Catalyst composition for oxidation of ethylene to ethylene oxide

This invention relates to catalysts for the manufacture of ethylene oxide, especially at commercial concentrations in the presence of carbon dioxide gas recycle, which contains impregnated silver on a support and a mixture of cesium salt and one or more alkali metal and alkaline earth metal salts in which the anions thereof are halide or oxyanions of elements other than the oxygen therein having an atomic number of 7 or 15 to 83 and being from groups 3b through 7b, inclusive, and 3a through 7a, inclusive, of the Periodic Table of the Elements, at least a portion of said oxyanions are oxyanions of group 3b to 7b elements.

BRIEF SUMMARY OF THE INVENTION 
TECHNICAL FIELD 
This invention relates to catalysts for the manufacture of ethylene oxide 
especially at commercial concentrations in the presence of carbon dioxide 
gas recycle, which contain impregnated silver on a support, e.g., an 
alpha-alumina support having an alpha-alumina content (inclusive of 
binder) of at least 98 percent (98%) by weight, and a mixture of (a) at 
least one cesium salt and (b) one or more alkali metal and alkaline earth 
metal salts of lithium, sodium, potassium, rubidium, magnesium, calcium, 
strontiun and barium, said mixture comprising (i) a cesium salt of an 
element other than the oxygen therein being selected from groups 3b 
through 7b, inclusive, of the Periodic Table of the Elements, and (ii) 
alkali metal and/or alkaline earth metal salt in which the anions of such 
salt comprise at least one of halide of atomic numbers of 9 to 53, 
inclusive, and oxyanions of elements other than the oxygen therein having 
an atomic number of 7 or 15 to 83, inclusive, and selected from the groups 
3a to 7a, inclusive, and 3b to 7b, inclusive, of the Periodic Table of 
the Elements. The mixture is preferably in an amount sufficient to provide 
an efficiency to ethylene oxide manufacture at a value at least about 79 
percent, as determined at STANDARD ETHYLENE OXIDE PROCESS CONDITIONS 
measured under oxygen process conditions. There is also described herein a 
process of making such catalysts and processes for producing ethylene 
oxide with such catalysts. 
BACKGROUND ART 
Introduction 
This invention is concerned in general with silver catalysts, their 
manufacture and their use in the manufacture of ethylene oxide in 
commercial concentrations in the presence of a gas phase inhibitor, 
especially a gas phase chloride inhibitor, and advantageously carbon 
dioxide recycle. The catalyst of this invention comprises a supported 
silver catalyst. The catalyst contains cesium salts of an oxyanion in 
combination with at least one other alkali metal and/or alkaline earth 
metal salt of a halide or an oxyanion. Preferably, another alkali metal is 
present and is lithium, sodium, potassium and/or rubidium. The oxyanions 
contain elements other than the oxygen therein having an atomic number of 
7 or 15 to 83, inclusive, and being from the groups 3b, through 7b, 
inclusive, and 3a through 7a, inclusive, of the Periodic Table of the 
Elements. Thus, the catalyst, when utilized in the manufacture of ethylene 
oxide, contains a select class of salts of cesium with one or more other 
select classes of salts of other alkali metals (excluding francium) and 
alkaline earth metals. The amount of these salts employed is not governed 
by prior art notions of weight or volume percentages because, as will be 
explained herein, such factors cease in general to be relevant. Thus, this 
invention allows the use of amounts of alkali metals and alkaline earth 
metals which cover a broad range to yield catalysts having desirable 
performances. 
SUMMARY ANALYSIS OF PRIOR ART 
In order to understand and appreciate this invention, it is desirable to 
review some basic facts about the science of making ethylene oxide by the 
gas phase reaction of ethylene and oxygen over a solid silver catalyst. 
A number of theories abound about the mechanism of the reaction of ethylene 
and oxygen. It is sufficient to say that none is universally accepted. 
What appears to be accepted is that oxygen in some fashion combines with 
solid silver and through that combination, oxygen is caused to react with 
ethylene to form ethylene oxide. Concomitant with that reaction is the 
combustion of ethylene and/or ethylene oxide to carbon dioxide and water 
(combustion products). Some have theorized that at least a portion of the 
carbon dioxide is generated by the isomerization of ethylene oxide to 
acetaldehyde which immediately goes to combustion products. 
It is these competing reactions that the workers in the art attempt to 
affect. Many additives have been used to enhance the reaction. To 
illustrate this point, it must be recognized that the best procedures 
employed today to make commercial silver catalysts when used to make a 
silver only catalyst, i.e., silver impregnated on a porous alpha-alumina 
support, will result in a catalyst which, under commercial ethylene oxide 
process conditions (exclusive of gas phase inhibitor addition), generates 
at best a selectivity or efficiency to ethylene oxide of about 35-50%, and 
reduced catalytic activity. The most significant contributor to improving 
selectivity or efficiency and activity is the addition of gas phase 
organic chloride compounds such as ethyl chloride, ethylene dichloride and 
vinyl chloride. Many other gas phase additives to enhance selectivity have 
been depicted in the art (See Law, et al., U.S. Pat. Nos. 2,279,469 and 
2,279,470) and they range from the addition of nitrogen oxides, ammonia to 
xylene. All of them, at one time or another, have been found to 
beneficially affect efficiency. 
Another class of additives are those incorporated into the silver catalyst 
and are not part of the gas phase fed or provided to the catalyst. There 
are many metals which when added into the silver catalyst beneficially 
affect the performance of the catalyst. Some say that they act as 
promoters and others attribute the benefit to an inhibiting or suppressing 
action. In the absence of the gas phase additives, these metals make 
little contribution, if any, to the catalyst's performance. However, in 
the presence of the gas phase additive, the net effect is an improvement 
in the amount of ethylene oxide produced and a concomitant reduction in 
carbon dioxide. Such metals cover the spectrum of the Periodic Table and 
their roles in the reaction are not understood at this time. Presently, 
certain of the alkali metals have found favor as additives for enhancing 
performance of the silver catalysts. This subject will be readdressed 
later. 
Though metals have received much attention relatively little attention in 
the literature has been given to the role of anions in this reaction. 
