Looking into Copper in CO-PROX Catalysts: A Multitechnique Approach

Guillermo Munuera

Departamento de Química Inorgánica. Universidad de Sevilla Instituto de Ciencia de Materiales de Sevilla

(Centro Mixto US-CSIC)

E-mail: munuera@us.es

The participants in the Projects

Instituto de Catalisis y Petroleoquimica CSIC, Madrid, Spain Dpto de Quimica Inorganica e ICMS, Univ. Sevilla-CSIC, Spain Dpto de Ciencia de Materiales, Ing. Met. y Q. Inorg., Univ. Cadiz, Spain Material Science Department, Univ. Cambridge, UK Chemistry Department, Brookhaven National Laboratory, USA

10 years using CuO-CeO2 catalysts for: - CO total oxidation with O2 (TOX) and - CO preferential oxidation in excess of H2 (PROX)

Last 10 years using CuO-CeO2 catalysts CO preferential oxidation in excess of H2 (PROX) Published Items in Each Year Citations in Each Year

Search: Web of Knowledge Period: 2002-2012 Topic: “CO-PROX AND CuO AND CeO2” Results: 49 references Impact: h-index = 17 (cites/item =19.22)

Looking into Copper in CO-PROX Catalysts: A Multitechnique Approach

Catalysis: An integrated Approach to Homogeneous, Heterogeneous and Industrial catalysis

J.A. Moulijn, P.W.N.M. Leeuwen, R.A. van Santen,1993

1- 300 bar.

10-6/10-10 bar

Characterization tecniques used in Catalysis

◊ The “operando” techniques ◊ The “pressure gap” debate

Catalysis: An integrated Approach to Homogeneous, Heterogeneous and Industrial catalysis

J.A. Moulijn, P.W.N.M. Leeuwen, R.A. van Santen, 1993

Proton Exchange Membrane Fuel Cell unit

Industrial Aplications

Proton Exchange Membrane Fuel Cell unit

Hydrogen Powered automotives

Fuel Cells: From PEMFC to SOFC electrolytes

PEMFC : Proton Exchange Membrane Fuel Cell SOFC: Solid Oxide Fuel Cell

Steam Reformer

HT-WGS LT-WGS PROX PEMFC 10 %

CO

3 %

CO

0.5 %

CO

<100 ppm

CO

HC

H2O

H2 generation from HC’s for its use in PEMFC

Thermodynamics of the WGS process

CO + H2O = CO2 + H2

H = - 40.6 kJ mol-1

45-75 % H2+ 0.5-2 % CO + 15-25 % CO2 + few % H2O + HC traces

CO-PROX: CO + H2 + (O2) = CO2 + H2

Catalytic Preferential Oxidation of CO

PROX LT-WGS 0.5-2 %

CO

45-75 % H2 + 0.5-2 % CO + 15-25 % CO2 + few % H2O + HC traces

<100 ppm

CO H2

10 %

CO

●High reactivity for CO oxidation

} CO2-Selectivity ● Low reactivity for H2 oxidation ● High resistence to poisoning by CO2 and H2O

Requirements for CO-PROX catalysts

Systems Supported PtGM

Pt; Pt-Ru; Pt-Rh (promoters; Ru, Rh)

Supported gold Au/Fe2O3; Au/TiO2;

Au/CeO2

Copper-ceria CuO/CeO2;

CuO/(Ce,M)Ox

Conversion window

100-200 oC 50-100 oC 120-200 oC

Selectivity

at full conversion

50 %

(could be enhanced by certain promoters)

50-100 % 80-100 %

Resistance to H2O-CO2

good poor fair

Overview of CO-PROX catalysts

S. Park, R.J. Gorte , J.M Vohs; Applied Catalysis A : General, 200 (2000) 55-61

How to prepare a CuO-CeO2 catalysts ?

3 nm

3.08 3.09 70o

2.7

54o

CuC

Microemulsion preparation

Mn+

Mn+

Mn+

Mn+

Microemulsion A

OH-

OH-

OH-

OH-

Microemulsion B

+ calcined support

A. Martínez-Arias et al. J. Power Sources 151 (2005) 32

1% w/w Cu was incorporated by incipient wetness impregnation

3 nm

3.05 3.01 72o

Sample

Cell parameter

(Å)a

Particle size (nm) (Ce/Tb)atc

Ratio XPS

SBET

(m2g-1)a HREMb XRDa

CuC 5.413 (5.412) 6.7 (8.2) 8.3 (7.9) - 92 (92)

CeTb1 50% Tb

5.367 (5.368) 5.5 (6.9)

6.1 (6.0)

0.89 0.13 95 (95)

CeTb4 20% Tb

5.393 (5.392) 6.6 (9.0)

7.2 (7.4) 4.25 0.75 104 (104)

The copper catalysts were prepared on CeO2 supports contaning 20% and 50% of Tb to examine posible electronic interactions of the support with the CuO active phase of the catalysts during CO-TOX. Data for the respective supports are given in parenthesis

8970 8980 8990 9000 9010 9020

CuC

CuCT1

Absorb

ance S

econd D

eri

vative

Energy (eV)

Cu-ZSM5

CuO

XANES Cu-K edge analysis of calcined CuC and CuCT1

The structure of copper in the original calcined CuC and CuCT1 catalysts is quite different to that 0f small clusters of CuO incorporated into ZSM 5 zeolites, it look more like bulk CuO but cannot be seen eithe by XRD or even by HRTEM

Catalytic tests in CO-TOX

CO-TOX: 1% CO + 0.5% O2 + Ar (balance)

300 350 400 450 500

0

20

40

60

80

100

CO

co

nve

rsio

n (

%)

Temperature (K)

CuC

CuCT1

CuCT4

T50

Temperature / K

Space velocity: 80.000 h-1; heating ramp: 5 K min-1

How work copper in CuC and CuCT catalysts during CO-TOX? Operando – DRIFTS Operando - XPS/XAES

Operando – DRIFTS analysis of CuC, CuCT4 and CuCT1

CuCT1CuCT4

2400 2300 2200 2100 2000 1900

493 K

443 K

413 K

373 K

K-M

Wavenumber (cm-1)

0.1

INIT

313 K

2111

2400 2300 2200 2100 2000 1900

K-M

Wavenumber (cm-1)

