Role of the Ru and Support in Sulfided RuNiMo Catalysts in

1364

Energy & Fuels 2009, 23, 1364–1372

Role of the Ru and Support in Sulfided RuNiMo Catalysts in Simultaneous Hydrodearomatization (HDA), Hydrodesulfurization (HDS), and Hydrodenitrogenation (HDN) Reactions ´ lvarez-Galvań,† and J. L. G. Fierro*,† B. Pawelec,† R. M. Navarro,† P. Castanõ,‡ M. C. A Instituto de Cata´lisis y Petroleoquı´mica, Consejo Superior de InVestigaciones Cientı´ficas (CSIC), c/Marie Curie 2, Cantoblanco, E-28049 Madrid, Spain, and Departamento Ingenierıá Quı´mica, UniVersidad del Paı´s Vasco, Apdo 644, E-48080 Bilbao, Spain ReceiVed October 8, 2008. ReVised Manuscript ReceiVed December 2, 2008

Simultaneous hydrodesulfurization (HDS), hydrodearomatization (HDA), and hydrodenitrogenation (HDN) reactions have been studied over sulfided RuNiMo/Al2O3 catalysts. The effects of Ru promotion and alumina support modification with HY zeolite and P on catalyst performance have been studied using a synthetic feed containing dibenzothiophene, toluene, naphthalene, and pyridine. Activity tests were carried out in a semiautomatic microplant equipped with a continuous flow reactor, working under conditions similar to industrial practice (P ) 5 MPa, T ) 285-360 °C, and liquid hourly space velocity (LHSV) ) 3 and 4.5 h-1). The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (TPD-NH3), and X-ray photoelectron spectroscopy (XPS) techniques. Activity tests revealed that optimal Ru loading is 1 wt % (nominal). Under fixed experimental conditions (300 °C, 5 MPa, and LHSV ) 3 h-1), ultra-low sulfur diesel (S < 20 ppm S) was obtained over a Ru(1%)Ni(5%)Mo(14%)/γ-Al2O3 catalyst from a feed containing 18361 ppm S. However, this catalyst showed similar capability toward aromatics and pyridine removal as a commercial NiMo/Al2O3 catalyst. At a reaction temperature of 345 °C, the 5% HY-Al2O3 substrate led to a small increase in the hydrogenation capability of this catalyst but without enhancement of its HDS/HDN capability. On the contrary, the P-modified substrate resulted in a lower activity. The properties of the supported catalysts are discussed in terms of the support effect and Ru promotion.

1. Introduction Supported nanoparticles of transition-metal sulfides are known to be efficient systems for catalyzing hydrotreating reactions. In particular, since the pioneering work by Pecoraro and Chianelli,1 RuS2 has been recognized as one of the most active compounds for hydrotreating reactions. However, despite the numerous studies on Ru-containing catalysts (see ref 2 and references within), there is a large discrepancy concerning the RuS2 supported on different materials. Explanations include, among others, the nature of precursors, activation procedures, and supports employed for this purpose (see ref 3 and references within). The formation of well-dispersed metal sulfide species on the carrier surface is essential for the preparation of highperformance hydrotreating catalysts. Surface properties, such as acidity, affect the dispersion and local environment of the metal sulfide species. Although the study by Sun et al.4 indicated that the number of acid sites is not the main factor for enhancing the activity of ruthenium sulfide dispersed in acidic Y zeolite,4 the activity of the later was superior compared that of its * To whom correspondence should be addressed. Fax: (+34) 915-854760. E-mail: [email protected]. † Consejo Superior de Investigaciones Cientı´ficas (CSIC). ‡ Universidad del Paı´s Vasco. (1) Pecoraro, T. A.; Chianelli, R. R. J. Catal. 1981, 67, 430–445. (2) De los Reyes, J. A. Appl. Catal., A 2007, 322, 106–112. (3) De los Reyes, J. A.; Go¨bo¨lo¨s, S.; Vrinat, M.; Breysse, M. Catal. Lett. 1990, 5, 17–24. (4) Sun, Ch.; Peltre, M.-J.; Briend, M.; Blanchard, J.; Fajerwerg, K.; Krafft, J.-M.; Breysse, M. Appl. Catal., A 2003, 245, 245–256.

alumina-supported counterpart5 and less acidic KY zeolite.6 Similarly, the ruthenium sulfide supported on the more acidic Zr-MCM-41 substrate recorded higher activity than catalysts supported on less acidic MCM-41 and Al2O3, suggesting that activity could be favored by the suitable textural and acidic properties of the support.7 However, in that study, the effect of the support acidity was masked by the effect of the Zr interaction with ruthenium sulfide, which could contribute to the stabilization of the Ru-S bond, thus impeding the formation of metallic ruthenium species under the reaction conditions used.7 In comparison to supported binary systems (see ref 2 and references within), the ternary Ru-Ni(Co)-Mo formulation has been far less studied.8-14 The doping of commercial NiMo8-10 (5) Harvey, T. G.; Matheson, T. W. J. Catal. 1986, 101, 253–261. (6) Moraweck, B.; Bergeret, G.; Cattenot, M.; Kougionas, V.; Geantet, Ch.; Portefaix, J.-L.; Zotin, J. L.; Breysse, M. J. Catal. 1997, 165, 45–56. (7) Eliche-Quesada, D.; Rodrı´guez-Castelloń, E.; Jimeńez-Lo´pez, A. Microporous Mesoporous Mater. 2007, 99, 268–278. ´ lvarez-Galvań, M. C.; Pawelec, B. (8) Navarro, R. M.; Castanõ, P.; A Catal. Today doi: 10.1016/j.cattod.2008.08.038. (9) Cattenot, M.; Geantet, C.; Glasson, C.; Breysse, M. Appl. Catal., A 2001, 213, 217–224. (10) Hirschon, A. S.; Wilson, R. B., Jr. Appl. Organomet. Chem. 2004, 6, 421–428. (11) Hirschon, A. S.; Wilson, R. B., Jr.; Laine, R. M. Appl. Catal. 1987, 34, 311–316. (12) Xiao, F. S.; Xin, Q.; Guo, X. X. Appl. Catal., A 1993, 95, 21–34. (13) Isoda, T.; Nagao, S.; Ma, X.; Korai, Y.; Mochida, I. Energy Fuels 1996, 10, 487–492. (14) Isoda, T.; Nagao, S.; Ma, X.; Korai, Y.; Mochida, I. Energy Fuels 1996, 10, 482–496.

