viously restricted t o the narrow boiling distillate under examination, at least an insight into the complexity of this petroleum product has been gained. The work already done is only the first step toward the characterization of light catalytic cycle stocks. The data obtained on this narrow fraction have to be extended, and fractions containing other interesting compound types, such as indanes and Tetralins, indenes and dihydronaphthalenes, etc., must also be investigated. Since mass spectrometry is the only conceivable tool for the routine detailed analysis of the complex gamut of compounds present in light catalytic cycle stocks, the high voltage and low voltage calibration data at present available must be improved and extended, so that definitive procedures for analysis may be developed.
(4) Chamberlain, N. F., ASAL. CHEM.
ACKNOWLEDGMENT
The authors thank D. J. Krisher, J. L. Taylor, G. R.Taylor, R. K. Saunders, T. J. Denson, The0 Hines, and H. W. Kinsey for their valuable contributions to experimental phases of this work and N.F. Chamberlain for discussion of the SAIR interpretations. They thank B. J. AIair, X P I Research Project 6, for donating synthetic mixtures of methylfluorenes and methylphenanthrenes. LITERATURE CITED
(1) Aczel, Thomas, Bartz, K. W,, Lumpkin, H. E., Stehling, F. C., ASAL. CHEU. 34, 1821 (1962). ( 2 ) Braude, E. 8., Jackman, L. M.,Linstead, R. P., J . Chern. SOC.1954, 3568. Linstead, R. P., Ibid., (3) Braude, E. 8., 1954,3544.
31,56 (1959). ( 5 ) Claesson, S., d r k i v Kemi, Xineral, Geol. 23A. S o . 1119461. (6) Hastings, S. H., Johnson, B. H., Lumpkin, H. E., ASAL. CHEM.28, 1243 (1956). ( 7 ) Hibbard, R. R., Ind. Eng. Chem. 41,197 (1949). ( 8 ) Hirschler, A. E., Amon, S., Ibid., 39,1585 (194i). ( 9 ) Lipkin, 11. R., Hoffecker, W. A., Martin, C. C., Ledley, R. E., ANAL. CHEM.20, 130 (1948). ( I O ) Lumpkin, H. E., Johnson, B. H., Ibzd.. 26. 1719 11954). (11) &iair,'B. J.,'Forziati, A. F., J . Res. .\-atl. Bur. Std., 32, 165 (1944). (12) Morrison, D. C., J . Org. Chem. 25, 1665 (1960). (13) Tiers. G. V.. J . Phus. Chem. 62.
RECEIVEDfor review July 23, 1962. Accepted October 8, 1962. Division of Petroleum Chemistry, 141st Meeting ACS, Washington, D. C., March 1962.
Characterization of Aromatics in Light Catalytic Cycle Stock by Spectrometric Techniques Compound Types of the General Formula THOMAS ACZEL,
K. W.
BARTZ, H.
E. LUMPKIN,
Research and Development, Humble Oil & Refining
,This paper describes the identification of aromatic compound types in a narrow fraction of a light catalytic cycle stock. Particular emphasis is given to the part of the investigation concerned with the analysis of compounds in the CnH2n--14series. The data obtained indicate that these compounds are naphthenonaphthalenes, such as tetrahydroanthracenes, tetrahydrophenanthrenes, and benzindanes, and the corresponding ketones. Analytical evidence in support of the conclusions reported is discussed in detail. The investigation was carried out on sharp chromatographic fractions obtained b y alumina gel percolation of the aromatic portion of a narrow distillate (622' to 625' F.). Individual fractions were examined mainly by mass spectrometry, but ultraviolet, nuclear magnetic resonance, infrared, and catalytic microdehydrogenation techniques were also employed.
x EXTEXSIVE program has been recently carried out in our laboratories for the characterization of the major aromatic components in light
CnH2,,--12
and
CnH2,,--14
and F. C. STEHLING
Co., Baytown,
Tex.
