Ind. Eng. Chem. Res. 1997, 36, 2521-2525
2521
KINETICS, CATALYSIS, AND REACTION ENGINEERING Hydrodesulfurization of Atmospheric Gas Oil over NiMo/Aluminum Borate Catalysts in a Trickle Bed Reactor Yu-Wen Chen* and Ming-Chang Tsai Department of Chemical Engineering, National Central University, Chung-Li, 32054 Taiwan, Republic of China
A precipitation technique at constant pH value was used to prepare a series of aluminum borates (ABs) with various Al/B atomic ratios. These samples have been characterized with respect to surface areas, pore volumes, and pore size distributions. These materials were used as the supports of Ni-Mo catalysts. Hydrotreating reactions of atmospheric gas oil (AGO) were carried out over these sulfided catalysts in a bench-scale trickle bed reactor. The results revealed that these catalysts are much more active than the conventional NiMo/Al2O3 catalysts on HDS reactions. They also demonstrate high aromatic saturation capabilities. The high hydrodesulfurization activities of catalysts on aluminum borate supports can be rationalized by the presence of boron. Several effects may concur in these catalysts and facilitate their HDS activity. On one hand, it can increase the metal dispersions and the hydrogenation capabilities of the catalysts. On the other hand, it can increase the surface acidities and the cracking abilities of the catalysts. Both are beneficial to the HDS reactions of AGO. An optimum B2O3 content, which gives the highest HDS activity, is located around 4 wt %. The overdose of boron in the catalyst will cause a formation of B2O3 on the surface leading to a decrease in the activity. Introduction The demand for low-sulfur distillates is increasing due to the increasing environmental concern of diesel engine emissions. It is known that low-sulfur distillate fuels (0.05 wt % S) can significantly reduce the contribution of sulfates to particulates from diesel engine emissions. Conventional hydrotreating processes can desulfurize petroleum distillates to low-sulfur contents (Asim et al., 1990; Dicks et al., 1981; Mann et al., 1987; Nash, 1989; Suchanek, 1990; Yitzhaki and Aharoni, 1987). Several authors (Ohtsuka, 1977; Stanislaus et al., 1988) have reported that hydrodesulfurization (HDS) is generally carried out over alumina-supported catalysts containing combinations of cobalt and molybdenum salts or nickel and molybdenum salts where cobalt and nickel play an important role in promoting the active sites of molybdenum-based sulfide catalysts in HDS. Changing the nature of the carrier is an interesting line of research to achieve more thorough hydrodesulfurization. Until now, various supports such as carbon (Duchet et al., 1983; Topsoe et al., 1986), silica (Muralidhar et al., 1984; Spozhakina et al., 1988), zeolite (Cid et al., 1987; Sambi and Mann, 1989), titania (Kim et al., 1989), zirconia (Nag et al., 1987; Duchet et al., 1991), alumina-aluminum phosphate (Chen et al., 1990), and mixed oxides (Wang and Chang, 1989; Daly, 1989) have been used to prepare hydrotreating catalysts. A detailed review of support effects on hydrotreating catalysts has been published by Breysse et al. (1991). Mixed oxides, particularly alumina-based binary oxides, are well suited catalytic materials. In a previous paper (Tsai et al., 1991; Li et al., 1993), the authors * To whom correspondence should be addressed. Fax: 8863-4252296. S0888-5885(97)00020-1 CCC: $14.00
demonstrated that CoMo/aluminum borate possesses high catalytic HDS activity for atmospheric residue oil and gas oil. Previous reports (Tanabe, 1970) have shown that alumina-boria catalysts can be used as cracking catalysts. Pine (1976) employed boria-alumina compositions in the hydrocarbon conversion process and proved that they are particularly useful in the hydrocracking of petroleum feedstocks over the boriaalumina supported for various combinations of zeolite, nickel oxide, and molybdenum oxide. Sato et al. (1987) reported that alumina-supported boria exhibited high catalytic efficiency for the vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactom. An optimum boria content occurred between 20 and 25 wt %. They suggested that boria, in excess of the optimum value, might have been deposited on active sites on alumina, so lowering the activity of the catalyst, since boria itself showed little activity in the absence of alumina. Later, the same experiment over aluminaboria was performed by Curtin et al. (1992), and