Selective Hydrogenolysis of Glycerol over Acid-Modified CoâAl

Subscriber access provided by READING UNIV

Article

Selective hydrogenolysis of glycerol over acidmodified Co-Al catalysts in a fixed-bed flow reactor Fufeng Cai, Xianghai Song, Yuanfeng Wu, Jun Zhang, and Guomin Xiao ACS Sustainable Chem. Eng., Just Accepted Manuscript • Publication Date (Web): 01 Dec 2017 Downloaded from http://pubs.acs.org on December 5, 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.

ACS Sustainable Chemistry & Engineering 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 30 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

ACS Sustainable Chemistry & Engineering

Selective hydrogenolysis of glycerol over acid-modified Co-Al catalysts in a fixed-bed flow reactor Fufeng Cai,†,‡,* Xianghai Song,‡ Yuanfeng Wu,‡ Jun Zhang,†,* Guomin Xiao‡,* †

CAS Key Laboratory of Low-Carbon Conversion Science and Engineering,

Shanghai Advanced Research Institute, Chinese Academy of Sciences, No. 99 Haike Road, Pudong District, Shanghai 201210, China ‡

School of Chemistry and Chemical Engineering, Southeast University, No. 2

Southeast University Road, Jiangning District, Nanjing 211189, China *Corresponding

authors.

E-mail

addresses:

[email protected]

(F.

Cai),

[email protected] (J. Zhang), [email protected] (G. Xiao). Tel./Fax: +86 25 52090612.

1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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 2 of 30

ABSTRACT In this study, different acid-modified Co-Al catalysts were prepared and employed for glycerol hydrogenolysis by the addition of B, Ce, Zr, and heteropolyacids (HSiW, HPW, HPMo) to Co-Al catalysts. The catalysts prepared in this work were thoroughly examined by various characterization methods such as BET, ICP, SEM, H2 chemisorption, TEM, XRD, H2-TPR, NH3-TPD, XPS, and FTIR. The results showed an increase in the acid strength and Co dispersion on the catalytic surface for the modified Co-Al catalysts. This facilitated the conversion of glycerol. When ethanol was used as a solvent, the selectivity of 1,2-propanediol (1,2-PDO) by the acid-modified Co-Al catalysts decreased slightly, attributable to the enhanced etherification activity of glycerol with ethanol. However when water was used as a solvent, the modified Co-Al catalyst with the B, Ce, and Zr species increased the selectivity of 1,2-PDO. Addition of heteropolyacids to Co-Al catalyst enhanced the selectivity of 1,3-propanediol (1,3-PDO) as compared to 1,2-PDO selectivity which was relatively low due to its association with Brønsted acid sites on the modified Co-Al catalysts. The optimal HSiW/Co-Al catalyst (in terms of both 1,2- and 1,3-PDO selectivity) showed 76.3% glycerol conversion and 18.3% 1,3-PDO selectivity with a good stability. This could be attributed to the existence of well-dispersed Co particles with strong interaction between Co and W species.

KEYWORDS: Glycerol, Hydrogenolysis, Propanediols, Acid-modified Co-Al catalysts, Heteropolyacids

2


Page 3 of 30 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


INTRODUCTION In recent years, large scale biodiesel production has yielded excess amount of glycerol as a by-product. This has resulted in a rapidly drop in the market price of glycerol.1 In this regard, how to utilize the oversupply of glycerol has received much attention in both industrial and academic communities.

Currently,

the

application

of

several

catalytic

technologies

including

transesterification, reforming, etherification, dehydration, oxidation, hydrogenolysis and carboxyalation in converting the cheap glycerol into other high-margin chemicals have been explored.2-4 Specifically, selective conversion of glycerol into propanediols (i.e., 1,2-PDO and 1,3-PDO) has received significant research attention. In industry, 1,2-PDO can be employed for produce cosmetics, pharmaceuticals, polyesters resins, and so on. 1,3-PDO is used primarily as a monomer for the manufacture of polytrimethylene terephthalate (PTT) with a higher flexibility and elasticity.5 Therefore, selective hydrogenolysis of glycerol can be view as a better alternative process to produce propanediols compared to the conventional method derived from the petroleum derivates. In general, the conversion of glycerol into propanediols catalyzed by a solid acid catalyst follows the dehydration-hydrogenation reaction pathway as reported in literature.6,7 Firstly, the glycerol conversion intermediates that are acetol or 3-hydroxypropionaldehyde, are generated from the dehydration of either the primary or secondary hydroxyl group of glycerol on the acid sites of the catalyst. Afterwards, the hydrogenation of the intermediates on the metal sites of the catalyst produces 1.2-PDO for acetol and 1,3-PDO for 3-hydroxypropionaldehyde. From the above analysis, it can be seen that both catalytic metal and acid sites have a significant influence in the production of propanediols from glycerol.8,9 Hydrogenolysis of glycerol involving different bifunctional metal-acid catalysts has been widely applied. Nakagawa et al.10 examined the catalytic performance for glycerol hydrogenolysis on modified Ir-ReOx/SiO2 catalysts with different solid acid co-catalysts, for example ZrO2, TiO2, HZSM-5, Amberlyst 70, and so forth. They noted that the catalytic activity significantly increased with the addition of solid acid co-catalysts. Among them, HZSM-5 was the best solid acid co-catalyst in view of the catalyst stability and activity. Slightly different from the report of Nakagawa et al, Li et al.11 claimed that the modification of Ru/Al2O3 and Ru/SiO2 with HZSM-5 3



promoted the conversion of glycerol, while the selectivity of propanediols decreased dramatically, which was attributed to the fact that the acidity of HZSM-5 enhanced the activity of Ru to break C-C bonds of glycerol. Zhu and co-workers12,13 reported that incorporation of the heteropolyacids (HSiW, HPW, HPMo) into Pt/ZrO2 catalyst exhibited a significant promoting effect on the production of 1,3-PDO from glycerol, attributable to the high levels of Brønsted acid sites and exceptional thermal stability. In order to raise the catalytic activity and stability of Cu/SiO2 catalyst, Zhu et al.14 prepared an admixture of B2O3 and Cu/SiO2 catalysts in different B/Cu weight ratios for glycerol hydrogenolysis. They found that addition of the B2O3 to Cu/SiO2 catalyst remarkably enhanced the acid strength and Cu metal dispersion, which led to the increased catalytic activity and stability. Likewise, Jiménez-Morales et al.15 in their study established that the Ce-modified Ni/SBA-15 catalysts possessed very high catalytic activity during the conversion of glycerol attributing this result to the strong acid sites and high Ni metal dispersion on the catalyst. However, the hydrogenolysis of glycerol involving acid-modified Co-Al catalysts has not been published in literature. Based on literature, generally cobalt catalyst exhibited relatively poor catalytic activity for glycerol hydrogenolysis as compared to some non-noble metal catalysts such as copper and nickel catalysts.14-17 According to the study of Guo et al.,16 a MgO supported cobalt catalyst for 1,2-PDO production from glycerol only exhibited 44.8% glycerol conversion and 42.2% selectivity of 1,2-PDO using an autoclave reactor at 200 ℃ and 2.0 MPa initial hydrogen pressure. Rekha et al.17 systematically investigated the activity of glycerol conversion on Co-ZnO catalysts with different mass ratios of Co and Zn at 180 ℃ and 4.0 MPa hydrogen pressure with a high catalyst loading in a batch reactor. Among the catalysts examined, a mass ratio of Co and Zn of 1:1 possessed the best catalytic activity giving rise to 70% of glycerol conversion and 80% of 2-PDO selectivity, but large quantities of byproducts such as ethylene glycol was observed. Several researches involving the dehydration-hydrogenation mechanism for propanediols production from glycerol has shown that modifying the catalyst by adding promoter with appropriate acidity significantly enhanced propanediols selectivity and also glycerol conversion.8,9 Therefore, in this work, different acid species such as B, Ce, Zr, HSiW, HPW, and HPMo were introduced into the Co-Al catalyst to investigate their catalytic activities focusing more on the structure-activity relationship of modified Co-Al catalysts for glycerol hydrogenolysis. The influences of reaction 4


Page 4 of 30

Page 5 of 30 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


variables, for example solvent, reaction temperature, and feeding rate, on glycerol hydrogenolysis were examined. Finally, the catalyst stability and reaction pathway for propanediols production from glycerol were also studied.

