Selective hydrogenation on copper chromite catalysts

243

Applied Catalysis, 22 (1986) 243-255 Elsevier Science Publishers B.V., Amsterdam -Printed

in The Netherlands

SELECTIVE

CATALYSTS

HYDROGENATION

V. REACTIONS

R. HUBAUT,

CHROMITE

ALCOHOLS

M. DAAGE and J.P. BONNELLE

Laboratoire

de Catalyse

des Sciences

(Received

ON COPPER

OF ALLYLIC

Heterogene

et Techniques

1 July

et Homogene,

de Lille,

1985, accepted

U.A. C.N.R.S.

59655 Villeneuve

10 December

No. 402, Universite

D'Ascq,

France.

1985)

ABSTRACT Reactions of various allylic alcohols were studied on a copper chromite catalyst. Three different reactions were observed: hydrogenation, isomerization and deoxygenation. By comparison with some other model compounds such as butanol, butanone and butadiene, analysis of the mechanism of the deoxygenation process suggests that, in fact, this reaction corresponds to a hydrodehydroxylation. Moreover, it is suggested that, in view of Siegel's model, the allylic alcohols constitute a good test model for characterizing the specificity and the nature of the catalytic sites on transition metal oxides.

INTRODUCTION

In previous

studies

that hydrogenation

(III)

ions and chromium species steric

saturated

are mainly

aldehydes

of the reactant

vity was excellent in the reactions the formation

involved, induced

with dienes,

in order to obtain and isomerization

the presence

whereas

large amounts compounds.

and high reactivity

The aim of this present

appeared whereas

1,4-additions

[S]. In addition,

of oxygenated

However,

of allylic

into copper

atom

in un-

of the high polari-

alcohols

low selectivity

chromite

by

1,2-hydro-

the mono-dihydrogenation

alcohols

(I)

hydride-like

to be controlled

because

selecti-

were formed

was attributed

to

[4].

work was to study the reactions

some insight

we found

on copper

for dienes

of an oxygen

of saturated

This

chromite,

respectively

with a particular

the olefins

effects.

or ketones

on copper

occur

are associated

between

and electronic

processes

of dienes

isomerization

ions, which

[l-33. The selectivity hindrance

genation

zation

on the reactions

and cis-trans

of allylic

catalyst

alcohols

for hydrogenation

reactions.

EXPERIMENTAL Samples Copper

chromium

and chromium nitrates,

oxide

hydroxides

according

with

ammonia

to a procedure

in a flow of nitrogen

0166-9834/86/$03.50

(Cu/Cr = 1) was prepared

at 37O"C,

solution

described

the catalyst

by coprecipitation

from a mixture previously was obtained

0 1986 Elsevier Science Publishers B.V.

of copper

of the corresponding

C51. After

decomposition

by reduction

in a flow

244 of hydrogen

at 150°C overnight.

were used after trans

further

Crotyl

alcohol

(Fluka, purum grade)

was a mixture

of the cis and

isomers.

Apparatus

and procedure

The catalytic

measurements

[6]. The reactants

were

a flow of hydrogen

(1 atm,

60-150°C. equipped

with

a flame

column.

dimethylsulpholane

were

introduced

carried

in a flow apparatus

at a constant

IO-60 ml min-')

Gas chromatographic

capillary

TABLE

The gases and hydrocarbons

purification.

analysis

ionization

The butene

detector

described

pressure

in an isothermal

was carried

was obtained

previously

(20 Tort-) in

reactor

on a Varian

operating

at

1440 apparatus

and a 100 x 0.2 mm I.D.

distribution

on firebrick

partial

Carbowax

20M

on a 10 m x l/8 in. I.D.

column.

1

Crotyl

alcohol

reactionsa

Total

conversion

/%

Butanal

Butanol

Butane

I-butene

/%

/%

/%

/%

trans-2-butene

cis-2-

/%

butene /%

1.0

3.0

28.2

64.8

2.5

1.5

3.0

4.5

30.3

61.4

2.5

1.3

5.6

5.2

29.8

61.0

2.6

1.4

17.8

5.0

29.4

62.1

2.3

1.2

37.8

5.1

30.0

61.0

2.4

1.5

40.6

4.9

30.5

< 0.1

60.6

2.5

1.4

50.0

5.2

29.7

0.1

61.4

2.3

1.3

60.0

4.8

29.9

0.2

61.1

2.5

1.5

aT = 335 K, palcohol

= 20 Torr, mass of catalyst

= 100 mg.

