Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on

Subscriber access provided by UQ Library

Article

Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on Different Titania Supports Mohong Lu, Hu Du, Bin Wei, Jie Zhu, Mingshi Li, Yuhua Shan, and Chunshan Song Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01498 • Publication Date (Web): 31 Aug 2017 Downloaded from http://pubs.acs.org on September 4, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

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

Energy & Fuels

Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on Different Titania Supports

Mohong Lu†,‡, Hu Du†, Bin Wei†, Jie Zhu†, Mingshi Li†,*, Yuhua Shan† and Chunshan Song‡,* †

Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, and

Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, Changzhou University, Changzhou, Jiangsu, 213164, PR China ‡

Clean Fuels and Catalysis Program, EMS Energy Institute, Department of Energy &

Mineral Engineering and Department of Chemical Engineering, Pennsylvania State University, 209 Academic Projects Building, University Park, PA, 16802, USA

*Corresponding author: 1、Professor Mingshi Li School of Petrochemical Engineering, Changzhou University, Changzhou, Jiangsu, 13164, P. R. China Tel: +86-519-86330360 Fax: +86-519-86330360 E-mail: [email protected] 2、Professor Chunshan Song Department of Energy & Mineral Engineering Pennsylvania State University University Park, Pennsylvania 16802, US Tel: +1-814-863-4466 E-mail: [email protected]

ACS Paragon Plus Environment

Energy & Fuels

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

Abstract Pd catalysts supported on TiO2 with different crystalline phases were prepared with formaldehyde as reducing agent and examined for hydrodeoxygenation (HDO) of guaiacol. Their properties were characterized by N2 adsorption, XRD, TEM and XPS. Compared to the carbon-supported Pd catalysts, TiO2-supported Pd catalysts exhibited higher C-O bond scission ability, which may be attributed to the presence of partially reduced titanium species originating from the reduction of Ti4+ by spillover hydrogen from Pd at 200 oC on the surface of TiO2. Guaiacol was hydrogenated on Pd sites to give 2-methoxycyclohexanol, which diffused to partially reduced titanium species and subsequently reacted with hydrogen from Pd to generate cyclohexane. Anatase TiO2-supported Pd catalyst gave the highest HDO activity of guaiacol among the Pd catalysts supported on three types of TiO2 (anatase, rutile and their mixed, P25) , suggesting that more partially reduced titanium species are in favor of the HDO reaction because anatase is facile to be reduced by H2 at 200 oC. Higher selectivity of cyclohexane for Pd/TiO2 reduced at 500 oC than that reduced at 200 oC further confirmed that the enhanced C-O bond scission ability of Pd/TiO2 is mainly attributed to the partially reduced titanium species on the surface of TiO2. Keywords: Palladium, Titania, partially reduced titanium species, Guaiacol, Hydrodeoxygenation


Page 2 of 35

Page 3 of 35

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

Energy & Fuels

Introduction The concerns for energy security and the global environmental issues have motivated the increasing research efforts on biomass as a promising renewable resource [1]. The development of pyrolysis technology for transforming biomass into bio-oils make the use of biomass possible [2,3]. Bio-oils made from biomass, however, cannot be utilized due to their high viscosity, low heating value and low thermal and chemical stabilities caused by high content of oxygen [4-7]. Therefore, it is necessary for bio-oil to be upgraded so that it can be used as a standard fuel. Catalytic hydrodeoxygenation (HDO) is considered to be an efficient technology to upgrade bio-oils, during which the oxygen in bio-oils are removed by reacting with hydrogen gas to give water in the presence of catalysts without unnecessary loss of carbon [8,9]. Supported CoMoS and NiMoS catalysts which exhibit high activities in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) process were examined for the HDO of bio-oils in earlier research [10-14]. The active sulfided state of catalyst can be maintained by the sulfur from fossil fuel. It is difficult, however, for the sulfided catalysts to keep active in HDO of bio-oils due to the low content of sulfur (typically < 0.1 wt%) in the bio-oil except when additional sulfur was added into the feed [15,16]. A number of catalysts were explored to replace the sulfided catalysts for HDO of bio-oils. Transition metal phosphides [17-19], carbide[20-22], and nitride [23-25] have been widely investigated because they exhibit excellent HDO performance. However, fast deactivation of these catalysts during HDO process is still an important problem. Recently noble metals, such as Pd, Rh, Pt and Ru and their alloys, have been


Energy & Fuels

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

received increasing attention as an effective alternative to sulfided catalysts in HDO of bio-oils [26-31]. Supported noble metal catalysts can have high HDO activity at mild reaction conditions. Supports of noble metal catalysts have remarkable influence on the HDO performance. Acidic supports, such as γ-Al2O3, SiO2–Al2O3, acid-treated carbon were considered as support for noble metal catalysts in the HDO of bio-oils. Bifunctional mechanism was proposed for HDO of guaiacol over the noble metal catalysts supported on acidic oxide [26]. The benzene ring of guaiacol was hydrogenated on noble metal sites and then deoxygenation occurred on acidic sites of the support. The transalkylation activity of catalysts was dramatically influenced by the type of acidic sites by comparison of catalytic HDO over Pt/γ-Al2O3 and Pt/HY [27]. Wang et al. studied the Pd-Fe supported on carbon catalyst for HDO of guaiacol and demonstrated that the synergy between Pd and Fe contributed to the high selectivity to benzene [30]. Palladium is commonly used as a heterogeneous catalyst for the selective hydrogenation [32-35]. The catalytic performance of Pd metal is significantly affected by the interaction between Pd particles and the supports [32-35]. TiO2 has been widely investigated as a support of noble metal catalyst due to its reducible property. It is well known that the strong metal support interaction (SMSI) between Pd and TiO2 occurred when Pd/TiO2 was reduced in hydrogen gas at high temperature. Partially reduced TiOx(x < 2) could migrate onto the surface of Pd and cover Pd particle, which will change the adsorption capacity and catalytic activity of Pd [36-38]. Crossley’s group compared the guaiacol conversion on Ru metal supported on TiO2 and non-reducible C, SiO2 and Al2O3 and found that Ru/TiO2 was more active than on other supports [39, 40]. They suggested that the high activity of Ru/TiO2 catalyst is attributed to spillover of hydrogen from the Ru metal to the reducible TiO2 to produce


