Modification of the structure sensitivity of supported Pt catalysts

Applied Elsevier

MODIFICATION

Jonn

161

Catalysis, 15 (1985) 161-173 Science Publishers B.V., Amsterdam

SENSITIVITY

in The Netherlands

Pt CATALYSTS

OF SUPPORTED

3utt

B.

Deljartment

60201,

OF THE STRUCTURE

- Printed

of Chenlcal

Englneerlnq,

Unlverslty,

Northwestern

Evanston,

IL

USC

At3STKAC'T A nuaber of probe reactIons lncludlng hydrogenstlon, hydroyenolysx, exchange and oxldatlon have been lnvestlgated over two series of Ft/S1C2 and Pt/AI 0 catalysts. These encompass a wide rance of percentage metal exposed, 2 3 and have been thoroughly characterized by hydrogen chenlsorptlon, reactlvxty of surface oxygen and x-ray line profIle analysis. While the orlqlnal Interest was to examine the relation between metal morphology and catalytic behavior, It turns out that pretreatment CondLtlonS are a~ important, or more SO, in the determlnatlon of catalytic actlvlty and selectlvlty. INTRODUCTION ;!:e questIon metals

of the relatlonshl~

ana their catalytic

&ecace.

At the first

of in average exposed.

metal

However,

S"Cr, as x

2 and SXhFS.

crystallite

much more

Thuslx].

al amplitude

the morphology

has been of Interest

level of characterlzatlon dlmenslon

1s possible

x-ray

chemlsorptlon,

size clstrlbutlon,

propertles

betaeen

one

might

shape,

or a correspondlnq

parameter,

percentage

electron

features

defect

cetal

1s used

microscopy,

s:;ctcas particle

population

and vlbratlon-

(cd. 2.0 no) particles.

here encompasses

2% wt. Pt, with percentage

analysis,

be able to define

-- even for very small

The work dIscussed

now well over s.

one can think of determlnatlon

If a conlblnatlon of methods

line profIle

lattice

of supported

exposed

a set of Pt/Sl02

catalysts,

from 6.3 to 61, and a slmllar

0.5 to

set of

0.3 to 0.4 wt. "6, with percentage exposed from 27 to 107. Physical Pt/Al 0 2 3' characterization was via x-ray dlffractlon plus H chernlsorptlon in our lab2 oratories [1,2,31. Addltlonal work h+s been conducted elsewhere [4,5!, but we focus on the first t:do methods as probe;; for the catalytic methylcyclopropane

hydrogenolysls,

anoe with cycloDentane. thst con&ucted

The thrust

elsewhere;

ea 1" thet only a single of catalysts collaborative Professor

however, reaction

has been studled. research

J.B. Cohen

0166-9834/85/$03.30

tere[1,2;3]

behavior

between

. Several

propene

hy2roqenatlon

of the work

much reported has been

have been

and deuterlun

literature

investigated

nave been used

primary

1s not greatly

different

exchfrom

1s more restrlct-

or only a small group

The results

discussed

here are the product

the author,

orofessor

R.L. 3urwel1,

over the past eight years.

0 1985

reactions

of these materials;

Elsevier

Science

Publishers

B.V.

Jr. and

of

162 PREPARATION

AND CHARACTERIZATION

pt/s10 -2 A wide pore slllca support

material.

gel

= 14 nm) was used as the P upon the support either by conventIona

(Davlso" Grade

Pt was deposIted

62, d

lmpregnatlon to lnclplent wetness with [H2PtC16]aq, or by lo" exchange with 2+ P~(NH~)~ . After preparation these catalysts were reduced I" H2, cooled I" in air. The percentage

N2 and stored

25OC, Dh, was determlned

after

1, then cool Ar to chemlsorptlon been described

I" detail

lvlty of adsorbed

the entlre

0 2 on these

range of particle

measured

temperature.

121. An extensive surfaces.

of H 2 gave values

chemlsorptlon

exposed

a pretreatment

A pulse

was used and has

Comparison

in a" even greater

reactlon

was structure

conslderable

with the 2-O2 about 20% smaller over

was substantially

increase

tltratio".