0.2

INIT

303 K

363 K

433 K

493 K

2110

2400 2300 2200 2100 2000 1900

443 K

433 K423 K413 K

403 K

393 K

383 K

373 K

363 K

353 K

343 K

333 K

323 K

313 K

303 K

K-M

Wavenumber (cm-1)

0.3

INIT2115

2110

CuCCuC (0% Tb) CuCT4 (20% Tb) CuCT1 (50% Tb)

The amount of Cu+-CO species, at 2110 cm-1 , decreases with increasing Tb content in the CeO2 support indicating a lost of Cu+ centers for CO

CO-TOX: 1% CO + 0.5% O2

Operando – DRIFTS vs. Catalytic tests

280 300 320 340 360 380 400 420 440 460 480

0

250

500

750

1000

1250

CO2(g) CuC

I Cu+-carbonyl CuC

CO2(g) CuCT4

I Cu+-carbonyl CuCT4

CO2(g) CuCT1

I Cu+-carbonyl CuCT1

I C

u+

-ca

rbo

nyl (a

.u.)

m/e

= 4

4 in

ten

sity (

a.u

.)

Temperature (K)

Cu+-CO

CO2

CuC

CuCT4

CuCT1

A. Martinez-Arias, Physical Chemistry and Chemical Physics, 14 (2012) 2144-2151

CO-TOX: 1% CO + 0.5% O2

Operando - XPS/XAES

Main Chamber XPS, XAES and LEIS Reaction Chamber: Gas manifold/MS, Ion-sputtering

Operando - XPS/XAES

250 300 350 400 450 500 550 600 650 700

0

20

40

60

80CuCT4

CuCT1 2CO + O

2 --> CO

2

"light off" / 7.5Kmin-1

CO/O2 = 2:1 (P

T=1.5 torr)

T50

=580KCuC

Temperature / ºK

% C

on

ve

rsio

n

500K

A. Martinez-Arias et al Phys. Chem Chem Phys 14 (2012) 2144-2151.

930 920 910 900 890 880 870

0

5

10

15

20

b)

a)

917.0

Ce3d_23.opj

a) O2

+-etched

b) Ar+-etched

Sample C1

XPS: Ce(3d)

Inte

nsity /

a.u

.

Binding Energy / eV1290 1280 1270 1260 1250 1240 1230

0

1

2

3

4

5

6 1241.3

Tb3d_3y4.opj

1276

XPS: Tb(3d)

H2.773K

O2.773K

Inte

nsity /

a.

un

its

Binding Energy / eV

Factor Analisis: Ce(3d) and Tb(3d) in CuCT1

XPS: Ce(3d) CeO2 vs. Ce2O3

XPS: Tb(3d) TbO2 vs. Tb2O3

1290 1280 1270 1260 1250 1240 1230

CuCT1_sel.opj

41.3%

Tb(III)

71.5%

Tb(III)

0%

Tb(III)

43.9%

Tb(III)

(d)

(c)

(b)

(a)

(a) Evac 473K 1h

(b) O2 / 1torr 473K 30min

(c) CO / 1torr 373K 30min

(d) CO+O2(2:1) 373K 30min

CuCT1: Tb(3d)

Fitting

B

C

Inte

nsity / a

.un

its

B.Energy / eV

920 910 900 890 880

99.0%

Ce(IV)

98.1%

Ce(IV)

100%

Ce(IV)

100%

Ce(IV)

CuCTCe_sel.opj

(d)

(c)

(b)

(a)

(a) Evac 473K 1h

(b) O2 / 1torr 473K 30min

(c) CO / 1torr 373K 30min

(d) CO+O2(2:1) 373K 30min

CuCT1: Ce(3d)

Fitting

C

B

Inte

nsity

/ a

.un

its

B.Energy / eV

Operando-XPS: Ce(3d) and Tb(3d) in CuCT1

Operando-XPS was carried out under O2 , CO and CO/O2(2:1) and Ce(3d) and Tb(3d) spectra analysed by Factor Analysis

J.P. Holgado et al. Appl. Surf Sci. 161,301-315, 2000

Factor Analysis

Operando XPS of CuCT1 and CuC catalysts

1: copper dispersion, measured as Cu/(Ce+Tb) ratios, only sightly changes with the treatments and are similar to those observed in the CuC catalyst under similar conditions. 2: terbium dispersion, measured as Tb/(Ce+Tb), is not modified by the treatments and is similar to that observed in the CT1 support. 3: terbium oxidation state changes with the treatments (Tb3+/Tb4+). 43.6% of the terbium is as Tb3+ in the original calcined catalyst 4: cerium remains fully oxidized after all the treatments (100% Ce4+) 5: cerium and copper in CuC (reference) are more easily reduce than in CuCT1 and CuCT4 under reducing treatments (i.e. CO or H2 )

G. Munuera et al. CONCORDE Conference, "Catalytic Nano-Oxides Research and Development in Europe: Present and Future"

Sevilla (Spiain), 2006.

Conclusions

What happen to Copper in CuCT1 ?

CO/O2 (2:1) reaction at 473K

Supports:

Ce3+ + Tb4+ Ce4+ + Tb3+

Copper:

Cu+ + Tb4+ Cu2+ + Tb3+

In priciple, Tb4+/Tb3+ acts as a “redox buffer” against Cu2+/Cu+ and Ce4+/Ce3+ what explains the differences in reactivity observed in the three catalysts (CuC > CuCT4 >> CuCT1). This implies a strong electronic interaction through the interfase CuO-CeO2 under CO-TOX operando conditions

A . Martinez-Arias et al. Phys. Chem Chem. Phys, 14 (2012) 2144-2151

But, how is copper under operando-XPS/XAES conditions in CuO-CeO2 catalysts ?

970 960 950 940 930 920

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

2,4

2,6

2,8

3,0

3,2

3,4

Cu2p_all.opj

933.6

932.7

932.5

932.6

Ar+,8min.

Ar+,1min.

Ar+,30seg.

original

CuO

CuOx

XPS: Cu(2p)

Ar+- etching

Inte

nsity / a

.u.

Binding Energy / eV

900 910 920 930

2

3

4

5

6

7

8

9

CuAES_all.opj

91

8.0

91

7.0

91

6.8

91

6.5

Ar+, 8min.

Ar+, 1min.

Ar+, 30seg.

original

CuO

CuOx

XAES: Cu(L3VV)

Inte

nsity / a

.u.

