PRODUCT REVIEW A ctivation of Catalytic Alumina Jc Faise M. Parera w i t a d de Ingenie& L?u;mia, Universidad Nacional del Litoal, SSinta Fe, Argentim
Jose M. Parera is currently professor a t the Chemical Engineering Department, Uniuersity of Litoral, Santa Fe, Argentina, where he graduated in 1958. His primary interests lie in heterogeneous catalysis. He is the author of manv DaDers nublished in international
Introduction Activated aluminas are widely used in industry. They are transition forms, produced by heating hydrated aluminas. By calcination of the activated aluminas a t very high temperature a chemically inert material is obtained. Activated aluminas are commonly used as desiccants for gases and liquids, as catalysts, and as catalyst supports. In addition to eliminating water from gases and liquids, they are used also to eliminate other contaminants or poisons in several substances as well as traces of fluorides, chlorides, SH2, etc. The most important forms of catalytic aluminas are the yand 7-aluminas. They are used as catalysts mainly in dehydration reactions (alcohol dehydration, alcohol and amine reactions, etc.) and in the Claus process to convert SH2 to ulfur. Alumina has no activity for hydrocarbon reactions which need a carbonium ion because it has no proton acidity. Nevertheless, if H F is added to alumina it presents protonic acidity and it is able to catalyze hydrocarbon cracking reactions. Presently one of the more important applications of ysnd 7-alumina is to support catalysts in naphtha reforming snd hydrocarbon isomerizations (Cd, CS,CS,xylene). Here the catalyst is a hifunctional one; the noble metal is supported on alumina where aciditv . is .nromoted with chlorine comDounds. [n this way the promoted acidity of alumina is able to catalyze Iisomerization and yet not able to promote cracking. As an inert support alumina has the advantage that it is not reduced by hydrogen, has high area, and a high melting point. y-Alumina is used as a carrier for nickel or platinum catalysts Iin hydrogenation reactions. As a support or added in very ~ 1 1 , I .>.. small amounts as a promoter (ammonla syntnesis), IC reauces 1;he velocity of heat sintering of metal crystals providing high 1zatalyst stability. When used as a support in reactions where icidity can provide parallel reactions i t is neutralized with ilkali. Another important use is in hydrodesulfurisation Nherehy cobalt and molybdenum oxides are supported on ilumina. Similar catalysts are able to hydrogenate olefins and iiromatic rings in gas-oil, lubricant oils, etc. The calcined alumina is an inert sinterized material that :orresponds to the OL form. It is used as a low area catalyst support (as in the case of nickel in steam reforming of hyIrocarbons a t very high temperature) or as an inert material catalyst bed supports, refractories, ceramics, abrasives). Because of the importance of activated alumina in the pe.roleum refining and petrochemical industries, it was the )hject of many studies. Pines and Haag (1960)established that I ictivated alumina shows intrinsic acidity, to which the cata1ytic activity was attributed. Since then, these authors and rthers performed several studies on the use of alumina in al:oh01 dehydration reactions and on the reaction mechanisms, IS quoted by Pines and Manassen (1966). MacIver e t al. (1963) ,tudied the surface properties of the y and ‘1 forms and vlacIver et al. (1964) investigated their catalytic properties. Many authors, including Munro and Horn (1935), Euken Ind Wicke (1944), Antipina and Frost (1948), Brey and ~~~~
~~~
~~
~
I
..
.
Four commercial aluminas were heated at 200-800 OC to study modifications in specific surface area, acidity, and catalytic activity for methanol dehydration and other acid-catalyzed reactions. This was also followed by DTA and TGA. Activity and total acidity changed similarly, showing both one maximum in y-alumina and two maxima in 7-alumina. The surface condition after heating (dehydration)determines catalytic activity. By rehydration after heating a new catalytic surface is obtained. The catalytic active surface appears to be a complex between reactants and alumina surface, which activity is nearly proportional to the acidity of the former bare surface. This function of the particular alumina is regulated by the sodium ratio.
