Alkylation of resorcinol with tertiary butanol over zeolite catalysts: Shape selectivity vs acidity

Article abstract of DOI:10.1016/j.catcom.2021.106291

The catalytic performance of various zeolites such as H-ZSM-5, H-Y, H-beta, H-Mordenite in resorcinol alkylation with tertiary butanol demonstrated that pore characteristics have major influence on product selectivity, whereas acid strength and number of acid sites influenced resorcinol conversion. The passivation of external surface of H-beta zeolite by silylation and amine poisoning produced shape selectively O-alkylated resorcinol methyl tert butyl ether (RMTBE) and 4-tert butyl resorcinol (4-TBR). We propose that 4-TBR formation goes over external acid sites through RMTBE isomerization, whereas formation of 4-TBR takes place inside the pores through direct C-alkylation mechanism.

Full text of DOI:10.1016/j.catcom.2021.106291

Catalysis Communications 152 (2021) 106291
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Catalysis Communications
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Short communication
Alkylation of resorcinol with tertiary butanol over zeolite catalysts: Shape
selectivity vs acidity
Vijaykumar S. Marakatti, Eric M. Gaigneaux*
´
Institute of Condensed Matter and Nanosciences (IMCN), MOlecular Chemistry, Materials and Catalysis (MOST), Universite Catholique de Louvain (UCLouvain), Place
Louis Pasteur 1, L4.01.09, B-1348 Louvain-la-Neuve, Belgium
A R T I C L E I N F O
A B S T R A C T
Keywords:
The catalytic performance of various zeolites such as H-ZSM-5, H-Y, H-beta, H-Mordenite in resorcinol alkylation
with tertiary butanol demonstrated that pore characteristics have major influence on product selectivity, whereas
acid strength and number of acid sites influenced resorcinol conversion. The passivation of external surface of H-
beta zeolite by silylation and amine poisoning produced shape selectively O-alkylated resorcinol methyl tert butyl
ether (RMTBE) and 4-tert butyl resorcinol (4-TBR). We propose that 4-TBR formation goes over external acid
sites through RMTBE isomerization, whereas formation of 4-TBR takes place inside the pores through direct C-
alkylation mechanism.
Acidity
Alkylation
Shape selectivity
Resorcinol alkylation
Zeolite
Particle size
1. Introduction
mesoporous materials [1–7]. However, reactions over these catalysts
were carried out at high temperature and/or pressure, and allowed only
Alkylation of aromatics is an important reaction in organic chemistry
due to its wide application in fine chemical, petrochemical, perfume,
dye and pharmaceutical industries [1,2]. Among different alkylation
reactions, Friedel-Crafts butylation of resorcinol to produce mono-tert
butylated products is one of the most noteworthy due to its involvement
in the synthesis of antioxidants, polymer stabilizers, therapeutics, and
organic synthetic applications [3,4]. The alkylation of resorcinol with
tertiary butanol (TBA) gives a mixture of alkylated benzenediols and
ethers. Being thermodynamically favoured (monoalkylated readily un-
dergoes a consecutive alkylation), dialkylated 4,6-di-tert-butyl resor-
cinol (4,6-DTBR) is usually the major product [5]. However, 4-tert-
butylresorcinol (4-TBR) is of particular interest as an antioxidant in
food preservatives and in treatment of skin diseases. Therefore, selective
synthesis of 4-TBR at a high conversion of resorcinol is a difficult and
challenging task for catalyst design [6,7].
moderate yields for 4-TBR. Zeolites with their tuneable acidity and high
thermal stability are promising and were well explored in various
alkylation, acylation, carbonylation, condensation and dehydrogenation
reactions [8–12]. Among the zeolite catalysts H-Y, ITQ-6 and H-ZSM-5
were studied for the butylation of resorcinol but low selectivity for 4-
TBR was reported, with only few details being given on the nature
and location of active sites for the reaction and the influence of their
respective pores on the product selectivity [1,3].
