Oxidative catalytic methane conversion

Catalysis Today, 1 (198’7) 357-363 Elsevier Science Publishers B.V., Amsterdam

CATALYTIC METHANE

OXIDATIVE

Manfred

-

Printed

357

in The Netherlands

CONVERSION

BAERNS

Chair of Technical Bochum, FRG

Chemistry,

Ruhr-University

Bochum,

Postfach

102148,

D-4630

INTRODUCTION Methane

chemistry

has received

years since huge amounts available

which

are not utilized

from where

its transport

different:

methane

which

are either

resulting chemistry:

excess,

(ii) by direct oxidation

solution

of methanol

since the amount

of CH4

thermally

by solid catalysts for methane

produced

liquified

of methane,

or catalytically

to acetylene

to be

either

and ethylene

which

catalysis

has not lead yet

eventual

process:

reactions

some promising

heterogeneous

any

success been

In heterogeneous

have been obtained The

has

present

catalytic

which might

contribution

is

catalytic

(i.e. methanol

or formaldehyde)

were discussed

during

at also

Liquid-phase

respect

to

an

catalytic

no

methane

conversion, for further

concerned

with

the (n ?

Workshop.

RESULTS

The catalytic to paraffinic, different

of CH4.

may

and Cn hydrocarbons

the Oxidation

or used

process

have potential only

can

phase

mainly

of HCN,

achieved,

2) as both the subjects

CATALYTIC

liquid

with

present

(ref. 1).

reaction

is presently

conversion

direct

appropriate

in the electric-arc

appreciable

activation

are known.

results

development.

to

although

oxidative

CH4,

methane

the

for further

2).

syngas

by

to gasoline

in a homogeneous

activation,

in the selective

(iii)

surpass

as additive

can via

most

are

(n Z

world-wide

the

significantly

its activation

fi)

or of

areas

objectives

than

achieved:

above 1500 to 2000 'C and also in the production

_gain some importance

consecutive

would

in remote

or Cn hydrocarbons

methanol:

does not appear

the

The research

be

to

during

To solve the problem

(ref. 2). Thermal

conversion

temperatures

few are

easily may

even when used in larger amounts

In the direct conversion be achieved

This

last

as its main constituent

particularly

into methanol

transportability.

of CH4 to Cn hydrocarbons.

comsumption,

process

but often flared,

as gas is often impossible.

liquid or which can be more

the production

attention

gas with methane

may be transformed

in better

coupling

considerable

of natural

conversion

olefinic

of methane

and aromatic

modes of reactor

operation.

to methanol

hydrocarbons

and fo~aldehyde

as

has been carried

out

In the first, methane

is

passed

well via over

as two a

multivalent oxygen

metal oxide as catalytic

required

for the reaction:

the lattice of the metal oxide,

which

simultaneously

provides

after consumption

material

of the oxygen

contained

it is

separately

steady-state

operation,

an oxidizing

agent such as 02 or N20) to the reactor

has been applied oxidation

to

the reader

Some comments the Oxidation

its

For further

details and

is referred

Bosch, van Ommen

Li O-promoted 2

magnesia

its

and

Ross

oxidative

work

on

coupling

to

given in Table 1. presented

(ref.

16)

Besidts

have

investigated

confirming

some

(pixid: partial pressure of oxidizing agent; oxidizing agent: ') = 02, 2, = N20)

T/K

Reaction Products

S/%

Y/%

Refer.

Pgxid Non-steady-state operation 5-10 wt% PbO/o-Al203

-

1073

C2 hc

43

2

/3/

5-10 wt% Sb203/o-A1203

-

1073

C2 hc

43

2

/3/

5-10 wt% Mn203/a-A1203

-

1073

C2 hc

45

5

/3/

Steady-state operation 22 wt% Pb0/4 wt% Na20/ Y-AT203

10

1)

1023

C2 hc

62

5

/4/

7 mole % Li2C03/Mg0

2

')

993

C2 hc

45

19

/S/

7 mole % Na20/Mg0

2

')

1073

C2 hc

57

22

/6/

43

')

1073

C2 hc

91

7

/6/

3.41)

998

C2 hc

24

5

/7/

5.2l)

La2o3 Sm203

1023

C2 hc

61

9

/8/

')

1023

C2 hc

98

1

/8/

IO mole % Li2C03/Sm203

2.51)

1023

C2 hc

52

20

/9/

20 mole % LiC1/Mn203

2

l)

1023

C2 hc

65

31

/lO/

1 mole % Rb20/SrC03

2

l)

1023

C2 hc

42

18

/Ill

16-49

*)

734

C2,C3,arom.hc 30

1

/l2/

0.32)

873

HCH0,CH30H

66

11

/13/

HCH0,CH30H

308

H-ZSM 5 MO/Cab-0-Sil

the

earlier

hydrocarbons (n 52), methanol and formaldehyde for various catalyst formulations

Reaction Conditions

at

paragraphes.

