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Al2O3: Its role and potential of HDS performance for steric hindered sulfur compound 4,6-DMDBT
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A novel catalyst of Ni,W-surface-Ti-rich-ETS-10/Al2 O3 : Its role and potential of HDS performance for steric hindered sulfur compound 4,6-DMDBT Shenyong Ren a , Jing Li a , Bing Feng a , Yandan Wang a , Wencheng Zhang b , Guangming Wen b , Zhihua Zhang b , Baojian Shen a,∗ a State Key Laboratory of Heavy Oil Processing, the Key Laboratory of Catalysis of CNPC, College of Chemical Engineering, China University of Petroleum, 18# Fuxue Rd., Changping, Beijing, 102249, China b Daqing Chemical Engineering Research Center, Petrochemical Research Institute of PetroChina Company Limited, 2# Chengxiang Rd., Longfeng, Daqing 163714, China
a r t i c l e
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Article history: Received 31 March 2015 Received in revised form 24 May 2015 Accepted 13 June 2015 Available online xxx Keywords: ETS-10 surface Ti rich WS2 phase HDS catalyst 4,6-DMDBT
a b s t r a c t There is growing interest in developing deep hydrodesulfurization (HDS) catalysts to obtain higher activity. This study provides an investigation of influence of surface-Ti-rich-ETS-10 (AT-ETS) on the performance of NiW-based catalyst (NiW-AT-ETS/Al2 O3 ) using NiW-ETS-origin/Al2 O3 as the reference. The HDS performance of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as model sulfur compounds were tested in fixed reactor. NiW-AT-ETS/Al2 O3 containing surface-Ti-richETS-10 lowered H2 reduction temperature compared to NiW-ETS-origin/Al2 O3 . NiW-AT-ETS/Al2 O3 had higher WS2 stacking numbers and shorter slab length though they showed similar sulfidation degree. Higher HDS performance was obtained over NiW-AT-ETS/Al2 O3 due to higher WS2 slab layers in contrast to NiW-ETS-origin/Al2 O3 . The advantage of NiW-AT-ETS/Al2 O3 for 4,6-DMDBT removal may be also related to easy accessibility of active sites on the catalyst surface as a result of the higher dispersion compared to NiW-ETS-origin/Al2 O3 . © 2015 Elsevier B.V. All rights reserved.
1. Introduction Large quantities of SOx gas emission are generated from automobile exhaust. The discharge of SOx gas emission could cause serious environmental pollution and human health problems. An efficient deep HDS process is needed to meet the increasingly stringent discharge standards in oil refining industry. Sulfur compounds removal, such as DBT and 4,6-DMDBT, are believed to be the hardest because the tremendous steric hindrance can restrain the accessibility of these compounds to the active sites of most HDS catalysts. Topsøe and co-workers have proposed the catalytic active site Co(Ni)Mo(W)S phase for industrial HDS catalysts Co(Ni)Mo(W)S/Al2 O3 , where Co(Ni) atoms as promoters are located on the edges of the Mo(W)S2 particles [1–3]. There are two types of Co(Ni)Mo(W)S phases: type I and type II. The type I active phase is less stacked and strongly interacted with support. The type II active phase is highly stacked and weakly interacted with
∗ Corresponding author. Tel.: +86 10 8973 3369; fax: +86 10 8973 3369. E-mail address: [email protected] (B. Shen).
support, exhibiting higher activity than type I active phase [4]. Novel supporting materials development is a promising approach for highly active HDS catalyst s with highly dispersed Co(Ni)Mo (W)S type II phase [5–8]. Various support materials such as carbon nanotube [9], silica [10], V2 O5 /Al2 O3 [11] and SiO2 /Al2 O3 [12] have been studied for HDS catalysts. Of these supports, titania-containing supports, such as TiO2 [13], nano-TiO2 [14,15], Al2 O3 -TiO2 [16,17], SiO2 -TiO2 [18], showed remarkable HDS activity compared to the traditional alumina catalysts. ETS-10, a microporous titanosilicate, has been attracting great attention and interest since it was synthesized and identified [19,20]. It is a molecular sieve with corner-sharing tetrahedral SiO4 and octahedral (TiO6 )2− link through bridging oxygen atoms, which composes three dimensional 12-membered ring porous system. The octahedral (TiO6 )2− are connected as linear chains, which run into two perpendicular directions of the crystal and space with siliceous matrix from one another. Ti-O-Ti chains network in ETS10 is similar to the structure of anatase. Generally Ti species can be octahedral (mainly in bulk titania) or tetrahedral (in framework of most molecular sieves) coordination in Ti-containing HDS catalysts. However, Ti–O–Ti chains in ETS-10 are spaced by siliceous