Silver salts such as silver nitrate, silver lactate and silver oxalate 
have long been used as a source of silver metal. Since the silver salts 
are reduced by roasting to the metal form, their selection would appear to 
have been arbitrary except when those salts deposit or occlude 
contaminating cations. Of course, the silver salts employed should have 
sufficient solubility in the solvating medium to effect the deposition of 
desired amounts of silver metal on the catalyst. For example, the 
manufacture of silver oxalate by the reaction of silver nitrate with 
potassium oxalate leaves behind in the silver oxalate a small amount of 
potassium which cannot be removed from the silver oxalate and it goes 
along for a ride with the silver in the remainder of the catalyst 
preparation steps. This is classically demonstrated in carrying out the 
processes of examples I and II F of U.S. Pat. No. 3,702,259. As it turns 
out, the amount of potassium occluded is sufficient to yield the 
beneficial results according to that patent of enhanced selectivity and 
activity (see, in addition, the Nielsen and LaRochelle U.S. Pat. Nos. 
3,962,136, 4,012,425, 4,010,115 and 4,356,312, part of a later series of 
patents which attribute selectivity gains to usage of relatively narrow 
amounts of the alkali metals potassium, rubidium or cesium). The manner in 
which silver is provided in the support (or carrier), with the exception 
of the erroneous conceptions of U.S. Pat. No. 3,702,259, seems not to be 
important except for one point. If the support contains a lot of leachable 
impurities, the acidity or basicity of the medium out of which the silver 
is deposited should not be so strong as to leach them from the support and 
become part of the silver catalyst in amounts to adversely affect the 
performance of the catalyst in the ethylene oxide reaction. However, if 
one wishes to employ such leachates to enhance the performance of the 
catalyst, then, of course, the leaching action is desirable. 
Some early references in the art have suggested the use of alkali metal 
halide (see Gould, Sears, Brengle, et al., and Sacken, infra) but they 
seemed to be more interested in providing a process for adding both 
alkali, the promoter, and chloride the inhibitor, to accommodate the known 
benefits of alkali promotion and chlorine inhibition, see Law, et al., 
supra. and Evans, infra. By the time of their work Law, et al., had 
already proven in commercial operations that gas phase chloride addition 
was a significant contributor to enhanced production of ethylene oxide. 
The role of chlorine or chloride was easily speculated about because of 
silver's known propensity for reaction with chlorine to form silver 
chloride. Whether right or wrong, it became and still is fashionable to 
presume that surface silver chloride plays some role in either achieving 
or controlling the reaction. Indeed, the concept that the alkali metals 
remain as salts in the silver catalyst after manufacture seems in some 
quarters to be unthinkable, see the aforementioned Nielsen and LaRochelle 
patents, where the alkali metal is perceived to be in its final form as 
the oxide. As a matter of fact the process of Nielsen 3,702,259 serves to 
convert the occluded potassium into its nitrate salt as shown by Nielsen 
and Schroer, Belgium Patent 779,699. The belief that such alkali metal 
addition converted the alkali to the oxide is also found in De Krijger and 
Wattimina U.S. Pat. No. 3,563,923, who added lithium compounds to the 
support prior to silver deposition. Rightly or wrongly, the authors 
thought the lithium went to the oxide form. We believe those positions are 
incorrect and that the alkali metals always form salts, either as the 
salts as deposited, or formed in situ either with the support (or the 
binder portion f the support) or formed in situ during catalyst 
manufacture (see Nielsen and Schroer, supra) or later converted during use 
by reaction with gas phase components which provides anions such as 
nitrate, chloride and/or carbonate. 
As viewed by the prior art, the role of alkali metal was presumed to 
provide a promoter component and, with the exception of when the halide 
salt was described for providing halide inhibition, the role of anion has 
been regarded to be unimportant. One exception is Sacken, U.S. Pat. No. 
2,671,764, who describes, the benefits derived from the provision of 
alkali metal sulfates. [This patent will hereinafter be called the "Sacken 
sulfate" patent to distinguish it from U.S. Pat. No. 2,765,283, in which 
Sacken employs alkali metal halide additive.] Unquestionably, the Sacken 
sulfate patent recognizes benefits from the use of alkali metal sulfate as 
promoters for the silver catalyzed ethylene oxide reaction. However, the 
Sacken sulfate patent practices the process in the absence of gas phase 
inhibitor such as organic chlorides. Consequently, the results depicted in 
the patent is a process which yields a low ethylene oxide selectivity. 
Even though the Sacken sulfate patent specifies the use of alkali metal 
sulfate, it is only compared with the corresponding hydroxide in showing 
that the sulfate anion plays a role in the ethylene oxide reaction. The 
prime variable in the Sacken sulfate patent appears to be the choice of 
alkali metal. Other exceptions are U.S. Pat. Nos. 4,414,135 and 4,415,476, 
in which the first patent proposes the use of cesium bromide or fluoride 
and the second patent proposes the use of more than 1000 ppm of sodium and 
cesium, both as their chlorides (compare U.K. Patent 2,043,481, page 18, 
Table VI). The last exception is U.S. Pat. No. 4,406,820 which employs 
certain alkali metal salts of organic acids such as m-hydroxy-benzoic acid 
and acrylic acid. Such anions would be expected to be converted to 
combustion products. 
The successful commercial employment of ethylene oxide catalysts depends in 
part upon a variety of factors other than the efficiency or selectivity 
and activity issues emphasized so frequently in the literature (especially 
the patent literature). Laboratory experimentations in this field run the 
gamut from testing and evaluating such catalysts in microreactors (i.e., 
tiny tubular reactors for testing crushed catalyst particles) to backmixed 
autoclaves of the Berty type (i.e., larger reactors which test full sized 
catalyst pellets and generally employ full gas recycle). Microreactors can 
yield the highest efficiency numbers, typically far greater than is 
obtainable in commercial tubular reactor operations for the same catalyst 
in non crushed condition, while backmixed autoclaves typically provide the 
lowest efficiency numbers because the entire catalyst is exposed to the 
outlet gas which has the lowest concentration of reactants and the highest 
concentration of products. Thus, direct comparisons between such reactor 
systems are not easily obtainable. Catalyst efficiency can be enhanced by 
a number of tricks such as by using unusually high amounts of ethylene or 
oxygen in the feed gas, low reaction rates, manipulation of inhibitor 
content in the gas feed, and by the reduction or elimination of carbon 
dioxide in the gas feed. Consequently, allegations of superiority or 
desirability of one catalyst over another have to be tested in controlled 
and comparable ways. But given that a catalyst provides under controlled 
and comparable conditions superior efficiency (or selectivity) values over 
another catalyst, such would be meaningless in the commercial world unless 
that superiority in performance is obtainable in respect to a 
commercially-usable catalyst size, a commercial size charge of such 
catalyst and such catalyst charge has respectable aging characteristics 
during commercial usage. Moreover, the catalyst should commercial usage 
has to satisfy a number of requirements. It must have a physical form and 
strength to allow proper gas flow in the reactor without being crushed. 
