Hydrogenolysis of Glycerol by the Combined Use of Zeolite and Ni

Apr 17, 2014 - David Lee Phillips,*. ,⊥ and Chenguang Liu. †,‡,∥. †. State Key Laboratory of Heavy Oil Processing, China University of Petro...
0 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/EF

Hydrogenolysis of Glycerol by the Combined Use of Zeolite and Ni/ Al2O3 as Catalysts: A Route for Achieving High Selectivity to 1‑Propanol Xufeng Lin,*,†,‡,§ Yanhong Lv,‡,∥ Yanyan Xi,†,∥ Yuanyuan Qu,‡,∥ David Lee Phillips,*,⊥ and Chenguang Liu†,‡,∥ †

State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East China), Qingdao 266555, China Key Laboratory of Catalysis of China National Petroleum Corporation, Qingdao 266555, China § College of Science, China University of Petroleum (East China), Qingdao 266555, China ∥ College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266555, China ⊥ Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China ‡

ABSTRACT: Sequential two-layer catalysts were used for the hydrogenolysis of glycerol to remove its oxygen content in a continuous-flow fixed-bed reactor. The acidic H-β catalyst layer was packed before the Ni/Al2O3 catalyst layer in the reactor. The sequential two-layer catalysts can provide good 1-propanol (1-PO) selectivities at high glycerol conversions (up to 69% selectivity at ∼100% conversion). To our knowledge, the catalytic system in this work presented one of the best selectivities to 1PO using non-noble metal based catalytic systems. A preliminary mechanistic study indicated that most of 1-PO in the products was generated from glycerol via a “sequential two-time dehydration-hydrogenation” mechanism.

1. INTRODUCTION The conversion of glycerol to more valuable chemical compounds1 is a hot topic in the area of sustainable chemistry due to the increasing amount of biodiesel produced industrially in this decade. A glycerol molecule has three hydroxyl groups, so removal of the oxygen content from glycerol by hydrogenolysis is one of the most important routes for upgrading glycerol.2 Alkanes are always much less valuable compared to oxygenated compounds, so complete removal of the oxygen content from glycerol to afford propane is not desirable. Instead, a selective removal of the oxygen content is preferred since this can produce more valuable products such as 1,2propanediol (12-PDO), 1,3-propanediol (13-PDO), 1-propanol (1-PO), isopropanol (2-PO), and ethylene glycol (EG), etc. The product selectivity to 12-PDO3−12 is currently the best (up to ∼98%11) among these oxygenated products, but the selectivities to the other oxygenated products listed above are often undesirably low. Compared to the abundant studies on the direct conversion of glycerol to 12-PDO3−12 and 13-PDO,13−19 the studies on the direct conversion of glycerol to propanols are far fewer in number,20−22 although 1-PO and 2-PO are also valuable chemicals.20 An indirect way for propanol production from glycerol may be achieved by conversion of glycerol to 12-PDO first, and 12-PDO is subsequently converted to propanol using catalysts such as an iridium pincer complex.23 In most of the studies dealing with propanol production from glycerol, noblemetal based catalysts are used.20,21,23 From a practical aspect, noble metal based catalysts are always quite expensive. Even using noble-metal based catalysts, the catalytic performance in obtaining either 1-PO or 2-PO still has a large room for improvement. Different to the noble metal cases, Friedrich et al.22 reported commercial Ni/Al2O3 and Ni/SiO2 catalysts can © 2014 American Chemical Society

be used for production of 1-PO from glycerol. Ni/Al2O3 gave 35.3% 1-PO selectivity and Ni/SiO2 gave 42.8% 1-PO selectivity at 320 °C. Removal of oxygen from glycerol by hydrogenolysis is generally believed to take place via the “dehydrogenationdehydration-hydrogenation” or the “dehydration−hydrogenation” mechanisms.3,13,15,24−26 Although the detailed catalytic reaction steps are still not clear, the dehydration step is generally believed to be directly responsible for the oxygen removal. Based on this point some researchers used “acid− metal” bifunctional catalysts for the hydrogenolysis of glycerol.25,26 On one catalyst the acid sites are responsible for the dehydration step and the metallic sites are responsible for the hydrogenation/dehydrogenation step, respectively. Mixing two catalysts in one catalytic system, one solid acid catalyst and one metal catalyst, was also employed in some reports.27−29 Up to now, this kind of study was usually carried out using autoclave batch reactors, where the solid acids such as ionexchanged resins or zeolites were fully mixed with noble-metal based catalysts. The use of two mixing catalysts was found to be beneficial to produce the C3 products over the cracking products. However, the selectivities to propanols are still low in these catalytic systems. It is well-known that the continuous-flow fixed-bed reactors are the preferred reactors for heterogeneous catalysis where the reactions take place on solid catalyst surfaces. In this study, we report using a sequential packing of the zeolitic and the Nibased catalysts in a fixed-bed reactor for hydrogenolysis of Received: January 16, 2014 Revised: April 17, 2014 Published: April 17, 2014 3345

