Competitive hydrogenation of benzene in reformate gasoline over Ni

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Competitive hydrogenation of benzene in reformate gasoline over Ni supported on SiO2, SiO2-Al2O3 and Al2O3 catalysts: Influence of support nature Mohammad Hassan Peyrovi, Taghi Rostamikia, and Nastaran Parsafard Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02952 • Publication Date (Web): 09 Oct 2018 Downloaded from http://pubs.acs.org on October 13, 2018

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Competitive hydrogenation of benzene in reformate gasoline over Ni supported on SiO2, SiO2-Al2O3 and Al2O3 catalysts: Influence of support nature M. H. Peyrovi a,*, T. Rostamikia a and N. Parsafard b a

Faculty of Chemistry Science and Petroleum, Department of Physical Chemistry, University of Shahid Beheshti, Tehran, 1983963113, Iran b

Kosar University of Bojnord, Department of Applied Chemistry, North Khorasan, Iran

* Corresponding author E-mail address: [email protected] (M. H. Peyrovi) Tel.: +98 21 29902892; Fax: +98 21 22431663. Address: Faculty of Chemistry Science and Petroleum, University of Shahid Beheshti, Tehran, Iran

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Abstract Nickel supported on SiO2, SiO2−Al2O3 and Al2O3 catalysts have been prepared and studied for reduction of benzene in reformate gasoline. The sol-gel method was used to prepare the catalysts. The evaluations were performed in a continuous fixed bed micro reactor fed by a flow of reformate gasoline at 398-473 K under atmospheric pressure. The physicochemical properties of the catalysts were obtained by XRD, FESEM, EDS-map, H2−adsorption and N2 adsorption/desorption to correlate the catalytic performances. To evaluate the performance of catalysts, different H2/Benzene molar ratios and space velocities were used. The Ni/SiO2-b, Ni/SiO2-c and Ni/FDU12 catalysts decreased benzene content to less than 1 volume percent at 423 K. The high toluene conversion by Ni/MSA and Ni/Mil-53(Al) catalysts in comparison to other catalysts indicates that toluene hydrogenation is favored on these catalysts. The highest conversion of benzene in competitive hydrogenation was achieved at 423 K by Ni/SiO2-c catalyst. In low H2/Benzene molar ratio and space velocity; benzene molecules find a greater chance of hydrogenation. Due to selective hydrogenation by Ni/SiO2-c; the RON is slightly reduced.

Keywords: Competitive hydrogenation; Reformate; Particle size; TOF; Space velocity.


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1. Introduction The quality of fuel used in vehicles is an important factor in environmental pollution. In order to meet the requirements of the environmental laws, refineries are forced to reduce the amount of benzene and aromatics in fuels. According to environmental regulations, gasoline produced by refiners, should have a maximum 35 and 1 volume percent of aromatic compounds and benzene, respectively.1,

2

These considerations are leading to process changes for refining and

reformulating gasoline until being suitable for environment and human health aspects. The conventional processes applicable to achieve benzene reduction in reformate are as follows: I. Benzene precursor removal (Fractionation). II. Benzene saturation (Hydrogenation) III. Solvent extraction (Extraction) IV. Benzene alkylation (Alkylation) Each of these processes has some advantages and disadvantages, but their implementation has high costs and requires a huge investment. The present work addresses reduction of benzene by selective hydrogenation. The cost of benzene reduction in this method will be much lower than other mentioned processes. The content of benzene varies widely with feedstock and conditions of catalytic reforming unit. 70 to 85 weight percent of benzene available in vehicles gasoline is generated from catalytic reforming.3 Therefore, reducing the amount of benzene plays a major role in producing environmental fuel. It is confirmed that the activity of the nickel supported catalysts for hydrogenation depends on the nature of the support, synthesis approach, the pre-treatment periods and the conditions of the reduction.4 According to literatures, the catalysts produced by sol-gel method have high thermal


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stability, persistence to deactivation and a good flexibility in controlling catalyst textural properties as particle size, surface area and pore size distribution.5,

6

Some researchers have

reported that the amount of toluene retained and hydrogenated on the Al2O3 and TiO2 catalysts are larger than benzene.6 However, Vannice and co-worker7 showed that the adsorption strength of toluene can be less than that of benzene on some supports. Benzene hydrogenation in a pure or unreal mixture has been widely studied, and a large number of catalysts with different metals were developed.8-10 Benzene hydrogenation in a real mixture such as reformate has been investigated very little.11 Considering the fact that refineries use hydrocarbon mixtures as feeds, there are still some deficiencies about understanding the behavior of aromatics in real mixtures. Hydrogenation in mild conditions is important to perform when safe and low energy consumption is required. Hydrogenation of benzene has been less studied using nickel catalysts in real mixtures. Because of the availability and a reasonable cost of nickel, high amount of nickel can be loaded on different oxides and used in industrial applications. In the present study, influence of various supports upon the characteristics of Ni catalyst and their activities in benzene hydrogenation were investigated. The main purpose of the present work, is to reduce the amount of benzene in reformate gasoline to less than 1 volume percent by competitive hydrogenation according to environmental regulations. While this reaction should be done selective to benzene to avoid reduction of other aromatics. By using real feed, we are going to adopt a realistic approach to hydrogenation of benzene. 2. Experimental section 2.1. Materials


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Anhydrous ethanol, 2-butanol, aluminum-tri-sec-butoxide, terephthalic acid, tetraethyl ortho silicate, nickel nitrate hexa hydrate, hydrochloric acid, xylene, potassium chloride and sulfuric acid with grade analysis were purchased from Merck Company. Pluronic P123 and Pluronic F127 were supplied from Aldrich. The reformate gasoline was used as a feed in catalytic experiments. The detailed hydrocarbon analyses of reformate gasoline according to the carbon number are presented in Table 1. 2.2. Synthesis of Support Silica-method A: For preparation of silica support, 10% liquid sodium ortho silicate (SiO2/Na2O ratio = 3.1) was added drop wise to 6% H2SO4 with slow stirring at ambient temperature until pH reached 4-5 and a wet gel-like precipitate was formed. The sediments obtained were filtered, washed and laid for 48 h at room temperature. Then, they were dried in the oven at 373 K for 24 h. The prepared support will be referred as SiO2-a. Silica-method B: The sol solution was synthesized by using 1:50:10:0.02 molar ratios of TEOS, distillated water, ethanol and hydrochloric acid as a speeding agent, respectively. To prepare liquid A, 1 mol of tetraethyl ortho silicate was mixed with ethanol (5 mol) and stirred at 298 K for 1 h. The B liquid includes of ethanol (5 mol) 50 mol of H2O (twice distilled) and 0.02 mol of HCl was added drop by drop to the A liquid and stirred. This stirring lasted for 1 h to facilitate the hydrolysis and condensation reactions. The formed sol was heated and vigorously stirred at 358 K for a few minutes until a wet gel was produced. The gel was filtered, washed and laid at 298 K for 24 h. The solid powder was calcined in air at 723 K for 4 h with heating rate 10 K/min.12 This support will be notified as SiO2-b. Silica-method C: To prepare this support, 4 g of tri block copolymer Pluronic P123 (EO20PO70EO20) was dissolved in 80 ml 2-butanol and the solution was mixed for 3 h at ambient


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temperature. Afterwards, 10.12 g tetraethyl ortho silicate was added to initial solution and mixed at room temperature for 5 h. The resulting solution was laid to an oven and heated to 373 K for 12 h. After filtration, the obtained gel was first dried at room temperature and then in the oven at 393 K. At the next step Pluronic P123 was extracted by Sechelt extractor with ethanol for 20 h. At the final step, the material was calcined for 3 h at 523 K and 2h at 823 K with heating rate 10 K/min. The prepared support will be referred as SiO2-c. L-FDU12: The synthesis was carried out using tri block copolymer Pluronic F127 (EO106PO70EO106) as a directing surfactant and xylene as a solvent. The synthesis method used is as follows: 2 g of F127, 5 g of KCl and 120 ml of 2 M HCl were mixed together. Thereupon, 4.8 g of xylene (isomeric mixture) was added and stirred at 288 K for 24 h in a closed bottle. Then, 8.2 g of tetraethyl ortho silicate was added to the resulting mixture and stirred for 24 h at 288 K. Subsequently, the mixture was moved to an oven and heated to 373 K for 72 h. The sediment was separated from the solution by filtration and left at room temperature in air. The resulting solid was calcined at 823 K for 5 h in air with heating rate 10 K/min to eliminate the copolymer template.13 The prepared support will be referred as FDU12. MSA: This support was prepared by 0.27 g aluminum-tri-sec-butoxide at 60 °C mixed with 3.29 g of tetra propyl ammonium hydroxide. The solution was cooled to 298 K. Then 13.88 g of tetraethyl ortho silicate mixed with 24.5 g of ethanol was added to first solution. After a few minutes, the clear solution turned into a homogeneous gel. After 15 h ageing at 298 K, the gel was dried at 373 K and calcined for 8 h in air at 823 K with heating rate 10 K/min.14 Mil-53(Al): The synthesis was carried out by dissolving 4.2 g of terephthalic acid in 28.8 g of H2O and 80 g of sodium hydroxide. The second solution consisting of 15 g of aluminum nitrate in 28.8 g of H2O was added to the first solution under stirring at 298 K. With this addition, a


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white precipitate was immediately created. The mixture was maintained under stirring at ambient temperature for one week. The white precipitate was washed and dried at 298 K overnight. The solid was calcined at 723 K for 3 h with heating rate 10 K/min.15 2.3. Catalyst preparation Catalysts containing 20% nickel were prepared by wet impregnation using appropriate Ni(NO3)2.6H2O aqueous solution and the synthesized supports. The materials were mixed at 298 K and then heated at 343 K to allow water to evaporate. The impregnated materials were dried at 373 K for 12 h and calcined in air at 723 K for 4 h. The prepared catalysts were reduced under pure H2 with 40 ml/min at 723 K for 6 h and cooled to evaluation temperature. 2.4. Catalyst characterization Surface properties of fresh catalysts were evaluated at 77 K using a BELSORP BET analyzerModel MINI II. To perform this analysis, the catalysts were degassed at 473 K for 2 h under vacuum. The specific surface area was measured from the Brunauer-Emmet-Teller (BET) isotherms. The total pore volume and average pore diameter was calculated from the gas adsorbed at a P/P0 = 0.99 and BJH model, respectively. The materials were analyzed by X-ray diffraction (XRD) with an STOE powder diffraction system utilizing Ni-filtered Cu Kα radiation at 45 kV and 50 mA with a 0.06o 2θ step and 1 s per step. Nickel particle size was estimated using Scherrer’s equation. TESCAN field emission scanning electron microscope - Model MIRA II coupled with an energy dispersive X-ray spectroscope and EDS-map were used to present the morphology and the distribution among the elements of fresh catalysts, respectively. Selected catalysts were dispersed in ethanol to be observed by scanning electron microscope.


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The dispersion of nickel (D) on the supports was measured by H2-adsorption analysis with a TPD/TPR analyzer−Model 2900 Micromeritics. The prepared catalysts were evacuated at 773 K for 1 h, reduced in hydrogen flow at 723 K for 1 h and evacuated again at the same temperature for 1 h before hydrogen adsorption. The average particle size (d) was estimated from the metal dispersion using the following relation: d = 97.1/D by assuming the spherical metal particle. D is the metal dispersion obtained from hydrogen adsorption results. 2.5. Catalyst Evaluation The hydrogenation of reformate gasoline was conducted in a continuous fixed bed micro reactor at 1 atm. 1 g of catalyst was pretreated with pure H2 at 473 K for 1 h. Then, the temperature was reduced to 398 K and feed with flow rate = 4 ml/h was added to the reactor inlet. Hydrogen was also used as a desired amount of H2/Benzene molar ratio. The products of reaction were collected in the one-hour interval and analyzed by a gas chromatograph (Agilent Technologies 7890A) equipped with an FID detector and a capillary column. Cyclohexane (CH) and methyl cyclohexane (MCH) were the major products obtained from hydrogenation of benzene and toluene. This method of catalytic performance was carried out at various temperatures (423−473 K) over each catalyst. The details about reformate gasoline components were presented in Table 1. As it is shown, the concentration of toluene is 6 times more than that benzene. The turnover frequency (TOF), specific rate (Sr), space velocity (Sv) and VVH were calculated as follows; .ρ × × ×% × ×

TOF =

.ρ ×

Specific rate =

(1)

!"#$

%&'( ×% )*+,

(2) 8

ACS Paragon Plus Environment

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Space velocity = VVH = -

./%!0"$1 2.3 "40! 2 05! "!41040#

9

1404.6#0 7!8 ./%!

./%!0"$1 2.3 "40! 2 2!!8 ./%! 2 1404.6#0

9

(3) (4)

Q, M, ρ and NA are the volumetric flow rate, molecular weight of benzene, density of feed and Avogadro constant, respectively. 3. Results and discussion 3.1. Catalyst characterization The X-ray diffractions of Ni/MSA, Ni/FDU12, Ni/SiO2-a, Ni/SiO2-b, Ni/SiO2-c and Ni/Mil53(Al) catalysts were presented in Fig. 1. These patterns exhibited a broad and sharp peak at low and high angles, which are related to amorphous area and high degree of crystallization of the Ni and NiO species phase, respectively.11, 16 This is confirmed by the high surface area obtained by these catalysts. The diffraction peaks at 44.5º, 51.8º and 75.5º can be attributed to Ni, and the characteristic peaks of NiO phase were observed at 61.2º. The narrow and intensive peaks at 44.5º reveal that Ni is the predominant crystal phase in these catalysts. The surface area (SBET) of catalysts was summarized with Table 2. The check of these results shows that all catalysts except Ni/SiO2-b exhibit relatively high surface area. The Ni/SiO2-c catalyst has the largest surface area. Although the Ni/SiO2-b has a lower surface area than other catalysts, it shows fairly high activity. By increasing the catalyst surface area, the reactants could be adsorbed more over the catalyst surfaces and promoting the reaction process. The results confirm that the surface area does not influence on dispersion of the nickel particles and there are other aspects in Ni/SiO2-b activity. These catalysts presented type IV isotherms, based on the IUPAC classification. The type H1 hysteresis loops characterize the cylindrical mesopores structure. Since the adsorption-desorption behaviors of the catalysts were similar, we showed some of them. As shown in Fig. 2 about 9 ACS Paragon Plus Environment

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Ni/MSA, at P/P0 < 0.25, the adsorption capacity increased slightly with raising the relative pressure, indicating that Ni/MSA passed through a small amount of micropores. The adsorption and desorption curves are not overlapping at P/P0 > 0.5, and the type of hysteresis loop shows the catalyst passes through a large number of mesopores. As shown in Fig. 2, Ni/MSA catalyst had a narrow pore size distribution. Most of the holes were in mesopores range (2-10 nm) with a small portion of micropores. The results (Table 2) show the dispersion of the nickel particles over the Ni/SiO2-c catalyst is better than others. Dispersion over the Ni/MSA and Ni/Mil-53(Al) probably due to the agglomeration of nickel and its interaction with support, are low. The homogeneous dispersion and the size of nickel particles over the catalysts surfaces depend on various factors, for example the synthesis method, interaction of metal with support and the metal loading content. Due to the same amount of nickel loaded in the prepared catalysts, dispersion of nickel depends on the nature of support and interaction between supports and metal nickel. Based on the studies, Nano scale particles that are homogeneously scattered over the surface, can be used as active sites for the reaction.17 The smaller particle size with a homogeneous dispersion provides a more accessible surface for the reactants. From the results obtained, it can be deduced that, benzene molecules have a higher chance of hydrogenation than larger molecules over the nickel catalyst with smaller size of nickel. The average particle size calculated using Scherrer’s equation from the full width at half maximum of the diffraction peak was also shown in Table 2. These results are confirmed by the results obtained of H2-adsorption. The Ni/SiO2-c catalyst with small particle size has achieved the best performance with respect to benzene reduction to less than 1 volume percent and research octane numbers.


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Field emission scanning electron microscopy images of the catalysts were demonstrated in Fig. 3. These images showed amorphous particles with relatively uniform diameters. Qualitative distribution maps of nickel phase in Ni/MSA, Ni/FDU12, Ni/SiO2-b and Ni/SiO2-c obtained from EDS-map were shown in Fig. 4. The Ni/SiO2-b and Ni/SiO2-c with small Ni particle size, show better distribution. Larger particles may be created due to agglomeration of metal particles during the reduction process. 3.2. Catalytic performance The conversions of benzene (CBz) and toluene (CTu) obtained over the prepared catalysts were presented in Fig. 5a and b, respectively. The catalytic performances of these catalysts strongly affected by the nature of supports. All catalysts exhibited high activity in benzene conversion at 423 K. While the highest benzene and toluene conversion were obtained by Ni/MSA catalyst at 423 K. The Ni/SiO2-c catalyst shows the lowest activity for toluene conversion. The high toluene conversion by Ni/MSA and Mil-53(Al) catalysts compared with other catalysts indicates that toluene hydrogenation is favored on these catalysts. The specific rate and TOF were calculated over the prepared catalysts at 398-473 K and presented in Table 3. As it can be seen, all catalysts have high activity at 423 K. The existence of a temperature dependent for maximum hydrogenation of aromatics can be ascribed to a decrease in surface coverage with aromatics at high temperatures, which can reduce reaction probability.18, 19 Lower activities were observed as the temperature increased in all cases. The Ni/SiO2-c, Ni/SiO2-b and Ni/MSA catalysts were more active than other catalysts at 423 K. The high activity achieved by Ni/SiO2-c is due to the proper dispersion of nickel particles. These results indicated that the nickel dispersion plays major role in activity of the catalysts. Also, it


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seems that by reducing the available surface area of the metal (Fig. 4b), the activity of Ni/FDU12 decreased. This is in agreement with dispersion obtained for Ni particle in Ni/FDU12 catalyst. The activity and selectivity of catalysts alter by hydrocarbon poisoning and deactivation during hydrogenation reaction. To study the catalytic stability, the performances were continued for 10 h. The relation between benzene conversion vs. time on stream at 448 K was given in Fig. 5c. As it is observed in this Figure, the conversion of all catalysts diminished with increasing the reaction time. Most of the changes in the conversion of benzene happens during the first 1-2 h on stream. Many research groups have suggested that the hydrogenation of aromatic compounds using the nickel catalyst occurs through hydrogen spillover.20, 21 In hydrogenation reactions over prepared catalysts, adsorbed hydrogen molecules on metal sites were converted to hydrogen atoms and moved from nickel to the support, followed by the hydrogenation of benzene adsorbed on the support. This action increases the catalytic activity and the reaction rate. It can be concluded that, due to the effect of hydrogen spillover resulting from the synergistic effect of metal and support significantly simplifies aromatic hydrogenation in these experiments. From a dynamic view point, catalytic reaction needs appropriate contact time to perform between reactants and catalyst. So, short or long time for reaction has an important effect on the creation of the products or by-products. In this work, except Ni/MSA, other catalysts show better benzene conversion at a high resident time of reaction. The results show that, in higher resident time (low space velocity) and low H2/Benzene molar ratio benzene molecules find a greater chance for hydrogenation. With decreasing the resident time in competitive adsorption of species, hydrogenation of aromatics such as toluene is provided.


