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Titanium-Silicalite: a Novel Derivative in the Pentasil Family
Titanium-Silicalite: a Novel Derivative in the Pentasil Family
A novel Ti derivative of Silicalite-l has been prepared by hydrothermal procedure with (n-C H7)4N-OH. X-ray, IR, EDX, and 29Si MAS NMR investigations in~icate an homogeneous distribution of Ti in the crystal while suggesting replacement of Ti for Si in the framework. TS-l catalyzes reactions involving HZO such as the direct hydroxylation of aromatics Z with high selectivity towards para isomers. Moreover, it selectively epoxidizes olefins and oxidizes alcohols to aldehydes or ketones, with high yield. Due to the pore structure of TS-l, minimization of useless byproducts is obtained in reactions involving aromatic hydrocarbons. INTRODUCTION The framework composition of porotectosilicates is an important factor which can affect the physical properties and catalytic behaviour of these materials. In the recent years, many efforts have been done to replace Si or Al in the framework of synthetic zeolites by several other elements. However, the results are reported mostly in the patent literature, without a real proof of the occurrence of isomorphous replacement. In the last decade, a research program has been carried out in our Laboratories, with the aim of synthesizing zeolite-type catalysts including in their framework elements capable to induce novel catalytic properties. This lead to the synthesis of borosilicates having the frame, ZSM-5 and ZSM-ll high silica zeolites, which work structure of NU-l,~ were termed boralites. The presence of boron in the tetrahedral sites of the framework was demonstrated by the unit cell parameters diminishing with rising boron content [1]. Moreover, we were successful in synthesizing a titanium derivative of Silicalite-l (TS-l) [2] , which represents the first example of a titanium-containing porotectosilicate. This result confirms the predictions recently given by Barrer on the basis of theoretical arguments [3]. Previously, the preparation of a porous titanosilicate was claimed in the patent literature [4] but the zeolitic nature of this material has been questioned [5]. It is the aim of this paper to report on the synthesis, structure characterization and catalytic behaviour of TS-l. EXPERIMENTAL 1. Synthesis Precursors of TS-l are prepared by the hydrothermal procedure at 175°C and autogeneous pressure from a reaction mixture containing tetraethylorthosilicate (TES) or silica sol (Ludox, from DuPont) to supply Si, tetraethylorthotitanate as the Ti source, tetrapropylammonium hydroxide (TPA-OH) and water. When working with silica sol, hydrogen peroxide has to be added to the reaction mixture for getting titanium in 129
130 (SY-8-1) the form of pertitanate species, which are known to be stable in strong basic solution. The organic containing precursor crystals have the empirical molar composition: y [(TPA)20]
.. xTi0
. (l-x)Si0 2 2 Typically, y is ca. 0.02 and x is ranging from 0 to 0.025. The latter value is not overcome even when large excess of Ti is used in the reaction mixture. The described route of synthesis leads to perfectly reproducible results. The organic material is removed by calcination in air at 550°C. For the samples investigated, additional treatments with ammonium acetate at 70°C were performed, followed by filtration, washing, drying and re-calcination at 550°C. More details about the synthesis of TS-l are reported elsewhere [2]. 2.Structure Characterization X-ray diffraction (XRD) analysis was performed on a Philips diffractometer equipped with a pulse-height analyzer, using CuK a radiation. Unit cell parameters were obtained by a least-squares fit to the interplanar spacings of 7-8 strong reflections, accurately measured in the as an internal standard [6]. 