Evaluation of transition metal phosphides supported on ordered mesoporous materials as catalysts for phenol hydrodeoxygenation

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Evaluation of transition metal phosphides supported on ordered

mesoporous materials as catalysts for phenol

hydrodeoxygenation

Received 00th January 20xx,

Accepted 00th January 20xx

a

b

a,b

a

a,b

DOI: 10.1039/x0xx00000x

A. Berenguer , T. M. Sankaranarayanan , G. Gómez , I. Moreno , J. M. Coronado , P. Pizarro , D.

P. Serrano*

a,b

www.rsc.org/

A series of transition metal phosphides (Ni

reduction of the corresponding metal phosphate precursors loaded over mesostructured Al-SBA-15, mesoporous ɣ-Al

m-Al ) and ordered mesoporous carbon (CMK-3). Both the dispersion and metal phosphide phases attained are strongly

influenced by the support features, such as its acidic and textural properties. XRD, TEM and H chemisorption results

revealed that MoP phase was probably formed but it undergoes a fast re-oxidation in air. On the other hand, metal

phosphide formation was hindered over m-Al as only metallic Ni and Co were detected. All the materials prepared have

been evaluated as catalysts in hydrodeoxygenation (HDO) using phenol as bio-oil model compound. The highest phenol

conversions were attained with the catalysts based on the acidic supports (Al-SBA-15 and m-Al ). Nevertheless, Co P/Al-

SBA-15, Ni P/m-Al and Co P/m-Al yielded cyclohexanol as main product denoting very low HDO efficiency. In

contrast, Ni P/Al-SBA-15 showed remarkable catalytic properties, being the only catalyst providing almost full phenol

2 2

P, Co P and MoP) have been synthesized by temperature programmed

2 3

O

(

2 3

O

2

O

3

2

O

3

2

O

3

2

2 3

O

2

conversion and extremely high HDO efficiency, with cyclohexane selectivity higher than 90 %. This may be due to a

α+

synergetic effect between the high electron deficiency, generated by the Ni (0 < α < 1) species owing to an electron

transfer from Ni to P, and the different acid sites present in the catalyst.

oxygenates (organic acids, aldehydes, ketones, sugars,

aromatics, etc.) leading to relatively low calorific value.

Likewise there are other poor properties, including high

Introduction

On account of the elevated consumption of non-renewable

viscosity, corrosiveness, immiscibility with hydrocarbon fuels,

etc., which hinders the direct use of pyrolysis bio-oil in vehicle

3

engines. Accordingly, it is necessary to apply additional

fossil fuels and the huge CO emissions associated with the

2

transport sector, the exploitation of renewable energy

resources has increased its importance significantly around the

world. Accordingly, the European Union has set a target of

downstream upgrading treatments in order to produce real

substitutes to conventional fuels from pyrolysis of

10% from renewable sources for energy of the transportation

4

,5

lignocellulosic biomass. In this sense, one of the most

promising upgrading routes is the catalytic

sector by the year 2020. Fuels derived from biomass, so-called

biofuels, could play an important role as substitutes of

petroleum-based fuels currently used. In particular,

lignocellulosic biomass has attracted great attention as raw

material because it is very abundant and does not compete

hydrodeoxygenation (HDO) reaction. This procedure consists

on subjecting the bio-oil to moderate temperatures (250-450

°

C) and high hydrogen pressure (20-300 bar) in the presence of

1

heterogeneous catalysts, so that the oxygen contained in

organic compounds is removed in the form of water without

unnecessary loss of carbon and, ideally, without undesired

with food industry. Lignocellulose, which is responsible of the

structural stability in the plant cell walls, is composed of two

carbohydrate polymers (cellulose and hemicellulose) and one

aromatic polymer formed by phenolic molecules (lignin).

Thermochemical treatments of lignocellulosic biomass, such as

pyrolysis, gasification and liquefaction are used to obtain bio-

6

,7

hydrogen consumption.

The investigation in this field started in the 1980’s and the

first catalytic systems explored were those used at industrial

scale in hydrodesulphurization (HDS) processes, such as Co-

2

oils which will be later converted into liquid bio-fuels. Among

7

–10

MoS

the sulphur anion vacancies or the coordinatively unsaturated

sites (CUS) located at the edges of MoS slabs have been often

2

and Ni-MoS

2

supported on alumina.

In those systems,

them, fast pyrolysis maximizes the production of bio-oil but,

unfortunately, this liquid fraction presents too high content of

2

proposed as the active sites for both HDS and HDO. However,

because of the substitution of sulphur by oxygen atoms as the

reaction progresses, deactivation of the sulphide catalysts

occurs. In order to maintain the stability and activity of these

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catalysts, it is necessary the addition of sulphur-containing “ligand” effect on the metal sites altering the electron density

compounds (e.g., H S and CS ) which react and preserve the of the metal cation, which facilitates the hydrogen

catalyst sulfurization. Nevertheless, the use of these reagents dissociation. Additionally, Ni P phase may have P–OH groups

associated with moderate acidity which favours the

2

1

1–13

leads to sulphur pollution of the final products.

Furthermore, the existence of acid sites on the alumina surface hydrogenation reactions.

favours the deactivation by coke deposition. As an attempt to reported that supported transition metal phosphides such as

avoid this last problem, active carbons have been proposed as Ni P/SiO , Fe P/SiO , MoP/SiO , Co P/SiO and WP/SiO lead to

supports, leading to a major selectivity towards deoxygenated high conversions in HDO of typical model compounds of bio-

2

9,30

In addition, several studies have

2

1

4

31

32

33

34

products but with lower conversions. Another option to oils such as phenol , guaiacol , furan and anisole.

prevent coke formation is supporting MoS over less acidic The method usually followed to prepare transition metal

2

metal oxides, such as zirconia and titania. It has been found phosphides (both bulk and supported) is by temperature-

that these materials not only reduce the coke deposition but programmed reduction (TPR) of the corresponding metal

3

5

also they favour the formation of small MoS

2

crystallites phosphates.

This reduction is carried out at high

1

5,16

leading to a better dispersion of the active phase. temperatures according to the high strength of the P-O

3

Noble metal catalysts, such as Ru, Pd, Pt, etc., have been bond. However, these severe conditions can reduce the

6

1

7

also studied for the HDO process. These materials have surface area and, therefore, the catalytic activity of the

shown to be active at lower temperatures and, therefore, they catalysts. Consequently, several studies have explored the use

could be able to inhibit secondary thermal reactions which of porous supports in order to enhance the dispersion of the

3

7

lead to an operational instability, aside from coke formation metal phosphides and hinder their sinterization.

and deactivation. In addition, these catalysts can be supported In this context, the aim of the current work is to report our

over materials with good hydrothermal stability, such as results concerning the dispersion and catalytic activity

1

8,19

carbons, zeolites and SBA-15.

