THE CATALYTIC DECOMPOSITION OF ETHYL ALCOHOL HERBERTE. Moms, UNIVERS~TY OP ALBERTA, EDMONTON, CANADA
The salientfeatures of the catalytic decomposition of ethyl alcohol have been outlined in this paper. The early studies on dehydration and dehydrogenation hawe been indicated and the mechanism of reaction outlined. The sources of some of the secondary products such as carbon dioxide, ethane, and methane have been identified from the awailable information. Some of the theories of catalytic action which hawe been deduced, following studies on alcohol decomposition, have been reviewed. Introduction The catalytic decomposition of ethyl alcohol has been the subject of numerous investigations since the first classical researches upon the activity of catalysts. Ethyl alcohol quite readily undergoes two main reactions involving either dehydration or dehydrogenation and is particularly useful for the determination of the specific nature of the activity of a catalyst. This variation in decomposition reactions permits a study of the mechanism of catalytic activity and many theories of the nature of a catalyst surface have been advanced as a result of studies on the decomposition of ethyl alcohol. For these reasons a brief review of the decomposition of ethyl alcohol should be of interest. This review is not intended as a comprehensive compilation of all results which have been published, but only those results which illu&rate the present development of the E subject are included. There are two main decompositions which ethyl alcohol readily undergoes due to the influence of catalytic agents; dehydration and dehydrogenation. Dependmg upon the catalyst there are also two possible dehydration reactions; intermolecular dehydration with the formation of ethyl ether; 2GHaOH = (C2H&0
+ HzO
and complete dehydration with the production of ethylene
Dehydrogenation produces acetaldehyde directly,
and any complexities in this reaction are produced by secondary reactions of the aldehyde. There are several other reactions which have been advanced by various workers and these will be discussed subsequently but these three abovementioned reactions are the most important. 1730
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DECOMPOSITION OF ETHYL ALCOHOL
1731
Early Researches The systematic study of the catalytic decomposition of ethyl alcohol was not started until early in the present century. With the exception of work on the preparation of ethyl ether, the information available on the reactions of alcohol was very meager. In 1839 Masson (38) observed that anhydrous zinc chloride produced ethyl ether from ethyl alcohol, and Greene (27) re-examined the same reaction in 1878, obtaining a great variety of products including ether, acetaldehyde, ethylene, ethane, hydrogen, and polymeric oils. Williamson's researches on the dehydration of ethyl alcohol by concentrated sulfuric acid were presented in 1852 (68) and a large number of papers have appeared since that time dealing with variations in the procedure. Grigoreff (28) was the first to observe that metallic oxides also possessed dehydrating power when he obtained ether and ethylene using alumina as the catalyst. Reiset and Millon (51) were the earliest to note that platinum sponge dehydrogenates alcohol at a temperature of 220'. These results indicated that two distinct types of reaction were possible with ethyl alcohol and the nature of the catalyst was the sole criterion of which route the decomposition would follow. General Results With this small amount of information available Ipatiev and Sabatier presented a long series of papers between 1901 and 1910 which indicated in great detail the type of reaction which might b e expected with a great variety of metals and metallic oxides. Ipatiev showed his results as pyrogenic decompositions, the studies being practically all high-temperature reactions in a range of 500-700°C. A large number of metals were studied and it was observed that both dehydration and dehydrogenation occurred in many cases (30). Sabatier and his co-workers, Senderens and Mailhe, investigated the iduence of catalysts over a much lower temperature range varying from 150°C. to 350°C. and rarely higher. The catalysts were quite specific and Rideal and Taylor (52) present a table (see p. 1732) which summarizes some of the results of Sabatier and Mailhe (54). The catalysts are arranged in their order of activity as dehydrating agents; the figures refer to the percentage of ethylene in the ethylene-hydrogen mixture obtained by passing alcohol vapor over the catalyst at 350°C. This table indicates the variation in the activity of many metals but is not complete and a more detailed summary of the activities of other catalysts may be found elsewhere (56). In addition to metals, however, other substances are also catalytically active. For example, Senderens (62) examined the action of amorphous carbon at 400°C. and found that
1732 Coiolyrl
-. l'hU*
JOURNAL OF CHEMICAL EDUCATION Per Cenl E l h v h r
.-IUU
