Bifunctional transalkylation and hydrodeoxygenation of anisole over a Pt/HBeta catalyst

Article abstract of DOI:10.1016/j.jcat.2011.03.030

The catalytic conversion of anisole (methoxybenzene), a phenolic model compound representing a thermal conversion product of biomass lignin, to gasoline-range molecules has been investigated over a bifunctional Pt/HBeta catalyst at 400 °C and atmospheric pressure. The product distribution obtained on the bifunctional catalyst was compared with those obtained on monofunctional catalysts (HBeta and Pt/SiO₂). This comparison indicates that the acidic function (HBeta) catalyzes the methyl transfer reaction (transalkylation) from methoxyl to the phenolic ring, yielding phenol, cresols, and xylenols as the major products. The metal function catalyzes demethylation, hydrodeoxygenation, and hydrogenation in sequence, resulting in phenol, benzene, and cyclohexane. On the bifunctional catalyst, both methyl transfer and hydrodeoxygenation are achieved at significantly higher rates than over the monofunctional catalysts, leading to the formation of benzene, toluene, and xylenes with lower hydrogen consumption and a significant reduction in carbon losses, in comparison with the metal function alone. In addition, on the bifunctional Pt/HBeta, the rate of deactivation and coke deposition are moderately reduced.

Full text of DOI:10.1016/j.jcat.2011.03.030

Journal of Catalysis 281 (2011) 21–29
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Bifunctional transalkylation and hydrodeoxygenation of anisole over a
Pt/HBeta catalyst
⇑
Xinli Zhu, Lance L. Lobban, Richard G. Mallinson, Daniel E. Resasco
Center for Biomass Refining, School of Chemical, Biological, and Materials Engineering, The University of Oklahoma, Norman, OK 73019, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The catalytic conversion of anisole (methoxybenzene), a phenolic model compound representing a ther-
mal conversion product of biomass lignin, to gasoline-range molecules has been investigated over a
bifunctional Pt/HBeta catalyst at 400 °C and atmospheric pressure. The product distribution obtained
on the bifunctional catalyst was compared with those obtained on monofunctional catalysts (HBeta
and Pt/SiO2). This comparison indicates that the acidic function (HBeta) catalyzes the methyl transfer
reaction (transalkylation) from methoxyl to the phenolic ring, yielding phenol, cresols, and xylenols as
the major products. The metal function catalyzes demethylation, hydrodeoxygenation, and hydrogena-
tion in sequence, resulting in phenol, benzene, and cyclohexane. On the bifunctional catalyst, both methyl
transfer and hydrodeoxygenation are achieved at significantly higher rates than over the monofunctional
catalysts, leading to the formation of benzene, toluene, and xylenes with lower hydrogen consumption
and a significant reduction in carbon losses, in comparison with the metal function alone. In addition,
on the bifunctional Pt/HBeta, the rate of deactivation and coke deposition are moderately reduced.
Ó 2011 Elsevier Inc. All rights reserved.
Received 1 December 2010
Revised 20 March 2011
Accepted 30 March 2011
Available online 19 May 2011
Keywords:
Bifunctional hydrodeoxygenation
Phenolic compound
Pt/HBeta
Anisole
Lignin
Hydrogenation
Hydrogenolysis
1. Introduction
catalysts can effectively reduce the oxygen content of phenolics
in the bio-oil [6–21]. However, this type of processing results in
Production of liquid hydrocarbon fuels from abundant lignocel-
lulosic biomass is being considered as a sustainable energy process.
Upgrading bio-oil derived from biomass via fast pyrolysis into
transportation fuels is an important step to accomplish this pro-
cess. Lignin is a biopolymer formed from three main monomers:
coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. In contrast
to cellulose and hemicellulose, from which thermal processing
produces high concentrations of relatively small oxygenates, lignin
breaks down the polymer leading to high concentrations of pheno-
lic molecules (phenol, guaiacol, syringol and their derivatives, see
Scheme 1). Therefore, phenolic compounds represent a significant
fraction of the biomass pyrolysis bio-oil [1–4] and remain a chal-
lenge for upgrading [3]. While building up the carbon chain is nec-
essary for small oxygenates conversion, most phenolics are already
in the gasoline range, but they require a deoxygenation process
that should preserve the carbon number within the range of gaso-
line. As previously proposed [5], model compound studies are of
crucial importance to establish the conditions for conversion of
phenolic-rich streams.
a significant loss of liquid yield, requires high hydrogen consump-
tion, and produces a sulfur containing stream. Zeolite upgrading
(including hydrocracking) is operated at atmospheric pressure
and high temperatures (300–600 °C) with lower hydrogen con-
sumption [22–28]. Though zeolites are effective in conversion of
small oxygenates (such as aldehydes and ketones) through acid
catalyzed reactions [22,29–31], their capability for deoxygenation
of phenolics is limited [23–28]. Increasing attention has been paid
to low temperature (<200 °C) and high pressure (3–5 MPa) hydro-
genation processes [32–36]. Full hydrogenation of the phenolic
ring over metal sites followed by dehydration and re-hydrogena-
tion yields aliphatic hydrocarbons. It is evident that the hydrogen
consumption is high in this process and the products are not as
valuable for gasoline blending. Minimizing carbon loss and also
hydrogen consumption (i.e. improving hydrogen efficiency [37])
are important parameters for the incorporation of biomass-derived
liquids in refineries. Therefore, while the addition of aromatics to
the gasoline and diesel fuel pools will still be limited by technical
and legislative caps, production of aromatics from the lignin frac-
tion of biomass is probably the most economically favorable pro-
cess. Also, aromatics are important building blocks in
petrochemical industry, and replacing their source from fossil to
renewable sources is certainly advantageous.
