Nano-IV(2005) Kanda


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Related Works in HDS Catalyst Development, Manuscript for Nano Materials Conference IV,Ottawa(2005)

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Nano-IV(2005) Kanda

  1. 1. Catalytic performance of noble metals supported on Al2O3-modifiedMCM-41 for thiophene hydrodesulfurizationY. Kanda, Y. Uemichi, T. Kobayashi, L. Andalaluna and M. SugiokaDepartment of Applied Chemistry, Muroran Institute of Technology,27-1 Mizumoto-cho, Muroran 050-8585, Japan Pt/Al2O3-MCM-41 catalyst showed high and stable activity for hydrodesulfurization ofthiophene at 350oC and this activity was higher than that of commercial CoMo/Al2O3hydrodesulfurization catalyst. Pt/Al2O3-MCM-41 catalyst has high hydrogenating ability inthe hydrodesulfurization of thiophene. The Broensted acid sites of Al2O3-MCM-41 and thespillover hydrogen formed on Pt particle in Pt/Al2O3-MCM-41 catalyst play an important rolefor the hydrodesulfurization of thiophene.1. INTRODUCTION Hydrodesulfurization (HDS) process of petroleum feedstocks is one of the importantprocesses in the petroleum industry to produce clean fuels. However, recently, thedevelopment of highly active HDS catalysts, which exhibit higher activity than commercialCoMo/Al2O3 HDS catalyst, have been claimed in the petroleum industry to produce lowersulfur content fuels. It has been accepted that metal zeolite catalysts have high possibility asnew HDS catalyst for petroleum [1, 2]. The authors have also investigated the development ofhighly active HDS catalysts based on zeolites [3-5]. Recently, mesoporous silicate materials such as FSM-16, MCM-41 and SBA-15, whichhave larger pore diameter than zeolites, have been attracting wide attention as new materialsfor catalysts and catalyst supports. Some attempts have been done to develop new HDScatalyst based on mesoporous silicates [6,7]. In the previous paper [8-11], e have reported that noble metals (NM), especially platinum,supported on FSM-16, MCM-41 and SBA-15 showed high and stable activity in the HDS ofthiophene and NM supported on mesoporous silicates have high possibility for usage of newHDS catalysts for petroleum feedstocks. In the present work, we examined the catalytic performance of NM supported onAl2O3-modified MCM-41 (Al2O3-MCM-41) for the HDS of thiophene in order to developmuch more highly active mesoporous silicates-based HDS catalysts for petroleum feedstocks.2. EXPERIMENTAL Al2O3-MCM-41 were prepared by an impregnation method using aluminum nitrate aqueous
