Top Catal (2009) 52:834–844 DOI 10.1007/s11244-009-9231-3
ORIGINAL PAPER
Hydrogenolysis of Glycerol to Propanediols Over Highly Active Ru–Re Bimetallic Catalysts Lan Ma Æ Dehua He
Published online: 28 April 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Several supported Ru–Re bimetallic catalysts (Ru–Re/SiO2, Ru–Re/ZrO2, Ru–Re/TiO2, Ru–Re/H-b, Ru–Re/H–ZSM5) and Ru monometallic catalysts (Ru/SiO2, Ru/ZrO2, Ru/TiO2, Ru/H-b, Ru/H–ZSM5) were prepared and their catalytic performances were evaluated in the hydrogenolysis of glycerol to propanediols (1,2-propanediol and 1,3-propanediol) with a batch type reactor (autoclave) under the reaction conditions of 160 °C, 8.0 MPa and 8 h. Compared with Ru monometallic catalysts, the Ru–Re bimetallic catalysts showed much higher activity in the hydrogenolysis of glycerol, and Re exhibited obvious promoting effect on the performance of the catalysts. The supported Ru monometallic catalysts and Ru–Re bimetallic catalysts were characterized by N2 adsorption/desorption, XRD, TEM-EDX, H2-TPR and CO chemisorption for obtaining some physicochemical properties of the catalysts, such as specific surface areas, crystal phases, morphologies/microstructure, reduction behaviors and dispersion of Ru metal. The results of XRD and CO chemisorption indicate that the addition of Re component could improve the dispersion of Ru species on supports. The measurements of H2-TPR revealed that the coexistence of Re and Ru components on supports changed the respective reduction behavior of Re or Ru alone on the supports, indicating the existence of synergistic effect between Ru and Re species on the bimetallic catalysts. The hydrogenolysis of some products (such as 1,2-propanediol, L. Ma D. He (&) Innovative Catalysis Program, Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China e-mail:
[email protected] L. Ma Institute of Chemical Defence, Beijing 102205, China
123
1,3-propanediol, 1-propanol and 2-propanol) were also examined over Ru and Ru–Re catalysts for evaluating influence of Re–Re on the reaction routes during glycerol hydrogenolysis. The results showed that over Ru–Re catalysts, glycerol was favorable to be converted to 1,2-propanediol, but not favorable to ethylene glycol, while 1,2-propanediol and 1,3-propanediol were favorable to be converted to 1-propanol. The influence of glycerol concentration in its aqueous solution on the catalytic performance was also evaluated over Ru and Ru–Re catalysts. Keywords Glycerol Hydrogenolysis Ru–Re bimetallic catalyst Re promoting effect
1 Introduction Glycerol is a by-product of bio-diesel production, and the development of the down-stream products of glycerol has recently attracted much attention because it is a low-cost renewable feedstock [1, 2]. There are several routes for converting glycerol to other chemicals, such as the hydrogenolysis of glycerol to propanediols [3, 4], the oxidation of glycerol to glyceric acid [5], the dehydration of glycerol to acrolein [6] and so on. Propanediols, both 1,2-propanediol and 1,3-propanediol, are high added-value chemicals. 1,2-propanediol is a non-toxic chemical material and it can be used as a humectant, antifreeze, brake fluid and humectant, or as a component of polyesters and alkyd resins [7, 8]. 1,3-propanediol is also an important compound and it is usually used for the manufacture of plasticizer, abluent, corrosion remover, paint and copolymers, especially for the production of polyester (polytrimethylene terephthalate) with terephthalic acid [7, 8]. However, both 1,2-propanediol and 1,3-propanediol are in industrially produced via
Top Catal (2009) 52:834–844
petroleum routes and the production of them from renewable resources is highly desired [7]. Several researches have recently focused on the conversion of glycerol to propanediols by catalytic hydrogenolysis method, and some heterogeneous catalysts, such as Ru-based catalysts [4, 9–14], Cu-based catalysts [3, 12, 15], Raney-nickel catalysts [12, 16] and other noble metal (Rh, Pt, Au et al.) catalysts [17–20], have been employed. Miyazawa et al. have made some progress on the research of glycerol hydrogenolysis with Ru catalysts [4, 9–11]. They found that the combination of 5%Ru/C and Amberlyst-15 resin was effective for the glycerol hydrogenolysis to 1,2-propanediol (12.9% glycerol conversion, 55.4% 1,2-PDO selectivity and 4.9% 1,3-PD selectivity) under the conditions of 393 K, 8 MPa and 20 h, compared with the combinations of the other noble metal catalysts (Rh/C, Pt/C and Pd/C) and acid promoters (Amberlyst-15, H2SO4 and HCl) [4]. When treating Ru(NO)(NO3)3 (Ru precursor) on active carbon support with Ar flow at 573 K, the activity of the catalytic system of 5%Ru/C ? Amberlyst-15 was enhanced (21.3% conversion and 76.7% 1,2-PDO selectivity) [10]. The different supports (active carbon, SiO2, Al2O3, TiO2 and NaY zeolite) of Ru catalysts also had great influence on the conversion of glycerol and the selectivity of 1,2-PDO [13]. Some base additives (LiOH, NaOH, Li2CO3, Na2CO3 and CaO) could increase the activity of Ru/TiO2, Ru/C and Pt/C catalysts [14, 20]. Chaminand et al. compared the catalytic performance of CuO/ZnO,Pd/C and Rh/C in the hydrogenolysis of glycerol, and found that CuO/ZnO catalyst showed high 1,2PDO selectivity (19% glycerol conversion and 100% selectivity to 1,2-PDO) [3]. On the other hand, Copperchromite also showed relatively high activity and selectivity to 1,2-PDO [12]. It was also reported that Pt/WO3/ ZrO2 catalyst could give 1,3-PDO in the yields up to 24% in glycerol hydrogenolysis [18]. On the other hand, PtRu/C and AuRu/C bimetallic catalysts were also examined in glycerol hydrogenolysis, but it seems that the activity and selectivity of AuRu/C or PtRu/C in the hydrogenolysis of glycerol was similar to the monometallic Ru/C [19]. Although efforts have been made so far and some progress has also been achieved in the hydrogenolysis of glycerol to propanediols, the glycerol conversion and propanediol selectivity are still not satisfying and the reaction mechanism is still unclear. Recently, bimetallic catalysts become more important in heterogeneous catalysis, because bimetallic catalysts can be superior to monometallic catalysts in the catalytic activity and selectivity for many reactions [21]. Similarly, in order to improve the catalytic activity and selectivity in the hydrogenolysis of glycerol, it is also desired to investigate bimetallic catalysts while on the development of monometallic catalysts. In our previous work, we found a remarkable promoting effect of Re2(CO)10 on the activity of
835
Ru/Al2O3, Ru/C and Ru/ZrO2 catalysts in the hydrogenolysis of glycerol to propanediols [22]. In our present work, we prepared some supported Ru–Re bimetallic catalysts and employed them in the hydrogenolysis of glycerol. The significant synergistic effect of Ru and Re on increasing the activity of the catalysts has been discovered. Some interesting results were also obtained.
