Hydrodeoxygenation of lignin derived monomers over supported metal catalysts

Presented by,

A. K. Deepa

Research guide: Dr. Paresh L. Dhepe

Catalysis & Inorganic Chemistry Division

CSIR-National Chemical Laboratory, Pune, India

Tel. 91-20-25902024, Fax. 91-20-25902633,

Email: pl.dhepe@ncl.res.in

Group Webpage: http://academic.ncl.res.in/pl.dhepe

M M M

R’ = H, -OCH3

R’’ = H, -CH2-CH=CH2

Hydrocarbons

HDO

H2

Lignin derived phenolic monomers

Hydrodeoxygenation (HDO) Depolymerization of lignin can produce aromatic monomers, which can be used as fuel

additives or octane enhancers Higher O-contents of aromatic monomers (27 %, C9.5H11O3) reduces the fuel efficiency

Hydrodeoxygenation (HDO) reactions upgrades the aromatic monomers Lignin derived aromatic monomers consists of several substitutions such as, alkyl, alkoxy,

hydroxyl, olefinic double bonds etc. Hence in the upgrading reactions of these types of compounds, there exists a competition between HDO and hydrogenation (reduction) of double bond or ring or aldehyde or ketone groups.

Lignin derived aromatic monomers like guaiacol, phenols, syringol, eugenol used to study HDO

reactions Sulfided CoMo and NiMo are conventional HDO catalysts, but has drawbacks like coke

formation and sulfur contamination Various combination of metals (Pt, Pd, Ru) and supports chosen from acidic [Al2O3 (AL), SiO2-

Al2O3 (SA)] neutral [carbon (C)], and basic [hydrotalcite (HT)] type The acidic supports are known to cleave C-O bonds and that the neutral and basic supports

may reduce the coke formation on the catalysts and thus increase the catalyst life. Hence we choose diverse supports in our work to study the activity difference.

Supported metals (for hydrodeoxygenation)

Synthesis technique: Impregnation

Support + Water

Stirred, 16h, R.T.

Calcined & Reduced (400 °C, 2h)

Dried

Aq. Solution of metal precursor

Metals: Pt, Pd, Ru

Supports: Acidic(SiO2-Al2O3, Ɣ-Al2O3 ),

Neutral(Carbon), Basic( HT)

M M M

R’ = H, -OCH3

R’’ = H, -CH2-CH=CH2

Hydrocarbons

HDO

H2

Lignin derived

phenolic monomers

Supported metals characterized using XRD, HRTEM, N2 sorption, ICP-OES techniques

Properties of supported metals Metals: Pt, Pd, Ru; Supports: Acidic(SiO2-Al2O3, Ɣ-Al2O3 ), Neutral(Carbon), Basic( HT)

HRTEM images of supported metal catalysts (a) AL (b) C (c) SA (d) HT.

Pd Pt

Ru

Catalyst

BET

surface

area[a]

[m2 g-1]

Average

particle

size[b]

[nm]

Carbon (C) 1000 -

Ɣ-Al2O3 (AL) 154 -

SiO2-Al2O3 (SA) 532 -

Hydrotalcite (HT) 250 -

Pd/C 1400 5

Pd/AL 122 10

Pd/SA 500 20

Pd/HT 187 15

Pt/C 1500 3

Pt/AL 174 15

Pt/SA 510 8

Pt/HT 159 3

Ru/C 850 3

Ru/AL 123 22

Ru/SA 490 15

Ru/HT 165 16 [a]N2 sorption study, [b]HRTEM analysis

30 40 50 60 70

Inte

nsity

(a.u

)

2

(111) (200) (220)

a

b

c

d

e

f

g

30 40 50 60 70

Inte

nsty

(a.u

)

2

a

b

c

d

(111) (200) (220)

30 40 50 60 70

Inte

nst

y(a

.u)

2

a

b

c

d

(111) (200) (220)

XRD patterns of supports and supported Pd catalysts. (a) AL (b) SA (c) HT (d) Pd/C (e) Pd/AL (f) Pd/SA (g) Pd/HT

XRD patterns of supported Pt catalysts (a) Pt/C (b) Pt/AL (c) Pt/SA (d) Pt/HT

XRD patterns of supported Ru catalysts (a) Ru/C (b) Ru/AL (c) Ru/SA (d) Ru/HT

XRD

Catalyst Theoretical

[wt%]

Actual

[wt%]

Pd/C 3 3

Pd/AL 3 3

Pd/SA 3 2.8

Pd/HT 3 2.9

Pt/C 3 3

Pt/AL 3.5 3.3

Pt/SA 2 2

Pt/HT 3.5 3.2

Ru/C 3 3

Ru/AL 3 2.8

Ru/SA 3 3.1

Ru/HT 3 2.9

ICP-OES

HDO of phenol

Possible products formed in HDO of phenol. Where ‘1’ is phenol, ‘2’ is cyclohexanol, ‘3’is cyclohexene, ‘4’ is

cyclohexane and ‘5’ is benzene.

