Hydrogenation of highly unsaturated hydrocarbons over highly dispersed Pd catalyst.

317

Applied Catalysis, 15 (1985) 317-326 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

HYDROGENATION

OF HIGHLY

PART II: LIGAND

J.P.

EFFECT

UNSATURATED

HYDROCARBONS

OVER HIGHLY

DISPERSED

Pd CATALYST.

OF PIPERIDINE

BOITIAUX, J. COSYNS and S. VASIJDEVAN

Institut

FranFais

(Received

du Petrole,

Rueil-Malmaison,

4 July 1984, accepted

22 November

France.

1984)

ABSTRACT The hydrogenation of highly unsaturated hydrocarbons like I-butyne, 1,3butadiene and isoprene was shown to be sensitive to metallic dispersion. Addition of an electrodonating compound like piperidine in the reaction mixture increases the hydrogenation rate and the selectivity for the formation of olefin. This effect is explained by a decomplexation or ligand effect.

INTRODUCTION

In the first part of this study [I] we showed the strong influence particle

size on the hydrogenation

turnover

number

decreases

electron

of the hydrogenation

at high dispersions.

a too strong

rate of highly

complexation

deficient

of i-butyne,

This particular

of these

unsaturated 1,3-butadiene

behaviour

hydrocarbons

highly

has been interpreted

unsaturated

to a ligand

which

as are

[l,ll].

improves

The additive

The

and isoprene

on the small particles

In this article we show that the use of an electrodonating piperidine,

of the metal

hydrocarbons.

the activity

of the catalyst

additive,

in the hydrogenation

like of these

hydrocarbons.

operates

as a moderator

in homogeneous

of the complexation

strength

and is similar

catalysis.

EXPERIMENTAL Complete

description

given elsewhere Apparatus

of preparation

[1,23. Catalyst

and procedure

and characterization

activity

tests are made

have been described

procedures

have been

in a batch CSTR reactor.

[7].

RESULTS

In a recent publication the hydrogenation low dispersion

rate of I-butyne.

the influence

We observed

(< 20%) and a sharp activity

ion of the substrate particular

[l] we studied

by the small particles

of palladium

a constant

turn-over

dispersion number

decrease

beyond.

A too strong

has been

invoked

to explain

of selectivity

0166-9834/85/$03.30

of palladium

catalysts

D 1985 Elsevier Science Publishers B.V.

by addition

at

complexat-

this

behaviour.

Improvements

on

of sulfur

318

5

10

20

15

25

1

I

30

35 40

Time (mid FIGURE

1

compound

Influence

or carbon

monoxide

at 100°C and more. are lethal

of piperidine

on the rate of consumption

are reported

In our operating

poisons.

Moreover

of hydrogen.

[3, 41. These additions

conditions

they improve

are generally

(room temperature)

the selectivity

used

these compounds

but not the catalytic

activity. The nitrogen genation

compounds

of acetylenics

into their corresponding

has been used to improve genation

the activity

of 1,3-butadiene

Our first experiments (2O"C, 2 MPa) pyridine additive

are also known as promoters

of soluble

of selectivity

olefins

of the hydro-

[5]. Further

palladium

catalysts

pyridine in the hydro-

[6]. with pyridine

is hydrogenated

indicated

that under our working

to piperidine.

conditions

Hence we used piperidine

as

in our study.

Activity The influence dispersion. Curve A. genated.The which occurs

of piperidine

Figure

10% Wt I-butyne hydrogenation

After

complete

with a similar

diluted

rateof

for a pressure

the hydrogenation

addition

has been examined

1 shows the consumption

in n-heptane

butyne

without

is low until

over a catalyst

as

a function

hydrogenation

which

follows

of I-butyne

(IO cm3 butyne

is on the other and butenes

of 37%

of time.

any additive

its complete

drop of 11 bar. The consumption

of I-butene

feedstock

of hydrogen

is hydro-

disappearance

of hydrogen

during

hand quicker.

we started

a second

in 90 cm3 heptane)

with an admixture

is notably

than

run of

0.8 cm3 piperidine. Curve B.

The I-butyne

hydrogenation

quicker

in the absence

of

319

0.26%Pd-Al$$ft

I5 Time (mid FIGURE

2

Influence

of piperidine

on the repartition

of products.