2 Experimental 2.1 General Comments ZrO(NO3)2 (analytic pure) was purchased from Beijing Chemical Reagent Company and used as the starting material of ZrO2. SiO2 was obtained from Tianjin Chemical Institute and used as a support, which was calcined at 400 °C for 4 h before used. TiO2 (P-25) was purchased from Degussa Company and used as received. Na–ZSM5 and Na-b zeolites were obtained from Shanghai Xinnian Chemical Company and used for preparing H–ZSM5 and H-b supports by proton exchange. Commercial catalysts, 5%Ru/Al2O3 and 5%Ru/C, were purchased from Alfa Aesar Company. Ru3(CO)12 and Re2(CO)10 were purchased from Strem Company. The commercial catalysts were used as received. RuCl3 4H2O was purchased from Institute of ShenYang Youse Jinshu and used for preparing Ru/ZrO2, Ru/SiO2, Ru/H-b, Ru/H–ZSM5, Ru/TiO2 and Ru–Re bimetallic catalysts. HReO4 was purchased from Alfa Aesar Company and used for preparing Re/SiO2 and supported Ru–Re bimetallic catalysts. Glycerol (ultra pure), the reaction substrate, was purchased from Alfa Aesar Company and used as received. Other reagents were purchased from Beijing Chemical Reagent Company. 2.2 Catalyst Preparation ZrO2 was prepared by precipitation method as described in our previous paper [22, 23]. The support ZrO2 was calcined at 550 °C for 5 h in flowing nitrogen gas (20 mL/min). H–ZSM5 and H-b were prepared by treating Na–ZSM5 and Na-b zeolites with 5wt% NH3Cl aqueous solution at 90 °C for three time (proton exchange) and finally calcining at 550 °C for 3 h before using as supports. Supported monometallic Ru catalysts (Ru/ZrO2, Ru/ SiO2, Ru/TiO2, Ru/H-b and Ru/H–ZSM5) and bimetallic Ru–Re (Ru–Re/ZrO2, Ru–Re/SiO2, Ru–Re/TiO2, Ru–Re/ H-b and Ru–Re/H–ZSM5) were prepared by impregnation method. The powder of supports was impregnated with RuCl3 4H2O aqueous solution or the mixture aqueous solution of RuCl3 4H2O and HReO4. After impregnation and solvent removal by evaporation, the precursors were
123
836
dried at 110 °C for 12 h, and calcined at 350 °C in air for 4 h. The as-prepared catalysts were directly used in the hydrogenolysis of glycerol and they would undergo in situ reduction during the hydrogenolysis reaction. The theoretic loading of Ru and Re on the prepared catalysts was 4.54wt% based on the devoted amount of RuCl3 4H2O and HReO4, respectively. The actual loading of Ru and Re on the prepared catalysts was analyzed by Inductive Coupling Plasma-Atomic Emission Spectroscopy (ICP-AES). 5 wt%Re/SiO2 was also prepared by impregnation method as above-described procedure. The commercial catalysts, 5%Ru/Al2O3 and 5%Ru/C, were used as received. 2.3 Characterization of Catalysts The specific surface areas, cumulative pore volume and average pore diameter of the catalysts and supports were measured by N2 adsorption/desorption with the BET and BJH methods on a Micromeritics ASAP 2010C analyzer. Before measurement, the samples were degassed at 473 K for 2 h. The phase structures of the catalysts were determined by X-Ray Diffraction (XRD) with a Bruker D8 Advance X-Ray Powder Diffractometer with Cu Ka (k = 0.15406 nm). The particle size was calculated from Scherrer formula: d ¼ 0:89k=Bð2hÞ cos h: Here, k is the wavelength of X-ray, B(2h) (rad) is the width of XRD pattern line at half peak-height, h is Bragg angle between the incident and diffracted beams, and d (nm) is the crystal size of the powder sample. The X-ray photoelectron spectroscopy (XPS) measurements were performed on a PHI Quantera Scanning X-ray Microprobe of ULVAC-PHI Inc. The spectra were referenced with respect to C1s line at 284.8 eV. The morphologies and microstructure of the catalysts were characterized by highresolution transmission electron microscopy (HR-TEM, JEM-2010 of JEOL) equipped with an energy dispersive X-ray detector (EDX). The accelerating voltage was 120 kV. The samples were ultrasonically dispersed in ethanol and deposited on a holey carbon copper grid before measurement. Temperature-programmed reduction (TPR) measurements were carried out on a dynamic-flow gas sorption instrument (Quantachrome, CHEMBET 3000 TPR/TPD). The catalyst samples (about 100 mg) were treated in Ar at 623 K for 0.5 h before TPR was performed. All TPR measurements were carried out in a flow of 5% H2/Ar (20 mL/min) at a heating rate of 15 K/min. A cold trap (liquid nitrogen ? iso propanol) was placed before the TCD to remove water produced during TPR measurements. The dispersion of Ru metal on supports was measured by CO chemisorption method. CO chemisorption was operated on dynamic-flow gas sorption instrument (Quantachrome, CHEMBET 3000 TPR/TPD). Before CO chemisorption was performed, catalyst samples (about 200 mg) were treated in a quartz reactor in a flow of H2 (20 ml/min) at 400 °C for 2 h
123
Top Catal (2009) 52:834–844
and then purged in He flow, and the temperature of quartz reactor was decreased to 40 °C in 2 h. The CO chemisorption was performed by pulse injection of pure CO gas at 40 °C. The stoichiometry of CO to Ru was 1 for CO chemisorption [24]. The particle sizes of Ru were calculated from CO adsorption =am Þ (dVA: characterization based on the formula D ¼ 6 ðvmdVA ˚ 3) particle size; D: dispersion) [25]. The parameter mm (13.65 A 2 ˚ and am (6.35 A ) of metal Ru were put into the formula and the ˚ ) was obtained. final formula d = 12.9/D (A 2.4 Hydrogenolysis Reaction of Glycerol The hydrogenolysis of glycerol was carried out in a stainless steel autoclave of 100 mL with a magnetic stirrer. Detailed procedure was described in our previous paper [22]. The standard reaction conditions were 160 °C, 8 MPa hydrogen pressure and 8 h reaction time, using 10 mL 40 wt% glycerol aqueous solution and 0.15 g supported catalyst in every run. After the reaction, the liquid and the solid catalyst in the mixture were separated by centrifugation and filtration. The procedure of the hydrogenolysis using some products as reactants, such as 1,2-propanediol (shorted as 1,2-PDO), 1,3-propanediol (1,3-PDO), 1-propanol (1-PO) and 2-propanol (2-PO), is same as above-described, and the concentration of these reactants was 40 wt% aqueous solution. The products in liquid phase were analyzed qualitatively by GC-Mass (GCMS-QP2010, SHIMADZU Corporation) and analyzed quantitatively with a gas chromatography (Lunan-SP 6890, PEG2 M, 30 m 9 0.25 mm; FID detector). The products in gas phase was not quantitatively analyzed, but qualitatively checked with a GC (TDX-01, TCD). The conversion in present study is denoted as ‘‘conversion of glycerol to liquid products’’ (shorted as conversion of glycerol, hereafter). The selectivity is denoted as ‘‘selectivity in liquid products’’ (shorted as selectivity, hereafter). The conversion of glycerol and the selectivity of each liquid product in all runs in present study were calculated based on the following equations. Conversion of glycerol ð%Þ Sum of C mol of all liquid products ¼ 100: Added glycerol before reaction (C mol) Selectivity ð%Þ C mol of each liquid product ¼ 100: Sum of C mol of all liquid products 3 Results and Discussion 3.1 Characterization of Catalysts The texture structure properties (specific surface areas, cumulative pore volume and average pore diameter) of the
