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

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(NMe 2 ) 3 , leads to homogeneous aluminosilicate xerogels containing Si – O – Al linkages through dimethylacetamide elimination. The addition of Pluronic P123 and F127 templates provides sti ﬀ gels that are, after calcination at 500 (cid:1) C, converted to stable mesoporous xerogels with a high surface area (>600 m 2 g (cid:3) 1 ) and wormhole-type pores ( d ¼ 5.9 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. 1,2They are usually prepared from alkoxide precursors under hydrothermal conditions by socalled molecular templating wherein a cationic organic species acts as a template for the formation of ordered pores and channels.This 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 A and typically 4-10 A. 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 prehydrolysis 4 or chelation methods. 5The discovery of ordered mesoporous silicates, such as MCM-41, with high surface areas, well-dened and tunable pore diameters from 1.5 to 10 nm was a signicant advancement in this eld.The catalysts with the hexagonal structure, such as Al-MCM-41, offered an opportunity for processing bulky molecules 6 and attracted much interest. 7Unfortunately, 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 uid (SCF) impregnation. 8Increase of hydrothermal stability was achieved also by 2-D hexagonal mesoporous SBA-15 materials 9 with large pores (4.6-30 nm), thick pore walls (3.1-6.4 nm), and high specic surface areas (up to 1000 m 2 g À1 ).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-synthesis 11 and graing or impregnation 12 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 graing 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. 13Al-SBA-15 materials with a large number of moderate acidic sites are very promising catalysts and supports allowing catalytic cracking, alkylation, and hydrotreating reactions. 14,15The preparation of Al-SBA-15 via the post-synthesis method was reported by Li 16 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. 17Recently, 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.9][20][21] A so-called coated route approach using a dilute clear solution of primary zeolite units was employed to synthesize ultrastable mesoporous aluminosilicate molecular sieves. 22,23This 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.
Recently, Liu 13 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% aer hydrothermal treatment in 100% water vapor at 800 C for 15 h.This group also reported a pH-adjusting method 24 based on the assembly of beta zeolite.An approach recently published by Enterría 25 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. 26In this method, condensations between SiCl 4 , AlCl 3 , Al(O i Pr) 3 , and Si(O i Pr) 4 in ethers or CH 2 Cl 2 provide monolithic homogeneous aluminosilicate gels 27 (Scheme 1).
This non-hydrolytic sol-gel technique has also been applied to the preparation of highly active mesoporous metathesis catalysts MoO 3 -SiO 2 -Al 2 O 3 28 and Re 2 O 7 -SiO 2 -Al 2 O 3 . 29Mullite precursor gel synthesis was described from AlCl 3 and TEOS in Et 2 O and CCl 4 in an autoclave at 110 C. 30 Catalytic efficiency of aluminosilicates was determined by a variety of test reactions.Kim reported Friedel-Cras acylation of bulky aromatic compounds in MFI zeolite nanosponge, 31 Neves 32 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. 33,34e have recently reported that non-hydrolytic acetamide elimination 35 can be successfully used for the synthesis of mesoporous titanium silicate 36 and zirconium silicate materials. 37In contrast to 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 nonhydrolytic 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 aer calcination at 700 C and convert to mullite only at 980-1000 C. We have successfully used these materials as catalysts for aminolysis 34,38 and alcoholysis 33 of styrene oxide and for the conversion of styrene oxide to phenylacetaldehyde. 39