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matrix, which is not only octahedrally coordinated but also highly dispersed by the framework Si atoms. Ti-site exposure on the surface of ETS-10 is considered to be the extremely dispersed titania chains. Accordingly, ETS-10 has given rise to wide applications on adsorption, ion exchange and shape-selective catalysis due to its particular properties [21,22]. In our previous works, ETS-10 supported NiW catalyst exhibited high HDS and HDA activity for a FCC diesel feed hydrotreating (sulfur content 1052 g/g) [23–26]. In our recent report, the surface-Ti-rich-ETS-10 was prepared by alkali-treatment process to remove Si atoms from the frameworks of ETS-10 [27]. To our knowledge, surface-Ti-rich-ETS-10 had not been used for HDS catalyst. The objective of this study was to develop a new support material to benefit the HDS reaction. The catalysts containing surface-Ti-rich-ETS-10 (AT-ETS) (NiW-AT-ETS/Al2 O3 ) and original ETS-10 (NiW-ETS-origin/Al2 O3 ) were characterized and evaluated for their role and potential in HDS of DBT and 4,6-DMDBT. 2. Experimental 2.1. Preparation of materials ETS-10: The starting material ETS-10 (abbreviated as ETS-origin) was synthesized through hydrothermal method as reported by Ji and Sacco Jr. et al. [28]. Surface Ti rich ETS-10 (abbreviated as ATETS) was obtained by the method described in our previous work [27]. ETS-origin and AT-ETS were transformed to H-ETS-origin and H-AT-ETS respectively by NH4 + ion exchange using NH4 Cl at 60 ◦ C for 12 h and calcination at 450 ◦ C for 2 h. Catalyst: The composite support was prepared by mixing 12.0 g H-ETS-origin (or H-AT-ETS) with 43.1 g pseudo-boehmite (Al2 O3 , 68 wt%) and extruding to form cloverleaf appearance support. The obtained extrudate was dried overnight at 120 ◦ C and calcined in the air at 500 ◦ C for 2 h. The corresponding NiW based catalysts (NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 ) were prepared by wetness impregnation of the composite supports using ammonium metal tungstate and nickel nitrate solution. The impregnated catalysts were dried at 120 ◦ C for 12 h and calcined at 500 ◦ C for 4 h. The amount of NiO and WO3 loading was 3.6 wt% and 18 wt%, respectively. The obtained catalysts (40–60 mesh particles) were evaluated in a 1 ml fixed bed micro-reactor for HDS reaction of DBT and 4,6-DMDBT, respectively. 2.2. Characterization The porosity of each sample was determined by measuring the N2 isotherm at −196 ◦ C on a Micromeritics ASAP 2020 automated system. The pore size distribution (PSD) was determined by the desorption branch of the data of N2 adsorption-desorption using BJH method. The total surface area was calculated according to the BET equation. The microporous volume, mesoporous volume, and external surface area were evaluated by the t-plot method. The bulk phase Si/Ti and Al/Ti molar ratios of the materials were determined on a Rigaku ZSX-100e X-ray fluorescence (XRF) spectrometer. The sampling depth was over than 2 m. The relative analysis error in quantification was ±5%. X-ray photoelectron spectroscopy (XPS) results were obtained on a VG ESCA Lab 250 photoelectron spectrometer using Al K␣ radiation (hv = 1486.6 eV). For these experiments, Ti 2p, Ni 2p and W 4f bands were recorded. Apparent atomic ratios in the XPS sampling region were evaluated from peak area integration ratios using sensitivity factors. The sampling depth was 2–5 nm. The relative analysis error in quantification was ±1%. Temperature-programmed reduction (TPR) experiments were carried out, prior to the reduction about 0.1 g sample in a quartz
Fig. 1. Adsorption–desorption curves (a) and pore size distribution (b) of catalysts.
Table 1 Pore structure data of composite supports and catalysts. Sample
Sext (m2 /g)
Vmeso (cm3 /g)
DAvg (nm)
ETS-origin/Al2 O3 AT-ETS/Al2 O3 NiW-ETS-origin/Al2 O3 NiW-AT-ETS/Al2 O3
300.6 313.5 214.5 230.2
0.549 0.570 0.405 0.440
7.31 7.27 7.56 7.65
tube reactor was pretreated in a nitrogen stream at 400 ◦ C for 30 min and then cooled down to room temperature. The temperature was then increased linearly at a rate of 10 ◦ C/min under a flow of H2 -N2 mixture (20% H2 by volume, 30 mL/min). The consumption of H2 was detected on an online thermal conductivity detector. The morphology of the Ni, W sulfide was observed by high resolution transmission electron microscopy (HRTEM) on a JEOL2100FX instrument operated at 200 kV (Samples were prepared by the drop method). 2.3. HDS catalytic activity of the catalysts The catalysts were first pre-sulfurized in situ with a sulfurizing feed of 10 vol% CS2 in decane at 4.0 MPa and 320 ◦ C for 3 h. The HDS of DBT (or 4,6-DMDBT) was evaluated in a continuous flow fixed bed microreactor under the following conditions: a model feed of 1000 ppm DBT (or 500 ppm 4,6-DMDBT) in decane, a catalyst load of 0.6 g, a reaction pressure of 4.0 MPa, a reaction temperature of 260 ◦ C, a feed flow rate of 6.6 mL/h, and an H2 /oil ratio of 370 (v/v). The liquid effluents were periodically collected and measured through microcoulometry instrument to give total S content when the steady-state conditions were reached. The products were analyzed on an Agilent 7890-5975C GC–MS.