8 d

I

20

FIGURE

l

3

Variation

hydrogenation

I

40

60

of the turn over number

of 1-butyne

presence

of piperidine,w

presence

of piperidine.

pure

100 Diipdllllo as a function

(from ref. El]), A

hydrogenation

8TI

I

60

of I-butene

of dispersion

hydrogenation formed

during

of I-butyne

ex 1 butyne

and in

the: in

IJ /

/

t

I

:

/

a 0

/

BO

f

I=

/ 80

cl

2:

ii-

21

3:

8 cm-l

FIGURE

I.R.

4

dispersion

spectra

catalyst

introduction

of CO, 3. After

piperidine,

in presence

of CO adsorption,

(0.76% Pd - Al203~~)

Oisp.:

introduction

but that of I-butene

of piperidine

over a low

27%. 1. Base line, 2. After

of piperidine.

is strongly

inhibited

by piperidine.

Selectivity In Figure product

2 are plotted

as a function

The hydrogenation little

butane

butyne

is consumed

of I-butyne

is formed

In this figure

the consumption

is very selective

from the beginning

before

the produced

we observe

again

ion. Nevertheless

the isomerisation

the hydrogenation

to butane:

piperidine

of I-butyne

and the evolution

of

of time.

but becomes

of the reaction.

I-butene

the strongly

inhibited

to 2-butenes

its addition.

only

1-butene.

Very

More than 90% of l-

is hydrogenated.

the butane/c2-butenes

4.0 after

and yields

rate of I-butene

seems to be more affected ratio

consurrptthan

has a value of 2 without

321

3200 2 pm-’ spectra

FIGURE 5

I.R.

dispersed

catalyst

of CO, 3. After

Influence

of adsorption

(0.76% Pd - A1203yt).

introduction

Various

catalysts

tested

including

becomes

We also observe hydrogenation

Whatever but 40 times

number

in our previous

of I-butyne

hydrogenation

without

that up to 20% dispersion of l-butyne

(dotted

publication

[I]

as a function

of

line) and with

number

by a factor

that the addition

the additive

but as dispersion

more and more significant.

has little

increases

At high dispersions

its promot-

the piperidine

of 4 to 5.

of piperidine

strongly

inhibits

the subse-

of I-butene.

the dispersion,

the activity

for I-butene

lower than for butene without

The influence

in a

per gram of catalyst.

have been obtained

from this figure

the turnover

was studied

line).

on the hydrogenation

ing effect

of l-butyne

the ones reported

cm3 piperidine

These activities (continuous

We observe

quent

on the hydrogenation

3 shows the turnover

piperidine

increases

1. Base line, 2. Introduction

dispersions.

with 0.8-1.0

dispersion.

influence

60%.

over a highly

of piperidine.

of additive

large range of metallic

Figure

Disp.:

of piperidine

of dispersion

The influence

were

of CO in presence

of piperidine

hydrogenation

is constant

piperidine.

on the hydrogenation

of 1,3-butadiene

was also

322 studied affect

for the high dispersions

and it was observed

the rate of hydrogenation

(the ratios

neither

I-butene/Q-butenes

that piperidine

the selectivity

and t-2 butene/c-2

does not

of the parallel

butene

are rounhly

reactions

unchanged).

DISCUSSION From the above 1)

The effect

hydrogenation catalysts. catalysts.

to I-butene

The positive

effect

is drastically

publications

dispersions:

1,3-butadiene

decrease

A too strong

supported

by the I.R.

bands consistent

In the present

work we again

and carbon

been tested,

utilized

monoxyde.

is

of the high

of I-butyne

and

20%. which

This interpretation

[Z], wherein

we observed

are

was

a frequency

a bond reinforcement

as the

one with 27%, another

4 shows the I.R.

introduction

new bands characteristic CO absorption adsorption

intensity

on yt alumina

with 0.76%

of CO adsorption

over the low dispersed

peaks at 2080 and 1980 cm-',

(in vapour of adsorbed

decreases

of

Fd have

with 60% dispersion.

spectra

of piperidine

the I.R. to study the coadsorption

Two catalysts

(27%) with the two characteristic

Figure

behaviour

on the small particles

with

lower).

