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Al2O3-TiO2/Al2O3-TiO2-SiO2 Composite-Supported Bimetallic Pt-Pd Catalysts for the Hydrodearomatization and Hydrodesulfurization of Diesel Fuel Guofu Wan,† Aijun Duan,† Zhen Zhao,*,† Guiyuan Jiang,† Dengqian Zhang,† Ruili Li,† Tao Dou,† and Keng H. Chung‡ State Key Laboratory of HeaVy Oil Processing, China UniVersity of Petroleum, Beijing 102249, People’s Republic of China, and Well Resources, Inc., 3919-149A Street, Edmonton, Alberta T6R 1J8, Canada ReceiVed August 22, 2008. ReVised Manuscript ReceiVed October 8, 2008
Al2O3-TiO2 and Al2O3-TiO2-SiO2 (denoted as AT and ATS) composite oxides were synthesized by the sol-gel method, which were used as supports for bimetallic Pt-Pd catalysts. The typical physicochemical properties of the catalyst samples were characterized by means of N2 adsorption, UV-vis diffuse reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The diesel hydrodearomatization (HDA) and hydrodesulfurization (HDS) activities of the catalysts were evaluated using a microreactor system. In comparison to the Pt-Pd/AT catalysts, all of the Pt-Pd/ATS catalysts showed much higher HDA activities. A 100 h test showed that the Pt-Pd/ATS catalyst had a high equilibrium HDA activity, with 432 ppm sulfur diesel. The enhanced HDA activity and sulfur tolerance of Pt-Pd/ATS were likely attributed to the incorporations of Ti and Si into Al2O3, which optimized the interaction between the catalyst support and active metals.
1. Introduction Stringent environmental legislation impels the rigorous specifications of ultra-clean fuels. New regulations on the composition of diesel fuels in EC and U.S.A. require a reduction of the aromatic contents.1-4 The total aromatic contents of clean diesel in the International Specification-IV is less than 15 vol %, and the content of polycyclic aromatics is lower than 2 m %, which leads to the development of new processes for aromatic saturation and the introduction of many new catalysts. Both supported transitional metal sulfide and supported noble metal catalysts for hydrodearomatization have been used in the industrial units. It is well-established that platinum catalysts exhibit an excellent hydrogenation promotion effect under moderate pressures.5 However, several restrictions, including the expensive price and the lower sulfur resistibility, limit the use of Pt catalysts.6 To develop sulfur-tolerant noble metal catalysts, many approaches have been introduced into the catalyst preparation.7-11 * To whom correspondence should be addressed. Fax: (+8610) 69724721. E-mail:
[email protected]. † China University of Petroleum. ‡ Well Resources, Inc. (1) Song, C. Catal. Today 2003, 86, 211–263. (2) Sun, C.; Peltre, M. J.; Briend, M.; Blanchard, J.; Fajerwerg, K.; Krafft, J. M.; Breysse, M.; Cattenot, M.; Lacroix, M. Appl. Catal., A 2003, 245, 245–255. (3) Cooper, B. H.; Donnis Bjorn, B. L. Appl. Catal., A 1996, 137, 203– 223. (4) Rojas, S.; Terreros, P.; Pen˜a, M. A.; Ojeda, M.; Fierro, J. L. G.; Otero, A.; Carrillo, F. J. Mol. Catal. A: Chem. 2003, 206, 299–311. (5) Cooper, B. H.; Stanislaus, A.; Hannerup, P. N. Hydrocarbon Process. 1993, 72, 86–87. (6) Vradmana, L.; Landaub, M. V.; Herskowitz, M. Fuel. 2003, 82, 633– 639. (7) Chiou, J. F.; Huang, Y. L.; Lin, T. B.; Chang, J. R. Ind. Eng. Chem. Res. 1995, 34, 4284–4289. (8) Chiou, J. F.; Huang, Y. L.; Lin, T. B.; Chang, J. R. Ind. Eng. Chem. Res. 1995, 34, 4277–4283.
