Role of hydroxyls on breaking Ether C-O bonds...

Managed by UT-Battellefor the Department of Energy

Florencia Calaza, T-L Chen,

David Mullins and Steven

Overbury

Oak Ridge National Laboratory

Oak Ridge, TN, USA

Role of hydroxyls on breaking Ether

C-O bonds adsorbed on CeO2(111)


Working at ORNL

San Luis V – April 2010

Oak Ridge National Laboratory

Main Goal is to get people working on Surface Science, Heterogeneous

Catalysis at real conditions and Theoretical Chemistry in the same room

and they don’t kill each other.

Study catalytic reactions of a variety of compounds (oxygenates,

hydrocarbons CO, etc) on CeO2.

Universidad Nacional de San Luis

Heterogeneous Catalysis at real conditions. Study the synthesis of

propylene through oxidative dehydrogenation of propane on MoOx –Al2O3

catalysts.

University of Wisconsin – Milwaukee

Surface Science applied to study catalytic processes. Study the synthesis

of vinyl acetate on Pd and Au-Pd model catalysts.

Managed by UT-Battellefor the Department of Energy San Luis V – April 2010

Outline

Real Catalysis vs. Surface Science

Preparation of cerium oxide films

Hydroxyls on CeO2(111)

Diethyl ether (DEE)

Dimethyl ether (DME)

Conclusions


Mimicking Real Catalysis


Real Catalysis:

High pressures (Torr range)

Possibility of several faces

involved in the catalytic

process

Constant high coverage of

adsorbates

Surface Science:

UHV conditions (10-10-10-9 Torr range)

Controlled exposed face of the solid

Probably low coverage of adsorbates

during the study of catalytic processes


Why Ethers?


Alcohols, and oxygenates in general, are closely tied to many aspects

of biofuel utilization.

Interest on R-O-R interaction with catalyst surfaces (R = H or alkyl

fragments)

From the Surface Science point of view:

H2O dissociates on oxides forming hydroxyls.

Alochols dissociate on oxides by breaking O-H bond and forming

alkoxyls on the surface which further decompose in a variety of

products.

Ether C-O-C bonds are more difficult to break on oxides.


Real Catalysis shows Ether

decomposition on Oxides


Diethyl ether has been studied on Al2O3 catalystsArai et al. J. Catal. 10 (1968) 128

Diethyl ether decomposes forming ethoxides at room temperature

Ethanol form ethoxides on Al2O3

Reaction at higher temperatures shows a variety of products desorbing:

• 300-380 K range DEE and ethanol and traces of ethylene

• 390-500 K range mainly ethylene and traces of DEE and MeOH

Dimethyl ether studied on different oxide catalysts shows formation of

methoxides on the surface which further decompose to CO and H2, CH4

and/or formaldehyde depending if the mehoxide group suffers partial or

total dehydrogenation.


Preparation of ceria films

Deposit Ce on Ru(0001) in oxygen to produce CeOX in situ

– highly oriented CeO2(111) films

– ability to control oxidation state by control of oxygen pressure

– films are stable from 100 K to 1000 K

– eliminates sample charging

– thin film more like “small” particle

– easily replenished


Ru(0001)

Ce

O2

CeO2(111)

adsorbates

Mullins, D. R., Radulovic, P. V., Overbury, S. H., Surf. Sci., 429, 186 (1999).

Mullins, D. R., Overbury, S. H., Huntley, D. R., Surf.Sci., 409, 307 (1998).


Structure of CeO2

films --STM

200x200 nm2200x200 nm2

27x21 nm227x21 nm2

9 x 9 nm2

d

9 x 9 nm2

d

Films exhibit (111) orientation

– LEED and high resolution STM

– Well ordered terraces

– But steps and clustered vacancies are common

– Strain patterns occur on thinnest films

Jing Zhou, D.R.Mullins, A.P. Baddorf, S. Kalinin, unpyublished


CeO2(111) & CeOx(111)

Preparing CeOx(111) films:

• Reduce CeO2 film by exposure to MeOH at high temperatures

• Sputter CeO2 film for a few minutes

• Grow reduced film by using lower pressures of O2

870 880 890 900 910 920

40000

50000

60000

70000

80000

Co

un

ts / a

.u.