RESULTS The reactionsofallylic alcohol

pressure

by varying crotyl

(ca. 20 Torr).

the hydrogen

alcohol,

alcohols

P-methylpropenol

reported

are observed:

an isomerization

ponding

aldehyde

a deoxygenation As shown

The variations

flow-rate.

distributions

were studied

leading

or ketone, a hydrogenation

in Figure

time under an alcohol

1, a sharp decrease flow occurred,

chosen

types of reactions

to the formation

are the major

no significant

of the corres-

saturatedalcohols products.

in the hydrogenation

whereas

were the

As shown by the product

reactionleadingto

in which monoolefins

partial

level were achieved

compounds

I,2 and 3, three different

reaction

at a constant

in conversion

The three model

and I-methylpropenol.

in Tables

process

at 60-80°C

activity

variation

versus

of the

and

245 TABLE

2

E-Methylpropenol

Total

reactionsa

conversion

/$

Z-methylpropanal

2-methylpropanol

isobutane

isobutene

1%

/%

I%

/%

2.2

10.8

88.3

0.9

4.5

10.4

88.6

1.0

8.8

10.3

88.4

1.3

17.0

9.0

89.1

1.9

26.1

8.2

89.9

1.9

38.0

6.3

91.9

46.7

5.5

92.0

aT = 335 K, paTcohoT

1.8 2.4

0.1

= 20 Torr, mass of catalyst

= 100 mg.

TABLE 3 I-Methylpropenol

reactionsa

Total conversion 0, I@

butanone

2-butanol

butane

I-butene

trans-2-

cis-Z-

/%

/%

/%

/%

butene

butene

1%

/%

3.0

1.5

1.8

47.2

48.2

0.1

2.8

47.4

48.3

0.2

2.9

1.2

4.1

47.1

48.0

0.1

3.1

1.7

8.0

47.6

48.0

0.1

3.0

1.3

11.1

48.0

47.5

0.2

2.8

1.5

13.0

48.1

47.3

0.1

3.2

1.6

26.3

47.7

47.2

E

0.2

3.2

1.7

37.9

48.0

46.9

0.1

0.2

3.3

1.5

aT = 335 K, palcohoT deoxygenation

and isomerization

that two different conclusion

drawn

hydrogenation of the

= 20 Torr, mass of catalyst

catalytic

has been ascribed

by chromium

hydrogenation

activity

presence

of dienes

(III)

contrasts

which

study on the reactivity

the isomerization

to be induced

was observed.

sites are involved,

in our previous

activity

catalyst,

activities

= 100 mg.

to the copper

and deoxygenation

cations. with

or a,ti-unsaturated

However,

suggests

is consistent

with the

of dienes

[2]; as the

(I) hydride-like

reactions

this slight

the activation aldehydes

This result

phenomenon

or ketones

are more decrease observed

species likely in the in the

[2,41. Therefore,

a

246

I

IO,6

-\._

5x3

FIGURE

1

Variation

the various cm3 min-'

FIGURE

2

catalyst

Crotyl

time under a flow of organic

alcohols.

Z-Methylpropenol;

= 20 Torr; mass of catalyst

alcohol

reactions,

compound

for

T = 335 K; Qh2 = 7.5

= 100 mg.

T = 335 K; Psubstrate

= 20 Torr; mass of

= 100 mg.

adsorption

be considered.

hydrogenation of the product

of the allylic As acetate

reactions

products.

isomerization

products

were never detected, occurred,

alcohol

anions

[7], the latter

distribution

and secondary

molecules

with

of allylic

; psubstrate

very strong should

of activity

reactions

.-.-.

hypothesis

to zero conversion

A71 three reactions were expected

we should

assume

or the formation

are reported

is more

levels

likely.

anions

poison

products

(Figures

that rapid protropic

as was shown for the 1,4-hydrogenation

of

Extrapolation

was used to identify

led to primary

to be secondary

of stable

to be a strong

primary

whereas

2,3,4).

Since

rearrangement

the I-enols

of these

of a,B-unsaturated

247

.-

u-

m--m-

-m--

.m=

20

Fl :GURE 3 catalyst

FIGURE

Z-Methylpropenol

I-Methylpropenol

reactions.

T = 335 K; Psubstrate

= 20 Torr; mass of

reactions.