EXPERIMENTAL SECTION Chemicals The purities of 1,2-PDO, 1,4-butanediol, Ce(NO3)3·6H2O, 1,3-PDO, ZrO(NO3)2·xH2O and acetol supplied from Aladdin Industrial Corporation were 99.5 wt.%, 99.5 wt.%, 99.0 wt.%, 99.5 wt.%, 99.5 wt.% and 90.0 wt.%, respectively. Other chemicals such as glycerol, cobaltous nitrate hexahydrate, ethylene glycol, H3BO3, methanol, aluminium nitrate nonahydrate, ethanol, H4[Si(W3O10)4]·xH2O, 1-propanol, H3[P(W3O10)4]·xH2O, 2-propanol, potassium carbonate and H3[P(Mo3O10)4]·xH2O, all of analytical grade, were acquired from Sinopharm Chemical Reagent Co., Ltd.. The aforementioned chemicals were employed for the experiments without undergoing further purification. In addition, deionized water self-made in the lab was used throughout the experiment.

Catalyst Preparation Preparation of the Co-Al catalyst was based on the co-precipitation method as in the literature.17 Following the general procedure, aqueous solution of aluminium nitrate nonahydrate (36.80 g) and cobaltous nitrate hexahydrate (4.94 g) was calculated and dispersed for 30 min at 50 ℃ with ultrasonic dispersion and stirred vigorously for 120 min at room temperature. Precipitation of the liquid mixture was done by adding a certain amount of concentrated solution of K2CO3 (0.2 g·mL-1) dropwise until pH of 9.0 was obtained. The suspension was then stirred (800 rpm) with a mechanical stirrer continuously for 48 h at 25 ℃. Then the precipitate was filtered by a Büchner funnel and repeated washing done five times (1000 mL × 5) with deionized water. Finally, the sample was dried at 100 ℃ in an oven for 24 h and calcined at 400 ℃ in a muffle furnace for 4 h to achieve the product. The acid-modified Co-Al catalysts were prepared by impregnating uncalcined Co-Al powder (> 120 mesh) after the drying procedure with a calculated amount of aqueous solution of H3BO3, H4[Si(W3O10)4]·xH2O, Ce(NO3)3·6H2O, H3[P(W3O10)4]·xH2O, ZrO(NO3)2·xH2O or H3[P(Mo3O10)4]·xH2O. After impregnation, the water was removed by 5



Page 6 of 30

heating and stirring at 90 ℃ under vacuum using a rotary evaporator. Subsequently, the sample underwent drying and calcination at 100 ℃ in the oven for 24 h and at 400 ℃ in the muffle furnace for 4 h, respectively. The catalysts produced were ground with a mortar and then pressed by a tablet machine at 10 MPa to form granules with sizes of 20 to 40 meshes. In the prepared catalysts, the nominal weight loadings for Co and promoters (i.e., B, Ce, HSiW, HPW, HPMo or Zr) were fixed at 20 wt.% and 8 wt.%, respectively on the Al2O3 support.

Catalyst Characterization The actual loadings of the Co and promoters in the catalysts were examined by inductively coupled plasma optical emission spectroscopy (Optima 7300 DV, PerkinElmer). The physical properties of modified Co-Al catalysts such as BET specific surface areas and total pore volume were measured at -196 ℃ by means of a Beishide 3H-2000PS1 instrument. Degassing the catalyst at 200 ℃ for 12 h using a vacuum was done prior to the characterization. The surface morphologies of the modified Co-Al catalysts were observed with a Philips XL-30 ESEM. During the measurements, the operating voltage of the instrument was 15 kV. Meanwhile, the morphologies of the modified Co-Al catalysts were also examined by using a FEI Tecnai G2 transmission electron microscope coupled with an energy dispersive spectrometer (EDS). The operating voltage of the instrument was 200 kV in the measurements. Using ultrasonic dispersion, the analyzed catalyst was mixed with ethanol for 30 min and then drops of the solution were mounted on a holey copper grid coated with an amorphous carbon film. Furthermore, hydrogen chemisorption was conducted to measure the Co dispersion of the catalysts. The 100 mg of modified Co-Al catalysts was first heated at 400 ℃ for 60 min in a flow of He (30 mL·min-1) and then decreased down to 30 ℃. After the pretreatment, the modified Co-Al catalysts were in situ reduced at 400 ℃ for 120 min in flowing 5% H2/N2 mixture gas at a flow velocity of 30 mL·min-1, and subsequently purified with flowing He for 30 min and decreased down to 100 ℃. Hydrogen chemisorption was carried out by injecting numbers of H2 pulses until saturation with H2 for the sample. The Co dispersion of the catalyst was calculated as in published literature.18,19 The phase composition of the modified Co-Al catalysts was verified by using a Bruker D8-Discover X-ray diffractometer with Cu Kα radiation. The operating voltage and electricity of the instrument were 40 kV and 30 mA, respectively. During the measurements, the scanning range 6


Page 7 of 30 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


was set from 10° to 90° at a scanning speed of 6°·min-1. The reducibility of modified Co-Al catalysts was studied by H2-TPR method. After pretreating at 400 ℃ for 60 min in a flow of He, the TPR was conducted by raising the temperature from 50 ℃ to 780 ℃ at a heating rate of 10 ℃·min-1 with a flow of 5% H2/N2 mixture gas. Measurement of the hydrogen consumption was done by means of the TCD. The NH3-TPD method was employed to analyze the acidity of the modified Co-Al catalysts. The 100 mg of modified Co-Al catalysts was first pretreated at 400 ℃ for 60 min in a flow of He and subsequently saturated at 100 ℃ for 30 min with pure NH3 stream. The modified Co-Al catalysts were purified at 100 ℃ for 60 min with a flow of He and then increased up to 750 ℃ at a heating rate of 10 ℃·min-1. The signal detection of the NH3 desorption was done using the TCD. The surface chemical composition of the modified Co-Al catalysts was probed by an X-ray Photoelectron Spectrometer with a Mg Kα radiation source. The obtained binding energies of all elements were calibrated by the C1s binding energy of 284.6 eV. Fourier transform infrared spectra of adsorbed pyridine (Py-IR) on the modified Co-Al catalysts were analyzed by a Nicolet 5700 FTIR spectrometer. The 30 mg of modified Co-Al catalysts was first heated at 300 ℃ for 60 min in a vacuum and subsequently decreased down to 30 ℃. Then, a FTIR spectrum was determined and expressed as spectrum Ⅰ. After adsorption of pyridine for 30 min, the modified Co-Al catalysts were purified at 150 ℃ for 30 min and then spectrum Ⅱ was measured. The final spectrum of the modified Co-Al catalysts was achieved by subtracting spectrum Ⅰ from spectrum Ⅱ.

