Progress in Catalyst Development for Hydrogen Production by Ethanol Steam 

Reforming

D.KunzruDept. of Chemical Engineering

Indian Institute of Technology KanpurKanpur,India

1st Chemistry in Energy ConferenceJuly 20‐22,2015,Edinburgh,UK

Introduction

• hydrogen is an ideal candidate for future sustainable energy systems ( high energy content, emission-free, can be used in a variety of applications)

• reforming of hydrocarbons (methane, naphtha, diesel, alcohols) can be used for producing hydrogen

• reforming is a highly endothermic reaction and requires high temperature

C2H5OH +3H2O                 2CO2+6H2 298 174 /oKH kJ mol

Advantages of Using Ethanol

• does not contribute to the greenhouse gas emissions (steam reforming of ethanol releases the same amount of CO2 as that consumed by biomass growth)

• easily available • non-toxic and sulphur-free• easy to transport• can be produced by fermentation

from renewable biomass sources

Reactions Involved during ESR

CH3CHO CH4 + CO

CO2 + H2CO + H2

CH4 CO2

CokeC2H4

C2H5OH

‐ H2‐ O2

+ H2O+ H2O

+ H2O

‐ H2O

+ H2 ‐ H2

WGS

Catalysts• Both metal and support affect the reaction

• Ethanol activated on the metal site; water activated on the support

• A variety of combination of metals and support have been reported

• Catalyst with higher WGS activity give higher hydrogen yields

Catalysts (contd.)

Noble metals : Rh, Pt, Pd, Ru Non-noble metals: Ni, Co, CuCombinations : Rh-Ni, Rh-Co, Rh-Pd, Rh-Pt, Pt-Ni,

Pt-Co, Ru-Ni, Ni-CuSupports : Al2O3, CeO2,ZrO2,TiO2, MgO, Zeolites,

CeO2-Al2O3, CeO2-ZrO2, Al2O3-ZrO2

Rh and Ni give the highest activity and selectivity to H2

Ni-based catalystsNi/γ Al2O3 : shows high activity and selectivity to H2

• Al2O3 promotes dehydration and cracking ofC2H5OH on the acidic sites; does not possesssignificant WGS activity

• Significant amounts of ethylene formed-polymerizesto coke

• Catalyst deactivates rapidly- deactivation correlateswell with the ethylene yield

Basic additives or promoters that favour wateradsorption and OH surface mobility added to lowercoke deposition

Catalysts Findings Ref.

Ni/Ce0.63Zr0.37O2,Ni/CeO2 , Ni/12%CeO2‐ɣAl2O3,Ni/ɣ‐Al2O3

T=873K, Steam/EtOH=3

Order of activity : Ni/Ce0.63Zr0.37O2>Ni/CeO2 > Ni/12%CeO2‐ɣAl2O3 >Ni/ɣ‐Al2O3The activity in the SR varied directly as the degree of mobility of surface OH groups 

Aupretre et al.(2002)

Ni/MxOy‐Al2O3 (M=Ce, La, Zr or Mg)

T=773K, Steam/EtOH=3

Metal dispersion :La2O3–Al2O3 > MgO–Al2O3 > CeO2–Al2O3 > Al2O3 > ZrO2–Al2O3Higher reforming activity of Ni/MgO‐Al2O3 due to  lower acidity and better dispersion than Ni/Al2O3.For Ce‐ and Zr‐promoted catalyststhe improvement in intrinsic activitydue to enhancement of wateradsorption/dissociation.Lower intrinsic activity of Ni/La2O3–Al2O3 : dilution effect caused by thepresence of lanthanum on Ni surfaces

Sánchez‐Sánchez et al.(2006)

Effect of Support

Catalysts Findings Ref.

Ni/Ce1−x ZrxO2 (x = 0, 0.26, 0.59, 0.84 and 1)T=673‐923K, Steam/EtOH=8

Ni/Ce0.74Zr0.26O2 with 30 wt% metalloading exhibited high catalytic activity andhydrogen selectivity

Biswas and Kunzru (2007)

Ni/Al2O3‐LaX ,(X =0‐12wt% La2O3)T=673‐873K, Steam/EtOH=3

Lanthanum improved the dispersion of the nickel oxide phase  and also increased the number of NiO species reducing at low temperature. Hydrogen yield was higher over La‐containing catalysts. Larger proportion of carbon deposits gasified at lower temperature with increasing La content .

Melchor‐Hernández et al.(2013)

CeO2‐ promoted Ni/SBA‐15T=923K,Steam/EtOH=4

Coke deposition and nickel metal sintering were significantly suppressed.

Li et al.(2015)

Effect of Support (contd.)

Rh-based catalysts• Supports commonly used: Al2O3,CeO2,CeO2-Al2O3,

La2O3-Al2O3 and CeO2-ZrO2

• Order of activity (Aupretre et al.,2002): Rh/Ce0.63Zr0.37O2 > Rh/12%CeO2-Al2O3 > Rh/CeO2 > Rh/Al2O3

• On Rh/CeO2, strong interaction between Rh and ceria inhibits particle sintering (Rh-O-Ce acts as an anchor).

