Novel non-hydrolytic templated sol-gel synthesis of mesoporous aluminosilicates and their use as aminolysis catalysts

Article abstract of DOI:10.1039/c5ra24563j

A novel non-hydrolytic sol-gel (NHSG) synthesis of mesoporous aluminosilicate xerogels is presented. The polycondensation between silicon acetate, Si(OAc)₄, and tris(dimethylamido)alane, Al(NMe₂)₃, leads to homogeneous alu

Full text of DOI:10.1039/c5ra24563j

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: D. Skoda, A.
Styskalik, Z. Moravec, P. Bezdicka, M. Babiak, M. Klementova, C. Barnes and J. Pinkas, RSC Adv., 2016,
DOI: 10.1039/C5RA24563J.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
Novel Non-hydrolytic Templated Sol-Gel Synthesis of Mesoporous
Aluminosilicates and Their Use as Aminolysis Catalysts
David Skoda,a,b Ales Styskalik,a,b Zdenek Moravec,a Petr Bezdicka,c Michal Babiak,a,b Mariana
Klementova,c Craig E. Barnes,d Jiri Pinkas*,a,b
a Masaryk University, Department of Chemistry, Kotlarska 2, CZ-61137 Brno, Czech Republic
b Masaryk University, CEITEC MU, Kamenice 5, CZ-62500 Brno, Czech Republic
c Institute of Inorganic Chemistry of the ASCR, v.v.i., CZ-25068 Husinec-Rez, Czech Republic
d
University of Tennessee, Department of Chemistry, Knoxville, TN 37996-1600, United
States
jpinkas@chemi.muni.cz
KEYWORDS. Sol-gel; Non-hydrolytic condensation; Templating; Acetamide elimination;
Mesoporous; Mixed oxides; Aluminosilicate; Aminolysis; Catalysis
Abstract
A novel non-hydrolytic sol–gel (NHSG) synthesis of mesoporous aluminosilicate xerogels is presented.
The polycondensation between silicon acetate, Si(OAc)4, and tris(dimethylamido)alane, Al(NMe2)3,
leads to homogeneous aluminosilicate xerogels containing Si–O–Al linkages through
dimethylacetamide elimination. The addition of Pluronic P123 and F127 templates provides stiff gels
that are, after calcination at 500 °C, converted to stable mesoporous xerogels with high surface area
(˃ 600 m2 g-1) and wormhole-type pores (d = 5.1 nm). The xerogels exhibit high catalytic activity in
aminolysis of styrene oxide (82 % conversion) with the turnover frequency up to 100.
Introduction
Aluminosilicate zeolites with their uniform molecular-sized pores, high surface acidity, and large
number of active sites have been extensively applied as molecular sieves, ion exchangers, and solid
acid catalysts in industrial catalytic processes since the last century.1, 2 They are usually prepared
from alkoxide precursors under hydrothermal conditions by so-called molecular templating wherein
a cationic organic species acts as a template for the formation of ordered pores and channels. This
1

RSC Advances
Page 2 of 27
View Article Online
DOI: 10.1039/C5RA24563J
approach generates highly ordered microporous materials whose pore diameters are controlled by
the size of the molecular templates. The pore sizes of zeolites are therefore below 15 Å and typically
4−10 Å.3 However, the conversion or adsorption of bulky organic molecules requires large pore
channels (>2 nm), which has not been achieved in stable microporous zeolites. A synthetic challenge
in this context is the disparate hydrolysis rates of Si and Al alkoxides which lead to precipitation of
alumina rich phases and has to be prevented by prehydrolysis4 or chelation methods.5 The discovery
of ordered mesoporous silicates, such as MCM-41, with high surface areas, well-defined and tunable
pore diameters from 1.5 to 10 nm was a significant advancement in this field. The catalysts with the
hexagonal structure, such as Al-MCM-41, offered an opportunity for processing bulky molecules6 and
attracted much interest.7 Unfortunately, the poor hydrothermal stability of the MCM-41-type
materials restricts their wider applications in industrial catalysis. Nevertheless, improved
hydrothermal stability of cubic Al-MCM-48 materials was achieved by supercritical fluid (SCF)
impregnation.8 Increase of hydrothermal stability was achieved also by 2-D hexagonal mesoporous
SBA-15 materials9 with large pores (4.6–30 nm), thick pore walls (3.1–6.4 nm), and high specific
surface areas (up to 1000 m2 g-1). However, electrically neutral frameworks of silica SBA-15 materials
exhibit very weak acidity derived from the silanol groups located on the pore walls. Therefore, much
effort have been devoted to increasing the acidity by introduction of Al into the framework by direct
synthesis,10 post-synthesis11 and grafting or impregnation12 strategies. The procedure of direct
synthesis is relatively simple, but only a small number of the heteroatoms can be introduced into the
mesophases. By contrast, the procedure of grafting or impregnation is complicated and difficult to
replicate. Moreover, there are always more 6-coordinated Al atoms in these materials than 4-
coordinated ones which are essential for Brønsted acidity.13 Al-SBA-15 materials with a large number
of moderate acidic sites are very promising catalysts and supports allowing catalytic cracking,
15
alkylation, and hydrotreating reactions.14, The preparation of Al-SBA-15 via the post-synthesis
method was reported by Li16 by treatment with aluminum isopropoxide. Han reported well-ordered
hexagonal mesoporous aluminosilicates synthesized by the re-crystallization of SBA-15 in a dilute
solution of aluminosilicate sol, glycerol, or both.17 Recently, the assembly of zeolite seeds or coating
of walls of mesoporous matrices (SBA-15, MCM-48) with zeolites was described as a promising way
to novel class of hydrothermally stable mesoporous aluminosilicate catalysts. The assembly of ZSM-5,
Beta, TS-1, and FAU zeolite seeds was achieved with the use of structure-directing agents, such as
cetyltrimethyl ammonium bromide (CTAB) or Pluronic P123.18-21 A so-called coated route approach
using a dilute clear solution of primary zeolite units was employed to synthesize ultrastable
23
mesoporous aluminosilicate molecular sieves.22,
This method produces a new type of
nanocrystalline zeolitic material with mesopore walls formed by a templated solid-state secondary
crystallization of zeolites into walls of SBA-15.
2

Page 3 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
Recently, Liu13 has obtained Al-rich mesoporous aluminosilicates with improved hydrothermal
stability by assembling zeolite Y and Beta precursors in the walls of mesophases. For example, the
retaining ratio of the total surface area was 33% after hydrothermal treatment in 100% water vapor
at 800 °C for 15 h. This group also reported a pH-adjusting method24 based on the assembly of Beta
zeolite. An approach recently published by Enterria25 provides a simple strategy based on the
overgrowing mesoporous silica (MCM-48) on crystalline zeolite particles. For this purpose, preformed
zeolite is added to mesoporous silica gel, which results in materials with a microporous zeolitic core
and a mesoporous silica cover (MCM-48).
The methods and procedures mentioned above all involve hydrolytic reactions. Aluminosilicates can
also be successfully prepared by non-hydrolytic routes. With these methods, it is possible to
overcome the problems of different hydrolysis rates and subsequent phase separation. These
techniques allow reaction control on atomic scale and homogeneous dispersions of silicon and
aluminum atoms in the gel network may be achieved. One type of non-hydrolytic sol-gel (NHSG)
reaction is alkylhalogenide elimination.26 In this method, condensations between SiCl4, AlCl3,
Al(OiPr)3, and Si(OiPr)4 in ethers or CH2Cl2 provide monolithic homogeneous aluminosilicate gels27
(Scheme 1).
Scheme 1. Non-hydrolytic alkylhalogenide elimination
This non-hydrolytic sol-gel technique has also been applied to the preparation of highly active
28
mesoporous metathesis catalysts MoO3–SiO2–Al2O3 and Re2O7–SiO2–Al2O3.29 Mullite precursor gel
synthesis was described from AlCl3 and TEOS in Et2O and CCl4 in an autoclave at 110 °C.30
Catalytic efficiency of aluminosilicates was determined by a variety of test reactions. Kim reported
Friedel-Crafts acylation of bulky aromatic compounds in MFI zeolite nanosponge,31 Neves32 used
mesoporous aluminosilicates with acid sites for conversion of furfuryl alcohol to ethyl levulinate and
Robinson described the alcoholysis and aminolysis of styrene oxide promoted by mesoporous
aluminosilicate catalysts.33, 34
We have recently reported that non-hydrolytic acetamide elimination35 can be successfully used for
the synthesis of mesoporous titanium silicate36 and zirconium silicate materials.37 In contrast to
3

