Subscriber access provided by UCL Library Services
Article
Development of a Bimetallic Pd-Ni/HZSM-5 Catalyst for the Tandem Limonene Dehydrogenation and Fatty Acid Deoxygenation to Alkanes and Arenes for Use as Bio-jet Fuel Jingjing Zhang, and Chen Zhao ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b00520 • Publication Date (Web): 26 May 2016 Downloaded from http://pubs.acs.org on May 29, 2016
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 Catalysis 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 17
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 Catalysis
Development of a Bimetallic Pd-Ni/HZSM-5 Catalyst for the Tandem Limonene Dehydrogenation and Fatty Acid Deoxygenation to Alkanes and Arenes for Use as Bio-jet Fuel Jingjing Zhang, Chen Zhao* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
Supporting Information Placeholder
ABSTRACT: A tandem process involving the dehydroaromatization of the terpene limonene and the hydrodeoxygenation of stearic acid has been found to be efficiently catalyzed by Pd-Ni/HZSM-5. The process involves the generation of pcymene from terpene with concomitant formation of H2, which leads to the one-pot hydrodeoxygenation of stearic acid to C17 and C18 alkanes; these products can be used as kerosene additives for aviation fuel. Screening a wide range of catalysts, the bimetallic Pd-Ni/HZSM-5 catalyst is the most efficient, leading to quantitative conversion of stearic acid to alkanes in limonene at 280°C at a H2 pressure of 2 bar after 120 min. It has been found that single Ni or Pd catalysts lead to a poor conversion of stearic acid in limonene at a H2 pressure of 2 bar. The combination of physically mixed Pd- and Ni- sites onto different supports (Pd/HZSM-5 or Pd/C, and Ni/HZSM-5, Ni/HY or Ni/HBEA) leads to catalysts which show satisfactory conversion to p-cymene, but generally have very low stearic acid conversion rates. Directly incorporating Pd and Ni onto the HZSM-5 scaffold forms the Pd-Ni/HZSM-5 bimetallic catalyst, which demonstrates a remarkable improvement in stearic acid conversion to C17 and C18 alkane products. In this catalyst system, Pd is shown to be the active site for limonene dehydroaromatization, while Ni catalyzes the separate stearic acid hydrodeoxygenation. The acidity of HZSM-5 (modified by the Si/Al ratios) influences the performance of the Pd-Ni bimetallic catalyst, and the proper pore size of HZSM-5 prevents side-reactions from limonene condensation. In addition, the alloyed Pd-Ni nanoparticles (optimized with higher Pd/Ni ratios) on the external surface of HZSM-5 enhance internal H· transfer between the two metals, thereby increasing the rate of stearic acid hydrodeoxygenation. The catalytic compatibility of the Pd and Ni sites, coupled with the proper pore sizes and optimized level of Brönsted acid sites in HZSM-5, result in the design of a multifunctional catalyst that is efficient for both steps of the cascade reaction. Hence, a bimetallic 5%Pd-10%Ni/HZSM-5 catalyst has been developed that allows for a simple, safe, and green approach for producing aromatics and hydrocarbon components present in bio-jet fuel derived from two biomass resources. KEYWORDS: terpene dehydroaromatization, stearic acid HDO, green biofuels, bimetallic catalysis, cascade reactions
INTRODUCTION The selective deoxygenation of lipids and fatty acids, which are considered to be potentially promising sustainable energy sources, to form “ready-to-use” hydrocarbons has been identified as one of the most challenging aspects in the conversion of biomass to biofuels.1-3 However, an approach for the conversion of oxygenated products in biomass into usable hydrocarbons via energy-efficient processes is highly desirable and requires further research.4-6 Sulfided CoMo and NiMo catalysts are frequently used for the conversion of lipids to biofuels by hydrodeoxygenation (HDO) in the presence of H2.7-10 The newly developed second generation sulfur-free metal catalysts include the noble metals Pd11-14, Pt15-17, and Ni18-24, Fe25, WC2/WO326,27. These catalysts can be employed for
the generation of green hydrocarbons, since they show considerably high activities and stabilities for lipid and fatty acid hydrodeoxygenation. However, HDO processes consume large amounts of H2 (~ at least a 3–4 molar ratio of H2/reactant), together with high pressures (~40 bar) at ambient temperature.18-22 These high H2 pressures require the use of expensive specialized equipment and, more importantly, are associated with potential serious safety hazards and problems with recycling H2 in scaled-up pilot tests. Therefore, there is a pressing need to develop methods to efficiently deoxygenate lipids and fatty acids at low H2 pressure conditions or in the absence of H2. In the absence of H2, zeolite catalysts, such as HZSM-5 and HUSY, can deoxygenate lipids via unselective catalytic cracking pathways,28-32 but this technique produces few liquid hydrocarbon products due to large amounts of gas (C1-C4 alkanes, CO, CO2, and CH4) and
ACS Paragon Plus Environment
ACS Catalysis
We envisaged the development of a catalytic system that worked in the absence of H2 and avoided the problems associated with the aforementioned catalysts. In addition, the catalyst should simultaneously form aromatics and hydrocarbons as part of the catalytic process. Therefore, the co-activation of cyclic compounds and lipids was considered to be a promising strategy for the production of bio-jet fuel with a fraction of aromatic hydrocarbons.38 Limonene, a C10 terpene natural product derived from orange peel waste, forms the aromatic pcymene and H2 through dehydroaromatization.39-42 The released H2 is then used for the hydrodeoxygenation of lipids or stearic acid for the generation of alkanes. In the present work, we present the results from further studies on the production of bio-jet fuel components from the coactivation of limonene and stearic acid. The compatibility of Pd and Ni as a bimetallic catalyst, and the effect of acidity and pore size of the zeolite scaffold (metal catalyst support) of various metal/zeolite combinations on catalytic activity was extensively investigated to develop an efficient catalyst system for the one-pot two-reaction process comprising limonene dehydroaromatization and stearic acid hydrodeoxygenation steps. In addition, an indepth characterization of the bimetallic Pd-Ni/HZSM-5 catalyst was performed to elucidate the relationship between catalyst properties and catalytic performance.
RESULTS AND DISCUSSION Characterization of Bimetallic Centers and Acidic Sites in the Selected Pd-Ni/HZSM-5 Catalyst. In this study, we used samples of parent HZSM-5 (SiO2/Al2O3 ratio: 300, as detected by inductively coupled plasmaatomic emission spectroscopy (ICP–AES)) and Pd and/or Ni incorporated into HZSM-5. N2 adsorption/desorption data indicated that parent HZSM-5 had a specific surface area of 438 m2 g−1, a pore volume of 0.57 cm3 g−1 and a pore width of 52 Å. After introduction of 20 wt.% Ni or 1 wt.% Pd to HZSM-5, the specific surface area of the zeolite decreased by 20%, while the pore volume and width
a.
HZSM-5 Pd/HZSM-5 Pd-Ni/HZSM-5
b.
400
400
300
300 200 100
200
0.86 0.88 0.90 0.92 0.94 0.96 0.98 1.00
P/P0
100 0 0.0
0.2
0.4
0.6
0.8
1.0
P/P0
c. BAS Absorbance (a.u)
coke formed. Alternatively, Pd/C can also exclusively decarboxylate fatty acids under He gas,11 although this process suffers from poor catalyst stability and results in lower yields compared to conventional deoxygenation reactions carried out in the presence of H2. Apart from problems associated with these catalysts, their use does not result in formation of aromatic components which are required in aviation jet fuel (max: 25 vol%) to provide a sufficient energy content. These components can be formed by aromatization of lighter alkanes (byproducts of triglyceride HDO) in a reactor at 600–800°C using Ga- or Zn- doped HZSM-5 catalysts.33-37 However, the energy intensive conditions, such as high working temperatures and the expensive reactor equipment required render the aromatization economically unfeasible. Hence, it is desirable to find solutions to these challenges by finding efficient and more ecologically friendly approaches for the formation of biofuels.
Vads(cm3/g)
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 17
HZSM-5
LAS
Pd/HZSM-5
Pd-Ni/HZSM-5
1580 1560 1540 1520 1500 1480 1460 1440 Wavenumber (cm-1)
Figure 1. Characterization of HZSM-5(300), 1%Pd/HZMS5(300), 5%Pd-10%Ni/HZSM-5(300) with (a) N2 adsorptiondesorption isotherms, (b) the inset shows P/P0 = 0.8–1.0 for details; (c) IR spectra of adsorbed pyridine.
