Effects of Phosphorus Content on Simultaneous Ultradeep HDS and

Article pubs.acs.org/IECR

Effects of Phosphorus Content on Simultaneous Ultradeep HDS and HDN Reactions over NiMoP/Alumina Catalysts Matheus Dorneles de Mello,*,†,‡ Flávia de Almeida Braggio,† Bruno da Costa Magalhaẽ s,† José Luiz Zotin,§ and Mônica Antunes Pereira da Silva*,† †

Escola de Química, Universidade Federal do Rio de Janeiro, C.P. 68542, 21949-900, Rio de Janeiro, Rio de Janeiro, Brazil R&D Center, PETROBRAS S.A., 950 Avenida Horácio Macedo, 21949-915 Rio de Janeiro, Rio de Janeiro, Brazil

§

S Supporting Information *

ABSTRACT: The effects of phosphorus content on competitive hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and hydrodenitrogenation (HDN) of quinoline (Q) over NiMo catalysts were evaluated. Reactions were carried out in a trickle-bed high-pressure flow microreactor. HDS of 4,6-DMDBT was strongly inhibited at Q concentrations of 90 ppmw N, mostly hydrogenation (HYD) route in HDS, suggesting that 4,6-DMDBT and Q compete for the same hydrogenation active sites, which was confirmed by the products’ distribution in HDN reactions. Morphology and nature of active sites promoted by phosphorus addition led to different activity performance on competitive HDS and HDN reactions, as evidenced by TOF values. At low concentrations of Q, promoted catalysts maintained activity for both HDS and HDN. High Q levels (above 90 ppmw N) decreased HDS and HDN activity due to stronger inhibition of catalysts. The addition of 1 wt % of phosphorus showed superior activity, attributed to a combination of better dispersed NiMoS active sites and Brønsted acidity.

1. INTRODUCTION Hydrotreating catalysts have played a crucial role in producing cleaner fuels by removing heteroatoms and saturating low aromatic compounds.1,2 The new ultralow S specifications for transportation fuels represent a major operational challenge for the petroleum refining industry since it is essential to achieve deep hydrodesulfurization (HDS) of most refractory sulfurcontaining compounds, such as 4,6-dimethyldibenzothiophene (4,6-DMDBT).3−6 It is known that 4,6-DMDBT reacts by two main reaction routes: direct desulfurization (DDS), with cleavage of a C−S bond, or a hydrogenation route (HYD), which promotes the formation of intermediates partially hydrogenated followed by desulfurization to cyclohexylbenzenes and bicyclohexyls. It is well established that 4,6-DMDBT HDS occurs predominantly through the HYD route.7−11 HDT catalysts are constituted by MoS2 clusters associated with Co or Ni at the crystallite edges, forming Co−Mo−S and Ni−Mo−S species, accepted as the active phase. These structures are complex in morphology and activity. There is evidence that confirms the existence of two types of structure for Ni−Mo−S phases. The first one is identified as type I, formed by a single layer of sulfide metals, with strong interaction with the support. The second possible morphology is denominated as type II, attributed to a multilayered structure with a weak interaction between metals and support. A type II structure would have more Ni atoms substituting the metal and © 2017 American Chemical Society

sulfur atoms at the edges of the crystals. Maximization of type II structure can be achieved by the addition of a secondary promoter, such as phosphorus, to the catalyst.12−14 It is usually accepted that those sites located along the periphery of the MoS2 crystal are responsible for catalytic activity.15 It is also important to consider the presence of different compounds in the feed to achieve the sulfur desired level required by regulations since those can also interfere with its desulfurization degree. In particular, the presence of nitrogencontaining compounds could lead to a strong inhibiting effect due to competitive adsorption and reaction between them and sulfur compounds on active sites.16−20 It has been reported that basic nitrogen-containing compounds, such as quinoline (Q), are the strongest inhibitors of HDS reaction compared to the corresponding nonbasic molecules, such as carbazole.19−21 Laredo et al.22 reported that nonbasic carbazole might have the same inhibitory effect of basic quinoline on HDS of DBT using CoMo/Al2O3 catalysts. Garcı ́a-Martı ́nez et al.10 concluded that nitrogen-containing compounds inhibit mostly the HYD route due to competition for hydrogenation sites. For hydrodenitrogenation (HDN) of Received: Revised: Accepted: Published: 10287

July 3, 2017 August 23, 2017 August 28, 2017 August 28, 2017 DOI: 10.1021/acs.iecr.7b02718 Ind. Eng. Chem. Res. 2017, 56, 10287−10299

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Industrial & Engineering Chemistry Research

understanding the promotive effect of phosphorus in catalyst formulation using a trickle-bed reactor at operational conditions relevant to the oil refining industry. Subsequently, we give insight on the competition between organonitrogen and organosulfur compounds by exploring their adsorption coupled to the catalytic activity.

