Aromatics Reduction over Supported Platinum Catalysts. 3. Effects of

Sep 15, 1996 - Fast Fourier transformation infrared spectroscopy was used to characterize the formation of bimetallic interactions of γ-Al2O3-support...
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Ind. Eng. Chem. Res. 1996, 35, 3893-3898

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Aromatics Reduction over Supported Platinum Catalysts. 3. Effects of Catalyst Precursors and Pretreatment Conditions on the Performance of Palladium-Promoted Platinum Catalysts Chou-An Jan,† Tzong-Bin Lin,‡ and Jen-Ray Chang*,† Department of Chemical Engineering, National Chung Cheng University, Chia-Yi, Taiwan, Republic of China, and Chinese Petroleum Corp., RMRC, Chia-Yi, Taiwan, Republic of China

Fast Fourier transformation infrared spectroscopy was used to characterize the formation of bimetallic interactions of γ-Al2O3-supported Pd-Pt catalysts. The effects of bimetallic interactions on catalyst performance were examined in long-term stability tests, carried out with a pilot plant under the same operating conditions and feed as those of a commercial diesel hydrotreating process. These tests are the hydrotreating of straight run distillate diesel at 340 °C, 580 psig, and H2/oil (mol) ) 2.5 over a 25 day period. The characterization results indicate that Pd precursors and pretreatment conditions affect Pd-Pt bimetallic interactions in the H2reduced catalysts and the catalyst performance. The Pd-Pt catalysts made from palladium(II) acetate without calcination pretreatment presented a significant Pd-Pt bimetallic interaction, as evidenced by a shift in the infrared absorption peak characteristic of terminal CO ligands adsorbed on the Pt clusters to higher energy, bridging CO on the Pd to lower energy, and a catalytic reduction of palladium(II) acetate by Pt. In contrast, no significant bimetallic interactions were observed for both catalysts made from palladium(II) acetate with a calcination at 450 °C in air and from palladium amine. The long-term stability tests further indicate that the Pd-Pt catalysts with bimetallic interactions have a relatively high selectivity for aromatics reduction and hydrodenitrogenation (HDN), whereas they have a relatively low selectivity for hydrodesulfurization (HDS). Introduction Platinum supported on γ-Al2O3 is known to be a highly active catalyst for the hydrogenation of aromatics. Cooper et al. (1993b) reported that 60-70% aromatics in Kuwait heavy gas oil (HGO) can be saturated by a Pt/Al2O3 catalyst at moderate conditions: a pressure of 650-870 psi, temperture of 277-307 °C, and a liquid hourly space velocity (LHSV) of 0.75-1.5 h-1. However, despite the catalyst’s excellent hydrogenation properties, it suffers from a high sensitivity to sulfur poisoning (Barbier et al., 1990). Therefore, a severe pretreatment is necessary to reduce the sulfur content to below 2 ppm. The low space velocity required in hydrodesulfurization (HDS) to obtain diesel with sufficiently low sulfur content thus limits the application of Pt/Al2O3 catalysts. In our previous paper (Lin et al., 1995), we reported that the addition of Pd markedly improved the performance of γ-Al2O3-supported Pt catalysts for the reduction of aromatics in diesel fuel; the aromatics conversion of diesel, with 369 ppm of sulfur, catalyzed by the Pt catalyst under weight hourly space velocity (WHSV) ) 1.5 h-1 at 340 °C and 580 psig, was only 9.6%, compared with 44% conversion by the Pd-Pt catalyst. Kinetic studies further indicated that the rate constant based on the zero-order rate expression for the Pd-Pt catalyst is about 4.5 times that for the Pt catalyst. The benefit of the addition of Pd has been attributed to the inhibition of sulfur poisoning caused by the formation of PdPt bimetallic interactions. However, similar to aluminasupported Re-Pt catalysts used in naphtha reforming processes (Purnell et al., 1993; Dossi et al., 1989; Isaacs and Petersen, 1982; McNicol, 1977), the formation of * Author to whom correspondence should be addressed. † National Chung Cheng University. ‡ Chinese Petroleum Corp., RMRC.