Depending on the catalyst evaluation in HDO reaction of three transition metal

P, Co P and MoP) over three types of

design, both conversion and deoxygenation degree were even phosphides (Ni

2

higher than in the case of traditional sulphide catalysts. mesoporous supports with different textural, physicochemical

Nevertheless, noble metal catalysts are expensive and they and acidic properties: mesostructured Al-SBA-15, ordered

need large hydrogen consumption to obtain high selectivity for mesoporous high surface area carbon CMK-3 and mesoporous

hydrogenation reactions. Additionally, these catalysts show ɣ-alumina (m-Al

2

O

3

). The catalysts have been characterized by

(77 K), XRD, TEM, ICP-OES, NH

2

TPD and H -TPR techniques in order to establish the

low resistance towards the poisoning caused by small amounts adsorption-desorption of N

2

3

-

2

0

of sulphur compounds.

As alternatives to the unstable sulphides and the expensive correlation between the catalyst properties and their HDO

noble metal catalysts, metal carbides and nitrides have been activity.

proposed for hydrogenation reactions, in particular

The catalytic reactions have been carried out using phenol

molybdenum nitrides and carbides due to their good hydrogen as model substrate because phenolic compounds represent

2

1,22

transfer properties.

Transition metal oxides have been also approximately 25% of oxygenates present in pyrolysis bio-oils,

3

8

investigated in the hydroprocessing field. Metal oxidized while they have shown low reactivity in HDO treatments , and

catalysts can be reduced producing anionic vacancies, which therefore, its study could provide important information for

create surface defects suitable to catalyze hydrogenolysis and improving the upgrading process of pyrolysis oils.

2

3–25

hydrogenation reaction at typical HDO conditions.

In the last years, transition metal phosphides have been

studied as a new type of catalysts. The physicochemical

Experimental

2

properties of metal-rich phosphides (MP and M P) are similar

Catalysts preparation

to those of ceramic compounds such as carbides, nitrides,

borides and silicides. These materials combine properties of

ceramics and metals, being remarkable their excellent heat

and electric conductivity, as well as high thermal and chemical

stability. Nevertheless, their crystal structure is essentially

Synthesis of Al-SBA-15. Al-SBA-15 mesoporous material was

3

9

synthesized according to the procedure described elsewhere.

In typical synthesis, 17 of silica source,

tetraethylorthosilicate (TEOS, Aldrich), and 0.249 of

aluminium isopropoxide (AIP, Aldrich) as Al source

(Si/Al)MOL=67] were added to 20 ml of an aqueous HCl solution

a

g

2

6

different than in carbides and nitrides. Numerous research

articles have stated the excellent properties in the

hydrotreating process of transition metal phosphides,

especially for HDS and HDN of petroleum feedstocks. Chen et

al. have reported that deoxygenation of methyl laurate is

[

of pH 1.5. This mixture was stirred about 3 h until a

homogenous solution was obtained. Then, this solution was

added to a second one containing 8 g of a non-ionic triblock

copolymer (Pluronic P123, Aldrich) solved in 300 ml of HCl at

pH 1.5. The final mixture was stirred for 20 h at 40 °C and aged

under static conditions and autogenous pressure at 110 °C for

2

higher using Ni P phase synthesized with a molar ratio of Ni/P

2

7

lower than the stoichiometric one. Likewise, Koranyi et al.

have concluded that it is necessary to introduce an excess of

phosphorous in order to achieve the formation of the most

2

4 h. The solid product obtained was filtered, dried overnight

and calcined in static air at 550 °C for 5 h with a heating rate of

.8 °C/min in order to remove the surfactant.

2

8

active phase Ni

2

P. The presence of phosphorus plays an

P activity. Firstly, P sites produce a

1

important role in Ni

2

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2 3

Synthesis of m-Al O . Mesoporous ɣ-alumina material was overnight, then at 120 °C for 24 h and subsequently calcined at

synthesized according to a sol-gel method described in 500 °C for 4 h under static air conditions.

4

0

literature. In this method 7.9 g of aluminium isopropoxide

were first dissolved in 40 g of isopropanol (Scharlau). Another Catalysts characterization

solution was prepared by mixing 7.3 g of HCl (35% wt. Porous properties were measured by nitrogen adsorption-

Scharlau), 4.3 g of hexadecyltrimethylammonium bromide desorption experiments at 77 K on a Quadrasorb system (from

(Aldrich) and 10 ml of deionized water. After stirring roughly Quantachrom). The surface area was calculated using the

both solutions for 30 min, they were mixed and further stirred B.E.T. equation, and the total pore volume was determined at

at room temperature for 4 h. Then the synthesis mixture was a relative pressure of 0.97. The Barrett-Joyner-Halenda (BJH)

heated at 80 °C and the obtained gel was dried at 110 °C for 15 method was used to estimate the pore size distribution using

h. Finally, the material was calcined in static air in two steps: the adsorption branch of the isotherm.

firstly, heating at 110 °C for 2 h with a heating rate of 10 °C/

min, and secondly, heating at 550 °C for 5 h using a heating recorded with a Philips PW 3040/00 X’Pert MPD/MRD

ramp of 1.8 °C/ min.

diffractometer using Cu Kα radiation operated at 45 kV and 40

X-ray diffraction (XRD) patterns of the catalysts were

Synthesis of CMK-3. Ordered mesoporous carbon (CMK-3) mA. Crystalline phases were identified by checking reflection

was synthesized using a nanocasting pathway with pure silica signals appearing in the XRD patterns with JCPDS (Joint

SBA-15 as hard template, following the procedure reported in Committee on Powder Diffraction Standards) data files. The

4

1,42

literature.

First, SBA-15 was prepared by a soft-templating route Scherrer´s equation. A high-temperature chamber was used to

metal phosphide crystallite size was calculated by the

4

3,44

described elsewhere

TEOS, Aldrich) and Pluronic P123 as silica source and structure to those employed in the reduction treatments. For these tests

directing agent, respectively. Typically, 4 g of Pluronic P123 the sample was subjected to the following temperature

were dissolved in mixture containing the following program under hydrogen flow (80 ml/min): a) heating from

composition: 0.0041 mol TEOS: 6.67 mol H O: 0.024 mol HCl. room temperature up to 350 °C at a rate of 5 °C/min; b)

, employing tetraethylorthosilicate check the formation of Mo phosphide under conditions similar

(

a

2

Afterwards, the solution was subjected to hydrolysis- heating from 350 °C to 600 °C at a rate of 1 °C/min, c)

condensation reaction at 40 °C for 6 h and hydrothermal isothermal conditions during 3 h and d) cooling down in H₂.

treatment at 90 °C during 3 days. Finally, the filtrated solids The highest temperature reached was 600 °C instead of 650 °C

were calcined at 550 °C during 6 h under static air.

because of the limitations of the chamber employed.