Kinetic Energy / eV

Differential Ar+-sputtering of CuO (bulk)

XPS: Cu(2p) XAES: Cu(L3M45M45, 1G)

Ar+–sputtering: CuO + Ar+(3.5 kV) Cu2O + O(g)

G. Munuera et al. CONCORDE Conference, "Catalytic Nano-Oxides Research and Development in Europe”, Sevilla (Spain) 2006.

Wagner “chemical state plots” for copper

936 935 934 933 932

914

915

916

917

918

919

Cu(OH)2(bulk)

EK (

Cu

L3V

V)

/ e

V

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Sample: ´

(eV)

1851

1850

1849

1848

1847

1846

NIST-XPS database

C.D. Wagner Anal. Chem 44 (1972) 967

NIST X-ray Photoelectron Spectroscopy Database; http://srdata.nist.gov/xps/

W. Grünert et al. J. Phys. Chem. 98 (1994) 10832

936 935 934 933 932

914

915

916

917

918

919

EK (

Cu

L3V

V)

/ e

V

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Sample: ´

(eV)

1851

1850

1849

1848

1847

1846

NIST-XPS database

EBE(Cu2p) vs. EK(CuL3VV) ● Blue dots, bulk CuO, Cu2O and Cu (foil) references and copper loaded ZSM-5 zeolites (W. Grünert et al.) ●“slope -1” full lines show the modified Auger parameter defined by Wagner as: α´= EBE(Cu2p) + EK(CuL3VV) α´ in eV (right scale) being related to the relaxation of the hole at the core-ionized copper atom (“final state effects” ) ● “slope -3” red guide dash lines indicate similar “chemical states” to those of the respective references

O

O

O

O

Copper oxides: A metal “stuffed” with oxygen (cationic eutaxy)

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

O O O O O O O O O O O O

O O O O O O O O O O O O

O O O O O O O O O O O O

O O O O O O O O O O O O

o o o

o o

o o o

o o

o o o

CuO (Tenorite) Cu2O (Cuprite) Cu (fcc)

The structure of the three stable copper oxides: cuprite (Cu2O, cubic) tenorite (CuO, monoclinic) and paramelaconite (Cu4O3, tetragonal mixed valence) all have the same fcc array of Cu atoms with O atoms occupying tetrahedral interstices. The occupied tetrahedral are those needed to satisfy the linear two-fold coordination of Cu (I) and

the planar four-fold coordination of Cu (II). This set of structures show an fcc eutaxy of cations, a concept first defined by O´Keeffe and Hyde.

M. O´Keeffe and B.G.Hyde Structure and Bonding 61 (1985) 77-144

A. Vegas, Crystallography Reviews, 7 (2000) 189-283

Looking into Copper: Operando-XPS/XAES from CuxO/CeO2/Si(111) films to CuxO/CeO2 real catalysts

930 920 910 900 890 880 870 860

200

250

300

350

400

450

500

550

600

650

Inte

nsity x

10

3 / K

cps

Binding Energy / eV

CeOx/Si(111)

XPS: Ce(3d)

886.0

904.0

917.0

CeO2

Ce2O3

200 400 600 800 1000

0

1

2

3

4

O

Ce

b)

a)

ISS.3.16.opj

LEIS spectra

CeO2-film

a) Ar+-etched

b) O2

+-etched

KE2

KE3

Inte

nsity /

a.u

.

Kinetic Energy / eV

CeO2/Si(111) vs. Ce2O3/Si(111) films

Low Energy Ions Scatering (LEIS/ISS) using He+ (1KV) detects exclusively the atoms at the topmost layer of the surface

920 910 900 890 880

0

5

10

15

20

Ce4+

Ce4+

Cu /Ce2O

3-film

XPS: Ce(3d)

917 e

V

Original

8 ML

5 ML

2 ML

1 ML

Inte

nsity / a

.u.

Binding Energy / eV

600 800 1000

0

2

4

6

Ce

Cu

O

LEIS_0.opj

8ML

5ML

2ML

1ML

LEIS spectra

Cu on Ce2O

3-film

Inte

nsity / a

.u.

Kinetic Energy / eV

Evaporation of copper (up to 8ML) on a highly reduced Ce2O3/Si(111) substrate followed by XPS (left) and LEIS (right) showing the progressive“shadowing” of the Ce2O3 sustract

Study of Cu/Ce2O3/Si(111) films: Copper evaporation

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

LEIS_XPS.opj

8 ML

Ce2O

3-film

4 ML

3 ML

2 ML

1 ML

Islands

(V-W mechanism)

monolayer

(FvdM mechanism)

LEIS vs XPS

lCu

= 10 A

lCeO2

=12 A

deq

= 4 A

LE

IS (

I/I 0

) valu

es

XPS Cu/Ce ratio

Study of Cu/Ce2O3/Si(111) films

V.M. Jimenez et al. Appl. Surf. Science 141 (1999) 186-192

Frank van der Merve “layer by layer” mechanism Volmer-Weber “Islands” mechanism Stransi-Krastinov mechanism “one layer + 3D islands” For metal deposited on oxidic supports the more general growing mode is the formation of “single layer islands” up to a coverage of 0.3-0.7 and then the formation of three-dimentional islands

936 935 934 933 932

913

914

915

916

917

918

919

O2 423K

O2473K

O2300K

O2 473K

O2 300K

Cu0/ 8ML

Cu0/1ML

EK (

Cu

L3V

V)

/ eV

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZSM-5

Cu2O (bulk)

Catalysts: Cu/CeO2

Cu0 oxidation

´

(eV)

1851

1850

1849

1848

1847

1846

Oxidation of Cu/Ce2O3/Si(111) to CuO/CeO2/Si(111)

970 960 950 940 930 920

16

18

20

22

24

26

28

30

32

Cu3d_treat1

c)

b)

a)

933.1

a) Original

b) + O2 / 15min

c) + O2 / 60min

Cu0/ Ce

2O

3-film

XPS: Cu(2p)

Inte

nsity /

a.u

.

Binding Energy / eV

880 890 900 910 920 930

35

40

45

50

55

60

65

70

CuAES_treat1

Cu0/Ce

2O

3-film

XPS: Cu(AES)

a) Original

b) + O2 / 15min

c) + O2 / 60min

915.6

917.4

c)

b)

a)

Inte

nsity /

a.u

.