10.1021/ef800861c CCC: $40.75  2009 American Chemical Society Published on Web 01/20/2009

Simultaneous HDA, HDS, and HDN Reactions

and CoMo catalysts8,11-15 with RuS2 was reported. The hybrid formulation by mixing CoMo/Al2O3 with Ru/Al2O3 was also studied.16 The RuNiMo/Al2O3 catalyst (obtained by adding Ru to a previously sulfided catalyst) was found to be more active and more selective for the HDN of quinoline to propylbenzene than a commercial NiMo/Al2O3 catalyst.10 For Ru-doped NiMo/ Al2O3 hydrotreating catalysts, Cattenot et al.9 studied the possibility of creating a mixed decorated site (NiRu)-Mo-S phase by varying the Ni/Ru atomic ratio. In this case, the promoting effect was explained as a result of the substitution of Ni atoms by Ru.9 However, our previous study on the effect of Ru incorporation to a commercial Ni(Co)Mo/γ-Al2O3 indicated that the presence of isolated RuS2 phases located on the catalyst surface contributed to the overall catalytic activity and improved the catalyst hydrogenation function,8 in good agreement with the study by Isoda et al.13,14 This might indicate that the preparation method is a critical step to enhance catalytic performance. Considering literature reports on ternary RuNiMo systems, one question remains open: what would be the effect if the simultaneous wet impregnation of alumina support with Ru, Ni, and Mo salt solutions were to be employed instead of successive impregnation? In this sense, the simultaneous incorporation of Ru and Ni precursors into the calcined Mo/γAl2O3 was reported to be more effective than the successive incorporation of Ru and Ni promoters,9 but this situation might be different if three Ru, Ni, and Mo precursors will be simultaneously incorporated into the alumina carrier. For the above reasons, the motivation and goals of this study are to examine the catalytic behavior of the sulfided RuNiMo/ Al2O3 systems in simultaneous HDS, HDN, and HDA reactions using a feed that resembles the composition of real feed: dibenzothiophene (DBT), naphthalene (NP), toluene (Tol), and pyridine (Py). All catalysts were prepared by the simultaneous wet impregnation method followed by calcination. This preparation method represents a new approach for producing such kind of catalysts. Additionally, the effects of Ru content (0.5, 1.0, and 1.5 nominal wt %) and alumina modification with P and HY zeolite have been studied. The aim to add HY zeolite on the alumina substrate is to increase the surface acidity of the alumina alone, needed for the HDS and HDA of diesel, without increasing the cracking level. The only published works to date followed the incorporation of Ru on zeolite HY and alumina separately.5 The originality of our idea involves impregnating a hybrid HY-Al material with the salts of Ru, Ni, and Mo. Similarly to HY, we decided to incorporate phosphorus into the alumina support because the positive influence of the presence of phosphate species on the alumina-based hydrotreating catalyst properties is widely recognized in the literature (see ref 17 and references within). Better insight on the structure and properties of these ternary systems appears of interest because there is no consensus about the effect of the Ru promoter and there are only a few papers published in the last 20 years. The physicochemical properties of the calcined and spent catalysts have been evaluated by various techniques, and catalyst activity was compared to that of a commercial NiMo/ Al2O3 catalyst. 2. Experimental Section 2.1. Catalyst Preparation. A total of 10 catalysts with different formulations and metal loadings were prepared to obtain two series (15) Lee, D. K.; Lee, I. C.; Woo, S. I. Appl. Catal., A 1994, 109, 195– 210. (16) Mochida, I.; Sakanishi, K.; Ma, X.; Nagao, S.; Isoda, T. Catal. Today 1996, 29, 185–189. (17) Iwamoto, R.; Grimblot, J. AdV. Catal. 2000, 44, 417–503.

Energy & Fuels, Vol. 23, 2009 1365 of catalysts with different loadings (Ni ) 3 wt %; Mo ) 12 wt % and Ni ) 5 wt %; Mo ) 14 wt %). The materials used as supports were (i) alumina [pore volume (Hg) ) 0.62 cm3 g-1, specific Brunauer-Emmett-Teller (BET) area ) 228 m2 g-1; and average pore diameter ) 11.8 nm] provided by Girdler (Sud Chemie), (ii) a physical mixture of this alumina with HY zeolite (5 wt % HY on alumina), and (iii) a P-modified alumina (phosphoric acid was incorporated simultaneously with the metal precursors). The characteristics of the pure HY zeolite (provided by Conteka) are as follows: SiO2/Al2O3 molar ratio of 5.6, Na2O content 0.14 wt %, and unit cell of 2.454 nm. Allcatalystswerepreparedbythesimultaneousadsorption-impregnation method using aqueous solutions of RuCl3 (Sigma, reagent for analysis), Ni(NO3)2 · 4H2O (Merck, reagent grade), and/or ammonium heptamolybdate (NH4)6Mo7O24 · H2O (Merck, reagent grade). Impregnates were dried at 100 °C (0.6 °C min-1) for 1 h. Finally, the precursors were calcined in air using a heating ramp of 1.8 °C min-1 from 100 to 450 °C (for catalysts containing 3% Ni and 12% Mo) or 420 °C (for catalysts containing 5% Ni and 14% Mo) and kept at that temperature for 2 h. Such careful calcination was used to avoid the sintering of ruthenium oxide during calcination.8 In the case of the Ru1Ni5Mo14/P-Al catalyst, the incorporation of phosphorus was performed simultaneously with the incorporation of metal precursors. The impregnate was dried at 100 °C and then calcined at 420 °C as above. The oxide precursors are labeled RuxNiyMoz/Al, where x, y, and z indicate nominal loadings of Ru, Ni, and Mo, respectively, whereas Al indicates alumina support. A commercial NiMo/Al2O3 catalyst (HR-348 from Procatalyse; SBET ) 164 m2 g-1; and Mo, Ni, and P loading of 10.7, 2.5, and 2.64 wt %, respectively) was used as a reference. 2.2. Catalyst Characterization Techniques. 2.2.1. Chemical Analysis. Chemical composition of the calcined samples was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) using a Perkin-Elmer Optima 3300DV instrument. The sample was treated with a solution of HNO3, H2SO4, and HClO4 in Anton Paar Multiwave 3000 apparatus at 200 °C for 1 h. The experimental error of the measurements was about 10%. 2.2.2. N2 Adsorption-Desorption Isotherms. The specific BET surface areas (SBET) of the oxide catalysts were determined from the adsorption-desorption isotherms of nitrogen at -196 °C, recorded with a Micromeritics TriStar 3000 apparatus. Prior to the experiments, the samples were degassed at 273 °C in vacuum for 5 h. The volume of the adsorbed N2 was normalized to standard temperature and pressure. The specific areas of the samples were calculated by applying the BET method to the nitrogen adsorption data within the 0.05-0.25 range of the relative pressures. 2.2.3. X-ray Diffraction (XRD). XRD patterns of the powdered calcined samples were recorded by scanning a 2θ range of 6-80° (0.04°; 20 s) using an X’Pert PRO X-ray diffractometer (PANalytical). Phase identification was carried out by a comparison to the JCPDS database cards. The particle size of RuO2 (RuS2) and MoO3 crystallites was determined by means of the Scherrer equation using the most intensive reflections. 2.2.4. Temperature-Programmed Reduction (TPR). TPR experiments were conducted on a Micromeritics 2900 device provided with a TCD and interfaced to a data station. Prior to the experiments, the oxide catalysts (ca. 50 mg) were heated at a rate of 15 °C min-1 to a final temperature of 400 °C and kept at that temperature for 1 h under a flow of He to remove water and other contaminants. Then, the samples were cooled to ambient temperature in the same flow of He and finally exposed to a 10% H2/Ar gas flow at a total flow rate of 50 mL min-1 while heating at a rate of 15 °C min-1 up to a final temperature of 1000 °C. 2.2.5. Temperature-Programmed Desorption of Ammonia (TPD-NH3). The acidity of the calcined catalysts was determined by TPD-NH3. Measurements were carried out with the same apparatus described for TPR. After loading, the sample of 50 mg was pretreated in a He (Air Liquide, 99.996%) stream at 200 °C for 1 h. Then, the sample was cooled to 100 °C and exposed to a

