Kinetic investigation of the reaction: CO+Cl2⇌COCl2 over ZSM-5 zeolites with transition metal ions

467

CatalysisToday, 3 (1988) 467-473 Printed in The Netherlands

Elsevier Science Publishers B.V., Amsterdam -

OVERZSM-5 ZEOLITESWITH

KINETIC INVESTIGATION OF THEREACTION:CO+C+ -COC12 TRANSITIONMETALIONS

P. FEJES, c. HAJOU,A. GILOE, Gy. SCH&EL, K. VARGAand I. HANNUS Applied Chemistry Department, Jozsef

Attila

University,

Szeged (Hungary)

ABSTRACT

The CO+Cl CrCOCl reaction was studied over a ZSM-5 zeolite (SiO /Al 0 = .s. A . . X Be= 80.0) contai ing tra sition metal ions. An Eley-Rideal type rate equ 2tie scribes the observed rates with acceptable accuracy. The proposed mechanism takes into account the interaction of CO arriving from the gas phase with cheyisorbed chlorine. 1.r. spectra convincingly show the presence of a charged COCl species under reaction conditions.

INTROOUCTION Because our paper deals primarily formation, discovery

we have to skip the history by Oavy (181’2) till

the production

of pigments,

its

another formulation

finds

Zeolites,

and 0.63 nm provide As regards

both easy access

that charcoals

phosgene with have hetero-

to the active

have to

pore openings between 0.6 sites

in the interior

of the

and easy removal of the product. sites,

by analogy with similar

mistry , ions of the Group 8 of the periodic they have partially

from its including

causes problems when spent catalysts those exhibiting

active

applications

for producing

in the fact

particularly

for the reactants

phosgene

and polymers.

as catalyst

explanation

of catalytic

important intermediate

present-day

herbicides

charcoal

channel systems and this

be replaced. grains

its

of this

extensive

dyes,

The idea to try to replace -disperse

with the kinetics

filled

orbitals

table

reactions

in organic

seem to be appropriate

for the interaction

che-

because

with CO and C12.

THERMOOYNAMICS OF THEREACTION.NON-CATALYTIC TRANSFORMATION Given the overall CO(gas) + C12(gas) the equilibrium the initial for defining

phosgene-forming

*COC12(gas)

constant

partial

(1)

of the reaction

pressures

the activities

lue of the extent

of overall

(pi),

can most conveniently

the pressure

(PO), the reactor reaction

Ka = exp(-A Gi T/RT) = P” yg(pEo-

3

Considering

reaction:

in the selected

by

standard state

volume (V) and the equilibrium

va-

(E >: FE)-‘(pFl-

FE)_1 2

that the Gibbs’

be expressed

free

energy of formation

(2) for phosgene from CO

468 = -46.61

and Cl2 at 473 K (200 ‘C), AG: CoCl that

the equilibrium

the reaction

is compleiely

can be regarded

kJ/mol,

‘displaced

it

follows

to the right

as irreversible

Tram equ. (2)

(Ka=1.4f3.105);

even at the highest

hence

experimental

temperature. Though the homogeneous, was not negligible

(it

times of reaction),

non-catalytic

because unavoidable

below this

level.

to the observed

about 5 % at the highest

reached

no correction

formation”

contribution

was applied errors

temperature

for this

of other

and longest

“empty reactor

origin

rate trans-

could not be diminished

EXPERIMENTAL The catalyst a molar ratio

base material

was a ZSM-5 zeolite

Si02/A1203 = 80.0,

Na+ ions of the as synthesized temperature

before

burning

using

with

bromide as template.

were exchanged for NH: ions at room

product

off the organics.