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Pd-Pt bimetallic interactions also depends strongly on the method of catalyst preparation and treatment. In the present paper, we report on the catalytic behavior of the Pd-Pt catalysts prepared from different precursors and pretreatment conditions to demonstrate the effect of the Pd-Pt bimetallic interactions. Fast Fourier transform infrared (FFT-IR) spectroscopy, characterizing CO adsorbed on a Pd-Pt catalyst sample, was used to examine the formation of bimetallic interactions; the interactions induce a shift of νCO to high frequency for terminal adsorbed CO on Pt, and concomitantly to low frequency for bridging CO on Pd. The effects of such bimetallic interactions on the selectivity of aromatics reduction, HDS, and hydrodenitrogenation (HDN) were examined in a long-term stability test, run at the same operating conditions (580 psig, 340 °C, and H2/oil mole ratio ) 2.5) and feed (straight run distillate diesel) as those of a commercial diesel hydrotreating process. The mechanism of the formation of the bimetallic interactions was proposed from FFTIR monitoring of the temperature-programmed decomposition of the catalyst precursors. Experimental Section Materials and Catalyst Preparation. γ-Al2O3 of 141 Å average pore diameter and 179 m2/g surface area was used as a catalyst support. The γ-Al2O3 was prepared from an equal ratio of Versal 250 and Capital B pseudoboehmitic alumina powder. The powder was digested by a nitric solution to form a gel, then neutralized by aqueous ammonia, followed by kneading and extruding, and finally calcined at 600 °C for 6 h. The Al2O3 support (cylindrical in shape, 1.1 mm diameter, and about 2-4 mm long) was first brought into contact with a solution of H2PtCl6 (strem) in doubly distilled deionized water, followed by removal of water © 1996 American Chemical Society

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in vacuum overnight, and then calcined at 450 °C for 8 h to prepare supported Pt catalysts. Some of the Pt catalysts were then brought into contact with an aqueous solution of Pd(NH3)4(NO3)2 precursors and then dried in vacuum for 12 h, followed by calcination in air at 450 °C for 8 h to produce the first supported Pd-Pt catalyst sample, denoted as [Pt-Pd(NH3)4/γ-Al2O3(c)]. The second Pd-Pt catalyst sample, [Pt-Pd(OAc)2/γAl2O3(c)], was prepared with the same procedure as that for the preparation of the first sample, but with a tetrahydrofuran (THF) solution of palladium(II) acetate, [Pd(O2CCH3)2], denoted as [Pd(OAc)2] (strem, used without purification) precursors. The preparation of the third sample, [Pt-Pd(OAc)2/γ-Al2O3], also followed the same procedure as that for sample 2 except that there was no calcination. To study the catalytic reduction effect of the third sample, a sample for comparison was prepared from the deposition of [Pd(OAc)2] on γ-Al2O3 and was denoted as [Pd(OAc)2/γ-Al2O3]. The supported Pd catalysts for the study of Pd-Pt bimetallic interactions were prepared from [Pd(OAc)2/γ-Al2O3] followed by calcination at 450 °C for 8 h. Long-Term Stability Tests. The stability tests were carried out in a continuous down flow trickle-bed reactor. The reactor is a stainless steel tube with a length of 0.924 m and an inside diameter of 2.07 cm. The reaction was run in an isothermal mode, and the temperature was controlled by a three-zone electric furnace with an independent proportional-integralderivative temperature controller. Diesel, a product of the no. 6 HDS unit of the Lin-Yuan refinery in Taiwan, was used as feedstocks. The diesel feed contained 28.4% aromatics, 369 ppm of sulfur, and 44.8 ppm of nitrogen (details of the analytical results are shown in Table 3 of our previous paper, Lin et al., 1995). The three PdPt catalyst samples were used for the stability tests. After the reaction system was purged with a dry nitrogen gas for 4 h, all the catalyst samples were reduced at 450 °C under 580 psig of pure hydrogen for 6 h. After reduction of the catalysts, the catalytic reactions were carried out at the following operation conditions: WHSV 3.0 h-1; H2/oil mole ratio 2.5; temperature 340 °C; pressure 580 psig. Product samples were collected periodically, and sulfur, nitrogen, and aromatics contents were measured. Details of the stability tests and sample analysis are shown in the previous paper (Lin et al., 1995). When aromatic conversion showed no significant changes, further kinetic study was conducted with WHSV ranging from 1.5 to 4.0 h-1. Catalyst Characterization Metal Surface Area. The metal surface area of the Pd-Pt catalysts was measured by the amount of CO chemisorbed on the catalysts. The measurement was made by the titration technique, in which an inert carrier gas (He), into which is injected a small volume (0.1 mL) of CO, is continuously passed over the catalysts. Gas composition is detected by a thermal conductivity detector. Before the measurements, fresh catalysts were reduced at the same operating conditions as those of stability tests, and the amount of chemisorption was calculated by summing up the proportions of all of the pulses consumed. Characterization of Catalyst Samples by FFTIR. Infrared Fourier transform spectra of surface species were recorded with a Shimadzu SSU-8000