10-35° 2~ angular region, using a-A1 Scanning electron micrographs were203obtained with a Philips PSEM-500 microscope equipped with EDX spectrometer. ~Si Magic Angle Spinning (MAS) NMR spectra were obtained at 59.6 MHz on a Bruker CXP-300 spectrometer equipped with a wide-bore superconducting magnet. The samples were put in Delrin-made sample holders and the spinning speed was typically 3 KHz. A flip angle of 45° and a pulse interval of 5 sec; were used.The experiments were performed without crosspolarization and proton decoupling. IR spectra were recorded on a Perkin Elmer 682 double beam grating spectrometer, using the KBr wafer technique. Chemical analysis of the crystallized products was made by conventional methods. RESULTS AND DISCUSSION A list of the samples investigated is reported in Table 1 together with data concerning the chemical composition of both the reaction mixture and the crystallized products. The titanium content was controlled by varying the composition of the reaction mixture. Inspection of X-ray powder pattern (Fig. 1) clearly indicates that TS-l possesses the pentasil-type framework structure [7]. Similarly to what observed in the case of the parent structure of ZSM-5 [8] and H-BOR-C boralite [1], the monoclinic lattice symmetry, characteristic of Silicalite-l, is preserved up to x ~ 0.01; for higher values of x, orthorhombic symmetry is detected. Significant increase of band c cell parameters with a resulting linear increase of unit cell volume are observed as a function of x (Fig. 2). This is consistent with the substitution of titanium in the silica the trend being in agreement with the higher value expected for the Ti-O bond length with respect to the Si-O bond lengtb. Accordingly, an opposite trend (contraction of the cell parameters) was found in the case of the parent structure of H-BOR-C [1]. Similarly to H-BOR-C [1], the unit cell volume, V(x), of TS-l having a content of Ti0 2 equal to x, can be related to the cell volume of pure Silicalite, VSi fhrough the equation V(x)
= VSi-VSi[I-(dTi!dSi) 3 ]x
(1)
G. Perego et al. d and dS' representing the Ti-O and Si-O bond lenghth respectively. T, Eq;(l) reqUires a linear dependence of Vex) on x. in agreement with the experimental trend. Table 1. Crystal data for TS-1 with different Ti content i) Unit cell parameters al Sample b ) RIc) R2d ) x e) a/X 1 2 3 4 5 6 7
133 66 33 5 20 5 20
0.21 0.21 0.22 0.89 0.25 2.00 0.25
0.005 0.008 0.012 0.017 0.019 0.023 0'.024
20.102(3) 20.121(4) 20.126(3) 20.126(3) 20.112(4) 20.133(5) 20.127(6)
b/X
c/X
19.896(12) 19.900 (4) 19.902 (3) 19.923 (4) 19.948 (4) 19.933 (3) 19.949 (7)
«/0
V/X3
13.373(3) 90.46(1) 5348.5(21) 13.373(3) 90.58(1) 5354.3(18) 13.393(3) 5364.7(17) 13.410(3) 5376.7(20) 13.414(3) 5381.7(18) 13.416(3) 5384.0(19) 13.423(4) 5389.3(21)
ii) Equations relating the unit cell parameters to the Ti content. fl a = 20.112 + 0.665x b = 19.876 + 2.935x c = 13.364 + 2.425x V 5341.8 + 1946x
a)
~;J
35
40
45
50
b)
10
....
so
Fig.1. X-ray diffraction patterns of orthorhombic TS-1 (a) and monoclinic Silicalite-1 (b).
131
132 (SY-8-1)
c.l
x
Fig.2. Unit cell parameters of TS-1 as a function of titanium content.
s., 0.000
It",O.005
It
0.023
·i08
Fig.3. IR spectra of TS-l compared to that of Silicalite-l (x=O). Arrow indicates the band at 970 cm~.
·UI
PPM 'roM''''
.1\.
Fig.4. 29Si MAS NMR spectra of TS-1 with different Ti content, compared to that of Silicalite-1 (x-O).
G. Perego et al. 29Si MAS NMR investigation shows that the multiplet characteristic of Silicalite-l [11] broadens in TS-l, while a shoulder appears in the high field side of the signal, with intensity increasing with rising Ti content (Fig. 4).
Fig.S. Scanning electron micrograph of a typical crystal of TS-l The inset shows the intensity of TiKa emission line (from EDX analysis) measured by scanning along the A-B line crossing the crystal.
