolites Beta an d USY, an d m esoporous m olecular sieves (Al)MCM-41 an d (Al)SBA-15, an d
2
+
3+
3+
3+
th eir ion -exch an ged form s (Zn , Fe , La an d Al ) were tested in acylation reaction s of
ferrocen e an d toluen e. Th e list of catalysts used with th eir structure ch aracterization , pore
dim en sion s an d Si/Al ratios is given in Table I.
+
All th e catalysts were used in acylation reaction s in proton ated (H ) an d ion -exch an ged
form s (Zn 2+, Fe , La an d Al ).
3+
3+
3+
Ion -exch an ged form s (Zn 2+, Fe3+, La3+ an d Al3+) of m olecular sieves were prepared by th e
followin g procedure. Zeolites were con verted to sodium form s by four tim es repeated ion ex-
ch an ge with 0.5 M sodium n itrate at room tem perature for 4 h . Th en th e Na-form s were
tran sform ed to correspon din g cation form s via four tim es repeated ion exch an ge with 0.25 M
n itrate of th e respective elem en t at room tem perature for 4 h . Fin ally, m olecular sieves were
recovered by filtration , wash ed out with distilled water, dried an d calcin ed at 550 °C for 6 h
of a h eatin g rate of 1 °C/m in .
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
30
Bejblová, Vlk, Procházková, Šiklová, Čejka:
Syn th esis of (Al)MCM-41 an d (Al)SBA-15
For th e syn th esis of (Al)MCM-41, sodium silicate, alum in ium isopropoxide an d trim eth yl-
tetradecylam m on ium brom ide as tem plate were used. In a typical syn th esis, 9.81 g of tri-
m eth yltetradecylam m on ium brom ide was dissolved in 500 m l of water in an autoclavable
polypropylen e bottle, th en 1.12 g of alum in um isopropoxide was added an d th is m ixture
was stirred for ca. 1 h . Later on , 450 m l of water was added, followed by 10 g of sodium sili-
cate an d it was stirred for 30 m in . Fin ally, 15 m l of eth yl acetate was added, th e m ixture was
aged at room tem perature for 5 h an d th en at 90 °C for 2 days.
Mesoporous m olecular sieve SBA-15 was prepared accordin g to th e followin g procedure19
0 g of triblock copolym er poly(eth ylen e oxide)–poly(propylen e oxide)–poly(eth ylen e oxide),
:
2
EO20PO70EO20 (tem plate) were dissolved in 645 m l of water an d 106 m l of 35% HCl an d
stirred at 35 °C. Th en 45.5 m l of tetraeth oxysilan e were added to th e clear solution an d th e
m ixture was stirred un til becam e h om ogen eous. Th e m ixture was allowed to stan d at 35 °C
for 24 h an d subsequen tly at 95 °C for 48 h . Th e resultin g solid ph ase was recovered by fil-
tration , wash ed with distilled water an d eth an ol, an d dried at room tem perature. Calcin a-
tion was carried out at 540 °C for 8 h with tem perature ram p of 1 °C/m in .
Alum in um was added to th e SBA-15 sam ples by post-syn th esis alum in ation 20. Th e reac-
tion m ixture of 5 g of SBA-15 an d 1 g of alum in um ch loroh ydrate in 125 m l of distilled wa-
ter was h eated at 80 °C for 2 h . Th e solid was recovered by filtration , wash ed with water an d
dried at am bien t tem perature. Calcin ation was carried out at 550 °C for 4 h with tem pera-
ture ram p of 1 °C/m in .
Ch aracterization of Catalysts
Th e crystallin ity of zeolites was determ in ed by X-ray powder diffraction with a Bruker D8
X-ray powder diffractom eter equipped with a graph ite m on och rom ator an d position -
sen sitive detector usin g CuKα radiation in th e Bragg–Bren tan o geom etry.