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Table 2 Composition analysis of oxidized catalysts through XRF and XPS methods. Sample
(NiO)XRF
(WO3 ) XRF
(Ni/W) XRF
(Ni/W) XPS
(Ni/Ti) XPS
(W/Ti) XPS
NiW-ETS-origin/Al2 O3 NiW-AT-ETS/Al2 O3
3.6% 3.6%
18.3% 18.4%
0.61 0.61
0.60 0.52
4.00 1.82
6.67 3.49
Fig. 2. H2 –TPR curves of two catalysts.
3. Results and discussion 3.1. Characterization Fig. 1 presents N2 sorption isotherms and BJH pore size distributions of the catalysts. The external area (Sext ) and mesopore volume (Vmeso ) of NiW-AT-ETS/Al2 O3 catalyst (230.2 m2 /g; 0.440 cm3 /g) were higher than those of NiW-ETS-origin/Al2 O3 (214.5 m2 /g; 0.405 cm3 /g) (Table 1). The trend is consistent with that of corresponding molecular sieves of ETS-origin and AT-ETS in our previous report [27]. Alkali-treatment slightly changes the porosity of the support material. Desilication of zeolites resulted in abundant surface Ti species exposure [29,30]. It was discussed that alkali-treatment can selectively remove the Si atoms from the framework of ETS-10, and enrich the surface Ti atoms [27]. Table 2 shows the elemental analysis of the catalysts. The surface phase (Ni/Ti)XPS ratio of oxidized NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 catalysts are 4.00 and 1.82, and the surface phase (W/Ti)XPS ratio of oxidized NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 are 6.67 and 3.49, respectively. Lower (Ni/Ti)XPS and (W/Ti)XPS of NiW-AT-ETS/Al2 O3 may be probably due to surface Ti rich of AT-ETS compared to those of NiWETS-origin/Al2 O3 . NiW-AT-ETS/Al2 O3 (0.52) showed lower surface phase (Ni/W)XPS ratio than oxidized NiW-ETS-origin/Al2 O3 (0.60) in spite of the same bulk phase (Ni/W)XRF (0.61), suggesting higher W species distribution on the surface of the catalyst containing Ti-rich-ETS-10. The catalysts of NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 displayed two well-developed peaks on H2 -TPR (Fig. 2). The lower temperature peak at about 600 ◦ C is corresponded to the reduction of octahedrally coordinated polymeric NiWO species [31,32]. There was no pronounced difference observed in this band between two catalysts. The higher temperature peak at around 900 ◦ C is attributed to the reduction of tetrahedrally coordinated monomeric NiWO species, which are mostly stabilized on the alumina containing support [33]. NiW-AT-ETS/Al2 O3 shows a relatively lower reduction temperature (915 ◦ C) than NiW-ETSorigin/Al2 O3 (930 ◦ C) in this band. Probably, surface-Ti-rich-ETS-10 may weaken the interaction between W species and surfaceTi-rich-ETS-10/Al2 O3 composite support due to the coordinately unsaturated sites at Ti-rich-ETS-10 surface, which results in easier
Fig. 3. XPS W 4f spectra of oxidized (a) and sulfidized (b) catalysts.
reduction of WO3 species by hydrogen. It was reported that W-TiO2 support formed a relatively weak interaction for WNi/TiO2 catalyst due to the presence of coordinately unsaturated sites at the TiO2 surface compared to that of WNi/Al2 O3 catalyst [34,35]. XPS W 4f spectra of oxidized and sulfidized catalysts respectively were showed in Fig. 3. There were two signals of W 4f5/2 and W 4f7/2 electrons at BE of 38.1 and 36.0 eV respectively (Fig. 3a) for oxidized catalysts. These signals are assigned to W6+ species, most like WO3 [36,37]. After sulfurization (Fig. 3b), a second doublet peak appeared at 33.7 and 31.6 eV, which was typical for W4+ as in the WS2 phase [38,39]. The XPS W 4f spectra of sulfided catalysts were simply divided into two regions. The first one was attributed to WO3 phase from 40.5 eV ranges to 35.3 eV and the second one was attributed to WS2 phase from 35.3 eV ranges to 29.0 eV. The sulfidation degree of oxidic W species was defined as the ratio of W4+ (WS2 ) to the sum of W4+ (WS2 ) and W6+ (WO3 ) [25], where the content of WS2 and WO3 were obtained from integration area on the XPS W 4f spectra of the catalysts. After the calculation, the sulfidation degree of NiW-ETS/Al2 O3 and NiW-ATS/Al2 O3 are 70% and 69% respectively. The XPS Ni 2p spectra of the oxidized catalysts showed (Fig. 4a) two sharp peaks of Ni 2p3/2 and Ni 2p1/2 at 856.6 and 874.1 eV, assigned to the spin-splitting of NiO [34] and two broad peaks, assigned to the envelopes of the corresponding shakeup satellite lines [40–42]. The peaks (Fig. 4b) of Ni 2p3 at 853.5 eV and Ni 2p1 at 871.0 eV may be associated to NiS [36].
