Effect of Sulfate Modification on Structure Properties, Surface Acidity

Article pubs.acs.org/IECR

Effect of Sulfate Modification on Structure Properties, Surface Acidity, and Transesterification Catalytic Performance of TitaniumSubmitted Mesoporous Molecular Sieve Shengping Wang, Yun Shi, and Xinbin Ma* Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China ABSTRACT: A series of sulfated titanium-submitted mesoporous molecular sieves denoted as S/Ti-MCM-41 were prepared by wet impregnation method with H2SO4 solution as promoter. The results of XRD, N2 adsorption−desorption, NH3-TPD, FTIR of pyridine adsorption, and XPS analysis indicated that S/Ti-MCM-41 samples possess well-ordered hexagonal mesostructure, although the pore diameter and specific surface area shrunk with the increasing coverage of sulfur species. As a result of the electron inductive effect from the SO bond of SO42−, Lewis acidity is intensified significantly and new Brönsted acid sites are generated from the activated hydroxyl groups. Brönsted acid sites are medium strength, while part of the Lewis acid sites are of weak strength and part of them are medium. The S/Ti-MCM-41 catalysts exhibited desirable activity for transesterification of dimethyl oxalate and phenol.

1. INTRODUCTION The M41S family of mesoporous molecular sieves has attracted extensive attention of many researchers since their discovery in 1990s.1,2 On behalf of these materials, MCM-41 is an important class of a hexagonally arranged cylindrical pores with a large surface area, regular pore diameters, and high thermal stability. Thus, these properties make MCM-41 material suitable for many catalytic applications, such as isomerization,3,4 selective oxidation,5−7 photocatalysis,8−10 and so forth. As reported, the incorporation of heteroatoms in MCM-41 could generate new acidity wherein Lewis and Brönsted acid sites are involved.11−14 The heteroatom-submitted MCM-41 has opened opportunities to obtain new acid sites for catalytic applications. Concerning the improvement of acidity, on the other hand, the sulfurcontaining catalysts are of interest because the modification of sulfate species has been reported to enhance both strength and amount of acidity on the surface of molecular sieves and metal oxide catalysts.15−17 Many of studies were carried out for the synthesis of TiMCM-41 catalysts.5,15−21 To the best of our knowledge, however, there are no reports on sulfated Ti-MCM-41 preparation. In this work, titanium containing MCM-41 material was prepared with the microwave irradiation method and modified by H2SO4 aqueous solutions to further improve the acidity. The structure and acid properties of the materials were characterized with XRD, N2 adsorption−desorption, NH3TPD and FT-IR of pyridine adsorption, and XPS analysis. Transesterification of dimethyl oxalate (DMO) with phenol, as an acid catalyzed reaction, was employed as a probe reaction to test the effects of sulfate modification on acid catalytic properties. In this route, DPO is synthesized via two steps; namely, the transesterification of DMO with phenol into methyl phenyl oxalate (MPO) (eq 1) followed the disproportionation reaction of MPO to DPO (eq 2), while a major byproduct during the above process was anisole (AN), © 2012 American Chemical Society

which could be formed via methylation of phenol and decarboxylation of MPO, as shown in eqs 3 and 4.

2. EXPERIMENTAL SECTION 2.1. Materials. Tetraethoxysilane (TEOS), tetrabutyl titanate (TBOT), cetyltrimethylammonium bromide (CTAB), sodium hydroxide (NaOH), and sulfuric acid (H2SO4, 98%) were all purchased from Kermel Fine Chemical Corporation (Tianjin, China). Dimethyl oxalate and phenol were obtained from Tianjin No. 1 Chemical Reagent Factory (Tianjin, China). All of these chemicals are analytical reagent-grade. Acetonitrile is HPLC grade and was acquired from Fisher Scientific Corporation (NJ, USA). 2.2. Synthesis of Ti-MCM-41. The titanium-submitted mesoporous molecular sieve was synthesized under a microwave-irradiation condition using cationic surfactant CTAB as template, and TEOS and TBOT as Si and Ti sources, respectively. Titanosilicate gel was prepared according to the detailed synthetic procedure described elsewhere.22 The Si/Ti Received: Revised: Accepted: Published: 5737

