Haiping Zhang, Hongfei Lin, Ying Zheng* Highly Dispersed Nanocrystalline Molybdenum Sulfide Prepared by Hydrothermal Synthesis as an Unsupported Model Catalyst for Ultra Clean Diesel Haiping Zhang, Hongfei Lin, Ying Zheng* Hydroprocessing Laboratory Department of Chemical Engineering University of New Brunswick May 11, 2010

Outline Introduction Experimental Results and discussion Conclusions

MoO3 (NR4)4MoS4 Introduction Precursors Solid-gas sulfidation MoO3+H2S+H2=MoS2+2H2O low surface area, incomplete sulfidation, low catalytic activities (NR4)4MoS4 Thermal decomposition (TD) of thiomolybdate Hydrothermal /solvothermal Expensive and toxic precursors preparation

Challenges Catalysts with desirable properties Low cost and easy scale-up Catalysts with desirable properties Well-dispersed nanocrystalline Highly-porous structure and high surface area High catalytic activities 4

Experimental MoS2-200°C MoS2-270°C MoS2-320°C MoS2-350°C Na2S MoO3 HCl Thermal couple Hydrothermal MoS2-200°C MoS2-270°C MoS2-320°C MoS2-350°C

Crystalline structure XRD spectra of MoS2 synthesized at temperature of 270-350°C showed typical diffraction MoS2 peaks. The broad diffraction peaks indicated a nanocrystalline structure. 110 100 103 MoS2 002 MoS2-200°C showed an amorphous structure. MoS2-200⁰C 002 100 103 110 MoS2-270⁰C Fig.1 XRD spectra of unsupported MoS2

TEM images a c b d Fig. 2 TEM images of unsupported MoS2; a, b, MoS2-200°C; c, d, MoS2-320°C. Amorphous MoS2-200°C, aggregated chuck appearance and burred layered structure. MoS2-320°C more dispersed dendritic morphology, and longer layered nanocrystallines.

Specific surface area MoS2-200°C MoS2-270°C MoS2-320°C MoS2350°C Fig. 3 Surface area of unsupported MoS2 at different temperatures 8

Hydrotreating conditions Batch reactor FEED Light cycle oil (LCO) S 15400 ppmw N 156 ppmw Catalyst-to-feed oil ratio 1:200 w.t. Hydrotreating temperature & pressure 375°C,1500psi

Fig. 5 HDN activities of MoS2 HDS/HDN activities As the synthesis temperature increased, the HDS/HDN activities increased. Fig. 5 HDN activities of MoS2 Fig. 4 HDS activities of MoS2 MoS2

Fig. 6 HDS conversion of MoS2 at different times HDS kinetics Fig. 6 HDS conversion of MoS2 at different times Fig.7 HDS kinetics MoS2-200°C MoS2-270°C MoS2-320°C MoS2350°C

Sulfur compounds analysis DBT BT-nMBT nMDBT Fig.8 Analysis of major sulfur compounds in hydrotreated LCO by GC-PFPD

Fig. 9 HDN conversion of MoS2 at different times HDN kinetics Fig.10 HDN kinetics Fig. 9 HDN conversion of MoS2 at different times MoS2-200°C MoS2-270°C MoS2-320°C MoS2350°C

S/Mo ratios in catalysts Table 2 S-to-Mo ratios and catalysts’ recovery at 320°C Catalysts S/ Mo ratios of catalysts * MoS2 recovery (%) ** MoS2-1 1.85 96.24 MoS2-2 2.05 55.1 MoS2-3 2.10 25.59 *: S/Mo ratio was tested by Microprobe. **: MoS2 recovery equals actual yield divided by theoretical yield. Different 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.

Specific surface area & Pore size distribution Fig.12 Pore size distribution of MoS2 Fig.11 Specific surface area of MoS2 MoS2-1 MoS2-2 MoS2-3 The highest specific surface area was as large as 262 m2/g. MoS2 catalysts are shown with bimodal pore size distribution, peaking at 2.75nm and ~10nm (mesopores).

Morphology The initial MoS2 crystal associate in bundles and twisted together forming a highly porous morphology. Fig.13 SEM images of MoS2-1.0 Figure 3 shows a nano-sized particles of unsupported MoS2, which exhibits a flower-like morphology. The average particle size is about 100nm.

Fig.14 HDS/HDN activities at different reactant ratios MoS2-1 S/Mo 1.85 MoS2-2 S/Mo 2.05 MoS2-1 S/Mo 1.85 MoS2-2 S/Mo 2.05 MoS2-3 S/Mo 2.10 Fig.14 HDS/HDN activities at different reactant ratios When S/Mo ratio equaled 1.85, the catalysts showed the highest activities.

kHDS VS Dev.of S/Mo ratio * Hydrotreating 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.

Acknowledgement This work is financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC).