Research Article pubs.acs.org/journal/ascecg
Environmentally Benign Bioderived Carbon Microspheres-Supported Molybdena Nanoparticles as Catalyst for the Epoxidation Reaction Dhananjay S. Doke,‡ Shubhangi B. Umbarkar,‡,§ Manoj B. Gawande,∥ Radek Zboril,∥ and Ankush V. Biradar*,†,‡,§
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Inorganic Materials and Catalysis Division, CSIR-Central Salt and Marine Chemical Research Institute, Bhavnagar 364002, Gujarat, India ‡ Catalysis Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, Maharashtra, India § Academy of Scientific and Innovative Research, ACSIR, Anusandhan Bhawan, New Delhi 110 001, India ∥ Regional Centre of Advanced Technologies and Materials, Faculty of Science, Department of Physical Chemistry, Palacký University, Šlechtitelů 27, 783 71 Olomouc, Czech Republic S Supporting Information *
ABSTRACT: A one-pot synthesis of molybdenum oxide nanoparticles (NPs) supported on bioderived carbon microspheres is reported. The catalyst was synthesized by the low temperature hydrothermal (LTH) method using D-glucose and bagasse as the carbon source. The carbonization of bagasse resulted in the formation of nonuniform carbon microspheres while glucose resulted in uniform carbon spheres. SEM and STEM elemental mapping show the uniform distribution of molybdenum oxide NPs over the carbon microspheres. XPS spectroscopy confirmed that molybdenum was in the Mo6+ oxidation state. The 1% MoO3 supported on carbon microspheres derived from D-glucose showed excellent catalytic activity up to 100% olefin conversion with 100% epoxide selectivity using organic tert-butyl hydroperoxide as an oxidant. The catalyst was successfully used for up to five cycles without losing substantial activity and selectivity. KEYWORDS: Carbon microspheres, Hydrothermal synthesis, Epoxidation, TBHP, Heterogeneous catalysis
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structures or morphologies of carbon such as carbon sphere8 and hollow carbon sphere,9,10 by low temperature hydrothermal (LTH) synthesis using readily available sugars (glucose). Furthermore, there are reports on the utilization of biomass (e.g., nut shells, wood, and peat) for the synthesis of different types of carbons. This biomass consists of a high amount of cellulose and hemicellulose. Therefore, they can be used as a raw material for carbon synthesis. Bagasse (BA) from sugar cane can be another very useful bioderived carbon source, which is produced annually in large quantities as a waste material by sugar mills. Generally, this bagasse is burned for the generation of steam for electricity production. However, during
INTRODUCTION Carbon-based materials have long been known for their versatile applications such as adsorbents, rubber enrichment materials, fuel-blending materials, or pigments.1 Recently, carbonaceous materials have attracted more attention in various types of applications such as adsorbents, gas storage, electrode, carbon fuel cells, and catalyst supports.2,3 The aforementioned carbon was synthesized by a carbonization method using petroleum coke and wood under controlled air.4 Lately, different morphologies of carbon have been reported using different methods including, for instance, laser ablation,5 hydrothermal carbonization,6 or high voltage arc.7 Among the various synthetic methodologies employed, hydrothermal synthesis has merit as the one-pot synthesis of metal oxides/ carbon having distinctive nano/micro assembly. Several reports appear in the literature concerning the synthesis of different © 2016 American Chemical Society
Received: September 15, 2016 Revised: November 11, 2016 Published: November 18, 2016 904
