【正文】 incorporate into the Sedge and nickel to the Moedge of MoS2 , and the promoted edge surfaces have more vacant sites under typical hydrotreating reaction conditions[6–8].Most nitrogen present in heavy crude oils is in the form of heterocyclic organonitrogen pounds containing basic (pyridinic) or nonbasic (pyrrolic) ring structures[9]. Non basic nitrogen pounds are a significant fraction of the total nitrogen content in heavy oils[10,11]. These nonbasic nitrogen pounds are more difficult to remove than basic nitrogen pounds using conventional NiMoS catalysts. Indeed, it has been shown that a narrow boiling fraction of coker gas oil containing more nonbasic carbazoles and tetrahydrocarbazoles was more inhibitory and deactivated the catalyst to a greater degree in the HDN of quinoline[12].This difference in reactivity has largely been attributed to the weaker adsorptivity of nonbasic nitrogen pounds pared to basic nitrogen pounds[13,14]. Basic and nonbasic nitrogen pounds have distinct electronic structures and properties that determine their differences in adsorption energetics and reaction pathways on catalyst surfaces[15]. Unfortunately, detailed information regarding the adsorption of oganonitrogen pounds on hydrotreating catalyst surfaces has not been reported, specifically for larger organonitrogen molecules in heavy oils containing two or three rings.There are several studies about the adsorption of sulfurcontaining molecules on the unpromoted MoS2 surface, including thiophene[16,17], benzothiophene[18], and diben zothiophene[19,20], which have provided some insights into hydrodesulfurization (HDS) reaction mechanisms. However, no similar work has been done for nitrogencontaining pounds, particularly on the industrially relevant nickel promoted MoS2 catalyst (NiMoS). Previous studies have been reported for the adsorption of pyridine on a hydrogenated MoS2 surface by the CNDO/UHF method[21], and we recently investigated the adsorption of pyridine and pyrrole on a NiMoS catalyst[22]. In the context of hydroprocessing heavy oils, higher molecular weight organonitrogen molecules such as quinoline, indole, acridine, and carbazole bee significant. Therefore, the objective of the present study is to investigate the adsorption of high molecular weight organonitrogen molecules on the active nickelpromoted NiMoS edge surface [4,7,8].2. Experimental methods The catalyst model used in the present study is shown in Fig. 1, which has also been used our previous study[22]. The model is repeated in the xdirection with a periodicity of six MoS2 units, and separated by vacuum layers of 15 ? in the yand zdirections. The volume of the supercell is ? ? .On the edge surface of this representation are nickel atoms that substitute surface molybdenum atoms. In the very large supercell, the interaction between the organonitrogen molecules and the catalyst surface will not be affected by molecules in the neighbouring cells. The calculations are based on densityfunctional theory (DFT), and have been performed using Material Studio DMol3 from Accelrys174。 (Version ) [23]. The DNP basis sets and GGAPW91 exchangecorrelation fuctionals are used in all calculations[24,25]. The real space cutoff radius is ? . All electron basis sets are used for light elements, such as hydrogen, oxygen, and sulfur. Effective Core Potentials[26,27] are used to treat core electrons of molybdenum and nickel, and a kpoint of (1 1 1) was used because of the large supercell. Spin polarization was applied to all calculations.Fig. 1. Catalyst model: black—nickel, dark grey—molybdenum, light greysulfur.3. Results and discussion In nickelpromoted molybdenum sulfide catalysts, nickel atoms prefer to incorporate into the MoS2 structure by substituting molybdenum atoms at the （10 ? 0）Moedge of MoS2[8], thus generating a socalled Niedge surface as shown in Fig. 1. In the following discussions, the adsorption of organonitrogen molecules was studied using a Niedge surface including six nickel atoms in a supercell。 however, only a part of the nickel layer is shown in subsequent figures to summarize the different adsorption modes. The adsorption energies (△Ea) are calculated as the differences in electronic energies between the adsorption plex and clean surface plus gasphase molecule. The negative DEa values indicate that adsorption is an exothermic process.. Adsorption of basic nitrogencontaining pounds Quinoline can be adsorbed on the Niedge of NiMoS with the molecular plane parallel to the Niedge plane via sideon adsorption, or with the molecular plane perpendicular to the Niedge plane as endon adsorption. Several possible adsorp tion modes were studied for both sideon and endon configurations. The sideon configurations resulted in very weak interactions as evidenced by small adsorption energies(△Ea 5 kcal mol1)。 thus, it can be concluded that no strong interaction exists between quinoline and NiMoS through sideon adsorption.Table 1 summarizes the most stable configurations of quinoline on the Niedge in which quinoline is perpendicular or titled to the Niedge surface bonding through N–Ni interaction. The endon configurations with the nitrogen atom bonding to a nickel site through a N–Ni bond (Structures 1a and1b) result in large adsorption energies (△Ea 21 kcal mol1).The repulsion effect between the hydrogen atoms of the phenyl ring and the Niedge surface results in a smaller adsorption energy when quinoline is orientated along the Niedge plane(Structure 1a, △Ea = kcal mol1) than when the phenyl moiety is away from the catalyst plane (Structure 1b, △Ea = kcal mol1). However, the presence of neighbouring slabs would interact with the outofplane phenyl ring, thus, affecting the stability of Structure 1b. Although Structure 1a would not be affected by the presence of neighbouring MoS2.Table 1Surface configurations of quinoline (1a and 1b) and acridine