- Email: [email protected]
Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2O2 as an environmentally friendly oxidant
G Model
ARTICLE IN PRESS
CATTOD-10615; No. of Pages 8
Catalysis Today xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant Keita Taniya a,b,∗ , Ryota Mori a , Atsushi Okemoto a , Takafumi Horie a,b , Yuichi Ichihashi a,b , Satoru Nishiyama a a b
Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan Center for Membrane and Film Technology, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan
a r t i c l e
i n f o
Article history: Received 30 September 2016 Received in revised form 20 January 2017 Accepted 21 February 2017 Available online xxx Keywords: Baeyer–Villiger oxidation Beta zeolite Hydrogen peroxide Cyclohexanone Cyclobutanone Acidic property
a b s t r a c t In this study, the Baeyer–Villiger (BV) oxidation of cyclic ketones to corresponding lactones using protontype -zeolite catalysts with various Al contents using an environmentally friendly oxidant (H2 O2 ) was investigated. With respect to the selective oxidation of cyclobutanone to the corresponding ␥butyrolactone, the hydrolysis of which hardly proceeded under the reaction conditions employed, the conversion of cyclobutanone and H2 O2 and yield of ␥-butyrolactone increased with increasing Al content of up to 418 mol/g (Si/Al ratio of 39.0), followed by marginal decrease at Al contents greater than 418 mol/g. These trends were clearly correlated to the amount of Brønsted acid sites as estimated by the combination of temperature programmed desorption of NH3 (NH3 -TPD) and Fourier transform infrared spectroscopy (FTIR) measurements for adsorbed pyridine. These results strongly indicated that the Brønsted acid sites in -zeolite catalysts serve as the active sites for the BV oxidation. On the other hand, for the BV oxidation of cyclohexanone to -caprolactone (the corresponding BV product), the selectivity of -caprolactone was maintained constant up to an Al content of 418 mol/g, but it gradually decreased at Al contents greater than 418 mol/g. An apparent correlation was observed between the amount of Lewis acid sites, attributed to the extra-framework Al species, and the trend of -caprolactone selectivity. These results suggested that the extra-framework Al species leads to the acceleration of the successive hydrolysis of -caprolactone. © 2017 Elsevier B.V. All rights reserved.
1. Introduction The Baeyer–Villiger (BV) oxidation involving the conversion of ketones or cyclic ketones to the corresponding esters or lactones, respectively, is an important transformation in synthetic organic chemistry; however, the use of peroxide or organic peroxy acids as the oxidant forms the desired product with the simultaneous generation of a significant amount of harmful waste [1]. For instance, -caprolactone is an important intermediate in the synthesis of polyesters, which is industrially produced by the oxidation of cyclohexanone with m-chloroperbenzoic acid, thereby affording a stoichiometric amount of m-chlorobenzoic acid [2]; this co-produced carboxylic acid must be neutralized, and the resultant salt must be disposed. Furthermore, organic peroxy acids are not
∗ Corresponding author at: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan. E-mail address: [email protected] (K. Taniya).
only expensive reagents, but also are difficult to transport, store, and handle because of their shock sensitivity and extremely high reactivity [3]. From the viewpoint of environmental considerations, several researchers have focused considerable efforts toward the development of an alternative catalytic process using an environmentally benign oxidant such as hydrogen peroxide (H2 O2 ). By using H2 O2 as the oxidant instead of organic peroxy acids, H2 O is the expected by-product. However, H2 O2 is a weak oxidant for the BV oxidation. Hence, to overcome this drawback, the use of heterogeneous catalysts with H2 O2 for the BV oxidation has been extensively investigated to activate the carbonyl group of ketone and/or hydrogen peroxide itself [4–21]. In this context, several heterogeneous catalysts, such as Ticontaining zeolite catalysts [4,5], Sn-containing zeolite catalysts [6–8], mesoporous ordered catalysts [9–11], solid acid catalysts [12–15], cationic clay-based catalysts [16–19], and polymeranchored metal complex catalysts [20,21], have been reported. Among these catalysts, our group has reported high activity for H-type -zeolite (HBEA) catalysts for the BV oxidation of cyclohexanone to -caprolactone using H2 O2 [15]. As has been mentioned
http://dx.doi.org/10.1016/j.cattod.2017.02.026 0920-5861/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
2
in our previous study, the Brønsted acid sites in these HBEA catalysts possibly activate H2 O2 and facilitate the BV oxidation, as demonstrated by the results obtained from the Fourier transform infrared spectroscopy (FTIR) measurement of H2 O2 adsorbed on the HBEA catalysts and the BV oxidation of cyclohexanone over Na+ exchanged -zeolites with varying percentages of ion-exchanged Na+ [15]. However, the maximum yield of -caprolactone was obtained at a Si/Al ratio of 85 for the HBEA catalyst although the amount of NH3 adsorption over the HBEA catalysts increased with decreasing the Si/Al ratio up to 55. Therefore, the role of Brønsted acid site in the HBEA zeolites for Baeyer–Villiger oxidation of cyclohexanone to -caprolactone still remains controversial. In order to clarify the role of Brønsted acid site, the considerable points seem to be still remained; one is the effect of the successive hydrolysis of -caprolactone during BV oxidation of cyclohexanone, and the other is the influence of the amount of Lewis acid sites in HBEA catalysts for BV oxidation of cyclohexanone. As for the former point, the yield of -caprolactone is affected by the successive hydrolysis of -caprolactone over the HBEA catalysts; these successive reactions make it difficult to elucidate the role of Al3+ in HBEA for the BV oxidation. We found that the successive hydrolysis of ␥-butyrolactone obtained by the BV oxidation of cyclobutanone barely proceeded. By using cyclobutanone for BV oxidation, the proper activity of HBEA catalysts for BV oxidation itself is expected to be elucidated. With respect to the latter point, it is well known that zeolites possess not only Brønsted acid site, but also Lewis acid site, and both acid sites can chemisorb NH3 . By a quantitative determination of both Brønsted and Lewis acid sites, it is expected to elucidate not only the proper relationship between the catalytic activity of HBEA for BV oxidation and Brønsted acid site, but also the effect of Lewis acid site on the catalytic performance of HBEA for BV oxidation. The present study was undertaken in order to elucidate the role of Al3+ species in the HBEA catalysts for BV oxidation of cyclic ketones by using H2 O2 . The effect of the Al content on the BV oxidation of both cyclobutanone to ␥-butyrolactone, which hardly gives any side reactions, and cyclohexanone to -caprolactone was investigated to compare the catalytic performance of the HBEA catalysts. The relationship between the catalytic performance and the amount of each acid site was also discussed.
