Solketal formation from glycerol and acetone over hierarchical zeolites of different structure as catalysts

Article abstract of DOI:10.1016/j.molcata.2016.11.018

Glycerol acetalization reaction with acetone was performed at 343?K and using a 1:1 molar ratio of glycerol to acetone in the feed over hierarchical zeolites comprising pores of different diameters (MFI, BEA, and MOR). The best catalytic performance for glycerol acetalization was exhibited by hierarchical (micro-mesoporous) MFI zeolites. Glycerol conversion over MFI zeolites exceeded 80%, with almost 100% selectivity to the desired product (4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane known as solketal). A significant increase in glycerol conversion and also selectivity to solketal in the studied reaction resulted from the easier accessibility of the active sites to reagents due to the formation of mesopores by means of desilication of the microporous zeolites.

Full text of DOI:10.1016/j.molcata.2016.11.018

Accepted Manuscript
Title: Solketal formation from glycerol and acetone over
hierarchical zeolites of different structure as catalysts
Author: J. Kowalska-Kus A. Held M. Frankowski K.
Nowinska
PII:
S1381-1169(16)30494-0
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.11.018
MOLCAA 10115
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Journal of Molecular Catalysis A: Chemical
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Revised date:
Accepted date:
6-9-2016
10-11-2016
11-11-2016
Please cite this article as: J.Kowalska-Kus, A.Held, M.Frankowski, K.Nowinska,
Solketal formation from glycerol and acetone over hierarchical zeolites of
different structure as catalysts, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2016.11.018
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Solketal formation from glycerol and acetone over hierarchical zeolites of different structure
as catalysts
J. Kowalska-Kus*, A. Held, M. Frankowski, K. Nowinska
Faculty of Chemistry, Adam Mickiewicz University, Poznan, Poland, *jolakow@amu.edu.pl

Highlights
Hierarchical zeolites significantly enlarge the glycerol conversion in acetalization
A shortening of diffusion path length results in almost 100% selectivity to solketal
Desilication of zeolites does not lead to significant modification of their acidity

ABSTRACT
Glycerol acetalization reaction with acetone was performed at 343 K and using a 1 : 1 molar
ratio of glycerol to acetone in the feed over hierarchical zeolites comprising pores of different
diameters (MFI, BEA, and MOR). The best catalytic performance for glycerol acetalization
was exhibited by hierarchical (micro-mesoporous) MFI zeolites. Glycerol conversion over
MFI zeolites exceeded 80 %, with almost 100 % selectivity to the desired product (4-
hydroxymethyl-2,2-dimethyl-1,3-dioxolane known as solketal). A significant increase in
glycerol conversion and also selectivity to solketal in the studied reaction resulted from the
easier accessibility of the active sites to reagents due to the formation of mesopores by means
of desilication of the microporous zeolites.

1. INTRODUCTION
Transesterification of vegetable oil and animal fats with methanol results not only in the
production of biodiesel but also in the formation of a significant amount of waste glycerol
phase (about 100 kG for every tonne of biodiesel) which, besides glycerol, is also comprised
of spent catalyst and excess methanol [1]. Considering that an increase in biodiesel production
brings about an increasing surplus of glycerol, its efficient utilization is very challenging.
Glycerol may be transformed into different chemicals that are intermediate for the production
of consumer goods. Among others are acroleine and acrylic acid obtained by the
oxydehydration process [2, 3], which are polymerized to acrylates; propylene glycol from
glycerol hydrogenolysis [4], applied in the pharmaceutical and food industry, and also
dihydroxyacetone (produced by glycerol oxidation [5, 6]), used for the production of
cosmetics and medicines. One promising procedure for glycerol utilization is the reaction of
glycerol with acetone or formaldehyde in the presence of acidic catalysts to produce acetals or
ketals [7-9].
A practical application of solketal, a product of glycerol acetalization with acetone, has been
found in a number of industrial processes [10]. It may be used in the polymer industry as a
plasticizer, in pharmaceutical production as suspending agent, and additionally as a fuel
additive, increasing the octane number of gasoline and reducing the emissions resulting from
fuel combustion.
The reaction of glycerol and acetone is a reversible process resulting in 2,2-dimethyl-1,3-
dioxolane-4-methanol (solketal) and water according to Scheme 1. Isomeric 1,3-dioxan-5-ol
may also be produced [11].
Our studies are concentrated on searching for the stable, easily accessible, and active catalyst
for the acetalization reaction. Traditionally, liquid inorganic acids have been applied as

