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A Novel Reaction-Controlled Foam-Type Polyoxometalate Catalyst for Deep Oxidative Desulfurization of Fuels Wenshuai Zhu, Yanhong Chao, Huaming Li, Peiwen Wu, Fang Zou, Suhang Xun, Fengxia Zhu, and Zhen Zhao Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 04 Nov 2013 Downloaded from http://pubs.acs.org on November 18, 2013

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Industrial & Engineering Chemistry Research

A Novel Reaction-Controlled Foam-Type Polyoxometalate Catalyst for Deep Oxidative Desulfurization of Fuels Wenshuai Zhu,* [a] Peiwen Wu,

[a]

Yanhong Chao, [b] Huaming Li,* [a] Fang Zou, [a] Suhang Xun, [a]

Fengxia Zhu, [a] Zhen Zhao[c]

a

School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, 212013 (P. R. China), Fax: (+86)

511-8879-1108 , E-mail: [email protected](H. M. Li); [email protected](W. S. Zhu) b

School of Pharmacy, School of the Environment, Jiangsu University, Zhenjiang, 212013 (P. R. China)

c

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249 (P.R. China)

1

ACS Paragon Plus Environment


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Abstract: A novel reaction-controlled foam-type catalyst has been designed by pairing 1-hexadecyl-3-methylimidazolium cation with peroxomolybdate anion. This catalyst switched from the powder to the foam-type active species, exhibiting high catalytic activity in oxidative desulfurization process. After reaction was finished, the foam became brittle and returned to the powder, which could be easily separated and reused. Reasons for this change were discussed detailed by experiments. The removal of DBT could reach 98.4% under the optimal condition of n(DBT): n(catalyst):n(H2O2) = 30:1:180, at 50℃ for 1 h. The catalyst could be recycled six times and the sulfur removal still remained to be about 93.9%.

Keywords: oxidative desulfurization, reaction-controlled, foam-type catalyst, heterogeneous catalysis , homogeneous catalysis

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1. Introduction Polyoxometalates (POMs), which are attractively researched in homogeneous and heterogeneous catalysis, exhibit different features in oxidation, esterification and dehydration etc. reactions1. Homogeneous catalysts are usually of high activity and selectivity, but their separation and reuse can be costly and difficult. Nevertheless, heterogeneous catalyst outweighs homogeneous one and show good recovery, except suffering from the relatively low activities. In view of both advantages and disadvantages of homogeneous and heterogeneous catalysts, the new strategies that facilitate the recycling of homogeneous catalysts have been developed2-3, such as reaction-controlled phase-transfer catalyst4-5, reaction-induced self-separation catalyst6-8 and temperature-responsive catalyst9-12. These catalysts can not only be recovered as those in the heterogeneous process but also exhibit high activity and selectivity as those in the homogeneous reaction. Here we expect our efforts can present a new catalyst strategy with high catalytic efficiency and easy recovery for oxidation reaction. Recently, oxidative desulfurization (ODS) in fuels has been attracting world-wide attentions13-16. Some refractory aromatic thiophenes, such as dibenzothiophene (DBT) and its derivatives in hydrodesulfurization (HDS)15, 17-18, are easy to be removed by the ODS, which is regarded as a promising strategy to achieve an ultra-low sulfur level19-23. Due to its advantages, such as low temperature, atmospheric pressure and high removal of aromatic sulfur compounds, ODS may present a post-treatment to the traditional HDS. Different oxidative systems have been used in ODS and proved to be highly efficient19, 24-27. Reported oxidative desulfurization catalysts included polyoxometalate28-36, organic acid37, ionic liquids38-52, Fenton reagent53, metal oxides hybrids15, 54-57, molecular sieves58-61 and so on. Especially, polyoxometalates as homogeneous catalysts, with 3



