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Rh-based catalysts supported on MCM-41-type mesoporous silica for dicyclopentadiene hydroformylation
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Rh-based catalysts supported on MCM-41-type mesoporous silica for dicyclopentadiene hydroformylation Yubo Ma a , Shaojun Qing c , Duo Yin a,b , Xamxikamar Mamat a , Jing Zhang d , Zhixian Gao a,c , Tianfu Wang a,e,∗ , Wumanjiang Eli a a
Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, Urumqi 830011, China University of the Chinese Academy of Sciences, Beijing 100049, China c Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China d Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50011, USA e Department of Power Engineering, Xinjiang Institute of Engineering, Urumqi 830011, China b
a r t i c l e
i n f o
Article history: Received 10 November 2014 Received in revised form 2 April 2015 Accepted 7 April 2015 Available online xxx Keywords: Dicyclopentadiene Diformyltricyclodecanes Hydroformylation Mesoporous silica
a b s t r a c t Impregnation method was used in this study to prepare five different Rh based catalysts supported on MCM-type mesoporous silica materials. These catalysts were evaluated based on their performance for the hydroformylation of dicyclopentadiene (DCPD) to produce diformyltricyclodecanes (DFTD). While a selectivity of DFTD was only 8.7% using monometallic Rh/MCM-41 as catalyst, the selectivity was enhanced to 76.2% at a similar DCPD conversion using bimetallic Co–Rh/MCM-41 catalyst, even when the Co loading was very low(25 mol% relative to Rh). Extensive catalyst characterization including TPR, TPD, XRD, XPS, BET and TEM was performed to study the nature of metal modification on Rh/MCM-41. It was found that modification on the Rh/MCM-41 by Co addition could substantially enhance the selectivity towards DFTD. This improvement was likely attributed to the formation of a more reactive Rh species on the catalyst surface. © 2015 Elsevier B.V. All rights reserved.
1. Introduction With a diminishing fossil reservation and increasing demand on materials and transportation fuels, it is widely recognized that replacing fossil feedstock with renewables is a potentially promising solution. However, before the complete replacement, a more practical strategy is to better utilize the existing fossil resources. In this regard, dicyclopentadiene (DCPD), which has been widely produced as a by-product from either the C5 fraction during ethylene cracking process or light benzene fraction from the coal-coking process, is amongst those potentially usable fossil feedstock. Traditionally, applications of DCPD were limited to the synthesis of low-grade resins and additives to transportation fuels. It was reported that a series of value-added fine chemicals such as monoformyltricyclodecenes (MFTD), diformyltricyclodecanes (DFTD), tricyclodecanedimethylol (TDDMeOH) could be derived from DCPD through hydroforrmylation and its subsequent
∗ Corresponding author at: Chinese Academy of Sciences, XJ Technical Institute of Physics & Chemistry, 41-1 South Beijing Road, Urumuqi 830011, China. Tel.: +86 9917880514; fax: +86 9917880514. E-mail address: [email protected] (T. Wang).
hydrogenation processing [1–4]. Several catalysis using cobalt, rhodium [5], and Co–Rh bimetallic catalysts [6–8], was reported to be capable of catalyzing the hydroformylation of DCPD. In addition, aqueous/organic biphasic catalytic system was also applied to perform the conversion of DCPD to MFTD or DFTD [9,10]. Although much progress has been achieved in homogeneous systems for DCPD hydroformylation, less success was reported regarding the heterogenization of these homogeneous catalysts. It is advantageous to develop processes based on heterogeneous catalysts where the active sites are immobilized on a porous support, contributing to its easy recovery, if comparable activity and selective could be achieved relevant to their homogeneous counterparts [11,12]. Heterogeneous Rh based catalyst has been also developed more than 20 years for the olefins hydroformylation. A multitude of organic polymers and inorganic materials such as SiO2 , Al2 O3 , MgO, ZnO, clays, active carbons and zeolites can be considered for catalyst support [13,14]. Due to the bulky size of DCPD, supports with large pore size are preferred for the desired reaction. Due to their high surface area, relatively large and tunable pore size, and facile surface functionalization properties, mesoporous silica materials are regarded as one of the most attractive catalyst supports, meanwhile, the larger pore size makes shape-selective reactions possible
http://dx.doi.org/10.1016/j.cattod.2015.04.007 0920-5861/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Y. Ma, et al., Rh-based catalysts supported on MCM-41-type mesoporous silica for dicyclopentadiene hydroformylation, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.007
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of larger molecules like cyclic compounds [15–18]. Given the above mentioned reasons, in the current work, we chose MCM41-type mesoporous silica as the support for the hydroformylation of DCPD. Unfortunately, catalytic activity could not be achieved for DCPD hydroformylation to form DFTD over monometallic Rh/MCM-41 catalyst, which motived us to tackle this challenge and explore a method to obtain an effective Rh based catalyst supported on the MCM-41. To achieve this goal, five types of Rh or Co–Rh bimetallic catalysts supported on MCM-type mesoporous silica materials were prepared by incipient wetness impregnation. These catalysts were evaluated based on their performance for the hydroformylation of DCPD to DFTD. The selectivity of DFTD was only 8.7% from monometallic Rh/MCM-41 catalysis. However, at a similar DCPD conversion, the selectivity was enhanced to 76.2% using the bimetallic Co–Rh/MCM-41 catalyst, even at a very low Co loading. Catalysis characterization including TPR, TPD, XRD, BET and TEM were carried out to study the nature of M modification on Rh/MCM41. This leads to the conclusion that Co modified Rh/MCM-41 catalysts can substantially enhance the selectivity of DFTD up to more than 65% at almost complete conversion of DCPD. 2. Materials and methods All chemicals used in the experiments were of analytical grade and were used without further purification. 2.1. Catalyst preparation The Rh/MCM-41 was prepared using MCM-41 mesoporous silica as a support and rhodium chloride as the Rh precursor. MCM-41(10 g) was impregnated with an aqueous solution (48 ml) containing (515 mg) rhodium chloride using the incipient wetness method. After the impregnation, the samples were first dried at 393 K for 4 h, then calcined at 673 K in a quartz tube for 4 h in the air and finally reduced in a H2 flow at 673 K for 2 h. For a nominal Rh loading of 2 wt%, the catalyst was denoted as 2% Rh/MCM-41. Similarly, the Co–Rh/MCM-41 catalysts with various Co loadings were prepared using the same method as 2% Rh/MCM-41. 2.2. Catalysts characterization 2.2.1. Porosity analysis Porosity analysis was performed to examine the surface area, pore volume and average pore diameter of various catalysts. Adsorption/Desorption isotherm of N2 at 76 K was obtained using an NOVA 2200e instrument. Before each measurement, the catalyst sample was degassed at 300 ◦ C for 4 h to remove adsorbed volatile species from the catalyst surface. The isotherms were plotted with pressure and BET method was adopted to calculate the surface area, while Horwarth–Kavazoe and BJH methods were used to determine the volumes of micropore and mesopore, respectively. 2.2.2. X-ray photoelectron spectroscopy X-ray photoelectron spectroscopy (XPS) analysis was performed with a VG ESCALAB 210 instrument equipped with an Mg anode and a multi-channel detector in order to determine the surface composition and metal speciation. Charge referencing was measured against adventitious carbon (C 1s, 285.0 eV). The surface speciation was determined from the peak areas of the corresponding lines using a Shirley-type background and empirical cross section factors for XPS. 2.2.3. Powder X-ray diffraction X-ray diffraction (XRD) was carried out using a Siemens D/max-RB powder X-ray Diffractometer. Diffraction patterns were
