The radiolysis of simple gas mixtures—II

Radiat. Phys. Chem. Vol. 23, No. 5, pp. 515 522, 1984 Printed in Great Britain.

0146-5724/84 $3.00+.00 Pergamon Press Ltd.

THE RADIOLYSIS OF SIMPLE GAS MIXTURES--II THE PRODUCTION

OF LOWER

ALKANES

AND

ALKENES

ALAN DYERt and GRAHAM E. MOORES~ Department of Chemistry and Applied Chemistry, University of Salford, Salford, M5 4WT, England (Received 15 December 1982; in revised form 6 May 1983) Abstract---Carbon dioxide based gas mixtures, similar to those used as coolants in the Advanced Gas-Cooled Reactors (AGR), have been radiolysed in stainless steel capsules at a dose rate of 3 Gy s using y radiation from a 6°C source. The concentrations of the lower alkanes and alkenes, so produced, have been determined under different conditions of temperature, pressure, gas composition and surface area. Observations showed that organic compounds were produced in concentrations of the order of of the methane concentration and that the production of these "trace organics" varied in a complex way with the experimental parameters. Mechanisms for the production of these organics have been proposed.

INTRODUCTION THE BASICchemistry of gas mixtures, similar to those used as coolants in the A G R , has been outlined elsewhere. °) The radiolytic products of methane, either alone or as the minor component in an inert gas mixture, have been studied extensively32-13) The major products were found to be hydrogen and ethane. The minor products were the higher alkanes, ethene and ethyne. It was soon discovered (2'3) that a polymeric liquid also was formed and it was assigned the formula C.Hz.. Various investigators (4~'t1'12) have shown the importance of ion-molecule reactions of the type given in equations (1)-(3).

(1)

both in the coolant of gas cooled reactors and in the liquors from the purification plants. The major product is ethane together with other alkanes, alkenes, alkanals, alkanones and alkanoic acids in smaller quantities °8-22) Their mode of formation has been the subject of such speculation and various sources have been proposed (molecular sieve driers, traces of lubricating oils, etc.) so it was anticipated that radiolysis at medium dose rates, i.e. " o u t of pile" could provide useful information as to mechanisms whereby organic compounds may be created from relatively simple gas mixtures.

CH4 + + CH4--~CH5 + + CH~

(2)

CH3 + + CH4--~C2H 5+ + H2

(3)

C2H5 + + CH4---~C3H7 + + H2.

The radiolysis of methane/carbon dioxide mixtures (2) lead to the formation of a white, wax-like solid of empirical formula CH20, assumed to be a polymer of methanal. Several groups of workers (t4-tT) have radiolysed hydrogen/carbon monoxide and hydrogen/carbon dioxide mixtures, and again white, wax-like solids were formed together with various alkanals and glycols. M a n y organic compounds have been observed

tAuthor to whom correspondence should be directed. ~Present address: Department of Physical Chemistry, The University, Leeds, LS2 9JT, England.

EXPERIMENTAL The carbon dioxide based gas mixtures were prepared in steel cylinders by U.K.A.E.A., Springfields, and had compositions as shown in Table 1. The mixtures were radiolysed in stainless steel capsules, one of which was demountable, of internal dimensions 16mm alia., 98mm length and 19ram dia., 150mm length. The y dose rate was ~ 3 Gy s- l, from a 370 TBq (10 kCi) 6°C source, measured as before. (I) Total dose was 1 kGy--1 MGy. The radiolyses were conducted at temperatures in the range 300-750 K and pressures in the range 0.5-5.5 MPa. After radiolysis gas samples were allowed to flow in a helium carrier gas through a gas chromatograph containing a Porapak Q column to a flame ionisation detector. The concentration of each component was determined from a measurement of the peak height and a calibration curve derived from a standard gas mixture supplied by U.K.A.E.A., Springfields. The usual estimated error in the measurements (2a) was ___59/0 although it was somewhat greater than this for the higer homologues. In certain experiments mild steel, stainless steel and graphite were in the demountable capsule. Detai!s of these materials are in Ref. 1. 515

516

A. DYERand G. E. MOORES TABLE

gas mixtures

1.