Page 4 of 35

Page 5 of 35

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

Energy & Fuels

defect sites. The results from Newman et al. demonstrated that uncalcined Ru/TiO2 catalysts with high dispersion of Ru metal exhibited high selectivity to direct deoxygenation in HDO of phenol when compared to Ru supported on carbon, alumina and silica. They hypothesized that the outstanding catalytic activity of Ru/TiO2 was attributable to Ti3+ site created by hydrogen spillover, interacting strongly with the oxygen in phenol to assist the breakage of C-O bond [41]. Ardiyanti investigated bimetallic Ni-Cu catalysts on various supports for the catalytic hydrotreating of fast pyrolysis oil and reported that NiCu/TiO2 showed the highest activity [42]. In our previous work, the introduction of TiO2 to Pd/SiO2 catalyst significantly enhanced the HDO activity [43]. In the present work, we use guaiacol as a model compound to examine the activity of Pd supported on TiO2 with different crystalline phase (anatase, rutile and their mixture, P25) for the HDO of guaiacol. For all the Pd/TiO2 catalysts, cyclohexane is the main deoxygenation product at elevated temperature, while 2-methycyclohexanol is the only product on carbon supported Pd catalysts. Pd supported on anatase TiO2 catalyst showed the highest HDO activity due to the more partially reduced titanium species formation on the surface of anatase TiO2. 2. Experimental 2.1. Materials and Catalyst Preparation PdCl2 solution (5 wt% in 10 wt% HCl), guaiacol (≥ 99.0% ) and n-dodecane (≥ 99% ) were bought from Sigma-Aldrich. Anatase TiO2, rutile TiO2 and Degussa P25 TiO2 were bought from Jingrui New Material Corporation (Xuancheng, China) Mesoporous Carbon (MC) was prepared by using the method reported in the literature [44]. The properties of obtained MC are shown in Table 1. All catalysts were prepared with formaldehyde as reducing agent. In a typical


Energy & Fuels

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

preparation, the slurry of 2.0 g supports in 50 mL water was added dropwise by 3.5 g of PdCl2 solution under stirring to achieve the desired Pd loading of 5 wt%. Then the obtained suspension was stirred for 1 h. After the pH was adjusted to approximately 11 using a 0.1 M NaOH solution, the solution was stirred for 2 h. Next, 1.0 mL formaldehyde (37 wt%) solution was slowly added to the suspension, and the obtained suspension was stirred for an additional 60 min at 80 oC. The mixture was filtered, washed and dried in a vacuum oven at 60 oC for 12 h. The obtained Pd/TiO2 (anatase), Pd/TiO2 (rutile), Pd/TiO2 (P25) and Pd/mesoporous carbon and Pd/activated carbon are referred to as Pd/TiO2(A), Pd/TiO2(R), Pd/TiO2(P), Pd/MC and Pd/AC, respectively. 2.2 Catalyst Characterization The adsorption of nitrogen was performed using a Micromeritics ASAP 2020 automated system at -196 oC to obtain the BET specific surface area, pore volume, and average pore diameter. The crystal structure of the catalysts were conducted by X-ray diffraction (XRD, Rigaku D/Max2400), using monochromatic Cu Ka radiation. The transmission electron microscopy (TEM) measurements were performed on a JEOL-2010 transmission electron microscope. The size distribution of Pd particles for every catalyst was estimated on the basis of 100 particles. X-ray photoelectron spectroscopy (XPS) measurements were performed by using a Multilab2000 X-ray photoelectron spectrometer. The binding energies (BEs) data were calibrated by using the BE of C1s at 284.8 eV as a reference. Prior to the characterization of XRD and XPS, the samples were treated by H2 (1 atm, 40 mL/min) at 200 oC for 3 h and then cooled to the room temperature followed passivation using 0.5% O2/Ar mixture.

2.3 Catalyst Activity Measurements The evaluation test of catalyst for HDO of guaiacol was carried out in a


Page 6 of 35

Page 7 of 35

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

Energy & Fuels

fixed-bed reactor with 6 mm inter diameter. In each run, 0.20 g sample (20-30 meshes) was placed in the center of the reactor. Prior to feed the solution of 3 wt% guaiacol in n-dodecane into the reactor, the palladium catalyst was treated by H2 (1 atm, 40 mL/min) at 200 oC for 3 h and then heated or cooled to the desired temperature. The HDO reaction were performed at 200, 240, 260, and 280 oC, total pressure 2 MPa, and H2 flow rate 150 mL/min (at atmospheric pressure). After the reaction was kept at the desired temperature for 6 h, the liquid product was collected by cooling the product mixture to room temperature and then separating liquid phase from gas phase and was analyzed by off-line GC equipped with an FID detector and a commercial HP-5 column. Guaiacol conversion (Xguaiacol), products selectivities (Sproducts-i) were calculated as follows: Xguaiacol = (Molguaiacol-in-Molguaiacol-out)/Molguaiacol-in; Sproducts-i = (Molproduct-i × ni)/(Molreacted guaiacol × 7), ni refers to the carbon number in product-i. 3. Results and Discussion 3.1. Catalyst Characterization The BET surface area, pore volume and average pore diameter of supports and as-prepared catalysts are shown in Table 1. Generally, the BET surface area and pore volume of TiO2 follows the order: TiO2(A)﹥TiO2(P)﹥TiO2(R) [45]. MC and AC have much larger BET surface area than TiO2. The slight decrease in BET surface area and pore volume for all of catalysts after Pd deposition compared to the supports indicates that palladium was deposited in the pores of the supports. The TEM photographs of the as-prepared catalysts are shown in Figure 1. It can be found that Pd particles are well dispensed on the surface of supports. The average size of Pd particles was estimated to be about 3.6 nm for Pd/TiO2(A), which is slightly smaller than those for Pd/MC and Pd/AC according to histogram analysis,


