Ni ratio and Ni content on performance of γ-Al2O3-supported nickel phosphides for deoxygenation of methyl laurate to hydrocarbons

Accepted Manuscript Title: Effects of P/Ni ratio and Ni content on performance of ␥-Al2 O3 -supported nickel phosphides for deoxygenation of methyl laurate to hydrocarbons Author: Zhena Zhang Mingxiao Tang Jixiang Chen PII: DOI: Reference:

S0169-4332(15)02601-X http://dx.doi.org/doi:10.1016/j.apsusc.2015.10.182 APSUSC 31663

To appear in:

APSUSC

Received date: Revised date: Accepted date:

1-8-2015 23-9-2015 13-10-2015

Please cite this article as: Z. Zhang, M. Tang, J. Chen, Effects of P/Ni ratio and Ni content on performance of rmgamma-Al2 O3 -supported nickel phosphides for deoxygenation of methyl laurate to hydrocarbons, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.10.182 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

*Highlights (for review)

Highlights 

The formation of AlPO4 was unfavorable for that of nickel phosphides. The phase compositions of nickel phosphide depended on the amount

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



cr

of reduced P.

Catalytic activity was determined by surface Ni site density and

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catalyst acidity.

HDO pathway was promoted by increasing P/Ni ratio and Ni content.



Nickel phosphide gave much higher carbon yield and lower H2

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Ac

ce pt

ed

consumption than Ni.

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

Page 1 of 54

Graphical Abstract (for review)

Graphical abstract 100

Conversion/%

Conversion/%

100

80

60

80

60

1.0 0.5

0

0.0

100

100

50 25

75 50

cr

75

25 0

90 60

C11/C12 ratio

613 K 593 K 573 K

120

30 0 0.0

0.5

1.0

1.5

2.0

2.5

613 K 593 K 573 K

8 6 4 2 5.0

7.5

10.0

12.5

15.0

Ni content/wt.%

Ac ce p

te

d

M

an

P/Ni molar ratio

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0

C11/C12 ratio

1.5

TOF/s

1

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-1

2

SC11+C12/%

SC11+C12/%

2.5 2.0

TOF/s

-1

3

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*Manuscript

Resubmitted the revision to Applied Surface Science Ref. No.: APSUSC-D-15-05628

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Effects of P/Ni ratio and Ni content on performance of

laurate to hydrocarbons

cr

γ-Al2O3-supported nickel phosphides for deoxygenation of methyl

an

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Zhena Zhang, Mingxiao Tang, Jixiang Chen*

Tianjin Key Laboratory of Applied Catalysis Science and Technology,

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Department of Catalysis Science and Engineering, School of Chemical

*

ce pt

ed

Engineering and Technology, Tianjin University, Tianjin 300072, China

Corresponding author

Tel.: +86-22-27890865.

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Fax: +86-22-87894301.

E-mail: [email protected] Postal

address:

Department

of

Catalysis

Science

and

Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.

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Abstract: γ-Al2O3-supported nickel phosphides (mNi-Pn) were prepared by the TPR method and tested for the deoxygenation of methyl laurate to

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hydrocarbons. The effects of the P/Ni ratio (n=1.0 - 2.5) and Ni content (m=5 - 15 wt.%) in the precursors on their structure and performance

cr

were investigated. Ni/γ-Al2O3 was also studied for comparison. It was

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found that the formation of AlPO4 in the precursor inhibited the reduction of phosphate and so the formation of nickel phosphides. With increasing

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the P/Ni ratio and Ni content, the Ni, Ni3P, Ni12P5 and Ni2P phases orderly

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formed, accompanying with the increases of their particle size and the amount of weak acid sites (mainly due to P-OH group), while the CO

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uptake and the amount of medium strong acid sites (mainly related to Ni sites) reached maximum on 10%Ni-P1.5. In the deoxygenation reaction,

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compared with Ni/γ-Al2O3, the mNi-Pn catalysts showed much lower activities for decarbonylation, C-C hydrogenolysis and methanation due

Ac

to the ligand and ensemble effects of P. The conversion and the selectivity to n-C11 and n-C12 hydrocarbons achieved maximum on 10%Ni-P 2.0 for the 10%Ni-Pn catalysts and on 8%Ni-P2.0 for the mNi-P2.0 catalysts, while the turnover frenquency (TOF) of methyl laurate mainly increased with the P/Ni ratio and Ni content. We propose that TOF was influenced by the nickel phosphide phases, the catalyst acidity and the particle size as well as the synergetic effect between the Ni site and acid site. Again, 1

Page 4 of 54

the hydrodeoxygenation pathway of methyl laurate was promoted with increasing P/Ni ratio and Ni content, ascribed to the phase change in the order of Ni, Ni3P, Ni12P5 and Ni2P in the prepared catalysts.

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Key words: P/Ni ratio; nickel content; nickel phosphide; methyl laurate;

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cr

hydrodeoxygenation; decarbonylation

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1. Introduction

Due to the fast consumption of fossil resources and the increase of

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environmental problem, it is very urgent to exploit renewable energy [1]. Biodiesel, a kind of renewable clean liquid fuel, is produced from

ed

vegetable oils and animal fat via transesterification [2]. Comparing with

ce pt

petroleum-based diesel, biodiesel has advantage of environment friendly, renewability, good lubricity, low sulfur and nitrogen contents, and low greenhouse gases emission [ 3 , 4 , 5 ]. However, it also has some

Ac

shortcomings such as low heating value, poor thermal and chemical stability, which are mostly ascribed to its high oxygen content [1,6,7]. In the last decade, hydrodeoxygenation (HDO) has attracted great attention to produce oxygen-free fuel. Through the HDO reaction, vegetable oils and animal fat are converted to diesel-like hydrocarbons (i.e., green diesel [6,8]). Green diesel is clearly superior to biodiesel in terms of high oxidation stability, low specific gravity and high cetane number. Also, 2

Page 5 of 54

HDO can be carried out with conventional hydrotreating process to lower the operating cost [9]. So far, many HDO catalysts have been investigated, such as metal

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sulfides (e.g. sulfided NiMo/Al2O3 [10,11]) and noble metals (e.g. Pt [11, 12]). Although the sulfided NiMo or CoMo catalysts have been

cr

commercialized to produce green diesel [ 13 ], the introduction of

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S-containing agent to feedstock, in order to avoid catalyst deactivation, leads to the formation of undesirable S-containing products and the

an

increase of investment [ 14 ]. From this view of point, to develop

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sulfur-free catalysts is very significant. Noble metal catalysts (Rh, Ru, Pt and Pd) are very active for the HDO process [13, 15], however, their cost

ed

is very high. Recently, metal carbides [16,17], metal nitrides [18] and transition metal phosphides [19,20,21,22] are tested for the HDO process

ce pt

and show good performance. Transition metal phosphides (especially Ni2P) have attracted great attention because of the excellent HDO

Ac

performance, which is due to their special structure resulted from the ligand and ensemble effects of phosphorus [23,24]. Supported nickel phosphide catalysts have been applied to the HDO

reaction of fatty acid esters in recent years. Yang et al. [22] reported that the HDO of methyl oleate on Ni2P/SBA-15 catalyst yielded a high content of long-chain hydrocarbons, whereas Ni/SBA-15 gave a broader hydrocarbon distribution due to the cracking reaction. Guan et al. [25] 3

Page 6 of 54

reported the synthesis of MCM-41 supported nickel phosphide catalysts and proved their excellent activities in the HDO of methyl palmitate. We investigated the effect of the supports on the structure and performance of

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nickel phosphides for the deoxygenation of methyl laurate, and found that the conversion of methyl laurate and the selectivity to C11 and C12

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hydrocarbons tended to decrease in the sequence of Ni2P/SiO2 >

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Ni3P-Ni12P5/Al2O3 > Ni2P/TiO2 > Ni2P/SAPO-11 > Ni2P-Ni12P5/HY > Ni2P/CeO2[26]. Moreover, we also found that Ni2P/SiO2 was more active