underwent only minimal changes implying that metal introduction leaves the zeolite pore structure essentially unchanged (Figures 1a–1b, Table S1a). In addition, the specific surface area and pore volume of 5 wt.%Pd-10 wt.%Ni/HZSM-5 (300) was 348 m2g−1 and 0.44 cm3 g−1, respectively. The micropore surface area and micropore volume of parent HZSM-5 (300) was 302 m2g−1 and 0.21 cm3 g−1, and after metal (Ni or/and Pd) incorporation, the micropore surface areas were decreased by ca. 16%, and the micropore volumes were lowered by ca. 43% (Table S1a). The decreased micropore surface areas and volumes is probably due to the presence of small metal particles in the micropores. The concentration of acidic sites was elucidated by the IR spectra of adsorbed pyridine (Figure 1c), which demonstrated that the 5 wt.%Pd-10 wt.%Ni/HZSM-5 (300) catalyst contained 0.003 mmol·g−1 of Brönsted acid sites (BAS) and 0.003 mmol·g−1 of Lewis acid sites (LAS). In comparison, BAS and LAS for parent HZSM-5 (300) was determined to be 0.017 and 0.0007 mmol·g−1, respectively. The loss of BAS sites suggested that impregnation with 5% Pd-10%Ni exchanged a large part of the protons of BAS sites within HZSM-5 pore.43 The bimetallic properties of the selected 5 wt.%Pd-10 wt.%Ni/HZSM-5 (300) catalyst were further characterized. The X-ray powder diffraction (XRD) patterns (Figure 2a) suggested that PdNi particles (nominal composition of 5 wt.%Pd-10 wt.%Ni/HZSM-5)
ACS Paragon Plus Environment
Page 3 of 17
contained a mixture of Ni (200) face-centered cubic, and Ni (111) face centered cubic phases (48% and 52%, respectively); a small peak corresponding to the presence of a Pd-Ni alloy at a peak of ~42.5° was also detected in the XRD pattern. X-ray photoelectron spectroscopy (XPS) spectra (Figure 2b–2c) revealed the Pd 3d and Ni 2p regions of the 5 wt.% Pd-10 wt.% Ni/HZSM-5 (300) catalyst, where the Pd 3d3/2 and 3d5/2 peaks were denoted by 339.5 eV and 334.1 eV, respectively. The peaks of Ni 2p1/2 and 2p3/2 were assigned to 877.6, 871.4 and 859.5, 852.8 eV, respectively. The Pd and Ni peak shifts, in comparison to Pd/HZSM-5 (300) and Ni/HZSM-5 (300) (Figure S1), were caused by the slight charge transfer between Ni and Pd, implying that the electronic structure of Ni and Pd was altered when they were alloyed together.
a.
Pd (111) Pd-Ni alloy
Intensity (a.u.)
Ni (111) Ni (200)
co-impregnated onto HZSM-5, newly-formed smaller particles (ca. 20 nm, probably Pd-Ni nanoclusters) appeared surrounding the HZSM-5 particle (Figure S2). This demonstrates that parent HZSM-5, 1 wt.% Pd/HZSM5 (300) and 5 wt.%Pd-10 wt.%Ni/HZSM-5 (300) formed via the impregnation method all show a distinct round particle shape with sizes of around 250 nm. The deposition-precipitation (DP) method generated ribbon shaped Ni nanoclusters (loading: 20 wt.%) covering the HZSM-5 support. The particle size of Pd-Ni on the external surface of the zeolite HZSM-5 was 8.6 ± 2.0 nm, as determined from transmission electron microscopy (TEM) imaging (Figure 3a). The dispersion of Pd-Ni metal particles was 18.6%, as calculated by the measurement of CO chemisorption.
HZSM-5
Pd/HZSM-5
Pd-Ni/HZSM-5
10
20
b.
30 40 50 2 θ (degree)
60
70
334.1 eV
Intensity ( a.u. )
339.5 eV
346
344
Pd 3d3/2
Pd 3d5/2
342 340 338 336 Binding Energy ( eV )
334
c. Intensity ( a.u. )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
332
852.8 eV 877.6 eV 871.4 eV
Ni 2p1/2
880
859.5 eV
Ni 2p3/2
870 860 Binding Energy ( eV )
850
Figure 2. (a) XRD patterns of HZSM-5 (300), 1%Pd/HZSM-5 (300), 5%Pd-10%Ni/HZSM-5(300). Characterization of 5%Pd10%Ni/HZSM-5(300) with (b)Pd 3d XPS spectra, (c) Ni 2p XPS spectra.
Based on scanning electron microscope (SEM) imaging, when Pd (loading: 5 wt.%) and Ni (loading: 10 wt.%) was
Figure 3. Characterization of 5%Pd-10%Ni/HZSM-5 (300) with (a) TEM image and particle size distribution, (b) HRTEM image, (c) HAADF-STEM image, two dimensional EELS mapping images of (d) Ni and (e) Pd, (f) EELS line scan, (g) SEM-EDX profile.
ACS Paragon Plus Environment
ACS Catalysis
Page 4 of 17 a
Table 1. Conversion of stearic acid in limonene with Pd- and/or Ni- supported catalysts.
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
Limonene Dehydroaromatization
En try
1
Catalyst
Conv. (%)
A
B
C
b
D
Conv. (%)
100
29
65
4
10% Pd/C
d
100
31
65
8
3
10% Pd/C
e
100
28
68
13
4 5 6
1% Pd/SiO2 1% Pd/ASA 1% Pd/HZSM-5 (450)
100 100 83
31 28 21
2 2 2
65 66 54
7 8 9
20% Ni/HBEA (20) 20% Ni/HY (30) 20% Ni/HZSM-5 (300)
100 100 89
28 21 14
4
10 11 12
10% Pd/C + 20% Ni/HBEA (20) f 10% Pd/C + 20% Ni/HY (30) f 10% Pd/C + 20% Ni/HZSM-5(300)
100 100 98
13
1% Pd/HZSM-5 (300), 260°C
100
14
1% Pd/HZSM-5 (300), 280°C
100
26
15
1% Pd/HZSM-5 (300), 300°C
100
27
2
10% Pd/C
Yield (C%)
Stearic Acid HDO
f
28
6
51 58 66
31 31 30
65 65 64
4
66
1 3 6
5 7 9
10 1
34 32 7 28 6 11
C17
Ester 4
17
3
5
20
7
5
26
5 7 7
15 16 16
34 32 5
16 16 22
5 2 1
16 19 16
2
2 5
20
71
26
23
1
68
69
61
2
16
1%Pd/HZSM-5 (300) + 20%Ni/Hβ(20), 260°C
100
5
55
44
21
17
1%Pd/HZSM-5 (300) + 20%Ni/HY(30), 260°C
100
32
65
29
15
24
C18
18 4 10 19
1
c
P (bar)
Yield (C%)
16
8
1
23 3
30
23
16
6
16
18
Pd/HZSM-5 (300) + Ni/HZSM-5 (300), 260°C
100
28
68
46
27
18
1
18
19
Pd/HZSM-5 (300) + Ni/HZSM-5 (300), 280°C
100
27
67
71
47
20
4
25
20
Pd/HZSM-5 (300) + Ni/HZSM-5 (300), 300°C
100
27
65
88
55
15
18
36
21
Pd/HZSM-5 (300) + Ni/HZSM-5 (300), 320°C
100
29
68
100
61
30
9
34
a
General conditions: 1.0 g stearic acid, 50 mL limonene, 0.2 g supported Pd (loading: 1 wt.%, prepared by impregnation method), b 0.2 g 20 wt.% Ni catalysts (prepared by DP method), 260 °C, 2 bar H2 and 6 bar N2, 120 min, stirring at 650 rpm. The additional c products contain cyclic ring-opening and limonene condensation products. Pressure measured for reactions lasting 120 min at d e f working temperature. 280°C. 300°C. 0.2 g Pd/C and 0.2 g Ni based catalysts.