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Fig. 6. HDS activities of two catalysts for DBT and 4,6-DMDBT feeds (reaction pressure, 4.0 MPa; temperature, 260 ◦ C; feed flow rate, 6.6 mL/h; H2 /oil ratio, 370 (v/v)).
type II NiWS phase on the catalyst. Higher WS2 slab layers can benefit for increase of hydrogenation activity [43]. Shorter average slab length of NiW-AT-ETS/Al2 O3 may suggest higher WS2 dispersion according to the previous study by Payen et al [44]. 3.2. HDS assessment
Fig. 4. XPS Ni 2p spectra of oxidized (a) and sulfidized (b) catalysts.
No presence of NiO phase signals (Fig. 4b) confirmed that the Ni species are fully sulfurized. The representative TEM images of two sulfided catalysts displayed (Fig. 5) thread-like layers WS2 slabs. The average layer number of per slab and average slab length were calculated from the measurement of about 100 WS2 crystallites. For NiWETS-origin/Al2 O3 catalyst, the average layer number was 2.3, the average layer spacing of per slab was 0.626 nm, and the average slab length was 3.74 nm. For NiW-AT-ETS/Al2 O3 catalyst, the average layer number, average layer spacing, and average length of the WS2 slabs were 3.3, 0.627 nm, and 2.66 nm, respectively. Both of two catalysts had almost equal average WS2 slabs layer spacing. The catalyst NiW-AT-ETS/Al2 O3 had higher WS2 slab layers and shorter slab length than NiW-ETS-origin/Al2 O3 . Considering the H2 -TPR temperature towards two catalysts, the surface Ti rich of ETS-10 in NiW-AT-ETS/Al2 O3 can relax the strong interaction between NiWS phase and Al2 O3 support and form higher stack of
The HDS results of catalysts NiW-ETS-origin/Al2 O3 and NiW-ATETS/Al2 O3 with DBT and 4,6-DMDBT feed at 260 ◦ C are shown in Fig. 6. HDS ratios of catalysts NiW-ETS-origin/Al2 O3 and NiW-ATETS/Al2 O3 for DBT are 95.2% and 96.5% respectively, while those for high steric hindered 4,6-DMDBT are 82.3% and 86.9%, respectively. NiW-AT-ETS/Al2 O3 showed the more advantage of HDS for 4,6-DMDBT than NiW-ETS-origin/Al2 O3 . NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 showed similar pore structure and sulfurization ability identified by BET and XPS analyses, respectively. The promoted HDS ratio of NiW-AT-ETS/Al2 O3 may be due to higher WS2 slab layers. The easy accessibility of active sites on the surface of NiW-AT-ETS/Al2 O3 catalyst can benefit the increase of 4,6-DMDBT HDS as a result of the higher dispersion compared to NiW-ETS-origin/Al2 O3 . 4. Conclusion A novel NiW-AT-ETS/Al2 O3 catalyst was developed by using surface Ti rich ETS-10, which was obtained by alkaline solution treatment of ETS-10, as the support component. NiW-AT-ETS/Al2 O3 was characterized by H2 -TPR, XPS and TEM, and assessed for HDS of DBT and 4,6-DMDBT using NiW-ETS-origin/Al2 O3 as reference. The enrichment of surface Ti species weakened the strong interaction between active phase WS2 and Al2 O3 support illustrated by H2 TPR. NiW-AT-ETS/Al2 O3 had higher WS2 stacked layers and shorter slab length. NiW-AT-ETS/Al2 O3 exhibited higher HDS ratios than
Fig. 5. TEM images of sulfidized catalysts NiW-ETS-origin/Al2 O3 (a) and NiW-AT-ETS/Al2 O3 (b).