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Activity of the catalysts was measured by the number of reacted molecules over the surface of catalysts. Therefore, the control of the space velocity is very important. Conversion of benzene at 423 K with different space velocity and H2/Benzene molar ratios were given in Table 4. As it was shown, benzene and toluene hydrogenation by the Ni/SiO2-a, Ni/MSA and Ni/Mil-53(Al) catalysts, initially increase with enhancing the molar ratios of H2/Benzene and space velocity then decrease. The Ni/SiO2-b, Ni/SiO2-c and Ni/FDU12 catalysts show different behaviors, benzene and toluene conversions decrease with increasing the H2/Benzene molar ratio. This behavior can be linked to the small particles of the nickel and the low probability of adsorption of the reactants at a low resident time. High space velocity and H2/Benzene molar ratios are suitable for benzene and toluene hydrogenation by the Ni/MSA catalyst. The Ni/SiO2-c catalyst presents a great performance at low space velocity and H2/Benzene molar ratios for benzene and toluene hydrogenation. These results show that the space velocity and resident time play very important roles in aromatic hydrogenation. As reported in literatures, presence of toluene in the feed due to its strong adsorption reduces benzene hydrogenation. By increasing toluene concentration, hydrogenation of benzene decreases more.11 The adsorption by a π-bond interaction of parallel ring to the metal surface is assumption that is made.7 Acidic support causes a competitive adsorption of aromatics on the active sites and expected that adsorbed toluene on acidic support can also react with spilled over hydrogen.22 In these experiments, the Ni/MSA and Ni/Mil-53(Al) catalysts display a higher activity in toluene conversion. This behavior could be due to the acidity of support used in these catalysts. These results indicate that the conversion of benzene and toluene depends on nature of support. Reducing toluene during benzene hydrogenation causes to a drastic drop in the research octane number (RON). As a result, the RON of the products reduces 10 and 7 units by Ni/MSA


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and Ni/Mil-53(Al) catalysts, respectively (Table 5). However, benzene conversion by Ni/SiO2-b and Ni/SiO2-c was about 3 and 5 times higher than that of toluene, respectively. High amount of benzene conversion over these catalysts indicates that this reaction is more favorable than other aromatics hydrogenation. Selectivity to cyclohexane (SCH) and methyl cyclohexane (SMCH), the volume percent of benzene and toluene in reformate gasoline and the RON of the products after selective hydrogenation were presented in Table 5. As it has shown, the highest and lowest selectivity to cyclohexane and methyl cyclohexane were obtained by Ni/SiO2-c catalyst. The research octane numbers for pure solution of benzene, toluene, cyclohexane and methyl cyclohexane are 98, 124, 85 and 67, respectively.23 Since about 2.5 and 0.9 volume percent of benzene and toluene are hydrogenate by Ni/SiO2-c catalyst, due to selective hydrogenation of benzene, the RON of product achieved by Ni/SiO2-c has been reduced a very small value. The Ni/SiO2-b and Ni/SiO2-c catalysts showed the best performance with respect to benzene reduction to less than 1 volume percent (Table 5). The remarkable behavior of these catalysts makes them more cost-effective for production of environmental fuel. 4. Conclusion The results show that the best temperature for benzene conversion in competitive hydrogenation is 423 K. Dispersion of nickel particles and their size play important roles in activity of catalysts. Benzene conversion obtained through Ni/FDU12 and Ni/SiO2-c catalysts in the presence of large quantity of toluene was about 3 and 5 times higher than that of the toluene, respectively. Ni/MSA and Ni/Mil-53(Al) effectively reduce benzene, but due to the greater reduction of toluene, the research octane number of the final product declined significantly. Despite the decrease of the benzene amount, the research octane number of products achieved by Ni/SiO2-c has been