Hydrotreating and zeolite upgrading are the two main ap-
proaches for bio-oil conversion, and have been and are being inten-
sively studied. High temperature (250–400 °C) and high pressure
(3–5 MPa) hydrotreating of bio-oil over sulfided CoMo or NiMo
As shown in Scheme 1, the hydroxyl (–OH) and methoxyl
(–OCH3) are the major functional groups of lignin derived
phenolics. In previous work, it has been shown that the methyl
⇑
Corresponding author. Fax: +1 405 325 5813.
E-mail address: resasco@ou.edu (D.E. Resasco).
0021-9517/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2011.03.030

22
X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
OH
OH
OH
OH
OH
Phenols
CH
3
(CH )
3
2
Phenol
Cresols
Xylenols
Catechol
OCH
OCH
3
3
CH
3
Anisoles
Anisole
Methylanisoles
OH
OH
OH
OH
OH
OCH
OCH
OCH
OCH
OCH
3
3
3
3
3
Guaiacols
CH CH=CH
CH=CHCH
CH COCH
2 3
CHO
2
2
3
Guaiacol
Eugenol
Isoeugenol 4-Acetonylguaiacol Vanillin
OH
OH
H CO
3
OCH H CO
OCH
3
3
3
Syringols
CH CH=CH
2
2
Syringol
4-Allylsyringol
Scheme 1. Structure of phenolic compounds.
in the methoxyl of phenolics could be transferred to the aromatic
ring through acid catalyzed transalkylation reactions over HZSM-
5; while the hydroxyl appears to be inert under the same reaction
conditions [28]. In this work, high temperature and low (atmo-
spheric) pressure operation for deoxygenation of phenolics over a
bifunctional metal/zeolite catalyst are demonstrated. Moreover,
this deoxygenation is accomplished with low carbon loss in the
form of methane and low hydrogen consumption by phenolic ring
hydrogenation. Anisole (methoxybenzene) has been chosen as a
model compound of phenolics because (1) anisole contains an iso-
lated methoxyl, one of the major functional groups of the lignin
phenolics; (2) the analysis of product distribution is relatively sim-
ple, i.e., after removal of the methyl from the methoxy group, the
hydroxyl group remains in the original molecule, while the source
of any methyl transferred to another molecule can be accounted
for; and (3) anisole is liquid at room temperature, no solvent is
needed for feeding, and thus, the influence of solvent on both reac-
tion and analysis is avoided. A well-known alkane isomerization
catalyst, Pt/HBeta, has been chosen as a bifunctional catalyst to
test, with the acid sites of HBeta catalyzing the alkyl transfer reac-
tion [28] and Pt catalyzing the deoxygenation reaction. Anisole
conversion over HBeta (acid zeolite function) and Pt/SiO2 (metal
function) is included for comparison.
The morphology of HBeta zeolite was studied by scanning elec-
tronic microscopy (SEM) on a Jeol JSM-880 electron microscope,
equipped with energy dispersive X-ray analysis. Powder X-ray dif-
fraction (XRD) patterns of the catalyst samples were obtained on a
Bruker D8 Discover diffractometer. The acid density of the HBeta
zeolite was determined by temperature programmed desorption
(TPD) of isopropylamine (IPA) [38,39] following the procedure de-
scribed previously [30]. The dispersion of Pt was estimated by dy-
namic pulse CO adsorption. Catalyst samples were reduced at
300 °C by flowing H2 for 1 h, and the temperature was held at
300 °C for another 0.5 h in flowing He to desorb the adsorbed H2.
After the sample was cooled down to room temperature in He,
100 lL of 5% CO/He gas mixture was pulsed onto the sample until
saturation of the surface of the catalyst was reached. The CO con-
sumption was monitored by a thermal conductivity detector (TCD,
SRI 310C GC). A CO/Pt stoichiometry of 1/1 was used to estimate
the Pt dispersion. Transmission electron microscopy (TEM) images
were obtained on a Jeol 2010F field emission system operated at
200 kV. A finely ground catalyst powder, pre-reduced at 300 °C
for 1 h, was dispersed ultrasonically in ethanol and then deposited
on a carbon coated copper grid for TEM measurement. The num-
ber-weighted (dn) and the surface-weighted average particle size
P
P
(ds) were calculated using dn =
R
nidi/Rni and ds ¼ nid3= nid2,
i
i
respectively, where di is the particle size of ni. Approximately 200
particles from images of different places of each sample were
counted to calculate the dn and ds. The coke deposition was evalu-
ated by temperature programmed oxidation of spent samples
using 5% O2/He with a Cirrus mass spectrometer (MS, MKS) detec-
tor. The temperature was ramped from room temperature to
900 °C with a heating rate of 10 °C/min. The quantification of car-
bon deposits was done by using calibrated pulses of CO2 and CO.
2. Experimental
2.1. Catalyst preparation and characterization
The ammonium form of Beta zeolite (Zeolyst, CP814C, Si/
Al = 19, SBET = 710 m2/g) was calcined at 550 °C for 4 h to obtain
HBeta. Pt/HBeta and Pt/SiO2 catalysts were prepared by incipient
wetness impregnation of HBeta and SiO2 (HiSil 210, SBET
=
2.2. Catalytic performance
135 m2/g) with an aqueous solution of H2PtCl6ꢀ6H2O (Aldrich)
overnight and were then dried at 110 °C for 12 h, followed by
calcination at 400 °C for 4 h.