For the synthesis of CMK-3 carbon, furfuryl alcohol (FA,

Transmission electron microscope (TEM) images were

Acros Organics) was used as precursor and oxalic acid (OA, obtained on a PHILIPS TECNAI 20T instrument, working at 200

Acros Organics) as polymerization catalyst. The pores of SBA- kV and equipped with an EDX spectrometer for measuring X-

15 were filled with a solution containing 0.012 g OA per 3 mL ray energy dispersive spectra. The powder sample was

FA through the wetness impregnation technique. ultrasonically dispersed in acetone and then deposited on a

Subsequently, the carbon precursor was polymerized within porous carbon film supported on a copper grid.

the SBA-15 pores by heat treatment at 50 °C for 1 day, and

Metal and phosphorus contents were measured by a Varian

later at 90 °C for 2 days. Then, carbonization was carried out VISTA-MPX Inductively Coupled Plasma-Optical Emission

under inert atmosphere with the following temperature Spectrometer (ICP-OES).

program: a) heating up to 150 °C for 3 h; b) heating up to 300

C at 1 °C/min; c) heating up to 850 °C at 5 °C/min and d) hydrogen temperature-programmed reduction (H -TPR) in a

The complete reducibility of the catalysts was checked by

°

2

keeping the last temperature for 3 h. Finally, the silica quartz U-tube reactor with 100 mg of sample loading in the

template was removed by dissolution with an ethanol-water thermostatic zone. The TPR profiles were obtained by passing

mixture containing 1 M NaOH. The black powders so obtained a 10 vol % H /Ar flow (50 ml/min) through the sample while

2

were then filtrated, washed and dried at 90 °C overnight. By heating from room temperature to 1000 °C, with a heating

thermogravimetric analysis it was confirmed the effective rate of 10 °C/min. The hydrogen consumption was determined

elimination of the silica template, whose concentration by calibration and further integration of the output signals of

remained below 5 wt.%.

the thermal conductivity detector (TCD). A cooling trap (liquid

N and isopropanol) placed between the sample and the TCD

2

Metal phosphide precursors incorporation

was used to retain the water produced during the reduction

Precursors of metal phosphides were loaded into the catalytic test.

supports by wetness impregnation technique. Thus, 1 g of

The acidity of materials was measured by temperature

-TPD) using the

-TPR measurements. The procedure

(Aldrich) or followed for the TPD measurements involved the pre-

O (Aldrich), using a Me/P molar ratio of 1.0 treatment of the catalyst by flowing He at 600 °C for 1h,

and with a total metal phosphide loading of 10 wt.%. cooling to 100 °C, flowing a He/NH mixture and removing the

support was dispersed into 1 mL of an aqueous solution programmed desorption of ammonia (NH

containing (NH HPO (Aldrich) and metallic salt, same setup as in the H

Ni(NO ·6H (Aldrich), Co(NO ·6H

NH Mo

3

4

)

2

4

a

2

3

)

2

O

3

)

2

O

(

4

)

6

7 2

O24·4H

3

Afterwards, the samples were dried at room temperature weakly physisorbed ammonia by passing helium at that

temperature for 30 min. Thereafter, the chemisorbed

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ammonia was desorbed by increasing the temperature up to

50 °C with a ramp of 10 °C/min, its concentration in the

Results and discussion

5

Physicochemical properties of the catalysts

effluent stream being monitored by a TCD signal.

Previously to the reaction tests, all samples were characterized

by a series of techniques with the aim to correlate their

physicochemical properties and metal phosphide-support

interactions with the activity results.

Catalytic activity measurements

The activity of the catalytic systems in phenol HDO was studied in a

100 ml stainless steel (SS) high-pressure stirred batch reactor.

Fig. 1 represents the N

2

adsorption-desorption isotherms at

Firstly, 50 ml of a solution containing 3.5 wt.% phenol (Aldrich) in

decalin (Aldrich), along with 0.1 g of catalyst was loaded into the

reactor.

7

7 K and the corresponding pore size distribution measured

for all the supported materials in reduced form, in addition to

the unloaded supports. In all cases type IV isotherms, typical of

mesoporous materials, were obtained. For Al-SBA-15 based

materials (Fig. 1a), the adsorption branch of the isotherms

Prior to the reaction tests, calcined samples were pelletized,

crushed and sieved with a 60-40 mesh (250-180 μm). Then, the

metal phosphide phases were prepared by Temperature-

Programmed Reduction (TPR) of the corresponding phosphate

shows a narrow hysteresis loop in the P/P

.4-0.8 due to capillary condensation within the mesopores.

This loop exhibits two steps in the desorption branch denoting

0

region between

46

35

0

precursors using a tubular furnace and the following

temperature program under H flow (80 ml/min): a) heating

2

47

the presence of bottle-neck shaped pores. As a general

trend, loading all the supports with 10 wt.% of metal

phosphides led to a severe decrease on the adsorbed volume

but without modifying the isotherm shape. This reduction on

from room temperature up to 350 °C at a rate of 5 °C/min; b)

from 350 °C to 650 °C at a rate of 1 °C/ min and c) isothermal

conditions during 3 h. After the last reduction step, the sample

was passivated by progressively introducing a stream of

4

5

2

the N adsorption was accompanied by a decrease on the

synthetic air at room temperature, as described in literature.

textural properties, as it can be seen in both BET surface area

and total pore volume values presented in Table 1

The reduction temperature was selected in order to preserve

the support structure since at temperatures above 700°C the

In general, the degree of surface area loss was higher in

2 3

mesoporous structure of m-Al O collapses. Likewise, in the

2 3

catalysts based on both Al-SBA-15 and m-Al O , exhibiting

case of ordered mesoporous carbon (CMK-3), the utilization of

higher temperatures could promote losses of carbon by

hydrogenation of the support.

surface areas between 40-60% lower than the original support,

than that observed for the CMK-3 supported materials, which

suffer a reduction close to 35%.

Prior to start the reaction, once the autoclave reactor was

Regarding the pore size distribution (Fig. 1d, 1e and 1f), no

significant changes were observed on the catalysts in

comparison with the supports, except in the case of Al-SBA-15-

based catalysts for which a slight reduction on the mean pore

diameter were always observed. This pore diameter decrease

suggests that some metal phosphides particles have been

deposited along the mesopores that formed the Al-SBA-15

structure during the impregnation process.

closed, it was purged by flowing pure N

2

at room temperature.

and

After that, the reactor was filled with 40 bar of pure H

2

immediately heated up to the reaction temperature (220 °C)

under vigorous stirring (1000 rpm). After 2 h of reaction, the

autoclave was cooled down rapidly with cold water and ice.