Figure 1. Product aromatics (HPLC) vs time on stream in longterm stability tests: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [Pt-Pd(OAc)2/ γ-Al2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

instrument having a spectral resolution of 4 cm-1. Catalyst samples were loaded as wafers into IR cells, and treatments were done in situ. To characterize the CO-adsorbed catalyst sample, before FFT-IR measurement, samples were reduced at the same operating conditions as those of the stability test, except at a H2 pressure of 1 atm. After the reduction, the sample was cooled to room temperature, and CO (flowing at 50100 mL/min at 1 atm) was introduced into the cell and maintained for about 20 min. After the CO treatment, the cell was evacuated to a pressure of approximately 10-2-10-3 Torr, and IR spectra were recorded. To investigate the catalytic reduction effect, the reduction process of [Pt-Pd(OAc)2/γ-Al2O3] and [Pd(OAc)2/γ-Al2O3] was monitored by FFT-IR. The powder samples were loaded into the IR cell. The cell was connected to a vacuum/gas handling manifold for in situ treatment. The samples were treated in H2 flowing at about 50 mL/min for 30 min at temperatures ranging from 25 to 350 °C. The H2 was purified by flowing through a trap containing particles of active zeolite 4A to remove moisture. Each sample was cooled to room temperature before the spectra were recorded. Results and Discussion As shown in the previous paper (Lin et al., 1995), the sulfur resistance of the supported Pt catalysts was greatly improved by addition of Pd. However, not all Pd-Pt catalysts have such good performance. The performance of the catalysts depends on the catalyst precursors and pretreatment conditions. Effects of Catalyst Precursors and Pretreatment on Aromatics Reduction. The hydrogenation of aromatics is a reversible reaction in which polynuclear aromatics are first converted to dinuclear aromatics and then to mononuclear aromatics, which are in turn converted to naphthenes. Since the reaction network is very complicated, it is very difficult to use a Langmuir-Hinshelwood-Hougen-Watson (LHHW) type of rate equation for representing the hydrogenation kinetics of industrial feedstocks. Therefore, simple powerlaw models have been used by most researchers to fit kinetic data, and percent aromatics hydrogenation has been used to represent the extent of saturation achieved during the hydrotreating (Stanislaus and Cooper, 1994). The product aromatics (total content of aromatics in the exit of the reactor) and percent aromatics hydrogenation versus time on stream of the Pd-Pt catalyst samples are shown in Figures 1 and 2, respectively. The

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Figure 2. Percent aromatics hydrogenation vs time on stream in long-term stability tests: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [PtPd(OAc)2/γ-Al2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

Figure 4. Product diaromatics (HPLC) vs time on stream in longterm stability tests: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [Pt-Pd(OAc)2/ γ-Al2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

Figure 3. Effect of space time on product aromatics (HPLC) at 340 °C, 580 psig, and H2/oil (mol) ) 2.7 catalyzed by M-Pt/γ-Al2O3 bimetallic catalysts: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [Pt-Pd(OAc)2/ γ-Al2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