Reaction conditions: Phenol (2 mmol), Catalyst

(Substrate/Metal = 200 mole ratio), Hexadecane (30 mL), H2

pressure at RT = 3 MPa, 250 °C, 1h.

Complete HDO activity achieved on supported metals were found to be far better than the earlier works

where cyclohexane (4) yield was very less (4 %) even when reactions were done at 400 °C over sulfided CoMo catalysts

HDO of guaiacol: Role of acidic support

Reaction conditions: Guaiacol (12 mmol), Catalyst (0.2 g), Hexadecane (30 mL), H2 pressure at RT=3 MPa, 250 °C, 1-6h

AL (0.1mmol/g) (less acidic)

100% 100%

12% 44%

75% 42%

13% 14%

3h 6h

SA (0.63mmol/g)

(acidic)

3h 6h

88% 99%

2% 0%

36% 77%

48% 20%

Conv.

-------

1h 100% 100%

Pd/C Pd/C

HDO of guaiacol

Possible products formed in HDO of guaiacol Reaction conditions: Guaiacol (12 mmol), Catalyst (0.2 g),

Hexadecane (30 mL), H2 pressure at RT = 3 MPa, 250 °C, 1h.

Catalytic studies using Pd catalysts

First step of ring hydrogenation is a metal catalyzed reaction however, further cleavage of C-O bond happens only when the support is acidic (SA)

C-O bond dissociation energy in guaiacol (6) (aromatic alcohol) (469 kJmol-1) is greater than that of methoxy cyclohexanol (7) (secondary alcohol) (385 kJmol-1). Therefore during HDO reactions, guaiacol (6) will first undergo hydrogenation to obtain methoxy cyclohexanol (7) , followed by deoxygenation to obtain cyclohexane (4)

HDO of guaiacol: Role of acidic support

Reaction conditions: Guaiacol (12 mmol), Catalyst (0.2 g), Hexadecane (30 mL), H2 pressure at RT=3 MPa, 250 °C, 1-6h

AL (0.1mmol/g) (less acidic)

100% 100%

12% 44%

75% 42%

13% 14%

3h 6h

SA (0.63mmol/g)

(acidic)

3h 6h

88% 99%

2% 0%

36% 77%

48% 20%

Conv.

-------

1h 100% 100%

Pd/C Pd/C

SA (0.63mmol/g)

(acidic)

AL (0.1mmol/g) (less acidic)

C (neutral)

HT (0.88mmol/g)

(basic)

HDO of guaiacol: Catalytic studies using Pt and Ru catalysts

76% 61%

75% 54% 10% 29%

7%

41% 66%

17% 5% 80% 19%

14% 11% 5%

87% 37% 49% 38%

12%

6%

47% 25%

Pt Ru

Pt Ru

Pt Ru

Pt Ru

Reaction conditions: Guaiacol (12 mmol), Catalyst (0.2 g), Hexadecane (30 mL), H2

pressure at RT=3 MPa, 250 °C, 1h.

5%

Conv.

Pt/AL

41% 50% 70%

10% 20% 25%

17% 14% 25%

14% 15% 20%

1h 3h 6h

Pd/SA

1h 3h 6h

52% 78% 88%

0% 0% 0%

50% 75% 80%

0% 0% 0%

Reaction conditions: Guaiacol (12 mmol), Catalyst (0.2 g), Hexadecane (30 mL), H2

pressure at RT=3 MPa, 250 °C, 1-6h

HDO of guaiacol: Time study

Conv.

Reaction conditions: Guaiacol (12 mmol), Pd/SA (0.2g),

Hexadecane (30 mL), H2 pressure at RT = 3 MPa, 200-250 °C,

3h.

0

10

20

30

40

50

60

70

80

90

100

200 230 250

Yie

ld(%

)

Temperature (°C) Reaction conditions: Guaiacol (12mmol), Pd/SA (0.2 g),

Hexadecane (30 mL), H2 pressure at RT = 1-3 MPa, 250 °C,

3h.