2. Experimental 2.1. Catalyst preparation HBEA catalysts with various Al contents were prepared under hydrothermal conditions [22]. HBEA catalysts were prepared in a hydrothermal synthesis reactor (Model KH-02, Hiro Company, Yokohama, Japan). An aqueous solution of tetraethylammonium hydroxide (TEAOH, 35%) as the structure-directing agent (30.25 g, Sigma–Aldrich), fumed silica (8.0 g, 0.007 m, Sigma–Aldrich), and Al(OH)3 (Nacalai Tesque) were stirred at room temperature for 4 h in a polyethylene beaker. An aqueous solution of HF (46%, 4.02 g, Nacalai Tesque) was slowly added into the hydrogel mixture prepared in the first step with vigorous agitation. The composition of each compound in the reaction mixture was SiO2 :yAl2 O3 :0.54TEAOH:0.54HF:9.3H2 O (y = 0.0036, 0.0050, 0.0063, 0.0100, 0.0125, 0.0185, 0.0250, and 0.0294). The mixture thus obtained was transferred to a Teflon-coated stainless steel autoclave reactor for crystallization at 423 K for 7 days. The obtained white solid was filtered and rinsed with 3 L of hot (ca. 343 K) deionized water. The as-synthesized sample was dried overnight at 393 K, followed by calcination in atmosphere at 853 K for 5 h for removing the structure-directing agent. The calcined sample was converted to its Na form via ion exchange with an
aqueous solution of 1 M NaNO3 at 353 K for 24 h. Na+ was ionexchanged with NH4 + from a 1 M aqueous NH4 NO3 solution at 353 K for 24 h. Finally, the sample was dried overnight at 393 K, followed by calcination in air flow at 773 K for 5 h, affording protontype -zeolites. Hereafter, the obtained catalysts will be referred to as HBEAX, where X represents the Si/Al ratio in the catalysts as estimated by X-ray fluorescence (XRF) analysis. In addition, -zeolite (Si/Al ratio of 37.5) was obtained from Zeolyst International (Pennsylvania, USA). This commercial zeolite was subjected to the same treatment as the HBEA catalysts described above: ion exchange with Na+ and NH4 + , followed by calcination. Hereafter, the catalyst thus obtained will be referred to as rHBEA37.5. 2.2. Characterization 2.2.1. X-ray fluorescence analysis The contents of Si and Al in the HBEA catalysts were estimated by XRF spectroscopy (Rigaku, Primini) under a vacuum of 1.7 Pa. The HBEA samples were excited using a Pd X-ray tube operated at 40 kV and 1.25 mA. 2.2.2. Powder X-ray diffraction (XRD) patterns Powder XRD patterns of the HBEA catalysts were recorded on a RINT-2000 (Rigaku) XRD instrument with Cu K␣ radiation for confirming the structure of each sample. The X-ray tube was operated at 40 kV and 20 mA. 2.2.3. N2 adsorption measurements Nitrogen adsorption measurements were performed at 77 K on a BELSORP-mini apparatus (MicrotracBEL Corp.) after pretreatment at 473 K under a N2 flow of 50 mL/min for 2 h. 2.2.4. Temperature-programmed desorption The temperature-programmed desorption (TPD) of adsorbed NH3 was performed in a static vacuum system for evaluating the amount of acid sites in the HBEA catalysts. The adsorption of NH3 on a sample was conducted at 373 K, followed by evacuation for 0.5 h. The amount of NH3 adsorbed on the sample was estimated by the difference between the total and reversible amounts of adsorbed NH3 . The adsorbed samples were heated at 10 K/min at temperatures ranging from 373 to 773 K. The pressure of desorbed ammonia was recorded using an ion gauge vacuum meter. 2.2.5. Infrared spectroscopy for the adsorption of pyridine on the HBEA catalysts The infrared (IR) spectra of the pyridine adsorbed on each catalyst were recorded using an in situ Pyrex glass cell equipped with KBr single-crystal windows. A sample disk with a diameter of 13 mm was compression-molded from 20 mg of -zeolite powder. The specimen was evacuated at 723 K for 2 h in the static vacuum system, followed by rapid transfer into the in situ IR cell with subsequent evacuation at 523 K for 2 h in vacuo. After pretreatment, pyridine was adsorbed at room temperature for 30 min, and the sample was evacuated at 523 K for 1 h. A total of 1000 scans for the sample IR spectra were recorded on a Nicolet 380 FTIR spectrometer, equipped with a highly sensitive MCT detector. The resolution of the spectrometer was 4 cm−1 . 2.3. Catalytic test 2.3.1. Baeyer–Villiger oxidation of cyclic ketones with H2 O2 The BV oxidation of cyclobutanone with H2 O2 was performed in an Erlenmeyer flask fitted with a condenser. Cyclobutanone (0.15 mL, 2.2 mmol, Tokyo Chemical Industry), 30% of a H2 O2 aqueous solution (0.18 mL, 2.2 mmol, Wako), acetonitrile (4 mL, Nacalai
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
3
Table 1 Physical properties of synthesized -zeolite with various Al content. Entry
1 2 3 4 5 6 7 8 a
Al content [mol/g]
Si/Al ratio
Surface area
Initial gel
Analysisa
Initial gel
Analysisa
[m2 /g]
119 165 208 327 407 598 798 932
117 169 200 335 418 578 782 890
139 100 79 50 40 27 20 17
141.2 97.3 82.5 48.6 39.0 27.0 20.3 17.0
552 562 540 520 551 470 520 470
Evaluated by XRF analysis.
Tesque), and 10 mg of catalysts were charged into the reactor. The reactor, equipped with a condenser, was purged several times with N2 to attain anaerobic atmosphere. The reactor was heated at 303 K for 2 h in a thermostatically controlled oil bath. After reaction, 1.0 mL of ethanol, serving as the internal standard, was injected into the solution, and the reaction mixture was centrifuged to separate the catalysts. Products were analyzed by GC-FID (GC-18A, Shimadzu) equipped with a G-300 column (Chemicals Evaluation and Research Institute, Japan). The oxidation of cyclohexanone with H2 O2 was performed in the same manner as that described above for the oxidation of cyclobutanone. The utilized reaction conditions were as follows: 0.2 mL of cyclohexanone (2.0 mmol, Nacalai Tesque), 0.1 mL of 30% H2 O2 , 4.0 mL of acetonitrile, and 20 mg of catalysts. The reaction was performed at 303 K for 3 h. For the BV oxidation of cyclohexanone over the mixture of rHBEA37.5 and ␥-Al2 O3 catalysts, the desired amount of ␥-Al2 O3 was added into the reaction mixture for BV oxidation.
2.3.2. Hydrolysis of -caprolactone The hydrolysis of -caprolactone was performed in a manner similar to that performed for the BV oxidation of cyclohexanone by using -caprolactone instead of cyclohexanone.
3. Results and discussion 3.1. Physical properties of the HBEA catalysts Table 1 summarizes the compositions of the as-prepared HBEA catalysts and their surface areas as calculated by the BET method. The synthesized HBEA catalysts consisted of various contents of Al from 117 to 890 mol/g. The surface areas of these samples ranged between 470 and 562 m2 /g. With increasing Al content, the surface area of the HBEA catalysts decreased at the higher Al content in HBEA catalysts. Fig. 1 shows the powder XRD patterns of the HBEA catalysts with various Al contents. The BEA structure was clearly observed for each catalyst. The unidentified peak at ca. 20◦ of 2 was observed for HBEA97.3 and HBEA141.2 catalysts. Although this peak is probably due to the presence of impurities and/or the interlayer stacking disorder in zeolite beta family [23], we cannot reach the identification in this study. For the HBEA catalysts with Al contents greater than 418 mol/g (Si/Al ratio of 39.0), peak intensity decreased with increasing Al content in the HBEA catalysts, attributed to decreased crystallinity and/or crystal size. Figure S1 shows the N2 adsorption isotherms of HBEA catalysts with Si/Al of 17.0, 20.3, 39.0 and 97.3, and their micropore volume estimated by a t-plot method. The estimated micropore volume of each catalyst showed almost constant value regardless of Si/Al atomic ratios. From the results of XRD and micropore volume, the crystal size of HBEA17.0 and HBEA20.3 was suggested to be smaller.
Fig. 1. XRD patterns of HBEA catalysts with various Al content.
3.2. Acidic properties of the HBEA catalysts Figure S2 shows the amount of adsorbed ammonia over the HBEA catalysts with various Al contents. Notably, the values obtained also include the amount of adsorbed ammonia on the non-acid sites [24–26], implying that the amount of irreversible adsorbed NH3 does not reflect the actual amount of acid sites in the HBEA catalysts. Fig. 2 shows the TPD spectra of adsorbed NH3 over the HBEA catalysts with various Al contents. Four peaks were observed at 413, 463, 563, and temperature greater than 673 K, respectively, with peak overlap. The peak observed at 413 K has been reported to be attributed to the interaction between ammonia molecules and the NH3 species adsorbed on the acid sites, namely, this NH3 species is adsorbed on non-acidic sites [24–26]. For precisely evaluating the amount of acid sites, this peak was extracted from the entire TPD spectra. On the other hand, the remaining three peaks observed at 463, 563, and temperature greater than 673 K were referred to as l, h, and h+ , respectively [27,28]; these peaks are typically observed in the NH3 -TPD profile of -zeolite. Niwa et al.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8 4
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
Fig. 3. Relationship between Al content of HBEA catalysts and the amount of acid sites.
Fig. 2. TPD spectra of NH3 adsorbed on HBEA catalysts with various Al content.
have reported that these desorbed ammonia peaks are attributed to weakly adsorbed NH3 on the Lewis acid sites, NH4 + on the Brønsted acid sites, and strongly adsorbed NH3 on the acid sites, respectively, as confirmed by the IRMS-TPD measurement of -zeolite [27]. This result indicated that l, h, and h+ peaks are related to the desorption of NH3 from the acid sites in the HBEA catalysts. Notably, NH3 species strongly adsorbed on acid sites (h+ peak) is desorbed in the complete temperature range during IRMS-TPD [27], indicating that the Brønsted and Lewis acid sites on the HBEA catalysts cannot be directly distinguished by NH3 -TPD measurements. Hence, the amount of NH3 corresponding to the l, h, and h+ peaks is evaluated by calculation from the total amount of adsorbed NH3 and the fraction of the l, h, and h+ peak areas from the total desorption spectrum. Moreover, the NH3 -TPD spectra for HBEA catalysts with various Al contents were analyzed on the basis of typical Gaussian distribution for extracting the physisorbed NH3 species (see Fig. S3). Fig. 3 shows the dependence of Al content in the HBEA catalysts on the total amount of acid sites. As shown in Fig. 3, the dashed line denotes an equivalent relationship between the Al content and the amount of total acid sites. The total amount of acid sites were almost equivalent to an Al content of up to 418 mol/g (Si/Al ratio of 39.0). At Al contents greater than 418 mol/g, the total amount of acid sites decreased as compared to the Al content, and the difference between the Al content and the total acid sites increased with increasing Al content. These results suggested that the excess Al introduced into the HBEA catalysts hardly serves as the acid sites at Al contents greater than 418 mol/g (Si/Al ratio of 39.0). Fig. 4 shows the FTIR spectra of the pyridine adsorbed on the HBEA catalysts with various Al contents. An IR band was observed at 1547 cm−1 , attributed to pyridine adsorbed on Brønsted acid sites (PyB) [29–33]. Three pyridine species were observed in the range between 1430 and 1470 cm−1 . Bands were observed at 1438,
Fig. 4. FT-IR spectra of adsorbed pyridine on HBEA catalysts with various Al content.