RSC Advances
Page 4 of 27
View Article Online
DOI: 10.1039/C5RA24563J
conventional hydrolysis-based routes for the preparation of SBA-15 and MCM-41 materials, our
approach excludes hydrolytic steps and the reactions proceed only by condensation of metal amide
with silicon acetate.
The work presented here introduces this novel non-hydrolytic acetamide elimination for the
preparation of aluminosilicate xerogels with a high Al content in the framework. This effective one-
pot reaction can be extended by the use of templates. With the Pluronic block copolymers we are
able to obtain homogeneous xerogels which exhibit their mesoporous character even after
calcination at 700 °C and convert to mullite only at 980─1000 °C. We have successfully used these
materials as catalysts for aminolysis34, 38 and alcoholysis33 of styrene oxide and for the conversion of
styrene oxide to phenylacetaldehyde.39
Experimental
General procedures
All manipulations were performed in dry nitrogen using Schlenk techniques or in an M. Braun drybox
with both H2O and O2 levels below 1 ppm. Al(NMe2)3 is highly flammable and reacts violently with
water, liberating flammable gases. It must be handled under dry inert gas at all times.
Chemicals, such as Pluronic P123 (EO20PO70EO20 Mav = 5845 g mol−1), Pluronic F127 (EO100PO65EO100
Mav = 12600 g mol−1), tris(dimethylamido)aluminium Al(NMe2)3 (99 %), styrene oxide (97 %), aniline
(97 %), methanol, and nonane, were purchased from Sigma-Aldrich. Si(OAc)4, Si2O(OAc)6, Me3SiOAc,
and Si2(CH2)2(OAc)6 were synthesized according to the published procedures.40 Toluene, methanol,
and isopropanol were dried by standard methods and distilled before use. Pluronic P123 and F127
were dried under vacuum at 60 °C, dissolved in dry toluene, and stored as 20.17 and 19.61 wt%
solutions, respectively.
Characterization
IR spectra were recorded on a Bruker Tensor 27 FTIR spectrometer from KBr pellets or on a Bruker
Alpha–Platinum ATR system. GC-MS measurements were performed on a mass spectrometer TSQ
Quantum XLS coupled with a gas chromatograph Trace GC Ultra by Thermo Scientific. The gas
chromatograph was equipped with a TS-SQC column (length 15 m, diameter 0.25 mm, film thickness
0.25 μm) using a temperature program: 50 °C (0 min), 5 °C min-1 to 80 °C, 15 °C min-1 ramp to 120 °C,
35 °C min-1 ramp to 200 °C, held at 200 °C for 0.5 min. Split injection mode was used with the
injector, interface, and detector temperatures all set to 200 °C. The column pressure was 31.5 kPa
4

Page 5 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
and the ionization energy was 70 eV. DIP MS measurements were performed with the temperature
program 30 °C for 30 s, 50 °C min-1 30–450 °C, and held at this temperature for 1 min; the ionization
energy was 44 eV. For liquid phase 1H and 13C NMR measurements, a Bruker Avance II DRX 300 MHz
spectrometer was used. The spectra were referenced to the residual proton or carbon resonances of
benzene-d6 (7.15 and 128.0 ppm) and CDCl3 (7.20 and 77.0 ppm). Solid state NMR spectra were
measured on a Bruker Avance III 700 MHz spectrometer with a MAS DVT 700S4 BL4 N-P/H probe and
on a Bruker Avance III 500 MHz spectrometer with a MAS VTN 500SB BL4 N-P/F-H probe. Chemical
shifts were referenced externally to 29Si δ [(Me3SiO)8Si8O20]: 11.72 ppm; 13C δ [adamantane] 38.68
ppm; 27Al δ [[Al(H2O)6]3+ (aq. solution)]: 0.0 ppm. High temperature PXRD diffractograms were
recorded on an X’PertPRO diffractometer equipped with a CoKα X-ray tube and a HTK 16 high-
temperature chamber (Anton Paar, Graz, Austria) with a Pt holder. Samples were measured from 500
to 1250 °C in 50 °C increments. The sample was held during scanning at a constant temperature for
12 min. Nitrogen adsorption/desorption experiments were performed at 77 K on a Quantachrome
Autosorb-1MP porosimeter. Prior to the measurements, the samples were degassed at 100 °C for at
least 24 h until the outgas rate was less than 0.4 Pa min−1. The adsorption-desorption isotherms were
measured for each sample at least three times. The specific surface areas (SA), total pore volumes
(Vtot at p/p0 = 0.98) and average pore size (d) were determined by volumetric techniques41, 42 and
analyzed by the multipoint BET method using at least five data points. The valid pressure ranges were
established by the Rouquerol transform and equivalent BET surface areas were calculated. Pore size
distributions were calculated by the NLDFT method from the adsorption branch of the isotherms
with the use of a nitrogen-on-silica kernel. Thermal analysis (TG/DSC) was performed on a Netzsch
STA 449C Jupiter apparatus in the stream of air (70 cm3 min-1) with a temperature ramp of 5 °C min-1
to 1000 °C, in a Pt crucible. Aluminium and silicon contents were determined on an ICP optical
emission spectrometer iCAP 6500 Duo (Thermo, UK) equipped with a solid-state generator with a
frequency of 27.12 MHz and a maximum power input 1350 W. The measurements of Al were
performed at 167.0, 308.2, and 309.2 nm. For Si analysis, wavelengths 212.4 and 251.6 nm were
used. Transmission electron microscopy (TEM) images were obtained from a JEOL JEM 3010
microscope operated at 300 kV (LaB6 cathode, point resolution 1.7 Å) with an Oxford Instruments
Energy Dispersive X-ray (EDX) detector attached. SAXS measurements were performed on a Rigaku
BioSAXS 1000 system at wavelength of 1.5408 Å with a PILATUS 100K detector, Dectris Lts. Scattering
curves were analyzed by ATSAS software package. Studies of surface acidity were performed on air-
calcined xerogels. Xerogels (cca 50 mg) were dried before adsorption under vacuum (1 h, 115 °C).
Then, the samples were exposed for 30 min to pyridine vapors under its autogenous pressure at 25
°C. After adsorption, samples were dried at room temperature under vacuum for 2 h. Adsorbed
pyridine was characterized by the IR technique.
5

RSC Advances
Page 6 of 27
View Article Online
DOI: 10.1039/C5RA24563J
The single-crystal X-ray diffraction data were collected at 120 K using Rigaku diffraction system
(MicroMax007HF DW rotating anode source with multilayer optic, partial χ axis goniometer, Saturn
724+ HG detector and Cryostream cooling device). Molybdenum Kα radiation (λ = 0.71075 Å) was
used. CrystalClear (Rigaku 2014) and CrysAlisPro (Agilent Technologies 2013) software packages were
used for data collection and data reduction. The structure was solved using SHELXT43 program and
refined (full matrix least-squares refinement on F2) using SHELXL program. Both symmetrically
independent cation fragments were disordered. One Me3Si- moiety of one anionic fragment was also
refined as disordered. Disordered fragments were treated by geometrical similarity restraints and by
ADP restraints. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms (of methyl
and hydroxyl groups) were placed at calculated positions and refined as riding and rotating, with
their Uiso set to 1.5 Ueq of carrier atom.
In reactions without a template, the yield of the product as well as the mass of starting precursors
were precisely weighed to allow gravimetric estimation of the degree of condensation, DC = 100(ntotal
– nresidual)/ntotal, where ntotal is the molar amount of organic groups in the starting materials and nresidual
is molar amount of residual organic groups in the xerogel based on the difference between
theoretical and experimental yields. As the condensation reactions were never quantitative, the
degree of condensation represents the relative difference between the maximum theoretical loss of
Me2NC(O)CH3 (eq. 1) in comparison to what is experimentally observed. This difference also defines
the number of acetoxy groups on silicon and dimethylamido groups on aluminium that are left in the
matrix.
Aluminosilicate xerogel prepared without template SiAl1 (Eq. 1)
Al(NMe2)3 (0.799 g; 5.02 mmol) dissolved in 15 cm3 of dry toluene was added dropwise by a syringe
to a stirred solution of Si(OAc)4 (1.033 g; 3.907 mmol) in 15 cm3 of dry toluene at 80 °C. After the
addition, a yellow gel formed. The reaction mixture was heated to 80 °C for 7 days, after which the
volatile byproducts were separated under vacuum and the yellow powder was dried under vacuum
for 24 h. Yield 1.098 g, theor. 0.494 g; DC = 56 %.
Identification of volatile by-products
1H NMR: (300 MHz, CDCl3) δ (ppm) 1.95 (s, CH3C(O)), 2.68 (s, NCH3), 2.85 (s, NCH3). GS-MS: 0.49 min
(N,N-dimethylamine) m/z = 45, 28; 1.92 min (N,N-dimethylacetamide) m/z = 87, 72, 44.
6

