Reverse Microemulsion Synthesis and Characterization of Nano

Apr 28, 2015 - Nickel Sulfide Catalyst for Residue Slurry-Phase Hydrocracking ... ABSTRACT: Nano nickel sulfide catalysts (NSCs) were successfully ...
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Reverse Microemulsion Synthesis and Characterization of Nano Nickel Sulfide Catalyst for Residue Slurry-Phase Hydrocracking Dong Liu,*,† Hui Du,† Jichang Zhang,‡ and Guohe Que† †

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266555, People’s Republic of China ‡ PetroChina Changqing Petrochemical Company, Xianyang, Shanxi 712000, People’s Republic of China ABSTRACT: Nano nickel sulfide catalysts (NSCs) were successfully prepared for residue slurry-phase hydrocracking, which were synthesized by precipitation reaction in cetyltrimethylammonium bromide (CTAB) or mixed-surfactant (CTAB and Tween-80)/1-butanol/toluene/water reverse microemulsion in the presence of NiCl2 as the nickel resource and (NH4)2S as the sulfiding reagent. The prepared catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experimental data revealed that both the kind and content of surfactants play a significant role in the morphology and size of NSCs. The particle size and crystallinity of NSC increased by thermal sulfiding at 300 °C in Karamay vacuum gas oil (KLVGO). Optical micrographs showed that NSCs could be well-dispersed in Karamay atmospheric residue (KLAR) without obvious aggregation. On the basis of the lower yields of gas, atmospheric residue (AR), and coke, the NSCs showed higher catalytic activity than a conventional water/oil-soluble Ni catalyst. NSCs had excellent coke suppression performance (coke yield is less than 0.65 wt %), and the produced coke mainly dispersed in liquid products. With the decrease of NSC particle size, the coke suppression performance enhanced and the size of toluene-insoluble fraction in liquid products (TI-LP) decreased. NSCs provided location for coke generation and deposition during the slurry-phase hydrocracking process. The crystal form of NSCs dispersed in the TI-LP was Ni3S2, which was confirmed by XRD analysis. phase.15 The “tiny pool” in reverse microemulsion can be applied as a “micro reactor” for the preparation of nanoparticles.16 A large number of studies has shown that a reverse microemulsion method has a distinct advantage to control the particle size.17−20 In that case, metal sulfide particles with high dispersity would be prepared in the “micro reactor” of a reverse microemulsion synthesis process. Sato et al. prepared ultrafine CdS, ZnS, and their composite particles by the injection of H2S into reverse micelles.21 Ultradispersed multimetallic catalysts from emulsified metallic aqueous solutions were prepared by adding ammonium sulfide, and the as-prepared catalysts exhibited excellent catalytic performances in the hydrocracking of Athabasca bitumen.22 Furthermore, in comparison to the metal sulfides from conventional water-soluble catalysts, the metal sulfide particles synthesized by a reverse microemulsion method could be easily well-dispersed in heavy oil because of the surface coating by surfactant and hydrocarbon. It will be of significance for the development of residue slurry-phase hydrocracking. In this study, nano-sized and effective sulfurized nickel sulfide catalysts were prepared in cetyltrimethylammonium bromide (CTAB) or mixed-surfactant (CTAB and Tween-80)/1butanol/toluene/water reverse microemulsion in the presence of NiCl2 as the nickel resource and (NH4)2S as the sulfiding agent. The dispersion in the Karamay atmospheric residue (KLAR) and the catalytic activity of the as-prepared nickel sulfide catalyst were compared to conventional water- and oil-

