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Octene hydroformylation by using rhodium complexes tethered onto selectively functionalized mesoporous silica and in situ high pressure IR study
Catalysis Today 164 (2011) 561–565
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Octene hydroformylation by using rhodium complexes tethered onto selectively functionalized mesoporous silica and in situ high pressure IR study Ki-Chang Song a , Ji Yeon Baek a , Jung A Bae b , Jin-Heong Yim b,∗ , Young Soo Ko a , Do Heui Kim c , Young-Kwon Park d , Jong-Ki Jeon a,∗∗ a
Department of Chemical Engineering, Kongju National University, 275 Budae-dong, Cheonan 331-717, Republic of Korea Division of Advanced Materials Engineering, Kongju National University, 275 Budae-dong, Cheonan 331-717, Republic of Korea Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352, USA d School of Environmental Engineering, Graduate School of Energy and Environmental System Engineering, University of Seoul, Dongdaemun-Gu, Seoul 130-743, Republic of Korea b c
a r t i c l e
i n f o
Article history: Available online 17 November 2010 Keywords: Heterogeneous rhodium catalyst SBA-15 Octene hydroformylation FT-IR
a b s t r a c t SBA-15-based heterogeneous catalysts were applied to 1-octene hydroformylation. The turn over frequency over SBA-15/␥-aminopropylmethyldimethoxysilane (AEAPMDMS)/Rh catalyst with triphenylphosphine (TPP) ligand prepared by conventional post grafting method was higher than that of the homogeneous catalyst, (Rh(CH3 COO)2 )2 with TPP. The SBA-15/AEAPMDMS/Rh catalyst can be easily recycled without rhodium loss. The molar ratio of linear to branched nonyl aldehydes was remarkably enhanced over the heterogeneous catalysts. The selectively functionalized rhodium catalyst (SBA15/Ph2 Si(OEt)2 /AEAPMDMS/Rh), in which rhodium was selectively tethered intra-pore of SBA-15, was beneficial for improving the selectivity to linear aldehyde. In situ high pressure FT-IR analysis suggested HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 to be active species over the SBA-15/AEAPMDMS/Rh catalyst with TPP. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Higher aldehydes and alcohols are very important high-value added substances in the chemical industry. Recently, there is growing interest in producing nonyl aldehydes through hydroformylation of octene compounds in the presence of hydrogen and carbon monoxide [1–4]. Homogeneous complex catalysts such as rhodium complex containing phosphorous ligands have been considered as an excellent catalyst for the hydrofomylation due to high activity obtained at mild reaction conditions [5]. In order to facilitate separation, recovery and recycling of catalyst, a lot of studies have been performed about rhodium catalysts supported in porous organic or inorganic supports such as polymeric resin [6,7], SiO2 [8,9] and hydrotalcite [10]. It is necessary, however, to develop a heterogeneous catalyst to present more superior activity and stability in comparison with the homogeneous catalysts. In addition, it is really important to enhance the ratio of linear to branched aldehydes (hereinafter designated L/B), because among isomers of the aldehydes produced, linear aldehyde is commercially more valuable than branched aldehydes.
Mesoporous silica has an ordered structure with a large surface area, thereby immobilizing a lot of metal complexes and having highly dispersed active sites for catalytic reaction. In addition, its pore size is larger than microporous supports, thereby leading to a shape selective reaction in production of aldehydes with high molecular weight [11]. Immobilization of rhodium complexes on the mesoporous supports has been widely studied in the last several decades [12–15]. Also the study on the surface functionalization of mesoporous materials has grown significantly [16,17]. Among these useful functional groups, amino groups show fairly good performance for 1-octene hydroformylation catalysts [18]. This study aims to immobilize the rhodium complexes to SBA-15 for a catalyst producing nonyl aldehydes through hydroformylation of 1-octene. We tried to enhance the ratio of linear to branched aldehydes through the selectively tethered rhodium to surface of mesoporous material. In addition, active species of the heterogeneous catalysts were investigated by using in situ high-pressure FT-IR measured during the in situ reaction at high pressure and high temperature. 2. Experimental
∗ Corresponding author at: Kongju National University, 275 Budae-dong, Cheonan 330-717, Republic of Korea. Tel.: +82 41 521 9397. ∗∗ Corresponding author at: Kongju National University, 275 Budae-dong, Cheonan 330-717, Republic of Korea. Tel.: +82 41 521 9363. E-mail addresses: [email protected] (J.-H. Yim), [email protected] (J.-K. Jeon). 0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2010.10.065
2.1. Catalyst preparation SBA-15 was synthesized according to the previous literature [19]. A conventional post grafting method and a selective functionalized method have been applied to mod-
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ify SBA-15. The post grafting method, which included reflux in a non-polar solvent in the presence of N(-aminoethyl) ␥aminopropylmethyldimethoxysilane (AEAPMDMS, GE Advanced Materials), was used. 0.5 g of as-synthesized SBA-15 was dispersed in 75 ml of toluene for 0.5 h at 50 ◦ C with stirring. After 3.5 mg of p-toluenesulfonic acid and 1.0 mmol of AEAPMDMS were added, the mixture was heated up to reflux temperature (nearly 120 ◦ C) and kept stirring for 2 h. After refluxing for 2 h the solid product was filtered, washed with ethanol several times. The resulting solid was dried at 100 ◦ C for 12 h. 1 g of amine functionalized SBA-15 was added to a solution of 0.037 g Rh4 (CO)12 in n-hexane under N2 . The mixture was stirred at room temperature under N2 atmosphere for 5 h. Finally the resulting solid was dried under vacuum and henceforth designated as SBA-15/AEAPMDMS/Rh. A selective functionalized method was applied for selectively tethering rhodium onto the internal surface (in pores). The as-calcined SBA-15 (3.0 g) was then dispersed in 80 mL of toluene and stirred at 50 ◦ C for 0.5 h. After sufficient immersion, 0.021 g of p-toluenesulfonic acid and 6.0 mmol of Ph2 Si(OEt)2 were added sequentially and stirred at 120 ◦ C for 2 h. The isolated solid product was washed with ethanol three times and dried at 100 ◦ C for 12 h, resulting in external grafting. For the internal grafting process, 3.0 g of SBA-15/Ph2 Si(OEt)2 was added to 80 mL of toluene. After stirring at 50 ◦ C for 0.5 h, 0.021 g of p-toluenesulfonic acid and 6.0 mmol of AEAPMDMS were added and the mixture was refluxed at 120 ◦ C for 2 h. The solid product was filtered and washed with ethanol three times. Then, the selective functionalized mesoporous silica SBA-15 was dried at 100 ◦ C for 12 h. For the purposes of Rh immobilization, the same process was performed. The final solid was designated as SBA15/Ph2 Si(OEt)2 /AEAPMDMS/Rh.