1366 Energy & Fuels, Vol. 23, 2009

Pawelec et al.

Table 1. Composition of the Synthetic Feed N (ppm) S (ppm)

aromatics (wt %)

compound

content

pyridine S2C + DBT S 2C DBT total mono-aromatics (toluene) di-aromatics (naphthalene) S-containing aromatics (DBT)

1079 18361 11943 6418 40.1 23.8 12.7 3.7

5% NH3/He (Air Liquide) flow stream (50 mL min-1) for 0.5 h. After catalyst equilibration in a helium flow at this temperature, the ammonia was desorbed using a linear heating rate of 15 °C min-1 up to 1000 °C. 2.2.6. X-ray Photoelectron Spectroscopy (XPS) of Spent Catalysts. Photoelectron spectra of the spent catalysts were recorded on a VG Escalab 200R electron spectrometer equipped with a hemispherical electron analyzer, using a Mg KR (hν ) 1253.6 eV, and 1 eV ) 1.603 × 10-19 J) X-ray source. After degassing at 10-6 mbar, the samples were transferred to the ion-pumped analysis chamber, where the residual pressure was kept below 4 × 10-9 mbar during data acquisition. The binding energy (BE) of the Al 2p peak at 74.5 eV was taken as an internal standard. The accuracy of the BE values was (0.1 eV. Peak intensities were estimated by calculating the integral of each peak after subtracting a S-shaped background and fitting the experimental peak to a combination of Lorentzian/Gaussian lines of variable proportions. Atomic surface contents were estimated from the areas of the peaks, corrected using the corresponding sensitivity factors. 2.3. Catalytic Activity Measurements. A synthetic feed stream containing DBT, pyridine, naphthalene, toluene, and S2C, added to produce H2S during on-stream, was employed. The detailed composition of the model feed employed is shown in Table 1. The reaction conditions were: total hydrogen pressure of 5.0 MPa, T ) 273-360 °C, catalyst weight ) 1.0 g (for catalysts containing 3% Ni and 12% Mo) or 1.5 g (for catalyst containing 5% Ni and 14% Mo), catalyst particle size ) 0.25-0.30 mm, liquid hourly space velocity (LHSV) ) 4.5 or 3 h-1, H2 flow ) 3 LN h-1, and H2/oil ratio ) 558 LN/L. Before the reaction, the oxide precursors were dried (200 °C for 1 h) and then sulfided with a 10% H2S/H2 (1:10 mol ratio) mixture, raising the temperature to 400 °C (ramp 3 °C min-1) and maintaining this temperature for 2 h. After sulfidation, the catalyst was purged with inert gas to eliminate H2S, which could be physisorbed on the catalyst surface. For each sample, the activity data were obtained after 3.5 h in reaction at each temperature. The products of DBT transformation were biphenyl (BP), cyclohexylbenzene (CHB), and dicyclohexane (DCH). The products of naphthalene and toluene hydrogenation were tetralin, decaline (cis and trans) and methylcyclohexane (MCH), respectively. For both naphthalene and toluene, no products derived from the hydrocracking/hydrogenolysis were detected. The sum of these products was considered in the calculation of the selectivity toward hydrogenation products (HYD). HDN conversion was calculated as the total pyridine removal. Considering the different simultaneous reactions, the reaction products were defined as follows: (i) monoaromatics (wt %) ) toluene + biphenyl + cyclohexylbenzene + tetralin, (ii) di-aromatics (wt %) ) naphthalene, (iii) aromatics with S (wt %) ) DBT, and (iv) total aromatics (wt %) ) mono-aromatics + di-aromatics + aromatics with S. The synergy percentage was calculated as the difference between the experimental and theoretical conversions with respect to the theoretical one; the latter was defined as the algebraic sum of the monometallic catalyst conversions corresponding to the composition in bimetallic catalysts. For the HDS and HDN reactions, the specific reaction rates were calculated according to the following expression:

ri )

FiXi m

where ri is the specific rate (mol molMe s-1), Xi is the conversion of reactant i (DBT, pyridine), Fi is the molar flow rate of the re-

Table 2. Labeling, Nominal Metal Loadings, SBET, and Crystal Sizes (from XRD) of the Oxide Precursorsa labeling referenced Ru1/Al Mo12/Al Ru1Mo12/Al Ru1Ni3Mo12/ Al Ni5Mo14/ Al Ru0.5Ni5Mo14/ Al Ru1Ni5Mo14/ Al Ru1.5Ni5Mo14/ Al Ru1Ni5Mo14/ P-Al Ru1Ni5Mo14/ HY-Al

Ru (wt %)

Ni (wt %)

Mo (wt %)

SBET (m2 g-1)

1.0 1.0

Lower Metal Loading 2.5 10.7 164 196 12.0 168 12.0 161 3.0 12.0 163

0.0

Higher Metal Loading 5.0 14.0 135

1.0

RuO2b (nm)

MoO3c (nm) nde

16.4 13.4 22.6

24.4 34.7 16.5

33.4

0.5

5.0

14.0

143

20.0

14.5

1.0 (0.36) 1.5 (0.45) 1.0 (0.29) 1.0 (0.26)

5.0 (3.7) 5.0 (3.7) 5.0 (3.7) 5.0 (5.1)

14.0 (10.1) 14.0 (10.0) 14.0 (9.8) 14.0 (13.1)

149

13.4

14.6

146

12.4

13.7

158

11.8

11.5

165

nd

nd

a Metal loading determined by the ICP analysis is given in parenthesis. b RuO2 (JCPDS card 00-040-1290). c MoO3 (JCPDS card 00-001-0706). d Commercial NiMo/Al catalyst from Procatalyse (HR-348). e nd ) not determined.

actant i (mol s-1), and m refers to the metal atoms per gram of catalyst (molMe gcat-1).