1" I" the surface

stored

greater Exposure

I" air

than that to 02,300oC

O2 content,

and this

The D = 81% gave O/Pt = 1.33, lndlcatlng h Into the crystallite lattice. At D = 40% this h 2 of the survival of a metallic core after 02 treat-

sensltlve.

penetration

of 0

lndlcatlve

rat10 was 0.50,

out on the reacttltratlon

of H

exposed

0 2 from the short exposure of the H2-02

resulted

method

It was found for catalysts

content

at

300°,1;Ar,4500,

study was carried

of percentage

sizes.

at 25'C for a year the surface resulting

by H2 chemlsorptlon

0 2,300°,0.5;H2,

for D = 6.3 the ratio approached 0.09. Reduction of stored h pt/s10 2; 02300°, 0.5*1" H also appeared to be structure sensltlve. At 25OC 0 2 2 was removed more rapldly from small Dh than large Dh.(Pretreat code 1" note a). ment, while

Characterlzatlon carried

"la Fourier

out for Pt/S102

full series

of samples

tlcle dimensions agreement

with

crystallltes

the Dh values.

were equlaxed,

exposed

posessed

with D h was the mea" vIbrationa linearly

correlated

measurement shown

I" Flqure

vestlgated "perfect

2. The catalyst

platinum".

one crystallographic particle results

I" Figure

that showed

no mlcrostraln

however

devlatlon

02,3000,0.5

size dlstrlbutlon

amplitude

correlation

Erom the XRD results

and the materlal as average

means

preparatron

of this are qlve"

flowing

I"-

growth

mlcrostralns.

pore dlmenslon,

1s

indlcatlng

of preferential

exhIbIted

during

growth

Details

h concernlnq size distrlbutlon and preparation *Note a) Pretreatment sequences are described example,

parameters varylnq

of Dh = 7.1 was the only one I" the range

may be due to an orlented

par-

I" good

this was found to be log-

of a typlcal

In this case there was evidence

= 6.3 was slmllar.

Average

were

and had lattice

1 and the vIbratIona

slgnlflcant

dIrectIon

D

was

to the

x' for the range of 21.5 to 40%, the

amplitude;

s1z.e was of the same order

axis. The D

as will be dlscussed.

from bulk Pt. The only property

with Dx or Dh. Results

are shown

of x-ray patterns

Erom dIffractlo",

Furthermore,

no different

analysts

[l]. This has been extended

to Dh = 81% recently,

and percentage

that were essentially

line proflle

of Dh = 7.1 to 40%

hence

these

along a pore

later. Some comments

were given earlier. These were by the following code; for

oxygen

in

The

at 300 OC for 0.5 hours.

163 (andare)

tentative.

While

D

= 40 % represents

h

tower limit to particle

an effective

size

301 ZO-

2-

0

(ca.

20

40

60

80

Dx

Figure 1. Typical particle size dlstrlbutlon, Dh = 40%, Lilll).

Figure 2. RMS vlbratlonal plltude vs. D x'

2.5 nm) accessible

via conventional

XRD equipment,

100

196

1=no,,8

finer particle

am-

SlZeS

= 63.5 and 81) have been lnvestlgated for wide angle patterns and EXAFS (Dh using the storage ring at Cornell University [6]. After exposure to air, 63.5% consists nearly

of particles

of crystalline

Pt304 with a core of Pt, while

81% 1s

fully oxidized.

Pt/A1203 These (American

catalysts CyanamId,

[Pt(Nt13)3("02)]N02. series

although

Direct

reduction

10001, d

by impregnation

on high purity

=12 nm, from an

ammoniacal

P nf 1mpregnatlon

TechnrGv-s

the presence

of chloride

of Incompletely

slred range of Dh age exposure

were prepared Aero

131. As wrth

chemisorptlon,

but the discrepancy

Dh. Equivalent

results

tltratlon

in the A1203

gave preparations

the case of Pt/S102,

from H2-O2

measurements

the results

differed

serves. of the de-

of percent-

from those

for H

2 of high

was more pror.ounced for Pt/A1203

were obtalned

of

were the same as for the S102

was avoided

dried materlal

v-alumina

solution

by the two methods

for Dh less than 45%,

smaller at larger Dh, approachthe H -0 values become progressively 2 2 ing approxunately 60% Dh for Dh above 90%. Again, a rather complex Interact-

however

10" of the Pt surface creasing

temperature

ough O,'Pts reactlon of o/pts increasing

with 0 2 was noted. of adsorptIon

with H 2 at 25OC became

for incomplete D

The ratio O/Pts

of O2 for all samples,

reactlon

from about

incomplete.