Reactant and products were analyzed off-line by gas

chromatography (Agilent, 7890 A) equipped with a FID

detector and a HP-INNOWAX column, as well as by GC-MS

The X-ray diffraction (XRD) patterns of both supports and

reduced catalysts are shown in Fig. 2. The ordered mesoporous

structure of Al-SBA-15 was evidenced at low angle (Fig. 2a),

both before and after the incorporation of the different active

phases. In the case of Al-SBA-15 support, three well defined

peaks corresponding to (100), (110) and (200) reflections,

representative of a 2D hexagonal pore system (p6mm) were

clearly detected. However, after loading the metal phosphides,

the last two reflections were imperceptible and the main

diffraction signal (100) was slightly shifted towards higher

angles. This result is in agreement with the drastic drop of the

textural properties exhibited by these samples, and is a

consequence of the very high metal phosphide dispersion

levels achieved over this support together with partial blocking

of the pores during the impregnation treatment. The ordered

mesoporous carbon, CMK-3, exhibited the same three

characteristic peaks at low angle, indicating that it has been

(

Bruker, BP-5ms; 5% diphenyl/ 95% dimethyl polysiloxane

column).

The catalytic activity of each material was evaluated in

terms of phenol conversion, XPHE (%), and deoxygenation

degree, HDO (%). These parameters were calculated using the

following equations:

0

n

PHE × XPHE - ∑

i

n

i

a

i

∑

n a

i i i

HDOꢀ%ꢁ =

X_P_H_Eꢀ%ꢁꢄ=ꢄ

× 100 = ꢂ1 - _n₀ꢃ × 100

× XPHE

PHE

(1)

(2)

0

PHE

n

× XPHE

0

F

n

PHEꢄ-ꢄnPHE

ꢄ× 100ꢄ

0

n

PHE

_W_h_e_r_e_n0 _i_s_t_h_e_i_n_i_t_i_a_l_a_m_o_u_n_t_o_f_p_h_e_n_o_l₍_m_o_l₎_,_nF is the final

PHE

amount of phenol (mol), n is the amount of i-product (mol) in the

i

liquid phase (except for unreacted phenol) and a is the number of

i

oxygen atoms in the molecule for each i-product.

4

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800

600

400

200

0

900

CMK-3

m-Al O

2 3

Al-SBA-15

Ni P/CMK-3

Ni P/Al-SBA-15

2

Ni P/m-Al O

2

2 3

2

Co P/CMK-3

2

MoP/CMK-3

300

Co P/Al-SBA-15

2

750

Co P/m-Al O

2

2 3

MoP/Al-SBA-15

MoP/m-Al O

2

3

600

2

00

0

450

3

00

50

0

1

A

B

0.0 0.2 0.4 0.6 0.8 1.0

Relative Pressure (P/P₀)

0.8^C

1.0

0

.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6

Relative Pressure (P/P₀)

6

5

4

3

2

1

0

D

2.1

E

1

.5

.0

F

1.8

1.5

1.2

0.9

0.6

0.3

1

0.5

0.0

40

80 120160

40

80 120 160

40

80 120160

Pore diameter (Å)

2

Fig 1 N adsorption-desorption isotherms at 77 K (A, B and C) and pore size distribution employing BJH method (D, E and F) corresponding to both the

supports and passivated supported catalysts.

successfully replicated the porous hexagonal symmetry of the species appeared (Fig. 2f). It is inferred that the establishment

hard template (SBA-15) used for its synthesis. Nevertheless, of different types of metal-support interactions promoted the

0

these peaks totally disappeared in the supported catalysts, preferential formation of Ni and Co . Regarding the MoP

denoting an apparent loss of mesoscopic order. In the case of phase, representative reflections were not detected in any

2 3

mesoporous alumina, m-Al O , a broad diffraction signal sample, which can be attributed to either a very high

appeared both in the support and supported catalysts, typical dispersion of this phase, leading to extremely small

of non-ordered materials but having some homogeneity of nanoparticles, or to an incomplete reduction of the metal

both the pore size and wall thickness along the particles.

High angle XRD patterns were collected in all prepared

phosphide precursor.

Fig. 3 shows representative TEM images of all the catalysts

materials in order to confirm the formation of metal prepared after the reduction and passivation treatment. It can

phosphide phases after the reduction treatment. For Ni P and be observed that the well-ordered hexagonal formation of

Co P over Al-SBA-15 and CMK-3 (Fig. 2b and 2d), reflections cylindrical channels was kept after active phase incorporation

corresponding to such phosphide phases were evidenced, the into both mesostructured supports, Al-SBA-15 and CMK-3, (Fig.

first support leading to more intense signals indicative of 3a-f), which is in agreement with the N physisorption

higher crystallinity and crystal sizes. On the contrary, these isotherms. The apparent partial or total loss of mesoscopic

metal phosphides were not observed over m-Al support order in CMK-3 based samples, suggested by the low angle

while characteristic peaks corresponding to metallic Ni and Co XRD patterns, is therefore attributed to the incorporation

2

2 3

O

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process of the metal phosphides, leading to a large coverage of exhibited a larger trend to form aggregates (Fig. 3g and 3h). In

both the internal and external surface of the support. Both conclusion, the general dispersion of the metal derived phases

2 2

Ni P and Co P nanoparticles are always clearly distinguished, over the supports increases in the following order: Al-SBA-15 <

independently of the support employed. However, MoP m-Al

2

O

3

< CMK-3.

particles were not observed in any case (Fig. 3c, 3f and 3i), in

The chemical composition of all the catalysts was

accordance with the high-angle XRD patterns, suggesting the determined by ICP-OES analysis, the results are presented in

formation of very well dispersed Mo species. Table 1. For Ni P and Co P-derived samples, it is noticed that

For Ni P and Co P supported catalysts, the distribution of the metal/phosphorus molar ratio was always higher than 1,

2

particle sizes was estimated from TEM images and it is which was the experimental ratio used for the metal

represented in Fig. 3, whereas the average size values are phosphide incorporation process. This value is due to the

displayed in Table 1. These data show that the average size of partial elimination of phosphorus during the reduction process

2

6,48

the active phase is smaller than 10 nm for Ni

2 3

Co P. In the case of ordered mesoporous carbon and m-Al O

2

P and 9.5 nm for in the form of gaseous P

x

y

H .