BE / eV

Ce3+

82 %

24%

2%

Ce3+ Ce3+ Ce4+


CeO2(111) & CeOx(111)


Hydroxyls on CeOx(111)


Ce

O

H

OH

OH2O + Ce

OO

CeO2(111)

H2O

H2O + Ce

OCe

O

H

O

H

CeOx(111)

T>500 K

538 536 534 532 530 528 526 524

6000

8000

10000

12000

14000

Inte

nsity / a

.u.

Binding Energy / eV

O1s XPS

533.2

530.9

OH(a)

lattice Oxygen

T>200 K

Mainly H2

& some H2O


Water (D2O) on Reduced CeO

x(111)

• Hydroxyls stable to >300 K– 16OD from water assumes vacancy

– D adsorbs on remaining lattice

oxygen (1st or 2nd layer)

– Resulting hydroxyls identical

(except isotopically) at 300 K

16v

Adsorbed

−D

3000 2900 2800 2700 2600 2500 2400

0 .0 0 0 0

0 .0 0 0 5

0 .0 0 1 0

0 .0 0 1 5

0 .0 0 2 0

0 .0 0 2 5

2 6 8 9

3 0 0 K

C e1 8

O x + D2

O

Ab

so

rba

nc

e

W a v e n um be rs , ( cm-1

)

30 0 K

30 0 K

2 7 0 5

C e O x + D2

O

3 0 0 Kb

a

−16OD


RAIRS & UHV System


Differentially

pumped bellows

Thermocouple

LN2

flow

Power

feedthroughs

Gate

valve

Sliding

Seals

(diff. pumped)

IR Spectrometer

CaF2

windows

(diff. pumped)

MCT Detector

Leak

valve

IR Cell

(Turbo

Pump)

Polarizer

IR beam

path purged

#3 #2 #1

Sample

holder

Ru(0001)


DEE on Ru(0001)


1000 1200 1400 1600 1800 2800 3200 3600

Ab

so

rba

nce

/ a

.u.

Frequency /cm-1

0.0002

2974

29

30

2865

14

42

13

87

12

78

11

69

10

02

(CH3CH

2)2O / Ru(0001) at 140 K * Warm up to 215 K

almost all desorbs

molecularly

~ 100 L

nCOC

O

fR

DEE and DME have C2v

symmetry in the gas phase


DEE on CeO2(111) and CeOx(111)


1000 1200 1400 1600 1800 2800 3200 3600

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

0.00022870

29

02

29

32

2968

14481388

1365

11

94

11

53

1004

940

10

58

10

98

~ 100 L

~ 100 L

CeOx

CeO2

(CH3CH

2)2O / CeO

2(111) (oxydized and reduced)

O

fR

•Warm up to 260 K

all desorbs molecularly

nCOC

O

CH2CH2

CH3H3C q


Geometry of adsorbed DEE


2500 2600 2700 2800 2900 3000 3100 3200 3300

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

Ru

CeO2

0.0005

2864

2975

~2

93

0

2970

2982

29

32

29

022868

va(CH3)

vs(CH2) +

0vertone dCH3va(CH2)

vs(CH3)


DEE on hydroxylated surfaces


2500 2600 2700 2800 2900 3000 3100 3200

2700

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

DEE

DEE/D2O

D2O

~25752700

2878

29

35

2977

2876 2974

2932

29

02

0.0005

Perturbed

ODFree

OD

In the presence of -OH

geometry of adsorption

very similar to the metal

case on Ru(0001)


DEE on hydroxylated surfaces


1200 1600 2000 2400 2800 3200 3600

2695

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

0.0005

(CH3CH

2)2O / OH / CeOx(111)