  2. 2. solution. After impregnation of aluminum nitrate, the samples were dried at 120oC and werecalcined at 500oC for 4 hrs. The amounts of Al2O3 loading were in the range of 0.1-43 wt%.NM/Al2O3-MCM-41 catalysts were prepared by an impregnation method using noble metalchloride aqueous solution; the amount of metal loading was 5 wt%. All catalysts were dried at120oC and then calcined at 500oC for 4 hrs in air. All catalysts were pretreated by heliumstream at 500oC for 1 hr and then reduced by H2 at 450oC for 1 hr prior to the reaction.Scheme 1 indicates the preparation of Al2O3-MCM-41 and NM/Al2O3-MCM-41 catalysts. HDS of thiophene was carried out at 350oC under 1 atm by the conventional fixed bed flowreactor. Thiophene was introduced into the reactor by passing hydrogen (30ml/min) through athiophene trap cooled at 0oC. The reaction products were analyzed by gaschromatograph (FID). The acidity of Al2O3-MCM-41 was evaluated by 2-Propanol (2-PA) dehydration (200oC)and cumene cracking (400oC) using pulse reactor with helium carrier gas. NM dispersion ofNM on Al2O3-MCM-41 was measured by XRD analysis, H2 adsorption method at 25oC andTEM technique. FT-IR spectra of pyridine and thiophene adsorbed Al2O3-MCM-41 wereobserved by using Jasco FT-IR spectrometer. ¡ §¥£ &©   ( ¨ )£ 0 ¦ £¢ # (¨ § ¨ )£ ¨ §0 ¦ £¢ )£0)%¡¥¤ § § §0)%¡¥¤ § )£ § §¨ § §¨ )£ 0 ) © )£ 0 ) © §0©¦ ¡¥ ) )£ ¡¢¥¡ ¤¢ % $ § ¨ § ©¨ ¢ ¢ ¦£¥£¤£¢¡   §§     ¡ ! £ ¨ §§ )£   (     #     ¨     ¨ Scheme 1. Preparation of Al2O3-MCM-41 and NM/Al2O3-MCM-41.3. RESULTS AND DISSCUSSION3. 1. Catalytic activities of NM supported on Al2O3-MCM-41 catalyst The catalytic activities of various NM (Pt, Pd, Rh, Ru) supported on Al2O3-MCM-41(4wt%Al2O3 loading) for the HDS of thiophene were examined at 350oC. It was found thatthe catalytic activities of NM/Al2O3-MCM-41 were remarkably varied with the kind of NMas shown in Figure 1. The order of the activities of these catalysts after 2 hrs reaction was asfollows: Pt Pd Rh Ru. The activity of Pt/Al2O3-MCM-41 was the highest amongNM/Al2O3-MCM-41 catalysts and this activity was higher than that of commercialCoMo/Al2O3 HDS catalyst. We also examined the catalytic activities of Pt supported on MCM-41 modified by variousamount of Al2O3 loading for the HDS of thiophene. It was revealed that there exists theoptimal amount of Al2O3 loading between the activity of Pt/Al2O3-MCM-41 and Al2O3loading and the optimal Al2O3 loading is 4 wt% as shown in Figure 2. Figure 3 shows thesummary of the activities of NM/MCM-41 and NM/4wt%Al2O3-MCM-41 catalysts for HDSof thiophene at 350oC. It can be seen that the activities of NM/Al2O3-MCM-41 catalysts were
  3. 3. higher than those of NM/MCM-41 and the Pt catalysts supported on Al2O3-MCM-41 showedhigh activities. 2 1 2 V# N 1 / % / 2 1 2 F# N 1 / % / %QPXGTUKQP % Q/ Q# N 12 1 2 1 4 J# N 1 / % / 2 1 4 W# N 1 / % / 6K G QP UVTGCO JQWT O H2/thiophene = 30 mol/mol, W/F = 37.9 g hr/molFigure 1. Catalytic activities of NM/Al2O3-MCM-41 for thiophene hydrodesulfurization at350{C. 338 w td e „ e ƒ w td e „ ed™ ˜– •“t — 37 h ‚ g 36 a ` f e €x d c 35 b q a ` Q PH A C pC i I Y yx 34 f… e… „ ™ ˜– • — 3 3 38 34 39 35 3@ r ru rt rs rv rrw X W V ECF SSR Q PH A GC F EDC B A F U TT ” “ †… ‰ˆ‡†… „ ’ ‘ I Figure 2. The effect of Al2O3-modifi- Figure 3. Activities of NM/MCM-41 cation of MCM-41 on HDS activities of and NM/Al2O3-MCM-41 catalysts for Pt/Al2O3-MCM-41 catalysts. HDS of thiophene at 350{C. The reaction products in the HDS of thiophene over Pt/4wt%Al2O3-MCM-41 were mainlyC4 hydrocarbons (butane 98%, butenes 2%) and trace amount of C1-C3 hydrocarbons,