3. Results and discussion 3.1. Textural properties of catalysts Nitrogen adsorption–desorption isotherms of the catalysts are shown in Fig. 1(a). All catalysts showed typical type IV isotherms with type-H1 hysteresis loop at P/P0 of between 0.5 and 0.7. The steep slope and sharp step are typical of multilayered adsorption followed by capillary condensation in well-ordered channel-like mesopores [20]. Despite the decrease in the amount of nitrogen adsorbed, the shape of hysteresis loop is almost same. It means that the pore shape may not be significantly changed through silane functionalization process and additional rhodium immobilization processes. In addition, the ordered hexagonal structures of the immobilized rhodium catalysts were confirmed with small-angle XRD results (Fig. 2). Textural properties of catalysts prepared in this study were displayed in Table 1. The BET surface areas of functionalized SBA15 materials decrease with functionalization and the subsequent immobilization process, because functionalized silanes and immobilized rhodium are attached to the surface of the mesoporous material. The pore volume of the rhodium-immobilized catalyst was greatly decreased, confirming that a tethering agent blocked pores of SBA-15, resulting in the reduction of surface area. The pore size distribution was shown in Fig. 1(b). The immobilized
2.2. Catalysts characterization Nitrogen adsorption–desorption isotherms were determined using a Micromeritics ASAP 2020 at −196 ◦ C. The surface area was calculated according to the BET equation. The pore volume was obtained from t-plot method. Small-angle powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/max-2500 X-ray diffractometer. 2.3. Catalytic reactions and in situ high-pressure FT-IR analysis 0.165 g of catalysts was added to a stainless steel autoclave reactor (80 mL) containing 50 ml THF and 4.26 g of 1-octene. And then 0.044 g of triphenylphosphine (PPh3 , TPP) was added to the mixture as a ligand. In the case of homogeneous catalytic reaction, we used (Rh(CH3 COO)2 )2 as a precursor for a homogeneous Rh catalyst for octene hydroformylation because (Rh(CH3 COO)2 )2 is not only stable in air, but also relatively inexpensive in comparison with those of other rhodium precursors, Rh(CO)4 , Rh6 (CO)16 , Rh4 (CO)12 , or Rh(acac)(CO)2 [3]. Subsequently, the autoclave was sealed and flushed with nitrogen gas. Syn-gas (CO/H2 = 1) was pressurized up to 20 bar in the reactor, and then the reactor was heated to 120 ◦ C. The reactor was kept at that temperature, and the syn-gas was filled up from a reservoir to maintain the pressure of 20 bar. After the completion of the reaction, the resulting products were analyzed by gas chromatography (GC-2014, Shimadzu). A home-made IR cell was used to observe the intermediates of 1-octene hydroformylation occurred in liquid phase. The IR cell was made of stainless steel and CaF2 windows, operating up to 400 ◦ C and 20 bar. Temperature was measured with a thermocouple and controlled by an external temperature controller. Spectrum GX (Perkinelmer) with an MCT detector was used for IR spectrum.
Fig. 1. (a) Nitrogen adsorption/desorption isotherms of SBA-15 (䊉: adsorption, : desorption), SBA-15/AEAPMDMS/Rh (: adsorption, : desorption), (:adsorption, : desorption), (b) SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh Pore size distribution of SBA-15 (), SBA-15/AEAPMDMS/Rh (), SBA15/Ph2 Si(OEt)2 /AEAPMDMS/Rh ().
K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
563
intensity
SBA-15 SBA-15 / AEAPMDMS/Rh SBA-15 / Ph2Si(OEt)2 / AEAPMDMS/Rh
1
2
3
4
5
2θ Fig. 2. XRD patterns.
rhodium catalysts had smaller pore size than that of SBA-15. Internal pores of two catalysts were functionalized using AEPMDMS, therefore, the degree of reduction in surface area and pore volume was similar in both nonselectively functionalized catalyst (SBA-15/AEAPMDMS/Rh) and selectively functionalized catalyst (SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh). 3.2. Hydroformylation of 1-octene Fig. 3 presented conversion, yield and selectivity in hydroformylation of 1-octene using SBA-15/AEAPMDMS/Rh with TPP ligand. 1-octene conversion and yield of nonyl aldehydes increased with reaction time and reached maximum after 30 min. The selectivity to nonyl aldehydes and octane isomers, which are desired products of 1-octene hydroformylation, and by-products through isomerization of 1-octene, respectively, were not significantly changed with reaction time. In addition, the molar ratio of linear to branched nonyl aldehydes (L/B) was not much varied with reaction time. Fig. 4 exhibited turn over frequency (TOF), nonyl aldehyde yield and L/B after 30 min of hydroformylation. The TOF of SBA-15/AEAPMDMS/Rh with TPP, non-selectively functionalized catalyst, was higher than that of the homogeneous catalyst (Rh(CH3 COO)2 )2 with TPP. It can be attributed to the high dispersion of active sites tethered onto mesoporous silica having a large surface area. The TOF of SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh with TPP, selectively functionalized catalyst, was lower than that of the non-selectively functionalized catalyst. Because rhodium active sites are tethered onto inner surface of the selectively functionalized catalyst, it appears to be limited by mass transfer of the reactant, compared to the non-selectively functionalized catalyst. The molar ratio of linear to branched nonyl aldehydes (L/B) was 0.8 in hydroformylation reaction over the homogeneous catalyst.