Recently, we reported heteropolyacid supported SiO2 and sulphated
zirconia as active catalysts for the alkylation of resorcinol [6,7]. In
continuation of our quest for simple, efficient and robust active catalysts
for this reaction, herein is reported the application of different zeolites
as solid acid catalysts for the conversion of resorcinol to 4-TBR. In this
work, zeolites (H-ZSM-5, H-Y, H-beta, H-Mordenite) with different
acidity, framework type, and particle sizes were studied. Insights on the
origin of product selectivity was gained by a systematic modification of
the zeolite catalysts by silylation and amine poisoning. The physico-
chemical properties of the catalysts, especially the porous characteris-
tics, were correlated with catalytic activity in the alkylation reaction.
Traditionally, homogeneous Lewis (AlCl3, FeCl3) and Brӧnsted acids
(H2SO4, H3PO4) are used to catalyse the reaction [7]. However, limita-
tions and hazardous nature of these soluble acid catalysts have led to
replace them by heterogeneous catalysts [7]. There are a few solid acid
catalysts that have been studied for the reaction so far, such as mont-
morillonite clay, zeolites, ZrO2 supported phosphotungstic acid,
dodecatungstophosphoric acid supported on K-10, sulphated meso-
porous Al2O3, sulphated zirconia and heteropolyacid supported
* Corresponding author.
E-mail address: eric.gaigneaux@uclouvain.be (E.M. Gaigneaux).
https://doi.org/10.1016/j.catcom.2021.106291
Received 18 December 2020; Received in revised form 8 February 2021; Accepted 9 February 2021
Available online 16 February 2021
1566-7367/© 2021 The Authors.
Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).

V.S. Marakatti and E.M. Gaigneaux
Catalysis Communications 152 (2021) 106291
Table 1
Physicochemical properties and catalytic activity/selectivity of zeolites for the resorcinol alkylation reaction.
Entry
Zeolite
SiO2/
Al2O3
(SAR)
SSAa
Micropore
Pore
Acidity
Resorcinol
Selectivity (%)
(m2/g)
Volumeb (cm3/g)
sizec (Å)
(mmol/g)
Conversion (%)
RMTBE
2-
4-
4,6-
Others
TON*
TBR
TBR
DTBR
1
2
ZSM-5
H-BEA
(nano)
H-BEA
H-BEA
H-Y
23
25
414
607
0.122
0.163
5.7
6.8
0.65
1.04
04
46
08
11
02
01
90
83
00
04
00
01
6
40
3
38
300
5
677
656
903
763
833
920
561
688
0.197
0.186
0.324
0.242
0.241
0.265
0.189
0.224
6.8
6.9
7.7
7.5
7.7
7.7
6.0
6.7
0.39
0.05
1.52
0.78
0.18
0.03
0.83
1.23
34
17
60
54
50
40
05
31
13
36
03
02
02
04
13
16
01
04
01
01
01
03
02
03
84
57
81
81
84
86
85
77
00
00
15
14
11
06
00
03
02
01
00
02
02
01
00
01
79
4
309
36
5
6
H-Y
12
30
80
20
28
62.9
252
1212
5
7
H-Y
8
H-Y
9
H-MOR
H-BEA
(Micro)
10
23
Reaction conditions: Resorcinol = 2.2 g, TBA = 4 ml, Chlorobenzene = 5 ml, T = 80 ◦C, Reaction Time = 14 h, o-xylene (internal standard) = 0.9 ml, Amount of
Catalyst = 0.22 g; *TON: calculated by mmol of resorcinol converted per mmol of acid sites.
a
b
Specific surface area determined by BET method.
Micropore Volume obtained from t-plot.
c
Average Pore Diameter determined by Horvath-Kawazoe method.
2. Experimental
(Bruker) equipped with a DTGS detector. The spectra were recorded
with100 scans between 400 and 4000 cmꢀ 1 with a resolution of 4 cmꢀ 1
.