DOI: 10.1021/acssuschemeng.6b02229 ACS Sustainable Chem. Eng. 2017, 5, 904−910
Research Article
ACS Sustainable Chemistry & Engineering this process, a large amount of carbon is released into the atmosphere, which adds to the increase in atmospheric carbon dioxide. Hence, possible use of this cellulosic material for carbon synthesis could be an interesting and valuable addition. To this end, some efforts have been made to utilize BA as a raw material for the synthesis of carbon by physical activation and carbonization.11 Various carbon-supported metal oxides were used as catalysts for different organic transformations.12 Among these, carbonsupported molybdena catalysts represent a special class owing to their catalytic applications in Fischer−Tropsch synthesis,13 alkane isomerization,14 hydrodesulfurization,15 higher alcohol synthesis,16 Fridel−Crafts alkylation,17 etc. For instance, Radovic et al.13 have used carbon-supported molybdena catalysts for hydrodesulfurization and Fischer−Tropsch synthesis. Del Gallo et al.14 have used MoO3-carbon for selective isomerization of n-butane. Zdražil and co-workers15 have synthesized MoO3 supported on carbon and used it for hydrodesulfurization activity. Shoja and co-workers16 synthesized alkalized MoO3 nanocatalyst supported on carbon nanotubes (CNTs) for higher alcohol synthesis in a fixed bed microreactor. Also, carbon microspheres-supported molybdena was used for a Friedel−Crafts alkylation reaction.17 Hong et al.18 have reported hydrodeoxygenation of maize oil by using molybdenum supported on reduced graphene oxide, activated charcoal, graphite, and fullerenes. Very few reports are available dealing with the utilization of molybdena supported on carbon catalysts for the epoxidation of olefins. Goto et al.19 have reported epoxidation of olefin using molybdena supported on activated carbon and tert-butyl hydroperoxide (TBHP) as an oxidant with 95% conversion and epoxide as the sole product. However, the recyclability of the catalyst was not studied. Chen and co-workers20 have reported the epoxidation of olefin using the magnetic γFe2O3@C@MoO3 core−shell catalyst. Despite an excellent catalytic activity as well as recyclability (97.3% conv and 99.9% sel), these approaches have used complicated synthesis procedures, high MoO3 loading (37.8%), and hazardous chemicals like HNO3. In another report, Hyeon et al.21 carried out olefin epoxidation by employing magnetically separable mesoporous molybdena silica microspheres. They obtained a 99% cyclooctene-oxide yield in 5 h. Recently, we utilized molybdena supported on oxide supports synthesized by the “resin burn method” for olefin epoxidation.22 The MoO3/SiO2 catalyst showed high activity in terms of >90% conversion, 96% selectivity, and recyclability. A large amount of research is being performed on the synthesis of high yields of epoxides which are used as synthons for the synthesis of a wide variety of chemicals such as drugs, agrochemicals, and food additives.23,24 Herein, we report synthesis and catalytic activity of molybdenum oxide NPs supported on bioderived carbon microspheres. The carbon microspheres (CMs) were synthesized using different precursors in one-step hydrothermal synthesis and used olefin epoxidation reactions.
Scheme 1. Schematic for Synthesis of MoO3/CMs from Bioderived Carbon Precursors