Fig. 3. Conversion of 1-octene, yield of nonyl aldehyde, and selectivity over SBA15/AEAPMDMS/Rh catalyst (reaction condition: 20 bar and 120 ◦ C, TPP/Rh = 20).
L/B were enhanced over the SBA-15/AEAPMDMS/Rh with TPP and the SBA-15/Ph2 Si(OEt)2 / AEAPMDMS/Rh, 2.5 and 2.8, respectively. It is remarkable that L/B can be enhanced by the selectively functionalized catalyst. It suggested that the catalyst in which rhodium was selectively tethered inside pores was beneficial for improving the selectivity to linear aldehyde, compared to the catalyst that rhodium was non-selectively immobilized inside and outside mesopores. It is well known that when bulky phosphine ligands are used in hydroformylation of higher olefins, it improves productivity of the linear aldehyde because of steric effects [21]. It may be interpreted that such steric effects are greater due to rhodium complex tethered inside the mesopore, thereby increasing the L/B, which are more clearly observed in the selectively functionalized catalyst. In addition to the catalytic activity, it is necessary to reduce the amount of rhodium loss during recycling of catalysts from the economic point of view, because the amount of rhodium loss during this process is very important factor of production cost. The results of recycling of SBA-15/AEAPMDMS/Rh with TPP were shown in Table 2. The nonyl aldehydes yield over the catalyst is not significantly changed upon the catalyst recycle. It is note-
Table 1 Textural properties of the catalysts. Catalyst
SBET (m2 g−1 )
Vtot (cm3 g−1 )
Pore size (nm)
Rh content (wt.%)a
SBA-15 SBA-15/AEAPMDMS SBA-15/AEAPMDMS/Rh SBA-15/Ph2 Si(OEt)2 SBA-15/Ph2 Si(OEt)2 /AEAPMDMS SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh
623 343 261 598 468 266
0.94 0.45 0.37 0.81 0.72 0.40
5.36 4.33 4.17 4.80 4.67 4.67
– – 0.92 – – 1.35
a
By ICP-AES with hydrofluoric acid treatment.
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3
a
2004
L/B
2
1945 1
0
60
3
-1
TOF (10 h )
4
40
2
20
A
C
B
D
Nonyl aldehyde yield (wt%)
80
6
0
absorbance
120 min 60 min 30 min 20 min 1978
10 min 5 min 2200
2100
2000
1900
Wavenumber (cm-1)
b
0
o
1945
2004
120 C
Catalyst o
100 C absorbance
Fig. 4. Turn over frequency (TOF), yield and L/B molar ratio of nonyl aldehyde on the 1-octene hydroformylation over the rhodium homogeneous and heterogeneous catalyst systems. (A: Homogeneous catalyst, [Rh(Ch3 COOH)2 ]2 + TPP, B: SBA-15/AEAPMDMS/Rh + TPP, C: SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh + TPP, D: SBA15/AEAPMDMS/Rh, Reaction condition: 20 bar and120 ◦ C, reaction time: 30 min, TPP/Rh = 20).
o
80 C
worthy, moreover, that rhodium in product was detected less than 0.5 ng/ml, suggesting that loss of rhodium during recycling is negligible. Consequently, the SBA-15/AEAPMDMS/Rh catalyst is believed to be easily recycled in comparison with the homogeneous catalysts. 3.3. High pressure in situ FT-IR analysis
o
50 C 2200
2100
2000
1900
-1
Wavenumber (cm ) The results of FT-IR analysis upon reaction time using SBA15/AEAPMDMS/Rh and TPP under 20 bar and 120 ◦ C were exhibited in Fig. 5(a). The peaks at 1945 cm−1 and 2004 cm−1 increased with reaction time, which could be assigned to HRh(CO)2 (PPh3 )2 and HRh(CO)(Ph3 P)3 , respectively [9,15,22]. According to previous results by Yan et al. [9], two broad peaks around 1938 and 2005 cm−1 appeared on HRhCO(PPh3 )3 /SiO2 . Also, Yan et al. [15] observed that two peaks at 1940 and 2000 cm−1 on HRhCO(PPh3 )3 /SBA-15. These results were well agreed with our results in Fig. 5(a). Fig. 5(b) displayed the FT-IR spectra of SBA15/AEAPMDMS/Rh with TPP, obtained during the reaction while ramping temperature at a rate of 5 ◦ C/min. The rhodium carbonyl complex in 1978 cm−1 observed at low temperature, then the characteristic peaks of HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 became apparent at 120 ◦ C. Meanwhile, it was difficult to fig-
Fig. 5. (a) Time-resolved FT-IR spectra obtained during the 1-octene hydroformylation over SBA-15/AEAPMDMS/Rh with TPP (reaction condition: 20 bar, 120 ◦ C), (b) FT-IR spectra obtained during temperature-programmed hydroformylation reaction of 1-octene over the SBA-15/AEAPMDMS/Rh with TPP (reaction condition: 20 bar).
ure out any other peaks except rhodium carbonyl complex at 1978 cm−1 in the FT-IR spectra of SBA-15/AEAPMDMS/Rh without ligand, obtained during the reaction while ramping temperature at a rate of 5 ◦ C/min, as shown in Fig. 6. It is noticeable that the heterogeneous catalyst without TPP ligand demonstrated very low activity in 1-octene hydroformylation as shown in Fig. 4. Therefore, TPP is thought to play an important role in readily forming active sites such as HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 which are only observed on the SBA-15/AEAPMDMS/Rh catalyst containing TPP.