Figure 5. Product monoaromatics (HPLC) vs time on stream in long-term stability tests: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [PtPd(OAc)2/γ-Al2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

highest aromatics saturation activity (lowest product aromatics and highest percent aromatics hydrogenation) at the start of the run is displayed by [Pt-Pd(NH3)4/γAl2O3(c)], while [Pt-Pd(OAc)2/γ-Al2O3(c)] presents the lowest activity. The initial activity trend among these three catalyst samples agrees with the CO chemisorption characterizing the metal dispersion of the catalysts: the amount of CO adsorbed on [Pt-Pd(NH3)4/γAl2O3(c)], [Pt-Pd(OAc)2/γ-Al2O3(c)], and [Pt-Pd(OAc)2/γAl2O3] is 0.85, 0.64, and 0.74 (mol of CO/mol of Pt), respectively. However, the stability maintenance of the catalysts is independent of the metal dispersion. Among these three catalyst samples, [Pt-Pd(NH3)4/γ-Al2O3(c)] had a much higher deactivation rate than the other two samples, although it has the highest metal dispersion. As for aromatics reduction, [Pt-Pd(OAc)2/γ-Al2O3] had the best catalytic performance. When the catalyst deactivation rate became insignificant (pseudo steady state), the reaction product catalyzed by this catalyst had the lowest aromatics content, and the turnover number (Boudart, 1981) of this catalyst is 0.0070 s-1, compared with 0.0030 s-1 for [Pt-Pd(OAc)2/γ-Al2O3(c)] and 0.0027 s-1 for [Pt-Pd(NH3)4/γ-Al2O3(c)]. In addition, consistent with findings of Cooper et al. (1993), as shown in Figure 3, the data of aromatics reduction fit zeroorder kinetics nicely and the rate constant of [PtPd(OAc)2/γ-Al2O3] is about 2.5 times the rate constants of [Pt-Pd(NH3)4/γ-Al2O3(c)] and [Pt-Pd(OAc)2/γ-Al2O3(c)]. Indicated in our previous paper (Lin et al., 1995), the aromatics saturation reactions over the Pd-Pt catalysts,

which were prepared from [Pd(OAc)2] precursors without calcination, are controlled by kinetics and polyaromatics are kinetically easier to hydrogenate than monoaromatics. This conclusion also holds for the other Pd-Pt catalysts prepared from different Pd precursors and pretreatment conditions. The conversion of aromatics with two rings is more than 50% for all samples (Figure 4). However, the conversion of monoaromatics is much lower; the highest conversion of monoaromatics among the samples is only about 12% (Figure 5). Effects of Catalyst Precursors and Pretreatment on HDS and HDN. The nitrogen (total content of nitrogen compounds, including nonheterocyclic and heterocyclic organonitrogen compounds, in diesel fuel) conversion versus time-on-stream of the Pd-Pt catalyst samples is shown in Figure 6. This figure indicates that the trend of HDN activity of the three catalyst samples at pseudo steady state agrees with that of the aromatics saturation; that is, [Pt-Pd(NH3)4/γ-Al2O3(c)] and [PtPd(OAc)2/γ-Al2O3(c)] have almost the same HDN activity, but the activity of both samples is lower than that of [Pt-Pd(OAc)2/γ-Al2O3]. In contrast, the trend of sulfur (total content of organosulfur compounds in diesel fuel) conversion, [Pt-Pd(OAc)2/γ-Al2O3(c)] > [Pt-Pd(OAc)2/γAl2O3] = [Pt-Pd(NH3)4/γ-Al2O3(c)], does not agree with the trend for aromatics saturation and HDN (Figure 7). Nonheterocyclic organonitrogen compounds, such as aliphatic amines and nitriles, are in considerably small amounts in diesel and are denitrogenated much more rapidly than the heterocyclic compounds (Katzer and

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Figure 6. Nitrogen conversion vs time on stream in long-term stability tests: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [Pt-Pd(OAc)2/γAl2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

Figure 8. Infrared spectra in the νCO stretching region characterizing the CO adsorbed on Pt, Pd, and Pd-Pt/γ-Al2O3 catalysts: (a) [Pt-Pd(OAc)2/γ-Al2O3(c)]; (b) [Pt-Pd(NH3)4/γ-Al2O3(c)]; (c) the summation spectra of the supported Pt and the Pd catalysts; (d) [PtPd(OAc)2/γ-Al2O3].