aromatic nitrogen-containing species, the reaction initially proceeds through heteroring saturation (hydrogenation) followed by cleavage of the C−N bond.10 The resulting aliphatic or aromatic amine intermediates are ultimately converted to hydrocarbons and ammonia. Thus, aromatic nitrogen-containing compounds, especially the basic ones, exhibit a strong affinity for the active sites associated with hydrogenation reactions.20,23,24 Quinoline is an excellent representative molecule to study HDN since it reacts via all pathways present in industrial HDN processes.25 The recent report by Rangarajan and Mavrikakis15 presented simulation evidence (DFT calculations) that inhibition by nitrogencontaining compounds is a combination of competitive adsorption between organonitrogen and organosulfur compounds and destabilization of HDS by strong adsorption of nitrogenated species. Several research groups have investigated the effects of phosphorus loading on HDS and HDN reactions separately,5,14,26−29 evaluating either catalysts with or without P or different amounts of phosphorus added to catalyst formulation. However, they have not reached an agreement about the role of phosphorus in HDT catalysts. Jian and Prins25 evaluated phosphorus addition to NiMo/Al2O3, and results showed that those catalysts were more active to quinoline HDN. This effect was attributed to an increase in sulfur vacancies in NiMoS phase, increasing the formation of active hydrogenation sites. However, the study was conducted comparing a nonpromoted with a promoted one (with P 2 wt %). On the other hand, van Veen et al.30 verified that the addition of 2.1 wt % P to NiMo/Al2O3 decreased the activity toward quinoline HDN. The authors concluded that P could act as an inhibitor instead of a promoter at loadings higher than 2.1 wt %.30 According to Xiang et al.,5 phosphorus loading up to 1.2 wt % favors Q adsorption in a planar position promoted by an enhancement in metals dispersion. The addition of 1.8 wt % of P would be enough to decrease this dispersion, leading to a decline in HDN conversion. Regarding HDS reactions, Ferdous et al.31 reported that phosphorus loading did not modify the catalytic activity for dibenzothiophene HDS but had a significant effect on HDN, associated with the high acidity of catalysts. On the other hand, Ali et al.32 found that the addition of 1 wt % of P2O5 to CoMo/Al2O3 catalysts promoted an enhancement in the HDS reaction rate of 4,6-DMDBT by about 50%. Eijsbouts et al.29 investigated the competitive thiophene HDS and quinoline HDN using catalysts with different amounts of P. They reported no benefit from phosphorus addition for HDS reaction. However, phosphorus intensified the HDN rates. Highest rates were observed for a P loading of 2 wt %. The authors also stated that P loading favors C−N bond cleavage but does not affect the C−S bond cleavage of thiophene. To the best of our knowledge, the effects of phosphorus loading on catalysts for simultaneous HDN of Q and HDS of 4,6-DMDBT competitive reactions were not previously investigated in continuous reactors. Even though this system is closer to industrial HDS plants, competition studies were mainly performed in batch reactors or with less refractory sulfur compounds.6,10,20,21,33 Furthermore, it would also be useful to accomplish this study adopting a wider range of operational conditions. Thus, in this work, we count on these studies to evaluate the catalytic performance of NiMoP/Al2O3 catalysts on competitive HDS of 4,6-DMDBT and HDN of quinoline,

2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation. A series of NiMoP/Al2O3 catalysts containing 15 wt % of MoO3 and Ni/(Ni + Mo) atomic ratio of 0.3 was prepared by the incipient wetness impregnation method using different phosphorus concentrations (0, 1, 2, and 4 wt %). The detailed synthesis procedure is provided in the Supporting Information. 2.2. Characterization. Samples were characterized in both oxide and sulfide states. Regarding characterization of oxide samples, the elemental composition was determined by X-ray fluorescence. Textural properties were obtained from nitrogen adsorption−desorption experiments. Structural characterization was measured by X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance spectroscopy (DRS). The samples were also characterized by temperature-programmed reduction (TPR), nuclear magnetic resonance (NMR) of 27Al and 31P and X-ray photoelectron spectroscopy (XPS). Acidity was determined by temperature-programmed desorption (TPD) of NH3 and n-propylamine. Sulfided samples were characterized by NO chemisorption, FT-IR of NO adsorption, hydrogen temperature-programmed reduction (H2-TPRS), temperature-programmed sulfidation (TPS), and FT-IR of pyridine adsorption. Detailed procedures of all characterization methods can be found in the Supporting Information. 2.3. Activity. HDS of 4,6-DMDBT (Sigma-Aldrich, 97%) and HDN of Q (Acros Organics, 96%) were carried out in a trickle-bed reactor (Microactivity-Reference Reactor of PID Eng & Tech), operated in downflow mode under different conditions. A typical procedure was as follows: about 1.0 g of the oxidic catalyst (60−100 mesh) was placed into the reactor middle zone diluted with silicon carbide. Before the activity test the catalyst was sulfided in situ with a solution of 4 wt % CS2 in n-hexane (0.1 mL min−1) from room temperature to 350 °C (2.5 °C min−1) under 3.1 MPa of hydrogen (flow rate 400 N mL min−1) for 2 h. The feedstock was composed of 4,6DMDBT (23.4 mmol L−1, 1000 ppmw of S) and Q (ranging from 1.0 to 6.2 mmol L−1, from 20 to 120 ppmw of N) in nhexadecane (Sigma-Aldrich, 99%). Reaction samples were periodically collected and analyzed by a gas chromatograph (Agilent 6890) coupled with a flame ionization detector (FID) and a capillary column (DB-1, J&W). Additionally, reaction products were identified by GC-mass spectrometry (Agilent 5975 MS/7820A GC). Steady state was reached after 5 h of reaction, considering a variation of less than 0.2% in reactant conversion. Mass balance was always better than 90%. The HDS or HDN rate constants (mol h−1 g−1) were computed according to eq 1 k=

F ⎛⎜ 1 ⎞⎟ ln M ⎝1 − x ⎠

(1)

The HDS or HDN activity regarding turnover frequencies (TOF, s−1) was determined according to eq 2 TOF = 10288

F M

( 1 −1 x )

ln

3600W

(2) DOI: 10.1021/acs.iecr.7b02718 Ind. Eng. Chem. Res. 2017, 56, 10287−10299

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Industrial & Engineering Chemistry Research where F is the reactant (4,6-DMDBT or Q) molar flow rate in the feed (mol h−1), x is the fractional conversion (of 4,6DMDBT or HDN), M is the catalyst mass (g), and W is the number of moles of active sites loaded (mol g−1) obtained from NO chemisorption measurements. The absence of mass transfer limitations was verified by the Weisz−Prater and Mears criteria (see Supporting Information for details). 2.4. HDS and HDN Competition Modeling. The kinetics of 4,6-DMDBT HDS in the presence of Q can be expressed by a Langmuir−Hinshelwood model considering a pseudo-firstorder reaction for 4,6-DMDBT.17 The reaction rate of 4,6DMDBT HDS can be calculated using eqs 3 and 4 rHDS =

k4,6‐DMDBTC4,6‐DMDBT (1 + KN CQ 0)n

rHDS = k′4,6‐DMDBT C4,6‐DMDBT

(3) Figure 1. X-ray photoelectron spectra of NiMoPx catalysts. NiMoP0: Mo 3d region (a) and Ni 2p region (b). NiMoP1: Mo 3d region (c), Ni 2p region (d), and P 2p region (e).

