Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production

Biomass and Bioenergy xxx (2017) 1e9

Contents lists available at ScienceDirect

Biomass and Bioenergy journal homepage: http://www.elsevier.com/locate/biombioe

Research paper

Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production Xiaoxiang Jiang a, Jiao Zhou b, Jing Zhao b, Dekui Shen b, * a Engineering Laboratory of Energy System Process Conversion & Emission Control Technology of Jiangsu Province, School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing 210042, PR China b Key Lab of Energy Thermal Conversion and Control, Ministry of Education, Southeast University, Nanjing 210096, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 7 October 2016 Received in revised form 27 June 2017 Accepted 29 June 2017 Available online xxx

Guaiacol, a mono-aromatic compound containing a hydroxyl and a methoxyl group, is one of the main products from lignin pyrolysis. In order to investigate the feasibility of aromatic hydrocarbons production from lignin, guaiacol was employed as the model compound for the catalytic conversion over HZSM-5 zeolites with different Si/Al ratios in a fixed-bed reactor under the temperatures from 500
C to 800
C. With the increased temperature, the yield of both aromatic hydrocarbons (such as benzene, toluene, styrene, naphthalene and 2-methylnaphtalene) and coke was increased from the mass fraction of 1.83%e24.27% and from 1.17% to 12.81%, respectively. At 600
C, the yield of benzene was promoted by the HZSM-5 catalyst with high Si/Al ratio (200) by the mass fraction of 2.94% and up to 1.94% for that of toluene. The production of monocyclic aromatic hydrocarbons (especially for benzene and p-xylene) was favored with the loading of Ni on HZSM-5(25), while the formation of polycyclic aromatic hydrocarbons was notably inhabited. The coke deposition was slightly increased with the increased loading of Ni during the catalytic conversion of guaiacol. The demethoxylation and dehydroxylation reactions were considered to be promoted by the increase of Brønsted acid sites, while the methyl substitution reaction was slightly influenced by the total acidity of catalyst. The experimental results provided the conceptual and technical support for the catalytic pyrolysis of lignin to produce aromatic hydrocarbons. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Guaiacol Catalytic conversion HZSM-5 Aromatic hydrocarbons

1. Introduction Lignin, a natural complex polymer composed of three kinds of aromatic units with different linkages, is a potential feedstock for the production of aromatic chemicals and gasoline additives (such as benzene and xylene) [1]. Guaiacol-type compounds, one of the main derivatives from the pyrolysis of lignin, accounted for the mass fraction of 15% of the liquid product [2]. Conversion of those guaiacol-type compounds to aromatic hydrocarbons would be a promising way for utilizing lignin. The difficulty of the cleavage of the phenolic hydroxyl group from the benzene ring resulted in the limitation of the formation of aromatic hydrocarbons from the cracking of guaiacol-type compounds [3]. Corma et al. [4] studied the conversion of two oxygenates (glycerol and sorbitol) from pyrolysis of biomass over six different catalysts, finding that the ZSM-5 catalyst could give the highest

* Corresponding author. E-mail address: [email protected] (D. Shen).

production of olefins and aromatics. HZSM-5, H-beta and HY zeolites were used in the catalytic fast pyrolysis of lignin model compounds containing beOe4 linkages by Neumann et al. [5]. HZSM-5 was found to be the most effective catalyst for producing the products such as BTX and alkylbenzenes. The strength, type and amount of acidity of HZSM-5 zeolite affected by Si/Al ratio play an important role in the conversion of the pyrolytic derivatives from biomass. Adjaye and Bakhshi [6,7] reported that HZSM-5 was the outstanding catalyst for the high yield and selectivity of hydrocarbons production due to its abundant acid sites. Foster and coworkers [8] reported that the ZSM-5 zeolite with the highest aluminum content presented the highest selectivity to smaller aromatic hydrocarbons such as benzene and toluene from the catalytic pyrolysis of glucose. Valle et al. [9] found 1%Ni/HZSM-5(30) catalyst produced a high yield of aromatics with the content of BTX higher than the mass fraction of 60% in the upgrading of crude biooil into hydrocarbons. Highest aromatic hydrocarbon selectivity attributed to the presence of strong Bronsted acid sites in HZSM-5 catalyst was demonstrated in the catalytic upgrading of bio-oil [10]. Coke deposition was proved to be a major cause of the catalyst

http://dx.doi.org/10.1016/j.biombioe.2017.06.026 0961-9534/© 2017 Elsevier Ltd. All rights reserved.

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

2

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

deactivation. The zeolite pore structure and the acidic properties, which were influenced by the type of catalysts and loading metal, play an important role in coke deposition for zeolite catalysts [11e13]. It needs to be noted that HZSM-5 zeolite can be widely used for conversion of the biomass-derived bio-oils for the production of aromatic hydrocarbons. However, the mechanism of the catalytic conversion of specific compounds from lignin over HZSM5 is not sufficiently investigated, confining the highly-valued commercial utilization of lignin. In order to fill the knowledge gap, guaiacol as one of the prominent compounds from the pyrolysis of lignin was selected to undergo the catalytic conversion over different HZSM-5 catalysts in a fixed bed reactor. The characteristics of the original and Nimodified HZSM-5 catalysts were characterized using BET, XRD, NH3-TPD, and Pyridine-FTIR to understand the inherent mechanism of catalytic conversion of guaiacol to aromatic hydrocarbons and the performance of coke deposition. 2. Materials and methods 2.1. Materials Guaiacol (purity >99.999%, reagent grade) was purchased from Aladdin Company, P.R.China and used as feedstock directly without any treatment. Commercial HZSM-5 zeolites separately with Si/Al ratio of 25, 38, 50, and 200 were provided by Catalyst Plant of Nankai University, China. Ni-modified HZSM-5 (Ni/HZSM-5) was prepared by a typical wet impregnation method using aqueous solutions of Ni (NO3)2$6H2O salt. Nickel loadings of 1, 3 and 5% mass fraction of the catalyst were obtained this way. The impregnation time was extended to about 24 h; the remaining paste was then dried in air at 105
C for 4 h and calcined at 600
C for 5 h. All catalysts were crushed and sieved to 50e60 mesh to obtain the particle size in the range of 0.25e0.3 mm. The Ni-modified catalysts were reduced in a H2 flow (100 cm3 min1) at 600
C for 1 h before the catalytic conversion experiments. 2.2. Characterization of catalysts The various catalyst samples were analyzed by low-temperature N2 adsorption (ASAP 2020 M) to determine the surface area (BET method), pore volume (calculated by the amount of the nitrogen adsorbed at P/P0 ¼ 0.99) and micropore parameters (t-plot method). X-ray diffraction (XRD) measurements were also performed using Smartlab XRD-3 diffractometer with Cu Ka radiation. The XRD patterns were accumulated in the range of 3e55
(2q). NH3-TPD experiments were carried out by temperatureprogrammed desorption of NH3 (FINESORB-3010) to estimate the strength of acid sites on the catalysts. Approximately 100 mg of the sample was used in each trial. The sample was loaded in a U-shaped quartz tube and pretreated in a He stream at 500
C for 1 h. The temperature was reduced to 120
C and pulse chemisorption was executed by injecting 5% volume fraction of NH3 in N2 (20 cm3 min1) pulses through the catalyst bed for 30 min. After the adsorption of NH3, the sample was scoured with He flow (20 cm3 min1) at 120
C for 1 h to obtain a smoothy baseline. Finally, NH3-TPD was performed in a He stream from 120 to 700
C with a 10
C$min1 heating rate. The whole desorption process was detected with thermal conductive detector (TCD). Fourier-Transform Infrared (FT-IR) spectroscopy experiments using pyridine as a probe molecule were performed on a Frontier FT-IR spectrometer (PE Company) for the determination of the Brønsted and Lewis type acid sites of the catalysts. Self-supported wafers of the catalyst were pressed and placed in the cell. Then,

