“BTX” from Guaiacol HDO under Atmospheric Pressure: Effect of

Jan 30, 2017 - The hydrodeoxygenation and transmethylation of guaiacol was performed over each individual Fe/Ni/HBeta, Fe/Ni/ZSM-5, Fe/Ni/HY, Fe/Ni/MC...
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“BTX” from Guaiacol HDO under Atmospheric Pressure: Effect of Support and Carbon Deposition Xiwei Xu*,†,‡ and Enchen Jiang*,† †

College of Materials and Energy, South China Agricultural University, Guangzhou 510640, China State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640, China

‡

S Supporting Information *

ABSTRACT: The hydrodeoxygenation and transmethylation of guaiacol was performed over each individual Fe/Ni/HBeta, Fe/ Ni/ZSM-5, Fe/Ni/HY, Fe/Ni/MCM-41, Fe/Ni/SiO2, and Fe/Ni/γ-Al2O3 catalyst in a fixed bed reactor under atmospheric pressure and low temperature. The effects of support and reaction time on the products distribution, the rate of transmethylation, and XHDO were studied. Among the different catalysts, Fe/Ni/HY zeolite demonstrated very good activity in both deoxygenation and transmethylation, giving 14% BTX (bezene, toluene, xylene) selectivity, 100% guaiacol conversion, and 26% tansalkylation ratio, thereby minimizing carbon loss and hydrogen consumption during the hydrodeoxygenation of guaiacol. Key upgrading reactions for the model chemical compound guaiacol, including aldol condensation, alkylation, hydrogenolysis, aromatization, and deoxygenation, were discussed. The fresh and spent catalysts were characterized by scanning electron microscopy (SEM), Xray diffraction (XRD), N2-physisorption, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and pyridine infrared spectroscopy (Py-IR) methods. The carbon deposition was also investigated.

1. INTRODUCTION Air pollution from using fossil fuels and environmental problems from the residues of the forest and agriculture have caused an increased interest in renewable sources. Fuel and chemical residues of the forest and agriculture are a most promising way to solve the problems.1 Among the manners of utilization of residues from agriculture and forestry as energy and resources, the upgrading of lignin has been generally discussed in recent years.2 Bio-oil is a promising way to reduce petroleum dependence.3 Currently, the direct liquid fuel from bio-oil gained from lignin is not available due to its high oxygen content and instability.4 The technology for the upgrading of bio-oil such as cracking and hydrolysis or HDO (hydrodeoxygenation) has been widely investigated. However, most of the research about HDO has been applied at high pressure with solvent and H-donor, which is strictly for equipment; it is difficult to use for separating products. Moreover, during the HDO process at high pressure, CH4, CO2, CH3OH, or other high volatiles will be produced by demethylation or demethoxylation of the methoxy groups,5,6 thereby decreasing the yield of carbon-atom and increasing the consumption of H2. Gas phase HDO at atmospheric pressure offers an efficient way to avoid solvent separation and high-pressure tolerant equipment. Transmethylation is a promising method to prevent losing carbon from conversion into a high-volatile product. The products of methylated phenolic or aromatic are also the building blocks that can be converted to highly valuable fuels or biobased chemicals by hydrodeoxygenation.7 Noble metals such as Pt, Ga, and Ru and transition metals such as Fe, Ni, and Co supported on zeolites are widely used in gas-phase HDO.8 Moreover, transition metals commonly serve the function of providing H species for hydrodeoxygenation.9 Zeolites such as ZSM-5, HBeta, HY, MCM-41, and SBA-15 are widely investigated and used to catalyze various kinds of © 2017 American Chemical Society

