Titration of hydrogen chemisorbed on supported platinum catalysts by ferric chloride solution

Appkd Catalysis, 16(1985)209~-214 Elsevier

Science

TITRATION CHLORIDE

S.

Publishers

B.V., Amsterdam

OF HYDROGEN

--Printed

CHEMISORBED

in The Netherlands

ON SUPPORTED

PLATINUM

CATALYSTS

BY FERRIC

SOLUTION

SZAB6 and

Central

F. NAGY

Research

Institute

Hungarian

for Chemistry,

Budapest,

P.O. Box 17, Hungary.

(Received

1 November

1984, accepted

2 January

Academlf of Sciences,

H-1525,

1985)

ABSTRACT It has been shown that titration of hydrogen chemisorbed on supported Pt catalyst by 0.1 M FeC13 solution in 1 M HCl electrolyte under oxygen free conditions can be used for surface determination. There is no hydrogen spillover in HCl solution.

INTRODUCTION Measurement routinely

gas-phase

to data published

methods

It follows

for surface

that a simple

in a suitable

which

It follows

Pt catalyst

that only

would

Taking

conditions

thereby

in a

adsorbed

on a supported

published

these compounds

agents

is still

earlier

may undergo

can be used for titration

falsifying

of the oxidizing

the above discussed

seemed

suitable

the oxygen

content

Pt has self-

On the other

in the presence

agent

but

of a supported

the results.

0 1985 Elsevier

conditions,

for this purpose

is higher

of

than the

ferric

Publishers

in

ions can

as organic

can only be made under oxygen-free

in different

electrolytes

in the final dispersity Science

an FeClS solution

because

ions and they do not decompose

such a titration disolved

cause discrepancies

0166-9834/85/$03.30

agent

system.

often do. Of course,

would

by an oxidizing of Pt dispersity

of the method

itself can be oxidized

the Pt nor the chloride

because

and

results.

but there

hydrogen

because

catalysts.

measurements

recognized,

be so high that the chloride

of a catalyst

in different

the same dispersity hydrogen

has almost

of the titration.

oxidizing

also be oxidized,

acid medium

neither

oxidants

titration

inorganic

into consideration

hydrochloric oxidize

agents

the results

of the PtClg-/Pt

gave

Deficiency

ions if the redox potential

potential

dispersity

is already

to measure

catalysts

electrochemical

of chemisorbed

14-51.

cannot

platinum

be used for determination

oxidizing

falsifies

hand, the Pt content chloride

method

solution

their redox potential

[l-3],

This possibility

been the use of organic oxidation

of platinum

determination

might

experimental

in water

on supported

earlier

titration

electrolyte

Pt catalyst.

no suitable catalyst

chemisorbed

been used for determination

According

supported

of hydrogen

B.V

used in the

results.

210 EXPERIMENTAL

METHODS

A three-compartment investigation

by titration

FeC13 solution.

curves

During

Deoxygenation

Titration

of hydrogen

cell as described

HCl electrolyte electrode

in which

the titrations

Platinum

powder

0.5 g Pt/ml

vacuum.

Introduction

Pt/A1203

platinum

ions without conditions

ads

of the charging solution

saturation

have

oxygen.

the catalysts

gas.

Pt catalyst

was made

electrode

in the same

in the same 1 M

A platinized

to indicate

the actual

Pt needle redox potentia

of the cells. by dissolving

the measured

from the solution

of H2PtC16

at 3-5°C with 50' KOH solution. with triply

catalyst

into an electrolvte

destroying

RFCELKIS

solution

in electrolyte

quantity

containing

structure

of platinum

and finally earlier

becomes

of chloride electrolyte

dried

in

Burette.

chloride

it should

solution

was

171.