1. INTRODUCTION Slurry-phase hydrocracking of a residue employs dispersed catalysts, which are disposable. Thus, the dispersed catalysts require the characteristics of high hydrogenation activity and high dispersibility.1−3 Water- and oil-soluble catalysts are commonly used because of the high dispersibility.4−8 Actually, it is metal sulfide that has the function of catalytic hydrogenation and coke suppression during the slurry-phase hydrocracking process. The metal sulfides produced by the sulfurization reaction are well-dispersed in heavy oil in the form of micro- and nano-sized particles; therefore, their ability of activating hydrogen and saturating macromolecular free radical are enhanced.9,10 Owing to the high cost of oil-soluble catalysts, water-soluble catalysts have been widely studied recently.6,11 However, the application of a water-soluble catalyst in residue slurry-phase hydrocracking still faces a series of problems. On the one hand, if the water-soluble catalyst is first dispersed in heavy oil and then sulfurized, the sulfurization degree of the water-soluble catalyst would be low because it is difficult to achieve the fully contact between catalyst emulsion and sulfiding reagent.11,12 On the other hand, the sulfurization reaction in catalyst emulsion will result in the large-sized metal sulfide particle if the water-soluble catalyst is sulfurized before dispersion. In that case, the catalytic activity would decrease because of the poor dispersibility. Hence, the dispersibility and sulfurization degree of a conventional water-soluble catalyst needs to be further improved. The reverse microemulsion process is an effective method to prepare superfine particles.13,14 Reverse microemulsion, a transparent, isotropic, and thermodynamically stable system, is composed of surfactant, co-surfactant, oil phase, and water © 2015 American Chemical Society

Received: January 12, 2015 Revised: April 27, 2015 Published: April 28, 2015 3353

DOI: 10.1021/acs.energyfuels.5b00067 Energy Fuels 2015, 29, 3353−3358

Article

Energy & Fuels Table 1. Composition and Properties of KLAR elemental composition (wt %) ρ20 (g cm−1)

ν (m2 s−1) −4

carbon residue (wt %)

C

H

2.0

86.6

12.5

S

N

0.9442

1.087 × 10

saturates

aromatics

resin

n-C7 asphaltene

Ni

V

Fe

50.4

22.2

27.2

0.2

11.8

0.35

10.8

(100 °C) SARA (wt %)

0.13 metal (μg g−1)

0.41

reactions of KLAR were carried out at 425 °C for 1 h. During the hydrocracking of KLAR, the pressure in the autoclave would reach 12.6 MPa. At the end of the hydrocracking reaction, the autoclave was cooled rapidly and vented. The liquid products were distilled to obtain the naphtha (350 °C) fractions. TI-LP was collected by centrifugation of the distilled bottom and washed with toluene until the used toluene became colorless. Meanwhile, the toluene-soluble product in the distilled bottom was atmospheric residue (AR). Toluene-insoluble products generated on the inside surface of autoclave (referred to as TI-AS) were also gathered and washed with toluene. Both TI-LP and TI-AS were dried at 110 °C for 4 h in a vacuum oven. During the hydrocracking progress, NSCs provided location for coke generation and deposition, indicating that the toluene-insoluble products was composed by coke and NSCs. Hence, the weight of NSCs in TI-LP and TI-AS were calculated according to the dosage of NSCs and the ratio of TI-LP/TI-AS. Then, the amounts of coke dispersed in liquid products (referred to as liquid coke) and coke generated on the inside surface of the autoclave (referred to as solid coke) were, therefore, calculated by subtracting the weight of NSCs as Ni3S2 from the corresponding toluene-insoluble product. Yields of hydrocracking products were calculated by the following equations:

soluble Ni catalysts. In addition, the toluene-insoluble fraction in liquid products (TI-LP) was separated and characterized.