reactions. Recently, some researchers found that zeolites play a key role in the transmethylation of phenol derivatives that are the typical compounds of bio-oil.10 Note that the property of supports has a significant effect on HDO. It was reported that the protons from the surface OH- of an oxide support would take the reaction with the aromatic ring lying planar or -OCH3 and OH- inside the phenolic compound.11,12 This would explain why, for some catalysts, the catalytic activity was significantly different even if they had the same active phase. For example, Van Ngoc et al.13 investigated the influence of support on HDO activity and selectivity. They investigated the zirconia, titania, and traditional industrially γ-alumina supports. Zirconia, as a support, induced a very efficient conversion of guaiacol to deoxygenated hydrocarbons. Wu investigated the HDO of guaiacol with Ni2P catalysts at atmospheric pressure and analyzed the effect of supports such as alumina, zirconia, and silica on catalytic performance.14 Olcese found that Fe/SiO2 was a potential catalyst for guaiacol hydrodeoxygenation (HDO).15 Nikulshin investigated the effect of the composition and the acidity of supporting sulfide catalysts on their activity and deactivation in guaiacol hydrodeoxygenation.16 Comparative research will indicate the role of supports in modifying catalyst morphologies and changing catalytic activity. In this paper, we prepared Ni/Fe/HBeta, Ni/Fe/ZSM-5, Ni/ Fe/HY, Ni/Fe/MCM-41, Ni/Fe/SiO2, and Ni/Fe/γ-Al2O3 catalysts and compared their catalytic performance in HDO and transmethylation. We also investigated their long time performances at atmospheric pressure and low temperature. Received: October 17, 2016 Revised: January 28, 2017 Published: January 30, 2017 2855

DOI: 10.1021/acs.energyfuels.6b02700 Energy Fuels 2017, 31, 2855−2864

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Energy & Fuels Table 1. N2 Physisorption Data of Catalysts with Different Support and the Content of Fe and Ni BET Surface area [m2/g] Fe/Ni/HBeta Fe/Ni/HY Fe/Ni/ZSM-5 Fe/Ni/MCM-41 Fe/Ni/γ-Al2O3 a

132 18 138 24 58

Total pore volumeBET [cm3/g] 0.2509 0.0344 0.1952 0.1792 0.3518

(P/P0 (P/P0 (P/P0 (P/P0 (P/P0

= = = = =

t-plot Micropore volume [cm3/g]

content of Ni [%]a

content of Fe [%]a

0.063 0.011 0.102 0.0109 0.166

10.42% 9.71% 9.19% 7.60% 9.79%

8.19% 8.02% 7.35% 6.55% 8.56%

0.9851) 0.99) 0.9856) 0.99) 0.9842)

The content of Ni and Fe was analyzed by AAS. The conversion percentage of products was calculated using eq 1. M(guaiacol)in is the initial molar amount of guaiacol, and M(guaiacol)out is the molar amount of guaiacol remaining after reaction.

Moreover, the carbon deposition of spent catalysts has also been studied.

2. EXPERIMENTAL SECTION

Ci% =

2.1. Catalysts preparation. The supports of HBeta, ZSM-5, HY, MCM-41, SiO2, and γ-Al2O3 (grounded and sieved Fe/Ni/ZSM-5 > Fe/Ni/HBeta > Fe/Ni/MCM-41, as shown in Table 2. For Fe/Ni/γ-Al2O3, although the amount of PyB is zero, the yield of BTX is 5.12%, as shown in Table 2, indicating that Lewis acid sites, not Bronsted acid sites, play an important role for HDO of guaiacol with Fe/Ni/γ-Al2O3 at atmospheric pressure.

Figure 2. X-ray diffraction patterns of catalysts with different supports: (a) fresh XRD (the catalysts were prereduced at 700 °C); (b) spent XRD. 2857