Catalyst breakage or abrasion is essentially unacceptable because of the 
pressure drop ad safety problems created. The catalyst should be able to 
withstand a certain amount of temperature rise in the reactor, and be 
regenerable when over chlorinated, which can and usually does happen on 
occasion during a catalyst's life in a commercial operation. It is 
desirable that an ethylene oxide catalyst be resistant to feed 
contaminations and regenerable when poisoned by inadvertent discharge of 
agueous caustic into the catalyst beds. Thus what may be an improvement in 
catalysis by one standard may be meaningless if the catalyst fails the 
other important characteristics and properties, and what may seem to be a 
highly efficient catalyst may only be so because of the method used to 
define such efficiency. 
DETAILED DISCUSSION OF PRIOR ART 
The manufacture of ethylene oxide by the reaction of oxygen or 
oxygen-containing gases with ethylene in the presence of a silver catalyst 
is an old and developed art. For example, U. S. Pat. No. 2,040,782, 
patented May 12, 1936, describes the manufacture of ethylene oxide by the 
reaction of oxygen with ethylene in the presence of silver catalysts which 
contain a class of metal promoters. In Reissue U. S. Pat. No. 20,370, 
dated May 18, 1937, Leforte discloses that the formation of olefin oxides 
may be effected by causing olefins to combine directly with molecular 
oxygen in the presence of a silver catalyst. From that point on, the prior 
art has focused its efforts on improving the catalyst's efficiency in 
producing ethylene oxide. 
In characterizing this invention, the terms "conversion", "selectivity", 
and "yield" are employed as defined in U. S. Pat. No. 3,420,784, patented 
Jan. 7, 1969, at column 3, lines 24-35 inclusive. This definition of 
"selectivity" is consistent with that disclosed in U. S. Pat. No. 
2,766,261 at column 6, lines 5-22, and U. S. Pat. No. 3,144,916, lines 
58-61. The definitions of "yield" and "conversion" have more varied 
meaning in the art and are not to be employed as defined, for example, in 
the aforementioned U. S. Pat. No. 2,766,261. The terms "efficiency" and 
"selectivity", as used throughout the specification and claims are 
intended to be synonomous. 
Silver catalysts employed in the manufacture of ethylene oxide have 
undergone significant changes since their initial period of development. 
As reported by the art, silver particles were first deposited upon support 
materials with little attention being paid to support properties, such as 
surface area, pore volume and chemical inertness. As the art evolved, 
there developed special technologies related to carriers or supports 
containing silver that were more effective for the reaction of ethylene 
with oxygen to produce ethylene oxide. Today, most supports for the silver 
catalysts are shaped particulate materials which can be loaded in the 
interior of a reactor wherein the reacting gases and the gaseous products 
of the reaction are capable of flowing in and about these particulate 
materials to pass through the reactor and be recovered. The size and shape 
of the support are variable factors and the particular size and shape 
selected are peculiar to the reactor employed, the gas flow required, and 
the pressure drop across the reactor, with other factors also being 
considered. 
The carriers that have been employed are typically made of inorganic 
materials, generally of a mineral nature. In most cases, the preferred 
carrier is made of alpha-alumina, such as has been described in the patent 
literature: see for example, U. S. Pat. Nos. 2,294,383; 3,172,893; 
3,332,887; 3,423,328; and 3,563,914. 
The carriers which are employed for the manufacture of most, if not all, 
commercially employed ethylene oxide catalysts are produced by companies 
who do not produce such catalysts. As a rule, the methods of making such 
carriers are trade secrets of significant value to the carrier 
manufacturers. Consequently, the catalyst manufacturer cannot know how the 
carrier is made. Critical to making a carrier which proves uniquely 
desirable for the manufacture of a successful catalyst can be a number of 
factors, such as the purity and other physical/chemical properties of raw 
materials used to make the carrier and the method by which the carrier is 
made. 
The silver that is deposited on these carriers is thought to be in the form 
of small particles because that is all that can be seen by current 
microscopic techniques. The patent literature indicates that the size of 
the silver is a factor in the effectiveness of the catalyst and in most 
cases fine particle silver is obtained utilizing the standard processes in 
the art; see, for example, U. S. Pat. Nos. 2,554,459; 2,831,870; 3,423,328 
(specifies that silver particles of 150-400 Angstroms are employed): 
3,702,259 (disclosed a preparation procedure for forming silver particles 
less than 1 micron in diameter) and 3,758,418 (discloses silver particles 
having a diameter less than 1000 Angstroms). Improvements in microscopic 
examinations of silver catalysts enable the observation that the particle 
size ranges to even smaller values. 
The deposition of silver onto the carrier can be achieved by a number of 
techniques but the two techniques which are most frequently employed 
involve, in one case, the impregnation of the support with a silver 
solution followed by heat treatment of the impregnated support to effect 
deposition of the silver on the support and in the other case, the coating 
of the silver on the support by the precipitation of silver or the 
preformation of silver into a slurry such that the silver particles are 
deposited on the support and adhere to the support surface when the 
carrier or support is heated to remove the liquids present. These various 
procedures are exemplified in various U. S. Pat. Nos. such as 2,773,844; 
3,207,700; 3,501,407; 3,664,970 (see British Patent 754,593) and 
3,172,893. 
The surface area provided by the support has been the subject of 
considerable interest in the development of silver catalysts. Disclosures 
concerning the surface area of the catalyst carrier can be found in U. S. 
Pat. No. 2,766,261 (which discloses that a surface area of 0.002-10 m2/gm 
is suitable); U. S. Pat. No. 3,172,893 which depicts a porosity of 35-65% 
and a pore diameter of 80-200 microns); U. S. Pat. No. 3,725,307 which 
depicts a surface area of less than 1 sg.m/gm and an average pore diameter 
of 10-15 microns): U. S. Pat. No. 3,664,970 (which utilizes a support 
having a minimum porosity of about 30%, at least 90% of the pores having 
diameters in the range of 1-30 microns, and the average of such diameters 
being in the range of 4-10 microns); and U. S. Pat. No. 3,563,914 which 
utilizes a catalyst support having a surface area of less than 1 sg. m/gm, 
a volume of 0.23 ml/gm and a particle size between 0.074 and 0.30 mm). Low 
surface area, inert alpha alumina is favored by the prior art. 