catalysts for the mentioned process. Owing to the problems involved with both product
separation and the utilization of spent catalysts, extensive research on the applications of
heterogeneous catalysts has been undertaken [12]. Among different solid acidic catalysts such
as heteropolyacids [13], mesostructure silica modified in a different manner (i.e. sulfonic
acid-functionalized materials) [14], acidic resins such as Amberlyst [15], and also various
kinds of zeolites were tested [16-19]. So far, the best catalytic performance for glycerol
acetalization exhibited Amberlyst. However, its application on a wide scale is limited due to
its low thermal stability hindering the regeneration of Amberlyst by calcination after several
using. Therefore, more suitable catalysts of acetalization seem to be zeolites. The highest
activity in the studied reaction was found over BEA zeolite. Despite significant activity of
BEA zeolite, its high price makes the process of glycerol utilization not profitable. On the
other hand, acetalization of glycerol performed over MFI zeolites, due to their relatively low
price, wide availability and high thermal stability, should be very attractive. The restriction
that brings about lower activity of MFI catalysts for this process is related to the shape-
selectivity properties associated with the relatively narrow channel size [20]. Our earlier
calculation using the GaussView programme exploitation [21] indicated that the diameter of
the acetalization products is situated in the range of 0.43-0.51 nm, which could result in
diffusion limitation.
The previous studies have therefore become an inspiration to improve the activity of zeolites
for glycerol acetalization by limitation of diffusion restriction. This goal has been attained by
application of hierarchical (micro-mesoporous) MFI, BEA and MOR zeolites as
heterogeneous catalysts used for glycerol with acetone acetalization. For this purpose, in the
present paper, zeolites of MFI structure (pore diameter 0.51 - 0.55 nm) as well as BEA, and
MOR, characterized with higher channel diameters (0.61-0.67 nm and 0.67-0.70 nm,
respectively [20]), were prepared by desilication procedure, which is relatively cheap and

easy modification. It was expected that the application of micro-mesoporous zeolites as
catalysts for glycerol acetalization should demonstrate excellent glycerol conversion and
selectivity to the desired product.
2. EXPERIMENTAL
2.1 Materials
H-MFI (Süd Chemie, Si/Al=12 and Alsi Penta, Si/Al=27; denoted as MFI-1-P, MFI-2-P,
respectively), H-Mordenite (PQ Corporation, Si/Al=17; designed as MOR-P) and H-Beta
(Sigma Aldrich, Si/Al=12; denoted as BEA-P) were used as raw materials for alkaline and
subsequent acidic treatment.
2.2 Catalyst modification
2.2.1. Alkaline treatment
All the commercial zeolites were alkali-treated using the following procedure. 5.0 g of zeolite
was added to a 0.2 M (150 ml) aqueous NaOH solution and stirred at 353 K for 2 h.
Afterwards, the slurry was cooled, filtered, and then washed with distilled water until the pH
of the filtration solution decreased to 7. After drying at 363 K for 12 h, the alkali-treated
zeolite was ion exchanged with 0.5 M NH4NO3 aqueous solution by stirring at 308 K for 24 h,
followed by filtering and rinsing with distilled water to remove sodium ions. After drying at
363 K for 12 h, the ammonium form of zeolite was subsequently calcined in static air at
823 K for 3 h to form the H-form, denoted as MFI-number-AT, MOR-AT and BEA-AT,
respectively.
2.2.2. Acidic treatment
Some of the alkaline treated samples were used for further acid treatment with aqueous
solutions of nitric or citric acids. The procedure of the acid treatment was as follows. One part
of zeolite was put into 0.5 M nitrate acid (NA) solution and the second one was placed in
0.5 M citric acid (CA) solution. The resulting mixtures were kept at 353 K for 3 h with