2.1. Catalyst preparation
NH3 adsorption and subsequent temperature-programmed desorption
(NH3-TPD) were performed in a Hiden CATLABPCS combined micro
reactor and mass spectrometer (MS) system as reported earlier. [7]
The zeolites H-ZSM-5, H-Y, H-BEA and H-Mordenite with different
SiO2/Al2O3 ratios (SAR) were purchased from Zeolyst International,
USA. The H-BEA (SAR 28) with bigger crystal size (Micro) obtained by
TOSOH, Japan. Before the reaction, catalysts were pre-treated to 550 ◦C
for 4 h in static air.
2.3. Catalytic studies
The alkylation of resorcinol with TBA was carried out in a liquid
batch reactor. In a typical reaction, 2.2 g of resorcinol was dissolved in 6
ml of TBA, 0.9 ml of o-xylene (internal standard) and 2–5 ml of solvent
in a 100 ml two neck round bottom flask fitted with a condenser. [7] The
reactor is placed in an oil bath under magnetic stirring (1200 rpm) and
heated to 80 ◦C. Then, 0.22 g of catalyst was added. The reaction was
Silylation of H-BEA: Tetra butyl orthosilicate (TBOS) corresponding
to loading of 15 wt% SiO2 mixed with a 100 ml toluene in a round
bottom flask. To this solution, around 5 g of H-BEA zeolite was added
and refluxed for 8 h followed by filtration. The solid obtained was dried
at 120 ◦C for 12 h, and finally calcined in air at 550 ◦C for 4 h. The above
procedure was repeated for successive SiO2 depositions.
monitored by GC-FID analysis. For sampling, 10 μl of reaction mixture
Amine poisoning: The zeolite beta initially dehydrated by heating to
550 ◦C for 4 h in static air. For the amine poisoning, dehydrated H-beta
zeolite was contacted with tri pentylamine, and then evacuated at
250 ◦C in vacuum to remove physiosorbed amine.
was mixed with 1.8 ml of methanol and was analysed by a gas chro-
matograph (Shimadzu- 2041, FID detector) equipped with an RTX-5
column (0.25 mm I.D. and 30 m length). All the products were identi-
fied by injecting the standard sample followed by NMR analysis as done
in our previous work. [6,7] The conversion and selectivity were directly
calculated from GC peak areas in mol% using a multi-point calibration
curve through the internal standard method. The mass balance calcu-
lated after the reaction is in the range 95–98%.
2.2. Catalyst characterization
The phase purity and crystalline properties of all the zeolites were
determined by X-ray diffraction on a Siemens D5000 diffractometer
equipped with a Cu Ka source. The samples were analysed in the 2-theta
range of 5 to 80◦ with a scan rate of 0.02◦ sꢀ 1. The amount of SiO2 after
silylation present on the catalyst was determined by ICP-OES analysis.
The BET surface area, pore volume, and pore size distributions were
obtained through N2 sorption experiments performed using a Micro-
metrics 3flex. Before the measurements, catalysts were degassed over-
night under a vacuum (6 Pa) at 300 ◦C. The measurements were
performed at ꢀ 196 ◦C with relative pressures in the range of 0.01–1.00
(p/p0).