Page 7 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
Characterization of xerogel
IR Spectra (KBr, cm-1): 443 w (δ C–N–C), 592 w, 634 w, 693 m (AlO6), 769 w (AlO4), 801 w (νsym Si–O–
Si), 1012 vs (νas Si–O–Si/Si–O–Al), 1186 w (ν NCH3), 1265 w (ν C–N–C), 1386 m (δ CH3), 1412 m, 1468
m (ν COO), 1510 m (ν C=O), 1596 vs (ν COO), 1536 vs (ν COO), 1718 vw (ν COO), 2799 vw (ν CH3),
2930 w (ν CH3), 3410 vw (ν NH).
NMR: 13C CPMAS (SiAl1, ppm) δ 21.9 (CH3C(O) – bidentate), 24.1 (CH3C(O) – monodentate), 33.4, 35.3
(CH3N), 38.2 (CH3N), 170.7 (CH3C(O) – monodentate), 179.4 (CH3C(O) – bidentate); 29Si CPMAS
(ppm) δ –89; 27Al MAS (ppm) δ 0 (AlVI = 6-coordinated Al), 29 (AlV = 5-coordinated Al), 54 (AlIV = 4-
coordinated Al).
TG/DSC (air, 5 °C min-1) weight loss at 1000 °C 53.83 %.
BET: SA = 607 m2 g-1, C = 146, Vtot = 0.35 cm3 g-1, d = 2.4 nm
Aluminosilicate xerogel C2SiAl with Si2(CH2)2(OAc)6 precursor was prepared with the same procedure
and under same conditions as in the case of SiAl1 xerogel. See Table 1.
Aluminosilicate xerogel prepared with Pluronic F127 template SiAlF2 (Eq. 1)
Al(NMe2)3 (0.814 g; 5.11 mmol) dissolved in 25 cm3 of the dry toluene was added dropwise by a
syringe to a stirred solution of Si(OAc)4 (1.029 g; 3.894 mmol) and Pluronic F127 (0.800 g) in dry
toluene (25 cm3) at 80 °C. After the addition, the mixture color changed to light yellow and a gel
formed. The reaction mixture was heated to 80 °C for 12 h forming a transparent light yellow stiff gel.
After 7 days of aging, the reaction was stopped, volatile byproducts were separated in vacuo and the
yellow-orange solid product was dried under vacuum for 24 h. Yield 1.689 g, theor. 0.496 g.
Identification of volatile by-products
GC-MS: 1.80 min (N,N-dimethylacetamide) m/z = 87, 72, 44.
Characterization of xerogel
IR Spectra (ATR, cm-1): 425 vw (δ C–N–C), 627 w, 689 w (AlO6), 766 w (AlO4), 860 w (CH), 972 s, 996
vs (ν Si–O–Al) , 1027 vs (ν Si–O–Si), 1034 vs (δ C–O–C), 1253 w (ν C–N–C), 1300 w, 1380 m (δ CH3),
1465 m (ν COO), 1516 m (ν C=O), 1586 s (ν COO), 2867 m (ν CH).
NMR: 13C CPMAS (SiAlF2, ppm) δ 26.9 (CH3C(O)), 40.7 (CH3N), 74.1 (CH2O), 79 (CHO), 173.3 (CH3C(O) –
monodentate), 184.6 (CH3C(O) – bidentate); 29Si CPMAS (SiAlF2, ppm) δ –87; 27Al MAS (SiAlF2, ppm)
δ 2 (AlVI), 32 (AlV), 61 (AlIV).
TG/DSC: (air, 5 °C min-1) weight loss at 1000 °C 70.06 %.
7

RSC Advances
Page 8 of 27
View Article Online
DOI: 10.1039/C5RA24563J
Portions of dried xerogel were calcined in a tube furnace under air at 500 and 700 °C for 3 h.
BET: (sample calcined at 500 °C) SA = 477 m2 g−1, C = 54, Vtot = 0.53 cm3 g−1, d = 4.5 nm.
ICP OES (sample calcined at 500 °C) wt%: Al 25.34 ± 0.04, Si 18.98 ± 0.01
Hydrothermal stability was studied after calcination at 500 °C. The xerogel was kept in refluxing
water for 24 hours. Then, water was evaporated and the sample was dried under vacuum at 100 °C.
Changes in the xerogel porosity and structure were studied by N2 porosimetry and MAS NMR
spectroscopy.
Calcined samples are labeled with a number corresponding to the particular calcination temperature,
e.g. SiAlF1-500, water-treated samples are labeled with H, e.g. SiAlF2-500H.
Reactions with the P123 template were carried out under the same conditions as in the case of F127.
Aluminosilicate xerogels from Si2O(OAc)6 precursor were prepared according to same protocol as in
the case of SiAlF2 sample. For details see the Table 1.
Condensation reaction between Me3SiOAc and Al(NMe2)3
A model condensation reaction between Me3SiOAc and Al(NMe2)3 (3:1) (Table 1) led to a molecular
product (1) containing the N,N-dimethylacetimidic acid cation [Me(C)OHNMe2]+ and [Al(OSiMe3)4]-
anion (Fig. 1 and 1S). Dimethylacetamide, hexamethyldisiloxane, and small amount of dimethylamine
were observed by GC-MS among the volatiles. The colorless crystalline product sublimed from the
dark orange viscous mass on the walls of a Schlenk flask. These crystals (292 mg, 14 %) were
separated in glove box and analyzed by single crystal X-ray diffraction analysis.
Characterizationof 1
27Al NMR (CDCl3, ppm) δ 59 ppm (AlO4)
EI-MS (m/z): 589 [Al2(OSiMe3)6H]+ (10 %); 574 [Al2(OSiMe3)5OSiMe2H]+ (100 %); 485 [Al2(OSiMe3)4
OSiMe2H]+ (20 %); 411 [Al2(OSiMe3)4H]+ (50 %).
Catalytic reactions
Aminolysis and alcoholysis reactions of styrene oxide33, 34, 38, 44 were performed in a 25 cm3 round-
bottomed Schlenk flask connected to a N2 source. Calcined (500 °C) aluminosilicate xerogels were
degassed before the reactions under vacuum at 100 °C for 20 min. The reaction mixture consisted of
catalyst (25 mg), dry toluene (5 cm3), styrene oxide (0.587 cm3, 5.00 mmol), and aniline (0.456 cm3,
5.00 mmol) or methanol (0.202 cm3, 5.00 mmol) in the case of aminolysis and alcoholysis,
8

