Comparison of the Reactive Adsorption Desulfurization Performance

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Comparison of Reactive Adsorption Desulfurization Performance of Ni/ZnO-Al2O3 Adsorbents Prepared by Different Methods Rooh Ullah, Peng Bai, Pingping Wu, Zhanquan Zhang, Ziyi Zhong, U. J. Etim, Fazle Subhan, and Zifeng Yan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00232 • Publication Date (Web): 22 Mar 2016 Downloaded from http://pubs.acs.org on March 23, 2016

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Comparison of Reactive Adsorption Desulfurization Performance of Ni/ZnO-Al2O3 Adsorbents Prepared by Different Methods Rooh Ullah, † Peng Bai, †,* Pingping Wu, † Zhanquan Zhang,§ Ziyi Zhong, ‡ U. J. Etim, † Fazle Subhan, ‖, † and Zifeng Yan †,* †

State Key Laboratory of Heavy Oil Processing, PetroChina Key Laboratory of Catalysis, China University of Petroleum, Qingdao, 266555, China §

Petrochina Petrochemical Research Institute, Beijing 102206, China

‡

School of Chemical & Biomedical Engineering, Nanyang Technological University (NTU), 62 Nanyang Drive, 637459 Singapore ‖

Department of Chemistry, Abdul Wali Khan University Mardan, K.P, Pakistan

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to)

* Corresponding authors. Tel: +86-532-86981856; 86981296; Fax: +86 532 86981295. E-mail address:[email protected] (P. Bai), [email protected] (Z. Yan)

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ABSTRACT: In this study, a series of Ni/ZnO-Al2O3 mixed oxide (MO) adsorbents were prepared by the one-step homogeneous precipitation method and the cation-anion double hydrolysis (CADH) method for reactive adsorption desulfurization (RADS) using thiophene as a model fuel in a fixed bed reactor. The synthesized adsorbents were characterized by N2 sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature programmed reduction (H2-TPR), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis) and Raman spectroscopy. Results show that both Ni loading and preparation method have a significant effect on adsorbent’s RADS activities. Among the studied adsorbents, 10%Ni/ZnO-Al2O3 prepared by the one- step urea precipitation method showed the best RADS performance with a thiophene conversion up to 96% and a sulfur adsorption capacity of 86 mg S/g, which is 34% larger than that of CADH adsorbents. In addition, upon five RADS-regeneration cycles, sample 10%Ni/ZnO-Al2O3 exhibited a drop of only 3% in thiophene conversion, indicating the high stability of Ni/ZnO-Al2O3 adsorbent prepared by homogeneous precipitation. Characterization results show that the one-step homogeneous precipitation method could facilitate the formation of small ZnO particles while suppressing the formation of inactive ZnAl2O4. On the other hand, by decreasing the formation of NiAl2O4, the homogeneous precipitation method could also generate high concentration of Ni0 sites, which are the active centers for the hydrogenolysis of C-S bonds. These findings indicate that a high-performance adsorbent for RADS can be obtained by employing a proper preparation method with a good control on the adsorbent structure.


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1.

INTRODUCTION

It has been recognized that sulfur oxides contribute to the accumulation of PM 2.5 and PM10 in atmosphere due to the formation of sulfates. Organosulfur compounds in gasoline not only cause the formation of acid rain by emitting sulfur oxides, but also deactivate catalysts in vehicle exhaust converters.

1-4

Therefore, one of the major worldwide concerns over the transportation

fuel quality is the sulfur content. In China and US, the sulfur concentration in gasoline will be regulated to be less than 10 ppm from 2017 onwards.

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In order to meet the more stringent

environmental protection legislations and regulations, ultra-deep desulfurization technologies are desired to produce ultra-low sulfur fuels. 6,7 Among the various technologies used for removing sulfur from gasoline, the reactive adsorption desulfurization technology (RADS) represented by S-Zorb process developed by Conoco Phillips Co. 8-10 has been implemented on an industrial scale by SINOPEC in China and is gaining increasing attention. This technology combines the advantages of both adsorption desulfurization

11,12

and catalytic hydrodesulfurization technologies.

13-15

In the S-Zorb process,

sulfur in gasoline is removed in moderate hydrogen pressure without severe decrease of octane number. 16-18 The reactive desulfurization of fluidized catalytic creaking (FCC) gasoline is achieved over Ni/ZnO-based adsorbents. Sulfur atoms in the organosulfur compounds are selectively captured by forming metal sulfides and the remaining hydrocarbon molecules without sulfur are released back to the main stream.

19-22

The RADS mechanism over Ni/ZnO-based adsorbent has already

been investigated by several groups. Tawara et al.

14

deduced that ZnO support had a kind of

strong metal-support interaction (SMSI) with Ni and could automatically regenerate Ni during


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the desulfurization process. Babich and Moulijin

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reported that the RADS process might

proceed via three series steps. In the first step, NiS was formed upon exposure to organosulfur compounds. In the second step, NiS reacted with H2 to restore Ni active sites with the release of H2S. In the final step, the resulting H2S reacted with ZnO to produce ZnS. Huang et al. 9 verified that sulfur species reacted with nickel to form Ni3S2 instead of NiS. Bezverkhyy et al.

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investigated the reaction kinetics of thiophene over Ni/ZnO adsorbent by thermal gravimetric analysis and identified a rapid sulfur chemisorption on Ni followed by a nucleation controlled conversion of ZnO to ZnS. The rate-limiting step was reported to be different during different stages of reaction. In the beginning, the thiophene decomposition was determined to be the ratelimiting step where a highly dispersed Ni metal was favorable, while with the partial sulfidation of ZnO, the thiophene diffusion could become the rate-limiting step because of the collapse of particle voids caused by the volume expansion during the transformation of ZnO to ZnS. 15 Based on the possible RADS mechanism described above, it is reasonable to conclude that an adsorbent with a highly porous structure and a high dispersion of metal components is the key to a high RADS activity. Besides that, the size of ZnO was found to have a significant impact on the RADS performance. ZnO particles with smaller particle size exhibited much higher RADS activity and larger sulfur capture capacity than those with larger particle size.