Th e con cen tration an d th e type of acid sites were determ in ed by adsorption of
aceton itrile-d3 or pyridin e as probe m olecules followed by FTIR spectroscopy (Nicolet
Protégé 460) usin g th e self-supported wafer tech n ique. Prior to adsorption of probe m ole-
cules, self-supportin g wafers of catalysts were activated in situ by overn igh t evacuation at
TABLE I
Structural an d ch em ical ch aracteristics of used catalysts
Ch an n el
structure
Ch an n el
diam eter, n m
Si/Al
ratio
Zeolite
Beta
Origin
Zeolyst
3D
0.64 × 0.70
an d
12.5
0
.56 × 0.56
USY
Zeolyst
3D
1D
1D
0.74
15
8.5
14
MCM-41
SBA-15
syn th esized
syn th esized
~3.4
~6.5
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
731
4
50 °C. Adsorption of aceton itrile-d3 proceeded at room tem perature for 30 m in at a partial
pressure of 950 Pa an d was followed by 20-m in evacuation . To obtain quan titative an alysis,
2
1
th e m olar absorption coefficien ts for aceton itrile-d adsorbed on Broen sted acid sites
3
–
1
–1
(
(
ν(C≡N)-B at 2297 cm , ε(B) = 2.05 ± 0.1 cm µm ol ) an d stron g an d weak Lewis acid sites
ν(C≡N)-L1 at 2325 cm an d ν(CN)-L2 at 2310 cm , respectively, ε(L) = 3.6 ± 0.2 cm µm ol
–
1
–1
–1
)
were used. In tegral in ten sities of in dividual ban ds were used an d spectra were n orm alized to
–
2
th e wafer th ickn ess 10 m g cm
.
Adsorption of pyridin e proceeded at 150 °C for 20 m in at partial pressure 900 Pa followed
by 15-m in evacuation . Th e con cen tration s of Broen sted an d Lewis acid sites were calculated
from in tegral in ten sities of in dividual ban ds ch aracteristic of pyridin e on Broen sted acid
–
1
–1
sites at 1545 cm an d ban d of pyridin e on Lewis acid site at 1455 cm an d m olar absorp-
2
2
–1
–1
tion coefficien ts of ε(B) = 1.67 ± 0.1 cm µm ol an d ε(L) = 2.22 ± 0.1 cm µm ol , respec-
–
1
tively (Table II). Th e spectra were recorded with a resolution of 4 cm by collection 64 scan s
for sin gle spectrum .
Ch em ical an alysis was carried out by X-ray fluorescen ce an alysis usin g a spectrom eter
Ph ilips PW 1404 provided with an an alytical program Un iQuan t.
Catalytic Experim en ts
Acylation reaction s were in vestigated in a Heidolph Syn th esis 1 (system of 16 parallel reac-
tors) in a liquid ph ase un der atm osph eric pressure. Prior to catalytic experim en ts, each zeo-
lite was activated at 450 °C for 90 m in an d th en cooled in a desiccator. Reaction products
TABLE II
Con cen tration s of Broen sted (BC) an d Lewis (LC) acid sites obtain by FTIR spectroscopy
FTIR, CD CN
FTIR, pyridin e
3
Zeolite
Zeolite
cLC
cBC
cLC
cBC
m m ol/g
m m ol/g
m m ol/g
m m ol/g
H-Beta
0.30
0.47
0.15
0.24
0.35
0.16
0.30
0.12
0.15
0.36
0.26
0.07
0.07
0.06
0.05
0.12
0.12
0.05
0.02
0.06
H-(Al)MCM-41
Zn -(Al)MCM-41
Fe-(Al)MCM-41
La-(Al)MCM-41
Al-(Al)MCM-41
H-(Al)SBA-15
0.21
0.40
0.10
0.16
0.27
0.15
0.28
0.16
0.11
0.17
0.04
0.04
0.01
0.04
0.04
0.01
0.02
0.02
0.01
0.03
Zn -Beta
Fe-Beta
La-Beta
Al-Beta
H-USY
Zn -USY
Fe-USY
La-USY
AlH-USY
Zn -(Al)SBA-15
Fe-(Al)SBA-15
La-(Al)SBA-15
Al-(Al)SBA-15
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
32
Bejblová, Vlk, Procházková, Šiklová, Čejka:
were an alyzed on a gas ch rom atograph (HP 6850 with FID detector) equipped with a h igh -
resolution capillary colum n DB-5 (len gth 10 m , diam eter 0.10 m m , ph ase th ickn ess 0.10 µm ).