Page 9 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
respectively. A blank reaction was performed without a catalyst. The reaction mixture was heated at
1
50 °C. Catalytic products were quantified by GC-MS and H NMR spectroscopy after 10 min and 1 h.
The reusability of catalyst was studied after washing the used catalyst with CH2Cl2 and toluene and
degassing under vacuum at 115 °C. We found that reused catalyst is still active. To investigate Al
leaching, 30 mg of the catalyst was refluxed in 15 cm3 of 2-propanol for 4 h. After centrifugation and
filtering off the catalyst powder, the filtrate was tested for the presence of Al species by ICP-OES.
Results and discussion
Aluminosilicate xerogels were synthesized by a novel acetamide elimination reaction according to eq.
1−3 from Si(OAc)4 (or bridged acetoxysilanes) and Al(NMe2)3 precursors in dry toluene under N2
atmosphere.
3 Si(OAc)4 + 4 Al(NMe2)3 → Al4Si3O12 + 12 Me2NC(O)CH3
(AcO)3SiOSi(OAc)3 + 2 Al(NMe2)3 → Al2Si2O7 + 6 Me2NC(O)CH3
(1)
(2)
(3)
(AcO)3Si-(CH2)2-Si(OAc)3 + 2 Al(NMe2)3
→ Al2Si2(CH2)2O6 + 6 Me2NC(O)CH3
The reaction proceeds with the formation of Si–O–Al network and release of dimethylacetamide
which was confirmed by GC-MS (Fig. 2S) and 1H NMR analysis of volatiles separated from the reaction
mixture. In the case of the reaction with excess Si(OAc)4, a small amount of acetic acid was observed
in GC-MS.
Hexaacetoxydisiloxane (AcO)3SiOSi(OAc)3 (eq. 2) and bis(triacetoxysilyl)ethane (AcO)3Si-(CH2)2-
Si(OAc)3 (eq. 3) were used for the modification of porosity and optimizing of the Si/Al ratio. Eq. 1
represents a complete condensation of functional groups to Si–O–Al network and quantitative
elimination of dimethylacetamide. However, under experimental conditions, the condensation is
incomplete (Scheme 2), and degree of condensation (DC) for the reaction without a template was
57 %.
9

RSC Advances
Page 10 of 27
View Article Online
DOI: 10.1039/C5RA24563J
Scheme 2 Synthesis of aluminosilicate gel with four-, five-, and six-coordinate Al atoms and residual acetate and
dimethylamide groups
Reaction parameters are summarized in Table 1. Systems without the templates produced yellowish
turbid gels which were dried under vacuum for 24 h to form yellow powders. With the use of
templates, stiff and transparent yellow gels were obtained. These gels were dried to form yellow-
orange rubbery or glassy products. Dried xerogels were afterwards calcined in a tube furnace at
500 °C for 3 h in air to remove the templates. The resulting yellowish powders possessed surface
areas that were substantially improved and pore sizes corresponded to mesoporous region (see
below).
Table 1 Precursors, reaction parameters, and residual masses after TG analysis
n
TG residual
TG residual
Sample
SiAl1
Si precursor n Si [mmol] n Al [mmol] Al mol %a Template Template mass at 1000 °C
mass calc. [%]b
[mmol]
[%]
46.17
50.09
7.71
45.10
40.45
-
Si(OAc)4
Si2(CH2)2(OAc)6
Me3SiOAc
3.907
5.108
5.018
5.100
4.478
56.2
49.9
24.6
-
-
-
-
-
-
C2SiAl
SiAl2
13.726
19.92
19.36
31.78
29.94
30.49
31.78
18.74
15.70
26.64
29.36
35.59
39.34
SiAlP1
SiAlF1
SiAlP2
SiAlF2
SiAlP3
SiAlF3
Si(OAc)4
Si(OAc)4
5.029
5.025
3.825
3.894
2.312
5.236
3.460
3.416
5.206
5.114
2.418
5.112
40.8
40.5
57.6
56.8
51.1
49.4
P123
F127
P123
F127
P123
F127
0.239
0.111
0.128
0.064
0.071
0.068
Si(OAc)4
Si(OAc)4
Si2O(OAc)6
Si2O(OAc)6
a nominal Almol% = nAl / (nAl + nSi)
b based on AlxSiyOz (see text) in precursors
10

Page 11 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
To study the condensation, a model reaction between Me3SiOAc and Al(NMe2)3 was carried out. It
provided molecular ionic compound [Me(C)OHNMe2]+ [Al(OSiMe3)4]─ (1) (Fig. 1 and 1S).
Crystallographic details and IR spectrum of 1 are summarized in Supporting materials (Table 1S, Fig.
3S). A similar compound has been prepared by Chisholm from Me3SiOH and Al(NMe2)3.45 This product
shows that condensation between acetoxy and dimethylamido groups takes place forming Si─O─Al
bonds.
Fig. 1 Tetrahedral tetrakis(trimethylsilyloxy)aluminate anion of compound 1
IR spectra of all dried products were recorded to identify Si–O–Al heterolinkages and also the
residual organic groups. Fig. 2 illustrates IR spectra of non-templated and F127 templated dried
samples synthesized by NHSG reactions. The absence of OH bands attests to the truly non-aqueous
nature of the xerogel synthesis. Vibrational bands located at 1030–1000 cm-1 are attributed to Si–O–
Si and Si–O–Al bonds on the basis that introduction of Si–O–Al bonds in a SiO2 matrix shifts the
absorption maxima toward the lower wavenumbers.46-48 Besides the bonds mentioned above,
vibrational bands of residual organic groups were observed as well. Dimethylamido groups give rise
to vibrational bands at 1250–1270, 1370–1380, 1510–1520, and 2970–2980 cm-1.49-51 Acetoxy
moieties are characterized by the asymmetric and symmetric COO stretches at 1580–1590 and 1460–
1470 cm-1, respectively. The difference between symmetric and asymmetric carboxylate vibrational
bands is 120–130 cm-1 and according to Deacon–Phillips rules, this is indicative of the bidentate
53
bridging mode on a metal center.52,
Pluronic templates P123 and F127 are represented by
vibrational bands of C–O–C bonds at 1090–1105 cm-1 and CH3 at 2860–2880 cm-1.54
11

RSC Advances
Page 12 of 27
View Article Online
DOI: 10.1039/C5RA24563J
7
2
1
F
SiAlF3
SiAlF2
SiAlF1
C2SiAl
SiAl1
3500
3000
2500
2000
1500
1000
500
wavenumber (cm-1)
Fig. 2 IR spectra of dried aluminosilicate xerogels prepared with and without F127 template
The thermal behavior of the prepared products was studied by TG/DSC analysis in air. Residual
masses are summarized in Table 1. These values are in an agreement with the calculated residual
masses corresponding to aluminosilicate AlxSiyOz, where x, y, and z represent moles of aluminium,
silicon, and oxygen in precursors. For example, the TG residual mass of sample SiAlF2 (Table 1) is
29.94 % while the calculated residual mass of aluminosilicate is 29.36 %. TG curves (Fig. 4S) of
xerogels synthesized without the templates display mass losses in two steps. The first mass loss is
observed between 50–225 °C (21–26 %) and the second one between 230–500 °C (24 %). These steps
are connected with oxidation of residual dimethylamido and acetoxy moieties. In the case of
templated samples the highest mass losses (52–56 %) are observed between 200–450 °C. Xerogels
with a lower content of Al show the highest mass loss between 125–400 °C (68–72 %). A lower
decomposition temperature than in the previous case could be explained by the oxidation of
unreacted monodentate acetoxy groups bound to silicon. DSC curves of the templated samples
(SiAlP2, SiAlF2) with 57–58 mol% of Al show exothermic peaks at 995 and 985 °C for the xerogel with
F127 and P123 copolymer, respectively. This observation could be connected to crystallization of the
mullite phase.46-48
Solid state NMR spectroscopy (Table 2) was employed for in-depth characterization of the
aluminosilicate xerogel matrix. 13C CPMAS NMR spectrum of non-templated sample (SiAl1) displayed
resonances of residual organic groups (Fig. 5S). Resonances at 33.1, 35.0, and 37.8 ppm are
attributed to dimethylamido groups while the acetoxy groups in bidentate and monodentate
coordination are characterized by the CH3 resonances at 22.0 and 24.1 ppm, respectively. The COO
12

