Hydrogenation and hydrogenolysis of acetophenone

Article abstract of DOI:10.1135/cccc20031969

Catalytic hydrogenation and hydrogenolysis of acetophenone was investigated on supported palladium catalysts in liquid phase at temperatures 30-130C and pressures 1-10 MPa. A number of supports like active carbon, alumina and zeolites Beta and ZSM-5 were

Full text of DOI:10.1135/cccc20031969

Hydrogenation and Hydrogenolysis of Acetophenone
1969
HYDROGENATION AND HYDROGENOLYSIS OF ACETOPHENONE
b
Martina BEJBLOVÁa1, Petr ZÁMOSTNÝa2, Libor ČERVENÝa3,* and Jiří ČEJKA
a
Department of Organic Technology, Institute of Chemical Technology, Prague,
1
Technická 5, 166 28 Prague 6, Czech Republic; e-mail: martina.bejblova@vscht.cz,
2
3
petr.zamostny@vscht.cz, libor.cerveny@vscht.cz
b
J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejškova 3, 182 23 Prague 8, Czech Republic; e-mail: jiri.cejka@jh-inst.cas.cz
Received July 14, 2003
Accepted August 18, 2003
Catalytic h ydrogen ation an d h ydrogen olysis of acetoph en on e was in vestigated on supported
palladium catalysts in liquid ph ase at tem peratures 30–130 °C an d pressures 1–10 MPa. A n um -
ber of supports like active carbon , alum in a an d zeolites Beta an d ZSM-5 were em ployed. Th e
effects of solven t an d support on th e reaction m ech an ism of acetoph en on e tran sform ation
were studied. Catalysts with acid zeolite support sh owed a very h igh activity in tran sform a-
tion of acetoph en on e to eth ylben zen e. Based on a kin etic m odel, th e reaction rates of
acetoph en on e tran sform ation to eth ylben zen e on Pd/C an d Pd/Al2O3 catalysts were dis-
cussed. Th e kin etic m odel con firm ed th at th e tran sform ation of acetoph en on e to eth yl-
ben zen e proceeds prim arily via a h ydrogen ation -deh ydration m ech an ism an d th e effect of
th e direct h ydrogen olysis of th e C=O bon d of acetoph en on e is in sign ifican t.
Keyw ord s: Hydrogen ation ; Hydrogen olysis; Carbon yl com poun ds; Acetoph en on e; Keton es;
Reduction s; Zeolites; Palladium ; Active carbon ; Heterogen eous catalysis; Solid support.
In a n um ber of ch em ical reaction s, carbon yl com poun ds are com m on ly re-
duced to correspon din g alcoh ols; n everth eless, in som e cases, it is desirable
to tran sform th e carbon yl group to m eth ylen e. Th e Clem m en sen 1,2 an d
Wolff–Kizh n er reduction 3,4 are th e first procedures applied to th e reduction
of carbonyl compounds to corresponding hydrocarbons. Subsequently, a num-
ber of agen ts were utilized for th ese reduction s, such as triisopropyl ph os-
ph ite5, lith ium alum in ium h ydride6,7 an d sodium boroh ydride8,9. At
presen t, h eterogen eous catalytic h ydrogen ation an d h ydrogen olysis are th e
m ost com m on ly utilized procedures to perform th ese reaction s.