Acylation of ferrocene. In a typical experim en t, 0.6 g of ferrocen e (Fluka), 8 m l of deca-
h ydron aph th alen e (Fluka; solven t), dodecan e (Aldrich ; in tern al stan dard) an d 0.6 g of an ac-
tivated catalyst were h eated to th e preset reaction tem perature. Th en 1.9 m l of acetic
an h ydride (Fluka) were added to th e reaction m ixture an d th e reaction started. Th e reaction
tem perature was 140 °C. Selectivity (S) to acetylferrocen e was calculated:
n
S =
,
(1)
∑n
i
wh ere n m ean s th e m olar am oun t of acetylferrocen e an d n th e m olar am oun t of th e reaction
i
product i.
Acylation of toluene. In a typical experim en t, 8.0 m l of toluen e (Lach em a, Czech Republic),
dodecan e (Aldrich ; in tern al stan dard) an d 0.7 g of an activated catalyst were h eated to th e
preset reaction tem perature. Th en 1.9 m l of isobutyryl ch loride (Fluka) were added to th e
m ixture an d th e reaction was started. Th e reaction tem perature was 110 °C. Selectivity (S) to
isopropyl p-tolyl keton e was calculated from Eq. (1), wh ere n was th e m olar am oun t of iso-
propyl p-tolyl keton e an d n th e m olar am oun t of th e reaction product i.
i
RESULTS AND DISCUSSION
Characterization of Acidity
FTIR spectra of zeolites Beta an d USY in th e region of OH vibration s con sist
–
1
of ban ds at 3745 cm correspon din g to th e term in al silan ol groups an d
–
1
ban ds ch aracteristic of bridgin g OH groups in zeolite Beta at 3610 cm an d
in zeolite USY at 3630 an d 3565 cm –1 (Figs 1A an d 2A). No ban d was ob-
–
1
served in th e region of Al–OH groups (ca. 3650–3660 cm ). A low-in ten sity
–
1
ban d at 3782 cm , frequen tly assign ed to OH groups on extrafram ework
3
+
alum in um oxide, was observed on ly in th e spectra of Al -form s of zeolite
Beta an d USY.
Th e adsorption of aceton itrile-d resulted in com plete disappearan ce of
3
ban ds of bridgin g OH groups an d form ation of n ew absorption ban ds at
–
1
2
297 an d 2326 cm ch aracteristic of th e adsorption of aceton itrile-d on
3
Si–OH–Al groups an d on Al-Lewis sites, respectively (Figs 1B an d 2B). In th e
case of ion -exch an ged form s of zeolites Beta an d USY it can be observed
th at som e am oun t of bridgin g groups rem ain ed after th e ion exch an ge, as
expected wh en usin g divalen t or even trivalen t cation s. Th is is also in
agreem en t with ch em ical an alysis data (Table III) sh owin g th e M/Al ratios
lower th an 1.
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
733
Th e in dividual m axim a of absorption ban ds correspon din g to th e adsorp-
tion of aceton itrile-d3 on Lewis sites sh ow a relation sh ip between th e
waven um ber an d acid stren gth of th e respective Lewis acid site. Th e order
–
1
–1
–1
of acid stren gth is Al (2325 cm ) > Zn (2310 cm ) > Fe (2300 cm ) > La
(
–
1
2275 cm ). It sh ould be n oted th at overlappin g of absorption ban ds of
aceton itrile-d3 in teractin g with Si–OH–Fe groups as well as with Fe-Lewis
FIG. 1
IR spectra in th e OH vibration region of zeolite Beta an d its ion -exch an ged form s before
aceton itrile-d3 adsorption (A) an d spectra of aceton itrile-d3 region after adsorption (B)
FIG. 2
IR spectra in th e OH vibration region of zeolite USY an d its ion -exch an ged form s before
aceton itrile-d3 adsorption (A) an d spectra of aceton itrile-d3 region after adsorption (B)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
34
Bejblová, Vlk, Procházková, Šiklová, Čejka:
acid sites was observed for both Fe-form s of zeolites Beta as well as USY (th e
–
1
absorption ban d with m axim um aroun d 2300 cm ).
Th e con cen tration s of Lewis an d Broen sted acid sites in th e sam ples were
2
1
calculated usin g th e m olar absorption coefficien ts 3.6 ± 0.2 an d 2.05 ± 0.1
–
1
cm µm ol , respectively. Th e results are given in Table II. Th e h igh est con -
2
+
cen tration of Lewis acid sites was foun d for th e ion -exch an ged Zn -form of
zeolite Beta. Th e con cen tration s decreased in th e order Al > H > La > Fe.