the sample was outgassed at 350
C for 2 h. Pyridine was adsorbed onto the sample at room temperature for 30 min and followed by desorption at 150
C and 350
C. It is generally acknowledged that the band at 1545 cm1 attributed to pyridinium ions corresponds to the Brønsted acid sites and the band at 1450 cm1 ascribed to pyridine coordinates to the Lewis acid sites [14]. The quantitative determination of acid sites was performed with the constants proposed by Emeis [15]. 2.3. Catalytic conversion of guaiacol The catalytic pyrolysis experiments were carried out on a fixed bed reactor, as shown in Fig. 1. The fixed-bed reactor was a quartz tube with an inner diameter of 20 mm and a length of 300 mm coupled with an effective heating section. The quartz tubular reactor was heated by the electrical heating coils and the temperature can be monitored by K-type thermocouples. In each experiment, about 0.5 g of the prepared catalyst was placed on the sand core of the reactor and silica sand was used as an inert solid carrier for comparison. Guaiacol was injected from the top of the reactor at the rate of 4 g h1 by a syringe pump. It was quickly evaporated and flew across the catalyst bed by carrier gas at the flow rate of 100 cm3 min1. The nitrogen was applied as carrier gas and the flow was controlled by the mass flow controller. The liquid product was collected by the two-step condensation system. Both two condensation equipment employed the mixture of water and ice to cool the condenser, where ethanol was used to absorb the volatile stream. The weight hourly space velocity (WHSV) was set to be 8 h1 according to the previous reports [16,17]. The chemical composition of the liquid captured from the catalytic conversion of guaiacol was analyzed by GC/MS (Agilent Technologies 7890A/5975C) via the helium sweeper gas stream. The GC separation was performed using a capillary column (HP5MS, 30 m  0.25 mm  0.25 mm). The GC inlet was 280
C and the split ratio was 30:1. The oven temperature was programmed from 40
C (3 min) to 180
C (2 min) with a 5
C$min1 heating rate and then ramp at 10
C$min1 to 280
C where it was held for 2 min. Typical operating conditions of MS were ionization energy 70 eV, and scan rate of 35e550 amu per second. Peak was identified using the NIST mass spectrum library and some published data [18e20]. Some of the identified phenolic compounds and aromatic hydrocarbons were quantified based on the external standard method. The authentic compounds (purity >99.999%, reagent grade, Aladdin or Keshi) were used as standards to produce calibration curves. The coke yield deposited on the reacted catalyst was estimated by thermogravimetric analyzer (ZRT-1). Each catalytic pyrolysis experiment was performed at three times. The experimental results can be obtained as the average value from the duplicated experimental runs. 3. Results and discussion 3.1. The characterization result of catalysts The physicochemical properties of the HZSM-5 with different Si/ Al ratio and the Ni-modified HZSM-5(25) zeolites used in the catalytic conversion of guaiacol are presented in Table 1. Among the HZSM-5 zeolites having different Si/Al ratio, the BET surface area of HZSM-5(200) was the largest one (about 366.1 m2 g1), while that of HZSM-5(50) was the smallest (only 287.46 m2 g1). As the Si/Al ratio of HZSM-5 was decreased from 200 to 25, the surface area and pore volume of micropore were respectively increased from 115.74 m2 g1 to 200.24 m2 g1 and from 0.052 cm3 g1 to 0.093 cm3 g1. The porosity characteristics of HZSM-5(25) catalyst were found

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

Temperature indicator

Thermo couple

Syringe pump

3

Mass flow controller

Furnace

N2 Quartz tubular reactor

Mass flow controlling box

Gas bag

H2 First condenser

Second condenser

Fig. 1. The schematics for the fixed-bed reactor system.

Table 1 The porosity characteristics of HZSM-5 zeolite catalysts. Sample

SBETa (m2$g1)

Smicrob (m2$g1)

Vmicrob (cm3$g1)

Vtotalc (cm3$g1)

HZSM-5(200) HZSM-5(50) HZSM-5(38) HZSM-5(25) 1%Ni/HZSM-5(25) 3%Ni/HZSM-5(25) 5%Ni/HZSM-5(25)

366.10 287.46 325.45 325.06 308.43 290.54 279.49

115.74 168.51 184.99 200.24 192.72 187.00 182.79

0.052 0.077 0.085 0.093 0.089 0.087 0.085

0.277 0.222 0.312 0.290 0.269 0.261 0.255

a b c

Based on the BET method. Based on the t-plot analysis. Based on the N2 adsorbance at P/P0 ¼ 0.99.

to be significantly changed by Ni loading. The BET surface area and the micropore surface area were gradually decreased with the increased metal loadings. Compared to HZSM-5(25), the total pore volume and micropore pore volume were obviously reduced for the Ni-modified HZSM-5(25). The alteration of porosity properties of the Ni-modified HZSM-5(25) were attributed to the pore blockage and the surface area coverage of the embedded crystalline HZSM5(25) zeolite by the formed metal Ni phases [21]. The XRD patterns of the unmodified and Ni-modified HZSM-5 catalysts are shown in Fig. 2. The characteristic peak of metal Ni was absent in the pattern of 1%Ni/HZSM-5(25) but was found at 44.35
(2q) in the profiles of HZSM-5(25) with higher Ni loadings. This phenomenon was probably ascribed to the bulk of Ni particles reflecting the inappropriate dispersion of Ni on HZSM-5(25) [21,22]. Fig. 3 depicts the NH3-TPD profiles of the HZSM-5 zeolites with different Si/Al ratio (Fig. 3)(a) and the Ni-modified HZSM-5(25) catalysts (Fig. 3)(b). It was noted that two desorption peaks were apparent in the NH3-TPD curves presented in Fig. 3(a). The peak position can give the information about the relative acid strength and the width of the peak represents the distribution of the strength [23]. The first peak appeared at 200e230
C in Fig. 3(a) could be ascribed to weak acid desorption peak in HZSM-5 zeolite, and the second peak at 325e440
C was associated with the