All08 W~OJ
98.5 98.5
Crn01 SiO, Ti02 Be0 zro2 U10r MozOa FelOs V~OS ZnO
91
Dehydrating
it acted as a mixed catalyst. One feature of this study was the identification of formaldehvde which Senderensbelieved
84 63 45 45 24 23 14 9 5
OCTOBER. 1932
to be formed directly according to the equation GH60H = CHI HCHO. A number of amorphous compounds and salts were found to give similar results with at least an equally great activity. The catalytic reactions of
+
Mixed dehydrating and dehydrogenating
ethyl alcohol are not limited to simple dehydrogenation and 0 dehydration and a variety of 0 Dehydrogenating products are possible which 0 will be discussed in detail 0 later. There are various fac0 tors, both physical and chemical, which also influence the action of catalysts with the regular reactions. The majority of studies on catalytic activity have been limited to single metal catalysts or small amounts of promoter. Studies by Boomer and Morris (12), (13) have indicated that there is a fundamental difference in the reactivity of metals when combined in a catalyst with other metallic elements. In mixed catalysts i t was absemed that nickel was more effective than chromium, which in turn was more active than copper hut the resistance to thermal de-activation was in the reverse order. The influence of pressure has been studied by Ipatiev (31). It was concluded that an increase of pressure diminished the decomposability of the alcohol, although the general course of reaction was much the same as that observed under ordinary pressure. The extent of decomposition varied inversely with the pressure. Similar results were obtained if the temperature was raised correspondingly to higher values. Rather interesting results were obtained a t high temperatures in which alcohol first decomposed to ether, and this was subsequently further dehydrated to ethylene; alcohol being apparently regenerated, was immediately dehydrogenated. A more recent paper by Ipatiev and Kliukvin (33) studied the influence of pressure upon the polymerization of the products of catalytic decomposition, using both iron and alumina as catalysts. In this case it was observed that both aldehyde and ethylene polymerized readily. Influence of Diluents The effect of diluting alcohol vapor with inactive substances has been investigated by many workers. One of the favorite diluents has been Mn02 SnO CdO MtllOl MgO Cu Ni
0 0
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DECOMPOSITION OF ETHYL ALCOHOL
1733
water vapor and Engelder (24) was probably the first to observe that water vapor decreased the rate of catalytic decomposition of ethyl alcohol. Constable (21) studied the influence of water vapor on the dehydration of alcohol over tboria and observed that in small concentrations water acted quite definitely as a promoter but a t higher concentrations acted as a poison. This was also confirmed by Hoover and Rideal (29) who noted a decrease in the velocity of the dehydration reaction. Armstrong and Hilditch (6) investigated the influence of water vapor on the dehydrogenation reaction over copper. It was found that the presence of water in alcohol improved the yield of acetaldehyde relative to that of hydrogen. Thus at 300° anhydrous alcohol only gave an aldehyde-hydrogenratio of 67%, while alcohol containing 8% water gave a 95y0 ratio. That is, with anhydrous alcohol there is a .much more pronounced decomposition of acetaldehyde and in this case water vapor apparently acts as a beneficial poison in suppressing secondary reactions. Russel and Marschner (53) studied the reaction on nickel below 200°C. and made similar observations on the fact that water increased the amount of alcohol undergoing reaction, but decreased the percentage of aldehyde decomposed. It was suggested that water reduced the length of time which the reacting molecules spend on the surface of the catalyst. There is a possible reaction between ethyl alcohol and water,
+ 3H20
C2HsOH
=
2C02 4- 6Hz
and Lazier and Adkins (36) observe without comment that water vapor increases the quantity of COz and hydrogen in Teaction products, although Boomer and Morris (14) were unable to find any direct indication of such a reaction with a variety of catalysts. Carbon dioxide as a diluent was studied by Gilfillan (26) with the anticipation of inducing reaction to produce diethyl carbonate. COI
+ 2CxH80H = CO(OC2Ha)p+ HrO
Instead of such a reaction, however, carbon dioxide promoted the formation of acetal with a thoria catalyst. CHICHO f 2GHaOH = CHsCH(OGH&
+ H20
Morris (40) found that the only influence of COz was indicated by inducing a greater decomposition of alcohol due to a slower space velocity. The reaction shown above is probably due to this same effect. Two other diluents have been examined by Hoover and Rideal (29). Acetaldehyde decreased the velocity of the dehydration reaction while chloroform in small quantities promoted the ethylene reaction. Chloroform in excess acted as a poison, however, and inhibited dehydrogenation whenever present.
