Methylation of cyclopentadiene on solid base catalysts with different surface acid-base properties

Article abstract of DOI:10.1016/j.jcat.2010.08.008

The methylation of cyclopentadiene with methanol has been studied over Al₂O₃ and KOH promoted MgO and unpromoted MgO. The dehydrogenation of methanol to formaldehyde was found to be a key-step in the generation of the active methylating species on these solid bases. The modification with Al₂O₃ or KOH favors the formation of methylcyclopentadienes and elevates the activity of MgO based on different reasons: introduction of acidic sites for Al₂O₃/MgO and superbasic effect for KOH/MgO. These catalysts present different deactivation behaviors due to the different surface acid-base properties. The heavy coking of cyclopentadiene on basic sites is responsible for the rapid deactivation of KOH/MgO along the catalytic test at 773 K. However, the coking can be well suppressed at 723 K, and KOH/MgO exhibits the catalytic performance apparently superior to MgO and Al₂O₃/MgO.

Full text of DOI:10.1016/j.jcat.2010.08.008

Journal of Catalysis 275 (2010) 257–269
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Methylation of cyclopentadiene on solid base catalysts with different surface
acid–base properties
⇑
Dongxue Lan, Li Ma, Yuan Chun , Chen Wu, Linbing Sun, Jianhua Zhu
Key Laboratory of Mesoscopic Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The methylation of cyclopentadiene with methanol has been studied over Al2O3 and KOH promoted MgO
and unpromoted MgO. The dehydrogenation of methanol to formaldehyde was found to be a key-step in
the generation of the active methylating species on these solid bases. The modification with Al2O3 or KOH
favors the formation of methylcyclopentadienes and elevates the activity of MgO based on different rea-
sons: introduction of acidic sites for Al2O3/MgO and superbasic effect for KOH/MgO. These catalysts pres-
ent different deactivation behaviors due to the different surface acid–base properties. The heavy coking of
cyclopentadiene on basic sites is responsible for the rapid deactivation of KOH/MgO along the catalytic
test at 773 K. However, the coking can be well suppressed at 723 K, and KOH/MgO exhibits the catalytic
performance apparently superior to MgO and Al2O3/MgO.
Received 21 June 2010
Revised 9 August 2010
Accepted 12 August 2010
Available online 16 September 2010
Keywords:
Cyclopentadiene
Methylation
Solid base
Ó 2010 Elsevier Inc. All rights reserved.
Magnesium oxide
Potassium hydroxide
Alumina
Reaction mechanism
Deactivation
Methanol
Formaldehyde
1. Introduction
procedure. It has been used for producing commercial MCPD [4].
However, this process concerns the expensive reactants, such as
The gasoline with high quality is extremely demanded with the
development of transportation vehicles manufacturing and stricter
regulations on environmental protection. The leaded antiknock
additive, which used to be an important component in gasoline,
should be replaced by unleaded antiknock additive. Methylcyclo-
pentadienyl manganese tricarbonyl (MMT), as one of the alternate
antiknock additives, has the advantage of low cost, improving the
octane number and combustion efficiency of gasoline as well as
reducing emission pollution [1]. As the precursor of MMT, methyl-
cyclopentadienes (MCPD) can be formed from the petroleum
cracking, however, the yield is quite limited. Contrarily, cyclo-
pentadiene (CPD) is a more abundant product, and thus many
researchers have endeavored to produce MCPD from the methyla-
tion of CPD.
metal sodium and methyl halides (usually methyl iodide), and
must be carried out in liquid ammonia in order to disperse and
stabilize sodium. Some researchers attempt to prepare alkylcyclo-
pentadiene with alcohol in the presence of a liquid strong basic
catalyst such as potassium or sodium hydroxide or alkoxide [5].
It should be noted that this reaction is still carried out in liquid-
phase and only a tarry product can be obtained when methanol
is involved. Yoshida et al. [6] report a vapor-phase reaction of
CPD with an aliphatic lower alcohol in the presence of a catalyst
containing oxides such as an alkaline earth metal oxide or alkali
metal oxide. They also utilize the basic zeolites in this process
but mainly for producing the multi-alkylated CPD derivatives [7].
Compared with liquid base, the use of solid base has apparent
advantages in many aspects, e.g. noncorrosive and environmen-
tally benign. The replacement of liquid-phase catalysis with
vapor-phase catalysis allows easier separation of the products as
well as the possibility of catalysts regeneration and reuse. There-
fore, the vapor-phase methylation of CPD is a very attractive route
to prepare MCPD.
In the earlier studies, the methylation of CPD is realized through
the following procedure: CPD reacts first with alkali metal sodium,
and the formed cyclopentadienyl sodium then reacts with methyl
halides to produce MCPD [2,3]. This method has the advantages
of high yield (76–85%) and relative simple post-treatment
Although the catalysts concerned in the patent [6] cover most of
the conventional oxide or mixed oxide solid bases, little work has
focused on the reaction process. In the previous work, we found
⇑
Corresponding author. Fax: +86 25 83317761.
E-mail address: ychun@nju.edu.cn (Y. Chun).
0021-9517/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2010.08.008

258
D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
that the base strength of catalysts plays a key role in vapor-phase
methylation of CPD with methanol [8,9]. In the present work, we
have investigated the catalytic behaviors and the deactivation of
unpromoted, KOH and Al2O3 promoted magnesium oxides in the
vapor-phase methylation of CPD with methanol. Our aim is to cor-
relate the catalytic performance in CPD methylation with the nat-
ure of catalysts and explore the possible reaction and deactivation
mechanisms.
and a delay time d1 = 5.0 s. The sample was spun in a 7-mm zircon
rotor at 6 kHz and 4200 scans. Adamantane was used as external
reference for the chemical shift.
2.3. Catalytic testing
The catalytic decomposition of isopropanol or methanol was
measured in a conventional flow reactor at atmospheric pressure.
The sample (50 mg, 20–40 mesh) was activated at 873 K in the
flow of N2 (30 mL/min) for 1 h and then was cooled to the reaction
temperature. The reactant isopropanol (Nanjing Chemical Reagent,
China, P99.7%) or methanol (Nanjing Chemical Reagent, China,
P99.7%) was introduced using a syringe pump with the space
velocity of 1.9 or 0.9 hꢀ1 in the flow of N2 (20 mL/min). The reac-
tion mixture was analyzed by on-line gas chromatography, using
a Varian 3700 instrument equipped with a flame ionization detec-
tor (FID) and a Propark-T column or a thermal conductivity detec-
tor and a TDX-01 column. Conversion was defined as Ci = (moles of
substrate reacted per mole of reactant in the feed); yields of H2,
dimethylether (DME) and other product i were defined as YH2 = (-
moles of product H2 formed per 2 moles of reactant in the feed),
YDME = (moles of product DME formed per 0.5 moles of reactant
in the feed), Yi = (moles of product i formed per mole of reactant
in the feed), respectively; selectivity was defined as Si = (moles of
product i formed per mole of reactant reacted).
The vapor-phase methylation of CPD with methanol was carried
out in a conventional flow reactor at atmospheric pressure [11].
The catalyst (50 mg, 20–40 mesh) was thermally activated at
873 K for 1 h in N2 and then was cooled to the reaction tempera-
ture. CPD was obtained by thermal depolymerization of dicyclo-
pentadiene (Aldrich) at 873 K, and the reactants CPD and
methanol (Nanjing Chemical Reagent, China, P99.7%) were intro-
duced by syringe pumps with a molar ratio of 0.9 or 1.8 (space
velocity of 1.6 or 2.5 hꢀ1) in the flow of N2 (20 mL/min). The reac-
tion was carried out in two modes: (1) the reaction was performed
at various temperatures with the same reaction time of 10 min, in
order to study the effect of temperature on the catalytic activity
and (2) the reaction was performed at various times with the same
reaction temperature, in order to compare the deactivation rate on
different catalysts. The reaction mixture was analyzed by on-line
GC (Varian 3700). In situ poisoning experiments were carried out
by doping methanol with a certain amount of acetic acid or pyri-
dine, and were ended by repumping pure methanol for reaction.
In order to study the regeneration of the deactivated catalyst, the
catalyst after reaction was calcined at 873 K for 1 h in the flow of
air, and then cooled to the reaction temperature for further reac-
tion. The coking was observed on these catalysts at higher reaction
temperatures, and the coking amount varied with the difference in
catalysts, temperatures and even the time. In order to better com-
pare the activity of these catalysts in CPD methylation, the calcula-
tions of the conversion and product selectivity were irrespective of
the contribution of the coking. Thus conversion and selectivity in
this reaction were defined as Ci = (moles of substrate reacted per
mole of CPD in the feed except what was transformed to the coke
deposit) and Si = (moles of product i formed per mole of CPD re-
acted), respectively. Carbon balance measurement indicated that
this treatment has little effect on the calculated values of conver-
sions in the temperature range of 673–723 K; however, the calcu-
lated value is lower than that including the contribution of the
coking in the temperature range of 773–823 K, especially for
KOH/MgO at a lower reaction time. For example, when the reaction
was carried out at 773 K for 10 min on 10%KOH/MgO, 41% of
conversion was calculated irrespective of the contribution of the
coking, while 68% of conversion was obtained including the contri-
bution of the coking.
2. Experimental
2.1. Catalyst preparation
KOH and Al2O3 promoted MgO catalysts were prepared by
impregnation of potassium hydroxide and aluminum nitrate from
their aqueous solution, respectively. Typically, a calculated amount
of potassium hydroxide or aluminum nitrate was dissolved in
20 mL of distilled water, and then 2 g commercial MgO (Shanghai
Chemical Reagent, China, P97.0%) was added into this solution.
After stirring at room temperature for 24 h, the mixture was evap-
orated to remove most of the water in a water bath and then dried
at 373 K overnight. The resulting solid was further calcined at
873 K for 2 h to form KOH- or Al2O3-modified MgO. These prepared
solid bases were denoted as x%KOH/MgO and x%Al2O3/MgO,
respectively, where x% indicated the mass percentage of KOH or
Al2O3 in the whole catalysts. For comparison, pure Al2O3 was pre-
pared by calcining aluminum nitrate at 873 K for 2 h, and portions
of these prepared Al2O3 powders were mechanically mixed with
MgO powders according to the mass ratio of 10%Al2O3 in the whole
catalyst, which was denoted as 10%Al2O3/MgO(mix).
2.2. Catalyst characterization
X-ray diffraction (XRD) patterns of samples were recorded on a
Rigaku, D/max-RA diffractometer with Cu K
a radiation in the 2h
range from 10° to 80°. N2 adsorption at 77 K was measured using
a Micromeritics ASAP 2020 system. Sample was evacuated at
573 K for 4 h prior to testing. Specific surface area of MgO was
determined using the Brunauer–Emmett–Teller (BET) equation
with adsorption data in the relative pressure range from 0.04 to
0.2. The base strength (H–) of samples was determined using Ham-
mett indicators [10], and sample was activated at 873 K for 1 h in
the flow of N2 (30 mL/min) before contacting with the indicators.
Acidity of sample was determined by using temperature-pro-
grammed desorption (TPD) of NH3. Sample (100 mg) was treated
in He (50 ml/min) at 873 K for 1 h and 40 ml of NH3 was injected
at room temperature. Weakly adsorbed NH3 was removed by flow-
ing He at 30 ml/min for 1 h. Temperature was then increased to
873 K at 8 K/min, and the liberated NH3 was detected by an on-line
gas chromatograph with a thermal conductivity detector (TCD) and
quantitatively measured by the external standard method. CO2-
TPD measurements were performed in the manner similar to
NH3-TPD measurements, except that CO2 was injected instead of
NH3. Inductively coupled plasma-optical emission spectrometric
(ICP-OES) analysis was performed in JA1100 ICP instrument. X-
ray photoelectron spectra (XPS) were acquired from Thermo Fisher
scientific K-Alpha spectrometer using a nonmonochromatized Al
Ka X-ray source (1486.6 eV). Base pressure in the analysis chamber
was maintained in the range of 10ꢀ9 mbar. Energy resolution of the
spectrometer was set at 0.9 eV. The error in the reported binding
energy (BE) values is 0.1 eV. Solid-state 13C MAS nuclear magnetic
resonance (NMR) spectrum of spent catalyst was performed on a
Bruker advance III NMR spectrometer, operating at a frequency of
100.62 MHz for 13C. To obtain quantitative data, single pulse
excitements (SPEs) were used with a 90° pulse length p1 = 3.5 s

