Facile Method for Synthesis of Polyamine-Functionalized Mesoporous

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Facile Method for Synthesis of Polyamine-Functionalized Mesoporous Zirconia and Its Catalytic Evaluation toward Henry Reaction Surjyakanta Rana, Sujata Mallick, and K. M. Parida* Colloids and Materials Chemistry Department, Institute of Minerals and Materials Technology, Bhubaneswar-751013, Orissa, India ABSTRACT: Different amine-functionalized mesoporous zirconia were prepared by a co-condensation method using silane [aminopropyltrimethoxysilane (APTES), N-(2 amino ethyl)-3-amino propyl trimethoxy silane (AAPTMS), and 3-[2-(2-amino ethyl amino) ethyl amino] propyl trimethoxy silane (AEPTMS)] and zirconium butoxide. The materials were characterized by X-ray diffraction, BET surface area analysis, 13C magic angle spinning-nuclear magnetic resonance (NMR), Fourier transfer infrared spectroscopy (FTIR), scanning electron micrography (SEM), and thermogravimetric analysis (TGA)-differential thermal analysis (DTA). FTIR and NMR results revealed the successful grafting of organic amines onto the surface of zirconia. The catalytic activities were investigated for liquid phase Henry reaction of aromatic aldehydes with nitro methane.

1. INTRODUCTION Numerous organic reactions such as addition, isomerization, condensation, alkylation, polymerization, and cyclization essential for production of drugs and fine chemicals are persuaded by using stoichiometric amounts of soluble bases, but solid base catalysts rather than soluble bases offer more economic and ecofriendly processes, lacking environmental problems that are associated with the salts formed on neutralization of soluble bases.1-5 Beside this, solid base catalysts are gifted with many advantageous properties like inexpensiveness and recyclability and they can be easily separable than the soluble solid base catalysts. Ordered mesoporous molecular sieves can act as good alternatives for these environmentally harmful homogeneous catalysts. Many research efforts, which have focused on preparing the organic/ inorganic hybrids through functionalization of the exterior and/ or interior surfaces, prompted the utilization of the resultant materials in the field of catalysis,6-8 separation,9,10 sensor design,11 adsorptions,12-17 and nano science.18 There are two methods for surface functionalization, i.e., grafting (also known as postsynthesis) and direct synthesis or co-condensation.19 In postsynthesis or the grafting method, organic functional groups are grafted through the reaction of a silane coupling agent with free and geminal silanol groups on the surface of mesopores. The resultant materials generally maintain highly ordered structures and show relatively high hydrothermal stability after the grafting reaction.20 However, in this method, the distribution of the functional groups on the surface of the pore wall is not uniform and the organic groups are mainly present near the pore mouth. Comparatively, the direct synthesis pathway by co-condensation of organic silane precursors controls the resultant materials in a better way. In this method, there is more uniform surface coverage of the organic functional groups without the blockage of mesopores. Several aminopropyl-functionalized mesostructures have been prepared through direct assembly as well as through grafting reactions of preassembled frameworks using amino propyl trimethoxy r 2011 American Chemical Society

silane as the functionalizing agent for some base-catalyzed reactions.21,22 Up to now, most of the work was on the modification of the small mesopores of MCM-type silica, on HMS-type silica, or SBA-15 mesoporous material. However, there are few reports on amine functionalized zirconia.23 Luo et al. reported amine-functionalized zirconia obtained by the postsynthesis method.24 However, preparation of poly amine functionalized zirconia using a direct method has never been reported before. The Henry reaction is one of the most useful carbon-carbon bond forming reactions and can be catalyzed by organic and inorganic bases. There are a few literature reports on functionalized mesoporous materials toward the Henry reaction. Sharma et al. reported amine-functionalized mesoporous MCM41 materials toward the Henry reaction.25 Moon Kim et al. reported copper complex immobilized on magnetically separable mesocellular supported mesoporous silica toward the Henry reaction,26 and Asefa et al. reported amine-functionalized mesoporous materials toward nitroaldol condensation,27,28 but no report on amine functionalized zirconia as catalyst toward the Henry reaction. In our previous work,29 we have reported a detail characterization and catalytic evaluation of monoamine-functionalized zirconia. Herein, we have made a comparative study between three different types of amine immobilized on mesoporous zirconia. The main objective of the present work is to study the effect various amines such as amino propyl triethoxy silane (APTES), N-(2 amino ethyl)-3-amino propyl trimethoxy silane (AAPTMS), and 3-[2-(2-amino ethyl amino) ethyl amino] propyl trimethoxy silane (AEPTMS) on the surface and textural characterization of mesoporous zirconia. The catalyst is found Received: August 25, 2010 Accepted: December 27, 2010 Revised: November 2, 2010 Published: January 19, 2011 2055

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Scheme 1. Schematic Presentation of Synthesis of Amine-Functionalized Zirconia

robust enough to achieve high catalytic activity toward Henry reactions.