stirring. The slurry was then cooled down, washed and dried at 363 K for 12 h and the
resulting samples were designated as MFI-number-NA, MOR-NA, BEA-NA and
MFI-number-CA, MOR-CA, BEA-CA, respectively. Finally, all the treated samples were
calcined at 823 K for 3 h.
2.3 Characterization
2.3.1 XRD
X-ray diffraction measurements were carried out on a Bruker AXS D8 Advance
diffractometer using CuKα radiation in order to confirm the structural correctness of the
prepared samples. Lowering of the crystallinity of alkali treated catalysts with comparison to
the parent ones was determined according to the method described in ref. [20, 22, 23]. The
relative crystallinity was calculated according to equation 1.
α = αo x I/Io
(Eq.1)
where we assume αo as equal to 100, I and Io are the areas of the reflexes characteristic of
parent and modified zeolites, respectively.
The I and Io values response to the sum of the areas of the most intense peaks at 2 Theta:
23.1°, 23.3° ,23.7°, 23.9°, 24.4° for MFI zeolite; 25.8°, 26.5°, 27.8° for MOR and 22.5° for
BEA zeolite.
2.3.2 Elemental analysis
Approximately 50 mg of the sample was weighed, placed in a Teflon bottle and 8 ml of supra
pure nitric acid (Sigma-Aldrich) was added. Then Teflon bottles were placed on the heating
plate with magnetic stirring for 30 min. After this time 2 ml of hydrofluoric acid (Sigma-
Aldrich) was added and placed again on the heating plate with magnetic stirring until
dissolution (around 30 min.). After cooling, the samples were placed in polyethylene
volumetric flasks and filled up to 100 ml with deionised water. The content of aluminium and
silicon were determined by atomic absorption spectrometry with acetylene-nitrous oxide

flame atomisation (F-AAS) using the 3D double-beam Shimadzu AA7000 analytical
technique (Shimadzu), equipped with an ASC-7000 autosampler (Shimadzu). The hollow
cathode lamps (HCL) employed were made by Photron.
2.3.3 BET
N2 adsorption/desorption isotherms were recorded on a Quantachrome Nova1000e analyzer at
77 K. The total surface area was calculated according to the BET equation. The micropore
and mesopore volume, and the external surface area were evaluated by the t-plot method. Pore
size was reported as the average pore diameter. Before measurements the samples were
preheated at 573 K for 4 h in vacuum.
2.3.4 FT-IR spectra of adsorbed pyridine
The FT-IR spectroscopic self-supporting wafer technique on a Bruker–Vector 22
spectrometer was used to determine the acidic properties of the parent and modified zeolites.
The wafers (20 mg/cm2) were prepared from powdered zeolites. Initially, the samples were
heated in vacuum at 673 K for 2 h. The samples were then cooled to the room temperature
(RT) after which the pyridine was adsorbed with following evacuation at 373 K to remove
physically adsorbed pyridine. The desorption temperature points were 373 K, 473 K, 573 K,
and 673 K. The spectrum was recorded after desorption in vacuum at a related temperature for
30 min. The number of acidic centers was calculated with equation 2 [21, 24]:
A
L
C
d
A
B
C
d
nT 

(Eq. 2)

L
m
 m
B
nT – total number of acidic sites expressed as micromoles of pyridine per 1 g of catalyst, AL
and AB – integrated absorbance of IR bands related to Lewis and Brønsted sites, Cd – cross
section of wafer in cm2 and m – mass in g of pressed pellet, and εL and εB molar absorption
coefficients for Lewis and Brønsted acid sites equal to 1.5 and 1.8 [μmol-1cm], respectively.
2.4 Catalytic activity measurement