• Ceria promotes the dissociation of H2O providing OH groups or mobile O-promotes carbon gasification.

TPR profiles (a) 2Rh/Al (b) 2Rh/10Ce/Al(c) 2Rh/20Ce/Al (d) 2Rh/30Ce/Al (e) 1Rh/20Ce/Al

SampleH2

uptake,μmol.g-1

Dispersion, %

Metal area Metal particlesize, nmm2.gcat

-1 m2.gmetal-1

2Rh/10Ce/Al 28.2 27.6 2.6 121.5 4.0

2Rh/20Ce/Al 89.4 86.0 8.1 378.4 1.3

2Rh/30Ce/Al 96.8 94.8 8.8 417.2 1.2

1Rh/20Ce/Al 52.5 90.8 4.8 399.4 1.2

2Rh/Al 15.7 16.5 1.4 72.4 6.7

Effect of ceria on metal dispersion and reducibility of Rh/Al2O3

Effect of ceria on conversion

0

20

40

60

80

100

120

650 700 750 800 850 900

Temperature, K

Con

vers

ion,

%

2Rh/Al2Rh/20Ce/Al2Rh/10Ce/Al2Rh/30Ce/Al

• Addition of ceria to Rh/Al2O3 increased the activity of catalyst at low temperatures.

• The higher activity was most probably due to higher dispersion and reducibility.

Peela et al.(2011)

The main reactions occurring during SRE were:Dehydrogenation:  CH3CH2OH  CH3CHO + H2 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐(1)Decomposition of acetaldehyde:     CH3CHO  CH4 + CO                 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐(2)Steam reforming of acetaldehyde:  CH3CHO + H2O  2 CO + 3 H2 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐(3)Steam reforming of methane:  CH4 +  H2O  CO + 3H2 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐(4)Water gas shift reaction:  CO +  H2O  CO2 + H2 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐(5)

Product selectivities on Rh/CeO2-Al2O3 catalyst

0

10

20

30

40

50

60

70

80

90

100

650 700 750 800 850 900

Temperature, K

Sect

ivity

, %

H2CO2COCH4CH3CHO

Catalyst: 2Rh/20Ce/Al

Bimetallic Catalysts• bimetallic catalysts can simultaneously promote the

SRE and WGS to increase the production of H2 and decrease the production of CO.

Ni-Cu

400 450 500 550 600 650

40

50

60

70

80

90

100

Etha

nol c

onve

rsio

n (%

)

Temperature (0C)

N NCu2 NCu5 NCu10

(A)

Addition of Cu  enhanced WGS and acetaldehyde reforming reactions for Ni/CeO2‐ZrO2.

Higher selectivity to CO2 and H2 ; lower  selectivity to CH3CHO.

Biswas and Kunzru (2007)

Rh-Ni

• Addition of Ni to Rh/CeO2‐Al2O3 did not affect the activity

• Addition of Ni reduced the CO selectivity and increased CH4selectivity due to CO hydrogenation

00.5

11.5

22.5

33.5

44.5

350 400 450 500 550 600 650

Sele

ctiv

ity, m

ol/m

ol o

f eth

anol

re

acte

d

Temperature, C

H2COCH4CO2

5Rh/10Ni/20Ce/Al

0

20

40

60

80

100

120

350 400 450 500 550 600 650

Etha

nol c

onve

rsio

n, %

Temperature, C

5Rh/20Ce/Al5Rh/10Ni/20Ce/Al

00.5

11.5

22.5

33.5

44.5

350 400 450 500 550 600 650

Sele

ctiv

ity, m

ol/m

ol o

f eth

anol

reac

ted

Temperature, C

H2COCH4CO2 5Rh/20Ce/Al

Rao and Kunzru,2011

Stability of 5Rh/10Ni/20Ce/Al

• Complete ethanol conversion at 873K and W/FA0 of 1.6 g.h.mol-1

• Dry reformate composition – 51 mol% H2, 7 mol% CO, 3 mol% CH4 and 13 mol% CO2 ( balance N2)

• Highly stable for 100h and no degradation in activity and selectivity to H2.

0

20

40

60

80

100

0

1

2

3

4

5

0 20 40 60 80 100

Etha

nol c

onve

rsio

n, %

Sele

ctiv

ity, m

ol/m

ol o

f eth

anol

re

acte

d

Time-on-stream, h

H2COCH4CO2Conversion

0

2

4

6

8

10

12

14

30 130 230 330 430 530 630 730

Wei

ght o

f the

sam

ple,

mg

Oxidation temperature, C

o Addition of  1 wt% Rh to 30 wt% Ni/CeO2‐ZrO2 promoted reducibiltyand   dispersion of NiO – Mondal et al.(2015)

Rh-Pd ( Scott et al.,2008)• 1/2wt.% Rh-1/2wt.% Pd/CeO2 gave higher conversion

and hydrogen yield in comparison to 1 wt.% Rh/CeO2or 1 wt.% Pd/CeO2

• Rh/CeO2 dissociates C-C bond; Pd catalyses WGS and hydrogen recombination

• active sites composed of very small particles (~1nm) of the transition metals, within the CeO2 support.