One of the effective methods is the addition of a second noble metal into the catalyst to obtain the bimetallic catalysts, typically the Pd-Pt bimetallic catalysts. Fujikawa and his cooperators12,13 studied the kinetics and long-term stability of the aromatic hydrogenation of diesel fuel over a SiO2-Al2O3-supported bimetallic Pt-Pd catalyst. The catalytic activities of Pt-Pd/SiO2-Al2O3 catalysts were tested using a mixed oil of hydrotreated light cycle oil (LCO) and straight-run light gas oil (SRLGO) as feedstocks. The test results showed that Pt (0.5 m %)-Pd (1.0 m %)/SiO2-Al2O3 catalyst exhibited the highest catalytic activity.13 In addition, the stability of this catalyst was kept stable in the long term test. Qian et al.14 studied the hydrodesulfurization (HDS) reactions of dibenzothiophene (DBT) and hydrogenation (HYD) of phenanthrene (PHE) over a series of alumina-supported noble metal catalysts. They found that the dual noble metal catalyst showed the better HYD activities compared to a conventional Co-Mo catalyst. Over the 10% Pd/Al2O3 and 2% Pt-10% Pd/Al2O3 catalysts, Qian and co-workers15 studied the effects of the presence of sulfur with the 35S radioisotope-labeled DBT feedstock. The results showed that the sulfided noble metal species on the alumina-supported platinum and palladium catalysts were presented in the form of PdSx (or PtSx) (x ) 0-0.25) in (9) Jan, C. A.; Lin, T. B.; Chang, J. R. Ind. Eng. Chem. Res. 1996, 35, 3893–3898. (10) Vı´t, Z.; Gulkova´, D.; Kalua, L.; Zdrail, M. J. Catal. 2005, 232, 447–455. (11) Landau, M. V.; Vradman, L.; Herskowitz, M.; Koltypin, Y.; Gedanken, A. J. Catal. 2001, 201, 22–36. (12) Fujikawa, T.; Idei, K.; Ohki, K.; Mizuguchi, H.; Usui, K. Appl. Catal., A 2001, 205, 71–77. (13) Fujikawa, T.; Idei, K.; Ebihara, T.; Mizuguchi, H.; Usui, K. Appl. Catal., A 2000, 192, 253–261. (14) Qian, W.; Yoda, Y.; Hirai, Y.; Ishihara, A.; Kabe, T. Appl. Catal., A 1999, 184, 81–88. (15) Qian, W.; Otani, K.; Li, L.; Ishihara, A.; Kabe, T. J. Catal. 2004, 221, 294–301.
10.1021/ef8006905 CCC: $40.75 2009 American Chemical Society Published on Web 11/19/2008
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the HDS reactions and that the existent states of noble metal sulfides on the catalysts changed with the partial pressure of H2S in the reaction atmosphere and approached the steady states with an increasing partial pressure of H2S to 5.2 kPa using a 35S radioisotope tracer method. Bihan and his cooperators adopted Yb-modifed USY zeolite to prepare the bimetallic Pt-Pd catalysts.16 Catalytic performances of the series of catalysts prepared under different conditions in the HDS of 4,6-DMDBT and hydrodearomatization (HDA) of tetralin showed that the low calcination temperature was favored for both deep HDS and deep HDA reactions, whereas the high calcination temperature depressed HDA reactions. Resende et al.17 used polymeric titanium oxides grafted on γ-Al2O3 as supports to prepare 1 m % Pt catalysts. The TiO2-Al2O3 supports were prepared by impregnation of titanium isopropoxide. The analysis results of TiO2-Al2O3 supports indicated that anatase crystallites and amorphous titanium oxides were coated on the alumina surface. The relative supported platinum catalysts indicated that the incorporation of titanium into alumina promoted the higher dispersions of platinum in the titania-modified catalysts compared to the alumina-supported catalysts, especially in preference to the high dispersion of platinum over the amorphous titanium oxide. Ishihara et al.18 systematically monitored the HDS activity of DBT and groups of substituted DBTs present in a SRLGO over a variety of alumina-supported noble metal catalysts (Ru, Rh, Ru-Rh, Pt, Pd, and Pt-Pd). The Pd-based catalysts exhibited excellent HDS performances compared to that of the conventional CoMo catalysts, especially for resolving the refractory compounds, i.e., 4,6-DMDBT. It could be attributed to the intensified HYD properties from the synergetic effect between the bimetallic Pt-Pd system. In this paper, a series of Al2O3-TiO2 and Al2O3-TiO2-SiO2 composite oxide supports were prepared by the sol-gel method using alumina as an aluminum source, and the catalytic performances of these composite-oxide-supported Pt-Pd catalysts for HDS and HDA of diesel oil were evaluated with the diesel feedstock to investigate the promoting effect of silicon/ titanium modification on HDS and HDA performances of catalysts. The exploration of the sol-gel method and the optimization of preparation conditions in this work were expected to obtain the composite support with high specific surface areas and suitable pore diameter for deep HDS and HDA of diesel oil. 2. Experimental Section 2.1. Feed Properties. A commercial diesel oil with 432 ppm wt sulfur was obtained from the PetroChina Fushun refinery. The typical physicochemical properties of the diesel feedstock are described in Table 1. 