(4)

where k4,6‑DMDBT and k′4,6‑DMDBT are the pseudo-first-order rate constants in the absence and presence of quinoline, respectively, KN is the adsorption equilibrium constant of Q, C4,6‑DMDBT is the concentration of 4,6-DMDBT, and CQ0 is the initial Q concentration. The adjustable parameter n in eq 3 considers adsorption of Q and 4,6-DMDBT on the same site of 4,6-DMDBT, Q, and H2 (n = 2). Combining eqs 3 and 4, the adsorption equilibrium constant can be determined by eq 5 k4,6‐DMDBT k′4,6‐DMDBT

= (KN CQ 0 + 1)2

NO uptakes of sulfided NiMoPx catalysts are provided in Table 1. NO chemisorption uptakes of different samples varied in a range from 113 to 165 μmol g−1. It can be observed that a phosphorus content up to 1 wt % promoted an increase in sulfide active sites density, being a maximum over the range studied. Simply based on total NO chemisorption experiments one would expect to achieve the highest catalytic activity for samples with the largest number of active sites. However, the nature of those sites is fundamental for catalytic activity. FT-IR NO experiments were thus carried out to provide such information. The infrared spectra of nitric oxide adsorbed on sulfided NiMoPx catalysts are displayed in Figure 2. The use of probe molecules to assign unpromoted (MoS2) and promoted (NiMoS) sites has been reported by either NO or CO adsorption.40,41 From our results three adsorption bands at about 1838, 1800, and 1700 cm−1 were identified. The band at 1838 cm−1 can be attributed to a stretching vibration of NO on sulfided Ni2+ ions, whereas the other two bands are assigned to the symmetric and antisymmetric stretching vibrations of NO of sulfided Mo2+ species, respectively.42 Herein, we assumed the band at 1838 cm−1 assigned to NO bonded to Ni is mainly due to NiMoS phase, considering the same approach used by Okamoto et al.43 and Yamada et al.44 for CoMo/Al2O3 catalysts. There are overlapping bands around 1800 cm−1, ascribed to Mo species with different degrees of sulfidation.45 Catalyst NiMoP0 presented a band at 1880 cm−1, assigned to Ni2+ oxidic species.42 Blue shifts of NO bands indicate the formation of less sulfided species.46,47 As shown in Figure 2, no significant differences could be observed. The intensity ratios of the bands associated with NiMoS phase (1840 cm−1) and MoS2 (1700 cm−1) coupled to the total number of active sites (from NO chemisorption experiments) provided quantitative information on the nature of those sites48 (Table 1). The sample with 1 wt % P showed a maximum in Ni-promoted edges. Further increase in phosphorus concentrations decreases those, attributed to an enlargement in the size and stacking of MoS2 clusters.45,47 Besides the nature of active sites, metal dispersion over support is also crucial for catalytic activity.38,49 The degree of dispersion (DP) for each sample was calculated according to eq 6 and is presented in Table 1

(5)

The adsorption equilibrium constant of Q can thus be determined by interpolation. This model also assumes that inhibition by H2S can be neglected considering its low concentration in the reactor in comparison with the H2 flow rate; the product KHCH and K4,6‑DMDBTC4,6‑DMDBT ≪ 1.

3. RESULTS AND DISCUSSION 3.1. Characterization. NiMoPx samples were characterized by different techniques. In this section, we present and discuss the XPS results and those involving sulfided samples (NO chemisorption, FT-IR NO, H2-TPRS, TPS, FT-IR Py). The characterization results for the remaining techniques are provided in the Supporting Information. XPS spectra of Mo 3d, Ni 2p, and P 2p over catalysts NiMoP0 and NiMoP1 are displayed in Figure 1. The spectra of the other P-containing catalysts (not shown) were like NiMoP1. Phosphorus loading generated species of Mo5+, decreasing Mo6+. Ayala-G et al.34 reported that this could be possible by redox properties in the heteropolyanion planar structure associated with heteropolymolybdates, which are easily reducible and generate the partially reduced compounds. Also, the presence of those species would improve catalysts sulfidation. For Ni 2p spectra, only one contribution was identified, indicating the presence of Ni2+ species. Similar behavior was observed in P 2p spectra where only P5+ species were observed.35−37 Quantitative XPS analyses of calcined catalysts are presented in Table 1. Phosphorus loading to NiMo catalysts promoted a slight decrease in the Mo/Al ratio, suggesting a high stacking degree of Mo.38 A linear increase between the P/Al ratio and the phosphorus content was observed, suggesting that phosphorus is well dispersed over the alumina surface.37,39 10289

DOI: 10.1021/acs.iecr.7b02718 Ind. Eng. Chem. Res. 2017, 56, 10287−10299

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Industrial & Engineering Chemistry Research Table 1. Surface Atomic Ratios for Calcined Catalysts and NO Uptake of Sulfided Catalysts surface atomic ratio

a

catalyst

Ni/Al

Mo/Al

Ni/Mo

P/Al

amount of total active sites (μmol NO g−1)

NiMoS active sitesa (μmol NO g−1)

MoS2 active sitesa (μmol NO g−1)

DPb (%)

NiMoP0 NiMoP1 NiMoP2 NiMoP4

0.02 0.02 0.02 0.01

0.11 0.09 0.07 0.08

0.16 0.17 0.23 0.16

0.00 0.04 0.08 0.15

150 165 146 113

136 151 116 88

14 14 30 25

52 61 48 47

Determined by FT-IR NO coupled to NO chemisorption. bDegree of dispersion (DP).

suggest that the maximum formation of NiMoS phase occurs for NiMoP1. Furthermore, H2-TPRS profiles also show that the presence of P in NiMo/Al2O3 catalyst increases the reduction temperature of the first peak, while it decreases the reduction temperature of the second one as compared to the P-free catalyst. The results can be associated with the formation of NiMoS species which are easily reducible.53 Table 2 shows the total hydrogen consumption of catalysts during H2-TPRS. The total hydrogen consumption is built up along the series, mostly due to the reduction of the last peak, associated with bulk MoS2 clusters. These results support the hypothesis of multilayered clusters connected to P loading. H2S consumption profiles observed during TPS experiments are shown in Figure 4. There is a peak at 35 °C associated with the release of physically adsorbed H2S.54 The TPS of the Pcontaining catalysts presented similar profiles to the P-free sample. All catalysts exhibited at least two peaks, around 125 and 180 °C. The first consumption peak was attributed to the exchange of sulfur for oxygen in MoO3, producing MoO2S species.52,53,55 The oxysulfide species of Mo(VI) were then decomposed to generate Mo(IV) oxysulfides around 165 °C. Those are further completely sulfided to MoS2. The formation of oxysulfides on catalyst surface depends on the interaction between Mo and support.53 As shown in Figure 4, all promoted catalysts showed an increase in H2S consumption regarding oxysulfides formation. However, for P loading higher than 1.0 wt %, oxysulfides reduction shifts from 165 to 190 °C, suggesting a stronger interaction with alumina and small dispersion of Mo crystals.53 These findings support our hypothesis that an increase in P loading leads to formation of more stacked layers of MoS2. NiMoP2 catalyst presented a release of H2S around 250 °C, possibly related to sulfidation of species with different interactions with alumina. The total amount of consumed H2S increased with P content catalysts, associated with development in sulfidation. H2S signals did not stabilize at the end of the experiment, related to an incomplete sulfidation given the experimental conditions. The degrees of sulfidation (DS) were calculated (eq 7) and are also summarized in Table 2

Figure 2. Infrared spectra of NO adsorbed on sulfided NiMoPx catalysts.