Total selectivity S and total yield Y of catalytic methane conversion to C,

p;H4

and

catalysts

Table 1

Catalyst

in

second,

(methane the

to the investigations

in the following

catalysts.

containing

the

of the most relevant

on

to the results

contributions

are given

In

feeding of the reactants,

oxygenates

and additional

Workshop

Roos, Bakker, oxidative

successfully.

of methane

hydrocarbons,

i.e. continuous

reoxidized.

the

7 wt% Mo03/Si02

0.32)

833

100

2

4 wt% NaOH/CaO

8.7l)

1013

C2,C3,C4 hc

74

10

051

/14/

2.4l)

1013

C2,C3,C4 hc

56

17

/15/

results of Ito and Lunsford 4). their

presentation

(ref. 5) as well as of Baerns and

dealt

with

deactivation

of the two different

was reported

for both catalysts:

a

it remained

activity

pattern

nearly constant observed

that no deactivation

occurs

been still sufficient complete

must,

under

oxygen conversion.

interesting

Time-independent

i.e. the oxygen

ca 100X. The selectivity only decreased while

rather

catalysts.

conversion

lifMg-oxide

experimental view

stayed

catalyst.

not necessarily

since the space velocity

This

aspect,

is

supported

150

constant

PbO The

by

constant proof

might to

deactivation

at

catalyst

as

of the reactants chosen

the

activity

be construed

conditions

(ref.

i.e.

constant

for the alumina-supported

for the

however,

the

associates

have

achieve results

200 tlh

150

200 tih

FIGURE

1

Deactivation

of ay-alumina-supported

time t of operation (T = 740 oC, p&4

28 wtX-PbO

= 0.7 bar, p&

catalyst during

= 0.07 bar)

Upper part: Change of activity (as conversion X of oxygen) Lower part: Change of selectivity S to Cz+hydrocarbons

360 obtained Baerns

for

a similar

during

the

observations during loss

clearly The

PbO due

to the

impairment is not

of

by PbO;

From

the

selective

Table and

catalysts.

It

compounds

exhibit

when

as catalysts

disadvantage

of Table similar

such

PbO.

rare-earth

metal

MECHANISM The

oxidative

formed and

but

Bhasin

proposed

(ref.

coupling

methyl

the

phase.

gas

contributes catalytic

catalyst

In

During

also

(see

the

experimental

results

surface

The which

oxidation,

and

are

long-time

stability

than

to

the

2, taken

that

of

from

as

may

occur

the

surface

system that

the

non-volatile

as shown

in

result

the

lead

results

in selectivities

by

using

certain

1).

as a solely reaction

oxidative

and

from

these

from

18)

believes

the

degree

at atmospheric

concentration oxidative (ref.

that

recombine

gas-phase

in

reaction

compared

to

the

pressure.

At

produced

reaction

leads

oxidative

evidence

lower

of thermally

coupling

Keller

previously

the

and

as

or

radicals

species

found

surface

that

to a small

have CH3

for

have

catalytic

surface

by

methane,

4)

adsorbed

suggestions

(ref.

the

of

(ref.

involving

catalytic

proceeds

coupling

coworkers

even

radicals

is

without

a

19)).

negatively-charged 2O- and 0 species

Barbaux,

by using

(ii)

CONVERSION

only

from

and

obtained

Table

the the

PbO-based

Li/Mg-oxide

15));

compounds be

in among

alkali/alkaline-earth the

(ref.

also (see

working

the

other

latter

author

process when

that to those

his group

originate

from

reported

reaction

Different

proposals,

Workshop,

a

observed 16).

those

a gas-phase

as Baerns

surface

however,

It is assumed the

For

and

be overcome

can

that

surface.

reaction

Figure

above

these

of methane

present

rise

been (ref.

non-selective

or Pb3(P04)2,

METHANE

be true

overall

to give

PbS04

15);

Lunsford

pressures,

sufficient

has

Workshop

to

negligible

catalysts

2. taken

of PbO may

CATALYTIC

The

is not

of the y-Al203

al.

