Comments on the papers on selective oxidation catalysis

Catalysis Today, l(1987) 337-340 Elsevier Science Publishers B.V., Amsterdam COMMENTS

R.K. 440

ON THE

PAPERS

ON

Center

Road,

Grzybowska

toluenes

(BA)).

The

molybdenum much

were

(Mn,

Co,

system

bonded

required

methyl

points for

Less

Mo=O

high

group

density

or the

She

transfer

study

that

complex

and

that

study

the

earlier

it was

first

as not

a ionic

support

that

data being

are the

mechanism,

intermediate

formation),

the

Sohio

is rate

limiting,

the

transition

surface

is much C-H

fast group

is on

formation

that

state

the

based

of

of

a

It

charge will

1) entailed and

decreased 2)

be the

that

0CH3 > which is

intermediate

on the

catalyst

of

(ref.

hydrogen

the

either

step.

(ref.

of

reactivity

catalysts,

on propylene

inferior.

bond

the

is

in

Cl

?

showed

abstracted

leading

to

the

the

C-H

complex.

insufficient rate

a

than

systems.

Mn3TeMo20,2

formation

Si-molybdate

aldehyde

the

that

more

reactions

vanadate

effect

the

by the

work

it will

(OCH3

to enhance

that

these

reactive,

> H irrespective

is as

over

for

while

respectively

argument

and

selective.

selectivities system,

less

the

main

follows

to previous

H-abstraction and

step

the

more

the

system of

group,

> C(CH3)3

limiting

However,

6 and 8

the

no substituent CH3

and are

at

of

MnMo04

Her

conducted

of

structure

step.

of the

alkylbenzenes

substituents

(expected

work

V=O

benzaldehyde V/Ti/K/O)

Mn3TeMo2012

Thus,

breaking

0CH3

are much

of

aldehydes

(300-36O'C)

systems.

of 25,

the

show

and

desirable

a Te doped

H-abstraction

is a radical-like

Grzybowska's breaking

length

rate

the

bonded

that

which

established

lent

as an H-radical, aldehyde

since

(V205 systems

respectively

yields

wolframite

decreases

that

with

is more

tightly

and

vanadium

15 respectively.

argument

the

of p-substituted

> H. This

obtained

corresponding

rate-limiting

toluenes

argues

remembered,

are

oxidation

(TBBA),

on vanadium The

37, 49

BA of 56,

the

bond

corresponding

Mn3TeMo2012,

calculations

substituted

type.

the

selective

the

in particular

less

is her

the

to

and

22 and

that

on

(300-5OO'C)

selectivity

is not

quantum-chemical charge

and

out

convincing

based

Te/Mo/O).

of the molybdates

reactive

H)

U.S.A.

molybdenum

gives

of 43.

44128.

reported

systems Ni)

68 respectively

selectivities

Grzybowska

TBBA

Ohio

C(CH3)3,

the

catalysts, of MBA.

55 and

is the more

and

than

active

yields

tightly

that

CATALYSIS

p-test-butylbenzaldehyde

used

V205-Ti02-K20

with

(MBA),

(Bi/Mo/O.

molybdenum-based

of 61,

Poland)

catalysts

more

Maximum

CH3

337

in The Netherlands

OXIDATION

Cleveland,

(OCH3,

(p-methoxybenzaldehyde

that

SELECTIVE

et al (Krakow,

p-substituted

the

Printed

GRASSELLI Warensville

the

-

to claim

limiting

step.

be necessary

an

ionic

mechanism

To distinguish

not only

to

and

between

use

a

radical

electron-donating

and C(CH

) ) (expected to enhance either cationic, or radical 33 but also electron withdrawing groups such as CN and Cl

radical

but

inhibit

cationic

intermediate

formation).