3. Results and discussion
The Friedel-Craft alkylation of resorcinol with TBA was carried out
over different zeolitic frameworks such as H-ZSM-5, H-MOR, H-BEA and
H-Y. The crystal structure using powder XRD and pore analysis (surface
area, pore volume, pore shape) of all the zeolites using N2 adsorption are
shown in Fig. S1. The conversion and selectivity for the different prod-
ucts are shown in Table 1 along with selected physicochemical proper-
ties of the catalysts. The resorcinol conversion was not same for these
zeolites although they have similar Si/Al ratio in the range 18–30, (Entry
1–2, 7, 9). Among the different tested zeolites, H-Y and H-BEA showed
higher resorcinol conversions (46 and 50%, respectively) compared to
H-MOR (5%) and H-ZSM-5 (4%) likely due to higher diffusion rates of
reactants and products in their large pores. The selectivity for 4-TBR
over both H-Y and H-BEA zeolites was ~85%, however, they differ in
their selectivity to 4,6-DTBR and RMTBE, which could be related to their
different texture and/or acidity. The selectivity for RMTBE was high for
H-BEA, whereas selectivity for 4,6-DTBR was dominant in the case of H-
Y. The NH3-TPD profile of H-BEA and H-Y zeolite exhibited similar acid
strength profiles (Fig. S2). Hence, the texture of zeolites appears as
Acidity measurements of zeolite catalyst done by the pyridine
adsorption technique. Wafers of the zeolite catalyst were prepared,
weighed and then placed in a sample holder inside a Pyrex cell specially
designed for a controlled heating of the sample under vacuum and
equipped with a NaCl window. In a typical measurement, the catalyst
was pre-treated at 300 ◦C under vacuum (between 10ꢀ 4 and 10ꢀ 5 Pa) for
2 h in order to remove impurities from the surface. After cooling under
vacuum, 1000 Pa of pyridine sent at room temperature into the cell and
adsorption was allowed for 30 min. The sample was then outgassed at
10ꢀ 5 Pa at 100 ◦C. FT-IR spectra were taken in transmission mode before
and after pyridine adsorption, using a spectrometer IFS55 Equinox
2

V.S. Marakatti and E.M. Gaigneaux
Catalysis Communications 152 (2021) 106291
Fig. 1. NH3-TPD profiles of a) H-Y and b) H-BEA zeolites with different Si/Al ratio (SAR).
crucial factor to explain the difference of selectivity to 4,6-DTBR and not
the acidity. Our interpretation is that H-Y zeolite having super cages
could form the 4,6-DTBR inside the pores or at the pore mouth, but for
H-BEA zeolite, due to smaller pore size, 4,6-DTBR formation is hindered.
The small amount of 4,6-DTBR (4%) formed on H-BEA would then have
proceeded on its external surface.
To check this hypothesis, we separately measured the ability of the
studied catalysts to achieve the butylation of 4-TBR to 4,6-DTBR. The
conversion of 4-TBR over H-BEA was possible but with extremely low
conversion (less than 1%), indicating internal acid sites are not acces-
sible in dialkylation reaction. At the opposite, H-Y zeolite exhibited 4-
TBR conversion ~15%, revealing that many of its acid sites are acces-
sible and active for dialkylation. Besides, it is reported in the literature
[2] that selectivity to 4-TBR vs 4,6-DTBR are dictated by the proportion
of Brønsted vs Lewis acid sites present in the catalyst. Thus, considering
this other factor, pyridine FT-IR measurements over H-Y and H-BEA
were conducted as shown in (Fig. S3). Both zeolites exhibit almost
similar Brønsted to Lewis acid site ratio (B/L ratio), confirming that
difference of acidity cannot be evoked to account for the difference in
selectivity between the two catalysts, and, therefore, that this difference
of selectivity should be more due to a textural effect as discussed earlier.
The selectivity for 2-TBR being identical for all the different zeolites,
suggests that on the contrary to the formation of 2-TBR, this is not
related to the zeolite structure. Interestingly, ZSM-5 and H-Mordenite
although with strong acid strength and large concentration of acid sites
(Fig. S2) resulted in low activity due to constraint of reactants to access
acid sites inside their small pores. Hence, the low activity observed in
these zeolites reflects the contribution of the reaction taking place on
external surface acid sites.
Fig. 2. Total acidity and catalytic activity and selectivity (%) of silylated H-
beta zeolite for the resorcinol alkylation with tertiary butanol reaction.
conversion of resorcinol. The selectivity for 4,6-TBR decreases with the
increase of SAR for H-Y and H-BEA zeolites, which could be due to the
decrease in strength and number of strong acidic sites, in harmony with
the TPD profiles (Fig. 1). The selectivity for RMTBE increases with SAR
for BEA zeolite, whereas for H-Y zeolite it remains almost constant,
which is attributed to pore characteristics of H-BEA as discussed earlier.
