王周君 吳平易, 蘭 玲 劉坤紅 胡亞瓊 季生福,*(北京化工大學(xué),化工資源有效利用國(guó)家重點(diǎn)實(shí)驗(yàn)室,北京0009;中國(guó)石油石油化工研究院,北京0095)

Mo-Ni2P/SBA-15催化劑的制備、表征及加氫脫硫催化性能

王周君1吳平易1,2蘭 玲2劉坤紅2胡亞瓊2季生福1,*
(1北京化工大學(xué),化工資源有效利用國(guó)家重點(diǎn)實(shí)驗(yàn)室,北京100029;2中國(guó)石油石油化工研究院,北京100195)

以介孔分子篩SBA-15為載體,通過(guò)分步浸漬硝酸鎳、磷酸氫二銨、鉬酸銨,然后在H2氣流下程序升溫還原(H2-TPR),制備了一系列不同Mo含量的Mo-Ni2P/SBA-15催化劑.采用X射線衍射(XRD)、氮?dú)馕摳?BET)、透射電子顯微鏡(TEM)和X射線光電子能譜(XPS)對(duì)催化劑的結(jié)構(gòu)進(jìn)行了表征,評(píng)價(jià)了催化劑對(duì)二苯并噻吩(DBT)的加氫脫硫(HDS)活性.結(jié)果表明,Mo-Ni2P/SBA-15催化劑仍然保留有介孔結(jié)構(gòu),催化劑的物相主要是Ni2P.催化劑表面的Ni以Niδ+和Ni2+形式存在;P以Pδ-和P5+形式存在;Mo以Moδ+和Mo6+形式存在.Mo能促進(jìn)催化性能的提高,其中Mo含量為1%(w,質(zhì)量分?jǐn)?shù))的Mo-Ni2P/SBA-15催化劑具有最好的二苯并噻吩加氫脫硫催化活性,在反應(yīng)溫度為380°C,反應(yīng)壓力為3.0 MPa的條件下,二苯并噻吩的轉(zhuǎn)化率可達(dá)99.03%,所有考察的Mo-Ni2P/SBA-15都以直接加氫脫硫(DDS)途徑為主.

Mo;Ni2P;二苯并噻吩;加氫脫硫;介孔

?Editorial office ofActa Physico-Chimica Sinica

1 Introduction

In recent years,environmental regulations have been tightened in many countries all over the world to limit the sulfur(S)content of fuel to ultra-low levels(10×10-6(mass fraction,w)),aiming at mitigating the exhaust emission of SO2and improving the air quality.1To fulfil such regulations,＞99.99%of S should be removed from a typical crude oil containing 1.5%(w)of S.This removal process is termed as deep hydrodesulfurization(HDS), in which the catalyst plays a key role.2,3The classic Mo(W)Co(Ni)/ Al2O3HDS catalyst cannot meet the requirements.Therefore,it is of great urgency to develop new catalysts with exceptional HDS performances.4,5

The transition metal phosphides are reported as a family of prospective catalysts with high activity,good stability,and excellent S resistance,among which nickel phosphide exhibits the best catalytic performances and molybdenum phosphide also possesses good activity.6,7Besides,it is well known that in the classic HDS catalysts,the addition of Ni toAl2O3-supported MoS2catalysts would efficiently promote the catalytic performances.8,9Therefore,it is of interest to study the effect of Mo on the structure and HDS performances of nickel phosphide catalysts.Up to now,a few studies have been conducted but controversial results were reported.10-12For example,Rodriguez et al.10reported that the MoNiP/SiO2catalyst is much less active than the monometallic phosphide catalysts in the HDS of thiophene,which was ascribed to the stronger interactions between MoNiP and SiO2due to the smaller size of the supported MoNiP particles relative to the supported Ni2P and MoP catalysts.On the contrary,Sun and coworkers11reported that the activities of the phosphides in the HDS of dibenzothiophene(DBT)followed the order of Ni2P/SiO2＞Ni-Mo-P/SiO2＞MoP/SiO2.The Ni sites in the Ni-Mo-P/SiO2catalysts were found to play a major role and no synergetic effect was observed between the phosphided Ni and the Mo atoms. Wang and Smith12reported similar activity trend on the unsupported metal phosphides for the HDS of 4,6-dimethyldibenzothiophene(4,6-DMDBT),which was interpreted by different electronic properties of the metal cations in Ni2P,Ni-Mo-P,and MoP.