In zeolite USY th e order of th e Lewis acid site con cen tration s was Al > Zn >
H > La > Fe.
FTIR spectra of (Al)MCM-41 an d (Al)SBA-15 con tain in th e OH region s
on ly a ban d at 3745 cm –1 correspon din g to th e term in al silan ol groups
(
Figs 3A an d 4A). Th e absorption ban d at 3660 cm –1 of OH groups on
alum in a was n ot observed an d n o absorption ban d in th e region 3600–
–
1
3
610 cm was foun d, wh ich m ean s th at n o bridgin g Si–OH–Al groups are
presen t in th e m olecular sieves.
TABLE III
Th e degree of ion exch an ge of catalysts used
Zeolite
BETA
Mn+
Mn+, wt%
Mn+/Al ratio
Zn 2+
Fe3+
La3+
Al3+
3.0
1.8
2.7
1.2a
0.40
0.87
0.20
0.29
USY
Zn 2+
Fe3+
La3+
Al3+
2.6
2.1
3.2
1.8a
0.49
0.56
0.33
0.45
(
Al)MCM-41
Zn 2+
Fe3+
Al3+
3.5
0.34
2.7
2.7
1.9a
0.32
(
Al)SBA-15
Zn 2+
Fe3+
Al3+
1.7
0.29
1.15
0.22
0.89
0.7a
a
Al3+ added by ion exch an ge.
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
735
To obtain a quan titative an alysis of th e con cen tration of Broen sted an d
Lewis acid sites, pyridin e adsorption was used for both m olecular sieves
(
Al)MCM-41 an d (Al)SBA-15 (Figs 3B an d 4B). Pyridin e adsorption resulted
–
1
in th e form ation of a n ew ban d at 1455 cm , wh ich correspon ds to th e in -
teraction between pyridin e an d Lewis acid23. Th e in ten sity of th is ban d de-
creased in th e order: Zn > Al > H > La > Fe for (Al)MCM-41 an d Zn > Al >
FIG. 3
IR spectra in th e OH vibration region of (Al)MCM-41 an d its ion -exch an ged form s before pyri-
din e adsorption (A) an d spectra of pyridin e region after adsorption (B)
FIG. 4
IR spectra in th e OH vibration region of (Al)SBA-15 an d its ion -exch an ged form s before
pyridin e adsorption (A) an d spectra of pyridin e region after adsorption (B)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
36
Bejblová, Vlk, Procházková, Šiklová, Čejka:
H > Fe > La for (Al)SBA-15. In La-form s of both m esoporous m olecular
–
1
sieves, form ation of a n ew ban d at 1446 cm was observed. Th is ban d in -
dicates th e presen ce of an oth er type of Lewis acid site. Th e sign al at
–
1
1
623 cm is assign ed also to pyridin e ion s on Lewis acid sites. On ly a n egli-
–
1
+
gible ban d at 1547 cm correspon din g to pyridin ium ion (PyH ) was foun d
in th e sam ples. Th is in dicates th at practically n o acid OH groups are pres-
en t in th e m esoporous m aterials un der in vestigation . Th e absorption ban d
at 1492 cm is assign ed to pyridin e adsorbed on both Broen sted an d Lewis
acid sites. In Zn - an d La-form s of m esoporous m olecular sieves, a n ew sig-
n al appears at ca. 1612 cm –1. Th e resultin g con cen tration s of Lewis an d
Broen sted acid sites calculated usin g m olar absorption coefficien ts 2.22 ±
–
1
–
1
0
.1 an d 1.67 ± 0.1 cm µm ol , respectively, are given in Table II. Th e spectra
in Figs 3B an d 4B clearly sh ow th at th ere are n o substan tial differen ces
between th e waven um bers of ban ds of pyridin e coordin ated to differen t
Lewis acid sites as it was in th e case of aceton itrile-d adsorption in cation -
3
exch an ged zeolites.
Th e con cen tration of cation s in catalysts was determ in ed by X-ray fluo-
n +
rescen ce an alysis. Th e degree of ion exch an ge determ in ed from th e M /Al
ratio is provided in Table III. Th ese data are in agreem en t with FTIR spectra
of aceton itrile-d adsorption sh owin g in com plete ion exch an ge of acid OH
3
groups.