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reduced a very small value that can be used with a very low cost for the benzene reduction and the production of environmental fuel. In higher resident time, benzene molecules find a greater chance of hydrogenation. Acknowledgment We would like to gratefully thank the research council of Shahid Beheshti University and central laboratory of Tehran refinery. References (1) de Leeuw, F. A. A. Set of Emission Indicators for Long-Range Transboundary Air Pollution. Environ. Sci. Policy. 2002, 5 (2), 135-145. (2) He, C.; Ge, Y.; Tan, J.; You, K.; Han, X.; Wang, J. Characteristics of Polycyclic Aromatic Hydrocarbons Emissions of Diesel Engine Fueled with Biodiesel and Diesel. Fuel. 2010, 89 (8), 2040-2046. (3) Palmer, R. E.; Shipman, R.; Kao, S. Options for Reducing Benzene in the Refinery Gasoline Pool. ACS, Petroleum Division Annual Meeting (San Diego) AM-08-10, 2008. (4) Wojcieszak, R.; Monteverdi, S.; Mercy, M.; Nowak, I.; Ziolek, M.; Bettahar, M. M. Nickel Containing MCM-41 and AlMCM-41 Mesoporous Molecular Sieves: Characteristics and Activity in the Hydrogenation of Benzene. Appl. Catal. A: Gen. 2004, 268 (1-2), 241-253. (5) Gonçalves, G.; Lenzi, M. K.; Santos, O. A. A.; Jorge, L. M. M. Preparation and Characterization of Nickel Based Catalysts on Silica, Alumina and Titania Obtained by Sol– Gel Method. J. Non-Cryst. Solids. 2006, 352 (32-35), 3697-3704. (6) Peyrovi, M. H.; Parsafard, N.; Hajiabadi, M. A. Ni‐W Catalysts Supported on HZSM‐5/HMS for the Hydrogenation Reaction of Aromatic Compounds: Effect of Ni/W Ratio on Activity, Stability, and Kinetics. Int. J. Chem. Kinet. 2017, 49, 283-292.


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(7) Poondi, D.; Vannice, M. A. Competitive Hydrogenation of Benzene and Toluene on Palladium and Platinum Catalysts. J. Catal. 1996, 161 (2), 742-751. (8) Zhao, W.; Liu, Y.; Wang, L.; Chu, J.; Qu, J.; Hao, Z.; Qi, T. Catalytic Combustion of Benzene on the Pd/Nanosize Al-HMS. Micropor. Mesopor. Mat. 2011, 138 (1-3), 215-220. (9) Zhu, L.; Sun, H.; Fu, H.; Zheng, J.; Zhang, N.; Li, Y.; Chen, B. H. Effect of ruthenium nickel bimetallic composition on the catalytic performance for benzene hydrogenation to cyclohexane. Appl. Catal. A Gen. 2015, 499, 124-132. (10) Zhu, L.; Yang, Z.; Zheng, J.; Hu, W.; Zhang, N.; Li, Y.; Zhong, C.J.; Ye, H.; Chen, B. H. Decoration of Co/Co3O4 Nanoparticles with Ru Nanoclusters: A New Strategy for Design of Highly Active Hydrogenation. J. Mat. Chem. A. 2015, 3 (22), 11716-11719. (11) Goundani, K.; Papadopoulou, C.; Kordulis, C. Benzene Elimination from Reformate Gasoline by High Pressure Hydrogenation in A Fixed-Bed Reactor. React. Kin. Catal. Let. 2004, 82 (1), 149-155. (12) Taira, M.; Yamaki, M. Preparation of SiO2-Al2O3 Glass Powders by the Sol-Gel Process for Dental Applications. J. Mater. Sci. Mater. Med. 1995, 6 (4), 197-200. (13) Yu, T.; Zhang, H.; Yan, X.; Chen, Z.; Zou, X.; Oleynikov, P.; Zhao, D. Pore Structures of Ordered Large Cage-Type Mesoporous Silica FDU-12s. J. Phys. Chem. B. 2006, 110 (43), 21467-21472. (14) Perego, C.; Amarilli, S.; Carati, A.; Flego, C.; Pazzuconi, G.; Rizzo, C.; Bellussi, G. Mesoporous Silica-Aluminas as Catalysts for the Alkylation of Aromatic Hydrocarbons with Olefins. Micropor. Mesopor. Mat. 1999, 27 (2-3), 345-354. (15) Díaz-García, M.; Mayoral, A.; Diaz, I.; Sánchez-Sánchez, M. Nanoscaled M-MOF-74 materials prepared at room temperature. Crys. Growth Des. 2014, 14 (5), 2479-2487.