Herein,the effect of Mo on the structure and HDS performances of nickel phosphide catalysts was further clarified.Silica has been most widely employed as the support for nickel phosphide because the support-precursor interaction is weak,which benefits the catalytic performances.13The ordered mesoporous silica SBA-15 has attracted particular attention due to its superior HDS performances than the traditional silica support.The unique textural properties(high specific surface areas,large pore volumes,and narrow pore size distributions)of SBA-15 lead to better dispersion of the active phases,thus improving the catalytic performances of the phosphide catalysts.14,15Therefore,the Ni2P/ SBA-15 catalysts were employed as the model phosphide catalysts.A series of Mo-promoted Ni2P/SBA-15 catalysts with various Mo contents(0.5%,1%,3%,5%,7%(w))were prepared by the temperature-programmed reduction(TPR)treatment following the subsequent incipient impregnation method.X-ray diffraction (XRD)and N2sorption analysis were employed to characterize the catalyst structure.The HDS of DBT was performed to evaluate the catalytic performances.

2 Experimental

2.1 Preparation of samples

The mesoporous molecular sieve SBA-15 was synthesized according to the method described in the literature16using a triblock copolymer(P123,EO20PO70EO20(EO:ethylene oxide,PO:propylene oxide),AR,Aldrich)as the structure-directing reagent and tetraethyl orthosilicate(TEOS,AR,Beijing Chemical Works)as the silica precursor.P123(4 g)was dissolved in a mixture of deionized water(90 mL)and hydrochloric acid(60 mL,4 mol·L-1) followed by a stirring at 40°C for 2 h.TEOS(8.5 g)was then slowly added to the mixture and subsequently stirred at 40°C for 22 h.After that,the gel mixture was transferred into a Teflon bottle and aged at 100°C for 24 h under static condition.The obtained solid sample was filtered,washed with the deionized water until neutral pH,and dried at room temperature.To remove the organic template,the sample was finally calcined at 550°C for 6 h.

The Mo-promoted Ni2P/SBA-15 catalysts with the initial P/Ni molar ratio of 2,the Ni2P content of 40%(w),and the Mo content varying from 0.5%to 7%(w)were prepared by the subsequent incipient impregnation method.Firstly,Ni2P/SBA-15 precursors were prepared by a co-impregnation method using Ni(NO3)2· 6H2O as the nickel source,(NH4)2HPO4as the phosphorus source, and SBA-15 as the support.The P/Ni molar ratio in the nickel and phosphorus sources was set at 2.SBA-15 was impregnated with the required amount of Ni(NO3)2·6H2O and(NH4)2HPO4aqueous solution at room temperature for 24 h,followed by drying at 100 oC for another 24 h.Then the sample was calcined at 500°C for 4 h to give the oxidic precursor of Ni2P/SiO2catalyst.Secondly, the Mo-promoted Ni2P/SBA-15 catalyst was prepared by impregnating an appropriate content of Mo(NO3)2·6H2O aqueous solution onto the obtained Ni2P/SBA-15 oxidic precursor at room temperature for 12 h,followed by drying at 120°C for 24 h.Then the sample was calcined at 500°C for 4 h to give the oxidic precursor of Mo-Ni2P/SiO2catalyst.After that,the Mo-Ni2P/SiO2oxidic precursors were pelletized to 40-60 mesh(250-420μm) and treated by TPR in a fixed-bed quartz reactor under atmospheric pressure in flowing H2(100 mL·min-1).The temperature was increased from room temperature to 300oC at a heating rate of 10°C·min-1,then to 650°C at 1°C·min-1,and held at 650°C for 2 h,followed by cooling to room temperature in the H2flow. Finally,the sample was passivated at room temperature with a 1.0%(volume fraction,φ)O2/Ar flow(50 mL·min-1)for 2 h.Such passivated sample was used for structure characterization or catalytic investigation.The sample was denoted as xMo-Ni2P/SBA-15 catalyst,where x%was the nominal mass fraction of Mo.