133
134 (5Y-8-l) Relatively large crystals of T5-l can be obtained, as shown by the SEM micrograph reported in Fig. S. EDX analysis indicates an homogeneous distribution of Ti within the crystals and the absence of other Ti contamination phases (Fig. 5). Evidence in favour of the structure homogeneity of TS-l was achieved also by FABM5 analysis [IZ]. TS-l is characterized by the same saturation adsorption pore volume of the parent 5ilicalite-l derivative, 0.19 cm3g-' [13]. Like the latter, it doesn't possess ion-exchange capacity, due to the fact that titanium is in the Ti(IV) chemical state. As a proof, no appreciable amount of Ti(III) species is detected by ESR analysis. TS-l possesses remarkable catalytic properties in reactions involving hydrogen peroxide (see Table z). TS-l catalyzes the epoxidation of both olefins [14,15] and diolefins [16], with high yield and high epoxide selectivity (>98% in the case of propylene). The reaction can be conducted with dilute aqueous hydrogen peroxide mixture «40% wt HZO This Z)' constitutes a big advantage with respect to conventional Os04' Ru04, VZO Mo0 TiO based catalysts [17], which require to work with 3, Z veryS' high (>95%) HZO concentration. Z Glycol monomethyl ethers are formed by reacting an olefinic compound with methanol and HZO in one step, with an ether selectivity higher Z than 95% Aldehyde and ketone derivatives are obtained from primary and secondary alcohols respectively, without subsequent oxidation of the reaction products to the corresponding carboxylic acids. Such reactions have been tested with benzyl alcohol, cyclohexanol and isopropyl alcohol, with selectivity exceeding 90% [18]. TS-l catalyzes the direct hydroxylation of aromatic hydrocarbons with hydrogen peroxide [19]. High yield and high selectivity (around 90%) are found. The isomers distribution can be modified by varying the solvent or the reaction temperature; however, a tendency towards para selectivity is clearly observed (Table 3). TS-l catalyst minimizes unwanted secondary reactions leading to useless polynuclear aromatic byproducts.
usr.
Table Z.
TS-l Catalyzed Products
Reactants l)b) R-C + HZO 6HS Z + HZO Z)b) R'-C 6H4-OH Z 3)C) R-CH=CH-R' + HZO
4)C) R-CH=CH-CH=CH-R' + HZO 5)d) R-CH=CH-R'+ CH 6)e) R-CHZOH + HZO
30H
Z
+ HZO
Z
7)e) R-CHOH-R' + H
°
R-C + HZO 6H4-OH
19
R'-C
19
6H3(OH)Z
R-C~~H-R'
Z
------------------~-~-------------------------------~------------------a) HZO conversion generally
Z
Ref.