Krieger (1949), Taylor (1949), Hindin and Weller (1956), Topchieva et al. (1959), Pines and Haag (1960), Echigoya and Shiba (1960), MacIver et al. (1964), Steinike (1965), and Rosolovskaya et al. (1966), have studied the physicochemical changes which are produced when alumina is heated, relating them to the water content. They found that there is an optimum amount of water, and therefore an optimum activation temperature, to which a maximum in catalytic activity for various reactions was found. Acidity also varies with the activation temperature, and it usually changes in a similar way to catalytic activity, as shown by Bailey e t al. (1958),Tanabe and Katayama (1959), Echigoya and Shiba (1960), MacIver e t al. (1963), Rosolovskaya et al. (1966), Bohl and Rebentish (1966), and Flockhart et al. (1968). Parry (1963) stated that the acidity of alumina is strong Lewis type and that if there are protons, they are very weak. I t was found by Schwab and Kral(1965), Tanabe et al. (1968), Rhee and Basila (19681, and Yamadaya et al. (1973) that the alumina surface in addition to acid sites has basic ones and that the acidity and basicity values follow similar variations. Tanabe et al. (1968) show that acidity and basicity both have a maximum in the alumina which has the greater catalytic activity. Alumina shows redox properties (Flockhart et al. (1968)), it takes electrons from aromatic hydrocarbons, such as perylene, and gives electrons to stronger acceptors, such as tetracyanoethylene. The preheating temperatures to which the electron accepting or donating properties have their maxima do not agree each other or with that of the maximum acidity. When alumina is heated to a high temperature, a decrease in the surface area takes place, as shown by MacIver et al. (1963), Brey and Krieger (1949), Hindin and Weller (1956), Echigoya and Shiba (1960), Bailey et al. (1958), Flockhart et al. (1968), Rhee and Basila (1968), de Boer e t al. (1963), Boreskov et al. (1963), and Vinnikova e t al. (1968). The differential thermal analysis shows several endothermal peaks, particularly one around 500 “C which corresponds to the irreversible dehydration of the y monohydrate stated by Say and Rase (1966). Several hypotheses have been proposed with regard to the nature of the active sites on the alumina catalyst and the mechanism of dehydration of alcohols. Cornelius et al. (1955) pointed out that the loss of OH surface groups as water produces highly strained A1-0-A1 bonds, which have a great chemical activity and on which water can be adsorbed regenerating both OH groups. They proposed that the strain disappears when water or another substance which dissociates is adsorbed. Something similar was expressed by Hindin and Weller (1956). Peri (1961) proposed that the loss of water takes place by means of a random combination of two neighbor surface OH groups, generating an 0 2 - ion in the outlet layer and an exposed aluminum ion in the lower layer, which is a Lewis acid. Afterwards, Peri (1965) presented a model for y-alumina dehydration which involves the creation of defective sites followed by the migration of surface groups or ions when the great dehydration requires a high temperature. Pines and Pillai (1960) established that the dehydration of alcohols takes place through a concerted mechanism which
involves an acid and a basic site. Knozinger (19681, according to his studies using infrared spectroscopy and kinetic methods, postulated that there are three kinds of sites which are necessary for the dehydration of alcohol to ether: incompletely coordinated aluminum ions (where an alcoxide is formed by dissociative adsorption of the alcohol), oxygen ions, and OH groups (in these groups alcohol molecules are adsorbed by H bonds). On the other hand, for methanol dehydration, the dissociative adsorption of methanol and the combination of the methoxy groups to give off dimethyl ether have been proposed by Soma et al. (1969) and Parera and Figoli (1969). The objective of this paper is the study of the activation of catalytic alumina by heating to have knowledge on the formation of the active surface and its properties. Four quite different commercial aluminas were used; they were activated by heating a t different temperatures and some of them were rehydrated and reactivated. The catalytic activity for dehydration of methanol and related acid catalyzed reactions, the acidity, and the specific surface area were determined in the different materials obtained. The physicochemical properties were compared with the differential thermal and thermogravimetric analysis of each catalyst. Actually, the terms “activation”, “heating” or “preheating” mean a reheating, because all of the commercial aluminas were previously heated by the manufacturers. They were materials received four or five years before being used and most of them were partially rehydrated during the storage period. Experimental Section Reactants. Methanol, 2-propanol, and methylaniline were B.D.H. pure grade. Methylaniline was vacuum distilled before use. Catalysts. Four commercial aluminas were used: (1)Alumina 992-C, supplied by Davison Chemical Division, W. R. Grace and Co.: composition: 0.002% NazO; 0.01% FeiO3; 0.009% S O ? ;3% HLO;q type; powder retained: 15%on 30 mesh (U.S.A.) and 65% on 200 mesh. (2) Alumina T-126, supplied by Girdler Catalyst, Chemetron Corp.; it has a very low sodium content (similar to 992-C), y type, pelleted in 4.3 X 5 mm cylinders, heated at 480 “C. (3) Alumina F-110, supplied by Aluminum Company of America; composition: 92-94% A120
f 800
w
L 0 400
TEMPERATURE, 'C
0
Figure 8. Acid strength distribution and catalytic activity as a function of heating temperature for y-alumina F-110. Standard catalytic activity run: temperature, 230 "C; catalyst, 20 g; feed of liquid methanol, 25 ml/h.