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(16) Savva, P. G.; Goundani, K.; Vakros, J.; Bourikas, K.; Fountzoula, C.; Vattis, D.; Lycourghiotis, A.; Kordulis, C. Benzene Hydrogenation over Ni/Al2O3 Catalysts Prepared by Conventional and Sol–Gel Techniques. Appl. Catal. B Env. 2008, 79 (3), 199-207. (17) Venezia, A. M.; La Parola, V.; Pawelec, B.; Fierro, J. L. G. Hydrogenation of Aromatics over Au-Pd/SiO2-Al2O3 Catalysts; Support Acidity Effect. Appl. Catal. A Gen. 2004, 264 (1), 43-51. (18) Peyrovi, M. H.; Toosi, M. R. Study of Benzene Hydrogenation Catalyzed by Nickel Supported on Alumina in A Fixed Bed Reactor. React. Kinet. Catal. Let. 2008, 94 (1), 115119. (19) Boudjahem, A. G.; Bouderbala, W.; Bettahar, M. Benzene Hydrogenation over Ni–Cu/SiO2 Catalysts Prepared by Aqueous Hydrazine Reduction. Fuel Process. Technol. 2011, 92 (3), 500-506. (20) Wang, L.; Liu, Q.; Jing, C.; Yin, J.; Mominou, N.; Li, S. Simultaneous Removal of Sulfides and Benzene in FCC Gasoline by in Situ Hydrogenation over NiLaIn/ZrO2-r-Al2O3. J. Hazard. Mat. 2018, 342, 758-769. (21) Zhang, H.; Zhang, X. G.; Wei, J.; Wang, C.; Chen, S.; Sun, H. L.; Wang, Y. H.; Chen, B. H.; Yang, Z. L.; Wu, D. Y.; Li, J. F. Revealing the Role of Interfacial Properties on Catalytic Behaviors by in Situ Surface-Enhanced Raman Spectroscopy. J. Am. Chem. Soc. 2017, 139 (30), 10339-10346. (22) Peyrovi, M. H.; Parsafard, N.; Mohammadian, Z. Benzene Selective Hydrogenation over Supported Ni (Nano-) Particles Catalysts: Catalytic and Kinetics Studies. Chin. J. Chem. Eng. 2018, 26, 521-528.


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(23) Ghosh, P.; Hickey, K. J.; Jaffe, S. B. Development of A Detailed Gasoline CompositionBased Octane Model. Ind. Eng. Chem. Res. 2006, 45 (1), 337-345.


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Table 1. Composition of the reformate gasoline as a feed employed in the catalytic tests. %w/w C4 C5 C6 C7 C8 C9 C10 C11 total

paraffins 1.5 2.4 2.8 2.9 0.9 0.1 10.6

isoparaffins 0.4 3.5 5.7 10.2 2.4 0.1 22.3

olefins 0.5 0.1 0.6

naphtenes 0.4 0.6 1.2 5.8 1.3 0.2 9.5


aromatics 3.6 21.2 19.4 10.1 2.1 0.4 56.8

unknown 0.2 0.2

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Table 2. Physicochemical properties of the prepared catalysts. Catalyst Ni/SiO2-a Ni/SiO2-b Ni/SiO2-c Ni/FDU12 Ni/MSA Ni/Mil-53(Al) a

SBET (m2/g) SPa (nm) Db (%) dNib (nm) 260 43 530 475 481 208

24.7 22.8 17.4 31.1 29.1 26.2

4.0 4.3 5.9 3.1 4.1 3.7

24.3 22.6 16.4 31.3 23.7 26.2

Particle size using the line broadening at half the maximum intensity (FWHM) of Nickel reflection, b Particle size (dNi) and nickel dispersion (D) by H2-adsorption.


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Table 3. The specific rate (Sr) and TOF achieved over the prepared catalysts. (P=1 atm, liquid feed rate=4 ml/h, hydrogen flow rate=600 ml/h, mass of catalyst=1 g) Sr (mmolBz gNi-1 h-1) TOF (h-1) 403 K 423 K 448 K 473 K 403 K 423 K 448 K 473 K Ni/SiO2-a 2.9 4.2 2.5 2.1 4.2 6.1 3.7 3.0 Ni/SiO2-b 3.9 5.2 4.3 2.8 5.3 7.1 5.9 3.9 Ni/SiO2-c 3.7 5.5 3.1 2.6 3.7 5.4 3.1 2.5 Ni/FDU12 3.2 4.8 4.3 3.9 6.1 9.1 8.1 7.5 Ni/MSA 4.3 5.6 3.3 3.0 6.8 8.0 4.7 4.3 Ni/Mil-53(Al) 3.4 5.2 4.2 2.7 5.4 8.3 6.7 4.3 Catalyst