1445, and 1455 cm−1 , attributed to gaseous pyridine and/or physically adsorbed pyridine on the surface, hydrogen-bonded pyridine, and pyridine adsorbed on the Lewis acid sites (PyL), respectively [29–33]. Another band was observed at 1491 cm−1 , attributed to the superposition of signals of pyridine adsorbed on both Brønsted and Lewis acid sites [29–33]. Moreover, the bands observed at 1430–1470 cm−1 were analyzed on the basis of typical Gaussian distribution for extracting the PyL band (Fig. S4). The concentrations of the Brønsted and Lewis acid sites were calculated via the
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
5
Fig. 5. Relationship between Al content of HBEA catalysts and the amount of Brønsted and Lewis acid sites estimated by the combination of NH3 -TPD and FTIR of adsorbed pyridine.
integration of the area corresponding to the PyB and PyL bands observed at 1547 and 1455 cm−1 , respectively. Fig. 5 shows the relationship between the Al content in the HBEA catalysts and the amount corresponding to each of Brønsted and Lewis acid sites as estimated by the combination of the amount of adsorbed NH3 on the acid sites (Fig. 3) and the concentrations of Brønsted and Lewis acid sites calculated from FTIR measurements. With increasing Al content of up to 418 mol/g (Si/Al ratio of 39.0), the amount of Brønsted acid sites increased, which was maintained constant at Al contents greater than 418 mol/g. In addition, with increasing Al content, the amount of Lewis acid sites gradually increased. These results suggested that the excess of Al species introduced into the HBEA catalysts serves as Lewis acid sites at an Al content greater than 418 mol/g. The amount of octahedral aluminum species has been reported to increase with decreasing Si/Al ratio (i.e., increasing Al content) [34]. Lavalley et al. and Detka et al. have independently reported that the Lewis acid sites in zeolites are possibly related to the extraframework Al species as the concentration of the Lewis acid sites, as compared with that of Brønsted acid sites, rapidly decreases after acid treatment [33,35]. These results suggested that the extraframework Al species are formed, which serve as the Lewis acid sites at Al contents greater than 418 mol/g (Si/Al ratio of 39.0). 3.3. Relationship between the acidity and performance of the HBEA catalysts for the BV oxidation of cyclobutanone Scheme 1 outlines the proposed reaction pathway for the BV oxidation of cyclobutanone. In the BV oxidation of cyclobutanone, ␥-butyrolactone was detected as the only product as confirmed by GC-FID. Some parts of the undetectable products, attributed to the polymerized product, should also be considered. Fig. 6 shows the catalytic performance of the prepared HBEA catalysts with various Al contents for the BV oxidation of cyclobutanone using H2 O2 . As shown in Fig. 6a, the conversion of cyclobutanone and yield of ␥-butyrolactone increased with increasing Al content of up to 418 mol/g (Si/Al ratio of 39.0), and marginally decreased at Al contents greater than 418 mol/g. The excess Al species introduced into the HBEA catalysts was not found to be effective for the BV oxidation. At Al contents of up to 418 mol/g (Si/Al = 39.0), the selectivity of ␥-butyrolactone was maintained at approximately 90%, followed by marginal decrease at Al contents greater than 418 mol/g (Fig. 6a). Notably, carbon
Fig. 6. BV oxidation of cyclobutanone over HBEA catalysts with various Al content.
balance over all catalysts was approximately 95% (not shown in figure). These results suggested that the successive hydrolysis of ␥-butyrolactone is difficult under the currently employed experimental conditions. Fig. 6b shows the conversion and efficiency of H2 O2 . The trend observed for H2 O2 conversion was quite similar to that observed for cyclobutanone conversion. H2 O2 efficiency was defined as the percentage of consumed H2 O2 for the formation of lactones. From the results, approximately a 100% H2 O2 efficiency was obtained over all HBEA catalysts. This result strongly indicated that H2 O2 is almost consumed during the BV oxidation of cyclobutanone, and its self-decomposition hardly proceeds over HBEA catalysts irrespective of Al content. Hence, the use of cyclobutanone as the reactant for the BV oxidation is advantageous for elucidating the role of the Brønsted acid sites in the HBEA catalysts as compared with the use of cyclohexanone as the reactant, because the effect of the successive hydrolysis on the catalytic performance for the BV oxidation over the HBEA catalysts can be excluded (Scheme 2). Fig. 7 shows the correlation between the amount of the Brønsted acid sites and the conversion of cyclobutanone and H2 O2 for the BV oxidation of cyclobutanone using HBEA catalysts with various Al contents. Notably, the dependence of Al content on the conversion of cyclobutanone and H2 O2 and the amount of Brønsted acid sites in the HBEA catalysts exhibited similar trends. As has
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8 6
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
Scheme 1. Reaction pathway of BV oxidation of cyclobutanone.
Scheme 2. Reaction pathway of BV oxidation of cyclohexanone.
Fig. 7. Correlation between the amount of Brønsted acid sites and the conversion of cyclobutanone and H2 O2 for BV oxidation of cyclobutanone over HBEA catalysts with various Al content.
been mentioned in our previous study, the Brønsted acid sites in these HBEA catalysts possibly activate H2 O2 and facilitate the BV oxidation, as demonstrated by the results obtained from the FTIR measurement of H2 O2 adsorbed on the HBEA catalysts and the BV oxidation of cyclohexanone over Na+ -exchanged -zeolites with varying percentages of ion-exchanged Na+ [15]. These results strongly suggested that the Brønsted acid sites in the HBEA catalysts play a crucial role as active sites for the BV oxidation of cyclobutanone with H2 O2 . 3.4. Relationship between the acidity and performance of the HBEA catalysts for the BV oxidation of cyclohexanone For the BV oxidation of cyclohexanone, -caprolactone (target molecule) was obtained as the main product, with low amounts of ␦-hexanolactone and 6-hydroxycaproic acid (representing the hydrolyzed product of -caprolactone) also detected. Some parts of the undetectable products, attributed to the polymerized product, should also be investigated. Fig. 8 shows the catalytic activity of the HBEA catalysts with various Al content for the BV oxidation of cyclohexanone with H2 O2 . At an Al content of up to 418 mol/g (Si/Al ratio of 39.0), the conversion of cyclohexanone and yield of -caprolactone increased, followed by gradual decrease at Al contents greater than 418 mol/g (Fig. 8a). On the other hand, at an Al content of up to 418 mol/g, the selectivity of -caprolactone was maintained at approximately 50%, followed by gradual decrease at Al contents
Fig. 8. BV oxidation of cyclohexanone over HBEA catalysts with various Al content.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
7
Fig. 9. Correlation between the amount of Lewis acid sites and the selectivity of -caprolactone for BV oxidation of cyclohexanone over HBEA catalysts with various Al content.
greater than 418 mol/g (Fig. 8a). Fig. 8b shows the conversion and efficiency of H2 O2 . At an Al content of up to 418 mol/g, H2 O2 efficiency was maintained at approximately 55%, followed by gradual decrease at Al contents greater than 418 mol/g (Fig. 8b). The trend observed for H2 O2 conversion was similar to that observed for cyclohexane conversion. These results implied that the excess Al species introduced into the HBEA catalysts are not effective for the BV oxidation of cyclohexanone and facilitate side reactions, such as hydrolysis and polymerization. The different Si/Al ratio where the maximum yield of caprolactone was obtained was observed between in this work (Si/Al = 39.0) and in our previous study (Si/Al = 84.3) [15]. In the previous study, we have mainly focused on understanding where Baeyer–Villiger oxidation of cyclohexanone proceeds on in HBEA catalysts. The range of Al content in HBEA catalysts, which the successive hydrolysis reaction hardly proceeded, has been employed. Additionally, we have regarded all the introduced Al3+ species in HBEA catalyst as Brønsted acid site in the previous study. Since the decrease of yield has been observed over the HBEA catalyst with Si/Al ratio of 55, we have assumed that the optimum Si/Al ratio is 85, and have not made the investigation into HBEA catalysts with Si/Al ratios smaller than 55 in the previous work. Therefore, we could not reach finding the actual optimum Si/Al ratio which showed the maximum yield of -caprolactone in the previous work. As mentioned earlier (Fig. 5), at Al contents greater than 418 mol/g, the amount of Lewis acid sites significantly increased. Thus, the Lewis acid sites adversely affect the catalytic performance of the HBEA catalysts for the BV oxidation of cyclohexanone. Fig. 9 shows the correlation between the amount of Lewis acid sites and the selectivity of -caprolactone for the BV oxidation of cyclohexanone over HBEA catalysts with various Al contents. Notably, with increasing the amount of Lewis acid sites at Al contents greater than 418 mol/g, the selectivity of -caprolactone decreased. As ester hydrolysis is well known to occur with protonic acids or bases, it would not be expected that the Lewis acid site itself catalyzes the hydrolysis reaction of -caprolactone. As described above, the Lewis acid sites in zeolites can be related to the extra-framework Al species. Furthermore, the extra-framework Al species has been reported to be composed of several aluminum species [36]. Hence, a part of the extra-framework species accelerates the successive hydrolysis of -caprolactone. For investigating the effect of the extra-framework Al species on the catalytic performance of the HBEA catalysts for the BV oxidation of cyclohexanone, ␥-Al2 O3 was added to the reaction mixture. The HBEA catalyst with a Si/Al ratio of 37.5 (rHBEA37.5) obtained from Zeolyst International and ␥-Al2 O3 (JRC-ALO-8) supplied by
Fig. 10. Dependence of the amount of added Al2 O3 to reaction mixture on the catalytic performance for BV oxidation of cyclohexanone over HBEA catalyst with a Si/Al ratio of 37.5 (rHBEA37.5).