November 8, 2011 April 5, 2012 April 6, 2012 April 6, 2012 dx.doi.org/10.1021/ie202563s | Ind. Eng. Chem. Res. 2012, 51, 5737−5742

Industrial & Engineering Chemistry Research

Article

bottomed flask (125 mL) equipped with a thermometer, a condenser, and a magnetic stirrer under refluxing condition at atmospheric pressure with Ti-MCM-41 as catalyst. The condenser consisted of a distillation column kept at 353 K by flowing recycled hot water in order to remove produced methanol to push the reaction toward the desired direction. In a typical experiment, 0.05 mol of DMO and 0.15 mol of phenol with a molar ratio of 1:3 and 0.9 g of Ti-MCM-41 were added into a batch reactor. Nitrogen gas was then flowed at 30 sccm for 10 min to purge the air from the reaction system. The reaction temperature was kept at 453 K, and the reaction time was 1 h. Quantitative analysis of reaction products was performed on an HP1100 series high-performance liquid chromatography (Agilent Technologies) equipped with a quaternary gradient pump, an online degasser, and an ultraviolet visible detector (VWD). A ZORBAX Eclipse XDBC18 column (150 mm × 4.6 mm, 5 μm, Agilent Technologies) was used for the liquid-chromatographic analysis of the products. The separation was achieved under a step-gradient elution condition with a mixed mobile phase consisting of water and acetonitrile and the UV detection at 254 nm at atmospheric temperature. TOF (mmol of converted DMO per acid sites (NH3 mmol) and hour), DMO conversion, and DPO, MPO, and AN selectivity and yield are used to show the catalytic performance of S/Ti-MCM-41 for the transesterification of DMO with phenol.

atomic ratio in the mixed gel was 50. The final gel was transferred into Teflon vessels and heated via nonpulsed microwave irradiation in a Multiwave 3000 microwave reaction system (Anton Parr) which could provide an efficient way for rapid and uniform crystallization heating. Crystallization was carried out in a temperature controlled mode where the temperature was ramped for 5 min and held for 40 min at 393 K. The solid products were filtered, washed with deionized water, and dried in air at 373 K for 12 h. The materials were calcined at 823 K for 6 h in air with a heating rate of 2 K/min to decompose the organic template and obtain white powder (Ti-MCM-41). 2.3. Synthesis of Sulfated Ti-MCM-41. A series of sulfated Ti-MCM-41 materials was prepared by the wet impregnation method. About 1 g of Ti-MCM-41 sample was treated with 4 mL of H2SO4 aqueous solution, in which H2SO4 concentration was adjusted to obtain different sulfur content varying from 2 wt % to 12 wt %, at room temperature for 30 min. The impregnated samples were dried at 353 K until complete dryness in an oven and subsequently calcined at 723 K for 3 h in a muffle furnace. The final products were abbreviated as xS/Ti-MCM-41, where x is the stoichiometric sulfur content. 2.4. Characterizations. SAXRD measurements were performed on a Rigaku D/max-2500 diffractometer using graphite filtered Cu Kα radiation (λ = 0.154056 nm) at 40 kV and 100 mA. Diffraction data were recorded at an interval of 0.02° and a scanning speed of 1° min−1 in the range of 1−10°. Nitrogen adsorption−desorption isotherms were obtained at 77 K using a Tristar 3000 surface area and porosity analyzer (Micrometritics). Before measurements, the samples were outgassed at 573 K for 3 h in a degas port of the analyzer. Surface areas were calculated by the Brunauer−Emmet−Teller (BET) method, and pore size distribution was determined via the Barrett−Joyner−Halenda (BJH) method based on the Kelvin equation.23 NH3-TPD experiments were conducted on Autochem 2910 chemical adsorption instrument (Micromeritics). The samples were heated to 823 K in flowing He (30 mL/min) for 1 h and then cooled to room temperature. Adsorption of ammonia was carried out at 323 K to saturation. And then ammonia was replaced with helium at 323 K for 1 h to remove the physical adsorption ammonia, followed by the desorption of ammonia with increasing temperature from 323 to 873 K at a rate of 10 K min−1. FT-IR spectra of samples were recorded in the range of 400 to 4000 cm−1 on a Nicolet 6700 spectrometer (Nicolet) with a KBr pellet. Acidity of catalysts was analyzed by FTIR measurement of adsorbed pyridine using the same IR spectrometer with a 4 cm−1 resolution. The samples were pressed into a self-supporting wafer followed by evacuation at 623 K for 0.5 h. After cooling to 333 K, pyridine was adsorbed on the samples until saturation. Subsequently, the samples were outgassed for 0.5 h at different temperatures, and the spectra were recorded. XPS analysis was conducted in a Perkin-Elmer PHI 1600 ESCA system with Mg Kα 1253.6 eV radiation as the excitation source. The sample was mounted on the specimen holder by means of double-sided adhesive tape. Spectra were collected in steps of 0.15 eV. The S 2p and Ti 2p binding energies were referenced to the C 1s peak at 284.6 eV. 2.5. Catalytic Reaction. Transesterification reaction of DMO with phenol was conducted in a three-necked round