2. EXPERIMENTAL SECTION 2.1. Synthesis of Mesoporous Zirconia. Mesoporous zirconia (m-ZrO2) was synthesized by the sol-gel route using zirconium butoxide, as the zirconia source, and cetyltrimethylammonium bromide (CTMAB), structure directing agent at a pH of 11.5, which was maintained by an ammonium hydroxide solution. Acetyl acetone (Acac) and ethanol controlled the rate of hydrolysis of zirconium butoxide in water. In a mixture of water (4 mol) and NH3 (0.03 mol), CTMAB (0.025 mol) was dissolved and stirred for 1 h. Then, a mixture of zirconium butoxide (0.1 mol), acetyl acetone (0.05 mol), and ethanol (0.5 mol) was added to the template solution slowly, and this mixture was stirred for 3 h. The mixture was then refluxed under stirring for 48 h at 90 °C. The resulting solid was filtered, washed with acetone, and dried for 10 h at 100 °C. To remove the surfactant species, the samples were heated in air at a ramp rate of 1 °C min -1 to 400 °C for 5 h. 2.2. Synthesis of Amine Functionalized Mesoporous Zirconia. In our previous study, we have found that 12.8 wt % amine functionalized mesoporous zirconia shows the highest activity.29 Therefore, the present study is confined to 12.8 wt % of mono-, di-, and triamine functionalized zirconia catalyst. The mixture containing cetyltrimethyl ammonium bromide, 2 M of NaOH (aq), and H2O was heated at 80 °C for 30 min at a pH of 12. To this clear solution, zirconium butoxide and APTES (for monoamine)/AAPTMS (for diamine)/AEPTMS (for triamine) were added sequentially and rapidly. Following the addition, a white precipitation was observed after 3 min of stirring. The reaction temperature was maintained at 80 °C for 2 h. The products were isolated by a hot filtration, washed with a sufficient amount of water followed by methanol, and dried under vacuum. For acid extraction, the as-obtained materials (1 g) were treated with a mixture of ethanol (100 mL) and concentrated HCl (1 mL, 38% in weight) at 80 °C for 6 h. The resulting (surfactant removed) solid products were filtered and washed with ethanol and then dried at 60 °C. Herein after, the samples are named as APTESZrO2, AAPT MS-ZrO2, and AEPTMS-ZrO2 (Scheme 1). 2.3. Physico-Chemical Characterization. The BET surface area and pore size distribution were determined by the multipoint N2 adsorption-desorption method at liquid N2 temperature

(-196 °C) by a Micromeritics ASAP 2020. Prior to analyses, all the samples were degassed at 200 °C and 10-4 Torr pressure for 2 h to evacuate the physisorbed moisture. The low angle X-ray diffractograms were recorded on a Philips PW 1710 powder diffractometer using Ni filtered Cu KR in the 2θ range of 080 °C. The Fourier transfer infrared spectroscopy (FTIR) spectra were recorded using Varian FTIR-800 in KBr matrix in the range of 4000-400 cm-1. The scanning electron microscopic figures of functionalized zirconia samples were recorded using a Hitachi S3400N. TG-differential thermal analysis (DTA) was carried out in static air using a METTLER TOLEDO TDA/SDTA 851e thermal analyzer in the temperature range of 30-1000 °C at a heating rate of 20 °C min-1. Solid state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were recorded on an AV300 NMR spectrometer. The CO 2 - temperature programmed desorption (TPD) of all the samples was carried out in a Micromeritics (Auto chem II) instrument. About 0.1 g of sample was taken inside quartz “U” tube and degassed at 150 °C for 1 h with He gas flow. The sample was then cooled to 30 °C, and at this temperature, the gas flow was changed to CO2. It was then heated at a heating rate of 10 °C/min up to 800 °C, and the spectra were recorded. 2.4. Catalytic Reaction. The Henry reactions were carried out using each of the organoamine-functionalized samples under N2 atmosphere in a flask that was equipped with a reflux condenser and a magnetic stirrer. The reactor was placed in a thermostat bath. In a typical experiment, 1 mmol of p-hydroxybenzaldehyde and 10 mL of nitromethane reactants were mixed and heated to the set temperature, and then, 0.2 g of the dried catalyst was rapidly added into the reactor. The reaction was stirred at 50 °C for 2 h under nitrogen atmosphere. After the reaction, the catalyst was recovered by centrifugation for reuse and the reaction mixture was characterized by an off-line Shimadzu gas chromatograph (GC-2010) equipped with ZB-WAX capillary column and flame ionization detector (FID) detector and by 1 H NMR.

