www.ecn.nl

Catalysts for Hydrogen Production in Membrane and Sorbent Reformers

Paul van Beurden, Eric van Dijk, Yvonne van Delft, Ruud van den Brink, Daan Jansen

Hydrogen Production with CO2 Capture

• Conventional CO2/H2 separation (PSA, scrubbers) involves many steps: Efficiency losses

GTCCGTCC

Air

O2, 79% N2

N2, H2O

LTS

Reformingor

Coal Gasification

Shift H2/CO2

separation CO2

H2

HTS

Natural gasor Coal

GTCCGTCCAir

N2, H2O

Reformingor

Coal Gasification

Separation-EnhancedWater Gas Shift

CO2

H2

Natural gasor Coal

Integration of shift- and CO2 capture steps

Separation-EnhancedReforming

Natural gas

One-step reforming and CO2 separation

GTCCGTCC

N2, H2O

Air

CO2

H2

Separation-enhanced Reforming

Steam reforming: CH4 + H2O 3 H2 + CO (H = 206 kJ/mol)

Water-gas shift: CO + H2O H2 + CO2 (H = – 41 kJ/mol)

Overall: CH4 + 2 H2O 4 H2 + CO2

CH4 + H2OCH4 + H2OCH4 + H2O

SMR-catalyst+

CO2 adsorbent

H2 (+ traces CO, CH4)

Sorption-

enhanced

reactors

CH4 + H2OCH4 + H2OCH4 + H2O

Pd-alloymembranecatalyst

Membrane

reactors

H2

H2

steamCO2 CO2 (+ traces CO, CH4, H2)

= Catalyst

The Water Gas Shift Equilibrium

CO + H2O H2 + CO2 (H = – 41 kJ/mol)

CO

con

vers

ion

Temperature

Water Gas Shift Catalysts

• Low-temperature shift catalysts‑ CuO /ZnO2 /Al2O3

‑ Operating Temperature: 185 – 275°C‑ Sulphur tolerance < 0.1 ppm

• High-temperature shift catalysts‑ Fe3O4 / Cr2O3

‑ Operating Temperature: 350 – 520°C‑ Sulphur tolerance 50 ppm

• Sulphur-tolerant shift catalysts‑ CoMoS‑ Operating Temperature: 250 – 500°C‑ > 100 ppm of sulphur is required in the feed

HTS catalyst in separation enhanced CO2 capture

H2 membranes CO2 sorbents

T > 520 °C In case of high CO concentration

Pre-shift necessary, high steam demand

Oxidation by steam May be an issue In regeneration mode:

Hydrogen co-feeding

Reduction because

CO2/CO ratio too low

- May be an issue at high temperature

Interaction with membrane / sorbent

Possible

Separate catalyst from membrane

Possible

Not observed in experiments

The Methane Steam Reforming Reaction

CH4 + 2 H2O 4H2 + CO2 (H = 165 kJ/mol)

CH

4 co

nver

sion

Temperature

Methane Steam Reforming Catalysts

• Ni-based catalysts‑ Used in industrial reforming at 800 – 1000 °C‑ Prone to oxidation and carbon formation

• Noble-metal based catalysts‑ Mainly Rhodium as active metal‑ Used/developed for low-temperature reforming

and more dynamic reforming

Activity at 400°C

• CeO2 and ZrO2 seem to promote activity at low temperature

0

5

10

15

20

25

Rh/LC

Z

Rh/CZA

Rh/ZrO

2

Rh/CeO

2

Rh/TiO

2

Rh/Al2O

3

Rh/M

gAl2O

4

Rh/M

orde

nite

Rh/La

CaCrO

x

Ac

tiv

ity

(a

.u.)

0

10

20

30

40

50

60

70

Dis

pe

rsio

n (

%)

CH4 2.9%

H2O 17.5%

N2 79.6%

Flow 25 sccm

T = 400 °C

P = 1 atm

Activity at higher temperatures

0

10

20

30

40

50

60

70

175 225 275 325 375 425 475 525

Temperature [C]

CH

4 C

onve

rsio

n [%

]

CH4 2.9%

H2O 17.5%

N2 79.6%

Flow 25 sccm

P = 1 atm

Dilution 1:5

Rh/CeZrO2

Rh/ZrO2

Rh/Al2O3

Rh/CeO2

Stability of commercial catalysts

0

10

20

30

40

50

60

70

0 20 40 60 80 100

Time [hr]