  4. 4. whereas those on Pt/MCM-41 were C4 hydrocarbons (butane 87%, butenes 13%). Theseresults indicate that Pt/Al2O3-MCM-41 catalyst has higher hydrogenating ability forunsaturated C4 hydrocarbons formed in the HDS of thiophene than Pt/MCM-41. Thissuggests that the dispersion of Pt on Al2O3-MCM-41 is higher than that on MCM-41.Table 1 Products distribution over reduced NM supported on MCM-41 and4wt%Al2O3-MCM-41 catalysts in HDS of thiophene at 350{C. Catalyst HDS (%) C3a) (%) C4b) (%) C4’c) (%) 1,3-C4’’d) (%) Pt/MCM-41 70.4 0.3 86.6 13.1 0.0 Pt/Al2O3-MCM-41 96.1 0.3 97.6 2.1 0.0 Pd/MCM-41 51.5 2.6 14.0 83.4 0.0 Pd/Al2O3-MCM-41 68.4 0.6 16.9 82.5 0.0 Rh/MCM-41 23.7 2.0 10.2 87.8 0.0 Rh/Al2O3-MCM-41 25.1 2.7 11.5 85.8 0.0 Ru/MCM-41 0.8 14.6 0.0 69.0 16.4 Ru/Al2O3-MCM-41 1.1 15.3 0.0 80.4 4.3a) C1-C3 hydrocarbons, b) butanes, c) butenes, d) 1,3-butadiene3. 2. Catalytic properties of Pt/Al2O3-MCM-41 We performed various characterization of Pt/4wt%Al2O3-MCM-41 in order to get definiteknowledge about the cause of high activity of Pt/4wt%Al2O3-MCM-41 for the HDS ofthiophene.(a) NM/MCM-41 (b) NM/4wt%Al2O3-MCM-41 †… †… §¦ §¦ †… … §¦ ¦ † †… †… †… †… § §¦ §¦ §¦ §¦ €‚ ‡… ¡¢£ ¨¦ € ¡  ~ rƒ rƒ rƒ Ÿ “¤ “¤ “¤ } rƒ rƒ ž “¤ “¤ y š {| œ x „ƒ ™ z › xy „ƒ „ƒ ™š ¥¤ w ˜ „ƒ „ƒ ¥¤ ¥¤ ¥¤ ¥¤ hg hi hj hk hl hm hn ho ‰ˆ ‰Š ‰‹ ‰Œ ‰ ‰Ž ‰ ‰ vssutsrq pi —””–•”“’ ‘ŠFigure 4. XRD patterns of noble metals supported on (a) MCM-41 and (b) 4wt%Al2O3-MCM-41 after H2 reduction at 450{C. Figure 4 shows the XRD analysis of NM/MCM-41 and NM/4wt%Al2O3-MCM-41catalysts after reduction at 450{C. It was found that the peak heights of Pd, Rh and Ru onMCM-41 and Al2O3-MCM-41 were not changed but that of Pt was significant decreased onAl2O3-MCM-41 compared to MCM-41. This indicates that the dispersion of Pt on
  5. 5. Al2O3-MCM-41 was higher than that on MCM-41. Table 2 shows the dispersion of NM and particle size on MCM-41 and 4wt%Al2O3-MCM-41 measured by H2 adsorption method. It was revealed that Pt dispersion (0.80) onPt/Al2O3-MCM-41 was the highest and particle size (1.18 nm) is the lowest amongNM/MCM-41 and NM/4wt%Al2O3-MCM-41.Table 2 Dispersion and particle size of NM on MCM-41 andAl2O3-MCM-41 measured by H2 adsorption. NM dispersion Particle size of NM Catalyst (H/NM) (nm) Pt/MCM-41 0.47 2.02 Pt/Al2O3-MCM-41 0.80 1.18 Pd/MCM-41 0.39 2.39 Pd/Al2O3-MCM-41 0.40 2.33 Rh/MCM-41 0.59 1.55 Rh/Al2O3-MCM-41 0.69 1.33 Ru/MCM-41 0.13 8.97 Ru/Al2O3-MCM-41 0.16 7.26 (a) Pt/MCM-41 (b) Pt/4wt%Al2O3-MCM-41Figure 5. TEM images of (a) Pt/MCM-41 and (b) Pt/4wt%Al2O3-MCM-41 catalysts. Figure 5 shows the TEM images of Pt/MCM-41 and Pt/Al2O3-MCM-41 catalysts. Large Ptparticles were observed on Pt/MCM-41 catalyst in image (a) in Figure 5. In thePt/Al2O3-MCM-41 catalyst, we didn’t observe any large Pt particle but only very fine Ptparticles in image (b) in Figure 5. These results indicate that Pt particles inPt/Al2O3-MCM-41 are loaded on Al2O3-MCM-41 with high dispersion and this high