dissolved in distilled water, and packed in an autoclave. The carbonization was carried out for 12 h by keeping the autoclave in the furnace at 180 °C under static conditions. The reaction occurred between the finely powdered BA, DG, and OA at the reaction temperature. For convenience, the respective catalysts were named BCM for carbon spheres synthesized from bagasse, and GCMs for carbon spheres synthesized from glucose. In addition, the following notation was used: 1A-MoO3/BCMs used 1% NH4Mo7O26·4H2O supported on BCMs; 1S-MoO3/ BCMs used 1% Na2MoO4·2H2O supported on BCMs; 1SMoO3/GCMs used 1% Na2MoO4·2H2O supported on GCMs; 1A-MoO3/GCMs used 1% NH4Mo7O26·4H2O supported on GCMs; and 10A-MoO3/BCMs used 10% NH4Mo7O26·4H2O supported on BCMs. The hydrothermal treatment of finely milled fibers of BA/DG led to the formation of CMs. The CMs were formed through two possible pathways. First, the hemicellulose in BA undergoes hydrolysis, which is catalyzed by a strong dicarboxylic acid, i.e., oxalic acid (OA)25 to yield glucose before further dehydration yielding 5-(hydroxymethyl)furfural (5-HMF). 5-HMF is further condensed and polymerized to form solid carbon with OH, CO, and COOH groups on the carbon surface. Also, owing to the autogenerated high pressure, the polymerized product tries to minimize the pressure by forming a spherical shape.26 The other possibility for the formation of CM is direct self-condensation and decarboxylation of cellulose and hemicellulose under the reaction conditions. The phase purity and crystallinity of synthesized catalysts were analyzed by powder X-ray diffraction. The Bragg diffraction patterns of the CMs and the MoO3/CMs catalyst showed a sharp diffraction peak at 25° which corresponds to the (002) plane of the graphitic carbon framework (Figure 1Aa,c),27 whereas a broad peak observed in the case of MoO3 NPs supported on D-glucose derived carbon clearly indicates that the CMs are amorphous in nature (Figure 1Ad,e). The 10A-MoO3/BCMs (10 wt %, MoO3/CMs prepared from
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RESULTS AND DISCUSSION A series of molybdenum oxide supported carbon microspheres (MoO3/CMs) were synthesized by one-pot hydrothermal carbonization using different carbon sources and molybdena precursors (Scheme 1). Different carbon sources such as bagasse (BA) or D-glucose (DG), oxalic acid (OA), and molybdena precursors, i.e., NH4Mo7O26·4H2O (AHM) or Na2MoO4·2H2O (SM), were
Figure 1. (A) Powder XRD patterns of the (a) BCM; (b) 1A-MoO3/ BCMs; (c) 1S-MoO3/BCMs; (d) 1S-MoO3/GCMs; (e) 1A-MoO3/ GCMs; (f) 10A-MoO3/BCMs. (B) FTIR spectra of (a) 1A-MoO3/ BCMs; (b) 1A-MoO3/GCMs; (c) 10A-MoO3/BCMs; (d) 1S-MoO3/ GCMs; and (e) 1S-MoO3/BCMs. 905
DOI: 10.1021/acssuschemeng.6b02229 ACS Sustainable Chem. Eng. 2017, 5, 904−910
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ACS Sustainable Chemistry & Engineering bagasse and ammonium heptamolybdate) (Supporting Information Figure S1) showed sharp Bragg reflections at 2θ = 23.4° (110), 26.2° (040), and 36.2° (060), which are characteristic peaks of the α-MoO3 orthorhombic phase having crystalline nature (Figure 1Af, JCPDS 05-0508).28 Other samples containing 1% MoO3 NPs supported on CMs did not show any diffraction peaks of molybdena due to its lower percentage (Figure 1Ab,e). The FTIR analysis (Figure 1B and for full range spectra see Figure S2) of all the samples showed distinct vibrational bands for CC, CO, and CH stretching. The bands at 1702 and 1613 cm −1 can be attributed to CO and CC, respectively.29−31 The bands at approximately 2900 and 3300−3700 cm−1 corresponded to stretching vibrations of aliphatic CH and OH, respectively (see Figure S2).32,33 The intensities of the hydroxyl or carboxyl groups are weaker in DG carbon as compared to BA carbon, thereby disclosing the dehydration reaction which was more prominent in DG carbon as compared to bagasse carbon. The