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A novel catalyst of Ni,W-surface-Ti-rich-ETS-10/Al2 O3 : Its role and potential of HDS performance for steric hindered sulfur compound 4,6-DMDBT Shenyong Ren a , Jing Li a , Bing Feng a , Yandan Wang a , Wencheng Zhang b , Guangming Wen b , Zhihua Zhang b , Baojian Shen a,∗ a State Key Laboratory of Heavy Oil Processing, the Key Laboratory of Catalysis of CNPC, College of Chemical Engineering, China University of Petroleum, 18# Fuxue Rd., Changping, Beijing, 102249, China b Daqing Chemical Engineering Research Center, Petrochemical Research Institute of PetroChina Company Limited, 2# Chengxiang Rd., Longfeng, Daqing 163714, China
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Article history: Received 31 March 2015 Received in revised form 24 May 2015 Accepted 13 June 2015 Available online xxx Keywords: ETS-10 surface Ti rich WS2 phase HDS catalyst 4,6-DMDBT
a b s t r a c t There is growing interest in developing deep hydrodesulfurization (HDS) catalysts to obtain higher activity. This study provides an investigation of influence of surface-Ti-rich-ETS-10 (AT-ETS) on the performance of NiW-based catalyst (NiW-AT-ETS/Al2 O3 ) using NiW-ETS-origin/Al2 O3 as the reference. The HDS performance of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as model sulfur compounds were tested in fixed reactor. NiW-AT-ETS/Al2 O3 containing surface-Ti-richETS-10 lowered H2 reduction temperature compared to NiW-ETS-origin/Al2 O3 . NiW-AT-ETS/Al2 O3 had higher WS2 stacking numbers and shorter slab length though they showed similar sulfidation degree. Higher HDS performance was obtained over NiW-AT-ETS/Al2 O3 due to higher WS2 slab layers in contrast to NiW-ETS-origin/Al2 O3 . The advantage of NiW-AT-ETS/Al2 O3 for 4,6-DMDBT removal may be also related to easy accessibility of active sites on the catalyst surface as a result of the higher dispersion compared to NiW-ETS-origin/Al2 O3 . © 2015 Elsevier B.V. All rights reserved.
1. Introduction Large quantities of SOx gas emission are generated from automobile exhaust. The discharge of SOx gas emission could cause serious environmental pollution and human health problems. An efficient deep HDS process is needed to meet the increasingly stringent discharge standards in oil refining industry. Sulfur compounds removal, such as DBT and 4,6-DMDBT, are believed to be the hardest because the tremendous steric hindrance can restrain the accessibility of these compounds to the active sites of most HDS catalysts. Topsøe and co-workers have proposed the catalytic active site Co(Ni)Mo(W)S phase for industrial HDS catalysts Co(Ni)Mo(W)S/Al2 O3 , where Co(Ni) atoms as promoters are located on the edges of the Mo(W)S2 particles [1–3]. There are two types of Co(Ni)Mo(W)S phases: type I and type II. The type I active phase is less stacked and strongly interacted with support. The type II active phase is highly stacked and weakly interacted with
∗ Corresponding author. Tel.: +86 10 8973 3369; fax: +86 10 8973 3369. E-mail address: [email protected] (B. Shen).
support, exhibiting higher activity than type I active phase [4]. Novel supporting materials development is a promising approach for highly active HDS catalyst s with highly dispersed Co(Ni)Mo (W)S type II phase [5–8]. Various support materials such as carbon nanotube [9], silica [10], V2 O5 /Al2 O3 [11] and SiO2 /Al2 O3 [12] have been studied for HDS catalysts. Of these supports, titania-containing supports, such as TiO2 [13], nano-TiO2 [14,15], Al2 O3 -TiO2 [16,17], SiO2 -TiO2 [18], showed remarkable HDS activity compared to the traditional alumina catalysts. ETS-10, a microporous titanosilicate, has been attracting great attention and interest since it was synthesized and identified [19,20]. It is a molecular sieve with corner-sharing tetrahedral SiO4 and octahedral (TiO6 )2− link through bridging oxygen atoms, which composes three dimensional 12-membered ring porous system. The octahedral (TiO6 )2− are connected as linear chains, which run into two perpendicular directions of the crystal and space with siliceous matrix from one another. Ti-O-Ti chains network in ETS10 is similar to the structure of anatase. Generally Ti species can be octahedral (mainly in bulk titania) or tetrahedral (in framework of most molecular sieves) coordination in Ti-containing HDS catalysts. However, Ti–O–Ti chains in ETS-10 are spaced by siliceous
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Please cite this article in press as: S. Ren, et al., A novel catalyst of Ni,W-surface-Ti-rich-ETS-10/Al2 O3 : Its role and potential of HDS performance for steric hindered sulfur compound 4,6-DMDBT, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.06.023