catalytic cycle stocks. The experimental details on the separation and analytical techniques used in this lvork, as well as our findings concerning the nature of the compound types in the C,HZn- 16 and C,H?,-18 series, have been described in detail (1). I n brief, the former consisted of an initial separation on alumina gel and repercolation of the cuts which appeared to be of interest on the same medium. Feed for the repercolation, heretofore referred t o as Percolation A, consisted of cuts 10, 11, 12, and 13 obtained in the first step. Feed for Percolation B consisted of cuts 14, 16, 17, and 18. The two percolations can be considered therefore as contiguous. I n fact, they are slightly overlapping, as noticeable in Figure 1. This paper deals with the identification of the other major compound types present in the narrow distillate fraction analyzed. For convenience, these are referred to as belonging t o the C,H2,-12 and C,H2,-14 series, although some of them, of identical molecular weights, contain heteroatoms such as sulfur and oxygen.
DISCUSSION
C,H2,-1?Series. As expected, this series consists of two compound types, naphthalenes a n d dibenzothiophenes (6). The bimodal distribution of the parent peak intensities, plotted against cumulative weight per cent of the chromatographic fractions, in the - 12 series is shown in both Figures 1 and 2. The separation between the Cl5 naphthalenes and the c13 dibenzothiophenes of the same molecular weight is particularly evident in Figure 2, as well as the carbon number separation, in order of decreasing molecular weight, achieved for the naphthalenes in Percolation A. These identifications are substantiated by the data shown in Figure 3, in which the characteristic fragment peaks are plotted. Fragment peaks characteristic of alkylnaphthalenes are predominant in Percolation A, coinciding with the first maximum in the parent peak plot, while the intense peak a t m/e 1 9 i , attributed t o dibenzothiophenes, coincides with the maximum in Percolation B. The presence of a compound of molecular formula CI3HlaSis proved also by VOL. 34, NO. 13, DECEMBER 1962
1821
the low voltage isotopic ratios reported below:
Exuerimental c u t No. (Percolation B) Peak height lg9 Peak height 198'
more abundant C13 carbon isotope (8). The difference, between the average isotopic value found and the theoretical value for ClaHloS,of 0.27%, is higher than exaected. and is urobablv due to the recording system rather than to a mixture of the hydrocarbon and sulfur compound, as high isotope ratios are also observed in other series.
Heteroatoms can be detected from isotopic ratios because of the relatively
+
Theoretical CISHI1 CIJHloS
15
20
25
30
35
15.29
15.12
15.44
15.21
15.30
16.49
15.00
I"
c15
-
c,s
c,, ClE
c 401-
!
Percolation A
Ci',"""
B
I\, !
c $
Percolation
-___-.
1
U
L
w33 -
4 O
r w3
0
2 20+ w
z
0
10-
00
WEIGHT PER CENT
i ikk?
1,
/5
io
25
30
35
40 4a'&
CUT NUMBER.
Figure 2.
CnH2,,-12
5
series
l o w voltage analysis
1822
ANALYTICAL CHEMISTRY
IO
115
io
25
3C
35 36
2 1-
4 0 4 2 44
lI_l l d l i
-I
-
-$
W
h
,
1
,
14 . . . . . . . . . . m/e 155 _.-_____ m/e 169--m/e l83--.-m/e 197-
m,c
,
I , ,
3567
11
15
,
20
Percolation A
I
25
33
I
35
J
40 44 CUT h
Figure 3.
1
I
I
5
10
15
20
25
30
35
4&%4
IER
C,H2,-12
series
Selected fragment peaks
two and possibly three compound types in this series, revealed b y t h e maxima in t h e plots of concentrations of individual carbon numbers us. weight per cent sample off t h e chromstographic column (Figure 4). Con-
Ultraviolet -pectra obtained on the above listed fractions contain characteristic dibenzothiophene absorption bands, in particular at 325 mp. C,,H2n-14Series. Mass spectral dat:r. indicate thp presence of at least
centrations u ere determined by low voltage analysis ( 7 ) . Since only approximate calibration data were available, these should be regarded only as indicative of trends, The first compound type is concm-
, Percolotion A
l
Percolation B
~~
**\
/'
'\
Y)
0
zt 2 0 -
00
Figure 4.