new band appearance at 1613 and 1510 cm−1 conforms to the increased aromatization of carbon. After completion of the glucose carbonization reaction, the band intensity at 1702 cm−1 (CO) and the wide band at approximately 3000−3700 cm−1 (OH) (Figure 1Bb,d) disappeared because of oxygen removal from parent carbon. The band intensity increased at 1613 cm−1 due to the more aromatic carbon (CC) in the carbon framework. These data reveal an increase in the aromatization as the reaction temperature rises, which is typical for a carbonization process.33 Due to low concentration of molybdenum on the catalyst surface, its FTIR adsorption peaks appeared with very low intensity (Figure S2). The characteristic absorption band at 970 cm−1 for the terminal MoO bond and the peaks at 902 and 801 cm−1 are attributed to the MoOMo vibrations of Mo6+, which indicates the presence of MoO3 nanoparticles on the carbon support. Other stretching bands did not appear prominently as most of the molybdenum might be buried in the carbon framework.34 The surface area and pore diameter of the synthesized carbon microspheres were determined by the Brunauer−Emmett− Teller (BET) method using N2 adsorption (Figure S3). The surface area of 1A-MoO3/GCMs was found to be 46.3 m2/g with average pore diameter 16.4 nm, whereas the 10A-MoO3/ GCMs sample showed 5 m2/g with pore diameter 30.91 nm. The porous material formed due to the evolution of ammonia from the AHM. TEM image of 1S-MoO3/BCMs (prepared from sodium molybdate precursor) disclosed that carbonization of bagasse results in nonuniformly sized CMs having MoO3 nanoparticles of size 5−10 nm uniformly distributed over CMs (Figure 2A,B). The reason for the appearance of separate molybdena nanoparticles was due to the weak interactions among sodium molybdate and the BCMs matrix. SEM elemental mapping of the same sample shows uniform distribution of all the metals over the carbon microspheres (Figure S4b). Furthermore, ICP-OES analysis showed 9.79 × 10−2 mmol/g molybdenum content. This result also corresponds with SEM (including elemental mapping), and EDAX analysis of other BA carbon-based materials is shown in Figures S4−S6. MoO3/ BCMs showed a nonuniform structure, as is the case for 1AMoO3/BCMs and 10A-MoO3/BCMs (prepared from ammonium heptamolybdate (AHM) precursor). The reason for the formation of nonuniformly sized particles in the case of BA carbon is that BA is composed of large polymeric units of
Figure 2. (A, B) HRTEM micrographs of 1S-MoO3/BCMs. (C) SEM elemental mapping of 1S-MoO3/BCMs. (D, E) HRTEM micrographs of 1A-MoO3/GCMs. (F) SEM elemental mapping of 1AMoO3/ GCMs. The yellow color represents molybdenum, the green color oxygen, and the red color carbon.
monosaccharides and the presence of ammonia which is released from AHM that inhibits the growth of uniform carbon microspheres. The CMs synthesized from the DG are monodispersed and spherical in shape. The average particle size of the MoO3 nanoparticle was 4.2 nm for the 1A-MoO3/ GCMs and 4.16 nm for 1S-MoO3/GCMs catalysts (see TEM and SEM including elemental analysis and average particle size of MoO3/GCMs; Supporting Information Figures S4 and S7− 10). No separate MoO3 NPs were observed for AHM supported on GCMs due to being embedded in the carbon matrix. Elemental mapping of various components is displayed in Figure 2C−F. STEM analysis of 1A-MoO3/GCMs is shown in Figure 3, and the results confirm the presence of Mo atoms
Figure 3. STEM image of 1A-MoO3/GCMs showing (A) Mo atoms; (B) O atom; (C) overall dispersion of Mo, O, and C of 1A-MoO3/ GCMs; (D) HAADF image of 1A-MoO3/GCMs; and (E) STEM-EDS of 1A-MoO3/GCMs.