The activity of the parent and modified zeolites was tested for the acetalization reaction of
glycerol with acetone. The reagents used in the experiments, glycerol (99.5 % purity) and
acetone (99 % purity), were purchased from Chempur. All the experiments were conducted at
a temperature of 343 K in closed glass vials of 4 cm3 capacity, under vigorous stirring (400
rpm) in a multiple-well parallel reaction block in the presence of catalyst in the amount of 1 %
related to glycerol. A 1 : 1 molar ratio of glycerol to acetone was used in the feed. Catalysts
were pre-activated in air at 623 K for 2 h followed by cooling down in a desiccator before the
catalytic run. Liquid products were analysed by GC, using a VARIAN CP-3800
chromatograph equipped with an FID detector with a VF-5ms column. Besides a predominant
product, a 5-membered ring ketal 2,2-dimethyl-1,3-dioxolane-4-methanol (solketal) and
unreacted glycerol and acetone, only a 6-membered ring ketal 2,2-dimethyl-1,3-dioxolane-5-
ol, a by-product, was identified by the Varian 4000 GC-MS apparatus. The catalytic activity,
reported as glycerol conversion (denoted as G C), selectivity to products: solketal (denoted as
S S) and isomer (denoted as S I), solketal yield (denoted as Y S), was calculated on the basis
of the equations presented in [25].
Conversion of glycerol (%)
mol of glycerol converted
C 
100
(Eq. 3)
(Eq. 4)
(Eq. 5)
initial mol of glycerol
where mol of glycerol converted = initial mol of glycerol – final mol of glycerol
Selectivity to solketal or isomer (%)
mol of X formed
S 
100
mol of glycerol converted
where X = solketal or isomer
Yield of solketal (%)
S C
100
Y 

3. RESULTS AND DISCUSSION
Catalyst characterization
XRD
The XRD patterns of parent and modified zeolites of MFI structure are presented in Fig. 1 and
BEA and MOR structures are demonstrated in Fig. 2. The patterns show that the proper
structure of the zeolites has been preserved in the samples after the alkaline treatment and
after the ionic exchange with aqueous solutions of NH4NO3. No additional phase was noted in
the modified samples. However, a small decrease in the intensities of the characteristic
reflexes was observed, which suggests a lowering of the crystallinity. The related crystallinity
of the modified samples with reference to the initial materials is listed in Table 1. These
results prove that alkali treatment induces some lowering in the crystallinity. A decrease in
crystallinity was visible for both MFI zeolites, at a similar level (about 30 % of the initial
value). A similar reduction of crystallinity was noted for MOR (30 % of the initial value),
while the crystallinity of BEA zeolite was practically unchanged (2 % of the initial value).
The following treatment of desilicated samples with HNO3 or C6H8O7 solutions in the next
step of catalyst modification was motivated by the literature suggestions [26], indicating the
possible occlusion of aluminum and hindrance of mesopores opening in alkaline treated
zeolites. The data showed that acidic treatment does not influence the crystalline structure of
the modified zeolites significantly, however, it results in an increase in the Si/Al ratio (Table
1). Only the treatment of desilicated BEA zeolite with nitric acid leads to some lowering in
the crystallinity up to 81 %. This may be due to the partial extraction of framework aluminum
from BEA zeolite, considering that BEA zeolite is relatively easy to dealuminate [20]. A
similar alteration of the crystallinity of BEA zeolite modified by means of desilication with
following treatment with nitric acid solution was reported by Wang et al. [27].