COMPOSITION

OF GAS MIXTURES

[H 2 ]

[CH 4 ]

vpm ~

[~2o]

[co]

vpm

v/o ##

vpm

53O

380

50

O. 25

580

520

90

2.00

750

500

lO0

0.25

420

1400

6O

1.00

tParts per million by volume. ttVolume per cent. RESULTS The data have been presented in terms of a concentration ratio (R), defined by equation (4)

R-

(4)

which is considerably higher than the steady-state concentration. The initial production rates of the alkanes increased with increasing temperature and Arrhenius plots of these rates are shown in Fig. 2. These plots yielded a mean apparent energy of activation of 23 kJ mol- ~ for ethane and 18 kJ m o l - 1 for propane. The variation in the steady-state alkane concentration with tempeature is shown in Fig. 3. It can be seen that the steady-state ethane concentration showed a similar trend with increasing temperature but propane was not detected at 750 K. Increasing the gas pressure from 2.1 to 4.1 MPa had little effect on the steady-state alkane concentration but increased the initial production rate, see Table 2. The introduction of mild steel into the capsule resulted in variable alkane concentrations which always were considerably higher than the corresponding empty capsule values. A typical example was a gas

Concentration, in vpm, of organic at a given dose Concentration, in vpm, of methane at the same dose

This presentation was adopted to eliminate methane concentration as a variable since it was changing with dose. Each determination was at least duplicated and many determinations were in triplicate. Their accuracy was of the order of + 10~. (i) The alkanes The alkanes studied quantitatively were ethane and propane. The compounds were found to be present in all the radiolysed gas samples with the exception of those radiolysed at ambient temperature. A plot of R vs dose is shown in Fig. 1. It can be seen that in the case of ethane, and to a lesser extent propane, there is a transient concentration

X

103.

mixture at 625 K, 4.1 MPa after an absorption of 24 kGy when in the presence of mild steel the ethane and propane ratios were 150 and 44, respectively compared to values of approximately 12 and 2, respectively, for the empty capsule. The effect of an increased area of stainless steel for a typical gas mixture is summarised in Table 3. The increased surface area tended to reduce the alkane concentration except for ethane at 625 K. The initial production rate of ethane was reduced at all temperatures by the introduction of more stainless steel. The effect on the concentration ratios of introducing graphite into the capsule is summarised in 1.5 7"

R 0.5

20

-0"5 \ x

-1.5

0

~

0

i

i 300

,

i oJ~ s_e

kGy

i 600

Variation in the concentration ratio with dose for ethane (0) and propane (*). Gas mixture A, 625K, 4.1 MPa. FIG. I.

-2"5 1.2

~ ' 1.6

' 2.0

103K T

Fig. 2. Arrhenius plots of ethane and propane production rates: (a) Gas C, ethane; (b) Gas A, ethane; (c) Gas B, ethane; (d) Gas A, propane. All gas mixtures at 4.1 MPa.

The radiolysis of simple gas mixtures--II Table 4. Again the alkane concentrations were reduced except for ethane at 680K. The effect of carbon monoxide concentration was examined and the effect on ethane and propane was as shown in Figs. 4 and 5. Under all the experimental conditions increasing the carbon monoxide concentration reduced the alkane production rate. The effect of carbon monoxide concentration on the steady-state alkane concentration is summarised in Table 5. Increasing the carbon monoxide concen-

517

tration did not have a marked effect on the ethane concentration except at 750 K where it was approximately doubled, in addition the concentration of propane was increased at 750 K but greatly reduced at 680 K. In certain experiments where the hydrogen concentration was increased from 1400 to 3000 vpm the concentration of both alkanes approximately was doubled. (ii) The alkenes The alkenes studied quantitatively were ethene and

TABLE 2. ALKANES: INITIAL PRODUCTION RATES Alkane

Temperature K

Ethane

500

Pressure FPPa

Production rate kGy-i

2.1

O.16

4.1

0.37

2.1

1.6

4.1

2.9

2.1

0.07

4.1

O. 10

2.1

0.15

4.1

0.25

750

500 Propane 750

TABLE 3. THE EFFECT OF ADDED STAINLESS STEEL ON THE STEADY-STATE ALKANE RATIO R !