2 3

Using m-Al O as support, the

2

metal to phosphorus ratios are closer to the initial ratio used in

catalysts, the mean diameter of the active phases is larger the synthesis (1), suggesting that, although the formation of Ni

than the pore size, indicating than the majority of particles are and Co metallic phases takes place, instead of metal

located at the external surface, as confirmed by TEM (Fig. 3). phosphides, a significant amount of phosphorus remain over

Crystallite size values determined by the Scherrer’s equation the support surface.

are shown in Table 1. In general, they are close to the mean

size of metal phosphide particles measured from TEM been probed by ammonia TPD (see Fig. 4a). In the case of

micrographs, suggesting the particles of the active phase are CMK-3, the NH -TPD analysis is not shown due to its lack of

monocrystalline. It is also remarkable significant acidity. The TPD profiles indicate that Al-SBA-15 presents a

The acidic properties of the Al-containing supports have

3

a

heterogeneity in the distribution of Ni and Co phosphide moderate amount of acid sites with medium strength, as

nanoparticles over Al-SBA-15, with significantly larger crystals evidenced by the peak centered at around 270 °C, which

3

over the external surface and others smaller and slightly corresponds with a NH loss of 0.11 mmol/g. Mesoporous

elongated inside the channels (Fig. 3a and 3b). On the other alumina exhibited a more intense and broader signal

hand, a more homogeneous particle distribution was observed extending in the range 125 - 400 °C. The amount of ammonia

over the CMK-3 carbon, this behaviour is especially more desorbed in this case is considerable larger (about 0.46

pronounced with Co

dispersion was achieved (Fig. 3d and 3e). In the case of m- a higher concentration of acid sites. However, the desorption

Al support, the nanoparticles corresponding to the active peak for this last support is quite asymmetric and seems to be

2 2 3

P as active phase, for which the highest mmol/g) than for Al-SBA-15, denoting that m-Al O possesses

2 3

O

phases, mainly in metallic form according to XRD results, the result of at least two contributions, one at

Table 1 Physicochemical properties of both supports and passivated supported catalysts.

b

c

a

2

-1

Total pore volume

Pore diameter

Impregnated

d

nanoparticles size (nm)

Me/P molar

e

ratio

S

BET (m g )

3

cm g )

-1

(

(nm)

Al-SBA-15

P/Al-SBA-15

869.60

523.59

391.16

329.45

1145

1.180

0.680

0.640

0.410

1.178

0.487

0.476

0.463

0.499

0.229

0.209

0.267

10.90

10.12

9.35

2.97

2.93

2.91

2.92

4.26

4.87

4.25

-

67*

1.42

1.22

0.96

-

Ni

2

10 (8.4)

Co

2

P/Al-SBA-15

8 (10.3)

MoP/Al-SBA-15

CMK-3

-

Ni

Co

MoP/ CMK-3

m-Al

P/m-Al

MoP/m-Al

2

P/ CMK-3

792.60

752.12

653.80

344.65

165.89

153.10

9.2 (9.2)

1.55

1.31

0.8

2

P/ CMK-3

4.9**

-

2

O

3

-

Ni

2

O

3

7.5 (7.9)

9.5 (6.3)

-

1.34

1.02

0.52

Co

2

O

3

2

206.10

4.28

a

b

isotherm (77 K). Total pore volume measured at P/P

c

= 0.97. Pore diameter calculated applying BJH method to the adsorption

BET surface area from N

2

0

d

branch. Metal phosphide size from TEM images. Values within brackets were calculated from Scherrer’s equation applied of the most intense diffraction

e

peak. Metal/Phosphorus molar ratio from ICP-AOS analysis. * Si/Al ratio from ICP- AOS analysis. **The signal of the most intense diffraction peak was

inadequate to use the Scherrer’s equation.

6

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Journal Name

Al-SBA-15

Ni P/Al-SBA-15

2

Ni P/Al-SBA-15

2

Ni P

Co P/Al-SBA-15

2

Co P/Al-SBA-15

2

Co P

MoP/Al-SBA-15

^A1

2

3

(º)

4

5

10

^B20

30

40

50

60

70

2

θ

2θ (º)

(002)

CMK-3

(101)

CMK-3

(

002)

Ni

2

P/CMK-3

Ni P/CMK-3

2

Ni₂P

(

Co P/CMK-3

2

Co P/CMK-3

2

Co P

(002)

MoP/CMK-3

(101)

^C1

2

3

(º)

4

5

10

^D20

30

40

50

60

70

2

θ

2

θ

(º)

(311)

m-Al O

(1 0 0)

(400)

2

3

(

440)

m-Al O₃

2

Ni P/m-Al O

3

2

(1 0 0)

(440)

Ni P/m-Al O

2

3

Ni

(400)

Co P/m-Al O

2

3

(1 0 0)

(440)

Co P/m-Al O

2

3

(311)

MoP/m-Al O

(400)

2

3

(1 0 0)

(440)

MoP/m-Al O₃

2

^E1

2

3

(º)

4

5

10

F

20

30

40

50

60

70

2θ

2

θ

(º)

Fig. 2 X-ray diffraction patterns at low (A, C and E) and wide angle (B, D and F) for both supports and passivated supported catalysts.

about 180 °C and other located around 270 °C, which would indication of the presence of a high proportion of oxidized P

correspond with acid sites of weak and medium strength, species as a consequence of the low stability of the the MoP

respectively. The high concentration of acid sites in m-Al O

2

phase when exposed to air. In addition, it can be observed that

3

may promote metal-support interactions, inhibiting the the ammonia TPD curve of the Ni P/Al-SBA-15 sample shows a

2

formation of the Ni and Co metal phosphides phases, as above shoulder at medium-high temperature (between 250 and 450

observed in the XRD patterns.

°C), leading to enhanced ammonia desorption compared to the

In order to clarify the relationship between the support. Interestingly, this fact is not observed for the Co P/Al-

2

incorporation of each metal phosphide and the overall acidity SBA-15 material, which indicates that the Ni phosphide phase

of the resulting material, the NH -TPD profiles corresponding presents some acidic features, which may affect its catalytic

3

to the catalysts prepared using Al-SBA-15 as support are drawn properties in HDO reactions, as further discussed.

in Fig 4b. After the metal phosphide loading, a new peak

appears at low temperatures, denoting the generation of weak Catalytic activity

acid sites. This effect is more pronounced in the case of Mo,

Once the catalysts were reduced at 650 °C and passivated,

followed by Ni and finally Co. Similar results have been earlier

they were tested in the phenol HDO reaction at 220 °C and 40

2

7

obtained by Chen et al. , being assigned to the Brönsted

acidity generated by P-OH groups. In particular, for the Mo-

containing sample, the sharp increase in the acidity is a clear

bar of pure hydrogen during 2 h. Both phenol conversion and

HDO efficiency attained are presented in Fig. 5. Under the

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Fig. 3 TEM images and particle size distribution of passivated supported catalysts: (A) Ni

2

P/Al-SBA-15, (B) Co

2

P/Al-SBA-15, (C) MoP/Al-SBA-15, (D)

Ni P/CMK-3, (E) Co P/CMK-3, (F) MoP/CMK-3, (G) Ni P/m-Al , (H) Co P/m-Al , (I) MoP m-Al O .

3

2

O

2

O

3

2 3

conditions employed, almost full conversion was obtained

over Ni P/Al-SBA-15, Ni P/m-Al O and Co P/m-Al O catalysts,

Al-SBA-15

m-Al O

Al-SBA-15

2

3

2

2 3

2

3

Ni P/Al-SBA-15

2

whereas Co P/Al-SBA-15 converted 82.9% of the initial phenol.