Figure 7. Sulfur conversion vs time on stream in long-term stability tests: 0, [Pt-Pd(OAc)2/γ-Al2O3(c)]; O, [Pt-Pd(OAc)2/γAl2O3]; 4, [Pt-Pd(NH3)4/γ-Al2O3(c)].

Sivasubramanian, 1979). Consequently, only heterocyclic compounds are important in considering the kinetics of nitrogen removal. Nitrogen heterocyclic compounds must first be hydrogenated before the nitrogen is removed (Marcilly, 1990). The requirement of the ring saturation implies that the denitrogenation rate is greatly dependent on the hydrogenation activity of the catalysts. The aromatics-saturation and HDN results thus suggest that, at pseudo steady state, [Pt-Pd(OAc)2/γ-Al2O3] presents the highest hydrogenation activity of the three catalyst samples. The higher hydrogenation activity of [PtPd(OAc)2/γ-Al2O3] was thought to be caused by less sulfur poisoning of the catalysts, and Pd-Pt bimetallic interactions were believed to play the crucial role. In the previous paper (Lin et al., 1995), we reported that the decrease of electron density of Pt particles caused by the Pd-Pt bimetallic interactions retards the rate of sulfur poisoning. The experimental results reported in this paper further demonstrate that the formation of Pd-Pt bimetallic interactions is determined by suitable precursors and preparation of the catalysts. Saturation of sulfur heterocyclic compounds is not a necessary step before the C-S breakage for HDS; hence, the trend of HDS activity (Figure 7) is not consistent with that of aromatics saturation and HDN. In comparing the results between HDS and HDN (Figure 6 and 7), we may conclude that the Pd-Pt bimetallic interactions have a greater influence on the activity maintenance of hydrogenation than on hydrogenolysis. FFT-IR Spectroscopy Characterizing the CO Adsorbed on the Pt-Pt Catalyst. As reported in the previous paper (Lin et al., 1995), the IR spectra of the CO adsorbed on Pt and Pd catalyst samples are consistent with spectra reported for CO adsorbed on similarly

prepared samples (Little et al., 1966). The band peaking at 2059 cm-1 of Pd + Pt (the summation of Pt and Pd) spectra was assigned as the terminal CO adsorbed on Pt particles, and the absorption peak located at 1911 cm-1 was assigned as the bridging CO adsorbed on Pd particles (Figure 8c). The infrared spectra characterizing CO adsorbed on [Pt-Pd(NH3)4/γ-Al2O3(c)] (Figure 8b) suggest that the Pt and Pd particles are segregated; the peaks characterizing CO adsorbed on Pt and Pd particles are close to those for the Pd + Pt spectra. Similar results were observed for [Pt-Pd(OAc)2/γ-Al2O3(c)] (Figure 8a), whereas the peaks characterizing CO adsorbed on the Pt and Pd particles are relatively broad in comparison to those of [Pt-Pd(NH3)4/γ-Al2O3(c)]. In contrast, the formation of bimetallic interactions was suggested for [Pt-Pd(OAc)2/ γ-Al2O3]; the terminal νCO band of the sample is approximately 20 cm-1 higher than that of the Pt sample, while the bridging νCO band of the Pd-Pt sample is abut 50 cm-1 lower than that of the Pd sample (Figure 8d). The shift of the CO absorption bands also suggests that the electron density of Pt is decreased by Pd-Pt bimetallic interactions; such a decrease causes less backbonding from Pt to the CO-π* orbital, resulting in a shift of νCO to high frequency, while an increase of electron density on Pd causes more Pd-carbonyl π-back-bonding, resulting in a shift of νCO to low frequency (Cotton and Wilkinson, 1988). FFT-IR Spectroscopy Characterizing the Temperature-Programmed Decomposition (TPDE) of [Pd(OAc)2]/γ-Al2O3 and [Pt-Pd(OAc)2/γ-Al2O3]. FFTIR spectra characterizing the TPDE of [Pd(OAc)2]/γAl2O3 and [Pt-Pd(OAc)2/γ-Al2O3] are shown in Figures 9 and 10, respectively. The absorption bands between 1350 and 1650 cm-1 were assigned as carboxylate ligands of [Pd(OAc)2] on γ-Al2O3. After both samples had been held for 30 min in H2 at 300 °C, the band intensities characterizing carboxylate ligands decreased to about 30% of those observed at 200 °C for [PtPd(OAc)2/γ-Al2O3], while there was nearly no change for [Pd(OAc)2]/γ-Al2O3. After 30 min at 350 °C, no significant bands were observed for [Pt-Pd(OAc)2/γ-Al2O3]. In