Automatic

first

ions

be

containing

or activity.

catalysts

even if a deoxygenated

The catalyst

containino

solutions

into an electrolyte

its original

the surface

water

as described

with a type OP-930

from the air, in the presence

Since

saturated

in with

ions some Pt may be is used, according

reaction:

7 4Cl- + 2H+

(PtCl$

distilled

was prepared

catalysts

from the catalyst

to the following

Pt + 0

was deposited

were performed

chemisorbed

dissolved

after

were performed.

was prepared

how to place the Pt catalyst

atmospheric oxygen

catalyst

of a Pt catalvst

studying

chloride

catalyst

in 0.1 M HCl solution.

free of electrolytes

The titrations

decided

solution

was completed

Supported

When

powder

. 4.5 ml 40. CH20 solution was added to every ml of H2PtC16 solution

and the reduction then washed

curve and the charging

due to dissolved

Pt hydrogen

electrode

in the main compartment

grade FeC13.6H20

errors

in the

161.

was a platinired

0.1 M FeC13 titrating of reagent

nitrogen

on supported paper

was used as an indicator

of the electrolyte

of hydrogen

by ourified

adsorbed

electrode

charging

on a platinum

or the measurement

in order to avoid

in our earlier

The reference

cell was used

of the cell and the FeC13 titrating

of traces

was effected

adsorbed

the titrations

deoxygenated

(and purging

hydrogen)

electrochemical

of electrochemical

of hydrogen

both the main compartment

been continuously

with

bottomed

of the similarity

curve measured with

platinum

+

(PtCl,)'-

ions can dissolve

+HO 2

and deposit

(I)

once more changing

thereby

the activity

of the catalyst. In accordance the gas-phase

with our earlier

and the catalyst,

into a deoxygenated For the above

experience

without

[S], Oads must be reduced

any contact

with

Hz in

with air, can be introduced

electrolyte.

reasons,

in our experiments

the catalyst

sample

was poured

into

211

‘8 FIGURE

1

1, Charging

curve of 0.3 g Pt powder

the same Pt powder measured

we switched

deoxygenated continued Having purified

with

to hydrogen

hydrogen

up to the saturation

of the catalyst the surplus

with hydrogen

in

and finally

Before

methods

carried

we had a catalyst

platinum

cathodic

chemisorbed

on massive _

the titration

of hydrogen

that the result

of surface

adsorbed

of our titration

determination

For this purpose,

catalysts,

out by strong

of hydrogen

be verified

in water

in the Pt-bottomed

0.3 g Pt powder at first by electric titration

with

converge,

it can be stated

Taking between

0.1 M FeC13

into consideration the two curves

catalysts

solution

sample whose

saturation

out of the cell by

surface

was saturated

on supported

Pt catalysts

electricity.

(curve

the charging

1 in Figure 1)

curve of

and then by

1). Since the two curves

have given

the same surface

of other measurements,

area.

the discrepancy

the hydrogen

adsorbed

on Pt

with 0.1 M FeC13 solution. to satisfy

Pt catalyst

In theory,

of other

solution.

5Z, therefore,

it is not enough

of a supported

it had to

was the same as the results

cell we determined

by titration

was

by FeC13 solution

current

the results

with hydrogen

Pt catalysts

(curve 2 in Figure

never exceeded

however,

potential

does not conduct

by hydrogen.

was flushed

polarization.

that the two methods

can be determined

In practice, electrode

sample

hydrogen

1 M HCl solution.

In the case of massive occasionally

When this was

electrolyte

to the cell and bubblingOf hydrogenWas

finished nitrogen

Titration

1 M HCl supporting

and finally

was added

saturation,

= 5 mA). 2, Charging curve of

out from the cell by nitrogen.

the dry cell and then air was purged finished,

(I

with 0.1 M FeC13 solution.

by titration

during

cannot

this condition be measured

titration

because

the

if the support

the catalyst

potential

212

0’ FIGURE 2 platinized solution

c

‘8

1, Titrated

charging

Pt needle

indicator

‘16

Q,C

curve of 0.5 g Pt powder. electrode

as a function

2, Potential

of the volume

of the of titrating

(in coulombs).

e

I

0 FIGURE

3

1, Titrated

of 0.2 g Pt powder

and the redox potential

‘4 charging

(platinized

Pt needle)

3, Titrated

of the electrolyte

of a supported

‘8

curve of 0.2 g Pt powder.

and 2 g alumina.

potential

Q. c

Pt catalyst

electrode.

charging

2, Titrated

charging

must be the same, therefore,

may be measured

This concept

curve

curve of 2 g alumina.

via the electrolyte

the by a small

has been tested with a massive

Pt

213

0,8.

6 V .

04 . .

.