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increasingly great importance, could be used under mild conditions for deep oxidative desulfurization10. Because of poor separation and reuse of these catalysts in homogeneous catalysis, polyoxometalates were usually immobilized on the carrier to facilitate the recycling62-63. However, these heterogeneous catalysts suffered from the relative long reaction time, cumbersome preparation procedures and loss of active species. In this paper, a novel reaction-controlled foam-type catalyst [(C16mim)2Mo2O3(O2)4·H2O] (abbreviated as (C16mim)2Mo2O11) was designed by pairing 1-hexadecyl-3-methylimidazolium cation with peroxomolybdate anion, which was fully characterized by FT-IR, TG/DSC, elemental analysis and

1

H and

13

C NMR spectroscopy. In the process of reaction, powder-like

peroxomolybdate catalyst gradually formed foam-type active species by the action of H2O2, and when the oxidative reaction was finished and the H2O2 was used up, the catalyst recovered powder for easy recycling. This catalyst was always heterogeneous in the reaction process. However, foam-type active species with large volume was like pseudo-liquid phase and exhibited high activity. This phenomenon manifested a powder-foam-powder transfer of the catalyst, which was controlled by the reaction, and so we referred to this catalyst as “reaction-controlled foam-type catalyst”.

2. Experimental Section 2.1. Materials. All the other chemicals were of an analytical grade and used as received. Hydrogen peroxide (30 wt.%), tetradecane (99.0%). n-octane, N-methylimidazole, hexadecyl bromide, Na2MoO4·2H2O, acetone, ethanol were analytical pure and purchased from Shanghai Sinopharm

Chemical

Reagent

Co.,

Ltd..

Dibenzothiophene

(98.0%,

DBT),

and

4,6-dimethyldibenzothiophene (97.0%, 4,6-DMDBT) were obtained from Sigma-Aldrich 4


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company. 2.2. Catalyst Characterization. The data of the catalyst elementary analysis was obtained by CHN-O-Rapid (Heraeus Corporation, Germany). NMR spectrum was recorded on an AV-400 spectrometer (Bruker Corporation, Germany) in CDCl3. The infrared spectrum (IR) of the catalyst (KBr pellets) was recorded with a Nicolet Nexus 470 FT-IR instrument. Thermogravimetry and differential scanning (TG/DSC) analysis was done on STA-449C Jupiter (NETZSCH Corporation, Germany). The testing process was 30-800℃ at a heating rate 10℃/min. The content of molybdenum (Mo) was measured by the gravimetric determination. The structure of the catalyst before and after catalysis was characterized by ESI-MS(Thermo LXQ, USA) 2.3. Preparation of [C16mim]2Mo2O3(O2)4·H2O. Na2MoO4·2H2O (5 mmol) was dissolved in water (10 mL) followed by the addition of 30 wt.% H2O2 (6 mL) in ice-water bath under stirring continuously. The formed orange-red solution was treated with diluted hydrochloric acid dropwise under stirring until the pH of the solution was just 4.2. [C16mim]Br (10 mmol) in 95% ethanol (15 mL) was added dropwise into the molybdate solution under stirring to get the white precipitate. The solid was filtered off, washed with water (10 mL) and diethyl ether (10 mL×2), respectively. The white solid was dried in vacuum at 50℃ for 24 h (yielding 96%), which was characterized by FT-IR, TG/DSC, elemental analysis, 1H and 13C NMR spectroscopy and ESI-MS. 2.4. Oxidative Desulfurization Process. Typical procedure for oxidative desulfurization of model oil: DT, DBT and 4,6-DMDBT were dissolved in n-octane to get the model oil with sulfur concentration of 250, 500 and 250 ppm while tetradecane was dissolved as an internal standard substance.

A

mixture

of

the

catalyst,

H2 O2

and

model

oil

(molar

ratio

n(S):

n(catalyst):n(H2O2)=30:1:180) was added into a two-necked flask. Then the reaction system was 5



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stirred under reaction conditions. After the reaction, the mixture was cooled down to room temperature. Model oil was taken out and further analyzed by gas chromatograph.