T = 335 K; Psubstrate

= 20 Torr; mass of

= 100 mg.

aldehydes

or ketones

importance

(Scheme

of each reaction

1) [4]. Moreover, was strongly

Table 4 gives the relative genation reactive, higher

of dienes,

obtained

respectively,

(III) site

activities

the least substituted

but the values

and lower,

chromium

and deoxygenation)

reactivity

chromium

ions, in contrast

to the copper

behaviour

low selectivity

of the double

on the hydrogenation of crotyl

between

alcohol,

isomerization

which

alcohol

the total activity

are of the

was in good agreement alcohol.

This result

bond is respected

site behaviour. reaction

to be the most

and crotyl

whereas

structure.

As for the hydro-

bond appeared

but was higher with crotyl

that the relative

effect

double

that the relative

on the reactant

for each reaction.

for Z-methylpropenol

suggests

the poisoning

it also appears

dependent

than expected,

(isomerization

for I- and P-methylpropenol

particular

converston

= 100 mg.

4

catalyst

Total

40

might

In the latter

instance

be associated

with the

is also demonstrated

and deoxygenation.

on the

by the very

-OH

&

Molecule

Relative

TABLE 4

OH

for reactions

0.4

0.6

1

Hydrogenation

activities

1.2

0.08

1

+ DOH

Isomerization

of allylic

0.036

1 .I6

0.04

9.0

9.0

I/DO

with dienes

0.008

0.1

DOH

comparison

0.072

0.9

I

alcohols:

-

b-A/

Hydrogenation

-+-

of diene

0.8

0.1

249

RI

A

/OH

R2

SCHEME

1

Isomerization

As shown Almost

R2

R,

in Tables

no saturated

reaction

I,2 and 3, the deoxygenation

hydrocarbons

were formed

were far from the thermodynamic crotyl

alcohol

equilibrium:

and I-methylpropenol,

reaction

I-butene

respectively,

(Table 5). This selectivity

process

a double

bond migration,

particular

formation conformation

alcohol

from

more than 90% of

to Scheme

2. Moreover,

from I-methylpropenol

of the adsorbed

obtained

shows that the deoxygenation

according

of trans-2-butene

of the olefins

and 2-butenes

represented

products

preferential

was very selective.

and the distributions

the deoxygenated requires

R,

R2

R4

molecule

suggests

is favoured

the

that a

on the cata-

lyst surface. In order alcohols, butanol

to verify

various

were

reaction.

that the deoxygenation

oxygenated

tested.

model

As reported

As the reactivity

of the rapid prototropic

oxygens

was performed

hydrogenolysis Therefore,

in Table

of enols

because

for allylic butanal

and

6, none of them led to a deoxygenation

rearrangement,

of the carbon-oxygen

is specific

such as 3-buten-l-01,

for deoxygenation

on the corresponding

the deoxygenation

reaction

compounds

cannot

a comparison

ethyl

propenyl

bond was observed

or carbon-oxygen

be measured of vinylic

ethers;

directly

and allylic

significant

only with ethyl ally1 ether.

bond cleavage

is specific

to allylic

compounds.

DISCUSSION Double

bond reactivities

We reported unsaturated

in previous

aldehydes

papers

or ketones

that the hydrogenation occurred

and that the selectivity

is controlled

hindrance

effects.

and electronic

also suggested

that occluded

C1,31. Therefore, bond would In general, instances.

one would

by the polarization

For the cis-trans

hydride expect

of dienes

ions and chromium

the least substituted For the isomerization was observed

higher

elementary

step of the reaction

was obtained

of allylic

corresponds

reactivity

alcohol

activity

to attack

should

reactive

alcohol.

[2-41 steric we

involved

of the double effect

occurred.

in all

on chromium

of dienes

for crotyl

of dienes

(III) ions were

bond is the most

with the isomerization

a slightly

polarization

reactivity

double

- deoxygenation

species

of the molecule,

isomerization

that the relative

or CY,B-

hydride-like

be the same on both types of sites as no particular

good agreement

higher

on a copper

ions,

(Table 4). However, As the first

by the hydride

lead to exclusive

ion, the

addition

on C-3.