DP(%) =

C NiMoS 100 C Ni

(6)

where C is the atomic concentration %. CNiMoS was determined considering 1 molecule of NO per site, and CNi was obtained from XPS. H2-TPRS patterns of sulfided NiMoPx catalysts are shown in Figure 3. Two main reduction peaks were identified: the first

DS(%) =

Figure 3. H2-TPRS profiles of sulfided NiMoPx catalysts.

one at 160−180 °C and the other at temperatures around 800 °C. The first peak can be assigned to the reduction of nonstoichiometric sulfur (Sx), which would form the coordinatively unsaturated sites (CUS) of Mo. The shoulder around 600 °C was assigned to the reduction of CUS in NiMoS phase. Finally, the last peak, around 800 °C, was attributed to the reduction of MoS2 in bulk phase.50−52 Catalyst NiMoP1 presented the lowest intensity in the Mo CUS peak and the highest intensity of the NiMoS CUS peak. These observations

C total sulfur 100 C total Ni + 2C total Mo

(7)

where Ci is atomic concentration %. The infrared spectra of pyridine adsorbed on sulfided NiMoPx catalysts are displayed in Figure 5. Five main bands were identified by spectral decomposition using a Gaussian function and provide information on the acidity distribution in the sulfided samples. Peak assignments were based on the recent report by Humbert et al.,56 which investigated pyridine adsorption on sulfided NiMo catalysts by DFT. Regarding Lewis acidity, two bands were assigned to either site connected 10290


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Industrial & Engineering Chemistry Research Table 2. H2-TPRS and TPS H2S Consumption of Sulfided Catalysts H2 consumption (μmol H2 g−1)

a

catalyst

total

peak 1 (100−200 °C)

peak 2 (200−600 °C)

peak 3 (600−800 °C)

H2S consumption (μmol H2S g−1)

DSa (%)

NiMoP0 NiMoP1 NiMoP2 NiMoP4

283 581 648 930

54 27 34 51

93 103 63 72

136 451 551 807

1552 1783 1946 3188

61 74 86 100

Sulfidation degree (DS) under experimental conditions.

to an enhanced decoration of Ni on the edges of sulfides. The acidity analyzes in the oxide phase also developed with P loading (see Table S4 in Supporting Information). This phenomenon may also help to create a fine dispersion of promoters on the surface upon sulfidation,57 correlating well with the increase in NiMoS phase formed. The catalyst without phosphorus did not fit in that trend. We thus hypothesize that the lower formation of Brønsted acids for that sample is related to a different active phase, less decorated with Ni. The effects of phosphorus on HDT catalysts are quite complex, and sometimes opposite trends are reported, as shown in the review of Iwamoto and Grimblot.58 The presence of phosphorus in the catalyst formulation may change the properties of the impregnation solution, such as the formation of heteropolyanions of Mo and P, pH, and stability significantly. The phosphate present in the impregnation solution also competes with the other active phase precursors for alumina surface sites. This competition can modify their distribution along the support and, upon sulfidation, the dispersion of the sulfide phase (stacking and length of MoS2 slabs). Moreover, the presence of phosphate in the final catalyst changes also its acidic properties, which can intervene in some hydrotreating reactions. Iwamoto and Grimblot also showed that these effects could be influenced by Mo and Ni contents, impregnation order, pH, the presence of impregnation additives, and calcination temperatures. Unfortunately, it is not easy (or even possible) to isolate a single effect and to evaluate the consequences in the catalytic performance. The purpose of characterizing samples in both oxide and sulfided phases was to contribute to a better understanding of phosphorus content effect on the main catalyst properties. The acidity measurements carried out in the oxide phase (see Table S4 in Supporting Information) correlate pretty well with the ones obtained for the sulfided phase because the support is a more determining factor regarding catalyst acidity than sulfidation itself.59,60 However, sulfidation leads to the formation of sulfhydryl groups on the surface, which contribute to catalyst acidity as well.61,62 Phosphorus addition enhanced the overall Brønsted acidity (M-edge plus S-edge), with a maximum of Brønsted sites associated with an M-edge for catalyst NiMo2P, as indicated by FT-IR pyridine adsorption of the sulfided samples. It is widely accepted that the active phase of NiMo hydrotreating catalysts is constituted by CUS which are associated with sulfur vacancies on the edges of MoS2 clusters and can be or not related to Ni on sulfide crystallites edges, forming Ni−Mo−S species of type I or type II.47 Apparently, phosphorus favors the formation of NiMoS and MoS2 phases, with the best ratio between these phases for NiMoP1 catalyst, according to FT-IR NO and H2-TPRS results. Another effect, related to H2-TPRS and TPS results, is the increase in reducibility and sulfidability of catalysts, an indication of the formation of multilayered NiMoS/MoS2 structures. The effect

Figure 4. TPS profiles of NiMoPx catalysts.