(i)

as catalysts,

radicals

surface

elevated

Table

3) as well

to the

be attributed

which

M.

latter decrease

Li/Mg-oxide

selectivities

conversion

of methane,

by

the

selectivity

operation the

presented 17));

probably

enhance

et

that

mentioned:

compounds

products.

gas-phase

Roos

better

show

(ref.

a catalytic

coupling

as

pressure

during

surfaces

selectivities

catalytic

that

involved.

from

most

a vapor

by a proportion

of

volatility

it may

on the

to the

be

OF OXIDATIVE

reaction

they

(see

Good

can

well

of PbO during

it appears

as CaS04-supported

3. taken to

as

as reported

alumina

comparable

of the

compounds,

it has

a loss

results

should

(ref.

from

4).

I),

that

as was

activity

is caused

such

selectivity (see

used

Such

(ref.

PbO catalyst, I, taken

in activity

that

et al.,

selectivity

elsewhere

literature most

by Roos

covered

outlined

fact

Figure

that

decrease

temperature.

quantified

(see

indicate

operation. of

at reaction and

alumina-supported

discussion

surface

or

participate

Elamrani

and

potential

measurements

Bonelle

lattice in

(ref. that

oxygen

the 20)

both

is

reaction. presented

species

are

361

Table

2

Activity

(as conversion

X of oxygen at modified

residence

time Wcat/F

and hydrocarbon

selectivity S of CaO-supported alkali-compound catalysts Ci (TP = 740 "C, piH4 = 0.65 bar, pi2 = 0.075 bar, time of operation: 18 to 20 h)

Alkali compound

W

cat'F

'02

'CH4

mole %

g s/ml

%

%

'C2H6

S

'C2H4

%

C3+

%

%

3)

"1 %

Na20

/8.7l)

0.64

94

15

41.4

28.6

9.0

79

Na2C03

/1.2 1)

0.18

92

14

45.4

23.1

7.5

76

NaOH

/6.01)

0.15

94

12

46.2

22.2

5.6

74

Li2S04

/1.42)

0.69

98

16

33.5

32.1

8.4

74

Na2S04

/3.52)

0.14

80

16

48.1

23.5

6.4

78

1) incip. wetness 2) mech. mixing 3) carbon

impregn.,

drying:

in the presence

130 "C/2 h

of H20;

number of hydrocarbons

drying:

130 "C/2h

formed Z 3

Table 3 Activity

(as conversion

hydrocarbon

X of oxygen at modified

selectivity

lead-compound

SC

catalysts

of various

residence

unsupported

time W,,JF)

and

and supported

i

(TP= 740 "C, p,!W4 = 0.65 bar, pi2 = 0.075 bar

lead cpd.

Wcat'F

'0

g s/ml

%

0.3

PbS04(100)

'C2

SC?

%

%

%

%

%

92

9

34

18

1.3

53

52.4

63

8

23

32

8.2

63

Pb3(P04)2(100)

13.6

87

9

32

18

1.8

51

PbS04(2)/CaS04

5.6

100

14

36

18

5.4

60

PbS04(19)/Ca3(P04)2

2.4

100

14

30

25

3.0

59

wt%

PbO(3O)/y-A1203

2

'CH4

Sc3+

=ci

362 Part a

-*-_

“:\ l

%“L ‘2’6

CO2 c 600

C3”6

60’

700

20

80

to

TlOC

x

100

Iti a,

Selectivity

FIGURE 2

of gas-phase

agent to Q+hydrocarbons Part a: Dependence pressures

(p&/pi2

of selectiLity

(symbols:

Part b: Dependence

coupling = ca 9

Si on temperature

open = 4.1 hatched of selectivity

of methane

with air as oxidizing

: i) T at various

total

= 6.0 full = 9.5 bar)

ST on oxygen conversion

X02 at T = 69i oC and

P = 4.1 bar) formed on a silica-supported agents. They assumed facilitate

Moo3 catalyst

that O- species

the formation

of

when 02 or N20 are used as

lead to total oxidation

partial

oxidation

besides some C hydrocarbons. n such as that reported by Otsuka,

products,

formaldehyde

from these

evidence,

Yokoyama

ussed electrochemical yttria-stabilized concluded should, adsorbed

oxygen-pumping

zirconia

that oxygen

however,

be emphasized,

with the dissociated

attached

to a metal

adsorption alumina who

process

system:

species

hydrogen

site,

giving

has been suggested

similar proposals

investigated

Li/Mg-oxide

ion

system,

containing

and

also

the

and other

(ref. 21).

migrated

in

species

methanol

Ag-Bi203),

as a result, while a

the

Me-CH3

by Larson

OH-groups remaining

species.

an

it

be

can

reaction.

and

Wall

exchange

reactions

methyl

(ref.

a 22)

It with

formed group dual

of by is site

for

the

and

Amenomiya

(23)

over

alumina.