2

Co P/Al-SBA-15

2

The rest of catalysts led to much smaller conversions, below

MoP/Al-SBA-15

50%. Comparing the same activity phase on different supports

the use of ordered mesoporous carbon is clearly the less

advantageous. The relatively low activity achieved with the

carbonaceous support is attributed to its non-acidic nature,

since acid sites have been found to strongly favour the HDO

4

9,50

reactions over other substrates such as anisole.

On the

other hand, molybdenum phosphide-based catalysts

presented the worst activity, with negligible conversions when

CMK-3 was used as support and reaching a maximum value of

2

1% over Al-SBA-15.

A

B

As an attempt to elucidate the reason of the activity

1

00 200 300 400 500 100 200 300 400 500

differences between the active phases, H

catalysts prepared using Al-SBA-15 as support was performed.

Fig. 6 shows the resultant H consumption curves of each

calcined catalyst before and after reduction treatments in the Fig. 4 NH

tubular furnace. Calcined Ni

P/Al-SBA-15 shows a broad peak phosphides supported on Al-SBA-15.

2

-TPR analysis of the

Temperature (ºC)

2

3

2 3

-TPD profiles of Al-SBA-15, m-Al O and passivated metal

2

from 500 °C to more than 900 °C, attributed to an overlapping

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in the reductions of both the nickel and phosphorous

Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins

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ARTICLE

2

7

precursors, respectively. When cobalt phosphide precursor

was loaded into the support, a main peak at higher

temperatures (890 °C) appeared. Despite this peak showed a

shoulder denoting overlapping with reduction reactions at

lower temperatures, it is much narrower than in the case of

1

00

Conversion

HDO (%)

80

2

Ni P formation and reveals a higher interaction with the

6

0

support. This result is in agreement with the smaller

nanoparticle sizes and higher dispersion achieved for cobalt

phosphide, as described before from TEM and XRD analysis. In

both cases, the estimated hydrogen consumption for the

40

3

catalysts reduction was similar (77.8 and 76.2 cm /g,

20

respectively). In the case of calcined MoP/Al-SBA-15 catalyst,

the behaviour was different comparing with the other two

active phases: two peaks emerged indicating that the

reduction of MoP precursor occurred in two steps. The first

one, at lower temperature (maximum at 426 °C), is attributed

0

5

-3

P

O

3

O

3

O

l

2

3

-

1

-

1

-1

K

o

K

i

l

2

l

2

A

i

M

-A

o

-A

M

-A

B

C

/C

m

/

m

S

-S

/

P

/

/m

P

l-

l

P

/A

o

M

N

P

N

C

i

o

N

C

M

to the reduction of MoO

3 2

to MoO while the second one

(

centered at 652 °C) reveals the consecutive reduction of both

5

1

Fig. 5 Phenol conversion and HDO (%) over Ni, Co and Mo phosphides

molybdenum and phosphorus precursors to obtain MoP.

After reduction treatment in a tubular furnace, the TPR

patterns obtained were quite different in the case of both Ni

and Co P/Al-SBA-15 materials, with still significant hydrogen

consumptions (24.04 and 12.52 cm /g, respectively) and

revealing the coexistence of different species. Thus, Ni P/Al-

supported catalysts.

2

P

2

3

Ni P/AlSBA-15 (calcined)-77.78 cm /g

2

760ºC

SBA-15 presented four peaks along a wide range of

temperatures: the first one appeared at 150 °C and it is

attributed to the chemical reaction between hydrogen and

3

Ni P/AlSBA-15 (reduced)-24.01cm /g

2

Ni P. The next peak, at around 394 °C, is assigned to the

6

62ºC

reduction of a nickel oxide layer generated around the nickel

phosphide particles during the passivation step with air.

Finally, a broad signal at higher temperatures with two

930ºC

90ºC

394ºC

1

50ºC

8

3

maximum H

2

consumptions (662 and 930 °C) are attributed to

Co P/AlSBA-15 (calcined)-76.24 cm /g

2

the reductions of nickel oxy-phosphates species and of P-O

bonds, respectively. Similar interpretation, concerning the

reduction of cobalt oxide layers and the existence of some

unreacted metal and phosphorous precursors, can be done for

3

Co P/AlSBA-15 (reduced)-12.52 cm /g

2

the reduced Co P/Al-SBA-15 sample, which exhibited two

4

16ºC

MoP/AlSBA-15 (calcined)-53.68 cm /g

26ºC

652ºC

760ºC

peaks at around 416 and 760 °C. Therefore, the reduction

treatment in the tubular furnace could not be totally efficient

since a small part of the initial precursors seemed to be in their

original form.

3

4

The most remarkable result was obtained in the case of

reduced MoP/Al-SBA-15, since its TPR curve and total

consumed hydrogen amount were quite similar to the same

sample before the reduction treatment. These results,

together with the difficulty to detect such active phase by

either XRD or TEM analysis, suggested that MoP is highly

unstable and with a high tendency to form the corresponding

3

MoP/AlSBA-15 (reduced)-50.41 cm /g

662ºC

413ºC

2

00 400 600 800 1000

Temperature (ºC)

oxidized species. To get further inside in this idea, several H

2

-

TPR assays with an in-situ reduction treatment of the reduced

sample have been done, the resultant curves being shown in Fig. 6 TPR profiles of fresh (calcined) and passivated metal phosphides

Fig 7.

supported Al-SBA-15.

The first assay consisted in reducing in situ the catalyst (Fig.

c) at the temperature of the HDO reaction tests (220 °C) and

7

no differences with the previous TPR results (Fig. 7a and b)

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formation of Mo

x

P

y

species. Once H

2

is replaced by air, the

3

5

3.68 cm /g of H

2

652ºC

peak generated during the reduction disappears even at room

temperature, corroborating the high instability of Mo

phosphide. This fact explains why these phases are not usually

observed in the ex-situ XRD patterns of the samples.

426ºC

(

a)

652ºC

Concerning the mechanisms by which phenol may undergo

HDO reactions, previous investigations have demonstrated

3

5

0.41 cm /g of H

2

4

,6,48

that there are two main parallel pathways.

hydrogenolysis of the C-O bond (DDO) leading to benzene as

product and b) hydrogenation (HYD) involving pre-

a) direct

421ºC

(

b)

a

hydrogenation of the aromatic ring to form cyclohexanol,

followed by elimination of water and subsequent

hydrogenation to form cyclohexane. However, from the GC

analysis of the reaction products, additional compounds

corresponding to addition or condensation reactions yielding

molecules with two C6 rings were detected in minor amounts.

Accordingly, Fig. 8 represents the proposed reaction pathways

for the conversion of phenol under the experimental

conditions employed in this work.