Si/Al ratio
The alkali treatment of zeolite should lead to a preferential desilication, which would then be
reflected in the changing of Si/Al ratio. The Si/Al ratios of the parent and modified zeolites
are presented in Table 1. The Si/Al ratio of all alkaline treated zeolites obtained via
the F-AAS analysis was found to be lower than that of the parent catalysts. The presented
results indicate that the higher Si/Al in applied MFI zeolites, the higher the degree of
desilication was observed. According to literature [26, 28, 29], desilication of zeolite depends
significantly on the Si/Al ratio of the initial material as well as on the applied conditions. A
high concentration of framework aluminum (low Si/Al ratio) results in restriction of the
silicon removal and in limitation of mesoporosity development. This is in accordance with the
lower degree of desilication in the MFI zeolite of Si/Al equal to 12, when compared to the
sample with Si/Al equal to 27 (Table 1). On the other hand, the relatively high mesoporosity
achieved in our experiment over MFI-1-AT may result from long duration of the treatment (2
h) at a relatively high temperature 353 K.
The influence of zeolite structure on the desilication process has been indicated in the
literature [30]. According to the results presented in Table 1 silicon removal as an effect of
alkaline treatment results in a decrease in the Si/Al ratio in the following way:
MFI(27)>MOR(17)~MFI(12)>BEA(12). Subsequent treatment with acids (HNO3 or C6H8O7)
brings about an increase in the Si/Al ratio as a result of aluminum removal. Susceptibility to
dealumination is especially visible for MOR and BEA zeolites. It has been shown by Groen et
al. [31] and also by Tian et al. [32] that resistance of BEA zeolite to dealumination is lower
when compared to MFI zeolites.
Textural properties
The influence of the alkali treatment on the porosity of the applied zeolites was studied by the
N2 adsorption–desorption procedure at 77 K and the results are listed in Table 1. Alkaline

treatment of the zeolites with NaOH solution and the following ionic exchange with aqueous
solution of NH4NO3 leads to spectacular mesopore formation. However, the enlargement of
the surface area and the mesoporosity depends on the structure of the initial samples. MFI
zeolites with a different Si/Al ratio show a similar increase in surface area (in the range of
20-25 % of the initial values), while the surface area of BEA zeolite increases by 10 % and
changes only slightly for MOR (3 % of the initial value). Desilication also results in an
increase of the surface of mesopores. The contribution of mesopores in total surface area
increased from approximately 10 % for initial zeolites of MFI structure to about 50 % for
modified ones, while for the BEA zeolite and MOR the contribution of mesopores increased
from 32 % to about 50 % and from 19 % to about 34 %, respectively. The following treatment
with HNO3 or C6H8O7 acid solutions influenced the textural parameters only slightly
(Figs 1 and 2). Even though, no significant changes in the modified zeolite texture were
recorded, the Si/Al ratio increased (Table 1) and Brønsted as well as Lewis acidity decreased
(Table 2) after acidic treatment, confirming partial aluminum removal.
As shown in Fig. 3, the isotherms of both MFI zeolites showed typical Langmuir Type-I
adsorption patterns prior to alkali-treatment. After alkaline treatment, all the isotherms
exhibited distinct hysteresis loops indicating Type-IV behavior as a result of mesopores
formation from the desilication process. This is in agreement with the observed increase in
pore volume as well as in enlargement of the contribution of mesopores surface in the total
surface area (Table 1). A similar alteration in zeolite texture was described in the literature as
a result of the desilication procedure [26].
Although the isotherms of parent BEA and MOR (Fig. 4) show some hysteresis due to the
presence of mesopores, the hysteresis loop increases visibly as a result of the desilication
process. The average pore diameter of modified samples was shifted towards higher values,