In order to assess the structural properties of Pd, Ni, Pd-Ni particles, high-resolution (HR) TEM imaging was utilized (Figure 3b). The HRTEM image revealed that PdNi was of high crystallinity and was composed of Pd-Ni alloy facets with a lattice distance of 0.21 nm. Single- or twin-crystallinity particles contained exposed Ni (111), Ni (200) and Pd (111), which was in agreement with XRD patterns (Figure 2a). SEM-mapping spectra (Figure S3) further revealed that the metallic nanoparticles were composed of dispersed Ni and Pd and alloyed Pd-Ni nanoparticles. A high angle annular dark field scanning transmission electron microscope (HAADF-STEM) image (Figure 3c) indicated that Pd-Ni nanoparticles were dispersed throughout the HZSM-5 support. Electron energy-loss spectroscopy (EELS) mappings of the selected 5%Pd-10%Ni/HZSM-5 (300) catalyst were operated with Ni (L-edge, 855 eV) and Pd (M-edge, 2122 eV) (Figures 3d–
3e). The plotted Pd and Ni element images also demonstrated that dispersed Pd and Ni and alloy Pd-Ni nanoparticles were loaded onto the external surface of HZSM-5. The scanning transmission electron microscopy STEM-EELS line scan profile of the 5%Pd-10%Ni/HZSM-5 (300) catalyst (Figure 3f) showed the relative distributions of Pd and Ni components in a single representative crystal (Figure 3c), illustrating that Pd and Ni atoms displayed typical alloy structure. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis (Figure 3g) indicated that the nanoparticles contained 1.04 atom% Pd and 3.33 atom% Ni, confirming the formation of bimetallic Pd-Ni nanoparticles with nominal composition (Pd0.22Ni0.78). Catalyst Screen. The green and energy efficient route for stearic acid hydrodeoxygenation in the presence of limonene can be summarized by two separate processes:
ACS Paragon Plus Environment
Page 5 of 17
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 Catalysis
1) limonene dehydroaromatization to p-cymene with concomitant formation of H2 and 2) stearic acid hydrodeoxygenation to alkanes aided with the in situ generated H2. The first catalyst system that was tested for this dehydroaromatization/hydrodeoxygenation cascade reaction sequence was Pd/C at 260°C. In order to maintain the high activity of the Pd site,39 H2 at low pressure (2 bar) and N2 (6 bar) were introduced into the reactor. Pd/C (10 wt.% loading) showed high activity for limonene dehydroaromatization to p-cymene (65% yield), but proved an inefficient catalyst for stearic acid hydrodeoxygenation because of the low H2 pressure (17 bar pressure at working condition), resulting in a conversion of only 4% after 120 min (Table 1, Entry 1). Even after increasing the temperature from 260 to 300°C, Pd/C only attained a stearic acid conversion of 13 %, with p-cymene being afforded in 68 % yield (Table 1, Entries 2– 3). Other Pd-supported catalysts on SiO2, amorphous silica alumina (ASA), and HZSM-5 (SiO2/Al2O3 ratio: 450) all successfully catalyzed the dehydroaromatization of limonene (yield ≥ 54%), but were poor candidates for the hydrodeoxygenation of stearic acid (conversion ≤ 9%) (Table 1, Entries 4–6). While the active Ni catalysts (Ni/HBEA (SiO2/Al2O3 ratio: 20), Ni/HY (SiO2/Al2O3 ratio: 300), Ni/HZSM-5 (SiO2/Al2O3 ratio: 300)) exhibited high activity for stearic acid hydrodeoxygenation in dodecane under a H2 pressure of 40 bar,18-24 these catalysts still performed poorly in the desired cascade reaction (Table 1, Entries 7– 9) yielding less than 30% ester and producing large amounts of undesired limonene condensation products after 120 min. These results suggested that a catalyst system comprising of individual -Pd or -Ni sites is ineffective for the required concomitant dehydroaromatization and hydrodeoxygenation steps, even under a H2 pressure of 2 bar with the Pd/C catalyst. In order to synergistically combine the catalytic capacities of Pd and Ni, we decided to screen catalysts containing physical mixtures of Pd/C and Ni catalysts (Table 1, Entries 10–12). Surprisingly, these mixtures exhibited even poorer catalytic performance, possibly as a result of difficulties in the compatibility of the catalysts for activating H2, adsorbing and desorbing reactants, intermediates and products in a one-pot system. This suggests that compatibility would require use of a proper scaffold in order to combine the abilities of the separate catalysts, not only for dispersing properly the bimetallic nanoclusters, but also for carrying out the two separate dehydrogenation and hydrogenation reactions in separate Pd and Ni sites. Searching for a scaffold to use with the Pd/Ni bimetallic catalyst system, we tested a Pd/zeolite system to use as a model, 1 wt.% Pd/HZSM-5 (SiO2/Al2O3 ratio: 300), which showed a slightly higher stearic acid conversion of 20 % and an unchanged p-cymene yield of 70 % at 260°C, compared to the 4 % conversion achieved with Pd/C (10 wt.% loading) catalyst (vide supra). Notably, close to 100% selectivity was achieved for C17 alkanes after 120 min (Table 1, Entry 13). Increasing the temperature up to
300°C, the C17 yield gradually increased to 69 %, and pcymene was formed in 68 % yield (Table 1, Entries 14-15), demonstrating this system as a promising candidate for catalyzing the two steps of the cascade reaction sequence in a one-pot system. With a catalyst system giving moderate yields of hydrogenated and dehydrogenated products at hand, we envisaged incorporating the Ni sites of Ni/HBEA or Ni/HY with Pd/HZSM-5; with this system conversion was slightly enhanced at 260°C, but produced a high yield of ester (Table 1, Entries 16–17). The combination of HZSM-5 (300) supported Ni/HZSM-5 with Pd/HZSM-5 at 260°C, sharply increased the yields of C17 and C18 to 27% and 18%, respectively. Temperature increases of 20°C intervals from 260 to 320°C gradually increased the conversion of stearic acid from 46% to 100% (Table 1, Entries 18–21), implying that HZSM-5 (300) is an adequate and compatible support for the separate Pd and Ni sites for the one-pot concomitant limonene dehydroaromatization and stearic acid hydrodeoxygenation. However, with individual Pd/HZSM-5 or Ni/HZSM-5 catalytic systems, stearic acid only attained conversions of 26% and 57% respectively in limonene at 280°C at a H2 pressure of 2 bar and N2 pressure of 6 bar (Figure S4). Encouraged by these results, our next attempt involved using a bimetallic 5%Pd10%Ni/HZSM-5 catalyst. It should be noted that the bimetallic 5%Pd-10%Ni/HZSM-5 catalyst is shown to be inactive for catalyzing stearic acid HDO in presence of 2 bar H2 at 280°C in dodecane. We were gratified to find that it resulted in 100% conversion of stearic acid to alkanes via hydrodeoxygenation (92% C17 and 8% C18), and in a 67% yield of p-cymene formed from limonene dehydroaromatization after 120 min (Figure S4; Table 2, Entry 3). This suggests that the HZSM-5 scaffold favors internal H· transfer from limonene to stearic acid among the dispersed Pd and Ni centers. In addition, the inactivity of stearic acid with 5%Pd-10%Ni/HZSM-5 in presence of introduced 2 bar H2 and 6 bar N2 in the dodecane solvent may be resulted from the mass transfer limitation in the gas-liquid-solid three phases. In comparison to Pd-Ni/HZSM-5, bimetallic Pd-Cu/HZSN-5 and Pd-Co/HZSM-5 performed poorly, with low stearic acid conversion rates leading exclusively to the formation of esters in 22% and 34%, respectively (Table 2, Entries 4– 5). Next, we evaluated the supportive effects of various scaffolds (HBEA, HY, HZSM-5, Silicalite-1, ASA, ZrO2, activated carbon, and nano-tube carbon) on the activity of the Pd-Ni bimetallic catalysts (Table 2, Entries 3, 6–14). In general, Pd-Ni nanoclusters supported on more acidic scaffolds (H-Zeolite and ASA) had higher conversion rates (13–45%) than those on neutral materials like ZrO2 and carbon (5–15% conversion rate). Catalyzed by three ASA supports with SiO2/Al2O3 ratios of (90:10, 80:20, 95:5) loaded Pd-Ni particles, the conversion attained 25%, 27%, and 45%, respectively. This suggests that the less acidic ASA support facilitates the coupling reaction. However, it was found that the large pores of HBEA, HY and open mesoporous ASA favored formation of limonene condensation products (Figure S5), and thus led to low
ACS Paragon Plus Environment
ACS Catalysis
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 6 of 17
Table 2. Conversion of stearic acid in limonene with supported mono- and bi-metallic Pd-, Ni- catalysts. Limonene Dehydrogenation Entry
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Catalyst
1% Pd/HZSM-5 20% Ni/HZSM-5 5%Pd-10%Ni/HZSM-5 5%Pd-10%Cu/HZSM-5 5%Pd-10%Co/HZSM-5 5%Pd-10%Ni/HBEA (20) 5%Pd-10%Ni/HY (30) 5%Pd-10%Ni/Silicalite-1 5%Pd-10%Ni/ASA (90:10) 5%Pd-10%Ni/ASA (80:20) 5%Pd-10%Ni/ASA (95:5) 5%Pd-10%Ni/ZrO2 5%Pd-10%Ni/C 5%Pd-10%Ni/Cnano tube
Conv. (%) 100 100 100 89 83 100 100 100 100 100 100 100 100 100
Yield (C%) A
B
C
18
26 26 8
71 69 67 22 52 62 64 68 42 58 70 74 71 66
10 28 19 24 30
21
7 9 27 1 3 27 23 25 10
a
Stearic Acid HDO
b
D
Conv. (%)
57 17
1
26 57 100 22 34 13 43 80 25 27 45 11 5 15
Yield (C%)
c
b
C17
C18
Ester
23 19 92
1 37 8
1 1
2 7 75
24 6 2 1
22 34 11 34 1
2
25 27 16 4 3 14
P (bar) 23 22 22 21 22 16 20 21 22 22 26 24 19
a
General conditions: 1.0 g stearic acid, 50 mL limonene, 0.2 g supported 5%Pd-10%Ni (Co, Cu) catalysts (synthesized by coimpregnation method), 280°C, 120 min, 2 bar H2 and 6 bar N2, stirring at 650 rpm. b A: Partial hydrogenation products, B: Full hydrogenation products, C: Dehydroaromatization products, D: Isomerization products. The additional products contain cyclic ring-opening and limonene condensation products. c Pressure measured for reactions lasting 120 min at working temperature.
ensured that only the desired tandem limonene dehydroaromatization and stearic acid hydrodeoxygenation reactions took place, to the exclusion of unwanted side reactions. The 5%Pd-10%Ni/Silicalite-1 catalyst led to 80% stearic acid conversion together with 93% C17 and 1% C18 alkane yields in limonene (Table 2, Entry 8). The much lower activity on Silicalite-1 compared to HZSM-5 (300) highlights the importance of BAS onto the acidic H-MFI.
Figure 4. (a) Chemical 3D structure of representative limonene condensation product; channel structures of (b) HZSM5 and (c) HBeta.
yields of stearic acid HDO products (C17 alkane yields of 2%, 7%, and 24%, respectively). It was demonstrated that the Brönsted acid sites (BAS) of HZSM-5 and HBEA were located in the 10-ring and 12-ring containing pores, respectively, while the BAS of the ASA scaffold were situated on the external surface of the open pores.47,48 The calculated diameter for the limonene condensation product was ~5.8–7.2 Å (Figure 4), while the pore sizes of HBEA and HZSM-5 were 5.6–7.7 Å and 5.1–5.6 Å, respectively. The larger pore sizes in ASA and HBEA facilitated access of limonene to the BAS of the pores, and facilitated the subsequent expulsion of limonene condensation products from the pores. Conversely, the smaller pore size (5.1–5.6 Å) and the appropriate acidity of HZSM-5 (SiO2/Al2O3 ratio: 300, BAS: 0.017 mmol·g−1, LAS: 0.0007 mmol·g−1)
Figure 5. Comparison of stearic acid conversion rates over various Pd-, and Ni- based catalysts. General conditions: 1.0 g stearic acid, 50 mL limonene, 0.2 g catalyst, 280°C, 2 bar H2 and 6 bar N2, 120 min, stirring at 650 rpm.