a correlation was observed between the concentration of surface acidic sites of catalyst and the selectivity to caprolactom. Peil et al. (1989) reported that aluminum borate is highly acidic. Wang and Chen (1991) also reached the same conclusion. Hydrothermal stability of aluminum borate was examined by Tsai and Chen (1990) under 1023 K for up to 48 h. Recently, Chen and Li (1992) investigated liquid-phase hydrogenation of cyclohexene over Pt/aluminum borate catalyst and found that high activity can be attributed to high metal dispersion and high turnover frequency as a result of boron support modification. Huang and Kang (1996) reported that the hydrogenation activity of naphthalene on Pt/aluminum borate catalyst is higher than that on Pt/Al2O3. This boron-modified catalyst effect has also been revealed by bulk and surface spectroscopic techniques for Co/Al2O3 catalyst (Stranick et al., 1987). In © 1997 American Chemical Society
2522 Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997
addition, Wendlandt and Unger (1990) investigated the properties and applications of boron-containing pentasil type zeolites and observed a higher stability and a more advantageous product selectivity than conventional ZSM-5-containing catalysts during the course of reforming and hydroisomerization reactions. In the previous study (Li et al., 1993), CoMo/ aluminum borate was reported to be a good catalyst in the hydrotreatment of atmospheric gas oil (AGO). The study reported here is a continuation of our previous work on hydrotreating reactions of AGO over NiMo/ aluminum borate catalysts. Conventional NiMo/Al2O3 catalyst was also included for comparison. The aim of this study mainly focused on the effect of boria content. Previous reported results (Li et al., 1993) of CoMo/ aluminum borate catalysts are included for comparison. In the present study, a precipitation technique at constant pH value was used to prepare a series of aluminum borates (ABs). Hydrotreatment of Kuwait atmospheric gas oil (AGO) with NiMo/AB catalysts was tested in a trickle bed reactor. A conventional NiMo/ Al2O3 catalyst and a commercial catalyst (HR-306) from Shell Oil Co. were included for comparison. The chemical and physical properties of these catalysts were characterized to obtain the correlation with their catalytic properties. The aim of this study mainly focused on the effect of boron (or B2O3) content. Most of the published data on hydrotreatment reactions were obtained with a noncontinuous batch reactor using model compounds as feedstock (Aegerter et al., 1996; Huang and Kang, 1995). This makes it difficult to interpret the performance results and to correlate them to commercial operations. Therefore, it is our intention to describe the results obtained by using AGO as feedstock in a continuous trickle bed reactor, which closely mimics a commercial operation. Experimental Section Support Preparation. The aluminum borate support was prepared from common solutions of aluminum nitrate (Al(NO3)3‚9H2O) and boric acid (H3BO3) using an ammonium hydroxide solution (pH ) 10.0 ( 0.1) as a precipitant. A well-stirred container was charged with distilled water. The previously described two solutions were slowly added to this distilled water with the rate of addition controlled in order to maintain the pH of the solution at a constant value of 8.0 ( 0.1. The resulting precipitate was filtered, washed with distilled water, and dried overnight at 373 K, followed by calcination at 773 K in a muffle furnace for 5 h. By altering the relative amount of aluminum nitrate and boric acid, a desired AB composite could be obtained. The alumina support was made by the same method as AB without adding boria acid. Catalyst Preparation. The oven-dried uncalcined aluminum borate material was ground to a powder, and then the solutions of (NH4)6Mo7O24‚4H2O and Ni(NO3)2‚ 6H2O (all from Merck) in an appropriate amount of distilled water were impregnated successively, where MoO3 content was 12 wt % and the Ni/Mo atomic ratio was 0.6. The mixture was extruded by adding an appropriate amount of water. The extrusion diameter was about 1/16 in. (1 in. ) 2.54 cm). The wet extrusion was dried at atmospheric pressure overnight and calcined at 373 K for 12 h, followed by 773 K for 5 h. This calcination temperature has been reported to give optimal HDS activity (Stanislaus et al., 1988). For