Temperature study Pressure study

0

10

20

30

40

50

60

70

80

90

100

1 2 3

Yie

ld(%

)

Pressure(MPa)

HDO of guaiacol

Recycle study: Catalysts were recycled upto4 cycles, without undergoing any deactivation

Catalyst stablity (spent catalyst) was also confirrmed using XRD and ICP-OES analysis

HDO of eugenol

Possible products formed in HDO of eugenol. Where ‘13’ is eugenol, ‘14’ is propylguaiacol, ‘15’ is propylphenol, ‘16’ is propylcyclohexanol, ‘17’ is propylcyclohexane, ‘18’ is propylmethoxycyclohexanol, ‘19’ is methoxypropylcyclohexane, ‘20’ is isoeugenol and ‘21’ is methylguaiacol

Catalytic studies over Pd catalysts

Reaction conditions: Eugenol (2 mmol), Catalyst (Substrate/Metal = 200 mole ratio), Hexadecane (30 mL), H2 pressure at RT = 3 MPa, 250 °C, 1 h.

HDO of eugenol:Catalytic studies over Ru and Pt catalysts

Reaction conditions: Eugenol (2 mmol), Catalyst (Substrate/Metal = 200 mole ratio), Hexadecane (30 mL), H2 pressure at RT = 3 MPa, 250 °C, 1 h. Conversion was 100 % for all the catalytic reactions

Ru

Pt

Recycle study: Catalysts were recycled upto4 cycles, without undergoing any deactivation. Catalyst stablity (spent catalyst) was also confirrmed using XRD and ICP-OES analysis

Effect of electron density (deficiency or richness) of metal particles on supports

When a metal is loaded on an acidic support, there occurs a polarization of electron density of metal atom towards the nearby cations on the acidic support (Brönsted acidity)

If metal-support interaction is present, XPS analysis of these matal show a poitive shift in B.E B.E. of Pd/SA and Pd/C appear at 333.5 and 340.7 eV corresponding to Pd3d5/2 and Pd3d3/2,

respectively which corresponds to fully reduced Pd nanoparticles XPS data shown here for Pd/SA doesn’t show a positive shift in the binding energy values of

Pd3d5/2 and Pd3d3/2, which indicates that the metal nanoparticles are less dependent on the support acidity.

330 335 340 345 350

Pd0 3d 3/2

Binding Energy (eV)

Inte

nsity (

a.u

.)

335.5

Pd0 3d 5/2

340.7

330 335 340 345 350

Pd0 3d5/2

Inte

nsity (

a.u

.)

Binding energy (eV)

335.4

Pd0 3d5/2

340.7

Pd/SA Pd/C

Reaction conditions: Guaiacol (0.164 g) + Eugenol (0.164 g), Catalyst (0.065 g), hexadecane (30 mL), H2 pressure at RT = 3MPa, 250 0C, 1 h.

HDO of guaiacol and eugenol mixture over Pt catalysts

SA

(acidic)

C (neutral)

88% 0% 0% 85%

99% 98% 0% 0%

100% 80% 0% 4% 0% 12%

100% 10% 0% 0% 80% 0%

Conv. Conv.

Metal supported on acidic supports can preferably perform maximum HDO under the optimized reaction conditions

The studies performed here will help in designing highly active catalysts for the complete HDO of lignin derived aromatic monomers

Complete HDO of lignin derived aromatic monomer mixture using supported metal catalysts which will finally help in the one pot HDO of lignin into hydrocarbon fuels using the best catalytic system.

For catalyst with acidic support, the phenol molecule will approach and adsorb on the catalyst surface in vertical manner resulting in deoxygenation. But in the case of catalyst with neutral support, planar interaction was observed between the aromatic ring and support

Mechanism proposed for ring hydrogenation versus HDO for lignin derived aromatic monomers

The main aim of this work was to understand the role of metal and support in HDO reactions of phenol, guaiacol and eugenol Combination of any metal with strong acidic support helps to achieve best HDO activity Neutral and basic supports, selectively ring hydrogenation products can be obtained

Catalyst recyclability study was performed (at least 4 times) Mixture of phenolic compounds (guaiacol and eugenol) which mimics actual lignin derived bio-oils was also studied The understanding of the catalysts functionalities will help to enhance the yields of desired products and develop active catalysts

Conclusions

For further reading………

• Function of metals and supports on the hydrodeoxygenation of phenolic compounds. A. K. Deepa and Paresh L. Dhepe, ChemPlusChem, 2014, 79, 1573-1583. http://onlinelibrary.wiley.com/doi/10.1002/cplu.201402145/abstract