Catalytic conversion of anisole was investigated in a fixed-bed
quartz tube (6 mm o.d.) reactor at atmospheric pressure. The

X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
23
Table 1
catalyst sample (40–60 mesh) was reduced in flowing H2 at 300 °C
Pt particle sizes estimated from XRD, TEM, and CO chemisorption.
for 1 h, and then the temperature was raised to 400 °C for reaction.
The anisole was fed using a syringe pump (kd scientific) and vapor-
ized before entering the reactor. All lines were heated to avoid any
condensation. The H2/Anisole molar ratio was kept at 50 in all runs.
The products were quantified online in a gas chromatograph (GC
6890, Agilent), equipped with an Innowax capillary column
(60 m) and a flame ionized detector (FID). The effluent was trapped
by methanol in an ice-water bath and its components identified by
GC-MS (Shimadzu QP2010s). A standard sample was injected for
isomer identification.
Sample
XRD
TEM
CO chemisorption
a
dXRD (nm)
dn (nm)
ds (nm)
DCO (%)
dCO (nm)
1% Pt/SiO2
1% Pt/HBeta
0.2% Pt/HBeta
7.1
–
–
4.1
1.6
1.4
8.3
2.4
1.6
20
71
78
5.5
1.6
1.4
a
Pt particle size was estimated using dCO = 1.1/DCO, where DCO is the Pt disper-
sion measured from CO chemisorption.
To analyze the product evolution from differential to integral
reactor conditions, the W/F was varied from 0 to 4 h, varying both
catalyst amount (5–240 mg) and organic feed flow rate (0.03–
0.48 mL/h). The W/F is defined as the ratio of catalyst mass (g) to
organic feed flow rate (g/h). In a standard run with W/F of 0.5 h,
the H2 flow rate, anisole flow rate, and catalyst amount were
20 scm3/min, 0.12 mL/h, and 60 mg, respectively. To determine
whether the measurements were conducted in the absence of
internal mass transfer limitations, the conventional Weisz–Prater
criterion was employed. Similarly, to test for external mass transfer
limitations, runs at varying gas velocities were compared. A fresh
catalyst sample was used for each W/F, and the data with a time
on stream (TOS) of 0.5 h were used for each W/F. The conversion
and yield are reported in Molcarbon%. To test the effect of cofeeding
water on anisole conversion, deionized water was fed with a paral-
lel syringe pump keeping a H2O/Anisole mass ratio of 1/4.
The XRD patterns of the Pt/SiO2 sample (Fig. S2) revealed the
presence of FCC Pt, superimposed to a broad feature produced by
the amorphous structure of SiO2. The estimated Pt particle size
from the full width at half maxima, using the Sherrer equation,
was 7.1 nm. By contrast, no Pt diffraction peaks were observed
with the Pt/HBeta samples (Fig. S2), indicating a high dispersion
of Pt on HBeta zeolite, i.e., particle size <5 nm.
Representative TEM images of 1% Pt/SiO2 and 1% Pt/HBeta are
displayed in Fig. 1, which include Pt particle size distributions as
insets. Although most of the Pt particles in the Pt/SiO2 samples
had sizes in the range of 2–4 nm, larger particles up to 20 nm in
diameter were occasionally observed. A much narrower Pt particle
size distribution was obtained over 1% Pt/HBeta, with most of the
particles in the 1–2 nm range. The Pt particle size distribution was
even narrower for the Pt/HBeta of lower Pt loading (0.2 wt.%)
(Fig. S3). It is expected that Pt particles smaller than 1 nm may re-
side inside the zeolite micropores.
The Pt dispersions (CO/Pt) estimated from CO uptakes were 0.2,
0.7, and 0.8, for 1% Pt/SiO2, 1% Pt/HBeta, and 0.2% Pt/HBeta cata-
lysts, respectively. As shown in Table 1, the estimated Pt particle
sizes from these CO chemisorption values are in good agreement
with those estimated from XRD and TEM, confirming that signifi-
cantly higher Pt dispersion is achieved over zeolite Beta than over
SiO2. As anticipated, the sizes derived from CO chemisorption are
consistently smaller than those derived from TEM and XRD, since
the chemisorption values weight more heavily the smallest parti-
cles, which may not be easily detected by TEM or XRD.
3. Results and discussion
3.1. Catalyst characterization
SEM observations of the HBeta zeolite show well ordered and
uniform crystallites with a quasi-spherical shape, with sizes in
the 0.5–1 lm range (see Fig. S1A). EDX elemental analysis
(Fig. S1B) indicates that the Si/Al ratio is near 24. The characteristic
BEA structure was the only phase identified by the XRD pattern in
the Beta zeolite sample (Fig. S2). The IPA/TPD measured Brønsted
acid density of HBeta was 0.665 mmol/g, in good agreement with
the EDX measured Al content, but somewhat lower than that cal-
culated from the Si/Al ratio specified by the manufacturer (i.e.,
19, instead of the measured 24). Also, the good agreement between
the measured density of Brønsted sites and the total density of Al
ions indicates that most of the Al are forming Brønsted sites.