convenience, we denoted aluminum borate supports as ABx, where x represents the measured Al/B atomic ratio. Characterization. Surface areas, pore volumes, and pore size distributions of catalyst samples were determined by nitrogen adsorption at 77 K using a Micromeritics ASAP 2400 analyzer. This enables us to measure pore size distributions in the radius range 1-30 nm. The measurements were performed on the oxidic form of the catalyst samples. Sample weights of about 500 mg were used. Since the average pore sizes were not large, the mercury penetration method was not valid for such catalysts in the present study. The metal contents of aluminum borate supports and NiMo/ aluminum borate catalysts were characterized by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Jarrell Ash Model 1100). Trickle Bed Reactor. The bench-scale cocurrent down-flow trickle bed reactor was used in this study by modifying the commercial-scale one from the petroleum industry. The schematic of the hydrotreatment system has been described in previous reports (Chen et al., 1990; Li et al., 1993). The cylindrical catalyst had a diameter of 1.5 mm and length of 4 mm. A stainless steel tube reactor of internal diameter 14.27 mm, outer diameter 25.40 mm, and length 430 mm was applied. In a typical run, the reactor was packed with 12 g of catalyst extrudates. The reactor was diluted with 5070 mesh sand (Merck) in order to reduce the dispersion effect and to make more homogeneous thermal distribution in the reactor. The reaction temperature was monitored with three thermocouples. One of the thermocouples was set in the center of tube reactor, and the other two were located outside the tube reactor along the length of the reactor. The catalyst was presulfided in the reactor. After the catalysts had been dried with a nitrogen purge at 393 K for 2 h, the diesel oil feedstock, which was doped to 1 wt % sulfur by addition of dimethyl disulfide, was passed through the reactor with the following temperature program: heated from room temperature to 448 K and kept for 2 h and then increased to 523 K and held for 4 h; after that, the temperature was increased to 598 K and retained until sulfiding was complete. The weight hourly space velocity (WHSV) of diesel oil was 2.4, the hydrogen flow rate was 300 mL(STP)/min, and the operation pressure was maintained at 2.8 MPa. After 24 h, the catalyst had been exposed to sulfur, which corresponded to four times the amount necessary to allow for complete conversion of the oxides of the active metals to their stoichiometric sulfides. The actual sulfur contents of the catalysts were not measured, since there would in any case be a reequilibration of the sulfur content during subsequent operations. HDS and aromatic saturation of heavy gas oils over the catalyst was conducted at 613 K and 2.8 MPa. After presulfiding of the catalyst, the Kuwait AGO was passed through the reactor with WHSV of 4. The hydrogen flow rate was the same as that in the presulfiding step. The characteristics of Kuwait AGO feedstocks are shown in Table 1. The hydrogen flow rate was 300 mL/ min at STP. The liquid feed and hydrogen gas were passed over the fixed bed of catalyst in a cocurrent down-flow mode. At an appropriate time, the hydrotreated oil samples were withdrawn to measure sulfur contents by X-ray fluorescence spectrometry (Oxford, LAB-X 2000) after the removal of dissolved
Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 2523 Table 1. Properties of Kuwait Atmospheric Gas Oil API, 60 °F sulfur, wt % composition saturate monoaromatic diaromatic 2diaromatic ASTM distillation IBP 5% 10% 20% 30% 40% 50% 60% 70% 80% 90% 95% FBP
34.2 1.45 69.7 17.0 10.2 3.1 426 K 527 K 546 K 563 K 572 K 577 K 581 K 586 K 590 K 597 K 607 K 618 K 621 K
Figure 1. Measured Al/B atomic ratio of aluminum borate vs nominal Al/B atomic ratio of the mother solution.
Table 2. Physical Properties of Aluminum Borate Supportsa nominal measured measured Al/B Al/B B2O3, wt % SA, m2/g PV, cm3/g PD, nm 1 3.5 12 Al2O3
2.7 10.0 34.1
11.3 3.8 1.0 0
158 225 239 203
0.55 0.43 0.39 0.41
13.9 7.6 6.5 8.1
a
SA: surface area. PV: pore volume. PD: average pore diameter PD ) 4 PV/SA. Table 3. Physical Properties of NiMo/Aluminum Borate Catalysts Al/B
B2O3, wt %
SA, m2/g
PV, cm3/g
PD, nm
Ni, wt %
Mo, wt %
2.7 10.0 34.1 NiMo/Al2O3 HR306
11.3 3.8 1.0 0 0
118 207 306 250 180
0.43 0.52 0.23 0.32 0.43
14.6 10.0 3.0 5.1 9.5
3.52 3.23 4.03 4.11 (3.0)a
9.49 8.85 11.15 11.10 12.0
a
Ni/Mo 0.61 0.60 0.59 0.60
The value is Co content (wt %).