To further improve the selectivity for 4-TBR and to understand that
RMTBE does form in BEA zeolite, pore engineering via silylation and
amine poisoning was achieved on H-BEA zeolites [14,15]. The crystal
structure and pore analysis (surface area, pore volume, pore diameter)
of all the silylated H-beta zeolites using nitrogen adsorption are shown
in Fig. S4. Successive systematic silylation of H-BEA using tetrabutyl
orthosilicate progressively narrows the pore size distribution of zeolites
along with passivation of external acid sites (Table S1). Small deposition
of SiO2 (3.7 wt%) at pore mouth and external surface improved the
selectivity for 4-TBR from 83 to 88% by decreasing 4,6-DTBR formation
(Fig. 2). This decrease in the formation of 4,6-TBR could be due to the
passivation of acid sites on the external surface of BEA zeolite. This
shows that formation of 4,6-DTBR is not taking place inside the pores
but on the external acid sites of zeolite. Further successive SiO2 depo-
sition (3.7 to 15 wt%) decreased resorcinol conversion from 41 to 10%
due to a decrease in the number of external acid sites, as seen from the
TPD profiles (Figs. 3a, 2). Moreover, with SiO2 deposition pore mouths
of zeolites were also narrowed (Table S1). SiO2 deposition above 3.7%
had 4-TBR selectivity dropped from 88 to 45%, and RMTBE selectivity
increased from 10 to 52%, even though strength of acid sites remains
similar for the pristine and silylated catalysts as seen in the TPD-NH3
The high selectivity for RMTBE over H-BEA zeolite is related to its
pore characteristics. Reaction of resorcinol with TBA inside the pores
could form RMTBE, but its isomerization to 4-TBR is not possible due to
pore constraints. Such formed RMTBE coming out of zeolite pores could
isomerize to 4-TBR on the external acid sites, and compete with resor-
cinol in the alkylation reaction. The resorcinol with its small molecular
diameter (ca. 5.6 Å) can easily penetrate into the pores of H-BEA zeolite,
whereas such diffusion is difficult for RMTBE [13]. As a result, the
concentration of RMTBE increases with reaction time. It should be noted
that the conversion of resorcinol to RMTBE is a reversible phenomenon,
which dictates RMTBE selectivity in the reaction [6]. Therefore, RMTBE
is shape selectively produced over zeolite H-BEA in the butylation re-
action. The presence of supercages in H-Y zeolite makes the isomeriza-
tion of RMTBE to 4-TBR feasible without any constraints, hence the low
selectivity to RMTBE.
Further, we investigated the effect of Si/Al ratio (SAR) on the cata-
lytic activity over H-BEA and H-Y (Table 1). As SAR increases for H-BEA
and H-Y zeolites, total acidity decreases with as a result the decreasing
3

V.S. Marakatti and E.M. Gaigneaux
Catalysis Communications 152 (2021) 106291
Fig. 3. a) NH3-TPD, and b) pyridine FT-IR spectra over silylated H-BEA catalysts of different wt% SiO2.
Scheme 1. Plausible reaction mechanism for the butylation of resorcinol.
profiles (Fig. 3b). Furthermore, Brønsted and Lewis acid sites (B/L ratio)
of silylated H-BEA, determined by pyridine FTIR, exhibits no variation in
B/L ratio indicating that a variation of this feature might not be the
reason for such a selectivity difference for RMTBE and 4-TBR. (Fig. 3b).
