Selective Hydroconversion of Oleic Acid into Aviation-Fuel-Range

The catalytic conversion of oleic acid was carried out with a fixed-bed flow reactor ... hydrocarbons (CxHy) in the OLPs were calculated according to ...
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Article Cite This: Ind. Eng. Chem. Res. 2019, 58, 5432−5444

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Selective Hydroconversion of Oleic Acid into Aviation-Fuel-Range Alkanes over Ultrathin Ni/ZSM‑5 Nanosheets Fuxiang Feng,† Li Wang,†,‡ Xiangwen Zhang,†,‡ and Qingfa Wang*,†,‡ †

Key Laboratory of Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China ‡ Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin 300072, China

Ind. Eng. Chem. Res. 2019.58:5432-5444. Downloaded from pubs.acs.org by UNIV PARIS-SUD on 04/26/19. For personal use only.

S Supporting Information *

ABSTRACT: Ultrathin Ni/ZSM-5 nanosheet catalysts with different acid concentrations, B/L (Brønsted/Lewis acid sites) ratios, and nanosheet thicknesses are designed for the hydroconversion of oleic acid into aviation-fuel-range alkanes (AFRAs). The role of acid concentration/distribution and nanosheet thickness was investigated. High acid concentration enhances the hydrodeoxygenation (HDO) reaction and intrinsic deoxygenation activity because of the synergistic effect between acid sites and metal sites. The selective cracking reaction can be enhanced by tailoring nanosheet thickness and acid distribution. The thin nanosheet favors isomerization, the selective cracking reaction, as well as the generation of central branched isomers. External acid sites dominate the primary cracking and central C−C cracking of the deoxygenated products, but internal acid sites promote the deeper cracking and terminal C−C cracking. Formation of aromatics is thoroughly suppressed at low reaction temperature (≤533 K). A high AFRA yield of 41.4% is achieved over the 3 nm nanosheet catalyst with Si/Al = 300 and B/L = 0.18.

1. INTRODUCTION To develop an alternative aviation fuel from biomass has become an important research area because of the incremental consumption with the rapid development of the aviation industry and the environmental problems derived from carbon emissions.1,2 For the stringent requirements (high energy content, low freeze point and viscosity) of the final products, two consecutive processes, catalytic deoxygenation of fatty acids or their derivatives and acid-catalyzed reactions (isomerization and cracking) of the deoxygenated products, are necessary.3,4 Recently, a single-step route has been developed to produce aviation-fuel-range hydrocarbons from vegetable oils and fatty acids over different types of bifunctional catalysts composed of metal and acid sites.5,6 With respect to the metal sites, catalystsupported noble metals (Pt, Pd, etc.) have been widely used because of their superior deoxygenation activity.7 However, the high cost and scarcity restrict their practical application. Sulfided transition metals (NiW, NiMo, CoMo) are an alternative class of catalysts but environmentally unfriendly.8 © 2019 American Chemical Society

In recent years, metallic Ni has been extensively used because of its low cost and noticeable deoxygenation activity.9 However, it usually needs high metal loading (>10 wt %) to achieve desired deoxygenation activity, which may result in a low metal dispersion due to the agglomeration at harsh treatments.10 As for the supports, moderate acidity and hierarchical porosity are beneficial for producing aviation fuel, because the deeper cracking reaction of bulky molecular is facilitated by high acidity and diffusion limitation.11,12 Different types of catalysts have been investigated to produce aviation fuel by a single-step route.13,14 For Al2O3-, SiO2− Al2O3-, SAPO-11-, MCM-41-, and USY-supported metal catalysts, a desired aviation fuel yield is usually obtained at a high reaction temperature (>653 K) because of their low acidity and pore structure.15,16 However, the β- and ZSM-5Received: Revised: Accepted: Published: 5432

January 7, 2019 March 9, 2019 March 18, 2019 March 18, 2019 DOI: 10.1021/acs.iecr.9b00103 Ind. Eng. Chem. Res. 2019, 58, 5432−5444