(red color) on the surface of carbon spheres (green color). Oxygen atoms (blue color) are homogeneously present on the bagasse carbon sample. The STEM result further corroborates the distribution of molybdena NPs within the material (Figure 3C). Figure 3D shows the high angle annular dark field (HAADF) STEM image of 1A-MoO3/GCMs. Elemental analysis results were found to be in agreement with EDAX analysis (Figure 3E). 906
DOI: 10.1021/acssuschemeng.6b02229 ACS Sustainable Chem. Eng. 2017, 5, 904−910
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ACS Sustainable Chemistry & Engineering XPS analysis was carried out to obtain the chemical and electronic state of molybdena on CMs. XPS spectra of 1AMoO3/GCMs are shown in Figure 4. XPS spectra of all other
Table 1. Results of Cyclooctene Epoxidation Using Different MoO3 wt % Supported on Different Carbon Spheresa entry
catalyst
% conv
% epoxide sel
1. 2. 3. 4. 5. 6. 7.
without catalyst CMs 10A-MoO3/BCMs 1A-MoO3/BCMs 1S-MoO3/BCMs 1S-MoO3/GCMs 1A-MoO3/GCMs
12 12 90 22 72 60 80 100b
100 100 100 69 100 100 100 100
rate constant, k (mol−1 s−1) 0.0076 0.0076 0.5000 0.0157 0.1429 0.0833 0.2222
a
Reaction conditions: cyclooctene, 2.5 mmol; oxidant, 5.5 M TBHP in decane (2.5 mmol); catalyst, 10 wt % of substrate (0.019 mM of MoO3); solvent, 1,2-dichloroethane, 6 g; chlorobenzene (internal standard), 15 mmol; time, 2 h; temperature, 80 °C. bIn this case, reaction time was 3 h.
A cyclooctene conversion of 72% was obtained with 100% selectivity for the epoxide. 1S-MoO3/GCMs catalyst showed 60% cyclooctene conversion and 100% epoxide selectivity. Among other catalysts, 1A-MoO3/GCMs showed a maximum catalytic activity of 100% cyclooctene conversion and 100% epoxide selectivity. The rate of reaction was found to be very high (0.2222 mol−1 s−1). 1A-MoO3/GCMs had a uniform size and shape; therefore, molybdena was more available for olefin epoxidation. The catalytic activity of molybdena supported on GCMs was superior to that of BA-derived catalysts. This may be due to the greater amorphous nature of the GCMs and the well-dispersed molybdena embedded in the GCM matrix compared to BCM. Also, the molybdena precursor AHM interacts more favorably with D-glucose or BA compared to SMA during the hydrothermal treatment. Thus, catalytic materials using AHM as the molybdena precursor gave better catalytic results. The progress of the reaction was monitored by periodically withdrawing the samples and injecting them into a gas chromatograph. The time versus conversion and selectivity curve for the aforementioned reaction showed linear increase in conversion with constant epoxide selectivity (Figure S14). Then, the best catalyst (1A-MoO3/GCMs) was chosen to study the wider applicability for different substrates. The epoxidation of a substrate like cyclohexene having more ring strain was also successfully converted into an epoxide (∼100%) product (Table 2, entry 1) a little slower reaction rate (0.0185 mol−1 s−1). Both cyclooctene and two-double-bond-containing alkenes converted efficiently. Alkenes with two double bonds took a longer reaction time along with less selectivity toward the second bond epoxidation, i.e., 58% and 48% selectivity for the 1,2-epoxide and 5,6-diepoxide, respectively (Table 2, entry 3). On the contrary, styrene did not show promising results under identical reaction conditions (Table 2, entry 4), as it gave 48% styrene conversion with only 44% epoxide selectivity; this may be attributed to the extra stability of styrene which may further cleave the double bond to yield benzaldehyde and the miscibility of styrene in the given reaction conditions which was much lower. Also, less reactive molecules like n-hexene, 3butene-2-ol, and 3-butene-1-ol were converted to epoxide with a high reaction rate (0.2222 mol−1 s−1) to selectively give epoxide as product. An industrially important fragrance molecule, limonene, also gave high epoxide selectivity. The obtained data revealed that 1A-MoO3/GCMs is one of the best among the reported catalysts based on molybdena
Figure 4. XPS spectra of (A) 1A-MoO3/GCMs, (B) Mo present in 1MoO3/GCMs, (C) carbon present in 1A-MoO3/GCMs, (D) oxygen present in 1A-MoO3/GCMs.