1

In industry, a

kneading method is commonly used to prepare the RADS adsorbent, where typically zinc oxide, nickel oxide, pseudoboehmite and SiO2 are physically mixed together to form the adsorbent. 16,24,25

Such kind of adsorbents have a poor pore structure and low dispersions of Ni and ZnO,

thus poor RADS performance is commonly observed. 25 Therefore, new approaches for synthesis of adsorbents with superior RADS performance are desirable. Due to the uniform composition at molecular level, homogeneous precipitation has been demonstrated to be effective to achieve 4 ACS Paragon Plus Environment

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uniformly dispersed particles. Especially, when urea is used as the precipitation agent, a metal carbonate hydroxide product is usually obtained. By decomposing the product at an elevated temperature, CO2, H2O and even NH3 will be released, leading to the formation of a porous metal oxide with abundant structural defects,

26,27

which may be suitable for the application as

RADS adsorbents. In addition, a versatile cation-anion double hydrolysis method (CADH) was reported for the preparation of mesoporous mixed oxide, where high dispersions of metal oxides were achieved even at high loadings. 28 Motivated by the above mentioned progress in adsorbent synthesis, we aim to develop effective and feasible approaches for preparing efficient adsorbents for RADS process and to understand the real structural factors that contribute to the good RADS performance. In this work, Ni/ZnO-Al2O3 adsorbents were prepared using the one-pot homogeneous precipitation approach and the CADH method. The adsorbents were evaluated in RADS reaction using a model fuel as the feedstock. The RADS performance of adsorbents prepared by the two methods was compared under identical conditions and the samples were characterized with a number of techniques.


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2. EXPERIMENTAL SECTION 2.1. Chemicals and Feedstock. In this study, a model fuel with a sulfur concentration of 3000 ppm was prepared by introducing thiophene (analytical grade, Aldrich) as a sulfur source in n-octane (analytical grade, Aldrich). ZnCl2 , Zn (NO3)2·6H2O, AlCl3·6H2O, NaAlO2, Pluronic P123 and urea were purchased from Sinopharm Chemical Reagent Co., Ltd. NiCl2 and Ni(NO3)2.6H2O were supplied by Shanghai Chemical Reagent Hanson. All chemicals were used without further purification. 2.2. Preparation of Adsorbents. For the one-pot homogeneous precipitation, typically 30 mL of ZnCl2 (1.36g) aqueous solution was mixed with 20 mL of AlCl3·6H2O (2.41g) aqueous solution with continuous stirring for 1 h. Then, 7.2 g of urea was added at room temperature. Subsequently, an aqueous solution of NiCl2 with different concentrations was added dropwise to the final mixture, followed by stirring for another 3 h. Finally, the mixture was transferred into a Teflon-lined stainless steel autoclave for hydrothermal treatment at 100⁰C for 24 h. The precipitate was filtered, washed with deionized water, dried at 80⁰C, and calcined at 550⁰C in air for 2 h. The synthesized samples are denoted as X%Ni/ZnO-Al2O3, where X represents the Ni loading. For comparison, a sample with the same composition of 10%Ni/ZnO-Al2O3 was also synthesized by the CADH method following our previous procedure

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. Typically, 2.32 g of

Pluronic P123 was dissolved in 30 mL of distilled water to obtain a clear solution, which was subsequently added with 2.97 g of Zn (NO3)2·6H2O and 20 mL aqueous solution of NaAlO2 (3.28 g) under continuous stirring. Afterwards, an appropriate amount of Ni(NO3)2•6H2O dissolved in 5 mL distilled water was added drop-wise, and the solution was further stirred for 4 h. The resultant solution was transferred into a stainless steel Teflon-lined autoclave and


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processed with similar procedures used in the one-pot homogenous approach and the material obtained was denoted as 10%Ni-ZnO-Al2O3. 2.3. RADS Performance Evaluation. The RADS performance evaluation of Ni/ZnOAl2O3 adsorbents was conducted in a fixed bed reactor system. A microreactor with an internal diameter of 8 mm and 250 mm in length was used for this study. Prior to desulfurization experiment; the reactor was washed thoroughly with ethanol for 24 h followed by purging with pure N2 for 30 min. 1 g (20-40 mesh) of adsorbent was loaded into the center of the microreactor column. Prior to the RADS reaction, the adsorbent was reduced in the presence of hydrogen with a flow rate of 20 mL/min under 0.5 MPa at 400 °C for 4 h. After the reduction process, the temperature and pressure were set at 350 oC and 1.5 Mpa. The model fuel was preheated to 120○C and injected along with H2 into the column by a micro-injection pump at a weight hourly space velocity (WHSV) of 4 h−1 with a H2/Oil ratio of 400. The sulfur content in the liquid product was analyzed with a BRUKER 450 Gas Chromatograph coupled with a PFPD detector.


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2.4. Characterization of Adsorbents. N2 sorption of the Ni/ZnO-Al2O3 adsorbents was carried out at 77K using a Micromeritics TriStar 3000 analyzer. Prior to adsorption analyses, all samples were degassed at 300⁰C for 12 h in vacuum. Brunaur-Emmett-Teller 2 method was used to calculate the specific surface area (SBET) in the relative pressure range of 0.05-0.25. BarrettJoyner-Halenda (BJH) method was used to calculate the pore size distribution (PSD).

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X-ray

diffraction (XRD) patterns were obtained on a PAN Analytical X’Pert PRO MPD X-ray diffractometer (XRD) coupled with nickel filtered Cu Kα radiation (40 kV, 40 mA) in a scanning range of 2 θ= 5-70o. Morphology of the calcined sample was studied with a S-4800 scanning electron microscope (SEM) operating at 15 kV. Elemental distribution mapping was analyzed by a JEM-2100 microscope equipped with energy-dispersive X-ray spectroscopy (EDX) at 200kV. The high resolution transmission electron microscopy (HRTEM) images were obtained on a JEM-2100 microscope. H2 temperature programmed reduction (H2-TPR) study of samples was conducted through Chem-BET 3000 TPD/TPR analyzer (Quantachrome, USA). Ultravioletvisible diffuse reflectance spectroscopy spectra were measured on a Hitachi U-4100 Spectrophotometer in the range of 200-800 nm. A Raman spectrophotometer (Thermo Fisher Scientifics, DXR) were employed to measure Raman spectra for adsorbents at room temperature with a backscattering geometry. 3. RESULTS AND DISCUSSION 3.1. Reactive Adsorbent Desulfurization Performances of Adsorbents. The reactive adsorption desulfurization performances of Ni/ZnO-Al2O3 adsorbents are shown in Figure 1. The corresponding sulfur adsorption capacities (mg S/g) are summarized in Figure 2. 10%Ni/ZnOAl2O3 exhibits a high RADS activity with the highest thiophene conversion of 99 % for the first 15 mL fuel flow, which gradually decreases to 96 % with increasing the oil volume to 30 mL,


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corresponding to a cumulative sulfur adsorption capacity of 78 mg S/g at 30 mL of oil flow (Figure 2). It is worthy to note that this sulfur adsorption capacity is three-fold higher than that of the Ni/ZnO-based adsorbents prepared by the conventional kneading method catalyst.