Table 2 Hydrolysis reaction of -caprolactone over each catalyst. Entry
Catalysts
Conversion of -caprolactone [%]
1 2 3
– Al2 O3 rHBEA37.5
0 0 6.2
the Catalysis Society of Japan were used. Since the catalytic performance for BV oxidation of cyclobutanone and cyclohexanone (Table S1 and S2, respectively) and NH3 -TPD spectrum over the rHBEA37.5 (Fig. S5) were similar to that over the HBEA39.0, the rHBEA37.5 catalyst was employed as a referential sample instead of HBEA39.0 in this study. Fig. 10 shows the effect of the amount of added ␥-Al2 O3 on the catalytic activity of the HBEA catalysts used for the BV oxidation of cyclohexanone. With increasing addition of ␥-Al2 O3 , the conversions of cyclohexanone and H2 O2 were maintained constant regardless of the amount of the added ␥-Al2 O3 , whereas the yield and selectivity of -caprolactone gradually decreased. These results clearly suggested that the aluminum oxides added to the reaction mixture facilitate the successive hydrolysis of -caprolactone. Table 2 summarizes the results obtained from the hydrolysis of -caprolactone over each catalyst. In the blank test (i.e. without catalysts) and using ␥-Al2 O3 , no conversion for -caprolactone was observed (Entries 1 and 2, respectively). The hydrolysis of caprolactone proceeded over HBEA with a Si/Al ratio of 37.5 (Entry 3). These results strongly suggested that the co-existence of the extra-framework Al species and HBEA catalysts leads to the acceleration of the successive hydrolysis of -caprolactone for the BV oxidation of cyclohexanone. At Al contents greater than 418 mol/g, the different trends of conversions of reactants and H2 O2 were observed by using different cyclic ketones; the conversions of cyclohexanone and H2 O2 decreased (Fig. 8), whereas that of cyclobutanone and H2 O2 insignificant decreased (Fig. 6). Since the conversion of cyclohexanone and H2 O2 decreased with increasing the amount of Lewis acid sites, these behavior were apparently attributed to the presence of extra-framework Al species. Nevertheless, their detailed behavior is currently under investigation.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
8
4. Conclusions (1) For the BV oxidation of cyclobutanone, the catalytic activity of the HBEA catalysts with various Al contents depended on the amount of Brønsted acid sites. (2) Extra-framework Al species negatively affected not only the selectivity of lactones but also the catalytic activity of the HBEA catalysts. (3) The successive hydrolysis of lactones was attributed to the coexistence of extra-framework Al species and the HBEA catalysts. Acknowledgments We greatly appreciate Mr. Norihisa Kumagai, Faculty of Engineering, Kobe University for the kind assistance with NH3 -TPD and FTIR measurements. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.cattod.2017.02. 026. References [1] C. Jiménez-Sanchidrián, J.R. Ruiz, Tetrahedron 64 (2008) 2011–2026. [2] H. Heaney, in: S.D. Burke, R.L. Danheiser (Eds.), Handbook of Reagents for Organic Synthesis—Oxidizing and Reducing Agents, Wiley, 1999, pp. 84–89. [3] G.-J. ten Brink, I.W.C.E. Arends, R.A. Sheldon, Chem. Rev. 104 (2004) 4105–4123. [4] A. Bhaumik, P. Kumar, R. Kumar, Catal. Lett. 40 (1996) 47–50. [5] R. Kumar, A. Bhaumik, Micropor. Mesopor. Mater. 21 (1998) 497–504. [6] A. Corma, L.T. Nemeth, M. Renz, S. Valencia, Nature 412 (2001) 423–425. [7] S.R. Bare, S.D. Kelly, S. Sinkler, J.J. Low, F.S. Modica, S. Valencia, A. Corma, J. Am. Chem. Soc. 127 (2005) 12924–12932. [8] P. Li, G. Liu, H. Wu, Y. Liu, J. Jiang, P. Wu, J. Phys. Chem. B 115 (2011) 3663–3670.
[9] A. Corma, M.T. Navarro, M. Renz, J. Catal. 219 (2003) 242–246. [10] M. Sasidharan, Y. Kiyozumi, N.K. Mal, M. Paul, P.R. Rajamohanan, A. Bhaumik, Micropor. Mesopor. Mater. 126 (2009) 234–244. [11] T. Chen, B. Wang, Y. Li, L. Liu, S. Qiu, J. Porous Mater. 22 (2015) 949–957. [12] Z.B. Wang, T. Mizusaki, Y. Kawakami, Bull. Chem. Soc. Jpn. 70 (1997) 2567–2570. [13] J. Fischer, W.F. Hölderich, Appl. Catal. A: Gen. 180 (1999) 435–443. [14] M. Lenarda, M. Da Ros, M. Casagrande, L. Storaro, R. Ganzerla, Inorg. Chim. Acta 349 (2003) 195–202. [15] R. Ohno, K. Taniya, S. Tsuruya, Y. Ichihashi, S. Nishiyama, Catal. Today 203 (2013) 60–65. [16] Z.Q. Lei, G.F. Ma, C. Jia, Catal. Commun. 8 (2007) 305–309. [17] U.R. Pillai, E.S. Demessie, J. Mol. Catal. A: Chem. 191 (2003) 93–100. [18] T. Hara, M. Hatakeyama, A. Kim, N. Ichikuni, S. Shimazu, Green Chem. 14 (2012) 771–777. [19] J.C. Sanchidrian, J.M. Hidalgo, R. Llamas, J.R. Ruiz, Appl. Catal. A: Gen. 312 (2006) 86–94. [20] C. Palazzi, F. Pinna, G. Strukul, J. Mol. Catal. A: Chem. 151 (2000) 245–252. [21] C. Li, J. Wang, Z. Yang, Z. Hu, Z. Lei, Catal. Commun. 8 (2007) 1202–1208. [22] H. Jon, B. Lu, Y. Oumi, K. Itabashi, T. Sano, Micropor. Mesopor. Mater. 89 (2006) 88–95. [23] http://asia.iza-structure.org/IZA-SC/ds.htm. [24] N. Katada, S. Iijima, H. Igi, M. Niwa, Stud. Surf. Sci. Catal. 105 (1996) 1227–1234. [25] F. Lónyi, J. Valyon, Micropor. Mesopor. Mater. 47 (2001) 293–301. [26] N. Katada, H. Igi, J. Kim, M. Niwa, J. Phys. Chem. B 101 (1997) 5969–5977. [27] M. Niwa, S. Nishikawa, N. Katada, Micropor. Mesopor. Mater. 82 (2005) 105–112. [28] H. Matsuura, N. Katada, M. Niwa, Micropor. Mesopor. Mater. 66 (2003) 283–296. [29] Y. Miyamoto, N. Katada, M. Niwa, Micropor. Mesopor. Mater. 40 (2000) 271–281. [30] W. Wu, E. Weitz, Appl. Surf. Sci. 316 (2014) 405–415. [31] M.I. Zaki, M.A. Hasan, F.A. Al-Sagheer, L. Pasupulety, Coll. Surf. A Physicochem. Eng. Asp. 190 (2001) 261–274. [32] J.P. Marques, I. Gener, P. Ayrault, J.C. Bordado, J.M. Lopes, F. Ramôa Ribeiro, M. Guisnet, Micropor. Mesopor. Mater. 60 (2003) 251–262. [33] M. Guisnet, P. Ayrault, C. Coutanceau, M.F. Alvarez, J. Datka, J. Chem. Soc., Faraday Trans. 93 (1997) 1661–1665. [34] A. Abraham, S. Lee, C. Shin, S.B. Hong, R. Prins, J.A. van Bokhoven, Phys. Chem. Chem. Phys. 6 (2004) 3031–3036. [35] M. Maache, A. Janin, J.C. Lavalley, J.F. Joly, E. Benazzai, Zeolites 13 (1993) 419–426. [36] R.D. Shannon, K.H. Gardner, R.H. Staley, J. Phys. Chem. 89 (1985) 4778–4788.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
ARTICLE IN PRESS
CATTOD-10615; No. of Pages 8
Catalysis Today xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant Keita Taniya a,b,∗ , Ryota Mori a , Atsushi Okemoto a , Takafumi Horie a,b , Yuichi Ichihashi a,b , Satoru Nishiyama a a b
Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan Center for Membrane and Film Technology, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan
a r t i c l e
i n f o
Article history: Received 30 September 2016 Received in revised form 20 January 2017 Accepted 21 February 2017 Available online xxx Keywords: Baeyer–Villiger oxidation Beta zeolite Hydrogen peroxide Cyclohexanone Cyclobutanone Acidic property
a b s t r a c t In this study, the Baeyer–Villiger (BV) oxidation of cyclic ketones to corresponding lactones using protontype -zeolite catalysts with various Al contents using an environmentally friendly oxidant (H2 O2 ) was investigated. With respect to the selective oxidation of cyclobutanone to the corresponding ␥butyrolactone, the hydrolysis of which hardly proceeded under the reaction conditions employed, the conversion of cyclobutanone and H2 O2 and yield of ␥-butyrolactone increased with increasing Al content of up to 418 mol/g (Si/Al ratio of 39.0), followed by marginal decrease at Al contents greater than 418 mol/g. These trends were clearly correlated to the amount of Brønsted acid sites as estimated by the combination of temperature programmed desorption of NH3 (NH3 -TPD) and Fourier transform infrared spectroscopy (FTIR) measurements for adsorbed pyridine. These results strongly indicated that the Brønsted acid sites in -zeolite catalysts serve as the active sites for the BV oxidation. On the other hand, for the BV oxidation of cyclohexanone to -caprolactone (the corresponding BV product), the selectivity of -caprolactone was maintained constant up to an Al content of 418 mol/g, but it gradually decreased at Al contents greater than 418 mol/g. An apparent correlation was observed between the amount of Lewis acid sites, attributed to the extra-framework Al species, and the trend of -caprolactone selectivity. These results suggested that the extra-framework Al species leads to the acceleration of the successive hydrolysis of -caprolactone. © 2017 Elsevier B.V. All rights reserved.