Figure 5. Infrared spectra of pyridine adsorbed on sulfided NiMoPx catalysts.

to an S-edge (1580 cm−1) or M-edge (1450 cm−1). Brønsted acid sites attached to an M-edge were assigned to the band at 1615 cm−1 and those related to an S-edge to the band at 1520 cm−1. The band at 1490 cm−1 represented an overlap between Lewis (L) and Brønsted (B) sites of different natures and was not used for comparison purposes. There is an increase in the overall Brønsted acidity of catalyst, mainly associated with H groups attached to a metal atom, which finds a maximum for NiMoP2 sample (see Table S6 in Supporting Information the normalized area for those peaks). Lewis acidity, on the other hand, presents a decrease upon phosphorus addition. In a general sense, P loading led to a decline in Lewis/Brønsted ratio for the series. We tried to correlate the nature of the acidity with the different possible active sites in sulfided samples. Indeed, the decrease in L/B ratio follows a linear relationship with the number of NiMoS sites for each sample, suggesting that the majority of Brønsted sites formed are related to Ni atoms on the edges of MoS2 crystals. This observation also points out that an increase in P loading leads 10291


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Figure 6. Effect of P loading on HDS of 4,6-DMDBT (41 bar and 6 h−1): (a) Conversion and (b) product yields.

experiments, identified by mass spectrometry. Since we were not able to discriminate between isomers, they were considered as the same product for yield calculation purposes. A typical chromatogram is provided in the Supporting Information (Figure S8). A smaller 4,6-DMDBT conversion under all conditions used for the catalyst with 4 wt % of P compared with the other promoted catalysts was observed. In fact, the conversion was similar to NiMoP0. The adverse effect of high phosphorus loading was reported previously in the literature.14,68 Moreover, NiMoP4 catalyst presented less formation of DMBCH (Figure 6b), which can be related to lower hydrogenation rates. TOF values increased with P content (Figure 7a), associated with formation of sites of higher activity. The difference in activity is more relevant comparing the nonpromoted with promoted catalyst samples, which could be attributed to the different degrees of sulfidation. In the first approach, we would expect that improved sulfidation would lead to higher HDS activity. However, it is important to consider that the active sites are mainly on the edges of sulfided Mo crystals, and during sulfidation, a fair amount of bulk MoS2 is formed, which is not necessarily available for reactions. Although there is a trend in values, a small variation range was expected since the metal content was also roughly the same for all samples. It is also worth mentioning that catalyst’s sulfidation prior to reaction was performed in the liquid phase using CS2, which provides higher sulfidation degrees when compared to sulfidation in H2S.69 This modification is evident considering the effect on HYD reactions (Figure 8a), where a good agreement between HYD yield and NiMoS sites was found for the promoted catalysts. The same trend was observed for a series of NiMo catalysts containing silica.70 One can also note that catalyst NiMoP1 presented the highest NiMoS density and HYD yield. On the other hand, it seems that DDS reaction (Figure 6b) occurs mostly at nonpromoted edges (Mo edges of NiMoS crystals or MoS2 crystals). Another trend can be observed in Figure 7b. TOF values appear to have an inverse linear relationship with the L/B ratio. In other words, the increase in Brønsted acidity in the samples is crucial for catalytic activity. The effect of P loading would be over 4,6-DMDBT isomerization reactions which occur on Brønsted acid sites. A smaller density of Brønsted acid sites would lead to less formation of isomerization products, which ends up disfavoring 4,6-DMDBT adsorption on the active sites. On the basis of FT-IR pyridine results, Brønsted acidity has a

of P on dispersion, as determined by a combination of characterization techniques, finds a maximum for P contents up to 1 wt %. A net dispersion decrease was observed for the catalysts with high P loading, attributed to the presence of more condensed/stacked MoS2 species. 3.2. HDS Activity. The conversions of 4,6-DMDBT and product yields over NiMoPx catalysts are presented in Figure 6. HDS of 4,6-DMDBT led to the formation of 3,3′dimethylbiphenyl (3,3′-DMBP), dimethylcyclohexane (DMBCH), and methylcyclohexyltoluene (MCHT). No sulfured intermediates (4,6-dimethyl-tetrahydrodibenzothiophene (4,6-DMthDT) or 4,6-dimethyl-hexahydrodibenzothiophene (4,6-DMphDT) were observed. A proposed reaction network is shown in Scheme 1. The results suggested that 4,6Scheme 1. Reaction Network for HDS of 4,6-DMDBT

DMDBT conversion occurred preferentially through the HYD reaction pathway because of the steric hindrance caused by the methyl groups in the compound, as widely accepted in the literature.10,63 Phosphorus addition up to 2 wt % promoted an increase in HDS of 4,6-DMDBT conversions. According to Mizutani et al.,64 phosphorus modifies the catalytic behavior in two ways: buildup of active sites density by enhanced metal dispersion and of Brønsted acidity. The Brønsted acidity diminishes the steric hindrance in compound adsorption on catalyst surface by promoting isomerization reactions of 4,6-DMDBT.64−66 Increasing the support acidity enhances mainly the catalytic performance for hydrogenation route.67 Indeed, isomerization products of hydrogenated products were observed in our 10292


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Figure 7. Relationship between TOFHDS of 4,6-DMDBT and (a) P loading and (b) L/B ratio (260 °C, 41 bar, 6 h−1).

Figure 8. HDS products distribution over active sites: (a) HYD vs NiMoS and (b) DDS vs CUS-Mo (230 °C, 41 bar, 6 h−1).

Figure 9. HDS of 4,6-DMDBT in the presence of Q (275 °C, 51 bar, 4 h−1): (a) 4,6-DMDBT conversion and (b) HDS product yields.

maximum for 2 wt % of P, which would explain the lower hydrogenation rates of catalyst NiMoP4 when compared to the others. Two phenomena can be taking place simultaneously: first, P loading from 0 to 1 wt % led to the formation of a different, more active, NiMoS phase. Moreover, the number of nonpromoted edges (CUS-Mo) decreased, as an indication of an enhanced concentration of Ni on sulfide crystals edges, supporting the hypothesis of the formation of type II phase structure. However, for phosphorus addition greater than 1 wt %, a reduction in NiMoS phase was observed. This was probably associated with the formation of more condensed Mo sulfide species, leading to the decline in the HYD yield. It is worth mentioning that if one compares the absolute values of

NiMoS density for catalysts NiMoP0 and NiMoP2, the one with a P loading of 2 wt % is smaller. However, it shows higher activity than the nonpromoted catalyst. For catalyst NiMoP4, the condensation and stacking of sulfided layers promoted by phosphorus appear to be crucial, reducing overall HDS activity. Gutiérrez and Klimova71 state that the excessive stacking of MoS2 layers makes remote NiMoS sites at the edges of crystals, limiting 4,6-DMDBT access due to steric hindrance inherent of the molecule. This hypothesis is consistent with H2-TPRS results, which showed growth in H2 consumption for the reduction of internal MoS2 slabs. Due to the similar conversion of 4,6-DMDBT over the NiMoP4 catalyst, as compared to the nonpromoted one, 10293


