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Highly Dispersed Nanocrystalline Molybdenum Sulfide Preparedby Hydrothermal Synthesis as an Unsupported Model Catalyst for Ultra Clean DieselHaiping Zhang, Hongfei Lin, Ying Zheng*Hydroprocessing Laboratory Department of Chemical EngineeringUniversity of New BrunswickMay 11, 2010OutlineIntroductionExperimentalResults and discussionConclusions2Introduction3Solid-gas sulfidationMoO3+H2S+H2=MoS2+2H2Olow surface area, incomplete sulfidation, low catalytic activitiesThermal decomposition (TD) of thiomolybdate Hydrothermal /solvothermalExpensive and toxic precursors preparationMoO3(NR4)4MoS4Precursors3ChallengesLow cost and easy scale-up

Well-dispersed nanocrystallineHighly-porous structure and high surface areaHigh catalytic activities Catalysts with desirable properties4Experimental5

Na2S MoO3HClThermal coupleHydrothermal

Crystalline structure6Fig.1 XRD spectra of unsupported MoS2 MoS2002110103100XRD spectra of MoS2 synthesized at temperature of 270-350C showed typical diffraction MoS2 peaks.

The broad diffraction peaks indicated a nanocrystalline structure.

002100103110MoS2-270C

MoS2-200CMoS2-200C showed an amorphous structure.

67Fig. 2 TEM images of unsupported MoS2; a, b, MoS2-200C; c, d, MoS2-320C.

TEM images

adcbAmorphous MoS2-200C, aggregated chuck appearance and burred layered structure. MoS2-320C more dispersed dendritic morphology, and longer layered nanocrystallines.

7Specific surface areaFig. 3 Surface area of unsupported MoS2 at different temperatures MoS2-200C MoS2-270C MoS2-320C MoS2350C 88Hydrotreating conditions9

Batch reactorFEED Light cycle oil (LCO)S 15400 ppmw N 156 ppmw

Catalyst-to-feed oil ratio1:200 w.t.

Hydrotreating temperature & pressure 375C,1500psi

9HDS/HDN activities10Fig. 4 HDS activities of MoS2Fig. 5 HDN activities of MoS2As the synthesis temperature increased, the HDS/HDN activities increased.

MoS211HDS kineticsFig. 6 HDS conversion of MoS2 at different timesFig.7 HDS kinetics MoS2-200C MoS2-270C MoS2-320C MoS2350C Sulfur compounds analysis 12

Fig.8 Analysis of major sulfur compounds in hydrotreated LCO by GC-PFPD BT-nMBTDBTnMDBT12HDN kinetics13Fig. 9 HDN conversion of MoS2 at different timesFig.10 HDN kinetics MoS2-200C MoS2-270C MoS2-320C MoS2350C S/Mo ratios in catalysts14CatalystsS/ Mo ratios of catalysts *MoS2 recovery (%) **MoS2-11.8596.24MoS2-22.0555.1MoS2-32.1025.59Different sulfur to molybdenum ratios in catalysts can be obtained through manipulating reactant (Na2S/ MoO3) ratios.

As the Sulfur (S) to Molybdenum (Mo) ratios in catalysts increased, MoS2 recovery decreased dramatically.

Table 2 S-to-Mo ratios and catalysts recovery at 320C*: S/Mo ratio was tested by Microprobe.**: MoS2 recovery equals actual yield divided by theoretical yield. 14Specific surface area & Pore size distribution15MoS2 catalysts are shown with bimodal pore size distribution, peaking at 2.75nm and ~10nm (mesopores).

The highest specific surface area was as large as 262 m2/g.

Fig.12 Pore size distribution of MoS2Fig.11 Specific surface area of MoS2 MoS2-1 MoS2-2 MoS2-3

15Morphology

Fig.13 SEM images of MoS2-1.0Figure 3 shows a nano-sized particles of unsupported MoS2, which exhibits a flower-like morphology. The average particle size is about 100nm.

16The initial MoS2 crystal associate in bundles and twisted together forming a highly porous morphology. HDS/HDN activities17When S/Mo ratio equaled 1.85, the catalysts showed the highest activities.

Fig.14 HDS/HDN activities at different reactant ratiosMoS2-1 S/Mo 1.85MoS2-2 S/Mo 2.05MoS2-1 S/Mo 1.85MoS2-2 S/Mo 2.05MoS2-3 S/Mo 2.10kHDS VS Dev.of S/Mo ratio *18Hydrotreating activities of catalysts were directly proportional with deviation of S/Mo ratio from stoichiometric ratio 2.

The lack or excess of sulfur element in crystal lattice can be related to the deformation of the crystalline and defects on the catalysts.Fig.15 Relationship between HDS conversion and deviation of S/Mo ratio*: Dev. of S/Mo ratio = S/Mo ratio -2

Conclusion A series of novel well-dispersed Nanocrystalline unsupported MoS2 with remarkable large surface area and pore volume were successfully synthesized using hydrothermal method. Catalysts prepared at higher synthesis temperature presented better hydrotreating performance. Temperature largely influenced crystal structure, and then affected hydrotreating activities, e.g. MoS2 with amorphous structure exhibited lowest activities. When the catalysts have nanocrystalline structure, the hydrotreating activities were directly proportional to deviation of S/Mo ratio from standard ratio 2. The lack or excess of sulfur can be related to the deformation of the crystal structure and defects on the catalysts.

19AcknowledgementThis work is financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC).20