0 pKo'-30
;=.
aoo
-04
a w
5 y
400 -
-03
>
200
LO0 630 800 TEMPERATURE, 'C
1(
Figure 10. Influence of rehydration and reheating on catalytic activity of alumina F-110. Standard catalytic activity run as in Figure 8. Curve 1, activity of catalyst heated at plotted temperature (same data as Figure 8 ) ; 2, catalyst heated a t 545 "C, rehydrated and reheated at plotted temperature; 3, catalyst heated at 380 "C, rehydrated and reheated a t plotted temperature; 4, catalyst heated a t plotted temperature and before the run rehydrated at 230 "C. Points A, three catalysts, one heated at 320 "C, one the former rehydrated and reheated at 320 "C, other the former rehydrated and again heated at 320 "C; B, like points of curve 4 and reheated at 515 'C; C, catalyst B after use and heated again at 515 "C; D, like points of curve 4 and kept 1 week in dry air before the run; E and F, like points of curve 4 and kept 1 week in dry and saturated air, respectively; points G, like points of curve 2 and kept 3 months in saturated air; H, catalyst heated at 685 "C and rehydrated at room temperature during 15 days; I, same as H and reheated at 685 O C .
5 w
E
I, W
E 0
u
-02 200 -
z'-
P 0
-01
0
rT)C
60TEMPERATURE,
-
800
lo
1000
O C
Figure 9. Acid strength distribution and catalytic activity as a function of heating temperature for alumina KA-201. Standard catalytic activity run: temperature, 230 'C; catalyst, 20 g; feed of liquid methanol, 25 ml/h.
Catalytic Activity. Figures 6-9 besides acidity show the catalytic activity for methanol dehydration in the standard run at 230 "C, expressed as the rate in ml/h of dimethyl ether reduced at normal conditions. From the figures it can be seen that the activity has remarkable variations in zones where the value of the specific surface area undergoes small changes. The activity follows a similar trend as the total acidity (stronger than pK, = 3.3). This is true for the catalysts that have only weak acidity (like those heated to less than 400 "C and KA-201) or for the ones that have mainly strong acidity (preheated a t temperatures close to the maximum). The temperatures for the maxima of activity agree aproximately with those for the maxima of acidity. The catalytic activity of 7-alumina is a little greater than that of y-alumina, as was already quoted by MacIver et al. (1964), de Boer et al. (1967), and Hall et al. (1964), but the difference is even greater between T-126 and F-110, both y, due to the difference in sodium content. 238 Ind. Eng. Chem., Prod. Res. Dev., Vol. 15,No. 4, 1976
Influence of Rehydration in Catalytic Activity. Alumina F-110 shows a sudden increase in catalytic activity when the heating temperature exceeds 450 "C, and a maximum at 545 "C. The great increase coincides with a similar increase in acidity and with the irreversible loss of water that show the DTA and the TGA. In order to see the influence of this loss of water and of the rehydration in the catalytic activity, samples of catalyst were first heated at 545 "C, and then rehydrated at room temperature during 15 days in a flask with air saturated with water vapor. Then they were heated at different temperatures lower than 545 "C and the standard activity runs a t 230 "C were performed. All of the samples show greater activity than the ones heated to the same temperature which were not previously heated to 545 "C and rehydrated. This is shown by the points of curve 2, Figure 10, plotted at the temperature of the second heating. For comparison, the curve of catalytic activity in Figure 8 is reproduced in Figure 10 as curve 1. As can be seen, the heating a t 545 "C, rehydration, and reheating increased the activity. T o see if the rehydration had little effect when heating at temperatures below the one of the irreversible loss of water, several samples of F-110 were heated a t 380 " C . Then they were rehydrated at room temperature as quoted before, heated at different temperatures lower than 380 "C, and finally the catalytic activity was measured. The activity, plotted at the temperature of the second heating, produces curve 3 in Figure 10, which shows a small difference with the original material heated only once (curve 1). Other experiments also showed that this rehydration, made more than once, had little effect on the catalytic activity. Three samples were heated at 320 "C: one was directly tested for activity, the second was rehydrated, heated again at 320