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than Ni12P5/SiO2 and Ni3P/SiO2 [27]. γ-Al2O3 is a typical support for

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commercial hydrotreating catalysts because of its large specific area, superior stability and the intrinsic acidity, which is favorable for the

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hydrotreating process. However, there are only a few articles about γ-Al2O3-supported metal phosphide catalysts since γ-Al2O3 interacts

ce pt

strongly with the phosphorus [20,28,29,30,31]. Consequently, to prepare Ni2P/γ-Al2O3

from

the

phosphate

precursor

via

the

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temperature-programmed reduction (TPR) method, a high P/Ni ratio in precursor is necessary. Sawhill et al. [31] prepared the NixPy/γ-Al2O3 catalysts from the oxidic precursors with the P/Ni molar ratios from 0.5 to 2.5, and found that the oxidic precursor with the P/Ni molar ratio of 2.0 yielded Ni2P/γ-Al2O3 that possessed the highest HDS activity. Li et al. [32] prepared a highly dispersed Ni2P/γ-Al2O3 through a solid phase reaction between nickel cations and hypophosphites at 533 K, and the 4

Page 7 of 54

catalyst exhibited high activity for the dehydrogenation of cyclohexane. To our knowledge, there have been no detail reports about the relationship between the structure and performance of γ-Al2O3-supported

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nickel phosphides for the HDO process of fatty acid esters. We consider

for the deoxygenation of triglyceride-based biomass.

cr

that this issue is very significant to obtain the optimal industrial catalyst

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In this work, we aim to investigate the effects of P/Ni ratio and Ni content on the structure and performance of the γ-Al2O3-supported nickel catalysts

and

to

give

insight

an

phosphide

into

the

catalyst

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structure-performance relationship. For this, a series of nickel phosphide catalysts with different compositions were prepared and characterized by

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UV-vis, H2-TPR, XRD, TEM, NH3-TPD, N2 sorption and CO chemisorption. Their performances were tested for the deoxygenation of

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methyl laurate as a model reactant to hydrocarbons. We propose the factors that affect the catalyst reactivity, which are useful for rationally

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designing the γ-Al2O3 supported nickel phosphide catalysts with high performance.

2. Experimental 2.1 Catalyst preparation A commercial γ-Al2O3 support (WYA-259) was purchased from Jiangsu Jingjing New Material Co., Ltd., China. The supported nickel phosphide catalyst was prepared by the temperature-programmed 5

Page 8 of 54

reduction (TPR) method. Firstly, γ-Al2O3 (40-60 mesh) was impregnated with a mixture aqueous solution of NH4H2PO4 and Ni(NO3)2·6H2O. After drying at 393 K for 12 h and calcination at 773 K for 4 h, the

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γ-Al2O3-supported nickel phosphate precursor was prepared. After that, 1.0 g precursor was loaded into a fix-bed quartz reactor (12 mm in

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diameter) and then reduced by H2 (320 mL/min) from 293 to 523 K at 10

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K/min and then from 523 to 923 K (or 1023 K) at 1 K/min and kept at 923 K (or 1023 K) for 3 h. The prepared catalyst was cooled to room

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temperature and passivated with a 0.5 vol% O2/N2 flow (320 mL/min) for

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4 h.

Here, two series of catalysts were prepared. One is from the

ed

precursors with the P/Ni ratios of 1.0, 1.5, 2.0 and 2.5 and the Ni content of 10 wt.%. The other is from the precursors with Ni content ranging

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from 5% to 15% and the P/Ni ratio of 2.0. The catalyst precursors, with P/Ni ratios above 2.0 and Ni content above 12%, were prepared by the

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consecutive impregnation method. That is, the support was firstly impregnated with a part of the mixture aqueous solution of NH4H2PO4 and Ni(NO3)2·6H2O. After drying at 393 K for 12 h and calcination at 773 K for 4 h, it was impregnated with the remainder solution, following by the drying and calcination. For simplicity, the prepared catalysts are denoted as mNi-Pn, where m and n represent the Ni content and the P/Ni ratio in precursor, respectively. 6

Page 9 of 54

For comparison, Ni/γ-Al2O3 (10 wt.% Ni) and Ni2P/SiO2 (8 wt.% Ni content) were also prepared. γ-Al2O3 (40-60 mesh) was impregnated with a solution of Ni(NO3)2·6H2O, while SiO2 (Qingdao Haiyang Chemicals

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Co. Ltd., Qingdao, China, 40 - 60 mesh) was impregnated with a mixture aqueous solution of NH4H2PO4 and Ni(NO3)2·6H2O where the P/Ni ratio

cr

was 1.0. After drying at 393 K for 12 h and calcination at 773 K for 4 h,

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the precursors were reduced at 923 K for 3 h by H2 (320 mL/min). And then the prepared catalysts were cooled to room temperature and

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passivated in a 0.5 vol% O2/N2 flow (320 mL/min) for 4 h.

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In addition, unsupported NiO and Ni3(PO4)2 and γ-Al2O3 supported phosphate (POx/γ-Al2O3) were prepared for references in the H2-TPR

ed

characterization. Ni(NO3)2·6H2O was calcined at 773 K for 4 h to produce NiO. POx/γ-Al2O3 was prepared in the following procedure.

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γ-Al2O3 (40 - 60 mesh) was impregnated with a solution of NH4H2PO4 and followed by drying at 393 K for 12 h and calcination at 773 K for 4 h.

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Ni3(PO4)2 was prepared from a mixture aqueous solution of NH4H2PO4 and Ni(NO3)2·6H2O. The solution was evaporated in an evaporating dish, and the resulting solid was calcined at 773 K for 4 h at a heating rate of 10 K/min. 2.2 Catalyst characterization Ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were acquired by a Perkin-Elmer Lambda 750S UV-Vis-NIR spectrometer to 7

Page 10 of 54

investigate the metal-oxygen species of the catalyst precursors. The powder samples (< 2 μm) were loaded into the holder with BaSO4 as the white standard and scanned over a wavelength range of 200-800 nm.

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H2-TPR, NH3 temperature-programmed desorption (NH3-TPD) and CO chemisorption were carried out on a home-made instrument to

cr

investigate the reducibility of the precursor, the catalyst acidity and the

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surface metal density, respectively. For H2-TPR, 50 mg catalyst precursor was loaded in a quartz U-tube micro-reactor (4 mm in diameter) and then

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reduced by a 10 vol% H2/N2 flow (60 mL/min) at a heating rate of 10

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K/min from 323 to 1273 K, during which the hydrogen consumption was determined by a thermal conductivity detector (TCD). NH3-TPD was

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performed in the same reactor loaded with 70 mg passivated catalyst. The passivated sample was firstly reduced with a H2 flow (60 mL/min) at 723

ce pt

K for 1 h, and it was then cooled to 373 K and exposed to NH 3 for 30 min. Afterward, it was swept by a He flow (40 mL/min) at 373 K for 1 h to

Ac

remove the physical adsorbed NH3. Finally, NH3-TPD was performed in the He flow at a heating rate of 15 K/min. The desorbed NH3 was detected by a TCD. In addition, the acid amount (i.e. the amount of desorbed NH3) was quantified by measuring the corresponding signal of the thermal decomposition of a known amount of hexaamminenickel (II) chloride ([Ni(NH3)6]Cl2). CO chemisorption was carried out on the same instrument with 100 mg passivated sample. Firstly, it was reduced with a 8

Page 11 of 54

H2 flow (60 mL/min) at 723 K for 1 h, and then the reduced sample was swept by a He flow (40 mL/min) at 723 K for 1 h to remove the adsorbed H2. And after the sample was cooled to 303 K and TCD was stable, the

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CO pulses were passed to the sample until the TCD detected effluent areas of consecutive pulses were constant.