16

In the

case of 8%Ni/ZnO-Al2O3 and 12%Ni/ZnO-Al2O3, the thiophene conversions after 15 mL fuel flow are reduced to 85 and 62%, along with the sulfur adsorption capacities of 61 and 41 mg S/g, respectively at 30 mL of fuel flow, implying the significant influence of Ni loading on RADS performance. By contrast, under the same RADS conditions, the 10%Ni-ZnO-Al2O3 adsorbent synthesized using the cation-anion double hydrolysis method displays a lower RADS performance than that of 10%Ni/ZnO-Al2O3. As revealed in Figure 1, the initial thiophene conversion at 15 mL of fuel is 86%, which is reduced to less than 71% after treating 30 mL of fuel with a corresponding capacity of 56 mg S/g, which is about two thirds of that of 10%Ni/ZnO-Al2O3. In short, the measured sulfur adsorption order is as follows: 10%Ni/ZnOAl2O3 ˃ 8%Ni/ZnO-Al2O3 ˃ 10%Ni-ZnO-Al2O3 ˃ 12%Ni/ZnO-Al2O3. 3.2. XRD Analysis. The XRD patterns of the adsorbents are shown in Figure 3a. Only gahnite phase (ZnAl2O4, JCPDS file No. 00-001-1146) is identified in all adsorbents, suggesting either existence of amorphous ZnO in highly dispersed form or non-existence of ZnO phase. The existence of ZnAl2O4, which is inactive in RADS process, between ZnO and Al2O3.

30

16

indicates the strong interaction

And, this interaction seems to be more prominent in 10%Ni-ZnO-

Al2O3 sample. In sample 12%Ni/ZnO-Al2O3, besides ZnAl2O4 phase, an additional nickel aluminum oxide phase (NiAl2O4, JCPDS card No. 00-001-1299) with reflections at 2θ of 45.1⁰, 59.5⁰ and 65.4⁰ is also observed, indicating the strong interaction of Ni with Al2O3. Eley et al. 31 investigated Ni species in Ni/Al2O3 based adsorbents and concluded that the amount of the inactive NiAl2O4 spinel was dependent on of the nickel loading and high loading of Ni favored


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the formation of this spinel either in dispersed or non-dispersed form. Furthermore, after reduction and before RADS test, the diffraction pattern of 10%Ni-ZnO-Al2O3-Red. is similar to that of unreduced 10%Ni-ZnO-Al2O3. The absence of reflections assignable to metallic Ni phase indicates that nickel particles were highly dispersed in the sample. The XRD patterns of spent adsorbents are shown in Figure 3b, where characteristic peaks of hexagonal zinc sulfide phase (ZnS JCPDF file no. 01-089-2191) are observed. This observation suggests the presence of ZnO, for ZnAl2O4 is well recognized to be in active in RADS process. As reported,16,32-35 ZnO is inactive toward thiophene but effectively reactive toward H2S to form ZnS, which is responsible for the sulfur capacity of Ni/ZnO-Al2O3 adsorbents (Figure 1). Therefore, the appearance of higher ratio of inactive ZnAl2O4 phase in 10%Ni-ZnO-Al2O3 sample will reduce the ZnO amount in the sample [34], thus decreasing the sulfur capacity. In comparison with 10%Ni-ZnO-Al2O3, evidently, 10%Ni/ZnO-Al2O3 shows higher peak intensities for ZnS with lower intensities for ZnAl2O4 phase, implying a larger amount of ZnO was converted to ZnS in 10%Ni/ZnO-Al2O3,

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which is in good agreement with the results

shown in Figure 1 and 2, where a larger sulfur capacity is observed on 10%Ni/ZnO-Al2O3 than on 10%Ni-ZnO-Al2O3. The presence of NiAl2O4 phase in sample 12%Ni/ZnO-Al2O3 after H2 reduction and RADS process indicates that NiAl2O4 could not be reduced to its active form of Niο,

36,37

but remained intact during the RADS process, resulting in a very low amount of active

Niο phase available for the hydrogenolysis of C-S bonds of thiophene. This is in well agreement with the results shown in Figure 1 and 2, where the poorest RADS performance of sample 12%Ni/ZnO-Al2O3 is observed. It is well accepted that the reaction of nickel with the organosulfur compound is the rate-limiting step in RADS technique, which breaks C-S bonds and generates H2S.

33,34

Huang et al.

21

verified the same phenomena by sulfur K-edge XANES 10

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study and concluded that the C-S bond cleavage is the rate limiting step in RADS technique which strongly relies on chemically free Ni0. Hence, to obtain a good RADS performance, Ni should be uniformly distributed over small ZnO particles.

1

Therefore, any effective synthetic

approach should be able to reduce the possibility of interaction between ZnO and Ni with Al2O3 preventing the formation of inactive NiAl2O4 and ZnAl2O4, but increase the loading of highly dispersed active species such as ZnO and Ni0. These results indicate the formation of welldispersed active ZnO and Ni0 species in Ni/ZnO-Al2O3 adsorbents may account for their superior RADS performance. 3.3. UV-visible DRS Analysis. To reveal the differences in phase composition,

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UV-

visible diffuse reflectance spectroscopy (UV-visible DRS) spectra were recorded for samples 10%Ni/ZnO-Al2O3 and 10%Ni-ZnO-Al2O3 (Figure 4). As shown in Figure 4, an absorbance peak at around 370 nm is observed for both samples, which are assigned to ZnO,30,38,39 demonstrating the presence of ZnO particles in the two samples. As compared with that of 10%Ni-ZnO-Al2O3, the higher intensity of ZnO peak at ca. 371 nm for 10%Ni/ZnO-Al2O3 indicates the larger amount of ZnO in the later, which can explain well their differences in RADS activities (Figure 1 and 2). However, the absorbance band reveals a red-shift from 371 to 381 nm for sample 10%Ni-ZnO-Al2O3 synthesized by CADH method, implying the ZnO crystal growth and coagulation with the effect of copolymer at high temperature.

38,40

In addition,

another peak is observed in UV region below 300 nm which is assigned to ZnAl2O4.

30,41,42

Obviously, the higher intensity of the absorbance peak below 300 nm in 10%Ni-ZnO-Al2O3 suggests the larger concentration of inactive ZnAl2O4, which can explain well its poorer thiophene conversion activity and lower sulfur adsorption capacity. This result is also consistent with the above XRD findings (Figure 3). Thus, it can be concluded that the higher RADS


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performance for 10%Ni/ZnO-Al2O3 may partially originate from its higher concentration of well dispersed ZnO. 3.4. Raman Spectroscopy Analysis. The Raman spectra measured at room temperature for 10%Ni/ZnO-Al2O3 and 10%Ni-ZnO-Al2O3 adsorbents are shown in Figure 5. The spectra exhibit a E2 active Raman mode at 99 cm-1 which mainly involves ZnO motion and is recognized as the lattice vibration of ZnO.