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351

Energy & Fuels

Article

the outlet of the reactor setup during reaction test by measuring the liquid volume change in a certain time. The flow rate of H2 was also checked with a bubble flow-meter at the gas exhaust. Typically the product flow was sampled 30 min after the temperature reached 220 °C unless specially specified, and then analyzed with an Agilent 6890 gas chromatograph (GC) equipped with a Stabilwax capillary column and a flame ionization detector. n-Butanol was used as the internal reference for the quantitative analysis of the reactant and product mixtures when carrying out an off-line GC measurement. A same amount of n-butanol was added to both of a sampled liquid product and a reactant solution with a same volume. The conversion of glycerol and the selectivity to a certain product, X, in this paper are based on carbon and are calculated by the following equations:

glycerol. The zeolitic catalyst layer was intended to be packed before the Ni catalyst layer, in order to ensure that the dehydration takes place before hydrogenation. The use of two catalysts in sequential layers was found to significantly improve the selectivity to 1-PO compared to the case of using one catalyst.

2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation and Characterization. The all-H type H-β zeolite with a Si/Al ratio of 15.8 was bought from Nankai Catalysts Company (Tianjin, China). Before use, this zeolite was dried at 110 °C overnight, followed by calcination in air at 450 °C for 4 h. The Al2O3 support was prepared in a common way as reported elsewhere.30 The NiO/Al2O3 sample was prepared by incipient wetness impregnation of Al2O3 with a Ni(NO3)2 solution. After impregnation, this sample was also dried at 110 °C overnight, followed by calcination in air at 450 °C for 4 h. Then, the NiO/Al2O3 sample was put into a fixed-bed reactor, and a H2 flow of ∼30 mL/min was used to reduce this sample at 450 °C for 8 h. The obtained black sample is denoted as Ni/Al2O3 in this paper. The as-prepared catalysts were further ground to >200 mesh particles and then X-ray fluorescence (XRF) spectroscopy was used to measure the elemental components of the catalysts. The Si/Al ratio of the H-β catalyst was confirmed and the Ni content of Ni/Al2O3 was measured to be 15.7%. The X-ray diffraction (XRD) patterns of the catalysts were recorded by a X’pert PRO MPD diffractometer (PANalytical Company, Netherlands) with Cu−K radiation (40 kV, 40 mA) at a speed of 5°/min. The 77 K−N2 BET surface area and the size distribution of the pores of the as-prepared catalysts were measured with the static BET method using a Micromeritcs ASAP2010 instrument. The amount of acid sites of the catalysts was obtained with temperature-programmed desorption of ammonia (NH3-TPD). About 200 mg of catalyst (20−40 mesh) was loaded in a quartz tube. The sample was heated from room temperature to 650 °C under a He flow (30 mL/min), which was then maintained at 650 °C for another 30 min to ensure complete removal of impurities. Then, the sample was cooled to 100 °C and saturated with a 10% NH3-in-He mixture, and then flushed by He for 1 h to remove physically adsorbed ammonia. Then, the sample was heated to 650 °C at a heating rate of 10 °C/min in the same He flow. The desorption profiles were recorded using a thermal conductivity detector (TCD), which was calibrated by a pulse gas with known amount of NH3. The CO chemisorption on Ni/Al2O3 was conducted using an Auto Chem 2950 HP equipment (Mircromeritics, U.S.A.). About 0.1 g of sample was placed in a U-shaped quartz tube, and was further reduced by H2 at 450 °C for 1 h. Then the sample was flushed with a He flow for 1 h and cooled to 30 °C. The CO chemisorption was operated by pulse injections of pure CO at 30 °C. The amount of exposed Ni sites was calculated by assuming one adsorbed CO molecule per surface Ni atom. 2.2. Catalytic Hydrogenolysis of Glycerol. The H-β catalyst was pressurized into a tablet and then crushed and sieved to 20/40 mesh particles for the catalytic reaction tests. The Ni/Al2O3 catalyst was also sieved to 20/40 mesh particles. The reaction tests for the catalytic hydrogenolysis of glycerol were performed in a stainless-steel fixed-bed reactor in the down-flow mode, with an i.d. of 8 mm and a length of 45 cm. These two catalysts were packed in this fixed-bed reactor to be two layers contacting with each other, with the H-β layer being at the upstream side. The volume of the reactor under the Ni catalyst layer was filled with quartz wool. The amount of the catalyst used in different times of reaction test will be specified in section 3. The reaction feed of 40% glycerol in aqueous solution (V/V) was introduced into the reactor at a flow rate of 0.2 mL/min, accompanied by a H2 flow of 96 mL/min. After the reactant feed flows were stable, the temperature of the catalyst layers was increased from room temperature to 220 °C, and the pressure of the reactor was 2 MPa. The product flow was cooled with a coolant of −6∼−1 °C. The flow rate of glycerol solution was double-checked both at the inlet and at