CnH2n-14
series
Low voltage analysis
VOL. 34, NO. 13, DECEMBER 1962
0
1823
m/,
165
m/r 167 m/e 181 m/e 195
m/e 209
.......... -.-
Percolation A
----
Percolation B
-
L W L
Y
0
52
2
1503-
I In ii
I
3a
1000-
0 W 0 W V
L
8 5000
a
0-
0 WEIGHT PER CENT
WEIGHT PER CENT
I
'
1 / 1 1 35"7
I
I
11
15
I
I
20 25 CUT NUMBER
I
I
I
Ill
30
35
40
44471
Figure 5.
CnH2n-14
I 5
I 10
I 15
I
I
I
I
Ill
20
25
30
35
40 4 4 42
CUT NUMBER
series
Selected fragment peaks
trated in fractions A-7 through A-40. The maxima for the individual carbon numbers appear again in order of decreasing molecular weight. The appearance of a second compound type is indicated by a second series of strong maxima in the C17 and Cle curves, respectively, a t A-44 and B-5 and at B-10. Fractions $-44 and B-5 are equivalent because of the overlap in Percolations A and B. The high voltage fragmentation pattern (Figure 5) offers sparse clues for the identification and differentiation of the two compound types. The most abundant peaks can be attributed to a loss of a methyl group from the molecule ion, indicating the presence of a t least two methyl substituents on the nucleus and possible nuclear molecular weights of 168 and 182. The two compound types were identified by auxiliary spectral techniques. The investigation was focused primarily on the fractions in which maximum concentrations of the C,&n-14 compound types were indicated by mass spectral data. First Compound Type. Examination of t h e high a n d low voltage mass spectra and precise isotope ratio measurements (Table 11) indicated t h a t this compound type is a hydrocarbon of molecular formula CnH2n--14, as expected, with a nuclear molecular weight of 168 or 182. NMR spectra obtained on fractions A-25 and A-35 contain absorption
1824
ANALYTICAL CHEMISTRY
bands a t chemical shifts characteristic of Aromatic H CH2 t o an aromatic ring CHI 01 t o an aromatic ring CH, p or p 2 t o an aromatic ring CH3 attached to an alicyclic ring (Y
This evidence is compatible with the following nuclear structures: Perinaphthane, nuclear MWl68
a & a
lJ::4Tetrahydroanthracene, nuclear MW
lJ2,3,4-Tetrahydrophenanthrene, nuclear MW 182 Benz [flindane, nuclear MW 168
n
Ben2 [elindane, nuclear MW 168 Kuclear magnetic resonance data definitely exclude the presence of acenaphthenes
6
5
although this compound type has been considered one of the major components in middle distillates. This contention is based on the fact that neither fraction A-25 nor A-35 has an NilIR absorption band a t about 6.8 to 7.0 r (tetramethylsilane standard = 10.0 p.p.m.). The methylene groups in acenaphthene absorb a t 6.85 7, and methyl substitution in the 3 or 8 position would be expected t o cause the ortho methylene resonance t o shift upfield from this value by about 0.15 p:p.m. The K'MR spectrum of A-35 given in Figure 6 shows no significant absorption in this range. It might be proposed that if the 1 and 2 carbon atoms in acenaphthene were each replaced by two methyl groups, no resonance at 6.85 r would be obtained. Assuming that the C,H2,-14 species in A-35 are acenaphthenes, then the mass spectrometric data indicate an average of 3.8 carbon atoms in side chains, predominantly as methyl groups. The intense absorption between 7.5 and 8.0 7 indicates that the substituents are largely attached t o aromatic rings; hence the 1 and 2 carbon atoms of acenaphthene could not be exhaustively methylated. The KMR spectrum of A-25 is very similar to that of A-35, except that the band assigned to CHS's attached to alicyclic ring is relatively more intense in the former fraction. This indicates that the decrease in the average carbon number observed by mass spectrometry in proceeding from A-25 to -2-35 is
Frequency: Solvent: Scan Rote: Int. Std.: Hi: Date:
60 mc CCI4 2 cps/s TMS 0.06 mi I I i gauss 6-13-61
BAND a b c d
e
ASSIGNMENT ArH C H 2 a A r and i n nophihene ring CH3QAr GH2P
CH3
/-
and P2Ar and in naphth'ene r i n g on nophthene r i n g
1NTEG R A L
T MS
L Figure 6.