Glycerol Hydrogenolysis Experiments In this study, the experiments were conducted in a vertical fixed-bed flow reactor with inner diameter of 11 mm and length of 950 mm as shown in Figure S1. Following the general procedure, 4.0 g of modified Co-Al catalysts with particles sizes of 20 to 40 meshes was fixed in the middle region of the reaction tube, filled with quartz sand (20-40 mesh) at both ends. Prior to the experiment, the modified Co-Al catalysts were reduced in situ in the reactor at 400 ℃ for 120 min with a pure H2 flow at a flow velocity of 100 mL·min-1. After the reduction process, the temperature of reactor was decreased down to 230 ℃ and then the system pressure was slowly increased to the 3.5 MPa with a back pressure regulator. Subsequently, a mixture of 20 wt.% 7



Page 8 of 30

glycerol in ethanol preheated to 230 ℃ was pumped into the reaction system at a flow velocity of 27.8 mL·h-1 by means of a metering pump combined with pure hydrogen (100 mL·min-1), which corresponded to WHSV of 1.21 h-1. After certain time of running, the reaction products were well cooled by ethylene glycol in a condenser and then stored in a gas-liquid separator. At regular intervals of time (30 min), the liquid samples in the gas-liquid separator were taken and analyzed by a gas chromatography (GC). The GC (Shimadzu GC-2014) was equipped with a FID, and the chromatographic column was Rtx-WAX (30 m × 0.25 mm). The GC analysis was done using 1,4-butanediol as an internal standard substance and also incorporated into the liquid sample. In addition, the liquid samples in the gas-liquid separator were also analyzed by means of GC-MS (Shimadzu GCMS-QP2010). The glycerol conversion, product selectivity and yield were calculated by means of the following equations:

Conversion (%) =

Selectivit y (%) =

Yield(%) =

moles of glycerol (in ) − moles of glycerol ( out ) × 100 moles of glycerol (in )

moles of carbon in a specific product × 100 moles of carbon in glycerol consumed

Conversion(%) × Selectivity(%) 100

(1)

(2)

(3)

RESULTS AND DISCUSSION Catalyst Characterization As depicted in Figure S2a, it was evident that the N2 adsorption-desorption isotherm of the Co-Al catalyst corresponded to the type Ⅳ isotherm and showed an obvious hysteresis loop of H1 type in the range of P/P0 = 0.5-0.95. The isotherm shapes of the catalysts remained unchanged after the introduction of promoters, but the pore diameter distribution for the acid-modified Co-Al catalysts decreased (Figure S2b), indicating that the promoters were small enough to enter the channels of Co-Al catalyst. As displayed in Table S1, the actual loadings of the Co and promoters measured by ICP-OES were very close to the nominal values, although there were small differences, most probably due to the metals loss in the preparation process. The specific surface areas and pore volumes of the acid-modified Co-Al catalysts were slightly lower than those of the 8


Page 9 of 30 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


Co-Al catalyst, which was likely attributable to the blockage of some pores by the promoters. As can be seen in Figure S3, all the acid-modified Co-Al catalysts had blocky texture with few particles deposited on the surface. It was also clear to see that more small particles existed in the Ce/Co–Al, HSiW/Co–Al, and Zr/Co-Al catalysts than in the Co-Al catalyst, indicating their superior structure. Together with TEM test, the EDS analysis was performed to estimate the chemical compositions of the catalysts. As shown in Figure S4, the results of EDS measurement indicated that the heteropolyacids (HSiW, HPW, HPMo) were present in the modified Co-Al catalysts and had a good stability. In addition, there were certain amounts of Cu and K in the catalysts, which were derived from copper grid used for TEM test and the residual precipitant (i.e., potassium carbonate), respectively. The TEM bright field images and dark field images of the catalysts are displayed in Figures S5 and S6, respectively. In Figure S5, the Co particles of the catalysts were seen to distribute evenly on the support surface, while the TEM dark field images (Figure S6) showed that the Co particles of acid-modified Co-Al catalysts were more dispersed than those of Co-Al catalyst. In order to clarify this point further, the Co dispersions of the acid-modified Co-Al catalysts measured by hydrogen chemisorption are given in Table S1. It is clear from these data in Table S1 that the addition of acid modifiers increased the Co dispersion of the catalysts. One possible explanation for this was that the introduction of promoters helped to restrain the aggregation of Co particles. Among the modified Co-Al catalysts prepared, the HSiW-modified Co-Al catalyst possessed the highest Co dispersion, which might be attributed to the existence of the strong interaction between the cobalt and W species (see below). As indicated in Figure S7, it is apparent that the presence of Co3O4 (PDF#42-1467)17 gave rise to diffraction peaks for calcined Co-Al catalyst at 36.8° and 44.8°. Also, in all the acid modified Co-Al catalysts, the Co3O4 phase was noted. However, no obvious characteristic peaks corresponding to the promoters were observed in acid-modified Co-Al catalysts except for Ce/Co-Al catalyst. After the reduction process, no noticeable diffraction peak of CeO2 (PDF#43-1002, 2θ = 28.5°)20 in the Ce/Co-Al catalyst was observed. However, the Co3O4 phase was still evident in all the acid-modified Co-Al. It was worthy to mention that the patterns of both Co (PDF#15-0806, 2θ = 44.2°)17 and Co3O4 phases were not evidently distinguished by XRD analysis. But for the Co3O4 phase, it was clear that the strength and width of diffraction peak were respectively weakened and broadened after the reduction process, indicating that some Co3O4 9



Page 10 of 30

species in the catalysts were reduced to CoO and/or Co.21 Furthermore, the peak intensity at 44.2° for the acid-modified Co-Al catalysts was weaker than that of Co-Al catalyst, suggesting the presence of higher dispersive Co species in the acid-modified Co-Al catalysts, in line with the measurement results of H2 chemisorption. The reducibility of the acid-modified Co-Al catalyst was examined by using H2-TPR method. As displayed in Figure S8, all the acid-modified Co-Al catalysts displayed two clear hydrogen consumption peaks α and β in the order of 150-500 ℃ and 600-780 ℃ respectively. According to literature, the peak α in the range of 150-500 ℃ is considered to be the reduction of Co3O4 to CoO, whereas the peak β in the range of 600-780 ℃ describes the reduction of CoO to Co.21,22 In comparison to Co-Al catalyst, the strength of low temperature peak α for the acid-modified Co-Al catalysts decreased, whereas that of high temperature peak β increased, despite almost the same Co content in the acid-modified Co-Al catalysts. This indicated that more CoO and/or Co species were formed because the promoters were introduced. Table S2 gives the amounts of consumed hydrogen during TPR measurement. It should be noted that the amount of consumed hydrogen of B/Co-Al catalyst was relatively low. In Figure S8, the reduction peaks of B/Co-Al catalyst slightly shifted to higher temperature, showing the existence of strong interaction between B and Co species, which might have led to the significant decrease in the amount of consumed hydrogen.23 In contrast, a high amount of consumed hydrogen at high temperature (> 600 ℃) was seen on HPMo/Co-Al catalyst, which might be due to the fact that molybdena could be partially reduced at high temperature.24,25 This notwithstanding, the results of H2-TPR showed that only parts of the Co3O4 species were reduced to CoO and/or Co0 in this study, which was probably attributed to the existence of strong interaction between Co3O4 species and promoters and/or support.26 Figure S9 presents the results of NH3-TPD analysis. For Co-Al catalyst, it was clear that a weak NH3 desorption peak existed in the range of 420-750 ℃, reflecting the presence of some strong acid sites.27 When different promoters were introduced into Co-Al catalyst, evidently, NH3 desorption peaks appeared in the range of 150-370 ℃, and also the strength of peaks in the range of 420-750 ℃ notably increased. Table S1 shows an analysis of the comparison of the acidities of the catalysts. It is evident that the addition of promoters into Co-Al catalyst enhanced both the acid quantity and strength. Among the prepared catalysts, the HSiW/Co-Al catalyst possessed the highest total acidity. 10