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XRD patterns were recorded on a D8 Focus powder diffractometer

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with Cu-Ka radiation (λ = 0.15406 nm). TEM images were obtained on a JEOL JEM-2100F instrument. N2 adsorption isotherm was measured on a

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Quantachrome QuadraSorb SI apparatus. The specific surface area (SBET)

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was calculated by Brunauer-Emmett-Teller (BET) equation. The total pore volume (VP) was estimated at a relative pressure of 0.99. The mean diameter

(d)

was

calculated

using

d

=

4VP/SBET.

The

ed

pore

Barrett–Joyner–Halenda (BJH) method was used to determine the pore

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diameter distribution using the desorption isotherm. X-ray photoelectron spectroscopy (XPS) was performed on a PHI

Ac

5000VersaProbe instrument with Al Kα radiation (1486.6 eV). Binding energies were determined with adventitious carbon (C1s at 284.8 eV) as the reference. To avoid the influence of the passivation on the catalyst surface property, the passivated catalysts were sputter-cleaned with an Ar+ ion beam (4 kV, 3.0 mPa) for 1.5 min. 2.3 Activity test The catalyst reactivity for the deoxygenation of methyl laurate was 9

Page 12 of 54

tested on a stainless-steel fixed-bed reactor (inner diameter of 12 mm). To eliminate the temperature gradient maintaining the isothermal catalyst bed, 0.35 g passivated catalyst diluted with the same size quartz sand was

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loaded in the reactor. A layer of quartz sand was placed on the catalyst bed to preheat the reactants. The passivated catalyst was reduced at 723 K

cr

for 1 h in a H2 flow (100 mL/min). After that, the temperature and H2

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pressure were adjusted to the desired values, and the reaction began when methyl laurate was continuously fed to the reactor through a pump. The

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gaseous products was analyzed on an on-line 102 GC equipped with a

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TCD and a TDX-101 packed column, and N2 was used as internal standard for quantitative analysis. The liquid products were identified by

ed

gas chromatograph (GC) standards and an Agilent GC6890-MS5973N, and quantified on a SP-3420 GC equipped with a FID and a HP-5

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capillary column (30 m × 0.33 mm × 0.5 µm). Tetrahydronaphthalene was used as internal standard for quantitative analysis.

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The conversion of methyl laurate(X) and the selectivity to product i (Si) were defined as follows:

X

n0  n n0

 100% ;

Si 

ni  100% n0  n

Where n0 and n denote the moles of methyl laurate in the feed and the product, respectively; ni denotes the mole of methyl laurate converted to product i (for example, n-undecane, n-dodecane and the oxygenated intermediates). 10

Page 13 of 54

The turnover frequency (TOF, s-1) of methyl laurate was calculated as follows: ln(1  X) TOF   （W / F） M

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Where X is the conversion, F is the amount of methyl laurate fed to the

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reactor per second (μmol/s), W is the catalyst weight (g) and M is the CO uptake (μmol/g). Since the conversions were much higher than 50%, far

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from differential conditions, we evaluated the TOF values with an

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integral analysis [33]. The formula, where −ln(1−X) substitutes for X, assumes a pseudo first-order reaction, which is reasonable because of the

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3. Results and discussion

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large excess of hydrogen and almost isothermal catalyst bed.

3.1 Catalyst characterization

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3.1.1 UV-Vis and H2-TPR

UV-vis DRS was used to determine the states of nickel species in the catalyst precursors. The results are shown in Fig. 1. For comparison, bulk

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NiO and Ni3(PO4)2 were also characterized. For the Ni/γ-Al2O3 precursor (shown in Fig. 1(A)), the strong bands around 208 and 273 nm are assigned to the Ni2+-O2+ charge-transfer transitions, and the weak bands at about 380 and 415 nm are ascribed to the octahedrally coordinated Ni2+ species in the NiO lattice [34]. Additionally, the broad band from 550 to 750 nm is related to the tetrahedrally coordinated Ni2+ species in the NiAl2O4 lattice [35]. For the nickel phosphide catalyst precursors, the 11

Page 14 of 54

remarkable band is visible at about 430 nm ascribed to the Ni2+ species coordinated with the phosphate ions (such as P2O72- and PO43-) [36]. The bands associated with the Ni2+ species in NiO and NiAl2O4 gradually

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decreased and disappeared with increasing the P/Ni ratio and the Ni content, indicating the absence of NiO and NiAl2O4 due to the formation

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of nickel phosphate. Particularly, for the 5%Ni-P2.0 precursor, the bands

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due to NiO and NiAl2O4 were still obvious, while the band due to nickel phaphate shifted to 420 nm (Fig. 1(B)). This may be ascribed to its low P

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content, and the strong interaction between PO43- and Al2O3 inhibited the

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formation of nickel phosphate, which is further confirmed by the H2-TPR results.

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Fig.2 shows the H2-TPR profiles of the catalyst precursors. As indicated in Fig. 2(A), POx/Al2O3 was initially reduced at about 1223 K.

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Such high reduction temperature is ascribed to the formation of stable AlPO4 [28]. The Ni/γ-Al2O3 precursor gave a peak at about 853 K with

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two shoulders at lower and higher temperatures, which are ascribed to the reductions of highly dispersed NiO, bulk NiO and surface NiAl2O4 spinel [37], respectively, in consistent with the UV-Vis results. Two peaks, a distinct one (723 ~ 1023 K) followed by a small one (1023 ~ 1223 K), are observed for all the nickel phosphide catalyst precursors. They are mainly attributed to the reductions of nickel-containing species (including NiO and nickel phosphate) and AlPO4, respectively. For the nickel phosphide 12

Page 15 of 54

catalyst precursors, the nickel species were reduced at higher temperature in comparison with those in the Ni/γ-Al2O3 precursor, while the phosphate was more easily reduced than that of POx/Al2O3 [38]. That is,

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the formation of nickel phosphate retarded the reduction of nickel species, whereas the nickel species accelerated the reduction of phosphate due to

cr

the activation of H2 on the nickel species [27]. In addition, as the P/Ni

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ratio increased for the 10%Ni-Pn catalyst precursors (Fig. 2(A)), the first peak became intense and shifted to high temperature, corresponding to

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the increasing amount of nickel phosphate. Different from other

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mNi-P2.0 catalyst precursors (Fig. 2(B)), the 5%Ni-P2.0 precursor gave smaller first peak than the second one due to the low content of nickel

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phosphate (in consistent with the UV-Vis results). With increasing the Ni content (accompanied with the increase of P content), the first peak

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remarkably increased in intensity and slightly shifted to high temperature, and the second peak also became intense. This is reasonable because

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there were more amounts of nickel phosphate and AlPO4 in the precursors and the nickel phosphate particles might grow up. 3.1.2 XRD and TEM Fig. 3 shows the XRD patterns of Ni/γ-Al2O3 and the nickel phosphide catalysts. In all patterns, the peaks at 2θ = 67.03º, 46.28º, 42.61º and 37.28º are ascribed to γ-Al2O3 (PDF#13-0373). For Ni/γ-Al2O3 (Fig. 3(A)), the small peaks at 2θ = 44.49º and 51.85º correspond to 13

Page 16 of 54

metallic Ni (PDF#65-2865). The introduction of phosphate into the catalyst precursors led to the disappearance of metallic Ni and the formation of the nickel phosphides. For 10%Ni-P1.0, the ill-defined and

the highly dispersed

nickel

phosphide

particles,

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broadened diffraction peaks (apart from the ones due to γ-Al2O3) indicate whose

phase

cr

compositions were determined by the following TEM characterization. In

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the patterns of 10%Ni-P1.5 and 10%Ni-P2.0, there are the peaks at 2θ = 48.96º and 46.96º ascribed to Ni12P5 (PDF#22-1190). For the catalysts

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prepared from the precursors with the P/Ni ratios between 1.0 and 2.0, the