As mentioned above, the workers in the field have determined that a variety 
of metals or metal cations when present in combination with the silver 
could act to promote a silver catalyst's ability to make ethylene oxide. 
These materials in themselves are not considered catalysts. Their presence 
in the catalyst has appeared to contribute to enhancing the rate or amount 
of oxide production but, as pointed out above, that contribution generally 
depends upon the presence of a gas phase additive such as the so-called 
gas phase inhibitor. Because the competing reactions in the reactor occur 
simultaneously and the critical factor in determining the effectiveness of 
the overall process is the measure of control one has over these competing 
reactions, inevitably a material which enhances the production of ethylene 
oxide might also be considered a material which inhibits the complete 
combustion of ethylene to carbon dioxide and water. Thus, there is a 
problem in defining whether that material which is termed a promoter is in 
fact an inhibitor of the combustion reaction. Where gas phase inhibitors 
are present and a so called promoted catalyst is used, a co action occurs 
which leaves one to question whether the "promoter" materials are in 
reality inhibitors or promoters. However, this matter seems to be an 
irrelevant issue. What is significant is that the outcome of the reaction 
is favorable to the efficient production of ethylene oxide. 
It has been known for a long time that impurities present in the catalyst 
and/or the gas phase can materially impact upon the reaction. In the early 
development of the art, there were no techniques available for identifying 
or measuring such impurities. Consequently, one could not isolate the role 
that such impurities played However, even in the earliest periods of the 
development of the art, the use of alkali metals as promoters for the 
silver catalyzed production of ethylene oxide was extremely well known in 
the art. U.S. Pat. No. 2,177,361, issued October 1939, has a teaching of 
the use of alkali metals in silver catalysts. U.S. Pat. No. 2,238,471 
discloses that lithium is very desirable as a promoter but that potassium 
and cesium are detrimental when used in amounts of essentially 10% by 
weight of potassium hydroxide or cesium hydroxide to the silver oxide 
employed in making the catalyst. Later, U.S. Pat. No. 2,404,438 states 
that sodium and lithium are effective promoters for this reaction. 
Essentially the same teaching can be found in U.S. Pat. No. 2,424,084. 
U.S. Pat. No. 2,424,086 generalizes about alkali metals as promoters and 
specifies sodium in particular. In U.S. Pat. No. 2,671,764 (the Sacken 
sulfate patent), the patentees believe that alkali metals in the form of 
their sulfates are effective as promoters for such silver catalysts. In 
particular, the patentees state that sodium, potassium, lithium, rubidium 
or cesium sulfates may be used as promoters. U.S. Pat. No. 2,765,283 
describes the pretreatment of a support with a dilute solution of a 
chlorine containing compound and indicates that such chlorine compounds 
should be inorganic. Particular illustrations cited of suitable inorganic 
chlorine compounds included sodium chloride, lithium chloride and 
potassium chlorate. This patent specifies that the amount of the inorganic 
chlorine containing compound which is deposited on the catalyst support is 
from 0.0001% to 0.2% by weight, based on the weight of the support. U.S. 
Pat. No. 2,615,900 to Sears describes the use of metal halide in the 
treatment of the supported catalyst and specifies that such halides can be 
of alkali metals such as lithium, sodium, potassium and cesium. The metal 
halide is present in the range of 0.01% to 50% based upon the weight of 
metallic silver. The patent also specifies that mixtures of the individual 
metal halides generally classified in the patent may be used to advantage 
to enhance the break-in period of a new catalyst composition while at the 
same time maintaining a moderate but steady activity of the catalyst over 
an extended period of time during normal operation. Thus, one particular 
metal halide treated catalyst would provide a short term high initial 
activity whereas another of the metal halides would provide a longer term 
moderate activity for the catalyst. This patent takes the position that 
the metal halides which are provided in the catalyst serve to inhibit the 
combustion of ethylene to carbon dioxide and thus classifies these 
materials as catalyst depressants or anticatalytic materials. U.S. Pat. 
No. 2,709,173 describes the use of a silver catalyst for making ethylene 
oxide in which there are provided simultaneously with the introduction of 
silver to the solid support, any of the alkali metal halides such as 
lithium, sodium, potassium, and rubidium compounds of chlorine, bromine 
and iodine, to enhance the overall production of ethylene oxide. The 
patent specifies small amounts "of less than about 0.5% are desirable". In 
particular, the patent emphasizes "proportions of alkali metal halide 
within the range of about 0.0001 to about 0.1%" are most preferred. The 
patent states that "although the preferred catalyst composition contains a 
separate promoter it is not always necessary since during preparation of 
the catalyst the alkali metal halide may be converted to some extent to 
the corresponding alkali metal oxide which acts as a promoter." U.S. Pat. 
No. 2,766,261 appears to draw from the teachings of U.S. Pat. No. 
2,238,474 in that cesium and potassium are said to be detrimental in 
silver catalysts; sodium and lithium are suggested as useful promoters. 
However, U.S. Pat. No. 2,769,016 finds that sodium, potassium and lithium 
are promoters when used in the silver catalysts. This latter patent also 
recommends the pretreatment of the support with dilute solutions of sodium 
chloride, lithium chloride or potassium chlorate. U.S. Pat. No. 2,799,687 
to Gould, et al., states that the addition of metal halides within the 
range described by Sears in U.S. Pat. No. 2,615,900 is not productive of 
optimum results. This is said to be especially true in the case of alkali 
metal halides, particularly the chloride and fluoride of sodium and 
potassium. The patentees recommend that the inorganic halide component of 
the catalyst be maintained within the range of 0.01-5 weight percent, 
preferably 0.01 to 0.1 weight percent, based on the weight of the "silver 
oxidative catalytic component," i.e., the silver salt transformed into 
elemental silver. U.S. Pat. No. 3,144,416 mentions a variety of metals as 
promoters and one of them is cesium. U.S. Pat. No. 3,258,433 indicates 
that sodium is an effective promoter. U.S. Pat. No. 3,563,913 recommends 
the use of alkali metals such as lithium compounds as promoters. The 
preferred amount of promoting material is said to be about 0.03 to 0.5%, 
by weight of metal oxide based on the weight of the support. U.S. Pat. No. 