H2S. The aromatic contents were analyzed by HPLC with an UV detector (Yoes and Asim, 1987). Results and Discussion Textural Properties. Surface areas, pore volumes, and average pore diameters of aluminum borate supports and NiMo/AB catalysts are given in Tables 2 and 3, respectively. Examination of Tables 2 and 3 shows that the incorporation of a small amount of boron into the alumina structure resulted in a slight increase in the specific surface area, whereas, further incorporation of boron into the alumina framework resulted in a decrease in the specific surface area. Tables 2 and 3 also show that the average pore diameter decreases with increasing the boron content on both AB and NiMo/AB materials. The results presented in Table 3 demonstrate that both the surface areas and pore diameters of ABs were decreased as the nickel and molybdenum were impregnated, possibly due to the deposition on the pore walls. The other interesting feature is that the measured Al/B atomic ratios are approximately two times those of nominal ones, as shown in Figure 1. It indicated that only a half of a boron was incorporated into the alumina matrix during the course of coprecipitation. This can be ascribed to high instability of transition boron materials (Tsai et al., 1991).
Figure 2. AGO HDS activity.
HDS Activity. The percentage of sulfur removal in a particular activity test is given by
%S)
[S in] - [S out] × 100% [S in]
where [S in] and [S out] are the experimentally measured inlet and outlet sulfur concentrations. Since all the catalysts tested were advanced HDS catalysts, under normally recommended operation conditions all samples gave greater than 95% conversion of the sulfur compounds to hydrogen sulfide. In order to magnify the difference in activity, the tests were conducted under conditions that were less severe for the catalysts than those used in practice. Under the conditions used in this study, the different catalysts showed differences of conversions varying over the range 40-80%. The temperature inside the catalyst bed was within the (5 K range. The heats of such reactions are usually small (of the order of 25-30 kcal/mol), and the concentrations of the reaction species are low. Therefore, the interparticle temperature gradients were not expected to be significant for the space velocity and particle used in the present study. The possible back-mixing was avoided by the catalyst bed dilution (Chen et al., 1990). However, the pore diffusion limitations are usually present in such reaction systems (Tsai et al., 1993; Li et al., 1995). In the present study, only the apparent conversions are reported. The relation between HDS activity of AGO and time on stream with various NiMo/AB catalysts is presented in Figure 2. The results showed that the NiMo/AB catalysts are not only more active than NiMo/Al2O3 but also more active than HR-306. The reasons for the high activities of CoMo/AB catalysts reported previously (Li et al., 1993) are also valid to portray NiMo/AB catalysts. The high activities of NiMo/AB catalysts can be interpreted in terms of the presence of highly dispersed boron on the support surface (Stranick et al., 1987). Since AB has a higher concentrations of hydroxyl groups on the surface than alumina (Chen and Li, 1992; Wang and
2524 Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 Table 4. Contents of the Saturation and Aromatic Compounds in the Product
Figure 3. Effect of B2O3 content on AGO HDS activity.
Chen, 1991) and BOH has a stronger acid strength than AlOH, this leads to the higher dispersion of Mo on the AB support surface. Therefore, it is speculative that more Co-Mo-O groups (which are the precursors of the Co-Mo-S groups) exist on the surface of AB than on the surface of Al2O3. This will produce more HDS active sites, generate higher hydrogenation capability, and make higher HDS activity (Topsoe et al., 1983; Topsoe and Clausen, 1984). However, the overdose of boron will form B2O3 and cause a decrease in metal dispersion. Stranick et al. (1987) reached the same conclusion. They reported that the presence of boron exhibited an increase in metal dispersion compared to boron-free sample due to the formation of surface aluminum borate. The overdose of boron will form B2O3 and cause a decrease of metal dispersion. The second explanation for the HDS activity behavior is based on the acidity of the catalyst. In a previous paper (Chen et al., 1994), it was shown that the acidities of NiMo/ABs are higher than that of NiMo/Al2O3. The