Phenol tert-butylation over zirconia-supported 12-molybdophosphoric acid catalyst

Article abstract of DOI:10.1016/j.molcata.2005.11.043

The alkylation of phenol with tert-butanol was investigated using zirconia-supported 12-molybdophosphoric acid (MPA) as catalyst. The catalysts with different MPA loading (5-25 wt.% calcined at 700 °C) and calcination temperature (15 wt.% calcined from 50

Full text of DOI:10.1016/j.molcata.2005.11.043

Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
Phenol tert-butylation over zirconia-supported
12-molybdophosphoric acid catalyst
Biju M. Devassy, G.V. Shanbhag, S.B. Halligudi∗
Inorganic Chemistry and Catalysis Division, National Chemical Laboratory, Pune 411 008, India
Received 7 October 2005; received in revised form 22 November 2005; accepted 23 November 2005
Available online 4 January 2006
Abstract
The alkylation of phenol with tert-butanol was investigated using zirconia-supported 12-molybdophosphoric acid (MPA) as catalyst. The catalysts
with different MPA loading (5–25 wt.% calcined at 700 ◦C) and calcination temperature (15 wt.% calcined from 500 to 750 ◦C) were prepared by
suspending zirconium oxyhydroxide in methanol solution of MPA followed by drying and calcination. These catalysts were characterized by X-ray
diffraction and 31P MAS NMR spectroscopy measurements. The XRD results indicated that MPA stabilizes the tetragonal phase of zirconia. 31
P
MAS NMR spectra showed the presence of three types of phosphorous species, phosphomolybdate in interaction with zirconia, decomposition
product of MPA and an unidentified species. FTIR pyridine adsorption on 15% MPA catalyst calcined at different temperatures showed the presence
of both Bro¨nsted and Lewis acidity and the catalyst calcined at 700 ◦C showed the highest relative Bro¨nsted acidity. Under the reaction conditions
of 140 ◦C, tert-butanol/phenol molar ratio of 2 and LHSV of 4 h−1, the phenol conversion was 80.6% at 2 h (selectivity to 2-TBP 11.5%, 2,4-DTBP
55.2%, and 4-TBP 25.7%), which decreased slowly with time and at 31 h, it was 58.5% (selectivity to 2-TBP 15.2%, 2,4-DTBP 41.6%, and 4-TBP
38.4%). The major reason for the catalyst deactivation was the reduction and leaching of MPA from the catalyst surface.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Zirconia; 12-Molybdophosphoric acid; Phenol; tert-Butylation
1. Introduction
[4,5]. Recently, we have shown that zirconia can be used as a
suitable support for heteropolyacids [6].
Heteropoly acids (HPAs) are a unique class of materials
active both in redox and acid catalysis [1,2]. These are polyox-
ometallates made up of heteropoly anions having metal–oxygen
Alkylation of phenol with tert-butanol is industrially impor-
tant as it is used for the production of tert-butylated phenols.
For instance, 2-tert-butyl phenol (2-TBP) is a starting material
for the synthesis of antioxidants and agrochemicals, whereas
4-tert-butyl phenol (4-TBP) is used to make fragrances and
phosphate esters, 2,4-di-tert-butyl phenol (2,4-DTBP) is used
in the synthesis of substituted triaryl phosphites. Commercially
tert-butyl phenols are produced by the reaction of phenol with
isobutene in presence of homogeneous catalysts. The use of
these catalysts gives rise to many problems concerning handling,
safety, corrosion, and waste disposal. Therefore, considerable
efforts have been made for the development of suitable hetero-
geneouscatalysts. Thevariouscatalystsreportedforthisreaction
include metal oxides [7], zeolites [8], various microporous and
mesoporous materials [9], clays and clay-based materials [10].