2. EXPERIMENTAL SECTION 2.1. Synthesis of NSCs. All of the reagents were of analytical grade and used without further purification. A 2 M NiCl2 solution was used as the nickel resource solution, and a 2 M (NH4)2S solution was used as the sulfiding agent solution. All of the preparation and mixing of reverse microemulsion were carried out at 40 °C with continuous magnetic stirring. 2.1.1. Synthesis of NSC-SS. NSC-SS refers to a nickel sulfide catalyst synthesized in the CTAB/1-butanol/toluene/water singlesurfactant reverse microemulsion. In a typical synthesis procedure, either 6.0 g of CTAB and 4.0 g of 1-butanol (as co-surfactant) or 7.0 g of CTAB and 3.0 g of 1-butanol were dissolved in 45 mL of toluene. NiCl2 solution or (NH4)2S solution (5 mL) were mixed with the above solution to form nickel resource reverse microemulsion or sulfiding agent reverse microemulsion, respectively. Then, the sulfiding agent reverse microemulsion was added dropwise to nickel resource reverse microemulsion with continuous magnetic stirring. After 30 min of sulfurization, the black precipitation were gathered by centrifugation (at 4000 rpm and 5 min for each time), washed by mixed solution of ethanol and water (1:1, v/v) 6 times, and finally dried at 50 °C for 4 h in a vacuum oven. 2.1.2. Synthesis of NSC-MS. NSC-MS refers to a nickel sulfide catalyst synthesized in the CTAB and Tween-80/1-butanol/toluene/ water mixed-surfactant reverse microemulsion. The mixed surfactants (3.6 g of CTAB and 2.4 g of Tween-80 or 3.0 g of CTAB and 3.0 g of Tween-80) and 4.0 g of 1-butanol were dissolved in 45 mL of toluene. Then, the reverse microemulsion preparation, sulfurization, and product isolation during the synthesis of NSC-MS were the same as the synthesis of NSC-SS. 2.1.3. Thermal Sulfiding of NSCs. The crystallinity of as-prepared NSCs were increased by thermal sulfiding in Karamay vacuum gas oil (KLVGO) under a hydrogen atmosphere at 300 °C for 1 h. Then, the treated catalysts were collected by centrifugation (at 4000 rpm and 5 min for each time), washed with hot toluene, and finally dried at 110 °C for 4 h in a vacuum oven. 2.2. Physical Characterization. X-ray diffraction (XRD) analysis was performed on a PANalyitcal X’Pert PRO MPD XRD using Cu Kα radiation (λ = 0.154 18 nm) with 2θ ranging from 10° to 70°. A JEOL JEM-2100F transmission electron microscope operated at an accelerating voltage of 200 kV was used to obtain the transmission electron microscopy (TEM) images of NSCs. The NSC samples were dispersed in ethanol by an ultrasonic bath for 30 min and then evaporated on a carbon-coated copper grid. The dispersion of NSCs in KLAR was observed by an optical microscope. NSCs (0.5 g) were added to 100 g of KLAR. Then, the mixture was heated to 80 °C and stirred by a slurry blender at the speed of 3000 rpm for 30 min. A slide was coated with one drop of the above stirred mixture while it was hot and observed after cooling to ambient temperature. The dispersion of the conventional watersoluble Ni catalyst was observed according to the literature.6 2.3. Catalytic Activity Test. KLAR was used as a feedstock for the catalytic activity test of NSCs. The composition and properties of KLAR are listed in Table 1. KLAR (150 g) and 500 μg g−1 of NSC (considered as Ni3S2 and calculated by the nickel content) were loaded in a 300 mL batch-type autoclave. Then, the autoclave was charged with hydrogen to 6.0 MPa at ambient temperature. The hydrocracking

yield of product (wt %) =

weight of product × 100 weight of feedstock

yield of gas (wt %) weight of feedstock − weight of autoclave contents = × 100 weight of feedstock where autoclave contents was liquid products and all of the coke. Hydrocracking of KLAR with different catalysts was performed 2 or 3 times to check the reproducibility, and the values reported were the average values. The dispersion of TI-LP in hydrocracked products was observed by an optical microscope. Besides, TEM and XRD were used to analyze the morphology and crystal structure of TI-LP. The catalytic activity of NSCs was compared to that of conventional water/oil-soluble Ni catalysts. The slurry-phase hydrocracking of KLAR with water- and oil-soluble Ni catalysts was carried out according to the literature.4,5 The water-soluble Ni catalyst was prepared following the steps: (a) forming the aqueous solutions of nickel chloride (NiCl2) and ammonium sulfide [(NH4)2S], (b) adding the NiCl2 aqueous solution to KLAR and dispersing with the stirring speed of 1000 rpm, (c) adding the (NH4)2S aqueous solution with continuous stirring for 30 min, and (d) removing water by nitrogen stripping.4 During the hydrocracking of KLAR with oil-soluble Ni catalyst, the oil-soluble precursor and elemental sulfur were added directly to feedstock oil and the metal sulfides were generated through a in situ sulfiding reaction.5 In addition, all of the other hydrocracking conditions were identical with the KLAR hydrocracking using NSCs.