3. Results and Discussion 3.1. Characterization of the catalyst. The characterization results were done as follows. Elementary analysis(mass percentage): Calc. for ([C16mim]2Mo2O3(O2)4·H2O): C, 48.00; H, 8.06; N, 5.60; Mo, 19.20. Found: C, 48.79; H, 7.64; N, 5.05; Mo, 18.87. The NMR spectral data and ESI-MS for [C16mim]2Mo2O3(O2)4·H2O was measured as follows. 1HNMR(400MHz, CDCl3) 0.81 (s, 3H, CH3), 1.22 (m, 26H, C13H26), 1.82 (s, 2H, CH2), 2.95(s, 2H, H2O ), 4.05(s, 3H, NCH3), 4.25(s, 2H, NCH2), 7.38(s, 1H, NCH),7.58(s,1H, NCH), 9.99 (s, 1H, NCHN), 13CNMR(100 MHz, CDCl3) δ 14.05, 22.61, 26.23, 29.00, 29.28, 29.36, 29.49, 29.57, 29.59, 29.60, 29.63, 30.29, 31.85, 36.65, 50.01, 77.20, 77.55, 121.85, 123.75, 137.32. ESI-MS: m/z (+) = 308, m/z (-) = 189. 3.2. Effect of Different Desulfurization System. To investigate the catalytic activity of (C16mim)2Mo2O11, the oxidation of model oil using hydrogen peroxide as an oxidant was performed. 4, 6-DMDBT and DBT were selected as sulfur compound representatives of those refractory sulfur compounds in fuels (Scheme 1). Sulfur removals in different desulfurization systems were shown in Table 1. Without the catalyst, the DBT removal was merely 2.8%. With the material Na2MoO4 or [C16mim]Br as a catalyst in the desulfurization system, the DBT removal kept low under the same conditions. When (C16mim)2Mo2O11 was used as a catalyst, the DBT removal increased sharply, reaching 98.4%. These results indicated that the designed catalyst (C16mim)2Mo2O11 played a vital role in catalytic oxidation desulfurization. The catalyst turned foam-type in the reaction process and the volume of the catalyst increased largely. Due to the 6


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sufficient contact between the catalyst and the substrate, the catalytic system exhibited high desulfurization efficiency. In this catalytic system, the sulfur removal for 4, 6-DMDBT, the most difficult one to be removed in HDS due to steric hindrance, could reach 78.0%. As expected, the sulfur removal for n-dodecanethiol (DT) was very high, reaching 100%. The oxidized sulfur compounds could be removed from the oil phase by a polar extractant. GC-MS of model oil in the reaction process indicated that the 4, 6-DMDBT and DBT were oxidized to 4, 6-DMDBTO2 and DBTO2. (see the supporting information Figure S1-8)

Scheme 1. Schematic illustration of oxidation of sulfur compounds

Table 1 Effect of different desulfurization systems

3.3. Effect of H2O2/DBT Molar Ratio on Desulfurization. The influence of the amount of H2O2 on the desulfurization and the oxidative efficiency of H2O2 were given in Fig. 1. Stoichiometrically, only 2 mol of H2O2 were consumed when per mole of sulfone was produced. Two competitive reactions were co-existent. One was the oxidation of DBT and the other was H2O2 self-decomposition. When n(H2O2)/n(DBT) was 3:1, sulfur removal was 69.8%. While n(H2O2)/n(DBT) got to 6:1, sulfur removal reached 98.4%. Therefore, increasing the amount of oxidant appropriately could improve the desulfurization. When the amount of H2O2 got a further increase after 6:1, there was no change with DBT conversion. The excess H2O2 could produce O2, which may be amenable for the change of foam-type catalyst. So the n(H2O2)/n(DBT) of 6.0 was proper. Figure 1. GC spectra of influence of the H2O2/Sulfur molar ratio (O/S) on the reaction

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3.5. Effect of Different Reaction Temperature and time on Desulfurization. To investigate the effect of the desulfurization system containing (C16mim)2Mo2O11 and H2O2, the experiments on sulfur removal of DBT versus reaction time at different temperature were done and the results were shown in Fig. 2. At the beginning, the higher the reaction temperature was, the higher the removal of DBT was. Hydrogen peroxide was easily decomposed at higher temperatures. DBT could be almost completely oxidized into sulfone at 50℃ in 1 h. The sulfur content of model oil decreased from 500 ppm to 8 ppm. The sulfur removal reached 79.3% and 93.0% at 40℃ and 60℃ in 1 h, respectively. There was no significant improvement for desulfurization when the reaction time was extended.