This indicates that pore size of zeolites plays the major role in the pre-
sent catalysis rather than their acidity. To further understand whether
reaction is indeed taking place inside the pores or outside, strong and
bulky basic amine, namely tripentyl amine (not able to penetrate pores
with a size of ~6.5 Å due to its large molecular diameter of 9–10 Å), was
adsorbed on the surface of H-BEA, and catalytic activity after such
modification will be limited to reactions proceeding only inside the
pores of the zeolites. Doing so, resorcinol conversion dropped from 46 to
20%, and selectivity for 4-TBR dropped from 85 to 43%. (Table S1). This
indicates that half of the reaction was taking place inside the zeolite
pores and half outside the pores. Similar resorcinol conversion (>15%)
and 4-TBR selectivity (61%) values as obtained with 13.3 wt% SiO2
deposition by silylation indicates that at this loading, the external sur-
face of H-BEA is completely covered with SiO2. The resorcinol conver-
sion of 10–15% observed even after passivating the external acid sites by
13.3 wt% SiO2 must originate from reaction taking place inside the pores
of zeolites.
Moreover, increased RMTBE selectivity with successive silylations
also supports that the formation of RMTBE occurs inside the pores and
its isomerization to 4-TBR on the external acid sites is inhibited. Not only
external acid sites are blocked, but also pore mouth of BEA zeolite is
narrowed by silylation, where this also restricts access of RMTBE inside
4

V.S. Marakatti and E.M. Gaigneaux
Catalysis Communications 152 (2021) 106291
Fig. 4. XRD pattern (a), nitrogen adsorption isotherms (b), Scanning Electron Microscopy (SEM) images of Nano (c), and Micro (d) H-beta zeolite. TPD-NH3 profiles
(e) of H-BEA zeolite with two different particle sizes, Nano and Micro. The broad peak for Nano H-beta at 2theta = 23◦ clearly differentiates it from the conventional
micro H-Beta, which has very narrow peak width. This is further supported by the SEM images.
the pores to form 4-TBR, hence RMTBE concentration in reaction in-
creases. We suspect that weak hydrogen bonded silanol groups present
after silylation on the zeolite surface could catalyse the formation of
RMTBE [16]. To check this hypothesis, reaction of resorcinol with TBA
over pure SiO2 catalyst was studied. Formation of RMTBE was not
observed, supporting the idea that silanol groups do not contribute to
RMTBE selectivity. This indicates that formation of RMTBE shape
selectively occurs inside the pores of zeolite, as due to pore constraints, it
cannot be isomerized to 4-TBR. Still ~45% of 4-TBR selectivity obtained
with surface passivated zeolite could be originated by direct C-alkyl-
ation of resorcinol with TBA and not through formation of RMTBE.
These studies show that part of the reaction (formation of 4-TBR)
proceeds within the zeolite pores, but another part proceeds on its sur-
face. Hence, reaction proceeding inside the BEA zeolite pores to form 4-
TBR (in case of silylated catalysts) must go through a direct C-alkylation
pathway (Scheme 1). In this case, TBA within the zeolite beta undergoes
dehydration over acid sites (to form either carbocation or isobutylene),
then attacks resorcinol to form the 4-TBR directly through C-alkylation.
The reaction over external acid sites may proceed through isomerization
of RMTBE; initially RMTBE is formed inside or over the external surface
of zeolite through O-alkylation of resorcinol and then isomerization to 4-
TBR occurs over external acid sites.
larger (sample named micro) particle size of ~400–500 nm and high
acidity (1.2 mmol NH3/g) exhibits lower catalytic activity compared to
smaller (sample named nano) particle size of 20–50 nm (Fig. 4 and
Table 1). This indicates that particle size effect is predominant over
acidity in H-Beta catalyst. The resorcinol conversion and selectivity for
RMTBE and 4-TBR depends on the particle size of the H-BEA zeolite. The
lower resorcinol conversion in case of large particles of H-BEA is due to
the reduced external surface acid density compared to smaller particles
in size having large external surface acid density. Moreover, a large
particle size of H-BEA could limit the diffusion of reactants along the
long length of zeolite channels. The high selectivity of RMTBE in case of
large particle sized H-BEA indicates that its isomerization to 4-TBR over
fewer external acid sites is reduced and further conversion of RMTBE to
4-TBR by direct C-alkylation inside the zeolite pores of longer dimension
is limited. This illustrates that particle size and pore characteristics of
zeolite have enormous effect on the product selectivity over BEA zeolite.