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absence of Ni2P phase is due to the formation of AlPO4 that is difficultly reduced. Consequently, there was no enough amount of reduced

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phosphorus reacting with metallic nickel to produce Ni2P phase. This is very different from the case using SiO2 as support, where Ni2P/SiO2 can

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be prepared from the precursor with the P/Ni ratio of 1.0 (Fig. 1S in supplementary information). Obviously, the peaks due to Ni2P at 2θ =

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40.84º, 44.74º, 47.44º and 54.28º (PDF#65-9706) are observed for 10%Ni-P2.5. In addition, the intense peaks due to Ni2P phase indicate the large particles. This is related to the consecutive impregnation companied with twice calcinations to prepare the 10%Ni-P2.5 catalyst precursor, leading to the remarkable decrease in the catalyst surface (see Table 1) and subsequently the sintering of Ni2P crystallites. Fig. 3(B) shows the XRD patterns of the mNi-P2.0 catalysts with 14

Page 17 of 54

different Ni contents. For 5%Ni-P2.0, no well-defined peaks due to nickel phosphides also indicate the highly dispersed nickel phosphide particles. With the increase of Ni content from 8 to 12 wt.%, the peaks due to

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Ni12P5 are observed and became intense, i.e., the Ni12P5 particles grew up. Interestingly, the peaks due to Ni2P rather than Ni12P5 are visible for

cr

15%Ni-P2.0.

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Because the highly dispersed nickel phosphide particles can not be detected by XRD for several catalysts (such as 10%Ni-P1.0 and

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5%Ni-P2.0), the TEM characterization was used to determine the nickel

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phosphide phases as well as their particle sizes (Fig. 4). In the HRTEM image of Ni/γ-Al2O3 (Fig. 4(a)), the interplanar distance (0.202 nm)

ed

corresponds to Ni (111) crystallographic plane. For 10%Ni-P1.0, the Ni (111) and Ni3P (231) crystallographic planes indicate the coexistence of

ce pt

the Ni and Ni3P phases. The Ni3P (231) and Ni12P5 (312) crystallographic planes were found in 5%Ni-P2.0, while only Ni12P5 phase existed in

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10%Ni-P2.0. The phase compositions for all the catalysts are presented in Table 1.

From the above, we conclude that the phase composition of nickel

phosphides on γ-Al2O3 is related to not only the P/Ni ratio but also the total phosphorus content. Since some amount of PO43+ interacted with γ-Al2O3 to form AlPO4 which was difficultly reduced at 923 K, there was no enough elemental P and PxHy (such as PH3) formed to react with the 15

Page 18 of 54

reduced Ni to form nickel phosphides during the reduction process. For instance, to obtain more amount of reduced phosphorus to prepare Ni2P/γ-Al2O3, increasing the reduction temperature of the precursor can

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be adopted. To confirm this, the 8%Ni-P2.0 and 12%Ni-P2.0 catalyst precursors were reduced at 1023 K (the resulting catalysts are denoted as

cr

8%Ni-P2.0-1023 and 12%Ni-P2.0-1023, respectively). Interestingly, Ni2P

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formed in 12%Ni-P2.0-1023 but not in 8%Ni-P2.0-1023 (Fig. 1S in supplementary information). This should be due to the low amount of

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phosphorus in the 8%Ni-P2.0-1023 precursor. In short, enough reduced P

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species are necessary to prepare Ni2P/γ-Al2O3.

As shown in Fig. 4(A)-(D), the metallic nickel and nickel phosphide

ed

particles uniformly dispersed on the support. 10%Ni-P1.0 and 10%Ni-P2.0 had larger nickel phosphide particles (average diameter of

ce pt

4.4 nm) than the metallic Ni particles on Ni/γ-Al2O3 (average diameter of 3.7 nm), ascribed to the incorporation of phosphorus into metallic Ni [39].

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Compared with 10%Ni-P2.0, 5%Ni-P2.0 possessed smaller particles (average diameter of 3.3 nm) because of its lower Ni content. Combined with the XRD results, it could be concluded that the particle size of nickel phosphide tended to be large with the increases of P/Ni ratio and Ni content. 3.1.3 XPS Fig. 5 shows the XPS spectra in the P 2p and Ni 2p3/2 regions for 16

Page 19 of 54

some catalysts. In P 2p XPS spectra, two peaks are observed at about 129.3 eV and 134.2 eV, ascribed to the reduced P species in the phosphides and the PO43- species derived from the unreduced AlPO4 [31],

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respectively. The reduced P species had smaller electron binding energy than the element P (130.2 eV), indicative of the charge transfer from Ni to

cr

P. In addition, the peaks of P 2p became intense as the P/Ni ratio and Ni

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content increased, corresponding to the increasing amount of AlPO4 and nickel phosphides. Due to the formation of difficultly reduced AlPO4, the

an

amount of the reduced P was much less than that of the PO43- species. In

M

Ni 2p3/2 region, for Ni/γ-Al2O3, the main peak centered at 852.4 eV is assigned to metallic Ni, and the small peak at around 857 eV corresponds

ed

to Ni2+ ions derived from the passivation. For the nickel phosphide catalysts, the electron binding energy of reduced Ni was larger than that

ce pt

of metallic Ni in Ni/γ-Al2O3, which is derived from the charge transfer from Ni to P leading to the positive charge of the Ni species [31]. This

Ac

further demonstrates the formation of nickel phosphides. Moreover, with the increase of P/Ni ratio and Ni content, the electron binding energy of Ni increased, corresponding to the enhanced charge transfer from Ni to P, due to that more and more P atoms interacted with Ni ones. This is consistent with the XRD and TEM results, that is, the nickel phosphide phase formed in the order of Ni3P, Ni12P5 and Ni2P with the increase of P/Ni ratio and Ni content. Indeed, Sawhill et al. [31] have also found that 17

Page 20 of 54

the electron binding energy of Ni site in Ni2P is larger than that in Ni12P5. 3.1.4 Textural properties and CO uptake Fig. 6 presents the N2 adsorption-desorption isotherms. All of the

ip t

catalysts gave the typical IV isotherms, indicating the presence of textural meso-pores. As shown in Table 1, with the increases of the P/Ni ratio and

cr

the nickel content, the BET surface area (SBET), the average pore diameter

us

(dp) and the pore volume (Vp) of the catalysts tended to decrease due to the blockage of the pores by the nickel phosphide particles and unreduced

an

AlPO4. Moreover, the pore size distribution became much narrower and

M

shifted to smaller diameter with increasing the P/Ni ratio and the nickel content (Fig. 7).

ed

Table 1 also shows the CO uptakes of Ni/γ-Al2O3 and the nickel phosphide catalysts. Ni/γ-Al2O3 gave the largest CO uptake of 70 μmol/g.

ce pt

For the 10%Ni-Pn catalysts, with increasing the P/Ni ratio, the decreased CO uptakes are ascribed to the coverage of the surface Ni sites by the

Ac

increased amount of phosphorus species as well as the growth of the nickel phosphide particles. For the mNi-P2.0 catalysts, the CO uptakes first increased and then decreased with increasing Ni content, and 8%Ni-P2.0 gave the largest CO uptake (34 μmol/g). Here, two factors affect the CO uptakes, that is, the Ni and phosphorus contents and the nickel phosphide particle size. The increase of Ni content was accompanied by that of P content for mNi-P2.0. Increasing Ni content 18

Page 21 of 54

favors CO uptake, whereas the increases of P content and nickel phosphide particle size made a contrary effect. As a circumstantial evidence, the CO uptakes remarkably increased to about 41 μmol/g when

ip t

the reduction temperature of the 8%Ni-P2.0 and 12%Ni-P2.0 precursors increased from 973 to 1023 K. The further reduction of P species led to

cr

the exposure of more surface Ni sites.