Conversion = 1 − ([Glycerol]product /[Glycerol]reactant ) × 100

Selectivity to X = ([X]/([Glycerol]reactant − [Glycerol]product )) × ((no. of C atoms in X)/3) × 100 2.3. Temperature-Programmed Surface Reaction of Glycerol. A typical temperature-programmed surface reaction (TPSR) of glycerol was carried out as described below. First, 1 g of the catalyst was immersed into the 40% glycerol solution for ∼12 h at room temperature. Then, the obtained slurry was filtered with a Buchner funnel and put into a vacuum oven for drying at 0.1 atm and at 70 °C for 4 h. Then, 20 mg of the sample obtained was put into a small ceramic boat. The ceramic boat was fixed into a reaction chamber and its temperature was controlled by a temperature controller. A 30 mL/ min N2 flow was used as the carrier gas to bring possible products to the detector. An online mass spectroscope (MS, Netzsh, Germany) was used as the product detector, and a few m/z values were set according to the molecular weights of the possible products. In order to remove the air in the reaction chamber and to obtain a stable background, pure N2 was purged into the reaction chamber at 40 °C for ∼2 h until the microbalance under the ceramic boat showed that its mass was unchanged. The temperature range 40−250 °C was examined for the TPSR study with an increasing rate of 5 K/min.

3. RESULTS AND DISCUSSION 3.1. Catalyst Characterization. Table 1 shows selected physiochemical properties which may be useful for the mechanistic understanding of glycerol hydrogenolysis described in section 3.3. Figure 1 shows the XRD patterns of the catalysts described in section 2.1. Figure 1a shows that using the H-β catalyst in a liquid-phase flow under the reaction conditions did not lead to an observable change in crystal structure. The XRD Table 1. Physicochemical Properties of Different Catalysts 77 K N2−BET results surface area (m2/g)

catalyst H-β Al2O3 Ni/Al2O3

catalyst

pore vol. (cm3/g)

pore size (nm)

618 0.25 0.62 331 0.71 6.2 251 0.55 6.3 amount of acid sites of the catalysts measured by TPD

NH3 desorbed before 350 °C (mmol NH3/g)

NH3 desorbed after 350 °C (mmol NH3/g)

total amount of acid sites (mmol/g)

H-β 0.975 0.465 1.44 0.824 0.302 1.13 Ni/ Al2O3 amount of exposed Ni atoms on Ni/Al2O3 measured with CO pulse chemisorption catalyst Ni/ Al2O3 3346

CO uptake (mmol/gcat)

amount of exposed Ni atoms (mmol/gcat)

dispersion (%)

0.188

0.188

7.0

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351

Energy & Fuels

Article

Figure 1. XRD patterns of (a) H-β zeolite before and after a catalytic reaction test and (b) the Al2O3 support and the Ni/Al2O3 catalyst before and after reduction by H2 at 450 °C for 4 h.