caused primarily by a decrease in the number of alicyclic methyl groups, the aromatic methyl content remaining approximately constant. Ultraviolet spectra obtained on fractions A-25, A-35, and A-40 (Figure 7) are broadly compatible with those published ( 3 ) for the five compounds depicted above. They are consistent with a perinaphthenic type structure, with the exception of an absorption band a t 255 mp present in fractions A-35 and -4-40 and a weak band a t 326 mp observed in all three fractions. The other suggested structures give rise to bands a t 326 mp, but not to the one at 255 mp. In addition, they present neak bands in the 300 to 320 mp region not detected in these fractions. The intensities of the ultraviolet bands attributed with certainty to the first compound type (at 233 and 326 mp) follow the same variation pattern through the fractions examined as the corresponding mass spectrometric parent peak intensities. Since the absorption band a t 255 mp is increasing in intensity from fraction A-27 to fraction A-40, it can be ascribed to the second compound type in this series. The band a t 282 mp is probably common t o both compound types. The presence of moderate concentrations of tetrahydroanthracenes and
Chemical S h i f t , p p m NMR spectrum of cut A-35
tetrahydrophenanthrenes in the above fractions has been verified by catalytic microdehydrogenation techniques. This approach has been described by Keulemans and Voge (4, Rowan (9), and Cousins, Clancy, and Crable (2). The dehydrogenation is carried out in a stream of carrier gas and the effluent products are examined by gas chromatography. According to their data, the compounds containing cyclohexyl rings are dehydrogenated to the corresponding aromatics, while the cyclopentyl rings remain essentially unaltered.
Table 1.
Slight modifications of the technique allowed its application to the problems encountered in this work. The equipment consisted essentially of a borosilicate glass reaction tube heated a t 700" F. containing a platinum on A1203 catalyst, connected on one side to a supply of the carrier gas (helium) and on the other to a cold trap. Reaction products collected in the cold trap were transferred to the mass spectrometer for analysis and the data obtained compared with those recorded prior t o dehydrogenation. The use of mass
Dehydrogenation Data
MS analysis by low voltage method, wt. yG Cut A-13 Cuts A-27, -28, -29, -31 Product A Feed Product A
A.
Compound type CnHzn- 6 CnHzn- B C,H,,- i n C,H,,- ;; CWHpn- 14 C J L - 16 CnHzn- 18
Feed 10.9 2.8 ... 45.5 36.6 4.2
...
12.8
+1.9 -2.8
3.8 1.8
50.6 22.4 7.1 7.1
+5.1 -14.2 +2.9 +7.1
18.0 70.8 5.6
... ...
Found after dehydrogenation Anthracenes (at 377 mp) Phenanthrenes (at 255 mp) Total CnH2,-
...
...
...