3.2. Anisole conversion over HBeta
The conversion of anisole was first studied over the acidic zeo-
lite. HBeta was chosen in this work for phenolics conversion, since
zeolite Beta has
a
three-dimensional 12-member ring pore
16
16
12
8
(A) (B)
12
8
4
4
0
0
0
4
8
12 16 20
0
4
8
12 16 20
Pt particle size (nm)
Pt particle size (nm)
Fig. 1. TEM images of (A) 1% Pt/SiO2 and (B) 1% Pt/Hbeta; insets: Pt particle size distribution. Both samples were reduced at 300 °C for 1 h, passivated, and brought to the TEM
minimizing exposure to ambient air.

24
X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
structure that is able to accommodate relatively large phenolic
compounds better than 10-number ring zeolites, such as ZSM-5.
As shown in Fig. 2, total conversion of anisole is achieved at W/F
of 0.33 h (Fig. 2A). At low W/F, the major products are phenol
(Ph) and methylanisole (MA), which are obtained in equal yields
(Fig. 2B), indicating that the first step of anisole conversion is a dis-
proportionation reaction. As we have previously indicated [28],
while this step is kinetically described as a bimolecular step, it does
not necessarily occur bimolecularly at the elementary step level. It
is possible that in the first step the methoxy group decomposes on
an acid site, while the methyl group is readily accepted by another
molecule in a subsequent step.
Increasing W/F leads to the consumption of MA and the produc-
tion of cresol isomers (Cr), xylenol isomers (Xol), and trimethyl-
phenol isomers (which is included in xylenols due to poor
separation). Similar to the behavior observed over HZSM-5 [28],
a number of transalkylation reactions (major paths), intramolecu-
lar rearrangements, and dealkylation reactions (minor paths) were
observed over the HBeta zeolite.
As shown in Fig. 2C, the minor products consisted of aliphatic
hydrocarbons (C1–9), aromatics (benzene, toluene, xylenes), dime-
thylanisole (DMA) isomers, and heavies (naphthalene, multiple
methylated benzenes). The low yields (<3%) of these minor prod-
ucts imply that the demethylation and deoxygenation reactions oc-
cur only to a limited extent. It must be noted that the yield of
dimethylanisoles is maximum at intermediate W/F, suggesting that
they are intermediates in the formation of xylenols. As summa-
rized in Fig. 2D, the main reaction catalyzed by the acidic function
is the methyl transfer from the methoxyl to the phenolic rings,
which include phenol, cresol, methylanisoles, finally forming the
major products of phenol, cresols, and xylenols.
3.3. Anisole conversion over Pt/SiO2
A Pt/SiO2 catalyst was employed to examine the behavior of the
metal function during anisole conversion. Even at the maximum
temperature and space time tested (400 °C, W/F = 4 h), the conver-
sion of anisole over the bare support was less than 2%, confirming
that SiO2 is inactive for this reaction. As shown in Fig. 3, total con-
version of anisole was achieved over Pt/SiO2 at a W/F of 1 h, while
complete deoxygenation was only obtained at a much higher W/F
(about 4 h). At low W/F, the rates of phenol (Ph) and methane (CH4)
production were very high, while those for other products were
nearly zero, indicating that, over Pt, demethylation of anisole is
the primary reaction. Contrary to the case on the acidic zeolites,
the decomposed methyl group does not remain on the surface
nor is it transferred to another molecule, but it is rapidly hydroge-
nated to form methane. Similar behavior has been observed in the
anisole conversion over CoMo and NiMo catalysts [7,9].
At intermediate W/F, the benzene (Ben) yield increases at the
expense of phenol, indicating the involvement of the direct hydro-
deoxygenation reaction. Further increase in W/F leads to the partial
hydrogenation of benzene to cyclohexane and further converted to
other aliphatic hydrocarbons. At this high temperature (400 °C),
the extent of aromatic hydrogenation is limited by equilibrium.
The major reaction pathway is summarized in Fig. 3C.
Two alternative pathways have been proposed in the literature
to describe the deoxygenation of phenolics: (1) direct hydrodeox-
ygenation forming aromatics and water; (2) hydrogenation of the
phenolic ring followed by dehydration forming a double bond in
the ring (cyclohexene derivative) and re-hydrogenation of the dou-
ble bond to cyclohexane derivatives [10]. The catalyst type and
reaction conditions play an important role on the reaction
100
(A)
(B)50
MA
Ph
40
80
60
40
20
0
Cr
Xol
30
20
15
10
10
0
5
0
0.00
0.04
0.08
0.0
0.1
0.2
0.3
0.4
0.5
0.0
0.1
0.2
0.3
0.4
0.5
W/F (h)
W/F (h)
OH
(C)
3.0
Hydrocarbons
Aromatics
(D)
OH
2.5
2.0
1.5
1.0
0.5
0.0
Dimethylanisoles
Heavies
OCH3
OH
OH
Acid site
Acid site
CH3
CH3
OCH3
CH3
H3C
0.0
0.1
0.2
0.3
0.4
0.5
W/F (h)
Fig. 2. Anisole conversion over HBeta: Effect of W/F on (A) anisole conversion; (B) major product distributions; (C) minor product distributions; and (D) major reaction
pathway. Reaction conditions: T = 400 °C, P = 1 atm, H2/Anisole = 50, TOS = 0.5 h for each W/F. The inset shows the distribution of products at very low W/F.