ACS Paragon Plus Environment
The overall catalyst screen for stearic acid hydrodeoxygenation in limonene is summarized and depicted in Figure 5. Through comparison of the investigated parameters, it can be concluded that separate Pd or Ni catalysts, regardless of the scaffold employed, result in low conversion rates of stearic acid in limonene under a H2 pressure of 2 bar, attaining a low conversion rate below 3 mmol·g−1·h−1 (Figure 5, A and B). The combination of physically mixed Pd- and Ni- sites onto various different supports (carbon and zeolites) was also inefficient with rates < 4.0 mmol·g−1·h−1 (Figure 5, C and D), even though it has been demonstrated that Pd acts as the active center for limonene dehydrogenation,39-42 and Ni functions as an efficient catalyst for stearic acid hydrogenation in presence of H2.18-24 In comparison, a unified combination of Pd/HZSM-5 and Ni/HZSM-5 enhances the rate up to nearly 5.0 mmol·g−1·h−1 (Figure S4). An optimal conversion rate was not achieved until both Ni and Pd sites were co-introduced onto HZSM-5 to form the bimetallic catalyst Pd-Ni/HZSM-5, attaining a rate of 8.8 mmol·g−1·h−1. In contrast, all the other tested supports (carbon, zirconium oxide, and large pore zeolite materials (HBEA and HY)) that were used to scaffold Pd-Ni bimetallic nanoclusters, led to relatively low activities (< 4.5 mmol·g−1·h−1; Figure 5, E), moreover limonene condensation products were formed in large amounts. In addition, the importance of Ni to catalyze the hydrodeoxygenation step was demonstrated by the low conversion rates of bimetallic Pd-Co and Pd-Cu catalysts supported on HZSM-5 (Figure 5, F), which were very similar to those of Pd/HZSM-5 (Figure 5, A-5). The high activity of Pd-Ni/HZSM-5 (Figure 5, G) for limonenefacilitated stearic acid HDO can be attributed to the appropriate pore sizes and well organized structure of HZSM-5, where Brönsted acidic sites are majorly present in the inner pores. In addition, HZSM-5 offers a high surface available for dispersal of the Pd, Ni, and alloy PdNi nanoclusters. Effect of Temperature on Stearic Acid Conversion in Limonene. The effect of temperature ranging from 260 to 320°C was investigated with the Pd-Ni/HZSM-5 catalyst (Figure 6). Increasing the temperature from 260 to 280°C increased the alkane yield from 47% to 100%, while the yield of p-cymene remained the same at 67%. Varying the temperature from 260 to 320°C did not affect the pattern in the proportions of the various products formed, suggesting that the reaction routes for limonene isomerization and dehydroaromatization and stearic acid conversion to C17 alkanes via initially formed esters followed by sequential decarbonylation of C18 fatty alcohol remained unchanged (Figure S6, Scheme 1). However, increasing the temperature to 280, 300, and 320°C
gradually increased the formation of toluene (formed from C-C cleavage of p-cymene) to 1%, 11%, and 14% yields, respectively. Hence, in order to obtain maximal pcymene and alkane yields, 280°C was chosen as the optimal temperature (Figure 6). From the obtained reaction rates as a function of temperature (from 260 to 320°C, Table S2), we obtained the Arrhenius plot in Figure 7. Based on the Arrhenius equation (ln k = ln A – Ea/RT), the apparent activation energy was calculated to be 93.8 kJmol−1. a. limonene dehydro-aromatization Conv. 100
100
p-Cymene Yield 100
Toluene Yield
100
100
80
C(%)
Based on these results, it can be concluded that the pore size and the presence of suitable BAS are important fators for determining the optimal scaffold for the cascade reaction.
67
60
68
67 57
40
20 14
11
0
0
260 °C
280 °C
1 1
300 °C
320 °C
b. Stearic Acid HDO Conv. 100
C17 + C18 Yield 100
100
100
100
100
99
80
C(%)
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 Catalysis
60 49
40
47
20
0
260 °C
280 °C
300 °C
320 °C
Figure 6. Liquid product distributions on stearic acid conversion in limonene as a function of temperature. General conditions: 1.0 g stearic acid, 50 mL limonene, 0.2 g 5%Pd10%Ni/HZSM-5 (300), 280°C, 2 bar H2 and 6 bar N2, 120 min, stirring at 650 rpm.
10 Ln rate ( mmol·g-1·h-1)
Page 7 of 17
8 6 y = -11.28x + 26.975
4 Ea = 93.8 kJ/mol
2 0 1.70
1.75
1.80
1.85
1000/T ( 1/K )
Figure 7. Arrhenius plot of the change in stearic acid conversion rate over the selected temperature range (from 260 to 320°C). Reaction conditions are displayed in Figure 6.
ACS Paragon Plus Environment
ACS Catalysis Impact of the SiO2/Al2O3 ratio in HZSM-5 on Stearic Acid Conversion in Limonene. The acidity of the HZSM-5 scaffold was adjusted by introducing different SiO2/Al2O3 ratios (100 to 400) during HSZM-5 synthesis and the impact of acidity on stearic acid conversion in limonene at 280°C at a H2 pressure of 2 bar was evaluated. The acidic properties of 5%Pd-10%Ni/HZSM-5 with increasing ratios of SiO2/Al2O3 were analyzed by IR with the adsorption/desorption of pyridine (Figure 8a). As expected, both the concentration of BAS (0.005, 0.005, 0.003, and 0.002 mmol·g−1) and LAS (0.013, 0.004, 0.003, and 0.003 mmol·g−1) decreased as the SiO2/Al2O3 ratios increased from 100 to 400. In addition, 5%Pd10%Ni/Silicalite-1 showed no BAS or LAS site.
highlighting the role of BAS and LAS in the reaction mechanism of stearic acid HDO leading to alkanes in the Pd-Ni bimetallic catalyst. In accordance with these results demonstrating that subtle changes in zeolite Si/Al ratios result in variations in reactivity, suggesting that the changes of acid sites may tailor the electronic structures and capabilities of supported metals. It has been reported that metal-support interaction can influence the activity of zeolite-supported metal catalysts in hydrogenation and hydrogenolysis reactions.44-45 Since 5%Pd-10%Ni/HZSM-5 (300) offered quantitative stearic acid conversion and formed C17 and C18 alkanes in a high yield of 83% and 17% respectively, this catalyst system was selected for further investigation (Figure 9).
LAS
a.
p-Cymene Yield C17 Yield
100
Pd-Ni/HZSM-5 (100)
Conv. / Yield ( C% )
Absorbance ( a.u. )
BAS
Pd-Ni/HZSM-5 (200) Pd-Ni/HZSM-5 (300) Pd-Ni/HZSM-5 (400) Pd-Ni/silicalite-1 1580
1560
1540
1520
1500
1480
1460
Stearic acid Conv. C18 Yield
80 60 40 20
1440
-1
Wavenumber ( cm )
b.
Ni (111) Ni (200)
0 Pd (111) Pd-Ni alloy
Pd-Ni/HZSM-5 ( 100 )
Intensity ( a.u. )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 17
Pd-Ni/HZSM-5 ( 200 )
Pd-Ni/HZSM-5 ( 300 )
Pd-Ni/HZSM-5 ( 400 ) Pd-Ni/silicalite-1
10
20
30
40
50
60
70
2 θ ( degree )
Figure 8. (a) IR spectra of absorbed pyridine and (b) XRD patterns on various 5%Pd-10%Ni/HZSM-5 with SiO2/Al2O3 ratios of HZSM-5 ranging from 100 to 400.