recorded with Cu K␣ radiation (40 mA, 40 kV) with a 2 range of 15–70◦ with step increment of 0.04◦ and a count time of 1 s. 2.2.4. Temperature-programmed reduction Temperature-programmed reduction (TPR) experiments were carried out on an FINESORB-3010 with a TCD detector. The catalyst (about 100 mg) was pretreated under dry air at 383 K for 1 h. The TPR profile was recorded with heating the sample from room temperature to 673 K at a ramping rate of 10 K/min under a H2 /Ar (10% v/v) flow. 2.2.5. Temperature-programmed desorption of H2 Metal dispersion was determined by temperature-programmed desorption (TPD) of H2 using an FINESORB-3010 analyzer with a mass detector (DM 300, AMETEK, USA). In a typical experiment, 100 mg of catalyst (dried at 383 K for 5 h before each measurement) with particle size ranging from 160 m to 200 m was placed in a U-shaped quartz tube. The sample was pretreated by passing hydrogen over the catalyst at a flow rate of 50 mL/min at 673 K for 1 h. The sample was then cooled to room temperature and kept in a flow of H2 (50 mL/min) for another 1 h. Pure Ar (flow rate of 50 mL/min) was then purged over the catalyst at room temperature for additional 1 h. TPD analysis was carried out from 20 ◦ C to 400 ◦ C with a ramping rate of 10 ◦ C/min with an Ar flow of 50 mL/min. The desorbed H2 was continuously monitored by a mass spectrum (m/z = 2). 2.2.6. Transmission electron microscopy The morphological properties of the catalysts were examined using a JEOL JEM-2010 instrument equipped with an energy dispersive X-ray spectroscopy (EDS) system. The JEOL JEM-1200 EXII electron microscope was operated at an accelerating voltage of 200 and 120 kV, respectively. To prepared the sample, 1 mg catalyst was dissolved in ethanol and thesolution was homogenized for 30 min by sonication. A copper grid was briefly dipped into the solution and the grid was then air dried to evaporate ethanol before measurement. 2.3. Reaction testing Hydroformylation of DCPD was performed in a 200 mL stainless steel autoclave reactor with an inserted glass liner. Reaction temperature was controlled by using an oil bath on a digital hotplate with thermocouple, before the reaction, the catalyst was tableted, broken and mesh screened, and the size of the catalyst should be between 165 and 198 m. In a typical experiment, the catalyst (200 mg), acetone (20 mL), triphenylphosphine (PPh3 ) (0.76 mmol) and DCPD (5.0 g) were first introduced into the reactor. Then, the autoclave was purged with syngas (CO/H2 = 1/1 in molar ratio) twice. The pressure was subsequently adjusted to an initial value (6 MPa) at room temperature. The reactor was heated to desired reaction temperature with a stirring rate of 650 rpm, which was found to be adequate for overcoming the diffusion limitations. An aliquot of liquid sample was taken at specified time for analysis. After the reaction, the catalyst can be recovered by filtration. For recyclability experiment of used catalyst, another addition of PPh3 was needed because PPh3 was soluble in the reaction medium and cannot be easily separated after the reaction. 2.4. Reaction product analysis The reaction effluents were analyzed using either GC–MS (Agilent 6890/5973) or GC (Shimadzu 2014) instrument equipped with a FID detector. The definitions being used in Section 3 include: the conversion of DCPD is defined as the moles of DCPD consumed divided by the moles of initial DCPD; the selectivity towards
Please cite this article in press as: Y. Ma, et al., Rh-based catalysts supported on MCM-41-type mesoporous silica for dicyclopentadiene hydroformylation, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.007
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MFTD or DFTD is defined as the moles of molecules produced divided by the moles of DCPD consumed; and the yield of MFTD or DFTD is defined as the DCPD conversion times the MFTD or DFTD selectivity, respectively. The possible leaching of Rh into the reaction medium after the reaction was determined on an inductively coupled plasma-atomic emission spectrometry (ICP-AES) (Thermo Elemental Company, USA) by dissolving the samples in aqueous nitric acid followed by measurement. 3. Results and discussions 3.1. Synthesis of DFTD over Rh based catalysts supported on MCM-41 The double hydroformylated product of DCPD, DFTD is the most desirable final product since it can be further oxidized or reduced to synthesize the corresponding di-acid and di-ol as valuable monomers. Thus, the variation of catalyst composition was carried out to explore the most effective catalyst systems. The results for hydroformylation of DCPD are summarized in Table 1. By comparison of entries 1 to 5, it was observed that the product distribution among MFTD (singly hydroformylated product), DFTD (doubly hydroformylated product) and other undesired byproducts would be greatly altered with different degree of Co modification. For 2%Rh–MCM41 (entry 1), only 8.7% DFTD selectivity could be achieved. For 2%Rh–0.5%Co–MCM41, the selectivity increased to 76.2% at a similar DCPD conversion (entry 2). Encouraged by these results, a series of other Rh–Co based bimetallic catalysts were prepared with increasing Co loading. As shown in entries 3–5, DFTD selectivity gradually increased until a loading of Co up to 2%. At higher Co loading such as 4% shown in entry
3
5, DFTD selectivity unexpectedly dropped to 75.2%, which was attributed to larger degree of side reactions(18.7% other products). This set of data suggested the Co addition could greatly improve the DFTD selectivity. Moreover, the optimal loading of Co in the Co–Rh bimetallic catalyst was found to be 2% in the tested range. This loading was chosen for further studies. In order to further understand the promotion effect of Co addition, a series of MCM-41 supported Rh catalysts modified with other early transition metals such as Cu, Ni, and Fe were synthesized and evaluated. Hydroformylation of DCPD catalyzed by these 2%Rh–2%M/MCM-41 materials was performed under the same reaction conditions as Co–Rh bimetallic system. By comparing entries 6–8 with 4, Ni modified catalysts was found to be a poor catalyst, resulting in negligible DFTD selectivity at a 20% conversion (entry 8). In contrast, Fe and Cu modified Rh/MCM-41 had a similar activity to Co (all greater than 99%). However, the selectivity towards DFTD was only 3.0% and 3.4% (entries 6–7) for Table 2 Porosity properties of MCM-41 and MCM-41-based materials. Sample
Rh loadings %
MCM41 2%Rh–MCM41 2%Rh–0.5% Co–MCM41 2%Rh–1% Co–MCM41 2%Rh–2% Co–MCM41 2%Rh–4% Co–MCM41
0 2 2
Rh3d5/2 307 Rh3d5/2 307.8 Co3d5/2 779.91 Rh3d5/2 308.24 Co3d5/2 779.66 Rh3d5/2 308.47 Co3d5/2 779.01 Rh3d5/2 308.61 Co3d5/2 778.77
2 2 2
Table 1 Hydroformylation of dicyclopentadiene over various catalysts. Entry Catalyst
Surface area (m2 /g)
Pore volume (cm3 /g)
907 774 804
0.775 0.551 0.536
762
0.535
699
0.446
670
0.417
2% Co-MCM41
DCPD con. % MFTD sel.% DFTD sel.% Others %
2%Rh–MCM41 2%Rh–0.5%Co–MCM41 2%Rh–1%Co–MCM41 2%Rh–2%Co–MCM41 2%Rh–4%Co–MCM41 2%Rh–2%Fe–MCM41 2%Rh–2%Cu–MCM41 2%Rh–2%Ni–MCM41 2%Rh–2%Co–MCM41a 2%Rh–2%Co–MCM41b
>99 >99 >99 >99 >99 >99 >99 20 >99 >99
87.0 18.8 12.9 6.0 6.1 84.3 87.4 19.5 7.6 3
8.7 76.2 78.6 87.3 75.2 3.0 3.4 0 85 88.7
4.3 5.0 6.5 6.7 18.7 12.7 4.0 0.5 7.4 8.7
2% Rh-4% Co-MCM41 2% Rh-2% Co-MCM41
Intensity
1 2 3 4 5 6 7 8 9 10
Binding energy (eV)
2% Rh-1% Co-MCM41 2% Rh-0.5% Co-MCM41 2% Rh-MCM41
Experimental conditions: reaction temperature: 140 ◦ C, reaction pressure: 6 MPa; reaction time: 6 h; DCPD: 5 g; catalyst: 0.2 g; PPh3 : 0.2 g. a The catalyst was reused at 5th time. b The reaction time, 12 h.