Acylation of Ferrocene
Friedel–Crafts acylation of ferrocen e with acetic an h ydride leads to th e for-
m ation of acetylferrocen es. Th is reaction catalyzed by zeolites is h igh ly se-
lective to m on oacylferrocen e (Sch em e 1).
SCHEME 1
Zeolites Beta, USY an d m esoporous m olecular sieves (Al)MCM-41 an d
(
Al)SBA-15 were tested as catalysts in acylation of ferrocen e with acetic an -
h ydride. As both Lewis an d Broen sted acid sites exh ibit catalytic activity in
2
+
3+
3+
3+
ferrocen e acylation , th e ion -exch an ged form s with Zn , Fe , La , Al of
th ese m olecular sieves were prepared an d we in vestigated th e effect of th e
type of Lewis acid on th e ferrocen e con version .
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
737
Figures 5–8 clearly depict th e effect of th e presen ce of added Lewis acid
sites on th e ferrocen e con version . In th e case of zeolite Beta (Fig. 5), th e
h igh est con version of ferrocen e was foun d for Al-Beta an d Zn -Beta zeolites.
FIG. 5
Th e effect of active site types on th e con version of ferrocen e in ferrocen e acylation with acetic
an h ydride over ion -exch an ged form s of zeolite Beta: H-Beta (᭿), Zn -Beta (᭹), Fe-Beta (ꢀ),
La-Beta (᭛) an d Al-Beta (✳). Ferrocen e/acetic an h ydride ratio 1:6
FIG. 6
Th e effect of active site types on th e con version of ferrocen e in ferrocen e acylation with acetic
an h ydride over ion -exch an ged form s of zeolite USY: H-USY (᭿), Zn -USY (᭹), Fe-USY (ꢀ),
La-USY (᭛) an d Al-USY (✳). Ferrocen e/acetic an h ydride ratio 1:6
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
38
Bejblová, Vlk, Procházková, Šiklová, Čejka:
Con version of ferrocen e over Zn -Beta was m arkedly lower up to 150 m in of
th e tim e-on -stream (TOS) com pared with Al-Beta. After 240 m in of th e re-
action , th e con version s over both catalysts were n early th e sam e reach in g
alm ost 100%. Th e ferrocen e con version s over La-Beta an d H-Beta after
3
00 m in of th e TOS were ca. 90%. However, th e in itial activity of th ese
zeolites differed sign ifican tly. After 60 m in of th e TOS, th e ferrocen e con -
version over H-Beta was 58% wh ile th e con version over La-Beta was on ly
2
3
2%. Th e lowest ferrocen e con version was ach ieved with Fe-Beta (38% after
00-m in reaction ). Th e order of th e in creasin g ferrocen e con version corre-
spon ds to th e in creasin g con cen tration of Lewis acid sites determ in ed by
adsorption of aceton itrile-d an d FTIR spectroscopy. Th e h igh est con cen tra-
3
tion of Lewis acid sites was foun d for Zn -Beta an d Al-Beta zeolites.
As to zeolite USY (Fig. 6), th e h igh est ferrocen e con version was ach ieved
again over Zn -Beta (ca. 80% after 300 m in of TOS). Som e decrease in th e
ferrocen e con version was observed with Al- an d H-form s. Th e con version of
ferrocen e over th ese two zeolites was ca. 10% lower in com parison with
Zn -USY. Th e lowest ferrocen e con version was again foun d for Fe-USY. Th e
results are in good agreem en t with th e con cen tration of Lewis acid sites in
USY zeolites. Al- an d Zn -form s exh ibited th e h igh est con cen tration of Lewis
acid sites wh ile Fe-USY exh ibited a 4.5 tim es lower con cen tration of Lewis
acid sites.
With m esoporous m olecular sieve (Al)MCM-41 (Fig. 7), th e h igh est con -
version of ferrocen e was reach ed with H-form (about 90%). Som e decrease
in th e con version was observed over Zn -(Al)MCM-41 (71%) an d th e lowest
con version was again obtain ed over Fe-(Al)MCM-41.