Energy & Fuels

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

indicating that TiO2 is favorable for the dispersion of Pd particles. The XRD patterns of all catalysts are shown in Figure 2. The TiO2 structures were not altered by Pd loading and subsequent thermal treatment. Crystalline Pd is hard to detect, except that a small peak at 40.0o assigned to the Pd (111) plane [46], can be observed for Pd/TiO2(P), Pd/TiO2(R) and Pd/AC. Compared to Pd/MC catalyst, Pd/AC catalyst exhibited a larger range of particle size, indicating that Pd is not well dispersed on the AC, which may be related to the pore texture of the AC support. It is well know that the pores in AC are mainly micropores. However, Pd nanoparticles are mainly in the internal surface of MC due to its larger pores. Almost no XRD peak of Pd species is observed for the Pd/TiO2(A) catalyst, suggesting that Pd particles on TiO2(A) surface are smaller. The smaller Pd particles obtained on TiO2(A) surface than on TiO2(P) and TiO2(R) surface may be the result of larger surface area (Table 1). The results indicate that Pd particles are well dispersed on supports, which are in good agreement with that obtained from TEM. The surface composition and oxidation states of all elements (Pd, Ti, and C species) in catalysts were analyzed by using XPS. Prior to the XPS test, the catalysts were treated at 200 oC, followed passivation with 0.5 % O2 in Ar flow after the catalysts were cooled to room temperature. The spectra of Pd3d, Ti2p, and C1s were collected. The atom compositions of Pd, Ti, and C on various catalysts surface are listed in Table 2. The Pd/Ti ratios in Pd/TiO2(A) and Pd/TiO2(P) catalysts are close and higher than that in Pd/TiO2(R) catalyst, indicating the properties of both Pd/TiO2(A) and Pd/TiO2(P) catalysts are similar, which is different from Pd/TiO2(R) catalyst. However, the Pd/Ti ratios for the three Pd/TiO2 catalysts obtained from XPS analysis are lower than the nominal value (0.04) for 5 wt% Pd/TiO2 catalyst, suggesting that Pd


Page 8 of 35

Page 9 of 35

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

Energy & Fuels

nanoparticles not only located on the external surface of TiO2 but in the pores of supports. For the Pd/MC catalyst, however, Pd nanoparticles mainly locate on the internal surface of MC due to its larger pore sizes; the Pd/C ratio obtained from XPS for the Pd/MC catalysts is lower than the nominal value (0.006). The reverse is true for Pd/AC. The surface chemical states of Pd determined by XPS are shown in Figure 3. The core level XPS spectra of Ti 2p recorded from various TiO2 samples (results not shown) show sharp and intense peaks at 464.2 and 458.5 eV, which are assigned to Ti4+ in the TiO2 [47,48]. However, No Ti3+ peaks were observed for all the TiO2 samples under these conditions. It is known that binding energies of metallic Pd0 are at 334.9±0.2 eV (3d5/2) [49-51] while binding energies of 336.4 eV (3d5/2) and 337.6 eV (3d5/2) are assigned to Pd2+ and Pd4+ in PdO and PdO2, respectively [52, 53]. For Pd/TiO2 catalysts, a main peak located at 335eV were observed companied a shoulder peak at 336.3eV indicating that Pd species are mainly presented as Pd0 metal and a passivated layer of PdO are formed on the surface of Pd nanoparticles. However, for the Pd/AC and Pd/MC catalysts, Pd species are mainly presented as PdO and PdO2 and no peak for Pd0 metal is observed. The results suggest that the interaction between Pd and TiO2 occurs when Pd/TiO2 catalysts were reduced at 200 oC. It is generally accepted that strong metal-support interaction between Pd and TiO2 support occurs after high-temperature (above 500 oC) reduction, which will lead to the migration of partial reduced Ti3+ species onto the surface of noble metal particles [36]. However, Riyapan et al. found it was possible for the reduction of Ti4+ to Ti3+ at relatively low reduction temperature in the presence of Pd [54]. The dissociatively chemisorbed hydrogen on the Pd may spill over to TiO2 surface and reduce Ti4+ to Ti3+[55-57]. The formation of TiOx( x < 2) species at lower temperature was observed [58]. Li et al. also reported that Ti4+ can be reduced to Ti3+ in the presence of Pd even


Energy & Fuels

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

Page 10 of 35

at low reduction temperature (200 oC) [32]. Partially reduced titanium species on the surface of TiO2 produced by the H2 reduction may be favorable to keep the palladium species in the form of metal Pd0. 3.2. Catalyst Activity The guaiacol hydrodeoxygenation was performed in the fixed-bed reactor at 200-280 oC under 3 MPa. The conversions of guaiacol on all the catalysts are shown in Figure 4. It can be seen that all catalysts have high HDO activity of guaiacol at the temperature employed. Especially, guaiacol is almost converted completely on all Pd catalysts except Pd/TiO2(R) suggesting that Pd catalysts have high hydrogenation activity. Compared to Pd/TiO2(R) catalyst, Pd/TiO2(A) and Pd/TiO2(P) catalysts exhibited higher hydrogenation, which may be due to the higher Pd content on the catalyst surface (Table 2) and better dispersion of Pd metal (Figure 1). The product distributions of guaiacol HDO over various catalysts with temperature are shown in Figure 5. The guaiacol HDO over a number of catalysts were investigated [59-62]. 2-Methoxycyclohexanol, cyclohexanol, cyclohexane and benzene are found to be the main products over Pd/TiO2 catalysts within the temperature range examined (Figure 5a-c). 2-Methoxycyclohexanol as the primary hydrogenation product at low reaction temperature (200 oC) for all the Pd catalysts confirms high hydrogenation ability of Pd catalysts. However, overwhelming amount of cyclohexane was found as the oxygen-free product on Pd/TiO2(A) and Pd/TiO2(P) while cyclohexane was hardly found over Pd/TiO2(R), which

suggests that the

breakage of C-O bond was facile on TiO2(A) and TiO2(P) supported Pd catalysts. The selectivity of cyclohexane increased with the decrease in 2-methoxylcyclohexanol when the reaction temperature was elevated. Especially, guaiacol almost transformed into cyclohexane and benzene completely at 260 oC over Pd/TiO2(A) catalyst further