3,585,217 states that alkali metal chlorides "are known to counteract the 
formation of carbon dioxide" and "may be incorporated into the catalyst". 
U.S. Pat. No. 3,125,538 discloses a supported silver catalyst containing a 
coincidentally deposited alkali metal selected from among potassium, 
rubidium and cesium in a specified gram atom ratio relative to silver. The 
weight of silver is preferably 2-5%, by weight, of the catalyst. The 
patentees characterize this catalyst as being especially suitable for the 
reaction of nitric oxide with propylene. This same catalyst is produced 
inherently by the processes of the examples of U.S. Pat. No. 3,702,259, 
as discussed previously, which patent promotes their use for making 
ethylene oxide. U.S. Pat. Nos. 3,962,136 and 4,012,425 also disclose that 
same catalyst as being useful for ethylene oxide production. U.S. Pat. No. 
3,962,136 describes the coincidental deposition of alkali metal with the 
silver on the support, the alkali metals being present in their final form 
on the support in the form of an oxide in which the oxide consists of 
cesium, rubidium or mixtures of both, optionally, combined with a minor 
amount of an oxide of potassium. The amount of such oxide is from about 
4.0.times.10.sup.-5 gew/kg to about 8.0.times.10.sup.-3 gew/kg of total 
catalyst. However, U.S. Pat. No. 4,010,115, patented Mar. 1, 1977, 
purports to distinguish itself from the other patents by employing as the 
oxide of the alkali metal the oxide of potassium optionally combined with 
a minor amount of an oxide of rubidium or cesium. U.S. Pat. No. 4,356,312 
describes the use of the same catalyst. Application Ser. No. 317,349, 
filed Dec. 21, 1972, which is a parent to U.S. Pat. Nos. 3,962,136 and 
4,010,115, and others, contains some interesting data deserving of 
comment. According to example 2 which contains some comparative 
experiments, there is described the manufacture of a catalyst which 
contains 310 parts per million by weight of coincidentally-added potassium 
and that catalyst when employed as an ethylene oxidation catalyst was 
found to be inactive for the production of ethylene oxide. 
U.S. Pat. No. 4,207,210 (corres. Belgium Patent 821,439, based upon British 
Patent Specification 1,489,335) discloses that a catalyst can be made that 
is equivalent to that produced in the so-called parent applications cited 
in U.S. Pat. Nos. 3,962,136, 4,012,425, and Patent 4,010,115 by using a 
sequential procedure by which the alkali metal is supplied to the support. 
Thus, the criticality in the method of deposition of alkali metal in the 
catalyst appears doubtful in the face of that type of disclosure and the 
disclosure of U.S. Pat. Nos. 4,033,903 and 4,125,480 which describe 
subjecting used silver-containing catalysts to a post-addition of one or 
more of potassium, rubidium or cesium. Apparently such treatment 
regenerates the catalyst's ability to enhance selectivity to ethylene 
oxide. Another patent which tends to indicate that a post addition of 
alkali metal such as cesium gives results equivalent to either 
pre-addition or simultaneous addition is U.S. Pat. No. 4,066,575. 
German Offenlegungsschrift 2,640,540 discloses in its examples a silver 
catalyst for ethylene oxide production containing sodium and either 
potassium, rubidium or cesium. 
Japanese Application Publication Disclosure No. 95213/75 is directed to a 
process for producing ethylene oxide using a catalyst composition 
comprising silver, barium, potassium and cesium in specified atomic 
ratios. Table I of this disclosure summarizes the efficiencies achieved 
with the various catalyst compositions of the examples. 
U.S. Pat. No. 4,039,561 discloses a catalyst for preparing ethylene oxide 
containing silver, tin, antimony, thallium, potassium, cesium and oxygen 
in specified atomic ratios. 
Belgium Patent 854,904 discloses silver catalysts containing various 
mixtures of sodium and cesium. U.K. Patent Application 2,002,252 
discloses, in Table 2, supported silver catalysts containing various 
mixtures of cesium and thallium, some of which additionally contain 
potassium or antimony. U.S. Pat. No. 4,007,135 broadly discloses (in 
column 2, lines 25-30) silver catalysts for alkylene oxide production 
containing silver "together with a promoting amount of at least one 
promoter selected from lithium, potassium, sodium, rubidium, cesium, 
copper, gold, magnesium, zinc, cadmium, strontium, calcium, niobium, 
tantalum, molybdenum, tungsten, chromium, vanadium and barium...". U. S. 
Pat. Nos. 3,844,981 and 3,962,285 disclose catalysts and processes for 
epoxidizing olefins in the presence of a multimetallic component. The 
catalyst in the 3,962,285 patent is said to comprise a minor amount of one 
or more of palladium, uthenium, rhenium, iron and platinum with a major 
amount of silver. The 3,844,981 patent discloses the preparation of the 
catalyst from a decomposible salt of group 7b, 1b or the iron group of 
group 8 of the Periodic Table of the Elements. Preferably, the salt is 
selected from the group of gold, copper, rhenium, manganese and iron 
salts. While the patentee contemplates that these metals are in the 
metallic state, oxidation during epoxidation conditions may occur with one 
or more of these metals, e.g., rhenium, to form oxyanions containing the 
metal. 
European Patent Publication No. 0003642 discloses, in Table 3, silver 
containing catalysts which include mixtures of potassium and cesium, and a 
catalyst containing sodium and cesium. 
Belgium Patent 867,045 discloses supported silver catalysts containing what 
is referred to as an effective proportion of lithium and a substantially 
lesser amount of alkali metal selected from among cesium, rubidium and/or 
potassium. 
Belgium Patent 867,185 discloses supported silver catalysts for ethylene 
oxide production containing a specified amount of potassium and at least 
one other alkali metal selected from rubidium and cesium. 
United Kingdom Patent No. 2,043,481, commonly assigned, describes the use 
of a synergistic combination of cesium and at least one other alkali metal 
in combination with silver on an inert support to provide catalysts which 
were superior to those known to the art at that time. Such catalysts have 
been widely employed commercially. The alkali metal components are 
provided to the support by a variety of ways. The alkali metal can be 
supplied to the support as a salt and many salts of the alkali metals are 
described. Specific illustration is made of the use of alkali metal 
sulfates as one of many usable alkali metal compounds. 