Both the formation of C- and O-alkylated products are possible
depending on reaction conditions such as reaction temperature
and type of catalyst. The catalyst with strong acidic sites or at
high reaction temperature, the reaction results in the formation
of C-alkylated products, while catalysts with weak acidic sites or
¨
octahedra as the basic structural unit. They are strong Bronsted
acid catalysts and their strength of acidity is higher than that of
conventional solid acids like zeolites and mixed oxides. HPAs
can be used either directly as a bulk material or in supported
form. The use in supported form is preferable because of its
high surface area compared to the bulk material (5–8 m2 g−1
)
and better accessibility of reactants to the active sites. Acidic or
neutral solids, which interact weakly with HPAs such as silica,
active carbon and acidic ion-exchange resin, have been reported
to be suitable as HPA supports [3].
In recent years zirconia has attracted much attention both as
catalyst and catalyst support because of its high thermal stabil-
ity and the amphoteric character of its surface hydroxyl groups
∗
Corresponding author. Tel.: +91 20 25893300; fax: +91 20 25893761.
E-mail address: sb.halligudi@ncl.res.in (S.B. Halligudi).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.11.043

B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
163
at low reaction temperature leads to the formation of O-alkylated
product [11,12].
diffractometer equipped with Ni filtered CuK␣ radiation
(␭ = 1.5418 A).
˚
The present work deals with alkylation of phenol with tert-
butanol using zirconia-supported 12-molybdophosphoric acid
as the catalysts. The reaction was carried out with an aim to
maximize phenol conversion together with the selectivity to 4-
tert-butyl phenol and 2,4-di-tert-butyl phenol. The influence of
MPA loading and catalyst calcination temperature on phenol
conversion and product selectivity is studied. The catalyst with
highest activity was used to study the effect of various reaction
parameters such as temperature, molar ratio, space velocity and
time-on-stream on phenol conversion and product selectivity.
31PMASNMRspectra(BrukerDSX-300spectrometer)were
recorded at 121.5 MHz with high power decoupling with a
Bruker 4 mm probe head. The spinning rate was 10 KHz and
the delay between two pulses was varied between 1 and 30 s to
ensure that complete relaxation of the 31P nuclei occurred. The
chemical shifts are given relative to external 85% H3PO4.
¨
The Bronsted and Lewis acidity of the catalyst 15 MZ cal-
cined at different temperatures are characterized by in situ FTIR
spectroscopy with chemisorbed pyridine. The pyridine adsorp-
tion studies were carried out in the DRIFT (diffuse reflectance
infrared Fourier transform) mode using a Shimadzu SSU 8000
instrument. A calcined powder sample in a sample holder was
placed in a specially designed cell. The samples were then heated
in situ from room temperature to 400 ◦C at a heating rate of
5 ◦C min−1 in a flowing stream (40 ml min−1) of pure N2. The
samples were kept at 400 ◦C for 3 h and then cooled to 100 ◦C
and then pyridine vapor (20 ␮l) was introduced under N2 flow
and the IR spectra were recorded at different temperatures up
to 400 ◦C. A resolution of 4 cm−1 was attained after averaging
over 500 scans for the IR spectra reported here.
2. Experimental
2.1. Materials
Zirconium oxychloride (ZrOCl2·8H2O) and ammonia (25%)
were procured from S.D. Fine Chemicals Ltd., Mum-
bai. Phenol, tert-butanol and methanol were obtained from
Merck (India) Ltd., Mumbai. 12-Molybdophosphoric acid
(H3PMo12O40·xH2O) was purchased from Aldrich. All the
chemicals were research grade and were used as received with-
out further purification.
2.4. Catalytic measurements
2.2. Catalyst preparation
The alkylation of phenol with tert-butanol was carried out
under atmospheric pressure using a fixed-bed down flow glass
reactor (30 cm length and 1.3 cm OD). The catalyst (2 g (1.5 ml),
30–40-mesh size) was loaded at the center of the reactor in such a
way that the catalyst bed was sandwiched between inert porce-
lain beads. The reactor was placed in a double-zone furnace
equipped with a thermocouple for sensing the reaction temper-
ature. The catalyst was activated at 500 ◦C for 5 h in a flow of
dry air and cooled to the reaction temperature in presence of dry
nitrogen before the reactions were conducted. The feed contain-
ing a mixture of phenol and tert-butanol of desired molar ratio
was introduced into the reactor with a fixed space velocity using
a syringe pump (Sage Instruments, Model 352, USA). Nitrogen
was used as a carrier gas with a flow rate of 35 ml/min. The prod-
ucts were collected in a cold trap and analyzed by Shimadzu 14B
gas chromatograph, equipped with a flame ionization detector
using SE-52 packed column. The products were identified by
GC-MS and by comparing with authentic samples. Conversion
is defined as the percentage of phenol converted into products.