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Figure 5 shows the TEM pattern of Fe/Ni/HY. The size of the particle is 200−400 nm according to the TEM pattern. The shape of the particle is cubic. From the EDX, we can know that the content of Fe is much less than that of Ni. but the results of AAS show that the ratio of Fe/Ni is 1:1. This indicates that most of the Ni is on the surface of catalysts but the Fe is inside the catalysts. And there is carbon deposition on the surface of the spent catalyst. This result is consistent with our previous research, which shows that the Ni is an active part and Fe plays the role of carbon resistance. 3.2. Effect of support. 3.2.1. Effect of support on the selectivity and yield of the product. As illustrated in Table 3, these catalysts with different supports showed obviously different catalytic performances. The products from HDO and transmethylation of guaiacol were BTX, phenol, and other hydrocarbons. The other hydrocarbons are mainly methylated benzenes (including 1-ethyl-3-methylbenzene; 1,2,3-trimethylbenzene; 1-ethyl-2-methylbenzene; 1-ethyl-2,4-dimethylbenzene; 1,3,5-trimethylbenzene; and so on) and oxygenated compounds (most of the oxygenated compounds are phenols (such as 2,3-dimethylphenol; 2-ethylphenol; 4-methylphenol; 2-ethyl-4-methylphenol; 3,4-dimethylphenol; 2,3,5,6-tetramethylphenol; 2,3,4,6-tetramethylphenol; 2,4,5-trimethylphenol; 1,3,4,5-trimethylphenol; 2,3,5-trimethylphenol; and so on). They also include nonphenolic derivatives (such as 4-(1,1dimethylethyl)benzenemethanol; 1-methoxy-2-methylbenzene; dibenzofuran; and fluorene). The main products include BTX, phenol, 2-methylbenzaldehyde,1-methyl-9H-fluorene, 2-hydroxy-6-methylbenzaldehyde, and so on. Methanol has not been detected in the liquid products, but we obtained CH4 at the gas product. Aromatic hydrocarbons were present in the products. However, no cyclohexane and cyclohexane derivatives were present, thereby indicating that the hydrogenolysis was not easy for π-bonding of the aromatic ring at atmospheric pressure with non-noble supported zeolites. Especially, for all catalysts, the contents of phenol and phenols were much higher than those of BTX and methylated benzenes. This indicates the hydrogenolysis of CH3O−Caromatic bonds is easier than the hydrogenolysis of Caromatic−OH external bond in guaiacol at atmospheric pressure. Table 3 shows the conversion and yield for BTX with different support catalysts. It indicates that supports play an important role in the product distribution. The yield of BTX from Fe/Ni/HY, Fe/Ni/HBeta, Fe/Ni/ZSM-5, Fe/Ni/MCM41, Fe/Ni/SiO2, and Fe/Ni/γ-Al2O3 is 14%, 5%, 6%, 0.2%, and 0%, respectively, which is consistent with the total amount of PyB and PyL (Fe/Ni/HY > Fe/Ni/ZSM-5 > Fe/Ni/HBeta > Fe/Ni/MCM-41 in Table 2). It is possible that the amount of acid plays an important role in the BTX yield. Moreover, for Fe/Ni/HY, the total content of BTX and other hydrocarbon is 26%, which is more than for the other catalyst. It is possible that pore structure (shape selectivity) and crystal property play an important role in the activity of Fe/Ni/HY. In Table 1, the BET surface area, the micropore surface area, and the micropore surface volume of Fe/Ni/HY are higher than for the other catalysts. This induces the high BET surface area and micropore volume, which are beneficial for guaiacol conversion and oxygen removal. Although the BET surface area is also very high for the MCM-41 catalyst, the conversion and selectivity are low. It is possible that the acid intensity of the surface is lower than for other zeolites. On the contrary, the BET surface of Fe/Ni/γ-Al23 is the lowest, but the BTX yield is still high. It is possible that the acid site plays an important role. The

For zeolite catalysts, the intensity of the Bronsted acid sites (PyB) and Lewis acid sites significantly decreases with increasing desorption temperature from 150 to 350 °C, thereby indicating that both PyB and PyL consist of weak, medium, and strong acids.23 As shown in Table 2, for Fe/Ni/HY, Fe/Ni/ HBeta, and Fe/Ni/MCM-41 catalysts, the amounts of PyB and PyL significantly decreased, and only approximately 25% was left, whereas they decrease a little for Fe/Ni/γ-Al2O3 and ZSM5 with the increase of desorption temperature from 150 to 350 °C, indicating that the acid site in Fe/Ni/HY, Fe/Ni/HBeta, and Fe/Ni/MCM-41 consists of weak, medium, and strong acids and the acid site in Fe/Ni/γ-Al2O3 and Fe/Ni/ZSM-5 is mainly composed of a strong acid. Besides, the intensity of the acid plays an important role in guaiacol HDO and the amount of carbon deposition. This will be explained further in the next section. 3.1.4. TPR analysis of catalysts. The H2-TPR of the Fe/Ni/ support catalysts are shown in Figure 4. It is well-known that