Fig. 2. XRD patterns of unmodified/Ni-modified HZSM-5 catalysts.

medium strong acid desorption peak. As the Si/Al ratio of HZSM-5 increased from 25 to 200, the temperature corresponding to weak acid sites shifted from 227
C to 200
C, suggesting a decrease of weak acid strength. Similarly, the temperature of medium strong acid sites decreased from 438
C to 326
C with the increase of Si/Al ratio of HZSM-5, indicating the medium strong acid strength also weakened in HZSM-5 with higher Si/Al ratio. Moreover, the temperature widths of the two peaks were both significantly narrowed when the Si/Al ratio of HZSM-5 was increased from 25 to 200. This suggested that the strength distribution of weak acid sites and medium strong acid sites both became weaker due to the increase of Si/Al ratio. It could be noted that the weak acid desorption peak was rarely influenced by the loadings of Ni, which still appeared at 225
C in accordance with the location of the temperature of weak acid sites in HZSM-5(25) (Fig. 3(b)). The distribution of medium strong acid sites was significantly changed with the addition of metal Ni. As the loadings of Ni increased from the mass fraction of 1%e5%, the peak corresponding to medium strong acid sites(about 350e450
C) gradually disappeared and the strong acid sites(>500
C) formed

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

4

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

TCD signal (a.u.)

HZSM-5(25) HZSM-5(38) HZSM-5(50) HZSM-5(200)

200

300

400

500

600

700

Temperature ( )

(a) unmodified HZSM-5 zeolites

TCD signal (a.u.)

1% Ni/HZSM-5(25) 3% Ni/HZSM-5(25) 5% Ni/HZSM-5(25)

200

300

400

500

600

700

(b) Ni-modified HZSM-5(25) Fig. 3. NH3-TPD curves of unmodified/Ni-modified HZSM-5 zeolites.

especially for 5%Ni/HZSM-5(25). One peak representing strong acid sites at 528
C was found in the NH3-TPD curve of 5%Ni/HZSM5(25) in Fig. 3(b). A shoulder peak at the range of 420e480
C was detected in 3%Ni/HZSM-5(25), reflecting the transition of medium strong acid sites to strong acid sites. A small strong acid desorption peak at 554
C in 1%Ni/HZSM-5(25) was also found with the appearance of medium strong acid desorption peak at 420
C. The surface acid sites played an important role on the products distribution. The acidity and distribution of acid sites in HZSM-5(25) catalysts were influenced by impregnation of metal Ni. The acidity-regulation by Ni addition would be responsible for the selectivity of products (poly-aromatics converted to monoaromatics) and the performance of coke deposition [24e28]. The distribution of Brønsted and Lewis acid sites of the HZSM-5 zeolites with Si/Al ratio from 25 to 200 and Ni-modified HZSM5(25) catalysts used in the experiments is summarized in Table 2. These sites could be divided into weak acid sites and strong acid sites respectively. The weak acid sites were defined as the quantitative amounts of acid sites at 150
C and the strong acid sites were defined as the quantitative amount of acid sites at 350
C. From Table 2, it could be observed that no matter weak acid sites or strong acid sites, the amount of Brønsted and Lewis acid sites of HZSM-5 catalyst were both increased with decreasing the Si/Al ratio of HZSM-5 from 200 to 25. For example, the amount of weak Brønsted acid sites was enhanced from 0.03259 mmol g1 in HZSM-5(200) to 0.18092 mmol g1 in HZSM-5(25). The total

amount of Brønsted acid sites of these HZSM-5 zeolites with different Si/Al ratio was markedly higher than that of the Lewis acid sites, except for HZSM-5(200). In the case of Brønsted acid sites, it could be seen from Table 2 that the amount of weak Brønsted acid sites was higher than the amount of strong Brønsted acid sites regardless of the Si/Al ratio of HZSM-5. And the same trend was found for the distribution of Lewis acid sites in HZSM-5 with different Si/Al ratio. The effect of the impregnation of metal Ni on the distribution of Brønsted and Lewis acid sites of HZSM-5(25) catalyst was pronounced. In comparison to the unmodified HZSM-5(25), the amount of Brønsted acid sites in the Ni-modified HZSM-5(25) were significantly lower while the amount of Lewis acid sites was much higher. The obvious decrease of the amount of Brønsted acid sites indicated that part of the acidic protons in HZSM-5(25) zeolite was ion-exchanged by Ni ions during the impregnation procedure [21]. The total amount of Brønsted acid sites reduced from 0.16869 mmol g1 to 0.13821 mmol g1 with the content of metal Ni in HZSM-5(25) increased from the mass fraction of 1%e5%. In contrast to the Brønsted acid sites, the total amount of Lewis acid sites was increased by 25%e36% with the impregnation of Ni, and the maximum of total amount of Lewis acid sites was achieved at 3%Ni/HZSM-5(25), about 0.18826 mmol g1. The incorporation of metal Ni into HZSM-5(25) zeolite also changed the distribution of weak and strong acid sites. For Brønsted acid sites, the strong Brønsted acid sites decreased to a higher extent (54%e65%) with the addition of Ni, while the weak Brønsted acid sites also decreased but not to such extent as the strong ones, about 32%e 43%. In the case of Lewis acid sites, the increase of the amount of strong Lewis acid sites (34%e47%) in the Ni-modified HZSM-5(25) catalysts was much higher than that of weak Lewis acid sites (20%e 32%). 3.2. Catalytic conversion of guaiacol over HZSM-5(25) under different temperatures Fig. 4(a) shows the distribution of the aromatic hydrocarbons produced from the catalytic conversion of guaiacol under four different temperatures(500, 600, 700 and 800
C). These aromatic hydrocarbons could be divided into two categories, monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs). Benzene and Toluene were the predominant products in monocyclic aromatic hydrocarbons, while the polycyclic aromatic hydrocarbons were mainly the dicyclic aromatic hydrocarbons, such as naphthalene and methylnaphthalene. Temperature, one of the reaction parameter, has a significant effect on aromatic hydrocarbons yield [4,29]. From Fig. 4(a), it was be found that the yield of aromatic hydrocarbons produced from the catalytic conversion of guaiacol was significantly influenced by the reaction temperatures. As the temperature was increased from 500
C to 800
C, the yield of aromatic hydrocarbons was enhanced from the mass fraction of 1.83%e24.25%. However, it should be noted that about the mass fraction of 8.19% guaiacol didn't decompose at 500
C (based on Table S1 in Supplementary Information). Among the distribution of aromatic hydrocarbons in Fig. 4(a), it was observed that the yield of monocyclic aromatic hydrocarbons was significantly higher than that of polycyclic aromatic hydrocarbons. The total yield of monocyclic aromatic hydrocarbons increased from the mass fraction of 1.47% at 500
C to 19.36% at 800
C, which suggested that the higher reaction temperature could enhance the cleavage of phenolic and methoxyl groups to produce light compounds such as benzene and toluene [30]. The proportion of benzene in all the detected aromatic hydrocarbons was enhanced from 38% to 61% with the temperature increased from 500
C to 800
C, indicating the side-chain in benzene was