increases.

piperidine

Figure

above

as an explanation.

study of CO adsorption

(40 times

rate of I-butyne

a particular

increased

The

at low dispersion.

of the hydrogenation

of these hydrocarbons

has been proposed

shift of the CO absorption dispersion

numbers

dispersed

altered.

lower).

inhibited

but negligible

when the dispersion

complexation

deficient

(40 times

is drastically

[I,21 we showed

the turnover

of I-butyne

of 4 to 5 over highly

on the hydrogenation

dispersions

number

is not significantly

inhibited

of l-butene

of piperidine

the turnover

by a factor

of I,3 butadiene

at high metallic

In our previous

electron

is increased

of I-butene

the following:

is very selective:

The hydrogenation

pronounced

metallic

we can deduce

The hydrogenation

hydrogenation 2)

results

of piperidine

phase along with a stream piperidine

appear

but no frequency

catalyst

respectively. of nitrogen),

Upon two

at 2960 and 2870 cm -I. The

shift

is produced

dispersed

catalyst

by the co-

of piperidine. 5 shows the same spectra

60%) wherein

over a highly

(dispersion

we observe

that the introduction of piperidine produces a large shift -1 -1 of the two CO bands from 2080 to 2050 cm and from 1950 to 1900 cm respectively. Thus the influence negligible

of piperidine

over low metallic

This behaviour

dispersion

of piperidine

donor compound

frequencies

of Lewis bases

film

(CH3)3N)

produced

particles

work

dispersion.

on the role

CO. The introduction

a small

produces

is

over higher

the published

on a highly

lower frequencies

This large shift over highly dispersed r back-donation

of CO adsorption

of adsorbed

[8], whereas

(NH3, H20,

band of CO by 15-75 cm -I, towards

increased

with

like (CH3)3N causes only

(1980 cm-') of CO on palladium the addition

spectra

and very pronounced

is consistent

of Lewis bases on the vibrational an electron

on the I.R.

of

shift in the L.F. band dispersed

displacement

Pt catalyst of the L.F.

[9]. has been attributed

by the electron enrichmentofthemetal

to an [14]. The

323

A Activity

4

;:::i-/i\, 1o-3 lo-4

:

I

I

pt

Ir

OS

c

I

I

I

I

_ AH a&for

.

Co Fe

Ni

Pd Rh Ru

+ I

,

I

I

I

ethylene

_ PEARSON acidity _ activity FIGURE 6

A typical

volcano

curve for the hydrogenation

Group VIII metals

(from ref. [IZ]).

electron

species

donating

transfers

this negative

dispersions particle

and the Metal-CO

In conclusion, reinforcement transfer towards

bonding

dispersed

catalyst

Clll. In the discussion

catalysts.

of the particular We concluded

in favour

the small electron ordination

of small

where

"ligand",

paper

at low

particles.

the bonding

induces

a

with a charge

hydrocarbons

of piperidine

catalysts,

transfer

like piperidine,

will be more pronounced

where

of the

poisons

several

possible

in the hydrogenation

This type of concept

the similarity.

belongs

are called

one

causes

in case of

to the coligands.

The piperidine,

of the hydrocarbons

a

of I-butyne.

of the hydrocarbon-metal

and the additives

energy

influence

ammonia

inert over a low dispersed

[l] we examined

bonding

the reagents

decreases

monoxide

of Lewis bases,

particles

In this present article we reinforce donating

However

on palladium

Such a type of selective

of a too strong

deficient

chemistry

orbital.

in turn

bonding.

it is relatively

of our previous

behaviour

over different

to the metal which

the unsaturated

over platinum

when

of ethylene

and carbon

CO chemisorbs

as for CO, the effect

Lewis base has been observed highly

of piperidine

bonding.

to the CO while

dispersed

shift

is little altered.

the hydrocarbon-metal

manner

bond

in the bulk of the large metal

[IO], hence the coadsorption

to reduce

over the highly

charge

gets diluted

the coadsorption

the metal

In a similar

electronic

to the CO IT* antibonding

charge

of the metal-CO

from the metal

is likely

transfers

charge

this negative

for double

an electro-

on small metal

DISPEBSHIN

50 25

1

0

FIGURE

7

Variation

shown

,

i

1BE 1.3BD 1B

1BE 1.3BD 1B

dispersions.

pdwy

of turnover

As dispersion

by the arrow.

number

increases

(I-butene

for 3 hydrocarbons

8

= 1 BE; 1,3-butadiene

in the turnover

Influence

particles

(influence

I-butyne.