Kinetic Energy / eV

8 ML

8ML

600 800 1000

0

2

4

6

8

+ O2 / 300K

1h

+ O2 /300K

15 min

8ML

O

Cu

Ce

LEIS_4.opj

LEIS spectra

Cu0 on Ce

2O

3-film

Inte

nsity / a

.u.

Kinetic Energy / eV

560 570 580 590 600 610 620

10

15

20

25

30

35

Ce_shd3.opj

b ) original

a) 8 ML Cu

XPS:Ce(3d)

a) Cu/Ce2O

3/Si(111) + O

2/473K

b) Ce2O

3/Si(111) + O

2/300K, 473K

Ce3+

Ce3+

Inte

nsity / a

.u.

Kinetic Energy /eV

Oxidation of Cu/Ce2O3/Si(111) to CuO/CeO2/Si(111)

Holgado J.P. et al., Applied Surface Sci. 158 (2000) 164-171

B. Skårman et al., J. Catal. 181 (1999) 6-15

0 200 400 600 800 10000

2

4

6

8

z (

nm

)

x (nm)

Zona 5

CuxO/CeO2/Si(111) Av.Disc diam.: 46 nm RMS roughness: 1.8 nm Peak to valley: 13.9 nm Avarge hight: 5.6 nm

0 200 400 600 800 10000

2

4

6

8

z (

nm

)

x (nm)

zona 3

CeO2/Si(111) Av. Disc diam: 30 nm RMS roughness: 2.0 nm Peak to valley: 16.2 nm Average hight: 7.2 nm

20.00 nm

0.00 nm

20.00 nm

0.00 nm

1 mμ x 1 mμ 1 mμ x 1 mμ

AFM study of CuO/CeO2/Si(111) films

C. Munuera, ICMM-CSIC

Copper oxides - Ceria interfaces

Since the cation lattice is essentialy maintained (cation eutaxy) appropiate cation lattice dimensions can be calculated. According to B. Skåman et al. a tensile strain is imposed to the copper oxides by ceria support which disminishes from 27% lattice mistfit for Cuprite to arround 8% for Tenorite. Misfit strain of this magnitude can only be maintained for a few monolayers of copper

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

O O O O O O O O

O O O O interface O O O O

O O O O O O O O

O O O O O O O O

o o o

o o

o o o

o o o o o

o o o o o

CuO-CeO2 Cu2O-CeO2

Tenorite Cuprite

B. Skårman et al. J. Catalysis, 181 (1999) 6-15

Cu2O – CeO2 interface: Extra-atomic relaxation (Rea)

O O O O

O O O O

O O O O

O O O O

o o o

o o

o o o

o o o o o

o o o o o

Cu2O-CeO2

O

o

O O O O

o o o CeO2

X-rays

electrons

+

“final state effects” The hole (+) left in the core-ionized copper polarizes the neighbour atoms. This “extra-atomic relaxation” process can be related to the Wagner modified Auger parameter shift (Δα´= 2ΔRea ). To a good approximation, the electrostatic Moretti´s simple model shows that the Auger parameter shift is a function of the number, distance, electronic polarizability and local symmetry of the first neighbour ligands of the core-ionized copper atom calculated taking into account dipole-dipole interactions between them

G. Moretti Surf. Interf. Anal. 16 (1990) 159-162 ; ibid Journal Electron Spectroscopy 95 (1998) 95-144

Wagner “chemical state plots” for copper

936 935 934 933 932

913

914

915

916

917

918

´> 0

´< 0

slo

pe -

3slop

e -1

I < 0 > 0

1844

Ek(L

3M

45M

45 ;

1G

)

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Wagner plot

Cu references

´

(eV)

1845

1850

1849

1848

1847

1846

C.D. Wagner Anal. Chem 44 (1972) 967; ibid.Faraday Discuss. Chem. Soc. 60 (1975) 291

T.D. Thomas, J. Electron Spectrosc. Relat. Phenom. 20 (1980) 117

G. Moretti, Surf. Interface Analysis, 17 (1991) 352-356

α´Cu= EB(2p3/2) + EK(CuL3M45M45 , 1G )

Moretti´s electrostatic model

Δα´= (α´Cu+ZSM5 - α´Cu2O ) Δα´= 2[ΔRia + ΔRea] for a non-local screening:

Δα´= 2ΔRea

EK = [const + 2(VM + kq] -3EB

I = [const + 2(VM + kq] Δ I = 2Δ(VM + kq) if ΔI = 0, same chemical state

G. Moretti et al.Surf. Interface Anal. 17 (1991) 352-356; ibid. Surf. Interface Anal. 31 (2001) 249-254

Structure (D∞h) RCu-O (Å) αo (Å3) n1 αo (Å

3) n2 2Rea (eV) Δα´ (eV)

Cu-O-Cu-O (Cu2O, bulk)

1.85 3.3 2 ---- ---- 7.18 0.0

Cu-O-Cu-O (Cu2O cluster)

1.95 3.3 ´ 2 ---- ---- 5.91 -1.27

Ce-O-Cu-O (CeO2 interface)

1.95 3.3 1 2.7 1 5.43 - 1.75

Si-O-Cu-O (ZSM5 interface)

1.95 3.3 1 1.22 1 4.25 -2.93

2Rea = (α´Cu+

(s)- α´Cu+

(g) ) ; Δα´ = (α´Cu+

(s) – α´Cu2O/bulk) ; α´Cu+

(g) = 1838.4 eV

Calculated Δα´ values for Cu2O on CeO2 and ZSM5 zeolites using Moretti´s simple electrostatic model

2Rea (eV)= 14.4 nαo/R4(1 + Dαo/R3) αo = polarizability of the ligands (Å3) n = number of nearneighbour R = distance to the core-ionized atom (Å) D = parameter taking into account the symmetry

936 935 934 933 932

913

914

915

916

917

918

919

O2 423K

O2473K

O2300K

O2 473K

O2 300K

Cu0/ 8ML

Cu0/1ML

EK (

Cu

L3V

V)

/ eV

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZSM-5

Cu2O (bulk)

Catalysts: Cu/CeO2

Cu0 oxidation

´

(eV)

1851

1850

1849

1848

1847

1846

Wagner Cu “chemical state plot” EBE(Cu2p) vs. EK(CuL3VV) ● XPS/XAES data of Copper in Cu/Ce2O3/Si(111) model catalyst ● Evaporated copper experiments (1ML and 8ML) followed by “in situ” oxygen treatments from 300K to 473K ●“slope -3” red guide dashed lines indicate similar “chemical states” to those of the respective “bulk” references (e.g. Cu, Cu2O and CuO) Differences along the lines must be related with size and interaction of the copper clusters with the ceria (or ZSM5) supports