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JOURNAL OF CHEMICAL EDUCATION
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Types of Reaction
It will be obvious that a variety of products are possible in the catalytic decomposition of ethyl alcohol and the nature and possible sources of some of these products make an interesting study. There are a t least five distinct reactions that may take place a t the surface of solid catalysts and of these the first four all occur within the same temperature range (65). CIHsOH = CpHsOH = C2HaOH = 2QHsOH = 2CsHsOH =
+
CHJCHO Hs CH4 CO 4- Hz C2H4 H20 C2H8 CHtCHO (CnHa)sO HsO
+ + +
+
+ HnO
These reactions will be elaborated in subsequent discussion and some of the complications arising from secondary reactions will also be considered. Dehydrogenation One of the most important decompositions of ethyl alcohol involves dehydrogenation with the formation of acetaldehyde and hydrogen over a variety of catalysts. This reaction is relatively simple chemically but the mechanism of the process possesses complications as indicated in the following extract. "We know that ethyl alcohol can he decomposed into acetaldehyde and hydrogen-but that is as far as people have gone hitherto. With pulverulent nickel as catalyst, the reaction is almost completely CHJCHBOH= CHsCFO
+ H,.
We do not know whether the hydrogen comes off in one stage or in two, though it is probable that i t comes off in two stages. If so, is the first stage CHaCHpOor CHaCHOH?" (8) There are two types of dehydrogenating catalysts exemplified by nickel and copper. Both tend to convert alcohol into aldehyde and hydrogen, but nickel is much more likely to decompose the aldehyde into methane and carbon monoxide. This activity is illustrated in the results of Armstrong and Hilditch (6) who obtained a ratio of aldehyde to hydrogen of only 36% of the theoretical with nickel a t 250°C. The gases from the reaction contained 60% He, 20% CO, and 1517% CHI. This same ratio was about 97% with copper a t 300' and the gas was practically pure hydrogen. A mass of experimental results has been published on this reaction but only a few examples will be cited. Palmer (46) made an extensive study of copper and various oxide catalysts to determine the influence of variations in reaction procedure. Adkims and Lazier (2) stated that a variation in temperature affected the amount but not the ratio of reaction products with nickel as the catalyst.
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9,
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10
DECOMPOSITION OF ETHYL ALCOHOL
1735
Both Ipatiev (32) and Armstrong and Hilditch (6) attempted to hydrogenate acetaldehyde to obtain an equilibrium but obtained only the normal decomposition products of acetaldehyde. Bancroft and George (10) were able to measure the equilibrium a t 140-145°C. both by hydrogenation and dehydrogenation over nickel and obtained a value of 96-97% alcohol by hydrogenation of acetaldehyde and 3% aldehyde by dehydrogenation of ethyl alcohol. Dehydration (a) Ethyl Ether.-Ethyl ether and ethylene are both produced by the dehydration of ethyl alcohol, although there is a marked difference in the methods of production. The formation of ether was first studied in detail by Williamson (68) who observed large yields of this product when using concentrated sulfuric acid a t 140°C. The mechanism of reaction is one of the classical examples of the intermediate compound theory, the first step producing ethyl sulfuric acid which reacts with another molecule of alcohol.