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

5

Table 2 Distribution of Brønsted and Lewis acid sites of the unmodified HZSM-5 zeolites and Ni-modified HZSM-5(25). Brønsted acid sites (mmol$g1)

Samples

HZSM-5(200) HZSM-5(50) HZSM-5(38) HZSM-5(25) 1%Ni/HZSM-5(25) 3%Ni/HZSM-5(25) 5%Ni/HZSM-5(25)

Total (mmol$g1)

Weak (150
C)

Strong (350
C)

0.03259 0.14795 0.16160 0.18092 0.12283 0.10499 0.10405

0.00815 0.08913 0.09970 0.09897 0.04586 0.03835 0.03416

0.04074 0.23708 0.26130 0.27989 0.16869 0.14334 0.13821

25 2-Methylnaphthalene Naphthalene Styrene Toluene Benzene

Yield（% ）

20

15

10

MAHs

MAHs

5 MAHs

0

MAHs

500

600

700

Temperature（ ℃）

25

Benzene Toluene Phenol o-Cresol p-Cresol Catechol 3-Methylcatechol

20

Yield（% ）

800

15 10 5

Total (mmol$g1)

Lewis acid sites (mmol$g1) Weak (150
C)

Strong (350
C)

0.03692 0.05633 0.05255 0.09904 0.11875 0.13033 0.12419

0.01385 0.02015 0.02524 0.03952 0.05443 0.05793 0.05280

0.05077 0.07648 0.07779 0.13856 0.17318 0.18826 0.17699

increased temperature. Apart from aromatic hydrocarbons, phenol-type compounds and catechol-type compounds were the other two main products in the catalytic conversion of guaiacol. In order to study deoxidation reaction mechanism for the formation of aromatic hydrocarbons during the guaiacol catalytic conversion process; seven typical compounds (benzene, toluene, phenol, o-cresol, p-cresol, catechol, and methylcatechol) were selected to observe the distribution of their yield under different temperatures. The changing trend of the yield of these compounds was presented in Fig. 4(b). Catechol, the primary product in the catalytic conversion of guaiacol, was mainly produced from the demethylation of methoxyl groups [31]. As the reaction temperature increased from 500
C to 700
C, the yield of catechol was significantly declined, and no catechol can be found at 800
C. The production of phenol was mainly caused by the directly demethoxylation of guaiacol or the dehydroxylation of catechol [32]. The yield of phenol was enhanced at first and then receded with the elevated temperature and the maximum was obtained at 600
C. Methyl-substitution products like 3-methylcatechol and methylphenols (o-cresol and p-cresol) were produced during the guaiacol transformation probably due to the formation and transfer methyl radical [33]. These methyl-substitution products was obviously decreased when reaction temperature was increased from 500
C to 700
C and was no longer produced at 800
C. The yield of benzene and toluene, the target products, was both enhanced significantly with the increased temperature. Fig. 5 shows the distribution of the total yield of aromatic hydrocarbons and the yield of coke deposited on the used catalysts. It could be noted that the yield of aromatic hydrocarbons and coke

25

25

0 500

600

700

800

Temperature（ ℃）

Y ield (% )

violently cracked at higher temperature to produce more benzene in the products. The production of naphthalene and methylnaphthalene was mainly resulted from the secondary polymerization of monocyclic aromatic hydrocarbons such as benzene and toluene. It could be found in Fig. 4 that the yield of polycyclic aromatic hydrocarbons was also increased with the elevated temperatures, for instance, the yield of naphthalene increased from the mass fraction of 0.37% at 500
C to 3.51% at 800
C
C. These polycyclic aromatic hydrocarbons were usually considered as coke precursors [22], the changing trend of which could provide an explanation for the increasing coke yield in the used HZSM-5(25) catalyst with the

20

15

15

10

10

5

5

0

500

600

700

Temperature ( )

800

Coke yield (w t.% )

Fig. 4. (a) Production of aromatic hydrocarbons from the catalytic conversion of guaiacol over HZSM-5(25) under different temperatures. (b) Production of typical aromatic compounds from the catalytic conversion of guaiacol over HZSM-5(25) under different temperatures.

Aromatic hydrocarbons Coke

20

0

Fig. 5. Yields of aromatic hydrocarbons and coke from the catalytic conversion of guaiacol over HZSM-5(25) under different temperatures.

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

6

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

were both increased as the temperature elevated from 500
C to 800
C. The coke deposition was attributed to the formation of polyaromatic species, which was also enhanced at higher reaction temperatures. The coke yield was increased from the mass fraction of 7.17% at 500
C to 12.81% at 800
C, demonstrating the inference about the effect of reaction temperature on the coke formation in the catalytic conversion of guaiacol. When selecting a suitable reaction temperature for the catalytic conversion of guaiacol, the production of aromatic hydrocarbons and the deposition of coke should be considered simultaneously. From Fig. 5, it is found that the intersection for the yield curve of aromatic hydrocarbons and the curve of coke yield appears at about 635
C. Therefore, 600
C was selected as the reaction temperature for the catalytic conversion of guaiacol with different HZSM-5 catalysts. 3.3. Catalytic conversion of guaiacol with different Si/Al ratios of HZSM-5 zeolites HZSM-5 zeolite has been reported to be very active for the production of aromatic hydrocarbons in catalytic lignin pyrolysis and catalytic upgrading of bio-oil [34e39]. The effect of HZSM-5 zeolites with different Si/Al ratio on the yield distribution of

8 2-Methylnaphthalene Naphthalene Styrene Toluene Benzene

7 6

Yield (%)

5 4 3

MAHs

2 MAHs

1

MAHs

MAHs MAHs

H ZS M -5 (2 00 ) H ZS M -5 (5 0) H ZS M -5 (3 8) HZ SM -5 (2 5)

Bl an k

0

60

Benzene Toluene Phenol o-Cresol p-Cresol Catechol 3-methylCatechol

50 40 30 20 Yield (%)

10 3 2 1

HZ SM -5 (3 8) HZ SM -5 (2 5)

50 ) HZ SM -5 (

HZ SM -5 (2 00 )

Bl an k

0

Fig. 6. (a) Production of aromatic hydrocarbons from the catalytic conversion of guaiacol with different HZSM-5 zeolite at 600
C. (b) Production of typical aromatic compounds from the catalytic conversion of guaiacol with different HZSM-5 zeolite at 600
C.