Study of CuxO/Ce2O3/Si(111) films

935 934 933

914

915

916

917

918

919

8

7

6

5

4

3

2

1

EK (

Cu

L3

VV)

/ e

V

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Catalysts:

CuC´

(eV)

1851

1850

1849

1848

1847

1846

Catalyst CuC: O2, CO, H2 and CO/H2

Exp

Nº Catalyst

Treatments Cu/Ce O/(Ce+Cu)

1 evac 473K, 1h. 0.106 2,23

2 O2/373K, 30 min 0.121 1.96

3 CO/573K, 15 min 0.100 2.13

4 H2/ 473K, 15 min 0.109 2.08

5 CO + H2 (1:1) 473K, 15 min

0.092 2.06

6 CO + H2 (1:1) 473K, 15 min

0.095 1.97

7 O2/573K, 30 min 0.106 1.92

8 CO + H2 (1:1) 473K, 15 min

0.090 1.99

Operando- XPS/XAES of 1CuO/CeO2 catalyst

Dispersion of copper remains almost unchanged for all the treatments even at temperatures higher than 473K without reduction to metallic copper

How is copper during CO-PROX ?

IMPREGNATION

Catalyst

name

Cu loading

(wt. %)

0.5CuO/CeO2 0.5

1CuO/CeO2 1

3CuO/CeO2 3

5CuO/CeO2 5

MICROEMULSION COPRECIPITATION

Catalyst

name

Ce:Cu atomic ratio

Ce0.95Cu0.05O2 9.5:0.5

Ce0.9Cu0.1O2 9:1

Ce0.8Cu0.2O2 8:2

Preparation of new copper oxide-ceria catalysts

D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026

Prepared by impregnation of a CeO2 support, obtained by microemulsion, with copper

Prepared by coprecipitation of microemulsions of copper and ceria

CuO/CeO2 catalysts: Structural characterization

5CuO/CeO2 Ce0.8Cu0.2O2

D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026

CuO/CeO2 catalysts. Structural characterization

D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026

0 10 20 30 40 50

0

20

40

60

80

100

ato

mic

%

test number

Ce

Cu

5CuO/CeO2

1CuO/CeO2

Ce0.8

Cu0.2

O2Ce

0.95Cu

0.05O

2

0 5 10 15 20 25

0

20

40

60

80

100

ato

mic

%

test number

Ce

Cu

0 10 20 30 40

0

20

40

60

80

100

ato

mic

%

test number

Ce

Cu

0 10 20 30 40 50 60

0

20

40

60

80

100

ato

mic

%

test number

Ce

Cu

Ce0.95

Cu0.05

O2

XEDS-STEM

X-ray Energy Dispersive Spectra

Catalyst SBET/m2g-1

0.5CuO/CeO2 115.9

1CuO/CeO2 106.5

3CuO/CeO2 106.0

5CuO/CeO2 100.8

Ce0.95Cu0.05O2 129.6

Ce0.9Cu0.1O2 135.8

Ce0.8Cu0.2O2 151.0

CuO-CeO2 catalysts: Textural/structural characterization

20 30 40 50 60 70 80

0

20

40

60

80

100

120

140

160

180

200

220

240

260

Inte

nsity

2

0.5CuO/CeO2

1CuO/CeO2

3CuO/CeO2

5CuO/CeO2

Ce0.95

Cu0.05

O2

Ce0.9

Cu0.1

O2

Ce0.8

Cu0.2

O2

XRD

CuO

XRD results for Ce1-xCuxO2 at room temperature

Sample Lattice constant, a (Å) Microstrain

(a.u.)

CeO2 5.400 0.85

Ce0.95Cu0.05O2 5.401 1.14

Ce0.9Cu0.1O2 5.401 1.24

Ce0.8Cu0.2O2 5.406 1.85 D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026

1750 1500 1250 1000

Wavenumber (cm-1)

2.0

3750 3500 3250 3000

K-M

Wavenumber (cm-1)

0.25

CO32-type species

OH- species

2400 2200 2000 1800

Wavenumber (cm-1)

2.0

INIT

303 K

313 K

323 K

473 K

Reaction T

CO-PROX: 1% CO + 1.25% O2 + 50% H2 over 1CuO/CeO2

Cu+ carbonyl CO2 (g)

D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026 and J. Am. Chem. Soc. 129 (2007) 12064

Difuse Reflectance Infrared Fourier Transformed Spectroscopy

CuxO-CeO2 catalysts: Operando-DRIFTS analysis

300 350 400 450 500

0

20

40

60

80

100

% R

en

dim

ien

to d

e C

O2

Temperatura / K

0,5CuO/CeO2

1CuO/CeO2

3CuO/CeO2

Ce0,95Cu0,05O2

Ce0,8Cu0,2O2

Evolución del CO2

QMS DATA for m/e = 44

300 320 340 360 380 400 420 440

-20

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

Inte

ns

ida

d (

u.a

.)

Temperatura / K

0,5CuO/CeO2

1CuO/CeO2

3CuO/CeO2

Ce0,95Cu0,05O2

Ce0,8Cu0,2O2

Cu+ carbonyl intensity

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CuO/CeO2 catalysts: Operando-DRIFTS analysis

D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026 and J. Am. Chem. Soc. 129 (2007) 12064

A correlation exist between the capacity to form Cu+-CO of each catalysts and its activity for CO oxidation

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CO oxidation activity correlates with the intensity of Cu+ carbonyls formed under reaction conditions; this, along with consideration that such carbonyls reflect interfacial copper oxide reduction, indicates that such activity is basically related to the interfacial redox activity

0 50 100 150 200 250 300

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Cu0.05

Ce0.95

O2

1CuO/CeO2

Sp

ecific

CO

oxid

atio

n r

ate

(m

mo

l g

ca

t-1m

in-1)

Integrated areaof the Cu+-carbonyl band (a.u.)