Very sim ilar results were obtain ed with (Al)SBA-15 (Fig. 8); h owever, th e
activity of Zn - an d H-(Al)SBA-15 were com parable. Al-form s of m esoporous
m olecular sieves were n ot so active in ferrocen e acylation as th e form s pre-
pared from zeolites Beta an d USY.
It is well kn own th at h eat treatm en t of zeolites above 600 °C leads to
deh ydroxylation of Broen sted acid sites. Molecules of water are split off
with con com itan t form ation of Lewis acid sites. We tried to study th e effect
of acid sites in ferrocen e acylation in th is way. Before acylation reaction ,
H-Beta was activated at 800 °C for 90 m in an d, after coolin g, th is zeolite
was used in ferrocen e acylation . We com pared th e ferrocen e con version s
obtain ed with zeolite activated at 450 an d at 800 °C, in wh ich we assum ed
in creasin g con cen tration of Lewis acid sites at th e expen se of Broen sted
acid sites. Figure 9 clearly depicts th e effect of activation tem perature on
th e ferrocen e con version . Th e con version of ferrocen e was about 8% h igh er
after 300 m in of TOS with zeolite Beta activated at 800 °C.
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
739
FIG. 7
Th e effect of active site types on th e con version of ferrocen e in ferrocen e acylation with acetic
an h ydride over ion -exch an ged form s of zeolite (Al)MCM-41: H-(Al)MCM-41 (᭿),
Zn -(Al)MCM-41 (᭿), Fe-(Al)MCM-41 (ꢀ), La-(Al)MCM-41 (᭛) an d Al-(Al)MCM-41 (✳).
Ferrocen e/acetic an h ydride ratio 1:6
FIG. 8
Th e effect of active site types on th e con version of ferrocen e in ferrocen e acylation with acetic
an h ydride over ion -exch an ged form s of zeolite (Al)SBA-15: H-(Al)SBA-15 (᭿), Zn -(Al)SBA-15
(
᭹), Fe-(Al)SBA-15 (ꢀ), La-(Al)SBA-15 (᭛) an d Al-(Al)SBA-15 (✳). Ferrocen e/ acetic an h ydride
ratio 1:6
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
40
Bejblová, Vlk, Procházková, Šiklová, Čejka:
All th ese data clearly sh ow th at th e presen ce of proper Lewis acid sites is
crucial for ach ievem en t of h igh activity in ferrocen e acylation with acetic
an h ydride. Ferrocen e con version in creases with in creasin g con cen tration of
Lewis acid sites an d probably also th e stren gth of th ese sites in fluen ces th e
resultin g ferrocen e con version .
Acylation of Toluene
Toluen e acylation with isobutyryl ch loride is a m odel reaction for th e syn -
th esis of isopropyl tolyl keton es (Sch em e 2). Th is reaction produces all
th ree isom ers of isopropyl tolyl keton e with preferen ce for para isom er,
SCHEME 2
wh ich is th e m ain product of toluen e acylation over zeolites due to
sh ape-selectivity. For H-form s of zeolites, th e selectivity to particular iso-
m ers depen ds on th e level of isobutyryl ch loride con version , on th e con -
8
cen tration of acid sites, an d on th e structure of th e zeolite used .
FIG. 9
Th e effect of activation tem perature on th e con version of ferrocen e in ferrocen e acylation with
acetic an h ydride over zeolite BETA: 450 °C (᭿), 800 °C (᭹). Ferrocen e/acetic an h ydride ratio
1
:6
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
741
Zeolites Beta an d USY an d m esoporous m olecular sieves (Al)MCM-41 an d
Al)SBA-15 an d th eir ion -exch an ged form s (Zn 2+, Fe , La an d Al ) were
3+
3+
3+
(
in vestigated in acylation of toluen e. Th e effect of th e presen ce of added
Lewis acid sites on th e isobutyryl ch loride con version is clearly seen in
Figs 10–13.
Al-, Zn - an d La-form s of zeolite Beta sh owed very sim ilar con version s of
isobutyryl ch loride (Fig. 10). Th e con version of isobutyryl ch loride ob-
tain ed over th ese zeolites was in th e ran ge 80–85% after 240 m in of TOS.