us

3.1.5 NH3-TPD

The NH3-TPD profiles of the catalysts and reference samples are

an

shown in Fig. 8, and the catalyst acid amounts are listed in Table 1. In the

M

profile of γ-Al2O3 (Fig. 8(A)), the weak and broad peak below 673 K corresponds to the NH3 desorption from the Lewis acid sites. Compared

ed

with γ-Al2O3, POx/γ-Al2O3 gave a larger peak centered at about 480 K due to the formed P-OH groups (i.e., weak Brönsted acids) [23], while the

ce pt

Ni/γ-Al2O3 catalyst gave a new peak at about 655 K derived from the unreduced Ni2+ sites (Lewis acid sites) [40]. All the γ-Al2O3 supported

Ac

nickel phosphide catalysts gave two peaks centered at about 473 and 648 ~ 748 K, corresponding to the weak acid and medium strong acid sites, respectively. The weak acid sites are mainly ascribed to the P-OH groups, while the medium strong acid sites are mostly related to the Ni species. In nickel phosphides, due to a charge transfer from nickel to phosphorus, the Ni sites bear small positive charges and act as Lewis acid sites [41]. As indicted in Table 1 and Fig. 8, the amount of weak acid sites 19

Page 22 of 54

increased with the increases of both P/Ni ratio and Ni content. This is reasonable that the increased phosphorus content led to more P-OH groups. As the P/Ni ratio and Ni content increased, the desorption peak

ip t

due to the medium strong acid sites shifted to high temperature, indicative of the increase of the acid strength. This is related to the charge change of

cr

the Ni species. As indicated by the XRD and TEM results, as the P/Ni

us

ratio and Ni content increased, the nickel phosphide phase formed in the order of Ni3P, Ni12P5 and Ni2P, while there are more charge transfer from

an

Ni to P in this order as shown in the XPS results, corresponding to the

M

enhancement of the acid strength. With the increase of P/Ni ratio and Ni content, the amount of medium strong acid sites firstly increased and then

ed

decreased, similar to the variation tendency of CO uptake. This can be explained by that the medium strong acid sites are mainly derived from

ce pt

the surface Ni sites.

3.2 Catalyst reactivity

Ac

In the deoxygenation of methyl laurate on Ni/γ-Al2O3 and nickel phosphide catalysts, n-undecane (n-C11), n-dodecane (n-C12), the oxygenated intermediates (including lauryl alcohol, lauraldehyde, and lauric acid and lauryl laurate), and cracked hydrocarbons (n-C6 ~ n-C10) and methanol were detected in the liquid products, and CO and CH4 were found in the gaseous products. According to the product distribution and our precious works [42], the deoxygenation pathway of methyl laurate is 20

Page 23 of 54

proposed (Scheme 1). n-C12 is produced via the HDO pathway of methyl laurate (shown in the area marked with dashed line), and the oxygen was removed as H2O and/or CH3OH. n-C11 was formed via the

intermediates, and the oxygen was removed as CO.

cr

3.2.1 Reactivities of Ni/γ-Al2O3 and 10%Ni-Pn catalysts

ip t

decarbonylation pathway of methyl laurate and the oxygenated

us

Fig. 9 shows the reactivities of Ni/γ-Al2O3 and 10%Ni-Pn. For all catalysts, the conversion of methyl laurate increased with the reaction

an

temperature. At each temperature, Ni/γ-Al2O3 gave the highest conversion,

M

ascribed to its largest density of surface Ni sites (i.e., the largest CO uptake). For the 10%Ni-Pn catalysts, as the P/Ni ratio increased from 1.0

ed

to 2.5, the conversion firstly increased and then decreased. 10%Ni-P2.0 gave the highest conversion although its CO uptake was not the largest.

ce pt

This indicates that the density of surface Ni sites was not the only factor influencing the conversion, and other factors might be involved such as

Ac

the intrinsic activity of Ni site and the catalyst acidity. Here, the intrinsic activity of each Ni site was represented by the

TOF of methyl laurate that was calculated on the base of the conversion of methyl laurate and the CO uptake (see Section 2.3). Similar to the conversion, TOF increased with the reaction temperature (Fig.9). However, at each temperature, Ni/γ-Al2O3 gave the smallest TOF, and the TOF on 10%Ni-Pn increased with the P/Ni ratio. This could partly be 21

Page 24 of 54

explained by the different nickel phosphide phases. As indicated by the XRD and TEM results, the phases in 10%Ni-Pn were detected in the sequence of Ni, Ni3P, Ni12P5 and Ni2P with the increase of P/Ni ratio. Our

ip t

previous work [27] indicates that Ni2P/SiO2 had higher conversion than Ni12P5/SiO2 and Ni3P/SiO2 in the deoxygenation of methyl laurate

cr

although it possessed lower CO uptake. Because there was less support

us

effect on SiO2-supported nickel phosphides, Ni2P had higher TOF than Ni12P5 and Ni3P. Additionally, it is important to note that the P-OH

an

groups (i.e., weak Brönsted acid sites) also catalyzed the conversion of

M

methyl laurate via decarbonylaton, hydrodeoxyenation and hydrolysis although their activity was lower than the Ni sites [27]. Thus, the TOF

ed

value must be influenced by the catalyst acidity. In other words, the TOF is a rough description about the activity of the Ni site, and its increase

ce pt

could also be ascribed to the increase of weak Brönsted acid amount with the increase of P/Ni ratio. Also, there might be a synergetic effect

Ac

between the Ni site and P-OH group on the conversion of methyl laurate [27]. To further confirm this suggestion, we compared the performance of the 8%Ni-P2.0 and 12%Ni-P2.0 prepared at different reduction temperatures (i.e., 923 and 1023 K). As shown in Fig. 2S in supplementary information, 8%Ni-P2.0 and 12%Ni-P2.0 gave higher TOFs than 8%Ni-P2.0-1023 and 12%Ni-P2.0-1023, even though Ni2P was formed in 12%Ni-P2.0-1023 (Fig. 1S). The higher TOFs on 22

Page 25 of 54

8%Ni-P2.0 and 12%Ni-P2.0 may be associated with the more weak acid amounts (Fig. 3S in supplementary information). Additionally, the large nickel phosphide particles also favor TOF as demonstrated in the

ip t

previous work [43]. As indicated in Fig. 9, the total selectivity to n-C11 and n-C12

cr

(SC11+C12) also increased with the reaction temperature, while the

us

selectivity to the oxygenated intermediates (Soxy) decreased. On a whole, Ni/γ-Al2O3 gave higher SC11+C12 than 10%Ni-Pn. Among 10%Ni-Pn,

an

10%Ni-P2.0 had the highest SC11+C12 and the lowest Soxy. SC11+C12 on

M

10%Ni-P2.0 reached 94.2% at 613 K, similar to that (94.8%) on Ni/γ-Al2O3. That is, 10%Ni-P2.0 possessed good performance.

ed

The C11/C12 molar ratio represents the selectivity between

ce pt

decarbonylation and HDO pathways. Compared with the HDO one, the decarbonylation pathway involves less hydrogen consumption but larger carbon loss. The increase of C11/C12 molar ratio on Ni/γ-Al2O3 was

Ac

more remarkable than those on the 10%Ni-Pn catalysts with the rise of reaction temperature (Fig. 9), and the C11/C12 molar ratio was slightly influenced by the temperature for 10%Ni-Pn (especially n=1.5 ~ 2.5). Ni/γ-Al2O3 gave much higher C11/C12 molar ratios (about 79 and 121 at 573 and 613 K, respectively) than 10%Ni-Pn, indicating that it was more favorable for the decarbonylation pathway. For 10%Ni-Pn, the C11/C12 ratio decreased with the increase of P/Ni ratio, and the largest C11/C12 23

Page 26 of 54

ratio was 11.8 at 613 K on 10%Ni-P1.0. Compared with that on Ni/γ-Al2O3, the much lower C11/C12 molar ratio on 10%Ni-Pn is mainly ascribed to the ligand effect of P. In nickel phosphides, the Ni sites bear

ip t

small positive charges due to the charge transfer from nickel to phosphorus [23,31], leading to the increase in the eletrophilicity of Ni site.

cr

Moreover, the eletrophilicity of Ni sites tended to increase in the

us

sequence of Ni3P, Ni12P5 and Ni2P [27]. The increased eletrophilicity facilitated the adsorption of the O atom of C=O band, subsequently

an

promoting the activation of C=O band and so the HDO pathway (i.e.,

M

reducing the C11/C12 molar ratio).