Table 2 Yield of 1-octene hydroformylation and Rh loss during recovery of catalyst. Catalysta
Nonyl aldehyde yield (wt%)
L/Bb
Rh concentration in product (ng/ml)c
Fresh Recycled Recycled twice
69.1 68.6 66.7
2.5 2.6 2.6
<0.5 <0.5 <0.5
a b c
Catalyst: SBA-15/AEAPMDMS/Rh, TPP/Rh = 20. Molar ratio of linear nonyl aldehyde to branched nonyl aldehyde. Determined by ICP after removal of catalyst.
K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
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Acknowledgement This work was supported by Mid-career Researcher Program through NRF grant funded by the MEST (No. R01-2007-000-201440).
absorbance
120 ºC
References
100 ºC 80 ºC
1978 50 ºC 2200
2100
2000
1900
Wavenumber (cm -1) Fig. 6. FT-IR spectra obtained during temperature-programmed hydroformylation reaction of 1-octene over the SBA-15/AEAPMDMS/Rh without TPP (reaction condition: 20 bar).
4. Conclusions A non-selectively functionalized rhodium catalyst (SBA15/AEAPMDMS/Rh) and selectively functionalized rhodium catalyst (SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh) were used as heterogeneous catalysts in 1-octene hydroformylation. The TOF of SBA-15/AEAPMDMS/Rh with TPP was higher than that of the homogeneous catalyst, Rh(Ch3 COOH)2 )2 with TPP. The molar ratio of linear to branched nonyl aldehydes was remarkably enhanced over the heterogeneous catalysts. The selectively functionalized rhodium catalyst was beneficial for improving the selectivity to linear aldehyde, compared to the non-selectively immobilized rhodium catalyst, where Rh is rather randomly located inside and outside mesopores. The SBA-15/AEAPMDMS/Rh catalyst can be easily recycled without rhodium loss. HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 are found to be active species over the SBA15/AEAPMDMS/Rh with TPP based on in situ high-pressure FT-IR results.
[1] M. Beller, B. Cornils, C.D. Frohning, C.W. Kohlpaintner, J. Mol. Catal. A: Chem. 104 (1995) 17. [2] D. He, D. Pang, T. Wang, Y. Chen, Y. Liu, Q. Zhu, J. Mol. Catal. A: Chem. 174 (2001) 21. [3] J.K. Jeon, Y.K. Park, J.M. Kim, Chem. Lett. 33 (2004) 174. [4] D. He, D. Pang, L. Wei, Y. Chen, T. Wang, Z. Tang, J. Liu, Y. Liu, Q. Zhu, J. Catal. Commun. 3 (2002) 429. [5] J.N. Armor, Catal. Today 163 (2011) 3–9. [6] F. Hung-Low, G.C. Uzcátegui, M.C. Ortega, A.B. Rivas, J.E. Yanez, J. Alvarez, A.J. Pardey, C. Longo, Catal. Today 107/108 (2005) 273–281. [7] S.I. Fujita, S. Akihara, S. Fujisawa, M. Arai, J. Mol. Catal. A: Chem. 268 (2007) 244. [8] H.J. Zhu, Y.J. Ding, L. Yan, J.M. Xiong, Y. Lu, L.W. Lin, Catal. Today 93–95 (2004) 389. [9] L. Yan, Y.J. Ding, H.J. Zhu, J.M. Xiong, T. Wang, Z.D. Pan, L.W. Lin, J. Mol. Catal. A: Chem. 234 (2005) 1. [10] S.K. Sharma, P.A. Parikh, R.V. Jasra, J. Mol. Catal. A: Chem. 301 (2009) 31. [11] L. Huang, Y. He, S. Kawi, Appl. Catal. A: Gen. 265 (2004) 247. [12] N. Sudheesh, S. Sharma, R.S. Shukla, R.V. Jasra, J. Mol. Catal. A: Chem. 296 (2008) 61. [13] Q. Peng, Y. Yang, Y. Yuan, J. Mol. Catal. A: Chem. 219 (2004) 175. [14] K. Mukhopadhyay, A.B. Mandale, R.V. Chaudhari, Chem. Mater. 15 (2003) 1766. [15] L. Yan, Y.J. Ding, L.W. Lin, H.J. Zhu, H.M. Yin, X.M. Li, Y. Lu, Mol. Catal. A: Chem. 300 (2009) 116. [16] N. Garcia, E. Benito, J. Guzman, P. Tiemblo, V. Morales, R.A. Garcia, Micropor. Mesopor. Mater. 106 (2007) 129. [17] J.A. Bae, S.H. Hwang, K.C. Song, J.K. Jeon, S.K. Young, J.H. Yim, J. Nanosci. Nanotechnol. 10 (2010) 290. [18] Q. Wei, Z.R. Nie, Y.L. Hao, L. Liu, Z.X. Chen, J.X. Zou, J. Sol. Gel. Sci. Technol. 39 (2006) 103. [19] J.A. Bae, K.C. Song, J.K. Jeon, Y.S. Ko, Y.K. Park, J.H. Yim, Micropor. Mesopor. Mater. 123 (2009) 289. [20] S.A. Bagshaw, N.I. Baxter, D.R.M. Brew, C.F. Hosie, N. Yuntong, S. Jaenicke, C.G. Khuan, J. Mater. Chem. 16 (2006) 2235. [21] R.H. Crabtree, The Organometallic Chemistry of the Transition Metals, Wiley, New York, 1988. [22] J. Zhao, Y. Zhang, J. Hana, Y. Jiao, J. Mol. Catal. A: Chem. 241 (2005) 238.