3. RESULTS AND DISCUSSION 3.1. Characterization. N2 adsorption-desorption is a common method to characterize mesoporous materials, which can provide information about the specific surface area, average pore diameter, pore volume, etc. BET surface area, pore size, and pore 2056

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Table 1. Surface Properties of Poly Amine Functionalized m-ZrO2 Samples

catalyst m-ZrO2 APTES-ZrO2 AAPTMS-ZrO2 AEPTMS-ZrO2

surface pore area volume pore basicity 2 -1 (m g ) (cm3/g) diameter (Å) (mmol/g) conversion (%) 156 107 101 98

0.25 0.19 0.18 0.17

32 27 26 25

2.2 4.5 5.8 6.3

10 82 87 92

Figure 2. BJH pore size distribution curves of m-ZrO2 and different amine-functionalized m-ZrO2.

Figure 1. N2 adsorption-desorption isotherms of m-ZrO2 and different amine-functionalized m-ZrO2.

volume for the various amine supported mesoporous zirconia materials are presented in Table 1. The specific surface area of mesoporous zirconia is 156 m2/g. After modification by amine, the specific surface area decreases significantly. The surface area of amine functionalized zirconia depends upon the chain length of the organo group. The surface areas of the samples containing the longer organodiamine and organotriamine groups in the mesoporores are slightly lower than the corresponding samples containing the shorter organoamines. The pore volume and pore diameter of the amine functionalized materials decrease compared to that of the parent zirconia due to the anchoring of amine groups. The basic sites of the amine functionalized zirconia catalysts were investigated by a pulse method using carbon dioxide as the probe molecule, and the results are given in Table 1. The results indicate that the basic sites of amine functionalized zirconia are higher than that of neat zirconia, which reveals that the functionalization of amine on zirconia induces an increase in the basic sites. The highest basic site corresponds to triamine functionalized zirconia followed by diamine and monoamine. This increasing trend of basic sites might be due to the presence of more amine group. N2 adsorption-desorption isotherms of the parent zirconia and various amine functionalized zirconia samples are shown in Figure 1. According the IUPAC classification, all the samples are of type IV isotherms with a typical hysteresis loop, featuring a sharp increase of capillary condensation at a relative pressure P/ P0 g 0.25, characteristic of mesoporous material with highly uniform size distribution. The relative pressure (P/P0) of the inflection points is related to a pore diameter in the mesopore range, and the sharpness of the step indicates the uniformity of pore size distribution The isotherms of pure ZrO2 and of APTES/ ZrO2 show hysteresis loops typical of type H1 or H2 curves, relative to the presence of cylindrical or bottleneck pores.

Figure 3. XRD (high) patterns of m-ZrO2 120 °C (a), APTES/ZrO2 120 °C (b), m-ZrO2 400 °C (c), m-ZrO2 550 °C [Inset: SXRD patterns of m-ZrO2 (a) and monoamine functionalized m-ZrO2 (b), diamine (c), and triamine (d)].

The isotherms of AAPTMS/ZrO2 and AEPTMS/ZrO2 are instead of type H4 which typically shows the presence of microporosity. Figure 2 shows the BJH pore size distribution of zirconia and amine modified zirconia. The pore size distribution exhibits sharp peaks, for the samples possess good mesoporous structure with ordering and uniform pore size distribution. The pore diameters decrease slightly with amine modification. The high angle X-ray diffraction (XRD) patterns of different calcined mesoporous zirconia and amine functionalized zirconia samples are shown in Figure 3. The XRD patterns of amine functionalized zirconia and zirconia recorded after calcined at 120 °C are amorphous in nature and shows very wide peaks characteristic of microcrystalline hydrated zirconia. In the XRD pattern of zirconia, recorded after calcining at 400 °C, a portion of the amorphous material crystallizes progressively to the tetragonal phase; as calcined temperature increases above 500 °C, zirconia exists mainly in the tetragonal phase with monoclinic phase. Small angle X-ray diffraction patterns of the mesoporous zirconia and various amine functionalized zirconia samples are shown in 2057



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Figure 4. FTIR spectra of m-ZrO2 and different amine-functionalized m-ZrO2.