Page 11 of 35

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

Energy & Fuels

indicating that Pd/TiO2(A) catalysts have high ability to improve the breakage of C-O bond. Benzene as oxygen-free product at elevated reaction temperature over Pd/TiO2(A) catalysts was also found. However no benzene was formed during the hydrodeoxygenation of cyclohexanol as the same conditions. Therefore it is likely that the direct breaking C-O bond of guaiacol rather than the dehydrogenation of cyclohexane leads to the formation of benzene, which suggests that a C-O direct breakage path exists besides the first hydrogenation and then deoxygenation path in the HDO reaction on Pd/TiO2(A) catalyst at elevated reaction temperature. Pd supported on carbon catalysts, however, exhibited dramatic difference in the products distribution compared to Pd supported on TiO2 catalysts. Guaiacol almost transformed to 2-methoxycyclohexanol completely, suggesting that carbon supported Pd catalysts have strong hydrogenation ability. A small amount of cyclohexanol and the almost absence of oxygen-free products demonstrate that the hydrogenolysis reaction of C-O bond is hard to occur on Pd/C catalysts likely because of the competing adsorption of aromatic ring with the C-O bonds in the hydrogenation intermediate products. Phenol and anisole, which are the main products for guaiacol HDO on Pd/C catalysts [9, 30], were not found over all the Pd catalysts in this study, indicating that the catalytic HDO performance of guaiacol was significantly influenced by the catalysts employed and reaction conditions. The relative low reaction temperature (< 280 oC) and high pressure of H2 benefit the high selectivity of hydrogenation product 2-mythoxylcyclohexanol. It is very clear that the supports play a key role in the HDO of guaiacol over supported Pd catalysts by analyzing the product distribution. Over all the Pd catalysts, 2-mythoxylcyclohexanol as the main product at low reaction temperature suggests that guaiacol was first hydrogenated on Pd particles. 2-Methoxylcyclohexanol was


Energy & Fuels

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

further transformed to cyclohexanol and then to cyclohexane over Pd/TiO2 catalysts while no further transformation of 2-methoxylcyclohexanol was found over Pd supported on carbon. It is indicated that the adsorption of 2-methoxylcyclohexanol on Pd/TiO2 cataysts is substantially different from that on Pd/carbon catalysts. The reduction of Ti4+ to Ti3+ at low temperature (200 oC) was confirmed by EPR in the presence of Pd [32, 55]. Ti3+ on the surface of TiO2 strongly interacts with the oxygen atom in the methanol and results in the C-O bond scission [63, 64]. Therefore we assume that the adsorption and breakage of C-O bond in 2-methoxycyclohexanol mainly occur on the partially reduced titanium species for Pd/TiO2 catalysts. Activated hydrogen spillover from dissociated H2 on Pd to partially reduced titanium species react with chemisorbed C-O bond to give the products (Scheme 1). The amount of partially reduced titanium species on the surface of TiO2 decreased with the content of rutile in TiO2 due to its more stable structure [65.]. So the difference of HDO activities of Pd supported on TiO2(A), TiO2(P) and TiO2(R) catalysts could be attributed to the different amount of partially reduced titanium species. To further investigate the active sites of Pd catalysts, the HDO of cyclohexanol over Pd/TiO2(A) and Pd/MC was carried out. The conversion of cyclohexanol is shown in Figure 6. It is clear that the scission of C-O bond can take place on both catalysts while the Pd/TiO2(A) exhibits higher C-O bond scission activity. The particle sizes of Pd on the both catalysts surface are comparable (Figure 1,2). Therefore partially reduced titanium species on the surface of TiO2 may play the substantial role in the C-O bond scission though Pd metal also can catalyze this reaction. For Pd/MC and Pd/AC catalysts, the hydrogenation of guaiacol and the C-O bond breakage could occur on the same sites and the competing adsorption of guaiacol and 2-methoxycyclohexanol may impede the occurrence of C-O bond scission, which


Page 12 of 35

Page 13 of 35

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

Energy & Fuels

results in the small amount of cyclohexane formed on Pd/MC and Pd/AC catalysts. However, for Pd supported on TiO2 catalysts, the hydrogenation of guaiacol takes place on Pd metal sites and produced 2-methoxycyclohexanol diffuses to partially reduced titanium species to react, which result in the high selectivity of cyclohexane. This process is remarkably analogical to the case of noble metal/acidic supports dual functional catalysts [27]. The effect of H2 treating temperature of Pd/TiO2(A) catalysts on the HDO property was investigated. The activity and selectivity of Pd/TiO2(A) catalyst treated at different temperatures are illustrated in Figure 7 and Figure 8, respectively. The Pd/TiO2(A) catalyst treated at 200 oC exhibited higher activity than that treated at 50 o

C. This may be due to the more partially reduced titanium species generated by

reduction at higher temperature. Surprisingly although the activity of Pd/TiO2(A) catalyst decreased dramatically, the selectivity of cyclohexane increased when the catalyst was treated at higher temperature (500 oC) (Figure 8). The treatment at high temperature does not alter the Pd particle size obviously (Figure 9), which is in line with the results reported in the literature [36]. It is generally accepted that Pd surface will be decorated by the migration of partially reduced TiOx when Pd/TiO2 was treated by H2 at higher temperature (500 oC), which will lead to the great decrease in the adsorption of H2 [36]. Therefore the decrease in activity of Pd/TiO2(A) could be attributed to the suppression of H2 chemisorption capacity of Pd covered by the TiOx. And the higher ability to C-O bond scission may result from more partially reduced titanium species produced by treatment at high temperature. The results further suggest that the partially reduced titanium species on the surface of TiO2 contribute to the high activity of guaiacol HDO over TiO2 supported Pd catalysts.


Energy & Fuels

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

4. Conclusion The HDO performance of Pd catalysts is substantially influenced by the properties of supports. When carbon materials, such as mesoporous carbon and activated carbon, were employed as support of Pd catalysts for guaiacol HDO, 2-methoxycyclohexanol as the dominating primary product was hardly transformed further. The C-O bond scission was suppressed by the presence of guaiacol and 2-methoxycyclohexanol. The guaiacol HDO process on Pd/TiO2 catalysts was proposed that 2-methoxycyclohexanol generated by hydrogenation of guaiacol on Pd sites diffused to partially reduced titanium species and reacted with the active H atom from Pd to give cyclohexane. Pd supported on anatase TiO2 catalyst showed the highest HDO activity might due to the more partially reduced titanium species formed on the surface of anatase TiO2.

Acknowledgements This work is financially supported by the National Natural Science Foundation of China (21761132006, 21676029). The financial supports from Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and the EMS Energy Institute of the Pennsylvania State University at University Park are also acknowledged. References

[1]

Patel, M.; Kumar, A. Production of renewable diesel through the hydroprocessing of lignocellulosic biomass-derived bio-oil: A review. Renew. Sust. Energ. Rev. 2016, 58, 1293–1307.