Top Catal (2009) 52:834–844
837
supports and catalysts are listed in Table 1. The supports SiO2, H-b, H–ZSM5 showed high specific surface areas (SBET), while the SBET of ZrO2 and TiO2 were considerable low. SiO2 had larger cumulative pore volume and average pore diameter than other supports (ZrO2, TiO2, H-b and H–ZSM5). The specific surface areas of these supports decreased when Ru or/and Re were supported on the supports, while the change of cumulative pore volume and average pore diameter were not obvious. The commercial catalyst Ru/C also showed very high specific surface areas. Although specific surface areas of the supports and catalysts were quite different, the catalytic activities of these catalysts were no direct relationship with the specific surface areas. For the investigation of crystal phases of Ru and Re on the supports prepared in this study, the as-prepared Ru/ SiO2, Re/SiO2 and Ru–Re/SiO2 catalysts were selected for XRD characterizations, because the XRD peaks of SiO2 support itself has less interference for observing the XRD peaks of Ru or/and Re species. The results are shown in Fig. 1. The as-prepared (calcined) Ru/SiO2 showed typical RuO2 diffraction peaks [JCPDS File 40-1290] (Fig. 1a), indicating that there were well-crystallized RuO2 [26] particles on SiO2 support. On the other hand, no diffraction peaks were detected on Re/SiO2 (Fig. 1b), and this implies that Re species might be well dispersed on SiO2 support. When Ru and Re components were simultaneously supported on SiO2, the diffraction peaks of RuO2 were weaker and broader (Fig. 1c), compared with the case of Ru/SiO2 Table 1 Specific surface areas, pore volume and average pore diameter of samples Catalyst
Specific surface area (m2/g)
Cumulative pore volume (cm3/g)
Average pore diameter (nm)
SiO2
301
1.69
19
ZrO2
66
0.23
11
TiO2
56
0.15
10
H-b
542
0.10
4
H–ZSM5
294
0.02
3
Ru/SiO2 Ru/ZrO2
284 54
1.56 0.21
18 12
Ru/TiO2
47
0.31
23
Ru/H-b
497
0.11
5
Ru/H–ZSM5
288
0.02
4
Ru/Al2Oa3
143
0.63
15
Ru/Ca
795
0.44
4
Ru–Re/SiO2
268
1.20
19
Ru–Re/ZrO2
62
0.17
11
Ru–Re/TiO2
50
0.29
21
Ru–Re/H-b
461
0.07
4
Ru–Re/H–ZSM5
283
0.04
3
a
Commercial catalyst
Ru RuO2 ReO3 e d
c b
a
10
20
30
40
50
60
70
80
2 Theta
Fig. 1 XRD patterns of catalysts (a) Ru/SiO2(calcined), (b) Re/ SiO2(calcined), (c) Ru–Re/SiO2(calcined), (d) Ru–Re/SiO2(after reaction), (e) Ru/SiO2(after reaction)
(Fig. 1a). Also, three very weak diffraction peaks at 2h & 24.1, 34.2 and 55.4°, which could be assigned to ReO3 phase [JCPDS File 84-0952], were observed (Fig. 1c). These results suggest that Ru–Re oxide particles could be well dispersed on the support when Ru and Re components were simultaneously supported on SiO2. On the other hand, the results of XRD characterizations of the spent Ru–Re/SiO2 and Ru/SiO2 samples (after hydrogenolysis under 160 °C, 8 MPa and 8 h) are also presented in Fig. 1d and e. It can be seen that the peaks assigned to Ru0 [JCPDS File 06-0663] phase were observed on the XRD profiles of the spent Ru–Re/SiO2 and Ru/SiO2, but there was no diffraction peak assigned to the phases of Re species being detected on the spent Ru–Re/SiO2 catalyst, suggesting that Re species could be well dispersed on the surface of the catalyst even after the reaction. The results that Ru0 phase was detected in the samples of spent Ru–Re/ SiO2 and Ru/SiO2 indicate that calcined Ru–Re/SiO2 and Ru/SiO2 samples went through an in situ reduction during the hydrogenolysis reaction and Ru oxide species could be reduced to Ru metal state. The valence state of Ru and Re surface species on spent Ru–Re/ZrO2 sample (after hydrogenolysis under 160 °C, 8 MPa and 8 h) and reduced Ru–Re/ZrO2 sample (reduced in hydrogen flow at 450 °C for 4 h) were analyzed by XPS, and the results are presented in Table 2. Ru species on the surface of both spent Ru–Re/ZrO2 and reduced Ru–Re/ZrO2 was in Ru0 metal state (binding energy of Ru3d5/2 = 280.3 eV, being coincident with reference data (280.1 eV) of Ru3d5/2 in Ru metal). However, Re species on the surface of the catalysts, both spent Ru–Re/ZrO2 and reduced Ru–Re/ZrO2, were in two states (Table 2). One was in
123
838
Top Catal (2009) 52:834–844
Table 2 Results of XPS measurement of catalysts
a
Ru3d5/2 (eV)
Re4f7/2 (eV)
Ru–Re/ZrOa2
280.3
46.3
41.1
Ru–Re/ZrOb2
280.3
46.3
41.2
Spot 2
Reference datac
a b c
Ru0
279.1–280.2
ReO3
46.5–47.0
Re0
40.3–41.0
Spot 1
Spot 3
Fresh catalyst Spent catalyst [27] Handbook of X-ray Photoelectron Spectroscopy