The total selectivity to cracked hydrocarbons (Scrack) also increased

ed

with the reaction temperature. Remarkably, Ni/γ-Al2O3 gave much higher

ce pt

Scrack than 10%Ni-Pn, especially at high reaction temperature. The lower Scrack on 10%Ni-Pn (less than 0.5% even at 613 K) is ascribed to the ligand and ensemble effects of P in nickel phosphides, which suppressed

Ac

the hydrogenolysis of C-C bond [27,44]. The CO/C11 molar ratio could reflect the methanation activity of the

catalyst. As indicated in Scheme 1, the decarbonylation of methyl laurate and its oxygenated intermediates would yield same amounts of CO and C11 if no methanation and C-C bond hydrogenolysis reaction took place. The CO/C11 ratio on Ni/γ-Al2O3 was close to 0, i.e., CO was almost converted to methane. This is not expected because of the large H2 24

Page 27 of 54

consumption. However, on the nickel phosphide catalysts, the CO/C11 ratio close to 1.0 indicates nearly no methanation. This is also ascribed to the ligand and ensemble effects of P in nickel phosphides. Because of the

ip t

lower electron density of the Ni site in the nickel phosphides, CO and H2 have less interaction with nickel phosphide than with metallic Ni [45].

cr

As shown in Scheme 1, if no C-C bond hydrogenolysis reaction and

us

methanation took place, CH4 could be only produced from the hydrogenolysis of the O-CH3 group (i.e., reaction (a)). The CO/CH4

an

molar ratio can reflect which pathway is dominating between the

M

conversion of methyl laurate to CH4 via reaction (a) and that to methanol via reactions (b) - (d). The CO/CH4 ratio on Ni/γ-Al2O3 was close to 0

ed

ascribed to the complete methanation of CO. The nickel phosphide catalysts gave larger CO/CH4 molar ratios than Ni/γ-Al2O3 due to their

ce pt

less activity for methanation. As the P/Ni ratio increased, the CO/CH4 molar ratio tended to increase. Because the 10%Ni-Pn catalysts gave

Ac

similar CO/C11 and C11/C12 ratios and low activity for the C-C bond hydrogenolysis, the increased CO/CH4 molar ratio reflects that the reaction (a) was suppressed with increasing P/Ni ratio. In addition, as the temperature increased, the CO/CH4 molar ratio increased from 0.5 to 1.5 while the C11/C12 ratio only slightly increased (apart from 10%Ni-P1.0), indicating that the reactions (b) - (d) were more dominating than the reaction (a), i.e., more amount of methanol was produced at higher 25

Page 28 of 54

temperature. This is expected because the formation of methanol consumes less amount of H2 than that of CH4. 3.2.2 Reactivities of mNi-P2.0 catalysts

ip t

The reactivities of the mNi-P2.0 catalysts are shown in Fig. 10 and Fig. 4S in supplementary information. The conversion and SC11+C12

cr

remarkably increased with the temperature. At each temperature, the

us

conversion and SC11+C12 first increased and then decreased with the Ni

an

content, while Soxy presented the contrary change trend (Fig. 4S). Among mNi-P2.0, 8%Ni-P2.0 exhibited the best deoxygenation performance.

M

As expected, the TOFs of the mNi-P2.0 catalysts also increased with the reaction temperature. Similar to those on the 10%Ni-Pn catalysts, the

ed

TOFs on the mNi-P2.0 catalysts exhibited different variation tendency to

ce pt

the conversion with increasing Ni contents. Surprisingly, at each temperature, the 5%Ni-P2.0 catalyst presents the highest TOF while the 8%Ni-P2.0 catalyst gave the lowest one. We speculate that this is related

Ac

to the less amount of P introduced into 5%Ni-P2.0, leading to less amount of AlPO4 formed and more amount of Lewis acid sites maintained on γ-Al2O3. As indicated by the UV-Vis spectra of mNi-P2.0 (Fig. 1), different from other nickel precursors, the 5%Ni-P2.0 precursor contained the large amount of NiO and NiAlO4 and the relatively low amount of nickel phosphate due to the insufficient P species. Here, Ni2P/SiO2 was tested to narrate for the effect of Lewis acid sites on γ-Al2O3 (Fig. 2S in 26

Page 29 of 54

supplementary information). Compared with 8%Ni-P2.0, Ni2P/SiO2 gave lower conversion, selectivity and TOF although it contained Ni2P phase (Fig. 1S in supplementary information). Also, 8%Ni-P2.0 gave a lower

ip t

C11/C12 molar ratio, that is, it was more favorable to catalyze the HDO pathway and so the carbon loss was reduced. Indeed, it has been reported

cr

that Lewis acid sites on γ-Al2O3 can catalyze the hydrolysis of carboxylic

us

esters into acids [10]. Although the Brönsted acid sites related to the P-OH groups on 8%Ni-P2.0 also contribute to TOF, their acid strength

an

was weaker than that of Lewis acid sites on γ-Al2O3 as indicated by the

M

NH3-TPD results. The stronger Lewis acid sites may more favorable for the hydrolysis reaction. However, the TOF increased with the increase of

ed

Ni content from 8% to 15%. Because the increase of Ni content companied with the increase of P one, the Lewis acid sites on γ-Al2O3

ce pt

were gradually covered, while the amount of Brönsted ones increased and the contribution of P-OH groups to TOF became dominating. Again, the

Ac

increased particle size of nickel phosphide also favored TOF. Thus, TOF was influenced by the nickel phosphide phases, the catalyst acidity (Brönsted and Lewis ones) as well as the particle size. At each temperature, the C11/C12 molar ratio slightly decreased with the increase of Ni content (Fig. 10), ascribed to the phase change from Ni3P to Ni2P. In addition, all the mNi-P2.0 catalysts gave very low Scrack (<0.5%) and the CO/C11 ratios of about 1.0, again demonstrating 27

Page 30 of 54

the low activity of nickel phosphides for the C-C bond hydrogenolysis and methanation. This is very significant for increasing the carbon yield and reducing H2 consumption.

ip t

4. Conclusions The P/Ni ratio and Ni content had a profound effect on the structure

cr

and performance of the mNi-Pn catalysts for the deoxygenation of methyl

us

laurate. In the catalyst precursors, the phosphate easily reacted with

an

γ-Al2O3 to form the stable AlPO4, decreasing the amount of reduced phosphorus and so inhibiting the formation of nickel phosphides during

M

the TPR process. With the increases of the P/Ni ratio and Ni content, the Ni, Ni3P, Ni12P5 and Ni2P phases formed in sequence, and their particle

ed

sizes became large. The single Ni2P phase was only formed in

ce pt

10%Ni-P2.5 and 15%Ni-P2.0 where the enough phosphorus was reduced at 923 K. Increasing reduction temperature (such as 1023 K) could promote the reduction of phosphate and so favored the formation of Ni2P

Ac

phase. As the increases of P/Ni ratio and Ni content, the amount of weak acid sites (mainly attributed to P-OH groups) increased, while the CO uptake and the amount of medium strong acid sites (mainly related to Ni sites) reached maximum for 10%Ni-P1.5. Among the mNi-Pn catalysts, 8%Ni-P2.0 gave the highest conversion and the total selectivity to n-C11 and n-C12 hydrocarbons in the deoxygenation of methyl laurate. The catalyst activity was mainly 28