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two catalysts are segregated. Inferred from this, we speculate that the reduction temperatures of Pd precursors higher than those of Pt oxide and the mobile Pd precursors are the necessary conditions for the formation of Pd-Pt bimetallic interactions. Conclusions

Figure 9. Infrared spectra of [Pd(OAc)2/γ-Al2O3] after (a) 30 min, 25 °C, in H2; (b) 30 min, 200 °C, in H2; (c) 30 min, 300 °C, in H2; (d) 30 min, 350 °C, in H2.

Both the precursors and pretreatment conditions of the γ-Al2O3-supported Pd-Pd catalysts play crucial roles in controlling the bimetallic interactions, thereby influencing the catalyst performance. In contrast to the samples either prepared from [Pd(NH3)4(NO3)2] with calcination or prepared from [Pd(OAc)2] with calcination, the sample prepared from [Pd(OAc)2] without calcination gave FFT-IR evidence of significant bimetallic interactions. These bimetallic interactions are formed from the catalytic reduction of Pd, inferred from the FFT-IR monitoring of the decomposition of carboxylate ligands of [Pd(OAc)2]. The decrease of electron density on Pt induced by such bimetallic interactions enhances the sulfur resistance of the catalysts, leading to relatively high activities for aromatics reduction and HDN at the pseudo steady state of the reaction; at the start of the run, the activities, however, increase with the metal dispersion. For HDS, since the saturation of sulfur heterocyclic compounds is not a necessary step before the C-S breakage, the activity is less influenced by the bimetallic interactions. Acknowledgment The support of the National Science Council of the Republic of China (NSC 85-2114-E-194-002), National Chung Cheng University, and the Refining & Manufacturing Research Center of Chinese Petroleum Corp. (RMRC) is acknowledged. Literature Cited

Figure 10. Infrared spectra of [Pt-Pd(OAc)2/γ-Al2O3] after (a) 30 min, 25 °C, in H2; (b) 30 min, 200 °C, in H2; (c) 30 min, 300 °C, in H2; (d) 30 min, 350 °C, in H2.

contrast, the band intensities were about 50% of those observed at 200 °C for [Pd(OAc)2]/γ-Al2O3. Inferred from the temperature-programmed reduction characterizing bimetallic interactions of Re-Pt catalysts (Boliver et al., 1975; McNicol, 1977; Isaacs and Petersen, 1982; Augustine and Sachtler, 1989; Purnell et al., 1993), the decrease of the reduction temperature of [Pd(OAc)2] for the sample with Pt presented, [Pt-Pd(OAc)2/γ-Al2O3], suggests a catalytic reduction of Pd. The catalytic reduction of Pd is thought to be the mechanism for the formation of bimetallic interactions; presumably, the mobile [Pd(OAc)2] on the support surface migrates to the hydrogen-covered Pt centers, where it is catalytically reduced by Pt. Since the reduction temperature of Pd oxide is lower than that of Pt oxide (Cheng et al., 1986; Chiou et al., 1995), no catalytic reduction will happen to [Pt-Pd(NH3)4/ γ-Al2O3(c)] and [Pt-Pd(OAc)2/γ-Al2O3(c)], and thus both Pd oxide and Pt oxide of these two catalysts are reduced separately. Consequently, Pd and Pt particles on these