100
200
300
400
Temperature / oC Co-Rh/MCM-41 Ni-Rh/MCM-41
Intensity
intensity
MCM-41 2Rh/MCM-41 0.5Co-2Rh/MCM-41 1Co-2Rh/MCM-41 2Co-2Rh/MCM-41 4Co-2Rh/MCM-41
Fe-Rh/MCM-41 Rh/MCM-41 Cu-Rh/MCM-41
0
10
20
30
40
50
60
70
80
90
2 Theta o Fig. 1. XRD patterns of MCM-41 and MCM-41-based materials.
50
100
150
200
250
300
350
400
Temperature oC Fig. 2. TPR profiles of various catalysts.
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3.2. ICP-AES, XRD, XPS and BET results In order to confirm whether the catalytic reaction occurred on the surface of the catalyst or in the solution, the reaction medium after the experiment was measured by ICP-AES. Negligible Rh content was detected, suggesting that the reaction should have occurred on the surface of the catalyst. XRD patterns of the MCM-41, 2% Rh/MCM-41, 0.5%Co–2%Rh/ MCM-41, 1%Co–2%Rh/MCM-41, 2% Co–2%Rh/MCM-41 and 4%Co– 2%Rh/MCM-41 are shown in Fig. 1. The results showed that the characteristic diffraction peaks of MCM-41 were observed for all samples. Moreover, characteristic diffraction peaks for Co and Rh were not discerned, suggesting that the Co and Rh species were highly dispersed on the MCM-41 matrix.
450
Temperature
400
2% Rh/MCM41
350
0.5C0-2% Rh/MCM41
300
1C0-2% Rh/MCM41
250
2C0-2% Rh/MCM41 4C0-2% Rh/MCM41
200 150
Intensity
2%Rh–2%Fe–MCM41and 2%Rh–2%Cu–MCM41, respectively, which was much lower compared to 2%Rh–2%Co–MCM41. These results revealed that the Co modification had the best selectivity towards DFTD among the tested catalytic materials. Further catalyst characterization was performed in order to understand why the Co modification had unique effect in terms of promoting DFTD formation. In addition, it can be seen that 85% DFTD selectivity can be obtained when 2%Rh–2%Co–MCM41 catalyst were used after 5 runs (entry 9), suggesting that the catalysts possessed moderately high stability. Also, a longer reaction time of 12 h with 2%Rh–2%Co–MCM41 as the catalyst was also investigated (entry 10). It is shown that only 1.5% increase of DFTD selectivity was achieved at an additional 4.6% MFTD conversion by prolonging the reaction time from 6 h to 12 h. This result demonstrated that the reaction time had a relatively small impact on altering the final product selectivity.
Temperature oC
4
100 50 0 1000
2000
3000
4000
5000
6000
7000
8000
Time /s Fig. 3. TPD profiles of various catalysts.
Porosity properties of different catalysts were summarized in Table 2. The BET surface area and pore volume of MCM-41 were 907 m2 /g and 0.775 cm3 /g, respectively. These two values for 2% Rh supported MCM-41 dropped to 774 m2 /g and 0.551 cm3 /g, due to the introduction of Rh. Further increasing Co loading, however, only slightly decreased the surface area and pore volume, which was in accordance with the homogenous Co distribution throughout the matrix of MCM-41. In order to probe the electronic properties of Rh and Co in the catalysts, the binding energies (B.E.) were tabulated. Standard binding energy for Co 2p3/2 and Rh 3d5/2 is 780 eV and 307 eV, respectively. For 2% Rh–MCM-41, the value of B.E. for Rh 3d5/2 was 307 eV, indicating negligible interaction between Rh and the MCM-41. Increasing Co loading altered the electronic structure of Rh, reflected by its shifting towards higher B.E. It was observed that the B.E. for Rh 3d5/2 shifted from 307.8 eV to 308.61 eV when
Fig. 4. HRTEM of various catalysts: (a) 2Rh/MCM-41, (b) 0.5Co–2Rh/MCM-41, (c) 2Co–2Rh/MCM-41(before the reaction), (d) 4Co–2Rh/MCM-41; (e) 2Co–2Rh/MCM-41(after the reaction).