Th e con version of a carbon yl com poun ds to correspon din g h ydrocarbon s
in a h ydrogen ation en viron m en t can proceed by several m ech an ism s. Th e
startin g carbon yl com poun d can be first h ydrogen ated to alcoh ol, wh ich is
deh ydrated in th e followin g step to form th e C=C bon d, th e latter bein g
h ydrogen ated in th e fin al step to th e desired h ydrocarbon . Th is m ech a-
Collect. Czech. Chem. Commun. (Vol. 68) (2003)
doi:10.1135/cccc20031969

1970
Bejblová, Zámostný, Červený, Čejka:
n ism 10–14 operates e.g. on bifun ction al catalysts with acid support (fre-
quen tly zeolites) an d a m etal com pon en t. Th e m etal h ydrogen ation
com pon en t of th e bifun ction al catalyst in itiates th e h ydrogen ation steps
(C=O → C–OH an d C=C → C–C) wh ile th e acid com pon en t is respon sible
for deh ydration of th e alcoh ol produced. Hydrogen olysis, th e secon d possi-
ble m ech an ism for th e con version of C=O group to CH2 group, in volves a
direct splittin g of th e oxygen –carbon bon d by h ydrogen . Th erefore, th e car-
bon yl com poun d can be first h ydrogen ated to a correspon din g alcoh ol,
followed15–18 by a h ydrogen olytic splittin g of th e C–OH bon d givin g th e
desired h ydrocarbon , or a direct h ydrogen olysis of th e C=O bon d of th e
startin g carbon yl com poun d takes place.
Palladium supported on active carbon 20–27, zeolites11,12,16 or silica28 is th e
m ost frequen tly em ployed catalyst for th e con version of carbon yl com -
poun ds to correspon din g h ydrocarbon s. Th e con version of a carbon yl
group to m eth ylen e is facilitated by in troduction of a sm all am oun t of an
acid to th e reaction m ixture (h ydroch loric an d sulfuric acid20–22,29 or m ore
often acetic acid15,23,24,30).
Reduction of carbon yl com poun ds to h ydrocarbon s takes place also by
usin g oth er h ydrogen ation catalysts based on e.g. copper(II)-ch ro-
m ium (III)31, iron 32, n ickel33 or sulfides34–36 an d W, Mo, CoMo, NiMo. How-
ever, th ese catalysts are substan tially less active for th e con version of C=O
to CH2 an d h en ce require h igh er tem peratures (200–300 °C) an d pressures
(up to 15 MPa).
Th e objective of th is work is to describe th e reaction m ech an ism of h y-
drogen ation an d h ydrogen olysis of acetoph en on e on palladium catalysts.
Th e effects of support an d solven t on th e kin etics of th e system of th ese re-
action s were m on itored. A detailed an alysis of kin etic data m ade possible to
describe th e m ech an ism of oxygen rem oval from th e m olecule of aceto-
ph en on e un der th e con dition s of h ydrogen ation .
EXPERIMENTAL
Catalysts
Supported catalysts with 5 wt.% of palladium were used for h ydrogen ation of acetoph en on e.
Zeolites ZSM-5 an d Beta with differen t Si/Al ratios ran gin g from 12.5 to 140 were used as
supports. Th e Pd/zeolite catalysts were prepared by im pregn ation of zeolites with a water so-
lution of PdCl2. A suspen sion of a zeolite (2.5 g) in 40% solution of PdCl2 in HCl (0.6 m l)
an d distilled water (100 m l) was stirred for 9 h , followed by evaporation usin g a vacuum ro-
tary evaporator, dryin g at 120 °C in a n itrogen atm osph ere (2 h ) an d calcin ation at 400 °C
(12–25 h ) in a stream of n itrogen .
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1971
For com parison , a com m ercial 5% Pd/C catalyst from Doduco Gm bH with dry m atter
con ten t of 41.9% an d 5% Pd/Al2O3 prepared at th e Departm en t of Organ ic Tech n ology,
were used37. No special activation was carried out prior to th eir use.
Apparatus an d Kin etic Measurem en ts
Catalytic tests were carried out in liquid ph ase in a 300 m l autoclave (Parr 4842) with a
m agn etic stirrer. An am oun t of 4.5 g of acetoph en on e (99%; Aldrich , U.S.A.), 10–80 m g of a
catalyst, 150 m l of m eth an ol p.a. or h exan e p.a. (both Pliva–Lach em a, Czech Republic) used
as th e solven t were ch arged to th e autoclave. Th en , th e autoclave was h eated to th e reaction
tem perature (30–130 °C), followed by pressurizin g with h ydrogen (1–10 MPa) an d stirrin g
was started.