Article

Industrial & Engineering Chemistry Research

supported Ni catalysts were synthesized by the incipient wetness impregnation method. According to the nanosheet thickness and Si/Al ratio, the resultant samples were denoted as NSx(y), where x is the nanosheet crystal thickness (3, 12, and 24 nm), and y is the Si/Al ratio (100, 150, 200, and 300). The commercial Ni/ZSM-5 catalyst with Si/Al = 300 was named as C200(300). Ni/ZSM-5 catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption/desorption (N2−BET), X-ray fluorescence (XRF), high-resolution 27Al MAS NMR, ammonia temperature-programmed desorption (NH3-TPD), pyridine (Py), and 2,6-ditert-butylpyridine (DBTPy)-IR. The detailed experimental procedures for catalyst preparation and characterizations are given in the Supporting Information. 2.3. Catalytic Conversion of Oleic Acid. The catalytic conversion of oleic acid was carried out with a fixed-bed flow reactor (1.0 cm i.d. and 45 cm in length). The reaction temperature was monitored with a thermocouple in the catalyst bed and controlled by three thermocouples on the reactor wall. A 1.00 g portion of catalyst was loaded and fixed by SiC in the center of the reactor. Oleic acid (33.3 wt % in cyclohexane) was used as feedstock, which was injected into the reactor at a flow of 0.2 mL/min using a high-pressure pump. The reactions were carried out at a corresponding reaction temperature under 3 MPa with flowing H2 of 100 mL/min. Before the reaction, the loaded catalysts were reduced at 773 K under flowing H2 for 3 h. The gas and liquid products of each experiment were successively collected by each 1 h interval under the given conditions. The gaseous products were analyzed online with an Agilent 3000 gas chromatograph equipped with a TCD detector using three columns (molecular sieve, plot U, and alumina). The liquid fraction was centrifuged in two parts: water and organic liquid products (OLPs). The OLPs were qualitatively analyzed with an Agilent 6890N gas chromatography/5975N mass spectrometry (GC/MS) instrument. A gas chromatograph (Bruker 456 GC, Bruker), equipped with a flame ionization detector (FID) and a commercially column (ZB-5 HT, 60 m × 0.25 mm × 0.25 m), was used to quantitatively analyze the hydrocarbons in OLPs. Icosane was used as internal standard to quantify the different products. The conversion of oleic acid, OLP yield, and selectivity/yield of corresponding hydrocarbons (CxHy) in the OLPs were calculated according to eqs 1−4:15,18 mOAfeed − mOAproducts conversion = mOAfeed (1)

supported metal catalysts favor deeper cracking of long-chain hydrocarbons as well as aromatization of the deeper cracking products even at a low reaction temperature (573 K).17,18 The aromatics selectivity in aviation fuel is relative high and increases with the elevation of reaction temperature over the β and ZSM-5 catalysts.13,19 Generally, the conversion significantly decreases below 573 K because of the low activity of catalysts.20,21 Therefore, the production of aviation-fuel-range hydrocarbons with high conversion and low or no aromatics is a great challenge. In addition, although extensive studies on the hydroconversion of fatty acids into aviation fuel have been investigated, the mechanism of acid sites on the deoxygenation pathways is still unclear. Further research on the critical factors tailoring the selective cracking of long-chain hydrocarbons is needed. In recent years, hierarchical zeolite catalysts have been rapidly developed because of their good diffusion characteristics and high activity.14,18 Ryoo et al.22 and Xiao et al.23 observed that bulky molecular reactions occurred at Al sites located at the external surface, and the catalytic activity is enhanced effectively by the introduction of mesopore.24,25 Choi et al.26 had reported a unit-cell-thick (2.5 nm) MFI nanosheet zeolite with abundant mesoporosity and large number of external acid sites. Upon comparison to others hierarchical MFI catalysts, this MFI nanosheet zeolite catalyst has higher external acid distribution and pore connectivity due to its ultrathin nanosheet structure, which is more beneficial for isomerization of n-alkanes (C7 and C10)27,28 and catalyst lifetime.29,30 Moreover, the acid distribution of the catalyst can be easily tailored by varying the nanosheet crystal thickness. In this context, ultrathin Ni/ZSM-5 nanosheet catalysts with different Si/Al ratio (100, 150, 200, and 300) and crystal thickness (3, 12, 24, and 200 nm) were synthesized. The role of acid concentration/distribution, reaction temperature, and nanosheet thickness on the hydroconversion of oleic acid into aviation-fuel-range alkanes was systematically investigated. The possible deoxygenation pathways of oleic acid and the C−C bond breaking mechanism of the deoxygenated products were also proposed.