rhenium oxide state, in which the binding energy of Re4f7/2 was in the range of 46.2–46.3 eV, and it coincided with reference data (46.4 eV) of Re4f7/2 in ReO3 [27]. The other, with binding energy being in the range of 41.1–41.2 eV, was in rhenium metal state [27]. The rhenium oxide on the surface of reduced Ru–Re/ZrO2 or spent Ru–Re/ZrO2 might be some kind of well-dispersed Re oxide species, which perhaps was hardly reduced during the reduction process or during the reaction in present study. The morphologies and microstructure Ru–Re/ZrO2 was characterized by HR-TEM and the images of TEM are shown in Fig. 2. The shapes of catalyst particles were approximately spherical particles, and the distribution of the particles was relatively uniform. The EDX analysis on the surface of Ru–Re/ZrO2 was done (Fig. 2a, three circled areas), and it confirmed the existence of both Ru and Re elements on the surface of ZrO2 support (Fig. 2c). Either in the shade contrast area (Fig. 2a, spot-1 and spot-2) or bright contrast area (Fig. 2a, spot-3) in the TEM observation of Ru–Re/ZrO2 sample, Ru and Re elements was all detected by EDX (Fig. 2c). This implies that Ru and Re were relatively uniformly combined and Ru–Re was well spread and dispersed on the surface of ZrO2. The reduction behaviors of Ru/SiO2, Re/SiO2, Ru–Re/ SiO2, Ru/ZrO2, Re/ZrO2 and Ru–Re/ZrO2 as well as the interaction of Ru and Re on Ru–Re/SiO2 and Ru–Re/ZrO2 were investigated with H2-TPR, and the results are shown in Figs. 3 and 4. The H2-TPR profile of Ru/SiO2 showed one reduction peak at 215 °C (Fig. 3), which was assigned to the reduction of Ru species from RuO2 to Ru0 [26]. Re/ SiO2 also showed only one reduction peak at 396 °C, which was attributed to the reduction of rhenium oxide [28, 29]. On the other hand, in the H2-TPR profile of Ru–Re/ SiO2, one strong and broad peak was appeared, in which the reduction temperature (279 °C) was lower than that (396 °C) in Re/SiO2 H2-TPR but higher than that (215 °C) in Ru/SiO2 H2-TPR. These results suggest that the interaction between Ru and Re on the surface of Ru–Re/SiO2 occurred, and the reduction behavior of Ru–Re/SiO2 was
123
b
Zr
c
O Cu C Cu Zr Re RuRu
Cu Zr Re
Ru
Cu Zr Ru Re 2
4
6
8
Re Re Re
Spot 1
Re Re
Spot 2
Re
Spot 3 10
12
14
KeV
Fig. 2 HR-TEM images (a, b) and EDX spectra (c) of Ru–Re/ZrO2
changed. As for Ru/ZrO2, H2-TPR profile revealed two intensive reduction peaks at 131 °C and 188 °C and one weak and broad peak at 456 °C (Fig. 4). It has been reported that low-temperature TPR peak (\140 °C) of Ru species was assigned to the reduction of well-dispersed RuOx species, and the peak at somewhat higher temperature (about 200 °C) was assigned to the reduction of well-
Top Catal (2009) 52:834–844
839 Table 3 The particle sizes of Ru on catalysts obtained from different characterization methods and total CO uptake on catalysts (Ru dispersion) during CO pulse chemisorptions
Intensity/a.u.
Average particle size (nm) from
0
100
200
300
400
500
600
XRD
TEM
CO adsorption
Ru/SiO2
18
15
28.0
c
Ru/ZrO2
–
7
6.1
21
b
Ru/Al2O3
–
–
5.6
23
a
Ru/C
–
–
4.5
29
Ru–Re/SiO2
7
6
5.6
23
Ru–Re/ZrO2
–
5
3.2
34
700
800
Intensity/a.u.
Fig. 3 TPR profiles of Ru/SiO2 (a), Re/SiO2 (c) and Ru–Re/SiO2 (b)
c b a 400
4.6
a
temperature(°C)
200
D (dispersion) %a
600
800
temperature
Fig. 4 TPR profiles of Ru/ZrO2 (a), Re/ZrO2 (c) and Ru–Re/ZrO2 (b)
crystallized RuO2 particles [30–34]. The weak and broad reduction peak at 456 °C in the H2-TPR of Ru/ZrO2 might be attributed to the interaction of Ru metal and ZrO2 support [35]. Re/ZrO2 showed one intensive reduction peak at 370 °C (Fig. 4). On the other hand, the H2-TPR profile of Ru–Re/ZrO2 revealed three reduction peaks at 120 °C, 182 °C and 342 °C (Fig. 4). The peaks at lower temperatures (120 °C and 182 °C) in the H2-TPR profile of Ru–Re/ ZrO2 were similar with those of Ru/ZrO2 in shape and position of the peaks. However, the reduction peak at 342 °C in the H2-TPR profile of Ru–Re/ZrO2 was much smaller and shifted to low temperature, compared with the peak in the H2-TPR profile of Re/ZrO2. This implies that part of Re component on Ru–Re/ZrO2 might interacted with Ru component. The dispersion of Ru metal on supports was measured by CO chemisorption, and CO uptake (the molar ratio of CO/Ru) on Ru/support or Ru–Re/support catalysts during CO pulse chemisorption is shown in Table 3. The molar ratio of CO/Ru over Ru/SiO2 was low (CO/Ru = 0.046), indicating the dispersion of Ru on SiO2 was not well. This
The dispersion of Ru metal was based on the CO chemisorption and actual loading of Ru on the catalysts: 3.55%Ru/SiO2, 3.77%Ru/ZrO2, 3.23%Ru-3.57%Re/SiO2, 3.64%Ru-4.12%Re/ZrO2 (obtained from ICP-AES characterization), and 5.17%Ru/Al2O3, 5.0%Ru/C (provided by manufacturer)
is coincident with the characterized results from XRD and H2-TPR. As mentioned above, the XRD pattern of Ru/SiO2 showed sharp diffraction peaks (Fig. 1a), and the H2-TPR profile of Ru/SiO2 revealed one intensive reduction peak (RuO2 to Ru0), indicating the existence of crystallized RuO2 on the surface of SiO2. When Ru and Re components were simultaneously supported on SiO2, the molar ratio of CO/Ru over Ru–Re/SiO2 increased remarkably, suggesting that Ru–Re particles were relatively well dispersed on the surface of SiO2. On the other hand, the molar ratio of CO/ Ru over Ru–Re/ZrO2 bimetallic catalyst was also higher than that over Ru/ZrO2 monometallic catalyst (Table 3), further indicating the promoting effect of Re component on increasing dispersion of Ru on the supports. Commercial catalysts Ru/Al2O3 and Ru/C also showed relatively high CO/Ru ratio. Here, the average particle sizes of metal Ru on the catalysts obtained from different characterizations (XRD, TEM and CO adsorption) are compared, and the results are listed in Table 3. From the results in Table 3, for every analyzed catalyst (Ru/SiO2, Ru/ZrO2, Ru–Re/SiO2 or Ru–Re/ZrO2), the average metal particle sizes obtained from different characterizations (XRD, TEM and CO adsorption) were close each other, except for the case of Ru/SiO2 measured by CO adsorption. The average metal particle size on Ru/SiO2 obtained from TEM characterization was 15 nm and it was close to that obtained from XRD characterization (18 nm). Although the average metal particle size on Ru/SiO2 obtained from CO adsorption (28.0 nm) was much larger than that obtained from TEM and XRD methods, the average metal particle sizes of Ru–Re/SiO2 obtained from CO adsorption (5.6 nm) was close to that obtained from TEM (6 nm) and XRD (7 nm). For the catalysts using ZrO2 as support, the average metal particle sizes of Ru/ZrO2 and Ru–Re/ZrO2 could not be obtained from XRD
123
840
Top Catal (2009) 52:834–844