was structure

with

III-

and at large en-

This

sensitive

llmitlng

value

and decreased

with

1.15 for Dh = 36% to 0.5 for Dh = 94%. For the

h' D 's, O/Pt s became about 2 after exposure h 100% this ratlo decreased to 1.15.

smallest

increased

to O2 at 300°C; at Dh near

164 X-ray dlffractlon than for Pt/SlO2

characterization

because

Pt and Al reflectlons. of relatively tenslty

weak

source

REACTION

of interferences

In general

lntenslty

one must work with a single peak,

for the Pt loadings

than those of conventIona

employed

(311),

here. A higher

diffractometers

1s required

I"-

for this.

STUDIES

The use of a number ectlvlty marlly

of Pt/Al 0 1s much more dlfflcult 2 3 I" the dIffractIon pattern between

factors

of probe

reactIons

has been mentIoned

on results

obtalned

(MCP) and the exchange

with

above.

to lnvestlgate The following

the hydrogenolysls

of deuterlum

actlvlty

and sel-

concentrates

pri-

of methylcyclopropane

with cyclopentane.

pt/s10 Initial

studies

hydrogenolysis were measured condltlons

being H2/HC

of D

procedure

was the same except

are shown

I" Figures

degree

of structure

beyond

the range of experImenta product

Figure

of approximately sensltlvlty

l-butane

Selectlvlty

5. Save

formatlo" 1at1on

of

1s not clear,

Mlcrostraln

density

was

Actlvatlon

shown

t the

with

values

l-butane

will be recalled to deviate

from

the favored

are shown

with prior

of a" enhanced

I" l-butane.

factor

I"

at O°C are roughly

20, In agreement

1s the result

clearly

The reason

reports.

rate of the for this var-

that the low D

perfect

con-

platinum

h

pt/s10

via

2

XRD.

to a dislocation detected in the D = 6.3%, corresponding h 11 dxlocatlo"s/cm2, a relatively hlqh value corresponding deformed

enerqles

Independent

in the preexponential correlation

metals

[61.

were measured

from MCP. These were

and were

metric

h of about

however,lt

at these of N

of 6 x 10

to that in heavily

butane

are

MCP a selectivity

For

is involved,

catalyst,the

h not a decrease

were the only catalysts

The results

the varlatlons

uncertainty.

D

to a

H2. For hydro-

three over the range of Dh. Although

1s not great,

for low D

n-butane,

subjected

350°, 2;cool

2' for H *,3ooo,1.

-53Oc

17/l,

were

for this base set of experiments

(l-C4/n-C4)

The lower selectlvlty

and

catalysts

with the base

3 and 4. In both cases the value

and n-butane

results

for the lowest

stant at a ratlo

(hydrogenolysls) the

frequencies

conversIons,

of 0 2,300o,O.i;H

by a factor

product.

O°C

and methylcyclopropane

(71. The turnover

at dlfferentlal

h

and

varies

between

cyclopropane

to hydrogenolysls

the procedure

base condltlons

involved

hydrogenation

= 15/l

Prior

pretreatment

genatlon

Pt/SiO,

as a function

(hydrogenatIonI. uniform

of

and propylene

of D

for the formatlon

for l-C4 and 43 kJ/mol

This

that structure

h' factor,

suggests

which

ln turn tempts

of these data. This exercise

I" terms of the coordlnatlve

unsaturatlon

as the ratlo of edge and corner this were not particularly

of both

ca. 39 kJ/mol

one to attempt

of the metal

I* that

sensltlvlty

was accordingly

atoms to total exposed

lnforuatlve,

I- and nfor n-C

plots

a qeo-

carried

crystallltes atoms. of N

t

4 resides

out,

expressed

The results

vs.

this

ratlo

of

165

O.l(j

Fiaure

I I 1 1 I I 20 40 60 Pwcmioga Espomd (D,, )

’

3. Nt-D

h

relatlonship,

Hz+

I 60

C H 36

,

I 100

-53OC.