D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
Table 1
259
3. Results
Base strength of selected catalysts detected
by Hammett indicator.
3.1. The characterization of catalysts
Catalyst
Base strength (H–)
Commercial MgO was used for solid base catalyst, which pos-
sesses a BET-specific surface area of 163 m2/g. The surface acidity
and basicity of MgO were modified by introducing various
amounts of Al2O3 and KOH. Fig. 1 compares the XRD patterns of
these catalysts. In the case of the unpromoted MgO, reflections
corresponding to both periclase MgO [JCPDS database, entry file:
45-0496] and brucite Mg(OH)2 [JCPDS database, entry file:
07-0239] are present. The appearance of Mg(OH)2 derives from
the hydration of MgO during storage. After impregnation of KOH,
the catalysts were hydrated, and reflections attributed to periclase
MgO disappeared. In fact, the existence of KOH is unnecessary for
the hydration of MgO, Mg(OH)2 can also be formed by treating
MgO with pure water, as indicated in Fig. 1A. Nevertheless, the
XRD patterns of calcined samples correspond overwhelmingly to
periclase MgO, indicating that Mg(OH)2 can be completely con-
verted to MgO by the thermal decomposition. The existence of
peak at 32.3° with very weak intensity indicates that a small
amount of KOH was converted to K2CO3 with CO2 in the air
[12,13]. Similarly, the XRD patterns of Al(NO3)3/MgO (uncalcined)
and Al2O3/MgO (calcined) correspond to those of brucite Mg(OH)2
and periclase MgO, respectively, as shown in Fig. 1B. It should be
MgO
18.4
ꢁ26.5
26.5
26.5
17.2
1%KOH/MgO
5%KOH/MgO
10%KOH/MgO
10%Al2O3/MgO
10% Al2O3/MgO
MgO
10%KOH/MgO
300
400
500
600
700
800
900
Δ Mg(OH)2 + K2CO3
* MgO
A
Temperature (K)
*
10% KOH/MgO
*
Fig. 2. TPD profiles of CO2 on MgO, 10%Al2O3/MgO and 10%KOH/MgO. CO2
adsorption at 303 K, 8 K/min heating rate.
*
*
*
+
Δ
10% KOH/MgO-uncalcined
Δ
Δ
pointed out that no alumina phase can be distinguished from the
XRD patterns of these Al2O3/MgO samples. One possible reason is
that Al2O3 is well dispersed on the surfaces of MgO, which pos-
sesses relatively larger specific surface area.
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
MgO treated with H2O
Δ
Δ
Δ
Δ
Δ
Table 1 lists the base strength of selected catalysts. The unpro-
moted MgO shows a base strength (H–) of 18.4, similar to the re-
sult reported in [14]. The base strength (H–) of catalyst increases
from 18.4 to 26.5 after loading 5% of KOH, similar to our previous
result on KNO3-loaded MgO [8] and Al2O3 [15]. According to Tana-
be’s definition [16], these KOH/MgO catalysts possess superbasic
sites. Contrarily, loading 10% of Al2O3 results in the decrease of
base strength (H–) from 18.4 to 17.2.
*
*
MgO-regenerated
*
*
*
*
*
MgO
*
Δ
Δ
Δ
*
Δ
*
20
40
60
80
2θ (degree)
The TPD profiles of CO2 preadsorbed at room temperature on
selected catalysts are presented in Fig. 2. The TPD profile of CO2
on the unpromoted MgO can be deconvoluted in three desorption
peaks with the peak temperature around 390, 470 and 555 K,
which are attributed to bicarbonates formed on Brønsted OH
groups, bidentate carbonates desorbed from metal–oxygen pairs
and unidentate carbonates released from low coordination oxygen
anions, respectively [17]. Among them, the desorption peaks
around 470 and 555 K are dominant, indicating that its basicity de-
rives mainly from the metal–oxygen pair and low coordination
oxygen anion. Few Brønsted OH groups are present on this MgO
activated at 873 K. The relative contribution of peaks at 470 and
555 K decreases after loading of 10%Al2O3, demonstrating that
10%Al2O3/MgO has weaker basicity than the unpromoted MgO.
Contrarily, a new desorption peak around 665 K appeared on the
TPD profile of CO2 on 10%KOH/MgO, indicating that this catalyst
shows stronger basicity than MgO, in agreement with the result
determined using Hammett indicators.
Δ Mg(OH)2
*MgO
B
*
*
10% Al2O3/MgO
5% Al2O3/MgO
*
*
*
*
*
*
*
*
32%Al(NO3)3/MgO-uncalcined
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
*
*
Δ
MgO
Δ
*
*
20
40
60
80
2θ (degree)
Acidity of MgO, 10%KOH/MgO and 10%Al2O3/MgO was investi-
gated by TPD of NH3 preadsorbed at room temperature, and the re-
sult is presented in Fig. 3. The TPD profile of NH3 on MgO can be
Fig. 1. XRD patterns of MgO and MgO promoted with Al2O3 or KOH with various
loading amounts under different treatments.