43,44

As is observed, 10%Ni/ZnO-Al2O3 shows a higher ZnO intensity

compared with 10%Ni-ZnO-Al2O3, probably due to the weaker interaction between ZnO and aluminates in 10%Ni/ZnO-Al2O3, which is in agreement with the XRD results (Figure 3), where lower intensity of ZnAl2O4 peaks is observed for 10%Ni/ZnO-Al2O3 than that of 10%Ni-ZnOAl2O3. Besides, a strong E1 longitudinal optical (LO) phonon mode is also detected at 580 cm─1 for sample 10%Ni/ZnO-Al2O3, attributed to the phonon structure of the ZnO-based materials. 4548

In contrast, this E1 (LO) phonon for sample 10%Ni-ZnO-Al2O3 is of higher intensity than that

of 10%Ni/ZnO-Al2O3 and exhibits a red shift to 588 cm-1, demonstrating the ZnO agglomeration in the bulky phase with intrinsic structure defects, Al2O3 than that in 10%Ni/ZnO-Al2O3.

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49

or larger ZnO particles in 10%Ni-ZnO-

This is in accord with the UV-visible DRS analysis

(Figure 4) and probably related to the templating effect of copolymer on the inorganic framework of 10%Ni-ZnO-Al2O3. Therefore, the Raman spectra verified the existence of small ZnO particles over 10%Ni/ZnO-Al2O3 adsorbent and provide a reasonable explanation for the RADS results shown in Figure 1 and 2 that the presence of small ZnO particles as an independent phase is one of the key factors contributing to the high RADS performance. 1 3.5. Textual Properties. Figure 6a exhibits N2 adsorption-desorption isotherms of adsorbents. All Ni/ZnO-Al2O3 adsorbents demonstrate type-IV adsorption isotherms with a H-2 hysteresis loop, proving the existence of ink-bottle mesopore in these samples.51 From the PSD


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curves and Table 1, it is observed that the pore size and pore volume of all Ni/ZnO-Al2O3 adsorbents have a decline trend with increasing Ni loading (Figure 6b). As can be seen from Table 1, Ni/ZnO-Al2O3 with 8% Ni loading has a higher pore volume and a larger average pore size than that with 12%Ni loading. A Similar trend was also observed for the specific surface area. This is possibly attributed to the occupation of mesoporous channels by Ni species.

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In

contrast, sample 10%Ni-ZnO-Al2O3 has a lower surface area compared with the other adsorbents, indicating the templating effect of copolymer at high crystallization temperature induces the crystal growth, consistent with studies showing that crystalline materials usually have a low surface area than the amorphous counterparts. 53,54 In order to understand the structural change of adsorbents during the RADS process, the N2 sorption characterization for spent adsorbents was performed. Figure 7 displays N2 adsorptiondesorption isotherms and PSD curves of spent Ni/ZnO-Al2O3 samples. The adsorbed amounts of N2 on the spent adsorbents become smaller, revealing the altering of the pores to lower level by sulfur adsorption and carbon deposition,

55

in accord with

the XRD results for the spent

adsorbents (Figure 3). Regarding 10%Ni/ZnO-Al2O3, its surface area, pore volume and pore size were reduced by 24.5%, 37.1% and 25.2% (Table 1), respectively, comparatively larger than all other adsorbents, consistent with its highest desulfurization activity among the investigated adsorbents as shown in Figure 2. In comparison with 10%Ni-ZnO-Al2O3, 10%Ni/ZnO-Al2O3 possesses higher surface area and proper pore structure, which can accommodate more phase transition and coke deposition, thus enhancing the RADS activity with a longer lifetime. 3.6. Morphology and Microstructure of Adsorbent. In order to obtain deep insights into the textural structure and morphology of 10%Ni/ZnO-Al2O3 sample, SEM, HRTEM and surface elemental distribution mapping analyses were conducted and the results are shown in Figure 8. It 13 ACS Paragon Plus Environment

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is clearly seen from SEM image (Figure 8a) that sample 10%Ni/ZnO-Al2O3 displays a spongylike morphology composed of small particles in the range of about 500-1000 nm. In addition, mesopores in the matrix of 10%Ni/ZnO-Al2O3 sample are clearly observed from TEM image in Figure 8b, confirming the porous features of 10%Ni/ZnO-Al2O3 as shown in Table 1. From the SEM-EDX images of the surface elemental distribution mapping for 10%Ni/ZnO-Al2O3 (Figure 8c-8f), it is verified that the ZnO and NiO particles are homogeneously dispersed over ZnAl2O4 and/or Al2O3 distributed inside the wide-ranging pores. The excellent dispersion of Ni and ZnO contributes to the higher RADS activity, which is responsible for hydrogenolysis of C-S bonds in thiophenic compounds and capturing of H2S, respectively. 25,56 3.7. H2-TPR Characterization. In the Ni/ZnO-Al2O3 based samples, Ni0 play an active role in the cleavage of C-S bonds in organosulfur compound with the release of H2S.33,34 The cleavage of C-S bonds is considered to be the rate limiting step in reactive adsorption desulfurization process, which strongly depends on the reducibility of Ni2+.21 In order to understand the reducibility of Ni2+ in the adsorbents, H2-TPR technique was used. As shown in Figure 9, two TCD signals were observed. The peak at around 300⁰C is attributed to the reduction of Ni2+ species weakly interacted with aluminate ions. The other peak in the range of 500-750⁰C is assigned to the reduction of strongly interacted Ni+2 species at the tetrahedral/octahedral vacancies of aluminate spinels and the decomposition of NiAl2O4 spinel phase.

52,57,58,59

Since the pre-reduction temperature used prior to RADS test was 400 oC, the

weakly interacted Ni2+ ions could be reduced to Ni0 atoms during the pre-reduction, which are active centers for the cleavage of C-S bonds. By contrast, strongly interacted Ni+2 species are inactive in the RADS process. As observed from Figure 9, the intensity of the peak for the weakly interacted Ni+2 species increases with the increase of Ni loading, indicating the same


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trend of RADS activity of the adsorbents. However, considering the high content of ZnAl2O4 phase in sample 12%Ni/ZnO-Al2O3, the produced H2S could not be effective stored by ZnO. Thus, the highest of sulfur capacity of sample 10%Ni/ZnO-Al2O3 should be attributed to its relatively high content of easily reducible Ni2+ and low content of ZnAl2O4 phase. 3.8. Regenerations of Catalyst Sample and RADS Mechanism. Adsorbent regeneration is an indispensable process in RADS process, where regeneration stability and long longevity of the catalyst are vitally important for their industrial utilization.