An alytical Meth ods
An alysis of th e reaction products was carried out on a gas ch rom atograph (GC 17A
Shim adzu) with the capillary colum n J&W Scientific (length 60 m , i.d. 0.32 m m , phase th ickn ess
0.25 µm ). Th e reaction in term ediates were an alyzed usin g GC-MS (Varian Saturn 2000).
RESULTS AND DISCUSSION
Figure 1 sh ows a typical tim e-on -stream depen den ce (T-O-S) of acetoph en -
on e con version s on Pd/C catalyst.
Usin g GC-MS, th e followin g in term ediates of acetoph en on e (1) tran sfor-
m ation to eth ylben zen e (4) were determ in ed, n am ely 1-ph en yleth an -1-ol
(2) an d styren e (3). Based on th e literature data an d th e results of our ki-
n etic experim en ts, th e followin g reaction sch em e of th e acetoph en on e
100
80
60
40
20
0
0
60
120
180
time, min
FIG. 1
Acetoph en on e h ydrogen ation on Pd/C catalyst in m eth an ol (130 °C, 6 MPa): ᭹ acetoph en on e,
᭿ eth ylben zen e, ᭺ 1-ph en yleth an -1-ol, ᭝ styren e)
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1972
Bejblová, Zámostný, Červený, Čejka:
tran sform ation to eth ylben zen e in cludin g possible h ydrogen ation , deh y-
dration an d h ydrogen olysis steps can be proposed:
Eth ylben zen e can be produced from acetoph en on e by a series reaction s,
in wh ich acetoph en on e is first h ydrogen ated to 1-ph en yleth an -1-ol (1 → 2),
th en con secutively deh ydrated to styren e (2 → 3), th e double bon d of
wh ich is fin ally h ydrogen ated to give eth ylben zen e (3 → 4).
Hydrogen olysis m ay also take part in th e tran sform ation of acetoph en on e
to eth ylben zen e, in cludin g a splittin g of th e C=O bon d of acetoph en on e
(1 → 4) or th e C–OH bon d of 1-ph en yleth an -1-ol with h ydrogen (2 → 4).
To verify th e proposed reaction m ech an ism , th e kin etic data of aceto-
ph en on e tran sform ation to eth ylben zen e on th e Pd/C an d Pd/Al2O3 cata-
lysts were processed by regression an alysis38 usin g th e program ERA 3.0. For
th e zeolite-based catalysts, th e an alysis of kin etic data will be publish ed
elsewh ere39. Two altern ative m ath em atical m odels form ally correspon din g
to Sch em e 1 were proposed to describe th e kin etics of th e Lan gm uir–
Hin sh elwood m odel an d th e m odel of n on -station ary kin etics.
Th e Lan gm uir–Hin sh elwood m odel was based on a com m on assum p-
tion 40 th at th e rate of a catalyzed reaction is con trolled by th e surface reac-
tion as th e rate-determ in in g step an d th e reaction rate was described in th e
m odel by th e followin g Eq. (1):
ki KA cA
ri =
,
(1)
1 + K1 c1 +K2 c2 +K3 c3 +K4 c4
CH3
CH3
O
k2
k1
CH CH2
H2
Pd/C
-H2O
OH
Pd/C
2
3
1
H2,Pd/C
H2,Pd/C
H2,Pd/C
k5
-H2O
k3
k4
CH2CH3
4
SCHEME 1
Reaction sch em e of acetoph en on e tran sform ation to eth ylben zen e
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1973
wh ere ri is th e rate of th e i-th reaction accordin g to Sch em e 1, ki its rate
con stan t, K th e form al adsorption coefficien t an d c th e con cen tration of
com poun ds 1–4 in th e reaction m ixture. Subscript A refers to a substan ce,
wh ich is a reactan t in th e i-th reaction .