2. MATERIALS AND METHODS 2.1. Chemicals. All the chemicals were used as received. 1Bromooctadecane (≥99.0 wt %, TCI), N,N,N′,N′-tetramethyl1,6-diaminohexane (≥99.0 wt %, Adamas Reagent Co., Ltd.), and 1-bromohexane (≥99.0 wt %, Tianjin Guangfu Fine Chemical Research Institute) were adopted to synthesize the multiammonium surfactant structure-directing agents. The sodium hydroxide, aluminum sulfate octadecahydrate, and tetraethyl orthosilicate (TEOS) were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd., and Ni(NO3)2· 6H2O (≥98.0 wt %, Alfa Aesar) was used as the Ni source. Oleic acid (98.0 wt %) was obtained from Shanghai Macklin Biochemical Co., Ltd. Commercial H-ZSM-5 zeolite with Si/Al = 300 was purchased from Nankai university catalyst plant. 2.2. Catalyst Preparation and Characterizations. Gemini-type quaternary ammonium surfactants with a formula of C22H45−N+(CH3)2−C6H12−N+(CH3)2−C6H13 were synthesized via a two-step reaction between tetramethyl diaminohexane and corresponding bromoalkanes. ZSM-5 nanosheet zeolites were synthesized using the Gemini surfactants as a structure-directing agent (SDA) by a onestep hydrothermal process. The nanosheet crystal thickness was tailored by changing the amount of SDA. Zeolite-

yieldOLPs =

mOLPs mOAfeed

selectivityC H = x

y

(2)

m(CH)n products ∑ (m(CH)n products)

(3)

yield C H = yieldOLPs × selectivityC H x

y

x

y

(4)

Where mOAfeed and mOAproducts are the mass of oleic acid in the feed and in the products, respectively. m(CH)nproducts is the mass of corresponding hydrocarbons in the OLPs. mOLPs is the mass of OLPs. 5433

DOI: 10.1021/acs.iecr.9b00103 Ind. Eng. Chem. Res. 2019, 58, 5432−5444

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Industrial & Engineering Chemistry Research

deviations of the crystal orientation in the a−c planes.26 The commercial ZSM-5 zeolite has an average thickness of about 200 nm. The pore properties of Ni/ZSM-5 nanosheet catalysts determined by N2 adsorption−desorption are shown in Figure 3. There is an inflection point at the low pressure from 0 to 0.1 atm (Figure 3a), suggesting the existence of a microporous structure.11 At the relatively high pressure from 0.45 to 0.90 atm, all the nanosheet catalysts show the type IV isotherm with a remarkable hysteresis loop, a known fingerprint of a hierarchical porous system. This means that abundant mesoporous structures exist in the samples. 9,23 The N2 adsorption−desorption isotherms of all the samples indicate that both micropore and mesopore exist in the nanosheet catalysts. The mesopore size distributions calculated from the adsorption branch of isothermal curves are illustrated in Figure 3b, and the structural properties of the Ni/ZSM-5 catalysts are listed in Table 1. The 3 nm nanosheet catalysts show similar mesopore size distribution at around 4.0 nm. As the nanosheets thickness increases, the mesopore specific surface area and mesopore volume of Ni/ZSM-5 catalysts reduce gradually, and the mesopore size distribution broadens because of the further crystal growth of 3 nm MFI nanosheets, causing the uniform mesopore structure to gradually reassemble in a randomly interconnected manner. 31 According to the definition of the hierarchy factors (HFs),32 the 3 nm nanosheet samples are very mesoporous materials with low microporosity, while the NS12(y) and NS24(y) samples are composed of zeolite nanocrystals with improved HF values, and the commercial C200(300) catalyst is a micropore material, which is consistent with the result in Figure 3. The acid properties of all the samples were investigated by NH3-TPD and Py-IR, and the number of accessible Brønsted acid sites was determined by DBTP-IR.33 The results are demonstrated in Figure 4 and Figure S2. As the Si/Al ratio decreases from 300 to 100, the ammonia desorption peak shifts to high temperature, indicating the increase of acid strength. Consequently, the total acid sites as well as Brønsted/Lewis acid sites (B/L) ratio also increase (Table 2). For the catalysts with the same Si/Al ratio (100 or 300) but different nanosheet thickness (3, 12, and 24 nm), the total acid concentrations are almost the same. However, the strong Brønsted acid sites and B/L ratio increase rapidly with the increased nanosheet thickness. The acid site accessibility factor (AF) is similar for the identical nanosheet thickness catalysts; meanwhile, it increases as the nanosheet thickness decreases attributed to the increased external surface and pore mouth amount. The C200(300) catalyst has the least accessible acid sites. The results of DTBPy-IR indicate that the accessible Brønsted acid sites decrease with the increase of Si/Al ratio and nanosheet thickness (Figure S2b). 3.2. Catalytic Conversion of Oleic Acid. The selective hydroconversion of oleic acid into aviation-fuel-range alkanes over the Ni/ZSM-5 nanosheet catalysts with different Si/Al ratios (100, 150, 200, and 300) was investigated at 533 K. The conversion of oleic acid and yield of organic liquid products (OLPs) over the series ZSM-5 nanosheet catalysts are given in Figure 5a. Almost complete conversion is achieved over all the catalysts. This indicates that the catalysts have high deoxygenation activity even with a low acid concentration. The OLP yield is 60.1% over the NS3(100) catalyst and gradually increases up to 75.4% with the decrease of Si/Al ratio to 300, suggesting that decreased Si/Al ratio increases the OLP

