Catalysis for clean renewable energy technologies

Moshe SheintuchDepartment of Chemical Engineering, Technion, Haifa, Israel

Catalysis for clean renewable energy technologies

Outline• 1. Introduction

• 2. Hydrogen productionSteam reforming Dry reforming Autothermal reforming Novel reactor concepts:

Membrane Reactor ;

Millisecond-contact Reactor;• 3. From renewable

sources to fuels• 4. Fuel Cells• 5. Hydrogen Storage

15% NiO and 85% MgAl2O4

CATALYTIC SCALES (1)

Fcc(110):

The surface atoms on a more open ("rougher") surface have a lower CN -this has important implications when it comes to the chemical reactivity of surfaces

fcc (111):

All surface atoms are equivalent and have a relatively high CN

The surface offers adsorption sites :

• On-top sites

Bridging sites, between two atoms

• Hollow sites, between three atoms

Actual solids:

(i) an angled corner

(ii) a spherical tip

CATALYTIC SCALES (2)

Methane Steam Reforming

222 HCOOHCO +=+224 3HCOOHCH +=+ ][206 11

−⋅=Δ molkJH

][41 12

−⋅−=Δ molkJH222 HCOOHCO +=+

2224 42 HCOOHCH +=+ ][165 13

−⋅=Δ molkJH

Drawbacks:

1. Equilibrium limitations

2. CO is poisonous for fuel cells

3. Heat supply is required

(combustion, nuclear?)

4. CO2 separation.

Drawbacks:

2. Hydrogen Production

Steps: Catalyst Selection

Reactor Design

Alternatives: Dry Reforming

Autothermal Design

MotivationFuel Cells

and Hydrogen

Fuel cells are more effective

than internal combustion engines

Fuel cells are quiet and

pollution-free; Extremely pure

hydrogen is required for effective

fuel cell operation

Hydrogen has the highest

energy content per unit of weight

of any known fuel; there is no

hydrogen fuel infrastructure

Hydrogen fuel is hard to transport

Hydrogen can be produced on-board using a small-

scale catalytic membrane reactor

Steam reforming: Catalyst selection depending on hydrogen source

Hydrogen source

Reforming reactionPromoterSupport2nd -

metal1-st metal

Gaseous hydrocarbons:

C1–C4

Dry R, steam R,

Rare earth oxide, ZrO2, IIA oxides

Al2O3–Co, Ru, Pt, Pd, Rh

C8–C18All reforming

reactionsGd, Sm

CeO2, La2O3, ZrO2,

Ce doped ZSM5,

Ce/Zr/Ladoped Al2O3

Co, Mo, Re

Ni, Pt, Ru, Pd, Rh

MethanolSteam RZnO, ZrO2CeO2, ZrO2,

Al2O3CoCu

EthanolSteam R, OSRLi, Na, KTiO2, ZnO, La2O3, MgO

Ru, Cr, Cu, FePt, Pd, Ni

Adapted from Saxena et al , Energy&Fuel, 2007

Carbon-induced catalyst deactivation is one of the main problems . DFT calculations demonstrate that the carbon tolerance of Ni can be improved by Ni-containing surface alloys that preferentially oxidize C atoms rather than form C–C bonds and have a lower thermodynamic driving force, associated with the nucleation of carbon atoms on low-coordinated Ni sites. Using the molecular insights obtained in the DFT calculations, Sn/Ni surface alloy was identified as a potential carbon-tolerant reforming catalyst in the steam reforming of methane, propane, and isooctane.