Page 14 of 35

Page 15 of 35

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

Energy & Fuels

[2]

Demirbas, A. Biomass resource facilities and biomass conversion processing for fuels and chemicals. Energy Convers. Manage. 2001, 42, 1357–1378.

[3]

van Haveren, J.; Scott, E. L.; Sanders, J. Bulk chemicals from biomass. Biofuels, Bioprod. Biorefin. 2008, 2, 41–57.

[4]

Echeandia, S.; Pawelec, B.; Barrio, V. L.; Arias, P. L.; Cambra, J. F.; Loricera,

C.

V.;

Fierro,

J.

L.

G.

Enhancement

of

phenol

hydrodeoxygenation over Pd catalysts supported on mixed HY zeolite and Al2O3. An approach to O-removal from bio-oils. Fuel, 2014, 117, 1061– 1073. [5]

Boullosa-Eiras, S.; Lødeng, R.; Bergem, H.; Stocker, M.; Hannevold, L.; Blekkan, E. A. Catalytic hydrodeoxygenation (HDO) of phenol over supported molybdenum carbide, nitride, phosphide and oxide catalysts. Catal. Today, 2014, 223, 44–53.

[6]

Jae, J.; Tompsett, G. A.; Foster, A. J.; Hammond, K. D.; Auerbach, S. M.; Lobo, R. F.; Huber, G. W. Investigation into the shape selectivity of zeolite catalysts for biomass conversion. J. Catal., 2011, 279, 257–268.

[7]

Li, K.; Wang, R.; Chen, J. Hydrodeoxygenation of anisole over silica-supported Ni2P, MoP, and NiMoP catalysts. Energy Fuels, 2011, 25, 854–863.

[8]

Wildschut, J.; Iqbal, M.; Mahfud, F. H.; Cabrera, I. M.; Venderbosch, R. H.; Heeres, H. J. Insights in the hydrotreatment of fast pyrolysis oil using a ruthenium on carbon catalyst. Energy Environ. Sci., 2010, 3, 962–970.

[9]

Shafaghat, H.; Rezaei, P. S.; Daud, W. M. A. W.; Catalytic hydrogenation of phenol, cresol and guaiacol over physically mixed catalysts of Pd/C and zeolite solid acids. RSC Adv., 2015, 5, 33990–33998.


Energy & Fuels

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

[10]

Page 16 of 35

Laurent, E.; Delmon, B. Influence of water in the deactivation of a sulfided NiMo/γ-Al2O3 catalyst during hydrodeoxygenation. J. Catal. 1994, 146 (1), 281–291.

[11]

Ferrari, M.; Bosmans, S.; Maggi, R.; Delmon, B.; Grange, P. CoMo/carbon hydrodeoxygenation catalysts: influence of the hydrogen sulfide partial pressure and of the sulfidation temperature. Catal. Today 2001, 65(2-4), 257–264.

[12]

Bui, V. N.; Laurenti, D.; Afanasiev, P.; Geantet, C. Hydrodeoxygenation of guaiacol with CoMo catalysts. Part I: Promoting effect of cobalt on HDO selectivity and activity. Appl. Catal. B 2011, 101 (3-4), 239–245.

[13]

Ruiz, P. E.; Frederick, B. G.; De Sisto, W. J.; Austin, R. N.; Radovic, L. R.; Leiva, K.; García, R.; Escalona, N.; Wheeler, M. C. Guaiacol hydrodeoxygenation on MoS2 catalysts: Influence of activated carbon supports. Catal. Commun. 2012, 27, 44−48.

[14]

Mora, I. D.; Méndez, E.; Duarte, L. J.; Giraldo S. A. Effect of support modifications for CoMo/γ-Al2O3 and CoMo/ASA

catalysts in

the

hydrodeoxygenation of guaiacol. Appl. Catal. A 2014, 474 (1), 59–68. [15]

Kubička, D.; Kaluža, L. Deoxygenation of vegetable oils over sulfided Ni, Mo and NiMo catalysts. Appl. Catal., A 2010, 372, 199−208.

[16]

Senol, O. I.; Viljava, T. R.; Krause, A. O. I. Effect of sulphiding agents on the hydrodeoxygenation of aliphatic esters on sulphided catalysts. Appl. Catal., A 2007, 326, 236−244.

[17]

Bui, P.; Cecilia, J. A.; Oyama, S. T.; Takagaki, A.; Infantes-Molina, A.; Zhao, H.; Li, D.; Rodríguez-Castellón, E.; Lopez, A. J. Studies of the synthesis of transition metal phosphides and their activity in the hydrodeoxygenation of a biofuel model compound. J. Catal. 2012, 294, 184–198.


Page 17 of 35

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

Energy & Fuels

[18]

Rensel, D. J.; Rouvimov, S.; Gin, M. E.; Hicks, J. C. Highly selective bimetallic FeMoP catalyst for C–O bond cleavage of aryl ethers. J. Catal. 2013, 305, 256–263.

[19]

Feitosa, L. F.; Berhault, G.; Laurenti, D.; Davies, T. E.; da Silva, V. T. Synthesis and

hydrodeoxygenation activity of Ni2P/C-Effect of the palladium salt on lowering the nickel phosphide synthesis temperature. J. Catal., 2016, 340, 154–165. [20]

Mortensen, P. M.; de Carvalho, H. W. P.; Grunwaldt, J. D.; Jensen, P. A.; Jensen, A. D. Activity and stability of Mo2C/ZrO2 as catalyst for hydrodeoxygenation of mixtures of phenol and 1-octanol. J. Catal., 2015, 328, 208–215.

[21]

Lee, W.S.; Kumar, A.; Wang, Z.; Bhan, A. Chemical titration and transient kinetic studies of site requirements in Mo2C-catalyzed vapor phase anisole hydrodeoxygenation. ACS Catal. 2015, 5, 4104−4114.

[22]

Zhang, W.; Zhan, Y.; Zhao, L.; Wei, W. Catalytic activities of NiMo carbide supported on SiO2 for the hydrodeoxygenation of ethyl benzoate, acetone, and acetaldehyde. Energy Fuels 2010, 24, 2052–2059.