3. RESULTS AND DISCUSSION 3.1. Chemical and Structural Properties. Figure 1 shows SAXRD patterns of the series of S/Ti-MCM-41 samples with

Figure 1. Small-angle XRD patterns of molecular sieves with different S contents: (a) Ti-MCM-41, (b) 2S/Ti-MCM-41, (c) 4S/Ti-MCM41, (d) 8S/Ti-MCM-41, and (e) 12S/Ti-MCM-41.

different S content. S/Ti-MCM-41 materials exhibit welldefined patterns, very similar to that of Ti-MCM-41, including a main reflection peak corresponding to the (100) plane at a small angle (2θ = 2−3°) and three other peaks around 3−7° indexed with (110), (200), and (210) facets. This indicates the excellent ordering degree of mesoporous molecular sieves.1,5 As the S content increases from 2% to 12%, the XRD peaks slightly shift toward higher diffraction angle, accompanied with a certain decrease of the peak strength, which could be associated with a trivial reduction in the long-range order of the structure. XRD patterns give evidence that the Ti-MCM-41 material 5738

dx.doi.org/10.1021/ie202563s | Ind. Eng. Chem. Res. 2012, 51, 5737−5742


Article

distribution and show another mesopore with a pore size of about 3.8 nm, which increases with the increasing S content. Thus, the loading of S species would give some interruption to the mesostructure of the titanium containing material. The texture parameters calculated from N2 adsorption−desorption isotherms are listed in Table 1. The specific surface area (SBET),

maintains the ordered hexagonal structure with surface modification of H2SO4. N2 adsorption−desorption isotherms and pore size distribution curves of the Ti-MCM-41 samples modified by H2SO4 are shown in Figures 2 and 3. All the samples show typical

Table 1. Structural Properties and Amounts of NH3 Desorbed for S/Ti-MCM-41 with Different S Contents catalysts Ti-MCM41 2S/TiMCM-41 4S/TiMCM-41 8S/TiMCM-41 12S/TiMCM-41

SBET (m2/g)

VBJH (cm3/g)

DBJH (Ǻ )

amount of NH3 desorbed (mmol NH3/g catalyst)

896

0.840

28.6

0.370

825

0.764

27.8

0.401

801

0.760

27.6

0.509

782

0.716

27.6

0.242

771

0.701

27.5

0.185

pore volume (VBJH), and average pore diameter (DBJH) are decreasing upon increasing S content, resulting from the S species covering the surface of the materials. Ammonia TPD characterization is a well-known method for determination of surface acid strength of solid heterogeneous catalysts. In the NH3-TPD curves, peaks are generally distributed into two regions: below and above 673 K, referred to as low-temperature (LT) and high-temperature (HT) regions, respectively. The peaks in the HT region can be attributed to desorption of NH3 from strong Brönsted and Lewis type acid sites, and the peak in the LT region is assigned as the desorption of NH3 from some relatively weak acid sites.25,26 NH3-TPD profiles of S/Ti-MCM-41 catalysts with different S contents are shown in Figure 4. From Figure 4, for

Figure 2. Nitrogen adsorption−desorption isotherms of molecular sieves with different S contents: (a) Ti-MCM-41, (b) 2S/Ti-MCM-41, (c) 4S/Ti-MCM-41, (d) 8S/Ti-MCM-41, and (e) 12S/Ti-MCM-41.

