An urgent demand for clean fraction oil makes a great pressure on the hydrotreating (HDT) technology due to progressively stringent environmental regulations.  Conventional HDT catalysts supported g-Al2O3 has been used for near 100 years. An alternative of taking anatase-type TiO2 (A-TiO2) as support other than g-Al2O3 could greatly improve the performance of the catalyst. The superior performance of Mo/TiO2 originates from the increasing of type II active sites numbers because of the presence of new MoS2-TiO2 interaction in an edge-bondingway3. However, the interaction was never reported from specific crystallography. The sulfidation process of Mo/TiO2 catalyst could be partly regarded as epitaxial growth of MoS2 on TiO2 support. And thus, the crystallographic orientation relationship (OR) between MoS2 and TiO2 is very important for understanding the active sites of the catalyst.

The TiO2 support was obtained by pressing anatase TiO2 powder, synthesized by hydrothermal method, into disc under 5 MPa pressure and breaking up into 20~40 mesh grains. Mo/TiO2 (10wt%) was synthesized by impregnating ammonium molybdate solution onto TiO2 support followed by dryness and calcination. Sulfiding experiments were carried out on a fixed-bed micro-reactor at 350°C under 10%H2S/H2 atmosphere. The catalysts were observed by HREM on a JEOL 2200FS microscope operated at 200kV.

HREM image in Figure 1A shows the interface relationship between MoS2 and TiO2 in sulfided Mo/TiO2 catalyst. MoS2 slab is anchored on (101) facet-exposing surface of A-TiO2 in edge-bonding way. The angle between (001)MoS2 and (101) A-TiO2 is 66°. The interface relationship could be elucidated by Coincidence Reciprocal Lattice Points (CRLP)4 theory, expressed by a scheme in Figure 2. The intersecting volume function of reciprocal lattice points of two crystals (hexagonal MoS2 and tetrahedral TiO2 shown in Figure 3A) could be computed from home-made program. The OR of two crystals at the initial orientation is (001)MoS2//(001)A-TiO2 and [100]MoS2//[100] A-TiO2 （Figure 3B）.The intersecting volume function V(a,b) is computed and plotted versus a and b angle. Figure 3C shows the corresponding 3D drawing. The same peak value presents at (0,15), (0,45) and (0,75) points, which reflects optimum OR presents at the orientations. At initial orientation, the deduced angle between (001)MoS2 and (101) A-TiO2 is 68 degree. At (0,15), (0,45) and (0,75) orientation, the values are 83°, 66°and 36°, respectively. The 66° angle between (001)MoS2 and (101) A-TiO2 at (0, 45) is highly consistent with that value observed by HREM. As a result, the conclusion could be drawn that CRLP theory could well predict interface relationship in MoS2/TiO2 HDT catalyst.

Acknowledgement
We thank the financial support of SINOPEC Project (115048)

References

1.M.Signorile, A. Damin, A. Budnyk, et al. J. cata. 2015, 328:225-235.

2. Edisson Morgado Jr，Jose′L. Zotin，Marco A.S. de Abreu，et al. Appl. Catal: A Gen. 2009,357 : 142–149.

3. SakashitaY, Araki Y,Honna k,et al. Appl. Catal, 1993, 105:69-75.

4. Susanne Stemmer, Pirouz Pirouz, Yuichi Ikuhara et al.Phy. Rev. Lett.，1996，77（9）:1797-1800.

Figures:

Figure 1 HREM image of sulfided Mo/TiO2 (A) and schematic of MoS2/TiO2 interface relationship (B)

Figure 2 The scheme of Coincidence Reciprocal Lattice Points (CRLP) theory.

Figure 3 Unit cells of MoS2 (Space group: P63/mmc, a=0.315nm,c=1.23nm) and Anatase-type TiO2 (Space group: I41/amd, a= 0.380nm,c=0.961nm) (A), the initial orientation between MoS2 and TiO2 at a=0 and b=0（B）and V(a,b)as a function of a and b (C).

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