XRD analysis (Figure 8b) indicated that the Pd-Ni particle sizes were not altered by the different Si/Al ratios, as calculated by the Scherrer equation. In general, the presence of BAS and LAS is essential for limonene isomerization and dehydroaromatization, as well as for stearic acid HDO. The p-cymene yield was not affected by changing the concentration of acidic sites; stearic acid conversion remained 100% with 5%Pd-10%Ni/HZSM-5 (200) and 5%Pd-10%Ni/HZSM-5 (300), but the lowest and highest ratios (100 and 400) showed an adverse effect on stearic acid conversion, decreasing by about 10% in both cases (Figure 9). However, acidic site concentration had a more significant effect on the yield of the C17 alkane,
100
200 300 400 silicalite-1 SiO2/Al2O3 molar ratio
Figure 9. Stearic acid conversion in limonene over 5%Pd10%Ni/HZSM-5 catalysts with different SiO2/Al2O3 molar ratios of HZSM-5. Reaction condition: 1.0 g stearic acid, 50 mL limonene, 0.2 g Pd-Ni/HZSM-5, 280°C, 2 bar H2 and 6 bar N2, 120 min, stirring at 650 rpm. Impact of Pd-Ni Weight Ratios on Stearic Acid Conversion in Limonene. The next step in the optimization of the Pd-Ni/HZSM-5 catalyst involved studying the impact of the Pd-Ni weight ratios (Pd/Ni wt.% from 0.5/10 t0 5/10) together with 5%Pd/HZSM-5 and 10% Ni/HZSM-5; from these studies we attempted to ascertain how changing the Pd/Ni molar ratio would affect the rate of the dehydrogenation/hydrogenation steps in the cascade reaction. The powder X-ray diffraction patterns suggested that the Pd-Ni/HZSM-5 (300) catalyst with different Pd/Ni ratios contained a mixture of single Pd and Ni particles (similar to those on individual 5%Pd/HZSM-5 and 10%Ni/HZSM-5), and a Pd-Ni alloy (Figure 10). The peak located at a 2ɵ value of ~42.5° was assigned to the Pd-Ni alloy phase,46 and this peak became more prominent as Pd/Ni ratios rose from 0.5/10 to 5/10, indicating that the incorporation of Pd precursor into HZSM-5 as a Pd-Ni alloy is facilitated with larger Pd-Ni ratios. Previously, it was observed that individual Pd and Ni particles on HZSM-5 leads to a low conversion of stearic acid (Table 2, entries 1, 2), but the presence of a Pd-Ni alloy peak on the XRD pattern does fully support
ACS Paragon Plus Environment
Page 9 of 17
its requirement for a reaction catalyst; the Pd and Ni on the same surface (at a particular wt% and ratio) are required instead of a physical mixture of Pd/HZSM-5 and Ni/HZSM-5. This suggests that the yield of alkanes, formed as a result of the cascade reaction where in situ generated H2 from limonene dehydroaromatization is followed by stearic acid HDO, can be maximized by increasing Pd/Ni ratios. Ni (111) Ni (200)
Intensity (a.u.)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis content up to 5.0 wt.%, sharply increased the conversion to 100% with C17 and C18 alkanes formed in close to 90% and 10% yield, respectively. This indicates that Pd-Ni bimetallic nanoparticles supported on HZSM-5 with higher Pd contents accelerate the rates for both fatty alcohol decarbonylation and stearic acid hydrogenation. This phenomenon is in accordance with previous reports showing that Pd can catalyze the decarbonylation/ decarboxylation of fatty acids.11, 12
Pd (111) Pd-Ni alloy
0.5%Pd10%Ni/HZSM-5 1%Pd10%Ni/HZSM-5
3%Pd10%Ni/HZSM-5 5%Pd10%Ni/HZSM-5 5%Pd/HZSM-5 10%Ni/HZSM-5
10
20
30
40
50
60
70
2θ θ (degree)
Figure 10. XRD patterns of PdxNiy/HZSM-5(300) with varying Pd-Ni weight ratios and 5%Pd/HZSM-5(300) and 10%Ni/HZSM-5(300).
The particle size distributions of Pd-Ni metal alloy nanoparticles (after counting 300 particles) on the HZSM5 (300) scaffold were determined by TEM images (Figure 11a-11d), which demonstrated that the mean diameter of the Pd-Ni alloy particles decreased (from 15.2, 11.6, 9.5, to 8.6 nm) as the amount of Pd increased (from 0.5:10 Pd/Ni to 5.0:10 Pd/Ni). In addition, the average metal particle sizes of 5%Pd/HZSM-5 and 10%Ni/HZSM-5 were 6.3 and 18.5 nm, respectively (Figure 11e and 11f), which indicates the individual Pd nanoparticles maybe much smaller than individual Ni nanoparticles on the bimetallic Pd-Ni catalyst. In addition, it was observed the particle sizes of bimetallic Pd-Ni (8.6-15.2 nm) was between the sizes of Pd (6.3 nm) and Ni (18.5 nm) particles. The XRD and TEM analyses together indicate that higher Pd/Ni ratios simultaneously lead to greater formation of Pd-Ni bimetallic alloy and decreased Pd-Ni nanoparticle sizes. Subsequently, the effect of varying the Pd/Ni weight ratios on Pd-Ni/HZSM-5 (300) catalysts on the conversion of stearic acid in limonene at 280°C at a H2 pressure of 2 bar and N2 pressure of 6 bar was investigated (Figure 12). The yields of p-cymene were almost constant at 70%, while the activity of the catalyst for stearic acid conversion showed great variability. Low Pd contents (0.5 to 3.0 wt.%) in Pd-Ni/HZSM-5 (300) resulted in moderate conversions of stearic acid (ranging from 50–60%) with large amounts of ester products formed, suggesting that low Pd content catalysts are not efficient for decarbonylation of the fatty alcohol intermediates to alkanes.11,12 We were gratified to find that raising the Pd
Figure 11. TEM images of Pd-Ni/HZSM-5 (300) with varying Pd-Ni weight ratios. (a) 0.5%Pd-10%Ni/HZSM-5 (300); (b) 1%Pd-10%Ni/HZSM-5 (300); (c) 3%Pd-10%Ni/HZSM-5 (300); (d) 5%Pd-10%Ni/HZSM-5 (300); (e) 5%Pd /HZSM-5 (300); (f) 10%Ni/HZSM-5 (300). D refers to average particle diameter.
To explore the quantitative roles of individual Pd, Ni, and Ni-Pd alloy on the 5% Pd-10% Ni/HZSM-5 (300), we conducted the reaction on three catalysts of 5%Pd/HZSM-5 (300), 10%Ni/HZSM-5 (300), and 5%Pd10%Ni/HZSM-5 (300) prepared by the impregnation method. If the Ni nanoparticle on 5%Pd/HZSM-5 (300) and the Pd nanoparticles on 10%Ni/HZSM-5 (300) roughly resembled the corresponding individual Ni and Pd nanoparticles on the bimetallic 5% Pd-10% Ni/HZSM-5 (300) catalyst, the contributions to C17 and C18 alkanes on individual 5%Pd and 10%Ni on the supported 5% Pd-10%
ACS Paragon Plus Environment
ACS Catalysis Ni/HZSM-5 (300) catalyst were 43% and 1%, respectively, and thus the Pd-Ni alloy contributed the major role of 56% to direct alkane formation. In addition, the XRD patterns showed that Pd-Ni bimetallic alloy formation (Figure 10), which can shorten the transfer distance of in situ produced H2 from Pd to Ni sites. Considering the results obtained thus in our efforts to improve p-cymene/alkanes yields, the 5 wt%Pd-10 wt% Ni/HZSM-5 catalyst system was chosen for further optimization (Figure 12).
a. 100
p-Cymene Yield C17 Yield
Stearic acid Conv. C18 Yield
Conv. /Yield ( C% )
80 60 40 20
0 0.5%Pd-10%Ni 1%Pd-10%Ni 3%Pd-10%Ni 5%Pd-10%Ni
b. C17+C18 Alkanes Yield ( % )
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
c. Contribution in 5%Pd10%Ni/HZSM-5
100
Page 10 of 17
10%Ni/HZSM-5 (300) catalyst while 16 bar pressure was gained in the absence of catalyst, implying that 4.0 bar pressure increase was originated from limonene dehydroaromatization. In addition, in the blank test with limonene in presence of 8 bar N2, limonene was very stable with a conversion lower than 4% at 280 °C attaining a pressure of 14 bar. While catalyzed by Pd/HZSM-5 (300), 70% p-cymene was formed and 18 bar pressure was observed at 280 °C. Thus, it can be reasonably estimated that 4 bar pressure H2 was in-situ produced from limonene at working temperature of 280 °C. The in-situ produced 4 bar H2 equals to 0.0264 mol, while in theory the generated H2 is calculated to be 0.0448 mol (limonene dehydroaromatization system substrates stearic acid hydrodeoxygenation system, detailed calculation is displayed in supporting information). The experimental data (0.0264 mol) for generating H2 is smaller than the theoretical data (0.0448 mol), and the plausible reason is attributed to the dissolved H2 in the limonene in the seal autoclave. It was indeed observed that substantial gas bubbles came out from the limonene liquid phase when the autoclaved was opened.
100
43% alkanes 56% alkanes by individual by Pd-Ni alloy Pd NPs
80 60 43
40 1% alkanes by individual Ni NPs
20
1
0 5%Pd
10%Ni
5%Pd-10%Ni
Figure 12. (a) Stearic acid conversion in limonene over x%Pd-y%Ni/HZSM-5 (300) catalysts with increasing Pd-Ni weight ratios (x/y from 0.5/10 to 5/10). (b) Alkane yields from 5%Pd/HZSM-5 (300), 10%Ni/HZSM-5 (300) and 5%Pd10%Ni/HZSM-5 (300). (c) Components on 5%Pd10%Ni/HZSM-5 (300) to contribute to form alkanes. Reaction condition: 1.0 g stearic acid, 50 mL limonene, 0.2 g catalyst, 280°C, 2 bar H2 and 6 bar N2, 120 min, stirring at 650 rpm.
A Kinetic Study on Stearic Acid Conversion in Limonene. In order to explore the reaction pathways of stearic acid HDO in limonene, a kinetic study was performed with 5%Pd-10%Ni/HZSM-5 (300) in a batch mode at 280°C at a H2 pressure of 2 bar and N2 pressure of 6 bar (Figure 13). The yield data at 0 min were calculated until the temperature reached 280 °C, and the changes of limonene conversion and pressure during the heating process with 5%Pd-10%Ni/HZSM-5 (300) catalyst were recorded at Table S3a, and the pressure changes without catalyst were comparatively listed at Table S3b. By comparing the data in Table S3a and S3b, from 24 to 180 °C the pressure increase was resulted from the temperature increase. But up to the higher temperature 280 °C, a higher pressure was obtained at 20 bar with 5%Pd-
Figure 13. Liquid product distributions on stearic acid conversion in limonene as a function of time. General conditions: 1.0 g stearic acid, 50 mL limonene, 0.2 g 5%Pd-10%Ni/HZSM5 (300), 280°C, 2 bar H2 and 6 bar N2, stirring at 650 rpm.