2.2 Catalyst characterization

The XRD patterns were collected on a Rigaku D/MAX2500VB 2+/PC system using Cu Kαradiation(λ=0.154056 nm)at 40 kV and 200 mA.The XRD patterns were collected at a scanning speed of 10(°)·min-1in the 2θ range of 10°-85°.The surface areas and porosity of the samples were characterized with N2sorption analysis.N2adsorption-desorption isotherms were measured at-196°C on a Sorptomatic 1990 analyzer(Thermo Corp.).Before the measurements,the samples were outgassed at 300°C for 4.0 h.The Brumauer-Emmett-Teller(BET)method was employed to calculate the specific surface areas.The pore volumes and pore size distributions were derived from the desorption branches of the isotherms using the Barrett-Joyner-Halanda(BJH)model.Transmission electron microscopy(TEM) experiments were carried out in a JEOL JEM-2100 microscope with an accelerating voltage of 200 kV.The microscope was equipped with an electron gun with LaB6and an objective lens (Focal length,2.3 mm;Spherical aberration,1.0 mm;Chromatic aberration,1.4 mm;point to point resolution,0.23 nm).The samples were dispersed in ethanol and placed on a copper grid before TEM examinations.The XPS experiments were carried out in an ESCALAB 250(Thermo Electron Co.)instrument using Al Kαas the exciting radiation at constant pass energy of 50 eV. Binding energies were calibrated using the carbon present as a contaminant(C 1s,285.0 eV).

2.3 Catalytic activity

The catalytic performance of the catalyst was evaluated by the HDS of DBT,which was carried out in a high pressure fixed-bed continuous flow stainless steel reactor(i.d.9.0 mm)with a central thermocouple to monitor the temperature of the catalyst bed.For each test,0.3 g of the catalyst(40-60 mesh)was diluted with quartz sands to fill the reactor.H2flow was regulated by a mass flow controller and the liquid feed consisting of 1.0%(w)DBT in decalin was introduced into the reactor by a piston pump.The S content in the feed corresponded to 1740×10-6(mass fraction,w). Aliquid hourly space velocity(LHSV)of 1.9 h-1was used in the present work.Preliminary tests have confirmed that both the internal and external diffusions were completely eliminated under the current experimental conditions.The catalyst was pre-reduced in-situ by flowing 40 mL·min-1H2at 500°C for 2 h.The catalytic activities were investigated under the total pressure of 3.0 MPa, at the temperature from 300 to 380°C,with the volume ratio of H2to liquid feed at 400.The activity data were collected after 0.5 h duration at each temperature.The liquid products were collected at 1.0 h intervals and analyzed off-line by a gas chromatography (SP 2100,Beijing Beifenruili Analytic Instrument(Group)Co., Ltd.)equipped with a flame ionization detector(FID)and a capillary column(HJ.PONA,50 m×0.20 mm×0.50 μm).The main liquid products of the reaction were biphenyl(BP)and cyclohexylbenzene(CHB)with the S content being converted to H2S.Therefore,the HDS performance of the catalysts can be evaluated by the conversion of DBT.

3 Results and discussion

3.1 XRD characterization

XRD characterization was employed to investigate the impact of the Mo on the bulk phase of metal phosphides in the Mopromoted Ni2P/SBA-15 catalysts.Fig.1 shows the XRD patterns of xMo-Ni2P/SBA-15 catalysts with various Mo contents.For the un-promoted 0Mo-Ni2P/SBA-15 catalyst(Fig.1(a)),a series of diffraction peaks at 2θ of 40.6°,44.5°,47.2°,54.1°,54.9°,74.8°, and 80.1°were observed,which were assigned to Ni2P(JCPDS No.03-0953).After introduction of Mo promoters(Fig.1(b-f)), the intensity of the peaks due to Ni2P phase was diminished. According to the Scherrer equation,the average crystalline size of Ni2P from Fig.1(a)to Fig.1(f)was calculated to be 21.7,20.5, 19.6,18.8,16.3,15.9 nm,respectively(Table 1).These results indicated that the dispersion of the Ni2P phase was improved in the Mo-promoted Ni2P/SBA-15 catalysts.Similar phenomena have been reported by Sun11and Chen17et al.with TEM characterizations.Such phenomena should be related with the different behaviors between Ni and Mo species during H2-TPR process. The precursor of Mo-containing phosphides is more difficult to be reduced than that of Ni2P phase;therefore,improved dispersion of Ni2P was observed after the addition of Mo.17Besides,no new diffraction patterns were detected.That is,no separate phase containing Mo was evident,either due to the low Mo loading or the high dispersion of the formed phases.18,19

Fig.1 XRD patterns of xMo-Ni2P/SBA-15 catalysts with various Mo contents

Table1 Pore structure parameters of xMo-Ni2P/SBA-15 catalysts with various Mo contents

3.2 N2adsorption-desorption

The xMo-Ni2P/SBA-15 catalysts with various Mo contentswere characterized by the N2adsorption-desorption measurement. Fig.2 illustrated that the isotherms for all of the samples belonged to type IV and exhibited a hysteresis loop,which were typical for the regular mesoporous materials.20These results suggested that the ordered mesoporous structure of Ni2P/SBA-15 catalysts was mainly maintained after the introduction of Mo promoters.