3. RESULTS AND DISCUSSION 3.1. Texture Properties of Ni/ZSM-5 Nanosheet Catalysts. The XRD patterns of the series catalysts with different Si/Al ratios and nanosheet thicknesses are illustrated in Figure 1. The catalysts present characteristic reflections of

Figure 1. XRD patterns of the series Ni/ZSM-5 nanosheet catalysts with different Si/Al ratio and nanosheet thickness. Nickel oxide reflections are highlighted with a square (◆).

MFI framework zeolites (JCPDS 44-0003) at 2θ = 8.3°, 9.2°, 23.5°, and 24.3° and the cubic structure nickel oxide (JCPDS 47-1049) at 2θ = 37.2°, 43.3°, 62.9°, 75.4°, and 79.4°.12 In addition, only the reflections of {h0l} are sufficiently sharp for indexing, which indicates that the zeolites possess wide a−c planes with large coherent domains and small b-axis framework thickness.26 The relative crystallinity (RC) of all the samples is calculated on the basis of the peak areas of four main characteristic peaks. Figure 1 shows that the relative crystallinity increases with the increase of nanosheet thickness, and the nanosheet catalysts have much lower crystallinity than the commercial catalyst due to their thin nanosheet structure. Moreover, the 27Al MAS NMR analysis demonstrates that no nonframework aluminum is detected in the different nanosheet thickness catalysts with Si/Al = 100 (Figure S1). The SEM and TEM images of calcined ZSM-5 zeolite samples are given in Figure 2. The obtained ZSM-5 nanosheet zeolites are three-dimensional intergrowth of laminas (SEM) composed of several alternating MFI nanosheets or one single nanosheet (TEM). The average thickness of ZSM-5 zeolite nanosheets along the b-axis is about 3, 12, and 24 nm for NS3, NS12, and NS24 samples, respectively. The results indicate that the nanosheet thickness is well-tailored from single unit cell thickness to multiple unit cell thickness along the b-axis. The mesoporosity formed from interlayer space between nanosheets is retained by the intergrowth of laminas and slight 5434

DOI: 10.1021/acs.iecr.9b00103 Ind. Eng. Chem. Res. 2019, 58, 5432−5444

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Figure 2. SEM (left) and TEM (right) images of the series ZSM-5 zeolites.

increasing the concentration of active H around metallic Ni particle for the hydrogenation process.35 The result suggests that acid sites participate in the HDO reaction, and their synergetic interaction with adjacent Ni sites enhances the HDO reaction. Meanwhile, the deoxygenation of oleic acid via DCOx reaction mainly depends on metallic Ni due to its high C−C hydrogenolysis activity of metallic Ni,37,38 which is consist with the previous work.9,39−41 Thus, as the acid concentration decreases, the HDO reaction selectivity decreases, but the DCOx reaction selectivity increases. The OLP distribution over the series catalysts was further determined. As shown in Figure 5c, no C16−C18 hydrocarbons but high C4−C8 hydrocarbon yield (42.7%) is obtained over the NS3(100) catalyst with only 17.4% of C9−C15 hydrocarbons. This indicates that the NS3(100) catalyst has high deep cracking activity. As the Si/Al ratio increases, the yield of C9−C15 hydrocarbons and C16−C18 hydrocarbons significantly increases with the decrease of C4−C8 hydrocarbon yield. The NS3(300) catalyst shows the maximum C9−C15 hydrocarbon yield of 38.1% with 15.2% of C16−C18 hydrocarbons and 22.1% of C4−C8 hydrocarbons. It is possible that high Si/Al ratio decreases the acid concentration as well as the B/L ratio, resulting in lower Brønsted acid site concentration, and thus

