Results of studies utilizing normal and rare oxygen isotopes in the catalytic oxidation of carbon monoxide over a platinum-tin oxide catalyst substrate are presented. Chemisorption of labeled carbon monoxide on the catalyst followed by thermal desorption yielded a carbon dioxide product with an oxygen-18 composition consistent with the formation of a carbonate-like intermediate in the chemisorption process. The efficacy of a method developed for the oxygen-18 labeling of the platinum-tin oxide catalyst surface for use in closed cycle pulsed care isotope carbon dioxide lasers is demonstrated for the equivalent of 10 to the 6th power pulses at 10 pulses per second

Hess, Robert V.

Hoyt, Ronald F.

Upchurch, Billy T.

Wood, George M., Jr.

English

NASA Technical Reports Server

N 8 7 - 2 0 5 3 8  
Rare i so tope  C1802 l a s e r  ope ra t ion  has  been c a r r i e d  out at  3OO0C with a 
Pt/A1203 c a t a l y s t  a t  Los Alamos Nat ional  Laboratory ( r e f .  4 ) .  I n  these  s t u d i e s ,  
whi le  t h e  alumina was consid ed an i n e r t  s u b s t r a t e  and not a p a r t i c i p a n t  i n  t h e  
c a t a l y t i c  recombination of CfgO and 1802 t o  form COP, s p e c i a l  a t t e n t i o n  and care were 
RARE ISOTOPE STUDIES INVOLVING CATALYTIC OXIDATION OF CO 
OVER PLATINUM-TIN OXIDE 
B i l l y  T. Upchurch 
Science and Technology Corporat ion 
Hampton, V i r g i n i a  
George M. Wood, Jr., Robert V. Hess, and Ronald F. Hoyt 
NASA Langley Research Center 
Hampt on, V i rg in i a  
SUMMARY 
I n  t h i s  repor t  r e s u l t s  of s t u d i e s  u t i l i z i n g  normal and r a r e  oxygen i so topes  i n  
t he  c a t a l y t i c  ox ida t ion  of carbon monoxide over a plat inum-t in  oxide c a t a l y s t  
s u b s t r a t e  are presented.  
followed by thermal deso rp t ion  y ie lded  a carbon d ioxide  product wi th  an oxygen-18 
composition c o n s i s t e n t  with t h e  formation of a carbonate- l ike in te rmedia te  i n  the  
chemisorpt ion process .  The e f f i c a c y  of a method developed f o r  t he  oxygen-18 
l a b e l i n g  of t h e  platinum-tin oxide c a t a l y s t  su r f ace  for  u s e  i n  c losed cyc le  pulsed 
rare i so tope  carbon d ioxide  lasers is demonstrated f o r  t he  equiva len t  of 10 6 pulses  
a t  10 pulses  per second. 
Chemisorption of labe led  carbon monoxide on the  c a t a l y s t  
INTRODUCTION 
I 193 
https://ntrs.nasa.gov/search.jsp?R=19870011105 2020-03-20T11:15:12+00:00Z
and t o  deve lop  t echn iques  t o  maximize i s o t o p i c  i n t e g r i t y  of rare  i s o t o p e  laser g a s e s  
t o  m a i n t a i n  laser  power at t h e  d e s i r e d  frequency.  A f u r t h e r  g o a l  was t o  u t i l i z e  
t h e s e  rare i s o t o p e  g a s e s  t o  de t e rmine  m e c h a n i s t i c  d e t a i l s  of CO o x i d a t i o n  on t h e  
Pt/Sno2 c a t a l y s t .  
Experiments d e s c r i b e d  i n  t h i s  paper  demons t r a t e  t h a t ,  w h i l e  oxygen exchange 
between t h e  gaseous oxygen and carbon monoxide s p e c i e s  and t h e  Pt /Sn02 s u b s t r a t e  
does indeed occur  a t  low r e a c t i o n  t e m p e r a t u r e s ,  t h e  i s o t o p i c  sc rambl ing  may be 
e l i m i n a t e d  by an inexpens ive  i s o t o p e  exchange s u r f a c e  l a b e l i n g  t e c h n i q u e  developed 
a t  Langley Research Center  ( r e f .  6 ) .  
EXPERIMENTAL 
The expe r imen ta l  a p p a r a t u s  f o r  i s o t o p e  measurements c o n s i s t e d  of a t e s t  gas  
c y l i n d e r  connected through a g a s  d r y i n g  chamber, f l ow c o n t r o l l e r ,  and a t e m p e r a t u r e  