2.2. Catalyst Preparation. Al2O3-TiO2 binary oxides were prepared by the sol-gel method. Titanium sol was prepared from the tetra-n-butyl-titanate, ethanol, nitric acid, and deionized distilled water in the molar ratio of 1:15:0.3:3, respectively. The alumina was dispersed with certain proportional ethanol and nitric acid at 303 K under gentle stirring for 1 h until an alumina slurry was formed. Titanium sol was added dropwise into the alumina slurry and formed a gel under drastic stirring condition. The gel was dried in air at 380 K for 10 h and then calcined at 773 K for 6 h. The solids obtained were denoted as AT-x (x is the TiO2 weight percent in AT). (16) Bihan, L. L.; Yoshimura, Y. Fuel 2002, 81, 491–494. (17) Resende, N. S.; Eon, J. G.; Schmal, M. J. Catal. 1999, 183, 6–13. (18) Ishihara, A.; Dumeignil, F.; Lee, J.; Mitsuhashi, K.; Qian, E. W.; Kabe, T. Appl. Catal., A 2005, 289, 163–173.
Wan et al. Table 1. Typical Physicochemical Properties of Feedstock properties density at 20 °C (g cm-3)a sulfur (ppm wt)b monoaromatics (m %)c diaromatics (m %)c triaromatics (m %)c total aromatics (m %) distillation (°C)d IBP 10% 30% 50% 70% 95% FBP
0.8391 432.0 13.9 5.2 0.8 19.9 154 218 258 290 316 365 450
a According to the ASTM D445 method. b Analyzed by the LC-4 coulometric sulfur analyzer. c According to the ASTM D2425 method. d According to the ASTM D2892 method.
In the case of Al2O3-TiO2-SiO2 composite oxides, titaniumsilicon sol was prepared from the tetra-n-butyl-titanate, ethylsilicate, ethanol, nitric acid, and deionized distilled water in various molar ratios of each component as (0-1):(0-1):15:0.3:3. The alumina was dispersed with certain proportional ethanol and nitric acid at 303 K under gentle stirring for several hours until an alumina slurry was formed. Then titanium-silicon sol was added dropwise into the alumina slurry to form the gel under drastic stirring. The gel was dried at 380 K for 10 h and then calcined at 773 K for 6 h. The solids obtained were denoted as ATS-1, ATS-2, and ATS-3. The weight ratios of Al2O3/TiO2/SiO2 were 5:3:2, 5:2.5:2.5, and 5:1:4 in the ATS composites, respectively. The pure TiO2 and SiO2 were also prepared according to the above-adopted method. The bimetallic catalysts were prepared by co-impregnations of either the AT or the ATS supports with PdCl2 and H2PtCl6 · 6H2O solutions using the incipient-wetness method. The samples were dried at 383 K for 12 h and calcined at 773 K for 4 h. The Pt and Pd loadings were kept constant at 0.5 and 1.0 m %, respectively. 2.3. Catalyst Characterization. The specific surface area and pore distribution of the catalyst samples were determined by the Brunauer-Emmett-Tellet (BET) method. X-ray powder diffraction (XRD) profiles were recorded in an XRD-6000 diffractometer using Cu KR radiation under 40 kV, 30 mA, and a scan range from 20° to 80°, at a rate of 4° min-1. The UV-vis diffuse reflectance spectroscopy (DRS) experiments were performed on a Hitachi U-4100 UV-vis spectrophotometer with the integration sphere diffuse reflectance attachment. The powder samples were loaded in a transparent quartz cell and were measured in the region of 200-800 nm under atmospheric conditions. The BaSO4 reflectance was used as the baseline for the corresponding sample measurement. 2.4. Catalytic Activity Measurement. Catalytic activity was evaluated in a high-pressure fixed-bed reactor with 2 g of catalyst (grain size of 0.3-0.5 mm). All of the catalysts were in situ reduced with H2 for 6 h at 573 K, 5 MPa total pressure, and 100 mL/min H2 flux. The HDA and HDS tests of diesel were carried out at 603 K, 5 MPa, 600 mL mL-1 (H2/oil), and 1.0 h-1 [liquid hourly space velocity (LHSV)]. Equilibrium catalytic activities of HDA and HDS were determined at steady state after 13 h on-stream. The sulfur contents of feedstock and products were analyzed using a LC-4 coulometric sulfur analyzer. The aromatic contents and distributions of the feed and products were determined according to the American Society for Testing and Materials (ASTM) D2425 method.