Page 13 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
resonances of acetate groups in unidentate and bidentate mode were observed at 170.4 and 179.5
ppm, respectively. Similar resonances of residual N(CH3)2 (34.1, 37.4 ppm), CH3 (20.7, 23.1 ppm) and
COO (169.8, 179.0 ppm) were observed also in the 13C CPMAS spectrum of the xerogel synthesized
from bis(triacetoxysilyl)ethane (C2SiAl). The ethylene (CH2–CH2) bridge is characterized by the signal
at 7.5 ppm. In the 13C CPMAS NMR spectrum of F127 templated xerogel (SiAlF2, Fig. 5S), the presence
of residual organic moieties was observed as well. The N(CH3)2 groups are seen at 40.8 ppm and CH3
of acetoxy species are displayed at 27.3 ppm. The carboxylate function features weak signals at 173.2
and 183.2 ppm. The template carbons are represented by chemical shifts at 21.0 (
76.8, and 78.8 ppm ( H2O and CH3
HO).55
The 29Si CPMAS NMR spectrum of non-templated sample (SiAl1) shows a broad signal with the
maximum at 89 ppm (Fig. 3). Compared to SiO2 ( 96 ppm) a downfield
110 ppm).56, 57 and Si(OAc)4 (
CH3CHO), 74.1,
C
C
−
−
−
shift is observed. This shift is caused by the presence of Si–O–Al linkages in the xerogel network.58-60
29Si CPMAS NMR spectrum of the sample C2SiAl with ethylene (CH2–CH2) bridges displays a broad
signal with the maximum at
broad signal at
−
54 ppm (Fig. 3). 29Si CPMAS NMR data of templated samples displays a
59
−
87 ppm assigned to Si(OSi)(OAl)3 species (Fig. 3).58, Similar resonances were
observed after calcination at 500 °C of these templated samples (Fig. 5). The resonance at
in 29Si CPMAS NMR corresponds to Si(OSi)(OAl)358, 59 In the case of templated samples with a lower Al
content (SiAlF1), 29Si CPMAS displays a signal with maximum at
106 ppm and a shoulder at 97
−90 ppm
−
−
ppm. This shift could be caused by the formation of Si–O–Si bonds because of excess Si(OAc)4 (Fig. 3).
Comparison of 29Si CPMAS NMR spectra before and after calcinations for the templated samples
SiAlF1, 2, 3 indicates there are not major differences (Fig. 4).
27Al NMR spectra of dried xerogels provide information about the coordination number of Al atoms
in the aluminosilicate network. 27Al spectra of dried non-templated xerogels (SiAl1, C2SiAl
) illustrate
three signals attributed to 4-coordinated (AlIV, 53 ppm), 5-coordinated (AlV, 28 ppm) and 6-
coordinated (AlVI, 0 ppm) Al3, 58, 61 (Fig. 6S). 27Al MAS NMR spectra of dried templated samples (SiAlF2,
3) show also the resonances for AlIV (58 ppm), AlV (31 ppm), and AlVI (2 ppm) atoms in the framework
(Fig. 6S). No significant change in the 27Al MAS NMR spectra of calcined templated xerogels was
observed and Al signals were found at 62 ppm (AlIV), 33 ppm (AlV), and 4 ppm (AlVI).58 27Al MAS NMR
spectrum of the sample SiAlF1 (lower Al content) displays signals for AlIV at 54 ppm and for AlVI at
and
4 ppm. After calcination of this sample, the resonances at 61 ppm (AlIV), 32 ppm (AlV), and 2
−2
−
ppm (AlVI) were observed (Fig. 5). Chemical shifts of xerogel samples are summarized in Table 2. From
these NMR data we can conclude, that the calcined xerogels still contain Si–O–Al bonds and no phase
separation takes place during the calcination. The 27Al NMR and EPR observations made by Chen et
al. show association of five-coordinated aluminum atoms to Lewis acid sites.62 Hence, the effect of
13

RSC Advances
Page 14 of 27
View Article Online
DOI: 10.1039/C5RA24563J
different aluminum coordination and their acid-base properties on the catalytic activity is a very
interesting subject. 27Al MAS spectrum of hydrothermally treated sample SiAlF2-500H shows
intensity decrease of signal corresponding to 5-coordinated Al while the signal of 6-coordinated Al
atoms increased (Fig. 7S). This change is caused by coordination of water and –OH groups. Solid state
MAS NMR spectra of the samples synthesized with the P123 template are similar and thus are not
shown here.
Table 2 MAS NMR chemical shifts of aluminosilicate xerogels
Chemical Shift [ppm]
Sample
29Si CPMAS
27Al MAS
28 0
SiAl1
−
−
89
54
53
54
54
61
61
64
61
69
C2SiAl
29
−1
SiAlF1
−106
−97
−2
−4
SiAlF1-500
SiAlF2
−
−
−
−
−
97
88
90
90
93
32
32
33
30
34
2
2
4
0
4
SiAlF2-500
SiAlF3
SiAlF3-500
29Si CPMAS
Q4
SiAlF3
SiAlF2
SiAlF1
C2SiAl
SiAl1
50 25
0
-25 -50 -75 -100 -125 -150 -175 -200
chemical shift (ppm)
Fig. 3 29Si CPMAS NMR spectra of dried aluminosilicate xerogels
14

Page 15 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
-93
29Si CPMAS
Q4
SiAlF3-500
SiAlF2-500
SiAlF1-500
20
0
-20 -40 -60 -80 -100 -120 -140 -160 -180 -200
chemical shift (ppm)
Fig. 4 29Si CPMAS NMR spectra of calcined (500 °C) aluminosilicate xerogels synthesized with F127 template
.
27Al MAS
d
r
.
o
o
c
d
r
o
o
-
5
l
c
-
A
4
l
A
SiAlF3-500
SiAlF2-500
SiAlF1-500
120 100 80 60 40
20
0
-20 -40 -60
chemical shift (ppm)
Fig. 5 27Al MAS NMR spectra of calcined (500 °C) aluminosilicate xerogels synthesized with F127 template
A very important feature of these aluminosilicate xerogels is their porosity. High surface area
materials with mesopores provide better catalytic efficiency for the processing of bulky organic
molecules. We investigated the N2 adsorption/desorption isotherms of the non-templated and
templated samples (Table 3). The results show that xerogels synthesized without copolymer
templates exhibit high surface areas after drying and feature the type-II isotherms63 (Fig. 6).
Equivalent BET surface areas of xerogels prepared from Si(OAc)4 (SiAl1) and from the ethylene
bridged acetoxysilane (C2SiAl, Fig. 8S) were 607 and 517 m2 g-1, respectively. However the pore
15

RSC Advances
Page 16 of 27
View Article Online
DOI: 10.1039/C5RA24563J
diameters correspond to micropores in both materials. After calcination of the C2SiAl sample at 200
°C, surface area decreased considerably to 36 m2 g-1. This change can be explained by the framework
collapse while the ethylene bridging groups are oxidized. Interestingly, according to the NLDFT
method, the pore diameter increased and shifted to the mesopore region (4.8 nm by NLDFT).
An improvement in morphological properties is achieved through the use of Pluronic templates
(Table 3). With this approach, framework collapse during heat treatment is avoided and high surface
areas are achieved after calcination at 500 °C. The shape of isotherms corresponds to type IV with
the H2 hysteresis consistent with significant mesopore content and narrower pore size distributions.
(Fig. 6, 9S).63 Calcined xerogel SiAlP2-500 synthesized with the P123 template containing 59.3 mol%
of Al exhibits surface area of 591 m2 g-1 and the pore volume 0.53 cm3 g-1. If (AcO)3SiOSi(OAc)3 is used
as the silicon precursor, the surface area increases to 627 m2 g-1. This change can be caused by better
crosslinking due to a higher number of functional groups. Pore diameters of these calcined samples
calculated by the NLDFT method are between 4.9 and 5.9 nm (Table 3). In the case of the
aluminosilicates synthesized with the F127 template, surface areas in the range 381–477 m2 g-1 are
achieved with a pore diameter of 4.9─5.9 nm (Fig. 10S). We observed that with increasing Al content
the surface areas and pore volumes increased as well. Pore diameters do not change with different
Si/Al ratios for P123 but increased for F127. For classification of thermal stability, we calcined the
sample SiAlF2 at 700 °C for 3 h and remeasured N2 adsorption isotherms (Fig. 7). Its surface area
reached 424 m2 g-1 (Vtot = 0.41 cm3 g-1) which is about 53 m2 g-1 lower than in SiAlF2-500 and the pore
volume and diameter decreased (Fig. 8, Table 3) and the distribution is narrower. To investigate
hydrothermal stability, the sample SiAlF2-500 was exposed to boiling water for 24 h (Fig. 7). The
surface area after this test was reduced to 166 m2 g-1 and pore volume to 0.28 cm3 g-1. The pore size
distribution maximum moved to 6.1 nm and the mesoporous character was preserved (Fig. 8).
Compared to this sample, the hydrothermally treated sample (SiAlF3-500H) synthesized with
(AcO)3SiOSi(OAc)3 exhibits also loss of surface area and pore volume while pore diameter increased
(Table 3, Fig. 11S).
16