Cu0.2

Ce0.8

O2

5CuO/CeO2

0.5CuO/CeO2

CuO-CeO2 catalysts. Operando-DRIFTS analysis

D. Gamarra et al. J. Am. Chem. Soc. 129 (2007) 12064

300 350 400 450 500 550

10

20

30

40

50

60

70

80

90

100

110

Sele

ctivid

ad

Temperatura / K

0,5CuO/CeO2

1CuO/CeO2

3CuO/CeO2

5CuO/CeO2

Ce0,95

Cu0,05

O2

Ce0,9

Cu0,1

O2

Ce0,8

Cu0,2

O2

300 350 400 450 500 550

0

20

40

60

80

100

%C

on

ve

rsió

n d

e C

O

Temperatura / K

0,5CuO/CeO2

1CuO/CeO2

3CuO/CeO2

5CuO/CeO2

Ce0,95Cu0,05O2

Ce0,9Cu0,1O2

Ce0,8Cu0,2O2

CO conversion CO2 Selectivity

The window for CO conversion of catalysts prepared by Cu/Ce coprecipitation are active for CO oxidation at lower temperatures but with a much lower CO2-selectivity while those prepared by impregnation shows much wider windows for both with a coincidence of ca 50-60 K

D. Gamarra et al. J. Phys Chem. C 111 (2007) 11026

CuxO/CeO2 catalysts: Catalytic activity

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CuO-CeO2 catalysts: Operando-XANES Cu-K edge

8950 8960 8970 8980 8990 9000 9010 9020 9030 9040

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

ab

so

rba

nce

(u

.a.)

Energy / eV.

Cu2+

Cu+

Cu0

Components detected

D. Gamarra et al. J. Am. Chem. Soc. 129 (2007) 12064

Calc.310

427437

448458

469480

490500

511521

532543

553563

573

8950 8960 8970 8980 8990 9000 9010 9020 9030

Ab

so

rba

nce

(a

.u.)

Tem

perature / K

Energy / eV

Ce0.8Cu0.2O2

CO-PROX: under 1% CO + 1.25% O2 + 50% H2 on Ce0.8Cu0.2O2

300 350 400 450 500 550 600

0.0

0.2

0.4

0.6

0.8

1.0

m.s

. in

ten

sity (

a.u

.)

T (K)

H2O

CO2

CO

O2

IIIII

Fra

ctio

n o

f p

ure

co

mp

on

en

t

Cu2+

Cu+

Cu0

I

H2 oxidation apparently proceeds when the copper reduction is extended from interfacial positions to the rest of the copper oxide clusters. This along with consideration that CO oxidation appears related to interfacial copper oxide sites suggests that the CO-PROX activity could be modulated upon changing the structural characteristics of the dispersed copper oxide component and its interface with the support

D. Gamarra et al. J. Am. Chem. Soc. 129 (2007) 12064

CuO-CeO2 catalysts: Operando-XANES Cu-K edge

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CuO-CeO2 catalysts. Operando-XANES Ce LIII-edge (difference spectra)

D. Gamarra et al. J. Am. Chem. Soc. 129 (2007) 12064

During the CO-PROX reaction some Ce3+ is seen also by XPS

5700 5720 5740 5760 5780

Inte

nsity (

a.u

.)

Energy (eV)

454 K

465 K

487 K

498 K

520 K

531 K

542 K

553 K

573 K

Ref. Ce3+

(Ce3+ vs. Ce4+)

Ce0.8Cu0.2O2 CO-PROX

Active oxygen species in CuO-CeO2. Operando-Raman

400 600 800 1000 1200

O2

2-

573 K

513 K

393 K

363 K

Inte

nsity (

a.u

.)

wavenumber / cm-1

457

463

323 K

343 K

O2

-

CO-PROX: under 1% CO + 1.25% O2 + 50% H2 on Ce0.8Cu0.2O2

D. Gamarra et al. J. Am. Chem. Soc. 129 (2007) 12064

oxidation mechanism using lattice O2- of CeO2 ?

Mars-van Krevelen Mechanism for oxidation

P. Mars, P. van Krevelen Chem.Eng. Sci. Suppl.. 1954,3.41

Sacrificial mechanism Some metal oxides that possess perovskite, fluorita or pyrochlore structures are prone to release their structural oxygen to an incoming reactant - such as hydrocarbons or carbon monoxide - and subsequently make good the loss by assimilating oxygen from the gas phase

Cu+-CO

CO2

2Ce3+V 2Ce4+O

Reduced 2Ce3+V centers at the CeO2, probably nearby the CuxO particles, were also detected during CO axidation in operando-XPS/XAES experiments

• Both CO and H2 oxidation activities are enhanced by CuxO dispersion. •

CO oxidation is related to formation of interfacial sites in CuxO particles.

• H2 oxidation is related to formation of reduced sites on top of CuxO particles.

CuO

CeO2

Reduced interface only Massive reduction of copper

CO+O2 H2+O2

Cu2O

•These hypotheses open the possibility to control the CO-PROX activity by acting separately on the CuxO/CeO2 interfaces and the CuO particles.

In summary

Optimization of CuO/CeO2 catalysts: inverse systems

A. Hornés et al. J. Am. Chem. Soc. 132 (2010) 34

CeO2

CuO

CuO

CeO2

Classic configuration Inverse configuration

CuO/CeO2 CeO2/CuO

Why ?

20 30 40 50 60 70 80 90

¤

¤¤¤

¤¤¤¤¤¤

¤

¤

¤

¤

¤

****

***

*

Inte

nsity (

a.u

.)

2(º)

¤*CeO

2

CuO

XRD

CeO2

CuO

HREM

A. Hornés et al. J. Am. Chem. Soc. 132 (2010) 34

Inverse CeO2/CuO. Structural and morphological characterization

300 350 400 450 500

0

20

40

60

80

100

T (K)

CeO2/CuO inverse catalyst

Cu0.2

Ce0.8

O2 reference

CO

co

nve

rsio

n (

%)

300 350 400 450 500

0

20

40

60

80

100

CeO2/CuO inverse catalyst

Cu0.2

Ce0.8

O2 reference

CO

2 s

ele

ctivity (

%)

T (K)

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CO conversion CO2 selectivity

A. Hornés et al. J. Am. Chem. Soc. 132 (2010) 34

Inverse CeO2/CuxO. Catalytic activity

CO Conversion: CO + ½O2 CO2

CO2 Selectivity: CO CO2 >> H2 H2O

Or … why not change the CuO-CeO2 interfaces ?

CuO/CeO2-NC CuO/CeO2-NP

CeO2 (111) CeO2(100)

50 nm 20 nm

General features of CuxO/CeO2 catalysts for CO-PROX and related processes

• In general terms, a correlation between redox and catalytic properties is observed, suggesting the existence of redox-type mechanisms in which both the copper oxide and the support components are involved.