3. Results and Discussion 3.1. Characterization of Oxide Precursors. The catalysts prepared are listed in Table 2 along with metal content, BET specific area, and crystal sizes (from XRD). Ruthenium oxide is known to be volatile.2 Thus, careful calcination was employed to avoid as much as possible ruthenium loses. Besides this, chemical analysis of the ternary catalysts by ICP showed much lower Ru content than the nominal one (Table 2). Chemical analysis of the catalysts containing 3 wt % Ni and 12 wt % Mo is similar to that of the commercial NiMo/γ-Al2O3 catalyst (2.5 wt % of Ni and 10.7 wt % of Mo). For the catalysts with nominal contents, 5 wt % Ni and 14 wt % Mo, chemical analysis of Mo approached that of the reference sample but that of nickel was somewhat higher but still below the nominal one. The BET area values of all catalysts (Table 2) in the 196-143 m2 g-1 range are relatively high. As expected, the catalysts with a higher metal loading have a slightly lower SBET than their counterparts with lower metal loadings. All catalysts have a lower SBET than the alumina carrier (228 m2 g-1). In addition, the Ru1/Al catalyst has the largest SBET among the catalysts studied (196 m2 g-1). All of the catalysts studied have the same average pore diameters (6.6 ( 0.1 nm), which are much lower than those of the pure alumina carrier (11.8 nm). The formation of crystalline phases was verified by X-ray powder diffraction of the oxide precursors (Figure 1). All samples showed the XRD features of the alumina, whose main diffraction lines overlap with that of nickel oxide species. All Ru-containing catalysts have the characteristic reflections of the RuO2 (JCPDS 00-040-1290), whereas all Mo-containing catalysts have the typical reflections of the MoO3 phase (JCPDS 00-001-0706). The exception is the monometallic Mo12/Al sample, which shows only diffraction lines of the Al2(MoO4)3 spinel phase (JCPDS 00-023-0764). The Ru1Ni3Mo12/HY-Al catalyst does not reveal any phases, probably because of the overlapping of their reflections with the zeolite peaks. The mean crystallite sizes, as calculated using the Scherrer equation, are compiled in Table 2. For all catalysts, the RuO2 crystallite sizes


Energy & Fuels, Vol. 23, 2009 1367

Figure 2. TPR profiles of the oxide precursors supported on (a) γ-Al2O3 and (b) γ-Al2O3 modified with HY or P.

Figure 1. XRD patterns of the oxide precursors: R, RuO2; M, MoO3; A, Al2O3.

are in the 12-23 nm range, whereas those of the MoO3 crystallites are in the 12-35 nm range. According to these results and that reported in our previous study on the RuNiMo/ γ-Al2O3 catalysts prepared by successive impregnation,8 we can conclude that metal oxide dispersion in samples prepared by simultaneous impregnation is poorer than that in samples obtained via successive impregnation. Considering the TPR results (Vide infra), the formation of well-dispersed NiMoO4 crystallites is possible, even though they were not detected as a result of the lower detection limit of the XRD technique. It is noteworthy that, irrespective of the total metal loadings, the molybdenum catalysts promoted by both Ru and Ni recorded a much lower MoO3 crystallite size than mono- and bimetallic catalysts. The redox behavior of the oxide phases was studied by TPR analysis. The TPR profiles of the catalysts supported on alumina are shown in Figure 2a, whereas those supported on HY- and P-loaded alumina are shown in Figure 2b. The two overlapping hydrogen consumption peaks at 188-213 and 222-252 °C are associated with a well-dispersed ruthenium oxide species, while the high-temperature peak is related to the reduction of RuO2 species.18 Thus, in good agreement with the study by Isoda et al.,13,14 the comparison of all TPR profiles indicates that Mo and Ru exist as separate phases on the surface of all of the supports. The TPR profile of the Mo12/Al catalyst (Figure 2a) shows two peaks at 458 and 776 °C associated with two reduction steps of the MoO3 species (the first, MoO3 f MoO2 and the second, MoO2 f Mo0).19,20 A third peak, which appears at an even higher temperature (>1000 °C), could be due to the (18) Betancourt, P.; Rives, A.; Hubaut, R.; Scott, C. E.; Goldwasser, J. Appl. Catal., A 1998, 170, 307–314.