Page 17 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
400
350
300
250
200
150
100
50
SiAlP2-500
with P123
SiAlF2-500
with F127
SiAl1
without template
adsorption
desorption
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
relative pressure (p/p0)
Fig. 6 N2 adsorption/desorption isotherms of aluminosilicate xerogels
Table 3 Surface areas, pore volumes and pore sizes of aluminosilicate xerogels
SA (BET)
V
d
[nm]
Sample
SiAl1
Template
Al mol%
[m2 g-1] [cm3 g-1]
-
56.2
49.9
42.2
40.6
59.3
58.1
58.1
58.1
54.1
50.7
50.7
607
517
429
381
591
477
424
166
627
442
171
0.34
0.38
0.37
0.37
0.53
0.53
0.41
0.28
0.55
0.46
0.31
2.4
2.9
4.9
4.9
4.9
5.9
5.1
6.1
4.9
5.3
6.1
C2SiAl
-
SiAlP1-500
SiAlF1-500
SiAlP2-500
SiAlF2-500
SiAlF2-700
SiAlF2-500H
SiAlP3-500
SiAlF3-500
SiAlF3-500H
P123
F127
P123
F127
F127
F127
P123
F127
F127
17

RSC Advances
Page 18 of 27
View Article Online
DOI: 10.1039/C5RA24563J
400
300
200
100
0
SiAlF2-500
SiAlF2-700
SiAlF2-500H
desorption
adsorption
0.0
0.2
0.4
0.6
0.8
1.0
relative pressure (p/p0)
Fig. 7 N2 adsorption/desorption isotherms of aluminosilicate xerogel SiAlF2 calcined at 500 (top) and 700 °C (middle).
Sample SiAlF2-500H after hydrothermal treatment (bottom).
SiAlF2-700
SiAlF2-500H
SiAlF2-500
0.020
0.015
0.010
0.005
0.000
0
2
4
6
8
10
12
14
diameter (nm)
Fig. 8 NLDFT pore diameters (adsorption branch) of aluminosilicate xerogels: SiAlF2 calcined at 500 and 700 °C. Sample
SiAlF2-500H after hydrothermal treatment
SAXS measurements of the calcined samples SiAlP2-500 and SiAlF2-500 synthesized with the P123
and F127, respectively, show a weak scattering maximum at 0.42° (0.06 Å−1) (Fig. 9). This behavior
points to the mesoscopic ordering with the uniform pore channels in the xerogel.
18

Page 19 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
0.06
dp = 4.9 nm
0.04
0.02
0.00
2
3
4
5
6
7
8
pore diameter (nm)
SAXS; d = 11 nm
0.2 0.3
0.0
0.1
0.4
0.5
q [Åꢀ1
]
Fig. 9 SAXS pattern of calcined aluminosilicate xerogel SiAlP2-500. NLDFT pore diameter distribution (inset).
The morphology of calcined mesoporous xerogels was studied by the TEM technique. The
micrographs illustrate “wormhole” structure of pores (Fig. 10).
Fig. 10 TEM micrographs of SiAlF3-500 aluminosilicate with mesoporous "wormhole" like morphology
The surface acidity of the calcined xerogels was studied by pyridine adsorption. The IR spectra of the
pyridine-treated samples (Fig. 11) display weak absorption bands at 1450, 1492, 1548, 1599, 1625,
and 1639 cm-1. The bands corresponding to Lewis acid sites (LPy) are present at 1450 and 1625 cm-
1 61, 64
.
Both Lewis and Brønsted acid sites are attributed to a vibrational band at 1492 cm-1. Brønsted
acidic sites (BPy) are characterized by the absorption bands at 1548 and 1639 cm-1.64 Pyridine
adsorbed by hydrogen bonds (HPy) of ≡Si–OH moieties can be assigned to the vibrational band at
19

RSC Advances
Page 20 of 27
View Article Online
DOI: 10.1039/C5RA24563J
1599 cm-1.61 These findings show that synthesized aluminosilicate xerogels exhibit surface acidity of
both Lewis and Brønsted type.
SiAlF1-500
BPy
LPy
LPy
+
BPy
LPy
HPy
BPy
1700
1650
1600
1550
1500
1450
1400
wavenumber (cm-1)
Fig. 11 IR spectra of calcined aluminosilicate xerogel (SiAlF1-500) after pyridine adsorption
High-temperature powder X-ray diffraction (HT PXRD) was used to determine the crystal phases that
arise during calcination (Fig. 12S). It was found that templated samples remain amorphous up to high
temperatures and then crystallize to mullite (PDF 82-1237).65-67 The xerogels SiAlP2 and SiAlF2 are
amorphous up to 950 °C before the diffraction lines of mullite are observed at 1000 °C (Fig. 12S).
These findings correspond to exothermic effects in DSC analysis (995 and 985 °C). In the case of
xerogels with a lower content of Al, diffraction evidence for mullite appeared at 1050 °C. Besides the
mullite phase, crystalline SiO2 (cristobalite PDF 85-0621) at 1100 °C was observed as well. The
presence of cristobalite could be explained by the excess of Si(OAc)4 in the starting mixture which
results in the phase separation during calcination. Samples synthesized with (AcO)3SiOSi(OAc)3
(SiAlF3-500 and SiAlP3-500) exhibit the mullite phase with crystallization temperature between 950–
1000 °C. Crystallization of mullite at ~980 °C indicates the homogeneity of aluminosilicate gels at the
atomic level.26, 68, 69 These findings show that our mesoporous aluminosilicates can be transformed to
homogeneous mullite phase.
Catalytic studies
Catalytic activities of the synthesized xerogels were tested in two types of model reactions (Fig 13S,
44
14S). At first, aminolysis of styrene oxide with aniline34,
was investigated with the calcined
aluminosilicate xerogel as a catalyst. The second model reaction was alcoholysis of styreneoxide with
20