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Co loading was gradually increased from 0.5% to 4%. Although there are some differences between the catalysts evaluated regarding the binding energy of Rh, the oxidation state of Rh species was Rh0 for all the experimented catalysts. On the other hand, the B.E. of Co 2p3/2 were remarkably lower than that of standard Co (Co 2p3/2 = 780 eV) when Co was introduced into Rh/MCM-41. The shift of binding energies for Co and Rh provided an evidence for the strong interaction between Co and Rh, which modified the electronic properties of the metals. This modification likely affected the DCPD conversion and DFTD selectivity in the catalysis. 3.3. TPR and TPD-H2 TPR was used to probe the status of Rh in these M-modified Rh–MCM-41 catalyst precursors (before reduction, existing as oxides). The results were summarized in Fig. 2. The reduction peak of RhOx in Fe-Rh/MCM-41 was superimposable with that of RhOx as a reference material. On the other hand, RhOx reduction peaks with all other metal (Cu, Ni and Co) modified materials shifted to higher temperatures compared to the reference RhOx. The extent of peak shift was in the order of Cu > Co ∼ Ni. In addition, the area under curve (AUC) for RhOx reduction was also altered after different M modification. Compared to Rh/MCM-41, the AUCs after Cu, Fe and Ni modification were greater than that of reference material RhOx. In the Co–Rh/MCM-41 catalyst, increasing the amount of Co added to Rh/MCM-41 resulted in a decrease in H2 consumption needed for RhOx reduction, indicating less Rh element was exposed on the surface. Thus, the improved activity of Co–Rh MCM-41 catalyst can be postulated to arise from the formation of more active Rh species on the surface which was likely induced and stabilized by the Co modification. H2 -TPD was used to study the nature of M modification on Rh/MCM-41. As shown in Fig. 3, all the catalysts had desorption peaks centered at similar temperature, indicating negligible change on the Rh dispersion after the metal modification. And the peak areas increased by following the order: 0.5Co–2%Rh/MCM-41 < 1Co–2%Rh/MCM-41 < 2%Rh/MCM41 ∼ 2Co–2%Rh/MCM-41 < 4Co–2%Rh/MCM-41. The Rh availability on the surface of MCM-41 was expected to decrease at a low Co loading (less than 1% in Rh/MCM-41), while a higher Rh availability on the surface of MCM-41 was observed at a higher Co loading (more than2% in Rh/MCM-41), which might be ascribed to the formation of a different Rh status. 3.4. TEM TEM images of different Rh based catalysts supported on MCM41 are shown in Fig. 4. It was observed that Rh nanoparticles with narrow size distributions were successfully deposited throughout the matrix of MCM-41 support, which was consistent with aforementioned results (e.g., XRD and metal dispersion on TPD-H2 ). The addition of Co had minimal influence on the size distribution of Rh nanoparticles, suggesting the modification primarily impacted the electronic properties rather than structural properties. TEM images of 2Co–2Rh/MCM-41 before and after the reaction are also shown in Fig. 4. As revealed by Fig. 4e, no appreciable change in Rh particle size was observed for the spent catalyst compared to fresh catalyst, suggesting that Rh nanoparticles were relatively stable under the reaction conditions (reaction temperature of 140 ◦ C). 4. Conclusion Five different Rh-based catalysts supported on MCM-41 were prepared by incipient wetness method, and were evaluated based on their catalytic performance for hydroformylation of DCPD. At almost complete conversion, the selectivity for desired product
5
DFTD was only 8.7% using monometallic Rh/MCM-41 catalyst. However, at a similar conversion, the selectivity was enhanced to 76.2% using the bimetallic Co–Rh/MCM-41 catalyst, even at a very lowing Co loading (0.5% in Rh/MCM-41). Extensive catalyst characterization was carried out to provide insights into the enhancement on selectivity after the Co addition. The TPR data indicated that the enhanced performance could arise from the presence of the more active Rh species on the surface, likely due to the Co modification. TPD-H2 , XRD, BET and TEM analysis showed little effect on the dispersion of Rh nanoparticles from the metal addition. Electronic properties of the M-modified Rh catalysts, however, were found to be greatly different from the monometallic Rh catalyst. It was speculated that the collective change in the electronics of Rh and the other added metals, would have an effect on the physichemical interaction between the reactant and product during the reaction, thereby changing the product distributions. In summary, Co modified Rh/MCM-41 catalysts can substantially enhance DFTD selectivity at almost complete DCPD conversion. This improvement was likely derived from the surface interactions between DCPD/DFTD and the active site on the bimetallic catalyst. This bimetallic catalytic system could be potentially promising in catalyzing hydroformylation reactions with other cyclic or acyclic di-enes for the selective production of valuable chemicals. Acknowledgments This work has been financially supported by Chinese Government “Thousand Talent” Program (Y42H291501), National Natural Science Foundation of China (U1139302, U1403192), Chinese Academy of Sciences (XBBS201114, 2015RC013) and Urumqi Science & Technology Bureau (Y121120006). References [1] Y.I.Y. Fujikura, N. Takaishi, H. Ikeda, Stereospecific hydroformylation of endo-dicyclopentadiene in the presence of rhodium complex catalysts. A route to endo-tricyclo[5.2.1.02,6]dec-8-exo-ylcarbinol, precursor of 4homoisotwistane, Synth. Commun. 6 (1976) 199–207. [2] Y.I.K. Aigami, N. Takaishi, Y. Fujikura, A. Takatsuki, G. Tamura, Biologicallyactive polycycloalkanes. 2. Antiviral 4-homoisotwistane derivatives, J. Med. Chem. 19 (1976) 536–540. [3] P.S.R. S.M. Barrington, Synthetic lubricants, US3005775, 1961. [4] A.C. P. Gloeckner, W. Andrejewski, Unsatrurated amorphous polyesters based on certain diciol isomers, US0526236, 2005. [5] P.W.N.M. Van Leeuwen, C.F. Roobeek, The hydroformylation of butadiene catalysed by rhodium-diphosphine complexes, J. Mol. Catal. 31 (1985) 345–353. [6] S.E.M.D.L. Hunter, P.E. Garrou, R.A. Dubois, Syn–gas reactions with cobalt subgroup clusters. 2. Dicyclopentadiene hydroformylation catalyzed by RhxCo4-x(CO)12 (x = 4, 2–0)/tertiary amine ctalysts, Appl. Catal. 19 (1985) 259–273. [7] G.E.H. P.E. Garrou, Hydroformylation of dicyclopentadiene to its dimethanolic derivatives, US 4 262 147, 1981. [8] M.M.L. Garlaschelli, M.C. Iapalucci, G. Longoni, Hydroformylation and hydrocarbonylation of dicyclopentadiene with cobalt rhodium catalytic-system promoted by triphenylphosphine—synthesis of monoformyltricyclodecenes, diformyltricyclodecanes and di(tricyclodecenyl)ketones, J. Mol. Catal. 68 (1991) 7–21. [9] X. Pi, Y. Zhou, L. Zhou, M. Yuan, R. Li, H. Fu, H. Chen, Dicyclopentadiene hydroformylation in an aqueous/organic two phase system in the presence of a cationic surfactant, Chin. J. Catal. 32 (2011) 566–571. [10] R. Luo, H.-r. Liang, X.-l. Zheng, H.-y. Fu, M.-l. Yuan, R.-x. Li, H. Chen, Highly efficient catalytic system for the formation of dialdehydes from dicyclopentadiene hydroformylation, Catal. Commun. 50 (2014) 29–33. [11] F.R. Hartley, Supported Metal Complexes, A New Generation of Catalysts, Reidel, Dordrecht, 1985. [12] Y. Iwasawa, Tailored Metal Catalysts, Reidel, Dordrecht, 1986. [13] M. Lenarda, L. Storaro, R. Ganzerla, Hydroformylation of simple olefins catalyzed by metals and clusters supported on unfunctionalized inorganic carriers, J. Mol. Catal. A: Chem. 111 (1996) 203–237. [14] L. Yan, Y.J. Ding, H.J. Zhu, J.M. Xiong, T. Wang, Z.D. Pan, L.W. Lin, Ligand modified real heterogeneous catalysts for fixed-bed hydroformylation of propylene, J. Mol. Catal. A: Chem. 234 (2005) 1–7.
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[15] L. Huang, Y. He, S. Kawi, Catalytic studies of aminated MCM-41-tethered rhodium complexes for 1-hexene hydroformylation, Appl. Catal., A: Gen. 265 (2004) 247–257. [16] L. Huang, J.C. Wu, S. Kawi, Rh4(CO)12-derived functionalized MCM-41-tethered rhodium complexes: preparation, characterization and catalysis for cyclohexene hydroformylation, J. Mol. Catal. A: Chem. 206 (2003) 371–387.
[17] S.K.L. Huang, {RhCl(CO)(2)}(2)-derived MCM-41-tethered rhodium complex catalysts via phosphine, amine and thiol ligands for cyclohexene hydroformylation, Bull. Chem. Soc. Jpn. 77 (2004) 295–302. [18] L. Huang, S. Kawi, An active and stable Wilkinson’s complex-derived SiO2 tethered catalyst via an amine ligand for cyclohexene hydroformylation, Catal. Lett. 92 (2004) 57–62.