12.2 2.5 0.8 31.8 31.1 13.0 8.6
$8.4 +0.7 t0.8 +'13.8 -39.7 +7.4
+8.6
B. Differential UV data, weight 70Cut -4-13 Cuts A-27, -28, -29, -31 1.5 7.2 8.7
3.3 13.1 16.4
VOL. 34, NO. 13, DECEMBER 1962
1825
spectrometry was warranted by the complexity of the materials under investigation. Experiments with pure compounds and literature data indicated that tetrahydroanthracenes and tetrahyrlrophenanthrenes dehydrogenate t o anthracenes and phenanthrenes belonging to the C,H2,- 18 series, while benzindanes and perinaphthanes either remain unaffected or dehydrogenate a t the most t o compounds in the C,H~,-16 series. The presence of anthracenes and phenanthrenes and the simultaneous decrease in the C,H2,-14 types detected by 110th mass spectrometry and ultraviolet, as shown in Table I, in the dehydrogenation products of cuts A-I3 and of a blend of cuts -4-27, -28, -29, and -31 indicate therefore that these fractions contain both tetrahydroanthracenes and tetrahydrophenanthrenes. Mass spectrometric data also bhow a n increase in the -12 and -16 series. These may be attributed to cracking of the -14 types to naphthalenes and to the dehydrogenation of perinaphthanes or benzindanes. The unreacted material in the C,H2,-14 series consists probably of benzindanes, although incomplete dehydrogenation of the other types cannot be excluded completely. Second Compound Type. The material giving origin t o t h e second series of maxima in Figures 4 and 5 is a n oxygenated type, possibly one of the follorring structures, appropriately substituted with methyl groups to account for their molecular weights from 210 to 224. Perinaphthanone, nuclear M W 182
a \
/
Benzindanone, nuclear MW 182
0
Tetrahydrophenanthrenone, nuclear P\IK 196 Tetrahydroanthracenone, nuclear MW 196 The experimental evidence in support of these structures furnished by exact mass spectrometric isotopic data, high resolution mass measurements. infrared, and ultraviolet spectra, is discussed below. The presence of a similar class of compounds, fluorenone?, in Wilmington petroleum has been reported recently by Latham, Ferrin, and Ball ( 5 ) . The measurement of isotope ratios from mass spectral data can be a very powerful technique in indicating the presence of a heteroatom in a mole1826
ANALYTICAL CHEMISTRY
I
i
i
i I
i i
i !
!
I
i
i
!
6 1
t
!
-
5 s
!
I '
80'/
,
Y
4
I
I
6 01
~3 40;
2
20
I
0
2tO
220
Figure 7,
230
240
250
260
270 280 290 300 WAVE LENGTH (MILLIMICROYSI
310
320
330
410
350
0
Ultraviolet spectra of cuts A-27, A-35, and A-40 in iso-octane
cule. The first clue that the second peak in the C,H2,-14 series was an oxygenated compound came from examining the ratios of the peak heights of masses 211 and 210 (CX) in the fractions shown in Table 11. The isotopic value at R-1 is in very good agreement with that expected for a Cl6HI8hydrocarbon; the value a t B-5 is intermediate; those for B-10 and B-15 are much lower. The isotope ratios for the latter two fractions check extremely \\-ell with the theoretical value of 16.47 for an oxygenated compound, C1bH140. This material is thus believed t o be an oxygenated compound. Fraction B-5 is a mixture of the hydrocarbon and the oxy-compound and the isotopic data are intermediate for this fraction, as Iyould he expected for a mixture. The isotopic data mentioned above, together with similar data for other fractions, are given in Table 11. I n examining these data one should bear in mind that an unexplained bias of about +O.l to +0.3yGhas been experienced recently in all of the isotopic data obtained on our instrument. Thi? is exemplified by
the measured isotopic values for the well identified C13 dihenzothiophenes (C,H2,- 12 series). Exact mass measurements, carried out on a CEC Model 21-110 high resolution mass spectrometer of the Mattauch design also confirmed the presence of oxygenated compounds in these fractions. Data obtained on fraction B-12 are reported below. Nominal mass 210 224
Theoretical Measured n1m5 for mass ClEH110 CI6H18 210 173 210 171 210 207 C16H160 C17& 224 187 224 191 224 227
The infrared spectrum of fraction B-10 contains two sharp carbonyl bands. One at 1682 em.-' is believed due to a conjugated carbonyl and the other a t 1725 em.-' is attributed t o a nonconjugated carbonyl. Examination of the ultraviolet spectra of several fractions containing the oxygenated material reveals that each has a weak, yet distinct, maximum at
Figure 8.