samples are given in Figures S10−13. XPS analysis of molybdena supported on CMs showed peaks at 232.6 and 235.6 eV due to Mo 3d5/2 and Mo 3d3/2, respectively (Figure 4B). Peak fitting of C 1s shows multiple signals between 284.6 and 288.1 eV, which arise from CC, CHx, CC, COR, CO, and COOH groups (Figure S13C).35,36 Also, the association of oxygen to carbon was validated by the O 1s spectrum, in which multiple signals appeared at 531.7 and 533.0 eV.36 These results correspond with those obtained from the FTIR revealing the presence of both aromatic and aliphatic carbon functional groups.
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CATALYST ACTIVITY The catalytic activity of the synthesized catalyst was evaluated for olefin epoxidation (Scheme 2). The model reaction was carried out with cyclooctene using different catalysts with TBHP as an oxidant at 80 °C. Scheme 2. Cyclooctene Epoxidation Reaction
Initially, the reaction was carried out without catalyst or active metal-loaded catalyst to test the catalytic properties of the only CMs. This gave only 12% conversion, which could be attributed to autocatalysis by the oxidant.37 When 10A-MoO3/ BCMs was used as the catalyst, 90% of the substrate was converted with 100% selectivity for the corresponding epoxide within 3 h (Table 1, entry 3). 1A-MoO3/BCMs gave only 22% conversion with 69% selectivity for the epoxide, because of the nonuniform size and shape of the former (Figure S4,A). 1SMoO3/BMCs were more catalytically active despite the nonuniform size and shape of the support. This may be attributed to the uniform distribution of molybdenum nanoparticles of 0.5−10 nm size over the carbon surface (Figure S7). 907
DOI: 10.1021/acssuschemeng.6b02229 ACS Sustainable Chem. Eng. 2017, 5, 904−910
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ACS Sustainable Chemistry & Engineering Table 2. Oxidation of Various Olefins Catalyzed by 1AMoO3/GCMs Using Organic TBHP as an Oxidanta
Figure 5. Recycle study of 1-MoO3/GCMs catalyst.
the carbon spheres. TEM analysis showed MoO3 nanoparticles 5−10 nm in size, uniformly distributed over BCMs. In comparison, no separate molybdena nanoparticles were observed in the case of GCMs as they were embedded in GCM matrix. 1A-MoO3/GCMs gave the best results in terms of catalytic activity and selectivity for olefin epoxidation. Recycle studies showed that this catalyst could be reused for up to five cycles without any loss of catalytic activity.
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EXPERIMENTAL SECTION
All of the reagents including ammonium heptamolybdate (AHM) (S. D. Fine Chemical India) and sodium molybdate (Molychem India Ltd.), cyclooctene, cyclohexene, D-glucose and 5.5 M TBHP in decane (Aldrich India), oxalic acid (Ranchem, India), ethanol (cymprangludt BV), and bagasse of sugar cane (from local sugar mills, India) were purchased and used without further purification. In a typical synthesis, the 150 mL Teflon coated closed pressure reactor was charged with 3 g of finely powered bagasse, 1 g of oxalic acid, 0.3 g of ammonium heptamolybdate, and 100 mL of deionized water. Subsequently, the autoclave was kept in a furnace for 12 h at 180 °C. After completion of reaction, the reactor was cooled to room temperature, and the reaction mixture was filtered through Whatman filter paper. The residue was washed with water and ethanol−water mixture (1:1). The final solid was dried at room temperature. The product was abbreviated as 10A-MoO3/BCMs. For the synthesis of the 1A-MoO3/BCMs catalyst, the abovementioned procedure was followed with NH4Mo7O26·4H2O (0.03 g) instead. For the synthesis of the 1S-MoO3/BCMs catalyst, the abovementioned procedure was followed with Na2MoO4·2H2O (0.03 g) instead. For the synthesis of the 1S-MoO3/GCMs catalyst, the abovementioned procedure was followed