[23]

Ghampson, I. T.; Sepúlvedac, C.; Garciac, R.; Fierrod, J. L. G.; Escalonac, N.; DeSisto, W. J. Comparison of alumina- and SBA-15-supported molybdenum nitride catalysts for hydrodeoxygenation of guaiacol. Appl. Catal. A 2012, 435–436, 51–60.

[24]

Ghampson, I. T.; Sepúlvedac, C.; Garciac, R.; Frederick, B. G.; Wheeler, M. C.; Escalona, N.; DeSisto, W. J. Guaiacol transformation over unsupported molybdenum-based nitride catalysts. Appl. Catal. A 2012, 413– 414, 78–84.

[25]

Ghampson, I. T.; Sepúlvedac, C.; Garciac, R.; Radovic, L. R.; Fierro, J. L.


Energy & Fuels

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

G.; DeSisto, W. J.; Escalona, N. Hydrodeoxygenation of guaiacol over carbon-supported molybdenum nitride catalysts: Effects of nitriding methods and support properties. Appl. Catal. A 2012, 439–440, 111–124. [26]

Gutierrez, A.; Kaila, R. K.; Honkela, M. L.; Slioor, R.; Krause, A. O. I. Hydrodeoxygenation of guaiacol on noble metal catalysts. Catal. Today 2009, 147 (3–4), 239–246.

[27]

Lee, C. R.; Yoon, J. S.; Suh, Y. W.; Choi, J. W.; Ha, J. M.; Suh, D. J.; Park, Y. K. Catalytic roles of metals and supports on hydrodeoxygenation of lignin monomer guaiacol. Catal. Comm. 2012, 17, 54–58.

[28]

Lin, Y. C.; Li, C. L.; Wan, H. P.; Lee, H. T.; Liu, C. F. Catalytic Hydrodeoxygenation of guaiacol on Rh-based and sulfided CoMo and NiMo catalysts. Energy Fuels 2011, 25, 890–896.

[29]

Zhao, C.; Kou, Y.; Lemonidou, A. A.; Li, X.; Lercher, J. A. Highly selective catalytic conversion of phenolic bio-oil to alkanes. Angew. Chem. Int. Ed. 2009, 121 (22), 4079–4050.

[30]

Sun, J.; Karim, A. M.; Zhang, H.; Kovarik, L.; Shari Li, X.; Hensley, A. J.; McEwen, J.; Wang, Y. Carbon-supported bimetallic Pd–Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol. J. Catal. 2013, 306, 47–57

[31]

Zacher, A. H.; Olarte, M. V.; Santosa, D. M.; Elliott, D. C.; Jones, S. B. A review and perspective of recent bio-oil hydrotreating research. Green Chem. 2014, 16, 491–515.

[32]

Li, Y.; Fan, Y.; Yang, H.; Xu, B.; Feng, L.; Yang, M.; Chen, Y. Strong metal-support interaction and catalytic properties of anatase and rutile supported palladium catalyst Pd/TiO2. Chem. Phys. Lett. 2003, 372 (1–2), 160–165.

[33]

Li, Y.; Xu, B.; Fan, Y.; Feng, N.; Qiu, A.; He, J. M.; Yang, H.; Chen, Y. The effect of titania polymorph on the strong metal-support interaction of


Page 18 of 35

Page 19 of 35

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

Energy & Fuels

Pd/TiO2 catalysts and their application in the liquid phase selective hydrogenation of long chain alkadienes. J. Mol. Catal. A: Chem. 2004, 216 (1),107–114. [34]

Koussathana,

M.;

Vamvouka,

N.;

Tsapatsis,

M.;

Verykios,

X.

Hydrogenation of aromatic compounds over noble metals dispersed on doped titania carriers. Appl. Catal. A 1992, 80 (1–2), 99–113. [35]

Binder, A.; Seipenbusch, M.; Muhler, M.; Kasper, G. Kinetics and particle size effects in ethene hydrogenation over supported palladium catalysts at atmospheric pressure. J. Catal. 2009, 268 (1), 150–155.

[36]

Fu, Q.; Wagner, T.; Olliges, S.; Carstanjen, H. Metal−oxide interfacial reactions: Encapsulation of Pd on TiO2 (110). J. Phys. Chem. B 2005, 109(2), 944–951.

[37]

Weerachawanasak, P.; Mekasuwandumrong, O.; Arai, M.; Fujita, S.; Praserthdam, P.; Panpranot, J. Effect of strong metal–support interaction on the catalytic performance of Pd/TiO2 in the liquid-phase semihydrogenation of phenylacetylene. J. Catal. 2009, 262(2), 199–205

[38]

Tapin, B.; Epron, F.; Especel, C.; Ly, B. K.; Pine, C.; Besson, M. Study of Monometallic Pd/TiO2 Catalysts for the hydrogenation of succinic acid in aqueous phase. ACS Catal. 2013, 3 (10), 2327−2335

[39]

Boonyasuwat, S.; Omotoso, T.; Resasco D. E.; Crossley, S. P. Conversion of guaiacol over supported Ru catalysts. Catal. Lett., 2013, 143, 783–791.

[40]

Omotoso, T.; Boonyasuwat, S.; Crossley, S. P. Understanding the role of TiO2 crystal structure on the enhanced activity and stability of Ru/TiO2 catalysts for the conversion of lignin-derived oxygenates. Green Chem. 2014, 16, 645–652.

[41]

Newman, C.; Zhou, X.; Goundie, B.; Ghampson, I. T.; Pollock, R. A.; Ross, Z.; Wheeler, M. C.; Meulenberg, R.; Austin, R. N.; Frederick, B. G. Effects


Energy & Fuels

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

of support identity and metal dispersion in supported ruthenium hydrodeoxygenation catalysts. Appl. Catal., A 2014, 477, 64−74. [42]

Ardiyanti, A. R.; Khromova, S. A.; Venderbosch, R. H.; Yakovlev, V. A.; Melian-Cabrera, I. V.; Heeres, H. J. Catalytic hydrotreatment of fast pyrolysis oil using bimetallic Ni–Cu catalysts on various supports. Appl. Catal. A 2012, 449,121–130.

[43]

Lu, M.H.; Zhu, J.; Li, M.S.; Shan, Y.H.; He, M.Y.; Song, C.S. TiO2-modified Pd/SiO2 for catalytic hydrodeoxygenation of guaiacol. Energy Fuels 2016, 30, 6671-6676.