European Patent Application 85,237 describes an ethylene oxide catalyst 
wherein the applicants believe they "chemically absorbed" by alcohol wash, 
cesium and/or rubidium onto the catalyst support, a procedure not unlike 
that described by Neilsen and Schroer, supra. for potassium treated 
catalysts. 
Japanese patent application Kokai 56/105,750 discloses, among other things, 
ethylene oxide catalysts containing cesium molybdate or cesium tungstate 
or cesium borate. The catalyst is stated to have an alumina carrier having 
a sodium content of less than 0.07 weight % and mainly consisting of alpha 
alumina having a specific surface area of 1 to 5 sg. m./gm. The carrier is 
impregnated with decomposible silver salt solution containing alkali metal 
boron complex, alkali metal molybdenum complex and/or alkali metal 
tungsten complex. No examples of mixtures of anions are disclosed, nor is 
there any disclosure or suggestion of mixtures of cesium with other alkali 
metals or alkaline earth metals. Japanese patent application Kokai 
57/21937 discloses thallium containing catalysts in which the thallium may 
be a borate or titanate salt. 
Since the date of filing of the Ser. No. 640,269 patent application, a 
number of patent documents have been published relating to ethylene 
epoxidation catalysts which may contain oxyanions. European patent 
application 247,414, published Dec. 12, 1987, discloses catalysts 
containing alkali metal and/or barium which may be provided as salts. The 
salts include nitrates, sulfates, and halides. European patent 
applications 266,015, published May 4, 1988, and 266,852, published May 
11, 1988, disclose catalysts containing a rhenium component, e.g., rhenium 
oxide, rhenium cation or rhenate or perrhenate anion. An example of a 
catalyst made from silver oxalate with cesium hydroxide, ammonium 
perrhenate, and ammonium sulfate is disclosed in the '852 application. 
Numerous examples of silver catalysts containing cesium, rhenate and co 
promoter salts are presented in the '015 application. For instance, 
Experiment 7-12 reports a catalyst having 13.5 weight percent silver, 338 
ppmw (parts per million by weight) cesium (CsOH), 186 ppmw rhenium 
(NH.sub.4 ReO.sub.4) and 55 ppmw manganese (KMnO.sub.4); Experiment 7-6, 
12.7 wt%, 421 ppm cesium, 186 ppmw rhenium, 32 ppm sulfur 
((NH.sub.4).sub.2 SO.sub.4) and Experiment 7-26, 14 7 wt% silver, 357 ppmw 
cesium and 78 ppmw potassium (as sulfate), 186 ppmw rhenium, 32 ppmw 
sulfur ((NH.sub.4).sub.2 SO.sub.4), and 184 ppmw tungsten (H.sub.2 
WO.sub.4). Experiments are presented in which vanadate, chlorate, 
molybdate, chromate, sulfite, phosphate and tungstate anion are added in 
combination with rhenate anion. 
DISCLOSURE OF THE INVENTION 
An aspect of this invention involves the manufacture of impregnated silver 
catalysts on a support, preferably an alpha-alumina support (having a size 
and configuration usable in commercially-operated ethylene oxide tubular 
reactors) having an alpha-alumina content (inclusive of binder) of at 
least 98 percent (98%) by weight, in which there is provided a mixture of 
at least one cesium salt and one or more alkali metal and alkaline earth 
metal salts. 
The anions of cesium salts comprise oxyanions, preferably polyvalent 
oxyanions, of elements other than the oxygen therein having an atomic 
number of at least 15 to 83 and being from groups 3b through 7b, 
inclusive, of the Periodic Table of the Elements (as published by The 
Chemical Rubber Company, Cleveland, Ohio, in CRC Handbook of Chemistry and 
Physics, 46th Edition, inside back cover). The salts of the alkali metals 
and/or alkaline earth metals present comprise at least one of halide of 
atomic numbers of 9 to 53, inclusive, and oxyanions of elements other than 
oxygen therein having an atomic number of either (i) 7 or (ii) 15 to 83, 
inclusive, and selected from the groups 3a to 7a, inclusive, and 3b to 7b, 
inclusive, of the Periodic Table of the Elements. Often the catalyst 
contains at least one anion other than an oxyanion of an element of groups 
3b to 7b. 
It is understood that in the preparation of the catalysts, regardless of 
the specific salts of cesium and the one or more other alkali metal and/or 
alkaline earth metal, intermixing will occur. Hence, a catalyst prepared 
using cesium sulfate and potassium molybdate will also contain cesium 
molybdate and potassium sulfate. 
The mixture is preferably in an amount sufficient relative to the amount of 
silver employed, to yield at STANDARD ETHYLENE OXIDE PROCESS CONDITIONS 
under oxygen process conditions, as hereinafter defined, a selectivity (or 
efficiency) of at least 79 percent. An aspect of the invention also 
involves the process of making ethylene oxide by feeding a gas phase 
mixture of ethylene, oxygen, recycled CO.sub.2 and a gas phase inhibitor 
to a bed of impregnated silver catalyst of this invention, to produce 
ethylene oxide. The process for making ethylene oxide is not limited to 
STANDARD ETHYLENE OXIDE PROCESS CONDITIONS for definition as is the 
catalyst. Catalysts which have been subjected to process conditions for 
ethylene oxide manufacture such as STANDARD ETHYLENE OXIDE PROCESS 
CONDITIONS are considered an important aspect of this invention. 
A remarkable aspect of a number of the various embodiments of this 
invention is the unique insensitivity of these catalysts to gas phase 
inhibitor addition. The catalysts of this aspect of the invention are 
active yet do not require critical doses of gas phase inhibitor for 
process control. Indeed, these catalysts tend to give a rather flat 
response to gas phase inhibitor addition making their use at commercial 
practice conditions efficient and free of upsets. Moreover, many of the 
catalysts of this invention exhibit unique high temperature responses 
yielding high selectivities at high temperatures (e.g., about 270.degree. 
C.) as are obtained at normal operating temperatures (e.g., about 
230.degree.-250.degree. C.). Many of the catalysts of this invention 
contain a cesium content which according to the prior art would be 
expected to poison the catalyst's capability for making ethylene oxide. 
Many of the catalysts of this invention depend upon a synergistic 
combination of alkali metal (in the salt form as herein defined) as 
spelled out in the aforementioned United Kingdom Patent No. 2,043,481, but 
the amounts of alkali metals to one another to achieve the desired synergy 
is now, according to this invention, not nearly as critical. 