Figure 4. H2-TPR of the Fe/Ni/support catalysts.

the reduction peaks of Ni oxide were at 450 °C and in the range of 600−750 °C.24 Moreover, the reduction of Fe2O3 to Fe3O4 is in the region 300−400 °C, and the region 400−700 °C is assigned to reduction of Fe3O4 to FeO and Fe.25,26 For all the Ni/Fe/γ-Al2O3 catalysts, the reduction of Ni/Fe oxides had two peaks at around 280−450 °C and in the range 450−700 °C, which were lower than those of the characteristic peaks of the monometallic Ni and Fe catalysts. The H2-TPR results indicated the formation of Ni−Fe bimetallic oxides (the result was consistent with the XRD pattern), which had a higher reducibility than the Ni and Fe monometallic oxides.24 The H2-TPR results also indicated Fe/Ni/MCM-41 catalysts had a higher reducibility than other catalysts. For example, the reduction peak for Ni−Fe bimetallic oxides starts from 220 °C, while it starts from 300 °C for Fe/Ni/zsm-5. The reduction peak from HY and γ-Al2O3 in the range 280−450 °C is much sharper than that for other catalysts. It is possible the reduction of Ni−Fe bimetallic oxides or of different crystal sizes occurs on the outer catalysts’ surface while the other catalysts are present in the zeolite channels.27 This is decided by the surface and pore sizes. The results in Table 1 also show that the BET surface are of HY is lower than those of other catalysts. It is also possible that the ratio of Ni−Fe bimetallic oxides to Ni/Fe monometallic oxides in HY is higher than those of other catalysts and the reducibility increased due to the reduction of less reducible Ni/Fe monometallic oxides and aluminates. 2858

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Figure 5. TEM and EDX patterns of fresh and spent Fe/Ni/HY catalysts.

Table 3. Effect of Different Catalysts on the Yield of Product from the Hydrodeoxygenation of Guaiacol Type of catalyst

Fe/Ni/HBeta

Fe/Ni/ZSM-5

Fe/Ni/HY

Fe/Ni/MCM-41

Fe/Ni/SiO2

Fe/Ni/γ-Al2O3

% Conversion % Yield CH4 Benzene Toluene Xylene Other hydrocarbon Phenol Oxygenated compound

100

99

100

69

11

76

0.96 0.5 2 3 7 38 50

1.93 1 3 2 0.4 44 48

0.87 1 6 7 12 54 20

0.78 0.1 0.1 0.0 2 36 30

0.42

0.67 2 3 0.3 4 50 16

8 4 3

is lower than that from Fe/Ni/HZSM-5. It is possible that the pore structure of the zeolites and acid site play an important role in the distribution of products. The BET surface area and pore diameter of Fe/Ni/ZSM-5 are slightly smaller than those for Fe/Ni/HBeta. And the ZSM-5 zeolite with 3D cross structure and 10-membered ring pore systems has a slightly lower HDO ability for phenol and phenols than the HBeta catalyst.28 Especially, acid intensity and amount is also another reason. The acid site Fe/Ni/HBeta consists of weak, medium, and strong acids, and the acid site in Fe/Ni/ZSM-5 is mainly composed of a strong acid. 3.2.2. Effect of supports on the transmethylation and XHDO. Transmethylation ratio is an important indicator for the carbon loss and hydrogen consumption. The supports have a