Figure 2. DBT removal versus the reaction time at 40, 50 and 60℃

3.6. Kinetics Study of Catalytic Oxidation on DBT. Reaction kinetic parameters of the oxidation of DBT were investigated. The rate constant for the apparent consumption of DBT was obtained from the pseudo-first-order equation. The plot of ln(C0/Ct) against reaction time, a straight line with slope k was obtained at 40℃, 50℃ and 60℃(Fig. 8). Half-live (t1/2= ln2/k) was calculated by t= [ln(C0/Ct)]/k, in which Ct was replaced with C0/2. The apparent rate constants of DBT were 0.0261 min-1, 0.0636 min-1, 0.2620 min-1 and the half-lives were 26.56 min, 10.90 min, 2.65 min at 40℃, 50℃ and 60℃, respectively. From the reaction rates determination at 40℃ and 50℃, the apparent activation energy for the oxidation of the DBT was derived from the Arrhenius equation. Through calculation, the activation energy Ea was about 76.2 kJ/mol.

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Figure 3. Pseudo-first-order kinetics for oxidation of DBT

3.7. Study of Reaction Process and Mechanism on Reaction-controlled Foam-type Catalyst. To clarify the process of catalytic oxidation, the pictures of different desulfurization systems were taken (Figure 4). At the beginning of the reaction, the catalyst itself as powder did not dissolve in model oil. With the addition of aqueous H2O2 and vigorous magnetic agitation, the powder-type catalyst turned foam-type and the volume obviously expanded. At the end of the reaction, with H2O2 decomposed, the catalyst returned to a powder-type material (Figure 4c), and the catalyst was precipitated from the model oil. The optical micrograph of the foam-type white solid was shown in Figure 4d. According to our observation, as H2O2 decomposed, oxygen bubbling evolved and voluminous bright white foam appeared spontaneously by the role of the surfactant-type catalyst. The volume of the foam increased rapidly and permeated through all the reaction room. After H2O2 was used up, the foam was brittle and could be easily crushed into the powder.

Figure 4. Photographs of (C16mim)2Mo2O11 switch process in oxidative desulfurization.

Figure 5 was scanning electron microscopy (SEM) microphotographs of the surface of the fresh catalyst and foam-type solid. The surface of the fresh catalyst was smooth (Figure 5a) and the surface of the freeze-fracture foam-type solid was rough (Figure 5b). The foam-type solid could be found the formation of many vesicles and the large volume of rough vesicle structure may contribute to the high catalytic activity.

Figure 5. SEM microphotographs showing the surface of the catalyst. 9



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To fully understand this interesting phenomenon, the composition and the structure of the catalyst before and after reaction have been measured by Electro Spray Ionization-Mass Spectroscopy (ESI-MS), TG/DSC and FT-IR. The results of ESI-MS were listed in Figure 6 and Figure 7. Positive ion ESI-MS spectra of the fresh (Figure 6a, m/z=308), the foam-type (Figure 6b, m/z=308) and the reclaimed catalyst (Figure 6c, m/z=308) were assigned to [C16mim]+, which indicated that the structure of the catalyst cation in the reaction process was stable. Negative ion ESI-MS spectra of the fresh (Figure 7a, m/z=189) and the reclaimed catalyst (Figure 7c, m/z=189) were identified as {[Mo=O(O2)2]2(u-O)}2-, which indicated that the structure of the catalyst anion before and after catalysis was similar. In the case of reaction intermediate, H2O2 in the system continuously supplied active oxygen to the anion forming other active peroxo structures [MoxOy(O2)z]n- (Figure 7b, m/z=177, 189, 209, etc.), and then these peroxo species reacted with DBT, forming DBTO2. Simultaneously, these peroxo structures were decomposed into {[Mo=O(O2)2]2(u-O)}2-.