Page 11 of 30 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


As regards the XPS measurement, Co 2p XPS profiles of the acid-modified Co-Al catalysts are illustrated in Figure S10. In Figure S10a, only two peaks centered at approximately 780 and 795 eV respectively assigned to Co 2p3/2 and Co 2p1/2 were evident in the calcined catalysts. This result suggested that the Co species in the modified Co-Al catalysts were principally in a trivalent state.17 In Figure S10b, the binding energy (B.E.) values of Co 2p3/2 and Co 2p1/2 for all modified Co-Al catalysts were increased to about 780.4 and 796.2 eV, respectively. Furthermore, two quite distinct satellite peaks at approximately 786.3 and 803.2 eV were noted. This could mean the presence of Co2+ and/or Co species in the reduced catalysts.21 Figure S10b again showed a slight shift to lower B. E. triggered by Co 2 peak of the acid modified Co-Al catalysts. This phenomenon could be attributed to the existence of strong interaction between the promoters and cobalt species.14 According to existing literatures,17,28,29 the peak of Co 2p3/2 for the reduced catalysts can be deconvoluted into three components, i.e., Co3+, Co2+, and Co0 species and the results are displayed in Figure S10c. As illustrated, the cobalt species in the reduced modified Co-Al catalysts were mainly presented in a state of Co2+. Meanwhile, the Co2+ species in the acid-modified Co-Al catalysts can be partially reduced to Co0. To identify the chemical valence of promoters on the acid-modified Co-Al catalysts, Figure S11 shows the B 1s, Ce 3d, W 4f, Zr 3d and Mo 3d XPS profiles of the reduced modified Co-Al catalysts. It was found that the B1s peak centered at 192.3 eV was associated with the presence of B3+ state.30 The peaks of Ce 3d5/2 and Ce 3d3/2 for the reduced Ce/Co-Al catalyst suggested that the cerium species were primarily in the state of Ce4+.15 The two peaks at about 35.1 and 37.2 eV for the reduced HSiW/Co-Al and HPW/Co-Al catalysts were respectively assigned to the W 4f7/2 and W 4f5/2 peaks of W6+.13 The binding energies of Mo 3d (232.4 and 235.5 eV respectively corresponding to Mo 3d5/2 and Mo 3d3/2) and Zr 3d (182.3 and 184.6 eV respectively corresponding to Zr 3d5/2 and Zr 3d3/2) were in concordance with the characteristic values of MoO3 and ZrO2, respectively.31,32

Glycerol Hydrogenolysis Study Catalytic Activity Test Table S3 gives the activity results for the experiment conducted on acid-modified Co-Al catalysts at 230 ℃ of reaction temperature and 3.5 MPa of hydrogen pressure in using ethanol as a solvent. As illustrated, the conversion of glycerol and selectivity of 1,2-PDO respectively were 11



70.2% and 60.5% when employing Co-Al as a catalyst. Meanwhile, there were still large numbers of byproducts such as glyceryl ethers and ethylene glycol in the liquid phase. When different promoters were added to Co-Al catalyst, the conversion of glycerol notably increased, but the selectivity of 1,2-PDO slightly decreased. High concentrations of glyceryl ethers were detected (see Table S4). This catalytic activity results indicated that the addition of the acid modifiers raised the etherification activity of glycerol with ethanol. It is well documented that the etherification activity of glycerol with ethanol can be improved in the presence of appropriate acid catalysts.33-35 In this study, the introduction of promoters into Co-Al catalyst significantly enhanced the acidities on the catalyst surface, as confirmed by NH3-TPD, which might have led to the increase of etherification activity. To minimize the effect of the glycerol etherification, the catalytic activity tests were also carried out at 230 ℃ of reaction temperature, 3.5 MPa of hydrogen pressure and 10 wt.% glycerol aqueous solution with 9.7 mL·h-1 liquid flow rate. The results are tabulated in Table 1. Furthermore, in order to identify the active sites for the production of propanediols from glycerol, Table 1 shows the activity results of glycerol hydrogenolysis on unreduced Co-Al and HSiW/Co-Al catalysts in using water as a solvent. It can be observed from Table 1 that the catalytic activities of unreduced Co-Al and HSiW/Co-Al catalysts were very low. In contrast, the catalysts activity after reduction notably increased, suggesting that the reduced cobalt species were effective for glycerol hydrogenolysis.21 On the other hand, it was found that no glyceryl ethers existed in glycerol hydrogenolysis conducted on acid-modified Co-Al catalysts in an aqueous solution. For Co-Al catalyst, the conversion of glycerol and selectivity of 1,2-PDO respectively were 48.6% and 77.2%. When the promoters were introduced into Co-Al catalyst, glycerol conversion was enhanced to some extent, but the selectivity to ethylene glycol slightly decreased. This could be attributed to the excellent properties in the acid-modified Co-Al catalysts, such as large amounts of acid sites and more highly dispersed Co species, as verified by NH3-TPD and H2 chemisorption respectively. There are two cases concerning the selectivity of 1,2-PDO for glycerol hydrogenolysis conducted on acid-modified Co-Al catalysts. The modification of Co-Al with B, Ce or Zr species raised the selectivity of 1,2-PDO. In contrast, relatively lower concentration of 1,2-PDO was achieved on heteropolyacids-modified Co-Al catalysts. Nevertheless, addition of the heteropolyacids raised the selectivity of 1,3-PDO, which was barely detected for glycerol 12


Page 12 of 30

Page 13 of 30 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


hydrogenolysis conducted on Co-Al catalysts modified with B, Ce or Zr species. Among the employed catalysts, the HSiW/Co-Al catalyst exhibited the highest 1,3-PDO yield, attaining 76.3% of glycerol conversion with 18.3% of 1,3-PDO selectivity. Documented evidence indicates that the production of 1,2- and 1,3-PDO from glycerol catalyzed by solid acid catalysts involves the dehydration of glycerol to obtain intermediates and their hydrogenation processes.36,37 According to the related literature, the type of acid sites on the catalyst surface has much influence on the distribution and yield of hydrogenolysis product. The 3-hydroxypropionaldehyde, an intermediate of glycerol hydrogenolysis, can be generated by the coordination of Brønsted acid sites on the catalyst surface to the secondary hydroxyl group of glycerol and further hydrogenation obtains 1,3-PDO, whereas Lewis acid sites on the catalyst surface preferentially produces 1,2-PDO by acetol hydrogenation pathway.38,39 To identify the nature of acid sites on the acid-modified Co-Al catalysts, in situ Py-IR spectra measurements were carried out. As displayed in Figure S12, the bands centered at about 1440 and 1540 cm-1 were considered to be pyridine ions formed by interaction with Lewis acid sites and Brønsted acid sites on the catalytic surface, respectively.39 As can be seen clearly in Figure S12, almost no Brønsted acid sites (expressed as B) existed on the Co-Al catalysts modified with B, Ce or Zr species, though these catalysts showed the high intensity band of Lewis acid sites (expressed as L) at ca. 1440 cm-1. In contrast, an obvious characteristic band corresponding to Brønsted acid sites at ca. 1540 cm-1 was observed on the Co-Al catalysts modified with HSiW and HPW, suggesting the presence of some Brønsted acid sites, which may have been derived from well-dispersed W species on the catalysts surface.13 In this study, the Co-Al catalysts modified with HSiW and HPW exhibited higher selectivity to 1,3-PDO, most probably be attributed to the existence of Brønsted acid sites on the catalysts surface. This is in concordance with the literature report.38,39 Because of its higher 1,3-PDO yield, the HSiW/Co-Al catalyst was selected for further investigation.