380 K

380 K

500 K

~600 L

~2000 L

88

5

10

54

11

05

14

32

13

38

13

68

~1

57

5

2695

29

63

29

27

Ethoxides are formed

Some OD species reacted

(negative peak ~2700 cm-1)

Probably acetate-like

Species are formed


Ethanol on CeOx(111)


900 1000 1100 1200 1300 1400 1500 1600 2800 2900 3000 3100

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

Ethanol on CeOx(111) dosed @ 100 K

450 K

886

1059

1111

13852958

0.001

Ethoxide species High coverage of

Ethoxide species


Some ideas for interaction


CH2-CH2-O-CH2-CH3

Ce

O

CH3

CH2

O

H

O

Ce

O

H

O

HH

C2H4(g)

+

@ 380 K

Seen on Al2O3

By decomposition

of ethoxides

Ce

OOO

CH3

C


DME on Ru(0001)


800 1000 1200 1400 1600 2600 2800 3000 3200

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

0.0002

919

1087

1170

1245

1452

1473 2811

28

28

2878

2916

2933

2983

DME / Ru(0001) @ LN2

O

fCH3

O

CH3H3C

q

DME desorbs molecularly

at <200 K

nCOC

sym

nCOC

asymdCH3

CH3

rock


DME on CeOx(111)


800 1000 1200 1400 2600 2800 3000 3200 3400 3600

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

0.0005

DME / CeOx(111)

918

1080

11

56

11

77

12

51

13

02

13

53

14

57

14732821

28

63

2930

~2

90

0

O

fCH3

CH3

rock

nCOC

sym

nCOC

asym dCH3

O

CH3H3C

q


DME on hydroxylated CeOx(111)


800 1000 1200 1400 2600 2800 3000 3200 3400 3600 3800

Ab

so

rba

nce

/ a

.u.

Frequency / cm-1

DME / OH / CeOx(111)

0.0005918

1090

11

61

11

75

1250

14

56

14

73

3663

3540

2923

28

862819

28

69

O

fCH3

O

CH3H3C

q

nCOC

sym

nCOC

asym

CH3

rock

dCH3 Perturbed

OH

Free OH


Differences between DEE and DME

reactivity on CeOx


DME doesn’t have b-hydrogens

DEE is a stronger base than DME

Al2O3 shows a much stronger acidity than CeO2

Activated adsorption: DME doesn’t stick to the surface at the pressures of DME and/or sample temperature used in the experiment.

Probably different face with different active sites exposed for breaking C-O bond in DME


Idealized CeO2

surfaces

M. V. Ganduglia-Pirovano, A. Hofmann, J. Sauer, Surface Science Reports 62 (2007) 219–270

We can prepare nanoparticles which specifically show different faces!!


Nano-octahedral CeO2

Terminate

exclusively in {111}

surfaces

SBET = 14 m2/g

Stable to 600 C in air


Conclusions

DME and DEE molecules adsorb weakly on Ru and CeOx films.

OH adsorbed on highly reduced CeOx interacts by hydrogen bonding with ether molecules perturbing their adsorbed geometry.

DEE C-O bonds breaks fairly easy in the presence of hydroxyls on CeOx (300-380 K)

Different than DME (probably because there are no b-H in the latter or other more open face is involved in this process



Acknowledgements


Group Leader: Steve Overbury

ORNL staff

David Mullins (CeO2(111))

Ye Xu (DFT)

Zili Wu (ceria NPs)

Jane Howe (microscopy)

Post-docs

Florencia Calaza (RAIRS)

Tsung-Liang (Alex) Chen (NSLS)

Wesley Gordon (RAIRS-FTIR formic)

Sanjaya Senanayake (NSLS)

Jing Zhou (STM)

Meijun Li (NP synthesis, FTIR)

Research funded by DOE Basic Energy Sciences, Division of

Chemical Sciences, Geosciences and Biosciences

Managed by UT-Battellefor the Department of Energy ACS – March 2009

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Role of hydroxyls on breaking Ether C-O bonds...

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