1. Introduction The Baeyer–Villiger (BV) oxidation involving the conversion of ketones or cyclic ketones to the corresponding esters or lactones, respectively, is an important transformation in synthetic organic chemistry; however, the use of peroxide or organic peroxy acids as the oxidant forms the desired product with the simultaneous generation of a significant amount of harmful waste [1]. For instance, -caprolactone is an important intermediate in the synthesis of polyesters, which is industrially produced by the oxidation of cyclohexanone with m-chloroperbenzoic acid, thereby affording a stoichiometric amount of m-chlorobenzoic acid [2]; this co-produced carboxylic acid must be neutralized, and the resultant salt must be disposed. Furthermore, organic peroxy acids are not
∗ Corresponding author at: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan. E-mail address: [email protected] (K. Taniya).
only expensive reagents, but also are difficult to transport, store, and handle because of their shock sensitivity and extremely high reactivity [3]. From the viewpoint of environmental considerations, several researchers have focused considerable efforts toward the development of an alternative catalytic process using an environmentally benign oxidant such as hydrogen peroxide (H2 O2 ). By using H2 O2 as the oxidant instead of organic peroxy acids, H2 O is the expected by-product. However, H2 O2 is a weak oxidant for the BV oxidation. Hence, to overcome this drawback, the use of heterogeneous catalysts with H2 O2 for the BV oxidation has been extensively investigated to activate the carbonyl group of ketone and/or hydrogen peroxide itself [4–21]. In this context, several heterogeneous catalysts, such as Ticontaining zeolite catalysts [4,5], Sn-containing zeolite catalysts [6–8], mesoporous ordered catalysts [9–11], solid acid catalysts [12–15], cationic clay-based catalysts [16–19], and polymeranchored metal complex catalysts [20,21], have been reported. Among these catalysts, our group has reported high activity for H-type -zeolite (HBEA) catalysts for the BV oxidation of cyclohexanone to -caprolactone using H2 O2 [15]. As has been mentioned
http://dx.doi.org/10.1016/j.cattod.2017.02.026 0920-5861/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
2
in our previous study, the Brønsted acid sites in these HBEA catalysts possibly activate H2 O2 and facilitate the BV oxidation, as demonstrated by the results obtained from the Fourier transform infrared spectroscopy (FTIR) measurement of H2 O2 adsorbed on the HBEA catalysts and the BV oxidation of cyclohexanone over Na+ exchanged -zeolites with varying percentages of ion-exchanged Na+ [15]. However, the maximum yield of -caprolactone was obtained at a Si/Al ratio of 85 for the HBEA catalyst although the amount of NH3 adsorption over the HBEA catalysts increased with decreasing the Si/Al ratio up to 55. Therefore, the role of Brønsted acid site in the HBEA zeolites for Baeyer–Villiger oxidation of cyclohexanone to -caprolactone still remains controversial. In order to clarify the role of Brønsted acid site, the considerable points seem to be still remained; one is the effect of the successive hydrolysis of -caprolactone during BV oxidation of cyclohexanone, and the other is the influence of the amount of Lewis acid sites in HBEA catalysts for BV oxidation of cyclohexanone. As for the former point, the yield of -caprolactone is affected by the successive hydrolysis of -caprolactone over the HBEA catalysts; these successive reactions make it difficult to elucidate the role of Al3+ in HBEA for the BV oxidation. We found that the successive hydrolysis of ␥-butyrolactone obtained by the BV oxidation of cyclobutanone barely proceeded. By using cyclobutanone for BV oxidation, the proper activity of HBEA catalysts for BV oxidation itself is expected to be elucidated. With respect to the latter point, it is well known that zeolites possess not only Brønsted acid site, but also Lewis acid site, and both acid sites can chemisorb NH3 . By a quantitative determination of both Brønsted and Lewis acid sites, it is expected to elucidate not only the proper relationship between the catalytic activity of HBEA for BV oxidation and Brønsted acid site, but also the effect of Lewis acid site on the catalytic performance of HBEA for BV oxidation. The present study was undertaken in order to elucidate the role of Al3+ species in the HBEA catalysts for BV oxidation of cyclic ketones by using H2 O2 . The effect of the Al content on the BV oxidation of both cyclobutanone to ␥-butyrolactone, which hardly gives any side reactions, and cyclohexanone to -caprolactone was investigated to compare the catalytic performance of the HBEA catalysts. The relationship between the catalytic performance and the amount of each acid site was also discussed.