260
D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
100
A
methanol conversion
H2 yield
CO yield
80
CH4 yield
10%Al2O3/MgO
CO2 yield
60
40
20
0
MgO
10%KOH/MgO
700
550
600
650
700
750
800
850
Temperature (K)
300
400
500
600
800
100
80
60
40
20
0
B
Temperature (K)
methanol conversion
H2 yield
Fig. 3. TPD profiles of NH3 on MgO, 10%Al2O3/MgO and 10%KOH/MgO. NH3
adsorption at 303 K, 8 K/min heating rate.
CO yield
CH4 yield
CO2 yield
Table 2
The catalytic performances in the decomposition of isopropanol and the contents of
carbon on catalysts before and after the methylation of CPD at 773 K for 300 min.
Catalyst
On clean surface (%)
On spent surface (%)
a
b
c
Yp
YA
YP
YA
CC
MgO
10%Al2O3/MgO
10%KOH/MgO
2
12
2
26
30
26
2
26
24
13
2.9
4.7
28
550
600
650
700
750
800
16
0.1
Temperature (K)
a
b
c
Yield of propylene.
Yield of acetone (T = 673 K, p = 101 kPa, space velocity = 1.9 hꢀ1).
Content of carbon determined by elemental analysis.
100
80
60
40
20
0
C
methanol conversion
H2 yield
CO yield
CH4 yield
deconvoluted in two desorption peaks, similar to the report in [17].
The lower temperature peak around 385 K may be attributed to the
reversible H-bond adsorption on Brønsted acidic sites, and the high-
er temperature peak around 570 K may result not only from the irre-
versible coordinated NH3 adsorption on Mg2+ cations but also from
the heterolytic dissociative adsorption leading to NH2ꢀ–H+ species
on Mg2+–O2ꢀ pairs [17,18]. The desorption amount of NH3 has an
apparent decrease after loading of 10%KOH, especially for those
preadsorbed on the Brønsted acidic sites. It indicates that the acidity
of 10%KOH/MgO is weaker than the unpromoted MgO. While the
desorption amount of NH3 has an apparent increase after loading
of 10%Al2O3, which mainly results from the contribution of the
Brønsted acidic sites on Al2O3 [17].
The acid–base properties of unpromoted MgO and MgO pro-
moted with KOH or Al2O3 were further investigated by the cata-
lytic decomposition of isopropanol, and the results are listed in
Table 2. It is well known that propylene and water are generated
on acidic sites, while acetone and hydrogen are formed on basic
sites in this probe reaction [11,19]. The conversion of isopropanol
and the selectivity to acetone on MgO at 773 K are 28% and 93%,
respectively. The high selectivity to acetone indicates that few
acidic sites exist on this solid base, similar to the report in [20].
After loading 10% of Al2O3, the conversion of isopropanol increases
but selectivity to acetone decreases. It indicates that 10%Al2O3/
MgO sample possesses more acidity compared with MgO, in agree-
ment with the result from TPD of NH3. The conversion of isopropa-
nol and the selectivity to acetone on 10%KOH/MgO are close to
those on unpromoted MgO. This result is surprising since it is well
known that KOH has much stronger basicity than MgO. One of the
possible reasons is that the dehydrogenation of isopropanol re-
quires weaker basicity [19], acetone is largely formed on the inter-
CO2 yield
DME yield
550
600
650
700
750
800
850
Temperature (K)
Fig. 4. Conversion of methanol, yields of H2, CO, CH4, CO2 and DME as functions of
temperature on (A) MgO, (B) 10%KOH/MgO and (C) 10%Al2O3/MgO (space veloc-
ity = 0.9 hꢀ1, p = 101 kPa).
mediate strong basic sites on this unpromoted MgO, and thus the
effect of KOH is not pronounced in this reaction. Another possible
reason is the formation of enolate under such strong basic condi-
tion, which may react with acetone and finally transform the oligo-
mer species over the catalyst surface. Therefore, actually the KOH/
MgO would be, intrinsically, more active, as expected, but the high-
er activity is quickly suppressed by these parallel reactions, with
the final effect to balance each other and to leave a final apparent
activity like MgO only.
3.2. Catalytic decomposition of methanol
The catalytic performances of MgO, 10%Al2O3/MgO and 10%KOH/
MgO in methanol decomposition are shown in Fig. 4, in which the
conversion of methanol and the yields of H2, CO, CH4, CO2 and even
DME are reported as functions of reaction temperature.

D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
261
It can be found that these solid base catalysts exhibit different
40
30
20
10
0
A
catalytic activities in methanol decomposition. The decomposition
of methanol starts at 623 K on unpromoted MgO; however, the
conversion of methanol is lower than 4% at 673 K. An appreciable
conversion can be observed at 723 K, which is similar to the re-
port in [21]. The conversion of methanol reaches 100% at 823 K
on this catalyst. Apparent increase in conversion is observed on
MgO modified with either Al2O3 or KOH. It can be found that
the conversions reach 95% and 100% at 773 K on 10%Al2O3/MgO
and 10%KOH/MgO, respectively, which are much higher than
61% on unpromoted MgO. The higher activity of 10%KOH/MgO
should be attributed to its stronger basicity compared with
MgO, which exhibits stronger dehydrogenating ability. While on
10%Al2O3/MgO, the formation of DME and its further transforma-
tion may have a certain contribution to the higher conversion of
methanol.
MgO
5% Al2O3 /MgO
10% Al2O3 /MgO
20% Al2O3 /MgO
50% Al2O3 /MgO
Al2O3
650
700
750
800
850
Temperature (K)
As shown in Fig. 4A and B, CO and H2 are the major products on
MgO and 10%KOH/MgO, and the yields of all products increase
with temperature. It is well known that H2 is obtained as a co-
product in the formation of C-containing compounds, and several
routes of the methanol transformations and the intermediates
decomposition have been reported to produce H2 [21]. The yield
of H2 approximately corresponds to the sum of yields of CO + 1/
2CH4 + 1/2CO2 at high temperature, indicating that the intermedi-
ates, i.e. formaldehyde, formic acid and methylformate, from meth-
anol transformation quickly decompose to the final products. It
should be pointed out that the selectivity to CO is over 88% among
the C-containing products under the conditions used for catalytic
tests, and the formation of CH4 is almost ignorable. This result
seems to suggest that most of the formaldehyde, which derives
from methanol dehydrogenation, directly decomposes to CO and
H2. Less formic acid and methylformate are formed on these cata-
lysts since the decomposition of these intermediates would pro-
duce CO2 and/or CH4 [21].
Due to the existence of a certain amount of the acidic sites,
dehydration of methanol also occurs on 10%Al2O3/MgO, and the
products DME may further transform to alkylbenzenes [21,22]. It
is reported that alkylaromatics are the prevailing compounds on
H-mordenite in the temperature range comprised between 523
and 623 K [21]. However, less alkylaromatics are formed on
10%Al2O3/MgO, since the acidity of this catalyst is apparently
weaker than that of acidic zeolites. As shown in Fig. 4C, DME is
the prevailing product on 10%Al2O3/MgO at 573 K. The yield of
CO dramatically increases with temperature, and CO becomes the
main product at a temperature higher than 623 K. Similar to the re-
sult on MgO and 10%KOH/MgO, the yield of H2 approximately cor-
responds to the sum of yields of CO + 1/2CH4 + 1/2CO2 at high
temperature on 10%Al2O3/MgO, and yield of CO is much higher
than those of CH4 and CO2. It indicates that the formation of the
light compounds undergoes a similar reaction process on these so-
lid base catalysts.
100
80
60
40
20
0
MgO
B
5% Al2O3/MgO
10% Al2 O3/MgO
20% Al 2 O3/MgO
50% Al 2 O3/MgO
Al2O3
650
700
750
800
850
Temperature (K)
100
80
60
40
20
0
C
MgO
5% Al2O3/MgO
10% Al2O3/MgO
20% Al2O3/MgO
50% Al2O3/MgO
Al2O3
650
700
750
800
850
Temperature (K)
Fig. 5. (A) Conversion of CPD, (B and C) selectivity to MCPD and DMCPD,
respectively, with methanol/CPD ratio of 1.8 (space velocity = 2.5 hꢀ1) as functions
of temperature on MgO promoted with various amounts of Al2O3 (p = 101 kPa).
3.3. Methylation of CPD with methanol
The catalytic performances of MgO and Al2O3 or KOH promoted
MgO in CPD methylation are shown in Figs. 5–7, in which the con-
version of CPD and the selectivity to MCPD and dimethylcyclopent-
adienes (DMCPD) are reported as functions of reaction temperature.
The target product of this reaction is MCPD, and by-products
consist mainly of DMCPD, accompanied with small amount of
hydrogenated products (i.e. cyclopentene, cyclopentane, methylcy-
clopentene, and dimethylcyclopentene). The sum of yields of these
hydrogenated products on these catalysts is lower than 1% in the
temperature range of 673–773 K and may reach 1–2% at 823 K.
Some light compounds, e.g. CO, CH4, CO2 and H2, can also be pro-
duced by the decomposition of methanol. The conversion of CPD
is only 1.4% at 673 K on the unpromoted MgO, as shown in
Fig. 5A. With the increase in reaction temperature, the conversion
of CPD increases and reaches 24% at 823 K. This unpromoted MgO
shows poor selectivity to MCPD and higher selectivity to DMCPD at
lower temperature, e.g. the selectivity to MCPD and DMCPD are
23% and 74%, respectively, at 673 K. Higher temperature favors
the formation of MCPD, and the selectivity to MCPD reaches 47%
at 823 K.
The catalytic performances on Al2O3 promoted MgO are shown
in Fig. 5, which are plotted as functions of reaction temperature.
Generally, the conversion curves on these solid bases present the
similar tendency to that on the unpromoted MgO. Modification