but with D-glucose (3 g) and Na2MoO4·2H2O (0.03 g). For the synthesis of the 1A-MoO3/GCMs catalyst, the abovementioned procedure was followed but with NH4Mo7O26·4H2O (0.03 g). Catalyst Characterization. All the catalysts were characterized by various physicochemical techniques, and details for the instruments and methods are given in Supporting Information section S1. Typical Reaction Procedure. The liquid phase catalytic epoxidation reaction was carried out in a 25 mL two-necked roundbottom flask equipped with a magnetic stirrer and immersed in a thermostat oil bath. The flask was charged with olefin (2.5 mmol) and oxidant (2.5 mmol) 5.5 M TBHP in decane; catalyst loadings were taken as 10 wt % of the substrate, and dichloroethane (6 g) was used as a solvent with chlorobenzene (15 mmol) internal standard. The samples were withdrawn periodically and analyzed on Agilent 7890B gas chromatograph equipped with a HP-5 column coated with 5%
a
Reaction conditions: substrate, 2.5 mmol; solvent, 1,2-dichloroethane, 6 g. TBHP, 2.5 mmol; catalyst, 1A-MoO3/GCMs, 10 wt % of substrate; chlorobenzene (internal standard), 15 mmol; reaction temperature, 80 °C. Asterisk (*) indicates that the remaining products were 1,2- and 5,6-diepoxides. Number sign (#) indicates that the remaining products were 1,2- and 9,10-diepoxides.
supported on carbon, with higher catalytic activity in terms of conversion and selectivity. The best catalyst, i.e., 1A-MoO3/GCMs, was used under optimized reaction conditions to test for the catalyst reusability by stopping the epoxidation reaction of cyclooctene at lower substrate conversion (∼80%). After each reaction cycle, the catalyst was separated by filtration from the reaction mixture and washed with 1,2-dichloroethane. There was no considerable decrease in the conversion and selectivity for epoxide even after five cycles (Figure 5). The GCM matrix embedding active MoO3 nanoparticles was responsible for the superior catalytic activity of 1A-MoO3/GCMs (see HRTEM and STEM images in Figures 2 and 3).
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CONCLUSIONS To conclude, we have used a simple environmentally benign bottom-up route for the synthesis of molybdenum oxide nanoparticles supported on bioderived carbon microspheres through the hydrothermal carbonization of bagasse and Dglucose as carbon precursors. The carbon spheres were formed by using a hydrolysis and condensation route catalyzed by oxalic acid. The bagasse source led to nonuniform carbon spheres, whereas glucose yielded uniformly shaped carbon spheres. SEM and STEM elemental mapping proved the uniform distribution of MoO3 nanoparticles (0.5−10 nm) over 908
DOI: 10.1021/acssuschemeng.6b02229 ACS Sustainable Chem. Eng. 2017, 5, 904−910
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ACS Sustainable Chemistry & Engineering phenyl 95% dimethylpolysiloxane (60 m length, 0.25 mm diameter, and 0.25 μm film thicknesses) and a flame ionization detector.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02229. Details on the preparation of the samples; complete description of the XPS, SEM, TEM, and STEM characterization tools; and detailed catalytic results (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Dhananjay S. Doke: 0000-0001-7906-7053 Ankush V. Biradar: 0000-0003-0111-3931 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS A.V.B. acknowledges the Director of CSIR-NCL for providing QHS, in-house project MLP 028026, and SERB (DST), Government of India, for fast tract project SERB/F/6598/ 2013-14. Authors are thankful to Dr A. Das, Director, CSMCRI Bhavnagar, for kind approval to carry out this work; to Dr S. Neogi for BET surface area measurements; and to Ondrej Tomanec for HRTEM images. CSIR-CSMCRI Communication No-141/2016.
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