FT-IR study of the δ(OH) mode of surface hydroxy groups on metal oxides

Journal o/Molecular Structure, 175 (1988) 453-458

453

Elsevier Science Publishers B.V., A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s

FT-IR

STUDY

OF

THE

6(OH)

MODE

OF

METAL J.C.

L A V A L L E Y °, M.

BUSCA*

and

V.

SURFACE

HYDROXY

GROUPS

ON

OXIDES

B E N S I T E L °, J.P.

G A L L A S °, J.

L A M O T T E °, G.

LORENZELLI*

° Laboratoire

de

* Istituto

Chimioa,

di

Spectrochimie,

ISMRa,

14032

CAEN

Fao. I n g e g n e r i a ,

16129

GENOVA

(France) (Italy)

ABSTRACT Bands

due

surface

hydroxy

sia

thoria

of

and

D20

related

by

and

to

suggesting

the

in-plane are

samples.

dehydration

using

to

groups

Their

heating

H2018 .

the

The

the

mode

the 60H

of

alumina, is

evacuation,

observed

of

of

on

assignment

under

position

a coupling

bending

observed

hydrogen-bonded zirconia,

based and

mode

of

effect exchange

are

limit

with

magne-

the

isotopic

frequencies

out-off

on

apparently

the

the ~ ( M - O H )

samples, mode.

INTRODUCTION Fourier-transform nique

for

the

heterogeneous hydroxy

free

from and

these

frequency

of

pure

has

vation

of

of

60H

the

been

gen

on

direct

ZnO

(3).

adsorption

on of

the

in

are

in-plane

a region

opaque, in

and ~+t

where to

case

combination

to

have

from

only

6OH m o d e s

samples or

after

hydrogen

of

mild on

the

are

modes,

pressed

in

is

activation

case of

or

of

hydro-

report groups

activated

obser-

evidence

the

to

hydroxy

of Their

the

Direct

adsorption

the

disks

from

(2).

the

expec-

absorptions.

paper

highly

bands. on

out-of-plane

these

silica

so m e

by

~OH

and

reported

present

of

the

water

been

the

aim

sharp

on

bands

heterolytic

of

oxide

of

as

covered

treatments

modes

bulk

the

The

are

tech-

solids,

informative

(6OH)

known

due

the

to

are

vibrational are

on

activation

lead

bands

data

few

estimated

observation

residual

i.e.

resulting

and

a useful

sites

surfaces

mild

Two o t h e r

falls

mode s e e m s

OH g r o u p s

after

these

is

surface

oxide

bondings oT

(1).

powders

the ~+8

the

which

However,

oxide

position

of

shape

which

the

Generally,

groups,

bendings.

spectroscopy

of

hydrogen

arrangements

for

(tOH) the

some

position

surface ted

catalysts.

groups,

become The

infrared

characterization

the either

produced

by

samples.

EXPERIMENTAL Alumina (ex-hydroxide)

0022-2860/88/$03.50

(Degussa and

thoria

C),

zirconia

(Rhone

(ex-isopropylate),

Poulenc)

© 1988 Elsevier Science Publishers B.V.

powders

have

magnesia been

pres-

454

sed

as

such

air

or

oxygen

into

IR-detectable been

and

the

pretreated

IR

cell

by N i o o l e t

MXt

in

the

vacuum

or

in

disappearance

adsorption.

transform

of

Spectra

have

spectrometers.

AND D I S C U S S I O N In

the

Fig.

I the

treated

presence

of

spectra

in a i r

water

at

vapour

of

at

tion

at

increasing

temperatures.

3660

cm-i

precisely

are

due

the

surface,

3600 tion

to f r e e

om-i,

comes

(more

main

increasing

such

do

cut-off

not

limit

spectra

any

show

at

surface

AI-O-A1

that

desorb

The

spectra

band

However,

that

high

other

a band

as is

temperatures, modes.

We s h o w

A'

3730

down

The at

already

progressively

formed 1050

that

cm-i, evacua-

pressed

(5),

centered here

by

on

below

disk

cm - i , w h e r e

reported near

band 3590

the

1000

3800 om-l)

coordinated

water

of

to

in

evacua-

3675

broad

about

as

been

between and

differently (1,4).

has

heated

after

observed

3770,

is c e n t e r e d

OH's

temperatures. show

occurs.

cuation

groups

discussed

that

later

reported

bands

3785,

sample

2 h and

°C a r e

The at

maximum

hydrogen-bonded

alumina

°C f o r

400

hydroxy

previously

whose

from at

surface

as

an

600

and

ce

water

Fourier

heating

to

Alumina

previously

as

by

up

before

impurities

recorded

RESULTS a)

disks

into

another

the

differen-

during cm-i,

band,

evadue

to

observable

B

A

a 0,019]

e

3900

FIG.