2. Experimental 2.1. Catalyst preparation HBEA catalysts with various Al contents were prepared under hydrothermal conditions [22]. HBEA catalysts were prepared in a hydrothermal synthesis reactor (Model KH-02, Hiro Company, Yokohama, Japan). An aqueous solution of tetraethylammonium hydroxide (TEAOH, 35%) as the structure-directing agent (30.25 g, Sigma–Aldrich), fumed silica (8.0 g, 0.007 m, Sigma–Aldrich), and Al(OH)3 (Nacalai Tesque) were stirred at room temperature for 4 h in a polyethylene beaker. An aqueous solution of HF (46%, 4.02 g, Nacalai Tesque) was slowly added into the hydrogel mixture prepared in the first step with vigorous agitation. The composition of each compound in the reaction mixture was SiO2 :yAl2 O3 :0.54TEAOH:0.54HF:9.3H2 O (y = 0.0036, 0.0050, 0.0063, 0.0100, 0.0125, 0.0185, 0.0250, and 0.0294). The mixture thus obtained was transferred to a Teflon-coated stainless steel autoclave reactor for crystallization at 423 K for 7 days. The obtained white solid was filtered and rinsed with 3 L of hot (ca. 343 K) deionized water. The as-synthesized sample was dried overnight at 393 K, followed by calcination in atmosphere at 853 K for 5 h for removing the structure-directing agent. The calcined sample was converted to its Na form via ion exchange with an
aqueous solution of 1 M NaNO3 at 353 K for 24 h. Na+ was ionexchanged with NH4 + from a 1 M aqueous NH4 NO3 solution at 353 K for 24 h. Finally, the sample was dried overnight at 393 K, followed by calcination in air flow at 773 K for 5 h, affording protontype -zeolites. Hereafter, the obtained catalysts will be referred to as HBEAX, where X represents the Si/Al ratio in the catalysts as estimated by X-ray fluorescence (XRF) analysis. In addition, -zeolite (Si/Al ratio of 37.5) was obtained from Zeolyst International (Pennsylvania, USA). This commercial zeolite was subjected to the same treatment as the HBEA catalysts described above: ion exchange with Na+ and NH4 + , followed by calcination. Hereafter, the catalyst thus obtained will be referred to as rHBEA37.5. 2.2. Characterization 2.2.1. X-ray fluorescence analysis The contents of Si and Al in the HBEA catalysts were estimated by XRF spectroscopy (Rigaku, Primini) under a vacuum of 1.7 Pa. The HBEA samples were excited using a Pd X-ray tube operated at 40 kV and 1.25 mA. 2.2.2. Powder X-ray diffraction (XRD) patterns Powder XRD patterns of the HBEA catalysts were recorded on a RINT-2000 (Rigaku) XRD instrument with Cu K␣ radiation for confirming the structure of each sample. The X-ray tube was operated at 40 kV and 20 mA. 2.2.3. N2 adsorption measurements Nitrogen adsorption measurements were performed at 77 K on a BELSORP-mini apparatus (MicrotracBEL Corp.) after pretreatment at 473 K under a N2 flow of 50 mL/min for 2 h. 2.2.4. Temperature-programmed desorption The temperature-programmed desorption (TPD) of adsorbed NH3 was performed in a static vacuum system for evaluating the amount of acid sites in the HBEA catalysts. The adsorption of NH3 on a sample was conducted at 373 K, followed by evacuation for 0.5 h. The amount of NH3 adsorbed on the sample was estimated by the difference between the total and reversible amounts of adsorbed NH3 . The adsorbed samples were heated at 10 K/min at temperatures ranging from 373 to 773 K. The pressure of desorbed ammonia was recorded using an ion gauge vacuum meter. 2.2.5. Infrared spectroscopy for the adsorption of pyridine on the HBEA catalysts The infrared (IR) spectra of the pyridine adsorbed on each catalyst were recorded using an in situ Pyrex glass cell equipped with KBr single-crystal windows. A sample disk with a diameter of 13 mm was compression-molded from 20 mg of -zeolite powder. The specimen was evacuated at 723 K for 2 h in the static vacuum system, followed by rapid transfer into the in situ IR cell with subsequent evacuation at 523 K for 2 h in vacuo. After pretreatment, pyridine was adsorbed at room temperature for 30 min, and the sample was evacuated at 523 K for 1 h. A total of 1000 scans for the sample IR spectra were recorded on a Nicolet 380 FTIR spectrometer, equipped with a highly sensitive MCT detector. The resolution of the spectrometer was 4 cm−1 . 2.3. Catalytic test 2.3.1. Baeyer–Villiger oxidation of cyclic ketones with H2 O2 The BV oxidation of cyclobutanone with H2 O2 was performed in an Erlenmeyer flask fitted with a condenser. Cyclobutanone (0.15 mL, 2.2 mmol, Tokyo Chemical Industry), 30% of a H2 O2 aqueous solution (0.18 mL, 2.2 mmol, Wako), acetonitrile (4 mL, Nacalai
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
3
Table 1 Physical properties of synthesized -zeolite with various Al content. Entry
1 2 3 4 5 6 7 8 a
Al content [mol/g]
Si/Al ratio
Surface area
Initial gel
Analysisa
Initial gel
Analysisa
[m2 /g]
119 165 208 327 407 598 798 932
117 169 200 335 418 578 782 890
139 100 79 50 40 27 20 17
141.2 97.3 82.5 48.6 39.0 27.0 20.3 17.0
552 562 540 520 551 470 520 470
Evaluated by XRF analysis.
Tesque), and 10 mg of catalysts were charged into the reactor. The reactor, equipped with a condenser, was purged several times with N2 to attain anaerobic atmosphere. The reactor was heated at 303 K for 2 h in a thermostatically controlled oil bath. After reaction, 1.0 mL of ethanol, serving as the internal standard, was injected into the solution, and the reaction mixture was centrifuged to separate the catalysts. Products were analyzed by GC-FID (GC-18A, Shimadzu) equipped with a G-300 column (Chemicals Evaluation and Research Institute, Japan). The oxidation of cyclohexanone with H2 O2 was performed in the same manner as that described above for the oxidation of cyclobutanone. The utilized reaction conditions were as follows: 0.2 mL of cyclohexanone (2.0 mmol, Nacalai Tesque), 0.1 mL of 30% H2 O2 , 4.0 mL of acetonitrile, and 20 mg of catalysts. The reaction was performed at 303 K for 3 h. For the BV oxidation of cyclohexanone over the mixture of rHBEA37.5 and ␥-Al2 O3 catalysts, the desired amount of ␥-Al2 O3 was added into the reaction mixture for BV oxidation.
2.3.2. Hydrolysis of -caprolactone The hydrolysis of -caprolactone was performed in a manner similar to that performed for the BV oxidation of cyclohexanone by using -caprolactone instead of cyclohexanone.
3. Results and discussion 3.1. Physical properties of the HBEA catalysts Table 1 summarizes the compositions of the as-prepared HBEA catalysts and their surface areas as calculated by the BET method. The synthesized HBEA catalysts consisted of various contents of Al from 117 to 890 mol/g. The surface areas of these samples ranged between 470 and 562 m2 /g. With increasing Al content, the surface area of the HBEA catalysts decreased at the higher Al content in HBEA catalysts. Fig. 1 shows the powder XRD patterns of the HBEA catalysts with various Al contents. The BEA structure was clearly observed for each catalyst. The unidentified peak at ca. 20◦ of 2 was observed for HBEA97.3 and HBEA141.2 catalysts. Although this peak is probably due to the presence of impurities and/or the interlayer stacking disorder in zeolite beta family [23], we cannot reach the identification in this study. For the HBEA catalysts with Al contents greater than 418 mol/g (Si/Al ratio of 39.0), peak intensity decreased with increasing Al content in the HBEA catalysts, attributed to decreased crystallinity and/or crystal size. Figure S1 shows the N2 adsorption isotherms of HBEA catalysts with Si/Al of 17.0, 20.3, 39.0 and 97.3, and their micropore volume estimated by a t-plot method. The estimated micropore volume of each catalyst showed almost constant value regardless of Si/Al atomic ratios. From the results of XRD and micropore volume, the crystal size of HBEA17.0 and HBEA20.3 was suggested to be smaller.
Fig. 1. XRD patterns of HBEA catalysts with various Al content.
3.2. Acidic properties of the HBEA catalysts Figure S2 shows the amount of adsorbed ammonia over the HBEA catalysts with various Al contents. Notably, the values obtained also include the amount of adsorbed ammonia on the non-acid sites [24–26], implying that the amount of irreversible adsorbed NH3 does not reflect the actual amount of acid sites in the HBEA catalysts. Fig. 2 shows the TPD spectra of adsorbed NH3 over the HBEA catalysts with various Al contents. Four peaks were observed at 413, 463, 563, and temperature greater than 673 K, respectively, with peak overlap. The peak observed at 413 K has been reported to be attributed to the interaction between ammonia molecules and the NH3 species adsorbed on the acid sites, namely, this NH3 species is adsorbed on non-acidic sites [24–26]. For precisely evaluating the amount of acid sites, this peak was extracted from the entire TPD spectra. On the other hand, the remaining three peaks observed at 463, 563, and temperature greater than 673 K were referred to as l, h, and h+ , respectively [27,28]; these peaks are typically observed in the NH3 -TPD profile of -zeolite. Niwa et al.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8 4
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
Fig. 3. Relationship between Al content of HBEA catalysts and the amount of acid sites.
Fig. 2. TPD spectra of NH3 adsorbed on HBEA catalysts with various Al content.
have reported that these desorbed ammonia peaks are attributed to weakly adsorbed NH3 on the Lewis acid sites, NH4 + on the Brønsted acid sites, and strongly adsorbed NH3 on the acid sites, respectively, as confirmed by the IRMS-TPD measurement of -zeolite [27]. This result indicated that l, h, and h+ peaks are related to the desorption of NH3 from the acid sites in the HBEA catalysts. Notably, NH3 species strongly adsorbed on acid sites (h+ peak) is desorbed in the complete temperature range during IRMS-TPD [27], indicating that the Brønsted and Lewis acid sites on the HBEA catalysts cannot be directly distinguished by NH3 -TPD measurements. Hence, the amount of NH3 corresponding to the l, h, and h+ peaks is evaluated by calculation from the total amount of adsorbed NH3 and the fraction of the l, h, and h+ peak areas from the total desorption spectrum. Moreover, the NH3 -TPD spectra for HBEA catalysts with various Al contents were analyzed on the basis of typical Gaussian distribution for extracting the physisorbed NH3 species (see Fig. S3). Fig. 3 shows the dependence of Al content in the HBEA catalysts on the total amount of acid sites. As shown in Fig. 3, the dashed line denotes an equivalent relationship between the Al content and the amount of total acid sites. The total amount of acid sites were almost equivalent to an Al content of up to 418 mol/g (Si/Al ratio of 39.0). At Al contents greater than 418 mol/g, the total amount of acid sites decreased as compared to the Al content, and the difference between the Al content and the total acid sites increased with increasing Al content. These results suggested that the excess Al introduced into the HBEA catalysts hardly serves as the acid sites at Al contents greater than 418 mol/g (Si/Al ratio of 39.0). Fig. 4 shows the FTIR spectra of the pyridine adsorbed on the HBEA catalysts with various Al contents. An IR band was observed at 1547 cm−1 , attributed to pyridine adsorbed on Brønsted acid sites (PyB) [29–33]. Three pyridine species were observed in the range between 1430 and 1470 cm−1 . Bands were observed at 1438,
Fig. 4. FT-IR spectra of adsorbed pyridine on HBEA catalysts with various Al content.