"C and tested, and the third one was rehydrated and reheated twice. The three have similar activities (points A), which means that for F-110 a t temperatures below that of the great loss of water, rehydration and dehydration by reheating are mostly reversible. Munro and Horn (1935) have stated that the catalytic activity depends on the amount of water on the surface. T o check it, other experiments were carried out. First, samples of F-110 were heated a t different temperatures; before starting the activity run, each sample was hydrated a t the run temperature, 230 "C. This was done by passing over the catalyst for 1h a nitrogen stream saturated with water in a bubbler a t room temperature and injecting in the vaporizer 1-ml pulses of water every 5 min. The catalyst was then swept 30 min with dry nitrogen and the activity run was carried out. The results are shown in curve 4, Figure 10, where it can be seen that although all catalyst samples were rehydrated a t 230 "C, the catalytic activity is not identical, but it depends on the temperature a t which it was first preheated. The decrease in catalytic activity is greater in samples with stronger acidity. As the reheating of a hydrated F-110 produces an increase in activity, a second reheating was done to see if the activity is increased; the sample of point B was heated a t 515 "C, water was added a t 230 "C as for the points of curve 4, and it was immediately reheated a t 515 "C in dry nitrogen for 4 h. After the run, the sample of point B was again heated a t 515 "C and the activity did not show an increment (point C). In order to see the influence of the time of adsorption on the catalytic activity, a sample heated a t 480 "C was hydrated a t 230 "C (similarly to points of curve 4) then kept for 1week in a closed flask with dry air and the standard activity run was finally performed (point D), showing that in this time span there is no influence upon the time of adsorption. The influence of the amount of water adsorbed was studied heating two samples a t 400 "C, hydrating them a t 230 "C and then one was kept for 1week in dry air and the other the same period of time but in air saturated with water. Both have similar catalytic activities (points E and F, respectively). The influence of the amount of water added was also studied under the conditions of curve 2. The points G show the activity of two samples heated and rehydrated similarly to points of curve 2, but one of them was kept three months longer in the saturated air flask before reheating. Heating a sample a t 685 "C and rehydrating by 15 days a t room temperature, the activity is represented by H on curve 4 (this curve represents rehydrating at 230 "C). If a sample similarly hydrated is reheated a t 685 "C, it has the activity of point I in curve 1.At temperatures higher than the maximum the reheating of a hydrated sample does not produce a great increase in the activity (perhaps because of the decrease in surface area). Studying the alumina T-126, a small increase in activity is produced upon heating a t 545 "C, rehydrating, and reheating (curve 2, Figure 7). This is due to the fact that this catalyst was originally heated by the manufacturer, whence it has already developed all of the active surface. Hydrating the alumina T-126 in the same way as the samples of curve 4, Figure 10 for F-110, curve 4 of Figure 7 was obtained. If samples of the rehydrated T-126 are reheated, the activities obtained are in curve 2 of Figure 7. In conclusion, from Figures 7 and 10, in the conditions of the activity test, the catalytic activity is decreased by hydrating the catalyst (curves 4), but the activity is still a function of the preheating temperature independent of the time of adsorption and the amount in excess of water added. If the heating temperature prior to hydration is higher than the one representing substantial loss of water (of F-110), a great in-
i
s __ '3
, -
203
400
600
TEMPERATdRE,
800
1000
"C
F i g u r e 11. Catalytic activity of alumina T-126; conversion of methylaniline to dimethylaniline and rate of production of propylene gas from 2-propanol, both as a function of heating temperature; catalyst, 3 g; temperature, 230 OC; in methylation of methylaniline with methanol the feed was 23 ml/h of 2:l molar basis methano1:methylaniline; in dehydration of 2-propanol t o propylene the feed was 23 ml/h liquid 2-propanol.