262
D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
60
40
20
0
50
A
MgO, M/C=0.9
MgO, M/C=1.8
10% Al2O3 /MgO, M/C=0.9
10% Al2O3 /MgO, M/C=1.8
10% KOH/MgO, M/C=0.9
10% KOH/MgO, M/C=1.8
A
MgO
1% KOH/MgO
5% KOH/MgO
10% KOH/MgO
20% KOH/MgO
40
30
20
10
0
650
700
750
800
850
650
700
750
800
850
Temperature (K)
Temperature (K)
100
80
60
40
20
0
100
B
B
MgO M/C=0.9
MgO M/C=1.8
10% Al2O3/MgO M/C=0.9
10% Al2O3/MgO M/C=1.8
10% KOH/MgO M/C=0.9
10% KOH/MgO M/C=1.8
MgO
80
60
40
20
0
1% KOH/MgO
5% KOH/MgO
10% KOH/MgO
20% KOH/MgO
650
700
750
800
850
Temperature (K)
650
700
750
800
850
Temperature (K)
100
80
60
40
20
0
C
Fig. 7. (A) Conversion of CPD and (B) selectivity to MCPD with methanol/CPD ratio
of 0.9 and 1.8 (space velocity was 1.6 and 2.5 hꢀ1, respectively) as functions of
temperature on unpromoted MgO, 10%Al2O3/MgO and 10%KOH/MgO (p = 101 kPa).
MgO
1% KOH/MgO
5% KOH/MgO
10% KOH/MgO
20% KOH/MgO
The highest conversion appears at 823 K on 1%KOH/MgO. How-
ever, when the loading amount of KOH reaches 5%, the conversion
of CPD declines at temperature higher than 773 K. Catalysts con-
taining 5–20%KOH exhibit the similar activity at the same reaction
condition and 80–90% of products are MCPD, while prevailing
product on the unpromoted MgO is DMCPD at a temperature lower
than 823 K. The existence of KOH greatly enhances the selectivity
to MCPD, i.e. suppresses the deep methylation of MCPD. These re-
sults seem to suggest that the methylation of CPD is dominated by
KOH species when its loading amount reaches 5%.
Fig. 7A and B shows the effect of the dosage ratio of methanol
and CPD on the catalytic performance of these solid bases. Higher
dosage of methanol favors the methylation of CPD, especially for
KOH promoted MgO. The conversion is doubled (e.g. from 16% to
34% at 773 K) on 10%KOH/MgO when the dosage ratio of methanol
and CPD increases from 0.9 to 1.8. On the other hand, lower dosage
of methanol favors the formation of MCPD. However, the effect of
the dosage ratio of methanol and CPD on selectivity is not as pro-
nounced as on conversion. The selectivity curves present a similar
tendency on each catalyst when different dosage ratios of the two
reactants are fed.
650
700
750
800
850
Temperature (K)
Fig. 6. (A) Conversion of CPD, (B and C) selectivity to MCPD and DMCPD,
respectively, with methanol/CPD ratio of 1.8 (space velocity = 2.5 hꢀ1) as functions
of temperature on MgO promoted with various amounts of KOH (p = 101 kPa).
with Al2O3 can enhance the conversion at lower temperature, how-
ever, the conversion decreases apparently when loading amount
exceeds 20%, as indicated in Fig. 5A. On the other hand, the selec-
tivity to MCPD almost linearly increases and the selectivity to
DMCPD decreases accordingly, when the loading amount of Al2O3
increases from 5% to 20% (Fig. 5B and C). It is reasonable to suggest
that the introduction of Al2O3 can suppress the deep methylation
of MCPD. The selectivity to MCPD decreases dramatically when
the loading amount of Al2O3 exceeds 20%, demonstrating that over-
loading Al2O3 is disadvantageous for the formation of MCPD.
Therefore, the appropriate loading amount of Al2O3 is between
10% and 20% in order to obtain the optimal catalytic performance.
The catalytic performances on KOH promoted MgO are shown
in Fig. 6, which are plotted as functions of reaction temperature.
3.4. Deactivation of catalysts
Fig. 8 illustrates the time-on-stream behaviors of these pro-
moted and unpromoted MgO catalysts during the methylation of
CPD. Generally, different deactivation behaviors can be observed

D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
263
on these solid bases. As shown in Fig. 8A, the activity of MgO in-
creases slightly along the catalytic test, while the activities of
Al2O3/MgO and KOH/MgO decrease apparently. It can be found that
the conversion of CPD on 10%Al2O3/MgO drops gradually from 25%
to 18% in 300-min run at 773 K. The deactivation of 10%KOH/MgO
is more serious than that of 10%Al2O3/MgO at 773 K. About 80% of
the initial activity is lost on 10%KOH/MgO in 120-min run, and the
conversion of CPD is only 4% in 300-min run. The final conversion
follows the order MgO > 10%Al2O3/MgO > 10%KOH/MgO, which is
just the reverse of the order for the initial conversion. As shown
in Fig. 8B and C, the change is not pronounced for the selectivity
to MCPD and DMCPD as a function of time at 773 K on 10%Al2O3/
MgO or 10%KOH/MgO. However, the selectivity to MCPD on unpro-
moted MgO increases progressively along the catalytic test and is
doubled in 300-min run, and the selectivity to DMCPD decreases
accordingly. This is obviously different from most of the base cat-
alytic processes [23,24]. Fig. 8 also depicts the time-on-stream
behavior of 10%Al2O3/MgO(mix), which was prepared by mechan-
ically mixing MgO with 10%Al2O3. It clearly shows that both the
activity of this mixed sample and the selectivity to MCPD increase
along the catalytic test, which is like the result on the unpromoted
MgO rather than on 10%Al2O3/MgO (prepared by impregnation of
aluminum nitrate). Therefore, the preparation method has the
apparent effect on the catalytic performance of Al2O3/MgO.
The deactivation curves at 723 K as functions of time are given
in Fig. 8D–F. The conversion of CPD diminishes gradually on
10%Al2O3/MgO and increases a little on the unpromoted MgO along
the catalytic test. It is important to note that the deactivation of
B
A
MgO
10% KOH/MgO
10% Al2O3/MgO
40
35
30
25
20
15
10
5
80
10% Al2O3/MgO-mix
60
MgO
40
10% KOH/MgO
10% Al2O3/MgO
10% Al2O3/MgO(mix)
20
0
0
0
50
100
150
200
250
300
0
0
0
50
50
50
100
100
100
150
200
250
300
Time (min)
Time (min)
30
25
20
15
10
5
100
80
60
40
20
0
D
C
MgO
MgO
10% Al2O3/MgO
10% KOH/MgO
10% KOH/MgO
10% Al2O3/MgO
10% Al2O3/MgO(mix)
50
100
150
200
250
300
150
Time (min)
200
250
300
Time (min)
100
80
60
40
20
0
100
80
60
40
20
0
E
F
MgO
10% KOH/MgO
10% Al2O3/MgO
MgO
10% KOH/MgO
10% Al2O3/MgO
50
100
150
200
250
300
150
200
250
300
Time (min)
Time (min)
Fig. 8. (A–C) Conversion of CPD, selectivity to MCPD and DMCPD, respectively, at 773 K; (D–F) conversion of CPD, selectivity to MCPD and DMCPD, respectively, at 723 K as
functions of time on unpromoted MgO, 10%Al2O3/MgO and 10%KOH/MgO (methanol/CPD = 1.8, space velocity = 2.5 hꢀ1, p = 101 kPa).