0 25’

.

E 0 20.

.'; al

.I,

z

0.15-

I 4.l

14 1

0.10-

0.05-

10

Figure

00

20

4. Nt-D

lb

h

20

Xl

40

60

relationship,

60

i-C 4

30

40

;o

60

.?O

60

formatlon,

70

80

Dh

Flqure

5. Selectivity-Dh

for MCP

hydrogenolysis.

OOC.

166 exhrbited detail,

the same shape as the origrnal

then, D

square vibrational reactions.

amplitude

was obtalned.

treatment

temperatures

of the lowest Dh catalyst reexamination

However,

the initial

with cyclopentane

ment of 0 2,300°,0.5;H2,3000,

at 81'C

for formation

any general

isotopic

and hydrogenation

trend

distributions

same value as for 6.3%. However,

cyclopentanes

pre-

[61.

in exchange

[8]. In this case a standard

of exchanged

mean

for MCP, an excellent

1;He,450° ,l;cool He was used.

by a factor of two for Dh between

between

of this after different

in H2 does not reveal

We also investigated

was attempted

and N t for the hydrogenolysrs

With the exception

over frequency

2, a correlation

of Figure

relation

deuterlum

vs. Dh data. TO this extent of t represents any geometric factors involved.

itself adequately

h Based on the results

N

of

pretreat-

The overall

turn-

in this case declined

6.3 and 63%, and then at 81% rose to the selectivity

to various

exchanged

species

varied with D

and, in particular the ratio of six exchange to ten exchange, h decreased substantially as Dh increased. This suggests that exchange

D6'D10' of H on both sides of the cyclopentane %,M-diadsorbed

species

on smaller

D

ring goes mainly h

via formation

and by rollover

catalysts,

of

on catalysts

of large Dh. At this point an investigation was initiated

for the exchange

H2,300°,1;He,3000,1,

threefold

frequency

over this range of conditions

were also significantly

D6'Dlo thus reaction

varies

This result focusing

ltivlty

[9]. Shown

function

with pretreatment

on the effect rn Figure

of pretreatment

periments

affected.

structure trated

sensitivity

37O'C are essentially

on apparent

is perhaps

1.

no apparent illus-

for pretreatment

the same as those shown previously

ex-

with Dh over

more clearly

7, where the results

variation

sensas a

shown in Table

sequence

of 200°C pretreatment

in the selectivity

plotted

of pretreatment

in the order

of the activity

at all. The phenomenon

inversions

of

on

structure

formation

in H2. The sequence

on the same catalyst

in the cross plot of Figure

Corresponding

study of MCP hydrogenolysis

of pretreatment

in the region

such as the

sensitivity

conditions.

From the figure one notes an inversion the series and, Indeed,

out for

in each case

was found to vary patterns

the structure

6 are N t for i-butane

temperature

was performed

(preceeded

for exchange

Thus,

conditions

were carried

and selectivity

led in turn to a similar

Pt/SiO*,

of pretreatment

Comparisons

and for H 2,3000,1

for H2, 450°,1,

The net turnover

by 02,300°,0.5L

of the effects

reactions.

In Figure

at

4.

with Dh were also seen.

Pt/A12D3 A similar and deuterium

sequence exchange

of Pt/Al203.