From the conversion of limonene, the small amount of isomerized limonene (20%) present initially gradually decreased to 0% after 2h (Figure 13a and Table S4), ac-
ACS Paragon Plus Environment
Page 11 of 17
companied by an increase in the formation of the fullyhydrogenated product methane (from 0 to 10%) and the dehydroaromatization product p-cymene (from 60 to 70%), the latter ultimately achieving a formation rate of 562 mmol·g−1·h−1. The 10% drop in isomerized product yield from 0 to 30 min (Table S4) and concomitant increase of 10% in dehydroaromatization product up to 70% yield suggests that isomerization can precede formation of dehydroaromatization product. With respect to the process of stearic acid deoxygenation to form long-chain alkanes, Figure 13b showed that a large amount of ester was initially present, formed from the HZSM-5 catalyzed esterification of stearic acid with stearic alcohol (produced from fatty acid hydrogenation), which had an initial conversion rate of 8.8 mmol·g−1·h−1 on stearic acid at 280°C (Figure 13b). The gradual decrease in the amount of ester over time accompanied by an increasing yield of C17 n-heptadecane (1% to 92%) and an increasing stearic acid conversion (Figure 13b) demonstrated that the ester was an intermediate to the formation of fatty alkanes. The reaction pathway involves initial reduction of the ester to hydrogenated fatty aldehyde,21 followed by further reduction to alkanes by the elimination of one mole of CO and hydrogenation of alkene. Only a very small amount of C18 n-octadecane was detected, with an 8% yield obtained after 120 min (see Figure 13b, Table S4).
depicted in Scheme 1. Limonene forms p-cymene and H2 via isomerization and dehydroaromatization steps. The reaction pathway for stearic acid reduction proceeds through an initial hydrogenation of the carboxylic group to produce the corresponding aldehyde from the in situ generated H2, followed by decarbonylation of 1octadecanal to produce C17 n-heptadecane and carbon monoxide (major route).18-24 Alternatively, the aldehyde can undergo hydrogenation to form 1-octadecanol, which reacts swiftly with stearic acid to form ester as the primary product. Consumption of 1-octadecanol by acidcatalyzed dehydration favors metal catalyzed ester hydrogenolysis and further aldehyde reduction to alcohol (minor route) leading to C18 n-octadecane formation. In the gas phase, CO reacts with H2 to produce methane and water.
Figure 14. Brief description of individual steps for stearic acid and limonene co-activation using the bimetallic PdNi/HZSM-5 catalyst.
dehydration
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 Catalysis
−1
−1
p-Cymene formation rate at 280°C: 562 mmol·g ·h −1 −1 Stearic acid conversion rate at 280°C: 8.8 mmol·g ·h Scheme 1. Reaction pathways for limonene participated stearic acid hydrodeoxygenation.
Considering our results showing the reaction progress of limonene dehydrogenation and stearic acid HDO with the various intermediates and side products formed in the process, the main reaction pathways of the multifunctional 5%Pd-10%Ni/HZSM-5 (300) catalyst are
Figure 14 briefly details the two separate reactions taking place on the bimetallic catalyst system comprising of both individual Pd and Ni nanoparticles and alloyed Pd-Ni clusters supported on the acidic, porous HZSM-5 scaffold. The limonene dehydroaromatization process follows the initial isomerization catalyzed by acid sites within the pore of HZSM-5 and subsequent dehydrogenation catalyzed by the Pd site on the external surface of HZSM-5. Due to the smaller pore sizes in HZSM-5 zeolites, the side-reaction of limonene condensation is mostly suppressed. In addition, the low H2 pressure employed hinders undesired limonene hydrogenation products from being formed, thus favoring catalysis of the dehydroaromatization reaction, primarily yielding aromatic p-cymene and H2 to be utilized in the HDO step. The presence of the Pd-Ni alloy facilitates transfer of H· (formed by dissociation of the in situ produced H2) to Ni, where it catalyses the hydrodeoxygenation of stearic acid to hydrocarbons. The
ACS Paragon Plus Environment
ACS Catalysis
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
metal catalysts are compatible and work in tandem in the Pd-Ni/HZSM-5 system catalyzing the two separate cascade reactions leading to high yields of value-added alkane fuels and aromatic hydrocarbons for the production of bio-jet fuel from two biomass resources. The composition of liquid products in the reaction mixture consisted of a mixture of hydrocarbons (C4 to C18) produced during stearic acid conversion in limonene using Pd-Ni/HZSM-5 at 280°C and a H2 pressure of 2 bar (Figure S7). The hydrocarbons (C4-C18) included products derived from both limonene and stearic acid conversion. Partially hydrogenated products (C10H18), the fully hydrogenated product p-menthane (C10H20), and dehydroaromatization product p-cymene (C10H14) appeared as the major products from limonene conversion, yielding 16%, 11%, 67%, respectively. A trace amount of toluene (1.3%) was observed, which was formed by elimination of the isopropyl group from pcymene, while limonene condensation products were formed in 0.48% yield. Stearic acid was fully converted to saturated fatty alkanes C17 n-heptadecane (major product) and C18 n-octadecane (minor product) after 120 min. Smaller C7 to C15 alkanes were also formed, and their presence in the mixture is beneficial for adjusting the properties (related to the carbon chain numbers) of jet fuel.
Page 12 of 17
remove organics, dried under vacuum overnight, and then was directly reused for subsequent catalytic runs. Even after reusing the Pd-Ni/HZSM-5 catalyst for an additional three runs, stearic acid could still be quantitatively converted to long-chain alkanes within 120 min (Figures 15b–15d). The resulting alkane product composition (C17 and C18 alkanes formed in ~90% and 10% yields, respectively) was similar to that obtained with the fresh catalyst, reaching initial rates of 5.7 mmol·g−1·h−1 in the three runs. After each reaction, the used 5%Pd-10%Ni/HZSM-5 (300) catalyst after four runs was subsequently characterized by XRD, SEM, HRTEM, STEM-ELLS, and STEM-Mapping (Figure 16). The XRD patterns (Figure 16a) and HRTEM imaging (Figure 16c) of the recycled catalyst showed the Pd-Ni alloy phase was present as expected. The XRD spectrum of the recycled Pd-Ni/HZSM-5 (300) catalyst exhibited the same peaks at 40.2°, 44.7°, and 52.1° as the fresh sample showing the presence of single Pd(111), Ni(111) and Ni(200) particles, respectively(Figure 2a). In addition, the peak at 42.5° on the used sample was assigned to Pd-Ni alloy phase. SEM imaging of the used 5%Pd-10%Ni/HZSM-5 (300) catalyst (Figure 16b) showed that the HZSM-5 scaffold was spherical and approximately ~100 nm in size.
As expected, the major component in the gaseous state was H2 (Figure S7 and Table S5), which is present from limonene dehydrogenation as well as from the H2 atmosphere at a pressure of 2 bar in the reaction system. The second largest fraction in the gas phase was CO, formed by decarbonylation of aldehyde intermediate formed as a result of fatty acid hydrogenation (Scheme 1). The other two major factions were CH4 and C3H8, with contents of 0.98% and 0.92%, respectively. CH4 was formed by methanation of CO with H2, and C3H8 was released by C-C cracking of p-cymene. In addition, trace amounts of lighter hydrocarbons were also detected: C2H6; C2H4; i-, n-C4H10; and i-, n- C5H12 (Table S5).
Catalytic Recycling Tests. In order to test for catalyst recyclability, a batch of 5%Pd-10%Ni/HZSM-5 catalyst was used repeatedly for stearic acid conversion in limonene at 280°C at a H2 pressure of 2 bar for 120 min (Figure 15). In the first run, the conversion rate of stearic acid at the end of the reaction period was 100%, forming C17 and C18 alkanes in 90% and 10% yields, respectively, at a rate of 6.0 mmol·g−1·h−1. Heptadecane was the most abundant product in the early stage of reaction progress, and the continual decrease in ester concentration showed that it was an intermediate leading to the formation of heptadecane via ester reduction to aldehyde followed by decarbonylation to form the corresponding alkane. Alternatively, the ester could be reduced to an alcohol via the aldehyde, which could undergo further reduction to alkane. In addition, limonene was dehydroaromatized to form p-cymene and H2 in 70% yield. After the first run, the catalyst was washed with acetone several times to
Figure 15. Stearic acid conversion in limonene as a function of time in four recycling runs. General conditions: 2.0 g stearic acid, 50 mL limonene, 0.4 g Pd-Ni/HZSM-5, 280°C, 2 bar H2 and 6 bar N2, stirring at 650 rpm.