Figure 3. Pore size distribution curves of molecular sieves with different S contents: (a) Ti-MCM-41, (b) 2S/Ti-MCM-41, (c) 4S/TiMCM-41, (d) 8S/Ti-MCM-41, and (e) 12S/Ti-MCM-41. Figure 4. NH3-TPD profiles of S/Ti-MCM-41 catalysts with different S contents: (a) 2% S, (b) 4% S, (c) 8% S, and (d) 12% S.

irreversible type IV adsorption isotherms as defined by IUPAC, including a steep increase at relative pressure of 0.2−0.4 characteristic of capillary condensation inside the primary mesopores.23,24 It means the S/Ti-MCM-41 samples retained mesostructure with uniform pore size distribution and large pore volume after surface modification of H2SO4. Furthermore, compared with the unmodified Ti-MCM-41, S/Ti-MCM-41 samples present inflection with a slight shift toward lower relative pressure with the increasing S content, indicating a decrease of mesopore volume. As shown in Figure 3, S/TiMCM-41 samples express narrow and uniform pore size

all S/Ti-MCM-41 samples with different S contents, there are two NH3 desorption peaks, of which one appears in the region below 473 K and another appears in the region of 473 to 673 K. It means the S/Ti-MCM-41 samples possess two types of acid sites with different acidic strengths including weak and medium strong acid sites. However, the amount of NH3 desorbed on S/ Ti-MCM-41 samples with different S contents are different, as illustrated in Table 1. The amount of NH3 desorbed on the S/ 5739



Article

Ti-MCM-41 samples is increased with the increase of S content from 2% to 4%, following a declining trend with the further increasing S content. It may be attributed to the coverage of excessive sulfur species, resulting in the decrease of the acid sites exposed to NH3 molecules. FT-IR measure of adsorbed pyridine has been performed to make further determination for the nature of acidity on the surface of S/Ti-MCM-41 samples. According to the literature, the adsorbed pyridine molecules can always be divided into three types: (i) the protonated pyridine characteristic for Brönsted acid sites, giving IR adsorption bands at about 1540 and 1639 cm−1; (ii) pyridine molecules coordinated with Lewis acid sites, which give bands at 1440−1460, 1575−1580, and 1600−1625 cm−1; and (iii) physisorbed pyridine connected to silanol groups by a weak hydrogen bonding, which gives bands at about 1445 and 1596 cm−1.13,27,28 As shown in Figure 5, S/ Figure 6. FTIR spectra of pyridine adsorbed on 8S/Ti-MCM-41 catalyst after desorption at different temperatures: (a) 333 K, (b) 373 K, (c) 423 K, (d) 473 K, (e) 523 K, and (f) 573 K.