Fig.2 N2adsorption-desorption isotherms of xMo-Ni2P/SBA-15 catalysts with various Mo contents

The pore size distribution of the xMo-Ni2P/SBA-15 catalysts was displayed in Fig.3.For the un-promoted 0Mo-Ni2P/SBA-15 catalyst(Fig.3(a)),only one peak was observed with the average size(DBJH)of 6.3 nm,which meant that the formed Ni2Pphase was uniformly distributed inside the mesoporous,consistent with our previous studies.18For the 0.5Mo-Ni2P/SBA-15 and 1Mo-Ni2P/ SBA-15 catalysts(Fig.3(b,c)),similar pore size distribution was observed while the DBJHwas slightly reduced to around 6.0 nm, indicating that the mesopores were well maintained after introducing a low content of Mo promoters.As the Mo content increased to 3%(w),a new aperture was developed with the DBJH= 3.8 nm,which became dominant as the Mo content further increased.The development of a new aperture with a lower DBJHmay be caused by the blockage of the mesoporous with the accumulated metal phosphides.It had been observed previously by our group on the Ni2P/SBA-15 catalysts.21The development of a new aperture with a specific DBJHshould be related with the uniform pore diameter of the SBA-15 support.

Fig.3 Pore size distributions of xMo-Ni2P/SBA-15 catalysts with various Mo contents

The pore structure parameters for the characterized samples were summarized in Table 1.It is clear that the pore structure parameters of the Mo-promoted Ni2P/SBA-15 catalysts depend on the content of the added Mo.At low Mo loadings(0.5%,1%,3%, and 5%(w)),a slight increase in the specific surface area and a slight decrease in the pore volume were observed in comparison with the un-promoted 0Mo-Ni2P/SBA-15 catalyst.The slight increase in the specific surface area may be related to the improved dispersion of Ni2P after the introduction of Mo promoters, as suggested by the aforementioned XRD results.The slight decrease of the pore volume should be caused by the larger amount of metal phosphides accumulated in the mesoporous.At high Mo loading(7%(w)),both the specific surface area and the pore volume decreased compared with the un-promoted counterpart, which suggested that the excess of Mo promoters blocked the mesoporous.

3.3 TEM measurement

Fig.4 TEM images of xMo-Ni2P/SBA-15 catalysts

TEM images were taken to investigate the dispersion and morphology of the xMo-Ni2P/SBA-15 catalysts with various Mo contents.Fig.4 shows the TEM images for the 0Mo-Ni2P/SBA-15, 1Mo-Ni2P/SBA-15,and 7Mo-Ni2P/SBA-15 catalysts.All of the catalysts exhibited a well-ordered mesoporous channel structure,which supported the aforementioned N2sorption results.Besides, dark particles were observed in the mesopores,which were assigned as Ni2P phases based on the EDS analysis.On the other hand,some relatively large particles were also noticed on the surface,which was consistent with the crystalline size of Ni2P calculated by Scherrer equation as in XRD analysis.

3.4 XPS characterization

XPS characterization was conducted to study the surface property of the Mo-Ni2P/SBA-15 catalysts.Fig.5 shows the XPS spectra of the 1Mo-Ni2P/SBA-15 catalyst.Characteristic Ni 2p peaks were observed at 853.3 and 857.4 eV,corresponding to Niδ+(0＜δ＜2)in Ni2P and Ni2+in Ni3(PO4)2,respectively.22P 2p XPS peaks were observed at 129.5,133.3,and 135.3 eV.Based on the literature,23the peak at 129.5 eV was ascribed as Pδ-in metal phosphides while the peaks at 133.3 and 135.3 eV were assigned as P5+in Ni3(PO4)2and P2O5,respectively.For Mo 3d XPS spectra, four peaks were observed at 228.4,231.6,232.8,and 236.1 eV. The peaks at 228.4 and 231.6 eV corresponded to Mo 3d5/2and Mo 3d3/2of Moδ+(0＜δ＜4)while the peaks at 232.8 and 236.1 eV were from Mo 3d5/2and Mo 3d3/2of Mo6+,respectively.24,18