The catalysts of many various embodiments of this invention can employ in 
their manufacture roasting conditions considerably different from those 
employed previously. For example, in making these catalysts, one may use 
lower temperatures for shorter periods of time to achieve a highly active 
catalyst at the onset of use in making ethylene oxide. 
DETAILED DESCRIPTION OF THE INVENTION 
The process for making the catalyst and the catalysts of the invention are 
characterized in their preferred embodiment by either cesium or a 
combination of (a) cesium and (b) at least one other alkali metal of 
lithium, sodium, potassium and rubidium and/or alkaline earth metal of 
magnesium, calcium, strontium and barium, so as to achieve a synergistic 
result, i.e., an efficiency greater than the greater value obtainable 
under common conditions from respective catalysts which are the same as 
said catalyst except that instead of containing both (a) and (b), one 
contains the respective amount of (a), and the other contains the 
respective amount of (b), or an improvement in aging characteristics or 
gas phase inhibitor response by reason of the presence of the amount of 
(b). Preferably, the catalyst contains other alkali metal. 
According to the most preferred aspects of this invention, the alkali 
metals are provided in the catalyst as salts whose anions are oxyanions as 
described previously. Catalysts in accord with this most preferred aspect, 
in general, are comprised of silver, cesium salts together with at least 
one other alkali metal (excluding francium) salt deposited onto the 
surface of a porous support, the particular mixture of silver and alkali 
metals being correlated in the most preferred embodiment to produce a 
synergistic result as defined in U.K. Patent 2,043,481 commonly assigned. 
The invention as hereinafter described defines the binary alkali metal salt 
combinations of cesium lithium, cesium-sodium, cesium potassium and 
cesium-rubidium which in combination with silver which when employed under 
STANDARD ETHYLENE OXIDE PROCESS CONDITIONS provide a synergistic result 
for a particular catalyst carrier and catalyst preparation. The catalysts 
of the invention are not, however, restricted to the above combinations of 
alkali metal salts and alkaline earth metal salts. Other alkali metal 
salts and/or salts of other cations may advantageously be added to any of 
the aforementioned synergistic combinations for the purpose of raising or 
lowering the catalyst operating temperature, improving the initial 
catalyst activity during the start up period and/or improving the aging 
characteristics of the catalyst over prolonged periods of operation. In 
some instances, the addition of a third or even a fourth alkali metal salt 
and/or alkaline earth metal salt and/or other salt to an otherwise 
synergistic binary combination will effect a further increase in catalyst 
efficiency thus contributing to the synergistic result. 
The techniques and relationships from which are derived synergistic binary 
alkali metal combinations for use in practicing the invention are 
described in considerable detail in United Kingdom Patent 2,043,481, and 
such description is incorporated herein by reference, specifically that 
disclosure at page 5, line 51 through page 11, line 6, inclusive. 
As with any catalyst for making ethylene oxide which provides optimum 
performance, there exists a correlation between 
(i) the nature of the support; 
(ii) the amount of silver on or in the support; 
(iii) the impurities or contaminants provided with the silver and other 
components; and 
(iv) the conditions under which the catalyst is used to produce ethylene 
oxide. 
In the above, for the purposes of this invention, "impurities or 
contaminants" can include the alkali metal salts defined above. 
However, in attempting to define any catalyst there must be a base value 
from which other factors are determined especially when the factors are 
variables, each dependent upon the base value for meaning. In the case of 
this invention, the base value can be the amount of silver or a 
combination of the amount of silver and the nature of the support. In most 
cases the latter combination will be the base value. Because at least two 
values will comprise the base value for catalyst performance, it is 
apparent that correlations between such combinations and other factors can 
be quite complex. There is no common thread of logic which integrates all 
of these combinations and/or factors To that extent, practice of the 
invention requires experimental efforts to achieve all or essentially all 
of the benefits of this invention. Without departing from this script, one 
skilled in the art can readily achieve the optimum performances of the 
catalysts of this invention. It should be recognized that such script is 
commonly followed by the artisan in making any commercially employable 
ethylene oxide catalyst. The elements of the script are dependent upon the 
technology employed in making the catalyst. 
The concentration of silver in the finished catalyst may vary from about 2 
to 40 or more, often, 2 to 20 or more, weight percent, a commercially 
preferred range being from about 6% to about 16% by weight of silver. 
Lower silver concentrations are preferred from a cost per unit catalyst 
standpoint. However, the optimum silver concentration for any particular 
catalyst will be dependent upon economic factors as well as performance 
characteristics, such as catalyst efficiency, rate of catalyst aging and 
reaction temperature. 
The concentration of cesium salt and other alkali metal and alkaline earth 
metal salts in the finished catalyst is not narrowly critical and may vary 
over a wide range. The optimum cesium salt and other alkali metal and/or 
alkaline earth metal salt concentration for a particular catalyst will be 
dependent upon performance characteristics, such as, catalyst efficiency, 
rate of catalyst aging and reaction temperature. The concentration of 
cesium salt in the finished catalyst may vary from about 0.0005 to 1.0 
weight percent, preferably from about 0.005 to 0.1 weight percent. The 
ratio of cesium salt to other alkali metal and alkaline earth metal 
salt(s) to achieve desired performance is not narrowly critical and may 
vary over a wide range. The ratio of cesium salt to other alkali metal and 
alkaline earth metal salt(s) may vary from about 0.0001:1 to 10,000:1, 
preferably from about 0.001:1 to 1,000:1. Preferably, cesium comprises at 
least about 1 to 95, e.g., about 5 to 90, and often about 10 to 80, mole 
percent of the total moles of alkali metal and alkaline earth metal in the 
finished catalyst. 
Carrier Selection 
The catalyst carrier employed in practicing the invention may be selected 
from conventional, porous, refractory materials which are essentially 
inert to ethylene, ethylene oxide and other reactants and products at 
reaction conditions. These materials are generally labelled as 
"macroporous" and consist of porous materials having surface areas less 
than 10 sg. m/g (square meters per gm of carrier) and often is less than 1 
sg. m/g. The surface area is measured by the conventional B.E.T. method 
described by Brunauer, S., Emmet, P., and Teller E., in J. Am. Chem. Soc. 