Figure 6. Positive ion ESI-MS spectra of the fresh and the reclaimed foam-type catalyst

Figure 7. Negative ion ESI-MS spectra of the fresh and the reclaimed foam-type catalyst

TG/DSC of the fresh catalyst and the reclaimed catalyst under nitrogen gas were shown in Figure 8. For the fresh catalyst, the results indicated that there was 1.9% mass loss before 100◦C and the corresponding endothermic peak of DSC curve emerged, which corresponded to the loss of one water molecule weakly bound to the catalyst. The catalyst decomposed with about 43.0% mass loss in the second step from 230.5 ℃ to 326.0℃, which indicated that long carbon chain of

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imidazole ring and peroxopolyoxometalate decomposed. Then, after 326.0℃, imidazole ring of the catalyst went on decomposing. The final remainder was molybdenum oxide. Compared the fresh catalyst with the reclaimed catalyst, TG/DSC results were similar. The water molecule in later was more than the former.

Figure 8. TG-DSC of [C16mim]2Mo2O3(O2)4·H2O

The IR spectra of the fresh, reclaimed catalyst and were shown in Figure 9. There were four characteristic bands of v(Mo=O)、v(O-O)、vsym[Mo(O2)] and vasym[Mo(O2)], which could confirm the anion structure of the fresh catalyst [C16mim]2Mo2O3(O2)4·H2O. Strong band at 946 cm-1 was assigned to v(Mo=O) of the terminal oxo group and near 852 cm-1 was due to v(O-O) of peroxo ligands. The (Mo2O) unit exhibited the band at 791 cm-1. The bands at 623 and 554 cm-1 were probably due to symmetric and asymmetric stretches of the Mo(O2) unit. The other peaks of 3480 cm-1 (OH), 3144、3063 cm-1 (CH of imidazolium ring), 2950、2917、2851 cm-1 (aliphatic CH), 1633 cm-1 (CN), 1574 cm-1 (CC), 1473、1384 cm-1 (CH), 1176 cm-1 (MeN) could be attributed to the organic cation. The IR spectra of the foam-type and reclaimed catalysts were similar to the fresh catalyst, indicating the main structure of the catalyst unchanged. The slight difference around 800 cm-1 may be attribute to anions of dimeric species converting into the monomeric species and H+ with the excess hydrogen peroxide in the reaction process64.

Figure 9. IR spectra of the fresh, foam-type and reclaimed catalyst

According to the observation of reaction phenomenon and experimental data, we concluded 11



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that the change of the catalyst from powder to foam may be attributed to the following reasons. To start with, the catalyst belonged to a surfactant. With the agitation and the self-decomposition of H2O2 (decomposing into oxygen bubbling), the cation of surfactant-type catalyst acted as foaming on the surface of the catalyst and oil. With the oxygen gas producing, the catalyst led to a foam-type structure, which had the similar mechanism to the vanadium oxide foam forming65. Moreover, the anion of the catalyst changed from {[Mo=O(O2)2]2(u-O)2-} to other peroxo species in the reaction process, which may be amenable for the change of the catalyst from powder to foam. In order to realize whether the similar structure polyoxometalates as (C16mim)2Mo2O11 were also behaved as reaction-controlled foam-type catalysts. Thus, the catalytic performance was studied using (C16mim)2Mo6O19 and (C16mim)2Mo8O26 with the different anions for oxidative desulfurization. Both of the two catalysts turned into sticky oily liquid in the process of reaction, which belonged to homogeneous reaction and exhibited high catalytic activity. Although their sulfur removal of DBT also can reach 99.0%, they were not reaction-controlled foam-type catalysts. After finishing reaction, the sticky oily liquid catalyst led to poor recovery. High catalytic activity was ascribed to the long carbon chain imidazole cation as phase-transfer agent in reaction process. These results still indicated that anion of the catalyst played a vital role in the feature of reaction-controlled foam-type catalyst. To investigate whether cations of catalysts were indispensable to the high activity and the feature of reaction-controlled foam-type catalyst, oxidative desulfurization was also carried out on the other two counterpart cations: [n-C16H33(π-C5H5N)]2Mo2O3(O2)4 (abbreviated as (C16Py)2Mo2O11) and [n-C16H33N(CH3)3]2Mo2O3(O2)4 (abbreviated as (C16NMe3)2Mo2O11). (C16Py)2Mo2O11 and (C16NMe3)2Mo2O11) catalysts exhibited emulsion feature, which was similar to Li group’s findings66-67. Though the two catalysts presented good sulfur removal of DBT, 12