264
D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
Table 3
50
40
30
20
10
0
Surface characterization (XPS) of the fresh and spent 10%KOH/MgO catalyst.
Catalyst
Binding Energy (eV)
K/Mg
O 1s
Mg 2p
K 2p3/2
(Atomic ratio)
10%KOH/MgO-fresh
10%KOH/MgO-spent
530.6
531.4
49.6
49.9
293.2
293.5
0.09
2.6
Methanol time
CPD accumulated time
CPD and Methanol time
CPD time
tures in the coke deposits are mainly condensed carbonaceous
materials [26]. The peak centered at 134.2 ppm corresponds to
the resonances of aromatics, which is possibly ascribed to carbon
bridges between aromatic rings (130–140 ppm) or substituted aro-
matic carbons (135–150 ppm) [26–28]. The peak centered at
170.7 ppm corresponds to carboxyl [28]. Other peaks in the 10–
100 ppm region might be distinguished from the NMR spectrum,
which can be ascribed to aliphatics. Nevertheless, their intensities
are very weak. Therefore, the coke deposit on spent 10%KOH/MgO
comprises mainly of the polycyclic aromatic products.
Methanol accumulated time
0
50
100
150
200
250
300
350
Time (min)
Fig. 9. Conversion of CPD as functions of contacting time of the reactants on
10%KOH/MgO based on various feeding modes: feeding methanol continuously and
CPD intermittently (5s), feeding CPD continuously and methanol intermit-
tently(dj) and feeding both CPD and methanol continuously (N) (T = 773 K,
methanol/CPD = 1.8, space velocity = 2.5 h–1, p = 101 kPa).
3.5. Poisoning test of catalysts
In order to further investigate the catalytic behaviors of these
solid bases in the methylation of CPD, acetic acid and pyridine
were used to poison the basic sites and acidic sites during the reac-
tion, respectively, and the results are plotted in Figs. 11 and 12. As
shown in Fig. 11, the conversion of CPD maintains around 25% after
co-feeding of pyridine on the unpromoted MgO, however, approx-
imate 50% of the activity is lost during co-feeding of acetic acid.
When acetic acid is removed from the feed stream, the conversion
of CPD is recovered. On the other hand, co-feeding of pyridine ele-
vates the selectivity to MCPD approximately from 45% to 60%. The
selectivity to MCPD maintains about 64% when pyridine is re-
moved from the feed stream, suggesting that the effect of pyridine
is permanent. While the selectivity to MCPD decreases a little dur-
ing co-feeding of acetic acid, it can be recovered by stopping acetic
acid feeding, indicating that the effect of acetic acid is temporary.
In the case of 10%Al2O3/MgO, both co-feeding of pyridine and ace-
tic acid can decrease the activity of catalyst to a certain extent, and
the effect of acetic acid is more pronounced. The conversion can be
recovered in both cases by removing the poison from the feed
stream. The selectivity to MCPD presents different variations in
pyridine and acetic acid poisoning on this catalyst. Pyridine poi-
soning has little effect on the selectivity to MCPD, while acetic acid
poisoning decreases the selectivity dramatically, and it can be
10%KOH/MgO is suppressed apparently at this temperature, only
22% of its initial activity is lost in 300-min run; while at 773 K, over
90% is lost. Therefore, the final conversion of CPD follows the order
of 10%KOH/MgO > 10%Al2O3/MgO > MgO, which is the same as the
initial one. Furthermore, it can be found from Fig. 8E and F that the
selectivities to MCPD and DMCPD on these catalysts keep nearly
constant throughout the test at 723 K.
In order to distinguish the effects of methanol and CPD to the
deactivation of catalyst, the methylation of CPD was carried out
in two feeding modes: (1) methanol was continuously fed into
reaction system while CPD was introduced at long intervals and
(2) CPD was continuously fed into reaction system while methanol
was introduced at long intervals. Fig. 9 depicts the time-on-stream
behavior of 10%KOH/MgO based on these two feeding modes at
773 K. It shows that the conversion of CPD is still close to 30% after
feeding methanol continually for 266 min in the first feeding mode,
which is far higher than that of 4% detected at the same reaction
time when methanol and CPD are co-fed. In fact, even the decrease
in conversion in the first feeding mode can be ascribed to the effect
of CPD, since the conversion trend based on CPD accumulated time
in this feeding mode is very similar to that in ordinary co-feeding
mode. Contrarily, the conversion of CPD drops more rapidly via
both CPD time and methanol accumulated time, if the second feed-
ing mode is used. It indicates that the deactivation rate of KOH/
MgO is faster if feeding CPD only. Therefore, the deactivation of
10%KOH/MgO derives from the CPD transformation.
Table 3 gives the BE values and the surface atomic ratios of the
fresh and spent 10%KOH/MgO catalyst. The BE value associated with
O 1s for the spent catalyst is apparently lower than that of the fresh
one (530.6 vs 531.4 eV), while the shift of the BE value of Mg 2p or K
2p3/2 is not pronounced. On the other hand, the spent 10%KOH/MgO
possesses much higher surface atomic ratio of K/Mg than the fresh
one (2.6 vs 0.09), indicating that the surface of catalyst is enriched
with K after the methylation of CPD. This phenomenon has also been
observed on KNO3 promoted MgO for O-methylation of dihydroxy-
benzenes [25] and soot combustion [12].
The solid-state 13C MAS-NMR spectrum of spent 10%KOH/MgO
catalyst is shown in Fig. 10. The NMR spectrum of spent 10%KOH/
MgO mainly exhibits two broad peaks in the chemical shift range
110–220 ppm centered at 134.2 and 170.7 ppm, respectively. It is
well known that the broad peak in NMR indicates that the struc-
300 280 260 240 220 200 180 160 140 120 100 80 60 40 20
0
δ (ppm)
Fig. 10. Solid-state 13C MAS NMR of spent 10%KOH/MgO catalyst.

D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
265
40
30
20
10
0
80
60
40
A
methanol
5% pyridine
methanol
5% acetic acid
methanol
0
100
200
300
Time (min)
400
500
Fig. 11. Conversion of CPD (dj) and selectivity to MCPD (sh)as functions of time on unpromoted MgO (ds) and 10%Al2O3/MgO (jh). Effect of the addition of pyridine and
acetic acid (T = 773 K, methanol/CPD = 1.8, space velocity = 2.5 hꢀ1, p = 101 kPa).
As shown in Fig. 12B, the conversion of CPD and the selectivity to
50
40
30
20
10
0
100
80
60
40
20
0
MCPD on 10%KOH/MgO diminish with co-feeding of acetic acid at
temperature below 773 K, but it is surprising to find that when the
temperature is higher than 773 K, both the activity and selectivity
increase. It seems that introducing acetic acid is helpful in lowering
the deactivation rate of KOH/MgO at high temperature.
A
methanol
5%acetic acid
methanol
3.6. Methylation of CPD with formaldehyde
The methylation of CPD with formaldehyde was also carried out
on these solid bases. Due to the difficulty to handle pure formalde-
hyde, formalin, which contains ca. 38% of formaldehyde, was used
for this reaction. Accordingly, 38% methanol aqueous solution was
employed for the comparison. Fig. 13 depicts the catalytic perfor-
mance of unpromoted MgO, 10%Al2O3/MgO and 10%KOH/MgO on
this reaction.
0
50
100
150
200
250
300
350
Time (min)
It can be found that the conversion of CPD (e.g. 4.5% at 773 K) on
unpromoted MgO with 38% of methanol is apparently lower than
that with pure methanol (e.g. 14.6% at 773 K), which can be as-
cribed to the effect of water. Replacing 38% methanol with forma-
lin (38% of formaldehyde) elevates the conversion of CPD on MgO
to a great extent, e.g. the conversion of CPD increases dramatically
from 0.3% to 13.1% at 673 K. It indicates that formaldehyde is a
more active methylating agent in CPD methylation. A similar
change can be observed on 10%Al2O3/MgO when formalin is used
as methylating agent instead of 38% methanol. As for 10%KOH/
MgO, the conversion of CPD with formalin has an apparent in-
crease at lower temperature compared to that with 38% methanol.
However, a dramatic decrease in conversion is observed at a tem-
perature higher than 723 K, which can be ascribed to the rapid
decomposition of formaldehyde at this higher temperature, since
this catalyst exhibits superbasicity. The selectivity to MCPD also in-
creases to a certain extent on unpromoted MgO and 10%Al2O3/
MgO, while it decreases a little on 10%KOH/MgO, when formalin
is used as methylating agent instead of 38% methanol. Neverthe-
less, the selectivity curves with temperature present the similar
tendency using both of the methylating agents.
100
80
60
40
20
0
100
B
5% acetic acid
methanol
90
80
70
60
50
40
650
700
750
800
850
Temperature (K)
Fig. 12. Conversion of CPD and selectivity to MCPD (A) as functions of time at
773 K; (B) as functions of temperature in 10-min run on 10%KOH/MgO. Effect of the
addition of acetic acid (methanol/CPD = 1.8, space velocity = 2.5 hꢀ1, p = 101 kPa).
recovered by removing acetic acid from the feed stream. Since
10%KOH/MgO possesses superbasicity, only the acid poisoning test
was carried out. As shown in Fig. 12A, co-feeding of acetic acid
does not alter the conversion curve tendency apparently, which
is different from the forenamed results. Considering that the deac-
tivation of this catalyst is too fast at this temperature before intro-
ducing acetic acid, the effect of acid poisoning may be enshrouded.
Therefore, the conversions were further compared at different tem-
peratures with or without co-feeding of acetic acid on this catalyst.
4. Discussion
4.1. The role of methanol in CPD methylation
A lot of work has been done on the transformation of methanol
on basic catalysts [21,29–36]. Chemisorption of methanol occurs
via heterolytic dissociation [37], involving the formation of hydro-
xyl groups and CH3Oꢀ anions [34]. Formate and methoxy species
occur via a nucleophilic attack reaction with intermolecular dis-

