31. K. GHARPUREY AND P. H. EMMETT
1182
m/e 45.--'I'his ion is the result of the formation of CHSf and neutral fragments of either CHs or CH, H. Considering the reaction to be C2H4S+ CHS+ CH3, a value of AHf+(CHS) = 271 kcal./ mole is calculated. This is a reasonable value in relation to the value of AHf+(CS) = 300 ked./ mole.g A value of 178 kcal./mole is calculated for AHr'(CHS) taking the neutral products to be CH? $- H. This latter value appears too low in relation to the value for AHf+(CS) and the value of AHf+(CH3S)= 222 kcal./mole.g m/e 46.-A value of 245 kcal./mole is calculated for AHf+(CIH2S) assuming the neutral fragment to be CH,. AHt+(CH2S) has not previously been determined, but our value appears reasonable in comparing it n-ith AHf+(CHS) = 271 kcal./mole, determined above, and AHr+(CH3S) = 222 kcal.1 mole. m/e 58.-Energetics indicate that the ion and neutral fraginents responsible for mle = 58 are C2H2S+ and 2H, respectively. The calculated AH( +(C,H,S ) is 261 kcal./mole, in agreement with the value of 265 kcal./mole given by Field and Franklin.g m/e 59.-This ion could only result from the
+
+
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ionization and dissociation of the parent molecule C2H4Sto give CzH3S+ H. The calculated AHt+(C2H3S) for this process is 230 kcal./mole. The relatively large (parent minus hydrogen) peak at m/e 59 for 70 e.v. electrons provides additional evidence for the weakened bonds in ethylene sulfide compared to those in ethylene oxide and ethylenimine. m /e 60.-This is the parent molecule-ion, C2H4S+. Lsing the observed ionization potential and the heat of formation of the parent compound, a value of AHf+(C2H4S)= 224 kcal./mole is calculated. It seems reasonable to assume that this ion retains its cyclic structure. Further theoretical considerations of the construction of the mass spectra of these three-membered heterocyclics will be given in more detail in a future publication.
+
Acknowledgment.-The authors wish to thank Dr. R. P. Ciula for providing the samples of ethylene sulfide. It is a pleasure to acknowledge the aid and comments of Dr. J. L. Franklin, and we wish to thank him for making available some of his data prior to publication.
STUDY OF THE HYDBOGENATIOS OF ETHYLENE OVER HOMOGENIZED COPPER-XICKEL ALLOY FILMS BY -11. K. GHARPUREY' XSD P.H. EMMETT The Johns Hopkins University, Baltimore, M d . Received January 6 , 1961
Heating t'hiri filnis of copper on nickel or nickel on copper a t 300" in hydrogen overnight, produced homogeneous filnis having the same color and the same activity for ethylene hydrogenation regardless of the order in which the metals were deposited. The !*elative reaction rates for ethylene hydrogenation per unit area a t 0" were 9.3, 13.9, 8.3, 8.8, 9.7 and 6.6 for pure Ki, and alloys containing 87.4,74.2,67.0, 63.0 and 18.3% nickel, respectively.
Introduction The activity of Cu-Ki alloy catalysts for the hydrogenaticm of ethylene was reported by Best and Russell2 to be several orders higher than that of a pure Xi catalyst. Hall and Emmett3 later reported a dependelice of the activity for this reaction on the pretreatment, for a series of alloy catalysts. When the catalysts, after reduction, were flushed with helium a t reduction temperature and then cooled 111 helium, the activity decreased with ai1 increase in copper content of the catalyst. On the other hand, if the catalysts were cooled in hydrogen, the actirity related to alloy composition showed two maxima (see Fig. l), and the initial additions of Cu to the S i increased the activity to nearly twice that of pure Ni. Hydrogen thus was shown to have a promoting effect on the activity of the alloy c.atalysts and a poisoning effect on thc activity of i,he pure Ni catalyst. These results were confirmed in substance by Pass4who studied a series of al1o:ys in the range 0-24y0 Cu. (1) National Chemical Laboratory, Poona, India. ( 2 ) R. J Best and F R'. Russell. J A m Chem. Soc , 7 6 , 838 (1954). (3) W' I) W K Hall, F. J. Cheselske and F E. Lutinski, International Confthience on Catal\sis, Paris 19h0 (b) J. G. Foss and H. Eyring, J . Pliys. Chem 62, 103 (1958), J G. I'oss, Ph.D., Thesis, Univ. of Utah, 1956.
July, 1961
HYDROGENATION OF ETHYLENE OVER HOMOGEKIZED Cu-Ni ALLOY
1183
vated by baking them in hydrogen for half an hour at' a temperat'ure of about 250-300'. This suggested the possibilithetiyo filaments were degassed by being heatid to a dull rvd heat. From this stage onwards, the reaction c~h:tl;nhcrhefore cooling was protected from t,he rest of the appariitus by a Dry Ice trap. The required qi1:tntitj- of Xi was evaporated by passing constant curwnt (-6.0 amp.) through the wire for certain lengths of time. The whole qutntity of Cu was evaporated off tlw JV-wire. The S i and the c'u mere evaporated one after thc, other to obtain possible extremes in surface rompoeitioii. On completion of the evaporation, the composite film \vas baked a t 300" in 5 cm. of H? overnight. -4fter :t dvse of E10:50mixture of ethylene and hydrogen (total pressure -1.5 mni.), was admitted, the course of the reaction \vas follo~wdwith a silicone oil manometer and :i travelling micro:rcope. The activity of the films wae normally mc:nsured successively at 0, -15, + l 5 and 0". Reactivation of the film between rims was carried out by pumping it for t r n minutes, baking it at about 230-300" in 5 cm. of hgdrogcln for 40 minutes, cooling it to reaction tcmperature, and primping it for 10 minutes. The fourth run, at O", a l ~ a y showed s the same acltivity 3s the first run. The surface area 'of the films \vas measured by the 13.E.T. method with rthaiilx (area :tssumed per ethane molecule = 20.5 A . Z ) a t liquid ox>.gen teinperitture. Pretreatment of the film wit11 c.thani. \ v w niadc at room temperature. The :iccur:icy of t h e ~ i i d : i e (:tre:L ~ mcasuren~entw t s estiimted to I)? :Lhout 10' < .