yield due to the suppressed deep cracking of long-chain hydrocarbons.34 For an exploration of the variation of the deoxygenation pathways, the distribution of H2O, CO2, and CO on different catalysts was analyzed and is illustrated in Figure 5b. The distribution of these oxygen-containing products is significantly influenced by the Si/Al ratio. Over the NS3(100) catalyst, H2O (47 mol %) and CO2 (32 mol %) are the main oxygencontaining products. As the Si/Al ratio increases, the selectivity of H2O decreases, but the selectivity of CO2 increases significantly. The maximum selectivity of CO2 (40 mol %) is obtained over the NS3(300) sample, indicating that DCO2 becomes the dominant reaction at high Si/Al ratio. Meanwhile, the CO selectivity only slight increases from 21 to 25 mol %. These results imply that decreased acid concentration inhibits the hydrodeoxygenation (HDO) reaction. This is because the basic oxygen atoms of oleic acid can interact with Lewis acid sites of catalysts by chemisorption as well as the Brønsted acid sites via H-bonding.35,36 The interaction between acid sites and oleic acid activates the C−O bonds, and thus favors its hydrogenation toward water by active H generated on the adjacent metallic Ni. Moreover, the Brønsted acid sites provide an additional delivery of the proton by hydrogen spillover, thus 5435

DOI: 10.1021/acs.iecr.9b00103 Ind. Eng. Chem. Res. 2019, 58, 5432−5444

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Industrial & Engineering Chemistry Research

Figure 3. (a) N2 adsorption and desorption isotherms and (b) pore size distributions of the series Ni/ZSM-5 catalysts.

Table 1. Physicochemical Properties of the Series Ni/ZSM-5 Catalysts catalyst

Si/Ala

Nia (wt %)

SBETb (m2/g)

Sext/mes (m2/g)

Smicro (m2/g)

Vmesoc (cm3/g)

Vmicro (cm3/g)

HFd

NS3(100) NS3(150) NS3(200) NS3(300) NS12(300) C200(300) NS24(300) NS12(100) NS24(100)

101 146 192 302 308 308 297 108 97

9.9 9.8 10.4 10.5 10.1 9.9 10.0 10.2 9.7

575 603 586 563 486 304 430 494 437

390 452 430 379 305 32 213 299 211

185 151 156 183 180 272 216 196 226

0.477 0.516 0.500 0.480 0.375 0.032 0.232 0.324 0.242

0.095 0.075 0.079 0.094 0.093 0.152 0.100 0.104 0.102

0.113 0.095 0.100 0.110 0.125 0.087 0.150 0.147 0.143

a Determined by XRF analysis. bSpecific surface area. cPore volume. dHierarchy factor (HF): determined as the product (Vmicro/Vpore) × (Smeso/ SBET).

the oleic acid conversion over the NS3(300) catalyst is 92% with an OLP yield of 72% at 513 K. As the reaction temperature increases up to 523 K, oleic acid conversion reaches 100%, and the OLP yield increases up to 79.1%, and then decreases to 75.4% at 533 K because of the enhanced deeper cracking of deoxygenated products. Figure 6b depicts that the HDO selectivity decreases with an increased DCOx selectivity as the reaction temperature increases. The result indicates that increased reaction temperature favors the DCOx reaction but restrains the HDO reaction. This is because HDO reaction is an exothermic reaction, while DCO and DCO2 are endothermic reactions.43,44 In contrast to the increased yield of C4−C8 hydrocarbons, the C16−C18 hydrocarbon yield decreases as the reaction temperature increases from 513 to 533 K (Figure 6c), and the maximum aviation-fuel-range hydrocarbon yield of 41.4% is obtained at 523 K. Moreover, the aviation fuel is dominated by

restrains the deeper cracking but enhances the selective cracking of the deoxygenated products into aviation-fuelrange alkanes. Figure 5d depicts that low-carbon-number (C9, C10) hydrocarbons are the main compounds of aviation-fuel-range alkanes over NS3(100) and NS3(150) catalysts. As the Si/Al ratio increases, high-carbon-number (>C11) hydrocarbon selectivity increases. The experiment and DFT calculation results of Song et al.42 showed that ZSM-5 with low Si/Al ratio favored the central cracking over terminal cracking due to the increased adjacent Brønsted acid sites. High Brønsted acid site concentration enhanced deeper cracking of long-chain hydrocarbons (>C11). Therefore, the catalysts with low Si/Al ratio result in more low-carbon-number hydrocarbons in aviationfuel-range alkanes. As for the NS3(300) catalyst, the selective hydroconversion of oleic acid to aviation-fuel-range alkanes at different reaction temperatures was further investigated. Figure 6a elucidates that 5436