Th e m odel of n on -station ary kin etics h as n ot used an y assum ption of th e
existen ce of th e rate-determ in in g step. All elem en tary steps in th e system s
of catalyzed reaction s were described by kin etic equation s of th e followin g
form :
adsorption
rj,ads = kj,adscjcL ,
(2)
(3)
(4)
surface reaction ri = kicjL
,
desorption
rj,des = kj,descjL ,
wh ere ri an d ki are th e rate an d th e rate con stan t of th e i-th surface reaction ,
rj,ads an d kj,ads th e rate an d th e rate con stan t of adsorption of j-th reaction
com pon en t an d rj,des an d kj,des th e rate an d th e rate con stan t of its de-
sorption . Th e sym bol cj refers to a con cen tration of a j substan ce in th e re-
action m ixture, cjL th e con cen tration of a j substan ce adsorbed on th e
catalyst surface relative to th e volum e of th e reaction m ixture an d cL th e
con cen tration of free active sites on th e catalyst surface. All con cen tration s
are defin ed as dim en sion less quan tities by Eq. (5).
cj [m ol m –3
cj [m ol m –3
]
]
cj =
(5)
∑
j
$
o =0
Th e results of th e regression an alysis clearly sh ow th at th e m odel of n on -
station ary kin etics m ade possible to satisfactorily describe th e m easured
data, wh ile th e Lan gm uir–Hin sh elwood m odel failed un der certain reaction
con dition s (Fig. 2). Th e lim ited applicability of th e Lan gm uir– Hin sh elwood
m odel can be explain ed by th e erron eous assum ption on th e rate-
determ in in g reaction step41. For th is reason , we h ave used th e n on -
station ary kin etic m odel for furth er evaluation of th e kin etic data.
Sin ce m ath em atic m odelin g was also used to com pare th e reaction course
in various solven ts an d in depen den ce on a catalyst support, an assum ption
was in troduced in to th e m odel, postulatin g th at an alteration of a solven t
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1974
Bejblová, Zámostný, Červený, Čejka:
itself affects on ly th e rate con stan ts of th e sorption processes an d does n ot
sign ifican tly in fluen ce th e value of th e rate con stan t of th e surface reaction .
Th is assum ption m ade it possible to assess all th e experim en tal data in vari-
ous solven ts togeth er, with out an y occurren ce of an in tolerable in crease in
th e n um ber of kin etic param eters. Figure 3 sh ows a com parison of th e m ea-
sured data an d th e data calculated from th e m odel for optim al values of pa-
ram eters.
1.00
a
c
0.50
0.00
0
175
350
time, min
1.00
0.50
0.00
b
c
0
175
350
time, min
FIG. 2
Com parison of th e m easured an d calculated data of acetoph en on e h ydrogen ation catalyzed by
Pd/Al2O3 in m eth an ol (130 °C, 6 MPa) usin g th e Lan gm uir–Hin sh elwood m odel (a) an d th e
n on -station ary kin etics m odel (b): ᭹ acetoph en on e, ᭿ eth ylben zen e, ᭺ 1-ph en yleth an -1-ol, ᭝
styren e
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1975
Table I sh ows th e estim ated param eters an d th eir reliability given by th e
ran ge of con fiden ce lim its42. Th e test of statistical sign ifican ce for th e esti-
m ated values was perform ed at a reliability level of 95%. Th e statistically in -
sign ifican t param eters were excluded from th e m odel. Based on th e values
of th e rate con stan ts of th e surface reaction s (param eters k1–k5), it could be
con cluded th at th e tran sform ation of acetoph en on e to eth ylben zen e pro-
ceeds prim arily th rough a system of h ydrogen ation -deh ydration reaction s
with th e followin g in term ediates: 1-ph en yleth an -1-ol (2) an d styren e (3)
(reaction path way: 1 → 2 → 3 → 4). A m in or effect of a direct
h ydrogen olytic splittin g of acetoph en on e to eth ylben zen e (reaction 1 → 4)