25,60,61

The key factors for

deactivation of adsorbents include carbon deposition, ZnS formation and sintering of the active metal particles, ZnO particles and the formation of impurity. The activity loss by carbon deposition and ZnO sulfurization can be recovered in regeneration process in lean oxygen/air gas flow at elevated temperatures, whereas the sintering of the catalyst is considered as the perpetual deactivation. 10%Ni/ZnO-Al2O3 was selected to evaluate its stability during the multi-cycle regeneration. Regeneration of the spent adsorbent was carried out in tubular furnace in air atmosphere at 550○C for 4 h. Figure 10 shows the stability and RADS activity after five consecutive regeneration cycles under similar conditions as the fresh adsorbent. The adsorbent achieves a desulfurization activity up to 96%, and a slight drop by 3% in thiophene conversion as compared with the initial activity, after the fifth cycle regeneration, indicating it good RADS stability. As such, Ni/ZnO-Al2O3 is relatively stable without significant change on Ni and ZnO particles upon calcination and Ni reduction. Since RADS is an incessant process, the used adsorbents should be repeatedly regenerated. Only a stable porous material with well dispersed active components will effectively reduce the mass transfer resistance of reactant molecules to contact with Ni/ZnO based materials and improve regeneration stability and RADS performance. It seems from the above discussion that 15 ACS Paragon Plus Environment

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Page 16 of 42

the homogeneous precipitation by urea can lead to the formation of highly dispersed small ZnO particles. That is because, when urea was decomposed at 100οC, the uniform increase of solution pH caused the homogeneous precipitation of Zn2+, Al3+ and Ni+2 ions, resulting in the formation of fine particles. The proposed RADS mechanism for NiO/ZnO-Al2O3 is illustrated in scheme 1. As can be seen, the organosulfur molecules can interact first with Ni particles and form Ni3S2 as revealed by Huang et al. 21 in their sulfur K-edge XANES investigation. Meanwhile, the sulfurfree fuel goes back to the main stream, while Ni3S2 react with H2 and generate H2S, which is very reactive toward ZnO to form ZnS through nucleation control sulfidation

9,21

as also shown

in our XRD study (Figure 3b). In this incessant RADS process, small and well dispersed ZnO particles are favorable for the continuous H2S interaction and sulfur mass transfer to ZnS formation, which is believed as a critical factor to achieve high sulfur adsorption capacity. After complete deactivation, the adsorbent can be used again for another RADS cycle after regeneration in air/O2 follow by reduction in H2. 4. CONCLUSIONS In this work, one-pot homogenous precipitation approach towards the preparation of Ni/ZnOAl2O3 is investigated, and the resulting samples are employed for RADS in high sulfur concentration model fuel. The 10%Ni/ZnO-Al2O3 sample achieves the highest thiophene conversion up to 96% with a processing amount of 30 mL of model fuel, corresponding to a 78 mg S/g sulfur adsorption capacity, which is 27% higher than that of the counterpart 10%Ni-ZnOAl2O3 prepared by the cation-anion double hydrolysis method. By tailoring the loading of Ni on these samples, it is found that too high Ni loading intends to form inactive NiAl2O4, and decreasing the expected activity. By comparing 10%Ni/ZnO-Al2O3 with 10%Ni-ZnO-Al2O3, it is revealed that there are several factors that can contribute to the higher RADS performance, 16 ACS Paragon Plus Environment

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namely: (1) the formation of small particles of ZnO and NiO with higher surface area and larger pore volume via homogenous precipitation using urea as the precipitation agent, as compared with that of the template assisted CADH method. However, the later usually leads to a relatively higher crystallinity with the sacrifice of surface area. (2) The reduced formation of ZnAl2O4 and NiAl2O4 phases by the homogenous urea precipitations, which are inactive for RADS, may be the reason for their higher performance. This study proves that the facile homogenous precipitation approach is effective to prepare the adsorbents with enhanced RADS performance, and obtains a clear structure-performance relationship for the adsorbents. ACKNOWLEDGEMENTS This work was financially supported by the Joint Funds of the National Natural Science Foundation of China and China National Petroleum Corporation (U1362202), Natural Science Foundation of China (21206195), the Fundamental Research Funds for the Central Universities (14CX02050A,

14CX02123A),

Shandong

Provincial

Natural

Science

Foundation

(ZR2012BM014), and the project sponsored by Scientific Research Foundation for Returned Overseas Chinese Scholar. Z. Z. ([email protected]) works at the Institute of Chemical Engineering in Singapore and also holds an adjunct associate professor position in the School of Chemical & Biomedical Engineering, Nanyang Technological University (NTU) in Singapore. REFERENCES (1) Zhang, Y.; Yang, Y.; Han, H.; Yang, M.; Wang, L.; Zhang, Y.; Jiang, Z.; Li, C. Ultra-deep desulfurization via reactive adsorption on Ni/ZnO: The effect of ZnO particle size on the adsorption performance. Appl. Catal. B: Environ. 2012, 119, 13-19.


Energy & Fuels

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(2) Dasgupta, S.; Gupta, P.; Nanoti, A.; Goswami, A. N.; Garg, M. O.; Tangstad, E.; Vistad, Ø. B.; Karlsson, A.; Stöcker, M. Adsorptive desulfurization of diesel by regenerable nickel based adsorbents. Fuel 2013, 108, 184-189. (3) Kašpar, J.; Fornasiero, P.; Hickey, N. Automotive catalytic converters: current status and some perspectives. Catal. Today 2003, 77 (4), 419-449. (4) Farrauto, R. J.; Heck, R. M. Catalytic converters: state of the art and perspectives. Catal. Today 1999, 51 (3), 351-360. (5) Kwasniewski, V.; Blieszner, J.; Nelson, R. Petroleum refinery greenhouse gas emission variations related to higher ethanol blends at different gasoline octane rating and pool volume levels. Biofuels Bioprod. Biorefin. 2016, 10 (1), 36-46. (6) Mansouri, A.; Khodadadi, A. A.; Mortazavi, Y. Ultra-deep adsorptive desulfurization of a model diesel fuel on regenerable Ni–Cu/γ-Al2O3 at low temperatures in absence of hydrogen. J. Hazard. Mater. 2014, 271, 120-130. (7) Ma, X.; Velu, S.; Kim, J. H.; Song, C. Deep desulfurization of gasoline by selective adsorption over solid adsorbents and impact of analytical methods on ppm-level sulfur quantification for fuel cell applications. Appl. Catal. B: Environ. 2005, 56 (1), 137-147. (8) Xu, G.; Diao, Y.; Zou, K.; Zhang, Z. Cause analysis of sorbent deactivation in S-Zorb unit for gasoline desulfurization. Pet. Process. Petrochem. 2011, 42, 1. (9) Huang, L.; Wang, G.; Qin, Z.; Dong, M.; Du, M.; Ge, H.; Li, X.; Zhao, Y.; Zhang, J.; Hu, T. In situ XAS study on the mechanism of reactive adsorption desulfurization of oil product over Ni/ZnO. Appl. Catal. B: Environ. 2011, 106 (1), 26-38.