Ultraviolet spectra of cuts B-1,
255 mp. This absorption band first appears in the ultraviolet spectrum of A-35 (shown in Figure 7 ) , and is consistent with the appearance of the Cp oxygenated compound, shown by the mass spectrometric data in Figure 4. T h e same 255-mp band also appears in A-40, and in the fractions of the B percolat,ion through B-15, as shown
Table
c
Yo.
20
CIS Cl8
(317
17.69 19.07
B-5,8-10,and B-15 in iso-octane
in Figure 8. The initial appearance, general variation of intensity, and disappearance of the ultraviolet features in the chromatographic fractions agree well with the mass spectrometric plots. A complete interpretation of the data is hindered b y the appearance in these fractions of two other compound types, dibenzothiophenes and dihydronnthra-
Isotope Ratios from MS Low Voltage Spectra
II.
C,,H,,-M series Experimental Percolation A. Fractions 25 30 35 40 16.72 16.67 16.92 17.86 17.87 17.81 17.84 18.03
Theoretical Oxygenated Hydrocarbon compd. 16.46 15 36 17.57 16.47 18.68 17.5s
Percolation B. Fractions CIS C18 c 1 7
1
5
10
15
16.69 17.69
16.76 17.01
16.50 16.48
16.58
17.60
16 46 17.57 18 68
15 36
16.47 17.58
cenes. Although not quite sufficient by themselves, the data obtained are consistent with the conclusions deduced from mass spectrometry and the infrared spectra, which clearly indicate that the second compound type found in the C,H2,1-14series is an aromatic ketone. I n addition t o the evidence discussed above, the similarity of the high voltage mass spectrum t o that of the first compound type indicates an analogous ring structure-Le., the structures of ketonaphthenonaphthalenes shown ab07 e. CONCLUSION
The investigation discussed. together with the data contained in the accompanying paper (I), has led t o a radical change in our ideas of the nature of certain compound types in light catalytic cycle stocks. W e deem particularly significant the proof5 obtained on the absence of acenaphthenes, a t least in the narrow distillate fraction studied. The discovery of a n olygenated compound type in rclntiwly high concentration is also mesningful. VOL 3 4 , NO. 1 3 , DECEMBER 1962
1827
The gathering of the detailed information obtained in the course of this m r k was made possible by the sharp Beparations achieved and the integration of complementary analytical techniques and tools. The role of mass spectrometry in Particular was s h o ~ nto be extremely valuable, both in indicating the presence of different compound types, and thus pinpointing the frattions t o be subjected t o further analysis, and in identifying the components contained in the same fractions. The data obtained by the use of high resolution mass spectrometry illustrate well the power of this technique.
ACKNOWLEDGMENT
We thank P. J. Klaas, formerly of Esso Research and Engineering Co., for the precise mass measurements obtained on the high resolution mass spectrometer. We also thank D. J. Krisher, J. L. Taylor, G. R. Taylor, R . K. Saunders, T. J. Denson, The0 Hines, and H, x n s e y for their valuable contributions t o experimental phases of this nTork.
w.
LITERATURE CITED
(1) Bartz, K. W., Aczel, Thomas, Lump-
kin, H. E., Stehling, F. CHEW34, 1814 (1962).
c.,
ANAL.
(2) Cousins, L. R., Clancy, D. J., Crable, G. F., Ihid., 33, 1875 (1961). (3) Friedel, R. A,, orchin, ST,,c catalog of Ultraviolet Spectra of Aromatic Compounds," Nos. 213, 214, 215> 216,
(47i",";ig!F'!2g2:, H. H., J . Phys. Chem. 63,476 (1959).
( 5 ) Latham, D. R., Ferrin, C. R., Ball, J. S., ANAL.CHEM.34, 311 (1962). ( 6 ) Lump% H. E., Johnson! B. H.1 Ibid., 26, 1719 (1954). (7) ~ ~H. E., hid,, ~ 30, 321 ~ (1958).k (8) Lumpkin, H. E., Sicholson, D. E., Ihid., 32, 74 (1960). ( 9 ) Rowan, Robert, Ibid., 33, 658 (1961).