takes also part on catalysts with active carbon as a support. A sim ilar split-
tin g of 1-ph en yleth an -1-ol (2 → 4) is n egligible. A relatively low reliability
of th e rate con stan t k1 (a broad in terval of th e con fiden ce lim its) is caused
1.00
1.00
b
a
c
c
0.50
0.50
0.00
0.00
0
150
300
0
150
300
time, min
time, min
1.00
1.00
d
c
c
c
0.50
0.50
0.00
0.00
0
175
350
0
180
360
time, min
time, min
FIG. 3
Com parison of th e m easured an d calculated data for Pd/C catalyst (a, b) an d Pd/Al2O3 catalyst
(c, d) in m eth an ol (a, c) an d h exan e (b, d) (130 °C, 6 MPa): ᭹ acetoph en on e, ᭿ eth ylben zen e,
᭺ 1-ph en yleth an -1-ol, ᭝ styren e
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1976
Bejblová, Zámostný, Červený, Čejka:
by th e rapid con version of acetoph en on e in th e reaction m ixture. Th e
value of th is rate con stan t is particularly projected in th e solution of th e
m odel on ly if th e con cen tration of acetoph en on e differs from zero an d
th us on ly several poin ts at th e begin n in g of each m easurem en t are effective
for th e estim ation of th e value of th is con stan t. Th erefore, th e reliability of
estim ation of th e rate con stan ts k2 an d k3 is m uch h igh er.
Th e differen t rates of acetoph en on e con cen tration decrease in various
solven ts an d on differen t catalysts are m ain ly caused by differen t rates of
acetoph en on e sorption on th e catalysts. In all cases, th e rate of surface reac-
tion was alm ost iden tical an d always m uch h igh er com pared to th e rate of
adsorption . Th e rates of con secutive reaction s differed for various catalysts,
wh ich was apparen tly caused by th e type an d acidity of th e support used.
Usin g th e Pd/C catalyst, th e rate con stan ts of deh ydration of 1-ph en yl-
eth an -1-ol an d h ydrogen ation of styren e were substan tially h igh er th an
th ose over th e Pd/Al2O3 catalyst.
TABLE I
Optim um values of kin etic param eters an d th eir 95% con fiden ce lim its (in paren th eses) esti-
m ated by regression an alysis for Pd/C an d Pd/Al2O3 catalysts in m eth an ol an d h exan e at
130 °C an d 6 Mpa, (≈0 in dicates statistically in sign ifican t param eters)
Rate
con stan ts
Pd/Al2O3, m eth an ol Pd/Al2O3, h exan e
Pd/C, m eth an ol
8.3 (6.7–300)
Pd/C, h exan e
8.3 (6.7–300)
k1
8.3 (1.7–32)
8.3 (1.7–32)
k2
0.56 (0.52–0.76) 0.56 (0.52–0.76)
0.029 (0.028–0.030) 0.029 (0.028–0.030)
k3
0.9 (0.7–1.4)
1.0 (0.03–4.8)
≈0
0.9 (0.7–1.4)
0.08 (0.07–0.09)
0.08 (0.07–0.09)
k4
1.0 (0.03–4.8)
≈0
≈0
k5
≈0
≈0
≈0
k1,ads
k2,ads
k3,ads
k4,ads
k1,des
k2,des
k3,des
k4,des
1.8 (1.1–2.4)
0.5 (0.3–6.4)
0.3 (0.1–3.7)
≈0
0.27 (0.22–0.33)
0.25 (0.22–0.31)
0.30 (0.26–0.41)
0.04 (0.03–0.05)
0.5 (0.2–110)
≈0
0.5 (0.2–7.1)
≈0
≈0
≈0
≈0
≈0
≈0
≈0
≈0
≈0
1.7 (1.1–3.7)
1.0 (0.3–7.5)
>>k3
3.4 (1.6–48)
0.12 (0.10–0.13)
2.7 (0.5–972)
>>k3
0.11 (0.08–0.13)
0.8 (0.2–170)
>>k3
≈0
>>k3
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1977
Table I sh ows th at certain estim ation s of th e sorption -desorption pro-
cesses are less reliable, wh ich is caused by a stron g correlation between in di-
vidual param eters. Th e in sign ifican ce of th e rate con stan ts of som e of th e
sorption processes can be in terpreted by assum in g th at a certain sorption
process is m uch slower th an th e com petitive surface reaction or th e reverse
sorption process. Th e value of th e rate con stan t of eth ylben zen e desorption
(k4,des) was such h igh com pared to th e rate con stan ts of its production th at
an addition al assum ption was in troduced in th e m odel assum in g th at th e
produced eth ylben zen e is, im m ediately after its production by th e surface
reaction , quan titatively desorbed from th e catalyst surface.