high acidity of the NiMo/ AB catalyst could enhance the cracking capability, which would result in the increase of HDS activity. Both hydrogenation and cracking capabilities of the catalysts are beneficial to the HDS activity. Generally speaking, the higher the boiling point of the oil is, the more difficult to perform HDS reaction. The boiling point of AGO is lower than that of the atmospheric tower bottom (ATB) residue. Consequently, the high AGO HDS activity of NiMo/AB catalyst is not surprising if one considers that it has a high ATB HDS activity. This is also the reason why the reaction temperature for AGO HDS in the present study is lower than that for ATB HDS. An interesting feature is that the decrease in activity during the initial period of time on stream for AGO is much slighter as compared with that for ATB. Indeed, further tests showed that the activity was maintained at a fairly constant level over a period of 300 h. This phenomenon can be attributed to the smaller formation of coke on the catalyst. Investigating the deposition of coke on the spent catalyst by thermogravimetric analysis with air suggested that the formation of coke is negligible for all the catalysts. The negligible coke level in this study can also be attributed to the excess hydrogen concentration (Richardson et al., 1996). Figure 3 shows the percentage of sulfur removal as a function of B2O3 content. It should be noted that the optimum B2O3 content is located around 4 wt %, regardless of NiMo/AB or CoMo/AB catalysts. This optimum composition occurred as a result of hydrogenation and hydrocracking functions appropriately balanced. According to the results of Li and Chen (1993), the acid strength of the support was increased dramatically on going from alumina to AB with an Al/B ratio of 20. However, a further increase in boron content does
catalyst
saturation, wt %
aromatics, wt %
feed NiMo/AB2.7 NiMo/AB10.0 NiMo/AB34.1 NiMo/Al2O3 HR306
62.3 72.2 74.6 73.5 72.1 73.2
37.7 27.8 25.4 26.5 27.9 26.8
not increase the acid strength of the catalyst. That is why adding boron to catalyst would increase hydrogenation activity. Too much boron is poisonous to the hydrogenation activity of the catalyst. At lower boron loadings, a surface-mixed oxide of alumina-boria is formed. However, at higher boron loading, boria (B2O3) itself is formed on the support surface. This is why too much boron is poisonous to the hydrogenation activity. Aromatics Saturation. A substantial decrease in the aromatics content of diesel fuel is expected to result in a significant decrease in hydrocarbon emissions. A summary of the results of aromatics saturation is shown in Table 4. The results demonstrated that the NiMo/ AB catalysts express a high activity for aromatics saturation, whereas the activity of CoMo/AB catalyst is not high (Li et al., 1993). However, regardless of whether NiMo/AB or CoMo/AB catalysts are used, both show better aromatics saturation capabilities than those of NiMo/Al2O3 or CoMo/Al2O3. This confirms our previous conclusion that the presence of boron can increase the hydrogenation ability of the catalyst. In addition, the hydrogenation ability using NiMo as component is higher than that of CoMo one. The catalyst with a B2O3 content of 4 wt % demonstrates the highest aromatic saturation capability, in agreement with the HDS results. Finally, it should be emphasized that the aromatic ring saturation reactions require more severe processing conditions, and thus, it is expected that the aromatic saturation will be increased to a large extent by increasing temperature and hydrogen partial pressure (Girgis and Gates, 1991; Mann et al., 1987; Nash, 1989; Suchanek, 1990; Yoes and Asim, 1987). Conclusion The results presented in this paper have shown that a new family of catalysts in which NiMo is dispersed on the aluminum borate support appears to be well suited for hydrotreating reactions of atmospheric gas oil. The activities of HDS and aromatics saturation of all NiMo/AB catalysts are higher than those of CoMo/ Al2O3. The HDS and aromatics saturation activities of NiMo/AB are a function of boria content. It shows a volcano plot. An optimum B2O3 content, which gives the highest activity, was observed at 4 wt %. The high activities of catalysts on AB supports can be rationalized on the presence of boron. Since boron has a higher electron negativity than aluminum, BOH has a stronger acid strength than AlOH. This leads to the conclusion that Mo7O24-6 links with B3+ rather than with Al3+. In addition, the AB support has a higher concentration of surface hydroxyl groups than Al2O3. Therefore, it is believed that more Co-Mo-O groups (the precursor of Co-Mo-S) exist on the surface of AB than on Al2O3. This produces more active sites and leads to higher hydrogenation capability and HDS activity. On the other hand, the stronger acidity on the AB support can enhance the cracking ability of the catalyst. Both are beneficial to the HDS reactions of