  6. 6. dispersion of Pt particle on Al2O3-MCM-41 is one of important factor for high activity in theHDS of thiophene. That is to say, it is assumed that highly dispersed Pt particle onAl2O3-MCM-41 acts as active site for the activation of hydrogen in the HDS of thiophene. We have also evaluated the acidic properties of MCM-41 and 4wt%Al2O3-MCM-41 by thereaction of 2-propanol (2-PA) dehydration (200oC) and cumene cracking (400oC) using pulsereactor. It was revealed that MCM-41 showed very low activity for both reactions but4wt%Al2O3-MCM-41 showed remarkable high activity for these reactions. These resultsindicate that 4wt%Al2O3-MCM-41 has high acidity and there exists the Broensted acid siteson Al2O3-MCM-41. Table 3 shows the catalytic properties of Pt/Al2O3-MCM-41 with other supported Ptcatalysts such as Pt/MCM-41, Pt/Al2O3, Pt/SiO2 Al2O3 and Pt/SiO2. It can be seen in Table 3that Pt/Al2O3-MCM-41 catalyst shows the highest HDS activity and this catalyst has high Ptdispersion and moderate Broensted acidity. That is, Pt/Al2O3-MCM-41 catalyst hasbifunctional properties with high hydrogenating ability and moderate Broensted acidity. Bythis reason, Pt/Al2O3-MCM-41 catalyst shows high and stable activities for HDS ofthiophene.Table 3 Catalytic properties of various supported Pt catalysts. HDS Dispersion of Dehydration Cracking of Catalyst a) conversion (%) Pt (H/Pt) of 2-PA (%)b) cumene (%)b) Pt/Al2O3-MCM-41 96.1 0.80 66.4 9.4 Pt/MCM-41 70.4 0.47 13.0 0.7 Pt/Al2O3 40.3 0.82 62.4 0.0 Pt/SiO2 Al2O3 38.0 0.12 98.4 37.7 Pt/SiO2 30.1 0.47 0.0 0.0a) Supported Pt catalyst, b) Activity of supports (0.03 g).3. 4. Mechanism of HDS of thiophene on Pt/Al2O3-MCM-41 catalyst It was revealed that Pt/Al2O3-MCM-41 catalyst showed the highest activity amongNM/Al2O3-MCM-41 catalysts for the HDS of thiophene. We studied the reaction mechanismof HDS of thiophene over Pt/Al2O3-MCM-41. We supposed that the Broensted acid site on Al2O3-MCM-41 acts as active site for theactivation of thiophene, whereas Pt particle acts as active site for the activation of hydrogenin the HDS of thiophene. We confirmed the existence of the Broensted acid sites at 1547 cm-1on 4wt%Al2O3-MCM-41 by the observation of FT-IR spectra of pyridine adsorbed onAl2O3-MCM-41 as shown in spectra (b) in Figure 6. It can be assumed that the surface silanolgroup on Al2O3-MCM-41 acts as Broensted acid site and the Broensted acid site acts as activesite for the activation of thiophene in the HDS of thiophene. Furthermore, we observed the FT-IR spectra of thiophene adsorbed on Al2O3-MCM-41 inorder to clarify the interaction of silanol group with thiophene molecule. In the backgroundspectra of Al2O3-MCM-41 evacuated at 500oC for 2 hrs, the silanol group (Si-OH) wasobserved at 3745 cm-1 as shown in spectra (a) in Figure 7.