Support Effect
Th e role of various supported catalysts with 5 wt.% of palladium in th e re-
action m ech an ism was in vestigated. Figure 4 depicts th e T-O-S depen den ce
of acetoph en on e con version to eth ylben zen e over in dividual catalysts.
Figure 4 in fers th at acetoph en on e tran sform ation to eth ylben zen e in m eth -
an ol easily proceeds on catalysts supported on active carbon an d zeolites,
wh ereas usin g alum in a, acetoph en on e is h ydrogen ated on ly to 1-ph en yl-
eth an -1-ol (Fig. 4b), n ot un dergoin g furth er tran sform ation .
Th e Pd/zeolite catalysts are th e m ost active in th e acetoph en on e tran sfor-
m ation to eth ylben zen e. Acid properties of zeolites apparen tly procure
water elim in ation from 1-ph en yleth an -1-ol as well as th e con secutive for-
m ation of styren e. Török et al.10 described th e sam e reaction m ech an ism
em ployin g Pt/K-10 m on tm orillon ite as th e catalyst for a broad ran ge of
con version s of various keton es to correspon din g h ydrocarbon s.
Neverth eless, styren e as a reaction in term ediate was described even wh en
an in ert support like active carbon was used (Fig. 4a). In th ese system s, acid
properties of th e catalyst are due probably to palladium -activated h ydrogen
as it was described by, e.g., Červen ý43,44
.
As it is apparen t from th e presen ted data, a sign ifican tly low con cen tra-
tion of styren e is produced over th e Pd/zeolite catalyst. Th erefore, it can be
assum ed th at h ydrogen olysis, i.e. th e direct splittin g of th e C=O bon d of
acetoph en on e or th e C–OH bon d of 1-ph en yleth an -1-ol by h ydrogen , is
sign ifican t in th ese tran sform ation s of acetoph en on e to eth ylben zen e.
Durin g h ydrogen ation of acetoph en on e catalyzed by palladium on zeo-
lite support, an oth er in term ediate – m eth yl (1-ph en yleth yl) eth er (5) (ᮀ in
Fig. 4c) – was foun d. Its form ation is assum ed to proceed, owin g to th e acid
properties of a zeolite, via in term olecular deh ydration of 1-ph en yleth an -1-ol
with m eth an ol.
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1978
Bejblová, Zámostný, Červený, Čejka:
100
80
a
60
40
20
0
0
60
120
180
time, min
100
80
b
60
40
20
0
0
60
120
180
240
300
time, min
100
80
c
60
40
20
0
0
10
20
30
time, min
40
FIG. 4
Th e course of h ydrogen ation an d h ydrogen olysis of acetoph en on e on Pd/C (a), Pd/Al2O3 (b)
an d Pd / Beta (c) catalysts (50 m g) with variou s su p p orts in m eth an ol (130 °C, 6 MPa): ᭹
acetoph en on e, ᭿ eth ylben zen e, ᭺ 1-ph en yleth an ol, ᭝ styren e, ٗ m eth yl (1-ph en yleth yl)
eth er
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1979
Effect of Support Acidity
Th e exten t of acidity of zeolite supports affects th e in itial rate of aceto-
ph en on e con version (k1 + k4). Th e effect of acidity of zeolites on th e rate of
acetoph en on e tran sform ation is apparen t from com parison of th e in itial
rates of reaction s catalyzed by palladium on zeolites Beta an d ZSM-5 em -
ployed as supports (Table II). Four types of zeolite Beta, differin g in th eir
Si/Al ratio, i.e. in th e con cen tration of th eir acid sites, an d two types of
ZSM-5 zeolite h avin g also differen t Si/Al ratios were utilized as a support for
h ydrogen ation catalysts. Th e in itial rates of acetoph en on e tran sform ation
are sign ifican tly in fluen ced by th e support acidity; with decreasin g Si/Al ra-
tio, th e in itial reaction rates in crease. On th e oth er side, it is n ecessary to
em ph asize th at th e ch an n el diam eter of th e zeolite used obviously does n ot
play a key role in th e reaction rate. For both zeolite ZSM-5 (with ch an n el size
of 0.53 × 0.55 n m ) an d zeolite Beta (large-pore zeolite, 0.76 × 0.64 n m )45, th e
in itial rates of acetoph en on e tran sform ation are sim ilar an d seem in gly
m ore depen den t on th e con cen tration of alum in um th an on th e ch an n el
size of th e particular zeolite.