The catalysts were prepared by suspending a known amount
of dried zirconium oxyhydroxide powder in a methanol solution
of MPA. Zirconium oxyhydroxide was prepared by hydrolysis
of 0.5 M zirconium oxychloride solution by the drop wise addi-
tion of aqueous NH3 (10 M) to a final pH of 10. The precipitate
was filtered and washed with ammonical water (pH 8) until free
from chloride ions by the silver nitrate test. The zirconium oxy-
hydroxide thus obtained was dried at 120 ◦C for 12 h, powdered
well and continued drying for another 12 h. Each time, 4 ml of
methanol per gram of solid support was used and the mixture
was stirred in a rotary evaporator for 8–10 h. After stirring, the
excess of methanol was removed at ca. 50 ◦C under vacuum.
The resulting solid materials were dried at 120 ◦C for 24 h and
ground well. A series of catalysts with different MPA loading
(5–25 wt.%) were prepared by changing the MPA concentra-
tion in methanol. The dried samples were then calcined in air at
700 ◦C. Samples with 15% MPA were calcined between 500 and
750 ◦C to understand the role of the calcination temperature on
the activity of the catalysts. The samples were heated at a rate
of 5 ◦C min−1 to the final temperature and held for 4 h under
static conditions, and cooled at a rate of 5 ◦C min−1 to room
temperature and stored in desiccator. The catalysts are repre-
sented by xMZ-T where x represents wt.%, M represents MPA,
Z represents zirconia and T denotes calcination temperature in
◦C.
3. Results and discussion
3.1. Characterization
3.1.1. X-ray diffraction
The XRD pattern of the catalysts with different MPA loading
calcined at 700 ◦C (Fig. 1A) shows that, the presence of MPA
strongly influences the crystallization of zirconium oxyhydrox-
ide into zirconia. Pure zirconia calcined at 700 ◦C is mainly
monoclinic with small amount of the tetragonal phase. For cata-
lysts with low MPA loading calcined at 700 ◦C, the XRD pattern
can be described as the sum of the monoclinic and tetragonal
2.3. Characterization
X-ray diffraction (XRD) measurements of the cata-
lyst powder were recorded using a Rigaku Geigerflex

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B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
Fig. 1. X-ray diffraction patterns of: (A) catalysts with different MPA loading calcined at 700 ◦C (a) 0, (b) 5, (c) 10, (d) 15, (e) 20, (f) 25% and (B) 15 MZ catalyst
calcined at different temperature (a) 400, (b) 500, (c) 600, (d) 700, (e) 750 ◦C; T = tetragonal ZrO2, M = monoclinic ZrO2, I = MoO3, H = ZrMo2O8.
phases of zirconia, this latter phase becoming dominant for
catalyst with 15% MPA. This can be explained as the strong
interactionofMPAwiththesupportreducesthesurfacediffusion
of zirconia, inhibits sintering and stabilizes the tetragonal phase
of zirconia. It can also be seen that up to a 15% MPA loading, no
diffraction lines, which could be attributed to the polyacid or to
its decomposition products, are observed. The catalyst 20 MZ-
700 shows the presence of new diffraction lines characteristic of
MoO3 and for 25% catalyst formation of ZrMo2O8 is observed.
This indicated that, MPA decomposed to molybdenum oxide,
forming relatively large particles and also reacting with the sup-
port forms ZrMo2O8 [13].