Influence of Solvent At present, different alcohols, e.g., methanol or ethanol, are often used as the solvents for the hydrogenolysis of glycerol except water. In general, hydrogen can dissolve more in alcohols than in water, which favors the increased glycerol conversion.40 On the other hand, H2 can be generated by the dehydrogenation of alcohols under suitable conditions.41 Therefore, the catalytic hydrogen 13



Page 14 of 30

transformation from the hydrogen donors such as methanol and 2-propanol to glycerol was also suitable for the conversion of glycerol.42 Moreover, several researchers suggested that the use of some organic reagents like sulfolane as solvents was helpful for the generation of 1,3-PDO from glycerol hydrogenolysis.43 By way of comparison, methanol and sulfolane were used to determine the influence of solvent on glycerol hydrogenolysis over HSiW/Co-Al catalyst. It can be seen from Figure 1 that the use of alcohols, i.e., methanol or ethanol, as solvents can obtain very high glycerol conversion (100%), which may be attributed to the presence of high concentration of hydrogen in the alcoholic solutions.44 However, there were high amounts of byproducts such as glyceryl ethers and the selectivity of 1,3-PDO was very low (< 2%) in the case of alcohols as solvents. In contrast, a certain amount of 1,3-PDO was achieved when water or sulfolane was used as solvents, though the glycerol conversions were relatively low, that were 76.3% and 82.4%, respectively. Among the solvents used, water was the best solvent for the conversion of glycerol into 1,3-PDO on HSiW/Co-Al catalyst in terms of catalytic activity, which was likely attributed to the higher polarity and proton transfer ability of water.45

Influence of Reaction Temperature As illustrated in Figure 2, the experiments were conducted at different reaction temperatures, i.e., 200, 230, 250 and 270 ℃ to study the influence of reaction temperature on glycerol hydrogenolysis over HSiW/Co-Al catalyst. Numerous studies suggested that the increasing of reaction temperature could promote the conversion of glycerol.46 As expected, glycerol conversion significantly enhanced from 43.5% to 91.6% when the reaction temperature was raised from 200 to 270 ℃. Nevertheless, it was found that the enhancement of reaction temperature was disadvantageous to the generation of 1,3-PDO and the maximal 1,3-PDO selectivity of 23.7% was attained for reaction carried out at 200 ℃ . After investigating the influence of reaction temperature on the selectivity and yield of hydrogenolysis product, Gong et al.39 claimed that increasing reaction temperature was more helpful for the activation of primary hydroxyl group of glycerol and tended to produce 1,2-PDO. Consistent with their reports, the selectivity of 1,2-PDO notably improved from 52.4% to 71.7% when the reaction temperature was enhanced from 200 to 250 ℃. However, further increase in reaction temperature resulted in a decrease in 1,2-PDO selectivity. Concurrently, large amounts of byproduct such as ethylene glycol were formed at high 14


Page 15 of 30 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


reaction temperature.

Influence of Liquid Flow Rate Figure 3 displays the activity results for the experiment performed on HSiW/Co-Al catalyst in different liquid flow rates ranging from 9.7 to 46.7 mL·h-1 at a reaction temperature of 230 ℃ and a hydrogen pressure of 3.5 MPa. As illustrated, there was an obvious decrease in the conversion of glycerol when the feed rate of glycerol-water mixture was remarkably increased. The explanation for this could be because the residence time for glycerol on the catalyst surface was short, which led to limited contact between the hydrogen and glycerol. For this reason, the production of acetol from glycerol increased at the expense of 1,2-PDO with the enhancement of the feed rate of glycerol-water mixture, indicating that the equilibrium states of glycerol dehydration favored the formation of acetol, and the rate of glycerol dehydration to 3-hydroxypropionaldehyde decreased. Thus, the selectivity of 1,3-PDO was significantly reduced from 18.3% to 7.2% when the feed rate of glycerol-water mixture was improved from 9.7 to 46.7 mL·h-1.

Stability Test To deepen investigation on the catalyst activity, the stability of the HSiW/Co-Al catalyst was examined at a reaction temperature of 230 ℃ and a hydrogen pressure of 3.5 MPa with a feed rate of glycerol-water mixture of 9.7 mL·h-1. It can be seen clearly in Figure 4 that the HSiW/Co-Al catalyst possessed a stable catalytic activity. After 50 h of continuous running under the reaction conditions applied in the experiment, the conversion of glycerol and selectivity of 1,3-PDO were 75% and 15% respectively. One possible explanation for this could be that the Co particles were properly dispersed resulting from a firm bonding between Co and W species.

Proposed Reaction Pathway To elucidate the reaction pathway for glycerol hydrogenolysis in using water as a solvent, catalytic activity tests using 1,2-PDO, acetol, 1,3-PDO, ethylene glycol, and 1-propanol as reactants on HSiW/Co-Al catalyst were performed under the reaction condition similar to that of glycerol hydrogenolysis. As displayed in Table S5, the acetol conversion was 100% and 87% 1,2-PDO selectivity was obtained when acetol was used as a reactant, demonstrating that the 15



hydrogenolysis product 1,2-PDO was generated from the hydrogenation of acetol. Furthermore, it was found that the conversion of 1,2-PDO (79.5%) was higher than that of 1,3-PDO (53.2%). When 1,2-PDO was used as a reactant, the selectivities to 2-propanol and 1-propanol were 59.3% and 34.1%, respectively. But in the presence of 1,3-PDO as a reactant, 1-propanol was the main product, suggesting that 2-propanol was generated from the excess hydrogenolysis of 1,2-PDO, and that 1-propanol can be formed from the hydrogenolysis of 1,2-PDO or 1,3-PDO. The conversion of 1-propanol was only 15.8% and propanal can be generated when using 1-propanol as a reactant. Similarly, the conversion of ethylene glycol was also very low (10.1%) and ethanol was the main product. Interestingly, the selectivity to ethylene glycol was 4.2% in the hydrogenolysis of glycerol, while no ethylene glycol was found in the catalytic activity tests using 1,2-PDO, acetol, 1-propanol or 1,3-PDO as reactants, implying that ethylene glycol could be generated directly from the C–C bond breaking reaction of glycerol. Documented evidence suggests that the conversion of glycerol into propanediols catalyzed by a solid acid catalyst proceeds via a dehydration-hydrogenation reaction route.6,7 Based on this reaction mechanism, acetol can be formed by the removal of primary hydroxyl group of glycerol on acid sites of support and further hydrogenation produces 1,2-PDO on metal sites of catalyst (i.e., acetol hydrogenation pathway); whereas the removal of secondary hydroxyl group of glycerol will produce 3-hydroxypropionaldehyde, which is further hydrogenated to achieve 1,3-PDO (i.e., 3-hydroxypropionaldehyde hydrogenation pathway).41,42 From the above analysis, it is evident that the types of propanediols obtained from glycerol hydrogenolysis mainly rely on the selective elimination of primary or secondary hydroxyl group of glycerol. It is well documented that Lewis acid sites on the catalyst tend to elimination of primary hydroxyl group of glycerol to form acetol, while the secondary hydroxyl group of glycerol can be removed by Brønsted acid sites on the catalyst to produce 3-hydroxypropionaldehyde.43 Therefore, Lewis acid sites on the catalyst were inclined to the conversion of glycerol into 1,2-PDO, while Brønsted acid sites on the catalyst facilitated the generation of 1,3-PDO. As indicated in Scheme 1, the possible reaction pathway for glycerol hydrogenolysis conducted on HSiW/Co-Al catalyst using water as a solvent was presented according to related literature and the authors’ experimental results. As confirmed by in situ Py-IR spectra analysis, the HSiW/Co-Al catalyst possessed abundant Lewis acid sites and a certain amount of Brønsted acid sites on the 16