1639 cm−1 are retained until the desorption temperature is raised to 573 K. According to the results of NH3-TPD detection, there are weak and medium strength acid sites presented on the surface of S/Ti-MCM-41 materials. Thus, it could be concluded that the weak acid sites belong to Lewis acidity, while the medium strength acid sites consist of both Lewis and Brönsted acidity. In addition, XPS spectra have been recorded for the intensive investigation of the chemical state of the elements on the surface of sulfate-modified Ti-MCM-41 materials. Table 2 enumerates the element surface content and binding energies of S/Ti-MCM-41 samples with different S contents. As the sulfur content in S/Ti-MCM-41 material is increased, the surface content of the titanium species declines gradually. From the results of XPS, the binding energy of S 2p(3/2) in S/TiMCM-41 materials presents at 169.3 ± 0.2 eV, which is attributed to S 2p of SO42−.30 SO42− species can link with Ti and Si atoms to generate the acid sites. As illustrated by the SO42− linkage with Ti in Scheme 1, the S(VI) sites are necessary for generation of new Lewis and Brönsted acidity. Due to the strong electron inductive effect caused by the SO bond of SO42−, Lewis acid sites have been intensified significantly. Moreover, the surface hydroxyl groups are further activated and formed H+, which generates new Brönsted acid sites.29,31 3.2. Catalytic Activities of S/Ti-MCM-41 Catalysts. The results of transesterification of DMO and phenol over different contents of sulfate modified Ti-MCM-41 catalysts are given in Table 3. Among the catalysts studied in this work, the 8S/TiMCM-41 sample shows the highest TOF, DMO conversion, and DPO yield, which have been up to 130.4, 72.0, and 17.5%, respectively. The conversion of DMO as well as the yield of DPO is gradually increased with the increase of sulfur content up to 8 wt % followed by a decrease. This phenomenon could be explained by the variation of Brönsted acidity proportion on the surface of the catalysts. The amount of Brönsted acid sites is also gradually raised to a maximum until the sulfur content increases to 8 wt %. Also, it is worth noticing that the byproduct anisole is generated using the sulfate modified TiMCM-41 as catalyst. The transesterification selectivity, namely, total selectivity of MPO and DPO, is decreased with the

Figure 5. FTIR spectra of pyridine adsorbed on molecular sieves with different S contents: (a) Ti-MCM-41, (b) 2S/Ti-MCM-41, (c) 4S/TiMCM-41, (d) 8S/Ti-MCM-41, and (e) 12S/Ti-MCM-41.

Ti-MCM-41 materials exhibit bands at 1447, 1578, and 1596 cm−1 the same as bare Ti-MCM-41, due to pyridine adsorbed on Lewis acid sites and hydrogen-bonded pyridine, respectively. Besides those, there are several new IR bands at around 1490, 1545, 1623, and 1639 cm−1, compared with bare Ti-MCM-41. Among them, the bands at 1545 and 1639 cm−1 are attributed to pyridine connected to Brönsted acid sites; the band at 1623 cm−1 is attributed to pyridine coordinated to Lewis acid sites; and the band at 1490 cm−1 is attributed to pyridine molecularly adsorbed on both the Lewis and the Brönsted acid sites. It suggests that sulfate modification generates new acidity on the surface of Ti-MCM-41 material, including Lewis and Brönsted acid sites. This result is coincident with the previous report that Brönsted acidity was generated by the impregnation method using H2SO4 as sulfatizing agent.15,29 Furthermore, the bands increased proportionally according to the amount of S species increasing from 2% to 4%, following a decrease with the further increasing of the S content, which is in line with the results of ammonia TPD characterization. Figure 6 shows the FTIR spectra of the S/Ti-MCM-41 sample recorded after the adsorption of pyridine and subsequent evacuation at different temperatures. As the desorption temperature increases, the IR adsorption intensity decreases gradually. The IR bands at around 1447 and 1578 cm−1 disappear after desorption of pyridine at 423 K. However, the bands at 1490, 1545, 1623, and 5740



Article

Table 2. Element Surface Content and Binding Energies of S/Ti-MCM-41 with Different S Contents Measured by XPS Analysis binding energies (eV)

a

element content (atom %)

S content (wt %)

S 2p(3/2)

Ti 2p(3/2)

S

Ti

O

Si

C

N

0 2 4 8 8a 8b 12

169.5 169.2 169.1 169.1 169.1 169.1

458.9 458.8 459.5 459.4 459.4 459.4 459.5

1.7 2.2 3.0 2.9 2.8 3.6

2.0 0.9 0.7 0.8 0.8 0.8 0.6

58.5 47.1 51.8 58.1 57.6 56.5 53.6

24.3 20.9 20.3 23.2 23.2 23.2 22.3

13.9 28.4 23.9 12.7 13.4 14.6 18.5

1.0 1.2 2.1 2.1 2.1 1.4

8S/Ti-MCM-41 after the first circle. b8S/Ti-MCM-41 after the second circle.