3. RESULTS AND DISCUSSION 3.1. XRD and TEM Analyses of NSC-SS. XRD patterns of the as-prepared NSC-SS are shown in Figure 1. Both of the patterns of NSC-SS synthesized with different dosages of CTAB and 1-butanol (curves a and b of Figure 1) show intense 3354

DOI: 10.1021/acs.energyfuels.5b00067 Energy Fuels 2015, 29, 3353−3358

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Figure 1. XRD patterns of NSC-SS synthesized with (a) 6.0 g of CTAB and 4.0 g of 1-butanol, (b) 7.0 g of CTAB and 3.0 g of 1butanol, (c) after thermal sulfiding of curve a at 300 °C, and (d) after thermal sulfiding of curve b at 300 °C. Figure 2. TEM images of NSC-SS synthesized with (A) 6.0 g of CTAB and 4.0 g of 1-butanol, (B) 7.0 g of CTAB and 3.0 g of 1butanol, and (C) after thermal sulfiding of panel A at 300 °C for 1 h.

reflections at 2θ = 21.8°, 31.2°, 38.3°, 44.5°, 50.3°, and 55.2° because of crystallographic peaks of Ni3S2 [Joint Committee on Powder Diffraction Standards (JCPDS) 30-0863]. At a lower mass ratio of CTAB/1-butanol, the XRD reflections of NSC-SS (curve a of Figure 1) are observed at 2θ = 30.2°, 34.6°, and 45.8°, which can be indexed to the hexagonal NiS (JCPDS 750613); meanwhile, the crystalline phase of Ni3S4 (JCPDS 431469) is observed at 2θ = 14.8°, 24.6°, and 38.1°. However, the absence of a relatively strong diffraction peak at 2θ = 45.7° indicates that the well-structured NiS did not form during reverse microemulsion synthesis. The intensities of these reflections increase after thermal sulfiding at 300 °C for 1 h, which reveals that the crystallinity of NSC-SS is enhanced by high temperatures. All of the major diffraction peaks of hexagonal NiS are also in the XRD pattern of thermal-sulfided NSC-SS synthesized at a higher mass ratio of CTAB/1-butanol (curve d of Figure 1). Moreover, the new diffraction peaks at 2θ = 27.3°, 31.3°, 43.0°, and 55.6° appear in both of the XRD patterns of thermal-sulfided NSC-SS synthesized with different dosages of CTAB and 1-butanol (curves c and d of Figure 1), which implies that part of the thermal-sulfided NSC-SS exists in the form of Ni9S8. The particle size and morphology of NSC-SS synthesized with different dosages of CTAB and 1-butanol were measured by TEM. As demonstrated in Figure 2A, the NSC-SS nanoparticles with a diameter ranging from 160 to 220 nm are synthesized at a lower mass ratio of CTAB/1-butanol. However, the NSC-SS synthesized at a higher mass ratio of CTAB/1-butanol has a wide particle size range of 100−310 nm, mainly in the size range of 180−270 nm (Figure 2B). The footprint similar to nanoparticles on TEM grids in panels A and B of Figure 2 was caused by the residual CTAB. The size of the nickel sulfide particles synthesized in reverse microemulsion was smaller than the size of a sulfided water-soluble catalyst (around 1.5 μm)23 and a sulfided oil-soluble catalyst (1−5 μm).5 Then, the NSC-SS with a smaller particle size (synthesized with 6.0 g of CTAB and 4.0 g of 1-butanol) was thermally sulfided in KLVGO under a hydrogen atmosphere at 300 °C for 1 h. As shown in Figure 2C, the particle size and shape of NSC-SS nanoparticles were kept nearly unchanged after thermal sulfiding. The TEM results consistent with the XRD patterns also indicate that the crystallinity of NSC-SS is increased by thermal sulfiding.