The

a Li'O- dual site as suggested in an ana‘iogous way.

are

Such

who

through

but that they may also serve as one

have been made by Quanzhi

deuterium-methane

(ref. 18). may be considered

anions

oxidizing 2-

that these oxygen anions do not only react

for CH4 adsorption:

reaction

results

Ag and

0

i.e.

and Morikawa

(O- and/or 02-) participate

CHG. CH3 or CH2 surface

two sites necessary

(i.e. oxygen

coated with catalytic

anions

while

by Lunsford

et

al

363 GO~~LUSIO~S AND OUTLOOK The results literature

presented

indicate

products:

(i) olefinic

aromatic

hydrocarbons:

for the

various

conditions catalyst

during

the Oxidation

that heterogeneous and

applied.

paraffinic

and (ii) methanol

products

depend

and the reaction

selectivity

and yield

development

of improved catalysts,

methane

on

molecules and/or the

for the desired

of the mechanistic

to the products

of the

to

a

used

concerned

conditions product.

leads to a

and,

in

oxidative

to

in the

variety

lesser

of

degree,

The

selectivities

and

the

with

order

Particularly

it is of importance

aspects

and those reported

formaldehyde.

catalysts

Thus, further work will be

formulations

knowledge

Workshop

methane-catalysis

optimizing

the

maximize

the

to

to

the

extend

our

with respect further

catalytic

reaction

converion

of

named above.

REFERENCES

Jezl, Overview of Methane Utilization: A Scenario of Success, in: 1 J.L. Proceed. of Workshop on Basic Research Opportunities in Methane Activation Chemistry, Houston, Texas. Febr. 4-6, 1985, (edited by E.D. Gibson, J.J. Stahr and A-6. Littlefield, for Gas research Institute, Chicago Ill.). M. Baerns, Nachr. Chem. Tech. Lab., 33 (1985) 292. P G.E. Keller, M.M. Bhasin. J. Catal., 73 (1982) 9. 4 W. Hinsen. W. Bvtvn and M. Baerns. Proc. 8th Int. Conar. ., Catal.. Berlin. 1984, Vol. 3, 581: T. Ito and J.H. Lunsford. Nature, 314 (1985) 721. 65 T. Morivama, N. Takasaki. E. Iwamatsu and K.-I. Aika. Chem. Lett.. (1986) i165. 7 C.-H. Lin, D. Campbell, J.-X. Wang and 3-H. Lunsford, J. Phys. Chem., 90 (1986) 534. K. Jinno, and A. Morikawa. J. Catal.. 700 (1986) 353. 8 K. &suka. 9 K. Otsuka, Q. Liu and A. Morikawa, J. Chem. Sot. Chem. Comm., (1986) 587. 10 K. Otsuka, Q. Liu, M. Hatano and A. Morikawa. Chem. Lett., (1986) 903. 11 K.-I. Aika, T. Moriyama, N. Takasaki and E. Iwamatsu. J. Chem. Sot. Chem. Comm.. (1986) 1210. J.R. Anderson and P. Tsai. Appl. Catal., 19 (1985) 141. R.S. Liu, M. Iwamotu, J.H. Lunsford, J. Chem. Sot. Chem. Comm., (1982) 78. R.F. Liu, R.S. Liu, K.Y. Liew, R.E. Johnson and J.H. Lunsford, J. Amer. Chem. Sot., 106 (1984) 4117. J.A.S.P. Carreiro, Doctoral Dissertation, Ruhr-University Bochum, 1986 (submitted). J.A. ROOS, A.G. Bakker, H. Bosch, J.G. van Ommen and J.R.H. Ross, Catal. Today, 1 (1987) 133. W. Bytyn, Doctoral Dissertation, Ruhr-University Bochum, 1986 (submitted). D.J. Driskoll, W. Martir. J.-X. Wang and J.H. Lunsford. J. Amer. Chem. Sot., 107 (1985) 58. M. Baerns and H. Zanthof, unpublished results. Y. Barbaux, A. Elamrani and J.P. Bonnelle. Catal. Today. 1 (1987) 147. K. Otsuka, S. Yokoyama and A. Morikawa, Chem. Lett., (i985)‘319. J.G. Larson and W.K. Hall, J. Phys. Chem., 69 (1965) 3080. L. Quanzhi and Y. Amenomiya, Appl. Catal., 23 (1986) 173.