conversion for Fe/Ni/HY is 100%, whereas this is only 11% for Fe/Ni/SiO2. The guaiacol conversion and the BTX yield for HBeta and HY zeolite are also very good. Moreover, the yield of BTX from Fe/Ni/γ-Al2O3 is 7%, which is a bit higher than those from Fe/Ni/HBeta (5%) and Fe/Ni/ZSM-5 (6%). With Fe/Ni/γ-Al2O3 catalysts, the yield for benzene and phenol is highest among all catalysts, which indicates that Fe/Ni/γ-Al2O3 is not beneficial for the transmethylation reaction. This is consistent with the results in Table 3. With Fe/Ni/HBeta and Fe/Ni/ZSM-5 catalysts, although the guaiacol conversion for both is 100%, the yield of products is significantly different. Especially for other hydrocarbons, the yield is 7% with Fe/Ni/HBeta and only 0.45% with Fe/Ni/ ZSM-5. Meanwhile, the content of phenol from Fe/Ni/HBeta 2859

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Energy & Fuels Table 4. Effect of Different Catalysts on the XHDO and the Ratio of Transmethylation

a

Type of catalyst

Fe/Ni/HBeta

Fe/Ni/ZSM-5

Fe/Ni/HY

Fe/Ni/MCM-41

Fe/Ni/SiO2

Fe/Ni/Al2O3

% XHDO % The ratio of transmethylationa % The ratio of transmethylationb

56 24 1

53 5 1

63 26 0.3

52 27 0.8

76 0.00 0.8

56 4 0.3

The ratio of transmethylation:the ratio of transmethylationhydrocarbon. bThe ratio of transmethylation:the ratio of transmethylationoxygenated compound.

significant influence on the transmethylation and XHDO, as shown in Table 4. The ratio of transmethylationhydrocarbon and transmethylationoxygenated compound for Fe/Ni/γ-Al2O3 is lower than that for other zeolites catalyst, which indicates that the BET surface area and pore structure are a key point for the transmethylation. And the zeolites with ion exchange performance and uniform pore size are beneficial for the transmethylation. For zeolite catalysts, the ratio of transmethylation for Fe/Ni/ZSM-5 is much lower than that for other catalysts. It is possible the channels in the ZSM-5 are not suitable for transmethylation due to shape selectivity. 3.3. Influence of reaction time. 3.3.1. Effect of reaction time on the yield of guaiacol HDO. We examined the effect of reaction time on the conversion of guaiacol and the yield of products. The conversion of guaiacol remained at 100% for the first 3 h and then decreased slowly to 91%. Figure 6 shows the

(CH3-) to the aromatic ring, phenol, or guaiacol. It has been shown that the methoxyl or methyl in guaiacol could be transferred to the phenol ring through acid-catalyzed transmethylation reactions over Fe/Ni/HBeta.10 3.3.2. Effect of reaction time on the transmethylation and XHDO. Figure 7 shows that the conversion of guaiacol is below

Figure 7. Effect of time on the XHDO and the ratio of transmethylation.

Figure 6. Influence of reaction time on the yield of guaiacol hydrodeoxygenation.

100% after 3 h and drops to 91% at 6 h. The XHDO gradually declines from 58% to 50% in 6 h. The ratio of transmethylation for hydrocarbon significantly drops from 21% to 15%. It is possible that the catalyst activity for hydrodeoxygenation decreases. 3.4. Possible principal reaction. Figure 8 shows the possible principal reaction network occurring on catalysts for guaiacol HDO at atmospheric pressure. The HDO of guaiacol with Fe/Ni/support catalysts at atmospheric pressure drastically improved products yield toward phenol and benzene by

yield of BTX, phenol, other hydrocarbons, and oxygenation compounds as a function of reaction time running for guaiacol HDO with Ni/Fe/HBeta catalyst at 350 °C and atmospheric pressure in the fixed bed. The liquid products were collected every 1 h. As indicated in Figure 6, the yield of BTX and other hydrocarbons declined significantly. However, the yield of phenol and oxygenation compounds gradually increased from 36% to 40% and from 48% to 54% after 6 h, respectively. It was possible that the HDO activity of the catalyst declined. The high concentration of phenol implied that most of the guaiacol was removed via the demethoxylation reactions, whereas less hydroxyl can be removed from phenol to form benzene or toluene and xylene by dehydroxylation and transmethylation. A low concentration of anisole confirmed that demethoxylation was more favored than dehydroxylation of guaiacol with the Fe/Ni/HBeta as catalyst. Moreover, the concentration of the oxygenated compound increased with time. Most of the oxygenation compound formed from the transfer of CH3−O