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(OPA) as hydrogenated intermediates and propylcyclohexene (PCHE), propylbenzene (PB), and propylcyclohexane (PCH) as denitrogenated products. At low concentrations of Q (20 and 50 ppmw of N), nitrogen-containing compounds were mainly converted to HDN products. However, at high levels of Q (90 and 120 ppmw of N) there was a decrease in the yields of those products associated with an increase in DHQ concentration. This behavior may occur due to a low rate of C−N bond breaking of DHQ or due to DHQ strong adsorption on catalysts surface.10,72,73 It can be observed that the addition of 1 wt % of P promoted a little increment in HDN products formation when compared to the catalyst without phosphorus. On the other side, NiMoP2 showed lower HDN conversions, indicating that a loading of P superior to 1 wt % decreased HDN activity. Since both catalysts showed similar Q conversions, increasing the loading of phosphorus was apparently leading to a reduction in hydrogenolysis of C−N bond activity. This could be due to a modification of the active sites (different phase type or less active sites) or to inhibition of that reaction caused by strong adsorption on hydrogenation sites. The effects of temperature on HDS and HDN reactions are shown in Figure 11. The results reveal that in the presence of N-compounds there is a higher sensitivity of HDS reaction to temperature and it may be attributed to two effects: (a) intrinsic reaction rate and (b) adsorption/desorption rates on catalyst sites. From Figure 11a, at 300 °C and 120 ppmw N of Q, catalyst NiMoP1 presented highest 4,6-DMDBT conversion and HYD/DDS ratio compared to the other two catalysts. The effects of H2 pressure on HDS of 4,6-DMDBT and HDN of Q were also investigated over catalyst NiMoP1 (see Figures S10 and S11 in Supporting Information). The increase in Q concentration decreased the HYD/DDS ratio, being more significant for experiments at 51 bar. In the absence of Q, 51 bar favors the formation of hydrogenated products, increasing 4,6-DMDBT conversion. However, this effect is neutralized in the presence of Q, mostly at concentrations higher than 50 ppmw N, due to a significant inhibition of HYD over DDS route. At Q levels of 90 and 120 ppmw N, raising the H2 pressure enhanced the formation of more N compounds, mainly DHQ, with a decrease in HDN products. This effect can be associated with a strong adsorption of N compounds on HYD sites.64 Another possibility would be that at the evaluated temperature the desorption of DHQ from HYD sites is disfavored and the reaction cannot proceed. Evidence for this hypothesis is that a small increase in temperature leads to almost total hydrogenolysis of DHQ (Figure 11b). The values of KN obtained are presented in Table 3. The high values for KN suggest that Q is mainly adsorbed on catalytic sites, favoring HDN over HDS reactions.21,73 Rising the H2 pressure also promoted an increase in KN, which agrees with results obtained for HDN of Q in the presence of 4,6DMDBT. Catalyst NiMoP2 also presented the highest KN. The values of KN also agree with the ones obtained in the literature for a NiMoP/Al2O3 catalyst.10,74 As shown in Figure 12a, before quinoline addition, promoted catalysts have higher TOF, confirming the existence of sites of enhanced activity and thus a better performance for HDS. Our TOF values are in agreement with reported ones in the literature.10,33 After Q addition, both catalysts showed a decrease in TOFHDS values, associated with the competition between 4,6-DMDBT and Q for the active sites. As expected,

evaluation of competition between HDS and HDN reactions was carried out only using the other catalysts. 3.3. Competitive HDS and HDN Reactions. The effects of initial Q concentrations on HDS of 4,6-DMDBT were investigated. As displayed in Figure 9, an increase in Q concentration modifies product distributions. The 3,3′-DMBP yield was almost unaltered, but HYD products (MCHT and DMBCH) showed a great decrease. These results agree with the literature, in which Q inhibits the HYD route of HDS reactions without affecting the DDS route significantly.28,63,64 At low concentrations of Q (20 and 50 ppmw N), the activity of P-containing catalysts decreased less when it is compared to the catalyst without phosphorus. Conversion of 4,6-DMDBT reduced 37% for NiMoP0 after the addition of 20 ppmw of N, while it presented a diminution of 23% for catalysts containing phosphorus. Garcı ́a-Martı ́nez et al.10 also found that the addition of 20 ppmw of N caused a decline in 30% of 4,6DMDBT conversion. Regarding HDS product yields, a reduction of 50% was observed for the catalyst without P, while for the promoted ones the reduction was 30%. At Q concentrations of 90 and 120 ppmw N, the inhibition effects were similar for all catalysts. Catalysts stability was also investigated evaluating HDS of 4,6-DMDBT before and after quinoline addition to the feed. A little deactivation (around 10% of activity loss) was observed after the reactions with Q for all catalysts (see Figure S9 in the Supporting Information). HDS product distribution was not modified after Q removal. The product distribution of Q HDN in the presence of 4,6DMDBT is shown in Figure 10, and its reaction network is

Figure 10. Product yields of the Q HDN in the presence of 4,6DMDBT (275 °C, 51 bar, 4 h−1).

presented in Scheme 2. The products detected were 1,2,3,4tetrahydroquinoline (1THQ), 5,6,7,8-tetrahydroquinoline (5THQ), decahydroquinoline (DHQ), and orthopropylaniline Scheme 2. Reaction Network for HDN of Q

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Figure 11. Effects of temperature on simultaneous HDS (a) and HDN (b) reactions (120 ppmw N, 51 bar, 4 h−1).

values for both reactions. The equilibrium adsorption constant of 4,6-DMDBT was estimated in the absence of Q to support the hypothesis that the small TOF values were mainly due to a strong adsorption of Q.75 K4,6‑DMDBT values are 1 order of magnitude smaller than those obtained for KN (see Table S7 in the Supporting Information). Table 4 shows the overall TOF values for reactions at different temperatures. In fact, at 290 and 300 °C, both HDS and HDN activities are recovered for all catalysts. NiMoP1 catalyst presented overall TOFHDS values higher than the other catalysts and had a great activity for HDN. On the other hand, the catalysts presented similar TOFHDN values at 300 °C, associated with an enhancement in the intrinsic rate constant and a decrease of adsorbed Q. Selectivity for HDS reactions over HDN reactions (see Figure S12 in the Supporting Information) decreases with Q concentration, as expected. P-containing catalysts are more selective for HDS compared to the one without P considering feeds at 20 ppmw N. Selectivities increased a small amount when 90 or 120 ppmw N of quinoline was used, mostly to a decrease in kHDN values. This observation supports the hypothesis that Q adsorbed on active sites also inhibits its reaction. Turaga et al.76 studied the competition between HDS and HDN reactions through molecular modeling methods. The authors concluded that 4,6-DMDBT and Q compete for hydrogenation sites. Q would occupy more active sites because of its high equilibrium adsorption constant compared to 4,6DMDBT and have a high reactivity for hydrogenation due to a higher bond order as compared to 4,6-DMDBT. Amines adsorb in the σ mode through an interaction of their lone pair of