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(10) Huan, H.; Salissou, M. N.; Dezhi, Y.; Xuan, M.; Li, S. Study on reactive adsorption desulfurization of model gasoline on Ni/ZnO-HY adsorbent. Chin. Pet. Process. Petrochem. Technol. 2013, 15 (3), 57-64. (11) Kim, J. H.; Ma, X.; Zhou, A.; Song, C. Ultra-deep desulfurization and denitrogenation of diesel fuel by selective adsorption over three different adsorbents: a study on adsorptive selectivity and mechanism. Catal. Today 2006, 111 (1), 74-83. (12) Srivastav, A.; Srivastava, V. C. Adsorptive desulfurization by activated alumina. J. Hazard. Mater. 2009, 170 (2), 1133-1140. (13) Tawara, K.; Nishimura, T.; Iwanami, H.; Nishimoto, T.; Hasuike, T. New hydrodesulfurization catalyst for petroleum-fed fuel cell vehicles and cogenerations. Ind. Eng. Chem. Res. 2001, 40 (10), 2367-2370. (14) TAWARA, K.; NISHIMURA, T.; IWANAMI, H. Ultra-deep hydrodesulfurization of kerosene for fuel cell system.(Part 2): Regeneration of sulfur-poisoned nickel catalyst in hydrogen and finding of auto-regenerative nickel catalyst. Sekiyu Gakkai Shi 2000, 43 (2), 114120. (15) Ryzhikov, A.; Bezverkhyy, I.; Bellat, J.-P. Reactive adsorption of thiophene on Ni/ZnO: Role of hydrogen pretreatment and nature of the rate determining step. Appl. Catal. B: Environ. 2008, 84 (3), 766-772. (16) Meng, X.; Huang, H.; Shi, L. Reactive Mechanism and Regeneration Performance of NiZnO/Al2O3-Diatomite Adsorbent by Reactive Adsorption Desulfurization. Ind. Eng. Chem. Res. 2013, 52 (18), 6092-6100. (17) Babich, I.; Moulijin, J. Recent advancement on deep desulfurization of gasoline and diesel oil. Fuel 2003, 82, 607-631.


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(18) Khare G. P. Sorbent composition, process for producing and use in desulfurization. U.S. Patent 6,274,533, Aug 14, 2001. (19) Bezverkhyy, I.; Ryzhikov, A.; Gadacz, G.; Bellat, J.-P. Kinetics of thiophene reactive adsorption on Ni/SiO2 and Ni/ZnO. Catal. Today 2008, 130 (1), 199-2055. (20) Ito, E.; Van Veen, J. On novel processes for removing sulphur from refinery streams. Catal. Today 2006, 116 (4), 446-460. (21) Huang, L.; Wang, G.; Qin, Z.; Du, M.; Dong, M.; Ge, H.; Wu, Z.; Zhao, Y.; Ma, C.; Hu, T. A sulfur K-edge XANES study on the transfer of sulfur species in the reactive adsorption desulfurization of diesel oil over Ni/ZnO. Catal. Commun. 2010, 11 (7), 592-596. (22) Saleh, T. A. Ni/ZnO Nano Sorbent for Reactive Adsorption Desulfurization of Refinery Oil Streams. Applying Nanotechnology to the Desulfurization Process in Petroleum Engineering, ed. Engineering Science Reference, Hershey PA: 2015, 216. (23) Bezverkhyy, I.; Ryzhikov, A.; Gadacz, G.; Bellat, J.-P. Kinetics of thiophene reactive adsorption on Ni/SiO2 and Ni/ZnO. Catal. Today 2008, 130 (1), 199-205. (24) Mesters, C. M. A. M. Catalyst and its use in desulphurisation. U.S. Patent 7,297,655, Nov 20, 2007. (25) Wen, Y.; Wang, G.; Wang, Q.; Xu, C.; Gao, J. Regeneration Characteristics and Kinetics of Ni/ZnO–SiO2–Al2O3 Adsorbent for Reactive Adsorption Desulfurization. Ind. Eng. Chem. Res. 2012, 51 (10), 3939-3950. (26) Bai, P.; Su, F.; Wu, P.; Wang, L.; Lee, F. Y.; Lv, L.; Yan, Z.-f.; Zhao, X. Copolymercontrolled homogeneous precipitation for the synthesis of porous microfibers of alumina. Langmuir 2007, 23 (8), 4599-4605.


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(27) Bai, P.; Wu, P.; Yan, Z.; Zhou, J.; Zhao, X. Self-assembly of clewlike ZnO superstructures in the presence of copolymer. The J. Phys. Chem. C. 2007, 111 (27), 9729-9733. (28) Bai, P.; Wu, P.; Yan, Z.; Zhao, X. A generalized approach to the synthesis of mesoporous mixed metal oxides using the cation-anion double hydrolysis method. Sci. Adv. Mater. 2011, 3 (6), 994-1003. (29) Barrett, E. P.; Joyner, L. G.; Halenda, P. P. The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. J. Am. Chem. Soc. 1951, 73 (1), 373-380. (30) Sampath, S. K.; Cordaro, J. F. Optical properties of zinc aluminate, zinc gallate, and zinc aluminogallate spinels. J. Am. Chem. Soc. 1998, 81 (3), 649-654. (31) Gorewit, B.; Tsutsui, M. Advances in Catalysis, ed.; DD Eley et al. Academic Press, New York: 1978. (32) TAWARA, K.; IMAI, J.; IWANAMI, H. Ultra-deep hydrodesulfurization of kerosene for fuel cell system.(Part 1): Evaluations of conventional catalysts. Sekiyu Gakkai Shi 2000, 43 (2), 105-113. (33) Tawara, K.; Nishimura, T.; Iwanami, H.; Nishimoto, T.; Hasuike, T. Ultra-deep hydrodesulfurization of kerosene for fuel cell system.(Part 3) Development and evaluation of Ni/ZnO catalyst. Sekiyu Gakkai Shi 2001, 44 (1), 43-51. (34) Fan, J.; Wang, G.; Sun, Y.; Xu, C.; Zhou, H.; Zhou, G.; Gao, J. Research on Reactive Adsorption Desulfurization over Ni/ZnO−SiO2−Al2O3 Adsorbent in a Fixed-Fluidized Bed Reactor. Ind. Eng. Chem. Res. 2010, 49 (18), 8450-8460.