3. Results and Discussion Table 2 shows the textural properties of Al2O3, SiO2, TiO2, and supported Pt-Pd catalysts. The specific surface areas of the PtPd/AT-x catalysts slightly decreased with the increasing Ti loading. High surface area is desirable for the high and uniform dispersion of active components (platinum and palladium). The pore volumes and average pore diameters of
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Table 2. Textural Properties of Supported Pt-Pd Catalysts, Al2O3, SiO2, and TiO2 samples
SBET (m2 g-1)
pore volume (cm3 g-1)
average pore diameter (nm)
Al2O3 SiO2 TiO2 Pt-Pd/AT-10 Pt-Pd/AT-22 Pt-Pd/AT-26 Pt-Pd/ATS-1 Pt-Pd/ATS-2 Pt-Pd/ATS-3
290.0 480.1 5.5 252.2 236.7 225.2 237.6 258.2 317.9
0.75 0.33 0.01 0.73 0.67 0.63 0.42 0.37 0.34
12.1 3.1 3.9 11.7 11.4 11.2 6.5 6.0 4.3
catalysts showed a slight decrease with TiO2 loading. Resende et al.17 suggested that the incorporation of TiO2 into the Al2O3 system facilitated the higher dispersions of platinum in the titania-modified catalysts. For Pt-Pd/ATS catalysts, the specific surface areas of the catalysts increased with the decreasing TiO2/SiO2 weight ratio. The pore volumes and average pore diameters of the catalysts were reduced with the decreasing TiO2/SiO2 weight ratio. A possible explaination is that SiO2 has a higher specific surface area and TiO2 has a lower specific surface area and lower pore volume than alumina. Therefore, an appropriate TiO2/SiO2 weight ratio would be an important factor affecting the specific surface area and pore properties of the Pt-Pd/ATS catalysts. Figure 1 shows the XRD patterns of AT with various TiO2 contents. The special peak corresponding to the anatase structure, particularly the characteristics of anatase TiO2, was at the 2θ of 25.3°, and the peak intensities also enhanced with Ti contents, indicating that the clusters of accumulated TiO2 became larger. Figure 2 shows the XRD patterns of ATS at various TiO2/ SiO2 weight ratios. No obvious peaks of anatase TiO2 and SiO2 crystals were found in ATS supports, indicating that TiO2 and SiO2 in the Al2O3 matrix were highly dispersed. Figure 3 and 4 show the XRD patterns of Pt-Pd supported on Al2O3 and titania-modified alumina (AT-x) and ATS catalysts, respectively. The XRD spectra of Pt-Pd/TA-x catalysts showed the special peaks corresponding to the anatase structure at the 2θ of 25.3°. Nevertheless, the XRD spectra of the Pt-Pd/ATS catalysts showed only a wide peak at this position. The broad peaks, corresponding to the support Al2O3 at the 2θ of 46° and 67° were detected in the XRD pattern of the Pt-Pd/Al2O3 catalyst. The peak intensity decreased as the titanium content increased. For all Pt-Pd catalysts, no obvious peaks of platinum and palladium crystallites were found, because the sensitivity of
Figure 2. XRD patterns of ATS with different TiO2/SiO2 weight ratios.
Figure 3. XRD patterns of the Al2O3- or AT-x-supported Pt-Pd catalysts.
Figure 4. XRD patterns of the ATS-supported Pt-Pd catalysts.
Figure 1. XRD patterns of AT with different TiO2 contents.
XRD was very low when the contents of platinum and palladium crystallites were low. On the other hand, the noble metal particles may exist as nanoparticles less than 4 nm, which is beyond the detection limit of XRD.
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Figure 5. UV-vis DR spectra of AT composite oxides.
Wan et al.
Figure 7. DRS spectra of calcined AT-supported Pt-Pd catalysts.
Figure 8. DRS spectra of calcined ATS-supported Pt-Pd catalysts. Figure 6. UV-vis DR spectra of ATS supports.