As shown in Fig. 1B, 15% catalyst was amorphous, when it
was calcined below 400 ◦C and the crystalline nature of zirco-
nia increases with calcination temperature. As the calcination
temperature increases from 500 to 700 ◦C, zirconia crystallizes
to tetragonal phase and at 750 ◦C, the formation of monoclinic
phase is indicated. Thus, the added MPA stabilizes the tetrago-
nal phase of zirconia and such stabilization of tetragonal ZrO2
in presence of other heteropoly acid is reported earlier [6].
MPA calcined from 600 to 750 ◦C shows that the state of phos-
phorous in catalysts depend on MPA loading and calcination
temperature. The spectra of catalysts with different MPA load-
ing (5–25 MZ-700) are shown in Fig. 2A. For 5% MPA catalyst,
NMR shows a peak at −8.6 ppm assigned to the presence of
phosphomolybdate in interaction with zirconia [20,21]. The up
field shift compared to pure MPA may be due to the strong
interaction of MPA with zirconia [21]. However, when the MPA
loading increased to 10%, NMR show peaks at −3.5, −8.2 and
18 ppm respectively. The peak at −3.5 ppm is assigned to micro-
crystalline MPA, similar to unsupported MPA [21,22] and the
chemical shift at −8.2 ppm is due to MPA interacting strongly
with the surface of zirconia. The origin of the peak at 18 ppm
is not clear at present. For catalysts with 15% MPA loading
and above, an additional peak at −30 ppm is observed, which
is attributed to phosphorous oxide (P–O–P) resulting from the
decomposition of the polyoxometallate [23]. However, the cata-
lyst 15 MZ-700 gave the highest phenol conversion and the 31
P
CP/MAS NMR spectrum of this catalyst showed the peak at
−8.5 ppm due the presence of MPA strongly interacting with
surface of zirconia (Fig. 2C).
The 31P MAS NMR spectra of 15 MZ catalyst calcined form
500–750 ◦CareshowninFig. 2B. Atacalcinationtemperatureof
500 ◦C, NMR spectrum shows two peaks, one at −8 ppm and the
other at 17.2 ppm. As the calcination temperature is increased to
600 ◦C, NMR spectrum shows peaks at −3.5, −8.2 and 18 ppm,
similar to the NMR spectrum of the catalyst 10 MZ-700. The
catalyst 15 MZ-750 shows a sharp peak at −30 ppm.
3.1.2. 31P MAS NMR
This is one of the most important characterization techniques
to study the state of phosphorous in heteropoly acids. The chem-
ical shift depends upon the phosphorous environment, which in
turn depends upon factors like hydration number, addenda metal
ion, support, etc [14–18]. The bulk MPA shows a sharp intense
peak at −3.5 ppm in the 31P MAS NMR spectrum, due to the
uniform phosphorous environment in highly hydrated structure
of the MPA, while the small peak observed near to the main
peak at 6.3 ppm may be due to part of the sample containing
different degrees of hydration [19]. The 31P MAS NMR spec-
tra of catalysts with 5–25% MPA calcined at 700 ◦C and 15%
3.1.3. FTIR pyridine adsorption
The nature of acidic sites present in the catalyst 15 MZ-
700 measured by FTIR pyridine adsorption spectroscopy in
the temperature range 100–400 ◦C is shown in Fig. 3. The

B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
165
spectrum recorded at 100 ◦C show peaks at 1609, 1579, 1487
and 1443 cm−1 termed 8a, 8b, 19a and 19b, respectively [24,25].
Additionally, the spectrum shows two other peaks, one at 1637
and the other at 1535 cm−1. The peak at 1579 cm−1 is found
to be very labile and its stability on the surface is temperature
dependant. When the temperature is increased to 200 ◦C, this
peak almost disappears, confirming its labile nature and hence,
it is concluded that this species bound to the surface OH groups
via H-bonding. Pyridine molecules bonded to Lewis acid sites
absorbed at 1609 and 1443 cm−1 (ascribed to the 8a and 19b-
¨
ring mode of pyridine), while those responsible for Bronsted
acid sites (pyridinium ion) show absorbance at 1535 and at
1637 cm−1 [26]. The band at 1487 cm−1 (19a-ring mode of pyri-
dine) is a combined band originating from pyridine bonded to
¨
both Bronsted and Lewis acid sites.