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(35) Wang, G.; Wen, Y.; Fan, J.; Xu, C.; Gao, J. Reactive Characteristics and Adsorption Heat of Ni/ZnO–SiO2–Al2O3 Adsorbent by Reactive Adsorption Desulfurization. Ind. Eng. Chem. Res. 2011, 50 (22), 12449-12459. (36) Ashrafi, M.; Pfeifer, C.; Pröll, T.; Hofbauer, H. Experimental study of model biogas catalytic steam reforming: 2. Impact of sulfur on the deactivation and regeneration of Ni-based catalysts. Energy Fuels 2008, 22 (6), 4190-4195. (37) Damyanova, S.; Dotceva, A.; Eliyas, A.; Vladov, C.; Petrov, L. Recent development of the hydrodesulfurization catalysts. J. Environ. Protec. Ecol. 2000, 1 (4), 478-484. (38) Monticone, S.; Tufeu, R.; Kanaev, A. Complex nature of the UV and visible fluorescence of colloidal ZnO nanoparticles. J. Phys. Chem. B 1998, 102 (16), 2854-2862. (39) Xie, W.; Li, Y.; Sun, W.; Huang, J.; Xie, H.; Zhao, X. Surface modification of ZnO with Ag improves its photocatalytic efficiency and photostability. J. Photochem. Photobiol. A: chem. 2010, 216 (2), 149-155. (40) Bai, P.; Xing, W.; Zhang, Z.; Yan, Z. Facile synthesis of thermally stable mesoporous crystalline alumina by using a novel cation–anion double hydrolysis method. Mater. Lett. 2005, 59 (24), 3128-3131. (41) Rafla-Yuan, H.; Cordaro, J. Optical reflectance of aluminum‐doped zinc oxide powders. J. Appl. Phys. 1991, 69 (2), 959-964. (42) Ragul, G.; Sumathi, S.; Nehru, M.; KC, S.; Kumar, S.; Bajpai, S.; Goel, C.; KC, S.; Ray, S. S.; Mandal, A. Synthesis, Characterization and Photocatalytic Study of Zinc Aluminate Nanopowders against Rhodamine–B and Crystal Violet Dyes. Intern. J. Appl. Eng. Res. 2013, 8 (19), 2013.


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(43) Chen, D.; Wang, Z.; Ren, T.; Ding, H.; Yao, W.; Zong, R.; Zhu, Y. Influence of Defects on the Photocatalytic Activity of ZnO. J. Phys. Chem. C. 2014, 118 (28), 15300-15307. (44) Cuscó, R.; Alarcón-Lladó, E.; Ibanez, J.; Artús, L.; Jiménez, J.; Wang, B.; Callahan, M. J. Temperature dependence of Raman scattering in ZnO. Phys. Rev. B. 2007, 75 (16), 165202. (45) Guo, S.; Du, Z.; Dai, S. Analysis of Raman modes in Mn‐doped ZnO nanocrystals. physica status solidi (b) 2009, 246 (10), 2329-2332. (46) Bundesmann, C.; Ashkenov, N.; Schubert, M.; Spemann, D.; Butz, T.; Kaidashev, E.; Lorenz, M.; Grundmann, M. Raman scattering in ZnO thin films doped with Fe, Sb, Al, Ga, and Li. Appl. Phys. Lett. 2003, 83 (10), 1974-1976. (47) Wei, X.; Man, B.; Liu, M.; Xue, C.; Zhuang, H.; Yang, C. Blue luminescent centers and microstructural evaluation by XPS and Raman in ZnO thin films annealed in vacuum, N2 and O2. Phys. B: Condens. Matter 2007, 388 (1), 145-152. (48) Decremps, F.; Pellicer-Porres, J.; Saitta, A. M.; Chervin, J.-C.; Polian, A. High-pressure Raman spectroscopy study of wurtzite ZnO. Phys. Rev. B. 2002, 65 (9), 092101. (49) Alim, K. A.; Fonoberov, V. A.; Balandin, A. A. Origin of the optical phonon frequency shifts in ZnO quantum dots. Appl. Phys. Lett. 2005, 86 (5), 53103-53103. (50) Calizo, I.; Alim, K. A.; Fonoberov, V. A.; Krishnakumar, S.; Shamsa, M.; Balandin, A. A.; Kurtz, R. In Micro-Raman spectroscopic characterization of ZnO quantum dots, nanocrystals and nanowires. Integrated Optoelectronic Devices; Int. Soc. Opt. Photonics: 2007. (51) Gregg, S.; Sing, K. Adsorption, Surface Area and Porosity, 2nd edn., Press, London, 1982. (52) Aslam, S.; Subhan, F.; Yan, Z.; Xing, W.; Zeng, J.; Liu, Y.; Ikram, M.; Rehman, S.; Ullah, R. Rapid functionalization of as-synthesized KIT-6 with nickel species occluded with template for adsorptive desulfurization. Microporous Mesoporous Mater. 2015, 214, 54-63.


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(53) Bai, P.; Wu, P.; Yan, Z.; Zhao, X. Cation–anion double hydrolysis derived mesoporous γAl2 O3 as an environmentally friendly and efficient aldol reaction catalyst. J. Mater. Chem. 2009, 19 (11), 1554-1563. (54) Zhang, Z.; Pinnavaia, T. J. Mesostructured γ-Al2O3 with a lathlike framework morphology. J. Am. Chem. Soc. 2002, 124 (41), 12294-12301. (55) Ju, F.; Liu, C.; Meng, C.; Gao, S.; Ling, H. Reactive Adsorption Desulfurization of Hydrotreated Diesel over a Ni/ZnO–Al2O3–SiO2 Adsorbent. Energy Fuels 2015, 29 (9), 60576067. (56) Wei, Q.; Chen, J.; Song, C.; Li, G. HDS of dibenzothiophenes and hydrogenation of tetralin over a SiO2 supported Ni-Mo-S catalyst. Fron. Chem. Sci. Eng. 2015, 9 (3), 336-348. (57) Hu, D.; Gao, J.; Ping, Y.; Jia, L.; Gunawan, P.; Zhong, Z.; Xu, G.; Gu, F.; Su, F. Enhanced investigation of CO methanation over Ni/Al2O3 catalysts for synthetic natural gas production. Ind. Eng. Chem. Res. 2012, 51 (13), 4875-4886. (58) Bazyari, A.; Mortazavi, Y.; Khodadadi, A. A.; Thompson, L. T.; Tafreshi, R.; Zaker, A.; Ajenifujah, O. T. Effects of alumina phases as nickel supports on deep reactive adsorption of (4, 6-dimethyl) dibenzothiophene: Comparison between γ, δ, and θ-alumina. Appl. Catal. B: Environ. 2016, 180, 312-323. (59) Barroso, M. N.; Gomez, M. F.; Arrúa, L. A.; Abello, M. C. Hydrogen production by ethanol reforming over NiZnAl catalysts. Appl. Catal. A: Gen. 2006, 304, 116-123. (60) Rohr, D. F.; Vogel, J. A. System and method of regenerating desulfurization beds in a fuel cell system. U.S. Patent 2014/0260964, Sep 18, 2014.


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(61) Liu, M.; Ye, X.; Liu, Y.; Wang, X.; Wen, Y.; Sun, H.; Li, B. Highly selective epoxidation of propylene in low-pressure continuous slurry reactor and the regeneration of catalyst. Ind. Eng. Chem. Res. 2015, 54 (20), 5413-5426.