3.2. XRD and TEM Analyses of NSC-MS. The XRD patterns in Figure 3 showed that the as-prepared NSC-MS

Figure 3. XRD patterns of NSC-MS synthesized with (a) 3.6 g of CTAB and 2.4 g of Tween-80, (b) 3.0 g of CTAB and 3.0 g of Tween80, (c) after thermal sulfiding of curve a at 300 °C, and (d) after thermal sulfiding of curve b at 300 °C.

before thermal sulfiding had the crystalline phase of Ni3S2 and NiS. Besides, the diffractions of Ni3S4 also exist in the XRD pattern (curve b of Figure 3) of NSC-MS synthesized with a higher mass ratio of CTAB/Tween-80. After the thermal sulfiding in KLVGO under a hydrogen atmosphere at 300 °C for 1 h, the diffraction intensity of XRD patterns increases, as shown in curves c and d of Figure 3. It indicates that the crystallinity of NSC-MS is increased, and no more crystal forms are produced by thermal sulfiding. As demonstrated in Figure 4, the NSC-MS synthesized in mixed-surfactant reverse microemulsion is spherical in shape, which is different from the morphology of NSC-SS. It indicates that the morphology of NSCs are influenced by the absorption of Tweeen-80 on the surface. The particle size of NSC-MS synthesized at a higher ratio of CTAB/Tween-80 is between 80 and 190 nm (Figure 4A), while the particle size is between 20 and 170 nm when the NSC-MS is synthesized at a lower ratio 3355

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mainly dispersed in KLAR with the size of a few micrometers as well as the residual water (Figure 5A). In comparison to the conventional water-soluble Ni catalyst, both NSC-SS and NSCMS can be well-dispersed into KLAR without obvious aggregation. First, the particle size of NSCs is on a nanometer scale. Second, the surfactants absorbed on the surface of NSCs during the reverse microemulsion synthesis, which can improve the compatibility of NSC particles and KLAR and also can prevent the aggregation of NSC nanoparticles by steric protection. 3.4. Catalytic Activity of NSCs. KLAR slurry-phase hydrocracking without and with different types of catalysts were carried out under an initial hydrogen pressure of 6.0 MPa at 425 °C for 1 h, and the product distribution is listed in Table 2. In comparison to KLAR hydrocracked without a catalyst, all Table 2. Product Distribution of KLAR Slurry-Phase Hydrocracking without and with Different Catalysts under an Initial Hydrogen Pressure of 6.0 MPa at 425 °C for 1 h

Figure 4. TEM images of NSC-MS synthesized with (A) 3.6 g of CTAB and 2.4 g of Tween-80, (B) 3.0 g of CTAB and 3.0 g of Tween80, and (C) after thermal sulfiding of panel B at 300 °C.

of CTAB/Tween-80 (Figure 4B). Besides, the particle size of NSC-MS in Figure 4B is mainly below 90 nm. As shown in Figure 4C, the shape of nanospheres changed from a regular sphere to an irregular ellipsoid and cube after thermal sulfiding. Moreover, the average particle size of NSC-MS increased and the size distribution decreased after thermal sulfiding, which is probably due to the coalescence of small nanospheres caused by a high surface energy. 3.3. Dispersion of NSCs in KLAR. The dispersion in KLAR and coke suppression performance of NSCs with a small particle size were tested. In the following contents, the NSC-SS means NSC synthesized in a single-surfactant reverse microemulsion with 6.0 g of CTAB and 4.0 g of 1-butanol, and the NSC-MS means NSC synthesized in a mixed-surfactant reverse microemulsion with 3.0 g of CTAB and 3.0 g of Tween-80. The dispersion of a conventional water-soluble Ni catalyst, NSC-SS, and NSC-MS in KLAR was observed by an optical microscope, as shown in Figure 5. The water-soluble Ni catalyst

product yield (wt %)

gas

naphtha

diesel

AR

coke

without catalyst W-cat.a O-cat.b NSC-SS NSC-MS

15.36 11.55 11.31 9.62 9.88

15.59 13.16 13.79 11.85 11.37

23.17 36.31 34.68 40.62 41.16

42.27 38.09 39.26 37.27 37.08

3.61 0.89 0.96 0.64 0.51

a

W-cat. = water-soluble Ni catalyst. bO-cat. = oil-soluble Ni catalyst.