. 0 FIGURE

4

‘4 charging

because,

Pt needle

testing

and A1203

consequently,

of a supported

of hydrogen

Before

2, the Pt needle

sample;

ion of the surface

Titration

curve of 5 g Pt/A120,

chemisorbed

in order

experiment

give information

the amount

no spillover

Figure

of hydrogen

4. In this experiment

The H/Pt

and the

ratio measured

the same potential

platinum

catalysts

a mixture

as

by FeC13 solution

of massive

to find out what differences

about

hydrogen

measured

under such experimental

The titration

sample

can be used for the determinat-

of the support.

3 it can be asserted

of hydrogen

indicated

this method

Pt catalyst,

due to the presence

On the basis of Figure

electrode

on supported

a real supported

powder was examined

not change

of both the catalyst

Pt catalyst.

in the titration might

Catalyst.

could be measured.

to Figure

did the catalyst

‘8

Q, c

in this case, the potential

electrode

According

.

.

.

I

Titrated

catalyst

l

l

Pt

catalyst

would

arise

On the other hand, this

spillover

in an aqueous

that the presence

by titration.

phase.

of alumina

It follows

does

that there

is

conditions.

chemisorbed

on a Pt/A1203

we used the same catalyst

by pulse adsorption

catalyst

is illustrated

as in our earlier

in

paper

was 0.105 and by TPD of hydrogen

[9].

1.36

191. On the basis of Figure 4, the H/Pt ratio and the surface sample

can also be calculated.

ion of adsorbed hydrogen

A=

adsorbed

7.5 x IO 5x

hydrogen on

From the figure

is 7.5 C. Since

and charge

of the catalyst

required

210 uC is required

for the oxidat-

for the oxidation

1 cm2 surface CZ], the surface of 1 g catalyst

of

is:

-4

210 x IO-6

=

0.7 m2/g

(2)

214 Not only the surface given catalyst

of a supported

can be determined

into consideration

Pt catalyst

but also the H/Pt ratio of the

by the titration

that the Pt content

illustrated

of our catalyst

in Figure

is about

4. Taking

0.5% and 5 g was

used in the titration:

H/Pt

=

(7.5/96500)/(5

which

is between

that pulse surface

x 0.5 x 10-2/195)

the results

adsorption

measurements

area than the real value,

Finally

it must be mentioned

the titration.

Reaction

and then it slowed down, catalyst. about

measured

(3)

by other methods

give a smaller,

that two periods

[9]. It is very probable

whereas

the TPD method

in our earlier

papers

could be distinguished

20% of the titrating

in our opinion,

It is interesting

0.6

as has been shown

of the first

the same as the result

=

solution

due to slow diffusion

a greater [lO,ll].

during

was very fast

in the pores

of the

that the result of the fast part of our titration

is

of pulse adsorption.

REFERENCES 1 2

10

11

L. Spenadel and M. Boudart, J. Phys. Chem., 64 (1960) 204. A.N. Frumkin, Advances in Electrochemistry and Electrochemical Engineering, Vol. 3, p.315, Interscience, New York (1963). J. Bett, K. Kinoshita, K. Routsis and P. Stonehart, J. Catal., 29 (1973) 160. L. Freidlin and K.G. Rudneva, Izvest. Acad. Nauk USSR, Otdel. Khim. Nauk. (1954) 491. D.V. Sokolskii, Hydrogenation in Solutions (in Russian), p.172, Alma-Ata (1962). S. Szab6 and F. Nagy, J. Electroanal. Chem., 70 (1976) 357. J. Margitfalvi, S. Szabd, F. Nagy, S. GUbolos and M. Hegediis, Preparation of Catalysts III, p.473, Elsevier, Amsterdam (1983). S. Szab6, F. Nagy and D. M6ger, Acta Chim. Acad. Sci. Hung., 93 (1977) 33. J. Margitfalvi, M. Hegedtis, S. Gobolos, E. Kern-T6las, P. Szedlacsek, S. Szabd and F. Nagy, Proc. 8th International Congress on Catalysis IV - 903 Verlag Chemie 1984. S. Szabb, D. Mdger, M. Hegedtis and F. Nagy, React. Kinet. Catal. Lett., 6 (1977) 89. F. Nagy, D. Mbger, M. Hegediis, Gy. Mink and S. Szab6, Acta. Chim. Acad. Sci. Hung., 100 (1979) 211.