crease in activity is obtained by reheating (curve 2). If not the activity is little affected (curve 3). Preheating does not increase the activity. Other Acid Catalyzed Reactions. The dehydration of 2-propanol to give propylene and the reaction of methanol with methylaniline are considered acid-catalyzed reactions. To check if they follow the same relationship with the acidity as the one of the dehydration of methanol to dimethyl ether, standard runs were made with alumina T-126 a t the conditions indicated in Figure 11.This shows that the activities for both reactions follow the same pattern as the activity for methanol; all have a maximum for the catalyst preheated a t about 500 "C. Conclusions and Discussion The results show that the modification by heating of the catalytic activity of alumina does not follow behavior similar to the one of the specific surface area, but rather to the modification of acidity. Catalytic activity and acidity stronger than pK, = 3.3 (which can be considered as the total acidity), both reach maxima a t the same temperatures. It is necessary to heat a t 500-550 "C to develop the greater catalytic activity, although the adsorbent capacity can be decreased because of destruction of the narrowest pores. ?-Alumina adsorbs more water than ?-alumina and desorbs it a t lower temperatures, thus being a better desiccant. Comparing catalysts with the same value of the total acidity, the activity follows the order 992-C > T-126 >> F-110 > KA201. 992-C and T-126 have activity values very far from the other two catalysts on account of their great purity independent of their different crystalline structure. In the order 992-C, T-126, F-110 and KA-201, the values of the properties a t the point of the maximum, relative to that of KA-201, are: catalytic activity per gram of catalyst, 9.7, 8.3, 1.4, and 1.0; total acidity, 1.36, 1.24, 1.00, and 1.00; sodium content, 0.0067, 0.007, 0.27, and 1.0. The strengths of the sites are: stronger than pK, = -8.3, -8.3, -5.6, and -3.0. The values of the total acidity are not much different in the four catalysts and in each one the shape of the curve of total acidity as a function of heating temperature is similar to that of catalytic activity. These properties change with the same trend but are not proportional. For the same value of acidity the value of the catalytic activity is a characteristic of each alumina, depending on preparation method. The preparation influences the composition (mainly sodium content) and the steric effects. Sodium decreases the activity and the strength of the acid Ind. Eng. Chem., Prod. Res. Dev., Vol. 15.
No. 4 , 1976 239
sites. Comparing F-110 with T-126, both 7,F-110 has 40 times more sodium, its catalytic activity is six times less, and the total acidity is similar but weaker. This great influence of sodium impurity in catalytic activity of alumina was demonstrated by Pines and Haag (1960). The catalysts heated a t low temperatures, highly hydrated, have zero or very small acidity shown by the standard titration method; nevertheless, they have catalytic activity with methanol in the standardized run. This could be due to the different experimental conditions. The acidity titration is carried out a t room temperature and by means of the adsorption of an indicator, while the dctivity is determined under reaction conditions (230 "C), with the surface covered by reactants. A t this conditions methanol can displace some water from the surface, as shown by Figoli et al. (1971), and transforms it into a catalytic active surface. The indicators are not able to detect this displacement a t room temperature and show the hydrated surface as nonacid. The behavior of alumina can be interpreted using the model of Peri (1965). This model is for the y-alumina surface and its dehydration: at lower temperature, once the weakly adsorbed water molecules are eliminated, the surface of the hydrated alumina is covered by hydroxyl groups, which minimize surface energy. Upon dehydration by heating, two hydroxyl groups form a water molecule and leave an 02-ion in the surface and an exposed aluminum ion in a lower layer, which are Lewis basic and acid