Turnover

pretreatment

(T above P

of studies

with methylcyclopropane

with cyclopentane frequencies 350°C)

has been carried

for hydrogenolysis

in this series were

hydrogenolysis out on the Series

after high temperature

independent

of D

h'

as were

167 TABLE

1

A typical Hun

pretreatment

experiment

Condltlons

a

O2'

b

of pretreatment

300°,0.5;He,3000,0.25;ti

25°,1;react,00 2' 300°,0.5;He,3000,0.25;H2,1350,1;react,00

c

O2' 02,3000,0.5;He,3000,0.25;H2,2600,

d

02,3000,0.5;He,3000,0.25;H

e

3oo" ,0.5;He,300°

2'

,0.25;H

O2' 02,3000,0.5;He,3000,0.25;H

f

2' 2'

0

l;react,O 370°,1;react,00

0

480° ,l;react,O 25°,1;react,00

e-7.1-Si02-PtCI-S (Y- 27-SiO

Figure as

6. Nt

a function

for

i-butane

of T

p' H2

at 0 (Table

Figure 7. Structure sensltlvlty for l-butane formatlon at low and high T . P

OC 1).

@-

-IonX-S 2 40-SiO2-PtCl-S

O-

63-Si02-IonX-S

l

81-SiO2-IonX-S

-

168 the actlvatlon

energies

Some dependence preparation subject

was noted,

This

series,

for the Pt/A1203 (l-~4/n-c4)

T

B

the

was

0.30

HIGH TEMPERATURE IN PREPARATION

as those t in the

temperature

are as well.

selectlvltles about

in

was

at hlqh temperature

9. Since Nt 1s Independent

corresponding series,

used

effect

gave the same N

and higher

in Flqure

15 for this

reduced

in pretreatment

III preparation

is Illustrated

respectively.

temperature

8. This memory

in Flqure

in that catalysts

though,

at lower temperature

36 and 43 kJ/mol,

on the reduction

as shown

and lower temperature

pretreatment.

latlc,

however,

to compensation,

in preparation reduced

for l-C4 and n-C4,

of the level of actlvlty

25% lower than that

of Dh The

obtalned

REDUCTION

Y i-4 020 2 I f

L

G

0

0.10

4LOW IN

)

IS

30

TEMPERATURE PREPARATION 45

A

A REDUCTION

60

n

60

Dh

Figure

8. N -Dh for MCP, 0 'C, on Pt/A1203. Solid circles, T = 400 - 500 'C t in preparation. Open circles, T = 300 OC in preparation. T 7 370 oc. P O Catalysts reduced at low T (300 "Cl in preparation, reduced at high T (480 "C) in pretreatment.

I in preparation,

I I6

30

46

60

so

76

Dh

Figure

9. Preparation

and pretreatment

effects

for N t*

i-butane:

MCP at 0 'C.

169 at ldentlcal

condltlons

(pretreatment

the range characteristic l-butane

formatlon

liar condltlons anlstlc

with that of metals

latter have seloctlvitles

have been confirmed

The same type of actlvlty H2 was obtained m~nlmum

In actlvlty

though given can

is at about

the rather

read too much

by recent

dependence

broad

125OC,

nature

by Chevreau

work

slm-

roughly

and Gault

[lo].

in this laboratory.

upon temperature

of pretreatment

in Figure

75OC lower than

of these mlnlma

in

10. Here the for Pt/SiO2,

It 1s doubtful

that

ane

Into this difference.

T

Figure

For the exchange were clearly

>n

for

such as Pd and Rh. Under

as for Pt/SlO 2, deplcted

for Pt/A1203

but still

on the order of 1 - 5; the mech-

~m,sllcat~ons of this have been dlscussed

Such differences

for Pt/SlO2,

Pt. Pt has a very high selectivity

of supported

compared

the

and reactron)

dependent

P’

Oc

10. The effect of T upon N i-butane from MCP, Al0 atO°C. ' Pretreitment sequence as in Ta g3le 1. Data for D = 66.7 and 103.8 of the origrnal figure [ll7 have been omitted for clarity.

reaction

at 81°C,

the isotoprc

upon D h, particularly

noted

distribution

patterns

as a decrease

in the value

of D = dlo/id2 - dlO) with increasing D Activation energy for overall 10 h' exchange was about 57 kJ/mol with some dependence on D h for the Individual drstrlbutions. Figure

General

11. Catalyst

increasing reduction

D

h

exchange

pretreatment

for reduction

1;cool He.

obtained

also affects

conditions

with Pt/A1203

the exchange;

at 100°C and Increases

at 450°C; pretreatment

H2,300°,1;He,4500,

patterns

with

for Figure

N

are shown decreases

t increasing

in with

D h for

11 data were o 2.300°,0.5;

170

.2 Di .I .08

.06

., .’ /

: -

.04

,!? !' I-

81 0, 67.5 0~'~~./~.,, \ \ 55* \b__&_~~

.02

f ;I '* I

\ .OlT

,

I

I

1

11.