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List of Tables Table 1. Physical properties of different adsorbents Adsorbents

SBET(m2/g) BRa

V (cm3/g) D(nm) AR b BR a

D(nm) ARb

177.6

SBET (m2/g) V ARb (cm3/g) BR a 145.9 0.43

8%Ni/ZnO-Al2O3

0.29

9.81

7.55

10% Ni/ZnO-Al2O3

174.5

131.8

0.37

0.24

7.66

5.73

12%Ni/ZnO-Al2O3

166.5

147.3

0.28

0.20

5.86

4.89

10%Ni-ZnO-Al2O3

119.8

98.9

0.25

0.17

8.29

6.67

a

BR: before reaction; bAR: after reaction;


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List of Figure and Scheme Captions Figure 1. Reactive adsorption desulfurization profiles of adsorbents using the model fuel as feedstock. Figure 2. Sulfur adsorption capacity of adsorbents at 30mL of fuel flow. Figure 3. XRD patterns of (a) fresh and (b) spent adsorbents Figure 4. UV-visible DRS spectra of 10%Ni/ZnO-Al2O3 and 10%Ni-ZnO-Al2O3 samples Figure 5. Raman spectra of samples 10%Ni/ZnO-Al2O3 and 10%Ni-ZnO-Al2O3 Figure 6. (a) N2 adsorption-desorption isotherms and (b) pore size distribution of fresh adsorbents Figure 7. (a) N2 sorption isotherms and (b) pore size distribution of adsorbents after RADS evaluation Figure 8. SEM image (a), TEM image (b), and elemental distribution mapping of oxygen (c), aluminum (d), nickel (e) and zinc (f) of sample 10%Ni/ZnO-Al2O3. Figure 9. TPR profiles of Ni/ZnO-Al2O3 adsorbents Figure 10. Regeneration performance of sample 10%Ni/ZnO-Al2O3 Scheme 1. Proposed RADS mechanism of thiophene over Ni/ZnO-Al2O3 adsorbent


Energy & Fuels

List of Figures and Scheme Figure 1

Thiophene 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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100 90 80 70 60

10% Ni/ZnO-Al2O3

50

12% Ni/ZnO-Al2O3

40

8% Ni/ZnO-Al2O3 10% Ni-ZnO-Al2O3

0 10 20 30 40 50 Volume of model fuel/g adsorbent (mL/g)


Page 29 of 42

Figure 2

80 70 60

20 10 0

10%Ni-ZnO-Al2O3

30

12%Ni/ZnO-Al2O3

40

8%Ni/ZnO-Al2O3

50 10%Ni/ZnO-Al2O3

Sulfur capacity mgS/g adsorbent

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

Energy & Fuels


Energy & Fuels

Figure 3a

∗ZnAl2O4 ♦NiAl2O4 ∗ ∗

10%Ni/ZnO-Al2O3

Intensity (a.u)

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

Page 30 of 42

∗

∗∗

∗

♦

♦

∗

♦

∗

∗

∗

∗ ∗

∗

8%Ni/ZnO-Al2O3 12%Ni/ZnO-Al2O3

∗ ∗

10%Ni-ZnO-Al2O3 10%Ni-ZnO-Al2O3 Red.

10

20

30 40 50 2 theta degree

60

70


Page 31 of 42

Figure 3b

(b)

Intensity (a.u)

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

Energy & Fuels

♥ZnS ∗ZnAl2O4 ♦NiAl2O4

♥ ♥ 10%Ni/ZnO-Al2O3 ♥

♥

*

♥ ♥

♥♥

* *


♥ * ♥ 10%Ni-ZnO-Al O 2

10

20

3

♥♦ ♦

♦ ♥

**

30 40 50 2 Theta degree

** * 60

70


Energy & Fuels

Figure 4

1.6 1.4 Absorbance

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

Page 32 of 42

1.2 ZnO

1.0

10%Ni/ZnO-Al2O3

0.8 0.6

10%Ni-ZnO-Al2O3

300

400 500 600 Wavelength (nm)

700

800


Page 33 of 42

Figure 5

10% Ni/ZnO-Al2O3

250 Raman intensity

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

Energy & Fuels

10% Ni-ZnO-Al2O3

-1

588cm

200 150 99

100

-1

580cm

50 0 0

200

400 600 800 -1 Raman shift (cm )

1000


Energy & Fuels

Figure 6a

(a) 600

10%Ni-ZnO-Al2O3

3

-1

Volume adsorbed (cm ⋅g STP)

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

Page 34 of 42

400

200

12%Ni/ZnO-Al2O3

10%Ni/ZnO-Al2O3

8%Ni/ZnO-Al2O3

0 0.0

0.2 0.4 0.6 0.8 Relative pressure (P/P0)

1.0


Page 35 of 42

Figure 6b

(b)

0.24

3

dV/dD (cm /g nm)

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

Energy & Fuels

10%Ni-ZnO-Al2O3

0.16 12%Ni/ZnO-Al2O3

0.08


0.00 5

10 15 Pore diameter (nm)

20


Energy & Fuels

Figure 7a

450

(a) 10%Ni-ZnO-Al2O3

3

-1

Volume adsorbed (cm ⋅g STP)

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

Page 36 of 42

300

150

12%Ni/ZnO-Al2O3

10%Ni/ZnO-Al2O3

8%Ni/ZnO-Al2O3

0 0.0

0.2 0.4 0.6 0.8 Relative pressure (P/P0)

1.0


Page 37 of 42

Figure 7b

(b) 0.15

3

dV/dD (cm /g nm)

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

Energy & Fuels

10%Ni-ZnO-Al2O3

0.10 12%Ni/ZnO-Al2O3

0.05

10%Ni/ZnO-Al2O3

8%Ni/ZnO-Al2O3

0.00 5

10 15 Pore diameter (nm)

20


Energy & Fuels

Figure 8

100

(a)

Thiophene 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

Page 38 of 42

(c)

(b)

90 80 70 60 (d)

50 40 30 O 0

(e)

Al

1

2

3 4 Cycles (f)

Ni

5

6

Zn


Page 39 of 42

Figure 9

8% Ni/ZnO-Al2O3

400

10% Ni/ZnO-Al2O3 12% Ni/ZnO-Al2O3

TCD Signal (a.u.)

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

Energy & Fuels

300 200 100 0 0

200

400 600 Temperature (°C)

800


Energy & Fuels

Figure 10

100 Thiophene 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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90 80 70 60 50 40 30

0

1

2

3 4 Cycles

5

6


Page 41 of 42

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

Energy & Fuels

Scheme 1


Energy & Fuels

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

Page 42 of 42

For Table of Content use only

Comparison of Reactive Adsorption Desulfurization Performance of Ni/ZnO-Al2O3 Adsorbents Prepared by Different Methods Rooh Ullah, † Peng Bai, †,* Pingping Wu, † Zhanquan Zhang,§ Ziyi Zhong, ‡ U. J. Etim, † Fazle Subhan, ‖,† and Zifeng Yan †,*


Comparison of the Reactive Adsorption Desulfurization Performance

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