(a) Transmission electron micrograph of a Ni particle covered by carbon. (b) DFT-calculated reaction energies for various elementary steps in steam reforming of methane on Ni(111). (from E. Nikolla et al, J. Catal. 2007)

Catalysis for clean renewable energy technologies:2. Hydrogen production

Mechanism of SR on Ni-based catalysts: Theoretical and experimental studies

Membrane reactor concept

D DD

A, B

A, B, C, D

A+B→C+D

A+B→C+D

Shift in reaction equilibrium 1

High perm-selectivity yields

high purity products 2

Schematic Representation: A typical lab-scale MR:

Changes in total olefin yield (f), cracking (y3) and isomerisation (yN) products during isobutanedehydrogenation in a Pd-tube packed with catalyst at 500 o C (Sheintuch and Dessau, 1996)

H2 Separation Membranes

Pd, Pd alloysSupported Pd

ZeoliticSilica

Almost 100% selectivity, high fluxes

High cost

Lower selectivities and fluxes

Potentially low cost

Well-developed preparation technology

Under-development preparation technology

Dense Metallic Nanoporous Ceramic

MEMBRANE ASSISTED FLUIDIZED BED REACTOR FOR H2PRODUCTION BY STEAM REFORMING OF CH4

C. S. PATIL, et al, Chem. Eng. Research and Design, 2006,

(Pd/Inconel membrane) CO selectivity is strongly suppressed due to the selective extraction of H2.

Methane Oxidation (MOx)

OHCOOCH 2224 22 +=+

The heat required for the endothermic reaction is supplied

by the exothermic reaction – reaction coupling 3 concept

Thermal Balancing

Methane Steam Reforming (MSR)

2224 42 HCOOHCH +=+ ][165 13

−⋅=Δ molkJHendothermic

][803 1−⋅−=Δ molkJHOx

exothermic

MEMBRANE REACTOR

Figure 2: Schematic diagram of the double-jacketed membrane reactor (Hou et al, CES 54, 3783-3791, 1999.) 900h of operation.

Combining Membrane Separation

and Thermal Balancing

CH4 + air

CH4

H2O

CO2

H2

CO2 +H2OH2

N2

Reactor schematic: Cross-sectional view:

Exothermic compartment (catalytic oxidation)

Membrane compartment

Endothermic compartment

(steam reforming)

Reactor Analysis

max, /)/(2

YFFY SRmf

MoutH= )/1(4max

SRt

Mt PPY −=2224 42 HCOOHCH +=+

Challenges:

• 1.Experimental verification.

• 2. Cheaper durable membranes.

• 3. CO2 sequestration.

• 4. Integrated vs. distributed design.

• 5. Alternative designs: Autothermal

Addition of small amount of Pd to Ni0.2Mg0.8Al2O4enhanced the catalytic activity and stability for the oxidative SR of methane, where Ni0.2Mg0.8Al2O4 deactivated due to the oxidation of Ni and carbon deposition. Formation of Pd–Ni alloy located preferentially on the surface improved the reducibility of Ni and the resistance to the carbon deposition.

Surface modification of Ni with Pd by a sequential impregnation method (Pd/Ni) was effective for the suppression of hot-spot formation during oxidative SR of methane (from K. Tomishige et al 2007)

2. Hydrogen production: Methane Oxidative Steam Reforming

Thermo-catalytic decomposition, TCD

TCD process, to produce hydrogen and carbon, is an alternative to reforming processes for small-to-medium size facilities

TCD of methane has several advantages over SMR process: no CO is obtained and the production of the ultra pure hydrogen issimpler and cheaper. Although theoretical hydrogen yield for SMRis twice of that for TCD, high reaction endothermicity and CO2sequestration would significantly reduce the net yield of hydrogen produced by SMR.

Metallic and carbonaceous catalysts have been used., The use of carbon catalyst offer several advantages: (i) higher fuel flexibility, (ii) lower price and (iii) the carbon formed can be used as catalyst precursor. But the direction of the ethanol reaction changed, when carbons were applied as a support.