The UV-vis DR spectroscopy was applied to determine the structures of AT and ATS composite oxides in the range from 200 to 800 nm as shown in Figures 5 and 6, respectively. No absorption arose from alumina was detected in Figure 5, because alumina was transparent in the detection range. In comparison to the pure γ-Al2O3, TiO2-Al2O3 binary oxides showed two broad absorption bands of 220-260 and 280-360 nm. These bands resulted from the charge-transfer transition of O2- to Ti4+. They corresponded to the excitation of electrons from the valence band (having the O 2p character) to the conduction band (having the Ti 3d character), which are the characteristics of anatase TiO2.19,20 These bands can be associated with the morphology of titania particles that have been formed on the surface of alumina, which are consistent with the XRD results. The DR spectrum of ATS was similar to that of AT. The ATS composite oxides showed two broad absorption bands of 220-255 and 260-340 nm, which are the characteristic bonds of anatase TiO2. Both the DRS and XRD results confirmed high dispersions of TiO2 in the Al2O3 matrix. Figures 7 and 8 show that the DRS spectra of calcined ATand ATS-supported Pt-Pd catalysts, respectively. The Pt-Pd/ Al2O3 had four bands centered at around 218, 280, 328, and 450 nm. The Pt-Pd catalysts after treatment at 773 K in air (19) Alejandre, A. G.; Ramı´rez, J.; Busca, G. Catal. Lett. 1998, 56, 29– 33. (20) Damyanova, S.; Spojakina, A.; Jiratova, K. Appl. Catal., A 1995, 125, 257–269.
resulted in the formation of new surface species with PtIV ([PtOxCly]s species17) and a superficial complex of Pd and chlorine (PdxOyClz21-23). According to the literature,22-24 the band at 218 nm is associated with the Pd-Cl charge transfer of PdCl2, and the band at 280 nm is assigned to Pd-O charge transfer and/or charge transfer from Cl- ligands to Pt in oxychloride surface complexes [PtOxCly]s.17 The observed shoulder at 328 nm is attributed to the d-d transition of Pt.17,25 In contrast, a broadband centered at 450 nm can be assigned to the d-d transitions of the bulk compound PtO217,25 and some PdO particles.26,27 The 200-350 nm UV-vis absorbance bands of Pt-Pd/AT and Pt-Pd/ATS were similar to those of AT and ATS supports. However, the bands centered at 450 nm of Pt-Pd/AT and Pt-Pd/ATS exhibited lower intensities than that of Pt-Pd/ Al2O3, indicating that the adsorption capacity of the noble metal on AT and ATS supports reduced. (21) Bozon-Verduraz, F.; Omar, A.; Escard, J.; Pontvianne, B. J. Catal. 1978, 53, 126–134. (22) Rakai, A.; Tessier, D.; Bozon-Verduraz, F. New J. Chem. 1992, 16, 869–875. (23) Tessier, D.; Rakai, A.; Bozon-Verduraz, F. J. Chem. Soc., Faraday Trans. 1992, 88, 741–749. (24) Pestryakov, A. N.; Lunin, V. V.; Fuentes, S.; Bogdanchikova, N.; Barrera, A. Chem. Phys. Lett. 2003, 367, 102–108. (25) Lietz, G.; Lieske, H.; Spindler, H.; Hanke, W.; Vo¨lter, J. J. Catal. 1983, 81, 17–25. (26) Zhang, Z.; Mestl, G.; Kno¨zinger, H. W.; Sachtler, M. H. Appl. Catal., A 1992, 89, 155–168. (27) Noronha, F. B.; Aranda, D. A. G.; Ordine, A. P.; Schmal, M. Catal. Today 2000, 57, 275–282.
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Table 3. HDA/HDS Results of Supported Pt-Pd Catalystsa sample
S (ppm wt)b
HDS (%)
monoaromatics (m %)c
diaromatics (m %)c
triaromatics (m %)c
total aromatics (m %)
HDA (%)
feed Pt-Pd/Al2O3 Pt-Pd/AT-10 Pt-Pd/AT-26 Pt-Pd/AT-32 Pt-Pd/ATS-1 Pt-Pd/ATS-2 Pt-Pd/ATS-3
432.0 11.8 32.2 3.5 16.6 10.0 7.7 0
97.3 92.5 99.2 96.1 97.7 98.2 100
13.9 14.2 12.3 9.2 13.2 1.1 1.0 3.3
5.2 2.0 2.3 1.0 2.0 0 0 0
0.8 0.1 0.1 0.0 0.1 0 0 0
19.9 16.3 14.7 10.2 15.3 1.1 1.0 3.3
18.1 26.1 48.7 23.1 94.5 95.0 83.4
a HDA and HDS reaction conditions: 603 K, 5 MPa, 600 mL mL-1 (H /oil), and 1.0 h-1 (LHSV). 2 analyzer. c According to the ASTM D2425 method.