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Rh-based catalysts supported on MCM-41-type mesoporous silica for dicyclopentadiene hydroformylation Yubo Ma a , Shaojun Qing c , Duo Yin a,b , Xamxikamar Mamat a , Jing Zhang d , Zhixian Gao a,c , Tianfu Wang a,e,∗ , Wumanjiang Eli a a
Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, Urumqi 830011, China University of the Chinese Academy of Sciences, Beijing 100049, China c Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China d Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50011, USA e Department of Power Engineering, Xinjiang Institute of Engineering, Urumqi 830011, China b
a r t i c l e
i n f o
Article history: Received 10 November 2014 Received in revised form 2 April 2015 Accepted 7 April 2015 Available online xxx Keywords: Dicyclopentadiene Diformyltricyclodecanes Hydroformylation Mesoporous silica
a b s t r a c t Impregnation method was used in this study to prepare five different Rh based catalysts supported on MCM-type mesoporous silica materials. These catalysts were evaluated based on their performance for the hydroformylation of dicyclopentadiene (DCPD) to produce diformyltricyclodecanes (DFTD). While a selectivity of DFTD was only 8.7% using monometallic Rh/MCM-41 as catalyst, the selectivity was enhanced to 76.2% at a similar DCPD conversion using bimetallic Co–Rh/MCM-41 catalyst, even when the Co loading was very low(25 mol% relative to Rh). Extensive catalyst characterization including TPR, TPD, XRD, XPS, BET and TEM was performed to study the nature of metal modification on Rh/MCM-41. It was found that modification on the Rh/MCM-41 by Co addition could substantially enhance the selectivity towards DFTD. This improvement was likely attributed to the formation of a more reactive Rh species on the catalyst surface. © 2015 Elsevier B.V. All rights reserved.
1. Introduction With a diminishing fossil reservation and increasing demand on materials and transportation fuels, it is widely recognized that replacing fossil feedstock with renewables is a potentially promising solution. However, before the complete replacement, a more practical strategy is to better utilize the existing fossil resources. In this regard, dicyclopentadiene (DCPD), which has been widely produced as a by-product from either the C5 fraction during ethylene cracking process or light benzene fraction from the coal-coking process, is amongst those potentially usable fossil feedstock. Traditionally, applications of DCPD were limited to the synthesis of low-grade resins and additives to transportation fuels. It was reported that a series of value-added fine chemicals such as monoformyltricyclodecenes (MFTD), diformyltricyclodecanes (DFTD), tricyclodecanedimethylol (TDDMeOH) could be derived from DCPD through hydroforrmylation and its subsequent
∗ Corresponding author at: Chinese Academy of Sciences, XJ Technical Institute of Physics & Chemistry, 41-1 South Beijing Road, Urumuqi 830011, China. Tel.: +86 9917880514; fax: +86 9917880514. E-mail address: [email protected] (T. Wang).
hydrogenation processing [1–4]. Several catalysis using cobalt, rhodium [5], and Co–Rh bimetallic catalysts [6–8], was reported to be capable of catalyzing the hydroformylation of DCPD. In addition, aqueous/organic biphasic catalytic system was also applied to perform the conversion of DCPD to MFTD or DFTD [9,10]. Although much progress has been achieved in homogeneous systems for DCPD hydroformylation, less success was reported regarding the heterogenization of these homogeneous catalysts. It is advantageous to develop processes based on heterogeneous catalysts where the active sites are immobilized on a porous support, contributing to its easy recovery, if comparable activity and selective could be achieved relevant to their homogeneous counterparts [11,12]. Heterogeneous Rh based catalyst has been also developed more than 20 years for the olefins hydroformylation. A multitude of organic polymers and inorganic materials such as SiO2 , Al2 O3 , MgO, ZnO, clays, active carbons and zeolites can be considered for catalyst support [13,14]. Due to the bulky size of DCPD, supports with large pore size are preferred for the desired reaction. Due to their high surface area, relatively large and tunable pore size, and facile surface functionalization properties, mesoporous silica materials are regarded as one of the most attractive catalyst supports, meanwhile, the larger pore size makes shape-selective reactions possible
http://dx.doi.org/10.1016/j.cattod.2015.04.007 0920-5861/© 2015 Elsevier B.V. All rights reserved.
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of larger molecules like cyclic compounds [15–18]. Given the above mentioned reasons, in the current work, we chose MCM41-type mesoporous silica as the support for the hydroformylation of DCPD. Unfortunately, catalytic activity could not be achieved for DCPD hydroformylation to form DFTD over monometallic Rh/MCM-41 catalyst, which motived us to tackle this challenge and explore a method to obtain an effective Rh based catalyst supported on the MCM-41. To achieve this goal, five types of Rh or Co–Rh bimetallic catalysts supported on MCM-type mesoporous silica materials were prepared by incipient wetness impregnation. These catalysts were evaluated based on their performance for the hydroformylation of DCPD to DFTD. The selectivity of DFTD was only 8.7% from monometallic Rh/MCM-41 catalysis. However, at a similar DCPD conversion, the selectivity was enhanced to 76.2% using the bimetallic Co–Rh/MCM-41 catalyst, even at a very low Co loading. Catalysis characterization including TPR, TPD, XRD, BET and TEM were carried out to study the nature of M modification on Rh/MCM41. This leads to the conclusion that Co modified Rh/MCM-41 catalysts can substantially enhance the selectivity of DFTD up to more than 65% at almost complete conversion of DCPD. 2. Materials and methods All chemicals used in the experiments were of analytical grade and were used without further purification. 2.1. Catalyst preparation The Rh/MCM-41 was prepared using MCM-41 mesoporous silica as a support and rhodium chloride as the Rh precursor. MCM-41(10 g) was impregnated with an aqueous solution (48 ml) containing (515 mg) rhodium chloride using the incipient wetness method. After the impregnation, the samples were first dried at 393 K for 4 h, then calcined at 673 K in a quartz tube for 4 h in the air and finally reduced in a H2 flow at 673 K for 2 h. For a nominal Rh loading of 2 wt%, the catalyst was denoted as 2% Rh/MCM-41. Similarly, the Co–Rh/MCM-41 catalysts with various Co loadings were prepared using the same method as 2% Rh/MCM-41. 2.2. Catalysts characterization 2.2.1. Porosity analysis Porosity analysis was performed to examine the surface area, pore volume and average pore diameter of various catalysts. Adsorption/Desorption isotherm of N2 at 76 K was obtained using an NOVA 2200e instrument. Before each measurement, the catalyst sample was degassed at 300 ◦ C for 4 h to remove adsorbed volatile species from the catalyst surface. The isotherms were plotted with pressure and BET method was adopted to calculate the surface area, while Horwarth–Kavazoe and BJH methods were used to determine the volumes of micropore and mesopore, respectively. 2.2.2. X-ray photoelectron spectroscopy X-ray photoelectron spectroscopy (XPS) analysis was performed with a VG ESCALAB 210 instrument equipped with an Mg anode and a multi-channel detector in order to determine the surface composition and metal speciation. Charge referencing was measured against adventitious carbon (C 1s, 285.0 eV). The surface speciation was determined from the peak areas of the corresponding lines using a Shirley-type background and empirical cross section factors for XPS. 2.2.3. Powder X-ray diffraction X-ray diffraction (XRD) was carried out using a Siemens D/max-RB powder X-ray Diffractometer. Diffraction patterns were