R T/K

Alkane

Empty Capsule

Ethane

500 625 680

9.1 8.3 iO

Propane

500 625 680

4.4 1.6 2.1

R Stain}ess steel

added 7.5 13 7.2

2.9 1.6 NOT DETECTED

TABLE 4.

THE EFFECT OF

Alkane

T/K

Ethane

500 625 680

9.1 8.3 iO

6.3 6.5 iO

Propane

500 625

4.4 i. 6

2.6 i. i

GRAPHITE ON THE STEADY-STATE ALKANE RATIO R

Empty ~apsule

R

Graphite added

R~

518

A. DYER and G. E. Mool~s

,I

R

12

a

b

/

4

//I

.

"

/ /

I

/

o II +'x 1i '. /

/' /

7 /

OoS;S-~,

"~

. . . . 3 0. . . . . . . ~

t / i

60 kGy

\,\

FIG. 3. Variation in the steady-state concentrations with tempeature: ( 0 ) Gas A, ethane; (,) Gas A, propane. Gas pressure, 4.1 MPa. propene. Both alkenes were detected in all experiments at 650 K and above. However, propene was an impurity in most of the unirradiated gas samples and was present in the low dose range of many experiments below 650K. A plot of R vs dose for the alkenes is shown in Fig. 6. Ethene and to a lesser ~xtent propene exhibited an initial transient concentration. Unlike the alkanes, the alkenes were seldom detected in steady-state gas mixture and when detected their concentrations were always lower than 0.05 vpm. The initial production rates of the alkenes increased with increasing temperature and Arrhenius plots of these rates yielded a mean apparent energy of activation of 170 kJ m o l - ' for ethene and 80 kJ mol - 1

R /c

20 / /

FIG. 5. Variation in the propane production rate with carbon monoxide concentration: (a) Gas A, 750 K; (b) Gas B, 750 K, (c) Gas A, 750 K; Gas B, 750 K, (c) Gas A, 500 K, (d) Gas B, 500 K. Gas pressure, 4. l MPa.

for propene. Figure 7 shows the dependence on temperature of the ethene ratio for several different gas mixtures in a temperature range of relevance to the AGR. The effect of gas pressure on the concentration ratio of the alkenes is summarised in Table 6. Increasing pressure reduced the ethene concentration whereas the trend was reversed for propene. The presence of mild steel resulted in the production of ethene at 625 K and of propene at 500 K, the latter persisting in steady-state gas mixtures. The effect of an increased area of stainless steel was pronounced: propene was no longer detected at temperatures of 680K and above and the ethene concentration was reduced, see Table 7. The presence of graphite had little effect on the alkene concentration although the first experiments with virgin graphite gave rise to higher ratios, approximately 3 compared to 0.45 for the empty cap-

/ /

/

/

TABLE 5. THE EFFECT OF CARBON MONOXIDE CONCENTRATION ON THE STEADY-STATE ALKANE RATION R I

/ /

b

/

i,/

/ /

/

10

i'

R1

/

"''"

Alkane

T/K

/ I /e

]e/!

R 1 2.0% CO

/'"

~/ Ethane

Ol

0.25% CO

J

J 30

i

I_ Dose kGy

300 625

750

9. i 8.3 ]0 4.5

500 625 680 750

4.4 I. 6 2. i Not detected

680

7.8 10

i] 8.8

60

FIG. 4. Variation in the ethane production rate with carbon monoxide concentration: (a) Gas A, 750K; (b) Gas B, 750 K; (c) Gas A, 500 K; (d) Gas B, 500 K. Gas pressure, 4.1 MPa.