It

will

be necessary Also,

toluene.

be achieved substitution

is the

Ruiz

that

work

that

oxides,

catalysts V205/Ti02

methacrolein

they

system, at a

at a IO/90

50/50

control Mechanism

opinion

the

that

and

they

can

mechanism

states,

active

oxidation

catalyst.

chemisorbing function,

and

and

active

site

three

oxygen

a redox

(i.e.

oxidation is the

catalysts. with

sophisticated one

phase,

compared

These

or NH

and

with

one

achieved

system

of the

that

by

by surface

O2

Mo=O

reduction

by

oxygen

an

match

insertion,

excellent is

within also

all and

required

Bi-0-Bi02

phase

and electron

and

of 8,

vacancy

in more

needed

a

transfer

most

multiphase its

faces

of

easily

be

Although

in this

(Bi-O-MO

and

provides

is

[OlO]

functions

than

functions

derives

can

as

properly,

this

4)

5)).

good

However,

to function

the

stated be

phase,

functions

which

(ref.

reduction

of I-FeMo04

As

will

For example,

0.5

reducing

site).

3,

and olefin

catalytically

other;

(refs.

Courtine

the

the

the

this

abstraction

oxygen,

Bi2(Mo04)3.

each

match

an

in a single

of

phases.

As

selective

functions

a catalyst

with

of the

(see

contains

epitaxially-matched

and dissociation

part

such

communicate

relaxation itself

For

reviewer's

as anti-H

these

Ma Z+M 10_a3tBixMoyOZ

having The

contain

a

to with

Mars-van

Mechanism.

gaseous

as

and

3).

function,

reside

such

a predominant

phase.

matching

formula

andp-FeMo04.

Bi2(Mo04)3

have

can

catalysts

the

this

for

to

to With

results

(ref.

inserting

these

functions

catalysts

phases

by epitaxial

Bi12(Mo04)3

cooperative

may

these

accomodated

the

these

or third

empirical

performance

abstraction,

all

Sohio

oxygen

and 0- or NH-

mixed

selectivity their

it is

as well

lattice

possessing

generation

phase

a second

easily

system,

thus-formed

abstracting

Now,

early

function,

of

isobutene

it from

abstracting

of chemisorbing

commercial

proprionitrile

maximum

necessary

anar-H

capable

catalysts

to the

are

all

of

Mechanism

it

limiting

rate

proprionitrile.

interpret

preliminary,

and

mixtures

of

and

They

according

inserting

the

q-H

to

et al.)

still

are:

advanced-generation

it is necessary

superior

an

oxidation

that

is observed,

heterolytic.

that

to differentiate

functions

function

occasions,

case

are

is

than

the

Mo03/Sb204

(Grasselli

data

rather

yields

Finally,

is suggested,

formamide

maximum

attempting

here

with effect

prove

effect

two mechanical

studied

of

conclusively isotope

out

toluene

substituent

intermediates.

observation

chose

of Mo03/Sb204.

Sohio

it to 02- -and transferring

on numerous

and

the

H-abstraction

the

They

be interpreted

latter

that

make

mixture

the

would

of N-ethyl

mixture

experimental

group

is homolytic

observe

mechanism",

radical

if a primary

confirm

multiphase.

substituted about

and

as pointed

breaking

the dehydration

methacrolein

Although

will

C-H

step

Belgium)

are

methacrolein

Krevelen

methyl

work

of each

conclusions

anion

and Mo03/Sb204.

and

the Mo03/Sb204

a "remote

the

Additional

et al.(Louvain,

oxidation

cation,

on

such

probably,

experiments

definitive

rate-limiting

be expected.

most

can

of H by D

is my belief and,

then

to distinguish

H-abstraction as would

to do pairwise

only

aC-H

dissociation).

for

a much

than

better

is feasible

339 by

the

Bi-0-Bi

of

the

Bi2(Mo04)3

phase

alone.

Thus.

in

the

multiphase

system. the Bi2(Mo04)3 phase contains the active site (W-H M 2+Mo 10_a3+BixMo40z a abstraction and 0 insertion) while the epitaxially matchedp-FeMoO4 contains the 2this rapidly replenishes the O2 activating and 0 transferring function: lattice

oxygens

course

of the

productive

of the

state.