Solvent Effect
Th e course of acetoph en on e h ydrogen ation can be also affected by sol-
ven t23. Th erefore, th e effect of solven t (polar m eth an ol an d n on -polar h ex-
an e) on th e in itial rate of acetoph en on e tran sform ation , r0, was in vesti-
TABLE II
Effect of support acidity on th e in itial reaction rates of acetoph en on e con version in m eth a-
n ol (130 °C, 6 MPa, 15 m g of catalyst)
–1 a
Catalyst
Si/Al of th e zeolite support
r0, m m ol m in –1 gcat
Pd/Beta (1)
Pd/Beta (2)
Pd/Beta (3)
Pd/Beta (4)
Pd/ZSM-5 (1)
Pd/ZSM-5 (2)
70
35
40.7
55.6
13.5
12.5
140
15
66.0
220.9
38.3
102.2
a
r0 is th e sum of th e rate of acetoph en on e h ydrogen ation to 1-ph en yleth an -1-ol an d th at of
h ydrogen olysis of acetoph en on e to eth ylben zen e.
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1980
Bejblová, Zámostný, Červený, Čejka:
gated (Fig. 5) as well as on th e selectivity of 1-ph en yleth an -1-ol production
(Fig. 6). In all cases, th e selectivity was determ in ed at 50% con version of
th e reactan t an d defin ed as follows:
S
= [conc. 2 (%)/conc. 2 (%) + conc. 3 (%) + conc. 4 (%) + conc. 5 (%)] × 100,
50
wh ere S50 is th e selectivity at 50% con version of acetoph en on e (1),
1-ph en yleth an -1-ol (2), styren e (3), eth ylben zen e (4), m eth yl (1-ph en yleth yl)
eth er (5).
350
300
250
200
150
100
50
0
Pd/C
Pd/Al O
Pd/Beta
2
3
FIG. 5
Effect of th e solven t (ᮀ m eth an ol, ᭿ h exan e) on th e in itial reaction rate of acetoph en on e
100
80
60
40
20
0
Pd/C
Pd/Al O
Pd/Beta
2
3
FIG. 6
Effect of th e solven t (ᮀ m eth an ol, ᭿ h exan e) on th e selectivity to 1-ph en yleth an -1-ol at 50%
acetoph en on e con version
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1981
As Fig. 5 sh ows, th e effect of solven t on th e in itial reaction rate is n ot
straigh tforward. Usin g th e Pd/C catalyst, th e in itial rate in m eth an ol was
twice as h igh as in h exan e. In con trast, for Pd/Al2O3 th e in itial rates did n ot
sign ifican tly differ an d usin g Pd/zeolite catalysts (e.g. zeolite Beta (2)), th e
rate was sign ifican tly h igh er in h exan e. Th e presen ted results im ply th at
th e acidity of differen t supports obviously affects th e in itial rate of aceto-
ph en on e decom position in depen den ce on th e type of th e solven t used.