Propane

4.4 l. 5 O . 79 O.17

The radiolysis of simple gas mixtures--II TABLE6. Trm

519

EFFECT OF PRESSURE ON THE ALKENE CONCENTRATION RATIo R 2

R2 Alkene

.... I.i MPa

2.1 MPa

4.1 MPa

5.1 MPa

C2H 4

13

9.1

I0

6.2

C3H 6

0.38

0.68

0.71

0.75

TABLE 7. TIlE EFFECT OF ADDED STAINLESS STEEL ON THE ETHENE CONCENTRATION RATIO R 3 R3

T/K

empty capsule

[ stainless steel added

I 680

0.67

0.63

715

3.0

0.53

sule experiments. The effect of gas composition on the ethene ratio is shown in Fig. 8. Increasing the carbon monoxide concentration appeared to increase the ethene concentration ratio whereas a high hydrogen concentration reduced the ratio. In the case of propene there was no consistent effect with changes of gas composition. Those gas mixtures in which a small steady-state alkene concentration was found were those containing a higher concentration of carbon monoxide.

DISCUSSION The concentrations of the components of the gas mixtures were a function of the relative rates of production and destruction. The two processes could have been either radiation-induced, purely thermal or a mixture of both. Experiments in the absence of radiation failed to produce any measureable quantifies of organics so thermal production below 680 K was thought to be negligible compared with the radiolysis. (i) The alkanes Of all the organics produced ethane was present in the highest concentration and was found in all experiments except those at 300 K. Its absence at 300 K was attributed to a low G( + C2I-I6)t (compared with tG(+/-organic) is the number of molecules of the organic produced/destroyed by the absorption of 1.6x 10-17J.

G(-C2H6)) at this temperature. The ethane ratio exhibited a temperature dependent peak at low dose (20 kGy at 625 K). Hummel o3) observed a similar transient behaviour attributed the "transient nature" of ethane in sealed systems to a destruction process involving oxygen atoms. If, however, production of ethane was via an n order reaction in methane then (5)

[ C 2 H 6 ] oc [ C H 4 ] n

25

10

I'

I I

s],I¢

k k k\ \

\

200

4 0 0 Dosl kG,

FIG. 6. Variation in the concentration ratio with dose for ethene (O) and propane (O). Gas mixture A, 750K, 4.1 MPa.

A. DYER and G. E. MOORES

520 and (6)

[C2H6] -- RC2H6 oc [CH4] n I. [CH4]

Now [CH4] decreased with increasing dose and if n > 1 then Rethanemight be expected to decrease until [CHa] : [CH4]~t~.ay .....-

o 10

/ / /

:/ // //

5

0 800

T K

800

FIG. 7. Variation in the low dose ethene concentration ratio with temperature. @, Gas A; [S], Gas B; O, Gas C; * Gas D. All gases at 4.1 MPa.

The activation energy for the ethane production process was found to be 23 kJ mol ~ (mean of three gases) similar to the value obtained by Hummel (26 kJ m o l - ~). The steady-state ethane concentration increased with increasing temperature except that at 750 K it fell to approximately one-half of the 680 K value. This behaviour was attributed to the activation energy of the production process being greater than that of the destruction process. The sudden fall in the steady-state concentration at 750 K could have been due to the onset of a second destruction process or to a fall in G(+C2H6). Norfolk et al. (2~) also noted a decreased yield of ethane above 720 K. At 680 K the mean value of the ethane ratio was eleven, i.e. 1.1 v/o of the methane concentration. This was somewhat lower than the ratio found in reactor coolants, "2) viz. approximately 4.5 v/o. The ethane production rate approximately was doubled by doubling the pressure from 2.1 to 4.1 MPa but, as the steady-state concentration was similar at the two pressures, it was likely that G ( + C2H6) and G ( - C 2 H 6 ) were similarly affected by pressure. The carbon monoxide concentration had a profound influence on the ethane ratio. A gas mixture containing 0.25 v/o carbon monoxide was found to produce ethane at approximately three times the rate of that in a 2 v/o carbon monoxide gas mixture. This can be explained by a competition mechanisms as shown in equations (7)-(9). (7)

~

10

(8)

(9)

CH 4 ~

CH 3 +

CH3 + + CH4~C2H5 + ---~C2H6 CH 3 ~ + C O ~ C H 3 C + O .