characterization, owing to the diffraction peaks of Ru metal being overlapped with that of support ZrO2 in XRD patterns. However, the average metal particle sizes of Ru/ ZrO2 obtained from TEM and CO adsorption were close each other (7 and 6.1 nm), and the same situation could also be observed in the case of Ru–Re/ZrO2. For commercial catalysts Ru/Al2O3 and Ru/C, the average metal particles sizes on Ru/Al2O3 and Ru/C obtained from CO adsorption characterization were 5.6 and 4.5 nm, respectively, indicating that metal particles on Ru/ Al2O3 and Ru/C were considerable fine. However, from the results of XRD characterizations of Ru/Al2O3 and Ru/C, it was difficult to distinctly observe Ru diffraction peaks from the XRD profiles probably due to the well dispersion of Ru on Ru/Al2O3 and Ru/C [22]. On the other hand, for TEM characterizations of Ru/Al2O3 and Ru/C, the boundaries of Ru particles in the TEM images of the catalysts were not clear, and it seems that Ru was highly spread and dispersed on the surface of Al2O3 and active carbon. It was difficult to exactly determine Ru particle size on Ru/Al2O3 and Ru/C samples from TEM [22]. Therefore, it was hardly to obtain the average metal particles sizes for Ru/Al2O3 and Ru/C by XRD and TEM characterizations in present study. Moreover, based on three characterization methods, all results revealed that the average metal particle sizes on Ru/ SiO2 was much larger than on other Ru/support catalysts, implying the metal Ru on the surface of SiO2 support might be favorable for aggregation. Average metal particle sizes
on Ru–Re/SiO2 measured by three different methods were in the range of 5.6–7 nm, and these were obviously smaller than that on Ru/SiO2 catalyst measured by same methods. On the other hand, by comparing Ru/ZrO2 and Ru–Re/ ZrO2, the same trend in the change of particle sizes could be also observed. That is, the average metal particle sizes on Ru–Re/ZrO2 obtained from TEM and CO chemisorption methods (5 nm and 3.2 nm) were somewhat smaller than that on Ru/ZrO2 catalyst obtained from same method (7 and 6.1 nm). 3.2 Hydrogenolysis of Glycerol 3.2.1 Catalytic Performance of Monometallic and Bimetallic Catalysts In the hydrogenolysis of glycerol over Ru-based catalysts, the reaction products were 1,3-propanediol (1,3-PDO), 1,2-propanediol (1,2-PDO), 1-propanol (1-PO), 2-propanol (2-PO), ethyl glycol (EG), ethanol and methanol (Table 4). In gas-phase products, methane was also detected, but it was only qualitatively analyzed in present study. In our previous research [22], we found a prominent promoting effect of Re2(CO)10 on the activity of Ru monometallic catalysts in glycerol hydrogenolysis to propandiols. In addition, the influence of reaction conditions (reaction temperature, hydrogen pressure and reaction time, etc.) in the hydrogenolysis of glycerol over Ru/ Al2O3 ? Re2(CO)10 catalyst has been already examined
Table 4 Results of glycerol hydrogenolysis over Ru/support and Re2(CO)10 ? Ru/support catalysts No.
Catalyst
Conv. (%)
Selec. (%) MeOH
EtOH
E.G
1-PO
2-PO
1,2-PDO
1,3-PDO
1 2
Ru/SiO2 Ru/SiO2 ? Re2(CO)10
16.8 37.0
0.8 0.2
6.3 3.4
18.2 5.4
27.2 24.2
2.1 4.4
39.0 51.7
6.4 10.7
3
Ru/ZrO2
25.4
1.8
10.9
18.9
30.5
4.2
31.9
1.8
4
Ru/ZrOa, 2
19.5
0.6
5.8
13.2
33.0
3.8
36.3
7.2
5
Ru/ZrO2 ? Re2(CO)10
37.0
0.2
2.6
2.3
22.8
4.7
55.7
11.8
6
Ru/H–ZSM5
20.5
0.6
6.2
15.0
28.1
1.8
42.2
6.0
7
Ru/H–ZSM5 ? Re2(CO)10
30.8
0.2
3.3
5.4
24.8
2.9
52.2
11.2
8
Ru/Al2Ob3
18.7
2.0
6.1
29.3
22.5
2.2
34.5
3.4
9
Ru/Al2O3 ? Re2(CO)b10
53.4
0.4
2.1
29.3
24.2
3.8
53.1
12.6
10
Ru/Cb
29.7
1.1
6.7
14.4
22.9
3.2
50.9
0.8
11
59.4
0.2
3.8
1.5
24.5
6.3
56.6
7.2
15.0
0.8
7.2
24.3
19.0
4.0
39.4
5.4
13
Ru/C ? Re2(CO)b10 Ru3(CO)c12 Re2(CO)c10
1.2
2.4
4.5
12.5
14.9
15.1
38.8
11.7
14
Ru3(CO)12 ? Re2(CO)c10
30.2
0.2
4.0
6.6
19.7
3.9
55.4
10.1
12
b
Reaction conditions: 160 °C, 8 MPa H2, 8 h, 10 mL 40 wt% glycerol aqueous solution, 150 mg Ru/support catalyst, mol ratio of Ru/Re = 1 a
Catalyst was reduced in hydrogen flow at 450 °C for 4 h before used
b
Data have already reported in previous paper [22]
c
Ru3(CO)12 = 0.0158 g, Re2(CO)10 = 0.0242 g, mol ratio of Ru/Re = 1
123
Top Catal (2009) 52:834–844
841
[22]. Therefore, 160 °C, 8.0 MPa and 8 h were chosen as the standard reaction conditions in present study. In present study, several supported Ru monometallic and Ru–Re bimetallic catalysts were prepared and their activities in glycerol hydrogenolysis were further investigated. Firstly, the catalytic performances of as-prepared Ru monometallic catalysts (Ru/SiO2, Ru/ZrO2 and Ru/H– ZSM5) and the promoting effects of Re2(CO)10 on the activity of these Ru/support were examined and compared with the cases of commercial catalysts of Ru/Al2O3 and Ru/C which have been tested in our previous paper [22], and the results are shown in Table 4. In our previous work [22], Ru/ZrO2 was pre-reduced in flowing H2 before being used in the reaction, and it showed 19.5% glycerol conversion (Table 4, No. 4). While in present study, calcined Ru/ZrO2 (Table 4, No. 3) went through an in situ reduction during the hydrogenolysis reaction (Ru metal phase being detected by XRD in spent Ru/ZrO2), and it showed somewhat higher activity (25.4% conversion) than prereduced Ru/ZrO2. Therefore, the as-prepared monometallic and bimetallic catalysts in present study were not prereduced in flowing H2 but went through an in situ reduction during the reaction. As shown in Table 4, as prepared monometallic catalysts Ru/SiO2 and Ru/H–ZSM5 also showed activities in the glycerol hydrogenolysis (the conversions of glycerol being 16.8% and 20.5%, respectively), which were comparable with the case of commercial catalyst Ru/Al2O3 (18.7% conversion). The promoting effect of Re2(CO)10 on the activity of monometallic Ru catalysts was further confirmed in the cases of Ru/SiO2 ? Re2(CO)10, Ru/ZrO2 ? Re2(CO)10, Ru/H–ZSM5 ? Re2 (CO)10 and Ru3(CO)12 ? Re2(CO)10 systems (Table 4, No. 2, 5, 7, 14). The conversion of glycerol increased from 1.5 to 2.2 times when addition of Re2(CO)10 to the Ru catalyzed reaction systems, and the selectivities of 1,2-PDO