General procedures
All manipulations were performed in dry nitrogen using Schlenk techniques or in an M. Braun drybox with both H 2 O and O 2 levels below 1 ppm.Al(NMe 2 ) 3 is highly ammable and reacts violently with water, liberating ammable gases.It must be handled under dry inert gas at all times.
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 Scientic.The gas chromatograph was equipped with a TS-SQC column (length 15 m, diameter 0.25 mm, lm thickness 0.   ] 3+ (aq.solution)]: 0.0 ppm.High temperature PXRD diffractograms were recorded on an X'PertPRO diffractometer equipped with a Co Ka 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 À1 .The adsorption-desorption isotherms were measured for each sample at least three times.The specic surface areas (SA), total pore volumes (V tot at p/p 0 ¼ 0.98) and average pore size (d) were determined by volumetric techniques 41,42 and analyzed by the multipoint BET method using at least ve 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 nitrogenon-silica kernel.Thermal analysis (TG/DSC) was performed on a Netzsch STA 449C Jupiter apparatus in the stream of air (70 cm 3 min À1 ) with a temperature ramp of 5 C min À1 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 (LaB 6 cathode, point resolution 1.7 A) 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 A with a PILATUS 100K detector, Dectris Lts.Scattering curves were analyzed by ATSAS soware package.Studies of surface acidity were performed on aircalcined xerogels.Xerogels (ca.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. Aer adsorption, samples were dried at room temperature under vacuum for 2 h.Adsorbed pyridine was characterized by the IR technique.
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 c axis goniometer, Saturn 724+ HG detector and Cryostream cooling device).Molybdenum K a radiation (l ¼ 0.71075 A) was used.CrystalClear (Rigaku 2014) and CrysAlisPro (Agilent Technologies 2013) soware packages were used for data collection and data reduction.The structure was solved using SHELXT 43 program and rened (full matrix least-squares renement on F 2 ) using SHELXL program.Both symmetrically independent cation fragments were disordered.One Me 3 Si-moiety of one anionic fragment was also rened as disordered.Disordered fragments were treated by geometrical similarity restraints and by ADP restraints.All non-hydrogen atoms were rened anisotropically.All hydrogen atoms (of methyl and hydroxyl groups) were placed at calculated positions and rened as riding and rotating, with their U iso set to 1.5U eq 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 ¼ 100(n total À n residual )/n total , where n total is the molar amount of organic groups in the starting materials and n residual 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 Me 2 NC(O)CH 3 (eqn (1)) in comparison to what is experimentally observed.This difference also denes the number of acetoxy groups on silicon and dimethylamido groups on aluminium that are le in the matrix.

Aluminosilicate xerogel prepared without template SiAl1 (eqn (1))
Al(NMe 2 ) 3 (0.799 g; 5.02 mmol) dissolved in 15 cm 3 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 cm 3 of dry toluene at 80 C. Aer the addition, a yellow gel formed.The reaction mixture was heated to 80 C for 7 days, aer 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 ¼ 56%.
Identication of volatile by-products.NMR: 13  Al(NMe 2 ) 3 (0.814 g; 5.11 mmol) dissolved in 25 cm 3 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 cm 3 ) at 80 C. Aer 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.Aer 7 days of aging at this temperature, 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.
Identication of volatile by-products.GC-MS: Calcined samples are labeled with a number corresponding to the particular calcination temperature, e.g.SiAlF1-500, watertreated 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 Si 2 O(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 Me 3 SiOAc and Al(NMe 2 ) 3
A model condensation reaction between Me 3 SiOAc and Al(NMe 2 ) 3 (3 : 1) (Table 1) led to a molecular product (1) containing the N,N-dimethylacetimidic acid cation [Me(C) OHNMe 2 ] + and [Al(OSiMe 3 ) 4 ] À 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 ask.These crystals (292 mg, 14%) were separated in glove box and analyzed by single crystal X-ray diffraction analysis.

Catalytic reactions
Aminolysis and alcoholysis reactions of styrene oxide 33,34,38,44 were performed in a 25 cm 3 round-bottomed Schlenk ask connected to a N 2 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 cm 3 ), styrene oxide (0.587 cm 3 , 5.00 mmol), and aniline (0.456 cm 3 , 5.00 mmol) or methanol (0.202 cm 3 , 5.00 mmol) in the case of aminolysis and alcoholysis, respectively.A blank reaction was performed without a catalyst.The reaction mixture was heated at 50 C. Catalytic products were quantied by GC-MS and 1 H NMR spectroscopy aer 10 min and 1 h.The reusability of catalyst was studied aer washing the used catalyst with CH 2 Cl 2 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 reuxed in 15 cm 3 of 2-propanol for 4 h.Aer centrifugation and ltering off the catalyst powder, the ltrate was tested for the presence of Al species by ICP-OES.