+
+ +
CBHSOH &SO& = H 2 0 CzHaOSOaH C H 6 0 H = H&O, (CzHshO CaH,OSOsH
+
This reaction has been the subject of much study since that time. The most favorable temperature for reaction is in the region of 140-145O according to Norton and Prescott (44); above 160° sulfurous acid is evolved with the destruction of sulfuric acid necessary for reaction. Pagliani (45) showed that SO2 under pressure is not sktisfactory for the reaction for it leads to the formation of many other product$? Senderens (64) made the observation that the addition of aluminum sulfate markedly promoted the reaction a t a lower temperature. An investigation of the sulfuric acid-ethyl alcohol equilibrium has been made by Pease and Yung (49) a t 130°C. and it was stated that a t this temperature there was a maximum conversion of 85% of the alcohol to ether which was evidently the equilibrium. (b) Ethylene.-The dehydration of alcohols by certain oxides, such as alumina or thoria, with the formation of ethylene is a well-known reaction. Senderens (63) observed that a t 240-260°C. the dehydration of alcohol over alumina produced ethyl ether but, a t 300°, ethylene to the amount of 99.5% was produced. Silica gave a similar yield a t 280°C. The mechanism of the reaction as suggested by Sabatier and Mailhe (55) bears a close analogy to Williamson's theory.
+
+
A1.01 2CzHaOH = HBO Aln02(OCH6)1 2CzHsOH f Ab02(OC2H& = Z(C2Hs)rO Ala0,(OH)2 AleOl(OH)n = Alson H 2 0
+
+
Boswell and Dilworth (15) have made another suggestion involving films of H+ and OH' on the catalyst surface which may react as shown.
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JOURNAL OF CHEMICAL EDUCATION
OCTOBER, 1932
The difficulties inherent in the selection of a suitable mechanism are indicated by the following excerpt. With pulverulent alumina the reaction is almost completely ethylene and water. Does water split off as such or do we get a preliminary splitting-off of hydrogen or hydroxyl? It seems improbable that water can split off as such because then it would be difficult to account for the intermediate formation of ether. If the first stage is a splitting-off of hydrogen, it probably is not the same hydrogen which comes off first with nickel, because then we should expect the reaction to go the same way in the two cases. If the first stage is a splitting-off of hydroxyl, does the other hydrogen come from the adjacent carbon atom, giving ethylene direct or does it come from the same carbon atom, forming a substituted methylene CHsCH, which then rearranges to ethylene? (8). The investigations of equilibrium in the dehydration of alcohol using alumina, by Pease and Yung (49), Clark, Graham, and Winter ( l a ) ,and Alvarado (5), all arrived a t a similar result indicating about 85% ether at 250-260°C. An interesting result on mixed catalysts showing both dehydration and dehydrogenation has recently been shown by Williamson and Taylor (69) using manganous salts as catalysts. It was observed that the ratio of dehydrogenation to dehydration increased with the valency of the ion in the salt as indicated by the oxide, sulfate, orthophosphate, and pyrophosphate. Taylor and Sickman (66) studied alcohol decomposition on zinc oxide catalysts and were impressed by the capriciousness of their catalysts and the difficulty of obtaining reproducible results.
Formation of Carbon Dioxide The sources of the carbon dioxide observed among the products of the decomposition of ethyl alcohol have given rise to several interesting postulations. Owing t o the variety of products formed in both primary and secondary reactions there are several fairly simple reactions leading t o carbon dioxide in the temperature ranges usually studied. These are indicated below with relevant references. 2CO = 2CO 2H2 = C 2H10 = CO H1O =
+ +
+
CO, Con C02 COa
+C + CH, + 2H2 + HS
( 3 0 . (61) (7h (17) (17) (67)
Certain of these reactions may be eliminated from consideration with some catalysts; if there is no trace of carbonization or dehydration, there is no possibility of reaction occurring.