266
D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
40
30
20
10
0
tion mechanism. In the current reaction, CPD is slightly
A
converted to the products at 673 K on MgO, and the conversion
of CPD greatly increases along with the increase in reaction tem-
perature. This variation is very similar to that in the formation of
light compounds from methanol on MgO (Fig. 4A). The yield of
H2 is observed approximately corresponding to the sum of yields
of CO + 1/2CH4 + 1/2CO2 (i.e. the amount of H2 produced approxi-
mately corresponds to the sum of 2CO + CH4 + CO2), and the yield
of CO is much higher than CH4 and CO2 on MgO, which indicates
that formaldehyde is formed on this catalyst and further decom-
poses to light products. Therefore, it is reasonable to suggest that
the dehydrogenation of methanol is also an important step in
CPD methylation. The reaction result in CPD methylation with
formaldehyde also supports this hypothesis. Replacing 38% metha-
nol with formalin can elevate the conversion of CPD on MgO to a
great extent, as indicated in Fig. 13. Therefore, the likely formation
of formaldehyde could promote the methylation of CPD with
methanol on MgO. This hypothesis is also supported by the com-
parison of the catalytic activities in CPD methylation and methanol
decomposition on different catalysts. Compared with MgO,
10%KOH/MgO is more active in methanol decomposition (Fig. 4),
and it also shows higher activity in CPD methylation (Fig. 6). More-
over, both 10%KOH/MgO and 10%Al2O3/MgO exhibit the catalytic
performances in CPD methylation with formaldehyde superior to
those with methanol in the temperature range of 673–723 K
(Fig. 13), indicating that formaldehyde may play an important role
in the conversion of CPD on all these solid base catalysts.
650
700
750
800
850
Temperature (K)
100
80
60
40
20
0
B
4.2. The role of acidic sites and basic sites in CPD methylation
In the methylation of CPD with methanol, loading Al2O3 or KOH
can greatly elevate the catalytic performance of MgO in the tem-
perature range of 673–773 K, as indicated in Figs. 5 and 6. How-
ever, their modifications bring totally different effects on the
surface properties. MgO possesses moderately strong basicity
(H– = 18.4) and weak acidity (see Tables 1 and 2 and Figs. 2 and
3). No Brønsted acidic sites exist on this conventional solid base
[20]. Loading Al2O3 enhances the acidity of MgO apparently and
decreases the base strength a little; while the modification of
KOH generates some superbasic sites, so it is unreasonable to as-
sume that they follow the same catalytic mechanism. It has been
discussed above that CPD reacts more efficiently with formalde-
hyde, which is likely to be formed by the dehydrogenation of
methanol on the basic sites. Due to relatively weaker basicity,
few methanol molecules are dehydrogenated on MgO at lower
temperature (e.g. 673 K), and accordingly, few products are
formed. Spoto et al. [47] reported that CPD can be dissociated into
cyclopentadienyl anions on MgO; however, this heterolytic dissoci-
ation of C–H bond preferentially occurs on the less frequent defec-
tive sites (e.g. sites located on or near the steps), the equivalent
Mg2+O2ꢀ pairs of the dominant {1 0 0} faces are inactive in CPD dis-
sociation. As a result, few CPD molecules are dissociated on this
catalyst at lower temperature. It might be another reason why
MgO shows lower activity in CPD methylation.
Al2O3/MgO contains a certain amount of the basic and acidic
sites, and both of them play the important roles in CPD methyla-
tion, as inferred from the higher activity on this catalyst compared
with pure MgO and Al2O3, and the lower activity during acetic acid
or pyridine poisoning (Fig. 11). It is well known that side chain
alkylation of toluene with methanol follows a co-operative action
of acid/base pairs [43,44,48]. Taking into account the similarity of
both reactions, it is reasonable to assume that the methylation of
CPD with methanol obeys a co-operative action of acid/base pairs
on Al2O3/MgO. It is important to note that the mechanically mixed
MgO with Al2O3 exhibits the catalytic behavior like unpromoted
MgO rather than Al2O3/MgO prepared by impregnation of alumi-
650
700
750
800
850
Temperature (K)
Fig. 13. (A) Conversion of CPD and (B) selectivity to MCPD, respectively, as
functions of temperature on unpromoted MgO (ds), 10%Al2O3/MgO (jh) and
10%KOH/MgO (ND) with 38% methanol solution (shD) and formalin (djN) as the
methylating agents, respectively (methylating agent/CPD = 1.8, space veloc-
ity = 2.5 hꢀ1, p = 101 kPa).
proportionation [38,39]. The formate may finally decompose to CO
and H2. The reactions between the adsorbed methoxy and formate
species or by direct dimerization of adsorbed formaldehyde (Tis-
chenko reaction) may yield methylformate, which finally decom-
poses at high temperatures to methane and CO2 [40]. Therefore,
several light products (CO, CH4, CO2 and H2) can be detected via
these reactions [21,41].
Formaldehyde plays an important role during the alkylation of
toluene or ethylbenzene with methanol [20,42,43]. It is generally
accepted that methanol is dehydrogenated to formaldehyde and
it is formaldehyde that serves as the alkylation agent to form sty-
rene [20,44]. Although the mechanism of reaction between phenol
and methanol catalyzed by basic oxides is usually believed to occur
by a direct electrophilic substitution on the aromatic ring, recent
studies [21,41,45,46] indicate that the dehydrogenation of alcohol
is also very important to the alkylation of phenol on MgO. Ballarini
et al. [21,45] suggest that the true methylating agent is formalde-
hyde or some compound formed by transformation of formalde-
hyde itself rather than methanol in phenol methylation, based on
their observation that the conversion of phenol begins exactly
when the conversion of methanol to light compounds starts.
Cavani et al. [41] take in situ IR technique combined with compu-
tational studies of sorbed molecules to further confirm this reac-