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Table 4. Effect of H2/Benzene molar ratios, space velocity (Sv) and residence time (Rt) on the activity at 423 K. CBz (%) CTu (%) H2/Bz Sv (h-1) Rt (s) VVH (h-1) 56.7 18.5 1.0 1320 2.7 58.9 23.3 1.4 1595 2.3 Ni/SiO2-a 3.6 34.8 14.9 1.8 1817 2.0 30.2 12.0 2.0 1960 1.8 73.2 23.1 0.5 1338 2.7 Ni/SiO2-b 65.4 20.0 1.2 1891 1.9 3.3 61.5 18.1 1.6 2258 1.6 77.0 16.5 0.4 736 2.7 Ni/SiO2-c 42.0 4.2 0.9 1075 1.9 2.1 40.0 3.5 1.7 1488 1.6 67.6 19.4 0.8 1200 3.0 Ni/FDU12 2.5 51.8 18.8 1.4 1600 2.3 49.3 15.9 1.9 1962 1.8 46.4 14.9 0.9 1673 2.2 57.6 22.0 1.8 2326 1.5 Ni/MSA 3.1 78.3 57.0 2.9 3226 1.1 62.7 32.5 4.6 4712 0.8 60.0 28.3 5.8 5696 0.6 36.6 8.1 0.9 1165 3.1 73.2 43.9 1.3 1475 2.4 Ni/Mil-53(Al) 2.4 66.2 38.1 2.1 1968 1.8 60.4 31.6 3.1 3104 1.2 catalysts


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Table 5. The products after selective hydrogenation obtained at 423 K. Benzene (v/v%) Toluene (v/v%) Aromatic (v/v%) SCH (%) SMCH (%) RON Reformate Ni/SiO2-a Ni/SiO2-b Ni/SiO2-c Ni/FDU12 Ni/MSA Ni/Mil-53(Al)

3.2 1.2 0.8 0.7 1.0 0.6 0.8

18.9 13.3 13.6 18.0 7.4 7.4 10.3

50.9 43.3 43.2 47.5 36.8 36.8 39.9


33.9 38.6 79.1 21.6 21.6 25.2

66.1 61.4 20.9 78.4 78.4 74.8

93.4 89.0 89.6 91.6 83.4 83.4 86.0

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Figure Captions Fig. 1. XRD patterns of as-prepared catalyst. Fig. 2. (a) N2 adsorption/desorption isotherms and (b) pore diameter distributions. Fig. 3. FESEM images of the prepared catalysts, (a) Ni/MSA, (b) Ni/FDU12, (c) Ni/SiO2-b and (d) Ni/SiO2-c. Fig. 4. EDS-map images obtained from SEM for Ni-phase in the prepared catalysts, (a) Ni/MSA, (b) Ni/FDU12, (c) Ni/SiO2-b and (d) Ni/SiO2-c. Fig. 5. (a) The benzene and (b) toluene conversions at 398-473 K and (c) benzene conversion vs. time on stream at 448 K (P=1 atm, liquid feed rate=4 ml/h, hydrogen flow rate=600 ml/h, mass of catalyst=1 g).


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Intensiyty (a. u.)

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10

Ni/MSA Ni/SiO2-b Ni/FDU12 Ni/SiO2-a Ni/Mil-53(Al) Ni/SiO2-c

Ni Ni NiO

26

42

58

Ni

74

2θ (degree) Fig. 1. XRD patterns of as-prepared catalyst.


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0.2

(a)

0

(b)

Ni/MSA Ni/SiO2-b Ni/FDU12

0.25

0.5

0.75

dVp /drp

0.15

Va /cm3(STP)g -1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.1 Ni/MSA Ni/SiO2-b Ni/FDU12

0.05

1

0 0

5

10

15

20

P/Po rp(nm) Fig. 2. (a) N2 adsorption/desorption isotherms and (b) pore diameter distributions.


25

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Fig. 3. FESEM images of the prepared catalysts, (a) Ni/MSA, (b) Ni/FDU12, (c) Ni/SiO2-b and (d) Ni/SiO2-c.


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Fig. 4. EDS-map images obtained from SEM for Ni-phase in the prepared catalysts, (a) Ni/MSA, (b) Ni/FDU12, (c) Ni/SiO2-b and (d) Ni/SiO2-c.


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100

Benzene Conversion (%)

Ni/SiO2-a Ni/SiO2-b Ni/SiO2-c Ni/FDU12 Ni/MSA Ni/Mil-53(Al)

(a)

75

50

25

60

Ni/SiO2-a Ni/SiO2-b Ni/SiO2-c Ni/FDU12 Ni/MSA Ni/Mil-53(Al)

45

(b)

30

15

0

0 398

423

448

473

398

423

Temperature (K)

448

473

Temperature (K)

80

Benzene Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Toluene Conversion (%)

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(c)

70

60

50

Ni/SiO2-a Ni/SiO2-c Ni/MSA

Ni/SiO2-b Ni/FDU12 Ni/Mil-53(Al)

40 0

2.5

5

7.5

10

Time on stream (h)

Fig. 5. (a) The benzene and (b) toluene conversions at 398-473 K and (c) benzene conversion vs. time on stream at 448 K (P=1 atm, liquid feed rate=4 ml/h, hydrogen flow rate=600 ml/h, mass of catalyst=1 g).


Competitive hydrogenation of benzene in reformate gasoline over Ni

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