Th e lowest isobutyryl ch loride con version reach ed ca. 57% with th e ion -
3
+
exch an ged Fe -form . Wh en we com pared th ese results with con cen tration
of Lewis acid sites of zeolite Beta an d its ion -exch an ged form s obtain ed by
adsorption of aceton itrile-d an d FTIR spectroscopy, we can see th at with
3
in creasin g con cen tration of Lewis acid sites th e ach ieved con version of th e
acylatin g agen t in creases. Th is is in a good agreem en t with th e results ob-
tain ed in ferrocen e acylation .
In th e case of zeolite USY, again very sim ilar con version s of isobutyryl
ch loride were obtain for all th e tested form s of th is zeolite (Fig. 11). Th e
con version s ran ged from 43 to 55% after 240 m in of TOS. Th e h igh est con -
version was foun d for th e Al-form possessin g th e h igh est con cen tration of
Lewis acid sites an d th e lowest con cen tration of Broen sted acid sites.
FIG. 10
Th e effect of active site types on th e con version of isobutyryl ch loride in toluen e acylation
over ion -exch an ged form s of zeolite Beta: H-Beta (᭿), Zn -Beta (᭹), Fe-Beta (ꢀ), La-Beta (᭛) an d
Al-Beta (✳)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
42
Bejblová, Vlk, Procházková, Šiklová, Čejka:
FIG. 11
Th e effect of active site types on th e con version of isobutyryl ch loride in toluen e acylation
over ion -exch an ged form s of zeolite USY: H-USY (᭿), Zn -USY (᭹), Fe-USY (ꢀ), La-USY (᭛) an d
Al-USY (✳)
FIG. 12
Th e effect of active site types on th e con version of isobutyryl ch loride in toluen e acylation
over ion -exch an ged form s of zeolite (Al)MCM-41: H-(Al)MCM-41 (᭿), Zn -(Al)MCM-41 (᭹),
Fe-(Al)MCM-41 (ꢀ), La-(Al)MCM-41 (᭛) an d Al-(Al)MCM-41 (✳)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
743
3
+
Ion -exch an ged Al -form s of m esoporous m olecular sieves (Al)MCM-41
an d (Al)SBA-15 (Figs 12 an d 13) were h igh ly active catalysts in toluen e acyl-
ation . Surprisingly, the conversion of isobutyryl chloride over Fe-(Al)MCM-41
was about 62% wh ile in ferrocen e acylation Fe-(Al)MCM-41 sh owed a very
low activity. Th is in dicates th at Fe-Lewis acid sites easily activate toluen e in
con trast to ferrocen e. H-form s of both m esoporous m olecular sieves were
n ot so active in toluen e acylation as in th e acylation of ferrocen e. Th e con -
version of isobutyryl ch loride in toluen e acylation over H-(Al)MCM-41 was
on ly 37% an d in th e case of H-(Al)SBA-15 43%.
Selectivities to isopropyl p-tolyl keton e at th e con version 20% over zeo-
lite Beta, USY, an d th eir ion -exch an ged form s with th e exception of
Fe-form s were h igh er th an 80% (Fig. 14). Th e selectivity to para isom er with
H-, Zn -, Al- an d La-Beta ran ged from 92 to 95%, over Fe-Beta it was ca. 78%.
In th e case of zeolite USY, th e h igh est selectivity to isopropyl p-tolyl keton e
was ach ieved with th e La- an d H-form s (96 an d 98%, respectively). Again ,
th e lowest selectivity (66%) to isopropyl p-tolyl keton e was reach ed with
Fe-USY. In an alogy with an oth er para-selective reaction (toluen e alkylation
2
4
with eth en e ), it can be speculated th at Fe cation s are also h igh ly active in
subsequen t isom erization , wh ich substan tially decreases th e selectivity to
para isom er.