indicating the formation of macropores in the modified samples. A similarly high pore
diameter was reported in the literature [20, 29].
Acidic properties
The acidity of the parent and modified zeolites was estimated on the basis of the FT-IR
spectra of adsorbed pyridine after desorption at a temperature in the range of 373-673 K.
Table 2 summarizes the acidic properties of all applied zeolites. Desilication of MFI and also
MOR and BEA zeolites with following ionic exchange with NH4NO3 resulted in the increase
of both total acidity estimated at 373 K (Figs 5 and 6) as well as strong acidity measured after
the evacuation of pyridine at 673 K (Table 2). Both Brønsted acidity and Lewis acidity were
responsible for the increase in total acidity in MFI zeolites. The high acidity after the
desilication process indicates that aluminum is still in tetrahedral coordination. On the other
hand, the lower Brønsted acidity and higher Lewis acidity observed on desilicated MOR and
BEA zeolites may evidence that the dealumination process occurs with desilication
(Tables 1 and 2).
When the desilicated samples were treated with aqueous solutions of HNO3 or C6H8O7, the
Lewis acidity was clearly lower in comparison with the samples exchanged with NH4NO3.
This suggests that the treatment of desilicated zeolites with acidic solutions results in
dissolution of aluminum debris, as suggested in the literature [26]. This is in accordance with
alteration in the Si/Al ratio (Table 1).
Catalytic activity for glycerol acetalization
Acetalization of glycerol with acetone to obtain solketal was tested over parent zeolites of
MFI, MOR and BEA structures and also on the materials subjected to desilication with
following ionic exchange with NH4NO3 solution and subsequent acidic treatment.
Protonic forms of commercial zeolites displayed very different activity for glycerol
acetalization depending on their pore arrangement. The initial MOR and BEA zeolites

characterized by a relatively large pore opening (diameter of about 0.67 nm) and higher
accessibility to active sites for the reactants show glycerol conversion in the range of 67-72 %
(Figs 9 and 10). The desilication process of MOR and BEA zeolites with generation of
mesoporosity resulted in some increase in glycerol conversion up to 81 %. The following
treatment with citric acid alters the glycerol conversion slightly, while treatment with nitric
acid results in a reduction of glycerol conversion. A similar tendency in the lowering of
glycerol conversion over all zeolites treated with nitric acid, compared to values obtained
after citric acid modification, may arise from a significant decrease in acidic sites resulting
from partial dealumination (Tables 1 and 2).
The activity of the parent zeolites of MFI structure, characterized by a different Si/Al ratio
equal to 12 and 27, was definitely lower (18 % and 37 %, respectively), because of the
diffusion limitation (Figs 7 and 8). According to the literature [33] the Si/Al ratio affects the
desilication process and a value in the range of 25-50 has been indicated as optimal. The
desilication process resulted in an increase in glycerol conversion. The glycerol conversion
over MFI-1-AT reached 30 %, whereas on the MFI-2-AT it increased up to 80 % (Figs 7 and
8). The following treatment with citric acid resulted in a significant increase in glycerol
conversion up to 82 % and 85 %, respectively. It seems that aluminum debris do not block the
mesopores for small nitrogen molecules (N2 applied for porosity estimation), while they are
not quite available for reagents. Therefore, the removal of aluminum debris results in a
significant increase in glycerol conversion.
The desilication of zeolites also resulted in an increase in selectivity to solketal, which
achieved nearly 100 %. Solketal, the main product of the acetalization reaction, is kinetically
favoured, while the isomer 1,3 dioxane is thermodynamically more stable. Longer contact
time with catalytically active sites may result in isomeric molecule formation (bringing about
the selectivity to 1,3 dioxane up to 25- 27 on MFI-1P and MFI-2P - Figs 7 and 8), therefore,

faster diffusion due to the presence of mesopores seems to be responsible for limitation of its
production up to 3 %. The obtained data confirm that an almost 80% yield of solketal, as the
predominant product, was obtained in the acetalization reaction. Interestingly, high glycerol
conversion (80 % or more) and near 100 % selectivity to solketal was achieved for the
stoichiometric acetone to glycerol ratio (acetone : glycerol = 1 : 1). Considering that the
acetalization of glycerol with acetone is a reversible reaction, a higher acetone to glycerol
molar ratio shifts the reaction towards the products. The best solketal yield reported in the
literature was achieved for an acetone to glycerol ratio equal to 4 : 1 [34]. The obtained results
indicate that the desilication of zeolites can create highly efficient catalysts for glycerol
acetalization.
4. CONCLUSIONS
Glycerol acetalization reaction with acetone performed for the very first time over large pores,
hierarchical zeolites (MFI, BEA and MOR) as catalysts resulted in a significant increase in
glycerol conversion, even exceeding 80 %. As a result of a dramatic shortening of diffusion
path length, selectivity to solketal reached almost 100 %. The most substantial increase in
activity for the acetalization reaction was recorded over hierarchical MFI zeolites which could
enable the utilization of commonly used MFI zeolites in an industrially relevant process of
glycerol transformation.