TBA as alkylating agent in reaction produces water as byproduct and
is known to poison acidity of catalyst during reaction leading to lower
activity. Therefore, an effort to use different butylating agents such as
tertiary butyl ether (MTBE) and di-tertiary butyl dicarbonate (DTBDC)
was performed and results are provided in Table S2. MTBE produces
methanol as by- product, which resulted in a lower conversion, likely
due to the blockage of acid sites. On the contrary, DTBDC produces CO2
gas as by-product, without influencing the acidity of the catalysts, hence
To further support this, the effect of particle size of H-BEA on cata-
lytic activity in the alkylation of resorcinol was studied. H-BEA with
5

V.S. Marakatti and E.M. Gaigneaux
Catalysis Communications 152 (2021) 106291
the relatively good conversion of resorcinol observed over DTBDC even
at the lower temperature of 60 ◦C. Moreover, the complete inhibition of
RMTBE, 2-TBR and other side-products formation indicates direct C-
alkylation with DTDBC (Table S2). The absence of side products for-
mation also could be due to the lower reaction temperature that we were
forced to apply with MTBE and DTBC as alkylating agent due to their
low boiling points. Overall, H-BEA and HY zeolite in the present work
exhibited good resorcinol conversion of ~70%with 91–97% selectivity
to 4-TBR at lower temperature (ca. 60 ◦C) using DTBDC as alkylating
agent than most of the previously reported catalysts (Table S3). The 10%
Ga-BEA zeolite and 20% DTP/K10 are the only catalysts exhibiting
100% selectivity for 4-TBR. However, for the 20% DTP/K10 and Ga-Beta
catalysts, reaction was carried out at higher temperature, namely 150 ◦C
and 80 ◦C, respectively [1,2]. Furthermore, the use of less abundant thus
more expensive metal like Ga makes it a less attractive process. ITQ-6
zeolite showed 45% resorcinol conversion with 78% selectivity to 4-
TBR at 100 ◦C [3]. The other catalysts such as ZrO2 supported phos-
photungstic acid (PTA), acidified montmorillonite K-10, sulphated zir-
conia and heteropolytungstate (HPW) supported SBA-15 exhibited
lower activity and selectivity in the alkylation reaction compared to H-Y
zeolite in the present work [5–7]. The zeolites in the current study
appear simple, efficient, and easily scalable, which makes them attrac-
tive catalysts for the alkylation reaction.
the work reported in this paper.
Acknowledgements
The authors thank FRS-FNRS for the Project de recherche n◦
T.0064.16, and the Postdoctoral position allocated to VSM. FRS-FNRS is
also thanked for the acquisition of the nitrogen physisorption equipment
used (project EQP U. N030.18). The authors also thank Francois Devred
for the technical support provided.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.catcom.2021.106291.
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The difference of pore size in zeolites H-ZSM-5, H-Y, H-beta, H-
Mordenite brings tremendous effect on resorcinol conversion and
product selectivity compared to their acidity. H-BEA and H-Y zeolites
with large pore size exhibit high resorcinol conversion compared to the
H-ZSM-5 and H MOR zeolites. The pore characteristics of H-BEA in-
creases the formation of RMTBE, whereas that of H-Y zeolite increases
dialkylation and produces more 4, 6-TBR. The external acid sites
passivation by silylation and amine poisoning of H-BEA shows that part
of reaction goes outside the pores (O-alkylation followed by isomeriza-
tion) and another part goes inside the pores (direct C-alkylation) with
different plausible mechanisms as supported by studying catalysts with
different particle sizes. The use of DTBDC butylating agent has shown
large catalytic activity via the direct C-alkylation route, without for-
mation of either RMTBE, or 2-TBR. H-BEA zeolite with DTBDC as
alkylating agent exhibits 68% of resorcinol conversion with 97% of 4-
TBR selectivity at the mild reaction temperature of 60 ◦C, which com-
petes very well with previously reported catalysts.
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Supporting information
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Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
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