aromatic hydrocarbons produced from the catalytic conversion of guaiacol at 600
C was presented in Fig. 6(a). Compared to the production of aromatic hydrocarbons from the pyrolysis without catalyst (the mass fraction of 1.38%), the total yield of aromatic hydrocarbons from catalytic conversion of guaiacol with the different four HZSM-5 catalysts was all significantly increased. The yield of monocyclic aromatic hydrocarbons (MAHs) was much higher than that of polycyclic aromatic hydrocarbons regardless of the change of Si/Al ratio of HZSM-5. Among the distribution of aromatic hydrocarbons produced from the catalytic conversion of guaiacol, benzene and toluene were the main compounds in monocyclic aromatic hydrocarbons, while naphthalene was dominated in the polycyclic aromatic hydrocarbons (PAH). Styrene, another product in monocyclic aromatic hydrocarbons [40], was mainly produced from the alkylation of benzene with ethylene. The yield of the above two PAHs was changed slightly with the HZSM-5 catalysts of different Si/Al ratios. 3-Methylnaphthalene cannot be detected in the non-catalytic pyrolysis of guaiacol, which was found to be produced with the yield of 0.23%e0.3% from the catalytic conversion process. The performance of HZSM-5 zeolites to promote the production of aromatic hydrocarbons was influenced by the Si/Al ratio of HZSM-5. The total yield of aromatic hydrocarbons was increased from the mass fraction of 2.78%e6.75% with the Si/Al ratio of HZSM-5 decreasing from 200 to 25, suggesting that HZSM-5 with higher acidity (lower Si/Al ratio) improved the production of aromatic hydrocarbons more effectively. This was probably attributed to the higher activity of the reactions such as dehydration, decarboxylation, dealkylation, conversion, isomerisation and oligomerisation, which was catalyzed by the strong acid sites of HZSM-5 in guaiacol catalytic conversion by HZSM-5 with lower Si/Al ratio [41,42]. The results of NH3-TPD analysis indicated that the strength of acid sites was gradually enhanced with the Si/Al ratio of HZSM-5 changing from 200 to 25. Meanwhile, the Pyridine-FTIR characterization also demonstrated the increase of the amount of acid sites (both Brønsted and Lewis acid sites) from HZSM-5(200) to HZSM-5(25). The yield of benzene and toluene were substantially enhanced from the mass fraction of 0.85% and 1% with HZSM5(200) to the mass fraction of 2.94% and 1.94% with HZSM-5(25), respectively. This can be ascribed to the increased amount of the Brønsted acid sites of HZSM-5 [36]. The effect of HZSM-5 acidity on the formation of naphthalene followed the similar trend as that of benzene and toluene, indicating that the higher acidity of HZSM-5 can facilitate the dimerization or dehydrocyclization reactions [43]. Fig. 6(b) shows the yield distribution of the selected typical compounds produced from the catalytic conversion of guaiacol in the presence of HZSM-5 with Si/Al ¼ 200, 50, 38, 25. The amount of catechol was the highest among the seven specific compounds produced from the guaiacol catalytic conversion. The yield of catechol was decreased as the Si/Al ratio of HZSM-5 changing from 50 to 25 due to the secondary reaction to form phenol or methylcatechol through the removal of the hydroxyl group or methyl substitution. However, the yield of catechol for the guaiacol catalytic conversion with HZSM-5(50) was higher than that with HZSM-5(200), which was possibly attributed to the smallest of pore volume of HZSM-5(50) inhibiting the diffusion of catechol in the secondary reaction. As shown in Fig. 6(b), the production of phenol by the influence of Si/Al ratio of HZSM-5 was slightly, but the yield of phenol was increased to the mass fraction of 19.36% rapidly in the presence of HZSM-5(25). This suggested the formation of phenol needed higher acid strength and more acid amount in HZSM-5 zeolite to improve the demethoxylation of guaiacol or the dehydroxylation of catechol. As the product of methyl substitution reaction of phenol, the production of cresols (p-cresol and o-cresol) was slightly affected by the acidity of HZSM-5 with the yield

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

2-methylNaphthalene Styrene Toluene

14 12

Naphthalene p-Xylene Benzene

10

Yield (%)

8 6

MAHs

MAHs

MAHs

MAHs

4

2,4-dimethylphenol 2-ethylphenol phenol

50 40

According to the investigation about the effect of the Si/Al ratio of HZSM-5 on the catalytic conversion of guaiacol, HZSM-5(25) performed as the best catalyst for the conversion of organic oxygenates to aromatic hydrocarbons such as benzene and toluene. Therefore, the impregnation of transition metal (Ni) on HZSM5(25) was further studied in this section to explore the influence of metal active component on the production of aromatic hydrocarbons. Fig. 8(a) depicts the yield distribution of aromatic hydrocarbons produced from the catalytic conversion of guaiacol with Ni-modified HZSM-5(25) catalysts at 600
C. It was found that the addition of the metal Ni to HZSM-5(25) catalyst induced a further small increase in the formation of aromatic hydrocarbons, except for the 5%Ni/HZSM-5(25) catalyst which made the total yield of aromatic hydrocarbons lower than that with HZSM-5(25). The total yield of aromatic hydrocarbons was decreased from the mass fraction of 12.15%e10.59% with the loadings of metal Ni increasing from 1% to 5%, suggesting the loadings of metal had an

30

Yield (%)

3.4. Catalytic conversion of guaiacol with Ni/HZSM-5

5% Ni /H ZS M -5 (2 5)

3% Ni /H ZS M -5 (2 5)

1% Ni /H ZS M -5 (2 5)

0

HZ SM -5 (2 5)

2

p-cresol o-cresol

20

5% Ni

/H ZS M 3% Ni

/H ZS M -5 (2 5)

-5 (2 5) /H ZS M 1% Ni

H ZS M

0

-5 (2 5)

10

-5 (2 5)

changed small with regard to the different Si/Al ratio of HZSM-5. The same trend was found in the yield distribution of 3methylcatechol produced from the catalytic conversion of guaiacol with different HZSM-5 zeolites. When the Si/Al ratio of HZSM-5 was changed from 200 to 25, the amount of Brønsted acid sites was increased from 0.04074 mmol g1 to 0.27989 mmol g1, which could improve the activity of deoxidation reaction such as dehydroxylation. Therefore, the yield of benzene and toluene were significantly increased with the Si/Al ratio of HZSM-5 decreasing from 200 to 25 due to the intense dehydroxylation of phenol and methylphenol. The coke yield deposited on the different HZSM-5 catalysts in the catalytic conversion of guaiacol at 600
C is shown in Fig. 9. Compared to the coke yield on the silica sand used in the blank condition, the yield of coke deposited on HZSM-5 zeolites was sufficiently increased due to the aromatization and polymerization reaction occurred on the acid sites in HZSM-5 catalyst. As shown in Fig. 7, the coke yield was increased from the mass fraction of 5.81% with HZSM-5(200) to the mass fraction of 9.29% with HZSM-5(25), which was attributed to the increase of the amount of acid sites in HZSM-5 with the decreasing of Si/Al ratio, especially the Brønsted acid sites.