of the water/oil-soluble Ni catalysts and NSCs have lower yields of gas, naphtha, AR, and coke products. Furthermore, similar results about the effect of the catalyst on hydrocracked product distribution were reported by Jeon et al.8 using an oilsoluble CoMo bimetallic catalyst for the hydrocracking of Athabasca bitumen and also by Rezaei et al. 24 using unsupported MoS2 catalysts for the hydroconversion of Cold Lake vacuum residue. Both NSC-SS and NSC-MS showed excellent effectiveness for KLAR hydroconversion as well as coke suppression. The main functions of the dispersed catalyst are promoting hydrogenolysis and inhibiting coke formation.25,26 Hydrogen is transformed into active hydrogen on the active sites of the dispersed catalyst. Then, active hydrogen is subsequently transferred and quenched with the macromolecule free radical near the catalyst, which suppress the condensation of the hydrocarbon free radical and the formation of coke. As demonstrated in Figure 6, the produced coke is mainly composed of liquid coke. The whole coke yield of KLAR hydrocracking with the presence of water- and oil-soluble Ni catalysts decreases to around 1 wt %, which decreases to even lower when KLAR hydrocracking with the presence of NSCs. Besides, the coke suppression performance of NSC-MS is better than that of NSC-SS. Besides being catalytically active, the dispersed catalysts also act as the obtainer of coke during residue slurry-phase hydrocracking. The seeds of coke that deposit on the fine catalyst particles are carried out in the reactor by the process streams. Otherwise, coke and other deposits would be formed on the inside surface of the reactor, which could impact the operation of the reactor.27 The NSC with a smaller particle size could provide more active sites for the activation of hydrogen and more obtainers for the deposition of coke. Therefore, NSC-MS exhibits a better coke suppression performance during the slurry-phase hydrocracking of KLAR.

Figure 5. Micrographs of different catalysts dispersed in KLAR (400×): (A) water-soluble Ni catalyst, (B) NSC-SS, and (C) NSCMS. 3356

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Figure 6. Coke composition of KLAR slurry-phase hydrocracking without and with different catalysts under an initial hydrogen pressure of 6.0 MPa at 425 °C for 1 h. (∗) W-cat., water-soluble Ni catalyst; (∗∗) O-cat., oil-soluble Ni catalyst.

Figure 8. XRD patterns of TI-LP from KLAR slurry-phase hydrocracking with NSCs.

slurry-phase hydrocracking process. Figure 8 also shows an intense reflection at 2θ = 25.6° as a result of crystallographic peaks of graphitic carbon.24 As shown in the TEM image of TILP from KLAR slurry-phase hydrocracking with NSC-SS (Figure 9), NSC-SS particles and the deposited coke together

3.5. Characterization of TI-LP. Experimental results show that the bulk TI-LP is obtained when KLAR hydrocracked without a catalyst. The morphology and dispersion of TI-LP in products of KLAR hydrocracked using different types of catalysts were observed by an optical microscope, as shown in Figure 7. The particle size of TI-LP in the products of KLAR

Figure 9. TEM image of TI-LP from KLAR slurry-phase hydrocracking with NSC-SS.

Figure 7. Micrographs (400×) of the morphology and dispersion of TI-LP in the products of KLAR hydrocracked using different catalysts: (A) water-soluble Ni catalyst, (B) oil-soluble Ni catalyst, (C) NSC-SS, and (D) NSC-MS.

form an irregular-shaped TI-LP particle, indicating that NSC-SS provided a location for coke generation and deposition. Besides, the diameters of NSC-SS in TI-LP are lower than 200 nm, which reveals no aggregation between NSC-SS particles during the hydrocracking process.

hydrocracked with NSCs is smaller than the particle size with a conventional water/oil-soluble Ni catalyst. In addition, the TILP of fine granular size is dispersed uniformly in the products of KLAR hydrocracked with NSC-MS, while a small amount of big TI-LP particles exists in the products of KLAR hydrocracked with NSC-SS. It indicates that the size of TI-LP can be reduced effectively by the uniform NSC nanoparticles. TI-LP products from KLAR slurry-phase hydrocracking with NSC-SS or NSC-MS were examined by XRD (Figure 8). Both patterns show strong reflections at 2θ = 21.8°, 31.2°, 38.3°, 44.5°, 50.3°, and 55.2°corresponding to Ni3S2 (JCPDS 300863). However, no XRD peaks corresponding to NiS, Ni3S4, and Ni9S8 are observed for TI-LP products. It indicates that the crystal form of NSCs completely converts to Ni3S2 during the