With acid form s of zeolites, com petitive adsorption of polar m eth an ol to-
100
80
60
40
20
0
0
60
120 180
240 300
360
time, min
FIG. 7
Hydrogen ation of acetoph en on e on Pd/Al2O3 in m eth an ol: ᭹ acetoph en on e, ᭿ eth ylben zen e, ᭺
1-ph en yleth an -1-ol, ᭝ styren e
100
80
60
40
20
0
0
60
120 180
240 300
360
time, min
FIG. 8
Hydrogen ation of acetoph en on e on Pd/Al2O3 in h exan e: ᭹ acetoph en on e, ᭿ eth ylben zen e, ᭺
1-ph en yleth an -1-ol, ᭝ styren e
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1982
Bejblová, Zámostný, Červený, Čejka:
geth er with acetoph en on e appears, wh ereas usin g h exan e, acetoph en on e
adsorption is preferen tially adsorbed.
Th e selectivity to 1-ph en yleth an -1-ol at 50% acetoph en on e con version
was sligh tly h igh er in h exan e with all types of th e catalysts.
Th e m ost apparen t effect of solven t was observed with 5 wt.% Pd/Al2O3.
In m eth an ol, th e fin al product of acetoph en on e h ydrogen ation led to
1-ph en yleth an -1-ol (selectivity ca 75%), wh ereas after 6 h , th e reaction m ix-
ture con tain ed on ly 4% of eth ylben zen e an d th e rest was styren e (Fig. 7),
wh ich was n ot furth er h ydrogen ated un der th e reaction con dition s used.
Th is un am biguously dem on strated th at catalyst deactivation occurred. On
th e oth er h an d, wh en h exan e was used as solven t un der th e sam e reaction
con dition s, 1-ph en yleth an -1-ol reacted furth er as an in term ediate an d after
th e sam e tim e period (6 h ), th e reaction m ixture con sisted of 65% of eth yl-
ben zen e an d 23% of 1-ph en yleth an -1-ol (Fig. 8).
CONCLUSIONS
Tran sform ation of acetoph en on e to eth ylben zen e successfully proceeds on
palladium catalysts supported on active carbon an d zeolites in m eth an ol
an d h exan e as solven ts. Wh ereas on Pd/C, th e in itial rate of acetoph en on e
reaction is h igh er in m eth an ol, on th e Pd/zeolite catalyst, th e rate is h igh er
in h exan e. On Pd/Al2O3 catalyst, th e reaction proceeds in m eth an ol on ly
givin g 1-ph en yleth an -1-ol, wh ich does n ot un dergo an y furth er reaction s,
wh ereas in h exan e, th e con version to eth ylben zen e con tin ues. Palladium
catalysts with zeolite supports were very active in th ese tran sform ation s.
Th e acidity of th e supports affected th e h ydrogen ation rate an d also con -
tributed to a large exten t to direct h ydrogen olysis durin g th e reaction .
Th e kin etic m odel describin g th e reaction system sh owed th at, on th e
Pd/C catalyst, h ydrogen ation -deh ydration m ech an ism s with in term ediates
of 1-ph en yleth an -1-ol an d styren e took place in th e tran sform ation of
acetoph en on e to eth ylben zen e (k1 = 8.3 s–1), wh ereas direct h ydrogen olytic
splittin g of th e C=O bon d of acetoph en on e h as on ly a m in or effect (k4 =
1.0 s–1). For th e reaction s catalyzed with Pd/Al2O3, th e rate con stan ts k4 was
zero an d, th us, n o direct h ydrogen olysis of th e C=O bon d in acetoph en on e
occurred. In addition , th e kin etic m odel excluded th e splittin g of th e C–OH
bon d of 1-ph en yleth an -1-ol to eth ylben zen e (k5 ≈ 0) on th e Pd/C as well as
Pd/Al2O3 catalysts in m eth an ol an d in h exan e.
The authors acknowledge the financial support of the Grant Agency of the Czech Republic (project
No. 203/03/0804).
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Hydrogenation and Hydrogenolysis of Acetophenone
1983
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