250

TABLE

5

Butene

distributions

Reactant

Crotyl

alcohol

I-butene

trans-Z-butene

%

%

94.3 * 0.5

1-Methylpropenol

cis-Z-butene %

3.75 + 0.25

3.4 * 1.4

65.2

trans/cis

2.07 f 0.25

+ 1.0

31.3

1.76 If.0.15

f 3.4

2.12 f 0.30

Butene thermodynamic 14.6

equilibrium

R2

51.9

33.5

R2

R4

RI

R.l

RI

OH

w

-

V

R3

SCHEME

2

R3

Deoxygenation

Therefore,

reaction.

the steric

hindrance

hydrogenation

of isoprene.

hydrogenation

of allylic

alcohols

alcohol.

copper

(I) site. As we reported

This suggests

effect

occurred

during

on C-3 crotyl

will

carbanionic

A probable of alcohol in Scheme alcohols, However,

of a stable

resulting

bond will

species

dehydration.

generates

never detected

site poisoning.

on the copper

poisoning

complex

we

is responsible

of the methyl with

substituent the oxygen

to an alcoholate

The apparent

reactivity

concentration

of the

(I) site.

mechanisms

Two different

allow

on the

intermediate

by the relative

pathways

corresponding

us to eliminate

and its hydrogenation,

reaction

can be given

can be considered,

to the dehydration

a diene as an intermediate,

reasons

the reactivity

that a strong

of the n-electrons

of the carbanionic

of the deoxygenation

3. The first route,

of

(I) alcoholate

the conjugation

in greater

interpretation

modifies section

for the

low reactivity

under a flow of substrate,

copper

then be governed

and isomerization

several

a surprisingly effect

than that in the

scale obtained

In that event the presence

increases

and alcoholate

Deoxygenation

indicates

in the preceding

the rearrangement

be favoured,

of the double

be less important

the reactivity

that another

behaviour.

alcohol

atom. Therefore,

would

the first few minutes

that the formation

for this particular

effect

In contrast,

crotyl

suggest

1.55

reported

from which

as represented

of unsaturated

the olefin

this possibility:

in terms

can be formed.

butadiene

was

in Table 6, leads to significant

aCalculated

Reactivities

TABLE 6

by assuming

<1o-4

2.5

0.02

<0.0007

1oo"c

40°C

>8O"C

>lOO"C

an actiation

energy

66%

55% /=+

80% A

none

none

none

of IO kcal/mole

9J.04

>8O"C

1.0

so.02

>8O"C

60°C

activitya

T"C relative

and dienic

p---A

+ EtOH

+ EtOH

compounds

m

4% -0

9%r\,/a/

none

traces of*

Isomerization

for all reactions.

3%

7% f+/

90%

Deoxygenation

oxygenated

conditons

for various

Reaction

and selectivities

OH

0+"+.

/\I\

30%

45%

MoH

AoN

11% /\DN

10% n

20% w

70% G@X/

100%

>wx

Hydrogenation

OH

DH

252

\ +H1

/

-H,O

MoH

SCHEME

3

SCHEME

4

‘I’

0 SCHEME

0

0

5

amounts expected

of Z-butenes

and is not observed

to the deoxygenation The second dehydration alcohols

(Q 30%); appreciable

route

of which

cannot

corresponds gives

a mixture

ration of the Z-butanol genation

reaction

one should

allylic

we conclude

alcohols.

be explained

in the cis-trans

reaction

pathway

should

should

in the preceding

attack

of dienes

alcohols,

In addition,

be obtained

it appears

with

occur

paragraph, on chromium

of the molecule

be applied

the

for

from the dehyd-

that the deoxy-

dehydration.

not be negligible process

cannot

show that the saturated

we used.

by simple alcohol

might

isomerization

thus involves

of saturated

Consequently,

that a direct

pathway

is

can be formed.

our results

of I- and 2-butenes

As we mentioned

involved

However,

under the conditions

note that such pathways

Therefore,

as no diene

to the formation

olefins.

intermediate.

cannot

of the 3-buten-l-01

(Table 6); and this reaction

of the 2-methylpropenol

be dehydrated

I-methylpropenol

deoxygenation

Nevertheless,

tertiary

alcohols.

specifically hydride

on

ions are

ions. A logical

by a hydride

ion and

253

SCHEP?E 6

SCHEME

7

Non concerted

isomerization

mechanism

(carbanion)

H 0

‘M

0

!; LI

0’1’0 0

1

‘M

6

c

iy

O’J’O 0

BH

00°

G

CH

to Scheme

4. Such a direct

8

elimination which

_:

0’1’0 0

B

SCHEME

~1

of the hydroxy

corresponds

the adsorbed

molecule

of the oxygen that event

observed

according

on the chromium

free electrons

a concerted

was postulated compound,

group,

to hydrodehydroxylation,

with

mechanism

a much

site should

the catalytic is favoured.

for the deoxygenation

while

suggests

be critical

alcohols

in the formation

of

as an interaction

site is required

The formation

of allylic

lower selectivity

process,

that the conformation

(Scheme

5). In

of a similar

complex

on a low-valent of the olefins

titanium was

[8].