DOI: 10.1021/acs.iecr.9b00103 Ind. Eng. Chem. Res. 2019, 58, 5432−5444

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Industrial & Engineering Chemistry Research

hydrocarbon selectivity decreases. This is because high reaction temperature favors the central C−C bond cracking over terminal cracking and enhances the deeper cracking of long-chain hydrocarbons to obtain low-carbon-number hydrocarbons. The selective hydroconversion of oleic acid into aviationfuel-range alkanes over the Ni/ZSM-5 nanosheet catalysts and commercial Ni/ZSM-5 catalyst was investigated. The conversion of oleic acid and yield of OLPs over the series Ni/ ZSM-5 catalysts with different nanosheet thicknesses are given in Figure 7a. Almost complete conversion of oleic acid is achieved over the NS3(300) catalyst. As the nanosheet thickness increases from 3 to 12, 24, and 200 nm, oleic acid conversion gradually decreases to 80.2%, 60.4%, and 45.7% over the NS12(300), NS24(300), and C200(300) catalysts, respectively, because of the decreased Ni dispersion and more wrapped Ni nanoparticles by micropore compared to the NS3(300) catalyst (Figure S5). Moreover, Figure S6a shows that the conversion over NS12(100) and NS24(100) catalysts is unexpectedly higher than that over the NS12(300) and NS24(300) catalysts in spite of the similar Ni dispersion (Figure S5) and pore structure (Table 1). The result reveals that high acid concentration enhances the deoxygenation activity, which is in accordance with previous work.9,35,46 As discussed above, the activated C−O bonds on acid sites are easily hydrogenated by active H around adjacent Ni particle. So the synergy between acid sites and metal sites accelerates the deoxygenation of oleic acid, resulting in high deoxygenation activity. As the nanosheet thickness increases from 3 to 200 nm, the OLP yield significantly decreases from 79.1% to 35.1% because of the decreased conversion of oleic acid. The distribution of H2O, CO2, and CO on the Ni/ZSM-5 catalysts with different nanosheet thicknesses is illustrated in Figure 7b. As the nanosheet thickness increases from 3 to 200 nm, the HDO selectivity gradually decreases from 50% to 32%. However, the DCO and DCO2 selectivity gradually increases from 19% to 26% and 31% to 42%, respectively. The result indicates that decreased nanosheet thickness favors HDO reaction over DCOx reaction. The decreased nanosheet thickness increases the accessible acid sites, which is beneficial for HDO reaction. Moreover, the decreased nanosheet thickness reduces Ni particles size, thus creating more Ni stepped sites to favor C−O hydrogenation toward water.47 Therefore the NS3(300) catalyst demonstrates the highest HDO selectivity.

Figure 4. NH3-TPD curves of the series Ni/ZSM-5 catalysts.

n-alkanes and their isomers; no aromatic is detected (Figure S3). This is probably due to the low reaction temperature and short micropore path which thoroughly restrains the aromatization of olefins.13,45 For the NS3(100) catalyst, as the reaction temperature increases from 513 to 533 K, the selectivity of C16−C18 hydrocarbons decreases from 28.1% to zero (Figure S4). The selectivity of C4−C8 hydrocarbons increases with the reaction temperature increasing from 513 to 573 K but decreases at 613 K, which is contrary to the variation of C9−C15 hydrocarbon selectivity. The aromatics content in C9−C15 hydrocarbons increases from 75% to 100% as the reaction temperature increases from 573 to 613 K. In our previous work, it was found that the olefins from cracking and dehydrogenation of long-chain hydrocarbons could be converted into aromatics on acid sites.13 The increased reaction temperature promotes the aromatization of shortchain olefins thus decreasing the selectivity of C4 −C 8 hydrocarbons but increasing aromatics selectivity in C9−C15 hydrocarbons. The carbon number distribution of C9−C15 hydrocarbons was further determined and is shown in Figure 6d. As the reaction temperature increases, the low-carbon-number hydrocarbon (