[44]

Huang, Y.; Hu, S.; Zuo, S.; Xu, Z.; Han, C.; Shen, J. Mesoporous carbon materials prepared from carbohydrates with a metal chloride template. J. Mater. Chem. 2009, 19, 7759–7764.

[45]

Ohno, T.; Sarukawa, K.; Matsumura, M. Photocatalytic activities of pure rutile particles isolated from TiO2 powder by dissolving the anatase component in HF solution. J. Phys. Chem. B 2001, 105, 2417–2420.

[46]

Wang, X.; Xia, Y. The influence of the crystal structure of TiO2 support material on Pd catalysts for formic acid electrooxidation. Electrochim. Acta 2010, 55, 851–856.

[47]

Jing, L.; Sun, X.; Cai, W.; Xu, Z.; Du, Y.; Fu, H. The preparation and characterization of nanoparticle TiO2/Ti films and their photocatalytic activity. J. Phys. Chem. Solids 2003, 64, 615–623.

[48]

Price, N. J.; Reitz, J. B.; Madix R. J.; Solomon, E. I. A synchrotron XPS study of the vanadia–titania system as a model for monolayer oxide catalysts. J. Electron Spectrosc. Relat. Phenom. 1999, 98–99, 257–266.

[49]

Kaichev, V.V. Morkel, M. Unterhalt, H. Prosvirin, I.P. Bukhtiyarov, V.I. Rupprechter, G. Freund, H.J. C–O bond scission on “defect-rich and perfect” Pd(1 1 1)?. Surf. Sci. 2004, 566–568 (Pt. 2), 1024–1029.


Page 20 of 35

Page 21 of 35

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

Energy & Fuels

[50]

Mamede, A.S.; Leclercq, G.; Payen, E.; Granger, P.; Gengembre, L.; Grimblot, J. XPS characterization of adsorbed reaction intermediates on automotive exhaust gas catalysts: NO and CO + NO interactions with Pd. Surf. Interface Anal. 2002, 34, 105–111.

[51]

Demoulin, O.; Navez, M.; Ruiz, P. The Activation of a Pd/γ-alumina catalyst during methane combustion: Investigation of the phenomenon and of potential causes. Catal. Lett. 2005, 103, 149–153.

[52]

Bi, Y.; Lu, G. Catalytic CO oxidation over palladium supported NaZSM-5 catalysts. Appl. Catal. B 2003, 41, 279–286.

[53]

Ketteler, G.; Ogletree, D. F.; Bluhm, H.; Liu, H.; Hebenstreit, E. L. D.; Salmeron, M. In situ spectroscopic study of the oxidation and reduction of Pd(111). J. Am. Chem. Soc. 2005, 127, 18269–18273.

[54]

Riyapana, S.; Boonyongmaneerat, Y. ; Mekasuwandumrong, O. ; Praserthdam, P. ; Panpranot, J. Effect of surface Ti3+ on the sol–gel derived TiO2 in the selective acetylene hydrogenation on Pd/TiO2 catalysts. Catal. Today 2015, 245, 134–138.

[55]

Xu, J.; Sun, K.; Zhang, L.; Ren, Y.; Xu, X. A highly efficient and selective catalyst for liquid phase hydrogenation of maleic anhydride to butyric acid. Catal. Commun. 2005, 6, 462–465.

[56]

Huizinga, T.; Prins, R. Behavior of titanium(3+) centers in the low- and high-temperature reduction of platinum/titanium dioxide, studied by ESR. J. Phys. Chem. 1981, 85, 2156–2158.

[57]

Conesa, J. C.; Soria, J. Reversible titanium(3+) formation by hydrogen adsorption on M/anatase (TiO2) catalysts. J. Phys. Chem. 1982, 86, 1392– 1395.

[58]

Panagiotopoulou, P.; Christodoulakis, A.; Kondarides, D. I.; Boghosian, S. Particle size effects on the reducibility of titanium dioxide and its relation to


Energy & Fuels

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

Page 22 of 35

the water–gas shift activity of Pt/TiO2 catalysts. J. Catal. 2006, 240, 114– 125. [59]

Gao, D.; Schweitzer, C.; Hwang, H. T.; Varma, A. Conversion of guaiacol on noble metal catalysts: Reaction performance and deactivation studies. Ind. Eng. Chem. Res. 2014, 53 (49), 18658–18667.

[60]

Lee, K.; Gu, G. H.; Mullen, C. A.; Boateng, A. A.; Vlachos, D. G. Guaiacol hydrodeoxygenation mechanism on Pt(111): Insights from density functional theory and linear free energy relations. ChemSusChem 2015, 8 (2), 315–322.

[61]

Pinheiro, A.; Hudebine, D.; Dupassieux, N.; Geantet, C. Impact of oxygenated compounds from lignocellulosic biomass pyrolysis oils on gas oil hydrotreatment. Energy Fuels 2009, 23 (2), 1007–1014.

[62]

Yan,

N.;

Yuan,

Y.;

Dykeman,

R.;

Kou,

Y.;

Dyson,

P.J.

Hydrodeoxygenation of lignin-derived phenols into alkanes by using nanoparticle catalysts combined with brønsted acidic ionic liquids. Angew. Chem. Int. Ed. 2010, 49 (32), 5549–5553. [63]

Zhang, Z.; Bondarchuk, O.; White, J.M.; Kay, B. D.; Dohnálek, Z. Imaging adsorbate O−H bond cleavage: methanol on TiO2(110). J. Am. Chem. Soc. 2006, 128, 4198–4199.

[64]

Henderson, M.A.; Otero-Tapia, S.; Castro, M.E. The chemistry of methanol on the TiO2(110) surface: the influence of vacancies and coadsorbed species. Faraday Discuss. 1999, 114, 313–329.

[65]

Panpranot, J.; Kontapakdee, K.; Praserthdam, P. Effect of TiO2 crystalline phase composition on the physicochemical and catalytic properties of Pd/TiO2 in selective acetylene hydrogenation. J. Phys. Chem.B 2006, 110, 8019–8024.