Page 16 of 30

Page 17 of 30 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


support surface. The primary hydroxyl group of glycerol was dehydrated by Lewis acid sites on HSiW/Co-Al catalyst to produce acetol, while Brønsted acid sites on HSiW/Co-Al catalyst promoted

the

elimination

of

secondary

hydroxyl

group

of

glycerol

to

form

3-hydroxypropionaldehyde. The intermediates of glycerol hydrogenolysis, i.e., acetol and 3-hydroxypropionaldehyde, can further react with hydrogen to generate 1,2-PDO and 1,3-PDO on Co active sites, respectively. However, excessive hydrogenolysis of 1,2-PDO will generate 2-propanol and 1-propanol. Also, 1-propanol was achieved from the hydrogenolysis of 1,3-PDO. Ethylene glycol was generated directly from the C–C bond breaking reaction of glycerol and released methanol on HSiW/Co-Al catalyst. Further hydrogenolysis of ethylene glycol produced ethanol. It was worthy to mention that 3-hydroxypropionaldehyde was not detected in the experiments. This could be due to its high activity, and if so, is in agreement with evidence in literature reports.36,37

CONCLUSIONS In this study, it has been proven that the modification of Co-Al with B, Ce, Zr, and heteropolyacids (HSiW, HPW, HPMo) increased the acid strength and Co dispersion on the catalytic surface, which facilitated the hydrogenolysis of glycerol. When water was used as a solvent for glycerol hydrogenolysis, the modification of Co-Al with B, Ce or Zr species increased the selectivity to 1,2-PDO. In contrast, relatively low selectivity of 1,2-PDO was obtained on heteropolyacids-modified Co-Al catalysts. However, the introduction of heteropolyacids increased the selectivity of 1,3-PDO, which could be attributed to the existence of Brønsted acid sites on the modified Co-Al catalysts. The HSiW/Co-Al catalyst (in terms of both 1,2- and 1,3-PDO selectivity) was proven to be highly effective for glycerol hydrogenolysis and showed a stable catalytic activity. The production of 1,2- and 1,3-PDO from glycerol through the dehydration-hydrogenation route was influenced by the nature of acid sites on the catalyst. Lewis acid sites on the catalytic surface were more suited to the conversion of glycerol into 1,2-PDO, while Brønsted acid sites on the catalytic surface facilitated the generation of 1,3-PDO. Further investigations on the influence of reaction variables on glycerol hydrogenolysis indicated that the 1,3-PDO selectivity was favorable when water was used as a solvent and when there was decrease in reaction temperature and liquid flow rate. 17



Page 18 of 30

ASSOCIATED CONTENT The schematic diagram of experimental apparatus, catalyst characterization results such as BET, SEM, TEM, EDS, XRD, H2-TPR, NH3-TPD, XPS, Py-IR and other catalytic activity results are provided in the Supplementary Information.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] (F. Cai) *Email: [email protected] (J. Zhang) *Email: [email protected] (G. Xiao)

ACKNOWLEDGEMENT The authors are very grateful for the financial support from the National Natural Science Foundation of China (No. 21276050, No. 21406034 and No. 21676054). The authors also thank Dr. Jessica Juweriah Ibrahim for helpful discussions.

REFERENCES (1) Salvi, B. L.; Panwar, N. L. Biodiesel resources and production technologies – A review. Renew. Sust. Energ. Rev. 2012, 16, 3680–3689, DOI: 10.1016/j.rser.2012.03.050. (2) Zhou, C.-H.; Beltramini, J. N.; Fan, Y.-X.; Lu, G. Q. Chemoselective catalytic conversion of glycerol as a biorenewable source to valuable commodity chemicals. Chem. Soc. Rev. 2008, 37, 527–549, DOI: 10.1039/b707343g. (3) Nakagawa, Y.; Tomishige, K. Heterogeneous catalysis of the glycerol hydrogenolysis. Catal. Sci. Technol. 2011, 1, 179–190, DOI: 10.1039/c0cy00054j. (4) ten Dam, J.; Hanefeld, U. Renewable chemicals: Dehydroxylation of glycerol and polyols. ChemSusChem 2011, 4, 1017–1034, DOI: 10.1002/cssc.201100162. (5) Martin, A.; Richter, M. Oligomerization of glycerol - a critical review. Eur. J. Lipid Sci. Tech. 2011, 113, 100–117, DOI: 10.1002/ejlt.201000386. (6) Gandarias, I.; Arias, P. L.; Requies, J.; Güemez, M. B.; Fierro, J. L. G. Hydrogenolysis of glycerol to propanediols over a Pt/ASA catalyst: The role of acid and metal sites on product 18


Page 19 of 30 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


selectivity and the reaction mechanism. Appl. Catal. B-Environ. 2010, 97, 248–256, DOI: 10.1016/j.apcatb.2010.04.008. (7) Miyazawa, T.; Kusunoki, Y.; Kunimori, K.; Tomishige, K. Glycerol conversion in the aqueous solution under hydrogen over Ru/C + an ion-exchange resin and its reaction mechanism. J. Catal. 2006, 240, 213–221, DOI: 10.1016/j.jcat.2006.03.023. (8) Bienholz, A.; Hofmann, H.; Claus, P. Selective hydrogenolysis of glycerol over copper catalysts both in liquid and vapour phase: Correlation between the copper surface area and the catalyst's activity. Appl. Catal. A-Gen. 2011, 391, 153–157, DOI: 10.1016/j.apcata.2010.08.047. (9) Vasiliadou, E. S.; Heracleous, E.; Vasalos, I. A.; Lemonidou, A. A. Ru-based catalysts for glycerol hydrogenolysis—effect of support and metal precursor. Appl. Catal. B-Environ. 2009, 92, 90–99, DOI: 10.1016/j.apcatb.2009.07.018. (10) Nakagawa, Y.; Ning, X.; Amada, Y.; Tomishige, K. Solid acid co-catalyst for the hydrogenolysis of glycerol to 1,3-propanediol over Ir-ReOx/SiO2. Appl. Catal. A-Gen. 2012, 433-434, 128–134, DOI: 10.1016/j.apcata.2012.05.009. (11) Li, Y.; Ma, L.; Liu, H.; He, D. Influence of HZSM5 on the activity of Ru catalysts and product selectivity during the hydrogenolysis of glycerol. Appl. Catal. A-Gen. 2014, 469, 45–51, DOI: 10.1016/j.apcata.2013.09.028. (12) Zhu, S.; Qiu, Y.; Zhu, Y.; Hao, S.; Zheng, H.; Li, Y. Hydrogenolysis of glycerol to 1,3-propanediol over bifunctional catalysts containing Pt and heteropolyacids. Catal. Today 2013, 212, 120–126, DOI: 10.1016/j.cattod.2012.09.011. (13) Zhu, S.; Gao, X.; Zhu, Y.; Cui, J.; Zheng, H.; Li, Y. SiO2 promoted Pt/WOx/ZrO2 catalysts for the selective hydrogenolysis of glycerol to 1,3-propanediol. Appl. Catal. B-Environ. 2014, 158-159, 391–399, DOI: 10.1016/j.apcatb.2014.04.049. (14) Zhu, S.; Gao, X.; Zhu, Y.; Zhu, Y.; Zheng, H.; Li, Y. Promoting effect of boron oxide on Cu/SiO2 catalyst for glycerol hydrogenolysis to 1,2-propanediol. J. Catal. 2013, 303, 70–79, DOI: 10.1016/j.jcat.2013.03.018. (15) Jiménez-Morales, I.; Vila, F.; Mariscal, R.; Jiménez-López, A. Hydrogenolysis of glycerol to obtain 1,2-propanediol on Ce-promoted Ni/SBA-15 catalysts. Appl. Catal. B-Environ. 2012, 117-118, 253–259, DOI: 10.1016/j.apcatb.2012.01.027. (16) Guo, X.; Li, Y.; Shi, R.; Liu, Q.; Zhan, E.; Shen, W. Co/MgO catalysts for hydrogenolysis of 19



glycerol

to

1,2-propanediol.