7

Fig. 8. (a) Production of aromatic hydrocarbons from the catalytic conversion of guaiacol with Ni-modified HZSM-5(25) catalysts at 600
C. (b) Production of phenoltype compounds from the catalytic conversion of guaiacol with Ni-modified HZSM5(25) catalysts at 600
C.

11

10

Coke yield (%)

Coke yield（ % ）

8

6

4

10

9

Fig. 7. Coke yield from the catalytic conversion of guaiacol with different HZSM-5 zeolite at 600
C.

5% N i/H ZS M -5 (2 5)

3% N i/H ZS M -5 (2 5)

H ZS M -5 (2 5)

H ZS M -5 (2 5)

H ZS M -5 (3 8)

H ZS M -5 (5 0)

H ZS M -5 (2 00 )

Bl an k

8

0

1% N i/H ZS M -5 (2 5)

2

Fig. 9. Coke yield from the catalytic conversion of guaiacol with Ni-modified HZSM5(25) catalysts under 600
C.

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

8

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

effect on the production of aromatic hydrocarbons due to the change of catalytic properties of HZSM-5(25) such as porosity and acidity with the addition of metal Ni. From the point of the production of monocyclic aromatic hydrocarbons, the total yield of monocyclic aromatic hydrocarbons from the catalytic conversion of guaiacol with Ni-modified HZSM-5(25) was higher than that with unmodified HZSM-5(25) regardless of the level of metal loading. However, the inhibition of polycyclic aromatic hydrocarbons was consistent with the addition level of metal Ni, which was reflected in that the total yield of naphthalene and 2-methylnaphthalene was decreased 19.86% in the case of 1%Ni/HZSM-5(25) compared to HZSM-5(25) to 38.53% in the case of 1%Ni/HZSM-5(25) compared to HZSM-5(25). This phenomenon was probably attributed to the decrease of the amount of Brønsted acid sites, especially the strong Brønsted acid sites, with the impregnation of metal Ni [26e28]. It could be noted from Fig. 8(a) that the yield of benzene produced from the catalytic conversion of guaiacol with Ni-modified HZSM-5(25) was higher than that with HZSM-5(25), which was possibly due to the synergistic effect between the strong adsorption of metal Ni and the acidity of catalyst. As the level of Ni loading increased from 1% to 5%, the yield of benzene was decreased accordingly because of the excessive coverage of Brønsted acid sites by the impregnation of metal Ni. But, the yield of toluene was decreased from the mass fraction of 3.41% with 1%Ni/HZSM-5(25) to the mass fraction of 2.81% with 5%Ni/HZSM-5(25), which were all lower than that from the catalytic conversion of guaiacol with HZSM-5(25), about the mass fraction of 3.51%. The decreased formation of toluene could be associated with the suppressed dehydroxylation reaction of methylphenol due to the decrease of Brønsted acid sites. In comparison to the catalytic conversion experiments with HZSM-5(25), all the Ni-modified HZSM-5(25) catalysts induced the production of p-xylene and the yield was slightly decreased with the increase of the level of Ni loading from 1% to 5%. Phenol-type compounds, as the precursor for the aromatic hydrocarbons, was the leading product from the catalytic conversion of guaiacol with Ni-modified HZSM-5(25) catalysts at 600
C (seen in Table S3 in Supplementary Information). The distribution of these phenol-type compounds (phenol, cresols, 2-ethylphenol, 2,4dimethylphenol) is shown in Fig. 8(b) to investigate the influence of metal active component on the production of phenol-type compounds from the catalytic conversion of guaiacol. As the shown in Fig. 8(b), phenol and 2-methylphenol were the dominant products in these phenol-type compounds with the proportion about 88%e 92%. The total yield of these phenol-type compounds achieved the maximum with 1%Ni/HZSM-5(25), about the mass fraction of 45.28% among the four catalysts used in this experiment. Compared to the unmodified HZSM-5(25), 1%Ni/HZSM-5(25) and 5%Ni/HZSM5(25) both enhanced the production of the phenol-type compounds, while the total yield in the catalytic conversion of guaiacol with 3%Ni/HZSM-5(25) was reduced. This was likely due to the absent of strong acid sites in 3%Ni/HZSM-5(25) catalyst (according to the analysis of NH3-TPD curve), suggesting that the strong acid sites in catalyst could improve the conversion of guaiacol to the phenol-type compounds. The production of cresols mainly resulted from the methyl substitution reaction, with the yield of o-cresol remarkably higher than that of p-cresol. This indicated that the methoxyl group in the ortho position of phenol existing in guaiacol was easier to occur the methyl substitution reaction. Nevertheless, the formation of cresols reported by Asmadi et al. [44] was thought that the OeCH3 bond was homolysed to form phenoxy and methyl radicals and radical induced the rearrangement (ipso-substitution) from aromatic OCH3 into aromatic CH3 structures. The yield of cresols from the catalytic conversion of guaiacol with Ni-modified catalysts (Fig. 8(b)) was higher than that with HZSM-5(25) while the yield of

toluene was decreased from the mass fraction of 3.51% with HZSM5(25) to the mass fraction of 2.81% with 5%Ni/HZSM-5(25) (Fig. 8(a)), which demonstrated that the addition of metal Ni to HZSM-5(25) inhibit the dehydroxylation reaction of cresols due to the decrease of Brønsted acid sites. 2-Ethylphenol was detected in the catalytic conversion of guaiacol, resulted from the alkylation reaction occurred between phenol and olefins [45]. But the yield of 2-ethylphenol produced from the guaiacol catalytic conversion in the presence of Ni-modified catalysts was decreased compared to that from the unmodified HZSM-5(25). This indicated that the impregnation of metal Ni on HZSM-5(25) reduced the activity of alkylation reaction that catalyzed by the Brønsted acid sites on zeolite. Fig. 9 presents the coke yield deposited on the catalysts in the catalytic conversion of guaiacol with Ni-modified HZSM-5(25) under 600
C. It should be noted that the impregnation of metal Ni to HZSM-5(25) induced a slight increase of coke yield compared to the unmodified HZSM-5(25). The level of metal Ni loading had a small effect on the coke yield which was increased from the mass fraction of 9.5%e9.78% as the metal loadings increased from 1% to 5%. According to the previous published literature and investigation results [21,46e48], the formation of coke on the catalysts was attributed to the enhancement of condensation reaction catalyzed by the acid sites in HZSM-5, especially the Brønsted acid sites. However, the amount of Brønsted acid sites in Ni-modified HZSM5(25) was decreased in comparison to the unmodified HZSM-5(25), which theoretically leaded to the decrease of coke yield in the guaiacol catalytic conversion with Ni-modified catalysts, while the fact was contrary. This phenomenon indicated that the metal itself had an effect on the formation of coke due to the strong adsorption performance of Ni, which could be validated by the variation trend of coke yield on the Ni-modified catalysts with the change of the level of metal loading.