Scheme 1. Genesis of Lewis and Brönsted Acidity on the Surface of S/Ti-MCM-41

Table 4. Recyclability of 8S/Ti-MCM-41 for the Transesterification of Dimethyl Oxalate with Phenola number of

conversion

yield (%)

selectivity (%)

MPO and DPO total selectivity

recycling

(%)

DPO

MPO

AN

DPO

MPO

(%)

1 2 3

56.8 54.8 52.9

6.0 5.7 5.6

46.3 44.7 43.2

0.9 0.9 0.9

10.6 10.4 10.5

81.5 81.6 81.6

92.1 92.0 92.1

a

Reaction conditions: DMO 0.05 mol, phenol 0.15 mol, catalyst 0.9 g, temperature 353 K, time 1 h.

increase of sulfur content, indicating that the side reaction would happen due to the catalytic action of Brönsted acidity. In conclusion, the results of catalytic test of S/Ti-MCM-41 catalysts showed that Brönsted acid sites could promote the transesterification reaction between DMO and phenol, although it would also lead to the formation of the byproduct anisole. Table 4 illustrates the activities of recycled 8S/Ti-MCM41catalysts under identical conditions. It was found that DMO conversion slightly dropped from 56.8% to 54.8% after the second recycle and further to 52.9% after the third recycle. The total selectivity of MPO and DPO still remained about 92.1% after three recycles. According to XPS analyses of the recovered catalysts as shown in Table 2, there was slight decrease in S content after three recycles, resulting in the decline of catalytic activities of 8S/Ti-MCM-41.

owing to the coverage of sulfur species. Furthermore, due to the strong electron inductive effect caused by the SO bond of SO42−, Lewis acid sites are intensified significantly and new Brönsted acid sites are generated from the activated surface hydroxyl groups. Moreover, weak acid sites belong to Lewis acidity, while the medium strength acid sites consist of both Lewis and Brönsted acidity. The results of the catalytic test of S/Ti-MCM-41 catalysts showed that Brönsted acid sites could promote the transesterification reaction between DMO and phenol, although it would also lead to the formation of the byproduct anisole. When the sulfur content reaches 8 wt %, S/ Ti-MCM-41 shows the highest DMO conversion and DPO yield of 72.0% and 17.5%, respectively.

■

4. CONCLUSIONS S/Ti-MCM-41 materials were prepared by the wet impregnation method with H2SO4 solution as the promoter. The mesostructure, surface chemical property, and acidity of the materials have been studied by XRD, N2 adsorption− desorption, NH3-TPD, FTIR of pyridine adsorption, and XPS. From the foregoing discussion it is concluded that the sulfate modification could not change the ordered hexagonal channel arrangement of Ti-MCM-41 material but rather gradually shrinks the pore diameter and specific surface area

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86-22-87401818. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial supports by Natural Science Foundation of China (NSFC) (Grant No. 20506018), the Program of Introducing Talents of Discipline to Universities (Grant B06006), the

Table 3. Catalytic Activities of S/Ti-MCM-41 with Different S contents for the Transesterification of Dimethyl Oxalate with Phenola yield (%)

a

selectivity (%)

S content (%)

TOF (h−1)

conversion (%)

DPO

MPO

AN

DPO

MPO

MPO and DPO total selectivity (%)

0 2 4 8 12

49.4 55.8 59.5 130.4 120.2

32.9 40.3 52.4 56.8 45.0

3.1 2.5 4.2 6.0 2.7

29.8 35.6 44.6 46.3 35.4

0 0.3 0.5 0.9 1.4

9.5 6.3 8.1 10.6 5.9

90.5 88.3 85.2 81.5 78.7

100 94.6 93.3 92.1 84.6

Reaction conditions: DMO 0.05 mol, phenol 0.15 mol, catalyst 0.9 g, temperature 353 K, time 1 h. 5741