CH

4 C

onve

rsio

n [%

]

Ni-catalystVendor A

Noble Metal catalyst Vendor B

Noble metal catalyst Vendor C

Noble metal catalystVendor A

Noble metal catalystECN

CH4 2.9%

H2O 17.5%

N2 79.6%

Flow 25 sccm

T = 500 °C

P = 1 atm

Membrane reformer:Experimental

• ECN PdAg-membrane on ceramic support

• Catalyst: Nickel based reforming catalyst

• T = 650°C

• Feed pressure = 11 bar(a)

• Steam/CH4 ratio = 3

Membrane reformer

• Equilibrium is shifted at lower space velocities

0%

25%

50%

75%

100%

0,0 1,0 2,0 3,0 4,0 5,0

CH4 feed flow [nl/min]

CH

4 co

nver

sion

MR

FBR

Thermo

Coke formation !

Experimental conditions- 100 ml/min flows- 1 – 5 grams sample- 1 – 4 bar(a)- Sorbent only or

sorbent/catalyst mixture

Materials Research – Experimental Apparatus

Materials- Commercially available noble-metal

based catalyst

- 22 wt% K2CO3-Hydrotalcites

Sorption-enhanced reforming: three individual cycles

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250Time [min]

conc

entr

atio

n [v

ol%

]

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%desorption desorption desorptionads ads ads ads

CH4

CO2

Conversion

Reaction conditions: 2.9% CH4, 17.5% H2O, 79.5% N2, 400°C Breakthrough of methane before CO2

CH

4 c

onv

ersi

on [

%]

Sorption-enhanced reforming

• Using a higher amount of catalyst suppresses methane breakthrough

• Amount of catalyst much higher than necessary to reach equilibrium

Reaction conditions: 2.9% CH4, 17.5% H2O, 79.5% N2, 400°C

0

0.2

0.4

0.6

0.8

0 10 20 30 40Elapsed time [min]

Con

cent

ratio

n [%

] adsorption desorptionsolid line: 3.0 g cat + 3.0 g ads

dashed line: 1.5 g cat + 3.0 g ads

CH4

CO2

Preliminary cost calculations for 400 MW NGCC

• For sorption-enhanced reformers, noble-metal catalyst costs are enormous.

• Rhodium-based catalyst costs are 5 times as high as Pd-membrane costs.

SESMR SESMR membraneCatalyst type 1wt% Rh Ni-based 1 wt% RhTemperature [°C] 400 400 650Sorbent/membrane [M Euro /yr] 2.7 2.7 0.9Catalyst [M Euro /yr] 138 8 4.6Natural gas [M Euro /yr] 96 96 97

Costs of Rhodium are very high at the moment…

Challenges for catalysts in separation enhanced reactions

• High activity at relatively low temperatures

• Resistant to carbon formation

Carbon formation

• Possible routes to carbon formation:

‑ Decomposition of CH4:

CH4 2H2 + C (high T)

‑ Boudouard:

2CO CO2 + C (low T)

0

2

4

6

8

10

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5O/C

H/C

400 °C500 °C600 °C700 °C

Carbon Formation

ATR

SR

H2 w

ithd

rawal

DR

Challenges for catalysts in separation enhanced reactions

• High activity at relatively low temperatures

• Resistant to carbon formation

• Stability under high carbon or strongly reducing conditions

• SERP: resistant to pure steam in sorbent regeneration step: Ni-based catalysts oxidise.

•Membrane: no negative interaction with PdAg-membrane

Conclusions

• The catalyst is an issue for both membrane and sorption-enhanced reforming!

• Nickel-based catalyst showed coking in membrane reactor experiment

• Rh-based catalysts are very active, but price is too high.‑ Ce and Zr promote low-temperature activity‑ Stability uncertain

Future work

• Continue study of (pre)commercial catalysts

• Study mechanism of low-temperature reforming and coke formation and development of low-cost catalysts.‑ Dutch CATHY-project with Technical University

of Eindhoven.

• Kinetics

Acknowledgement

CATO is the Dutch national research programme on CO2 Capture and Storage. CATO is financially supported by the Dutch Ministry of Economic Affairs (EZ) and the consortium partners. (www.co2-cato.nl)

GCEP: Global Climate and Energy Program:

‑ Stanford University

‑ ExxonMobil, GE, Toyota, Schlumberger