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reaching 98.0 % and 99.0%, these emulsion droplets were too stable to be easily demulsified and it was still difficult to separate the catalyst from oil after reaction. Further investigation of other reasons for this change, effect of reaction medias and temperatures were done. Different solvents, such as benzene, toluene, H2O, methanol, ethanol, acetonitrile, n-octane, actual diesel and FCC gasline were used to replace model oil. The results in Table 2 indicated that the change of the reaction-controlled foam phenomenon could be found in weak-polar or non-polar solvent, such as benzene, toluene, n-octane, actual diesel and FCC gasline. However, this change could not be found in polar solvents, such as H2O, methanol, ethanol, acetonitrile. Reaction temperatures were also investigated whether played a vital role in reaction-controlled foam-type catalyst phenomenon. Different temperatures, such as 25℃, 50℃ and 75℃ were plotted to investigate self-decomposition of H2O2 and oxygen bubbling producing rate. According to experiment (Figure 10), decomposition of H2O2 hardly happened at 25℃, but presented acutely at 75℃, where reaction-controlled foam-type catalyst phenomenon could not be found. The results indicated that the oxygen producing rate played an important role to this phenomenon and low or high temperature was not conducive to this phenomenon. It is appropriate at about 50℃ for self-decomposition rate and oxidation rate of H2O2, where reaction-controlled foam-type catalyst phenomenon could appear. Based on these findings, we could help explore the reaction-controlled foam catalyst in other areas, such as oxidation of alcohols, olefins, amines and epoxidations, developing a novel catalyst strategy with high catalytic efficiency and easy recovery.

Table 2 Effect of different reaction medias for reaction-controlled foam-type catalyst phenomenon

Figure 10. Investigating the decomposition of hydrogen peroxide at different temperatures with [C16mim] 2Mo2O11 as the catalyst. 13



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3.8. Effect of the Recycle of the Catalyst. The recycling of the [(C16mim)2Mo2O11] catalyst was investigated by choosing DBT as a substrate in the desulfurization system. The result was shown in Table 3. After reaction, the catalyst self-precipitated and then pored out the treated oil and adding new oil and H2O2 for the next cycle. The catalyst could be easily recovered by decantation and recycled six times without significant decrease in desulfurization. The sulfur removal still remained to be about 93.9%. After the reaction, these oxygenated DBTs were highly polarized and decreased solubility in model oil. Some white sulfone substances were precipitated from model oil and adsorbed by the catalyst. To a certain extent, sulfone might affect the desulfurization efficiency. After being recycled several times, catalysts were extracted by CCl4 at room temperature. Then, CCl4 was distilled until white crystal solid was produced. The white crystal solid was characterized by IR. The appearance of characteristic frequencies at 1288 cm-1 (νas , SO2 ) and 1161 cm-1 (νs, SO2) confirmed the sulfone was the only product, which was in accordance with the results of GC-MS.

Table 3 Recycling of [C16mim]2Mo2O11 in desulfurization system

4. Conclusion In summary, a novel reaction-controlled foam-type catalyst [C16mim]2Mo2O3(O2)4·H2O has been synthesized, which is an active catalyst in desulfurization system. The removal of DBT could reach 98.4% under the optimal condition of n(DBT):n(catalyst):n(H2O2) = 30:1:180, at 50℃ for 1 h. The catalyst switched from powder to large volume foam-type material and finally to all the catalyst self-precipitating from the model oil. So the catalyst could be easily separated by decantation and could be recycled at least six times, which has provided an effective approach to circumventing the 14


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difficulty in separating polyoxometalate catalysts from the fuels.