Table 3. Apparent Adsorption Constants of Q for Catalysts catalyst NiMoP0 NiMoP1 NiMoP2 a

a

H2 pressure (bar)

KN (L mol−1)

determination coefficient (R2)

51 31 51 51

584 47 770 824

0.99 0.90 0.97 0.97

Evaluated at 275 °C and 4 h−1.

those values decreased rapidly as Q concentration increased, associated with a decrease in HDS rate constants. TOFHDN values increased up to a Q concentration of 4.9 mmol L−1, associated with an enhancement in HDN rates for both catalysts (Figure 12b). At this concentration, catalyst NiMoP2 has the highest value compared to the other two. TOFHDN values drop considerably for concentrations above that, especially for catalyst NiMoP2. The results point out that Q, besides inhibiting HDS of 4,6-DMDBT, also inhibits its own reaction. This phenomenon is probably due to adsorption not only of Q but also of other intermediates, especially DHQ, which have a strong interaction with active sites.10,74 TOFHDN are also slightly higher than TOFHDS values at the referred Q concentration regime. In that case, since Q and its intermediates are mostly adsorbed on active sites, those are mostly performing HDN reactions. At Q concentrations of 90 and 120 ppmw N, there is a stronger inhibition due to nitrogencompounds adsorption, which leads to a decrease in the number of available active sites for both reactions. This could cause variations in the rate constants and indirectly in TOF

Figure 12. Turnover frequencies at different Q concentrations: (a) TOFHDS and (b) TOFHDN. 10295


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Industrial & Engineering Chemistry Research Table 4. Overall TOF Values of Simultaneous HDS of 4,6-DMDBT and HDN of Q NiMoP0

NiMoP1

temperature (°C)

TOFHDSa (×10 4 s−1)

TOFHDNa (×10 4 s−1)

275 290 300

0.15 0.84 2.23

0.36 1.76 2.48

a

NiMoP2

TOFHDSa (×10 4 s−1) TOFHDNa (×10 4 s−1) 0.15 1.08 3.55

0.37 1.84 2.27

TOFHDSa (×10 4 s−1)

TOFHDNa (×10 4 s−1)

0.17 0.72 3.00

0.28 1.53 2.40

TOFs calculated based on the total amount of NO adsorbed on catalyst active sites evaluated at 6.2 mmol L−1 of Q, 51 bar, and 4 h−1.

Figure 13. Relationship between NiMoS actives sites and products distribution on the competitive HDS and HDN reactions at different Q concentrations: (a) HYD/DDS ratio and (b) HDN (%) (275 °C, 51 bar, 4 h−1).

(Figure 13b), which can be explained by a few factors: first, NiMoS active sites that are more inhibited by Q due to the overall catalyst acidity, as evidenced by equilibrium adsorption constants and pyridine adsorption experiments; second, less overall NiMoS active sites formed (FT-IR NO and H2-TPRS), which increases the competition between 4,6-DMDBT and Q. Since there are stronger Q and DHQ adsorptions, activity decreases more significantly.

electrons on the nitrogen atom with the catalyst surface. In their standing-up configuration, they hinder the plane π adsorption of 4,6-DMDBT aromatic molecules and thus their hydrogenation.6,63 Ho and Qiao77 investigated the competition between 3-ethylcarbazole and 4,6-diethyldibenzotiophene for the active sites of a CoMo catalyst. They reported that nitrogen-containing compounds had a stronger adsorption affinity for HYD sites than hydrogenolysis ones. Those findings are also in agreement with the values for adsorption constants of Q and 4,6-DMDBT reported by Garcı ́a-Martı ́nez et al.,10 who studied the competitive HDS and HDN reactions between 4,6-DMDBT and Q using a NiMoP/Al2O3 catalyst. The results showed that phosphorus loading to NiMo catalyst contributed to an enhancement of HDS activity, despite the fact that it also contributes to a stronger inhibition effect by Q. The high equilibrium adsorption constant determined for all catalysts can be attributed, in part, for catalysts acidity. It is worth noting that the overall acidity of the catalysts increased with P loading, as evaluated by NH3 TPD analyses. Catalysts with high acidity are more inhibited by basic Q, leading to an increase in equilibrium adsorption constants.19 At low concentrations of Q (20 and 50 ppmw N), the enhancement in HDS activity promoted by phosphorus in NiMoP1 and NiMoP2 catalysts can maintain their activity for HDS and HDN. This is probably not associated with an inhibition of active sites but only a competitive effect between Q and 4,6-DMDBT (Figure 13). Raising Q concentration results in a decrease in HDS activity due to stronger inhibition of P catalysts. In this case, all catalysts have similar HDS activity, but NiMoP1 shows greater activity for HDS and HDN reactions comparing reactions at 275 °C. An increase in the temperature (Table 4) leads to higher HDS activity for catalyst NiMoP1 and similar HDN activity for all catalysts. There is a linear relationship between NiMoS sites for HDN products yield and HYD/DDS ratio. NiMoP2 catalyst presented the lowest yields of HDN products

4. CONCLUSIONS The effects of phosphorus content on competitive reactions of HDS of 4,6-DMDBT and HDN of quinoline were investigated. All catalysts showed a significant inhibition of HDS activity at 120 ppmw N of quinoline, the HYD route being more inhibited. These results also suggest that 4,6-DMDBT and quinoline compete for hydrogenation sites, as confirmed by product distribution for HDN reactions. An enhancement in HDS activity was observed with the addition of phosphorus for small concentrations of quinoline. This was associated mostly with the formation of more active NiMoS phase (probably type II). Under those conditions, P-promoted catalysts were able to perform HDS and HDN simultaneously, also evidenced by TOF values. For quinoline concentrations of 90 and 120 ppmw N and at 290 and 300 °C, the catalyst with 1 wt % of P was more active for HDS as compared to the others. The catalyst with 2 wt % of P was more inhibited in the presence of quinoline. However, it remained an active catalyst for HDN. This was associated with its higher acidity (mainly Brønsted) and lower dispersion of NiMoS sites, inaccessible to 4,6DMDBT due to the exaggerated stacking of MoS2 layers as evidenced by H2-TPRS. P loading of 4 wt % did not present a promotive effect on HDS reactions under the evaluated conditions. 10296