It is also corresponding as represented is involved.

interesting aldehyde

that the isomerization

or ketone can be explained

in Scheme

6, where

Nevertheless,

like intermediate

as shown

a trans

by a very

conformation

the isomerization in Scheme

of the allylic

reaction

7. Therefore,

alcohols

to the

similar mechanism,

of the double may occur with

bond-oxygen a carbanion-

the isomerization/deoxygenation

254 should

be dependent

conformation reaction

of the conformation

of the double

and all other

conformation effects

and steric

hindrance.

alcohol

oxygen

and the absence

we suggest

instances

molecule

occurs

would

as greater

of steric

effects

reaction.

In addition,

very substantial

will

cis adsorption.

favour

a concerted

mechanism

a non-concerted

the

by electronic

deoxygenation

of the double

through

as a cis

affected

conjugation

requires

preferentially

molecule

lead to a deoxygenation

will be strongly

In that sense,

is predictible

that the deoxygenation

isomerization

system

to an isomerization

state of the adsorbed

crotyl

state of the adsorbed

bond-oxygen

of

bond with the Consequently,

whereas

mechanism

the

and carbanion-

like intermediate.

Nature

and specifity

Several

years

on transition

of the catalytic

ago, Siegel

metal

oxides

such as hydrogenation applications

Scheme

and isomerization

vacancies

Isomerization hydride,

catalyst

reactions

previously

dehydroxylation According

as two vacancies

petitive

isomerization

ratio

only

cannot

of allylic

and one hydride

the oxygen

of dienes

hydrogenations

in

or two

be detected.

because

on copper

chromite

that more

insight

by using

the reactions as specific

type of sites which

a good complementary

to adsorb

and hydrodehydroxylation,

test.

CH sites

the molecule

alcohols

do

the hydro-

to non-hydrogenation

allylic

and one

8).

In that sense,

represents

are required

(one vacancy

are reported

any of these

is specific

and proportional

represented

vacancies

(Scheme

it is interesting

alcohols

atom. Moreover,

is significant

respectively

sites can be obtained

5, this reaction

eliminate

three coordination

[9]. Therefore,

properties

by the structures

that the reactions

[I]. In effect,

reaction

to Scheme

numerous

ion (sites C and CH, respectively).

with this model,

of C and CH sites

not have hydrogenation

sites

of test reactions,

[9]. Since then,

with BH and CH structures

of the catalytic

alcohols

with

and one hydride,

are in agreement

of allylic

described

ion associated

sites are associated

into the specifity

of alkenes

and one hydride

or two vacancies

Since we reported

of the catalytic

by using a group

have been reported.

sites are generally

8, i.e. a metal

coordination

that the structure

could be characterized

of this model

Hydrogenation

sites

proposed

and to

can undergo

com-

the isomerizationldeoxygenation

to the relative

concentration

of B, BH and

C, CH sites. Finally,

it is noteworthy

on the number

of vacancies

in the reaction. transfers stable perties

being

of which

with an anion species

The copper

the hydride

system

that the properties

(I) hydride

ion and induces

a copper

system,

of the metallic

which

an irreversible

induces

reported,

a reversible

and a hydroxyl

group.

would

cation

is known to be very hydrogenation

(I) ion]. The chromium(III)

have been extensively

and therefore

such as a hydride

of the sites do not depend

but also on the nature

cation,

reactive,

process

[the

the acidic

pro-

rather exist

process

only

involved

in association

by exchanging

nucleophilic

255 CONCLUSION We have shown that, alcohols

can be deoxygenated

the mechanism, more

in addition

likely

that allylic of model

Siegel's alcohols,

reactions

chromite

known model

in addition

catalyst.

to olefins

for characterizing

metal

and dienes,

the catalytic

reaction

of

and

To our knowledge

on a heterogeneous

for transition

allylic

From the analysis

any dehydration

hydrodehydroxylation.

of this reaction

well

and isomerization,

does not involve

to a concerted

this is the first example by considering

on a copper

this deoxygenation

corresponds

to hydrogenation

catalyst. oxides,

constitute

Moreover,

we suggest a better

set

sites.

REFERENCES 1 2 3 4 5 6 7 8 9

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