By ion exchange in aqueous COG’+ and RhC13 solutions,

specimen synthesized

tetrapropyl-ammonium

four catalyst

La(N03)3, Pd(NH3)4C12, Pt(NH3j4C12

specimens

were prepared

with the approximate

compositions: H(Na)l 14Pt0 59 (A102)2e32(Si02)92

Sample 1.:

2': H(Na)0.74C00.65La0.09

(A102)2.32(sio2)92.68

3.: H(Na)0.16Pd1.08

(A102)2.32(sio2)92.68

4 .: H(Na)0.15Rh0.72

(A102)2. 32(sio2)92.

The acidity -exchange

(H+> values capacity

the respective Provided

are uncertain

of the zeolite

that

every active their

For infrared

studies

Pt

(i.e.

2+

2+ , Co , etc.

concentration, of less

analysis

of

self-supporting

lying

up to 700 K and contacting

permitting

between 0.103 2 ny 5

cell

was connected

in situ

to a high vacuum

gas reservoires. heat-treatment

the wafer with the gaseous reactants

were recorded

was accessib-

wafers of about 5-10 mg/cm2 thickness

The infrared

facility

ions)

than 2.

pump and to the respective

with a heating Spectra

site

by a factor

from the powders.

system with oil-diffusion

temperatures.

(=0.412 meq/g> and the elemental

initial

5 0.188 mmol/g, would differ were pressed

68

as they were computed from the known ion-

specimen.

le for the reactants,

provided

68

at beam temperature

using

It

was

in vacua at preselected

a Specord 75-IR

type spectrometer. The reaction

was carried

out in a batch reactor

over catalyst

samples of approximately

parated)

of the reactor

part

the preparation

(volume:

of gas mixtures

with gas recirculation

1 g (~0.025 g). Vl =

(CO and Cl,)

The unheated

(and se-

0.0891 dm3, Tl = 29823 K) permitted of known amount and composition.

469

After

admission of the mixture into

~0.02%

dm3), the reaction

pressure

using a special

ducer,

the heated part of the reactor

was followed

by continuous

sensor for agressive

(volume:V2

registration

gases (Datametrics

of the total pressure

trans-

type 1590 A).

Approximate extents

of adsorption

for each component were obtained

metric measurements on the same catalyst the threshold

of detection

adsorption

and linearity

tent of the overall

KT and KT (see

reaction

by volu-

of CO was below The isotherms

was also presumed to be valid

These data were used for determining

coefficients,

unreacted

The adsorption

even at the lowest temperature applied.

for Cl2 and COC12 were linear the mixtures.

samples.

later)

the equilibrium

for

values of

for Cl2 and COC12. The final

(or the conversion

ex-

of CO) was determined from the

out the Cl2 and COC12. This was used for checking the

CO by freezing

value of Kg. THERATE EQUATION Gaseous chlorine

(and also phosgene)

ALPO-s even at elevated CO are therefore theoretical

fully

is strongly

(T >500 K) temperatures; occupied

bound in zeolites

potential

adsorption

by C12. This has to be considered

and sites

for

when deriving

a

rate equation.

The interaction

between CO and Cl2 can be visualized

as follows,

ki/ki, Lc1I

i=l

iz1 + Cl2 _-.

2

2

[C121+ co

k2/k2 c

3

cc0c1,3

.

k;/k3

*

COC12 + [zl

specifically

where 1.. . I : stands for sorbed species,

(4)

[COC121

iZ] for unoccupied active

sites. The catalytically cavities tion,

active

in interaction

sites

are unspecified

with chemisorbed chlorine.

above a few tenths of 1 mnol/g,

be responsible).

Reaction

and the surface coverage

chlorine,

corresponds

This picture pressed

2

this

2

r2 = k2%12PC0 - ki%OCl,

The actual

phosgene

mechanism which can be ex-

formalism: (6)

(fast> (rate

may

from the “gas” phase

equilibrium.

is in accord with an Eley-Rideal

- ki”C1

high sorp-

over the “oxygen-lattice”

step being rate-determining.

mathematical

in the zeolitic

(For the relatively

between CO arriving

to the adsorption

by the following

‘1 = kl~p~l

takes place

physisorption

ions present

determining)

(7)

(8)