Augustine, S. M.; Sachtler, W. M. H. On the Mechanism for the Platinum-Catalyzed Reduction of Rhenium in PtRe/γ-Al2O3. J. Catal. 1989, 116, 184-194. Barbier, J.; Lamy-Pitara, E.; Marecot, P.; Boitiaux, J. P.; Cosyns, J.; Verna, F. Role of Sulfur in Catalytic Hydrogenation Reactions. Adv. Catal. 1990, 37, 279. Boliver, C.; Charcosset, H.; Frety, R.; Primet, M.; Tournayan, L.; Betizeau, C.; Leclercq, G.; Maurel, R. Platinum-Rhenium/ Alumina Catalysts J. Catal. 1975, 39, 249-259. Boudart, M.; Dje´ga-Mariadassou G. Kinetics of Heterogeneous Catalytic Reactions; Princeton University Press: Princeton, NJ, 1981; pp 1-37. Cheng, Y.-M.; Chang, J.-R.; Wu, J.-C. Kinetic Study of Pyrolysis Gasoline Hydrogenation over Supported Palladium Catalyst. Appl. Catal. 1986, 24, 273-285. Chiou, J.-F.; Huang, Y.-L.; Lin, T.-B.; Chang, J.-R. Aromatics Reduction over Supported Platinum Catalysts. 1. Effect of Sulfur on the Catalyst Deactivation of Tetralin Hydrogenation. Ind. Eng. Chem. Res. 1995, 34, 4277-4283. Cooper, B. H.; Stanislaus, A.; Hannerup, P. N. Hydrotreating Catalysts for Diesel Aromatics Saturation. Hydrocarbon Process. 1993a, June. Cooper, B. H.; Pøgaard-Andersen, P., A.; Hannerup, P. N. Production of Swedish class I diesel using dual-stage process. AIChE Spring National Meeting, Houston, 1993. Cotton, F. A.; Wilkinson, G. Adv. Inorg. Chem., 5th ed.; John Wiley & Sons: New York, 1988; pp 58-68. Dossi, C.; Tsang, C. M.; Sachtler, W. M. H. Reforming-Type Catalysis with Zeolite-Supported PtRe. Energy Fuels 1989, 3, 468-474. Isaacs, B. H.; Petersen, E. E. The Effect of Drying Temperature on the Temperature-Programmed Reduction Profile of a Platinum/Rhenium/Alumina Catalyst J. Catal. 1982, 77, 43-52.

3898 Ind. Eng. Chem. Res., Vol. 35, No. 11, 1996 Katzer, J. R.; Sivasubramanian, R. Process and Catalyst Needs for Hydrodenitrogenation. Catal. Rev.-Sci. Eng. 1979, 20, 155208. Lin, T.-B.; Jan, C.-A.; Chang, J.-R. Aromatics Reduction over Supported Platinum Catalysts. 2. Improvement in Sulfur Resistance by Addition of Platinum to Supported Platinum Catalysts. Ind. Eng. Chem. Res. 1995, 34, 4284-4289. Little, L. H.; Kiselev, A. V.; Lygin, V. I. Infrared Spectra of Adsorbed Species; Academic Press: New York, 1966; p 62. Marcilly, C. Hydrotreating Hydrosulfurization; ENSPM-Formation Industri, Institute Francais du Petrole: 1990. McNicol, B. D. The Reducibility of Rhenium in Re on γ-Alumina and Pt-Re on γ-Alumina Catalysts. J. Catal. 1977, 46, 438. Purnell, S. K.; Chang, J.-R.; Gates, B. C. NaY Zeolite-Supported Re-Pt Catalysts Prepared from Organometallic Precursors:

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Received for review March 7, 1996 Revised manuscript received July 2, 1996 Accepted July 17, 1996X IE960134E

X Abstract published in Advance ACS Abstracts, September 15, 1996.