Results and discussion
The reaction proceeds with the formation of Si-O-Al network and release of dimethylacetamide which was conrmed by GC-MS (Fig. 2S †) and 1 H 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.
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 aerwards 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).
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.7][48] Besides the bonds mentioned above, vibrational bands of residual organic groups were observed as well.0][51] Acetoxy moieties are characterized by the asymmetric and symmetric COO stretches at 1580-1590 and 1460-1470 cm À1 , respectively.The difference between symmetric and asymmetric carboxylate vibrational bands is 120-130 cm À1 and according to Deacon-Phillips rules, this is indicative of the bidentate bridging mode on a metal center. 52,53luronic templates P123 and F127 are represented by vibrational bands of C-O-C bonds at 1090-1105 cm À1 and CH 3 at 2860-2880 cm À1 . 54he 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 Al x Si y O z , 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 rst 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.][48] Solid state NMR spectroscopy (Table 2) was employed for indepth 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 CH 3 resonances at 22.0 and 24.1 ppm, respectively.The COO resonances of acetate groups in unidentate and bidentate mode were observed at 170.4 and 179.5 ppm, respectively.Similar Scheme 2 Synthesis of aluminosilicate gel with four-, five-, and six-coordinate Al atoms and residual acetate and dimethylamide groups.The 29 Si CPMAS NMR spectrum of non-templated sample (SiAl1) shows a broad signal with the maximum at À89 ppm (Fig. 3).Compared to SiO 2 (À110 ppm) 56,57 and Si(OAc) 4 (À96 ppm) a downeld shi is observed.This shi 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 (CH 2 -CH 2 ) bridges displays a broad signal with the maximum at À54 ppm (Fig. 3). 29Si CPMAS NMR data of templated samples displays a broad signal at À87 ppm assigned to Si(OSi)(OAl) 3 species (Fig. 3). 58,59Similar resonances were observed aer calcination at 500 C of these templated samples (Fig. 4).The resonance at À90 ppm in 29 Si CPMAS NMR corresponds to Si(OSi)(OAl) 3 58,59 In the case of templated samples with a lower Al content (SiAlF1), 29 Si CPMAS displays a signal with maximum at À106 ppm and a shoulder at À97 ppm.This shi could be caused by the formation of Si-O-Si bonds because of excess Si(OAc) 4 (Fig. 3).Comparison of 29 Si CPMAS NMR spectra before and aer calcinations for the templated samples SiAlF1, 2, 3 indicates there are not major differences (Fig. 4).