∼30%. The selectivity of 1-PO increased significantly to 60% when the sequential layers of the catalysts were used. On the other hand, the selectivity to 12-PDO was dramatically decreased to ∼4%. Accompanied with these changes, the selectivity to acetol also dramatically decreased from ∼33% when using pure Ni/Al2O3 as the catalyst to ∼1% when using the two-layer catalysts. Obviously the addition of the zeolitic catalyst directed the hydrodeoxygenation of glycerol toward a higher degree, to improve the selectivity to 1-PO. Varying amounts of H-β combined with 1g of Ni2O3/Al was used to examine the effect of the catalyst weight ratio on the product selectivity. Figure 3 shows that increasing the amount of the H-β catalyst led to higher glycerol conversion as well as higher selectivity to 1-PO, while the selectivity to 12-PDO decreased at the same time. For example, the selectivity to 12PDO decreased from 29.8% to 3.7% while the selectivity of 1PO increased from 45.3% to 69.3% when the amount of H-β increased from 0.5 to 1.25 g. When the amount of H-β was increased to 1.25 g, the glycerol conversion reached 100%, and the selectivities to 1-PO and 12-PDO stayed almost unchanged. To our knowledge, our system of two-layer catalysts gave one of the highest selectivities to propanol from glycerol using a continuous-flow fixed-bed reactor with a non-noble metal based catalytic system.22 Here, the catalytic reaction results reported from similar studies, which also aim at propanol production are compared to our results. Friedrich et al.22 showed an overall selectivity of 69% for lower alcohols (methanol, ethanol, and propanol) with a single-layer Ni/SiO2 catalyst at a 99% glycerol conversion. The temperature was 320 °C and the liquid hourly space velocity (LHSV) was 3.0 h−1. However, the selectivity to 1-PO was 42.8% and the selectivity to ethanol was 20.2%. They claimed that they have obtained the highest selectivity to lower alcohols from glycerol using a continuous-flow fixed-bed reactor with an inexpensive catalytic system. In contrast to that, our catalytic system presented the 1-PO selectivity much higher than 42.8% with a similar glycerol conversion and LHSV. In addition, a much lower temperature was used in this work (220 °C vs 320 °C in ref 22). Nevertheless, the stability of our catalytic system was relatively poor compared to the single-

pattern of Ni/Al2O3 shown in the top curve in Figure 1b indicates that most of the Ni content exists in the metallic state as reflected by the Ni(111) and Ni(200) peaks located at 44.5° and 51.9°, respectively (Joint Committee on Powder Diffraction Standards number: 01-070-0989). Figure 2 shows the TEM image of Ni/Al2O3 which indicates that the reduced Ni content became nanoparticles with sizes ranging from 10− 30 nm.

Figure 2. TEM image of the Ni/Al2O3 catalyst after reduction by H2.

3.2. Catalytic Hydrogenolysis of Glycerol. Table 2 summaries the glycerol conversion and the selectivities to different products for the catalytic hydrogenolysis of glycerol. It can be seen that the single-layer Ni/Al2O3 gave moderate selectivity to 12-PDO (∼52%) at a moderate glycerol conversion (60.5%). The main byproducts were acetol (selectivity of ∼33%) and ethanol (selectivity of ∼8%). Ethylene glycol, methanol, acrolein, and propanal were also observed as minor products, and 1-PO was not observed. When 1.0 g of H-β catalyst was packed in the layer before the 1.0 g Ni/Al2O3 layer, the product selectivity changed significantly and the glycerol conversion had an increase of 3347

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351

Energy & Fuels

Article

Table 2. Catalytic Performances of the Hydrogenolysis and the Dehydration of Glycerol Using Different Catalysts hydrogenolysisa catalyst conversion (%) of glycerol selectivity (%) to

12-PDO 13-PDO EG 1-PO acetol acrolein propanal acetone ethanol methanol unidentifiedd

dehydrationb

1 g Ni/Al2O3

1 g H-β//1 g NiO/Al2O3

1 g Al2O3

1 g H-β

60.5

89.9

4.8

74.7

51.7 0.2 2.4 0.2 32.7  0.9  8.0 1.5 2.4

3.7 2.6 1.5 60.3 1.1 0.2 0.2 10.3 11.6 0.9 7.6

c        82.2  18.8

    1.0 48.8 3.9 5.2 34.6  6.5

The reaction condition is described in section 2.2. bThe reaction condition was same as hydrogenolysis except no hydrogen flow was used. c represents “not detected”. dThe selectivity was calculated by 100% subtracted by the overall selectivity of all of the known compounds.