VOL. 9, NO. 10
DECOMPOSITION OF ETHYL ALCOHOL
1737
Sabatier and Mailhe (54) have shown that oxide catalysts may be reduced by alcohol vapor, producing COI, but obviously this reaction would cease when the oxide bad been completely reduced. Brown and Reid (16) have suggested that the carbon dioxide is due to the condensation of acetaldehyde to an ester, which on decarboxylation yields COz and a hydrocarbon. The decarboxylation of ethyl acetate has been reviewed by Sabatier (59) and further investigated by Adkius (1) and found to proceed readily over certain catalysts. This is of further interest in view of the fact that acetic acid bas been reported as a frequent product in alcohol decomposition &d would tend to promote ester formation; Armstrong and Hilditch (6) have reported ethyl acetate as a product obtained over nickel a t 350°C. Lazier and Adkins (36) believed that the above mechanisms were unsatisfactory and emphasized several factors which must be taken into consideration. These include the presence of carbon dioxide itself, the acidic nature of all condensates and the frequent observance of a brown, water-insoluble resin, and Lazier and Adkins developed a new mechanism to account for all of these facts. They suggest that the catalyst is dehydrogenating and the aldehyde produced by this reaction is still further dehydrogenated to yield a ketene.
The reaction between this ketene and more acetaldehyde would produce COI and an unsaturated hydrocarbon, which latter would polymerize to produce the resin so often observed.
A reaction between the keteue and water would produce acetic acid, while a reaction between this ketene and ethyl alcohol yields ethyl acetate. Recently Boomer and Morris (14) have examined these reactions in detail and obtained confirmation of the reaction suggested by Lazier and Adkins with some catalysts. However, it was also observed in several cases that the resin was an oxygenated product rather than a hydrocarbon, which indicated other reactions. To account for this it was suggested that the ketene might react further to produce allene and carbon dioxide: 2H2CC0 = C 0 2
+ HzCCCHS
This reaction would account for the larger amounts of COz observed while a secondary reaction between allene and acetaldehyde would produce a compound with the. composition and properties indicated by the oxygenated resin obtained.
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JOURNAL OF CHEMICAL EDUCATION
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OCTOBER, 1932
Formation of Ethane The formation of ethane has been a subject of consideration in several research papers. Greene (27) observed its formation on hot ZnClz while Ehrenfeld (23) noted ethane when ethyl alcohol was passed over heated carbon and stated that the hydrocarbon was formed as a primary reduction product. Engelder (24) studied alcohol decomposition over titania and claimed the formation of ethane by the hydrogenation of ethylene, the latter being produced in a primary dehydration reaction. This reaction was said to be due to hydrogen present as "nascent hydrogen." Bischoffand Adkins (11)studied this mechanism in detail and believed it more probable that the formation of ethane involved an anto-oxidation and reduction reaction. 2GHsOH = CHKHO
+ HBO+ CIH,
Boomer and Morris (12) reported results with a catalyst containing copper and chromium on silica. The results indicated that ethane was due to the primary reaction of Bischoff and Adkiis. In a later study these workers (43) investigated a number of catalysts and concluded that both primary formation and secondary hydrogenation yielded ethane, the reaction being dependent upon the catalyst. Formation of Methane Methane has been frequently olkerved among the products of the catalytic decomposition of ethyl alcohol &d several sources of the hydrocarbon are possible. One of the main sources of methane involves the decomposition of acetaldehyde, a reaction which has been studied by Sabatier and Senderens (60) over many catalysts. Razuvaev (50) added the reaction betweenC0 and hydrogen CO
+ 3H2 =
CH4
+ H20
as a source of methane. Morris and Boomer (42) investigated the sources of methane possible with the reactants produced in the decomposition of ethyl alcohol. It was concluded that there were a t least seven reactions which might yield methane. In addition to the two mentioned above the following reactions were considered:
+
.