reduction of a minor proportion of molybdenum species strongly interacting with the alumina surface or even to sulfate impurities in the alumina.21 The reduction of MoO2 to Mo0 is more difficult than the reduction of the MoO3 species because the former species are interacting more strongly with the support. On the other hand, the reduction peak of the Ni2+ species in the octahedral coordination is known to overlap with another of the Mo6+ species,21 whereas the reduction of bulk NiO to Ni0 occurs at 363 °C. Thus, a broad peak with maximum at 432 °C in the TPR profiles of ternary RuNiMo catalysts is probably due to the reduction of both the NiO and R-NiMoO4 phases, whose small crystallites cannot be detected by XRD. Considering the intensity of the peaks, it seems that the amount of the R-NiMoO4 phase increases when the molybdenum catalyst is doubly promoted with Ru and Ni. In comparison to the Mo12/ Al, the Ni5Mo14/Al sample records an additional peak at 620 °C, which can be assigned to the reduction of Ni2+ species in the tetrahedral coordination.22 Finally, it can be noted that all ternary samples have a much larger H2 consumption in the hightemperature region than the binary Ni5Mo14/Al catalyst because of a spillover effect from the Ru0 particles.8 Finally, an increase of catalyst acidity in P- and HY-modified alumina was confirmed by the TPD-NH3 technique. The TPD-NH3 profiles of the calcined Ru1Ni5Mo14/Al, Ru1Ni5Mo14/ HY-Al, and Ru1Ni5Mo14/P-Al catalysts are shown in Figure 3. From these profiles, it is clear that the HY-Al-supported catalyst has a slightly larger amount of weak acid sites than its P-loaded counterpart. Considering the area under the curves (Figure 3), both catalysts showed much larger total acidity than unmodified Ru1Ni5Mo14/Al. Thus, from TPD-NH3 profiles, one might to conclude that P and HY modification of the alumina substrate led to the formation of weak strength acid sites. 3.2. Characterization of the Spent Catalysts by XPS. Because the activity behavior discussed below has been attributed to the formation of metal sulfides, the XPS technique has been used to examine the chemical state of the elements of (19) Arnoldy, P.; de Jong, J. C. M.; Moulijn, J. A. J. Phys. Chem. 1985, 89, 4517–4526. (20) Chary, K. V. R.; Reddy, K. R.; Kumar, C. P. Catal. Commun. 2001, 2, 277–284. (21) Burch, R.; Collins, A. Appl. Catal. 1985, 18, 389–400. (22) Barrio, V. L.; Arias, P. L.; Cambra, J. F.; Guëmez, M. B.; Pawelec, B.; Fierro, J. L. G. Appl. Catal., A 2003, 242, 17–30.


Pawelec et al.

Figure 3. TPD-NH3 profiles of the oxide Ru1Ni5Mo14/Al, Ru1Ni5Mo14/ HY-Al, and Ru1Ni5Mo14/P-Al catalysts. Table 3. Binding Energies (eV) of the Core Electrons of the Spent Catalysts catalyst

Al 2pa Ru 3d5/2b Mo 3d5/2

Ru1/Al Mo12/Al Ru1Mo12/Al Ru1Ni3Mo12/Al referencec

LHSV ) 4.7 h-1 74.7 279.6 74.7 229.3 74.7 279.7 229.3 74.7 279.8 229.3 74.7 229.2

Ni5Mo14/Al Ru0.5Ni5Mo14/Al

LHSV ) 3.0 h-1 74.7 229.3 74.7 280.7 229.3

Ru1Ni5Mo14/Al Ru1.5Ni5Mo14/Al Ru1Ni5Mo14/HY-Al

74.7 74.7 74.7

280.0 279.9 280.6

229.3 229.3 229.3

Ru1Ni5Mo14/P-Al

74.7

280.6

229.3

referencec

74.7

229.2

Ni 2p3/2

854.5 854.5 854.3 854.3 (71) 856.3 (29) 854.2 854.3 854.2 (60) 856.3 (40) 853.2 (18) 854.2(37) 856.3 (45) 854.5

S 2p 162.1 162.2 162.1 162.1 162.0 162.0 162.0 162.0 162.1 162.0 161.9 162.0

The Al 2p peak was taken as an internal pattern (BE of Al 2p ) 74.5 eV). b The BE of the Ru 3d5/2 core level was estimated after deconvolution of the C 1s peak. c Commercial NiMo/γ-Al2O3 catalyst from Procatalyse (HR-348). a

the spent catalysts. It is noteworthy that the calcined catalysts in this study were presulfided with a H2/H2S mixture at 400 °C for 2 h and then additionally sulfided during an on-stream reaction by S2C added to the feed. Employing such a procedure, one might expect a total sulfidation of the oxide phases. The BE values of Ru 3d5/2, Mo 3d5/2, Ni 2p3/2, and S 2p core levels are compiled in Table 3. For the Ru1Ni5Mo14/HY-Al catalyst, the Si 2p peak (from zeolite) with BE at 103.3 eV was also observed. Similarly, the Ru1Ni5Mo14/P-Al catalyst displayed the P 2p peak with a BE of 134.4 eV. The S 2p energy region of all catalysts showed a single component with BE in the 161.9-162.2 eV range, which is a characteristic of sulfide (S2-) species.23 Large differences in the BE of the Ru 3d5/2 peak were observed for the Ru-containing catalysts (Table 3). The BE of the Ru 3d5/2 peak was considered only after deconvolution of the C 1s peak because the Ru 3d3/2 component overlaps with the C 1s peak, arising from hydrocarbon contaminations. In addition, the identification of ruthenium species is difficult (23) Pawelec, B.; Damyanova, S.; Mariscal, R.; Fierro, J. L. G.; Sabrados, I.; Petrov, L. J. Catal. 2004, 223, 86–97.