X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
25
100
80
60
40
20
0
(A)
CH4
C6-9
Ben
Tol
Ph
(B)70
60
50
40
30
20
10
0
20
10
0
0.0 0.1 0.2
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
W/F (h)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
W/F (h)
OCH3
OH
(C)
Pt
Pt
Pt
CH4
Fig. 3. Anisole conversion over 1% Pt/SiO2: Effect of W/F on (A) anisole conversion; (B) product distribution; and (C) major reaction pathway. Reaction conditions: T = 400 °C,
P = 1 atm, H2/Anisole = 50, TOS = 0.5 h for each W/F. The inset shows the distribution of products at very low W/F.
pathways [8,10,12–14,16,18,20]. For example, while on sulfided
NiMo catalyst hydrogenation followed by dehydration seems to
be the preferred path, direct hydrodeoxygenation has been
proposed to be the major path for a sulfided CoMo catalyst
[8,20]. Increased H2S partial pressures decrease the surface con-
centration of coordinative unsaturated sites and shifts the reaction
pathway to the hydrogenation/dehydration route [13,16,18].
Theproductdistributionobservedinthiswork forthePt/SiO2 cat-
alyst shows that the direct hydrodeoxygenation reaction is the dom-
inant reaction under our current operating conditions. However, one
cannot expect a direct hydrogenolysis of the Caromatic–OH bond. In
fact, theoretical calculations show that the bond strength of
aromatics have been completely converted. It is interesting to note
that almost no aromatics saturation was observed when full deox-
ygenation was achieved over Pt/HBeta catalysts. In contrast, in a
recent study of the conversion of phenol over Pt/HY catalyst [34],
mostly saturated rings were observed in the product. The differ-
ences in the results from that study with the current contribution
may be ascribed to their higher pressures and lower temperatures
(4 MPa and 200 °C), which are more conducive to ring saturation.
This is an interesting point for selecting a given process strategy;
since dehydrogenation/hydrogenation are significantly faster reac-
tions than deoxygenation, they are usually pseudo-equilibrated
and therefore the combination of appropriate temperature and
pressure conditions can be used to tailor the naphthenic/aromatic
ratio, depending on the desired product.
It is apparent that the simultaneous presence of the two cata-
lytic functions greatly enhances the deoxygenation. This enhance-
ment could be not only due to the independent contributions of the
Brønsted sites (methyl transfer reaction) and the metal sites
(hydrodeoxygenation), but also to a synergistic bifunctional path,
as discussed later.
Fig. 5 compares theyield ofthemajor products at thesame overall
conversion of anisole (ꢁ80%) over HBeta, Pt/HBeta, and Pt/SiO2. To
illustrate the influence of Pt in the acid-catalyzed alkyl transfer, the
deoxygenated products (Ben, Tol, Xy) are added together with their
corresponding oxygenates (Ph, Cr/MA, and Xol/DMA). Thus, the ef-
fect of deoxygenation on product distribution is eliminated for com-
parison purposes. A clear trend is obvious among the three catalysts.
At thesameanisoleconversion, theyield of C6 aromatics(Ben + Ph) is
highest over Pt/SiO2 and gradually decreases for Pt/HBeta and HBeta.
By contrast, no C7 or C8 aromatics are observed for Pt/SiO2, while they
are significant for Pt/HBeta and, more so, for HBeta. These results
clearly show that Pt alone only catalyzes demethylation, and it inter-
feres in the transalkylation process when it is simultaneously pres-
ent with the Brønsted sites responsible for this reaction. It is
apparent that some methyl groups left on the surface from the
demethylation of anisole are hydrogenated over Pt, yielding CH4 in-
stead of transalkylating to another aromatic. This conclusion is sup-
ported by the observed CH4 yields, which over Pt/HBeta are higher
than over HBeta, but significantly lower than over Pt/SiO2.
Caromatic–OH bond (e.g., phenol) is 84 kJ/mol higher than that of the
Caliphatic–OH (e.g., aliphatic alcohols) [6]. This significant difference
in bond strength is due to the delocalization of the out of plane lone
pair orbital of oxygen onto the
p orbital of the phenolic ring. In
addition, formation of a surface intermediate that would bind both
C and O to the surface would require a sp2–sp3 transformation that
is not favored if the aromatic ring remains intact. Thus, the apparent
direct hydrodeoxygenation may involve a partial hydrogenation of
the phenolic ring near the Caromatic–OH bond, resulting in the
temporary removal of the delocalization effect followed by rapid
dehydration. The result would be the formation of benzene and
water. A similar reaction pathway has been proposed for deoxygen-
ation of phenol on CoMo catalysts [19] and hydrogenation of cresol
on Rh catalysts [40].