Article

(19) Guidotti, M.; Batonneau-Gener, I.; Gianotti, E.; Marchese, L.; Mignard, S.; Psaro, R.; Sgobba, M.; Ravasio, N. The Effect of Silylation on Titanium-Containing Silica Catalysts for the Epoxidation of Functionalised Molecules. Microporous Mesoporous Mater. 2008, 111, 39. (20) Wu, P.; Iwamoto, M. Metal-Ion-Planted MCM-41. Part 3. Incorporation of Titanium Species by Atom-Planting Method. J. Chem. Soc., Faraday Trans. 1998, 94, 2871. (21) Chen, L. Y.; Jaenicke, S.; Chuah, G. K. Thermal and Hydrothermal Stability of Framework-Substituted MCM-41 Mesoporous Materials. Microporous Mater. 1997, 12, 323. (22) Shi, Y.; Wang, S.; Ma, X. Microwave Preparation of TiContaining Mesoporous Materials. Application As Catalysts for Transesterification. Chem. Eng. J. 2011, 166, 744. (23) Barrett, E. P.; Joyner, L. G.; Halenda, P. P. The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms. J. Am. Chem. Soc. 1951, 73, 373. (24) Uphade, B. S.; Yamada, Y.; Akita, T.; Nakamura, T.; Haruta, M. Synthesis and Characterization of Ti-MCM-41 and Vapor-Phase Epoxidation of Propylene Using H2 and O2 over Au/Ti-MCM-41. Appl. Catal., A 2001, 215, 137. (25) Sawa, M.; Niwa, M.; Murakami, Y. Relationship between Acid Amount and Framework Aluminum Content in Mordenite. Zeolites 1990, 10, 532. (26) Lónyi, F.; Valyon, J. On the Interpretation of the NH3-TPD Patterns of H-ZSM-5 and H-mordenite. Microporous Mesoporous Mater. 2001, 47, 293. (27) Eimer, G. A.; Casuscelli, S. G.; Chanquia, C. A.; Elias, V.; Crivello, M. E.; Herrero, E. R. The Influence of Ti-loading on the Acid Behavior and on the Catalytic Efficiency of Mesoporous Ti-MCM-41 Molecular Sieves. Catal. Today 2008, 133, 639. (28) Saikia, L.; Satyarthi, J. K.; Srinivas, D.; Ratnasamy, P. Activation and Reactivity of Epoxides on Solid Acid Catalysts. J. Catal. 2007, 252, 148. (29) Guo, D. S.; Ma, Z. F.; Jiang, Q. Z.; Xu, H. H.; Ma, Z. F.; Ye, W. D. Sulfated and Persulfated TiO2/MCM-41 Prepared by Grafting Method and their Acid-Catalytic Activities for Cyclization of Pseudoionone. Catal. Lett. 2006, 107, 155. (30) Fourches, N.; Turban, G.; Grolleau, B. Study of DLC/Silicon Interfaces by XPS and In-Situ Ellipsometry. Appl. Surf. Sci. 1993, 68, 149. (31) Xu, H. H.; Guo, D. S.; Jiang, Q. Z.; Ma, Z. F.; Li, W. J.; Wang, Z. Catalytic Performance of Sulfated Silica MCM-41 for Cyclization of Pseudoionone to Ionones. Chin. J. Catal. 2006, 27, 1080.

National Key Project for the 11th Five Year Plan (Grant No. 2006BAE02B00), and Hebei Science and Technology Support Program (11215633) are gratefully acknowledged.