2CO 2H2 COX 4Hz 4C0 2 8 0 2H1 C nCHa
+ +
+
= CH,
+
CO* CH4 2Hz0 = CHI 3C02 = CH* = CHa, &Ha, C. H2, etc. =
+ +
VOL. 9, NO. 10
DECOMPOSITION OF ETHYL ALCOHOL
1739
All of these reactions occur within the temperature range usually studied in alcohol decomposition. It was therefore decided that it was extremely difficult to determine the exact source of methane in the catalytic decomposition of ethyl alcohol although certain reactions may be expected with specific catalysts. In addition to the products discussed above many organic liquids have been found in the condensates obtained in reactions with many catalysts. Only small quantities of such materials have been obtained and exact identification appears difficult but acetic acid, ethyl acetate, butyraldehyde, croton aldehyde, etc., have been detected by various workers. Such products further complicate an analysis of reaction mechanisms and it must be concluded that studies of alcohol decomposition are usually limited to qualitative determinations on catalytic activities: Various Reactions While this paper has been concerned primarily with the catalytic decomposition of ethyl alcohol, an indication of some other catalytic reactions seems to be in order. A review of the catalytic oxidation of alcohol may be found elsewhere (41). Catalytic esterification with the formation of ethyl acetate in both liquid and vapor phase has been studied on several occasions. Mailhe and de Godon (37) and Frolich, Carpenter, and Knox (25) used zirconia as the catalyst while Milligan and Reid (39) found silica to be an excellent catalyst. Ethyl formate may he prepared in an analogous manner. C The production of ethyl mercaptan has been studied in two quite distinct reactions. Kramer and Reid (35) passed ethyl alcohol and hydrogen sulfide over thoria at 380' and obtained 35% conversion to the mercaptan. Gilfillan (26) promoted the formation of this product by passing a mixture of alcohol and carbon bisulfide over several catalysts. In some cases appreciable quantities of ethyl mercaptan were formed. Ethyl amine is fairly readily prepared by passing a mixture of ammonia and alcohol over various catalysts (9). Sabatier and Mailhe (55) found thoria especially favorable for this reaction. Knoevenagel (34) heated ethyl alcohol and aniline a t 230' with iodine as a catalyst and obtained a good conversion to ethyl aniline. It has also been stated that the formation of acetal from ethyl alcohol and acetaldehyde is favored by the presence of various catalysts (58). These few examples of the formation of esters. mercaptan, amines, and acetal have been presented to show some of the many other catalytic reactions of ethyl alcohol. Theories of Catalytic Action from Alcohol Studies The catalytic decomposition of ethyl alcohol has been a prolific source of theories of the action of a catalytic surface and some of these merit study
1740
JOURNAL OF CHEMICAL EDUCATION
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OCT~BER, 1932
Sabatier (57) firmly believed that catalysis could be explained by the formation of intermediate compounds and cited the formation of nickel hydrides as the most outstanding example. A finely divided metal which gives a quickly formed and readily decomposable, unstable hydride should be able to remove hydrogen from compounds and thus act as a dehydrogenation catalyst. While such a theory may seem satisfactory in certain cases, the extension of the idea to all results presents many difficulties. Palmer (47) concluded from a series of studies that the active surface of a catalyst was covered by a layer of alcohol several molecules thick, but only in the layer next to the catalyst was the intensity of radiation strong enough to induce activation. As the temperature increased the adsorbed layer decreased in thickness with the resultant increase in ease of evolution of the products. The radiation theory of chemical action is not necessary for the visualization of this concept and adsorption is generally accepted as an important factor in catalytic decomposition. A study of decomposition products of primary alcohols led Palmer and Constable (48) to an extension of the above theory. It was believed that reaction occurred in the adsorbed film covering the surface. In this case i t was observed that the film was not monomolecular below 280°C. but had a thickness which increased as the temperature decreased. In view of the fact that various alcohols indicated a similar reaction velocity in spite of a