Further information concerning the Pd-Ni bimetallic phase on recycled catalyst was confirmed by a STEMEELS line scan profile and the STEM-mapping images in Figures 16e–16h. The line-scan profile (Figure 16f) and the two dimensional EELS mapping micrographs of Pd (Figure 16g) and Ni (Figure 16h) elements indicated that the uniform chemical distributions of individual Pd and Ni nanoparticles as well as alloyed Pd-Ni particles were unchanged after catalytic runs. The SEM-EDX measurement showed that the nanoparticles contained 1.31 atom% Pd and 3.93 atom% Ni (see Figure S9),
ACS Paragon Plus Environment
Page 13 of 17
suggesting that the Pd/Ni ratio in the used catalyst approached to that in the fresh catalyst (Pd0.22Ni0.78).
a.
fresh catalyst used catalyst
Vads(cm3/g)
400
300
200
100
0 0.0
0.2
0.4
0.6
0.8
1.0
p/p0
b.
fresh catalyst used catalyst
Absorbance ( a.u. )
LAS
BAS
1580
1560
1540
1520
1500
1480
1460
1440
Wavenumber ( cm-1 )
c. 0.4
DTG ( %/min )
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 Catalysis
0.0 fresh catalyst used catalyst
-0.4 -0.8 -1.2 -1.6 0
100
200
300
400
500
600
700
800
Temperature ( °C )
Figure 17. Measurements of fresh and used 5%Pd10%Ni/HZSM-5 (300) catalysts by (a) N2 sorption, (b) IR spectra of adsorbed pyridine, (c) differential thermal gravity analysis.
Figure 16. (a) XRD patterns of bare HZSM-5, fresh PdNi/HZSM-5, and reused 5%Pd-10%Ni/HZSM-5 (300) catalyst. Measurement of used 5%Pd-10%Ni/HZSM-5 (300) after four runs by (b) SEM image; (c) HRTEM image and (d) STEM image; (e) TEM image; (f) STEM-EELS line scan profile; Two dimensional EELS mapping image of (g) Pd and (h) Ni elements.
Then the fresh and spent 5%Pd-10%Ni/HZSM-5 (300) catalyst was further comparatively characterized by N2 sorption, IR of adsorbed/desorbed pyridine, and thermogravimetric analysis (TGA) (Figure 17a-17c). The specific surface area of used catalyst was slightly changed from 348 to 328 m2·g−1, and pore volumes remained at 0.42-0.44 cm3·g-1 (Table S1). The micropore surface areas and volumes were maintained at 253-262 m2·g−1 and 0.120.13 cm3·g-1, suggesting a high stability of the selected 5%Pd-10%Ni/HZSM-5 (300) catalyst during the catalytic test. In addition, the micro-, meso- pore distributions of the used catalyst were almost not changed compared to the fresh catalyst. The results of IR-Py showed that Brönsted acid densities was unchanged at 0.003 mmol·g−1, while Lewis acid densities were decreased from 0.003 to 0.0.0015 mmol·g−1. The differential thermal gravity (DTG) analysis (Figure 17c) of fresh/used 5%Pd-10%Ni/HZSM-5
ACS Paragon Plus Environment
ACS Catalysis
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 14 of 17
We conclude that the optimized 5%Pd-10%Ni/HZSM-5 (300) catalyst has been demonstrated to be durable under the tested reaction conditions. The consistent activity and selectivity performances of the reused catalysts indicate that the bimetallic 5%Pd-10%Ni/HZSM-5 (300) catalyst is highly active and stable in such gas-liquid-solid three phase catalytic system for the conversion of two bioresources (fatty acid and terpene) with a minimal pressure of hydrogen (2 bar).
Pd/Ni ratios simultaneously lead to greater formation of Pd-Ni bimetallic alloy and decrease Pd-Ni nanoparticle sizes. The developed multifunctional 5%Pd10%Ni/HZSM-5 (300) catalyst is shown to possess high stability and remains highly active even after four consecutive recycling tests. In conclusion, a simple, efficient, green process is established for the formation of bio-jet fuel components by converting two bio-resources into hydrocarbons (mostly C17 and C18) and p-cymene at low H2 pressures. This presents itself as a methodology of great potential for solving the great demand of high energy-density aviation liquid.
CONCLUSIONS
EXPERIMENTAL SECTION
A one-pot process has been developed for the conversion of limonene to p-cymene with concomitant in situ formation of H2, followed by the hydrodeoxygenation of stearic acid to hydrocarbons under low H2 pressure (2 bar). The heterogeneous 5%Pd-10%Ni/HZSM-5 (300) catalyst is effective for the full conversion of stearic acid and limonene via a cascade reaction sequence. The main pathway of limonene conversion to p-cymene involves initial isomerization, followed by further dehydroaromatization (Scheme 1). Stearic acid reacts with stearic alcohol to produce an ester as the primary product, and sequential reduction and decarbonylation of the corresponding aldehyde leads to long-chain C17 alkane formation. In the gas phase, the main molecules detected are H2, CO, and CH4 (formed from methanation of the two previous components).
Catalyst Synthesis: Preparation of Bimetallic Pd-M Catalysts by Incipient Wetness Impregnation (IWI). A typical Pd-Ni/HZSM-5 was synthesized as follows. Firstly an H2PdCl4 solution (0.05 M, 9.4 mL) was prepared, and Ni(NO3)2·6H2O (0.495 g) was dissolved in distilled water (10 mL) to form a second solution. Then the Ni and Pd precursor solutions were mixed and well-dropped onto HZSM-5 (0.85 g), which kept magnetic stirring at ambient temperature for 10 h. Subsequently the slurry was filtered, dried at 80 °C overnight, calcined in flowing air (flowing rate: 100 mL/min) at 460 °C for 4 h, and finally reduced in flowing H2 (flowing rate: 100 mL/min) at 460 °C for 240 min. Synthesis of Pd-M catalysts (M refers to Cu, Co) was similar to the procedure for Pd-Ni/HZSM-5 preparation, but the temperatures for calcination and reduction were increased to 600 °C. For synthesis of catalysts with different Pd, Ni weight ratios of 0.5 : 10, 1.0 : 10 and 3.0 : 10, the amounts of H2PdCl4 solution above were adjusted to 0.94 mL, 1.88 mL, and 5.64 mL, respectively.
(300) under an air flow demonstrated around 1.4 wt% coke was detected.
With respect to the bimetallic Pd-Ni catalyst loaded onto HZSM-5 (300), Pd has the important role of catalyzing limonene dehydroaromatization to p-cymene with concomitant formation of H2, while Ni displays a high catalytic ability for the hydrodeoxygenation of stearic acid to alkanes. Bimetallic 5%Pd-10%Ni/HZSM-5 catalysts are screened with different SiO2/Al2O3 ratios to optimize the amount of BAS to obtain maximum conversion of stearic acid and the highest yields of C17/C18 alkanes. In addition, the presence of Pd-Ni alloy nanoparticles in the bimetallic 5%Pd-10%Ni/HZSM-5 (300) facilitates the transfer of H· between Pd and Ni which speeds up the hydrodeoxygenation step of the cascade reaction. The bimetallic Pd-Ni nanoparticles are compatible with other scaffolds such as HBEA, HY, and ASA, which have large pores or external acidic sites. However, these supports catalyze the formation of large amounts of limonene condensation products, but form the target dehydroaromatization and HDO products in low yields. The small pore sizes of the HZSM-5 based scaffold is proven to be important to hinder formation of undesired limonene condensation side products. The acidic site concentration of HZSM-5 has a significant effect on the yield of the C17 alkane, highlighting the role of BAS and LAS in the reaction mechanism of stearic acid HDO leading to alkanes in the Pd-Ni bimetallic catalyst. The XRD and TEM analyses together indicate that smaller
Catalyst Characterization. The specific surface area and pore size distribution were performed by N2 adsorption at 77 K on a BELSORP-MAX instrument after activating the samples under vacuum at 573 K for 10 h. Inductively coupled plasma atomic emission spectroscopy (ICP–AES) was performed on a Thermo IRIS Intrepid II XSP emission spectrometer after dissolving the catalyst in the HF solution. The IR spectra of adsorbed pyridine (IR-Py) were recorded with a Bruker VERTEX 70 spectrometer equipped with an insitu IR cell. The samples were activated in vacuum at 673 K for 60 min before equilibrated with pyridine at 423 K, then evacuated at 423 K for 60 min. Powder X-ray diffraction (XRD) patterns were measured on Rigaku Ultima IV X-ray diffractometer utilizing Cu-Kα radiation (λ = 1.5405 Å) operated at 35 kV and 25 mA. X-ray photoelectron spectroscopy (XPS) were performed with a Al Ka X-ray source (hγ = 1486.6 eV) on Kratos Axis Ultra DLD spectrometer device, and an aperture slot of 300 × 700 microns were used to record spectra data. Scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis unit (Oxford, UK) was operated on a Hitachi S-4800 microscope to illuminate crystal morphology and size. Transmission electron microscopy (TEM) images were 2 performed on a FEI Tecnai G F30 microscope working at 300 kV. STEM-mapping and line-scan profiles were observed by transmission electron microscopy (TEM, JEM-2100, JEOL,
ACS Paragon Plus Environment
Page 15 of 17
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 Catalysis
Japan) and energy dispersive X-ray (EDX, Oxford, UK). Pulse CO chemi-sorption was used to determinate metal dispersion with a Micromeritics AutoChem 2910 device. For catalyst pre-treatment, 50 mg catalyst was reduced in 10 vol% H2 in He at 500 °C for 120 min. Then 5 vol% in He CO gas pulse was purged after cooling to 35 °C. Thermogravimetric analysis (TG) was performed on a Mettler TGA/SDTA 851e instrument with a heating rate of 10 °C/min under an air flow.