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Octene hydroformylation by using rhodium complexes tethered onto selectively functionalized mesoporous silica and in situ high pressure IR study Ki-Chang Song a , Ji Yeon Baek a , Jung A Bae b , Jin-Heong Yim b,∗ , Young Soo Ko a , Do Heui Kim c , Young-Kwon Park d , Jong-Ki Jeon a,∗∗ a
Department of Chemical Engineering, Kongju National University, 275 Budae-dong, Cheonan 331-717, Republic of Korea Division of Advanced Materials Engineering, Kongju National University, 275 Budae-dong, Cheonan 331-717, Republic of Korea Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352, USA d School of Environmental Engineering, Graduate School of Energy and Environmental System Engineering, University of Seoul, Dongdaemun-Gu, Seoul 130-743, Republic of Korea b c
a r t i c l e
i n f o
Article history: Available online 17 November 2010 Keywords: Heterogeneous rhodium catalyst SBA-15 Octene hydroformylation FT-IR
a b s t r a c t SBA-15-based heterogeneous catalysts were applied to 1-octene hydroformylation. The turn over frequency over SBA-15/␥-aminopropylmethyldimethoxysilane (AEAPMDMS)/Rh catalyst with triphenylphosphine (TPP) ligand prepared by conventional post grafting method was higher than that of the homogeneous catalyst, (Rh(CH3 COO)2 )2 with TPP. The SBA-15/AEAPMDMS/Rh catalyst can be easily recycled without rhodium loss. The molar ratio of linear to branched nonyl aldehydes was remarkably enhanced over the heterogeneous catalysts. The selectively functionalized rhodium catalyst (SBA15/Ph2 Si(OEt)2 /AEAPMDMS/Rh), in which rhodium was selectively tethered intra-pore of SBA-15, was beneficial for improving the selectivity to linear aldehyde. In situ high pressure FT-IR analysis suggested HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 to be active species over the SBA-15/AEAPMDMS/Rh catalyst with TPP. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Higher aldehydes and alcohols are very important high-value added substances in the chemical industry. Recently, there is growing interest in producing nonyl aldehydes through hydroformylation of octene compounds in the presence of hydrogen and carbon monoxide [1–4]. Homogeneous complex catalysts such as rhodium complex containing phosphorous ligands have been considered as an excellent catalyst for the hydrofomylation due to high activity obtained at mild reaction conditions [5]. In order to facilitate separation, recovery and recycling of catalyst, a lot of studies have been performed about rhodium catalysts supported in porous organic or inorganic supports such as polymeric resin [6,7], SiO2 [8,9] and hydrotalcite [10]. It is necessary, however, to develop a heterogeneous catalyst to present more superior activity and stability in comparison with the homogeneous catalysts. In addition, it is really important to enhance the ratio of linear to branched aldehydes (hereinafter designated L/B), because among isomers of the aldehydes produced, linear aldehyde is commercially more valuable than branched aldehydes.
Mesoporous silica has an ordered structure with a large surface area, thereby immobilizing a lot of metal complexes and having highly dispersed active sites for catalytic reaction. In addition, its pore size is larger than microporous supports, thereby leading to a shape selective reaction in production of aldehydes with high molecular weight [11]. Immobilization of rhodium complexes on the mesoporous supports has been widely studied in the last several decades [12–15]. Also the study on the surface functionalization of mesoporous materials has grown significantly [16,17]. Among these useful functional groups, amino groups show fairly good performance for 1-octene hydroformylation catalysts [18]. This study aims to immobilize the rhodium complexes to SBA-15 for a catalyst producing nonyl aldehydes through hydroformylation of 1-octene. We tried to enhance the ratio of linear to branched aldehydes through the selectively tethered rhodium to surface of mesoporous material. In addition, active species of the heterogeneous catalysts were investigated by using in situ high-pressure FT-IR measured during the in situ reaction at high pressure and high temperature. 2. Experimental
∗ Corresponding author at: Kongju National University, 275 Budae-dong, Cheonan 330-717, Republic of Korea. Tel.: +82 41 521 9397. ∗∗ Corresponding author at: Kongju National University, 275 Budae-dong, Cheonan 330-717, Republic of Korea. Tel.: +82 41 521 9363. E-mail addresses: [email protected] (J.-H. Yim), [email protected] (J.-K. Jeon). 0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2010.10.065
2.1. Catalyst preparation SBA-15 was synthesized according to the previous literature [19]. A conventional post grafting method and a selective functionalized method have been applied to mod-
562
K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
ify SBA-15. The post grafting method, which included reflux in a non-polar solvent in the presence of N(-aminoethyl) ␥aminopropylmethyldimethoxysilane (AEAPMDMS, GE Advanced Materials), was used. 0.5 g of as-synthesized SBA-15 was dispersed in 75 ml of toluene for 0.5 h at 50 ◦ C with stirring. After 3.5 mg of p-toluenesulfonic acid and 1.0 mmol of AEAPMDMS were added, the mixture was heated up to reflux temperature (nearly 120 ◦ C) and kept stirring for 2 h. After refluxing for 2 h the solid product was filtered, washed with ethanol several times. The resulting solid was dried at 100 ◦ C for 12 h. 1 g of amine functionalized SBA-15 was added to a solution of 0.037 g Rh4 (CO)12 in n-hexane under N2 . The mixture was stirred at room temperature under N2 atmosphere for 5 h. Finally the resulting solid was dried under vacuum and henceforth designated as SBA-15/AEAPMDMS/Rh. A selective functionalized method was applied for selectively tethering rhodium onto the internal surface (in pores). The as-calcined SBA-15 (3.0 g) was then dispersed in 80 mL of toluene and stirred at 50 ◦ C for 0.5 h. After sufficient immersion, 0.021 g of p-toluenesulfonic acid and 6.0 mmol of Ph2 Si(OEt)2 were added sequentially and stirred at 120 ◦ C for 2 h. The isolated solid product was washed with ethanol three times and dried at 100 ◦ C for 12 h, resulting in external grafting. For the internal grafting process, 3.0 g of SBA-15/Ph2 Si(OEt)2 was added to 80 mL of toluene. After stirring at 50 ◦ C for 0.5 h, 0.021 g of p-toluenesulfonic acid and 6.0 mmol of AEAPMDMS were added and the mixture was refluxed at 120 ◦ C for 2 h. The solid product was filtered and washed with ethanol three times. Then, the selective functionalized mesoporous silica SBA-15 was dried at 100 ◦ C for 12 h. For the purposes of Rh immobilization, the same process was performed. The final solid was designated as SBA15/Ph2 Si(OEt)2 /AEAPMDMS/Rh.
