Robert Schlögl

Fritz-Haber-Institut, Berlinwww. fhi-berlin. mpg.de

MPI CEC, Mülheimwww.cec.mpg.de

Energy Transformation:Heterogeneous Catalysis from a

Fundamental Perspective

A. Trunschke, A. Knop-Gericke, M. Willinger

H.J Freund and teamR. Horn and team F. Neese and team

Energy systems: sustainability

• One element in sustainable systems are closed material cycles for harmful and rare resources.

• Many different realizations and socio-economic boundary conditions (Europe, US, China).

• De-carbonisation is not the target.

• Closing the CO2 cycle is!

3

Who is doing what?• Few large emitters and a

many small ones like Germany.

• The climate is protected only if a substantial number of emitters take steps against growing CO2.

• Even without this the growing scarcity of useful fossil resources and security arguments call for a change of the energy supply.

• Measures that impede a joint action are counterproductive for the targets of energy transformation.

How large is the systemic challenge ?• Power generation is the

largest contribution to CO2 in Germany.

• All REN in Germany save 220.000 tpd CO2.

• Almost overcompensated by using more lignite than gas.

• Germany emits daily ca. 2.2 Mt CO2 from energy, (2.6 MT total).

• To contribute significantly to sustainability we need to process ca. 325.000 tpdCO2 with hydrogen from renewable sources.

A systemic solution is best• Reduction of

emission by substitution and saving.

• Renewable electricity for power and heat.

• Better use of domestic thermal energy.

• Chemistry provides energy carriers for mobility and chemical transformations.

Targets for CEC

Summary I• The chemical industry is a small player in the global energy

consumption and in its CO2 emission; this does not exclude the deep involvement of chemistry in the energy transformation.

• Chemical industry is advanced in energy integration and utilization. Some potential in better processes.

• The main levers for the energy system are competence and technology of chemical industry to generate sustainable chemical energy carriers: larger operation than all present activities.

• The raw material change offers challenges: fossil (and limited biomass) sources need novel upgrading now: save fossils for materials!

• CO2 hydrogenation (power to X) as alternative is not yet ready as business case and as technology system.

• The critical science in this endeavour is catalysis (chemo- electro-photo-) through heterogeneous interfaces.

• Let us create now the solutions needed.

Catalysis is system chemistry

We want to know the working structure in order to control the function

9

Reaction networks in raw material change

• Constructed only for the „organic“ part of the overall process.

• Universal form of oxygen for C-H activation, water formation, oxygen transfer and stabilization of oxidiccatalysts.

• Mean field approximation, static catalyst (*) that performs all functions.

10

Details on active sites: beyond models

• In VxOy catalysts a pressure gap between NAP and atmospheric pressure can exist.

• M1 seems to be insensitive to this artefact.

• The valence change in VxOy occurs at the vanadyl group.

reaction mix (C4/O2)

oxygen

total pressure (mbar)

103,3100

1000

10

10100

1000

total pressure (mbar)

H.J. Freund et al. (2003)11

Can we see the surface structure ?

20s

10s

500ms

2s

1s

100ms

1 nm12

The bulk of a catalyst is „frustrated“

• Perfect crystals are catalytically inactive: they exhibit stable terminations and are inert towards adsorption.

• Nanostructuring and bulk defects are critical for operation:

• Static surface sites for dissociation and reaction-induced dynamics.

Mo rich

V rich

oxygen

channel sites13

Precision of structure

M1M2 M4

M9M10

M11

M8M6

M5

M3

M7

89°

89°(109±4)°

(69±5)°

14

Summary II• Catalysts are homogeneous

metastable solids.• They form in mesoscopic

dimensions dynamical active sites on their way to greater stability.

• Kinetic enabling of surface activation needs to be accompanied by kinetic stabilization of the bulk against segregation and defect healing.

• We need insight into catalyst kinetics forming active sites in addition to reaction kinetics using active sites.

15

The grand challenge of catalysis in chemical energy conversion

• CEC for storing electrical energy needs electrons to reduce oxidized molecules.

• These electrons can in sustainable manner only come from oxidation of water.

• This reaction requires a catalyst capable of splitting water and transferring several charges onto an oxoanion.

This reaction is the source of electrons to generate hydrogen and reduction equivalents for all chemical energy storage reactions.

This is independent of electro-or photocatalysis 16

Master Nature• Nature also uses water

oxidation as platform reaction to store free energy and generate reduced carbon species.

• Molecular water splitting with individual free electrons from photo activation.

• Dynamics and 3-D architecture: still issues with stability.

CP43CP47

D1 D2

lumenPsbOPsbU

PsbV

cytoplasm

C2-Axis

cyt b-559

The best we can do: Ir electro catalyst

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

0.0

0.5

1.0

1.5 1 2

curre

nt /

mA

potential / V

# 18281 Pt/Nafion/Ir

18

Status of the working surface• In-situ XPS reveals

a mixture of metal, oxide and oxi-hydroxides at the working surface.

• Intricate mixture of semiconducting and metallic properties.

• Origin of over-potential? Surface analysis with less than 1 nm depth informtion

19

Practical relevance• Explanation for

notorious instability of diluted and supported systems.

• Corrosion of carbon support a critical issue.

• Prototypical behaviour for other electrodes such as Pt , Ru or Mn-oxides.

0 30 60 90 120 150 180

0

10

20

30

40

50

j (m

A/cm

2 geo.)

Time (min)

Ir/C Ruβ A

0.5 M H2SO41.55 V vs. SCE

Chronoamperometry

In collaboration with BASF (Prof. Walther and team)

Summary III• Electro-catalysts behave

chemically like chemo-catalysts.• They develop under significant

chemical potential a dynamical interface and active sites.

• This is a 3-D hierarchical structure that is only poorly modelled by a flat metal surface.

• Reaction intermediates (like HOO*) and uncontrolled charge carrier transport hold complex challenges for stability at operation conditions above the biological equivalent. (1 mA/cm2

at 100% FE).

Future strategy

• The combination of model studies with rational synthesis and advanced in-situ analysis provided foundations for the physical understanding of interfacial reactions

• The conversion into a design concept based upon full reaction networks including molecular and catalyst transformations is the next target.

• We have developed a strategy for collaborative creation of a knowledge base for interfacial catalytic reactions.

22

Predictions in science„Ich vertraue auf das Pferd“

„Das Auto ist eine vorübergehende

Erscheinung“

Oder doch besser:

„Dem Anwenden muss das Erkennen vorausgehen“

(Max Planck)

23

Thank You24

25

How large is the real challenge• Power generation is the

largest contribution to CO2 in Germany.

• All REN in Germany save 220.000 tpd CO2.

• Almost overcompensated by using more lignite than gas.

• Germany emits daily ca. 2.2 Mt CO2 from energy, (2.6 MT total).

• To contribute significantly to sustainability we need to process ca. 250.000 tpdCO2 with hydrogen from renewable sources.

Data: Germany 2013Source BMWI

A practical realization of systemic energy supply:power from two independent systems!

• Fossil fuels forcompensatingnegative volatiliy.

• Excess renewable energy is first converted in high-value chemicals: solar fuels.

• Not possible without suitable catalysis: now?

27

The way to sustainability: only with chemistry

• Reduction of the energy-related emissions in the first world.

• Soft landing of the emission growth trends in Asia.

• Become technically and societal more energy efficient.

• The big things first: Systemic character

28