(1) Luterbacher, J. S.; Rand, J. M.; Alonso, D. M.; Han, J.; Youngquist, J. T.; Maravelias, C. T.; Pfleger, B. F.; Dumesic, J. A. Science 2014, 343, 277-280.
Catalytic Measurements. A typical experiment was carried out as follows: stearic acid (1.0 g), limonene (50 mL), and PdNi/HZSM-5 catalyst (0.2 g) were charged into a batch autoclave (Parr Instrument, 300 mL). The reactor was firstly flushed with N2 at ambient temperature for three times, and was then heated up to 280 °C when 6 bar N2 and 2 bar H2 was purged, and the reaction started at a stirring speed of 650 rpm. The liquid products were in situ sampled during the catalytic runs. Conversion = (weight of converted reactant / weight of the starting reactant) × 100%. Yield of liquid products (C%) = (C atoms in liquid products/C atoms in the starting reactant) × 100%. Selectivity (C%) = (C atoms of each product/C atoms in all the liquid products) × 100%.
(4) Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107, 24112502.
After reaction, liquid products were analyzed on a gas chromatograph equipped with a mass spectrometer (GC-MS, Shimadzu QP-2010 Ultra) with a Rtx-5Sil MS capillary column (30 m×0.25 mm×0.25 μm). Analysis for gaseous products was performed on a GC (Techcomp 7900) equipped with thermal conductivity detector (TCD) and columns (TDX-01: 30 cm×3 mm, TDX-01: 2 m×3 mm), as well as flame ionization detector (FID) and a HP-PLOT Q capillary column (50 m×0.53 mm×25 μm).
(2) Ragauskas, A. J.; Williams, C. K.; Davison, B. H.; Britovsek, G.; Cairney, J.; Eckert, C. A.; Frederick Jr, W. J.; Hallett, J. P.; Leak, D. J.; Liotta, C. L.; Mielenz, J. R.; Murphy, R.; Templer, R.; Tschaplinski, T. Science 2006, 311, 484–489. (3) Zhao, C.; Brück, T.; Lercher, J. A. Green Chem. 2013, 15, 1720-1740.
(5) Kunkes, E. L.; Simonetti, D. A.; West, R. M.; Serrano-Ruiz, J. C.; Gärtner, C. A.; Dumesic, J. A. Science 2008, 322, 417-421. (6) Huber, G.W.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044-4098. (7) Huber, G. W.; Connor, P. O.; Corma, A. Appl. Catal. A 2007, 329, 120-129. (8) Kumar, R.; Rana, B. S.; Tiwari, R.; Verma, D.; Kumar, R.; Joshi, R. K.; Garg, M. O.; Sinha, A. K. Green Chem. 2010, 12, 2232-2239. (9) Liu, Y.; Boyas, R. S.; Murata, K.; Minowa, T.; Sakanishi, K. Energy & Fuels 2011, 25, 4675-4685. (10) Kubička, D.; Kaluža, L. Appl. Catal. A 2010, 2, 199-208. (11) Snare, M.; Kubickova, I.; Maki-Arvela, P.; Chichova, D.; Eranen, K.; Murzin, D. Y. Fuel 2008, 87, 933-945. (12) Simakova, I. L.; Simakova, O. A.; Romanenko, A. V.; Murzin, D. Y. Ind. Eng. Chem. Res. 2008, 47, 7219-7225. (13) Ping, E. W.; Wallace, R.; Pierson, J.; Fuller, T. F.; Jones, C. W. Micro. Meso. Mater. 2010, 132, 174-180. (14) Morgan, T.; Grubb, D.; Santillan-Jimenez, E.; Crocker, M. Top Catal. 2010, 53, 820-829.
ASSOCIATED CONTENT Supporting Information This material is available free of charge via the Internet at http://pubs.acs.org.
(15) Snare, M.; Kubickova, I.; Maki-Arvela, P.; Eranen, K.; Murzin, D. Y. Ind. Eng. Chem. Res. 2006, 45, 5708-5715. (16) Murata, K.; Liu, Y.; Inaba, M.; Takahara, I. Energy & Fuels 2010, 24, 2404-2409. (17) Kon, K.; Onodera, W.; Takakusagi, S.; Shimizu, K. Catal. Sci. Technol. 2014, 4, 3705-3712.
AUTHOR INFORMATION
(18) Ma, B.; Zhao, C. Green Chem. 2015, 17, 1692-1701.
Corresponding Author *Email:
[email protected] (19) Ma, B.; Hu, J. B.; Wang Y. M.; Zhao, C. Green Chem. 2015, 17, 4610-4617.
Notes
(20) Peng, B.; Yuan, X.; Zhao, C.; Lercher, J. A. J. Am. Chem. Soc. 2012, 134, 9400-9405.
The authors declare the following competing financial interest(s): portions of this work have been disclosed in a Chinese Patent: ZL201410593592.2.
(21) Peng, B.; Zhao, C.; Kasakov, S.; Foraita, S.; Lercher, J. A. Chem. Eur. J. 2013, 19, 4732-4741.
ACKNOWLEDGMENT
(23) Kandel, K.; Frederickson, C.; Smith, E. A.; Lee, Y. ACS Catal. 2013, 3, 2750-2758.
This research was supported by the Recruitment Program of Global Young Experts in China, National Natural Science Foundation of China (Grant No. 21573075), and Shanghai Pujiang Program (PJ1403500).
REFERENCES
(22) Song, W., Zhao, C.; Lercher, J. A. Chem. Eur. J. 2013, 19, 9833-9842.
(24) Yang, Y.; Ochoa-Hernández, C.; de la Peña O’Shea, V. A.; Coronado, J. M.; Serrano, D. P. ACS Catal. 2012, 2, 592-598. (25) Kandel, K.; Anderegg, J. W., Nelson, N. C.; Chaudhary, U.; Slowing, I. I. J. Catal. 2014, 314, 142-148. (26) Gosselink, R. W.; Stellwagen, D. R.; Bitter, J. H. Angew. Chem. Int. Ed. 2013, 52, 5089-5092. (27) Hollak, S. A. W.; Gosselink, R. W.; van Es, D. S.; Bitter, J. H. ACS Catal. 2013, 3, 2837-2844.
ACS Paragon Plus Environment
ACS Catalysis
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 16 of 17
(28) Immer, J. G.; Kelly, M. J.; Lamb, H. H. Appl. Catal. A 2010, 375, 134-139.
(38) Zhang, J. J.; Zhao, C. Chem. Commun. 2015, 51, 1724919252.
(29) Renzo, F. D.; Fajula, F. Stud. Surf. Sci. Catal. 2005, 157, 112.
(39) Zhao, C.; Gan, W.; Fan, X.; Cai, Z.; Dyson, P. J.; Kou, Y. J. Catal. 2008, 254, 244-250.
(30) Twaiq, F. A.; Zabidi, N. A. M.; Bhatia, S. Ind. Eng. Chem. Res. 1999, 38, 3230-3237.
(40) Kamitsou, M.; Panagiotou, G. D.; Triantafyllidis, K. S.; Bourikas, K.; Lycourghiotis, A.; Kordulis, C. Appl. Catal. A 2014, 474, 224-229.
(31) Katikaneni, S. P. R.; Adjaye, J. D.; Bakhshi, N. N. Energy & Fuels, 1995, 9, 1065 -1078.
(41) Roberge, D. M.; Buhl, D.; Niederer, J. P. M.; Hölderich, W. F. Appl. Catal. A 2001, 215, 111-124.
(32) Benson, T. J.; Hemandez, R.; White, M. G.; French, W. T.; Alley, E. E.; Holmes, W. E.; Thompson, B. Clean, 2008, 36, 652-656.
(42) Buhl, D.; Weyrich, P. A.; Sachtler, W. M. H.; Hölderich, W. F. Appl. Catal. A 1998, 171, 1-11.
(33) Choudhary, V. R.; Kinage, A. K.; Choudhary, T. V. Science 1997, 275, 1286-1288.
(43) Zhao, C.; Yu, Y.; Jentys, A.; Lercher, J. A. Appl. Catal. B 2013, 132– 133, 282–292.
(34) Choudhary, V. R.; Kinage, A. K.; Sivadinarayana, C.; Devadas, P.; Sansare, S. D.; Guisnet, M. J. Catal. 1996, 158, 3450.
(44) Mojet, B. L.; Miller, J. T.; Ramaker, D. E.; Koningsberger D. C. J. Catal. 1999, 186, 373-386.
(35) Choudhary, V. R., Kinage, A. K.; Sivadinarayana, C.; Guisnet, M. J. Catal. 1996, 158, 23-33. (36) Nishi, K.; Komai, S.; Inagaki, K.; Satsuma, A.; Hattori, T. Appl. Catal. A 2002, 223, 187-193. (37) Naccache, C. M.; Mériaudeau, P.; Sapaly, G.; Tiep, L. V.; Taârit, Y. B. J. Catal. 2002, 205, 217-220.
(45) Kappinski, Z.; Gandhi, S. N.; Sachtler, W. M. H. J. Catal. 1993, 141, 337-346. (46) Saha, J.; Bhowmik, K.; Das, I.; De G. Dalton Trans. 2014, 43, 13325-13332. (47) Busca, G. Chem. Rev. 2007, 107, 5366-5410. (48) Clark, J. H. Acc. Chem. Res., 2002, 35, 791-797.
ACS Paragon Plus Environment
Page 17 of 17
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 Catalysis
SYNOPSIS TOC
Table of Content:
ACS Paragon Plus Environment
17