IA.

water 400°C

'

'

FT-IR

36'00

spectra

pretreatment (c),

FIG.

iB.

pect

to

500°0

that

of

(4000-3000

and (d),

Difference

evacuation

600°0 spectra

highly

33'00

'

' c m 4"

om-i) at

of

1300

'

1"100

an A l z 0 3

: 200°0

(a),

sample 300°0

after

(b),

(e). in

activated

the

1300-1050

alumina.

om-i

range

with

res-

455 in

the

of

t h e above

ring

ratioed

drying

decrease heavy ved om-I

(D-bonded

assignment

to

is

b)

not

at

ii00

c m -I

at

the

beginning

the

pretreatment

and

By

2710

om -I

surface at

(free

such

groups,

all.

bands

OD's)

samples

This

but

the

behaviour

but

using

are

obser-

and

show

at

2650

again

the

confirming above

Ii00

allows

hydrogen-bonded

The

t h e band a t

repeated

the ~OD

du-

600°0.

of

c m -I , u n p e r t u r b e d ,

1050

60H mode o f

that

is

water,

evacuation

b a n d at

AI-O-AI

band p a r a l l e l s

normal

2750

the

t e m p e r a t u r e s up t o

us

hydroxy

to

its o m -I

assign

groups.

Ziroonia In

band after at

of

observable

to

this

above

OD's).

of

band

of

instead

2775,

appearance

this

evacuation at the

D20

2790,

band

detected

is

intensity When

water

at

under

in

cm- I .

3590

spectra,

e v a c u a t i o n treatment but d i s a p p e a r s c o m p l e t e l y

at

and

previous

be

has

well

ziroonia,

Fig.

2 shows

apparent

even

in

°0.

not

shown

out its

with

shift

assigned

activation are

200

also

carried causes

of well

at

is

study

is

H2018 must

case

om -I ,

activation

450°0

ment

the

953

to

at

450°0, at

band

before

that

does

it

heavy to

when

3775

cm -I

mode.

D20, (6).

The

the ~OH

and

3670

any not

water

948

the

presence

unratioed

disappears

present

a 60H

evident

This

the

after

while

if

at

the

the

bands

of

of

this

this

free

band

hydroxy

o m -I , e x c l u d e s

r.t..

its

with band after groups

assignment

'\

A

i a

/b

o.o

0.0

~

c

m

!

~/d J

/

3900 FIG.

2.

FT-IR

and evacuation

' k . ~ "/ i

3600

spectra

at

(a)

3300

of

r.t.,

a

ZrOz

w

sample

200°0

9,50 CFh"I

1000

(b),

after

water

300°0

(c)

A

pretreat-

exchange

Consequently,

absence

a

evacuation

evacuation

appear

of

spectra,

pretreatment

and 450°0

(d).

456 to

the

bending

mode

H-bonded

OH's

A further

stronger

les, any

could

be

whose

of

the

vOH

free

is

too

hydrogen

responsible

groups.

broad

bonding,

for

We

assign

to be

well

possibly

non-appearance

it,

then,

to

distinguishable.

with of

water

this

molecu-

band

before

activation.

o) Magnesia Similar been

first

vapour

at

r.t.

(Fig.3). the

results

evacuated and

Difference

region

1000-800

evacuation

are

at

finally

evacuated show

cm-l.

Its

and

3400

cm -1

and

a

When

the

previous

treatment

at

and

observed

cm -I , w h i l e

2765 the

one

The

bands

at

the

therefore

assigned

respectively,

cm-i

and

although

60H

D20

OD's)

i000

cm-I of

a weak

of

of ~ O H free

at

at

at

at

3740

unperturbed. at

800

bands

are

2650, om-i

1000-800

855

bands

OH's

hydrogen-bonded band

in

increasing

the Q O D

and

and

has

water

temperatures

with

and

that

with

absorption

apparently

with

(free

3400

broad

those

band

are

between

3550,

to ~ O H

cm-i

MgO

increasing

with

is d o n e

of

contact

decreases

main ~OH

3615

2675

at

at

case

into

a relatively

intensity

absorption

observed. groups

while

the

put

in p a r a l l e l

3550

weaker

in

later

spectra

temperature, om-1,

observed

750°0,

cm-i

2600

is

not

cm-i

are

surface

OH

persists

on

A '~ A

B

a

0'07I a

3/oo

3~oo . ~oo

900

FIG. 3A. FT-IR s p e c t r a (3800-3300 o m - i ) t e r p r e t r e a t m e n t a n d e v a c u a t i o n at i00 FIG.

38.

dro×ylated

Difference sample.

spectra

with

76o c m d of a MgO sample a f t e r (a),

respect

to

200 that

(b) of

an~

wa-

300°C(0).

a fully

dehy-

457

0.01

_J

3800

'

4.