Page 21 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
methanol.33 Catalytic yields for aminolysis are summarized in Table 4. The blank reaction without a
catalyst was performed as well and no product was obtained after 4 h. We observed that our
calcined mesoporous xerogels are efficient catalysts for aminolysis reaction of epoxides. The 1H NMR
spectra of the reaction mixture (in C6D6) display resonances attributed to two products: 2-phenyl-2-
(phenylamino)ethanol (Ia) and 1-phenyl-2-(phenylamino)ethanol) (IIa) (Fig. 13S, 15S). These products
were also confirmed by the GC-MS technique. Catalytic yields were analyzed after 10 and 60
minutes. The highest conversion was observed with the catalyst SiAlF1-500 (82 % after 1 hour).
However, high catalytic efficiencies (up to 80 %) were reached in all cases (Table 4). Catalyst with a
high content of Al exhibits a lower catalytic activity which could be caused by the presence of larger
alumina clusters. Xerogels synthesized with (AcO)3SiOSi(OAc)3 provide higher homogeneity and
better dispersion of Al in framework and furthermore a higher catalytic activity. We also investigated
recycling the catalysts in the second reaction run. The styrene oxide conversion with 7 mg of reused
xerogel (SiAlF3-500) reached 21 % after 1 h which represents nearly the same activity (TOF = 20) as
the fresh catalyst. A report describing aluminosilicates as catalysts for aminolysis was published by
Robinson.70 These nanoporous catalysts are prepared by conventional hydrolytic sol-gel process from
TEOS and aluminium nitrate nonahydrate in the presence of cetyltrimethylammonium bromide. The
comparison between these catalysts and our mesoporous aluminosilicates is presented in Table 5.
Table 4 Aminolysis of styrene oxide. Catalytic yields and selectivities
Selectivity [%]
n Al in cat
(25 mg)
[mmol]
Al mol%
(ICP)
Conversion
[%]
Sample
t [min]
TOFa
Ia
IIa
10
60
10
60
10
60
10
60
10
60
46
79
50
82
43
69
50
79
56
80
96
95
97
98
96
95
96
96
96
96
4
5
3
2
4
5
4
4
4
4
86
25
100
27
56
15
79
21
80
19
SiAlP1-500
SiAlF1-500
SiAlF2-500
SiAlF3-500
SiAlP3-500
42.2
40.6
58.1
50.7
54.1
0.16
0.15
0.23
0.19
0.21
a TOF - apparent turnover frequency [mmol mmol-1 h-1]
Table 5 Aminolysis of styrene oxide. Comparison with other aluminosilicate catalysts synthesized by hydrolytic sol-gel
Temperature
[°C]
Time
[h]
m
[mg]
Conversion Selectivity
Sample
Si/Al
1.5
[%]
(Ia:IIa) [%]
SiAlF1-500
50
1
25
82
98 : 2
21

RSC Advances
Page 22 of 27
View Article Online
DOI: 10.1039/C5RA24563J
SiAlF2-500
SiAlF3-500
AS-(14)70
0.7
1.0
14
14
14
10
50
50
1
1
25
25
50
50
50
50
69
80
37
53
28
87
95 : 5
96 : 4
95 : 5
95 : 5
95 : 5
-
r. t.
r. t.
40
6
AS-(14)70
24
6
AS-(14)70
AlKIT-5(10)38
r. t.
0.5
In the case of styrene oxide alcoholysis, our catalysts exhibit a lower efficiency than in aminolysis
reactions. Catalytic products confirmed by GC-MS and 1H NMR were (Fig. 15S, 16S) (1,2-
dimethoxyethyl)-benzene (Ib) and phenylacetaldehyde (IIb) (Fig. 14S, Table 6). Catalyst SiAlF1-500
exhibits 28 and 44 % conversion of styrene oxide after 2 and 5 h, respectively. Selectivity for (1,2-
dimethoxyethyl)-benzene after 5 h reached 54 %.
Table 6 Alcoholysis of styrene oxide. Catalytic yields and selectivities.
n Al
in catal
[mmol]
Selectivity [%]
Al mol%
(ICP)
Conversion
[%]
Sample
t [h]
Ib
63
59
54
IIb
37
41
46
2
3
5
28
32
44
SiAlF1-500
40.6
0.15
We also performed a catalytic reaction with the catalyst SiAlF1-500 where no methanol was used. In
this case, phenylacetaldehyde was observed as the only product and the catalytic yield after 1 h was
35 %. A leaching test confirmed that no Al was released into the solution. Only 0.3 % of the total
aluminium amount in catalyst was found in the filtrate.
Conclusions
The non-hydrolytic sol-gel (NHSG) reactions based on acetamide elimination described here provide
a very effective route to homogeneous aluminosilicate xerogels with high Al loading. This one pot
reaction proceeds as polycondensation between acetoxysilanes and aluminium(III) dimethylamide
and leads to the formation of Al–O–Si networks. In all cases N,N-dimethylacetamide was confirmed
as the only reaction byproduct attesting to the absence of homocondensation reactions. Al–O–Si
bonds were identified by IR spectroscopy and 29Si and 27Al MAS NMR spectroscopy. We observed 4-,
5-, and 6-coordinated Al atoms in the frameworks of both dried and calcined xerogels. These
materials exhibit high surface areas (up to 607 m2 g-1) but are microporous. Calcination causes
22

Page 23 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
framework collapse and samples lose porosity. With the use of block copolymer templates such as
Pluronic P123 and F127, homogeneous, stiff gels were obtained. After calcination at 500 and 700 °C
mesoporous aluminosilicate materials with high surface areas ranging from 380 to 627 m2 g-1 with
the pore diameters 4.9 (P123) and 5.9 (F127) nm were obtained. After hydrothermal treatment, the
surface area decreased but mesoporous character was preserved. Calcined xerogels were
investigated as catalysts for the aminolysis and alcoholysis of styrene oxide. The presence of catalytic
active acidic sites (Lewis, Brønsted) was determined by pyridine adsorption. All xerogels exhibit good
catalytic activity. Especially in the aminolysis model reaction, very high conversions (69–82 %) were
observed.
Acknowledgements
This research has been financially supported by the Ministry of Education, Youth and Sports of the
Czech Republic under the project CEITEC 2020 (LQ1601). Authors thank the project KONTAKT II
LH11028, the X-ray Diffraction and Bio-SAXS Core Facility of CEITEC, L. Simonikova for ICP-OES
analyses, and V. Vykoukal for the SAXS measurements.
23

RSC Advances
Page 24 of 27
View Article Online
DOI: 10.1039/C5RA24563J
References
1.
2.
D. S. Santilli and S. I. Zones, Catal. Lett., 1990, 7, 383-387.
G. F. Wan, A. J. Duan, Y. Zhang, Z. Zhao, G. Y. Jiang, D. Q. Zhang, Z. Y. Gao, J. Liu and K. H.
Chung, Energy Fuels, 2009, 23, 3846-3852.
3.
4.
5.
6.
E. Masika and R. Mokaya, Chem. Mater., 2011, 23, 2491-2498.
G. A. Pozarnsky and A. V. McCormick, J. Non-Cryst. Solids, 1995, 190, 212-225.
J. Ren, L. Zhang and H. Eckert, J. Sol-Gel Sci. Technol., 2014, 70, 482-490.
C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 1992, 359, 710-
712.
7.
8.
9.
R. Mokaya and W. Jones, Chem. Commun., 1998, 1839-1840.
K. Wang, Y. Lin, M. A. Morris and J. D. Holmes, J. Mater. Chem., 2006, 16, 4051.
D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc., 1998, 120, 6024-
6036.
10.
11.
A. Sakthivel, S. J. Huang, W. H. Chen, Z. H. Lan, K. H. Chen, H. P. Lin, C. Y. Mou and S. B. Liu,
Adv. Funct. Mater., 2005, 15, 253-258.
C. Li, Y. Wang, Y. Guo, X. Liu, Y. Guo, Z. Zhang, Y. Wang and G. Lu, Chem. Mater., 2007, 19,
173-178.
12.
13.
S. Li, Q. Xu, J. Chen and Y. Guo, Ind. Eng. Chem. Res., 2008, 47, 8211-8217.
H. Liu, L. Wang, W. Feng, L. Cao, X. Gao, H. Liu and C. Xu, Ind. Eng. Chem. Res., 2013, DOI:
10.1021/ie302604m, 130228111721009.
14.
15.
16.
17.
G. M. Kumaran, S. Garg, K. Soni, M. Kumar, L. D. Sharma, K. S. Rama Rao and G. M. Dhar, Ind.
Eng. Chem. Res., 2007, 46, 4747-4754.
A. Vinu, D. P. Sawant, K. Ariga, M. Hartmann and S. B. Halligudi, Microporous Mesoporous
Mater., 2005, 80, 195-203.
Q. Li, Z. Wu, B. Tu, S. S. Park, C.-S. Ha and D. Zhao, Microporous Mesoporous Mater., 2010,
135, 95-104.
C. Han, H. Wang, L. Zhang, R. Li, Y. Zhang, Y. Luo and X. Zheng, Adv. Powder Technol., 2011,
22, 20-25.
18.
19.
20.
Y. Liu, W. Zhang and T. J. Pinnavaia, Angew. Chem. Int. Ed., 2001, 40, 1255-1258.
Y. Liu and T. J. Pinnavaia, Chem. Mater., 2002, 14, 3-5.
Z. Zhang, Y. Han, L. Zhu, R. Wang, Y. Yu, S. Qiu, D. Zhao and F.-S. Xiao, Angew. Chem. Int. Ed.
2001, 40, 1258-1262.
,
21.
22.
23.
24.
H. Wang, Y. Liu and T. J. Pinnavaia, J. Phys. Chem. B, 2006, 110, 4524-4526.
D. Trong On and S. Kaliaguine, Angew. Chem. Int. Ed., 2002, 41, 1036-1040.
D. Trong On and S. Kaliaguine, J. Am. Chem. Soc., 2003, 125, 618-619.
H. Liu, K. Guo, X. Li, S. Liu, X. Gao, H. Liu, L. Cao, Y. Chen and C. Xu, Microporous Mesoporous
Mater., 2014, 188, 108-117.
25.
M. Enterría, F. Suárez-García, A. Martínez-Alonso and J. M. D. Tascón, J. Alloys Compd., 2014,
583, 60-69.
26.
27.
A. Vioux, Chem. Mater., 1997, 9, 2292-2299.
S. Acosta, R. Corriu, D. Leclercq, P. H. Mutin and A. Vioux, J. Sol-Gel Sci. Technol., 1994, 2, 25-
28.
28.
29.
30.
31.
D. P. Debecker, K. Bouchmella, M. Stoyanova, U. Rodemerck, E. M. Gaigneaux and P. Hubert
Mutin, Catal. Sci. Technol., 2012, 2, 1157.
K. Bouchmella, P. Hubert Mutin, M. Stoyanova, C. Poleunis, P. Eloy, U. Rodemerck, E. M.
Gaigneaux and D. P. Debecker, J. Catal., 2013, 301, 233-241.
D. Janackovic, A. Orlovic, D. Skala, S. Drmanic, L. Kostic-Gvozdenovic, V. Jokanovic and D.
Uskokovic, Nanostruct. Mater., 1999, 12, 147-150.
J.-C. Kim, K. Cho, S. Lee and R. Ryoo, Catal. Today, 2015, 243, 103-108.
24