+ HZO
+ HZO
R-CH-CH-CH=CH-R' + H
°
R-CH(OH)-C(OCH
HZO
'cI
R-CHO + ZHZO R-CO-R' + ZH
Z
3)-R'+
°
14,15 16 15 18 18
close 1)-5) and ca. 90% for 6) Z and 7J. Reaction temp. in the range in Table 3. c) Typical epoxide select.: 85-100%. ether select. in the range 95-100%. e)Typical aldehyde or ketone select. close to 100%. This suggests the "restricted transition state selectivity" [ZO] to be effective, due to the peculiar pore structure of TS-1. For batch runs concerning the reactions listed in Table Z, the cata-
G. Perego et al. lyst can be regenerated many times by calcination in air at 550°C without appreciable loss of Ti as well as of catalytic activity. Thermal, chemical and catalytic stabilities of TS-1 constitute another proof of the presence of Ti in the framework. Table 3. Examples of direct hydroxylation of aromatic hydrocarbons with hydrogen peroxide by TS-1 catalyst. a) Hydrocarbon
Solvent
Phenol Methanol Phenol Acetone Toluene Acetone Toluene Water Ethylbenzene Acetone Anisole Acetone o,m-Cresol Acetone p-Cresol Acetone
F.R.% Conv.% Select.% %para %ortho b) c) d) e) 65 20 100 91 70 35 43 30 100 92 80 57 10 90 65 70 15 98 45 10 98 85 65 26 70 10 98 90 65 30 15 98 90 73 64 36 60 10 98 87 61 24 10 98 87 70 100
%meta
15 29 16
performed batchwise at 60-100 oC, Ref.(19). Ratio: (moles H 02 fed) x 100!(moles hydrocarbon fed). hydrox. hydrocarbon)x100!(moles reacted hydro(males hydrox. hydrocarbon) x lOa! ( males reacted H 202). CONCLUSIONS A navel Ti derivative of Silicalite-1 (TS-1) has been prepared fallowing a route leading to highly reproducible results. By referring to the empirical formula xTi0 2 • (1-x)Si0 2 , a maximum content of Ti has been-obtained, to x = 0.025. Investigation of TS-1 by several techniques (XRD, IR, 29Si MAS NMR, EDX) suggests that Ti replaces Si in the tetrahedral sites of the framework with and homogeneous distribution within the crystal. TS-1 displays unusual nan-acidic catalytic properties in reactions involving hydrogen peroxide. The incorporation of titanium in the framework and the peculiar pare structure account for the catalytic behaviour (high yields, high selectivities and minimization of by· products) as well as for the thermal and chemical stabilities of TS-l. ACKNOWLEDGEMENTS The authors wish to thank Dr. B. Notari and Dr. V. Fattore for helpful discussions and for their interest in this work. Dr. C. Neri, Dr. U. Romano, Dr. M.G. Clerici and Dr. F. Maspero are gratefully acknowledged for their contribution to the reactivity studies. The authors are indebted to Mr. M. Buroni, Dr. G. Santi, Dr. S. Ghelli and Dr. C. Busetto for providing SEM, IR, NMR and ESR experiments respectively. REFERENCES 1. M. Taramasso, G. Perego and B. Notari, Proc •.Fifth Int. Conf. an Zeolites, Naples, L.V.C. Rees Ed., p.40, Landon Heyden and Sans (1980) • 2. M. Taramasso, G. Perego and B. Notari, U.S. Pat 4,410,501 (1983). 3. R.M. Barrer, Proc. Sixth Int. Conf. an Zeolites, Rena (USA), A. Bisio and D.H. Olson Ed.s, p.870, Butterworth (1984). 4. D.A. Yaung, U.S. Pat 3,329,481 (1967). 5. D.W. Breck, in "Zeolite Molecular Sieves", p.322, J. Wiley and Sans (1974).