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Captions figures
Fig.1. XRD patterns of parent and modified MFI-1 (A) and MFI-2 (B) zeolites with Si/Al
ratio equal to 12 and 27, respectively
Fig.2. XRD patterns of parent and modified BEA (A) and MOR (B) zeolites with Si/Al ratio
equal to 12 and 17, respectively
Fig. 3. N2 sorption isotherms of parent and modified MFI-1 (A) and MFI-2 (B) zeolites with
Si/Al ratio equal to 12 and 27, respectively.
Fig. 4. N2 sorption isotherms of parent and modified BEA (A) and MOR (B) zeolites with
Si/Al ratio equal to 12 and 17, respectively.
Fig. 5. FT-IR spectra of pyridine adsorbed at RT and desorbed at 373 K for 0.5 h, related to
total acidity, recorded on parent and modified MFI-1 (A) and MFI-2 (B) zeolites with Si/Al
ratio equal to 12 and 27, respectively
Fig. 6. FT-IR spectra of pyridine adsorbed at RT and desorbed at 373 K for 0.5 h, related to
total acidity, recorded on parent and modified BEA (A) and MOR (B) zeolites with Si/Al ratio
equal to 12 and 17, respectively
Fig. 7. Conversion of glycerol (G C), selectivity to products: solketal (S S) and isomer (S I),
yield of solketal (Y S) over parent and modified MFI-1 zeolite with Si/Al ratio equal to 12
Fig. 8. Conversion of glycerol (G C), selectivity to products: solketal (S S) and isomer (S I),
yield of solketal (Y S) over parent and modified MFI-2 zeolite with Si/Al ratio equal to 27
Fig. 9. Conversion of glycerol (G C), selectivity to products: solketal (S S) and isomer (S I),
yield of solketal (Y S) over parent and modified BEA zeolite with Si/Al ratio equal to 12
Fig. 10. Conversion of glycerol (G C), selectivity to products: solketal (S S) and isomer (S I),
yield of solketal (Y S) over parent and modified MOR zeolite with Si/Al ratio equal to 17
Scheme 1 Acetalization reaction of glycerol with acetone

Tables
Table 1 Physicochemical and textural characterization of the parent and modified zeolites
b
Zeolite
Molar SBET
Sextc Mespor Average Vtotalb Vmesoc Relative
Si/Al (m2/g) (m2/g)
ratioa
esc
pore
diamete
rb
(cm3/g) (cm3/g) Crystallini
tyd
(%)
(nm)
MFI-1-P
12
242
292
293
308
252
307
310
308
490
525
539
538
398
399
410
409
24
10
46
46
49
12
53
54
51
32
48
48
52
32
48
48
52
3.06
0.19
0.30
0.31
0.32
0.19
0.31
0.32
0.30
0.71
1.21
1.21
1.25
0.35
0.57
0.63
0.60
0.05
0.20
0.21
0.22
0.05
0.30
0.22
0.29
0.50
1.03
1.02
1.08
0.14
0.39
0.45
0.42
100
72
MFI-1-AT
MFI-1-CA
MFI-1-NA
MFI-2-P
9.2
135
135
151
29
4.08
4.16
4.17
3.04
3.98
3.94
4.06
5.84
9.19
9.31
9.00
3.54
5.73
5.87
6.12
12.9
13.6
27
74
72
100
74
MFI-2-AT
MFI-2-CA
MFI-2-NA
BEA-P
13.2
21.5
25.7
12
164
167
158
159
252
259
282
74
79
77
100
98
BEA-AT
BEA-CA
BEA-NA
MOR-P
9.3
12.0
18.3
17
95
81
100
67
MOR-AT
MOR-CA
MOR-NA
10.8
20.2
25.8
117
129
138
70
65
a F-AAS; b BET-method; c T-plot method; d according to ref. [20, 22, 23]