(fast.1 where the ej-s free

active

partial

(j=Cl,, sites

COC12) are coverages,

and the pi-s

f+ is the relative

proportion

(i=CO, Cl2, COC12) are the corresponding

of actual

pressures. Kinetic

equation, fined

and balance

expressing

as: AP = p:l

equations

the rate

can be transformed

into

a single

differential

(in mol/s> by the change of the total

+ pEo - p; the pp-s are initial

partial

pressure

pressures,

(de-

and p is

2 the actual cients,

pressure,

so: AP 201,

equilibrium

constants

d(A

P> _ k2KT a - + a~cl; “2 where

are adsorption

and

equilibrium

constants

; yzl+Ky

As approximate tion

experiments,

determined

parameters

(rate

coeffi-

(9)

K”3= “~oc12’“coc12

ve amounts in the adsorbed Pzl+K;

constant

- + AP)(P;~ -

dt

KY = $.12/nC12

and containing

etc.):

defined

and gas phase, andazP/y

values kg/n;

in a closed

and the Greek letters

stand

for

+Ky

(10)

for KY and KY are available

es n2

system by the respecti-

(s-1 kPa-1)

from (9) by the method of linear

and k$/r$ least

from independent s

H; (s-l>

adsorp-

can be

squares.

RESULTSAN0 DISCUSSION A representative (r) as a function

example showing the of t is given in Fig.

BP*

t curve and the computed rates

1.

50.0

.0

-2 m %

+++-+

=

XXXX =

2

PRESSURE RflTE

-4

f

Fig.

~.AP -

t and r ++

t curves

for catalyst

(ny = 0.103 nnrol; T = 363 K).

No.1 (Pt)

471

The evaluation and (10).

of data strictly

The derivatives

approximation

of the

followed

the mathematical

were obtained

from a fourth

AP versus t curve followed

and xi from the linear by nultiplying

dAP/dt regression

by analytical

were transformed

by the amount of active

The most important equilibrium termined from two or three parallel

sites

expressions

into

derivation.

actual

for each catalyst

data and kinetic

(9)

degree polynomial ~2

rate coefficients ($1.

parameters,

as averages de-

runs, are summarized in Table 1.

TABLE1 Sorption

coefficients

Catalyst No.

1 (Pt)

t-$=0.103 mmol No. 2 (Co) ny=O.lll

mm01

No. 3 (Pd) r$=0.182 mm01 No. 4 (Rh) n0=0.118 mm01 2

and rate constants

for the catalytic

k2*10’/(mol/s

kPa)

phosgene formation ki*107/(mol/s)

T/K

K?

K;

363 383 399 418

0.65 0.45 0.32 0.22

0.97 0.66 0.81 0.56

6.90 9.51 7.57 12.13

0.71 0.59 2.4-l 1.85

363 383 398 418

0.82 0.46 0.32 0.20

0.95 0.80 0.60 0.40

3.25 5.15 9.15 17.98

0.42 0.75 1.17 1.90

365 383 400 418

0.46 0.25 0.21 0.13

0.70 0.65 0.45 0.19

1.19 1.52 8.46 21.15

2.19 1.46 1.51 2.59

364 385 398 419

0.53 0.33 0.27 0.16

0.72 0.50 0.38 0.22

1.11 4.43 8.24 19.82

0.71 0.86 1.07 1.98

From (2) and (7) follows

that Ka = P’(k,/ki)(K;/K;);

as K;/K; changes with-

in one order of magnitude, the value of k2 should exceed that of k; by at least 2-3 orders ptotic

of magnitude which does not materialize

behaviour

tardation

of the

AP+

t curves

by COC12 which should be considered

In order to rationalize (see e.g.

the same authors

zeolites:

of phosgene is actually are dealing

with phosgene,

ward two similar racteristic

ionic

and the asym-

of product re-

the kinetics.

to phosgene formation interactions

it should

are dominating

ref.1).