1445, and 1455 cm−1 , attributed to gaseous pyridine and/or physically adsorbed pyridine on the surface, hydrogen-bonded pyridine, and pyridine adsorbed on the Lewis acid sites (PyL), respectively [29–33]. Another band was observed at 1491 cm−1 , attributed to the superposition of signals of pyridine adsorbed on both Brønsted and Lewis acid sites [29–33]. Moreover, the bands observed at 1430–1470 cm−1 were analyzed on the basis of typical Gaussian distribution for extracting the PyL band (Fig. S4). The concentrations of the Brønsted and Lewis acid sites were calculated via the
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
5
Fig. 5. Relationship between Al content of HBEA catalysts and the amount of Brønsted and Lewis acid sites estimated by the combination of NH3 -TPD and FTIR of adsorbed pyridine.
integration of the area corresponding to the PyB and PyL bands observed at 1547 and 1455 cm−1 , respectively. Fig. 5 shows the relationship between the Al content in the HBEA catalysts and the amount corresponding to each of Brønsted and Lewis acid sites as estimated by the combination of the amount of adsorbed NH3 on the acid sites (Fig. 3) and the concentrations of Brønsted and Lewis acid sites calculated from FTIR measurements. With increasing Al content of up to 418 mol/g (Si/Al ratio of 39.0), the amount of Brønsted acid sites increased, which was maintained constant at Al contents greater than 418 mol/g. In addition, with increasing Al content, the amount of Lewis acid sites gradually increased. These results suggested that the excess of Al species introduced into the HBEA catalysts serves as Lewis acid sites at an Al content greater than 418 mol/g. The amount of octahedral aluminum species has been reported to increase with decreasing Si/Al ratio (i.e., increasing Al content) [34]. Lavalley et al. and Detka et al. have independently reported that the Lewis acid sites in zeolites are possibly related to the extraframework Al species as the concentration of the Lewis acid sites, as compared with that of Brønsted acid sites, rapidly decreases after acid treatment [33,35]. These results suggested that the extraframework Al species are formed, which serve as the Lewis acid sites at Al contents greater than 418 mol/g (Si/Al ratio of 39.0). 3.3. Relationship between the acidity and performance of the HBEA catalysts for the BV oxidation of cyclobutanone Scheme 1 outlines the proposed reaction pathway for the BV oxidation of cyclobutanone. In the BV oxidation of cyclobutanone, ␥-butyrolactone was detected as the only product as confirmed by GC-FID. Some parts of the undetectable products, attributed to the polymerized product, should also be considered. Fig. 6 shows the catalytic performance of the prepared HBEA catalysts with various Al contents for the BV oxidation of cyclobutanone using H2 O2 . As shown in Fig. 6a, the conversion of cyclobutanone and yield of ␥-butyrolactone increased with increasing Al content of up to 418 mol/g (Si/Al ratio of 39.0), and marginally decreased at Al contents greater than 418 mol/g. The excess Al species introduced into the HBEA catalysts was not found to be effective for the BV oxidation. At Al contents of up to 418 mol/g (Si/Al = 39.0), the selectivity of ␥-butyrolactone was maintained at approximately 90%, followed by marginal decrease at Al contents greater than 418 mol/g (Fig. 6a). Notably, carbon
Fig. 6. BV oxidation of cyclobutanone over HBEA catalysts with various Al content.
balance over all catalysts was approximately 95% (not shown in figure). These results suggested that the successive hydrolysis of ␥-butyrolactone is difficult under the currently employed experimental conditions. Fig. 6b shows the conversion and efficiency of H2 O2 . The trend observed for H2 O2 conversion was quite similar to that observed for cyclobutanone conversion. H2 O2 efficiency was defined as the percentage of consumed H2 O2 for the formation of lactones. From the results, approximately a 100% H2 O2 efficiency was obtained over all HBEA catalysts. This result strongly indicated that H2 O2 is almost consumed during the BV oxidation of cyclobutanone, and its self-decomposition hardly proceeds over HBEA catalysts irrespective of Al content. Hence, the use of cyclobutanone as the reactant for the BV oxidation is advantageous for elucidating the role of the Brønsted acid sites in the HBEA catalysts as compared with the use of cyclohexanone as the reactant, because the effect of the successive hydrolysis on the catalytic performance for the BV oxidation over the HBEA catalysts can be excluded (Scheme 2). Fig. 7 shows the correlation between the amount of the Brønsted acid sites and the conversion of cyclobutanone and H2 O2 for the BV oxidation of cyclobutanone using HBEA catalysts with various Al contents. Notably, the dependence of Al content on the conversion of cyclobutanone and H2 O2 and the amount of Brønsted acid sites in the HBEA catalysts exhibited similar trends. As has
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8 6
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
Scheme 1. Reaction pathway of BV oxidation of cyclobutanone.
Scheme 2. Reaction pathway of BV oxidation of cyclohexanone.
Fig. 7. Correlation between the amount of Brønsted acid sites and the conversion of cyclobutanone and H2 O2 for BV oxidation of cyclobutanone over HBEA catalysts with various Al content.
been mentioned in our previous study, the Brønsted acid sites in these HBEA catalysts possibly activate H2 O2 and facilitate the BV oxidation, as demonstrated by the results obtained from the FTIR measurement of H2 O2 adsorbed on the HBEA catalysts and the BV oxidation of cyclohexanone over Na+ -exchanged -zeolites with varying percentages of ion-exchanged Na+ [15]. These results strongly suggested that the Brønsted acid sites in the HBEA catalysts play a crucial role as active sites for the BV oxidation of cyclobutanone with H2 O2 . 3.4. Relationship between the acidity and performance of the HBEA catalysts for the BV oxidation of cyclohexanone For the BV oxidation of cyclohexanone, -caprolactone (target molecule) was obtained as the main product, with low amounts of ␦-hexanolactone and 6-hydroxycaproic acid (representing the hydrolyzed product of -caprolactone) also detected. Some parts of the undetectable products, attributed to the polymerized product, should also be investigated. Fig. 8 shows the catalytic activity of the HBEA catalysts with various Al content for the BV oxidation of cyclohexanone with H2 O2 . At an Al content of up to 418 mol/g (Si/Al ratio of 39.0), the conversion of cyclohexanone and yield of -caprolactone increased, followed by gradual decrease at Al contents greater than 418 mol/g (Fig. 8a). On the other hand, at an Al content of up to 418 mol/g, the selectivity of -caprolactone was maintained at approximately 50%, followed by gradual decrease at Al contents
Fig. 8. BV oxidation of cyclohexanone over HBEA catalysts with various Al content.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
7
Fig. 9. Correlation between the amount of Lewis acid sites and the selectivity of -caprolactone for BV oxidation of cyclohexanone over HBEA catalysts with various Al content.
greater than 418 mol/g (Fig. 8a). Fig. 8b shows the conversion and efficiency of H2 O2 . At an Al content of up to 418 mol/g, H2 O2 efficiency was maintained at approximately 55%, followed by gradual decrease at Al contents greater than 418 mol/g (Fig. 8b). The trend observed for H2 O2 conversion was similar to that observed for cyclohexane conversion. These results implied that the excess Al species introduced into the HBEA catalysts are not effective for the BV oxidation of cyclohexanone and facilitate side reactions, such as hydrolysis and polymerization. The different Si/Al ratio where the maximum yield of caprolactone was obtained was observed between in this work (Si/Al = 39.0) and in our previous study (Si/Al = 84.3) [15]. In the previous study, we have mainly focused on understanding where Baeyer–Villiger oxidation of cyclohexanone proceeds on in HBEA catalysts. The range of Al content in HBEA catalysts, which the successive hydrolysis reaction hardly proceeded, has been employed. Additionally, we have regarded all the introduced Al3+ species in HBEA catalyst as Brønsted acid site in the previous study. Since the decrease of yield has been observed over the HBEA catalyst with Si/Al ratio of 55, we have assumed that the optimum Si/Al ratio is 85, and have not made the investigation into HBEA catalysts with Si/Al ratios smaller than 55 in the previous work. Therefore, we could not reach finding the actual optimum Si/Al ratio which showed the maximum yield of -caprolactone in the previous work. As mentioned earlier (Fig. 5), at Al contents greater than 418 mol/g, the amount of Lewis acid sites significantly increased. Thus, the Lewis acid sites adversely affect the catalytic performance of the HBEA catalysts for the BV oxidation of cyclohexanone. Fig. 9 shows the correlation between the amount of Lewis acid sites and the selectivity of -caprolactone for the BV oxidation of cyclohexanone over HBEA catalysts with various Al contents. Notably, with increasing the amount of Lewis acid sites at Al contents greater than 418 mol/g, the selectivity of -caprolactone decreased. As ester hydrolysis is well known to occur with protonic acids or bases, it would not be expected that the Lewis acid site itself catalyzes the hydrolysis reaction of -caprolactone. As described above, the Lewis acid sites in zeolites can be related to the extra-framework Al species. Furthermore, the extra-framework Al species has been reported to be composed of several aluminum species [36]. Hence, a part of the extra-framework species accelerates the successive hydrolysis of -caprolactone. For investigating the effect of the extra-framework Al species on the catalytic performance of the HBEA catalysts for the BV oxidation of cyclohexanone, ␥-Al2 O3 was added to the reaction mixture. The HBEA catalyst with a Si/Al ratio of 37.5 (rHBEA37.5) obtained from Zeolyst International and ␥-Al2 O3 (JRC-ALO-8) supplied by
Fig. 10. Dependence of the amount of added Al2 O3 to reaction mixture on the catalytic performance for BV oxidation of cyclohexanone over HBEA catalyst with a Si/Al ratio of 37.5 (rHBEA37.5).