a

of 80% was achieved at the glycerol conversion of 99.7%, when Pt−HSiW/ZrO2 was used as the catalyst. In addition, the selectivity to 2-PO was 11%, making the overall selectivity to propanols quite high. However, the LHSV they used was relatively low (0.045 h−1, compared to ∼3.0 h−1 for H-β//Ni/ Al2O3 in this work) to obtain the above performance. The glycerol conversion and the 1-PO selectivity dropped dramatically when the LHSV increased from 0.045 to 0.18 h−1. When the LHSV was 0.18 h−1, the glycerol conversion was ∼50% and the 1-PO selectivity was ∼40%. In addition, one may note that the Pt−HSiW/ZrO2 catalyst is much more expensive than the Ni-based catalysts used in the work of Friedrich et al.22 and in this work. 3.3. Preliminary Study of the Reaction Mechanism of Glycerol Hydrogenolysis on the Two-Layer Catalysts. To produce a propanediol molecule from a glycerol molecule requires removal of one O atom and to produce a propanol molecule requires removal of two O atoms. In principle removal of two O atoms in a glycerol molecule by hydrogenolysis requires a deeper degree of deoxygenation than the removal of one O atom, however, the complete removal of the O atoms should be avoided. Therefore, the production of propanol from glycerol requires a sophisticated control of the catalytic hydrogenolysis process. There are many reports on understanding the mechanism for transition metalcatalyzed hydrogenolysis of glycerol in the literature.3,13,15,24−26,29,31,32 The “dehydrogenation−dehydration− hydrogenation” and “dehydration−hydrogenation” mechanisms are widely considered for this type of catalytic reactions. Although Ni-based catalysts are often used in hydro-treating, the reports dealing with the hydrogenolysis of glycerol using catalysts containing Ni as the only active metal component, are not frequently seen in the literature.12,22,32−36 Thus, the reports dealing with the reaction mechanism of Ni-catalyzed hydrogenolysis of glycerol are few in number.22,32 The main goal of the preliminary work described in this section is not to obtain a more detailed reaction mechanism on the single-layer Ni catalyst, but to understand whether and how the two-layer catalysts change the reaction mechanism compared to the case of the single-layer Ni catalyst. In order to obtain mechanistic insights for the hydrogenolysis of glycerol catalyzed by single Ni/Al2O3 layer and by the sequential two-layer catalysts, the temperature-programmed surface reaction (TPSR, see section 2.3 for detail) of glycerol

Figure 3. Hydrolysis of glycerol using 1g Ni/Al2O3 and varying mass of H-β in the catalyst layer before the Ni/Al2O3 layer in a fix bed reactor. Temperature = 220 °C; pressure = 2 MPa; flow rate of glycerol solution = 0.2 mL/min; flow rate of H2 = 96 mL/min.

layer Ni catalyst. For example for the 1 g H-β//1 g NiO/Al2O3 catalysts, when the time-on-stream changed from 30 to 60 min and to 100 min, the glycerol conversion decreased from 100% to ∼92% and to ∼70%, respectively, and the 1-PO selectivity decreased from ∼60% to ∼52% and to ∼43%, respectively. It has been shown that the catalytic performance of the singlelayer Ni/Al2O3 catalyst was relatively stable over 72 h.22 Since the crystal structure of β-zeolite was quite stable during the reaction test as indicated from the XRD measurement (Figure 1a), the relative instability of the two-layer catalysts may be mainly accounted for the carbon deposit on the β-zeolite layer. Noble metal based catalyst may be able to present good selectivity to propanols for hydrogenolysis of glycerol.20,21 It is also interesting to compare the overall catalytic performance of our two-layer catalysts with those of noble metal based catalysts. In a study reported by Zhu et al.20 for transformation of glycerol to propanols, one of the highest selectivities to 1-PO 3348

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351

Energy & Fuels

Article

Figure 4. Temperature dependence of the mass spectroscopic signal (TPSR profile) for H-β, Al2O3, and Ni/Al2O3 catalyzed dehydration of glycerol with the m/z signal of 56 (a) and 74 (b), respectively. Scan rate: 5 K/min.

PDO may be produced from the hydrogenation of acetol. Since acetol is the product from the first dehydration of glycerol at a primary site, the “primary dehydration−hydrogenation” mechanism seems to be more plausible than the “dehydrogenation− dehydration−hydrogenation” mechanism. This is also consistent with the conclusion of the TPSR experiment, and consistent with the proposed mechanisms of glycerol hydrogenolysis using first-row transition metal catalysts.31 The reluctance of Ni based catalysts to remove a secondary OH group in glycerol can be reflected by the case that almost in all of the reports dealing with the generation of 13-PDO from glycerol, noble metal systems such as Pt, Ru-based catalysts were used.13−19 It has been well established that acidic zeolites can be used as dehydration catalysts for glycerol.37−39 In most of the investigations on zeolite catalyzed glycerol dehydration, relatively high temperatures were used (typically 270−350 °C) and the reactants were in the gas phase. This is somewhat different to our present reaction conditions. Thus, a similar reaction condition as the hydrolysis reaction was employed to perform H-β catalyzed dehydration of glycerol, and the results are shown in the right-most column in Table 2. The main product was acrolein, the two-time dehydration product of glycerol, and other products such as ethanol also had moderate contributions. Compared to the relatively weak signals observed at m/z of 56 and 74 in the TPSR profiles for glycerol dehydration on Al2O3 and on Ni/Al2O3, the signals at these two m/z ratios for the H-β case were much larger, especially for the one observed at m/z = 56 (see Figure 4). Since TPSR is a transient state technique for characterization, the signal at m/z = 56 indicated that the two-time dehydration of glycerol took place quickly on H-β. Therefore, by comparing the data in the fourth and the right-most columns in Table 2, one can see that for the sequential two-layer catalysts, most of 1-PO was produced from hydrogenation of acrolein, which was generated when the reactant feed flow went through the H-β layer. Ni is one of the most frequently used metals for the hydrogenation of unsaturated aldehydes.40 However, a direct comparison between the reaction rates of glycerol dehydration on zeolites and that of acrolein hydrogenation on Ni catalysts is presently unavailable from the kinetic studies in the literature. In contrast to that, some hints can be obtained by comparing the results from two density functional theory studies by Jiao et al.41 and by Limtrakul et al.,42 respectively. Jiao et al. reported that hydrogenation of acrolein to produce propanal has an