3.4. Anisole conversion over Pt/HBeta
As shown in Fig. 4, complete conversion of anisole over Pt/HBe-
ta was achieved at a W/F of 0.1 h, which is 10 times shorter than
that required to reach the same conversion over Pt/SiO2. At low
conversions, the products obtained on Pt/HBeta are similar to those
observed with the HBeta catalyst, which include methylanisole
(MA), phenol (Ph), cresol isomers (Cr), xylenol isomers (Xol), and
dimethylanisole isomers (DMA). However, above a given conver-
sion level, these oxygenates start being converted into aromatic
hydrocarbons, benzene (Ben), toluene (Tol), xylene isomers (Xy),
and C9+ aromatics (Fig. 4C). At a W/F of about 0.3 h, the oxygenated

26
X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
35
100
80
60
40
20
0
(A)
(B)
20
10
0
30
25
20
15
10
5
0.00 0.02 0.04
MA
DMA
Ph
Cr
Xol
0
0.0
0.1
0.2
0.3
0.4
0.5
0.0
0.1
0.2
0.3
0.4
0.5
W/F (h)
W/F (h)
60
50
40
30
20
10
0
(C)
(D)
C1-2
C3
C4-9
OH
Pt
Ben
Tol
Xy
CH3
OCH3
OH
OH
Acid site
Pt
Pt
CH3
CH3
C9+
Acid sites
CH3
CH3
H3C
0.0
0.1
0.2
0.3
0.4
0.5
W/F (h)
Fig. 4. Anisole conversion over 1% Pt/HBeta: Effect of W/F on (A) anisole conversion; (B) oxygenate distributions; (C) hydrocarbon distributions; and (D) major reaction
pathway. Reaction conditions: T = 400 °C, P = 1 atm, H2/Anisole = 50, TOS = 0.5 h for each W/F. The inset shows the distribution of products at very low W/F.
Table 2
W/F for catalyst to achieve 30% total anisole conversion and 30% deoxygenation, and
turn over frequency (TOF) for deoxygenation.
Sample
W/F (h)
TOFb (sꢂ1
)
30% Conversion
30% Deoxygenationa
HBeta
1% Pt/SiO2
1% Pt/HBeta
0.027
0.079
0.008
0.90
0.12
0.104
0.330
a
Benzene, toluene, xylenes, and C9+ aromatics are considered as deoxygenation
products.
b
TOF is defined as moles of anisole conversion to deoxygenation products over
per mole surface Pt per second. The TOF is obtained from anisole conversion to
deoxygenation products less than 10% by adjusting W/F. The Pt dispersion esti-
mated from CO chemisorption was used for TOF.
C6 Aromatics
(Ph + Ben)
C7 Aromatics
(MA + Cr + Tol)
C8 Aromatics
(Xol + Xy + DMA)
Fig. 5. Yield of different C-number oxygenated and deoxygenated aromatics, at
similar anisole conversion (ꢁ80%) over the different catalysts. Open bar: HBeta;
shaded bar: Pt/HBeta; solid bar: Pt/SiO2.
enhances the overall reaction rate. For example, it was shown in
the previous study that addition of water improves the overall
reaction rate by a factor of 2.5 due to the acceleration of O–CH3
bond cleavage via hydrolysis over Brønsted acid sites by H2O [28].
What is even more remarkable is that the rate of anisole con-
sumption on Pt/HBeta is even higher than on Pt/SiO2. However,
the evolution of methane is much lower on the former than on
the latter. This result indicates that the methyl groups that are pro-
duced by demethylation on Pt are effectively transferred to other
aromatics. This transfer does not occur on Pt alone (see Fig. 5);
therefore, these should necessarily involve the participation of
the Brønsted sites in a synergistic phenomenon that can only occur
when Pt is in intimate contact with the Brønsted site.
An important result that requires further analysis is the en-
hanced conversion of anisole observed on the Pt/HBeta catalyst.
For instance, as shown in Table 2, to achieve a given anisole con-
version (e.g. 30%), the W/F required over Pt/HBeta (0.008 h) is only
a third of that required over HBeta (0.027 h). At this relatively low
conversion, most of the anisole consumed is involved in demethyl-
ation and transalkylation. The enhanced activity observed in the
presence of Pt indicates that the metal accelerates the cleavage
of the methoxy group (O–CH3) in anisole. As previously discussed
in our recent study on HZSM-5 [28], this is the first step in the reac-
tion and an enhancement in the rate of the O–CH3 bond breaking
At the same time, a synergistic effect is observed for deoxygen-
ation, which is a metal-catalyzed reaction. As shown in Table 2,

X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
27
achieving 30% deoxygenation of the oxygenated aromatics over Pt/
3.5. Stability test and coke analysis
SiO2 requires a W/F seven times greater than that required over the
Pt/HBeta catalyst having the same Pt loading. To further quantify
the difference in specific deoxygenation rates over the two cata-
lysts, the turn over frequency (TOF) was calculated using the data
obtained under differential reaction conditions with a deoxygen-
ation conversion lower than 10%. As shown in Table 2, the TOF over
Pt/HBeta was three times higher than that over Pt/SiO2, which sug-
gests that the zeolite environment plays an important role in
enhancing the deoxygenation activity of Pt.
Fig. 6 shows the stability tests of the HBeta, 1% Pt/HBeta, and 1%
Pt/SiO2 catalysts during the anisole conversion runs. The W/F was
adjusted to obtain a comparable initial conversion level over the
three different catalysts. A more rapid deactivation was observed
on HBeta than on either Pt/SiO2 or Pt/HBeta, indicating that Pt
plays a role in cleaning adjacent acid sites by hydrogenation of
coke precursors. Also, SiO2 being an inert support does not adsorb
coke precursors as strongly as the acidic zeolite [42].