because the binding energy of the Ru 3d5/2 peak of Ru0 is very close to that of RuS2.24 Taking into account the literature reports, we assume that the higher BE (ca. 280.7 eV) corresponds to RuS2 species, which has a pyrites structure, whereas the lower BE (in the 279.6-280.0 eV range) corresponds to ruthenium intermediate compounds between metallic and sulfide. These species were observed previously,25,26 and they were called “surface sulfide ruthenium” species.25 These intermediate Ru species are present on the surface of the spent catalysts, with theexceptionofRu0.5Ni5Mo14/Al,Ru1Ni5Mo14/P-Al,Ru1Ni5Mo14/ HY-Al samples, in which the RuS2 phase was present. Interestingly, the formation of RuS2 is observed only for the catalysts showing partial sulfidation of their nickel species (Vide infra). In the case of the Ru0.5Ni5Mo14/Al, Ru1Ni5Mo14/P-Al, and Ru1Ni5Mo14/HY-Al catalysts, this might indicate that the sulfidation of the Ru species is facilitated when NiMoO4 species are formed. The Mo 3d5/2 peak of all spent catalysts exhibited binding energy at 229.3 eV because of MoS2 species.27 In this study, all catalysts showed complete sulfidation of molybdenum species. On the contrary, partial sulfidation of the molybdenum species was observed by us previously for the spent RuNiMo/ γ-Al2O3 catalysts prepared by successive impregnation.8 Concerning the nickel species, the BE at ca. 856.3 eV indicates the presence of unsulfided nickel species, whereas the peak at about 854.2 eV is due to nickel sulfide species.24 The former BE coincides with that reported for the NiMoO4 species,28 indicating a strong interaction between Ni and Mo. The Ru1Ni5Mo14/P-Al catalyst is the only one showing two types of nickel sulfide species, as inferred from the components at BE values of 853.2 and 854.2 eV. Considering the percentage of nickel sulfide (Table 3), the Ru1Ni5Mo14/Al catalyst records the total sulfidation of nickel species, whereas both Ru1Ni5Mo14/HY-Al and Ru1Ni5Mo14/P-Al catalysts showed partial sulfidation of nickel species. This points to the difficulty of sulfide nickel species in the latter catalysts. The atomic ratios calculated from the peak intensities of the elements are given in Table 4. Considering the surface exposure of the molybdenum and nickel species, as deduced from the Mo/Al and Ni/Al atomic ratios, respectively, two observations are made: (i) the Ru-promoted samples revealed a larger molybdenum and nickel species surface exposure than their unpromoted Ni5Mo14/Al counterpart, and (ii) HY- and Pmodified alumina led to the enhancement of molybdenum and nickel species surface exposure, with the former modification being more effective than the latter. In good agreement with the Ru loadings (0.5-1.5 wt %), all ternary catalysts have small differences in the Ru species surface exposure. The Ru/Al catalyst is the only one that showed a S/Ru atomic ratio much larger than those expected for the formation of the ruthenium sulfide species. This high atomic ratio can be explained considering the formation of -SH groups attached to the catalyst surface. Finally, because the S/(Ru + Ni + Mo) atomic ratio for complete sulfided components (MoS2, Ni3S2, and RuS2) is in the order of 1.73, the experimental values of this ratio ranging from 1.39 to 1.56 points to the incomplete sulfidation of all ternary catalysts. (24) Mitchell, P. C. H.; Scott, C. E.; Bonnelle, J.-P.; Grimblot, J. G. J. Catal. 1987, 107, 482–489. (25) Kuo, Y.-J.; Tatarchuk, B. J. J. Catal. 1988, 112, 229–249. (26) De Los Reyes, J. A.; Vrinat, M.; Geantet, Ch.; Breysse, M. Catal. Today 1991, 10, 645–664. (27) Arias, P. L.; Cambra, J. F.; Guëmez, M. B.; Legarreta, J. A.; Pawelec, B.; Fierro, J. L. G. Bull. Soc. Chim. Belg. 1995, 104, 197–204. (28) Hernańdez-Huesca, R.; Me´rida-Robles, J.; Maireles-Torres, P.; Rodrı´guez-Castelloń, E.; Jimeńez-Lo´pez, A. J. Catal. 2001, 203, 122–132.



Table 4. Surface Atomic Ratios of the Spent Catalysts catalyst

Ru/Al Nitotal/Al Ni-S/Al Mo/Al S/Al

S/(Ru + Ni + Mo)

LHSV ) 4.7 h-1 Ru1/Al Mo12/Al Ru1Mo12/Al Ru1Ni3Mo12/ Al referencea Ni5Mo14/Al Ru0.5Ni5Mo14/Al Ru1Ni5Mo14/ Al Ru1.5Ni5Mo14/ Al Ru1Ni5Mo14/ HY-Al Ru1Ni5Mo14/ P-Al referencea a

0.013 0.007 0.003

0.066

0.066

0.079 0.103 0.122

0.052

0.052

0.078 0.181 0.217 0.266

6.0 2.3 1.97 1.39

0.107

0.222

1.40

0.003 0.005

LHSV ) 3.0 h-1 0.070 0.070 0.139 0.098 0.070 0.537 0.083 0.083 0.162

0.326 0.989 0.360

1.56 1.55 1.44

0.007

0.074

0.074

0.155

0.363

1.54

0.005

0.126

0.076

0.256

0.565

1.46

0.005

0.178

0.066

0.450

0.880

1.39

0.055

0.055

0.137

0.291

1.52

Commercial NiMo/γ-Al2O3 catalyst from Procatalyse (HR-348).

Summarizing, the XPS data indicate that the degree of sulfidation of the catalysts depends upon both the metal loadings and the support composition, being more difficult for the catalysts with lower metal loadings and supported on alumina modified with zeolite. 3.3. Effect of Ru Doping on the Activity of Mo12/Al Catalyst. 3.3.1. HDS. To clarify whether Ru might exert a synergic effect on the catalytic activity of the NiMo/Al2O3 base catalyst, the Ru1/Al, Mo12/Al, Ru1Mo12/Al, and Ru1Ni3Mo12/ Al catalysts were tested in simultaneous HDS/HDA/HDN reactions performed at P ) 5.0 MPa, T ) 285-360 °C, and LHSV ) 4.5 h-1. A commercial NiMo/γ-Al2O3 catalyst (with similar Ni and Mo loadings as the ternary sample) was used as a reference. The synthetic feedstock contains toluene, naphthalene, dibenzothiophene, and pyridine, whose contents are shown in Table 1. In this feedstock, both toluene and naphthalene resemble the structure of aromatic compounds found in the diesel fraction [typical light gas oil (LGO)]. Moreover, this model feed provides additional information on the inhibition of the HDS reaction by both naphthalene and pyridine. The effect of the promotion of the Mo catalyst and the influence of the reaction temperature on the remaining sulfur, di-aromatic, and mono-aromatic content in the reactor effluents are shown in parts a-c of Figure 4, respectively. The sulfur content in the reactor effluents decreased upon raising the temperature from 280 to 360 °C. In the HDS reaction at 360 °C, the sulfur concentration remaining in the reactor effluent was much lower in the case of Ru1Mo12/Al (711 ppm S) as compared to the Mo12/Al and Ru1/Al catalysts (2116 and 3712 ppm S, respectively), indicating the Ru promotion of the HDS reaction, in good agreement with another report.24 However, the synergy effect between Ru and Mo did not occur. Considering the XRD and TPR results (Table 2 and Figure 3, respectively), this is probably due to the relatively large MoO3 crystals (34.7 nm) present in the Ru1Mo12/Al catalyst, which were separated from smaller RuO2 crystals (13.4 nm). We will come to this point later when discussing the activity of the ternary RuxNi5Mo14/Al catalysts. Contrary to binary Ru1Mo12/Al, the ternary Ru1Ni3Mo12/Al catalyst fully eliminated sulfur in the hydrotreating of feedstock at 300 °C. The HDS activity of this ternary catalyst is larger than that of the commercial NiMo/γ-Al2O3 sample, indicating that Ru incorporation was effective in promoting HDS activity. Finally, considering product distribution, BP and CHB were the main products of DBT transformation over all of the catalysts

Figure 4. Hydrotreating of the synthetic feed over catalysts with lower metal loadings. Influence of the reaction temperature on the remaining (a) sulfur, (b) di-aromatics, and (c) mono-aromatics in the reactor effluents (P ) 5.0 MPa, T ) 285-360 °C, and LHSV ) 4.5 h-1).