Figure

Effect

cyclopentane,

I

di

3

’

of temperature

Pt/A1203,

/

*--*-* I I 7

I

I

on isotopic

f .

I-

I 9

exchange

Dh = 47.6. Di = di/(dl-dlOi

patterns

vs. number

introduced.

/

0.4 -

T

Pt/sIo, E

- 0.3.

/

ti 2 &b 0.2-

/

+

/ /

f

Z -4-

+

I L

0.1 -

I5

45

30

I L

Pt/AI,O,

L

60

75

**

90

Oh

Figure pretreat

12. Comparison

of N

Hz, 370 O, 1.

t

i-butane

vs. Dh at 0 "C after

r

of of D

171

Comparison:

Pt/SiO2-Pt/A1203

In Figure

12 is presented

the two series

of catalysts

0.25;H2,370°,1;cool values

ditions midrange

of Dh about

Pt/A1203

Ill].

exchange Dh

However,

h' different.

"C, H2/RC

turnover

2

= 15/l)

conditions

on two Pt/Si02

(65%). These patterns

after H2,25O

a comparison

and Pt/A1203

catalysts

between

catalysts

are of the same general

for

[ll] . These

is about three

an order of magnitude

13 is presented

freqUenCy

~02,300°,0.5;He,300a,

2 for other pretreatment

comparison

For example,

35% show Pt/SiO

in Figure

patterns

of i-butane

pretreatment

the same at low Dh, but the Pt/SiO

at high D

can be quite

Finally,

(0

H2) and reaction

are essentially

times as active

a comparison

at identical

con-

in the

more active than

the isotopic

of about

type, however

the same

variation

of

with D

on Pt/Al 0 is the opposite of that found with Pt/Si02. In h d6'd10 2 3 terms of total N t, the Pt/Si02 is again about three times as active as the Pt/A1203,

but this also varies

ilar to the hydrogenolysis

with pretreatment

conditions

in a manner

sim-

reaction.

I

1

aCyclopentane

+ Deuterium,

63.5-Si02-IonX,

0.49

%

Pt

81 'C O2' o-

300", 0.5; Hz, 300",

He, 450', 1 66.7-A1203-PtNN,

0.28

1;

% Pt

Same Pretreatment Conditions = Davison Grade 62 SiO 2 1000 = Aero A1203

Figure 13. Comparison of initial isotopic distribution pattern for cyclopentane + D2 at 81 OC for Pt/Si02 and Pt/A1203.

DISCUSSION The overall erally

similar.

morphological

behavior

differences

but the similarities are unaware ment effects

of Pt/SiO

and Pt/A1203 for these reactions is gen2 noted at high D may be suggestive of some h between the Pt crystallites on the two supports,

The differences

at low Dh would

of the nature

indicate

of the support

for the two series

at low D

that large

particles

[12]. The similarity h

also argues

of Pt

of pretreat-

in favor of this view,

172 but the logic does not seem to extend Details

of morphological

resolution

transmission

differences electron

we have proposed

to high percentage could perhaps

microscope

materials.

exposed

be resolved

by future

high

studies.

[9] on the basis of literature

data that for large par-

ticles of Pt exposure

to 02 at elevated

produces

a large concentration

of vacancies

300' followed

by H 2,25O would

well as, perhaps, is increased,

rncomplete

produce

anneals

vacancies.

This annealing

since they intrinsically Thus one might

pretreatment

temperature

to Dh below the mInimum in the subsequent suggestion

process

and the ordering

increase

ln N

for high Dh than for low D

h in removal

face for the former. either

D h of coordinative

for MCP hydrogenolysis, in Nt. Different t

wth

factors,

This

however,

pretreatment

at the metal

with the result of blockage

in N

with respect

temperature.