Appl.

Catal.

A-Gen.

2009,

Page 20 of 30

371,

108–113,

DOI:

10.1016/j.apcata.2009.09.037. (17) Rekha, V.; Sumana, C.; Douglas, S. P.; Lingaiah, N. Understanding the role of Co in Co–ZnO mixed oxide catalysts for the selective hydrogenolysis of glycerol. Appl. Catal. A-Gen. 2015, 491, 155–162, DOI: 10.1016/j.apcata.2014.10.042. (18) Jacobs, G.; Das, T. K.; Zhang, Y.; Li, J.; Racoillet, G.; Davis, B. H. Fischer–Tropsch synthesis: support, loading, and promoter effects on the reducibility of cobalt catalysts. Appl. Catal. A-Gen. 2002, 233, 263-281, DOI: 10.1016/S0926-860X(02)00195-3. (19) Opris, C.; Cojocaru, B.; Gheorghe, N.; Tudorache, M.; Coman, S. M.; Parvulescu, V. I.; Duraki, B.; Krumeich, F.; van Bokhoven, J. A. Lignin fragmentation over magnetically recyclable composite

Co@Nb2O5@Fe3O4

catalysts.

J.

Catal.

2016,

339,

209–227,

DOI:

10.1016/j.jcat.2016.04.002. (20) Mallesham, B.; Sudarsanam, P.; Reddy, B. V. S.; Reddy, B. M. Development of cerium promoted copper–magnesium catalysts for biomass valorization: Selective hydrogenolysis of bioglycerol. Appl. Catal. B-Environ. 2016, 181, 47–57, DOI: 10.1016/j.apcatb.2015.07.037. (21) Guo, X.; Li, Y.; Song, W.; Shen, W. Glycerol hydrogenolysis over Co catalysts derived from a layered

double

hydroxide

precursor.

Catal.

Lett.

2011,

141,

1458–1463,

DOI:

10.1007/s10562-011-0642-y. (22) Tang, C.-W.; Wang, C.-B.; Chien, S.-H. Characterization of cobalt oxides studied by FT-IR, Raman, TPR and TG-MS. Thermochim. Acta 2008, 473, 68–73, DOI: 10.1016/j.tca.2008.04.015. (23) Zhao, S.; Yue, H.; Zhao, Y.; Wang, B.; Geng, Y.; Lv, J.; Wang, S.; Gong, J.; Ma, X. Chemoselective synthesis of ethanol via hydrogenation of dimethyl oxalate on Cu/SiO2: Enhanced stability with boron dopant. J. Catal. 2013, 297, 142–150, DOI: 10.1016/j.jcat.2012.10.004. (24) Santos, R. C. R.; Braga, D. M. V.; Pinheiro, A. N.; Leite, E. R.; Freire, V. N.; Longhinotti, E.; Valentini, A. Role of Cu, Ni and Co metals in the acidic and redox properties of Mo catalysts supported on Al2O3 spheres for glycerol conversion. Catal. Sci. Technol. 2016, 6, 4986–5002, DOI: 10.1039/c6cy00096g. (25) Mota, C. J. A.; Goncalves, V. L. C.; Mellizo, J. E.; Rocco, A. M.; Fadigas, J. C.; Gambetta, R. Green propene through the selective hydrogenolysis of glycerol oversupported iron-molybdenum catalyst: The original history. J. Mol. Catal. A-Chem. 2016, 422, 158–164, DOI: 20


Page 21 of 30 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


10.1016/j.molcata.2015.11.014. (26) Shimura, K.; Miyazawa, T.; Hanaoka, T.; Hirata, S. Preparation of Co/Al2O3 catalyst for Fischer–Tropsch synthesis: Combination of impregnation method and homogeneous precipitation method. Appl. Catal. A-Gen. 2014, 475, 1–9, DOI: 10.1016/j.apcata.2014.01.012. (27) Feng, Y.; Yin, H.; Wang, A.; Shen, L.; Yu, L.; Jiang, T. Gas phase hydrogenolysis of glycerol catalyzed by Cu/ZnO/MOx (MOx=Al2O3, TiO2, and ZrO2) catalysts. Chem. Eng. J. 2011, 168, 403–412, DOI: 10.1016/j.cej.2011.01.049. (28) Chu, X.; Liu, J.; Sun, B.; Dai, R.; Pei, Y.; Qiao, M.; Fan, K. Aqueous-phase reforming of ethylene glycol on Co/ZnO catalysts prepared by the coprecipitation method. J. Mol. Catal. A-Chem. 2011, 335, 129-135, DOI: 10.1016/j.molcata.2010.11.024. (29) Kungurova, O. A.; Khassin, A. A.; Cherepanova, S. V.; Saraev, A. A.; Kaichev, V. V.; Shtertser, N. V.; Chermashentseva, G. K.; Gerasimov, E. Y.; Paukshtis, Е. A.; Vodyankina, О. V.; Minyukova, T. P.; Abou-Jaoudé, G. δ-Alumina supported cobalt catalysts promoted by ruthenium for FischerTropsch synthesis. Appl. Catal. A-Gen. 2017, 539, 48–58, DOI: 10.1016/j.apcata.2017.04.003. (30) Liaw, B. J.; Chen, Y. Z. Liquid-phase synthesis of methanol from CO2/H2 over ultrafine CuB catalysts. Appl. Catal. A-Gen. 2001, 206, 245–256, DOI: 10.1016/s0926-860x(00)00601-3. (31) Sun, Z.; Yang, C.; Liu, G.; Lu, H.; Zhang, R.; Wang, L.; Wang, H. Largely enhanced electrochemical performance in MoO3-x nanobelts formed by a “sauna reaction”: Importance of oxygen vacancies. Electrochim. Acta 2017, 239, 16–24, DOI: 10.1016/j.electacta.2017.04.052. (32) Zhu, Y.; Kong, X.; Zhu, S.; Dong, F.; Zheng, H.; Zhu, Y.; Li, Y. W. Construction of Cu/ZrO2/Al2O3 composites for ethanol synthesis: Synergies of ternary sites for cascade reaction. Appl. Catal. B-Environ. 2015, 166, 551–559, DOI: 10.1016/j.apcatb.2014.12.015. (33) Pariente, S.; Tanchoux, N.; Fajula, F. Etherification of glycerol with ethanol over solid acid catalysts. Green Chem. 2009, 11, 1256–1261, DOI: 10.1039/b905405g. (34) Melero, J. A.; Vicente, G.; Paniagua, M.; Morales, G.; Muñoz, P. Etherification of biodiesel-derived glycerol with ethanol for fuel formulation over sulfonic modified catalysts. Bioresource Technol. 2012, 103, 142–151, DOI: 10.1016/j.biortech.2011.09.105. (35) Yuan, Z.; Xia, S.; Chen, P.; Hou, Z.; Zheng, X. Etherification of biodiesel-based glycerol with bioethanol over tungstophosphoric acid to synthesize glyceryl ethers. Energ. Fuel. 2011, 25, 3186–3191, DOI: 10.1021/ef200366q. 21