Table 2 Hydrolysis reaction of -caprolactone over each catalyst. Entry
Catalysts
Conversion of -caprolactone [%]
1 2 3
– Al2 O3 rHBEA37.5
0 0 6.2
the Catalysis Society of Japan were used. Since the catalytic performance for BV oxidation of cyclobutanone and cyclohexanone (Table S1 and S2, respectively) and NH3 -TPD spectrum over the rHBEA37.5 (Fig. S5) were similar to that over the HBEA39.0, the rHBEA37.5 catalyst was employed as a referential sample instead of HBEA39.0 in this study. Fig. 10 shows the effect of the amount of added ␥-Al2 O3 on the catalytic activity of the HBEA catalysts used for the BV oxidation of cyclohexanone. With increasing addition of ␥-Al2 O3 , the conversions of cyclohexanone and H2 O2 were maintained constant regardless of the amount of the added ␥-Al2 O3 , whereas the yield and selectivity of -caprolactone gradually decreased. These results clearly suggested that the aluminum oxides added to the reaction mixture facilitate the successive hydrolysis of -caprolactone. Table 2 summarizes the results obtained from the hydrolysis of -caprolactone over each catalyst. In the blank test (i.e. without catalysts) and using ␥-Al2 O3 , no conversion for -caprolactone was observed (Entries 1 and 2, respectively). The hydrolysis of caprolactone proceeded over HBEA with a Si/Al ratio of 37.5 (Entry 3). These results strongly suggested that the co-existence of the extra-framework Al species and HBEA catalysts leads to the acceleration of the successive hydrolysis of -caprolactone for the BV oxidation of cyclohexanone. At Al contents greater than 418 mol/g, the different trends of conversions of reactants and H2 O2 were observed by using different cyclic ketones; the conversions of cyclohexanone and H2 O2 decreased (Fig. 8), whereas that of cyclobutanone and H2 O2 insignificant decreased (Fig. 6). Since the conversion of cyclohexanone and H2 O2 decreased with increasing the amount of Lewis acid sites, these behavior were apparently attributed to the presence of extra-framework Al species. Nevertheless, their detailed behavior is currently under investigation.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026
G Model CATTOD-10615; No. of Pages 8
ARTICLE IN PRESS K. Taniya et al. / Catalysis Today xxx (2017) xxx–xxx
8
4. Conclusions (1) For the BV oxidation of cyclobutanone, the catalytic activity of the HBEA catalysts with various Al contents depended on the amount of Brønsted acid sites. (2) Extra-framework Al species negatively affected not only the selectivity of lactones but also the catalytic activity of the HBEA catalysts. (3) The successive hydrolysis of lactones was attributed to the coexistence of extra-framework Al species and the HBEA catalysts. Acknowledgments We greatly appreciate Mr. Norihisa Kumagai, Faculty of Engineering, Kobe University for the kind assistance with NH3 -TPD and FTIR measurements. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.cattod.2017.02. 026. References [1] C. Jiménez-Sanchidrián, J.R. Ruiz, Tetrahedron 64 (2008) 2011–2026. [2] H. Heaney, in: S.D. Burke, R.L. Danheiser (Eds.), Handbook of Reagents for Organic Synthesis—Oxidizing and Reducing Agents, Wiley, 1999, pp. 84–89. [3] G.-J. ten Brink, I.W.C.E. Arends, R.A. Sheldon, Chem. Rev. 104 (2004) 4105–4123. [4] A. Bhaumik, P. Kumar, R. Kumar, Catal. Lett. 40 (1996) 47–50. [5] R. Kumar, A. Bhaumik, Micropor. Mesopor. Mater. 21 (1998) 497–504. [6] A. Corma, L.T. Nemeth, M. Renz, S. Valencia, Nature 412 (2001) 423–425. [7] S.R. Bare, S.D. Kelly, S. Sinkler, J.J. Low, F.S. Modica, S. Valencia, A. Corma, J. Am. Chem. Soc. 127 (2005) 12924–12932. [8] P. Li, G. Liu, H. Wu, Y. Liu, J. Jiang, P. Wu, J. Phys. Chem. B 115 (2011) 3663–3670.
[9] A. Corma, M.T. Navarro, M. Renz, J. Catal. 219 (2003) 242–246. [10] M. Sasidharan, Y. Kiyozumi, N.K. Mal, M. Paul, P.R. Rajamohanan, A. Bhaumik, Micropor. Mesopor. Mater. 126 (2009) 234–244. [11] T. Chen, B. Wang, Y. Li, L. Liu, S. Qiu, J. Porous Mater. 22 (2015) 949–957. [12] Z.B. Wang, T. Mizusaki, Y. Kawakami, Bull. Chem. Soc. Jpn. 70 (1997) 2567–2570. [13] J. Fischer, W.F. Hölderich, Appl. Catal. A: Gen. 180 (1999) 435–443. [14] M. Lenarda, M. Da Ros, M. Casagrande, L. Storaro, R. Ganzerla, Inorg. Chim. Acta 349 (2003) 195–202. [15] R. Ohno, K. Taniya, S. Tsuruya, Y. Ichihashi, S. Nishiyama, Catal. Today 203 (2013) 60–65. [16] Z.Q. Lei, G.F. Ma, C. Jia, Catal. Commun. 8 (2007) 305–309. [17] U.R. Pillai, E.S. Demessie, J. Mol. Catal. A: Chem. 191 (2003) 93–100. [18] T. Hara, M. Hatakeyama, A. Kim, N. Ichikuni, S. Shimazu, Green Chem. 14 (2012) 771–777. [19] J.C. Sanchidrian, J.M. Hidalgo, R. Llamas, J.R. Ruiz, Appl. Catal. A: Gen. 312 (2006) 86–94. [20] C. Palazzi, F. Pinna, G. Strukul, J. Mol. Catal. A: Chem. 151 (2000) 245–252. [21] C. Li, J. Wang, Z. Yang, Z. Hu, Z. Lei, Catal. Commun. 8 (2007) 1202–1208. [22] H. Jon, B. Lu, Y. Oumi, K. Itabashi, T. Sano, Micropor. Mesopor. Mater. 89 (2006) 88–95. [23] http://asia.iza-structure.org/IZA-SC/ds.htm. [24] N. Katada, S. Iijima, H. Igi, M. Niwa, Stud. Surf. Sci. Catal. 105 (1996) 1227–1234. [25] F. Lónyi, J. Valyon, Micropor. Mesopor. Mater. 47 (2001) 293–301. [26] N. Katada, H. Igi, J. Kim, M. Niwa, J. Phys. Chem. B 101 (1997) 5969–5977. [27] M. Niwa, S. Nishikawa, N. Katada, Micropor. Mesopor. Mater. 82 (2005) 105–112. [28] H. Matsuura, N. Katada, M. Niwa, Micropor. Mesopor. Mater. 66 (2003) 283–296. [29] Y. Miyamoto, N. Katada, M. Niwa, Micropor. Mesopor. Mater. 40 (2000) 271–281. [30] W. Wu, E. Weitz, Appl. Surf. Sci. 316 (2014) 405–415. [31] M.I. Zaki, M.A. Hasan, F.A. Al-Sagheer, L. Pasupulety, Coll. Surf. A Physicochem. Eng. Asp. 190 (2001) 261–274. [32] J.P. Marques, I. Gener, P. Ayrault, J.C. Bordado, J.M. Lopes, F. Ramôa Ribeiro, M. Guisnet, Micropor. Mesopor. Mater. 60 (2003) 251–262. [33] M. Guisnet, P. Ayrault, C. Coutanceau, M.F. Alvarez, J. Datka, J. Chem. Soc., Faraday Trans. 93 (1997) 1661–1665. [34] A. Abraham, S. Lee, C. Shin, S.B. Hong, R. Prins, J.A. van Bokhoven, Phys. Chem. Chem. Phys. 6 (2004) 3031–3036. [35] M. Maache, A. Janin, J.C. Lavalley, J.F. Joly, E. Benazzai, Zeolites 13 (1993) 419–426. [36] R.D. Shannon, K.H. Gardner, R.H. Staley, J. Phys. Chem. 89 (1985) 4778–4788.
Please cite this article in press as: K. Taniya, et al., Role of Al3+ species in beta zeolites for Baeyer–Villiger oxidation of cyclic ketones by using H2 O2 as an environmentally friendly oxidant, Catal. Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.02.026