was carried out on H-β, Ni/Al2O3 as well as the Al2O3 support. From the TPSR profiles (Figure 4) in the form of the temperature dependent mass spectroscopic signal, no signal was observed at positions of m/z =2 and of m/z = 90 in the temperature range examined. If a catalytic dehydrogenation process takes place, the products are expected to be H2 (molecular weight of 2) and glyceraldehyde or dihyroxylacetone (molecular weights of 90).32 Very weak signals at the positions of m/z = 56 (two-time dehydration product of glycerol) and m/z = 74 (first dehydration product of glycerol) were observed on both of Ni/Al2O3 and Al2O3. This indicated that the dehydration process may take place on Ni/Al2O3, although not obviously. Then the TPSR results were inclined to the “dehydration−hydrogenation” mechanism over the “dehydrogenation−dehydration−hydrogenation” mechanism. From the data of product selectivities obtained from the single layer Ni/Al2O3 (see the third column in Table 2) one may see that the secondary C−O bond cleavage seemed reluctant to take place, since the overall selectivity to the primary O removal reactions (producing 12-PDO and acetol) was ∼89%. The decrease of the LHSV from 7.06 to 3.53 led to an improved selectivity to 12-PDO by ∼20% and a decreased selectivity to acetol by ∼26% (Figure 5). This implied that 12-

Figure 5. LHSV dependent on glycerol conversion and product selectivities to 12-PDO and acetol for the single-layer Ni/Al2O3 catalyzed hydrogenolysis of glycerol. Temperature = 220 °C; pressure = 2 MPa; flow rate of glycerol solution = 0.2 mL/min; flow rate of H2 = 96 mL/min. 3349

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351

Energy & Fuels

■

energy of activation (EA) of 0.72 eV (69.4 kJ/mol). Further hydrogenation of propanal to produce propanol requires an EA of 1.33 eV (128.3 kJ/mol). In contrast to that Limtrakul et al. reported in their DFT study that the first dehydration of glycerol on zeolite H-ZSM-5 to produce 3-hydroxypropanal (HPA) requires an EA of 260 kJ/mol, and the dehydration of HPA to produce acrolein requires an EA of 164.4 kJ/mol. These theoretical findings show that Ni-catalyzed acrolein hydrogenation may be much easier to undergo than zeolite-catalyzed glycerol dehydration. They support our way of using catalysts, where a larger amount of acid sites in the zeolite layer was required than that of the exposed metal sites in the Ni catalyst layer. For example the amount of acid sites in H-β was 7.6 times larger than that of the exposed Ni atoms in Ni/Al2O3 with a same mass as H-β (see Table 1). However, from Table 2 it can be seen that not all of the 1-PO was produced from the hydrogenation of acrolein. This is because the selectivity to 1-PO on the two-layer catalysts was higher than the selectivity to acrolein from the H-β catalyzed dehydration of glycerol, and Ni/Al2O3 did not give acrolein. Previous reports12,22 showed the single-layer supported Ni catalyst can directly give 1-PO with a noticeable selectivity. After investigating on the role of the intermediates in the hydrogenolysis reaction,32 they proposed that 1-PO can be generated from “dehydration−hydrogenation” of 13-PDO, which is formed from the hydrogenation of 3-hydroxylpropanal. Interestingly 13-PDO was also obverted as a minor product in our system (Table 2). In addition, it is also possible that the hydrogenation of propanal as well as some unidentified liquid products may have minor contributions to the formation of 1PO. To briefly summarize the preceding results, the detailed reaction mechanism for the hydrogenolysis of glycerol on the single-layer Ni/Al2O3 catalyst is still not well understood in the present status, although the preliminary results showed consistence with a “primary dehydration−hydrogenation” mechanism. However, obviously the two-layer catalysts changed the reaction mechanism of hydrogenolysis compared to the case of one-layer catalyst. For the sequential two-layer catalysts, most of 1-PO came from the hydrogenation of acrolein that was produced from the two-time dehydration of glycerol. The results suggested that a “sequential two-time dehydration−hydrogenation” mechanism may make the main contribution to the final products.