Nevertheless

idine addition

curve,

as

= 1 By).

(neither

maximum

This type of volcano

VIII

influence

with

taking

catalytic

of metal

between

activity

strength

(See Figure

6).

at 100% as

activity

dispersion

hydrogenation

for

and piper-

what can be said

and I-butene? adsorbed

species,

for an optimum

one would

strength

Thus the variation

can be represented

curve has been reported metals

the hydrogenation

1,3-butadiene

place

studied

to the left of the curve

for the I-butyne

too weak nor too strong).

of adsorption

group

for 3 hydrocarbons

to CO) and improves

obtained

reaction

expect

1BE 1.3BDlBY

is to shift

if the opposite

results

The hydrogenation

different

opposite

is well established

on the different

number

of piperidine

by the arrow.

as a function

at 3 different

= I,3 BD; I-butyne

,

indicated

isorption

studied

py

Variation

consequently

1BE 1,3BDlB

we move to the right of the volcano

I FIGURE

1

I

1BE 1.3BD1B

‘~~~~~

dispersion.

K

01100% b

of chem-

of reaction

by a volcano

for the hydrogenation

rate

type curve.

of ethylene

over

325 In the case of hydrogenation palladium

the adsorption

strength

I-butyne

> 1,3-butadiene

results,

where we observed

and lastly

the butenes

ion of the adsorption

by the arrow

numbers

on an arbitrary

7. The T.O.N.

values

dispersions.

the points

that is coherent

effect

This sequence

is hydrogenated

turnover

strength

As far as the influence spectacular

in the followin?! order

> 2-butenes.

that I-butyne

different

increases

with an increase

at high dispersions.

curve at 100% dispersion by the arrow the addition

the left. Thus the presence

of the three

hydrocarbons

representation

The unsaturated

dispersed

catalysts

hydrocarbons

by our

second

as a funct-

we build a Volcano from our earlier

of the adsorption

is concerned

As indicated

results.

butadiene

CUrVeI

publications

From this figure we can deduce that as

of the volcano

This simplified

cl31

shift to the right side of the curve as indicated

of piperidine

is observed

scale,

are taken

piperidine.

adsorption

over

is confirmed

first,

of these

the nature

to move towards

hydrocarbons

formed.

like the one of Figure [1,2] for three

varies

> I-butene

If we plot the hydrogenation

dispersion

C4 unsaturated

of different

Hence

hydrocarbons

in presence

of piperidine

our earlier

complex

and the addition

in Figure 8 we compare and in absence

of piperidine

and acts contrary

confirms

strength.

we have shown that the most

more

reduces

of

the points

the force of

to the metallic observation

strongly

of an electron

causes

dispersion.

and unifies

the

over the highly

donating

species

decreases

this "self-inhibition". The highly additive

dispersed

acting

Unlike

homogeneous

same central different

catalysts

behave

similarly

to homogeneous

catalysts,

the

as a ligand. catalysts

where

atom, on heterogeneous

sites and the electronic

the ligand

catalysts effect

and the reactive

both species

coadsorb

can chemisorb

on the

on two

could be a "long range" one [15].

CONCLUSION Our studies highly

unsaturated

a too strong

Further

in a same manner

on highly

low hydrogenation dispersed

by the observed

both activities

effect

and selectivities

work will show that such effects with

palladium

of the metal with the hydrocarbon.

is supported

increases

ligand.

that the relatively

hydrocarbons

complexation

interpretation which

indicate

several

other metals

turnover

number

catalyst

is due to

The validity

of

of this

of a Lewis base-piperidineby acting

as a "decomplexing"

can be observed

of group

and interpreted

VIII.

ACKNOWLEDGEMENT One of the authors the grant of study do this work.

(S.V.) wishes

to thank

leave and the French

Engineers

Government

India Ltd.,

for providing

(India),

for

a scholarship

to

326

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