3. Results and discussion 3.1. Textural properties of catalysts Nitrogen adsorption–desorption isotherms of the catalysts are shown in Fig. 1(a). All catalysts showed typical type IV isotherms with type-H1 hysteresis loop at P/P0 of between 0.5 and 0.7. The steep slope and sharp step are typical of multilayered adsorption followed by capillary condensation in well-ordered channel-like mesopores [20]. Despite the decrease in the amount of nitrogen adsorbed, the shape of hysteresis loop is almost same. It means that the pore shape may not be significantly changed through silane functionalization process and additional rhodium immobilization processes. In addition, the ordered hexagonal structures of the immobilized rhodium catalysts were confirmed with small-angle XRD results (Fig. 2). Textural properties of catalysts prepared in this study were displayed in Table 1. The BET surface areas of functionalized SBA15 materials decrease with functionalization and the subsequent immobilization process, because functionalized silanes and immobilized rhodium are attached to the surface of the mesoporous material. The pore volume of the rhodium-immobilized catalyst was greatly decreased, confirming that a tethering agent blocked pores of SBA-15, resulting in the reduction of surface area. The pore size distribution was shown in Fig. 1(b). The immobilized
2.2. Catalysts characterization Nitrogen adsorption–desorption isotherms were determined using a Micromeritics ASAP 2020 at −196 ◦ C. The surface area was calculated according to the BET equation. The pore volume was obtained from t-plot method. Small-angle powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/max-2500 X-ray diffractometer. 2.3. Catalytic reactions and in situ high-pressure FT-IR analysis 0.165 g of catalysts was added to a stainless steel autoclave reactor (80 mL) containing 50 ml THF and 4.26 g of 1-octene. And then 0.044 g of triphenylphosphine (PPh3 , TPP) was added to the mixture as a ligand. In the case of homogeneous catalytic reaction, we used (Rh(CH3 COO)2 )2 as a precursor for a homogeneous Rh catalyst for octene hydroformylation because (Rh(CH3 COO)2 )2 is not only stable in air, but also relatively inexpensive in comparison with those of other rhodium precursors, Rh(CO)4 , Rh6 (CO)16 , Rh4 (CO)12 , or Rh(acac)(CO)2 [3]. Subsequently, the autoclave was sealed and flushed with nitrogen gas. Syn-gas (CO/H2 = 1) was pressurized up to 20 bar in the reactor, and then the reactor was heated to 120 ◦ C. The reactor was kept at that temperature, and the syn-gas was filled up from a reservoir to maintain the pressure of 20 bar. After the completion of the reaction, the resulting products were analyzed by gas chromatography (GC-2014, Shimadzu). A home-made IR cell was used to observe the intermediates of 1-octene hydroformylation occurred in liquid phase. The IR cell was made of stainless steel and CaF2 windows, operating up to 400 ◦ C and 20 bar. Temperature was measured with a thermocouple and controlled by an external temperature controller. Spectrum GX (Perkinelmer) with an MCT detector was used for IR spectrum.
Fig. 1. (a) Nitrogen adsorption/desorption isotherms of SBA-15 (䊉: adsorption, : desorption), SBA-15/AEAPMDMS/Rh (: adsorption, : desorption), (:adsorption, : desorption), (b) SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh Pore size distribution of SBA-15 (), SBA-15/AEAPMDMS/Rh (), SBA15/Ph2 Si(OEt)2 /AEAPMDMS/Rh ().
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intensity
SBA-15 SBA-15 / AEAPMDMS/Rh SBA-15 / Ph2Si(OEt)2 / AEAPMDMS/Rh
1
2
3
4
5
2θ Fig. 2. XRD patterns.
rhodium catalysts had smaller pore size than that of SBA-15. Internal pores of two catalysts were functionalized using AEPMDMS, therefore, the degree of reduction in surface area and pore volume was similar in both nonselectively functionalized catalyst (SBA-15/AEAPMDMS/Rh) and selectively functionalized catalyst (SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh). 3.2. Hydroformylation of 1-octene Fig. 3 presented conversion, yield and selectivity in hydroformylation of 1-octene using SBA-15/AEAPMDMS/Rh with TPP ligand. 1-octene conversion and yield of nonyl aldehydes increased with reaction time and reached maximum after 30 min. The selectivity to nonyl aldehydes and octane isomers, which are desired products of 1-octene hydroformylation, and by-products through isomerization of 1-octene, respectively, were not significantly changed with reaction time. In addition, the molar ratio of linear to branched nonyl aldehydes (L/B) was not much varied with reaction time. Fig. 4 exhibited turn over frequency (TOF), nonyl aldehyde yield and L/B after 30 min of hydroformylation. The TOF of SBA-15/AEAPMDMS/Rh with TPP, non-selectively functionalized catalyst, was higher than that of the homogeneous catalyst (Rh(CH3 COO)2 )2 with TPP. It can be attributed to the high dispersion of active sites tethered onto mesoporous silica having a large surface area. The TOF of SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh with TPP, selectively functionalized catalyst, was lower than that of the non-selectively functionalized catalyst. Because rhodium active sites are tethered onto inner surface of the selectively functionalized catalyst, it appears to be limited by mass transfer of the reactant, compared to the non-selectively functionalized catalyst. The molar ratio of linear to branched nonyl aldehydes (L/B) was 0.8 in hydroformylation reaction over the homogeneous catalyst.