¨
The Bronsted/Lewis (B/L) site ratio of 15 MZ catalyst cal-
cined at different temperatures (600, 700 and 750 ◦C) calcu-
lated from the IR absorbance intensities of bands at 1536 and
1442 cm−1 [27] are shown in Fig. 4. The results indicate that
¨
an increase of activation temperature decreases both Bronsted
¨
and Lewis acidity but an overall increase in Bronsted character
of the catalyst up to an activation temperature of 200 ◦C for 15
MZ-650 and 15 MZ-750 catalysts and up to 300 ◦C for 15 MZ-
¨
700 catalyst. This indicates the presence of stronger Bronsted
acid sites in 15 MZ-700 catalyst and this catalyst also possesses
¨
relatively higher Bronsted acidity.
3.2. Catalytic activity
The main products of the tert-butylation of phenol were
2-tert-butyl phenol (2-TBP), 4-tert-butyl phenol (4-TBP), 2,4-
di-tert-butyl phenol (2,4-DTBP) and tert-butyl phenyl ether
(TBPE). The products like 2,6-di-tert-butyl phenol and 2,4,6-
tri-tert-butyl phenol (TTBP) were formed in small amounts. C8
and C12 olefins, formed by the oligomerization of isobutene,
were also observed in the reaction, where isobutene is formed
by the acid catalyzed dehydration of tert-butanol. Scheme 1 rep-
resents the formation of different products during tert-butylation
of phenol.
Fig. 2. 31P MAS NMR spectra of: (A) catalysts with different MPA loading (a)
pure MPA, (b) 5, (c) 10, (d) 15, (e) 20, (f) 25% (where b–f calcined at 700 ◦C);
(B) 15 MZ catalyst calcined at different temperature (a) 500, (b) 600, (c) 700,
(d) 750 ◦C and (C) 31P CP/MAS NMR spectrum of 15 MZ catalyst calcined at
700 ◦C.
3.2.1. Effect of MPA loading
In order to investigate the effect of MPA loading, catalysts
with 5–25% MPA on zirconia calcined at 700 ◦C were used in
alkylation of phenol with tert-butanol at 120 ◦C with a space
velocity of 4 h−1 (Fig. 5). Out of the catalysts with different
MPA content, the 5% MPA catalyst showed the lowest phenol
conversion (41.9%), while the catalyst with 15% MPA gave the
highest conversion (64.6%). Further increase in MPA loading
decreases phenol conversion as for 25% catalyst it was 60.8%.
Theselectivitytodifferentalkylatedproductsalsodependson
the loading of MPA. The catalyst with 5% MPA shows the high-
est selectivity to TBPE. As the phenol conversion increased from
51.9% for 5% catalyst to 64.6% for 15% catalyst, the selectivity
to TBPE decreased from 10.3 to 1.6%. The 5% catalyst shows
2-TBP selectivity of 25% and 4-TBP selectivity of 21.1%. When
MPA content was increased to 10%, the selectivity to 2-TBP was
decreased to 20.2%, while selectivity to 4-TBP was similar to
Fig. 3. The IR spectra of pyridine adsorbed on 15 MZ-700 catalyst after in situ
activation at: (a) 100; (b) 200; (c) 300; (d) 400 ◦C.

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B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
Fig. 4. The change in Bro¨nsted acidity (ꢀ ) (B), Lewis acidity (᭹) (L) and B/L ratio (ꢁ) (I(B)/I(L)) with activation temperature for the catalysts: (A) 15 MZ-600,
(B) 15 MZ-700 and (C) 15 MZ-750.
that of 5% catalyst. The catalysts with higher MPA content gave
products with similar selectivity to 2-TBP and 4-TBP as that of
10% catalyst. The selectivity to 2,4-DTBP increased up to 15%
MPA loading (52.2%) and further increases in MPA loading
decreases its selectivity.
alyst calcined at 500 ◦C, shows 40% phenol conversion and it
increased to 64.6% at a calcination temperature of 700 ◦C. Fur-
therincreaseincalcinationtemperaturedecreasestheconversion
of phenol.