One can speculate that a Brønsted acid site adjacent to a Pt par-
ticle could facilitate the deoxygenation reaction by protonating the
oxygen in phenol, which would inhibit the delocalization of the O
Deactivation of the catalyst with time on stream reduces the de-
gree of deoxygenation, even when the anisole conversion is still
100%. Fig. 7 shows the effect of reaction time on the distribution
of major products obtained over 1% Pt/HBeta at anisole conversions
significantly lower than 100%. In this case, it is seen that catalyst
deactivation causes the reduction in both hydrodeoxygenation
and transalkylation reactions, resulting in decreases in yields of
both deoxygenation products (Ben, Tol, Xy, and C9+ aromatics)
and transalkylation products (Ph, Cr, Xol) except MA, which in-
creases as catalyst deactivates, since MA is both a primary and
an intermediate product for transalkylation.
lone pair orbital with the aromatic
p orbital and thus would facil-
itate the Pt-catalyzed partial hydrogenation of aromatic ring at the
bond close to the Caromatic–OH. With this partial hydrogenation, the
electron delocalization is removed and water elimination can read-
ily happen over the adjacent Brønsted acid site. Due to the high
temperatures used in this study, the formation of aromatics is fa-
vored, so partially hydrogenated products are not observed.
In summary, addition of Pt to HBeta has a synergistic effect on
activity (Fig. 4D). In the first place, Pt accelerates the rate of alkyl
transfer from the methoxy group to the phenolic ring catalyzed
by Brønsted acid sites. At the same time, the Brønsted acid sites
adjacent to Pt accelerate the hydrodeoxygenation rate occurring
in a bifunctional reaction.
The Pt/HBeta catalyst exhibits a unique advantage for the con-
version of aromatics containing a methoxy group compared with
any other deoxygenation catalyst, in which carbon loss is unavoid-
able. That is, in the low temperature hydrolysis process catalyzed
by acid sites, the methyl of the methoxy group is eliminated as
methanol [32,33]; in the high temperature hydrotreating processes
over sulfided catalysts or the Pt/SiO2 catalyst studied here, carbon
is lost as CH4 [7,9,12,14,16,18,41]. In contrast, over the bifunctional
Pt/HBeta catalyst, most of methyl is transferred to the phenolic
ring and retained after deoxygenation, minimizing carbon loss.
Since alkylated aromatics are more attractive than benzene for
fuel applications, and to further limit the carbon losses, a Pt/HBeta
with reduced metallic function was tested. As shown in Table 3,
when a 0.2% Pt/HBeta catalyst was used, five times longer W/F
was needed to achieve full deoxygenation of anisole than over
the 1% Pt/HBeta. However, a noticeable increase in toluene, xy-
lenes, and C9+ aromatics at the expense of benzene was observed,
indicating a decreased loss of carbon as CH4. This result indicates
that adjusting the metal/acid balance, one could control product
distribution and improve liquid yield in the upgrading of bio-oils
containing phenolics.
It seems that deactivation affects hydrodeoxygenations more
strongly than transalkylation, as evidenced by the decrease in
100
Pt/HBeta (W/F=0.083 h)
HBeta (W/F=0.25 h)
Pt/SiO (W/F=0.5 h)
2
80
60
40
20
0
1
2
3
4
5
Time on stream (h)
Fig. 6. Effect of time on stream on anisole conversion over HBeta, 1% Pt/SiO2, and 1%
Pt/HBeta catalysts. Reaction conditions: T = 400 °C, P = 1 atm, H2/Anisole = 50. The
W/F was adjusted for each catalyst in order to achieve similar initial conversion.
35
30
25
20
15
10
5
35
30
25
20
15
10
5
MA
Ph
Cr
Ben
Tol
Xy
(A)
(B)
Xol
C9+
Table 3
Major product distributions for complete conversion of anisole over HBeta and
complete deoxygenation of anisole over Pt/SiO2 and Pt/HBeta catalysts.
Catalyst
HBeta
0.5
1% Pt/SiO2
4
1% Pt/HBeta
0.33
0.2% Pt/HBeta
1.5
W/F (h)
Major product yield (%)
Phenol
Cresols
Xylenols
C1–2
C3
C4–9
Benzene
Toluene
Xylenes
C9+ aromatics
39.5
33.5
24.2
0.2
0.2
0.2
0.1
0.1
0.3
0.3
0.2
0
0.1
0.2
0
6.0
0.4
1.6
51.2
27.6
10.6
1.7
0.7
0.6
0.3
4.2
0.7
1.5
40.2
31.8
14.4
3.4
0
0
0
15.4a
0
50 60 70 80 90 100
Anisole conversion (%)
50 60 70 80 90 100
Anisole conversion (%)
14.1
69.2
0.8
0
Fig. 7. Product yield as a function of overall anisole conversion over 1% Pt/HBeta.
Different conversions were achieved by catalyst deactivation (solid symbols) and by
varying W/F (open symbols). (A) Oxygenates and (B) aromatics. The reaction
conditions for deactivation were the same as Fig. 6; the data for the W/F series are
reproduced from Fig. 4, with anisole conversions lower than 100%.
0
a
CH4 is the only product for C1–2 aliphatic hydrocarbons.

28
X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
selectivity to deoxygenated aromatics as the catalyst deactivates
(Fig. 8). However, this difference is mostly due to the sequence of
reactions. Transalkylation steps are involved in the primary
reactions, while all hydrodeoxygenation steps occur in secondary
reactions. Therefore, as the overall conversion drops, the latter
are more affected. As a result, a decrease in selectivity to deoxy-
genated aromatics is clearly observed as the catalyst deactivates
(Fig. 8). Therefore, when comparing two different catalysts, the
comparison must be made at the same level of anisole conversion.
For instance, it is seen that, at the same overall conversion, the
selectivity to deoxygenation is much higher over Pt/HBeta than
over Pt/SiO2, confirming that Pt/HBeta is more effective for
hydrodeoxygenation.