135
136 (SY-8-l) 6. "Powder Diffraction File", JCPDS Ed., Pennsylvania, USA (1978). 7. G.T. Kokotailo and W.M. Meier, "Properties and Applications of Zeolites" R. P. Townsend Ed., Spec. Pub!. No33, p, 133, The Chemical Society, London (1980) 8. E.L. Wu, S.L. Lawton, D.H. Olson, A.C. Rohrman Jr., and G.T. Kokotailo, J. Phys. Chem. 83, 2777 (1979). 9. J.A. Bland, Acta Cryst. 14;-875 (1961). 10. M.F. Best and R.A. Condrate Sr.,J. Material Sci. Lett. ~,994 (1985). B.G. Varshal, V.N. Denisov, B.N. Mavrin, G.A. Pavlova, V.B. Podobedov and KH. E. Sterin, Opt. Spectrosc. (USSR) iI, 344 (1979). 11. C.A. Fyfe, G.C. Gobbi, J. Klinowski, J.M. Thomas and S. Ramdas, Nature 296, 530 (1982). 12. A.G. AshtOn, J. Dwyer, I.S. Elliot, F.R. Fitch, G. Qin, M. Greenwood and J. Speakman, Proc. Sixth Int. Conf. on Zeolites, Reno (USA), D. Olson and A. Bisio Eds., p.704, Butterworth (1984). 13. E.M. Flanigen, J.M. Bennett, R.W. Grose, J.P. Cohen, R.L. Patton, R.M. Kirchner and J.V. Smith, Nature 271, 512 (1978). 14. C. Neri, A. Esposito, B. Anfossi and ~Buonomo, Eur. Pat. 100119 (1984) F. Buonomo, Eur. Pat. 100118 (1984). 15. C. Neri, B. Anfossi 16. F. Maspero and U. Romano, Pat. pending. 17. R.A. Sheldon, J. Mol. Catal. 7, 107 (1980). 18. A. Esposito, C. Neri and F. B~onomo, It. Pat. Appl. 22607 A/82 19. A. Esposito, M. Taramasso, C. Neri and F. Buonomo, U.K. Pat. 2116974 (1985); G. Bellussi, F. Buonomo, A. Esposito, M.G. Clerici, U. Romano and B. Notari, Pat. Pending. 20. E.G. Derouane, in "Catalysis by Zeolites", p.5, B. Imelik et a!. Eds. (Elsevier Sci. Pub. Co., Amsterdam, 1980).
A novel Ti derivative of Silicalite-l has been prepared by hydrothermal procedure with (n-C H7)4N-OH. X-ray, IR, EDX, and 29Si MAS NMR investigations in~icate an homogeneous distribution of Ti in the crystal while suggesting replacement of Ti for Si in the framework. TS-l catalyzes reactions involving HZO such as the direct hydroxylation of aromatics Z with high selectivity towards para isomers. Moreover, it selectively epoxidizes olefins and oxidizes alcohols to aldehydes or ketones, with high yield. Due to the pore structure of TS-l, minimization of useless byproducts is obtained in reactions involving aromatic hydrocarbons. INTRODUCTION The framework composition of porotectosilicates is an important factor which can affect the physical properties and catalytic behaviour of these materials. In the recent years, many efforts have been done to replace Si or Al in the framework of synthetic zeolites by several other elements. However, the results are reported mostly in the patent literature, without a real proof of the occurrence of isomorphous replacement. In the last decade, a research program has been carried out in our Laboratories, with the aim of synthesizing zeolite-type catalysts including in their framework elements capable to induce novel catalytic properties. This lead to the synthesis of borosilicates having the frame, ZSM-5 and ZSM-ll high silica zeolites, which work structure of NU-l,~ were termed boralites. The presence of boron in the tetrahedral sites of the framework was demonstrated by the unit cell parameters diminishing with rising boron content [1]. Moreover, we were successful in synthesizing a titanium derivative of Silicalite-l (TS-l) [2] , which represents the first example of a titanium-containing porotectosilicate. This result confirms the predictions recently given by Barrer on the basis of theoretical arguments [3]. Previously, the preparation of a porous titanosilicate was claimed in the patent literature [4] but the zeolitic nature of this material has been questioned [5]. It is the aim of this paper to report on the synthesis, structure characterization and catalytic behaviour of TS-l. EXPERIMENTAL 1. Synthesis Precursors of TS-l are prepared by the hydrothermal procedure at 175°C and autogeneous pressure from a reaction mixture containing tetraethylorthosilicate (TES) or silica sol (Ludox, from DuPont) to supply Si, tetraethylorthotitanate as the Ti source, tetrapropylammonium hydroxide (TPA-OH) and water. When working with silica sol, hydrogen peroxide has to be added to the reaction mixture for getting titanium in 129