3

4

8.58 cm /g of H

2

627ºC

419ºC

(c)

3

4

.80 cm /g of H

2

(

d)

Fig 9 illustrates the distribution of products, in terms of

selectivity, obtained for every catalyst tested. Strong

differences can be observed, revealing the important influence

of both the support nature and the type of metal phosphide

loaded. The three catalysts based on Mo as precursor of the

metal phosphide exhibit, not only low conversions, but also

poor selectivity since the variety of compounds produced

denoted the occurrence of two main reaction pathways: direct

hydrogenolysis of the C-O bond (DDO) and hydrogenation

2

00 400 600 800 1000

Temperature (ºC)

Fig. 7 TPR profiles of MoP/Al-SBA-15, (A) calcined, (B) passivated, (C)

calcined and reduced in situ at 220°C and (D) calcined and reduced in

situ at 650°C.

were detected. On the other hand, when the sample was (HYD). On the other hand, the major product of both Ni and Co

subjected to an in-situ treatment with H

at 650 °C (Fig 7d), phosphides supported on mesoporous carbon was found to be

which is the reduction temperature in the tubular furnace; the cyclohexanol (73.4 and 85.9% respectively), in addition to

consumption was very low. This result confirmed that the much lower amounts of cyclohexanone (11.8 and 6.9%) and

2

H

2

molybdenum phosphide phase is generated during the cyclohexene (12.29 and 3.9%). These results suggest that the

standard reduction treatment but is highly unstable in principal pathway of phenol reaction over both catalysts is the

presence of air, being quickly re-oxidized and it explains the complete hydrogenation of the aromatic ring (HYD) following

very low catalytic activity observed for their derived catalysts.

To get further insights about the formation of Mo phosphide

this route: phenol → cyclohexanone → cyclohexanol (Fig. 8).

Similarly to CMK-supports, when both Ni and Co were supported

2 3

phases during the reduction process, in situ XRD analyses using over m-Al O , the main product obtained was cyclohexanol (74 and

a high-temperature chamber under conditions similar to those 82%, respectively) and the second major product was cyclohexane

employed in the reduction treatments have been performed. (22.2 and 17%). However, there are three discrepancies denoting

While during the heating ramp no new diffraction peak was different reaction pathways: a) the conversion achieved was quite

observed (see SI Figure), when reaching a temperature of 600 higher, close to 100%, b) benzene was negligible or even not

°

C, a broad low intensity peak appeared in the 33ᵒ-47ᵒ 2θ detected and c) larger molecules formed by condensation reactions

range. This signal remained unaltered during both the constant were detected in small amounts. The absence of benzene, denoting

temperature step and the cooling of the sample provided that that direct deoxygenation route did not occur, together with the

a H

through the chamber, after reaching a temperature of 30 °C, formation of metallic Ni and Co species instead of their

the broad XRD peak rapidly disappeared.

corresponding phosphides, as it was concluded from the XRD

2

atmosphere is kept. However, when air was passed extremely high conversion of phenol was attributed to the

These results confirm that the Mo reduction takes place analyses. Besides, several studies have reported the strong

even at a relatively low temperature of 600 °C. The interaction between Ni and Co with alumina and the weak Me-P

52,53

appearance of a broad XRD signal could be related with the interaction for metal phosphides in the same support.

formation of different types of highly dispersed Mo phosphide

This strong interaction could promote the formation of

species. In this respect MoP, Mo P and MoP

phases present mixed oxides with alumina, such as the NiAl or CoAl

3

2

O

4

2 4

O

reflections in this interval, so it is not possible to determine the spinels, decreasing the acidity of the support and, therefore,

exact stoichiometry by this technique. Nevertheless, it can be limiting the deoxygenation capacity by reducing the availability

5

2

concluded that the temperature program used in the of metallic sites. Nevertheless, some acidic properties must

reduction process in this work is enough to achieve the be retained on the catalyst since small concentrations of large

1

0 | J. Name., 2012, 00, 1-3

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molecules formed by condensation of two C6 rings have been longer times, phenol conversion rapidly increased and

observed, the condensation reactions being catalyzed by acidic deoxygenation of cyclohexanol to yield cyclohexane was

sites.

In the case of Ni and Co phosphides supported on Al-SBA- cyclohexane was about 90%. According to this analysis, it was

5, phenol conversions were ~100% and 82.9%, respectively. confirmed that hydrodeoxygenation of phenol over Ni P/Al-

For Ni P, the product distribution was different in comparison SBA-15 occurred preferentially through the HYD route, with

with the results obtained using CMK-3 and m-Al as minor contribution of direct hydrogenolysis pathway (DDO). In

supports: cyclohexane was the main product with 91% of the case of Co P/Al-SBA-15, the overall reaction proceeded

observed, so that at the end of the test the selectivity to

1

2

2 3

O

2

selectivity. Since, according to Fig. 8, cyclohexane is the more slowly and the selectivity to cyclohexanol was much

product corresponding to the complete hydrodeoxygenation higher and stable during the progress of the reaction.

reaction of phenol, this result evidences that this catalyst is Moreover, a limit on the phenol conversion at 80% seems to

very effective with high reaction rates of the intermediate appear, which can be interpreted as a signal of catalyst

steps. On the other hand, Co

2

P/Al-SBA-15 showed higher deactivation.

In order to check the effect of the possible presence of

selectivity to cyclohexanol (77.8 %) and, hence, lower HDO

capacity. Due to the mild acidic nature of the support, minor metal oxide phases and metallic species when using the Al-

amounts of larger ether molecules formed by condensation SBA-15 support, two additional reactions were carried out

0

using NiO/Al-SBA-15 and Ni /Al-SBA-15 as catalysts. In the case

reactions were observed over both catalysts.

Both phenol conversion and product evolution was followed of NiO/Al-SBA-15 no phenol conversion was observed,

in more detail for the Ni P and Co P/Al-SBA-15 catalysts by confirming that the oxide has negligible activity in the HDO

2

0

carrying out reactions at shorter times (Fig. 10). In the former reaction. In contrast, when Ni /Al-SBA-15 was tested as a

case, during the first hour of reaction, with phenol conversions catalyst, phenol conversion was close to 100 %, similarly to

2

below 60%, both cyclohexanol and cyclohexane were the most that observed over Ni P/Al-SBA-15. However, great changes

abundant products, while other intermediates appeared in occurred in the products distribution. Thus, although

0

much smaller amounts according to faster conversion rates. At cyclohexane was also the major product obtained over Ni /Al-

OH

Etherification route

[

+

]

[

+ 3 H₂]

2]

O

[

4]

DDO route

[

+ H ,- H O]

2

[+2 H₂]

[2]

2

[

1]

[6]

HYD route

OH

O

OH

CH₃

[

+2 H₂]

2]

[+ H₂]

[2]

[- H O]

2

[+ H₂]

[2]

[

[1]

[5]

Alkylation route

HO

[

6]

HO

[

+

]

[

+ 3 H₂]

2]

[- H O]

2

[+ H₂]

[2]

[

3]

[

[1]

Fig. 8 Reaction network in phenol transformation 1) Hydrogenolysis, 2) Hydrogenation, 3) Alkylation, 4) Etherification, 5) Isomerization, 6) Dealkylation and

detherification.