Acknowledgements We thank the National Nature Science Foundation of China (Nos. 21106055, 21076099, 21276117, 21376111), the Natural Science Foundation of Jiangsu Province (No. BK2011506, BK2012697), Doctoral Innovation Fund of Jiangsu Province (CXLX12_0667), Zhenjiang Scientific Research Funding (NY2010030).

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16


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Saha,

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Thermochemical, structural, and reactivity indexes analyses. J. Catal. 2011, 282, 201. (57) Ramos-Luna, M. A.; Cedeno-Caero, L., Effect of Sulfates and Reduced-Vanadium Species on Oxidative Desulfurization (ODS) with V2O5/TiO2 Catalysts. Ind. Eng. Chem. Res. 2011, 50, 2641. (58) Wang, Y. H.; Yang, R. T.; Heinzel, J. M., Desulfurization of Jet Fuel JP-5 Light Fraction by MCM-41 and SBA-15 Supported Cuprous Oxide for Fuel Cell Applications. Ind. Eng. Chem. Res. 2009, 48, 142. (59) Sengupta, A.; Kamble, P. D.; Basu, J. K.; Sengupta, S., Kinetic Study and Optimization of Oxidative Desulfurization of Benzothiophene Using Mesoporous Titanium Silicate-1 Catalyst. Ind. Eng. Chem. Res. 2012, 51, 147. (60) Wang, W. H.; Li, G.; Li, W. G.; Liu, L. P., Synthesis of hierarchical TS-1 by caramel templating. Chem. Commun. 2011, 47, 3529. (61) Kim, T. W.; Kim, M. J.; Kleitz, F.; Nair, M. M.; Guillet-Nicolas, R.; Jeong, K. E.; Chae, H. J.; Kim, C. U.; Jeong, S. Y., Tailor-Made Mesoporous Ti-SBA-15 Catalysts for Oxidative Desulfurization of Refractory Aromatic Sulfur Compounds in Transport Fuel. ChemCatChem 2012, 4, 687. (62) Yu, R. M.; Kuang, X. F.; Wu, X. Y.; Lu, C. Z.; Donahue, J. P., Stabilization and immobilization of polyoxometalates in porous coordination polymers through host-guest interactions. Coord. Chem. Rev. 2009, 253, 2872. 21



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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Schematic illustration of oxidation of sulfur compounds

23



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Page 24 of 37

internal standard

1

a

n(H2O2)/n(DBT)=3:1

69.8%

b

n(H2O2)/n(DBT)=4:1

84.6%

c

n(H2O2)/n(DBT)=5:1

90.0%

d

n(H2O2)/n(DBT)=6:1

98.4%

e

n(H2O2)/n(DBT)=7:1

98.6%

2

3

4

5

6

Retention time/min Figure 1. GC spectra of influence of the H2O2/Sulfur molar ratio (O/S) on the reaction Experimental conditions: model oil = 5 mL, t = 1 h, T = 50℃, n (DBT):n (catalyst) = 30:1 (molar ratio)

24


Page 25 of 37

100 90

Conversion(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 70 60 50 40

0

40 C 0 50 C 0 60 C

30 20 10 0 0

10

20

30

40

50

60

70

Time/min Figure 2. DBT removal versus the reaction time at 40, 50 and 60℃ Experimental conditions: model oil = 5 mL, n(DBT) : n(catalyst) : n(H2O2) = 30:1:180 (molar ratio)

25



16 o

60 C o 50 C o 40 C

14 Ln(C0/Ct)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 37

12

2 R DBT = 0.9852 kDBT = 0.2620

10 8 6

2 R DBT = 0.9971 kDBT = 0.0261

4

2 R DBT = 0.9907 kDBT = 0.0646

2 0 0

10

20

30

40

50

60

Time / min Figure 3. Pseudo-first-order kinetics for oxidation of DBT

26


Page 27 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Photographs of (C16mim)2Mo2O11 switch process in oxidative desulfurization. a)Mixture of model oil (the upper lay) and (C16mim)2Mo2O11 (white solid at bottom) before reaction; b) With addtion of H2O2, the mixture of model oil and (C16mim)2Mo2O11 with magnetic agitation; c) Completion of the reaction, the catalyst has precipitated.; d) Optical micrograph of the foam-type white solid in picture b