Table 2 Acidic properties of the parent and modified zeolites
Acidity ( µmol/g)
Totala
L
Strongb
L
Zeolite
B
B+L
B
B+L
MFI-1-P
234
327
256
262
279
368
170
157
464
282
219
94
73
272
229
199
63
307
599
485
461
342
464
369
339
674
752
388
280
456
550
337
242
75
35
143
94
110
276
249
248
215
297
159
148
345
458
250
124
232
335
251
214
MFI-1-AT
MFI-1-CA
MFI-1-NA
MFI-2-P
133
155
151
187
263
86
97
28
MFI-2-AT
MFI-2-CA
MFI-2-NA
BEA-P
96
61
199
182
210
470
169
186
78
73
75
73
139
155
139
69
206
303
111
55
BEA-AT
BEA-CA
BEA-NA
MOR-P
378
301
235
149
133
165
130
164
99
MOR-AT
MOR-CA
MOR-NA
249
102
93
170
121
50
a calculated after pyridine adsorption at RT and desorption at 373 K for 0.5 h;
b calculated after pyridine adsorption at RT and desorption at 673 K for 0.5 h;

*Graphical Abstract
Hierarchical zeolites demonstrated very excellent glycerol conversion and selectivity to the
desired product (solketal) for acetalization reaction.
O
OH
O

Figure
Fig.1
B
A
MFI-2-CA
MFI-1-CA
MFI-2-NA
MFI-2-AT
MFI-1-NA
MFI-1-AT
MFI-1-P
MFI-2-P
10 20 30 40 50 60
10 20 30 40 50 60
2 Theta(°)
2 Theta(°)

Figure
Fig. 2
B
A
MOR-CA
BEA-CA
MOR-NA
MOR-AT
BEA-NA
BEA-AT
BEA-P
MOR-P
10 20 30 40 50 60
10 20 30 40 50 60
2 Theta(°)
2 Theta(°)

Figure
Fig. 3.
A 320
280
240
200
160
120
80
B 320
280
240
200
160
120
80
MFI-1-CA
MFI-1-NA
MFI-2-CA
MFI-2-NA
MFI-2-AT
MFI-1-AT
MFI-2-P
MFI-1-P
1.0
0.0
0.2
0.4
0.6
0.8
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Relative pressure (p/p0)

Figure
Fig. 4.
A
1200
1000
800
B 450
400
350
300
250
200
150
100
50
BEA-CA
BEA-NA
MOR-CA
MOR-NA
BEA-AT
BEA-P
600
400
MOR-AT
MOR-P
200
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Relative pressure (p/p0)

Figure
Fig. 5.
A
B
0.25
0.25
1490
1490
1456
1546
1546
1456
MFI-2-NA
MFI-2-CA
MFI-1-NA
MFI-1-CA
MFI-2-AT
MFI-2
MFI-1-AT
MFI-1
1575
1500
Wavenumber(cm-1)
1425
1575
1500
Wavenumber(cm-1)
1425

Figure
Fig. 6.
A
B
0.25
0.25
1490
1490
1456
1456
1546
1546
BEA-NA
BEA-CA
MOR-NA
MOR-CA
BEA-AT
MOR-AT
MOR
BEA
1575
1500
Wavenumber(cm-1)
1425
1575
1500
Wavenumber(cm-1)
1425

Figure
Fig. 7.
G C
Y S
S S
S I
100
80
60
40
20
0
MFI-1-P
MFI-1-AT
MFI-1-CA
MFI-1-NA