Fig. 3. Conversion of 1-octene, yield of nonyl aldehyde, and selectivity over SBA15/AEAPMDMS/Rh catalyst (reaction condition: 20 bar and 120 ◦ C, TPP/Rh = 20).
L/B were enhanced over the SBA-15/AEAPMDMS/Rh with TPP and the SBA-15/Ph2 Si(OEt)2 / AEAPMDMS/Rh, 2.5 and 2.8, respectively. It is remarkable that L/B can be enhanced by the selectively functionalized catalyst. It suggested that the catalyst in which rhodium was selectively tethered inside pores was beneficial for improving the selectivity to linear aldehyde, compared to the catalyst that rhodium was non-selectively immobilized inside and outside mesopores. It is well known that when bulky phosphine ligands are used in hydroformylation of higher olefins, it improves productivity of the linear aldehyde because of steric effects [21]. It may be interpreted that such steric effects are greater due to rhodium complex tethered inside the mesopore, thereby increasing the L/B, which are more clearly observed in the selectively functionalized catalyst. In addition to the catalytic activity, it is necessary to reduce the amount of rhodium loss during recycling of catalysts from the economic point of view, because the amount of rhodium loss during this process is very important factor of production cost. The results of recycling of SBA-15/AEAPMDMS/Rh with TPP were shown in Table 2. The nonyl aldehydes yield over the catalyst is not significantly changed upon the catalyst recycle. It is note-
Table 1 Textural properties of the catalysts. Catalyst
SBET (m2 g−1 )
Vtot (cm3 g−1 )
Pore size (nm)
Rh content (wt.%)a
SBA-15 SBA-15/AEAPMDMS SBA-15/AEAPMDMS/Rh SBA-15/Ph2 Si(OEt)2 SBA-15/Ph2 Si(OEt)2 /AEAPMDMS SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh
623 343 261 598 468 266
0.94 0.45 0.37 0.81 0.72 0.40
5.36 4.33 4.17 4.80 4.67 4.67
– – 0.92 – – 1.35
a
By ICP-AES with hydrofluoric acid treatment.
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3
a
2004
L/B
2
1945 1
0
60
3
-1
TOF (10 h )
4
40
2
20
A
C
B
D
Nonyl aldehyde yield (wt%)
80
6
0
absorbance
120 min 60 min 30 min 20 min 1978
10 min 5 min 2200
2100
2000
1900
Wavenumber (cm-1)
b
0
o
1945
2004
120 C
Catalyst o
100 C absorbance
Fig. 4. Turn over frequency (TOF), yield and L/B molar ratio of nonyl aldehyde on the 1-octene hydroformylation over the rhodium homogeneous and heterogeneous catalyst systems. (A: Homogeneous catalyst, [Rh(Ch3 COOH)2 ]2 + TPP, B: SBA-15/AEAPMDMS/Rh + TPP, C: SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh + TPP, D: SBA15/AEAPMDMS/Rh, Reaction condition: 20 bar and120 ◦ C, reaction time: 30 min, TPP/Rh = 20).
o
80 C
worthy, moreover, that rhodium in product was detected less than 0.5 ng/ml, suggesting that loss of rhodium during recycling is negligible. Consequently, the SBA-15/AEAPMDMS/Rh catalyst is believed to be easily recycled in comparison with the homogeneous catalysts. 3.3. High pressure in situ FT-IR analysis
o
50 C 2200
2100
2000
1900
-1
Wavenumber (cm ) The results of FT-IR analysis upon reaction time using SBA15/AEAPMDMS/Rh and TPP under 20 bar and 120 ◦ C were exhibited in Fig. 5(a). The peaks at 1945 cm−1 and 2004 cm−1 increased with reaction time, which could be assigned to HRh(CO)2 (PPh3 )2 and HRh(CO)(Ph3 P)3 , respectively [9,15,22]. According to previous results by Yan et al. [9], two broad peaks around 1938 and 2005 cm−1 appeared on HRhCO(PPh3 )3 /SiO2 . Also, Yan et al. [15] observed that two peaks at 1940 and 2000 cm−1 on HRhCO(PPh3 )3 /SBA-15. These results were well agreed with our results in Fig. 5(a). Fig. 5(b) displayed the FT-IR spectra of SBA15/AEAPMDMS/Rh with TPP, obtained during the reaction while ramping temperature at a rate of 5 ◦ C/min. The rhodium carbonyl complex in 1978 cm−1 observed at low temperature, then the characteristic peaks of HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 became apparent at 120 ◦ C. Meanwhile, it was difficult to fig-
Fig. 5. (a) Time-resolved FT-IR spectra obtained during the 1-octene hydroformylation over SBA-15/AEAPMDMS/Rh with TPP (reaction condition: 20 bar, 120 ◦ C), (b) FT-IR spectra obtained during temperature-programmed hydroformylation reaction of 1-octene over the SBA-15/AEAPMDMS/Rh with TPP (reaction condition: 20 bar).
ure out any other peaks except rhodium carbonyl complex at 1978 cm−1 in the FT-IR spectra of SBA-15/AEAPMDMS/Rh without ligand, obtained during the reaction while ramping temperature at a rate of 5 ◦ C/min, as shown in Fig. 6. It is noticeable that the heterogeneous catalyst without TPP ligand demonstrated very low activity in 1-octene hydroformylation as shown in Fig. 4. Therefore, TPP is thought to play an important role in readily forming active sites such as HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 which are only observed on the SBA-15/AEAPMDMS/Rh catalyst containing TPP.