■

REFERENCES

(1) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T. W.; Olson, D. H.; Sheppard, E. W. A New Family of Mesoporous Molecular Sieves Prepared with Liquid Crystal Templates. J. Am. Chem. Soc. 1992, 114, 10834. (2) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Ordered Mesoporous Molecular Sieves Synthesized by a LiquidCrystal Template Mechanism. Nature 1992, 359, 710. (3) Zou, J. J.; Zhang, M. Y.; Zhu, B.; Wang, L.; Zhang, X. W.; Mi, Z. T. Isomerization of Norbornadiene To Quadricyclane Using TiContaining MCM-41 as Photocatalysts. Catal. Lett. 2008, 124, 139. (4) Silva, T. N.; Lopes, J. M.; Ribeiro, F. R.; Carrott, M. R.; Galacho, P. C.; Sousa, M. J.; Carrott, P. Catalytic and Adsorption Properties of Al- And Ti-MCM-41 Synthesized at Room Temperature. React. Kinet. Catal. Lett. 2002, 77, 83. (5) Blasco, T.; Corma, A.; Navarro, M.; Pariente, J. P. Synthesis, Characterization, and Catalytic Activity of Ti-MCM-41 Structures. J. Catal. 1995, 156, 65. (6) Iglesias, J.; Melero, J. A.; Sanchez-Sanchez, M. Highly Ti-Loaded MCM-41: Effect of the Metal Precursor and Loading on the Titanium Distribution and on the Catalytic Activity in Different Oxidation Processes. Microporous Mesoporous Mater. 2010, 132, 112. (7) Jha, R. K.; Shylesh, S.; Bhoware, S. S.; Singh, A. P. Oxidation of Ethyl Benzene and Diphenyl Methane over Ordered Mesoporous MMCM-41 (M = Ti, V, Cr): Synthesis, Characterization and StructureActivity Correlations. Microporous Mesoporous Mater. 2006, 95, 154. (8) Kosuge, K.; Singh, P. S. Synthesis of Ti-Containing Porous Silica with High Photocatalytic Activity. Chem. Lett. 1999, 1, 9. (9) Lihitkar, N. B.; Abyaneh, M. K.; Samuel, V.; Pasricha, R.; Gosavi, S. W.; Kulkarni, S. K. Titania Nanoparticles Synthesis in Mesoporous Molecular Sieve MCM-41. J. Colloid Interface Sci. 2007, 314, 310. (10) Do, Y. J.; Kim, J. H.; Park, J. H.; Park, S. S.; Hong, S. S.; Suh, C. S.; Lee, G. D. Photocatalytic Decomposition of 4-Nitrophenol on TiContaining MCM-41. Catal. Today 2005, 101, 299. (11) Gianotti, E.; Bisio, C.; Marchese, L.; Guidotti, M.; Ravasio, N.; Psaro, R.; Coluccia, S. Ti(Iv) Catalytic Centers Grafted on Different Siliceous Materials: Spectroscopic and Catalytic Study. J. Phy. Chem. C 2007, 111, 5083. (12) Hunger, M.; Schenk, U.; Breuninger, M.; Glaser, R.; Weitkamp, J. Characterization of the Acid Sites in MCM-41-Type Materials by Spectroscopic and Catalytic Techniques. Microporous Mesoporous Mater. 1999, 27, 261. (13) Rajagopal, S.; Marzari, J. A.; Miranda, R. Silica-AluminaSupported Mo Oxide Catalysts: Genesis and Demise of BrønstedLewis Acidity. J. Catal. 1995, 151, 192. (14) Dutoit, D. C. M.; Schneider, M.; Hutter, R.; Baiker, A. TitaniaSilica Mixed Oxides: IV. Influence of Ti Content and Aging on Structural and Catalytic Properties of Aerogels. J. Catal. 1996, 161, 651. (15) Parida, K. M.; Rath, D. Studies on MCM-41: Effect of Sulfate on Nitration of Phenol. J. Mol. Catal. A: Chem. 2006, 258, 381. (16) Wang, X.; Yu, J. C.; Liu, P.; Su, W.; Fu, X. Probing of Photocatalytic Surface Sites on SO42−/TiO2 Solid Acids by in Situ FTIR Spectroscopy and Pyridine Adsorption. J. Photochem. Photobiol., A 2006, 179, 339. (17) Samantaray, S. K.; Mohapatra, P.; Parida, K. Physico-Chemical Characterisation and Photocatalytic Activity of Nanosized SO42‑/TiO2 Towards Degradation of 4-Nitrophenol. J. Mol. Catal. A: Chem. 2003, 198, 277. (18) Galacho, C.; Carrott, M. M. L. R.; Carrott, P. J. M. Structural and Catalytic Properties of Ti-MCM-41 Synthesised at Room Temperature up to High Ti Content. Microporous Mesoporous Mater. 2007, 100, 312. 5742


Effect of Sulfate Modification on Structure Properties, Surface Acidity

Recommend Documents