variation in length of hydrocarbon chain, it was concluded that reaction occurred on the -CH20H group a t the end of each chain. This group was adsorbed on the catalyst in contact with the surface while the hydrocarbon chain remained perpendicular to the copper surface. The analogy between this concept and that concerning oriented fatty acid films on water is evident. In an interesting series of papers Constable (19) advanced the theory that chemical reaction occurred only when alcohol molecules were adsorbed over a characteristic arrangement of atoms which was called a "reaction center." There may be a variation in the number of atom centers beneath one adsorbed molecule and consequently the density of reaction centers may also vary considerably with a variation in activity. It was further stated (20) that alcohol decomposition only occurred when the alcohol molecule possessed an energy above that characteristic of the temperature of the film. Since the -CH20H group was changed it seemed possible that this group contained this excess energy called the energy of activation. Somewhat later Constable (22) stated that catalytic action was due to the effect of strong specific fields of force emanating from special configurations of atoms upon the catalyst, this theory representing an extension of the radiation concept to the postulated reaction centers. Adkins (1) maintained that the activity of a catalyst depended on the
VOL.9, NO.10
DECOMPOSITION OF ETHYL ALCOHOL
1741
molecular size of cavities in the mass. A series of alumina catalysts prepared by different methods indicated varying activities. It is evident that alumina prepared by the methods shown would have a markedly different structure. 2AI(OH)r 2AI(OCzHsh
= =
ALOJ ALOa
+ 3&0
+ 3(CmHshO
Adkins has shown that the activity of such catalysts presented a marked variation. Several factors must be considered in catalytic reactions according to results of Adkins and his co-workers (3). The adsorbing power of the catalyst, the variation in the spacing of the active points of the surface; and the degree of unsaturation of catalyst atoms are variables which change with catalysts and each needs separate attention. A later paper with Millington ( 4 ) stressed the fact that the activity of a catalyst depended upon the molecular aggregation within the catalyst rather than on the catalyst itself. Hoover and Rideal (29) stated that the action of mixed dehydration and dehydrogenation catalysts was explicable on the theory of different active patches on the surface of the catalyst, each area possessing its characteristic and specific activity. It also seemed probable that both the orientation of surface atoms and the adsorptive power of the active patches played a part in the determination of the type of reaction which would proceed upon an active patch. Such a theory can be apparently substantiated by the variation in the energies of activ~tionfor each reaction. The conception of active areas is not a new one and Russel and Marschner (53) employed this device in a study of a nickel catalyst. Such areas possessed various activities and it was suggested that the most active portions of a surface might adsorb poisons and decomposition would then proceed on the less active areas. It was further postulated that water in the reaction mixture would leave the active areas available for action and increase the activity of the catalyst. This brief review of some theories is not complete but these examples have been selected as indicative of the trend of the theoretical treatment of catalysis as indicated by studies of the catalytic decomposition of ethyl alcohol. Conclusion In this paper the present status of our knowledge of the catalytic decomposition of ethyl alcohol has been indicated. It is evident that the reactions are extremely complex and many products may be obtained, but in most cases the course of reaction may be predicted from the nature of the catalyst used. No effort has been made to make this a comprehensive review but as far as possible most of the important developments have been included. It is hoped that this arrangement will indicate leads for
1742
JOURNAL OF CHEMICAL EDUCATION
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OCTOBER, 1932
further research and prove a concise summary for those having a limited knowledge of t h e field.
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VOL.9, NO. 10
DECOMPOSITION OF ETHYL ALCOHOL
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