Reaction pathways steam reforming (for ethanol)

RemarksEquationReactionIdeal pathway, the highest hydrogen

productionC2H5OH+3H2O→2C

O2+6H2Steam reforming

Undesirable products, lower hydrogen production

C2H5OH+H2O→2CO+4H2

Steam reforming

Reaction pathways for hydrogen production in practiceC2H5OH→C2H4O+H2Dehydrogenation

Undesired pathway, main source of coke formationC2H5OH→C2H4+H2ODehydration

Coke formation, low hydrogen production

C2H5OH→CO+CH4+H2

Decomposition

CO+3H2→CH4+H2OMethanationReduce coke formation, enhance

hydrogen productionCO+H2O→CO2+H2Water gas shift reaction

(WGSR)

List of steam reforming using noble metal catalyst (for ethanol)

Hydrogen selectivity (%)

Ethanol conversion

(%)

Steam/Ethanol molar

ratioTemp. (K)Suppo

rtCatalyst

951003:11073γ-Al2O3Rh (1 wt%)5542Ru (1 wt%)6560Pt (1 wt%)5055Pd (1 wt%)9199 (10 h)8.5:1923MgORh (3 wt%)7010 (10 h)Pd (3 wt%)

59.758.58:1573CeO2Rh (2 wt%)66.3100673

energy efficiency (%)

cost ($/kg H2)aplant size and technology

central plant

66b2.11 natural gas steam reforming

60c2.17 coal gasification

midsize plant

70d3.94 methane steam reforming

45-50c7.07 biomass gasification

distributed plant

27c7.36 water electrolysis

70-80c3.68 natural gas steam reforming

56-73e6.82 water electrolysis

Cost and Energy Efficiency from the Selected Technologies to Produce Hydroge

Catalysis for clean renewable energy technologies:3. From renewable sources to fuels

Current methods for transformation of biomass into gaseous and liquid fuels(fromG. Huber and J. Dumestic, Catal. Today, 2006

Biodiesel from Low Cost Vegetable Oil and Waste Fats:

Various biodiesel production TE processesSCMeOHmethod enzymatic methodheterogeneous

catalytic methodhomogeneous catalytic

method120-240 s1-8 h 0.5-3 h 0.5-4 h reaction time

C C C C reaction conditions

none immobilized lipase metal oxide or carbonate acid or alkali catalyst

methyl esters methyl esters methyl esters saponified products free fatty acids

high low to high normal normal to high yield

methanolmethanol or methyl acetate methanol methanol, catalyst, and

saponified product removal for purification

none none none wastewater waste

high normal or

triacetylglycerol as byproduct

low to normal low glycerin purity

simplecomplicated complicated complicated process

Adapted from D. Mohan, Energy&Fuels,2006

R.R. Davda, J.W. Shabaker, G.W. Huber, R.D. Cortright and J.A. Dumesic, Appl. Catal. B Environ. 43 (2002), p. 13.

Aqueous-phase reforming (ethylene glycol at 483 K and 22 bar )

Conclusions

1. Hydroprocessing of vegetable oils using transition metal type catalysts is being produced commercially. One of the main drawbacks is that it it requires high pressure. It produces a diesel like products composed of linear hydrocarbons.

2. The use of molecular sieve type catalysts is very promising for the conversion of vegetable oils to highly aromatic gasolines.

3. Heterogeneous catalysis is the backbone of the chemical / petrochemical industry. Few biorefining processes use heterogeneous catalysis. The processing of biomass-derived feedstocks is different due to low thermal stability and a high degree of functionality (typically being hydrophilic in nature), thus requiring unique reaction conditions, such as aqueous-phase processing.

4. Catalytic pyrolysis of vegetable oils can be grouped into : (1) molecular sieve catalysts, (2) activated alumina catalysts, (3) transition metal catalysts and (4) sodium carbonate.

5. The applications of novel solid feed mixtures for pyrolysis, catalysts, co-gas feeds, and related approaches have not been explored very much.

7. The electricity costs from biomass, geothermal and solar sources are within the range of US$ 7–25 cents/kWh, compared to the conventional (coal, natural gas, etc.) electricity costs of US$ 4–6 cents/kWh.

Hydrogen storage in carbon nanotubes

Storage capacity

Concluding remarks

• 1. Short term effort will probably yield small gains using SR with new process designs.

• 2. Long term effort should be addressed to renewable resources. Its economic advantages still debated, may not be economical here (water).

• 3. Catalysis is still an art, basic research that allows computational catalyst selection is required.