• Their high catalytic activity for CO oxidation (either with or without H2 ) seems to be due to the existence of strong synergetic CuO-support interactions.

• Such interaction appears to facilitate copper oxide reduction which help to activate the reactants. Stabilization of reduced states of copper by such interaction has been observed under operando conditions.

• The physicochemical properties of CuxO/CeO2 interfaces strongly depend on the nature or type of both the copper oxide and the support entities.

Who is who?

• Daniel Gamarra (ICP-CSIC) • Aitor Hornés (ICP-CSIC) • Ana B. Hungría (ICP-CSIC, Univ. Cádiz) • Parthasarathi Bera (ICP-CSIC) • Antonio López Cámara (ICP-CSIC) • Laura Barrio (BNL- USA, ICP-CSIC)

• Marcos Fernández-García (ICP-CSIC) • José A. Rodríguez (BNL -USA) • Arturo Martínez-Arias (ICP-CSIC) • J. Carlos Conesa (ICP-CSIC) • Javier Soria (ICP-CSIC) • Guillermo Munuera (Univ. Sevilla, ICMS) • Jonathan C. Hanson (BNL - USA)

Looking into Copper in CO-PROX Catalysts: A Multitechnique Approach

“ Although concepts and ideas occupy a central place in the grand sweep of our understanding of the nature of the world arround us, it is a mistake to imagine that they play a greater role than tools and techniques in achieving scientific progress. ” Prof. Sir John Meuring Thomas

Opening lecture (Turning Points in Catalysis)

First European Congress on Catalysis (EUROPACAT-1, Montpellier 1993)

Angew. Chem. Intern. Ed. Engl. 1994, 33, 913-937

Some Highlights in Heterogeneous Catalysis 1990-2000 M/CeO2 (M = Pt, Rh) for TWC car catalysts Rh-Pt/Ce1-xZrxO2/γ-Al2O3-La2O3 2000-2012 CuO/CeO2 catalysts for CO oxidation (TOX and CO-PROX)

CO-PROX: CO + H2 + (O2) = CO2 + H2

Catalytic Preferential Oxidation of CO

PROX LT-WGS 0.5-2 %

CO

45-75 % H2 + 0.5-2 % CO + 15-25 % CO2 + few % H2O + HC traces

< 100 ppm

CO H2

10 %

CO

●High reactivity for CO oxidation

} CO2-Selectivity ● Low reactivity for H2 oxidation ● High resistence to poisoning by CO2 and H2O

Requirements for CO-PROX catalysts

Active sites in CuO-CeO2 catalysts: Kinetic analysis

CO 2 2

10

CO

0.91 -0.37 -0.62

CO H O

-94.4 kJ/mol3.4 10 exp

RT

× p p p mol/kg/s

r

2

2 2 2

13

H

-0.48 -0.69

H CO H O

-142 kJ/mol6.1 10 exp

RT

× p p p mol/kg/s

r

H.C. Lee, D.H. Kim. Catal. Today 132 (2008) 109

CuxO/(Ce,M)Oy catalysts: General characteristics

Catalyst Support employed and Ce/M atomic ratiosa

Copper loading (wt. %)

SBET

(m2g-1)

Structural properties: phases detected and crystal

sizeb

CuO/CeO2 CeO2 ---- 1 92 Fluorite CeO2 8 nm

CuO/CT1 (50% Tb)

Ce-Tb mixed oxide

Ce/Tb = 1.10

1 95 Fluorite Ce-Tb

mixed oxide 6 nm

CuO/CT4 (20% Tb)

Ce-Tb mixed oxide

Ce/Tb = 3.93

1 104 Fluorite Ce-Tb

mixed oxide 7 nm

a ICP-AES values. b Based on XRD, HRTEM and Raman

A. Martínez-Arias et al. J. Power Sources 151 (2005) 32

The copper catalysts (1% w/w Cu) were prepared on supports contaning 20% and 50% of Tb to examine posible electronic interactions of the modified support with the CuxO active phase of the catalysts during CO-TOX

930 920 910 900 890 880 870

0

5

10

15

20

b)

a)

917.0

Ce3d_23.opj

a) O2

+-etched

b) Ar+-etched

Sample C1

XPS: Ce(3d)

Inte

nsity /

a.u

.

Binding Energy / eV1290 1280 1270 1260 1250 1240 1230

0

1

2

3

4

5

6 1241.3

Tb3d_3y4.opj

1276

XPS: Tb(3d)

H2.773K

O2.773K

Inte

nsity /

a.

un

its

Binding Energy / eV

Factor Analisis: Ce(3d) and Tb(3d) in CuCT1

XPS: Ce(3d) CeO2 vs. Ce2O3

XPS: Tb(3d) TbO2 vs. Tb2O3

Operando-XPS of CuCT1 and CuC catalysts

Column 1: copper dispersion only sightly changes after the treatments and is similar to that observed in the CuC catalyst, given in parenthesis. Column 2: terbium dispersion is not modified by the treatments and is similar to that observed in the CT1 support, given in parenthesis. Column 3: terbium oxidation state changes with the treatments (Tb3+/Tb4+) Column 4: cerium remains fully oxidized after all the treatments (Ce4+) Column 5: cerium in CuC (reference) is more reducible than in CuCT1 under reducing treatments (i.e. CO or Ar+-etching)

G. Munuera et al. CONCORDE Conference, "Catalytic Nano-Oxides Research and Development in Europe”, Sevilla (Spain) 2006.

Wagner “chemical state plots” of copper for CuC and CuCT1

936 935 934 933 932

914

915

916

917

918

919

Cu2+

ZSM-5

Cu+

ZSM-5

Cu2O

(bulk)

CuO

(bulk)

Cu0

(bulk)

O2473K

CO300K

vac

473K

vac

300K

Wag_Cu_redox.opj

1846

1847

1848

1849

1850

1851

´

(eV)

EK (

Cu

L3

VV)

/ e

V

B. Energy / eV

Catalysts: CuC1 Catalyst: CuC

936 935 934 933 932

914

915

916

917

918

919

8

Ar+/2 min

7

Ar+/1 min

Ar+/30 s

6

CO/373K

5

CO/O2773K

4

3

vac 773K

O2/473K

2

1

vac 473KCu(OH)

2

(bulk)

EK (

Cu

L3V

V)

/ e

V

B. Energy / eV

Cu0

(bulk) CuO

(bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O

(bulk)

Sample:

CuCT1´

(eV)

1851

1850

1849

1848

1847

1846

Catalyst: CuCT1

Inverse CeO2/CuO Preparation

Cu2+

Cu2+

Cu2+

Cu2+

+ OH-

OH-

OH-

OH-

1st: CuO

Ce3+

Ce3+

Ce3+

Ce3+

OH-

OH-

OH-

OH-

+

2nd: CeO2/CuO CuO

Calc.