130 (SY-8-1) the form of pertitanate species, which are known to be stable in strong basic solution. The organic containing precursor crystals have the empirical molar composition: y [(TPA)20]
.. xTi0
. (l-x)Si0 2 2 Typically, y is ca. 0.02 and x is ranging from 0 to 0.025. The latter value is not overcome even when large excess of Ti is used in the reaction mixture. The described route of synthesis leads to perfectly reproducible results. The organic material is removed by calcination in air at 550°C. For the samples investigated, additional treatments with ammonium acetate at 70°C were performed, followed by filtration, washing, drying and re-calcination at 550°C. More details about the synthesis of TS-l are reported elsewhere [2]. 2.Structure Characterization X-ray diffraction (XRD) analysis was performed on a Philips diffractometer equipped with a pulse-height analyzer, using CuK a radiation. Unit cell parameters were obtained by a least-squares fit to the interplanar spacings of 7-8 strong reflections, accurately measured in the as an internal standard [6]. 10-35° 2~ angular region, using a-A1 Scanning electron micrographs were203obtained with a Philips PSEM-500 microscope equipped with EDX spectrometer. ~Si Magic Angle Spinning (MAS) NMR spectra were obtained at 59.6 MHz on a Bruker CXP-300 spectrometer equipped with a wide-bore superconducting magnet. The samples were put in Delrin-made sample holders and the spinning speed was typically 3 KHz. A flip angle of 45° and a pulse interval of 5 sec; were used.The experiments were performed without crosspolarization and proton decoupling. IR spectra were recorded on a Perkin Elmer 682 double beam grating spectrometer, using the KBr wafer technique. Chemical analysis of the crystallized products was made by conventional methods. RESULTS AND DISCUSSION A list of the samples investigated is reported in Table 1 together with data concerning the chemical composition of both the reaction mixture and the crystallized products. The titanium content was controlled by varying the composition of the reaction mixture. Inspection of X-ray powder pattern (Fig. 1) clearly indicates that TS-l possesses the pentasil-type framework structure [7]. Similarly to what observed in the case of the parent structure of ZSM-5 [8] and H-BOR-C boralite [1], the monoclinic lattice symmetry, characteristic of Silicalite-l, is preserved up to x ~ 0.01; for higher values of x, orthorhombic symmetry is detected. Significant increase of band c cell parameters with a resulting linear increase of unit cell volume are observed as a function of x (Fig. 2). This is consistent with the substitution of titanium in the silica the trend being in agreement with the higher value expected for the Ti-O bond length with respect to the Si-O bond lengtb. Accordingly, an opposite trend (contraction of the cell parameters) was found in the case of the parent structure of H-BOR-C [1]. Similarly to H-BOR-C [1], the unit cell volume, V(x), of TS-l having a content of Ti0 2 equal to x, can be related to the cell volume of pure Silicalite, VSi fhrough the equation V(x)
= VSi-VSi[I-(dTi!dSi) 3 ]x
(1)
G. Perego et al. d and dS' representing the Ti-O and Si-O bond lenghth respectively. T, Eq;(l) reqUires a linear dependence of Vex) on x. in agreement with the experimental trend. Table 1. Crystal data for TS-1 with different Ti content i) Unit cell parameters al Sample b ) RIc) R2d ) x e) a/X 1 2 3 4 5 6 7
133 66 33 5 20 5 20
0.21 0.21 0.22 0.89 0.25 2.00 0.25
0.005 0.008 0.012 0.017 0.019 0.023 0'.024
20.102(3) 20.121(4) 20.126(3) 20.126(3) 20.112(4) 20.133(5) 20.127(6)
b/X
c/X
19.896(12) 19.900 (4) 19.902 (3) 19.923 (4) 19.948 (4) 19.933 (3) 19.949 (7)
«/0
V/X3
13.373(3) 90.46(1) 5348.5(21) 13.373(3) 90.58(1) 5354.3(18) 13.393(3) 5364.7(17) 13.410(3) 5376.7(20) 13.414(3) 5381.7(18) 13.416(3) 5384.0(19) 13.423(4) 5389.3(21)
ii) Equations relating the unit cell parameters to the Ti content. fl a = 20.112 + 0.665x b = 19.876 + 2.935x c = 13.364 + 2.425x V 5341.8 + 1946x
a)
~;J
35
40
45
50
b)
10
....
so
Fig.1. X-ray diffraction patterns of orthorhombic TS-1 (a) and monoclinic Silicalite-1 (b).