The selectivity to different alkylated products also varies with
calcination temperature as that observed in the case of cata-
lysts with different MPA loading. As the conversion increased
from 40% for the catalyst calcined at 500 ◦C to 64.6% for
the one calcined at 700 ◦C, the selectivity to TBPE decreased
from 12.5 to 1.6%, 2-TBP from 26.5 to 19% and 4-TBP
from 25.8 to 20.5%. However, the selectivity to 2,4-DTBP was
increased with calcination temperature up to 700 ◦C (52.2%)
and further increase in calcination temperature decreases its
selectivity.
3.2.2. Effect of calcination temperature
Thecatalystwith15%MPAcalcinedfrom500to750 ◦Cwere
used to study the change in catalytic activity with calcination
temperature (Fig. 6). From the figure it is clear that calcination
temperature has a profound effect on catalytic activity. The cat-
The acidity measurements of the catalysts by FTIR pyridine
adsorption shows that the catalyst 15 MZ-700 possess the high-
¨
est relative Bronsted acidity, which indicates that alkylation of
¨
phenol by tert-butanol is catalyzed by Bronsted acid sites present
in the supported-catalyst.
3.2.3. Effect of reaction temperature
The reaction was studied in the temperature range of
80–180 ◦C using 15 MZ-700 catalyst. The changes in the conver-
sion of phenol and selectivity to different products as a function
of temperature are shown in Fig. 7. At 80 ◦C, phenol conversion
was 21.3% and increased to 76.5% at 140 ◦C. An increase of
reaction temperature above 140 ◦C decreases the conversion of
phenol. The decrease in conversion of phenol could be due to
the dealkylation of tert-butyl phenol to phenol at high temper-
ature and also the diminishing availability of tert-butanol as it
undergoes oligomerization rather than alkylation [9].
At 80 ◦C TBPE obtained as the major product (53.5%) and
as phenol conversion increases, TBPE selectivity decreases and
it was completely absent at 140 ◦C. The decrease in TBPE
selectivity with temperature may be due to its rearrangement
Scheme 1. (A) tert-Butyl phenyl ether, (B) 2-tert-butyl phenol, (C) 4-tert-butyl
phenol and, (D) 2,4-di-tert-butyl phenol.

B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
167
Fig. 5. Effect of MPA loading on phenol conversion and product selectivity. Reaction conditions: temperature, 120 ◦C; tert-butanol/phenol molar ratio = 2;
LHSV = 4 h−1; time, 2 h.
to C-alkylated product. Indeed, it has been shown that such
rearrangement occurred on heating by contact with an acid cat-
alyst [6(c)]. The highest selectivity to 2-TBP was found to be at
100–120 ◦C (21%), while, selectivity to 2,4-DTBP (45%) was
highestat140 ◦C. Thehigherselectivityof2,4-DTBPatthistem-
perature may be due to the higher stability and the availability
of tert-butyl cation at this reaction temperature. The formation
of 4-TBP is favored at high temperature as it is the thermody-
namically stable product and hence an increase of temperature
always results in an increase of its selectivity.
3.2.4. Effect of molar ratio
The effect of molar ratio on phenol conversion and prod-
uct selectivity was studied at 120 ◦C with tert-butanol/phenol
molar ratio of 1–4 (Fig. 8). Generally, the phenol conversion
was increased with an increase in the amount of tert-butanol.
At a molar ratio of 1, phenol conversion was 58.1%, which
increased to 80.6% at a molar ratio of 3. A further increase
in molar ratio had no appreciable effect on phenol conversion.
It was shown that the polar molecule, such as methanol and
higher alcohols compete with phenol for adsorption sites and
Fig. 6. Effect of catalyst calcination temperature on phenol conversion and product selectivity. Reaction conditions: same as that in Fig. 5.