Table 3 lists the HDS and HDA activities of Pt-Pd catalysts. Sulfur contents were reduced from 432 to below 33 ppm wt for all Pt-Pd catalysts. Total aromatic contents were reduced from 19.9 to less than 4 m % for Pt-Pd/ATS catalysts. For Pt-Pd/AT catalysts, the optimal TiO2 loading was 26 m %. Pt-Pd/AT-26 achieved the highest HDS and HDA activities (99.2 and 48.7% conversions, respectively), which were much higher than those of Pt-Pd/Al2O3 (97.3% HDS and 18.1% HDA conversions, respectively). For Pt-Pd/ATS catalysts, the optimal TiO2/SiO2 weight ratio was unity. Pt-Pd/ATS-2 showed the highest HDA activity (95.0% conversion) among all of the catalyst samples. All of the Pt-Pd/ATS catalysts had much higher HDA activities (from 83 to 95% conversion) than those of Pt-Pd/Al2O3 and Pt-Pd/AT catalysts. The Pt-Pd/ATS catalysts also had high HDS activities, and the sulfur contents of diesel products were reduced below 10 ppm wt (above 97% HDS conversion). From the data in Table 3, in comparison to the aromatic distributions in the feed and products, the effectiveness of HDA activities for all Pt-Pd catalysts were as followed: monocyclic aromatics < dicyclic aromatics < tricyclic aromatics. In the case of the Pt-Pd/Al2O3 catalyst, its low HDA activity was mainly due to low monoaromatics conversion. For all Pt-Pd/AT catalysts, tricyclic aromatics were reduced from 0.8 to below 0.1 m % and dicyclic aromatics were reduced from 5.2 to below 2.3 m %. Especially for the Pt-Pd/AT-26 catalyst, the product had 0.0 m % triaromatics and 1.0 m % diaromatics. In comparison to polycyclic aromatics, monocyclic aromatics are much more difficult to be removed. Even Pt-Pd/ AT-26, the best active Pt-Pd/AT catalyst, monoaromatics were reduced from 13.9 to 9.2 m %. All Pt-Pd/ATS catalysts showed excellent HDA activities. Di- and tricyclic aromatics were completely removed over all of the Pt-Pd/ATS catalysts, and monoaromatics were reduced from 13.9 to less than 3.3 m %. For all of the Pt-Pd/ATS catalysts, sulfur contents, total aromatic contents, and polycyclic aromatic contents of the product oils all met the sulfur or aromatic regulations of Internaitonal Specification-IV of ultraclean diesel fuel. Figures 9 shows the HDS and HDA activities of the Pt-Pd/ ATS-3 catalyst in the 100 h time-on-stream test, indicating that the equilibrium catalyst activity was kept stable. High HDS/HDA activities of the Pt-Pd catalyst were attributed to the improved dispersion of Pt-Pd over the surface
b
Analyzed by the LC-4 coulometric sulfur
Figure 9. HDS and HDA activities of the Pd-Pt/ATS3 catalyst in the 100 h time-on-stream test.
of the support. High HDA activity of Pt-Pd/ATS was likely a result in the incorporation of Ti and Si into Al2O3, which adjusted the interactions between the support and active metals. 4. Conclusions (1) The appropriate contents of Ti and Si incorporated into Al2O3 increased the HDS and HDA activity and stability of the Pt-Pd catalyst. (2) From the activity test results, the Pt-Pd/ ATS-2 catalyst was the most active catalyst for HDA and HDS under the applied conditions, and the sulfur contents, total aromatic contents, and polyaromatic contents of the product oils all met the sulfur or aromatic regulations of International Specification-IV of ultra-clean diesel fuel. Therefore, ATS composite oxide was proven to be a kind of excellent support candidate for Pt-Pd HDS/HDA catalysts. (3) A 100 h timeon-steam test result demonstrated that the Pt-Pd/ATS catalyst had excellent stability in HDS and HDA reactions. Acknowledgment. The authors acknowledge the financial support from the 973 National Basic Research Program of China (2004CB217806) and Natural Science Foundation of China (20876173 and 20773163). EF8006905