In view of the decreased production rate the steady-state concentration might have been expected to be lower in high carbon monoxide gas mixtures but this was not found to be the case. The steady-state concentration was increased, if anything, and this presumably due to a decreased destruction rate in high carbon monoxide gases, so protecting ethane via a mechanism, equation (10), involving competition for oxidising species similar to that proposed for this protection of methane. (26~

0

CO (10)

I

0

Dose kGy

20

FIG. 8. Variation in the ethene production rate with gas composition: (a) Gas B; (b) Gas A; (c) Gas D. All gases at 750K, 4.1 MPa.

C O 2 - - - ) . C O 2 + ~-

CH 4 C2H6

Carbon monoxide concentration had little effect on the steady-state ethane ratio which may be assigned

521

The radiolysis of simple gas mixtures--II to a balancing effect of decreased production and increased protection. Smith et al. ~2~)noted the same effect in reactors presumed to be at steady state. Propane was detected in all experiments except those performed at 300K, when G(+C3Hg) was probably too low to sustain a measurable concentration. The activation energy for the propane concentration was reduced by increasing temperature, the values at 625 and 680 K being approximately half that at 500 K. This was probably because G ( - C 3 H s ) increased significantly in the range 500-625 K. The steady-state concentration of propane was approximately 0.6 of the ethane concentration at 500 K but only 0.2 at 625K. The latter ratio agreed with W . A . G . R . t results, (22) although the actual concentrations of both ethane and propane were higher in W.A.G.R. The mean propane ratio at 625 K was found to be approximately 2 whereas in reactors it was 7 in high carbon monoxide and 12 in low carbon monoxide gases. Doubling the pressure from 2.1 to 4.1 MPa increased the production rate of propane although not as markedly as for ethane. The steady-state concentration was increased at 500 K by this pressure change, probably due to an increase in G ( + C3Hs) if propane was assumed to behave similarly to methane (1), but was unchanged at 625 K presumably because of the balancing effect of an increased G(-C3H8). Carbon monoxide reduced the production rate of propane probably by a similar competition mechanism to that proposed for ethane. An increase in the carbon monoxide concentration from 0.25 v/o to 2.0 v/o halved the rate above 500 K. The steady-state value was not greatly affected by carbon monoxide at 500 or 625 K since the protection effect probably counterbalanced the reduced production.

presence of ethene in detectable quantities at the steady-state was almost certainly due to a lower G(-C2H4) value. The carbon monoxide concentration had little effect on the ethene production rate and the increased ethene concentration, at the steadystate, in the "high carbon monoxide" gases, could not have been attributable to a higher G(+C2H4). The increased concentration was probably due to a competition/protection mechanism similar to that outlined for the alkanes. Propene was not detected in a steady-state mixture above 680 K. The effect of pressure on the production rate and steady-state concentration of both ethene and propene was small. Increasing the hydrogen concentration markedly reduced the ethene production rate and hydrogenation was a possible mechanism:

(12)

CH2" +

(ii) The alkenes The alkenes were detected consistently only at temperatures above 650 K. Propene was present as an impurity in most of the sample gas mixtures and this tended to complicate the low dose results. Both ethene and propene were formed via processes with much higher activation energies than for the formation of the corresponding alkanes. Taking the mean value for three gases, the activation energy of the ethene production process was 170 kJmo1-1 (cf. ethane 23 kJ mol - 1) and for propene 80 kJ m o l (cf. propane 18 kJ mol-1). This indicated a predominant thermal step in alkene production. Ethene was detected in a steady-state mixture at 750 K only in "high carbon monoxide" gases, the

(13)

CH2" + CH2"--*C2H4

tW.A.G.R.--Windscale AGR.