Figure 3. The low-angle XRD patterns of zirconia samples demonstrated the mesostructure because there was only one broad peak at around 1 o which translates to a spacing of 6.94 nm, calculated from the Bragg Equation, 2d sin θ = nλ. The intense and narrow XRD peak of zirconia sample suggested a relatively organized and oriented mesostructure. 30 The XRD pattern of various amine functionalized m-ZrO 2 are similar to that of m-ZrO 2 , but the modification with amine slightly reduces the intensities of the XRD peaks. However, the structure of amine functionalized zirconia is still mesoporous. The FTIR spectra of mesoporous zirconia and 12.8% amine functionalized zirconia are presented in Figure 4. The FTIR spectrum of zirconia shows a broad band in the region of 3410 cm-1 due to asymmetric stretching of OH group, and two bands at 1621 and 1386 cm-1 are due to bending vibrations of -(H-O-H)- and -(O-H-O)- bonds. The band at 503 cm-1 resulted from the existence of both tetragonal and monoclinic zirconia. The spectra at 730 cm-1 are attributed to the presence of the Zr-O bond. The presence of N-H bending vibration at 690 cm-1 and of NH2 symmetric bending vibration at 1532 cm-1 of amine functionalized ZrO2 nanoparticles, absent in neat zirconia, indicate the successful grafting of organic amine onto the surface. Two new absorption bands, namely, 8001200 cm-1 and 2800-3000 cm-1, are observed on the spectrum of amine functionalized ZrO2 nanoparticles, suggesting that APTES has been successfully attached to the ZrO2 nanoparticles. The thermogravimetric analysis (TGA) profile showed three distinct weight losses due to organic functional groups, including methanol, and a small weight loss due to the dehydration of the surface hydroxyl group (Figure 5). The DTA pattern of the zirconia sample showed one endothermic peak at 108 °C for dehydration and dehydroxylation of zirconia. The exothermic peak at 556 °C was due to the crystallization of microcrystalline hydrated zirconia into metastable tetragonal zirconia in agreement with our XRD results31,32(see Figure 3). The DTA pattern of various anime modified sample show four peaks, Figure 5b-d. The endothermic peak around 110 °C is due to water loss. The exothermic peaks around 350-550 °C and 700-750 °C are attributed to the loss of amine. The small exothermic peak around the zirconia sample undergoes a total loss of nearly 18% due to physisorbed, chemisorbed, decomposed oxide phases, etc., while in the case of the amine modified sample the

Figure 5. TGA and DTA patterns of m-ZrO2 (a), monoamine-functionalized m-ZrO2 (b), diamine (c), and triamine (d).

total loss is ∼20%, 22%, and 24% for mono-, di-, and triamine, respectively, TGA (Figure 5a). This indicates the modification of zirconia surface by various amines. C13 magic angle spinning NMR is a powerful tool to characterize the functionalization of amines of zirconia surface. The C13 NMR spectra of various amine modified zirconia are shown in Figure 6a-c. C13 CP MAS NMR spectra showed the presence of functionalized organic groups attached to the zirconia surface and the absence of surfactant species after the solvent extraction process. The absence of signals at 15 and 58 ppm, assigned to the SiO-CH2-CH3 species and in the range of 50-70 ppm, for surfactant groups, indicates that the hydrolysis of the organosilane monomers is complete and the surfactant is completely removed from the zirconia pore channels. The monoamine functionalized zirconia (Figure 6a) shows the sharp peak at 11.4 ppm, which is ascribed to the carbon atom bonded to silicon. The signal at 25.4 ppm corresponds to methylene group carbon, and the peak around 45 ppm can be attributed to methylene group carbon atoms attached to the anime group. In the case of diamine functionalized zirconia (Figure 6b), the sharp peak at 8.7 ppm is attributed to the carbon atom bonded to silicon. The signal at 20 ppm corresponds to the methylene group carbon, and the peaks around 38.5, 50.5, and 65.7 ppm can be assinged to methylene group carbon atoms attached to the amine groups. In the case of triamine functionalized zirconia (Figure 6c), the sharp peak at 8.9 ppm is attributed to the carbon atom bonded to silicon. The signal at 19.5 ppm corresponds to the methylene group carbon, and the peaks around 38.5, 45.1, 49.6, 52.2, and 56.2 ppm can be assigned to methylene group carbon atoms attached to the amine groups. Scanning electron micrographs of amine functionalized zirconia materials are shown in Figure 7. The scanning electron micrography (SEM) micrographs demonstrated a variety of particle shapes and sizes. It has been found that the catalysts are well-ordered and uniformly distributed over the support surface. The SEM image of monoamine functionalized zirconia (Figure 7a) material showed curved hexagonal shaped tubular morphology, but in the case of diamine and triamine functionalized zirconia (Figure 7b,c), the shapes transformed into micrometer-sized spheres. For monoamine, each crystal has a cylindrical 2058