The formation zeolites

environments

This fact

indication

in refining

the pathways leading

be remembered that in zeolitic

here.

are a clear

with since

Fejes et al.

an “overture”

(refs.2-3)

and Lok et al.

mechanisms which can be modified

for the interactions

to dealumination

about 1980. As concerns to express

which

dealumination (ref.41

put for-

the main steps

taking place between some halogen,

of

X2, and

cha-

{ A104,2- 1. Me+ + X2-+ ({ A104,2- 1. Me+. . .X While the indicated orine,

steps with a highly

lead to completion

even at Ts350

mation stops at the intermediate Infrared

spectra

6-_

x6+

) --t{AlO+}.X-+

electronegative K (cf.

MeX + 0

J

X2 as reactant,

Lok), with chlorine

(11)

like

flu-

the transfor-

stage.

registered

at beam temperature with sample 2. in the pre-

sence of CO+C12 mixtures, equal intensity

or COC12 alone, exhibit two intense features of nearly -1 as shown in Fig. 2. They can be assigned at 1805 and 1718 cm

to the

01 vibration node (symmetric stretching; in gaseous phosgene absorbing -1 at 1827 cm ; see ref.5) in Fermi resonance with the overtone 2 04 ( “4 being an asymmetric stretching 01/2

o2 diad.

giving

The position

rise

to absorption

at 845 cm-l)

of the two bands differ

570 and 281 cm-’ found by Jacox et al. ces at 14 K and interpreted

(ref.61

which results

in an

markedly from those at 1880,

in irradiated

solid

as being due to the free radical

CO+HClmatri-

COCl’.

80

40

lj50

1 sQ0

Fig.

2. Infrared

wawenumber (cm-‘>

spectrum of the COCl+ spec?ls

Fermi-resonance It is believed rise

17BE

at 1718 and 1805 cm

that in the case of zeolites

the surface

to the bands mentioned is the ion COCl+, in fact

form of phosgene: by Eaily

ID-CO It/a

species

a stabilized

which gives mesomeric

of which was postulated

already

(ref. 5) -

As a consequence, that’the

I-, the existence

showing

.

lone electron

by interaction

the i.r.

data give support to the previous

pair of CO may cause complete heterolysis

with the Cl6 + end of the molecule.

mediate Cl-CO+*Cl- either

(with AlOCl, MeCl and CO2 as products) As pretreatment

The relatively

desorbs as COC12, or else

picture

in

of Cl6 --Cl6 stable

+

inter-

causes “dealumination”

above about 600 K.

in high vacua at 773 K reduced the level

sample 2. by about 40 %, also Erdnsted acid sites

are active

of activity

of

in forming phosgene.

473 Though the most active previous Y> attain

reasonings

follows

a large

(e.g.

of charcoals

number of questions

had to be clarified

working catalysts

varieties

that the best catalyst

or even exceed the activity

from Japan), etc.)

catalyst

before

by zeolitic

sample 2.;

from the

were an H+-type ultrastable (e.g.

that of type H6W-761

(time on stream effects,

even suggestions

hint:

can be raised

regeneration to replace

the

materials.

REFERENCES 1 2 3 4 5 6

J.A. Rabo, P.E. Pickert, D.N. Stamires, J.E. Boyle, Deuxikme International Congrks de Catalyse (Editions Technip, Paris, 1960); Section II. p. 104 P. Fejes, I. Kiricsi, I. Hannus, A. Kiss and Gy. SchBbel, React. Kinet. Catal. Lett., 14 (1980) 481. P. Fejes, I. Hannus, I. Kiricsi, Zeolites, 4 (1984) 73. 8.M. Lok, F.P. Gortsema, C.A. Messina, H. Rastelli, ACS Symposium Series, No. 218 (Intrazeolite Chemistry), 1982; p. 41. C.R. Bailey, J.8. Hale, Phil. Mag., 25 (1983) 274. M.E. Jacox, D.E. Milligan, J. Chem. Phys., 43 (1965) 886.