27
Al 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 (Al IV , 53 ppm), 5-coordinated (Al V , 28 ppm) and 6-coordinated (Al VI , 0 ppm) Al 3,58,61 (Fig. 6S †). 27Al MAS NMR spectra of dried templated samples (SiAlF2, 3) show also the resonances for Al IV (58 ppm), Al V (31 ppm), and Al VI (2 ppm) atoms in the framework (Fig. 6S †). Al MAS NMR spectrum of the sample SiAlF1 (lower Al content) displays signals for Al IV at 54 ppm and for Al VI at À2 and À4 ppm.Aer calcination of this sample, the resonances at 61 ppm (Al IV ), 32 ppm (Al V ), and 2 ppm (Al VI ) were observed (Fig. 5).Chemical shis 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 27 Al NMR and EPR observations made by Chen et al. show association of ve-coordinated aluminum atoms to Lewis acid sites. 62Hence, the effect of 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.
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 N 2 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 aer drying and feature the type-II isotherms 63 (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 m 2 g À1 , respectively.However the pore diameters correspond to micropores in both materials.Aer calcination of the C2SiAl sample at 200 C, surface area decreased considerably to 36 m 2 g À1 .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 shied to the mesopore region (4.8 nm).
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 aer calcination at 500 C. The shape of isotherms corresponds to type IV with the H2 hysteresis consistent with signicant mesopore content and narrower pore size distributions (Fig. 6 and 9S †). 63Calcined xerogel SiAlP2-500 synthesized with the P123 template containing 59.3 mol% of Al exhibits surface area of 591 m 2 g À1 and the pore volume 0.53 cm 3 g À1 .If (AcO) 3 SiOSi(OAc) 3 is used as the silicon precursor, the surface area increases to 627 m 2 g À1 .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 m 2 g À1 are achieved with a pore diameter of 4.9-5.9nm (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 classication of thermal stability, we calcined the sample SiAlF2 at 700 C for 3 h and remeasured N 2 adsorption isotherms (Fig. 7).Its surface area reached 424 m 2 g À1 (V tot ¼ 0.41 cm 3 g À1 ) which is about 53 m 2 g À1 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 aer this test was reduced to 166 m 2 g À1 and pore volume to 0.28 cm 3 g À1 .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) 3 SiOSi(OAc) 3 exhibits also loss of surface area and pore volume while pore diameter increased (Table 3, Fig. 11S †).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 A À1 ) (Fig. 9).This behavior points to the mesoscopic ordering with the uniform pore channels in the xerogel.
The morphology of calcined mesoporous xerogels was studied by the TEM technique.The micrographs illustrate "wormhole" structure of pores (Fig. 10).
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 À1 .The bands corresponding to Lewis acid sites (LPy) are present at 1450 and 1625 cm À1 . 61,64Both Lewis and Brønsted acid sites are attributed to a vibrational band at 1492 cm À1 .Brønsted acidic sites (BPy) are characterized by the absorption bands at 1548 and 1639 cm À1 . 64Pyridine adsorbed by hydrogen bonds (HPy) of ^Si-OH moieties can be assigned to the vibrational band at 1599 cm À1 . 61These ndings show that synthesized aluminosilicate xerogels exhibit surface acidity of both Lewis and Brønsted type.
High-temperature powder X-ray diffraction (HT PXRD) was used to determine the crystal phases that arise during calcination (Fig. 12S †).6][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 ndings 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 SiO 2 (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) 3 SiOSi(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. 26,68,69These ndings 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 and 14S †).At rst, aminolysis of styrene oxide with aniline 34,44 was investigated with the calcined aluminosilicate xerogel as a catalyst.The second model reaction was alcoholysis of styrene oxide with methanol. 33atalytic yields for aminolysis are summarized in Table 4.The blank reaction without a catalyst was performed as well and no product was obtained aer 4 h.We observed that our calcined mesoporous xerogels are efficient catalysts for aminolysis reaction of epoxides.The 1 H NMR spectra of the reaction mixture (in C 6 D 6 ) display resonances attributed to two products: 2-phenyl-2-(phenylamino)ethanol (Ia) and 1-phenyl-2-(phenylamino)ethanol (IIa) (Fig. 13S and 15S †).These products were also conrmed by the GC-MS technique.Catalytic yields were analyzed aer 10 and 60 minutes.The highest conversion was observed with the catalyst SiAlF1-500 (82% aer 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) 3 SiOSi(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% aer 1 h which represents nearly the same activity (TOF ¼ 20) as the fresh catalyst.A report describing aluminosilicates as catalysts for aminolysis was published by Robinson. 70These 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.
In the case of styrene oxide alcoholysis, our catalysts exhibit a lower efficiency than in aminolysis reactions.Catalytic products conrmed by GC-MS and 1 H NMR were (Fig. 15S and 16S †) (1,2-dimethoxyethyl)-benzene (Ib) and phenylacetaldehyde (IIb) (Fig. 14S, † Table 6).Catalyst SiAlF1-500 exhibits 28 and 44%  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 aer 1 h was 35%.A leaching test conrmed that no Al was released into the solution.Only 0.3% of the total aluminium amount in catalyst was found in the ltrate.

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 conrmed as the only reaction byproduct attesting to the absence of homocondensation reactions.Al-O-Si bonds were identied by IR spectroscopy and 29 Si and 27 Al 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 m 2 g À1 ) but are microporous.Calcination causes framework collapse and samples lose porosity.With the use of block copolymer templates such as Pluronic P123 and F127, homogeneous, stiff gels were obtained.Aer calcination at 500 and 700 C mesoporous aluminosilicate materials with high surface areas ranging from 380 to 627 m 2 g À1 with the pore diameters 4.9 (P123) and 5.9 (F127) nm were obtained.Aer 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.

Fig. 2
Fig.2IR spectra of dried aluminosilicate xerogels prepared with and without F127 template.
). 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 shis were referenced externally to 29 Si d [(Me 3 SiO) 8 Si 8 O 20 ]: 11.72 ppm; 13 C d [adamantane]: 38.68 ppm; 27 Al d [[Al(H 2 O) 6

Table 1
Precursors, reaction parameters, and residual masses after TG analysis a Nominal Al mol% ¼ n Al /(n Al + n Si ).b Based on Al x Si y O z (see text) in precursors.

Table 2
MAS NMR chemical shifts of aluminosilicate xerogels

Table 5
Aminolysis of styrene oxide.Comparison with other aluminosilicate catalysts synthesized by hydrolytic sol-gel

Table 6
Alcoholysis of styrene oxide.Catalytic yields and selectivities This Open Access Article.Published on 25 February 2016.Downloaded on 3/27/2024 8:29:16 AM.This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.