It is interesting to note that when changing conversion level
over Pt/HBeta by either catalyst deactivation or by varying W/F
(Fig. 7), the yields of all the major products fall near the same trend
line when they are plotted as a function of anisole conversion, indi-
cating that deactivation only reduces numbers of active sites with-
out altering the chemistry. A type of deactivation that would show
this behavior is pore blocking. This behavior is in line with a uni-
form distribution of Pt throughout the HBeta zeolite; otherwise,
the metal/acid balance would be altered when pore blockage
occurs.
HBeta
x2
Pt/HBeta
Pt/SiO
2
0
200
400
600
oC)
800
Temperature (
Fig. 9. Temperature programmed oxidation profiles of spent catalysts after 5 h on
stream. Reaction conditions were the same as those in Fig. 6 for each catalyst.
Table 4
Coke formation over HBeta, 1% Pt/HBeta, 1% Pt/SiO2 after 5 h reaction.a
Catalyst
Coke formation
gcarbon/gcatalyst (%)
gcarbon/gconverted
(%)
anisole
Quantification of the carbon deposited during anisole conver-
sion was accomplished by TPO of the spent catalysts. As shown
in Fig. 9, a broad CO2 evolution peak centered at 636 °C was ob-
served for the HBeta catalyst. In contrast, two smaller peaks cen-
tered at 183 and 522 °C were observed over Pt/SiO2. Addition of
Pt to HBeta resulted in shift and a reduction in size of the intense
peak observed for HBeta resulting in three peaks at around to 332,
507, and 569 °C. These shifts could be due to the presence of Pt that
catalyzes the oxidation of coke, lowering the oxidation tempera-
ture significantly. The percentage of coke formed over Pt/HBeta
was slightly reduced compared with that over the HBeta, but
was significantly higher than that over Pt/SiO2 (Table 4), suggest-
ing that the extent of coke deposition is not only dependent on
the presence or absence of Pt, but also on the acidity and pore
structure of the support. However, when the amount of coke
deposited was compared on the basis of converted anisole
(Table 4), the ratios obtained over Pt/SiO2 and Pt/HBeta were com-
parable, but significantly lower than the one over HBeta. In addi-
tion to the expected conclusion that Pt improves the coke
tolerance, these results generate another interesting implication.
That is, the products of anisole conversion (e.g. phenol, cresol)
may be responsible for deactivation.
HBeta
Pt/HBeta
Pt/SiO2
12.0
10.2
1.6
13.4
3.2
3.0
a
Reaction conditions were the same in Fig. 6 for each catalyst.
As in most studies dealing with upgrading of phenolics, deacti-
vation is a crucial effect. Future commercial applications of lignin
biomass conversion will require catalysts with improved resis-
tance to deactivation. Improved catalysts might involve special
preparations such as introducing mesopores inside the zeolite
crystallite [30], improving metal dispersion through anchoring,
adding effective promoters, optimizing the metal/acid balance in-
side the zeolite micropores. Alternatively, or in parallel, reactor
engineering may also be needed to implement continuous catalyst
regeneration.
The effect of water addition on anisole conversion was briefly
studied since significant amounts of water are always present in
bio-oil. These experiments were carried out under the same condi-
tions as those shown in Fig. 6, except that between 2 and 3.5 h on
stream, H2O was fed to the reactor (Fig. 10). Remarkably, the addi-
tion of water caused an immediate enhancement in anisole conver-
sion. It is believed that the addition of H2O helps hydrolyzing the
O–CH3 bond of the methoxy group in anisole [28]. The observed
improvement is more pronounced over the zeolite-based catalysts
than over Pt/SiO2, implying that the acid site may be more effective
in catalyzing hydrolysis than Pt alone.
When the flow of water was interrupted after 3.5 h, the anisole
conversion over HBeta dropped immediately to the level observed
in the absence of water (Fig. 6). This behavior is similar to that pre-
viously observed for anisole conversion over HZSM-5 [28] and con-
firms that addition of water only enhances the anisole conversion
rate, without affecting the rate of coke formation. In contrast, on
the supported Pt catalysts, anisole conversion dropped much more
slowly to the level of the dry run (Fig. 6), and it remained some-
what higher than in the dry run, even after 5 h. These results would
indicate that, in the presence of Pt, water may help clean the sur-
face to some extent.
30
Pt/HBeta
25
20
15
Catalyst
Deactivation
Pt/SiO2
10
50
60
70
80
90
Anisole conversion (%)
It was also observed that the presence of water had only a small
effect on the distribution of the major products as a function of ani-
sole conversion. To make a direct comparison, the results of the
water-containing runs have been included in Fig. 8 together with
Fig. 8. Effect of deactivation on selectivity to deoxygenation during anisole
conversion over 1% Pt/HBeta and 1% Pt/SiO2. The reaction conditions were the
same as those in Fig. 6. Solid symbol, without water; open symbol, with water (H2O/
An molar ratio = 1.5).

X. Zhu et al. / Journal of Catalysis 281 (2011) 21–29
29
Oklahoma Bioenergy Center is greatly appreciated. The authors
thank Gregory W. Strout and Preston Larson for their help with
TEM and SEM measurements, respectively.
100
80
60
40
20
0
H2O on
H2O off
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jcat.2011.03.030.
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Financial support from the National Science Foundation EPSCOR
(0814361), the Department of Energy (DE-FG36GO88064), and the