Figure 8. Principal reaction network occurring on catalysts for guaiacol HDO at atmospheric pressure. 2860

DOI: 10.1021/acs.energyfuels.6b02700 Energy Fuels 2017, 31, 2855−2864

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Energy & Fuels DDO and demethoxylation pathways. The products phenol and benzene will form anisole, 2,4-dimethoxylphenol, toluene, and xylene by transmethylation or transmethoxylation pathways. In our experiments, completely hydrogenated products such as cyclohexane are found as traces. This indicated that the HYD pathway is prevented at atmospheric pressure by Fe/Ni/ support catalysts. The result concers with that of Gevert et al.,29 who proposed that the HDO of phenolic compounds prefers πbonding adsorption through the oxygen atom and would give C−O hydrogenolysis with π-bonding of the aromatic ring. Besides, with different supports, the principal reaction network is different. For HBeta supported catalyst, it favored transmethylation or transmethoxylation of phenol and benzene due to the high yield of other hydrocarbons and oxygenated compounds. For HY supported catalysts, it prefers to produce phenol by demethoxylation pathways. It also drastically enhanced the transalkylation of benzene pathways, as we observed a higher yield for toluene and xylene than for the other supported catalysts. At last, the use of γ-Al2O3 support catalyst drastically improved products yield toward benzene. 3.5. Carbon deposition. 3.5.1. FTIR Characterization. The FT-IR spectra of the spent Fe/Ni/HBeta, Fe/Ni/ZSM-5, Fe/Ni/HY, Fe/Ni/MCM-41, Fe/Ni/SiO2, and Fe/Ni/γ-Al2O3 (all the catalysts were used at 350 °C for 1 h, the WHSV was 3.5 h−1) are presented in Figure 9. Some researchers have

The detail of the six spectra show that there is an obvious mismatch below 1000 cm−1. In the region 880−450 cm−1, there are four different moderate absorption bands which are attributed to the formation of bonds between Fe, Ni particles, and the Si−Al structure of the support37 for Fe/Ni/HY, Fe/Ni/ HBeta, and Fe/Ni/ZSM-5. However, there are only two strong adsorptions at 750 and 590 cm−1 for Al2O3 support and at 800 and 471 cm−1 for the SiO2 support because of the absence of Si or Al in the support. 3.5.2. SEM Imaging. Figure 10 shows the surface morphology of fresh catalysts and the carbon deposition on the surface of spent catalysts. For all catalysts, a part of the pore in the surface was lost in the carbon deposition. Regarding the spent Fe/Ni/HBeta catalyst, the carbon deposition is a cubical crystal structure and the diameter is approximately 2−9 μm. On the contrary, the shape of the carbon on the surface of MCM41 is less than 2 μm. In addition, the fresh Fe/Ni/HY catalyst comprises a considerable amount of the agglomerated crystal particles with about 1.5 μm diameter, which is expected to have a substantial contributory effect on their catalytic activities. Also, there are obvious pores among the particles. However, carbon deposition with carbon-rich flat plates on Fe/Ni/HY catalyst is obviously on the spent catalysts. In addition, the microsized cubical crystal structures shown in the fresh particle of SiO2 are covered by sheets of compact carbon deposition on the spent one. 3.5.3. TG Analysis. To investigate the source of carbon deposition formation, the thermal experiments were performed. From Table 5, we can identify that the total weight losses were 10.5%, 10.63%, 5.13%, 2.12%, 10.55%, and 2.04%, corresponding to Ni/Fe/HY, Ni/Fe/HBeta, Ni/Fe/HZSM-5, Ni/Fe/γAl2O3, Ni/Fe/MCM-41, and Ni/Fe/SiO2 catalysts, respectively. Figure 8 shows that there are three stages of weight loss, from 30 to 250 °C, from 250 to 450 °C, and from 450 to 600 °C. The first stage connects with moisture and alcohol release, which shows the catalysts and carbon deposition to be hydrophilic. The second and third stages present the formation of aromatic derivatives and soft coke. To our surprise, there is no carbon deposition in the range 600−800 °C, which usually corresponds to the graphite.38,39 This result is consistent with the result from XRD analysis of spent catalysis in Figure 11. In addition, the amount of carbon deposition on Fe/Ni/Al2O3 and Fe/Ni/ZSM-5, as shown in Table 5, is less than those on Fe/ Ni/HY, Fe/Ni/HBeta, and Fe/Ni/MCM-41. The result is consistent with the amount of the weak and medium acid sites in catalysts in Table 2. Thereby, it indicates that the weak and medium acid sites are attributed to the formation of carbon deposition. Comparing all spent catalysts, we determined that γ-Al2O3 showed the least mass loss from the second stage at only 0.48%. On the contrary, the mass loss from Ni/Fe/MCM-41 reaches the maximum. It is possible that the effectivity of guaiacol conversion with Ni/Fe/MCM-41 is lower than others; therefore, most of the guaiacol is absorbed on the surface of MCM-41 and forms polyaromatics, which is the main composition of carbon deposition from the FI-IR results. Regarding Ni/Fe/HZSM-5, we found that the mass loss was lower than Ni/Fe/HY and Ni/Fe/HBeta in the second stage. However, the HDO activity is lower than others. This indicates that the carbon deposition does not play an important role for the inactivity of Ni/Fe/HZSM-5. It is possible that the pore structure of Ni/Fe/ZSM-5 is not suitable for the entrance of guaiacol; therefore, most of the guaiacol can only take the