773 K

Calc.

773 K

Cu/Ce = 1.13; SBET = 91 m2g-1 A. Hornés et al. J. Am. Chem. Soc. 132 (2010) 34

Average

crystal size

~ 22 nm

CuxO

CeO2-NC

CeO2-NP

CuxO

Sample Crystal

size (nm)

Lattice parameter

a (Å)

Microstrain (d/d)

F2g frequency

(cm-1)

F2g FWHM (cm-1)

SBET (m2g-1)

CeO2-NC 46 5.406 0.0001 464 15.5 20

CeO2-NP 7 5.410 0.0019 462 23.3 130

Cu/CeO2-NC 42 5.404 0.0002

463

15.5

14

Cu/CeO2-NP 7 5.410 0.0025

460

28.2 115

CeO2-NP

CuxO CuxO

CeO2-NC

1700 1600 1500 1400 1300 1200 1100

0.515471463 1394

1335 1277

Cu/CeO2-NPCu/CeO

2-NR

2400 2300 2200 2100 2000 1900 1800

wavenumber / cm-1

0.5

CO2 (g) 2115

2400 2300 2200 2100 2000 1900 1800

wavenumber / cm-1

2.0

2110CO

2(g)

1700 1600 1500 1400 1300 1200 1100

1583

13991297

1216

1478

1356

1.0

1700 1600 1500 1400 1300 1200 1100

1600 12171298

1354

13921469

1546

5.0

1568

2400 2300 2200 2100 2000 1900 1800

2099

K-M

wavenumber / cm-1

3.0

2115CO2(g)

Cu/CeO2-NC

1700 1600 1500 1400 1300 1200 1100

0.515471463 1394

1335 1277

Cu/CeO2-NPCu/CeO

2-NR

2400 2300 2200 2100 2000 1900 1800

wavenumber / cm-1

0.5

CO2 (g) 2115

2400 2300 2200 2100 2000 1900 1800

wavenumber / cm-1

2.0

2110CO

2(g)

1700 1600 1500 1400 1300 1200 1100

1583

13991297

1216

1478

1356

1.0

1700 1600 1500 1400 1300 1200 1100

1600 12171298

1354

13921469

1546

5.0

1568

2400 2300 2200 2100 2000 1900 1800

2099

K-M

wavenumber / cm-1

3.0

2115CO2(g)

Cu/CeO2-NC

936 935 934 933 932

913

914

915

916

917

918

5

4

3

21

slo

pe -

3

slope

-1

1844

Ek(L

3M

45M

45 ;

1G

)

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Sample: CuC-nc

SBET

= 20 m2g

-1

´

(eV)

1845

1850

1849

1848

1847

1846

936 935 934 933 932

913

914

915

916

917

918

5

2

1

43

slo

pe -

3slope

-1

1844

Ek(L

3M

45M

45 ;

1G

)

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Sample: CuC-ns

SBET

= 130 m2g

-1

´

(eV)

1845

1850

1849

1848

1847

1846

Treatments/473K: (1) evac. ; (2) red CO ; (3) CO-TOX ; (4) CO-PROX; (5) red H2

Operando-XPS/XAES CO-TOX and CO-PROX reactions: CuC-NP and CuC-NC catalysts

300 350 400 450 500

0

20

40

60

80

100

T (K)

CeO2/CuO inverse catalyst

Cu0.2

Ce0.8

O2 reference

CO

co

nve

rsio

n (

%)

300 350 400 450 500

0

20

40

60

80

100

CeO2/CuO inverse catalyst

Cu0.2

Ce0.8

O2 reference

CO

2 s

ele

ctivity (

%)

T (K)

CO-PROX: under 1% CO + 1.25% O2 + 50% H2

CO-conversion CO2-selectivity

A. Hornés et al. J. Am. Chem. Soc. 132 (2010) 34

Catalytic conversion vs. selectivity in CuO-CeO2 catalysts

CO-Conversion: CO + ½O2 CO2

CO2-Selectivity: CO CO2 >> H2 H2O

936 935 934 933 932

913

914

915

916

917

918

´= 2 eV

´= 2 eV

slo

pe -

3slop

e -1

1844

Ek(L

3M

45M

45 ;

1G

)

B. Energy / eV

Cu0 (bulk)

CuO (bulk)

Cu2+

ZSM-5

Cu+

ZMS-5

Cu2O (bulk)

Sample:

CuO (bulk)

(sputtered)

´

(eV)

1845

1850

1849

1848

1847

1846

EBE(Cu2p) vs. EK(CuL3VV) ● XPS/XAES data of copper in Ar+-etched bulk CuO (Tenorite) ● Differential sputtering of CuO produce reduced CuxO surfaces ● “slope -3” red dash lines indicate similar “chemical states” to those of the respective references ● Thus, the copper loaded in ZSM-5 zeolites prepared by W. Grünert et al. have the same “chemical states” as CuO and Cu2O ● Differences are in the modified Auger parameter (Δα´≈ 2.4 eV) which are related to those“final state effects”

Wagner “chemical state plot” for copper

W. Grünert et al. J. Phys. Chem., 1994, 98, 10832

“Aunque ideas y conceptos ocupan un lugar central en la expansión del conocimiento sobre la naturaleza del mundo que nos rodea, es un error creer que juegan un papel mayor que el de

las herramientas y las técnicas en el progreso científico”

Looking into Copper in CO-PROX Catalysts: A Multitechnique Approach

“ Although concepts and ideas occupy a central place in the grand sweep of our understanding of the nature of the world arround us, it is a mistake to imagine that they play a greater role than tools and techniques in achieving scientific progress”

Opening lecture (Turning Points in Catalysis)

First European Congress on Catalysis (EUROPACAT-1, Montpellier 1993)

Angew. Chem. Intern. Ed. Engl. 1994, 33, 913-937

John Meuring Thomas