RECEIVEDfor review dugust 20, 1962. ilccepted October 22, 1962.
An Adsorption Flow Method for Specific Metal Surface Area Determination HANS L.
GRUBER
Research and Development Departmenf, The Aflantic Refining Co., Philadelphia, Pa.
b A slug flow
CO chemisorption method is described for the determination of metal dispersion or specific metal surface area of multicomponent catalysts whose metal area correof the sponds to about only 0.1 to 1 A stream of total surface area. helium is passed over the reduced catalyst sample and a known amount of CO is injected in front of the catalyst bed. The amount of CO not adsorbed and therefore remaining in the helium stream is measured by a thermal conductivity detector. The amount of CO adsorbed is obtained b y difference. The effect of temperature, particle size, slug size, and flow rate is discussed. The method was applied extensively to platinum-on-alumina reforming catalysts. As an example, the decrease of platinum dispersion due to sintering is shown.
%
W
commercial importance of supported metal catalysts of low metal concentration, the physical structure of such catalysts, especially their specific metal surface area, has become of considerable interest. Several investigations have recently been described in the literature (1, 6-9, 19) using adsorption techniques t o measure specific metal surface area, even if this metal area amounts t o about only 1% of the total surface area of the catalyst. Most of this nork was carried out in static, volumetric adsorption systems. Because of the high vacuum technique involved, the static 1828
ITH THE INCREASISG
ANALYTICAL CHEMISTRY
method, although probably the most accurate one, is inherently slow and tedious to operate. We have, therefore, in addition to our volumetric procedure described previously (6), developed a fast, dynamic method free from the disadvantages of the static high vacuum adsorption procedure. It can also be used to determine metal surface area on a routine basis. Although such a flow method might be open t o more experimental errors, the gain in speed and simplicity would be worth a certain sacrifice in precision. A great variety of different flow systems has been used in the past to study adsorption of gases on solids and t o measure surface area as reviewed in detail by Brunauer (2) and by Orr and Dallavalle (11). Cremer and Roselius (5) have first pointed out that the chromatographic technique can be used not only t o separate and identify gases or vapors, but also to characterize adsorbents or catalysts. The surface area of the adsorbent and the heat or free energy of adsorption of the test gas used can be calculated from gas chromatographic data, such as retention time and volume (3, 4). Kelsen and Eggertsen (10) have recently developed a simple flow technique t o measure B E T areas. A mixture of helium and nitrogen is passed over the sample at - 190' C. until adsorption equilibrium is established. The sample is then allowed t o warm to room temperature, and the amount of gas desorbed is measured b y a conventional detector-e.g.,
a thermal conductivity cell. Hughes, Houston, and Sieg (8) were the first t o study specific metal surface area of supported bifunctional catalysts b y chemisorption of carbon monoxide in a flow system. The amount of carbon monoxide adsorbed from a helium carbon monoxide mixture was determined by frontal analysis of the effluent gas stream. The carbon monoxide concentration was measured with a Geiger counter, using radioactive tagged ~ 1 4 0 .
The method developed here utilizes the specific, irreversible adsorption of a test gas on the metal surface. A stream of helium is passed over the reduced catalyst sample and then through a thermal conductivity cell. A known amount of a test gas is injected as a slug into the helium stream in front of the catalyst bed. I n passing over the catalyst, part of the gas is adsorbed b y the metal surface. The amount of gas remaining in the helium stream is measured by the thermal conductivity detector. The difference between the amount injected and the amount recorded by the detector is due t o adsorption on the catalyst and is, therefore, a measure of metal surface area. EXPERIMENTAL
Apparatus. A schematic diagram of t h e flow adsorption apparatus is shown in Figure 1. A constant stream of carrier gas is obtained from a positive displacement pumping syst e m as described by Hughes, Houston,
~