  7. 7. ±¯ ° ±´³² ,736,+2-/ ,736,+2-/ « ­® µ ³´² E µ ³³² D « ­¬ C ª© 9 CXGPWO DGT EO ª© 9 CXGPWO DGT EOFigure 6. FT-IR spectra of pyridine (a) after evacuation at 500{C, (b) thio-adsorbed on (a) MCM-41 and (b) 4wt% phene 15 Torr coexistence and (c) afterAl2O3-MCM-41. Pyridine was adsorbed at evacuation at 100{C150oC followed by evacuation at 150oC for30 min. Figure 7. FT-IR spectra of thiophene adsorbed on 4wt%Al2O3- MCM-41. After introduction of 15 Torr of thiophene onto the Al2O3-MCM-41, the absorption band ofsilanol group at 3745 cm-1 decreased considerably and large and broad peak at 3600 cm-1,which is assigned to silanol group interacting with thiophene molecule, appeared as shown inspectra (b). However, the decreased absorbance of silanol group was almost regenerated bythe evacuation at 100oC as shown spectra (c). These results indicate that the thiophenemolecule interacts with surface silanol group, i.e. Broensted acid site, on Al2O3-MCM-41, butthe interaction between silanol group and thiophene is not so strong. By these results, it wasconfirmed that thiophene is adsorbed and activated on silanol group on Al2O3-MCM-41 in theHDS of thiophene over Pt/4wt%Al2O3-MCM-41 catalyst. Furthermore, we tried to confirm the existence of spillover hydrogen in the HDS ofthiophene over Pt/Al2O3-MCM-41. The catalytic activity of Pt/SiO2 (quartz) (A) mixedmechanically with Al2O3-MCM-41 (B) was examined. It was found that the activity of mixedcatalyst obtained experimentally was higher than that of calculated one (A+B). This suggeststhat there exists spillover hydrogen on Pt/Al2O3-MCM-41 in the HDS of thiophene. On the basis of these results, we propose a possible mechanism for the HDS of thiopheneover Pt/Al2O3-MCM-41 catalyst as shown in Scheme 2. In the proposed mechanism,thiophene is activated on the silanol group of Al2O3-MCM-41 and hydrogen is activated on Ptto form spillover hydrogen. The spillover hydrogen formed on Pt particle attacks theactivated thiophene on the silanol group of Al2O3-MCM-41.
  8. 8. Ä » · Ó ÏÇÒÊÑÐÇÊÍÌ · »· »· S ÊÉÈǽ Å Ä ½Æ ÍɺÑȺ Ð ¼ Æ ÏÉÎÇÊÍÌË É ÏÉ ËÅÇ Ë Æº S · · · · ÍÉºÔ ÏÉÇÊ × ¸ · ɺ Ô Í ÐÑ Æ Æ ¶ · º¹ º¹ · · · ÍÉÔÊÉÅÔ Í Ì ËÎ · Æ ½ Æ » à ¿ À Á À¿¾ ¶½ ¼ ɺ Ô Í Ð ¼ Æ Æ ÖÕÏºÑ Å Æ ½Scheme 2. The possible mechanism of thiophene hydrodesulfurization over Pt/Al2O3-MCM-41 catalyst.4. CONCLUSION It was found that the Pt/Al2O3-MCM-41 catalyst showed high and stable activity for theHDS of thiophene and both platinum particle and silanol group on Pt/Al2O3-MCM-41catalyst act as active sites for the HDS of thiophene. It can be concluded thatPt/Al2O3-MCM-41 might be a promising new HDS catalyst for organic sulfur compounds inthe petroleum feedstocks.ACKNOWLEDGEMENTS This work was partially supported by a Grant-in-Aid for Scientific Research, Japan.REFERENCES1. M. Laniecki and W. Zmierczak, Zeolites, 11(1991)18.2. Y. Okamoto, Catal. Today, 39(1997)45.3. M. Sugioka, Erdol Kohle, Erdgas, Petrochemie, 48(1995)128.4. M. Sugioka, F. Sado, T. Kurosaka and X. Wang, Catal. Today, 45(1998)327.5. T. Kurosaka, M. Sugioka and H. Matsuhashi, Bull. Chem. Soc. Jpn., 74(2001)7476. K. M. Reddy, B. Wei and C. Song, Catal. Today, 43(1998)261.7. A. Wang, Y. Wang, T. Kabe, Y. Chen, A. Ishihara and W. Qian, J. Catal., 199(2001)19.8. M. Sugioka, L. Andalaluna, S. Morishita and T. Kurosaka, Catal. Today, 39(1997)61.9. M. Sugioka, S. Morishita, T. Kurosaka, A. Seino, M. Nakagawa and S. Namba, Stud. Surf. Sci. Catal., 125 (1999)531.10. M. Sugioka, T. Aizawa, Y. Kanda, T. Kurosaka, Y. Uemichi and S. Namba, Stud. Surf. Sci. Catal., 142 (2002)739.11. M. Sugioka and T. Kurosaka, J. Japan Petrol. Inst., 45(2002)342.