Article

AUTHOR INFORMATION

Corresponding Authors

*Email: [email protected]. *Email: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Supports from the National Natural Science Foundation of China (21003159, 21306230), from the Natural Science Foundation of Shandong (ZR2012BQ020), from the Fund for Distinguished Young Scientists of Shandong Province (BS2013NJ008), and from a Research Grants Committee of Hong Kong grant (HKU-7048/11P) and Collaborative Research Fund HKU1/CRF/08 to D.L.P., are gratefully acknowledged.

■

REFERENCES

(1) Zhou, C.-H.; Beltramini, J. N.; Fan, Y.-X.; Lu, G. Q. Chem. Soc. Rev. 2008, 37, 527−549. (2) Peng, B.; Zhao, C.; Mejía-Centeno1, I.; Fuentes, G. A.; Jentys, A.; Lercher, J. A. Catal. Today 2012, 183, 3−9. (3) Wu, Z.; Mao, Y.; Song, M.; Yin, X.; Zhang, M. Catal. Commun. 2013, 32, 52−57. (4) Feng, Y.; Yin, H.; Shen, L.; Wang, A.; Shen, Y.; Jiang, T. Chem. Eng. Technol. 2013, 36, 73−82. (5) Gandarias, I.; Arias, P. L.; Fernandez, S. G.; Requies, J.; El Doukkali, M.; Güemez, M. B. Catal. Today 2012, 195, 22−31. (6) Guo, X.; Li, Y.; Song, W.; Shen, W. Catal. Lett. 2011, 141, 1458− 1463. (7) Yuan, Z.; Wang, L.; Wang, J.; Xia, S.; Chen, P.; Hou, Z.; Zheng, X. Appl. Catal., B 2011, 101, 431−440. (8) Kim, N. D.; Park, J. R.; Park, D. S.; Kwak, B. K.; Yi, J. Green Chem. 2011, 14, 2638−2646. (9) Kwak, B. K.; Park, D. S.; Yun, Y. S.; Yi, J. Catal. Commun. 2012, 24, 90−95. (10) Jiménez-Morales, I.; Vila, F.; Mariscal, R.; Jiménez-López, A. Appl. Catal., B 2012, 117−118, 253−259. (11) Zhu, S.; Gao, X.; Zhu, Y.; Zhu, Y.; Zheng, H.; Li, Y. J. Catal. 2013, 303, 70−79. (12) Huang, L.; Zhu, Y.-L; Zheng, H.-Y.; Li, Y.-W.; Zeng, Z.-Y. J. Chem. Technol. Biotechnol. 2008, 83, 1670−1675. (13) Zhu, S.; Qiu, Y.; Zhu, Y.; Hao, S.; Zheng, H.; Li, Y. Catal. Today 2013, 212, 120−126. (14) ten Dam, J.; Djanashvili, K.; Kapteijn, F.; Hanefeld, U. ChemCatChem. 2013, 5, 497−505. (15) Amada, Y.; Shinmi, Y.; Koso, S.; Kubot, T.; Nakagawa, Y.; Tomishige, K. Appl. Catal., B 2011, 105, 117−127. (16) Shinmi, Y.; Koso, S.; Kubota, T.; Nakagawa, Y.; Tomishige, K. Appl. Catal., B 2010, 94, 318−326. (17) Huang, L.; Zhu, Y.; Zheng, H.; Ding, G.; Li, Y. Catal. Lett. 2009, 131, 312−320. (18) Wang, K.; Hawley, M. C.; DeAthos, S. J. Ind. Eng. Chem. Res. 2003, 42, 2913−2923. (19) Zhu, S.; Gao, X.; Zhu, Y.; Zhu, Y.; Xiang, X.; Hu, C.; Li, Y. Appl. Catal., B 2013, 140−141, 60−67. (20) Zhu, S.; Zhu, Y.; Hao, S.; Zheng, H.; Mo, T.; Li, Y. Green Chem. 2012, 14, 2607−2616. (21) van Ryneveld, E.; Mahomed, A. S.; van Heerden, P. S.; Friedrich, H. B. Catal. Lett. 2011, 141, 958−967. (22) van Ryneveld, E.; Mahomed, A. S.; van Heerden, P. S.; Green, M. J.; Friedrich, H. B. Green Chem. 2011, 13, 1819−1827. (23) Ahmed Foskey, T. J.; Heinekey, D. M.; Goldberg, K. I. ACS Catal. 2012, 2, 1285−1289. (24) Auneau, F.; Delbecq, C. M. F.; Pinel, C.; Sautet, P. Chem.Eur. J. 2011, 17, 14288−14299.