The binding energy and surface atom concentration of the Mo-Ni2P/SBA-15 catalysts with various Mo contents were summarized in Table 2.Compared with the Ni2P/SBA-15 catalyst,little change was observed in the binding energy of Ni 2p and P 2p in the Mo-Ni2P/SBA-15 catalysts.Mo 3d peaks were detected after the added Mo content increased up to 1.0%(w).Since Niδ+,Pδ-, and Moδ+species are the constituents of metal phosphides,it is crucial to study the concentration ratio of Niδ+/ΣNi,Pδ-/ΣP,and Moδ+/ΣMo on the surface.As revealed in Table 2,after addition of Mo,study the concentration ratio of Niδ+/ΣNi and Pδ-/ΣP increase slightly while study the concentration ratio of Moδ+/ΣMo keeps almost constant.That is,the addition of Mo would promote the formation of nickel phosphides on the surface,which may provide more active sites for the HDS reactions.

Fig.5 XPS spectra of the 1Mo-Ni2P/SBA-15 catalyst

Table2 XPS results of xMo-Ni2P/SBA-15 catalysts with various Mo contents

3.5 Catalytic activity evaluation

The effect of Mo contents on the DBT conversion of xMo-Ni2P/ SBA-15 catalysts was investigated at reaction temperature from 300 to 380°C.As demonstrated in Fig.6,the DBT conversion increased with the temperature for all of the xMo-Ni2P/SBA-15 catalysts.In a whole,all of the Mo-promoted Ni2P/SBA-15 catalysts exhibited a superior DBT conversion than the un-promoted counterpart.The XRD results have documented that the dispersion of the Ni2Pphases in the Mo-promoted Ni2P/SBA-15 catalysts was improved after the introduction of the Mo promoters,which may explain the superior DBT conversion on the Mo-promoted Ni2P/ SBA-15 catalysts.Among the Mo-promoted Ni2P/SBA-15 cata-lysts,the 1Mo-Ni2P/SBA-15 catalyst exhibited the best activity at temperature from 340 to 380oC while the 7Mo-Ni2P/SBA-15 catalyst exhibited the best activity at lower temperature,which demonstrated that the promotion effect depended on the Mo contents at various temperatures.The addition of Mo leads to the improved dispersion of Ni2P,which benefits the HDS activity.On the other hand,the addition of Mo results in the blockage of the surface Ni species by Mo,which deteriorates the HDS activity. Therefore,an optimal amount of Mo exists in the present work.

Fig.6 Catalytic activity of xMo-Ni2P/SBA-15 catalysts with various Mo contents for HDS of DBT

Fig.7 BPand CHB selectivities over xMo-Ni2P/SBA-15 catalysts with various Mo contents

It is well established that the HDS of DBT proceeds mainly via two parallel reaction pathways.11,25,26One is the direct desulfurization(DDS)with BP as the product.The other is the hydrogenation followed by the desulfurization(HYD)with CHB as the final product.Fig.7 illustrates the selectivity profiles for the HDS of DBT on xMo-Ni2P/SBA-15 catalysts with various Mo contents at reaction temperature from 300 to 380°C.For all of the tested catalysts,the BP selectivity was much higher than the CHB selectivity at each temperature,indicating that DBT was mainly converted via the DDS pathway.After introduction of the Mo promoters,the CHB selectivity was slightly enhanced compared with the un-promoted counterpart.The Mo content was found to have little impact on the BP/CHB selectivity of the Mo-promoted Ni2P/SBA-15 catalysts.A recent study27,28showed that two types of sites,tetrahedral Ni(1)sites and square pyramidal Ni(2)sites, presented in the nickel phosphides.The Ni(1)sites carried out DDS route while the Ni(2)sites were responsible for the HYD route.The present work suggested that the addition of Mo would increase the portion of the Ni(2)sites in the nickel phosphide phases,thus accelerating the HYD route.Sun et al.11reported that the Ni-Mo-P/SiO2catalyst exhibited a slightly higher CHB selectivity than the Ni2P/SiO2catalyst,in agreement with our results.