27



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Page 28 of 37

Figure 5. SEM microphotographs showing the surface of the catalyst. a) fresh catalyst; b) freeze-fracture foam-type white solid

28


100 80 60 40 20 0

a fresh catalyst

308

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1400

1600

1800

2000

1400

1600

1800

2000

m/z

100 80 60 40 20 0

relative abundance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


relative abundance relative abundance

Page 29 of 37

308

0

200

b foam-type catalyst

400

600

800

1000

1200

m/z

100 80 60 40 20 0

308

0

200

c recycled catalyst

400

600

800

1000 1200

reclaimed foam-type catalyst Figure 6. Positive ion ESI-MS spectra of the fresh and them/z

29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

relative abundance relative abundance relative abundance


100 80 60 40 20 0

189

0

a fresh catalyst

200

400

600

800

100

177

80 60

Page 30 of 37

1000 1200 m/z

1400

1600

1800

2000

1800

2000

1800

2000

b foam-type catalyst

189

40 20 0

0

100 80 60 40 20 0

200

400

600

800

189

0

200

1000 1200 m/z

1400

1600

c recycled catalyst

400

600

800

1000 1200 m/z

1400

1600

Figure 7. Negative ion ESI-MS spectra of the fresh and the reclaimed foam-type catalyst

30


Page 31 of 37

15

100 -43.0%

TG2

10

60 -13.8%

40

5

DSC/(mw/mg)

exo

TG1

80 -1.9%

TG / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


DSC1

20

DSC2

0

0 100

200

300

400

o

500

600

Temperature / C

Figure 8. TG-DSC of [C16mim]2Mo2O3(O2)4·H2O

31



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Page 32 of 37

reclaimed catalyst

fresh catalyst

foam-type catalyst

4000 3600 3200 2800 2400 2000 1600 1200

800

400

-1

Wavenumbers(cm )

Figure 9. IR spectra of the fresh, foam-type and reclaimed catalysts

32


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decomposition percentage of H2O2/%

Page 33 of 37

100 90 80

o

25 C o 50 C o 75 C

70 60 50 40 30 20 10 0

0

10 20 30 40 50 60 70 80 90 100 110 120

t / mins

Figure 10. Investigating the decomposition of hydrogen peroxide at different temperatures with [C16mim]2Mo2O11 as the catalyst. m(catal)=0.0052 g, n(H2O2)=1.0 mmol, p=1.0167x105 pa, Room temperature: 301 K

33



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Page 34 of 37

Table 1 Effect of different desulfurization systems Sulfur removal/% 1 DBT — 1 2.8 2 DBT Na2MoO4 1 2.0 3 DBT [C16mim]Br 1 3.3 4 DBT catalyst I 1 98.4 5 4,6-DMDBT catalyst I 2 78.0 6 DT catalyst I 1 100 Experimental conditions: model oil=5 mL, T=50 ℃ , n(S):n(catalyst): n(H2O2)=30:1:180(molar ratio). Sulfur content of DBT, 4,6-DMDBT and DT was 500, 250 and 500 ppm, respectively. Catalyst : [C16mim]2Mo2O11 Entry

Substrate

Catalyst

t/h

34


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Table 2 Effect of different reaction medias for reaction-controlled foam-type catalyst phenomenon Entry Solvent polar reaction-controlled foam-type catalyst phenomenon 1 none Yes benzene 2 weak toluene Yes 3 strong H2 O No 4 strong methanol No 5 strong ethanol No 6 strong acetonitrile No 7 weak n-octane Yes 8 weak actual diesel Yes 9 weak FCC gasline Yes

35



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Page 36 of 37

Table 3 Recycling of [C16mim]2Mo2O11 in desulfurization system Run Sulfur removal Run Sulfur removal 1 4 97.7 98.4 2 5 97.4 93.9 3 6 98.3 93.9

Experimental conditions: model oil = 5 mL, t = 1 h, T = 50℃, n(DBT) : n(catalyst) : n(H2O2) = 30:1:180.

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A Novel Reaction-Controlled Foam-Type ... - ACS Publications

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