Figure 6.

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C MAS NMR of monoamine-functionalized m-ZrO2 (a), diamine (b), and triamine (c). 2059



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Figure 7. SEM figures of monoamine-functionalized m-ZrO2 (a), diamine (b), and triamine.(c).

form, having a diameter ranging from 0.4 to 1.0 μm. The total length of the crystals is 1 to 2 μm and consists of packages of cylindrical fibers (Figure 7a). The SEM image of diamine functionalized material shows micrometer-sized oval shape morphology where as for triamine functionalized zirconia the particles are of spherical shape morphology with diameters in the 0.1-1 μm range. 3.2. Catalytic Activity. The catalytic activity of the amine modified zirconia catalysts were evaluated for the nitroaldol reaction of p-hydroxybenzaldehydes with nitromethane, and the results are summarized in Table 1. Mesoporous zirconia grafted with amines or polyamines could effectively catalyze nitroaldol reactions to produce nitroalkenes in high yields, whereas the pure zirconia gave rise to only small amounts of nitroalkene. The triamine functionalized zirconia catalyst showed the highest conversion (92%) due to the presence of more basic sites. The conversion of p-hydroxybenzaldehde follows the same trend as basic sites as monoamine < diamine < triamine. The Henry reaction is mainly a base catalyzed reaction based on the cabon-carbon bond forming process. The surfaces of functionalized zirconia are occluded by organic amine templates, which provide high activity as a base in mild conditions. The reaction pathway can be rationalized by the possible mechanism illustrated in Scheme 2. Amine functionalized zirconia, when reacting with nitro methane, acts as the proton scavenger to generate nitro methane anion, which acts as the attacking reagent. It attacks the carbonyl group of benzaldehyde to form an enolate species. This in a subsequent step abstracts a proton from protonated amine functionalized zirconia and loses a water molecule to produce

p-hydroxynitrostyrene. Without catalyst, no reaction was observed. The effect of various reaction parameters on the condensation of p-hydroxybenzaldehyde with nitromethane was studied using triamine functionalized zirconia as catalyst. 3.2.1. Effect of Catalyst Amount. The variation of catalytic activity with the amount of catalyst is shown in Figure 8. It is not of practical interest to use a large amount of catalyst. Again, the removal of high molecular weight adsorbed products from the catalyst is quite expensive too. It is observed that the product conversion increases from 79% to 98%, with increasing the amount of catalyst from 0.01 to 0.04 g. With an excess amount of catalyst, the conversion obviously increased because of the availability of more basic sites, which favors the dispersion of more active species. 3.2.2. Influence of Reaction Time. Results showing the influence of reaction time on the conversion of p-hydroxybenzaldehyde and product selectivity in the condensation reaction over triamine functionalized zirconia catalyst are presented in Figure 9. With increasing the reaction time from 0.5 to 3 h, the selectivity for p-hydronitrostyrene is decreased while the conversion is increased. As with increasing reaction time, the product may undergo further condensation and give dinitro product, which decreased the selectivity of p-hydronitrostyrene. The conversion and selectivity values show no appreciable change with further rise in reaction time to 4 h. 3.2.3. Effect of Substituents. With the optimal conditions in hand, the different aldehydes were examined in the presence of a catalytic amount of triamine functionalized zirconia for the Henry 2060



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Scheme 2. Schematic Presentation of Henry Reaction

Figure 8. Effect of catalyst on base catalyzed Henry reaction using triamine-functionalized m-ZrO2 as catalyst.