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matrix, which is not only octahedrally coordinated but also highly dispersed by the framework Si atoms. Ti-site exposure on the surface of ETS-10 is considered to be the extremely dispersed titania chains. Accordingly, ETS-10 has given rise to wide applications on adsorption, ion exchange and shape-selective catalysis due to its particular properties [21,22]. In our previous works, ETS-10 supported NiW catalyst exhibited high HDS and HDA activity for a FCC diesel feed hydrotreating (sulfur content 1052 g/g) [23–26]. In our recent report, the surface-Ti-rich-ETS-10 was prepared by alkali-treatment process to remove Si atoms from the frameworks of ETS-10 [27]. To our knowledge, surface-Ti-rich-ETS-10 had not been used for HDS catalyst. The objective of this study was to develop a new support material to benefit the HDS reaction. The catalysts containing surface-Ti-rich-ETS-10 (AT-ETS) (NiW-AT-ETS/Al2 O3 ) and original ETS-10 (NiW-ETS-origin/Al2 O3 ) were characterized and evaluated for their role and potential in HDS of DBT and 4,6-DMDBT. 2. Experimental 2.1. Preparation of materials ETS-10: The starting material ETS-10 (abbreviated as ETS-origin) was synthesized through hydrothermal method as reported by Ji and Sacco Jr. et al. [28]. Surface Ti rich ETS-10 (abbreviated as ATETS) was obtained by the method described in our previous work [27]. ETS-origin and AT-ETS were transformed to H-ETS-origin and H-AT-ETS respectively by NH4 + ion exchange using NH4 Cl at 60 ◦ C for 12 h and calcination at 450 ◦ C for 2 h. Catalyst: The composite support was prepared by mixing 12.0 g H-ETS-origin (or H-AT-ETS) with 43.1 g pseudo-boehmite (Al2 O3 , 68 wt%) and extruding to form cloverleaf appearance support. The obtained extrudate was dried overnight at 120 ◦ C and calcined in the air at 500 ◦ C for 2 h. The corresponding NiW based catalysts (NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 ) were prepared by wetness impregnation of the composite supports using ammonium metal tungstate and nickel nitrate solution. The impregnated catalysts were dried at 120 ◦ C for 12 h and calcined at 500 ◦ C for 4 h. The amount of NiO and WO3 loading was 3.6 wt% and 18 wt%, respectively. The obtained catalysts (40–60 mesh particles) were evaluated in a 1 ml fixed bed micro-reactor for HDS reaction of DBT and 4,6-DMDBT, respectively. 2.2. Characterization The porosity of each sample was determined by measuring the N2 isotherm at −196 ◦ C on a Micromeritics ASAP 2020 automated system. The pore size distribution (PSD) was determined by the desorption branch of the data of N2 adsorption-desorption using BJH method. The total surface area was calculated according to the BET equation. The microporous volume, mesoporous volume, and external surface area were evaluated by the t-plot method. The bulk phase Si/Ti and Al/Ti molar ratios of the materials were determined on a Rigaku ZSX-100e X-ray fluorescence (XRF) spectrometer. The sampling depth was over than 2 m. The relative analysis error in quantification was ±5%. X-ray photoelectron spectroscopy (XPS) results were obtained on a VG ESCA Lab 250 photoelectron spectrometer using Al K␣ radiation (hv = 1486.6 eV). For these experiments, Ti 2p, Ni 2p and W 4f bands were recorded. Apparent atomic ratios in the XPS sampling region were evaluated from peak area integration ratios using sensitivity factors. The sampling depth was 2–5 nm. The relative analysis error in quantification was ±1%. Temperature-programmed reduction (TPR) experiments were carried out, prior to the reduction about 0.1 g sample in a quartz
Fig. 1. Adsorption–desorption curves (a) and pore size distribution (b) of catalysts.
Table 1 Pore structure data of composite supports and catalysts. Sample
Sext (m2 /g)
Vmeso (cm3 /g)
DAvg (nm)
ETS-origin/Al2 O3 AT-ETS/Al2 O3 NiW-ETS-origin/Al2 O3 NiW-AT-ETS/Al2 O3
300.6 313.5 214.5 230.2
0.549 0.570 0.405 0.440
7.31 7.27 7.56 7.65
tube reactor was pretreated in a nitrogen stream at 400 ◦ C for 30 min and then cooled down to room temperature. The temperature was then increased linearly at a rate of 10 ◦ C/min under a flow of H2 -N2 mixture (20% H2 by volume, 30 mL/min). The consumption of H2 was detected on an online thermal conductivity detector. The morphology of the Ni, W sulfide was observed by high resolution transmission electron microscopy (HRTEM) on a JEOL2100FX instrument operated at 200 kV (Samples were prepared by the drop method). 2.3. HDS catalytic activity of the catalysts The catalysts were first pre-sulfurized in situ with a sulfurizing feed of 10 vol% CS2 in decane at 4.0 MPa and 320 ◦ C for 3 h. The HDS of DBT (or 4,6-DMDBT) was evaluated in a continuous flow fixed bed microreactor under the following conditions: a model feed of 1000 ppm DBT (or 500 ppm 4,6-DMDBT) in decane, a catalyst load of 0.6 g, a reaction pressure of 4.0 MPa, a reaction temperature of 260 ◦ C, a feed flow rate of 6.6 mL/h, and an H2 /oil ratio of 370 (v/v). The liquid effluents were periodically collected and measured through microcoulometry instrument to give total S content when the steady-state conditions were reached. The products were analyzed on an Agilent 7890-5975C GC–MS.