and 1,3-PDO increased too, while the selectivity of ethylene glycol, which was a degradation product, decreased obviously. For the homogeneous catalysts Ru3(CO)12 and Re2(CO)10, Ru3(CO)12 alone showed a little activity (15% conversion) for converting glycerol to 1,2-PDO (Table 4, No. 12), while Re2(CO)10 alone showed nearly no activity on the glycerol hydrogenolysis (Table 4, No. 13). However, when the combination of Ru3(CO)12 and Re2(CO)10 was employed in the hydrogenolysis of glycerol, the activity of the catalytic system increased dramatically, and the selectivity of 1,2-PDO also increased, while the selectivity of ethylene glycol decreased (Table 4, No. 14). It is clear that the catalytic behaviors of Ru3(CO)12 ? Re2(CO)10 system was same with that of Ru/support ? Re2(CO)10 systems. Therefore, there existed a synergistic effect between Ru and Re in the reaction system, and this effect was the rational reason of why Ru/support ? Re2(CO)10 systems possessed high activities in glycerol hydrogenolysis. In order to further investigate the behaviors of Ru–Re on supports in the hydrogenolysis of glycerol, a series of supported bimetallic Ru–Re catalysts were examined in the glycerol hydrogenolysis, and the results are listed in Table 5 and compared with those of supported monometallic Ru catalysts. As shown in Table 5, among SiO2-supported catalysts, Re/SiO2 showed very low catalytic activity (the conversion of glycerol was merely 1.7%). This result further confirmed that Re species alone did not possess the catalytic activity for glycerol hydrogenolysis. Compared with the reaction result of Ru/SiO2 glycerol hydrogenolysis, Ru–Re/SiO2 bimetallic catalyst manifested much higher activity than Ru/SiO2. Similarly, the comparisons between other Ru monometallic catalysts (Ru/ZrO2, Ru/H–ZSM5, Ru/H-b and Ru/TiO2) and Ru–Re bimetallic catalysts (Ru–Re/
Table 5 Comparison of Ru/support and Ru–Re/support catalysts in glycerol hydrogenolysis Catalyst
Conv. (%)
Selec. (%) MeOH
EtOH
EG
1-PO
2-PO
1,2-PDO
1,3-PDO
1
Re/SiO2
1.7
2.1
6.2
11.4
20.9
6.8
44.4
8.1
2
Ru/SiO2
16.8
0.8
6.3
18.2
27.2
2.1
39.0
6.4
3
Ru–Re/SiO2
51.7
0.4
8.4
6.4
29.1
6.7
44.8
4.2
4
Ru/ZrO2
25.4
1.8
10.9
18.9
30.5
4.2
31.9
1.8
5
Ru–Re/ZrO2
56.9
0.2
7.4
4.0
27.7
8.1
47.2
5.5
6
Ru/H–ZSM5
20.5
0.6
6.2
15.0
28.1
1.8
42.2
6.0
7
Ru–Re/H–ZSM5
54.2
0.3
9.4
4.7
33.9
7.2
41.5
2.9
8
Ru/H-b
32.0
0.6
8.6
9.7
29.4
4.1
43.6
4.0
9
Ru–Re/H-b
52.8
0.3
8.4
4.5
33.2
8.1
42.8
2.7
10 11
Ru/TiO2 Ru–Re/TiO2
6.0 36.3
1.0 0.3
3.4 5.5
19.0 6.3
23.4 28.1
1.5 5.2
44.9 46.4
6.8 8.1
Reaction conditions: 160 °C, 8 MPa H2, 8 h, 10 mL 40 wt% glycerol aqueous solution, 150 mg catalyst
123
842
Top Catal (2009) 52:834–844
ZrO2, Ru–Re/H–ZSM5, Ru–Re/H-b and Ru–Re/TiO2) also proved the synergistic effect of Ru and Re on the supports, and revealed that the Ru–Re bimetallic catalysts possess higher activity and less selectivity to degradation product (ethylene glycol) than Ru monometallic catalysts (Table 5). On the other hand, it is interesting to take notice of the comparison of some Ru–Re/support bimetallic catalysts (Ru–Re/SiO2, Ru–Re/ZrO2, Ru–Re/H–ZSM5) and Ru/ support ? Re2(CO)10 systems (Ru/SiO2 ? Re2(CO)10, Ru/ ZrO2 ? Re2(CO)10, Ru/H–ZSM5 ? Re2(CO)10). The Ru– Re/support bimetallic catalysts showed higher activity than Ru/support ? Re2(CO)10 systems, but in the increase of the selectivities of 1,2-propanediol and 1,3-propanediol, Ru/support ? Re2(CO)10 systems were more obvious (Tables 5, No. 3, 5, 7 and 4, No. 2, 5, 7). While for the effect on decreasing the formation of degradation product (ethylene glycol), Ru–Re/support bimetallic catalysts and Ru/support ? Re2(CO)10 systems were similar, compared with Ru/support alone catalysts (Table 5, No. 2, 4, 6). The promoting effect of Re species on the activity of Ru based catalysts was discussed preliminarily. Firstly, compared the average metal particle sizes on Ru/SiO2 with Ru– Re/SiO2, and Ru/ZrO2 with Ru–Re/ZrO2 (Table 3), it can be seen that Re component had an effect on promoting the dispersion of Ru component on the surface of the supports. On the other hand, it is suggested that the existence of Re component could also prevent the aggregation of Ru metal particles during the reaction. Secondly, it is suggested that Re component (rhenium oxide species) would act as a solid acid and it would promote the glycerol dehydration step, and subsequently increased the activity of Ru–Re catalysts and the selectivity of PDO. Based on the literatures [36, 37], it has been reported that rhenium oxide showed surface acidity, and this has been proved by FT-IR and TPD studies of adsorbed pyridine [36] and by the characterization of IR and ammonia thermo-desorption [37]. Furthermore, in present study, the results of XPS characterization showed that rhenium oxide species existed on the surface of the spent Ru–Re/ZrO2 catalyst after the reaction. Although
as-prepared Ru–Re catalysts would undergo in situ reduction during the hydrogenolysis, rhenium oxide on the surface of the catalysts was not easy to be reduced at 160 °C during the reaction. The results of TPR characterization showed that the reduction temperatures of Re/ZrO2 and Re/ SiO2 (around 400 °C) were much higher than that of Ru/ ZrO2 and Ru/SiO2. The hydrothermal circumstance reaction (glycerol aqueous solution) might also favor the existence of rhenium oxide species during the reaction. Synthetically considering the results obtained in the experiments in present study, we suggest that rhenium oxide species played a role in the hydrogenolysis. 3.2.2 Influence of Glycerol Concentration The catalytic hydrogenolysis of glycerol is usually carried out in liquid phase with glycerol aqueous solution. On the other hand, the dehydration and hydrogenation reactions will occur during glycerol hydrogenolysis, and water will be formed in the dehydration step. Water content in reaction system, in other words, the concentration of glycerol in its aqueous solution could influence the activity of catalysts and the selectivities of products [4, 12]. In present study, influence of glycerol concentration on the catalytic performance was examined over Ru/Al2O3 ? Re2(CO)10 and Ru/Al2O3 catalysts in the ranges of 10–40 wt% glycerol concentration under the reaction conditions of 160 °C, 8 MPa H2 and 8 h, and the results are presented in Table 6. In the case of using Ru/Al2O3 catalyst, almost no change in the conversions of glycerol, but an increase in 1,2-PDO selectivity was observed with the glycerol concentration changing from 10 wt% to 40 wt%. In contrast, the conversions of glycerol over Ru/Al2O3 ? Re2(CO)10 catalytic system increased with the increase of glycerol concentration. A similar tendency in the influence of water content on glycerol conversion over a copper-chromite catalyst was also observed by Dasari et al. [12]. In addition, the selectivity of 1,2-PDO over Ru/Al2O3 ? Re2(CO)10 also increased with the increase of glycerol concentration, while formation of degradation product (ethylene glycol) decreased.