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Journal Name

Ni₂P/Al-SBA-15

Ni P/Al-SBA-15

Co P/Al-SBA-15

MoP/Al-SBA-15

2

1

00

100

90

80

70

60

50

40

30

20

10

0

OH

100

90

80

70

60

50

40

30

20

10

0

2

9

8

7

6

5

4

3

2

1

0

O

OH

O

CH

3

P

E

N

C

Oⁿ^e

C

L

er^s

P

E

N

C

Oⁿ^e

C

L

er^s

P

E

N

C

Oⁿ^e

-

O

H

L

er^s

C

H

E

O

C

H

E

O

C

H

E

C

B

-

C

B

-

C

B

-

M

C

th

M

C

th

M

C

th

H

O

C

O

Ni P/CMK-3

Co P/CMK-3

MoP/CMK-3

2

OH 2

00

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

Ni P/CMK-3 OH

Co

P/CMK-3

MoP/CMK-3

2

9

8

7

6

5

4

3

2

1

0

O

OH

P

C

E

N

C

Oⁿ^e

C

L

er^s

P

C

E

N

C

Oⁿ^e

C

L

er^s

P

C

E

N

C

Oⁿ^e

-

O

H

L

er^s

H

C

H

C

H

E

O

H

E

O

C

H

E

M

C

B

-

th

M

C

B

-

th

M

C

B

-

th

H

O

C

O

Ni P/m-Al O

Co P/m-Al O

MoP/m-Al O

2

3

2

3

2

3

00

100

90

80

70

60

50

40

30

20

10

0

OH

100

90

80

70

60

50

40

30

20

10

0

Ni P/m-Al O OH

Co

P/m-Al

O

MoP/m-Al

O

2

3

2

3

2

3

9

8

7

6

5

4

3

2

1

0

O

HO

O

OH

P

C

E

N

C

Oⁿ^e

C

L

er^s

P

C

E

N

C

Oⁿ^e

C

L

er^s

P

C

E

N

C

Oⁿ^e

-

H

L

er^s

H

C

H

C

H

E

-

O

H

E

-

O

C

H

E

O

M

C

B

-

th

M

C

B

-

th

M

C

B

-

th

H

O

C

O

MCP- Methylcyclopentane, CH- Cyclohexane, CHE- Cyclohexene,

BEN- Benzene, CH-One- Cyclohexanone, CH-OL- Cyclohexanol

Fig. 9 Product distribution (%) reached over Ni, Co and Mo phosphides supported catalysts.

SBA-15, it was produced with a selectivity significantly lower nickel phosphide itself, enhance the interaction with the

than over Ni P/Al-SBA-15 (57.4 % and 91%, respectively) phenol molecules, causing their adsorption and favouring their

Moreover, cyclohexanol was the second major product, with subsequent transformation through aromatic ring

2

a selectivity of 41.8%, revealing that the presence of metallic hydrogenation and HDO reactions.

Ni leads to the complete hydrogenation of the aromatic ring

but with a lowered HDO efficiency.

Conclusions

Taking into account all the catalytic results previously

described, it is clearly evidenced that Ni P/Al-SBA-15 is the

2

2 2

The synthesis of Ni P, Co P and MoP over three supports

only catalyst providing extremely high HDO efficiency

exhibiting almost full phenol conversion together with

cyclohexane selectivity higher than 90 %. This may be due to a

synergetic effect between the high electron deficiency,

presenting different physicochemical properties (mesoporous

acidic ɣ-Al ; ordered mesoporous acidic aluminosilicate, Al-

2 3

O

SBA-15, and ordered mesoporous carbon, CMK-3) has been

investigated. The physicochemical analysis indicated that both

the dispersion and metal phases attained are strongly

influenced by the support nature and, in particular, its acidity.

The dispersion of metal derived nanoparticles over the

α+

generated by the Ni (0 < α < 1) species owing to an electron

transfer from Ni to P, and the different acid sites present in the

catalyst. As a result, Ni sites show enhanced capability for

adsorbing and activating

2

H , facilitating the hydrogen

supports increases in the following order: Al-SBA-15 < m-Al

2 3

O

2

7,54

activation causing both HDO and aromatic ring saturation.

<

CMK-3. From XRD, TEM and H -TPR results, it was revealed

2

On the other hand, it is probable that the acidic features of

this system, arising from both the Al-SBA-15 support and the

that MoP phase is probably formed but very rapidly re-

oxidized in presence of air. On the other hand, metal

J. Name., 2013, 00, 1-3 | 12

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Page 13 of 15

Journal Name

Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins

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DOI: 10.1039/C5GC02188J

ARTICLE

together with cyclohexane selectivity higher than 90 %. This

remarkable behaviour can be assigned to a synergetic effect

α+

100

between the high electron deficiency, generated by the Ni (0

Ni P/Al-SBA

Ni P/Al-SBA-1 5- 15

2

<

α < 1) species owing to an electron transfer from Ni to P, and

80

the different acid sites present in the catalyst.

60

Acknowledgements

40

This work has been supported by the Spanish Ministry of

Economy and Competitiveness though LIGCATUP project

2

20

0

(ENE2011-29643-C02-01), the European Union Seventh

Framework Programme (FP7/ 2007-2013) under grant

agreement n°604307 (CASCATBEL project) and by the regional

government of Madrid through RESTOENE research project

0

30

60

90

120

0

30

60

90

120

(Ref: P2009/ENE-1743, Consejería de Educación de la

Reaction time (min)

Comunidad de Madrid).

1

0

1

0

Notes and references

Co P/Al-SBA-15

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4 | J. Name., 2012, 00, 1-3

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Green Chemistry

View Article Online

DOI: 10.1039/C5GC02188J

A series of transition metal phosphides (Ni P, Co P and MoP) supported over three mesoporous

2

materials: Al-SBA-15, m-Al O and CMK-3 have been probed as potential catalysts in

2

3

hydrodeoxygenation (HDO) for upgrading pyrolysis bio-oils using phenol as bio-oil model

compound.

(

A) Ni P/Al-SBA-15 (E) Co P/CMK-3

2

B) Ni P/m-Al O

(F) Ni P/CMK-3

2

3

2

C) Co P/m-Al O

(G) MoP/Al-SBA-15

2

3

1

00

D) Co P/Al-SBA-15 (H) MoP/m-Al O

2

3

(I) MoP-CMK-3

80

60

40

A

B

C

20

D

E

F

G

H

O

-

CYCL

HEX

ANO

0

O

-

%) CY^C^L

(

HDO

I

L

RSIO

N

NVE

HEX

ANE

CO

1

Article Doi

Evaluation of transition metal phosphides supported on ordered mesoporous materials as catalysts for phenol hydrodeoxygenation

DOI: 10.1039/c5gc02188j

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c5gc02188j

Full text of DOI:10.1039/c5gc02188j

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