Table 2 Yield of 1-octene hydroformylation and Rh loss during recovery of catalyst. Catalysta
Nonyl aldehyde yield (wt%)
L/Bb
Rh concentration in product (ng/ml)c
Fresh Recycled Recycled twice
69.1 68.6 66.7
2.5 2.6 2.6
<0.5 <0.5 <0.5
a b c
Catalyst: SBA-15/AEAPMDMS/Rh, TPP/Rh = 20. Molar ratio of linear nonyl aldehyde to branched nonyl aldehyde. Determined by ICP after removal of catalyst.
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Acknowledgement This work was supported by Mid-career Researcher Program through NRF grant funded by the MEST (No. R01-2007-000-201440).
absorbance
120 ºC
References
100 ºC 80 ºC
1978 50 ºC 2200
2100
2000
1900
Wavenumber (cm -1) Fig. 6. FT-IR spectra obtained during temperature-programmed hydroformylation reaction of 1-octene over the SBA-15/AEAPMDMS/Rh without TPP (reaction condition: 20 bar).
4. Conclusions A non-selectively functionalized rhodium catalyst (SBA15/AEAPMDMS/Rh) and selectively functionalized rhodium catalyst (SBA-15/Ph2 Si(OEt)2 /AEAPMDMS/Rh) were used as heterogeneous catalysts in 1-octene hydroformylation. The TOF of SBA-15/AEAPMDMS/Rh with TPP was higher than that of the homogeneous catalyst, Rh(Ch3 COOH)2 )2 with TPP. The molar ratio of linear to branched nonyl aldehydes was remarkably enhanced over the heterogeneous catalysts. The selectively functionalized rhodium catalyst was beneficial for improving the selectivity to linear aldehyde, compared to the non-selectively immobilized rhodium catalyst, where Rh is rather randomly located inside and outside mesopores. The SBA-15/AEAPMDMS/Rh catalyst can be easily recycled without rhodium loss. HRh(CO)2 (PPh3 )2 and HRh(CO)(PPh3 )3 are found to be active species over the SBA15/AEAPMDMS/Rh with TPP based on in situ high-pressure FT-IR results.
[1] M. Beller, B. Cornils, C.D. Frohning, C.W. Kohlpaintner, J. Mol. Catal. A: Chem. 104 (1995) 17. [2] D. He, D. Pang, T. Wang, Y. Chen, Y. Liu, Q. Zhu, J. Mol. Catal. A: Chem. 174 (2001) 21. [3] J.K. Jeon, Y.K. Park, J.M. Kim, Chem. Lett. 33 (2004) 174. [4] D. He, D. Pang, L. Wei, Y. Chen, T. Wang, Z. Tang, J. Liu, Y. Liu, Q. Zhu, J. Catal. Commun. 3 (2002) 429. [5] J.N. Armor, Catal. Today 163 (2011) 3–9. [6] F. Hung-Low, G.C. Uzcátegui, M.C. Ortega, A.B. Rivas, J.E. Yanez, J. Alvarez, A.J. Pardey, C. Longo, Catal. Today 107/108 (2005) 273–281. [7] S.I. Fujita, S. Akihara, S. Fujisawa, M. Arai, J. Mol. Catal. A: Chem. 268 (2007) 244. [8] H.J. Zhu, Y.J. Ding, L. Yan, J.M. Xiong, Y. Lu, L.W. Lin, Catal. Today 93–95 (2004) 389. [9] L. Yan, Y.J. Ding, H.J. Zhu, J.M. Xiong, T. Wang, Z.D. Pan, L.W. Lin, J. Mol. Catal. A: Chem. 234 (2005) 1. [10] S.K. Sharma, P.A. Parikh, R.V. Jasra, J. Mol. Catal. A: Chem. 301 (2009) 31. [11] L. Huang, Y. He, S. Kawi, Appl. Catal. A: Gen. 265 (2004) 247. [12] N. Sudheesh, S. Sharma, R.S. Shukla, R.V. Jasra, J. Mol. Catal. A: Chem. 296 (2008) 61. [13] Q. Peng, Y. Yang, Y. Yuan, J. Mol. Catal. A: Chem. 219 (2004) 175. [14] K. Mukhopadhyay, A.B. Mandale, R.V. Chaudhari, Chem. Mater. 15 (2003) 1766. [15] L. Yan, Y.J. Ding, L.W. Lin, H.J. Zhu, H.M. Yin, X.M. Li, Y. Lu, Mol. Catal. A: Chem. 300 (2009) 116. [16] N. Garcia, E. Benito, J. Guzman, P. Tiemblo, V. Morales, R.A. Garcia, Micropor. Mesopor. Mater. 106 (2007) 129. [17] J.A. Bae, S.H. Hwang, K.C. Song, J.K. Jeon, S.K. Young, J.H. Yim, J. Nanosci. Nanotechnol. 10 (2010) 290. [18] Q. Wei, Z.R. Nie, Y.L. Hao, L. Liu, Z.X. Chen, J.X. Zou, J. Sol. Gel. Sci. Technol. 39 (2006) 103. [19] J.A. Bae, K.C. Song, J.K. Jeon, Y.S. Ko, Y.K. Park, J.H. Yim, Micropor. Mesopor. Mater. 123 (2009) 289. [20] S.A. Bagshaw, N.I. Baxter, D.R.M. Brew, C.F. Hosie, N. Yuntong, S. Jaenicke, C.G. Khuan, J. Mater. Chem. 16 (2006) 2235. [21] R.H. Crabtree, The Organometallic Chemistry of the Transition Metals, Wiley, New York, 1988. [22] J. Zhao, Y. Zhang, J. Hana, Y. Jiao, J. Mol. Catal. A: Chem. 241 (2005) 238.