Table 6 Effect of reactant concentration on glycerol hydrogenolysis over Ru/Al2O3 and Ru/Al2O3 ? Re2(CO)10 Catalyst
Concentration of glycerol (wt%)
Conv. (%)
Selec. (%) MeOH
EtOH
EG
1-PO
2-PO
1,2-PDO
1,3-PDO
Ru/Al2O3 ? Re2(CO)10
10
36.4
1.6
10.9
13.4
29.0
8.6
36.5
0
Ru/Al2O3 ? Re2(CO)10
20
47.7
0.9
10.0
9.2
30.7
7.3
38.1
4.0
Ru/Al2O3 ? Re2(CO)10
40
53.4
0.4
6.8
7.8
23.4
5.1
50.1
6.4
Ru/Al2O3
10
17.5
5.1
5.0
49.2
16.9
1.0
22.2
0.4
Ru/Al2O3
20
17.9
3.1
4.0
44.6
15.2
1.0
31.9
0.2
Ru/Al2O3
40
18.8
2.0
7.0
29.1
22.3
1.9
34.3
3.3
Reaction conditions: 160 °C, 8 MPa H2, 8 h, 10 mL glycerol aqueous solution, 150 mg Ru/Al2O3, mol ratio of Ru/Re = 1
123
Top Catal (2009) 52:834–844
843
3.3 Hydrogenolysis of 1,2-PDO, 1,3-PDO, 1-PO and 2-PO From the results of glycerol hydrogenolysis over Ru monometallic and Ru–Re bimetallic catalysts (Tables 4, 5), it can be seen that the existence of Re component increased not only glycerol conversion, but also the selectivities of 1,2-PDO and 1,3-PDO, while decreased the selectivity of ethylene glycol. These results imply that Re component could inhibit the degradation reaction during glycerol hydrogenolysis. In order to examine the influence of Re component on the reaction routes and the distribution of the products during glycerol hydrogenolysis, Ru/Al2O3 and Ru/Al2O3 ? Re2(CO)10 catalysts were use in the hydrogenolysis of 1,2-PDO, 1,3-PDO, 1-PO and 2-PO, and the obtained results are compared with the hydrogenolysis of glycerol over the same catalysts under same reaction conditions, as shown in Table 7. When the hydrogenolysis of 1,2-PDO was carried out over Ru/Al2O3 catalyst, the main products were EtOH (48.4% selectivity) and 2-PO (31.3% selectivity), and the selectivity (19.5%) of 1-PO was much lower than that of 2-PO (Table 7). While over Ru/Al2O3 ? Re2(CO)10 catalyst, the hydrogenolysis of 1,2-PDO was more favorable (40.9% conversion) than over Ru/Al2O3 (6.4% conversion), the main products of 1,2-PDO hydrogenolysis were 2-PO (53.2% selectivity) and 1-PO (38.4% selectivity), and the formation of degradation product (EtOH) was greatly suppressed (9.3% EtOH selectivity). These results also revealed that Re component also had the effect on inhibiting the degradation of 1.2-PDO to EtOH. On the other hand, 1,3-PDO could also be converted over both Ru/ Al2O3 and Ru/Al2O3 ? Re2(CO)10 catalysts, and the conversion of 1,3-PDO was 24.1% (over Ru/Al2O3) and 40.4% (over Ru/Al2O3 ? Re2(CO)10), respectively. The main products formed in 1,3-PDO hydrogenolysis over Ru/
Al2O3 were 1-PO (49.0% selectivity) and EtOH (49.6% selectivity), and almost no 2-PO was formed. This is consistent with the results reported in literature [4], in which 1,3-PDO hydrogenolysis was performed over Ru/C and Ru/C ? Amberlyst resin. Over Ru/Al2O3 ? Re2(CO)10 catalyst, 1,3-PDO was mainly converted to 1-PO (75.6% selectivity), while the selectivity of EtOH (23.5%) was much lower than that of 1-PO (Table 7). On the other hand, in 1-PO hydrogenolysis, both Ru/ Al2O3 and Ru/Al2O3 ? Re2(CO)10 catalysts showed almost no activity. This indicates that 1-PO was stable under the given reaction conditions in the hydrogenolysis over both Ru/Al2O3 and Ru/Al2O3 ? Re2(CO)10. This results is coincident with the fact that there was no difference in the selectivity of 1-PO in glycerol hydrogenolysis between over Ru/Al2O3 and Ru/Al2O3 ? Re2(CO)10. On the other hand, for the hydrogenolysis of 2-PO, almost no reactant was converted over Ru/Al2O3 (2-PO conversion \0.3%), while the conversion of 2-PO was 9.7% over Ru/Al2O3 ? Re2(CO)10 and the formed product was mainly EtOH. These results suggest that 2-PO was less stable over Ru/Al2O3 ? Re2(CO)10 catalyst than over Ru/ Al2O3 under the same reaction conditions. Based on the reaction results of the hydrogenolysis of 1,2-PDO, 1,3-PDO, 1-PO and 2-PO as well as glycerol, we proposed a scheme of reaction routes which were favorable or not favorable over Ru–Re catalysts, as shown in Scheme 1. It could be suggested that glycerol was favorable to be converted to 1,2-PDO, but not favorable to 1,3-PDO and ethylene glycol over Ru–Re catalysts. Both 1,2-PDO and 1,3-PDO were favorable to be converted to 1-PO, while 1,2-PDO was also favorable to be converted to 2-PO. In addition, 1-PO was not favorable to be converted, but 2-PO, in some sort, was favorable to be converted to ethanol. Therefore, in order to get higher selectivities of
Table 7 The results of various compounds Cat.