studied. BP, which appears as the main product, is produced via the direct desulfurization pathway (DDS), whereas CHB is produced from tetrahydrodibenzothiophene (THDBT) via the hydrogenation route (HYD) of this reaction. 3.3.2. HDA. The influence of the reaction temperature on the remaining di-aromatic and mono-aromatic content in the reaction effluents is displayed in parts b and c of Figure 4. The comparison of both figures clearly indicates that the amount of mono-aromatics increases simultaneously with a decrease in the amount of di-aromatics, as a consequence of the cracking of di-aromatics and thus forming mono-aromatics. Considering the feed composition (DBT, naphthalene, toluene, and pyridine), a stronger adsorption of naphthalene than that of toluene onto the catalyst surface could be expected. This is because the strength of adsorption is related to the molecular weight of the molecule. Naphthalene is generally believed to adsorb in flat mode through its π electrons onto the catalyst surface,29 and its hydrogenation is easier than toluene.30 This is related to a decrease in the resonance energy per aromatic ring as well as to differences in the π-electron cloud density in the aromatic ring as a result of the inductive effect of the methyl group.31 Considering the di-aromatic content in the reactor effluents at 300 °C, the activity trend is Ru1Ni3Mo12/Al > industrial > (29) Girgis, M. J.; Gates, B. C. Ind. Eng. Chem. Res. 1991, 30, 2021– 2058. (30) Pawelec, B.; Mariscal, R.; Navarro, R. M.; van Bokhorst, S.; Rojas, S.; Fierro, J. L. G. Appl. Catal., A 2002, 225, 223–237.


Figure 5. Comparison of remaining N content after hydrotreating of the model feed over sulfided catalysts with lower metal loadings (285 °C, P ) 5 MPa, LHSV ) 4.5 h-1, and steady-state conditions).

Ru1Mo12/Al ≈ Mo12/Al > Ru1/Al (Figure 4b), in close agreement with the HDS activity trend (Vide supra). It is noteworthy that an increase in the reaction temperature from 300 to 360 °C led to a decrease in the mono-aromatics formed (Figure 4c) because of their cracking at high reaction temperatures. Furthermore, it is important to mention that, in the reaction at 360 °C, the Ru1Ni3Mo12/Al catalyst records a lower amount of remaining mono-aromatics than the reference catalyst and the Mo12/Al and Ru1Mo12/Al catalysts, confirming the enhancement of the activity achieved employing ternary catalyst formulation (Ru1Ni3Mo12/Al). 3.3.3. HDN. With the exception of the monometallic Ru1/ Al catalyst, the pyridine conversion over all 3 wt % Ni and 12 wt % Mo catalysts was the total at temperatures higher than 285 °C. Considering the feed composition (DBT, naphthalene, toluene, and pyridine), one might expect that both basic organonitrogen compounds and polycyclic aromatics inhibit the HDS reaction.32 In particular, basic organonitrogen compounds, such as pyridine, are ranked among the strongest inhibitors of the HDS reaction. For a high concentration of nitrogen- and sulfur-containing compounds, as is the case of the model feedstock used in this study, such inhibition is sufficiently wellunderstood.29 The HDN activity of the catalysts in the reaction at 285 °C is compared in Figure 5. As seen in this figure, catalyst activity follows the trend: Ru1/Al (872 ppm N) > Mo12/Al (333 ppm N) > Ru1Mo12/Al (140 ppm N) > a conventional NiMo/Al2O3 (60.7 ppm N) > Ru1Ni3Mo12/Al (none). Two main conclusions could be drawn from this trend: (i) the inhibition of the HDN reaction on the Ru1Mo12/Al catalyst by Ru and (ii) the larger HDN capacity of the ternary Ru1Ni3Mo12/Al catalyst with respect to the commercial NiMo/γ-Al2O3 sample, indicating that Ru inhibition of the HDN reaction could be eliminated when double Ru and Ni promotion of the Mo catalyst is used. For the binary Ru1Mo12/Al catalyst, the Ru inhibition of the HDN reaction was eliminated by raising the reaction temperature from 285 to 300 °C (data not shown here). At a higher reaction temperature of 360 °C, pyridine conversion over sulfided Ru1/ Al was only 84.5% (167 ppm of N in the reactor effluent). Summarizing, the HDN activity trend is the same as for sulfur removal. Moreover, the catalysts record similar activities in both pyridine and di-aromatic elimination (Ru1Ni3Mo12/Al > conventional NiMo/Al2O3 > Ru1Mo12/Al ≈ Mo12/Al > Ru1/Al). It is generally assumed that hydrogenolysis and hydrogenation (31) Moreau, C.; Geneste, P. In Theoretical Aspects of Heterogeneous Catalysis; Moffat, J. B., Ed.; Van Nostrand Reinhold: New York, 1990; p 256. (32) van Looij, F.; van der Laan, P.; Stork, W. H. J.; DiCamillo, D. J.; Swain, J. Appl. Catal., A 1998, 170, 1–12.

Pawelec et al.

Figure 6. Influence of the Ru loading on the HDS, total aromatic, and di-aromatic conversions in the hydrotreating of the synthetic feed over sulfided RuxNi5Mo14/Al catalysts (x ) 0.5, 1.0, and 1.5 nominal wt % Ru). Reaction conditions were T ) 300 °C, P ) 5.0 MPa, LHSV ) 3 h-1, and TOS ) 3 h.