131
132 (SY-8-1)
c.l
x
Fig.2. Unit cell parameters of TS-1 as a function of titanium content.
s., 0.000
It",O.005
It
0.023
·i08
Fig.3. IR spectra of TS-l compared to that of Silicalite-l (x=O). Arrow indicates the band at 970 cm~.
·UI
PPM 'roM''''
.1\.
Fig.4. 29Si MAS NMR spectra of TS-1 with different Ti content, compared to that of Silicalite-1 (x-O).
G. Perego et al. 29Si MAS NMR investigation shows that the multiplet characteristic of Silicalite-l [11] broadens in TS-l, while a shoulder appears in the high field side of the signal, with intensity increasing with rising Ti content (Fig. 4).
Fig.S. Scanning electron micrograph of a typical crystal of TS-l The inset shows the intensity of TiKa emission line (from EDX analysis) measured by scanning along the A-B line crossing the crystal.
133
134 (5Y-8-l) Relatively large crystals of T5-l can be obtained, as shown by the SEM micrograph reported in Fig. S. EDX analysis indicates an homogeneous distribution of Ti within the crystals and the absence of other Ti contamination phases (Fig. 5). Evidence in favour of the structure homogeneity of TS-l was achieved also by FABM5 analysis [IZ]. TS-l is characterized by the same saturation adsorption pore volume of the parent 5ilicalite-l derivative, 0.19 cm3g-' [13]. Like the latter, it doesn't possess ion-exchange capacity, due to the fact that titanium is in the Ti(IV) chemical state. As a proof, no appreciable amount of Ti(III) species is detected by ESR analysis. TS-l possesses remarkable catalytic properties in reactions involving hydrogen peroxide (see Table z). TS-l catalyzes the epoxidation of both olefins [14,15] and diolefins [16], with high yield and high epoxide selectivity (>98% in the case of propylene). The reaction can be conducted with dilute aqueous hydrogen peroxide mixture «40% wt HZO This Z)' constitutes a big advantage with respect to conventional Os04' Ru04, VZO Mo0 TiO based catalysts [17], which require to work with 3, Z veryS' high (>95%) HZO concentration. Z Glycol monomethyl ethers are formed by reacting an olefinic compound with methanol and HZO in one step, with an ether selectivity higher Z than 95% Aldehyde and ketone derivatives are obtained from primary and secondary alcohols respectively, without subsequent oxidation of the reaction products to the corresponding carboxylic acids. Such reactions have been tested with benzyl alcohol, cyclohexanol and isopropyl alcohol, with selectivity exceeding 90% [18]. TS-l catalyzes the direct hydroxylation of aromatic hydrocarbons with hydrogen peroxide [19]. High yield and high selectivity (around 90%) are found. The isomers distribution can be modified by varying the solvent or the reaction temperature; however, a tendency towards para selectivity is clearly observed (Table 3). TS-l catalyst minimizes unwanted secondary reactions leading to useless polynuclear aromatic byproducts.
usr.
Table Z.
TS-l Catalyzed Products
Reactants l)b) R-C + HZO 6HS Z + HZO Z)b) R'-C 6H4-OH Z 3)C) R-CH=CH-R' + HZO
4)C) R-CH=CH-CH=CH-R' + HZO 5)d) R-CH=CH-R'+ CH 6)e) R-CHZOH + HZO
30H
Z
+ HZO
Z
7)e) R-CHOH-R' + H
°
R-C + HZO 6H4-OH
19
R'-C
19
6H3(OH)Z
R-C~~H-R'
Z
------------------~-~-------------------------------~------------------a) HZO conversion generally
Z
Ref.