Figure 9. FT-IR images of catalysts after the catalytic tests.

found that the strongly bonded zeolitic water in the 3665−2980 cm−1 region with a maximum peak at 3400 cm−1 and another peak at approximately 1635 cm−1 was due to physic-absorbed water molecules vibration.30−32 Previous studies31,33 have reported that these water molecules, which caused the active metal particle rearrangement and agglomerate, are not beneficial for the activities of the catalysts. This observation corroborates with the result in the sample TG profile. The bands at 2925 and 2980 cm−1 represent aliphatic groups. The bands at 1630 cm−1 and approximately 1450 cm−1 represent stretching vibrations of the CC group in an aromatic ring/rings. The band at 1100 cm−1 may be attributed to the stretching vibration of C−N or the bending of the C−O bond.34 The peaks at 800−500 cm−1 correspond to the vibration of −CH2− groups and the aromatics.35 The wavenumber in the 900−400 cm−1 region corresponds to the incorporation of active metals in aluminosilicates.36 2861

DOI: 10.1021/acs.energyfuels.6b02700 Energy Fuels 2017, 31, 2855−2864

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Figure 10. SEM photographs of the fresh and spent catalysts with different supports.

Table 5. Amount of Mass Loss and Temperature Range with Corresponding Mass Loss Peaks Peak temperature range (°C)/Mass loss (wt/%) Catalyst

Total mass loss (wt/%)

Stage 1

Stage 2

Stage 3

Ni/Fe/HY Ni/Fe/HBeta Ni/Fe/HZSM-5 Ni/Fe/γ-Al2O3 Ni/Fe/MCM-41 Ni/Fe/SiO2

10.50% 10.63% 5.13% 2.12% 10.55% 2.04%

36−255/(6.25%) 36−210/(5.20%) 36−233/(3.49%) 36−231/(2.12%) 36−181/(4.01%) 36−218/(2.72%)

255−424/(2.34%) 210−449/(4.01%) 234−417/(1.04%) 231−426/(0.48%) 182−460/(6.31%) 219−453/(1.13%)