(36) Priya, S. S.; Bhanuchander, P.; Kumar, V. P.; Dumbre, D. K.; Periasamy, S. R.; Bhargava, S. K.; Lakshmi Kantam, M.; Chary, K. V. R. Platinum supported on H-mordenite: A highly efficient catalyst for selective hydrogenolysis of glycerol to 1,3-propanediol. ACS Sustainable Chem. Eng. 2016, 4, 1212–1222, DOI: 10.1021/acssuschemeng.5b01272. (37) Mai, C. T. Q.; Ng, F. T. T. Effect of metals on the hydrogenolysis of glycerol to higher value sustainable and green chemicals using a supported HSiW catalyst. Org. Process Res. Dev. 2016, 20, 1774–1780, DOI: 10.1021/acs.oprd.6b00245. (38) Zhu, S.; Gao, X.; Zhu, Y.; Li, Y. Promoting effect of WOx on selective hydrogenolysis of glycerol to 1,3-propanediol over bifunctional Pt–WOx/Al2O3 catalysts. J. Mol. Catal. A-Chem. 2015, 398, 391–398, DOI: 10.1016/j.molcata.2014.12.021. (39) Gong, L.; Lu, Y.; Ding, Y.; Lin, R.; Li, J.; Dong, W.; Wang, T.; Chen, W. Selective hydrogenolysis of glycerol to 1,3-propanediol over a Pt/WO3/TiO2/SiO2 catalyst in aqueous media. Appl. Catal. A-Gen. 2010, 390, 119–126, DOI: 10.1016/j.apcata.2010.10.002. (40) Vasiliadou, E. S.; Lemonidou, A. A. Kinetic study of liquid-phase glycerol hydrogenolysis over Cu/SiO2 catalyst. Chem. Eng. J. 2013, 231, 103–112, DOI: 10.1016/j.cej.2013.06.096. (41) Gandarias, I.; Arias, P. L.; Fernández, S. G.; Requies, J.; El Doukkali, M.; Güemez, M. B. Hydrogenolysis through catalytic transfer hydrogenation: Glycerol conversion to 1,2-propanediol. Catal. Today 2012, 195, 22–31, DOI: 10.1016/j.cattod.2012.03.067. (42) Gandarias, I.; Arias, P. L.; Requies, J.; El Doukkali, M.; Güemez, M. B. Liquid-phase glycerol hydrogenolysis to 1,2-propanediol under nitrogen pressure using 2-propanol as hydrogen source. J. Catal. 2011, 282, 237–247, DOI: 10.1016/j.jcat.2011.06.020. (43) Chaminand, J.; Djakovitch, L. a.; Gallezot, P.; Marion, P.; Pinel, C.; Rosier, C. C. Glycerol hydrogenolysis

on

heterogeneous

catalysts.

Green

Chem.

2004, 6, 359–361, DOI:

10.1039/b407378a. (44) Baranenko, V. I.; Kirov, V. S. Solubility of hydrogen in water in a broad temperature and pressure range. At. Energy 1989, 66, 30–34, DOI: 10.1007/bf01121069. (45) Wang, C.; Jiang, H.; Chen, C.; Chen, R.; Xing, W. Solvent effect on hydrogenolysis of glycerol to 1,2-propanediol over Cu–ZnO catalyst. Chem. Eng. J. 2015, 264, 344–350, DOI: 10.1016/j.cej.2014.11.113. (46) Balaraju, M.; Rekha, V.; Prasad, P. S. S.; Devi, B. L. A. P.; Prasad, R. B. N.; Lingaiah, N. 22


Page 22 of 30

Page 23 of 30 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


Influence of solid acids as co-catalysts on glycerol hydrogenolysis to propylene glycol over Ru/C catalysts. Appl. Catal. A-Gen. 2009, 354, 82–87, DOI: 10.1016/j.apcata.2008.11.010.

23



Page 24 of 30

Table 1 The activity results for the experiment performed on acid-modified Co-Al catalysts when using water as a solvent Conversion

Selectivity (%)

(%)

1,2-PDO

1,3-PDO

1-Propanol

Ethylene glycol

Others

Co-Al

48.6

77.2

0.6

0.4

11.9

9.9

Co-Ala

2.0

68.9

0.2

0.4

15.7

14.8

B/Co-Al

61.9

81.2

1.1

0.9

6.4

10.4

Ce/Co-Al

68.3

79.5

1.3

0.8

7.6

10.8

HSiW/Co-Al

76.3

60.2

18.3

9.5

4.2

7.8

HSiW/Co-Ala

2.8

64.6

3.7

2.1

10.0

19.6

HPW/Co-Al

65.8

65.1

15.1

7.8

4.8

7.2

HPMo/Co-Al

57.4

74.3

3.4

2.9

6.9

12.5

Zr/Co-Al

72.5

85.0

1.7

1.0

5.1

7.2

Catalyst

Process parameters: solvent, water; glycerol concentration, 10 wt.%; the feed rate of glycerol-water mixture, 9.7 mL·h-1; the flow velocity of pure hydrogen, 100 mL·min-1; the mass of catalyst, 4.0 g; the temperature of preheater, 230 ℃; the temperature of reactor, 230 ℃; the pressure of reactor, 3.5 MPa; data collection after 180 min running. Others include 2-propanol, acetol, methanol, etc. a Without the reduction process.

24


Page 25 of 30 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


Figure 1. The activity results for the experiment performed on HSiW/Co-Al catalyst in the presence of different solvents. Process parameters: glycerol concentration, 10 wt.%; the feed rate of liquid mixture, 9.7 mL·h-1; the flow velocity of pure hydrogen, 100 mL·min-1; the mass of catalyst, 4.0 g; the temperature of preheater, 230 ℃; the temperature of reactor, 230 ℃; the pressure of reactor, 3.5 MPa; data collection after 180 min running.

25



Page 26 of 30

Figure 2. The activity results for the experiment performed on HSiW/Co-Al catalyst in different reaction temperatures. Process parameters: solvent, water; glycerol concentration, 10 wt.%; the feed rate of glycerol-water mixture, 9.7 mL·h-1; the flow velocity of pure hydrogen, 100 mL·min-1; the mass of catalyst, 4.0 g; the pressure of reactor, 3.5 MPa; data collection after 180 min running.

26


Page 27 of 30 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


Figure 3. The activity results for the experiment performed on HSiW/Co-Al catalyst in different liquid flow rates. Process parameters: solvent, water; glycerol concentration, 10 wt.%; the flow velocity of pure hydrogen, 100 mL·min-1; the mass of catalyst, 4.0 g; the temperature of preheater, 230 ℃; the temperature of reactor, 230 ℃; the pressure of reactor, 3.5 MPa; data collection after 180 min running.

27



Page 28 of 30

Figure 4. The stability study of HSiW/Co-Al catalyst. Process parameters: solvent, water; glycerol concentration, 10 wt.%; the feed rate of glycerol-water mixture, 9.7 mL·h-1; the flow velocity of pure hydrogen, 100 mL·min-1; the mass of catalyst, 4.0 g; the temperature of preheater, 230 ℃; the temperature of reactor, 230 ℃; the pressure of reactor, 3.5 MPa.

28


Page 29 of 30 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


Scheme 1. Proposed reaction pathway for glycerol hydrogenolysis performed on HSiW/Co-Al catalyst in using water as a solvent.

29



Page 30 of 30

Selective hydrogenolysis of glycerol over acid-modified Co-Al catalysts in a fixed-bed flow reactor Fufeng Cai, Xianghai Song, Yuanfeng Wu, Jun Zhang, Guomin Xiao

For Table of Contents Use Only

The acid-modified Co-Al catalysts exhibited superior catalytic performance for glycerol hydrogenolysis, which was attributed to the increased acid strength and high Co dispersion.

30


Selective Hydrogenolysis of Glycerol over Acid-Modified CoâAl

Recommend Documents

Selective Hydrogenolysis of Glycerol over Acid-Modified CoâAl