Page 23 of 35

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

Energy & Fuels

Captions of scheme and figures Figure 1. TEM images and particle size distribution of catalysts. Figure 2. XRD profiles of catalysts.(A: anatase; R: rutile) Figure 3. The XPS spectra of Pd3d of the catalysts. Figure 4. Conversion of guaiacol as a function of temperature on different catalysts. Figure 5. Selectivity of products as a function of temperature over (a) Pd/TiO2(A), (b) Pd/TiO2(P), (c) Pd/TiO2(R), (d) Pd/MC and (e)Pd/AC. Figure 6. Conversion of cyclohexanol as a function of temperature over catalysts. Figure 7. Conversion of guaiacol as a function of temperature on Pd/TiO2 (A) treated by H2 at different temperature. Figure 8. Selectivity of products as a function of temperature over Pd/TiO2(A) treated by H2 at (a) 50 oC, (b) 200 oC, (c) 500 oC. Figure 9. XRD profiles of Pd/TiO2(A) treated by H2 at different temperature. (A: anatase) Scheme 1. Hydrodeoxygenation reaction pathways of guaiacol on Pd/TiO2 and Pd/C catalysts. .


Energy & Fuels

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

Table1. The physical properties of supports and catalysts. Catalysts TiO2(A) Pd/TiO2(A) TiO2(P) Pd/TiO2(P) TiO2(R) Pd/TiO2(R) MC Pd/MC AC Pd/AC

Surface area (m2/g) 71 64 66 50 30 26 626 615 1297 1284

Pore volume (m3/g) 0.22 0.20 0.17 0.16 0.07 0.06 0.81 0.73 1.23 1.16

Average pore diameter (nm) 13.3. 12.4 13.1 12.8 10.6 9.6 4.5 4.7 2.7 3.6


Page 24 of 35

Page 25 of 35

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

Energy & Fuels

Table 2. The XPS data of catalysts Samples Pd/TiO2(A) Pd/TiO2(P) Pd/TiO2(R) Pd/MC Pd/AC

Pd 0.81 1.03 0.55 0.33 0.74

Atomic composition Ti C Pd/Ti Pd/C 26.26 0.031 31.42 0.033 20.50 0.027 90.17 0.0036 85.49 0.0086


Energy & Fuels

Pd/TiO2(A)

Frequency (%)

40 35 30 25 20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10 11

Particle size (nm) 30

Frequency (%)

Pd/TiO2(P)

25 20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10 11


Frequency (%)

Pd/TiO2(R)

20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10 11

Particle size (nm)

Frequency (%)

30

Pd/MC

25 20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10 11


Pd/AC

Frequency (%)

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

Page 26 of 35

25 20 15 10 5 0 0

1

2

3

4

5

6

7

8

9

10 11

Particle size (nm)

Figure 1. TEM images and particle size distribution of catalysts


Page 27 of 35

A

Pd/TiO2(A)

Pd A A

A

A A A

Pd/TiO2(P)

Intensity (a.u.)

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

Energy & Fuels

R R

R

Pd/TiO2(R) R R R R

R

Pd/MC

Pd/AC

10

20

30

40

50

o

60

70

80

2 Theta ( )

Figure 2. XRD profiles of catalysts. (A: anatase; R: rutile)


Energy & Fuels

Pd/TiO2(A)

Intensity (a.u.)

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

338.3

336.3

Page 28 of 35

335.0

Pd/TiO2(P)

Pd/TiO2(R)

Pd/MC

Pd/AC

346

344

342

340

338

336

334

B.E.(eV) Figure 3. The XPS spectra of Pd3d of the catalysts.


332

Page 29 of 35

100

Conversion (%)

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

Energy & Fuels

90

80 Pd/TiO2(A) Pd/TiO2(P) 70

60 200

Pd/TiO2(R) Pd/MC Pd/AC 220

240

260

o

Temperature ( C)

Figure 4. Conversion of guaiacol as a function of temperature on different catalysts.


Energy & Fuels

100

Cyclohexane Benzene Methoxycyclohexanol Cyclohexanol

80

80

60 40 20 0 200

220

240

60 40 20 0 200

260

o

Temperature ( C)

220

240 o

260

Temperature ( C)

100

100

d

c 80

Selectivity (%)

Selectivity (%)


b

a Selectivity (%)

Selectivity (%)

100


60 40 20 0 200

220

240 o

260

80 60 40


20 0 200

Temperature ( C)

220

240 o

260

Temperature ( C)

100

e Selectivity (%)

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

Page 30 of 35

80 60 40


20 0 200

220

240 o

260

Temperature ( C)

Figure 5. Selectivity of products as a function of temperature over (a) Pd/TiO2(A), (b) Pd/TiO2(P), (c) Pd/TiO2(R), (d) Pd/MC and (e)Pd/AC.


Page 31 of 35

100 Pd/TiO2(A)

Conversion (%)

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

Energy & Fuels

80

Pd/MC

60 40 20 0 200

220

240 o

260

Temperature ( C)

Figure 6. Conversion of cyclohexanol as a function of temperature over catalysts.


Energy & Fuels

100

Conversion (%)

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

80 60 40 o

50 C o 200 C o 500 C

20 0 200

220

240

260

o

Temperature ( C)

Figure 7. Conversion of guaiacol as a function of temperature on Pd/TiO2 (A) treated at different temperature.


Page 32 of 35

Page 33 of 35

Selectivity (%)

100

a


80 60 40 20 0 200

220

240

260

o

Temperature ( C)

100


Selectivity (%)

b 80 60 40 20 0 200

220

240

260

o

Temperature ( C)

100

Selectivity (%)

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

Energy & Fuels


c

80 60 40 20 0 200

220

240

260

o

Temperature ( C)

Figure 8. Selectivity of products as a function of temperature over Pd/TiO2(A) treated by H2 at (a) 50 oC, (b) 200 oC, (c) 500 oC.


Energy & Fuels

A

o

500 C Pd A

A A A AA

Intensity (a.u.)

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

o

200 C

o

50 C

10

20

30

40

50

60

70

80

o

2 Theta ( ) Figure 9. XRD profiles of Pd/TiO2(A) treated by H2 at different temperature. (A: anatase)


Page 34 of 35

Page 35 of 35

Pd/TiO2 O

benzene OH

O HO

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

Energy & Fuels

OH

Pd/TiO2

2-methoxy cyclohexanol

guaiacol

cyclohexanol

cyclohexane

O

Pd/C OH

2-methoxy cyclohexanol

Scheme 1. Hydrodeoxygenation reaction pathways of guaiacol on Pd/TiO2 and Pd/C catalysts.


Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on

Recommend Documents