recorded with Cu K␣ radiation (40 mA, 40 kV) with a 2 range of 15–70◦ with step increment of 0.04◦ and a count time of 1 s. 2.2.4. Temperature-programmed reduction Temperature-programmed reduction (TPR) experiments were carried out on an FINESORB-3010 with a TCD detector. The catalyst (about 100 mg) was pretreated under dry air at 383 K for 1 h. The TPR profile was recorded with heating the sample from room temperature to 673 K at a ramping rate of 10 K/min under a H2 /Ar (10% v/v) flow. 2.2.5. Temperature-programmed desorption of H2 Metal dispersion was determined by temperature-programmed desorption (TPD) of H2 using an FINESORB-3010 analyzer with a mass detector (DM 300, AMETEK, USA). In a typical experiment, 100 mg of catalyst (dried at 383 K for 5 h before each measurement) with particle size ranging from 160 m to 200 m was placed in a U-shaped quartz tube. The sample was pretreated by passing hydrogen over the catalyst at a flow rate of 50 mL/min at 673 K for 1 h. The sample was then cooled to room temperature and kept in a flow of H2 (50 mL/min) for another 1 h. Pure Ar (flow rate of 50 mL/min) was then purged over the catalyst at room temperature for additional 1 h. TPD analysis was carried out from 20 ◦ C to 400 ◦ C with a ramping rate of 10 ◦ C/min with an Ar flow of 50 mL/min. The desorbed H2 was continuously monitored by a mass spectrum (m/z = 2). 2.2.6. Transmission electron microscopy The morphological properties of the catalysts were examined using a JEOL JEM-2010 instrument equipped with an energy dispersive X-ray spectroscopy (EDS) system. The JEOL JEM-1200 EXII electron microscope was operated at an accelerating voltage of 200 and 120 kV, respectively. To prepared the sample, 1 mg catalyst was dissolved in ethanol and thesolution was homogenized for 30 min by sonication. A copper grid was briefly dipped into the solution and the grid was then air dried to evaporate ethanol before measurement. 2.3. Reaction testing Hydroformylation of DCPD was performed in a 200 mL stainless steel autoclave reactor with an inserted glass liner. Reaction temperature was controlled by using an oil bath on a digital hotplate with thermocouple, before the reaction, the catalyst was tableted, broken and mesh screened, and the size of the catalyst should be between 165 and 198 m. In a typical experiment, the catalyst (200 mg), acetone (20 mL), triphenylphosphine (PPh3 ) (0.76 mmol) and DCPD (5.0 g) were first introduced into the reactor. Then, the autoclave was purged with syngas (CO/H2 = 1/1 in molar ratio) twice. The pressure was subsequently adjusted to an initial value (6 MPa) at room temperature. The reactor was heated to desired reaction temperature with a stirring rate of 650 rpm, which was found to be adequate for overcoming the diffusion limitations. An aliquot of liquid sample was taken at specified time for analysis. After the reaction, the catalyst can be recovered by filtration. For recyclability experiment of used catalyst, another addition of PPh3 was needed because PPh3 was soluble in the reaction medium and cannot be easily separated after the reaction. 2.4. Reaction product analysis The reaction effluents were analyzed using either GC–MS (Agilent 6890/5973) or GC (Shimadzu 2014) instrument equipped with a FID detector. The definitions being used in Section 3 include: the conversion of DCPD is defined as the moles of DCPD consumed divided by the moles of initial DCPD; the selectivity towards
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MFTD or DFTD is defined as the moles of molecules produced divided by the moles of DCPD consumed; and the yield of MFTD or DFTD is defined as the DCPD conversion times the MFTD or DFTD selectivity, respectively. The possible leaching of Rh into the reaction medium after the reaction was determined on an inductively coupled plasma-atomic emission spectrometry (ICP-AES) (Thermo Elemental Company, USA) by dissolving the samples in aqueous nitric acid followed by measurement. 3. Results and discussions 3.1. Synthesis of DFTD over Rh based catalysts supported on MCM-41 The double hydroformylated product of DCPD, DFTD is the most desirable final product since it can be further oxidized or reduced to synthesize the corresponding di-acid and di-ol as valuable monomers. Thus, the variation of catalyst composition was carried out to explore the most effective catalyst systems. The results for hydroformylation of DCPD are summarized in Table 1. By comparison of entries 1 to 5, it was observed that the product distribution among MFTD (singly hydroformylated product), DFTD (doubly hydroformylated product) and other undesired byproducts would be greatly altered with different degree of Co modification. For 2%Rh–MCM41 (entry 1), only 8.7% DFTD selectivity could be achieved. For 2%Rh–0.5%Co–MCM41, the selectivity increased to 76.2% at a similar DCPD conversion (entry 2). Encouraged by these results, a series of other Rh–Co based bimetallic catalysts were prepared with increasing Co loading. As shown in entries 3–5, DFTD selectivity gradually increased until a loading of Co up to 2%. At higher Co loading such as 4% shown in entry
3
5, DFTD selectivity unexpectedly dropped to 75.2%, which was attributed to larger degree of side reactions(18.7% other products). This set of data suggested the Co addition could greatly improve the DFTD selectivity. Moreover, the optimal loading of Co in the Co–Rh bimetallic catalyst was found to be 2% in the tested range. This loading was chosen for further studies. In order to further understand the promotion effect of Co addition, a series of MCM-41 supported Rh catalysts modified with other early transition metals such as Cu, Ni, and Fe were synthesized and evaluated. Hydroformylation of DCPD catalyzed by these 2%Rh–2%M/MCM-41 materials was performed under the same reaction conditions as Co–Rh bimetallic system. By comparing entries 6–8 with 4, Ni modified catalysts was found to be a poor catalyst, resulting in negligible DFTD selectivity at a 20% conversion (entry 8). In contrast, Fe and Cu modified Rh/MCM-41 had a similar activity to Co (all greater than 99%). However, the selectivity towards DFTD was only 3.0% and 3.4% (entries 6–7) for Table 2 Porosity properties of MCM-41 and MCM-41-based materials. Sample
Rh loadings %
MCM41 2%Rh–MCM41 2%Rh–0.5% Co–MCM41 2%Rh–1% Co–MCM41 2%Rh–2% Co–MCM41 2%Rh–4% Co–MCM41
0 2 2
Rh3d5/2 307 Rh3d5/2 307.8 Co3d5/2 779.91 Rh3d5/2 308.24 Co3d5/2 779.66 Rh3d5/2 308.47 Co3d5/2 779.01 Rh3d5/2 308.61 Co3d5/2 778.77
2 2 2
Table 1 Hydroformylation of dicyclopentadiene over various catalysts. Entry Catalyst
Surface area (m2 /g)
Pore volume (cm3 /g)
907 774 804
0.775 0.551 0.536
762
0.535
699
0.446
670
0.417
2% Co-MCM41
DCPD con. % MFTD sel.% DFTD sel.% Others %
2%Rh–MCM41 2%Rh–0.5%Co–MCM41 2%Rh–1%Co–MCM41 2%Rh–2%Co–MCM41 2%Rh–4%Co–MCM41 2%Rh–2%Fe–MCM41 2%Rh–2%Cu–MCM41 2%Rh–2%Ni–MCM41 2%Rh–2%Co–MCM41a 2%Rh–2%Co–MCM41b
>99 >99 >99 >99 >99 >99 >99 20 >99 >99
87.0 18.8 12.9 6.0 6.1 84.3 87.4 19.5 7.6 3
8.7 76.2 78.6 87.3 75.2 3.0 3.4 0 85 88.7
4.3 5.0 6.5 6.7 18.7 12.7 4.0 0.5 7.4 8.7
2% Rh-4% Co-MCM41 2% Rh-2% Co-MCM41
Intensity
1 2 3 4 5 6 7 8 9 10
Binding energy (eV)
2% Rh-1% Co-MCM41 2% Rh-0.5% Co-MCM41 2% Rh-MCM41
Experimental conditions: reaction temperature: 140 ◦ C, reaction pressure: 6 MPa; reaction time: 6 h; DCPD: 5 g; catalyst: 0.2 g; PPh3 : 0.2 g. a The catalyst was reused at 5th time. b The reaction time, 12 h.