4. CONCLUSION In summary, the significance of this work is 2-fold for upgrading glycerol. First, to best of our knowledge, we have shown one of the highest selectivities to 1-propanol using inexpensive nonnoble metal-based catalysts working with a fixed-bed reactor. Second, methodologically we report for the first time using a sequential two-layer catalytic system in a fixed-bed reactor for the hydrogenolysis of glycerol. In addition, the use of two-layer catalysts may make the hydrogenolysis of glycerol take place via a “sequential two-time dehydration−hydrogenation” mechanism. Obviously this paper also offers a new approach for hydrodeoxygation of biomass derived polyols, such as glucose, xylose etc. It is interesting to apply a similar two-layer catalytic system to the chemical transformation of these biomass resources. 3350

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351

Energy & Fuels

Article

(25) Wawrzetz, A.; Peng, B.; Hrabar, A.; Jentys, A.; Lemonidou, A. A.; Lercher, J. A. J. Catal. 2010, 269, 411−420. (26) Gandarias, I.; Arias, P. L.; Requies, J.; Guemez, M. B.; Fierro, J. L. G. Appl. Catal., B 2010, 97, 248−256. (27) Nakagawa, Y.; Ning, X.; Amada, Y.; Tomishige, K. Appl. Catal., A 2012, 433−434, 128−134. (28) Balaraju, M.; Rekha, V.; Sai Prasad, P. S.; Prabhavathi Devi, B. L. A.; Prasad, R. B. N.; Lingaiah, N. Appl. Catal., A 2009, 354, 82−87. (29) Miyazawa, T.; Kusunoki, Y.; Kunimori, K.; Tomishige, K. J. Catal. 2006, 240, 213−221. (30) Liu, B.; Chai, Y. M.; Wang, Y. J.; Zhang, T. T.; Liu, Y. Q.; Liu, C. G. Appl. Catal., A 2010, 388, 248−255. (31) Nakagawa, Y.; Tomishige, K. Catal. Sci. Technol. 2011, 1, 179− 190. (32) van Ryneveld, E.; Mahomed, A. S.; van Heerden, P. S.; Green, M. J.; Holzapfel, C.; Friedrich, H. B. Catal. Sci. Technol. 2014, 4, 832− 837. (33) Perosa, A.; Tundo, P. Ind. Eng. Chem. Res. 2005, 44, 8535−8537. (34) Zhao, J.; Yu, W.; Chen, C.; Miao, H.; Ma, H.; Xu, J. Catal. Lett. 2010, 134, 184−189. (35) Hang, J.; Chen, J. Chin. J. Catal. 2012, 33, 790−796. (36) Hu, J.; Liu, X.; Wang, B.; Pei, Y.; Qiao, M.; Fan, K. Chin. J. Catal. 2012, 33, 1266−1275. (37) Kim, Y. T.; Jung, K.-D.; Park, E. D. Microporous Mesoporous Mater. 2010, 131, 28−36. (38) Kim, Y. T.; Jung, K.-D.; Park, E. D. Appl. Catal., A 2011, 393, 275−287. (39) Gu, Y.; Cui, N.; Yu, Q.; Li, C.; Cui, Q. Appl. Catal., A 2012, 429−430, 9−16. (40) Mäki-Arvela, P.; Hájek, J.; Salmi, T.; Murzin, D. Y. Appl. Catal., A 2005, 292, 1−49. (41) Luo, Q.; Wang, T.; Beller, M.; Jiao, H. J. Phys. Chem. C 2013, 117, 12715−12724. (42) Kongpatpanich, K.; Nanok, T.; Boekfa, B.; Probste, M.; Limtrakul, J. Phys. Chem. Chem. Phys. 2011, 13, 6462−6470.

3351

dx.doi.org/10.1021/ef500147k | Energy Fuels 2014, 28, 3345−3351