sites, respectively. These are strained or defective sites, but their strain is small if neighboring OH is eliminated leaving alternatively on the surface an 02-and an aluminum ion. As the temperature increases, OH groups, which require more energy on account of being further away from each other, start leaving. In this way the strain or distortion of the new A1-0-A1 link produced is larger and can be shown by a great increase in acidity (which is stronger) and in catalytic activity. According to this pattern, when the temperature is raised, increasingly strained sites would continue to appear. At still higher temperatures this process is overcome by the mobility of the protons, OH groups, or 02ions, which cause the tensions to be gradually eliminated. Thus, the surface energy, as well as its ability to turn the indicators to acid color (acidity and acid strength) and to adsorb activately the alcohol molecules, pass through a maximum. A t a higher temperature than that of the maximum, few strained sites remain and they are relieved by increasing the temperature. The 7-alumina, due to its surface structure, would also have other hydroxyls which are more stable: after the first maximum, strained sites are relieved, then the elimination of other OH groups (which have a greater activaiion energy and are less mobile) is continued, new acid sites are formed, the disappearance of which requires a higher temperature, and this produces the second maximum. Tanabe (1970) explains this as a change in the crystallinity degree of the g-alumina. The condition on the surface during the reaction is a function of its status prior to the arrival of the reactants. The contact of methanol vapors to the catalyst a t 230 "C does not always produce the same conditions on the surface, but it forms superficial compounds which depend on the state of the surface (preheating temperature). When methanol or water are adsorbed there is no strain elimination, as supposed by Cornelius et al. (1955).If there were strain elimination, activity under standard conditions (230 "C) would always be the same. If only the amount of water were important, hydrating the catalyst at different temperatures and heating at 230 "C in dry nitrogen before the run should always produce the same catalytic activity because the hydration equilibrium should be the same. But as this is not the case, the catalytic activity depends on the preheating temperature. The number of 240
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 4, 1976
methoxyl groups which are formed depends on the number of aluminum ions exposed when methanol is introduced. This number remains constant during the reaction (Knozinger (1968)) and the rate constant is proportional to it. Therefore if all, or a fixed proportion, of the exposed aluminum ions form active methoxyls, activity and acidity will be proportional. The results show that they are not perfectly proportional, perhaps so because the strength of the indicators used in measuring the acidity does not coincide with the strength of the acid sites able to form active methoxyls. If it is accepted that the existence of acid sites is responsible for catalytic activity, according to our results it seems that all of them behave catalytically in the same way, independently of their ability to give the acid color only to the weak indicators or also to the strong ones. Perhaps when methanol is adsorbed on the active sites, it causes the same state of strength or activity in all of them. At 230 "C methanol, the same as for pyridine in Knozinger and Stolz (1971) experiments, could not differentiate strong sites from weak ones. This uniformity of the alumina surface in these working conditions was also indicated before by Soma et al. (1969) and by Figoli et al. (1971). But the relation between activity and acidity does not mean that active sites and acid sites are identical. They could be different sites, which are similarly, but independently, formed during surface dehydration. Perhaps the catalytic active surface acts as a whole whose properties depend on the state of the bare catalytic surface when the reactants reach it and on the surface