Page 31 of 54

determined by the density of surface Ni sites and the catalyst acidity. The TOFs of methyl laurate increased with the P/Ni ratio and Ni content, and they depended on the nickel phosphide phases, the catalyst acidity as well

ip t

as the particle size. The deoxygenation pathway was mostly determined by the active phase compositions. The HDO pathway was promoted by

cr

increasing P/Ni ratio and Ni content due to the formation of nickel

us

phosphides in the order of Ni3P, Ni12P5 and Ni2P. Compared with Ni/γ-Al2O3, mNi-Pn showed much lower activity for the decarbonylation,

an

C-C hydrogenolysis and methanation attributed to the ligand and

M

ensemble effects of P. This is very expected because of increasing the carbon yield while reducing the H2 consumption. Particularly, 8Ni-P2.0

ed

had superior performance to Ni2P/SiO2 with the same Ni content. Thus, we propose that γ-Al2O3 is an attractive support for the nickel phosphide

ce pt

catalysts catalyzing the HDO reaction of fatty acid ester to hydrocarbons. Acknowledgements

Ac

The authors gratefully acknowledge the support from the National Natural Science Foundation of China (No. 21176177), the Natural Science Foundation of Tianjin (No. 12JCYBJC13200) and the Program of Introducing Talents to the University Disciplines (B06006). References： [1] C. Zhao, Y. Kou, A.A. Lemonidou, X. Li, J.A. Lercher, Highly

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ed

with γ-Al2O3 supporter of NiO/γ-Al2O3 catalysts, Acta Phys-Chim. Sin.

[38] H. Shi, J. Chen, Y. Yang, S. Tian, Catalytic deoxygenation of methyl laurate as a model compound to hydrocarbons on nickel phosphide

Ac

catalysts: Remarkable support effect, Fuel Process. Technol. 118 (2014) 161-170.

[39] S. Yang, C. Liang, R. Prins, A novel approach to synthesizing highly active Ni2P/SiO2 hydrotreating catalysts, J. Catal. 237 (2006) 118-130. [40] J.A. Cecilia, I.J. Morales, A.I. Molinab, E.R. Castellona, A.J. Lopez, Influence of the silica support on the activity of Ni and Ni 2P based catalysts in the hydrodechlorination of chlorobenzene. Study of factors 35

Page 38 of 54

governing catalyst deactivation, J. Mol. Catal. A: Chem. 368-369 (2013) 78-87 [41] K. Li, R. Wang, J. Chen, Hydrodeoxygenation of Anisole over

ip t

Silica-Supported Ni2P, MoP, and NiMoP Catalysts, Energy Fuels 25

cr

(2011) 854-863.

[42] J. Chen, Y. Yang, H. Shi, M. Li, Y. Chu, Z. Pan, X. Yu, Regulating distribution

in

deoxygenation

of

methyl

us

product

laurate

on

an

silica-supported Ni-Mo phosphides: Effect of Ni/Mo ratio, Fuel 129 (2014) 1-10.

M

[43] Y. Yang, J. Chen, and H. Shi, Deoxygenation of methyl laurate as a model compound to hydrocarbons on Ni2P/SiO2, Ni2P/MCM-41, and

ce pt

3400-3409.

ed

Ni2P/SBA-15 catalysts with different dispersions, Energy Fuels 27 (2013)

[44] P. Liu, J.A. Rodriguez, T. Asakura, J. Gomes, K. Nakamura, Desulfurization reactions on Ni2P(001) and α-Mo2C(001) surfaces:

Ac

Complex role of P and C sites, J. Phys. Chem. B 109 (2005) 4575-4583. [45] P. Liu, J.A. Rodriguez, Catalysts for hydrogen evolution from the [NiFe] hydrogenase to the Ni2P(001) surface: The importance of ensemble effect, J. Am. Chem. Soc. 127 (2005) 14871−14878.

36

Page 39 of 54

Figure

Figure captions Fig. 1 UV-Vis spectra of catalyst precursors. Fig. 2 H2-TPR profiles of catalyst precursors. Fig. 3 XRD patterns of Ni/γ-Al2O3 and mNi-Pn catalysts.

ip t

Fig. 4 TEM images of (A) and (a) Ni/γ-Al2O3; (B) and (b) 10%Ni-P1.0;

cr

(C) and (c) 5%Ni-P2.0; (D) and (d) 10%Ni-P2.0.

Fig. 5 XPS spectra of P 2p and Ni 2p3/2 for Ni/γ-Al2O3 and mNi-Pn catalysts

us

Fig. 6 N2 adsorption-desorption isotherms of Ni/γ-Al2O3 and mNi-Pn catalysts.

an

Fig. 7 Pore diameter distributions of Ni/γ-Al2O3 and mNi-Pn catalysts. Fig. 8 NH3-TPD profiles of Ni/γ-Al2O3 and mNi-Pn catalysts

M

Fig. 9 Reactivities of Ni/γ-Al2O3 and 10%Ni-Pn catalysts for deoxygenation of methyl

ed

laurate

Fig. 10 Reactivities of mNi-P2.0 catalysts for deoxygenation of methyl laurate.

Ac

ce pt

Scheme 1 Proposed deoxygenation pathway of methyl laurate

Page 40 of 54

ip t cr

SBET

dp

Vp

(m2/g)

(nm)

(cm3/g)

Ni/γ-Al2O3

148

11.1

0.41

an

us

Table 1 Properties of Ni/γ-Al2O3 and mNi-Pn catalysts

10%Ni-P1.0

108

10.2

0.28

10%Ni-P1.5

104

9.1

10%Ni-P2.0

102

10%Ni-P2.5

61

5%Ni-P2.0

107

Catalysts

12%Ni-P2.0 15%Ni-P2.0 a

CO uptake

Acid amount (μmol/g)

(μmol/g)

Weak (T<623 K)

Strong(T>623 K)

Ni

70

50

46

Ni,Ni3P

40

244

75

0.24

Ni3P, Ni12P5

42

336

92

8.3

0.21

Ni12P5

26

410

52

7.3

0.11

Ni2P

10

486

0

11.1

0.30

Ni3P, Ni12P5

14

228

33

111

8.6

0.24

Ni12P5

34

232

38

66

7.0

0.12

Ni12P5

17

453

40

54

6.3

0.08

Ni2P

16

524

14

ep te

d

M

compositionsa

Ac c

8%Ni-P2.0

Phase

based on XRD and HRTEM characterizations

Page 41 of 54

(A) NiO Ni/-Al2O3

200

300

400

500

600

700

800

(B)

ce pt

ed

15% Ni-P2.0 12% Ni-P2.0 10% Ni-P2.0 8% Ni-P2.0 5% Ni-P2.0

Ac

Absorbance/a.u.

M

an

Wavelength/nm

us

cr

ip t

Absorbance/a.u.

10% Ni-P1.0 10% Ni-P1.5 10% Ni-P2.0 10% Ni-P2.5 Ni3(PO4)2

200

300

400

500

600

700

800

Wavelength/nm

Fig. 1 UV-Vis spectra of catalyst precursors. (A) NiO, Ni3(PO4)2, Ni/γ-Al2O3 and the 10%Ni-Pn catalyst precursors with different P/Ni ratios; (B) the mNi-P2.0 catalyst precursors with different Ni loadings.

Page 42 of 54

(A)

10%Ni-P2.0

ip t

10%Ni-P1.5

cr

10%Ni-P1.0 Ni/-Al2O3 POx/Al2O3

473

673

873

1073

1273

ed

(B)

ce pt

H2consumption/a.u.

M

an

Temperature/K

us

H2 consumption/a.u.

10%Ni-P2.5

15%Ni-P2.0

12%Ni-P2.0

10%Ni-P2.0

Ac

8%Ni-P2.0

5%Ni-P2.0

473

673

873

1073

1273

Temperature/K

Fig. 2 H2-TPR profiles of catalyst precursors. (A) POx/ Al2O3, Ni/γ-Al2O3 and the 10%Ni-Pn catalyst precursors with different P/Ni ratios; (B) the mNi-P2.0 catalyst precursors with different Ni loadings.