4. CONCLUSION NSCs were successfully prepared for residue slurry-phase hydrocracking via reverse microemulsion synthesis, and both the kind and content of surfactants play a significant role in the morphology and size of NSCs. The particle size and crystallinity of NSCs increased by thermal sulfiding at 300 °C in KLVGO. NSCs could be well-dispersed into KLAR without obvious aggregation. On the basis of the lower yields of gas, AR, and coke, the NSCs showed higher catalytic activity than that of a conventional water/oil-soluble Ni catalyst. NSCs had excellent coke suppression performance (coke yield is less than 0.65 wt %), and the produced coke mainly dispersed in liquid products. In addition, with the decrease of the NSC particle size, the coke suppression performance enhanced and 3357

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(17) Zhang, X.; Chan, K. Y. Water-in-oil microemulsion synthesis of platinum−ruthenium nanoparticles, their characterization and electrocatalytic properties. Chem. Mater. 2003, 15 (2), 451−459. (18) Garti, N.; Spernath, A.; Aserina, A.; Lutza, R. Nano-sized selfassemblies of nonionic surfactants as solubilization reservoirs and microreactors for food systems. Soft Matter 2005, 1 (3), 206−218. (19) Amir, M.; Reza, A. Partial oxidation of butane to syngas using nano-structure Ni/zeolite catalysts. J. Ind. Eng. Chem. 2014, 20 (4), 1542−1548. (20) Boyjoo, Y.; Pareek, V. K.; Liu, J. Synthesis of micro and nanosized calcium carbonate particles and their applications. J. Mater. Chem. A 2014, 2 (35), 14270−14288. (21) Sato, H.; Tsubaki, Y.; Hirai, T.; Komasawat, I. Mechanism of formation of metal sulfide ultrafine particles in reverse micelles using a gas injection method. Ind. Eng. Chem. Res. 1997, 36 (1), 92−100. (22) Galarraga, C. E.; Pereira-Almao, P. Hydrocracking of Athabasca bitumen using submicronic multimetallic catalysts at near in-reservoir conditions. Energy Fuels 2010, 24 (4), 2383−2389. (23) Luo, H.; Deng, W.; Gao, J.; Fan, W.; Que, G. Dispersion of water-soluble catalyst and its influence on the slurry-phase hydrocracking of residue. Energy Fuels 2011, 25 (3), 1161−1167. (24) Rezaei, H.; Liu, X.; Ardakani, S. J.; Smith, K. J.; Bricker, M. A study of Cold Lake vacuum residue hydroconversion in batch and semi-batch reactors using unsupported MoS2 catalysts. Catal. Today 2010, 150 (3), 244−254. (25) Matsumura, A.; Kondo, T.; Sato, S.; Saito, I.; de Souza, W. F. Hydrocracking Brazilian Marlim vacuum residue with natural limonite. Part 1: Catalytic activity of natural limonite. Fuel 2005, 84 (4), 411− 416. (26) Matsumura, A.; Sato, S.; Kondo, T.; Saito, I.; de Souza, W. F. Hydrocracking Marlim vacuum residue with natural limonite. Part 2: Experimental cracking in a slurry-type continuous reactor. Fuel 2005, 84 (4), 417−421. (27) Furimsky, E. Catalysts for Upgrading Heavy Petroleum Feeds; Elsevier: Amsterdam, Netherlands, 2007.

the size of TI-LP decreased. NSCs provided location for coke generation and deposition during the slurry-phase hydrocracking process. Moreover, the crystal form of NSCs dispersed in the TI-LP was Ni3S2, which was confirmed by XRD analysis.

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AUTHOR INFORMATION

Corresponding Author

*Telephone/Fax: +86-0532-86984629. E-mail: ldongupc@vip. sina.com. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (21176259).

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REFERENCES

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DOI: 10.1021/acs.energyfuels.5b00067 Energy Fuels 2015, 29, 3353−3358