• Active sites at Rh-Ce and Pd-Ce interface.

• At steam/EtOH of 6 and 777K, the catalyst was stable for 2 weeks.

Rh-Pt ( Cobo et al.,2013)

• Rh-Pt supported on La2O3 showed high catalytic performance and good stability.

• Rh-Pt-Rh2O3 proposed as the active sites.

• At steam/EtOH of 7 and 873 K, the catalyst was stable for 120 h.

Kinetic Modeling• kinetics studied over various catalysts

• power law rate expressions or Langmuir –Hinshelwood/Eley-Rideal models used

• reports on kinetics show significant differences

• maybe due to the different catalyst used and/or the different reaction conditions

Power law kinetics• Normally fitted as –rSRE =  • Wide variation in the reported values of α and β

Catalyst Temp. range, K

Steam/EtOH

α β Reference

Ni/Al2O3 673 4.3 2.52 7.0 Therdthianwong et al. (2001)

Ni‐Al‐LDH 550‐923 5.5 0.8 0 Mas et al.(2008)

Ni/MgO‐Al2O3

673‐873 3‐18 0.71 2.71 Mathure et al.(2007)

Ru/Al2O3 873‐973 10 1.0 0 Vaidya and Rodrigues(2006)

Pt/CeO2 573‐723 1.5‐6 0.5 0 0.015 Ciambelli et al.(2010)

Rh‐Pt / monolith

837‐973 3‐10 0.2/1.2 0 Simson et al. (2009)

L-H and Eley-Rideal kinetic modelsCatalyst Temp. 

range, K

Steam/EtOH

Reactions considered RDS Ref.

Ni‐Al‐LDH 823‐923 5.63 ED:C2H5OHCH4+CO+H2ESR:C2H5OH+H2OCH4+

CO2+2H2MR:CH4+H2OCO+3H2MR1:CH4+2H2OCO2+4H2

C2H5OH*+H2O*CO2+CH4*+2H2+*

CH4*+H2O*CO+3H2+2*

CH4*+2H2O*CO2  +4H2+3*

Mas et al. (2008)

Rh/CeO2 623‐933 4‐8 ED, MR and WGS C2H5OH +*C2H5OH*

CH4*+H2O*CO+3H2+*

CO2*CO2+*

Gorkeet al. (2009)

Rh/MgAl2O4‐Al2O3

773‐873 11.25 ED,ESR,MR, and WGS CHO*+*CO*+H*CHO*+OH*CO2* +   

H2+*CH3*+OH*CO*+

2H2+*CO*+OH*CO2*+H*

Graschinsky et al.(2010)

L-H and Eley-Rideal kinetic models (contd).

Catalyst Temp. range, K

Steam/EtOH

Reactions considered RDS Ref.

Skeletal Ni 573‐673 8 ED, MR and WGS C2H5OH* +*CH4*+CO*+H2

CH4*+H2OCO*+3H2CO*+H2OCO2*+H2

Zhang et al. (2014)

Rh/CeO2‐Al2O3

723‐823 4‐8 ESR,ED, MR and WGS C2H5OH* +H2O*C2H5OOH*+H2* 

C2H5OH*C2H4O*+H2CH4*+H2O*CH4O*+

H2*CO*+H2O*CO2*+H2*

Peelaand Kunzru(2011)

Ni/ɣ Al2O3 473‐873 10 9 elementary steps  CH4+2*CH3*+ H* Wu et al.(2014)

Probable elementary steps during SRE

C2H5OH +*C2H5OH*

C2H5OH*+*CH3CH2O*+H*

CH3CH2O*+*CH3CHO* +H*

CH3CHO* CH3CHO+*

2H*2*+ H2

ETD

CH3CHO+*CH3CHO*

CH3CHO* +*  CH3*+ CHO*

CHO*+ *CO*+H*

CH3*+H*2*+CH4* 

CO* CO+*

ACD

CO+*CO* 

H2O+*H2O*

H2O* +*H*+OH*

CO*+OH*COOH*+*

COOH*+*CO2*+H*

CO2*CO2+*

WGS

MR

CH4+2*CH3*+H*

CH3*+*CH2*+H*

CH2*+*CH*+H*

CH*+H*C*+H*

H2O+*H2O*

H2O* +*H*+OH*

C*+OH*CHO*+*

CHO*+*CO*+H*

2H*H2

CO*CO+*

Conclusions• Rh and Ni show the highest activity for SRE• Basic additives (eg La2O3) or promoters that favour

water adsorption and OH surface mobility(eg CeO2; CeO2-ZrO2) lower the coke deposition

• Addition of another metal can improve the performance.

• The important reactions during SRE are ethanol decomposition, ethanol dehydrogenation, acetaldehyde decomposition, acetaldehyde reforming, MR and WGS.

• The rate determining steps depend on the catalyst and the support.

Acknowledgements• N.R.Peela, P.Biswas• Dept. of Science &Technology, N.Delhi