4. Conclusion The catalytic conversion of guaiacol to produce aromatic hydrocarbons was investigated in this work, regarding the influence of reaction temperature and catalyst species. As the temperature was increased from 500
C to 800
C, the production of aromatic hydrocarbons was significantly increased to a yield of the mass fraction of 14.07% for benzene and 4.04% for toluene. HZSM-5 zeolite with high Si/Al ratio can promote the total yield of monocyclic aromatic hydrocarbons (benzene, toluene and styrene) from the mass fraction of 2.23%e5.44%, along with the coke yield increased from the mass fraction of 5.81%e9.29% during the catalytic conversion of guaiacol. HZSM-5(25) with the increased Ni loadings from 1% to 5% could promote the formation of benzene from the mass fraction of 5.72%e6.08%, but decrease that of toluene from the mass fraction of 2.81%e3.41%. The deoxygenation reaction such as demethoxylation and dehydroxylation can be favored by the higher temperature and higher acidity of HZSM-5, promoting the formation of benzene and toluene. With the above discussion, the results could provide the conceptual guide for the catalytic conversion of lignin to monocyclic aromatic hydrocarbons as the important additive of transportation liquid fuel.

Acknowledgement The authors would like to acknowledge financial support from the National Natural Science Foundation of China (project references: 51476034 and 51676047), Natural Science Foundation of Jiangsu Province (project reference: BK20161423 and BK20141451).

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026

X. Jiang et al. / Biomass and Bioenergy xxx (2017) 1e9

Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.biombioe.2017.06.026. References
n-Leshkov, Insights into the [1] T. Prasomsri, M. Shetty, K. Murugappan, Y. Roma catalytic activity and surface modification of MoO3during the hydrodeoxygenation of lignin-derived model compounds into aromatic hydrocarbons under low hydrogen pressures, Energy Environ. Sci. 7 (2014) 213e217. [2] G.W. Huber, S. Iborra, A. Corma, Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering, Chem. Rev. 106 (2006) 4044e4098. [3] E. Furimsky, Catalytic hydrodeoxygenation, Appl. Catal. A Gen. 199 (2000) 147e190. [4] A. Corma, G. Huber, L. Sauvanaud, P. O'Connor, Processing biomass-derived oxygenates in the oil refinery: catalytic cracking (FCC) reaction pathways and role of catalyst, J. Catal. 247 (2007) 307e327. [5] G.T. Neumann, B.R. Pimentel, D.J. Rensel, J.C. Hicks, Correlating lignin structure to aromatic products in the catalytic fast pyrolysis of lignin model compounds containing beOe4 linkages, Catal. Sci. Technol. 4 (2014) 3953e3963. [6] J.D. Adjaye, N.N. Bakhshi, Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part I: conversion over various catalysts, Fuel Process Technol. 45 (1995) 161e183. [7] J.D. Adjaye, N.N. Bakhshi, Production of hydrocarbons by catalytic upgrading of a fast_pyrolysis bio-oil. Part II :Comparative catalyst performance and reaction pathways, Fuel Process Technol. 45 (1995) 185e202. [8] A.J. Foster, J. Jae, Y.-T. Cheng, G.W. Huber, R.F. Lobo, Optimizing the aromatic yield and distribution from catalytic fast pyrolysis of biomass over ZSM-5, Appl. Catal. A Gen. 423e424 (2012) 154e161. [9] B. Valle, A.G. Gayubo, A. Alonso, A.T. Aguayo, J. Bilbao, Hydrothermally stable HZSM-5 zeolite catalysts for the transformation of crude bio-oil into hydrocarbons, Appl. Catal. B Envir. 100 (2010) 318e327. [10] S.T. Srinivas, A.K. Dalai, N.N. Bakhshi, Thermal and catalytic upgrading of a biomass-derived oil in a dual reaction system, Can. J. Chem. Eng. 78 (2000) 343e354. [11] E. Epelde, A.G. Gayubo, M. Olazar, J. Bilbao, A.T. Aguayo, Modified HZSM-5 zeolites for intensifying propylene production in the transformation of 1butene, Chem. Eng. J. 251 (2014) 80e91. [12] Y. Li, C. Zhang, Y. Liu, X. Hou, R. Zhang, X. Tang, Coke deposition on Ni/HZSM-5 in bio-oil hydrodeoxygenation processing, Energy & Fuels 29 (2015) 1722e1728. [13] P.M. Mortensen, J.-D. Grunwaldt, P.A. Jensen, K. Knudsen, A.D. Jensen, A review of catalytic upgrading of bio-oil to engine fuels, Appl. Catal. A General 407 (2011) 1e19. €nen, T. Salmi, M. Hupa, D.Y. Murzin, Catalytic pyrolysis [14] A. Aho, N. Kumar, K. Era of woody biomass in a fluidized bed reactor: influence of the zeolite structure, Fuel 87 (2008) 2493e2501. [15] C. Emeis, Determination of integrated molar extinction coefficients for infrared absorption bands of pyridine adsorbed on solid acid catalysts, J. Catal. 141 (1993) 347e354. [16] W. Song, J.F. Haw, Improved methanol-to-olefin catalyst with nanocages functionalized through ship-in-a-bottle synthesis from PH3, Angew. Chem. Int. Ed. 42 (2003) 891e894. [17] S. Shao, H. Zhang, R. Xiao, D. Shen, J. Zheng, Comparison of catalytic characteristics of biomass derivates with different structures over ZSM-5, BioEnergy Res. 6 (2013) 1173e1182. [18] D. Shen, S. Gu, K.H. Luo, S.R. Wang, M.X. Fang, The pyrolytic degradation of wood-derived lignin from pulping process, Bioresour. Technol. 101 (2010) 6136e6146. [19] A.M. Azeez, D. Meier, J. Odermatt, T. Willner, Effects of zeolites on volatile products of beech wood using analytical pyrolysis, J. Anal. Appl. Pyrolysis 91 (2011) 296e302. [20] D. Shen, J. Zhao, R. Xiao, S. Gu, Production of aromatic monomers from catalytic pyrolysis of black-liquor lignin, J. Anal. Appl. Pyrolysis 111 (2015) 47e54. [21] E.F. Iliopoulou, S.D. Stefanidis, K.G. Kalogiannis, A. Delimitis, A.A. Lappas, K.S. Triantafyllidis, Catalytic upgrading of biomass pyrolysis vapors using transition metal-modified ZSM-5 zeolite, Appl. Catal. B Envir. 127 (2012) 281e290. [22] W.-L. Fanchiang, Y.-C. Lin, Catalytic fast pyrolysis of furfural over H-ZSM-5 and Zn-H-ZSM-5 catalysts, Appl. Catal. A Gen. 419e420 (2012) 102e110.
lez, F. Hermes, M. Bertmer, E. Rodríguez-Castello
n, [23] L. Rodríguez-Gonza
nez-Lo
pez, U. Simon, The acid properties of H-ZSM-5 as studied by A. Jime NH3-TPD and 27Al-MAS-NMR spectroscopy, Appl. Catal. A Gen. 328 (2007)