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Table 2 Composition analysis of oxidized catalysts through XRF and XPS methods. Sample
(NiO)XRF
(WO3 ) XRF
(Ni/W) XRF
(Ni/W) XPS
(Ni/Ti) XPS
(W/Ti) XPS
NiW-ETS-origin/Al2 O3 NiW-AT-ETS/Al2 O3
3.6% 3.6%
18.3% 18.4%
0.61 0.61
0.60 0.52
4.00 1.82
6.67 3.49
Fig. 2. H2 –TPR curves of two catalysts.
3. Results and discussion 3.1. Characterization Fig. 1 presents N2 sorption isotherms and BJH pore size distributions of the catalysts. The external area (Sext ) and mesopore volume (Vmeso ) of NiW-AT-ETS/Al2 O3 catalyst (230.2 m2 /g; 0.440 cm3 /g) were higher than those of NiW-ETS-origin/Al2 O3 (214.5 m2 /g; 0.405 cm3 /g) (Table 1). The trend is consistent with that of corresponding molecular sieves of ETS-origin and AT-ETS in our previous report [27]. Alkali-treatment slightly changes the porosity of the support material. Desilication of zeolites resulted in abundant surface Ti species exposure [29,30]. It was discussed that alkali-treatment can selectively remove the Si atoms from the framework of ETS-10, and enrich the surface Ti atoms [27]. Table 2 shows the elemental analysis of the catalysts. The surface phase (Ni/Ti)XPS ratio of oxidized NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 catalysts are 4.00 and 1.82, and the surface phase (W/Ti)XPS ratio of oxidized NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 are 6.67 and 3.49, respectively. Lower (Ni/Ti)XPS and (W/Ti)XPS of NiW-AT-ETS/Al2 O3 may be probably due to surface Ti rich of AT-ETS compared to those of NiWETS-origin/Al2 O3 . NiW-AT-ETS/Al2 O3 (0.52) showed lower surface phase (Ni/W)XPS ratio than oxidized NiW-ETS-origin/Al2 O3 (0.60) in spite of the same bulk phase (Ni/W)XRF (0.61), suggesting higher W species distribution on the surface of the catalyst containing Ti-rich-ETS-10. The catalysts of NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 displayed two well-developed peaks on H2 -TPR (Fig. 2). The lower temperature peak at about 600 ◦ C is corresponded to the reduction of octahedrally coordinated polymeric NiWO species [31,32]. There was no pronounced difference observed in this band between two catalysts. The higher temperature peak at around 900 ◦ C is attributed to the reduction of tetrahedrally coordinated monomeric NiWO species, which are mostly stabilized on the alumina containing support [33]. NiW-AT-ETS/Al2 O3 shows a relatively lower reduction temperature (915 ◦ C) than NiW-ETSorigin/Al2 O3 (930 ◦ C) in this band. Probably, surface-Ti-rich-ETS-10 may weaken the interaction between W species and surfaceTi-rich-ETS-10/Al2 O3 composite support due to the coordinately unsaturated sites at Ti-rich-ETS-10 surface, which results in easier
Fig. 3. XPS W 4f spectra of oxidized (a) and sulfidized (b) catalysts.
reduction of WO3 species by hydrogen. It was reported that W-TiO2 support formed a relatively weak interaction for WNi/TiO2 catalyst due to the presence of coordinately unsaturated sites at the TiO2 surface compared to that of WNi/Al2 O3 catalyst [34,35]. XPS W 4f spectra of oxidized and sulfidized catalysts respectively were showed in Fig. 3. There were two signals of W 4f5/2 and W 4f7/2 electrons at BE of 38.1 and 36.0 eV respectively (Fig. 3a) for oxidized catalysts. These signals are assigned to W6+ species, most like WO3 [36,37]. After sulfurization (Fig. 3b), a second doublet peak appeared at 33.7 and 31.6 eV, which was typical for W4+ as in the WS2 phase [38,39]. The XPS W 4f spectra of sulfided catalysts were simply divided into two regions. The first one was attributed to WO3 phase from 40.5 eV ranges to 35.3 eV and the second one was attributed to WS2 phase from 35.3 eV ranges to 29.0 eV. The sulfidation degree of oxidic W species was defined as the ratio of W4+ (WS2 ) to the sum of W4+ (WS2 ) and W6+ (WO3 ) [25], where the content of WS2 and WO3 were obtained from integration area on the XPS W 4f spectra of the catalysts. After the calculation, the sulfidation degree of NiW-ETS/Al2 O3 and NiW-ATS/Al2 O3 are 70% and 69% respectively. The XPS Ni 2p spectra of the oxidized catalysts showed (Fig. 4a) two sharp peaks of Ni 2p3/2 and Ni 2p1/2 at 856.6 and 874.1 eV, assigned to the spin-splitting of NiO [34] and two broad peaks, assigned to the envelopes of the corresponding shakeup satellite lines [40–42]. The peaks (Fig. 4b) of Ni 2p3 at 853.5 eV and Ni 2p1 at 871.0 eV may be associated to NiS [36].