Ind. Eng. Chem. Res., Vol. 36, No. 7, 1997 2525
AGO. However, the overdose of boron in the catalyst will cause a formation of B2O3 on the surface and lead to a decrease in the HDS activity. Acknowledgment This research is supported by the National Science Council (NSC-81-0402-E008-012) and Chinese Petroleum Co. of the Republic of China. Literature Cited Aegerter, P. A.; Quigley, W. W. C.; Simpson, G. J.; Ziegler, D. D.; Logan, J. W.; McCrea, K. R.; Glazier, S.; Bussell, M. E. Thiophene Hydrodesulfurization over Alumina-Supported Molybdenum Carbide and Nitride Catalysts: Adsorption Sites, Catalytic Activities, and Nature of the Active Surface. J. Catal. 1996, 164, 109-121. Asim, M. Y.; Keyworth, D. A.; Zoller, J. R.; Plantenga, F. L.; Lee, S. L. Hydrotreating for Ultra-Low Aromatics in Distillates. NPRA Paper No. AM-90-19, 1990. Breysse, M.; Portefaix, J. L.; Vrinat, M. Support Effects on Hydrotreating Catalysts. Catal. Today 1991, 10, 489-505. Chen, Y. W.; Hsu, W. C.; Lin, C. S.; Kang, B. C.; Wu, S. T.; Leu, L. J.; Wu, J. C. Hydrodesulfurization Reactions of Residue Oils over CoMo/Alumina-Aluminum Phosphate Catalysts in a Trickle Bed Reactor. Ind. Eng. Chem. Res. 1990, 29, 1830-1840. Chen, Y. W.; Li, C. Liquid Phase Hydrogenation of Cyclohexene over Pt/Aluminum Borate Catalysts. Catal. Lett. 1992, 13, 359361. Chen, Y. W.; Tsai, M. C.; Li, C. Hydrodesulfurization of Residue Oils over NiMo/Alumina-Aluminum Borate Catalysts: Effect of Boria Content. Ind. Eng. Chem. Res. 1994, 33, 2040-2046. Cid, R.; Orellana, F.; Lopez-Agudo, A. Effect of Cobalt on Stability and Hydrodesulfurization Activity of Molybdenum Containing Y Zeolite. Appl. Catal. 1987, 32, 327-336. Curtin, T.; McMonagle, J. B.; Hodnett, B. K. Influence of Boria Loading on the Activity of B2O3/Al2O3 Catalysts for the Conversion of Cyclohexanone Oxime to Caprolactom. Appl. Catal. 1992, 13, 359-361. Daly, F. P. The Use of Binary Oxides as catalyst Supports for Hydrodesulfurization and Hydrodenitrogenation. J. Catal. 1989, 116, 600-603. Dicks, A. L.; Ensell, R. L.; Phillips, T. R.; Szczepura, A. K.; Thorley, M.; Williams, A.; Wragg, R. D. A Study of Relationship Between Pore Size Distribution, Hydrogen Chemisorption, and Activity of Hydrodesulphurisation Catalysts. J. Catal. 1981, 72, 266273. Duchet, J. C.; Tilliette, M. J.; Cornet, D.; Vivier, L.; Perot, G.; Bekakra, L.; Moreau, C.; Szabo, G. Catalytic Properties of Nickle Molybdenum Sulfide supported on Zirconia. Catal. Today 1991, 10, 579-592. Girgis, M. J.; Gates, B. C. Reactivaties, Networks, and Kinetics in High Pressure Catalytic Hydroprocessing. Ind. Eng. Chem. Res. 1991, 30, 2021-2058. Huang, T. C.; Kang, B. C. Kinetic Study of Naphthalene Hydrogenation over Pt/Al2O3 Catalyst. Ind. Eng. Chem. Res. 1995, 34, 1140-1148. Huang, T. C.; Kang, B. C. Hydrogenation of Naphthalene with Platinum-Aluminum Borate Catalysts. Chem. Eng. J. 1996, 63, 27-36. Kim, D. S.; Kurusu, Y.; Wachs, I. E.; Hardcastle, F. D.; Segawa, K. Physicochemical Properties of MoO3-TiO2 Prepared by an Equilibrium Adsorption Method. J. Catal. 1989, 120, 325-336. Li, C.; Chen, Y. W.; Yang, S. J.; Wu, J. C. Hydrodesulfurization Reactions of Atmospheric Gas Oil over CoMo/Alumina-Aluminum Borate Catalysts. Ind. Eng. Chem. Res. 1993, 32, 15731578. Li, C.; Chen, Y. W.; Tsai, M. C. Highly Restrictive Diffusion under Hydrotreating Reactions of Heavy Residue Oils. Ind. Eng. Chem. Res. 1995, 34, 898-905. Mann, R. S.; Sambi, I. S.; Khulbe, K. C. Catalytic Hydrofining of Heavy Gas Oil. Ind. Eng. Chem. Res. 1987, 26, 410-414. Muralidhar, J.; Massoth, F. E.; Shabtai, J. Catalytic Functionalities of Supported Sulfides I. Effect of Support and Additives on the CoMo Catalyst. J. Catal. 1984, 84, 44-52. Nag, N. K. A Comparative Study on the Dispersion and carrierCatalyst Interaction of Molybdenum Oxides Supported on
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Received for review January 2, 1997 Revised manuscript received April 17, 1997 Accepted April 23, 1997X IE970020I
Abstract published in Advance ACS Abstracts, June 1, 1997. X