424−582/(1.91%) 450−614/(1.42%) 418−649/(0.60%) 427−659/(−0.48%) 461−595/(0.23%) 454−782/(−1.81%)

methylnaphthalene. The difference of quantity and variety of the organic soluble coke among the catalysts with different supports is attributed to the difference of mass loss and degeneration temperature of carbon deposition. The amount of phenol and phenols is much higher for Ni/Fe/HBeta and Ni/ Fe/MCM-41 (with about 46% and 50%, respectively); therefore, the mass loss at stage 2 is higher than that for the other catalysts (in Table 5), for the organic reactants, intermediate products, and products that were left on the surface.39 The appearance of heptadecane, 2,6,10,14-tetramethylpentadecane, and 2,6,10,14-tetramethylhexadecane induced a part of “organic carbon” that continued to take the deoxygenation reaction on the surface of the catalyst. Moreover, the variety of oxygenated compounds increased with reaction time. This result is consistent with the activity of the catalyst decreasing with time, which confirmed that oxygenated compounds are the coke precursors in the formation of carbon deposits.

reaction on the surface of ZSM-5 but not inside the pore. On the contrary, the guaiacol can easily go inside the pore in Ni/ Fe/HY. And some products, together with guaiacol, are left in the pore, which causes the increase of carbon deposition. This is in agreement with the research report for shape selectivity. Regarding Ni/Fe/γ-Al2O3 and Ni/Fe/SiO2 catalysts, it is remarkable that there is a weight gain stage (in Table 5, the mass increased 0.48% and 1.81% in the third stage). It is possible that the Ni and Fe left from the catalyst reduction are oxidized again under air atmosphere, indicating that the reduced Ni and Fe in pure Si−O or Al−O structure formed some new structures which were not active for guaiacol HDO. 3.5.4. GC-Mass analysis of carbon deposition. Table 6 shows the quantitative and variety distribution of the organic soluble coke on Ni/Fe/HBeta, Ni/Fe/HY, Ni/Fe/γ-Al2O3, and/Fe/MCM-41 catalysts based on GC-MS analyses. The variety of organic coke from Ni/Fe/HBeta, Ni/Fe/HY, and Ni/ Fe/γ-Al2O3 catalysts is much more than from Ni/Fe/MCM-41, such as the isomer of 2-methylbenzaldehyde, the isomer of 1(2-methylphenyl)ethanone,1-methyl-3-phenoxybenzene, and 12862

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Article

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b02700. Table 6: Quantitative and variety distribution of the organic soluble coke on Ni/Fe/HBeta, Ni/Fe/HY, Ni/ Fe/γ-Al2O3 and Ni/Fe/MCM-41 catalysts based on GCMS analyses (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*(Xiwei Xu) E-mail: [email protected]. *(Enchen Jiang) E-mail: [email protected]. ORCID

Enchen Jiang: 0000-0002-8431-5717 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Supported by the Science and Technology Planning Project of Guangdong Province, China (Grant No. 2016A020210073), the National Science Foundation of China (Grant No.51576071), and the State Key Laboratory of Pulp and Paper Engineering (Grant No. 201618).

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REFERENCES

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Figure 11. TG and DTG curves for spent catalysts under air atmosphere.

4. CONCLUSION (1) BTX was produced from hydrodeoxygenation and transmethylation of guaiacol under atmospheric pressure. (2) Fe/Ni/support catalysts were prepared with different supports. The catalytic activity of hydrodeoxygenation and transmethylation of guaiacol was Fe/Ni/HY > Fe/ Ni/HBeta > Fe/Ni/ZSM-5 > Fe/Ni/γ-Al2O3 > Fe/Ni/ MCM-41 > Fe/Ni/SiO2. (3) Supports of Fe/Ni/support catalysts influenced the pore structure and crystal property of the active part, the surface morphology, the amount, and the composition of the carbon deposition in catalysts. (4) The Py-IR analysis displayed that the total amounts of PyB and PyL were attributed to the yield of BTX, and the presence of weak and medium acid sites was attributed to the formation of carbon deposition. (5) Key upgrading reactions include aldol condensation, alkylation, hydrogenation, aromatization, and deoxygenation. Moreover, the phenol amount indicated the hydrogenolysis of CH3O−caromatic bonds is the main reaction. 2863

DOI: 10.1021/acs.energyfuels.6b02700 Energy Fuels 2017, 31, 2855−2864

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