c o n t r o l l e d  ca t a lys t  r e a c t o r  chamber t o  a mass s p e c t r o m e t e r  g a s  sampling i n l e t .  The 
d r y i n g  chamber was charged w i t h  anhydrous magnesium p e r c h l o r a t e .  A H a s t i n g s  mass 
f low c o n t r o l l e r  was p l aced  upstream from t h e  c a t a l y s t  chamber. Excess  gas flow no t  
p a s s i n g  i n t o  the  mass s p e c t r o m e t e r  w a s  d i v e r t e d  through a H a s t i n g s  mass f low meter 
t o  t h e  o u t s i d e  atmosphere. The mass s p e c t r o m e t e r  w a s  a DuPont CEC Model 21-104 
magnet ic  s e c t o r  u n i t .  The c a t a l y s t  r e a c t o r  chamber was b u i l t  from components and 
ma in ta ined  t empera tu re  c o n t r o l  w i t h i n  0.5OC. The c a t a l y s t  of 1%Pt/Sn02 w a s  o b t a i n e d  
from Englehard I n d u s t r i e s .  A l l  c a t a l y s t  c h a r g e s  were p laced  i n  t h e  chamber enc losed  
w i t h i n  a 6.35 nun i n t e r n a l  d i a m e t e r  by approximately 40 cm q u a r t z  tube.  The c a t a l y s t  
was h e l d  i n  p l a c e  by q u a r t z  wool p l u g s  on each end of  t h e  c h a r g e .  A l l  rare  i s o t o p e  
g a s  composi t ions were o b t a i n e d  from Cambridge I s o t o p e  L a b o r a t o r i e s  w i t h  s t a t e d  
p u r i t i e s  of b e t t e r  t h a n  98 atom p e r c e n t  and were ana lyzed  mass s p e c t r o m e t r i c a l l y  i n  
ou r  l a b o r a t o r y  prior t o  use.  A l l  o t h e r  gases  were from S c o t t  S p e c i a l t y  g a s e s .  
Chemisorpt ion measurements were c a r r i e d  ou t  u s i n g  a Shimadzu the rma l  c o n d u c t i v i t y  
d e t e c t o r  gas  chromatograph. A l l  t e s t  g a s  f low ra tes  were 5 s t a n d a r d  c u b i c  
c e n t i m e t e r s  per  minute .  
A l l  O2 c o n c e n t r a t i o n s  were 1 p e r c e n t  by volume i n  neon. A l l  s t o i c h i o m e t r i c  m i x t u r e s  
of  CO and O2 were 2 p e r c e n t  and 1 p e r c e n t ,  r e s p e c t i v e l y ,  w i t h  a 2 p e r c e n t  neon s p i k e  
and t h e  ba l ance  helium. Hydrogen was 7.5 p e r c e n t  by volume i n  helium. 
A l l  CO c o n c e n t r a t i o n s  were 2 p e r c e n t  by volume i n  neon. 
RESULTS AND DISCUSSION 
During carbon monoxide chemiso rp t ion  s t u d i e s ,  it w a s  found t h a t  some CO 
chemisorbed onto t h e  Pt /Sn02 c a t a l y s t  a t  room t e m p e r a t u r e  w h i l e  some CO 
s i m u l t a n e o u s l y  ox id ized  and evolved as C02 w i t h  t h e  subsequent  r e d u c t i o n  of t h e  
c a t a l y s t  s u r f a c e  by removal of s o m e  ox ide .  A room t empera tu re  CO c h e m i s o r p t i o n  
t i t r a t i o n  of  a 1.0 gram sample of 1% Pt/SnOZ c a t a l y s t  was found t o  b ind  
42 m i c r o l i t e r s  of CO. 
mass s p e c t r o m e t r i c a l l y .  
d i sp l acemen t  by gaseous hydrogen c h l o r i d e  e v o l v e  C02 as d e t e c t e d  w i t h  t h e  mass 
s p e c t r o m e t e r .  Subsequen t ly ,  chemiso rp t ion  of  Cl'O upon a normal i s o t o p e  Pt/SnO 
c a t a l y s t  s u b s t r a  e f o l l  wed by hermal d e s o r p t i o n  of  C02  y i e l d e d  an approx ima te fy  
4:4:1 r a t i o  of C € 6  0 2 : C  18 0 18 0 : C  lk O2 as would be expected from a c a r b o n a t e  s p e c i e s  
t h u s  l e n d i n g  f u r t h e r  suppor t  f o r  t h e  e x i s t e n c e  of such an i n t e r m e d i a t e  s p e c i e s  i n  
t h e  recombinat ive redox mechanism. 
Thermal d e s o r p t i o n  y i e l d e d  42 m i c r o l i t e r s  of CO as measured 