2 f'
,
I
10
20
30
I
,
40
50
60
70
80
90
I00
ATOM PER CENT Ni Fig. 1.-Hydrogenation of ethylene over Si-Cu alloy films: 0. present data (temp. 0"); A, data of Hall and Emmett (temp. 200°K.). The activity units for the two sets of data have been made to coincide for nickel.
111 the later experiments, however, the films were left overnight in 5 cm. of hydrogen a t 300" before measuring the activities. (It was fouiid that Curich films took slightly longer for homogenization.) The results of these later experiments are summarized in Table I and Fig. 1. The following points may be noted: (a) The specific activity a t 0" of a Cu-topped 87.4% S i film is decidedly higher (-1.5 X ) than that of pure Si film. (b) The specific activities of Si-topped 63% S i film and Cutopped 67(% S i film lie in the same range within experimeni a1 error of surface area measurement. (e) The activity of the Cu-topped 81.7% Cu film is higher than that of pure Cu by a t least two orders, and comparable to that of the pure Ni film. (d) The initial coppery appearance (on the outside) of the Si-topped films would disappear in a short time when they were baked at 300°, thus indicating substaiitial homogenization in this short time. (e) The above results are consistent with a good homogenization of the films throughout their thickness. Variation in the composition of the Results 1wo cxperinients were performed initially : film over thc surface i. expected due to directional 1. The activity of 12.5 m g . of S i film was deter- oon-uniformi ty of deposition leading to variation mined at a series of tempcrutures. 2.05 n-g. of Cu in the relative layer thickness of the individual then was e~\~aporatcd oii top of the reactivated film. metals. Such variations can of course he minimized The activily of this composite film wa,s measured with proper geometry, etc., of the eraporatioii :titer a half' hour bake-out in 5 cni. of hydrogen a t sct-up. (f) The above results follow similar trends nlmut 300" and was fouiid to I)c iicarly double to those of Hall and I h m e t t oil hydrogen-cooled that of the pure S i film. 2 . 12.5 mg. of S i \vas catalysts (Fig. 1). (g) l r o i n the activity detercvaporsted on top of u 2.05 mg. of Cu film. The tniiiationq at only three tempcraturcs, it is not coract,ivity of this film after s similar hake-out in r w t to deterrniiic the exact value of the artlvatiori hydrogen7 \vas fouiid to he equal to that of the r.iiergies. However. the activatioii energy appeared composite film in the first experimeiit where Cu t o lie in the range 6-8 kcal. /mole with no systematic variation with composition. This also i>in approxiwas evaporated ciii top of the Xi. The abo7:e runs indicated that a half hour treat- mate agreement with the results of Hall and Emment a t 300" n-as enough to homogenize the films. mett, though they found the activation energy to he more nearly 4 kcal./mole. (h) The rextion (7) The liorriogenizntion liere o b s e r r e d is not unrrasonahle when nab found to he zero order in ethylene and about cuiiipared to tiiat for 1000 A. Xi-Cu films recently reported by Belser 0.4 order in hydrogen over both pure Cu and 74.2% 1.7. A p p l . I'h!,s:'cs, 31, Xi2 (1Q1;O)l in vacuo at -400O. The present films nickel films. liad a n averagc tliickne.36 of 300 t o 500 A. r 7
MICHAEL HOCHAND HERRICK L. JOHNSTON
1184
TABLE I Mass
evapd. mg.
Atom % Ni
Metal deposited on top
Activity a t 0' (arbitrary units) ka
Surface Specific area, activity a t cm.2 O', k~ = k / A
11.77 100 Ni 4521 5-19 9.3 15.7 87.4 Cu 5815 418 13.9 15.7 74.2 Cu 4563 550 8.3 12.55 67.0 Cu 4452 509 8.8 11.3 63.0 Ni 6582 680 9.7 15.15 18.3 Cu 4563 695 6.6 15.8 0 CU 8.314 5300 7 ,028 a The k as h':re specified - lo6 k' where k' is defined by -dP/di = k' .PH*= k' (2P, 7 P0)/2. P is the total pressure a t tJimet, and POis the initial pressure. t is in seconds.
Summary The above experiments show a simple means of obtaining homogeneous alloy films for catalytic work. The results are in approximate agreement
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with those of Hall and Emmett both as regards the variation of activity with alloy composition and the near constancy of the activation energy. They suggest that the presence of unreduced oxide in the bulk catalyst does not appear to be essential to the rather high activities (compared to that of pure Ni) of some of the Cu-Ni alloy catalysts observed for the ethylene hydrogenation reaction. Acknowledgments.-Thanks are due to Dr. Colin T . H. Stoddart for many helpful djscussions. The appointment of &I,I