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(10) García-Martínez, J. C.; Castillo-Araiza, C. O.; De los Reyes Heredia, J. A.; Trejo, E.; Montesinos, A. Kinetics of HDS and of the Inhibitory Effect of Quinoline on HDS of 4,6-DMDBT over a Ni-MoP/Al2O3 Catalyst: Part I. Chem. Eng. J. 2012, 210, 53. (11) Egorova, M.; Prins, R. Hydrodesulfurization of Dibenzothiophene and 4,6-Dimethyldibenzothiophene over Sulfided NiMo/γAl2O3, CoMo/γ-Al2O3, and Mo/γ-Al2O3. J. Catal. 2004, 225 (2), 417. (12) Topsøe, H. The Role of Co-Mo-S Type Structures in Hydrotreating Catalysts. Appl. Catal., A 2007, 322, 3. (13) Lauritsen, J. V.; Kibsgaard, J.; Olesen, G. H.; Moses, P. G.; Hinnemann, B.; Helveg, S.; Norskov, J. K.; Clausen, B. S.; Topsoe, H.; Laegsgaard, E.; Besenbacher, F. Location and Coordination of Promoter Atoms in Co- and Ni-Promoted MoS2-Based Hydrotreating Catalysts. J. Catal. 2007, 249 (2), 220. (14) Zhou, T.; Yin, H.; Han, S.; Chai, Y.; Liu, Y.; Liu, C. Influences of Different Phosphorus Contents on NiMoP/Al2O3 Hydrotreating Catalysts. J. Fuel Chem. Technol. 2009, 37 (3), 330. (15) Rangarajan, S.; Mavrikakis, M. On the Preferred Active Sites of Promoted MoS2 for Hydrodesulfurization with Minimal Organonitrogen Inhibition. ACS Catal. 2017, 7 (1), 501. (16) Nagai, M.; Sato, T.; Aiba, A. Poisoning Effect of Nitrogen Compounds on Dibenzothiophene Hydrodesulfurization on Sulfided NiMo/Al2O3 Catalysts and Relation to Gas-Phase Basicity. J. Catal. 1986, 97 (1), 52. (17) Lavopa, V.; Satterfield, C. N. Poisoning of Thiophene Hydrodesulfurization by Nitrogen Compounds. J. Catal. 1988, 110 (2), 375. (18) Sumbogo Murti, S. D.; Yang, H.; Choi, K. H.; Korai, Y.; Mochida, I. Influences of Nitrogen Species on the Hydrodesulfurization Reactivity of a Gas Oil over Sulfide Catalysts of Variable Activity. Appl. Catal., A 2003, 252 (2), 331. (19) Kwak, C.; Lee, J. J.; Bae, J. S.; Moon, S. H. Poisoning Effect of Nitrogen Compounds on the Performance of CoMoS/Al2O3 Catalyst in the Hydrodesulfurization of Dibenzothiophene, 4-Methyldibenzothiophene, and 4,6-Dimethyldibenzothiophene. Appl. Catal., B 2001, 35 (1), 59. (20) Farag, H.; Kishida, M.; Al-Megren, H. Competitive Hydrodesulfurization of Dibenzothiophene and Hydrodenitrogenation of Quinoline over Unsupported MoS2 Catalyst. Appl. Catal., A 2014, 469, 173. (21) Laredo, G. C.; Montesinos, A.; De Los Reyes, J. A. Inhibition Effects Observed between Dibenzothiophene and Carbazole during the Hydrotreating Process. Appl. Catal., A 2004, 265 (2), 171. (22) Laredo, S. G. C.; De Los Reyes, J. A.; Luis Cano, D. J.; Castillo, M. J. J. Inhibition Effects of Nitrogen Compounds on the Hydrodesulfurization of Dibenzothiophene. Appl. Catal., A 2001, 207 (1−2), 103. (23) Adam, F.; Bertoncini, F.; Dartiguelongue, C.; Marchand, K.; Thiébaut, D.; Hennion, M. C. Comprehensive Two-Dimensional Gas Chromatography for Basic and Neutral Nitrogen Speciation in Middle Distillates. Fuel 2009, 88 (5), 938. (24) Zeuthen, P.; Knudsen, K. G.; Whitehurst, D. D. Organic Nitrogen Compounds in Gas Oil Blends, Their Hydrotreated Products and the Importance to Hydrotreatment. Catal. Today 2001, 65 (2−4), 307. (25) Jian, M.; Prins, R. Kinetics of the Hydrodenitrogenation of Decahydroquinoline over NiMo(P)/Al2O3 Catalysts. Ind. Eng. Chem. Res. 1998, 37 (97), 834. (26) Liu, C.; Yu, Y.; Zhao, H. Hydrodenitrogenation of Quinoline over Ni-Mo/Al2O3 Catalyst Modified with Fluorine and Phosphorus. Fuel Process. Technol. 2005, 86 (4), 449. (27) Jian, M.; Prins, R. Existence of Different Catalytic Sites in HDN Catalysts. Catal. Today 1996, 30, 127. (28) Rabarihoela-Rakotovao, V.; Brunet, S.; Berhault, G.; Perot, G.; Diehl, F. Effect of Acridine and of Octahydroacridine on the HDS of 4,6-Dimethyldibenzothiophene Catalyzed by Sulfided NiMoP/Al2O3. Appl. Catal., A 2004, 267 (1−2), 17. (29) Eijsbouts, S.; Gruijthuijsen, L. v.; Volmer, J.; De Beer, V. H. J.; Prins, R. The Effect of Phosphate on the Hydrodenitrogenation

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b02718. Detailed preparation and characterization methods, oxide and sulfided forms; characterization results for catalysts in oxide form, XRD, TPR, DRS, Raman, NMR, and TPD; chromatograms for HDS and HDN reactions; stability test after HDS + HDN reactions (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *Tel: +55 (21) 39387606. E-mail: [email protected]. ORCID

Mônica Antunes Pereira da Silva: 0000-0003-0779-7959 Present Address ‡

M.D.d.M.: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis, Minnesota 55455-0132, United States. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for financial support by PETROBRAS S.A (Grant 00500071477119). M.M. and F.B. acknowledge ANP, FINEP, CNPq, and PRH-13 for their financial support.

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REFERENCES

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