Another sample a f t e r  CO chemiso rp t ion  f o l l o w e i  by chemical  
194 
Since  our primary goal  w a s  t o  develop a c a t a l y t i c  r egene ra t ion  system fo r  t he  
ope ra t ion  of a r a r e  i so tope  c losed  cyc le  pulsed C 0 2  laser system, i so tope  exchange 
s t u d i e s  were subsequent ly  c a r r i e d  out t o  thoroughly i n v e s t i g a t e  t h e  Pt/Sn02 c a t a l y s t  
system with regard  t o  i s o t o p i c  i n t e r a c t i o n s  with a l l  l a s e r  gas s p e c i e s  a s  shown i n  
t a b l e  1. 
18 As is noted i n  t a b l e  I,  C 0 was found t o  r e a d i l y  e x t r a c t  oxygen-16 from the  
unlabeled Pt/Sn02 at temperatures  from room temperature upwards. 
i s o t o p i c a l l y  unlabeled c a t a l y s t  cannot be used fo r  regenera t ion  of t h e  d i s s o c i a t i o n  
products  which would be encountered i n  a closed cyc le  r a r e  i so tope  C 0 2  l a s e r .  Rows 
2, 3, and 4 i n  t a b l e  I show t h a t  t h e r e  w a s  no exchan e o r  scrambling r e a c t i o n  
observed between 1802 (alone or  i n  combination wi th  f602) and t h e  Pt/Sn02 c a t a l y s t  
s u b s t r a t e  u n t i l  temperatures  s u b s t a n t i a l l y  g r e a t e r  than t h e  expected ope ra t ing  
temperatures  of t he  laser c a t a l y s t  bed were a t t a i n e d .  
Thus, t h e  
When a s to i ch iomet r i c  mixture of t he  oxygen-18 labe led  carbon monoxide and 
oxygen w a s  pa sed over t he  normal i so tope  Pt/Sn02 c a t a l y s t  a t  100°C, 85 percent  and 
15 percent  C1'02 and C 16 0 18 0, r e s p e c t i v e l y ,  were i n i t i a l l y  formed (row 5, t a b l e  I ) .  
These y i e l d s  g radua l ly  changed t o  90 percent and 10 percent  a f t e r  8 hours o r  more of 
opera t ion .  Evident ly ,  t he re  a r e  two poss ib le  recombinative mechanisms occurr ing ,  
one of which is  perhaps a t  the  s u r f a c e ,  and one which i s  i n t e r a c t i v e  with the  SnO 
su r face .  I n  add i t ion ,  t he  Sn02 su r face  must slowly become i s o t o p i c a l l y  labe led  with 
oxygen-18 v i a  the i n t e r a c t i v e  exchange mechanism. Complete su r face  l a b e l i n g  by t h i s  
technique would r e q u i r e  an i n o r d i n a t e l y  long t i m e  fo r  s u f f i c i e n t  i so tope  l a b e l i n g  t o  
be a t t a i n e d  even i f  d i f f u s i o n  from the  bulk were inope ra t ive .  
2 
With t h e  foregoing d a t a  i n  hand, it was decided tha t  an attempt would be made 
16 t o  l a b e l  t h e  su r face  of t h e  Pt /Sn 
reducing the  su r face  t o  e lemental  t i n  followed by r eox ida t ion  of t h e  t i n  
su r face  t o  Sn'%i wi th  '*02. Should a l l  of t h e  a c t i v e  normal-isotope oxygen a t  t h e  
s u r f a c e  be exchanged i n  t h i s  way, then t h e  c a t a l y s t  would be s u i t a b l e  f o r  use i n  a 
rare i so tope  c losed  cyc le  C 0 2  l a s e r  i f  d i f f u s i o n  of t he  bulk mat r ix  oxygen-16 t o  t h e  
s u r f a c e  does not occur.  
O2 c a t a l y s t  with oxygen-18 by f i r s t  chemical ly  
The  chemical reduct ion  of t h e  Pt/Sn02 c a t a l y s t  w a s  accomplished by exposing it 
t o  a flowing s t ream o f  7.5 percent  H2 i n  helium a t  225OC. 
removal w a s  judged complete a f t e r  t he  mass spec t romet r i ca l ly  monitored H20 
concen t r a t ion  i n  the  s t ream had dropped t o  the  instrument background l e v e l .  The 
redyged s u b s t r a t e  su r face  was then reoxidized a t  225OC with a gas stream con ta in ing  