D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
267
Scheme 1. Proposed reaction mechanism for the methylation of CPD on MgO.
num nitrate, which should be ascribed to the different dispersion
state of Al2O3 on MgO. It is well known that the interaction be-
tween Al2O3 and MgO on the mechanically mixed catalyst is far
weaker than that prepared by impregnation method, and Al2O3
can be highly dispersed on the surface of MgO via the impregna-
tion route [49]. Based on the reaction result in Fig. 8, highly dis-
persed acidic species around the basic sites on MgO are required
for this reaction, not only by the simple makeup of MgO and
Al2O3. In fact, 10%Al2O3/MgO(mix) shows the activity inferior to
MgO due to the decrease in MgO content in catalyst. The highly
dispersed acidic species can activate methanol or formaldehyde,
and make it easier to react with CPD adsorbed even on {1 0 0} faces
of MgO catalyst, and thus elevate the activity of catalyst. The sur-
face nature of catalyst becomes more and more like the property
of coating layer when the loading amount exceeds 20%, thus cata-
lysts with high loading amount of Al2O3 show poor catalytic per-
formance in CPD methylation.
The acidity is very weak and some superbasic sites are formed
on KOH/MgO. This catalyst exhibits stronger dehydrogenation abil-
ity, and more CPD and methanol are then converted to cyclopenta-
dienyl potassium and formaldehyde, respectively, at lower
temperature. It is helpful to the methylation of CPD. The XPS result
supports this suggestion. As shown in Table 3, the surface K con-
tent on the spent 10%KOH/MgO catalyst is much higher than that
on the fresh one. This significant surface segregation of K should
be ascribed to the formation of cyclopentadienyl potassium, simi-
lar to the liquid-phase methylation of CPD with methylating agent,
e.g. CH3I, under the existence of strong base, e.g. NaNH2 [2,3,50].
Although the basicity of KOH is weaker than that of NaNH2 and
methanol (or formaldehyde) is not as active as CH3I, higher reac-
tion temperature used in this vapor-phase catalysis enables the
considerable conversion of CPD. These KOH/MgO samples exhibit
the catalytic performance like KOH rather than MgO in CPD meth-
ylation except for 1%KOH/MgO, in which the surface of MgO is not
fully covered by KOH and thus both the catalytic behaviors of MgO
and KOH are observed (Fig. 6). When the whole surface of MgO is
covered by KOH, the resulting KOH/MgO should have the similar
catalytic performance. It can explain why the similar reaction re-
sults are observed on KOH/MgO with the loading amount between
5% and 20%, as indicated in Fig. 6.
basic sites, e.g. the O2ꢀ sites on or near the steps, at lower temper-
ature (e.g. 673 K). The heterolytic dissociation of CPD also occurs
on these stronger basic sites and Mg2+ sites stabilize the formed
cyclopentadienyl anions. Due to the stronger interaction between
cyclopentadienyl and Mg2+, the formed MCPD is readily dissociated
on the nearby O2ꢀ sites (as indicated in Scheme 1) and further con-
verted to DMCPD. Therefore, MgO shows poor selectivity to MCPD
and high selectivity to DMCPD at lower temperature. With the in-
crease in reaction temperature, desorption of MCPD from the Mg2+
sites speeds up, thus the deep methylation of MCPD is weakened.
Unlike MgO, KOH/MgO catalyzes the methylation of CPD via a
mechanism more like the liquid-phase reaction (Scheme 2), and
the actual active sites derive mainly from KOH. CPD first reacts
with KOH and is converted to cyclopentadienyl potassium, and
then reacts with formaldehyde (or methanol) to form MCPD. Be-
cause the formed intermediate is unbounded on Mg2+ and O2ꢀ sites
of MgO, product MCPD can be easily taken away with carrier gas
and has little chance to take the further reaction. Therefore, high
selectivity to MCPD is observed on KOH/MgO. As for Al2O3/MgO,
introducing Al2O3 provides highly dispersed acidic species around
the basic sites on MgO to activate formaldehyde (or methanol),
which enables some weaker basic sites on {1 0 0} faces of MgO to
take part in this reaction. Because only limited amount of methy-
lating agents can be activated, the MCPD formed on {1 0 0} faces
of MgO is relatively difficult to be converted into DMCPD, and thus
Al2O3/MgO also exhibits higher selectivity to MCPD compared with
MgO.
4.3. Deactivation of catalysts
Different deactivation behaviors are observed on MgO, Al2O3/
MgO and KOH/MgO in vapor-phase methylation of CPD with meth-
anol. In order to better understand the change of catalyst nature
after this methylation reaction, the elemental analysis and cata-
lytic decomposition of isopropanol were employed to detect the
coking extent on spent catalysts and their acid–base properties,
respectively, and the results are listed in Table 2.
It is unexpected that the selectivity to MCPD and the activity of
MgO has a certain elevation during the reaction, which seems to
suggest that the methylation of CPD contains an induction period
on MgO. The result from elemental analysis (see Table 2) indicates
that MgO contains small amount of carbonaceous species (2.9% of
carbon) after 300-min run. However, this coking is not the reason
for the elevation of activity and selectivity to MCPD. In fact, if
calcining the spent catalyst at 873 K in the air, the activity of
MgO can further increases to 33% (data not given in tables or
The difference of active sites also brings about the dramatic
change of selectivities to MCPD and DMCPD on these catalysts.
Scheme 1 explains the high selectivity to DMCPD on MgO at lower
temperature, which is proposed according to the reports on the
alkylation of aniline [51] and toluene [43,48] with methanol on
MgO. During the reaction, formaldehyde is formed on the stronger

268
D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
Scheme 2. Proposed reaction mechanism for the methylation of CPD on KOH/MgO.
figures), indicating that the coking is detrimental to the conversion
of CPD. Therefore, the surface property of MgO must have been
altered after CPD methylation. This change derives not from the
formation of new component or phase after reaction, since the
spent catalyst still presents the phase of periclase MgO (see
Fig. 1). One possible reason is that more defective sites are formed
during the methylation of CPD. It is known that some neutral oxy-
gen vacancies could be formed on MgO during N2 treatment at high
temperature, which could enhance the catalytic activity. Moreover,
CO2 is one of the decomposition products of methanol, they could
react with MgO during the methylation reaction, and the resulting
carbonaceous or carbonated species could create distortions in the
MgO lattice, which may have some effect on the final activity of
catalyst. More work is still needed to interpret this change.
Al2O3/MgO possesses a higher initial activity than unpromoted
MgO, however, the activity decreases to a lower value than that
on MgO after a long run at 773 K. The result from elemental anal-
ysis (see Table 2) demonstrates that 10%Al2O3/MgO contains 4.7%
of carbon after 300-min run due to the coke deposit, which is high-
er than that on the unpromoted MgO (2.9%). The result from the
catalytic decomposition of isopropanol (see Table 2) indicates that
the coking on 10%Al2O3/MgO mainly diminishes the yield of ace-
tone, i.e. it decreases the basicity. Accordingly, the activity of
Al2O3/MgO drops a little after this coking.
Fig. 8 shows that the deactivation of 10%KOH/MgO is serious at
773 K. Although it exhibits the highest initial activity, the conver-
sion of CPD is only 6% after 300-min run. The result from elemental
analysis (see Table 2) demonstrates that this spent catalyst con-
tains 28% of carbon, which is about nine times of that on the
unpromoted MgO. Obviously, this heavy coking should be respon-
sible for the serious deactivation on KOH/MgO. This coke deposit
comprises mainly of the polycyclic aromatic products, as indicated
in Fig. 10. ICP-OES analysis indicates that 14% of K is lost after 300-
min run (data not given in tables or figures), which may have a cer-
tain effect on the activity of catalyst. However, after calcining at
873 K in the air, the activity of KOH/MgO can be recovered (data
not given in tables or figures) and the color of catalyst changes
from black to original white, which gives further evidence that
the deactivation is due to the coke deposition [52]. This spent cat-
alyst shows apparent decrease in acetone yield in the catalytic
decomposition of isopropanol (Table 2), indicating that the basicity
on 10%KOH/MgO diminishes after the methylation of CPD. Further-
more, an apparent reduction in BE value associated with O 1s core
level can be observed after the methylation of CPD from the XPS re-
sult (Table 3),which can be ascribed to electronic interaction be-
tween O2ꢀ ions and reactants. Therefore, this coking occurs
mainly on the basic sites and most possibly relates to KOH. The
reaction result based on two feeding modes, i.e. feeding methanol
continuously and CPD intermittently or feeding CPD continuously
and methanol intermittently, indicates that the deactivation of cat-
alyst and the coking derive from CPD transformation (Fig. 9). The
deactivation mechanism on 10%KOH/MgO is different from that
on acidic catalyst. As has been confirmed, the hexamethylbenzene
and polynuclear aromatics formed by transformation of methanol
on acidic sites are mainly responsible for the deactivation of
catalyst in phenol methylation with methanol [21,22,53–55]. The
heavy coking on KOH/MgO should be ascribed to the superbasicity
of KOH/MgO, which possesses stronger electrodonating ability
than MgO [24]. The superbasicity favors both the formation of
cyclopentadienyl anion and the decomposition of methanol. The
formed cyclopentadienyl anions can be converted to MCPD and
polymers with methylating agent and CPD, respectively. At lower
temperature, the cyclopentadienyl anions mainly react with
methylating agent to form product MCPD. However, these cyclo-
pentadienyl anions are more likely to polymerize due to the rapid
decomposition of the methylating agent, and transform to polycy-
clic aromatic products (coking deposits) by further condensation
and methylation. This deactivation mechanism can give a reason-
able explanation for the abnormal phenomenon on 10%KOH/MgO
during the acetic acid poisoning at higher temperature (Fig. 12B).
Although the competitive adsorption of acetic acid would inhibit
the transformation of CPD on basic sites, the existence of the
superbasic sites induces heavy coking of CPD on 10%KOH/MgO at
773 K or higher temperature, which turns to be the overwhelming
factor for the deactivation of catalyst. Co-feeding acetic acid de-
creases the basicity of catalyst, thus weakens both the coking of
CPD and the decomposition of methanol, which are helpful to the
formation of MCPD.
It should be pointed out that the deactivation rate on KOH/MgO
decreases dramatically when temperature drops from 773 to
723 K, and accordingly, carbon content decreases from 28% to
4.8% (data not given in tables and figures) after 300-min run. Obvi-
ously, the coking on KOH/MgO can be well suppressed by lowering
reaction temperature. One of the reasons is that the decomposition
rate of methanol decreases remarkably as the reaction temperature
drops to 723 K, as indicated in Fig. 4B. Thus, more methanol mole-
cules are provided for the methylation reaction, and the polymer-
ization of cyclopentadienyl anion is suppressed accordingly.
Compared with other catalysts, KOH/MgO exhibits higher activity
and selectivity to MCPD even after a long run at 723 K, and displays
the potential as an effective catalyst in the methylation of CPD.
5. Conclusions
This work compares the catalytic performances of MgO and
MgO promoted with Al2O3 or KOH in the methylation of CPD with
methanol. The dehydrogenation of methanol is a key-step on these
solid bases, with generation of the active species, e.g. formalde-
hyde, for the methylation of CPD. The modification with either
Al2O3 or KOH can enhance the initial activity of MgO and the selec-
tivity to MCPD at lower temperature; however, their catalytic
mechanisms present apparent difference. As for Al2O3/MgO, both
the acidic and basic sites play the important roles in CPD methyl-
ation; while for KOH/MgO, the existence of superbasic sites is
responsible for the higher activity and selectivity to MCPD, and
KOH rather than MgO catalyzes this reaction. Due to different ac-
tive sites, these catalysts display different deactivation behaviors.
The superbasicity of KOH/MgO makes it easy to deactivate at
773 K, due to the heavy coking of CPD on the basic sites. However,
the coking effect can be greatly suppressed when the reaction tem-
perature decreases to 723 K, and this catalyst exhibits much better