reactions proceed over separate sites.33 Because pyridine adsorbs either flat or end-on through the sp2 lone-pair electrons of the nitrogen atoms on both Lewis and Brønsted acid sites,34 the decrease of the mono-aromatic formation at the reaction temperature of 360 °C over the Ru1Ni3Mo12/Al catalyst (Figure 4c) could be due to the competitive adsorption of the pyridine on the sites where hydrogenation occurs. 3.4. Optimization of Ru Loading. In this section, simultaneous DBT, naphthalene, toluene, and pyridine conversions have been investigated by comparing the activity of ternary RuNiMo catalysts having a slightly larger Ni and Mo loading with respect to a conventional NiMo/Al2O3 catalyst (total metal loading in the range of 10-20.5 wt %). The feed composition is described in Table 1. The influence of the Ru loadings (0.5, 1.0, and 1.5 wt %) on total sulfur, aromatic, and di-aromatic conversions in the reaction at 300 °C is shown in Figure 6. As seen in this figure, the maximum HDS, total aromatic, and di-aromatic conversions were achieved on the catalyst doped with 1 wt % (nominal content) Ru. 3.5. Effects of the Reaction Temperature and Support Modification. The influence of the alumina modification by P and HY on the catalytic response of ternary RuNiMo catalysts in the simultaneous HDS, HDN, and HDA reactions was studied with the same synthetic feed employed in the experiments described above and under the same reaction conditions (P ) 5 MPa, T ) 285-360 °C, and LHSV ) 3 h-1). Figure 7A shows the influence of the temperature and support on the HDS and HYD capabilities of the Ru1Ni5Mo14/HY-Al, Ru1Ni5Mo14/ P-Al, and Ru1Ni5Mo14/Al catalysts. The data in this figure indicate that (i) the total HDS conversion was obtained in the reaction at 300 °C over Al- and HY-Al-supported catalysts, (ii) temperatures as higher as 320 °C are needed for total HDS conversion over P/Al-supported catalyst, (iii) irrespective of the support, the HYD capability increases upon raising the temperature from 285 to 360 °C, and (iv) the HYD conversion at 360 °C follows the trend: Ru1Ni5Mo14/HY-Al > Ru1Ni5Mo14/ Al > Ru1Ni5Mo14/P-Al. At 300 °C, the catalyst supported on HY-modified alumina showed a larger HDS than HYD capacity than its counterparts supported either on P-modified or nonmodified alumina (Figure 7B). The top panel of Figure 8 compares the HDS conversion at 300 °C for bimetallic Ni5Mo14/Al and reference catalysts to those of the ternary Ru1Ni5Mo14 catalysts. Both Ru1Ni5Mo14/ Al and Ru1Ni5Mo14/HY-Al catalysts record the same HDS activities. A similar conclusion might be reached concerning (33) Nagai, M.; Sato, T.; Aiba, A. J. Catal. 1986, 97, 52–58. (34) Kno¨zinger, H. AdV. Catal. 1976, 25, 184–271.



Figure 7. (A) Influence of the temperature and support composition on the HDS and HYD capabilities of the Ru1Ni5Mo14 catalysts supported on P-Al, HY-Al, and Al2O3 (T ) 265-360 °C, P ) 5 MPa, and LHSV ) 3 h-1). (B) Comparison of the HDS and HYD capabilities of those catalysts in the reaction at 300 °C.

total aromatic and di-aromatic conversions at 300 °C (middle and bottom panels of Figure 8, respectively). Figure 9 compares the HDS and HDN reaction rates at 285 °C for the Ru1Ni5Mo14 catalysts supported on Al, P-Al, and HY-Al materials to those of the commercial NiMoP/γ-Al2O3 catalyst. All catalysts were more active in HDS than in the HDN reaction because the latter is more difficult than the former.35 Interestingly, all ternary catalysts were less active in HDN than the commercial sample. For the HDS reaction, the reaction rates follow the trend: Ru1Ni5Mo14/Al ≈ Ru1Ni5Mo14/HY-Al > commercial NiMoP/γ-Al2O3 > Ru1Ni5Mo14/P-Al, indicating that only both former catalysts were more active in the HDS reaction at 285 °C than the commercial one. 3.6. Catalyst Activity-Structure Correlation. The generally accepted description for sulfided Ni-Mo catalysts is that small MoS2 crystallites lie with their basal planes parallel to the Al2O3 surface or are edge-bonded to the support surface and Ni ions, as promoters, are deposited on the edges of the MoS2 crystallites.35 Because the ternary systems studied in this work are more complex than the binary one, the contribution of the metallic Ru or RuS2 species to catalytic activity is superimposed by the contribution of Ni and Mo species. Considering the literature reports (see ref 2 and references therein), we assume that the presence of RuS2 on the catalyst surface is more favorable than the formation of Ru metal species because the former species might chemisorb much larger quantities of hydrogen than metallic ruthenium surfaces covered by partial monolayers of adsorbed sulfur.36 In this study, catalyst activation by sulfidation with a 10% H2S/H2 mixture (1:10 molar ratio) at 400 °C followed by (35) Ho, T. C. Catal. ReV. Sci. Eng. 1988, 30, 117–160.

Figure 8. Influence of the support and Ru promotion on the HDS, total aromatic, and di-aromatic conversions in the hydrotreating of the synthetic feed over Ni5Mo14/Al and Ru1Ni5Mo14 catalysts supported on Al, P-Al, and HY-Al (T ) 300 °C, P ) 5.0 MPa, LHSV ) 3 h-1, and TOS ) 3 h).

Figure 9. Comparison of the HDS and HDN reaction rates of the Ru1Ni5Mo14 catalysts supported on Al, P-Al, and HY-Al to those of a conventional NiMoP/γ-Al2O3 (T ) 285 °C, P ) 5.0 MPa, LHSV ) 3 h-1, and TOS ) 3 h).

resulfidation during on-stream conditions led to the formation of Ru0 and RuS2 species of pyrite-like structure in the spent Ru1Ni5Mo14/Al and Ru1Ni5Mo14/HY-Al catalysts, respectively. For both catalysts, the ruthenium species are isolated from nickel


and molybdenum species. The active sites of the ruthenium sulfide species of the Ru1Ni5Mo14/HY-Al catalyst consist of superficial anionic vacancies (similar to those of the molybdenum sulfide phase).37 The small RuS2 particles show some preferential exposed planes, favoring hydrogenation properties, as already mentioned for alumina-supported ruthenium sulfide catalysts.26 Additionally, in comparison to the Ru1Ni5Mo14/Al catalyst, the Ru1Ni5Mo14/HY-Al sample shows more favorable structural and morphological properties, such as (i) a larger Mo surface exposure (Table 4), (ii) a larger metal oxide dispersion, as deduced from XRD (Table 2), (iii) an easier reduction of the RuO2 phase, as derived from TPR (Figure 2b), (iv) a larger SBET (Table 2), and (v) a larger acidity linked to the presence of zeolite HY. For the most active Ru1Ni5Mo14/Al catalyst, the absence of sintering of Ru particles during sulfidation was confirmed by X-ray line broadening (data not shown here). After sulfidation, this sample showed the RuS2 species (JCPDS 00012-0737) having a mean particle size of 13 nm, whereas its oxide precursor showed RuO2 particles with a size of 13.4 nm, as determined from XRD line-broadening measurements of the peak at 54.43° of 2θ. The sulfided Ru1Ni5Mo14/Al catalyst did not show the crystalline MoS2 phase, indicating that this phase could be amorphous or with a crystal size below the detection limit of the technique (

Role of the Ru and Support in Sulfided RuNiMo Catalysts in

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