1% O2 u n t i l  t h e  1802 concen t r a t ion  ex i t i ng  the  c a t a l y s t  chamber had a t t a i n e d  and 
remained at  t h e  1 percent  concent ra t ion  leve l  f o r  a t  l e a s t  one hour as measured on 
the  mass spectrometer .  The temperature was then reduced t o  ambient under neon 
flow. The preceding i so tope  exchange l abe l ing  of t he  metal oxide c a t a l y s t  w a s  
accomplished i n  about 5 hours and is p a r t l y  the  b a s i s  f o r  our pa ten t  a p p l i c a t i o n  
( r e f .  6 ) .  
The a c t i v e  su r face  oxygen 
18 The 1% Pt/Sn O2 s u r f a c e  labe led  c a t a l y s t  w a s  then eva lua ted  under cond i t ions  
l i s t e d  i n  row 6 of t a b l e  I and was found t o  main ta in  t h e  i s o t o p i c  i n t e g r i t y  of t h e  
rare  i so tope  gas composition f o r  a per iod of 30 hours  of ope ra t ion  before  s h u t t i n g  
down t he  r e a c t o r  v o l u n t a r i l y .  The subsurface narmal oxygen-16 i so tnpe  i n  the  bulk 
of  t h e  c a t a l y s t  material obviously does not d i f f u s e  t o  the  su r face  at  or below t h e  
tes t  temperature  of 100°C. While the e f f i cacy  of the  su r face  l abe led  c a t a l y s t  has  
been demonstrated dur ing  cont inuous operat ion fo r  30 hours  at  t h e  e l eva ted  
195 
temperature, as well as other periods at lower temperatures, longer term evaluative 
tests are needed and will be performed during 1987. 
CONCLUDING KEMARKS 
To summarize our accomplishments and ongoing efforts involving oxygen isotope 
labels we have demonstrated supportive evidence for the existence of a carbonate- 
like intermediate species involving the catalyst and chemisorbed CO for the redox 
mechanism. We have discovered an economical method for preparing a catalyst for use 
in a closed cycle rare isotope pulsed carbon dioxide laser and have demonstrated its 
efficac in our surrogate test facility over test periods which would be comparable 
with 10 pulses at 10 pps. However, studies of longer duration are needed and the 
ultimate test should, of course, be carried out in a rare isotope pulsed carbon 
dioxide laser. We are also currently considering developing our own normal and rare 
isotope Pt/Sn02 catalyst coatings on high surface-area-to-weight ratio inert support 
spheres. 
8 
REFERENCES 
1. Freed, C.; ROSS, C.; and O'Donnell, R. G., J. Mol. Spec., 49, 439-453 (1974). -
2. Freed, L. E.; Freed, C.; and O'Donnell, R. G., IEEE J. Quant. Elect., QE-18, 
1229-1239, (1982). 
3. Hess, R. V.; Brockman, B.; Schryer, D. R.; Miller, I. M . ;  Bair, C. H.; 
Sidney, B. D.; Wood, G. M.; Upchurch, B. T.; and Brown, K. G., NASA TM-86415, 
1985. 
4. Sorem, M. S. and Faulkner, A., Rev. Sci. Instrum., 5 2 ,  1193-1196 (1981). -
5 .  Brown, K. G.; Sidney, B. D.; Schryer, D. R.; Upchurch, B. T.; Miller, I. M . ;  
Wood, G. M.; Hess, R. V.; Burney, L. G.; Paulin, P. A.; Hoyt, R. F.; and 
Schryer, J.: Laser Radar Technology and Applications, SPIE Proceedings, 663, 
136-144 (1986). 
-
6. NASA Langley Research Center Case No. LAR 13542-1-SB, U. S. Patent Application 
No. 847,304, June 1986. 
196 
React ant 8 
c180 
02 
02 + 02 
18 
16 18 
1802 + 16 02 
TABLE 1.- OXYGEN ISOTOPE LABEL STUDIES 
T ,  OC -Catalyst 
P ~ / S ~ " O ~  24-150 
P t / sn1602 25-225 
P t /Sn1 6 ~ 2  25-225 
~t /sn1602 > 350 
P t / ~ n l  6 ~ 2  100 
P t  /Sn1802 100 
~~~~ 
Product Y i e l d s  
16 18 c o o  
No Reaction 
No Reaction 
1 601 80 
85-903 C 1 8 0 2  
15-10% C 16 0 18 0 
P o 2  
197 


Rare isotope studies involving catalytic oxidation of CO over platinum-tin oxide

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server