One

obviously

plausible

interface

be more

that high temperature

important

pretreatment

of sites at the metal-support

It is true that several

Pt/SiO 2 or Pt/Al 0 are an effective 2 3

monolayers

poison

with

t

must be involved

crystallite-support

factor would

fewer

for higher

degree

the rapid decline

in the activation.

is more effective

with

be able to explain

is that hydroxylation

is important

a higher

2'

(as

of pretreatment

structure

be less pronounced

contain

with to 0

of vacancies

As the temperature

to a more ordered

would

a surface

Thus, exposure

layer.

a high concentration

reduction).

the Pt surface

materrals,

unsaturation.

temperatures

in the outer

of water

inter-

adsorbed

on

for the hydogenolysls

reaction.

ACKNOWLEDGMENT This work was supported of Basic Energy

Scelnces,

Fund of Northwestern x-ray diffraction University, and 4 -12

University.

facility

supported reprInted

by the United

Contract

States Department

DE-AC02-77ER04254,

The x-ray work

of the Materials

by the NSF-MRL by permission

in part was conducted

Research

program, of Academic

of Energy,

grant

Office

and by the Ipatieff

Center,

Northwestern

DMR82-16972.Figures

Press,

in the

1.2

Inc.

REFERENCES 1 S.R. Sashital, J.B. Cohen, R.L. Burwell, Jr. and J.B. Butt, J. Catal., 50 (1977) 479. 2 T. Uchijima, J.M. Herrmann, Y. Inoue, R.L. Burwell, Jr., J.B. Butt and J.B. Cohen, J.Catal., 50 (1977) 464. 3 M. Kobayashi, Y. Inoue, N. Takahashi. R.L. Burwell, Jr., J.B. Butt and J.B. Cohen, J. Catal., 64 (1980) 74. 4 P.J. Angevine, J.C. Vartuli and W.N. Delgass, Proc. 6th Int. Cong. Catalysis (1976) 611. 5 K. Aika, L.L. Ban, I. Okura, S. Namba and J. Turkevich, Inst. Catal. Hokkaido Univ., 24 (1976) 54. 6 R.K. Nandi, F. Molinaro, C. Tang, J.B. Cohen, J.B. Butt and R.L. Burwell, Jr., J. Catal., 78 (1982) 289.

173 7 P.H. Otero-Schlpper, W.A. Wachter, J.B. Butt, R.L. Burwell, Jr. and J.B. Cohen, J. Catal., 50 (1977) 494. See also: E. Rorris, PhD Dissertation, Northwestern University, Evanston, IL, 1983 (Unlverslty Mlcrofllms). 8 Y. 1XXle, J.M. Herrmann, H. Schmidt, R.L. Burwell, Jr., J.B. Butt and J.B. Cohen, J. Catal., 53 (1978) 401. 9 P.H. Otero-Schlpper, W.A. Wachter, J.B. Butt, R.L. Burwell, Jr. and J.B. Cohen, J. Catal., 53 (1978) 414. 10 T. Chevreau and F.G. Gault, J. Catal., 50 (1977) 124. 11 S.S. Wong, P.H. Otero-Schlpper, W.A. Wachter, Y. Inoue, M. Kobayashi, J.B. Butt, R.L. Burwell, Jr. and J.B. Cohen, J. Catal., 64 (1980) 84. 12 R.L. Burwell, Jr. 1n B. Pullman (Ed), Catalysis in Chemistry and Blochem1stry. Theory and Experiment, D. Reldel Publishing Co. 1979, p. 207.

NOMENCLXTURE CP - cyclopropane di - number

exchanged,

CP + D2

d

- pore diameter P Di - percent exchanged, - percentage

CP + D2

exposed

metal

measured Dh D - percentage exposed metal measured x AC - hydrocarbon, normally CP or MCP

by H2 chemlsorption by x-ray dlffraction

RCP - methylcyclopropane N

t Pt

T

- turnover S

- surface

frequency, platinum

- pretreatment p

reactions/Pt

atoms

temperature

S

-set

at 25 OC