Figure 9. Effect of reaction time on base catalyzed Henry reaction using triamine-functionalized m-ZrO2 as catalyst. 2061



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Table 2. Henry Reactions of Various Aldehydes with Nitromethane

reaction, and the results are summarized in Table 2. The derivatives of benzaldehydes bearing electron withdrawing groups (nitro group and halo group) were more reactive toward the Henry reaction and give more conversion than those with electron donating groups (-CH3, -OCH3, -NH2, and OH). In the case of electron withdrawing groups, the possibility of attack of the carbanion (generated from the nitromethane group) at the carbonyl carbon is enhanced compared to that of electron donating groups. Generally, the electron donating substituents in meta position are more favorable than that of

ortho and para positions toward the Henry reaction. This may be due to the resonating effect of the lone pair on the substituents. 3.3. Reusability of the Catalyst. Reusability of the catalyst was investigated by carrying out repeated runs on the same batch of the used triamine functionalized zirconia as catalyst toward the Henry reaction of p-hydroxybenzaldehyde and nitromethane. The catalyst was separated by centrifugation after the reaction, washed several times with distilled water, dried, and used in the reaction with a fresh reaction mixture. 2062


Industrial & Engineering Chemistry Research The yield decreased by 3% in the regenerated sample after three cycles. One prominent feature, which was exhibited by the IR spectra obtained after the catalytic runs, was the growth of the so-called coke band around 1600 cm-l. This band is ascribed to highly unsaturated carbonaceous deposits.33 In our case, the absence of the IR band around 1600 cm-l gives evidence of no coke formation after the catalytic run.

’ CONCLUSIONS The conclusions were as follows: (1) The nitrogen adsorption-desorption study reveals that the catalyst retains the mesoporosity. (2) There is a slight decrease in pore diameter after functionalization of various amines in zirconia. (3) The C13 NMR and FTIR spectra confirmed the successful functionalization of amine groups on zirconia surface. (4) Mesoporous zirconia grafted with amines or polyamines could effectively catalyze nitroaldol reactions to produce nitroalkenes in high yields. (5) The reusability test exhibits the good recycling capacity of the amine-functionalized material.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: 91674-2581637.

’ ACKNOWLEDGMENT The authors are thankful to Prof. B.K. Mishra, Director, IMMT, and Bhubaneswar for his keen interest, encouragement, and kind permission to publish this work. One of the authors, S. M., is obliged to CSIR for a senior research fellowship. ’ REFERENCES (1) Kloetstra, K. R.; Van Bekkum, H. Base and acid catalysis by the alkali-containing MCM-41 mesoporous molecular sieve. J. Chem. Soc., Chem. Commun. 1995, 1005. (2) Subba Rao, Y. v.; De Vos, D. E.; Jacobs, P. A. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene Immobilized in MCM-41: A Strongly Basic Porous Catalyst. Angew. Chem., Int. Ed. Engl. 1997, 36, 2661. (3) Koteswara Rao, K.; Gravelle, M.; Sanchez, J.; Figueras, F. Activation of Mg-Al Hydrotalcite Catalysts for Aldol Condensation Reaction. J. Catal. 1998, 173, 115–121. (4) Cavani, F.; Trifiro, F.; Vaccari, A. Hydrotalcite-type anionic clays: Preparation, properties and applications. Catal. Today 1991, 11, 173–301. (5) Lakshmi Kantam, M.; Choudary, B. M.; Venkat Reddy, Ch.; Koteswara Rao, K.; Figueras, F. Aldol and Knoevenagel condensations catalysed by modified Mg-Al hydrotalcite: a solid base as catalyst useful in synthetic organic chemistry. J. Chem. Soc., Chem. Commun. 1998, 1033–1034. (6) Stein, A. Advances in Microporous and Mesoporous Solids-Highlights of Recent Progress. Adv. Mater. 2003, 15, 763–775. (7) Mbaraka, I. K.; Radu, D. R.; Lin, V.S.-Y.; Shanks, B. H. Organosulfonic acid-functionalized mesoporous silicas for the esterification of fatty acid. J. Catal. 2003, 219, 329–336. (8) Wang, X. G.; Chen, C.-C.; Chen, S.-Y.; Mou, Y.; Cheng, S. Arenesulfonic acid functionalized mesoporous silica as a novel acid catalyst for the liquid phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam. Appl. Catal., A: Gen. 2005, 281, 47–54. (9) Dai, S.; Burleigh, M. C.; Shin, Y. C.; Morrow, C.; Barnes, C.; Xue, E. Z. Imprint Coating: A Novel Synthesis of Selective Functionalized Ordered Mesoporous Sorbents. Angew. Chem., Int. Ed. 1999, 38, 1235– 1239.

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Facile Method for Synthesis of Polyamine-Functionalized Mesoporous

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