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Fig. 6. HDS activities of two catalysts for DBT and 4,6-DMDBT feeds (reaction pressure, 4.0 MPa; temperature, 260 ◦ C; feed flow rate, 6.6 mL/h; H2 /oil ratio, 370 (v/v)).
type II NiWS phase on the catalyst. Higher WS2 slab layers can benefit for increase of hydrogenation activity [43]. Shorter average slab length of NiW-AT-ETS/Al2 O3 may suggest higher WS2 dispersion according to the previous study by Payen et al [44]. 3.2. HDS assessment
Fig. 4. XPS Ni 2p spectra of oxidized (a) and sulfidized (b) catalysts.
No presence of NiO phase signals (Fig. 4b) confirmed that the Ni species are fully sulfurized. The representative TEM images of two sulfided catalysts displayed (Fig. 5) thread-like layers WS2 slabs. The average layer number of per slab and average slab length were calculated from the measurement of about 100 WS2 crystallites. For NiWETS-origin/Al2 O3 catalyst, the average layer number was 2.3, the average layer spacing of per slab was 0.626 nm, and the average slab length was 3.74 nm. For NiW-AT-ETS/Al2 O3 catalyst, the average layer number, average layer spacing, and average length of the WS2 slabs were 3.3, 0.627 nm, and 2.66 nm, respectively. Both of two catalysts had almost equal average WS2 slabs layer spacing. The catalyst NiW-AT-ETS/Al2 O3 had higher WS2 slab layers and shorter slab length than NiW-ETS-origin/Al2 O3 . Considering the H2 -TPR temperature towards two catalysts, the surface Ti rich of ETS-10 in NiW-AT-ETS/Al2 O3 can relax the strong interaction between NiWS phase and Al2 O3 support and form higher stack of
The HDS results of catalysts NiW-ETS-origin/Al2 O3 and NiW-ATETS/Al2 O3 with DBT and 4,6-DMDBT feed at 260 ◦ C are shown in Fig. 6. HDS ratios of catalysts NiW-ETS-origin/Al2 O3 and NiW-ATETS/Al2 O3 for DBT are 95.2% and 96.5% respectively, while those for high steric hindered 4,6-DMDBT are 82.3% and 86.9%, respectively. NiW-AT-ETS/Al2 O3 showed the more advantage of HDS for 4,6-DMDBT than NiW-ETS-origin/Al2 O3 . NiW-ETS-origin/Al2 O3 and NiW-AT-ETS/Al2 O3 showed similar pore structure and sulfurization ability identified by BET and XPS analyses, respectively. The promoted HDS ratio of NiW-AT-ETS/Al2 O3 may be due to higher WS2 slab layers. The easy accessibility of active sites on the surface of NiW-AT-ETS/Al2 O3 catalyst can benefit the increase of 4,6-DMDBT HDS as a result of the higher dispersion compared to NiW-ETS-origin/Al2 O3 . 4. Conclusion A novel NiW-AT-ETS/Al2 O3 catalyst was developed by using surface Ti rich ETS-10, which was obtained by alkaline solution treatment of ETS-10, as the support component. NiW-AT-ETS/Al2 O3 was characterized by H2 -TPR, XPS and TEM, and assessed for HDS of DBT and 4,6-DMDBT using NiW-ETS-origin/Al2 O3 as reference. The enrichment of surface Ti species weakened the strong interaction between active phase WS2 and Al2 O3 support illustrated by H2 TPR. NiW-AT-ETS/Al2 O3 had higher WS2 stacked layers and shorter slab length. NiW-AT-ETS/Al2 O3 exhibited higher HDS ratios than
Fig. 5. TEM images of sulfidized catalysts NiW-ETS-origin/Al2 O3 (a) and NiW-AT-ETS/Al2 O3 (b).
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Please cite this article in press as: S. Ren, et al., A novel catalyst of Ni,W-surface-Ti-rich-ETS-10/Al2 O3 : Its role and potential of HDS performance for steric hindered sulfur compound 4,6-DMDBT, Catal. Today (2015), http://dx.doi.org/10.1016/j.cattod.2015.06.023