The

no new

phases

excluded

by the

data

two

types

of sites,

sites

opinion that

being

that

they

Sb204.

probably

implies

also

probably lead

The

jury

and

The

both

advanced

over

et

yields

covering

the

vanadia

and

vanadium

that

an

and

anatase

the

NH

One

pressures.

sequence

two

Sohio

number

of

reviewer's

sites

of Moo3

observed

some

mechanism,

and

at 10%

Sb204;

with

be

possesses

the

Mo03/50%

phases,

cannot

this

optimum

the

fullest

many-fold.

Moo3

is

acidic

this lattice

this

surface

This site

would

probably

one

and

that the

in propylene

one

indicating

same.

This

and

has how work

mechanistic

alkylaromatics

and

effect

that

the

valent lattice

interesting

observed

at

adsorption

is in good (ref.

lower

is

the

vanadia

slight

it was

that

of

between

some

aromatics

ammoxidation

was

monolayer

that

activity alkyl

the

of

Mechanistically,

the

states

observations

have

cooperative

aromatic

reaction little

experimental

further

inductivity)

occurs. alkyl

very

catalysts.

important

a

oxdiation

given

system,

ammoxidation

which

suggests

indicates

are

involved

on the

a

More

redefine oxidation

most

(valance

of the

of selective for

of oxidation

catalyst.

to

catalysts

titania.

points needed

stabilization oxidation

of their

This

fine

or a multi-phase

reported

with

is stabilized.

inserting

site,

It

50%

to the

the

selective

Italy)

supporting

effect

and

at

functions

structural,

support.

vanadia

mechanistic

the

all the

relative

obtained

of the

partial

acid

selectivity

According

a superior

inhibition

NH3

between

identify

the

catalysts.

the

at the

that

the

during its

compounds

6)

sites.

modifies

up to

is probably

surface

(ref.

is observed

matched.

Sb204

a Bronsted

to Moo3

optimum

sophisticated

were

species

distortion

about

kinetic

V205/Ti02

known

and

in a single-phase

al (Bologna,

highest

and

authors,

of oxidizing

interpreting

to yield

is needed,

Cavani

out

operate

picture

Sb204

contact

we can

far

site

used site

activity.

is still

thus

It is well

get

reaction

Moo3

by the

that

as they

the

between

inactivated

a maximum

interplay

of

of

activity

although

said

these

addition

epitaxially

how these

been

4 times

phase

up

observed

an oxidizing

to maximum

catalysis:

active

pumping

presented.

practically

Mo03/90%

phase

were

about

the

are

thus

interaction

Although

acid

Bi2(Mo04)3

reaction,

analogy

high site

to

3).

REFERENCES 1 J.D. Burrington. C.T. Kartisek and R.K. Grasselli. J. Org. Chem.. 46 (1981) 1877. 2 R.K. Grasselli and J.D. Burrington. Adv. Catal.. 30 (1981) 133. 3 (a) R.K. Grasselli. J.F. Brazdil and J.D. Burrington. Proc. 8th Internat Berlin, 5 (1984) 369.; (b) R.K. Grasselli. Appl. Catal.. Congr. Catal.,

the

340

4

15 (1985) 127; (c) R.K. Grasselli, J. Chem. Educ., 63 (1986) 216. L.C. Gleaser, M.A.S. Hazle and R.K. Grasselli. (a) J.F. Brazdil, M. Mehicic, ACS Symp. Series (Ed's M.L. Deviney and J.L. Glaud) 288 (1985) 26; (b) J.F. Brazdil, R.G. Teller, R.K. Grasselli and E. Kostiner, ACS Symp. Series (Ed's

R.K. Grasselli and J.F. Brazdil), 279 (1985) 58. 5 P. Courtine, ACS Symp. Series (Ed's R.K. Grasselli and J.F. Brazdil) 279 (1985) 38. 6 (a) J.D. Burrington, C.T. Kartisek and R.K. Grasselli, J. Catal. 63 (1980) 235: (b) R.K. Grasselli and J.D. Burrington, I&EC, Prod. Res. & Dev., 23 (1984) 393.