+ HZO
+ HZO
R-CH-CH-CH=CH-R' + H
°
R-CH(OH)-C(OCH
HZO
'cI
R-CHO + ZHZO R-CO-R' + ZH
Z
3)-R'+
°
14,15 16 15 18 18
close 1)-5) and ca. 90% for 6) Z and 7J. Reaction temp. in the range in Table 3. c) Typical epoxide select.: 85-100%. ether select. in the range 95-100%. e)Typical aldehyde or ketone select. close to 100%. This suggests the "restricted transition state selectivity" [ZO] to be effective, due to the peculiar pore structure of TS-1. For batch runs concerning the reactions listed in Table Z, the cata-
G. Perego et al. lyst can be regenerated many times by calcination in air at 550°C without appreciable loss of Ti as well as of catalytic activity. Thermal, chemical and catalytic stabilities of TS-1 constitute another proof of the presence of Ti in the framework. Table 3. Examples of direct hydroxylation of aromatic hydrocarbons with hydrogen peroxide by TS-1 catalyst. a) Hydrocarbon
Solvent
Phenol Methanol Phenol Acetone Toluene Acetone Toluene Water Ethylbenzene Acetone Anisole Acetone o,m-Cresol Acetone p-Cresol Acetone
F.R.% Conv.% Select.% %para %ortho b) c) d) e) 65 20 100 91 70 35 43 30 100 92 80 57 10 90 65 70 15 98 45 10 98 85 65 26 70 10 98 90 65 30 15 98 90 73 64 36 60 10 98 87 61 24 10 98 87 70 100
%meta
15 29 16
performed batchwise at 60-100 oC, Ref.(19). Ratio: (moles H 02 fed) x 100!(moles hydrocarbon fed). hydrox. hydrocarbon)x100!(moles reacted hydro(males hydrox. hydrocarbon) x lOa! ( males reacted H 202). CONCLUSIONS A navel Ti derivative of Silicalite-1 (TS-1) has been prepared fallowing a route leading to highly reproducible results. By referring to the empirical formula xTi0 2 • (1-x)Si0 2 , a maximum content of Ti has been-obtained, to x = 0.025. Investigation of TS-1 by several techniques (XRD, IR, 29Si MAS NMR, EDX) suggests that Ti replaces Si in the tetrahedral sites of the framework with and homogeneous distribution within the crystal. TS-1 displays unusual nan-acidic catalytic properties in reactions involving hydrogen peroxide. The incorporation of titanium in the framework and the peculiar pare structure account for the catalytic behaviour (high yields, high selectivities and minimization of by· products) as well as for the thermal and chemical stabilities of TS-l. ACKNOWLEDGEMENTS The authors wish to thank Dr. B. Notari and Dr. V. Fattore for helpful discussions and for their interest in this work. Dr. C. Neri, Dr. U. Romano, Dr. M.G. Clerici and Dr. F. Maspero are gratefully acknowledged for their contribution to the reactivity studies. The authors are indebted to Mr. M. Buroni, Dr. G. Santi, Dr. S. Ghelli and Dr. C. Busetto for providing SEM, IR, NMR and ESR experiments respectively. REFERENCES 1. M. Taramasso, G. Perego and B. Notari, Proc •.Fifth Int. Conf. an Zeolites, Naples, L.V.C. Rees Ed., p.40, Landon Heyden and Sans (1980) • 2. M. Taramasso, G. Perego and B. Notari, U.S. Pat 4,410,501 (1983). 3. R.M. Barrer, Proc. Sixth Int. Conf. an Zeolites, Rena (USA), A. Bisio and D.H. Olson Ed.s, p.870, Butterworth (1984). 4. D.A. Yaung, U.S. Pat 3,329,481 (1967). 5. D.W. Breck, in "Zeolite Molecular Sieves", p.322, J. Wiley and Sans (1974).
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