Difference

FIG.

activated b)

3~00

sample

deuterium.

species face

species

fully

before

that

while

disappear

upon

samples

860 c m -1'

spectra

adsorption

increase

adsorption

dehydroxylated

a multiphonon

'

theFT-IR

and

bands

by

that

1{00

between after

The

formed

'

in

of

a thoria

of

a)

intensity

inverse

bands

highly

hydrogen

and

correspond are

due

to

to

sur-

adsorption.

evacuated

at

750°C,

certainly

due

to

mode.

d) T h o r i a A the by

previous

appearance adsorption

(7).

of

A similar

cases in

these

groups

also

not

by

a transparence

previously bands

heavy

thoria,

but

shown

that

conditions,

at (8).

1115, The

of

a strong

band

dehydroxylated spectra,

study

of

water band

water,

hydrogen producing

860

and

above

data

by

shown

treatment window

800

670

in

and

confirm

not

assigned

to

a 5QH

adsorption

Fig. at

deuterium

Th-H-Th cm - t ,

and

4 655

on

mode highly

difference

from

in

cm-1.

has

Th-D-Th

previous

shown formed

However, dissociate

respectively) the

has

is

deuterium.

observed

thoria

that

hydrogen

with is

on

cm-1,

therefore

appears as

adsorption at

It

on

species and

OH

assignment

both also

thoria (broad or of

OD the

458 band

at

cm-i

may

670

cm-i

be

intensity

to a 6 0 H

due

to

decreases

the by

mode

and

suggest

that

band

of

surface

Th-O-Th

hydrogen

or

deuterium

the

window

at

groups

635

whose

adsorption.

CONCLUSIONS The

above

evidence

the

60H

on s o m e

oxides.

In

than

the

band

is v a r i a b l e ,

cut-off

data

This

stretching

M-O

alumina

the

band

and due

distinction,

be

thoria

;

deuterium

It

exchange.

down

mode o f

the

directly

as,

~OH b a n d ,

free

OH's

it w i l l

(i)

the

by

the

50H

mode

is p r e d i c t e d

band

the

that

that

not

therefore

be

the

at 6 3 0

the

cm -i

the

of

from

the

cases

upon

the

generally

using

of

that

observable

However

I" O H ' s

position

water

bending

combination.

"type

near their

bonding,

region.

the 9 + 6

so-called

mode

The

distinguished

6OH o n e ;

black-out

the

60H

difficult

inversely

be

this of

is s i t u a t e d

hydrogen

up

observation of

can

the

groups.

band

of

metal-oxygen

between

varies

shifts in

bulk

surface

groups defined

position

This makes

they

directly

better

the

the

this

groups.

to

hydroxy

The position to

of

MOH

known

will

fall

band.

intensity

is

is e v e n

related

moreover

the

be a c c e s s i b l e example,

M-O-M

their

bonded

to a c o u p l i n g of

evidence

adsorption/desorption shifts

due

is p o s s i b l e

band

eventually,

mode

to s u r f a c e although

this

stretching

and,

can

it

hydrogen

apparently

oxide

stretching.

that

least

cases

OH

being

the

at

some

and of

of

corresponding of

the

indicate

band

of

the

it m a y As

an

alumina

combination

(9).

REFERENCES i.

H.P.

Boehm and H.

technology", 2.

L.M.

Kustov,

Phys.

Chem.

Boocuzzi,

3.

F.

J.

Catal.

4.

J.C.

5.

59

51

J.C.

kavalley

6.

Bensitel,

7.

X.

8.

J.

Chem. 9.

L.

J.

on

A.

39.

p.

Kazanskii,

Zecchina,

Benaissa,

and

M.

G.

Busoa

Benaissa,

Elsevier, V. J.

J.

Aota,

Lynch, Soc.

E.

in p.

Russian

J.

A.

Bossi

and

M.

Oamia,

and

V.

Lorenzelli,

Appl.

"Adsorption

Hemidy

catalysis

Lamotte,

0.

Saur

and

J.C.

Lamotte

and

J.C.

in p r e s s . Freund, V.

(1985)

surfaces",

and

251

J.

Faraday I, 83

Lavalley, I, 81

J.F.

oxide

1985,

Moravek,

J.C.

Faraday

Mariette,

catalysis

V.B.

s c i e n c e and

(1983),

249.

Chem.

Lamotte, Soc.

and

4

150.

Spectrochim.

Montagne,

Lavalley,

Vol.

1314.

Borello, M.

(1986)

surfaces",

M.

E.

"Catalysis,

Berlin,

8orovkov

(1985)

(1978)

oxide

Lavalley,

Chemie,

V.Yu.

Lavalley, 24

Catal.

Knozinger, in

Verlag

and

(1987)

Lorenzelli

1417. and

E.

Freund,

J.

215. D.

Cornet,

Elsevier

in

(1985),

"Adsorption p.

263.

and

on