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B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
Fig. 7. Effect of reaction temperature on phenol conversion and product selectivity. Reaction conditions: tert-butanol/phenol molar ratio = 2; LHSV = 4 h−1; time,
2 h.
an increase in the molar excess of alkylating agent results in an
increase in phenol conversion as observed in the present study
[8(c)].
3.2.5. Effect of space velocity
The effect of space velocity was studied at 140 ◦C using tert-
butanol/phenolmolarratioof3fromLHSVof2to10 h−1 andthe
results are shown in Fig. 9. With an increase of space velocity
from 2 to 10 h−1, phenol conversion was changed from 82 to
62.4%. The decrease in conversion with an increase in space
velocity is due to the lower time available for the reactants to be
in contact with the active sites of the catalyst. With decrease in
the conversion of phenol, the selectivity to 2,4-DTBP decreased
from 60.5 to 44.6%. However, change in space velocity had no
appreciable effect on the selectivity of other products.
The formation of TBPE was observed in small amount under
these conditions. The selectivity to 2-TBP was low and it
decreased from 17.3 to 9.8% when the molar ratio increased
from 1 to 4. With an increase in molar ratio from 1 to 4 the
selectivity to 4-TBP decreased from 41.3 to 21.3%, while 2,4-
DTBP selectivity increased from 38 to 64.6%. This could be
due to the higher availability of tert-butanol, which leads to the
formation of the dialkylated product.
Fig. 8. Effect of molar ratio on phenol conversion and product selectivity. Reaction conditions: temperature, 120 ◦C; LHSV = 4 h−1; time, 2 h.

B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
169
Fig. 9. Effect of space velocity on phenol conversion and product selectivity. Reaction conditions: temperature, 140 ◦C; tert-butanol/phenol molar ratio = 3; time,
2 h.
3.2.6. Effect of time on stream
4-TBP 38.4%. However, the major drawback of MPA/ZrO2 cat-
alyst is its deactivation, which is in sharp contrast with the
catalytic behavior of zirconia-supported silicotungstic acid cat-
alyst, where the catalyst is found to be stable and regenerable
[6(c)]. The color of the product mixture obtained from 15 MZ-
700 catalyst was found to be dark blue and it indicated the major
reason for the catalyst deactivation is due to the reduction [28]
and leaching of MPA from the catalyst surface.
In order to study the deactivation behavior of the catalyst,
the reaction was studied at 140 ◦C with LHSV of 4 h−1 using
tert-butanol/phenol molar ratio of 3, for 31 h (Fig. 10). The
conversion of phenol was found to be 80.6% after 2 h with selec-
tivity to 2-TBP 11.5%, 2,4-DTBP 55.2%, and 4-TBP 25.7%,
and after 31 h, the conversion of phenol was decreased to be
58.5% with selectivity to 2-TBP 15.2%, 2,4-DTBP 41.6%, and
Fig. 10. Effect of time-on-stream (TOS) on phenol conversion and product selectivity. Reaction conditions: temperature, 140 ◦C; LHSV = 4 h−1; tert-butanol/phenol
molar ratio = 3.

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B.M. Devassy et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 162–170
(c) R.F. Parton, J.M. Jacobs, D.R. Huybrechts, P.A. Jacobs, Stud. Surf.
4. Conclusions
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zirconia-supported 12-molybdophosphoric acid (MPA) as the
catalysts in a continuous fixed-bed down flow reactor. The activ-
ity of the catalyst depends on both MPA loading and calcination
temperature and catalyst with 15% MPA on ZrO2 calcined at
700 ◦C was found to be the most active catalyst. The catalyst
shows good conversion and selectivity to alkylation under mild
conditions but deactivate with time due to reduction and leaching
ofMPAfromthecatalystsurface. ThedeactivationofMPA/ZrO2
catalyst by leaching of MPA from the catalyst surface restricts
the use of this catalyst in presence of highly polar reactants.
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This work was carried under DST-SERC project. BMD
acknowledges CSIR New Delhi for the award of research asso-
ciateship.
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