(11)

C2H4 + H2--*C2H6.

The effect on propene production increasing the hydrogen concentration was mixed; at 680 K the build-up rate was increased but at 750 K was reduced. The ethene ratio vs dose graph (Fig. 6) exhibited a similar transient region to that exhibited by ethane, and at a similar dose. Thus the ethene concentration at low doses was considerably higher than the steadystate concentration. The maximum observed peak concentration ratio was 15 compared with a typical reactor coolant ratio of 5. Indeed, in experiments at 750 K the ethene concentration at low doses was comparable with, and sometimes larger than, the ethane concentraion. This observation tended to cast doubts on the mechanisms

CH4--~C2H6

since these would have been expected always to produce a lower concentration of ethene than ethane. The temperature for the onset of ethene production (cf. 680 K) was similar to the temperature at which the steady-state ethane ratio fell to approximately one half its lower temperature value and this suggested that ethane to ethene conversion was taking place. Other researchers (2L22) have reported a similar threshold temperature for the onset of ethene production. However, if ethene has been produced from ethane one would have expected carbon monoxide to reduce the ethene production rate since it decreased the ethane production rate. Also, one would have expected the ethane build-up rate to be reduced at 750 K when comparable amounts of ethene were produced. If both compounds were formed from the

522

A. DYER and G. E. MOORES

same species then, yet again, the e t h a n e p r o d u c t i o n rate would have fallen, viz.

(14)

C2HT"--~C2H6+ IT

(15)

C2H 4 + H 2 + IT.

It seemed p r o b a b l e that the fall in the e t h a n e steady-state c o n c e n t r a t i o n at 750 K was due to the onset of a n o t h e r destruction process (which m i g h t have p r o d u c e d some ethene) at a r o u n d 680 K a n d t h a t ethene was p r o d u c e d by some m e c h a n i s m which had little effect o n ethane, e.g. one involving the ethyl radical. (iii) Effects o f different surfaces inside the capsule (a) Graphite. T h e presence o f graphite was f o u n d to have little effect on the c o n c e n t r a t i o n o f alkanes or alkenes o t h e r t h a n possibly to reduce the p r o d u c t i o n threshold t e m p e r a t u r e of the latter species. (b) M i l d steel. T h e presence o f mild steel was found to increase e t h a n e a n d p r o p a n e c o n c e n t r a t i o n s , Dwyer a n d Somorjai (24) have observed the f o r m a t i o n o f CI-C5 h y d r o c a r b o n s from CO/H2 mixtures in the presence of iron foils a n d the increased c o n c e n t r a t i o n of alkanes observed in the present work p r o b a b l y arose in a similar manner. They also reported ethene a n d p r o p e n e formation, as observed herein (ethene at 625 K a n d p r o p e n e at 500 K) a n d n o t e d rapid carbonaceous deposition on the iron which was similar to the present o b s e r v a t i o n of a comparatively thick c a r b o n a c e o u s deposit o n the mild steel. (c) Stainless steel. A n increased area o f stainless steel decreased the p r o d u c t i o n rate o f e t h a n e b u t p r o b a b l y ' r e d u c e d the destruction rate also, since the steady-state values were similar. The effect for propane was m o r e p r o n o u n c e d a n d at the higher temperatures studied p r o p a n e was not detected. It was p r o b a b l e t h a t p r o p a n e was b r o k e n d o w n at the stainless steel surface a b o v e 680 K, but the fact t h a t there was a steady-state at 680 K pointed to the destruction o f p r o p a n e via a reversible process. (16)

C3H8 Stainless steel ~ 680 K products.

gas mixtures at m e d i u m dose. Whilst not a t t e m p t i n g complete solutions it is h o p e d t h a t the results will be o f some practical value towards a n u n d e r s t a n d i n g of "out-of-pile" p h e n o m e n a observed in working gas cooled reactors. F u r t h e r work is c o n t i n u i n g to follow up the effects o f stainless steel reported herein.