D. Lan et al. / Journal of Catalysis 275 (2010) 257–269
269
[22] M. Bregolato, V. Bolis, C. Buscob, P. Ugliengo, S. Bordigac, F. Cavani, N. Ballarini,
L. Maselli, S. Passeri, I. Rossetti, L. Forni, J. Catal. 245 (2007) 285.
[23] Y. Wang, J.H. Zhu, J.M. Cao, Y. Chun, Q.H. Xu, Micropor. Mesopor. Mater. 26
(1998) 175.
performance than the unpromoted MgO even after a long run.
Moreover, the activity of this spent catalyst can be recovered by
calcining at 873 in the air.
[24] J.I. Di Cosimo, C.R. Apesteguía, J. Mol. Catal. A 130 (1998) 177.
[25] M. Vijayaraj, C.S. Gopinath, J. Catal. 243 (2006) 376.
[26] A.R. Pradhan, T.S. Lin, W.H. Chen, S.J. Jong, J.F. Wu, K.J. Chao, S.B. Liu, Appl.
Catal. A: Gen. 218 (2001) 81.
Acknowledgments
[27] R. Golembiewski, J. Kornatowski, Chem. Mater. 13 (2001) 609.
[28] Z. Fan, A.P. Watkinson, Ind. Eng. Chem. Res. 45 (2006) 6428.
[29] R.C. Greenler, J. Chem. Phys. 37 (1962) 2094.
We would like to thank the financial support from the NSF of
China (20873061), the Ministry of Science and Technology of China
(Grant 2008 AA06Z327 from the 863 Program), and the testing
fund of Nanjing University.
[30] R.O. Kagel, J. Phys. Chem. 71 (1967) 844.
[31] J. Shabtai, L.H. Klemm, D.R. Taylor, J. Org. Chem. 35 (1970) 1075.
[32] P. Mars, J.J. Scholten, P. Zwietering, Adv. Catal. 14 (1963) 35.
[33] U. Heiz, J. Phys. Chem. B 106 (2002) 11961.
[34] M. Ziolek, J. Kujawa, O. Saur, J.C. Lavalley, J. Phys. Chem. 97 (1992) 9761.
[35] J.S. Francisco, J. Am. Chem. Soc. 125 (2003) 10475.
[36] J. Hu, K. Zhu, L. Chen, C. Ku1bel, R. Richards, J. Phys. Chem. C 111 (2007) 12038.
[37] J. Günster, G. Liu, J. Stultz, S. Krischok, D.W. Goodman, J. Phys. Chem. 104
(2000) 5738.
References
[1] F.J. Wu, B.C. Berris, D.R. Bell, US Patent 4 946 975, to Ethyl Co., Ltd., 1990.
[2] S. Mclean, P. Haynes, Tetrahedron 21 (1965) 2313.
[3] V.A. Mironov, E.V. Sobolev, A.N. Elizarova, Tetrahedron 19 (1963) 1939.
[4] S.J. Rajan, US Patent 4 547 603, to Ethyl Co., Ltd., 1982.
[5] H.E. Fritz, D.W. Peck, US Patent 3 255 267, to Union Carbide Co., Ltd., 1966.
[6] Z. Yoshida, S. Kato, Y. Amemiya, K. Yanai, US Patent 4 567 308, to Asahi
Chemical Co., Ltd., 1985.
[7] Z. Yoshida, S. Kato, Y. Amemiya, EP Patent 0 256 228, to Asahi Chemical Co.,
Ltd., 1987.
[8] L.B. Sun, Z.Y. Wu, J.H. Kou, Y. Chun, Y. Wang, J.H. Zhu, Z.G. Zou, Chin. J. Catal. 27
(2006) 725.
[38] X.D. Peng, M.A. Barteau, Langmuir 5 (1989) 1051.
[39] N.D. Lazo, D.K. Murray, M.L. Kieke, J.H. Haw, J. Am. Chem. Soc. 114 (1992) 8552.
[40] T. Mori, S. Hoshino, A. Neramittagapong, J. Kubo, Y. Morikawa, Chem. Lett.
(2002) 390.
[41] F. Cavani, L. Maselli, S. Passeri, J.A. Lercher, J. Catal. 269 (2010) 340.
[42] C.S. Huang, A.N. Ko, Catal. Lett. 19 (1993) 319.
[43] A. Borgna, J. Sepúlveda, S.I. Magni, C.R. Apesteguía, Appl. Catal. A 276 (2004)
207.
[9] L.B. Sun, L. Gong, X.Q. Liu, F.N. Gu, Y. Chun, J.H. Zhu, Catal. Lett. 132 (2009) 218.
[10] J.H. Zhu, Y. Chun, Y. Qin, Q.H. Xu, Micropor. Mesopor. Mater. 24 (1998) 19.
[11] R.Q. Sun, L.B. Sun, Y. Chun, Q.H. Xu, Carbon 46 (2008) 1757.
[12] R. Jimenez, X. Garcia, C. Cellier, P. Ruiz, A.L. Gordon, Appl. Catal. A 314 (2006)
81.
[44] A.E. Palomares, G. Eder-Mirth, M. Rep, J.A. Lercher, J. Catal. 180 (1998) 56.
[45] N. Ballarini, F. Cavani, L. Maselli, S. Passeri, S. Rovinetti, J. Catal. 256 (2008) 215.
[46] A.H. Padmasri, A. Venugopal, V. Durgakumari, K.S. Rama Rao, P. Kanta Rao, J.
Mol. Catal. A 188 (2002) 255.
[47] G. Spoto, S. Bordiga, A. Zecchina, J. Mol. Catal. 49 (1988) 187.
[48] A.E. Palomares, G. Eder-Mirth, J.A. Lercher, J. Catal. 168 (1997) 442.
[49] D. Jiang, B. Zhao, Y. Xie, G. Pan, G. Ran, E. Min, Appl. Catal. A 219 (2001) 69.
[50] E.I. Becker, J. Chem. Edu. 36 (1959) 119.
[51] K. Tanabe, M. Misono, Y. Ono, H. Hattori, New Solid Acid and Bases, Elsevier
Science & Technology Publishing, Amsterdam, 1990. p. 1.
[52] A.S. Ndou, N.J. Coville, Appl. Catal. A 275 (2004) 103.
[53] Ø. Mikkelsen, S. Kolboe, Micropor. Mesopor. Mater. 29 (1999) 173.
[54] M. Bjørgen, U. Olsbye, S. Kolboe, J. Catal. 215 (2003) 30.
[55] W.C. Choi, J.S. Kim, T.H. Lee, S.I. Woo, Catal. Today 63 (2000) 229.
[13] J. Diaz-Teran, D.M. Nevskaia, J.L.G. Fierro, A.J. Lopez-Peinado, A. Jerez,
Micropor. Mesopor. Mater. 60 (2003) 173.
[14] J.H. Zhu, Y. Wang, Y. Chun, Z. Xing, Q.H. Xu, Mater. Lett. 35 (1998) 177.
[15] Y. Wang, W.Y. Huang, Y. Chun, J.R. Xia, J.H. Zhu, Chem. Mater. 13 (2001) 670.
[16] K. Tanabe, in: B. Imelik, C. Nacceche, G. Condurier, Y. Ben Taarti, J.C. Verdrine
(Eds.), Catalysis by Acids and Bases, Elsevier, Amsterdam, 1985, p. 1.
[17] V.K. Díez, C.R. Apesteguía, J.I. Di Cosimo, J. Catal. 215 (2003) 220.
[18] F. Prinetto, G. Ghiotti, R. Durand, D. Tichit, J. Phys. Chem. B 104 (2000) 11117.
[19] P.E. Hathaway, M.E. Davis, J. Catal. 116 (1989) 263.
[20] P.E. Hathaway, M.E. Davis, J. Catal. 119 (1989) 497.
[21] N. Ballarini, F. Cavani, L. Maselli, A. Montaletti, S. Passeri, D. Scagliarini, C.
Flego, C. Perego, J. Catal. 251 (2007) 423.