Page 43 of 54

Al2O3

Ni2P

Ni

Ni12P5

Ni3P

(A) 10%Ni-P2.5

10%Ni-P1.0 Ni/-Al2O3

40

50

60

70

80

an

30

us

Al2O3

ip t

10%Ni-P1.5

cr

Relative intensity/a.u.

10%Ni-P2.0

M

2 Theta/degree

Al2O3

(B)

Ni2P

Ac

ed

15%Ni-P2.0 12%Ni-P2.0 10%Ni-P2.0

ce pt

Relative intensity/a.u.

Ni12P5

8%Ni-P2.0 5%Ni-P2.0

Al2O3 30

40

50

60

70

80

2 Theta/degree

Fig. 3 XRD patterns of Ni/γ-Al2O3 and mNi-Pn catalysts. (A) Ni/γ-Al2O3 and10%Ni-Pn catalysts; (B) mNi-P2.0 catalysts

Page 44 of 54

(A)

(a)

cr

ip t

dNi(111)=0.202nm

us

(B)

(b)

dNi3P(231)=0.190nm

Ac

ce pt

ed

M

an

dNi(111)=0.202nm

(C)

dNi12P5(312)=0.186nm

(c)

dNi3P(231)=0.190nm

Page 45 of 54

(D)

(d)

cr

ip t

dNi12P5(312)=0.186nm

us

Fig. 4 TEM images of (A) and (a) Ni/γ-Al2O3; (B) and (b) 10%Ni-P1.0;

Ac

ce pt

ed

M

an

(C) and (c) 5%Ni-P2.0; (D) and (d) 10%Ni-P2.0.

Page 46 of 54

134.2

Relative intensity/a.u.

P 2p

ip t

129.3

15%Ni-P2.0

cr

10%Ni-P2.0 5%Ni-P2.0

140

us

10%Ni-P1.0

135

130

125

M

an

Binding energy/eV

Ni 2p2/3

853.2 852.8

ed

852.6

10%Ni-P2.0

ce pt

Relative intensity/a.u.

15%Ni-P2.0

5%Ni-P2.0

852.6

10%Ni-P1.0

852.4

Ac

Ni/-Al2O3

860

858

856

854

852

850

Binding energy/eV

Fig. 5 XPS spectra of P 2p and Ni 2p3/2 for Ni/γ-Al2O3 and mNi-Pn catalysts Note: black lines correspond to the original curves and the red lines correspond to the smoothed ones.

Page 47 of 54

300

(A)

Ni/-Al2O3 10% Ni-P1.0 10% Ni-P1.5 10% Ni-P2.0 10% Ni-P2.5

200

ip t

150

100

cr

Quantity adsorbed/cm g

3 -1

250

us

50

0 0.0

0.2

0.4

0.6

0.8

-1

an

Relative pressure/pp0

M

200

(B)

ed

5% Ni-P2.0 8% Ni-P2.0 10% Ni-P2.0 12% Ni-P2.0 15% Ni-P2.0

ce pt

3 -1

150

100

50

Ac

Quantity adsorbed/cm g

1.0

0

0.0

0.2

0.4

0.6

0.8

1.0

-1

Relative pressure/pp0

Fig. 6 N2 adsorption-desorption isotherms of Ni/γ-Al2O3 and mNi-Pn catalysts. (A) Ni/γ-Al2O3 and10%Ni-Pn catalysts; (B) mNi-P2.0 catalysts

Page 48 of 54

0.06

(A) Ni/-Al2O3 0.05

0.04

3

-1

Pore volume/cm .g .nm

-1

10% Ni-P1.0 10% Ni-P1.5 10% Ni-P2.0 10% Ni-P2.5

ip t

0.03

cr

0.02

0.00 0

5

10

15

M

0.08

25

30

(B) 5% Ni-P2.0 8% Ni-P2.0 10% Ni-P2.0 12% Ni-P2.0 15% Ni P2.0

ed

-1

0.06

ce pt

3

-1

Pore volume/cm .g .nm

20

an

Pore diameter/nm

us

0.01

0.04

Ac

0.02

0.00

0

5

10

15

20

25

30

Pore diameter/nm

Fig. 7 Pore diameter distributions of Ni/γ-Al2O3 and mNi-Pn catalysts. (A) Ni/γ-Al2O3 and10%Ni-Pn catalysts; (B) mNi-P2.0 catalysts

Page 49 of 54

(A)

NH3 desorption/a.u.

10%Ni-P2.5 10%Ni-P2.0

ip t

10%Ni-P1.5 10%Ni-P1.0

cr

Ni/-Al2O3

POx/-Al2O3

373

473

573

673

773

873

Ac 373

ed 473

(B)

15%Ni-P2.0

ce pt

NH3 desorption/a.u.

M

an

Temperature/K

us

-Al2O3

12%Ni-P2.0 10%Ni-P2.0 8%Ni-P2.0 5%Ni-P2.0

573

673

773

873

Temperature/K

Fig. 8 NH3-TPD profiles of Ni/γ-Al2O3 and mNi-Pn catalysts (A) Ni/γ-Al2O3 and 10%Ni-Pn catalysts; (B) mNi-P2.0 catalysts;

Page 50 of 54

100

Conversion/%

90 80 70 60

ip t

613 K 593 K 573 K

3

TOF/s

-1

2

1

0 0.5

1.0

1.5

P/Ni molar ratio

SC11+C12/%

80 60

M

40 20 0 120

613K 593K 573K

ed

100 80 20 10

ce pt

C11/C12 molar ratio

2.5

an

100

2.0

us

0.0

cr

50

0

0.0

0.5

1.0

1.5

2.0

2.5

P/Ni molar ratio

Ac

15

Soxy/%

10

5

0 5

613 K 593 K 573 K

Scrack/%

4 3 2 1 0 0.0

0.5

1.0

1.5

2.0

2.5

P/Ni molar ratio

Page 51 of 54

2.0

CO/CH4

1.5 1.0 0.5 0.0

ip t

613K 593K 573K

0.5

0.0 0.5

1.0

1.5

P/Ni molar ratio

2.0

2.5

us

0.0

cr

CO/C11

1.0

Fig. 9 Reactivities of Ni/γ-Al2O3 and 10%Ni-Pn catalysts for deoxygenation of methyl

an

laurate.

Ac

ce pt

ed

M

Reaction conditions: 3.0 MPa, WHSV of 14 h-1, H2/methyl laurate ratio of 25

Page 52 of 54

100

Conversion/%

90 80 70 60

TOF/s

-1

2

ip t

613K 593K 573K

1

0 7.5

10.0

Ni content/%

60

M

40 20 0 8

ed

SC11+C12/%

80

6 4

613K 593K 573K

2

ce pt

C11/C12 molar ratio

15.0

an

100

12.5

us

5.0

cr

50

0

5.0

7.5

10.0

12.5

15.0

Ni content/%

Ac

Fig. 10 Reactivities of mNi-P2.0 catalysts for deoxygenation of methyl laurate. Reaction conditions: 3.0 MPa, WHSV of 14 h-1, H2/methyl laurate ratio of 25

Page 53 of 54

(d) +H2, -CO, -CH3OH

C11H23COOH

(b) +H2O, -CH3OH

(c) +H2, -CH3OH

-CO

C11H23 OH

+H2, -H2O C11H23CHO

-H2O -CO, -H2O

C11H22 -CO

+H2 -H2 O

C12H24

+H2

n-C12H26

us

-H2O

C12H25OH

n-C11H24

cr

+C11H23COOH C11 H23COOC12 H25

+H2

ip t

(a) +H2, -CH4 C11H23COOCH3

Ac

ce pt

ed

M

an

Scheme 1 Proposed deoxygenation pathway of methyl laurate

Page 54 of 54