9

174e182. €nsted and [24] N. Fellenz, J. Bengoa, S. Marchetti, A. Gervasini, Influence of the Bro Lewis acid sites on the catalytic activity and selectivity of Fe/MCM-41 system, Appl. Catal. A Gen. 435 (2012) 187e196. [25] C. Zhao, J.A. Lercher, Upgrading pyrolysis oil over Ni/HZSM-5 by cascade reactions, Angew. Chem. 124 (2012) 6037e6042. [26] S. Telalovi
c, J.F. Ng, R. Maheswari, A. Ramanathan, G.K. Chuah, U. Hanefeld, Synergy between Brønsted acid sites and Lewis acid sites, Chem. Commun. (2008) 4631e4633. [27] V.V. Kumar, G. Naresh, M. Sudhakar, J. Tardio, S.K. Bhargava, A. Venugopal, Role of Brønsted and Lewis acid sites on Ni/TiO 2 catalyst for vapour phase hydrogenation of levulinic acid: kinetic and mechanistic study, Appl. Catal. A General 505 (2015) 217e223. [28] P. Sun, G. Gao, Z. Zhao, C. Xia, F. Li, Acidity-regulation for enhancing the stability of Ni/HZSM-5 catalyst for valeric biofuel production, Appl. Catal. B Environ. 189 (2016) 19e25. [29] T.R. Carlson, Y.-T. Cheng, J. Jae, G.W. Huber, Production of green aromatics and olefins by catalytic fast pyrolysis of wood sawdust, Energy Environ. Sci. 4 (2011) 145e161. [30] J. Zhao, W. Xiuwen, J. Hu, Q. Liu, D. Shen, R. Xiao, Thermal degradation of softwood lignin and hardwood lignin by TG-FTIR and Py-GC/MS, Polym. Degrad. Stab. 108 (2014) 133e138. [31] A.L. Jongerius, R. Jastrzebski, P.C.A. Bruijnincx, B.M. Weckhuysen, CoMo sulfide-catalyzed hydrodeoxygenation of lignin model compounds: an extended reaction network for the conversion of monomeric and dimeric substrates, J. Catal. 285 (2012) 315e323. [32] J. Hu, D. Shen, R. Xiao, S. Wu, H. Zhang, Free-radical analysis on thermochemical transformation of lignin to phenolic compounds, Energy & Fuels 27 (2012) 285e293. [33] V.N. Bui, D. Laurenti, P. Afanasiev, C. Geantet, Hydrodeoxygenation of guaiacol with CoMo catalysts. Part I: promoting effect of cobalt on HDO selectivity and activity, Appl. Catal. B Envir. 101 (2011) 239e245. [34] U.V. Mentzel, M.S. Holm, Utilization of biomass: conversion of model compounds to hydrocarbons over zeolite H-ZSM-5, Appl. Catal. A Gen. 396 (2011) 59e67. [35] H.J. Park, J.-K. Jeon, D.J. Suh, Y.-W. Suh, H.S. Heo, Y.-K. Park, Catalytic vapor cracking for improvement of bio-oil quality, Catal. Surv. Asia 15 (2011) 161e180. [36] S. Stephanidis, C. Nitsos, K. Kalogiannis, E.F. Iliopoulou, A.A. Lappas, K.S. Triantafyllidis, Catalytic upgrading of lignocellulosic biomass pyrolysis vapours: effect of hydrothermal pre-treatment of biomass, Catal. Today 167 (2011) 37e45. [37] R.W. Thring, S.P. Katikaneni, N.N. Bakhshi, The production of gasoline range hydrocarbons from Alcell® lignin using HZSM-5 catalyst, Fuel Process. Technol. 62 (2000) 17e30. [38] T.P. Vispute, H. Zhang, A. Sanna, R. Xiao, G.W. Huber, Renewable chemical commodity feedstocks from integrated catalytic processing of pyrolysis oils, Science 330 (2010) 1222e1227. [39] X. Li, L. Su, Y. Wang, Y. Yu, C. Wang, X. Li, et al., Catalytic fast pyrolysis of Kraft lignin with HZSM-5 zeolite for producing aromatic hydrocarbons, Front. Environ. Sci. Eng. 6 (2012) 295e303. [40] T. Parsell, S. Yohe, J. Degenstein, T. Jarrell, I. Klein, E. Gencer, et al., A synergistic biorefinery based on catalytic conversion of lignin prior to cellulose starting from lignocellulosic biomass, Green Chem. 17 (2015) 1492e1499. [41] T.S. Nguyen, S. He, L. Lefferts, G. Brem, K. Seshan, Study on the catalytic conversion of lignin-derived components in pyrolysis vapour using model component, Catal. Today 259 (2016) 381e387. [42] Z. Ma, E. Troussard, J.A. van Bokhoven, Controlling the selectivity to chemicals from lignin via catalytic fast pyrolysis, Appl. Catal. A General 423 (2012) 130e136. €nen, T. Salmi, M. Hupa, D.Y. Murzin, Catalytic pyrolysis [43] A. Aho, N. Kumar, K. Era of biomass in a fluidized bed reactor: influence of the acidity of H-Beta zeolite, Process Saf. Environ. Prot. 85 (2007) 473e480. [44] M. Asmadi, H. Kawamoto, S. Saka, Thermal reactions of guaiacol and syringol as lignin model aromatic nuclei, J. Anal. Appl. Pyrolysis 92 (2011) 88e98. [45] I. Graça, F.R. Ribeiro, H.S. Cerqueira, Y.L. Lam, M.B.B. de Almeida, Catalytic cracking of mixtures of model bio-oil compounds and gasoil, Appl. Catal. B Envir. 90 (2009) 556e563. [46] Q. Zhang, J. Chang, T. Wang, Y. Xu, Review of biomass pyrolysis oil properties and upgrading research, Energy Convers. Manage. 48 (2007) 87e92. [47] C.-q. Dong, Z.-f. Zhang, Q. Lu, Y.-p. Yang, Characteristics and mechanism study of analytical fast pyrolysis of poplar wood, Energy Convers. Manage. 57 (2012) 49e59. [48] A. Galadima, O. Muraza, In situ fast pyrolysis of biomass with zeolite catalysts for bioaromatics/gasoline production: a review, Energy Convers. Manage. 105 (2015) 338e354.

Please cite this article in press as: X. Jiang, et al., Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production, Biomass and Bioenergy (2017), http://dx.doi.org/10.1016/j.biombioe.2017.06.026