Besides,the 1Mo-Ni2P/SBA-15 catalyst has been employed to test the stability up to 50 h at 380°C under 3.0 MPa with the volume ratio of H2to liquid feed at 400.It was found that both the DBT conversion and BP/CHB selectivity possessed a good stability under the current conditions.XRD characterizations confirmed that the phosphide phase and dispersion of the 1Mo-Ni2P/ SBA-15 catalyst were well maintained after the stability test.

4 Conclusions

A series of xMo-Ni2P/SBA-15 catalysts with the initial P/Ni molar ratio of 2,the Ni2P content of 40%(w),and the Mo content varying from 0.5%to 7%(w)were prepared by the TPR treatment following the subsequent incipient impregnation method and characterized with XRD and N2sorption for the HDS of DBT reaction.Only Ni2P phases was detected with the Mo contents up to 7%(w).The dispersion of the Ni2P phase was improved after the introduction of Mo promoters.The 0.5Mo-Ni2P/SBA-15 and 1Mo-Ni2P/SBA-15 catalysts showed a narrow pore size distribution with DBJHclose to 6.0 nm,while an extra aperture with DBJH=3.8 nm was developed on the xMo-Ni2P/SBA-15 catalysts with higher Mo contents.All of the Mo-promoted Ni2P/SBA-15 catalysts exhibited a superior DBT conversion than the un-promoted counterpart,which may be related to the improved dispersion of the Ni2P phase.Among the Mo-promoted Ni2P/SBA-15 catalysts,the promotion effect depended on the Mo contents at various temperatures.DBT was mainly converted via the DDS pathway on the tested catalysts.The HYD pathway was slightly enhanced after the addition of Mo promoters.The Mo content had little impact on the selectivity of the Mo-promoted Ni2P/SBA-15 catalysts.

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Preparation,Characterization and Hydrodesulfurization Catalytic Performances of Mo-Ni2P/SBA-15 Catalysts

WANG Zhou-Jun1WU Ping-Yi1,2LAN Ling2LIU Kun-Hong2HU Ya-Qiong2JI Sheng-Fu1,*
(1State Key Laboratory of Chemical Resource Engineering,Beijing University of Chemical Technology,Beijing 100029, P.R.China;2Petrochemical Research Institute,PetroChina,Beijing 100195,P.R.China)

A series of Mo-Ni2P/SBA-15 catalysts with various Mo loadings were prepared by impregnating nickel nitrate,diammonium hydrogen phosphate,and ammonium molybdate onto an SBA-15 support,followed by temperature-programmed reduction(TPR)under H2.The structure of the catalysts was characterized by X-ray diffraction(XRD),N2adsorption-desorption,transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).The catalytic performance was evaluated in the hydrodesulfurization(HDS)of dibenzothiophene(DBT).The results indicate that the mesoporous structure was maintained and the Ni2P phase was present in all of the catalysts.The chemical states of Ni were Niδ+and Ni2+,the chemical states of P were Pδ-and P5+,and the chemical states of Mo were Moδ+and Mo6+.Mo was shown to promote the HDS catalytic performance of Ni2P/SBA-15 catalysts.The Mo-Ni2P/SBA-15 catalysts with 1%(w,mass fraction)Mo loading exhibited the highest HDS activity.The conversion of the DBTreached 99.03%under reaction conditions of 380°C and 3.0 MPa.The HDS of DBT proceeded mainly via the direct desulfurization(DDS)pathway over all of the tested Mo-Ni2P/SBA-15 catalysts.

Mo;Ni2P;Dibenzothiophene;Hydrodesulfurization;Mesoporous

O643

10.3866/PKU.WHXB201501094www.whxb.pku.edu.cn

Received:October 31,2014;Revised:January 7,2015;Published on Web:January 9,2015.

?Corresponding author.Email:jisf@mail.buct.edu.cn;Tel:+86-10-64419619.

The project was supported by the National Key Basic Research Program of China(973)(2006CB202503)and PetroChina Innovation Foundation, China(2010D-5006-0401).

國(guó)家重點(diǎn)基礎(chǔ)研究發(fā)展規(guī)劃項(xiàng)目(973)(2006CB202503)及中國(guó)石油科技創(chuàng)新基金(2010D-5006-0401)資助