groups formed after reactant adsorption. During reaction the surface groups of alumina (Al, 0, OH) are covered by reactants, products, or other groups, which remain on the surface irreversibly on evacuating (as in the case of determination of the ir spectrum) or can be exchanged with other reactants when they are introduced (as adsorption with interaction). In this way the reactants see an active surface different to the one after heating, but related to it (to its exposed aluminum ions which constitute acid sites). Acknowledgments The author is grateful to E. R. Rincbn for the DTA and TGA determinations, to H. E. Olivera for the specific surface area measurements, and to J. C. Brengio for the acidity titrations. Literature Cited Antipina, T. V.. Frost, A. V., Compt. Rend. Acad. Sci. URRS, 53, 45 (1948). Bailey, G. C., Holm, V. C., Blackburn, D. M.. J . Phys. Chem., 62, 1453 (1958). Beretka, J., Ridge, M. J., J . Chem. Soc., A, 2106 (1967). Bohl, K., Rebentisch, G.. Chem. Tech. (Berlin), 18, 496 (1966); Chem. Abstr., 65,6340 (1966). Boreskov, G. K., Dzisko, V. A,, Borisova, M. S., Zh. Fiz. Khim., 27, 1176 (1963). Brey, W. S., Jr., Krieger, K . A,, J . Am. Chem. Soc., 71, 3637 (1949). Churruarh R. A,, Hillar, S. A,, Rev. Fac. lng. Quim., 37, 363 (1968). Cornelius, E. B., Milliken, T. H., Mills, G. A,. Oblad. A. G., J. Phys. Chem.. 59, 809 (1955). Cranston, R. W., Inkley, F. A,, Adv. Catal. Re/. Subj., 9, 143 (1957). de Boer, J. H., Fortuin, J. M., Lippens. B. C., Meijs, W. H., J . Catal., 2, 1 (1963). de Boer. J. H.. Fahim. R. B.. Linsen, B.G., Visseren. W. J., de Vleesscha-Uwer, W.F.N.M., J. Catal., 7, 163 (1967). Echigoya, W., Shiba, T., Bull. Tokyo lnst. Techno/. Ser. 6, 133 (1960). Euken, A,. Wicke, W., Naturwissenschaften, 32, 161 (1944). F;yoli, N. S., Parera, J. M., J . Res. lnst. Catal., Hokkaido Univ., 18, 142 11971) Figoli, N. S., Hillar, S. A., Parera, J. M., J . Catal., 20, 230 (1971). Flockhart, B. D., Uppal, S. S., Leith, I. R., Pink, R. C., Paper 79, lnt. Congr. Catal. 4 t h Moscow (1968). Hall, W. K., Lutinski, F. W.. Gerberich, H. R.. J. Catal., 3, 512 (1964). Hindin, S. G., Weller, S. W., J. Phys. Chem.. 60, 1501 (1956). Irazoqui, H., Oberto, S. C., Rev. fac. lng. Quim., 37, 399 (1968). Knozinger, H., Angew. Chem. lnt. Ed., 7, 791 (1968). Knozinger, H., Stolz, H., An. Quim.. 67, 999 (1971). Maclver, D. S., Tobin. H. H., Barth. R. T., J . Catal., 2, 485 (1963). Maclver. D. S., Wilmont, W. H.. Bridges, J. M., J . Catal., 3, 502 (1964) Munro. L. A,, Horn, W. R., Can. J. Res.. 12, 707 (1935).
Parera, J. M., Fjgoli, N. S., J. Catal., 14, 303 (1969). Parry, E. P., J. Catal., 2, 371 (1963). Peri. J. E., Actes lnt. Congr. Catal. Znd., 1, 1333 (1961). Peri, J. E., J. Phys. Chem., 69, 211, 220, 231 (1965). Pines, H., Pillai, C. N., J. Am. Chem. SOC.,82, 2401 (1960). Pines, H.,Haag, W. O., J. Am. Chern. Soc., 82, 2471 (1960). Pines, H.,Manassen, J., Adv. Catal. Re/. Subj., 16, 49 (1966). Rhee, K. H., Basila, M. R., J. Catal., IO, 243 (1968). Rosolovskaya, E. N., Shakhnovskaya, 0. L., Topchieva, K. V., Kinet. Katal., 7, 750 (1966). Say, G. R., Rase, H.F., lnd. Eng. Chem., Prod. Res. Dev., 5, 250 (1966). Schwab, G. M., Kral, H..Proc. lnt. Congr. Catal. 3rd, 7964, 1, 433 (1965). Soma, Y., Onishi, T., Tamaru, K., Trans. Faraday SOC.,65, 2215 (1969). Steinike, U., 2. Anorg. Allg. Chem., 338, 78 (1965). Tanabe, K., Kaiayama. M.. J. Res. lnst. Catal. Hokkaido Univ.. 7, 106 (1959).
Tanabe, K., Yamaguchi, T., Takeshita, T., J. Res. lnst. Catal. Hokkaido Univ., 16, 425 (1968). Tanabe, K., "Solid Acids and Eases, Their Catalytic Properties", Kodansha, Tokyo, 1970. Taylor, R . J., J. SOC.Chem. lnd., 68, 23 (1949). Topchieva, K. V., Rosolovskaya. W. N.,Sharaev, 0. K., Vestnik Moskov. Univ.. Ser. Mat. Mekh, Astron., Fiz, Khim., 14 (1). 217 (1959). Vinnikova, T. S., Dzis'ko, V. A., Kefeli. L. M., Plyasova, L. M., Kinet. Katal., 9, 1331 (1968). Wheeler, A., Adv. Catal. Re/. Subj.. 3, 250 (1950). Yamadaya, S., Shirnonura, K.. Kinoshita, T., Uchida. H., J. Nat. Chem. Lab. lnd., 68, 132 (1973).
Receioed f o r reuiew January 7, 1956 Accepted August 16,1976
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 4, 1976
241