FIG. 13
Th e effect of active site types on th e con version of isobutyryl ch loride in toluen e acylation
over ion -exch an ged form s of zeolite (Al)SBA-15: H-(Al)SBA-15 (᭿), Zn -(Al)SBA-15 (᭹),
Fe-(Al)SBA-15 (ꢀ), La-(Al)SBA-15 (᭛) an d Al-(Al)SBA-15 (✳)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
44
Bejblová, Vlk, Procházková, Šiklová, Čejka:
FIG. 14
Th e effect of active site types on th e con version of isobutyryl ch loride an d selectivity to iso-
propyl p-tolyl keton e in toluen e acylation over ion -exch an ged form s of zeolites Beta an d USY:
᭿
con version (at 240 m in ), ᮀ selectivity (at isobutyryl ch loride con version 20%)
FIG. 15
Th e effect of active site types on th e con version of isobutyryl ch loride an d selectivity to iso-
propyl p-tolyl keton e in toluen e acylation over ion -exch an ged form s of (Al)MCM-41 an d
(
Al)SBA-15: ᭿ con version (at 240 m in ), ᮀ selectivity (at isobutyryl ch loride con version 20%)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

The Effect of Type of Acid Sites in Molecular Sieves
745
Th e selectivities to isopropyl p-tolyl keton e at th e con version of iso-
butyryl ch loride of 20% over m esoporous m olecular sieves (Al)MCM-41 an d
(
Al)SBA-15 an d th eir ion -exch an ged form s were a little lower com pared
with th e zeolites used (Fig. 15). Th is is due to larger ch an n el diam eters of
th ese m aterials, wh ich en able th e form ation of th e bulkier ortho-isom er an d
also con secutive acylation of toluen e to diisobutyryltoluen es. Th e selectiv-
ity to para-isom ers over (Al)MCM-41 ran ged from 78 to 86%. Th e lowest
selectivities com pared with oth er m olecular sieves, were obtain ed over
ion -exch an ged form s of (Al)SBA-15.
CONCLUSIONS
Th e role of th e acid site type (Broen sted vs. Lewis) in th e activity an d selec-
tivity of differen t m olecular sieve catalysts was in vestigated in acylation of
ferrocen e with acetic an h ydride an d in acylation of toluen e with isobutyryl
ch loride. H-, Zn -, Fe-, Al- an d La-form s of zeolite Beta, USY an d m esoporous
m olecular sieves (Al)MCM-41 an d (Al)SBA-15 were in vestigated.
Th e con cen tration of Lewis an d Broen sted acid sites was determ in ed by
adsorption of aceton itrile-d3 or pyridin e as probe m olecules followed by
FTIR spectroscopy. Th e h igh est con cen tration s of Lewis acid sites were
foun d for Zn - an d Al-form s of th e m olecular sieves used. On th e oth er h an d,
th e lowest con cen tration of Lewis acid sites was foun d for th e Fe-form s.
No gen eral relation sh ip between th e type of cation an d substrate was
foun d. In acylation of ferrocen e over zeolites Beta an d USY, th e h igh est
con version s of ferrocen e were ach ieved with Zn - an d Al-form s. Th e h igh est
con version s of ferrocen e over m esoporous m olecular sieves (Al)MCM-41
an d (Al)SBA-15 were reach ed over Zn - an d H-form s. It was foun d th at
Al-form s of m esoporous m olecular sieves were n ot so active in ferrocen e
acylation com pared with th e activity of th ese form s prepared from zeolites
Beta an d USY. Th e lowest con version s were obtain ed with Fe-form s of all
th e m olecular sieves used. Th e correlation between con cen tration of Lewis
acid sites an d ferrocen e con version was foun d.
In acylation of toluen e, Al-form s of zeolites as well as m esoporous cata-
lysts were th e m ost active. Th e lowest activity in toluen e acylation was
foun d for Fe- an d H-form s of th e m olecular sieves used. Th e selectivities to
isopropyl p-tolyl keton e at th e con version 20% over zeolite Beta, USY an d
th eir ion -exch an ged form s with th e exception of Fe-form s were h igh er th an
8
0%. Th e h igh est selectivity (m ore th an 95%) to para-isom er was obtain ed
with H- an d La-form s of both zeolites Beta an d USY an d also with Al-form
of zeolite Beta. Th e selectivities over m esoporous m olecular sieves
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 728–746

7
46
Bejblová, Vlk, Procházková, Šiklová, Čejka:
(
Al)MCM-41 an d (Al)SBA-15 an d th eir ion -exch an ged form s were lower
com pared with zeolites. Th is was due to larger ch an n el diam eters of th ese
m aterials, wh ich en ables th e form ation of sterically m ore dem an din g ortho-
isom er an d also con secutive acylation of toluen e to diisobutyryltoluen es.
The authors thank the Grant Agency of the Czech Republic (Grants No. 104/07/0383 and
No. 203/03/H140) for financial support.
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