Acknowledgements---The authors are grateful to Dr. P. Campion, Mr. A. Blanchard, Dr. P. A. V. Johnson and their colleagues at Springfields Nuclear Power Developments for many helpful discussions and to the U.K. Atomic Energy Authority Northern Division for financial support during the tenure of this work.

REFERENCES 1. A. DYER and G. E. MOORES,Radiat. Phys. Chem. 1982, 20, 315. 2. S. C. LIND and D. C. BARDWELL, J. Am. Chem. Soc. 1926, 48, 2335. 3. R. E. HONIG and C. W. SHEPPARD, J. Phys. Chem. 1946, 50, 119. 4. D. P. STEVENSONand D. O. SCHISSLER, J. Chem. Phy~s. 1955, 23, 1353. 5. D. P. S~'iTVENSONand D. O. SCHISSLER, J. Chem. Phys. 1956, 24, 926. 6. G. G. MEISELS, W. H. HAMILL and R. R. WILLIAMS, J. Chem. Phys. 1956, 25, 790. 7. F. H. FIELD, J. L. FRANKLIN and V. W. LAMPE, J. Am. Chem. Soe. 1956, 78, 5697, 8. F. H. FIELD, J. L. FRANKLINand F. W. LAMPE, J. Am. Chem. Soc. 1957, 79, 2419. 9. F. W. LAMPE, J. ,4111. Chem. Soc. 1957, 79, 1055. 10. L. H. GEVANTMANand R. R. WILLIAMS,J.

l I. 12. 13. 14. 15. 16. 17. 18. 19. 20.

(

Stainless steel e n h a n c e d destruction rates of b o t h alkenes at 680 a n d 715 K. T h e alkenes were p r o b a b l y removed from the gas phase by irreversible processes such as c a r b o n i s a t i o n at the steel surfaces. CONCLUSIONS All cases studied were complex processes related to working conditions e n c o u n t e r e d by reactor coolant

21. 22. 23. 24. 25. 26.

Phys.

Chem.

1952, 56, 569. G. G. MEISELS, W. H. HAMILL and R. R. WILLIAMS,J. Phys. Chem. 1957, 61, 1456. S. WEXLER and N. JF,SSE, J. Am. Chem. Soc. 1962, 84, 3425. K. YANG and J. MANNO,J. ~tin. Chem. Soc. 1959, 81, 3507. S. C. LIND and D. C. BARDWELL, J. Am. Chem. Soc. 1925, 47, 2675. F. MOSELEY, A. E. TRUSWELL and C. D. EDWARDS, AERE Report R2913, 1559. D. C. DOUGLAS, J. Chem. Phys. 1955, 23, 1558. W. H. BEATTIE, Int. J. Chem. Kinetics 1972, 4, 463. P. CAMPION, M.Sc. Thesis, University of Salford, 1972. P. CAMPION, Ph.D. Thesis, University of Salford, 1977. P. CAMPION, Gas Chemistry in Nuclear Reactors and Large Industrial Plant, p. 53 (Edited by A. Dyer). Heyden, London 1980. D. J. NORFOLK, R. F. SKINNER and W. J. WILLIAMS,as Ref. 20, p. 67. R. SMITH, L. O. GREEN and P. A. V. JOHNSON, as Ref. 20, p. 248. R. W. HUMMEL, Unpublished work. D. J. DWYER and G. A. SOMORJAI,J. Catalysis 1978, 52, 291. J.-C. FESSLER, Ph.D. Thesis, University of Grenoble, 1971. D. A. DOMINEY, A.E.R.E. Report R.3481, 1961.