100
200
300
400
Temperature / oC Co-Rh/MCM-41 Ni-Rh/MCM-41
Intensity
intensity
MCM-41 2Rh/MCM-41 0.5Co-2Rh/MCM-41 1Co-2Rh/MCM-41 2Co-2Rh/MCM-41 4Co-2Rh/MCM-41
Fe-Rh/MCM-41 Rh/MCM-41 Cu-Rh/MCM-41
0
10
20
30
40
50
60
70
80
90
2 Theta o Fig. 1. XRD patterns of MCM-41 and MCM-41-based materials.
50
100
150
200
250
300
350
400
Temperature oC Fig. 2. TPR profiles of various catalysts.
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3.2. ICP-AES, XRD, XPS and BET results In order to confirm whether the catalytic reaction occurred on the surface of the catalyst or in the solution, the reaction medium after the experiment was measured by ICP-AES. Negligible Rh content was detected, suggesting that the reaction should have occurred on the surface of the catalyst. XRD patterns of the MCM-41, 2% Rh/MCM-41, 0.5%Co–2%Rh/ MCM-41, 1%Co–2%Rh/MCM-41, 2% Co–2%Rh/MCM-41 and 4%Co– 2%Rh/MCM-41 are shown in Fig. 1. The results showed that the characteristic diffraction peaks of MCM-41 were observed for all samples. Moreover, characteristic diffraction peaks for Co and Rh were not discerned, suggesting that the Co and Rh species were highly dispersed on the MCM-41 matrix.
450
Temperature
400
2% Rh/MCM41
350
0.5C0-2% Rh/MCM41
300
1C0-2% Rh/MCM41
250
2C0-2% Rh/MCM41 4C0-2% Rh/MCM41
200 150
Intensity
2%Rh–2%Fe–MCM41and 2%Rh–2%Cu–MCM41, respectively, which was much lower compared to 2%Rh–2%Co–MCM41. These results revealed that the Co modification had the best selectivity towards DFTD among the tested catalytic materials. Further catalyst characterization was performed in order to understand why the Co modification had unique effect in terms of promoting DFTD formation. In addition, it can be seen that 85% DFTD selectivity can be obtained when 2%Rh–2%Co–MCM41 catalyst were used after 5 runs (entry 9), suggesting that the catalysts possessed moderately high stability. Also, a longer reaction time of 12 h with 2%Rh–2%Co–MCM41 as the catalyst was also investigated (entry 10). It is shown that only 1.5% increase of DFTD selectivity was achieved at an additional 4.6% MFTD conversion by prolonging the reaction time from 6 h to 12 h. This result demonstrated that the reaction time had a relatively small impact on altering the final product selectivity.
Temperature oC
4
100 50 0 1000
2000
3000
4000
5000
6000
7000
8000
Time /s Fig. 3. TPD profiles of various catalysts.
Porosity properties of different catalysts were summarized in Table 2. The BET surface area and pore volume of MCM-41 were 907 m2 /g and 0.775 cm3 /g, respectively. These two values for 2% Rh supported MCM-41 dropped to 774 m2 /g and 0.551 cm3 /g, due to the introduction of Rh. Further increasing Co loading, however, only slightly decreased the surface area and pore volume, which was in accordance with the homogenous Co distribution throughout the matrix of MCM-41. In order to probe the electronic properties of Rh and Co in the catalysts, the binding energies (B.E.) were tabulated. Standard binding energy for Co 2p3/2 and Rh 3d5/2 is 780 eV and 307 eV, respectively. For 2% Rh–MCM-41, the value of B.E. for Rh 3d5/2 was 307 eV, indicating negligible interaction between Rh and the MCM-41. Increasing Co loading altered the electronic structure of Rh, reflected by its shifting towards higher B.E. It was observed that the B.E. for Rh 3d5/2 shifted from 307.8 eV to 308.61 eV when
Fig. 4. HRTEM of various catalysts: (a) 2Rh/MCM-41, (b) 0.5Co–2Rh/MCM-41, (c) 2Co–2Rh/MCM-41(before the reaction), (d) 4Co–2Rh/MCM-41; (e) 2Co–2Rh/MCM-41(after the reaction).