Reactant
Conv. (%)
Selec. (%) MeOH
EtOH
EG
1-PO
2-PO
1,2-PD
1,3-PDO
Ru/Al2O3 ? Re2(CO)10
Glycerol
53.4
0.4
6.8
7.8
23.4
5.1
50.1
6.4
Ru/Al2O3 Ru/Al2O3 ? Re2(CO)10
Glycerol 1,2-PDO
18.8 40.9
2.0 0
7.0 9.3
29.1 0
22.3 38.4
1.9 52.3
34.3 –
3.3 0
Ru/Al2O3
1,2-PDO
6.4
0.8
48.4
0
19.5
31.3
–
0
Ru/Al2O3 ? Re2(CO)10
1,3-PDO
40.4
0.2
23.5
0.4
75.6
0.2
0.1
–
Ru/Al2O3
1,3-PDO
24.1
0.2
49.6
0.3
49.0
0.4
0.6
–
Ru/Al2O3 ? Re2(CO)10
1-PO
\0.3
–
a
–
–
–
–
Ru/Al2O3
1-PO
\0.3
–
a
–
–
–
–
–
Ru/Al2O3 ? Re2(CO)10
2-PO
9.7
0.3
97.2
–
–
–
–
–
Ru/Al2O3
2-PO
\0.3
–
a
–
–
–
–
–
–
Reaction conditions: 160 °C, 8 MPa H2, 8 h, 10 mL 40 wt% reactant aqueous solution, 150 mg Ru/Al2O3, mol ratio of Ru/Re = 1 a
Trace amount of EtOH was detected, but the selectivity was not calculated owing to too lower conversion
123
844 Scheme 1 Influence of Ru–Re catalysts on reaction routes in glycerol hydrogenolysis. Y: the route that was favorable over Ru–Re catalysts. N: the route that was not favorable over Ru–Re catalysts
Top Catal (2009) 52:834–844 OH
N
H 2C
H2 C
Y
CH2
OH
Y OH H2 C
OH HC
OH
OH CH 2
Y
H 2C OH
N
1,2-PDO and 1,3-PDO, the inhibiting the further conversion of 1,2-PDO and 1,3-PDO to 1-PO and 2-PO could be one of the key points, and the further efforts on the modification of the catalysts are still required. 4 Conclusion Ru–Re bimetallic catalysts showed high activity in the hydrogenolysis of glycerol and Re exhibited obvious promoting effect on enhancing the activity of the catalysts and the selectivities of propanediols. Of 56.9% conversion of glycerol and 47.2% selectivity of 1,2-propanediol were achieved over Ru–Re/ZrO2 bimetallic catalyst under the reaction conditions of 160 °C, 8.0 MPa and 8 h. There existed a synergistic effect between Ru and Re species on the bimetallic catalysts, and the existence of Re component on Ru–Re/ support catalysts improved the dispersion of Ru species on supports and changed the respective reduction behavior of Re or Ru alone on the supports. Glycerol was favorable to be converted to 1,2-propanediol over Ru–Re catalysts under the reaction conditions in present study, but not favorable to ethylene glycol. The inhibiting of the further conversion of 1,2-propanediol and 1,3-propanediol to 1-propanol and 2-propanol might be one of the key points for further enhancing the selectivities of 1,2-PDO and 1,3-PDO. Acknowledgments This work is supported by the Analytical Foundation of Tsinghua University, China. Authors are grateful of Mr. Zhanping Li for his discussion and advice on XPS measurements.
References 1. Behr A, Eilting J, Irawadi K, Leschinski J, Lindner F (2008) Green Chem 10:13 2. Chheda JN, Huber GW, Dumesic JA (2007) Angew Chem Int Ed 46:7164 3. Chaminand J, Djakovitch L, Gallezot P, Marion P, Pinel C, Rosier C (2004) Green Chem 6:359 4. Miyazawa T, Kusunoki Y, Kunimori K, Tomishige K (2006) J Catal 240:213 5. Demirel-Gulen S, Lucas M, Claus P (2005) Catal Today 102– 103:166 6. Chai SH, Wang HP, Liang Y, Xu BQ (2007) Green Chem 9:1130 7. van Haveren J, Scott EL, Sanders J (2008) Biofuels Bioproducts Biorefining 2:41
123
OH
H 2C
HC OH
H2 C
Y
OH
CH 3
OH
Y
CH3
H 2C
H 3C
HC
N CH 3
Y
OH H 2C
H3 C
N
H2 C
8. Smidova D, Mikulasek P, Stloukal R, Hirschmann S (2006) Desalination 200:466 9. Kusunoki Y, Miyazawa T, Kunimori K, Tomishige K (2005) Catal Commun 6:645 10. Miyazawa T, Koso S, Kunimori K, Tomishige K (2007) Appl Catal A 318:244 11. Miyazawa T, Koso S, Kunimori K, Tomishige K (2007) Appl Catal A 329:30 12. Dasaria M, Kiatsimkula P, Sutterlinb R, Suppesa G (2005) Appl Catal A Gen 281:225 13. Feng J, Fu HY, Wang JB, Li RX, Chen H, Li XJ (2008) Catal Commun 9:1458 14. Feng J, Wang JB, Zhou YF, Fu HY, Chen H, Li XJ (2007) Chem Lett 36(10):1274 15. Wang S, Liu HC (2007) Catal Lett 117(1–2):62 16. Alvise P, Pietro T (2005) Ind Eng Chem Res 44:8535 17. Furikado I, Miyazawa T, Koso S, Shimao A, Kunimori K, Tomishige K (2007) Green Chem 9:582 18. Kurosaka T, Maruyama H, Naribayashi I, Sasaki Y (2008) Catal Commun 9:1360 19. Maris EP, Ketchie WC, Murayama M, Davis RJ (2007) J Catal 251:281 20. Maris EP, Davis RJ (2007) J Catal 249:32 21. Stytsenko VD (1995) Appl Catal A 126:1 22. Ma L, He DH, Li ZP (2008) Catal Commun doi:10.1016/ j.catcom.2008.07.009 23. Song YQ, He DH, Xu BQ (2008) Appl Catal A 337:19 24. Han WF, Liu HZ, Zhu H (2007) Catal Commun 8:351 25. Ertl G, Knoinger H, Weitkamp J (2008) Handbook of heterogeneous catalysis, vol 2, 2nd edn. Wiley-VCH, Weinheim 26. Lanza R, Jaras SG, Canu P (2007) Appl Catal A 325:57 27. John FM, William FS, Peter ES, Kenneth DB (1995) Handbook of X-ray photoelectron spectroscopy. Physical Electronics, Inc., Minnesota USA 28. Jacobs G, Chaney JA, Patterson PM, Das TK, Davis BH (2004) Appl Catal A 264:203 29. Breen JP, Burch R, Griffin K, Hardacre C, Hayes M, Huang X, O’Brien SD (2005) J Catal 236:270 30. Hosokawa S, Kanai H, Utani K, Taniguchi Y, Saito Y, Imamura S (2003) Appl Catal B 45:181 31. Yan QG, Wu TH, Weng WZ, Toghiani H, Toghiani RK, Wan HL, Pittman CU Jr (2004) J Catal 226:247 32. Faroldi B, Carrara C, Lombardo EA, Cornaglia LM (2007) Appl Catal A 319:38 33. Sun GL, Xu AH, He Y, Yang M, Du HZ, Sun CL (2008) J Hazard Mater 156:335 34. Bi JL, Hong YY, Lee CC, Yeh CT, Wang CB (2007) Catal Today 129:322 35. Nurunnabi M, Murata K, Okabe K, Inaba M, Takahara I (2008) Appl Catal A 340:203 36. Kawai T, Jiang KM, Ishikawa T (1996) J Catal 159:288 37. Nahama FS, Clause O, Commereuc D, Saussey J (1998) Appl Catal A 167:237