Page 25 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J
32.
33.
34.
P. Neves, S. Lima, M. Pillinger, S. M. Rocha, J. Rocha and A. A. Valente, Catal. Today, 2013,
218-219, 76-84.
M. W. C. Robinson, R. Buckle, I. Mabbett, G. M. Grant and A. E. Graham, Tetrahedron Lett.
,
2007, 48, 4723-4725.
M. W. C. Robinson, D. A. Timms, S. M. Williams and A. E. Graham, Tetrahedron Lett., 2007,
48, 6249-6251.
35.
36.
A. Styskalik, D. Skoda, J. Pinkas and S. Mathur, J. Sol-Gel Sci. Technol., 2012, 63, 463-472.
D. Skoda, A. Styskalik, Z. Moravec, P. Bezdicka, C. Barnes and J. Pinkas, J. Sol-Gel Sci. Technol.
,
2015, 74, 810-822.
37.
38.
39.
D. Skoda, A. Styskalik, Z. Moravec, P. Bezdicka and J. Pinkas, J. Mater. Sci., 2015, 50, 3371-
3382.
R. Chakravarti, H. Oveisi, P. Kalita, R. R. Pal, S. B. Halligudi, M. L. Kantam and A. Vinu,
Microporous Mesoporous Mater., 2009, 123, 338-344.
D. Barreca, M. P. Copley, A. E. Graham, J. D. Holmes, M. A. Morris, R. Seraglia, T. R. Spalding
and E. Tondello, Appl. Catal., A, 2006, 304, 14-20.
40.
41.
J. Goubeau and R. Mundiel, Z. Anorg. Allg. Chem., 1953, 272, 313-325.
J. Rouquerol, F. Rouquerol, P. Llewellyn, G. Maurin and K. S. W. Sing, Adsorption by Powders
and Porous Solids: Principles, Methodology and Applications, Elsevier Science, 2013.
S. Lowell, J. Shields, M. Thomas and M. Thommes, in Characterization of Porous Solids and
Powders: Surface Area, Pore Size and Density, Springer Netherlands, 2004, vol. 16, ch. 5, pp.
58-81.
42.
43.
44.
45.
46.
G. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008, 64, 112-122.
R. Kore, R. Srivastava and B. Satpati, ACS Catal., 2013, 3, 2891-2904.
M. H. Chisholm, J. C. Huffman and J. L. Wesemann, Polyhedron, 1991, 10, 1367-1372.
Y. Hirata, K. Sakeda, Y. Matsushita, K. Shimada and Y. Ishihara, J. Am. Ceram. Soc., 1989, 72,
995-1002.
47.
E. Ruiz de Sola, F. Estevan, F. J. Torres and J. Alarcón, J. Non-Cryst. Solids, 2005, 351, 1202-
1209.
48.
49.
50.
C. S. Blackwell, J. Phys. Chem., 1979, 83, 3251-3257.
A. M. Dwivedi, S. Krimm and S. Mierson, Spectrochim. Acta, Part A, 1989, 45, 271-279.
G. Socrates, Infrared and raman characteristic group frequencies : tables and charts, John
Wiley & Sons, West Sussex, 2007.
51.
52.
53.
54.
55.
56.
V. Venkata Chalapathi and K. Venkata Ramiah, Proc. Indian Acad. Sci., 1968, 68, 109-122.
G. Deacon and R. Phillips, Coord. Chem. Rev., 1980, 33, 227-250.
S. Doeuff, M. Henry, C. Sanchez and J. Livage, J. Non-Cryst. Solids, 1987, 89, 206-216.
Y.-l. Su, J. Wang and H.-z. Liu, Langmuir, 2002, 18, 5370-5374.
H.-M. Kao, C.-L. Chen and S.-W. Chiao, J. Chin. Chem. Soc., 2005, 52, 693-699.
R. Simonutti, A. Comotti, S. Bracco, A. Simonelli and P. Sozzani, Chem. Mater., 2002, 14,
3377-3381.
57.
58.
D. W. Sindorf and G. E. Maciel, J. Phys. Chem., 1982, 86, 5208-5219.
M. Toba, F. Mizukami, S.-i. Niwa, T. Sano, K. Maeda and H. Shoji, J. Mater. Chem., 1994, 4,
1131.
59.
E. Lippmaa, M. Maegi, A. Samoson, M. Tarmak and G. Engelhardt, J. Am. Chem. Soc., 1981,
103, 4992-4996.
60.
61.
62.
63.
64.
I. Jaymes, A. Douy, D. Massiot and J.-P. Coutures, J. Non-Cryst. Solids, 1996, 204, 125-134.
C. Hernandez and A. C. Pierre, Langmuir, 2000, 16, 530-536.
F. R. Chen, J. G. Davis and J. J. Fripiat, J. Catal., 1992, 133, 263-278.
M. Thommes, Chem. Ing. Tech., 2010, 82, 1059-1073.
M. A. Betiha, M. F. Menoufy, A. M. Al-Sabagh, H. M. A. Hassan and S. A. Mahmoud,
Microporous Mesoporous Mater., 2015, 204, 15-24.
65.
H. Schneider, J. Schreuer and B. Hildmann, J. Eur. Ceram. Soc., 2008, 28, 329-344.
25

RSC Advances
Page 26 of 27
View Article Online
DOI: 10.1039/C5RA24563J
66.
S. Satoshi, C. Contreras, H. Juárez, A. Aguilera and J. Serrato, Int. J. Inorg. Mater., 2001, 3,
625-632.
67.
68.
69.
70.
D. M. D. D. R. Treadwell, I. A. Aksay, Chem. Mater., 1996, 8, 2056-2060.
A. Navrotsky, Chem. Mater., 1994, 6, 160-170.
F. He and W. T. Petuskey, Mater. Lett., 2009, 63, 2631-2634.
M. W. C. Robinson, A. M. Davies, I. Mabbett, T. E. Davies, D. C. Apperley, S. H. Taylor and A. E.
Graham, J. Mol. Catal. A: Chem., 2010, 329, 57-63.
26

Page 27 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA24563J