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Co loading was gradually increased from 0.5% to 4%. Although there are some differences between the catalysts evaluated regarding the binding energy of Rh, the oxidation state of Rh species was Rh0 for all the experimented catalysts. On the other hand, the B.E. of Co 2p3/2 were remarkably lower than that of standard Co (Co 2p3/2 = 780 eV) when Co was introduced into Rh/MCM-41. The shift of binding energies for Co and Rh provided an evidence for the strong interaction between Co and Rh, which modified the electronic properties of the metals. This modification likely affected the DCPD conversion and DFTD selectivity in the catalysis. 3.3. TPR and TPD-H2 TPR was used to probe the status of Rh in these M-modified Rh–MCM-41 catalyst precursors (before reduction, existing as oxides). The results were summarized in Fig. 2. The reduction peak of RhOx in Fe-Rh/MCM-41 was superimposable with that of RhOx as a reference material. On the other hand, RhOx reduction peaks with all other metal (Cu, Ni and Co) modified materials shifted to higher temperatures compared to the reference RhOx. The extent of peak shift was in the order of Cu > Co ∼ Ni. In addition, the area under curve (AUC) for RhOx reduction was also altered after different M modification. Compared to Rh/MCM-41, the AUCs after Cu, Fe and Ni modification were greater than that of reference material RhOx. In the Co–Rh/MCM-41 catalyst, increasing the amount of Co added to Rh/MCM-41 resulted in a decrease in H2 consumption needed for RhOx reduction, indicating less Rh element was exposed on the surface. Thus, the improved activity of Co–Rh MCM-41 catalyst can be postulated to arise from the formation of more active Rh species on the surface which was likely induced and stabilized by the Co modification. H2 -TPD was used to study the nature of M modification on Rh/MCM-41. As shown in Fig. 3, all the catalysts had desorption peaks centered at similar temperature, indicating negligible change on the Rh dispersion after the metal modification. And the peak areas increased by following the order: 0.5Co–2%Rh/MCM-41 < 1Co–2%Rh/MCM-41 < 2%Rh/MCM41 ∼ 2Co–2%Rh/MCM-41 < 4Co–2%Rh/MCM-41. The Rh availability on the surface of MCM-41 was expected to decrease at a low Co loading (less than 1% in Rh/MCM-41), while a higher Rh availability on the surface of MCM-41 was observed at a higher Co loading (more than2% in Rh/MCM-41), which might be ascribed to the formation of a different Rh status. 3.4. TEM TEM images of different Rh based catalysts supported on MCM41 are shown in Fig. 4. It was observed that Rh nanoparticles with narrow size distributions were successfully deposited throughout the matrix of MCM-41 support, which was consistent with aforementioned results (e.g., XRD and metal dispersion on TPD-H2 ). The addition of Co had minimal influence on the size distribution of Rh nanoparticles, suggesting the modification primarily impacted the electronic properties rather than structural properties. TEM images of 2Co–2Rh/MCM-41 before and after the reaction are also shown in Fig. 4. As revealed by Fig. 4e, no appreciable change in Rh particle size was observed for the spent catalyst compared to fresh catalyst, suggesting that Rh nanoparticles were relatively stable under the reaction conditions (reaction temperature of 140 ◦ C). 4. Conclusion Five different Rh-based catalysts supported on MCM-41 were prepared by incipient wetness method, and were evaluated based on their catalytic performance for hydroformylation of DCPD. At almost complete conversion, the selectivity for desired product
5
DFTD was only 8.7% using monometallic Rh/MCM-41 catalyst. However, at a similar conversion, the selectivity was enhanced to 76.2% using the bimetallic Co–Rh/MCM-41 catalyst, even at a very lowing Co loading (0.5% in Rh/MCM-41). Extensive catalyst characterization was carried out to provide insights into the enhancement on selectivity after the Co addition. The TPR data indicated that the enhanced performance could arise from the presence of the more active Rh species on the surface, likely due to the Co modification. TPD-H2 , XRD, BET and TEM analysis showed little effect on the dispersion of Rh nanoparticles from the metal addition. Electronic properties of the M-modified Rh catalysts, however, were found to be greatly different from the monometallic Rh catalyst. It was speculated that the collective change in the electronics of Rh and the other added metals, would have an effect on the physichemical interaction between the reactant and product during the reaction, thereby changing the product distributions. In summary, Co modified Rh/MCM-41 catalysts can substantially enhance DFTD selectivity at almost complete DCPD conversion. This improvement was likely derived from the surface interactions between DCPD/DFTD and the active site on the bimetallic catalyst. This bimetallic catalytic system could be potentially promising in catalyzing hydroformylation reactions with other cyclic or acyclic di-enes for the selective production of valuable chemicals. Acknowledgments This work has been financially supported by Chinese Government “Thousand Talent” Program (Y42H291501), National Natural Science Foundation of China (U1139302, U1403192), Chinese Academy of Sciences (XBBS201114, 2015RC013) and Urumqi Science & Technology Bureau (Y121120006). References [1] Y.I.Y. Fujikura, N. Takaishi, H. Ikeda, Stereospecific hydroformylation of endo-dicyclopentadiene in the presence of rhodium complex catalysts. A route to endo-tricyclo[5.2.1.02,6]dec-8-exo-ylcarbinol, precursor of 4homoisotwistane, Synth. Commun. 6 (1976) 199–207. [2] Y.I.K. Aigami, N. Takaishi, Y. Fujikura, A. Takatsuki, G. Tamura, Biologicallyactive polycycloalkanes. 2. Antiviral 4-homoisotwistane derivatives, J. Med. Chem. 19 (1976) 536–540. [3] P.S.R. S.M. Barrington, Synthetic lubricants, US3005775, 1961. [4] A.C. P. Gloeckner, W. Andrejewski, Unsatrurated amorphous polyesters based on certain diciol isomers, US0526236, 2005. [5] P.W.N.M. Van Leeuwen, C.F. Roobeek, The hydroformylation of butadiene catalysed by rhodium-diphosphine complexes, J. Mol. Catal. 31 (1985) 345–353. [6] S.E.M.D.L. Hunter, P.E. Garrou, R.A. Dubois, Syn–gas reactions with cobalt subgroup clusters. 2. Dicyclopentadiene hydroformylation catalyzed by RhxCo4-x(CO)12 (x = 4, 2–0)/tertiary amine ctalysts, Appl. Catal. 19 (1985) 259–273. [7] G.E.H. P.E. Garrou, Hydroformylation of dicyclopentadiene to its dimethanolic derivatives, US 4 262 147, 1981. [8] M.M.L. Garlaschelli, M.C. Iapalucci, G. Longoni, Hydroformylation and hydrocarbonylation of dicyclopentadiene with cobalt rhodium catalytic-system promoted by triphenylphosphine—synthesis of monoformyltricyclodecenes, diformyltricyclodecanes and di(tricyclodecenyl)ketones, J. Mol. Catal. 68 (1991) 7–21. [9] X. Pi, Y. Zhou, L. Zhou, M. Yuan, R. Li, H. Fu, H. Chen, Dicyclopentadiene hydroformylation in an aqueous/organic two phase system in the presence of a cationic surfactant, Chin. J. Catal. 32 (2011) 566–571. [10] R. Luo, H.-r. Liang, X.-l. Zheng, H.-y. Fu, M.-l. Yuan, R.-x. Li, H. Chen, Highly efficient catalytic system for the formation of dialdehydes from dicyclopentadiene hydroformylation, Catal. Commun. 50 (2014) 29–33. [11] F.R. Hartley, Supported Metal Complexes, A New Generation of Catalysts, Reidel, Dordrecht, 1985. [12] Y. Iwasawa, Tailored Metal Catalysts, Reidel, Dordrecht, 1986. [13] M. Lenarda, L. Storaro, R. Ganzerla, Hydroformylation of simple olefins catalyzed by metals and clusters supported on unfunctionalized inorganic carriers, J. Mol. Catal. A: Chem. 111 (1996) 203–237. [14] L. Yan, Y.J. Ding, H.J. Zhu, J.M. Xiong, T. Wang, Z.D. Pan, L.W. Lin, Ligand modified real heterogeneous catalysts for fixed-bed hydroformylation of propylene, J. Mol. Catal. A: Chem. 234 (2005) 1–7.
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[15] L. Huang, Y. He, S. Kawi, Catalytic studies of aminated MCM-41-tethered rhodium complexes for 1-hexene hydroformylation, Appl. Catal., A: Gen. 265 (2004) 247–257. [16] L. Huang, J.C. Wu, S. Kawi, Rh4(CO)12-derived functionalized MCM-41-tethered rhodium complexes: preparation, characterization and catalysis for cyclohexene hydroformylation, J. Mol. Catal. A: Chem. 206 (2003) 371–387.
[17] S.K.L. Huang, {RhCl(CO)(2)}(2)-derived MCM-41-tethered rhodium complex catalysts via phosphine, amine and thiol ligands for cyclohexene hydroformylation, Bull. Chem. Soc. Jpn. 77 (2004) 295–302. [18] L. Huang, S. Kawi, An active and stable Wilkinson’s complex-derived SiO2 tethered catalyst via an amine ligand for cyclohexene hydroformylation, Catal. Lett. 92 (2004) 57–62.
Please cite this article in press as: Y. Ma, et al., Rh-based catalysts supported on MCM-41-type mesoporous silica for dicyclopentadiene hydroformylation, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.04.007