Vol. 60, pp. 309-16, (1938). They are further characterized by pore 
volumes ranging from about 0.15-0.8 cc/g, preferably from about 0.2-0.6 
cc/g. Pore volumes may be measured by conventional mercury porosimetry or 
water absorption techniques. Median pore diameters for the above described 
carriers range from about 0.01 to 100 microns. a more preferred range 
being from about 0.5 to 50 microns. The carriers may have monomodal, 
bimodal pore, or multimodal distributions. 
For ease of repeatability in the use and reuse of impregnating solutions, 
the carrier should preferably not contain ions which are exchangeable with 
the alkali and alkaline earth metals supplied to the catalyst, either in 
the preparation or use of the catalyst, so as to upset the amount of 
alkali metal which provides the desired performance and/or catalyst 
enhancement. If the carrier contains such ions, the ions should generally 
be removed by standard chemical techniques such as leaching. However, if 
the carrier contains an amount of alkali metal or alkaline earth metal, 
which is transferable to the silver, then either (i) the carrier may be 
treated to remove such excess alkali metal or alkaline earth metal or (ii) 
the amount of alkali metal or alkaline earth metal supplied to the 
catalyst should take into account the transferred alkali metal or alkaline 
earth metal. 
The chemical composition of the carrier, which may be an inert refractory 
oxide, is not narrowly critical. Carriers may be composed, for example, of 
alpha alumina, silicon carbide, silicon dioxide, zirconia, magnesia and 
various clays. The preferred carriers are alpha-alumina particles often 
bonded together by a bonding agent and have a very high purity, i.e., at 
least 98 wt. % alpha alumina, any remaining components being silica, 
alkali metal oxides (e.g., sodium oxide) and trace amounts of other metal 
and non-metal impurities; or they may be of lower purity, i.e., about 80 
wt. % alpha-alumina, the balance being a mixture of silicon dioxide, 
various alkali oxides, alkaline earth oxides, iron oxides, and other metal 
and non metal oxides. The carriers are formulated so as to be inert under 
catalyst preparation and reaction conditions. A wide variety of such 
carriers are commercially available. Alumina carriers are manufactured by 
United Catalysts, Inc., Louisville, Kentucky, and the Norton Company, 
Akron, Ohio. As stated above, processes for making carriers is often kept 
a trade secret by the manufacturers. Various alpha-alumina carriers are 
disclosed, for instance, U.S. Pat. Nos. 3,172,866; 3,908,002; 4,136,063; 
4,379,134; 4,368,144; 4,389,338, 4,645,754; and 4,701,437; European Patent 
Applications 207,550; 207,541; 244,895; 266,852; and 266,015; and the 
Peoples Republic of China Patent application CN 85 1-02281A. 
The carriers may be in the shape of pellets, extruded particles, spheres, 
rings and the like. The size of the carriers may vary from about 1/16" to 
1/2". The carrier size is chosen to be consistent with the type of reactor 
employed. In general, sizes in the range of 1/8" to 3/8" have been found 
to be most suitable in the typical fixed bed, tubular reactor used in 
commercial operations. 
While as with any supported catalyst, the optimal performance will depend 
upon optimizing the carrier in terms of its chemical composition 
(including impurities), surface area, porosity and pore volume. However, 
the enhancement in performance provided by this invention may be most 
pronounced when using less than optimized carriers. Thus, in demonstrating 
the invention in the examples, a variety of carriers are used. 
It has been stated in some patents that there exists a correlation between 
surface area of the support and the amount of alkali metal promoter one 
may employ to maximize the selectivity capabilities of the catalyst, see 
U.S. Pat. Nos. 3,962,136 and 4,207,210. This invention demonstrates that 
by the use of the alkali metal salts of this invention, such a 
relationship does not exist and amounts of alkali metal salts far greater 
(based on alkali content) than that previously urged desirable can be 
employed to produce the best performing catalysts as judged by present day 
commercial standards. 
Oxyanions and Other Anions 
The types of oxyanions suitable as counterions for the alkali and alkaline 
earth metals provided in the catalysts of this invention comprise by way 
of example only, sulfate, SO.sub.4.sup.-2, phosphates, e.g., 
PO.sub.4.sup.-3, manganates, e.g., MnO.sub.4.sup.-2, titanates, e.g., 
TiO.sub.3.sup.-2,tantalates, e.g., Ta.sub.2 O.sub.6.sup.-2, molybdates, 
e.g., MoO.sub.4.sup.-2, vanadates, e.g., V.sub.2 O.sub.4.sup.-2, 
chromates, e.g., CrO.sub.4.sup.-2, zirconates, e.g., ZrO.sub.3.sup.-2, 
polyphosphates, nitrates, chlorates, bromates, tungstates, thiosulfates, 
cerates, and the like. The halide ions include fluoride, chloride, bromide 
and iodide. It is well recognized that many anions have complex 
chemistries and may exist in one or more forms, e.g., manganate 
(MnO.sub.4.sup.-2) and permanganate (MnO.sub.4.sup.-1); orthovanadate and 
metavanadate; and the various molybdate oxyanions such as 
MoO.sub.4.sup.-2, Mo.sub.7 O.sub.24.sup.-6 and Mo.sub.2 O.sub.7.sup.-2. 
While an oxyanion, or a precursor to an oxyanion, may be used in solutions 
impregnating a carrier, it is possible that during the conditions of 
preparation of the catalyst and/or during use, the particular oxyanion or 
precursor initially present may be converted to another form which may be 
an anion in a salt or even an oxide such as a mixed oxide with other 
metals present in the catalyst. In many instances, analytical techniques 
may not be sufficient to precisely identify the species present. The 
invention is not intended to be limited by the exact species that may 
ultimately exist on the catalyst during use but rather reference herein to 
oxyanions is intended to provide guidance to understanding and practicing 
the invention. 
Frequently, in the finished catalyst the calculated ratio of A/n:Cs, 
wherein A is the moles of oxyanion of elements of group 3b to 7b and n is 
the valence of such oxyanion and Cs is the moles of cesium, is at least 
about 1:10, preferably at least about 3:10. When a nitrate anion is 
employed, generally the catalyst contains sodium or, preferably, 
potassium, and the nitrate comprises at least 20, say, at least 50, mole 
percent of the total anion associated with alkali metals and alkaline 
earth metals. In some instances, it has been found beneficial to add more 
anion than is required to associate with the alkali metal and alkaline 
earth metal being provided to the catalyst. The reason why such additional 
anion is beneficial in these situations is not known. The additional anion 
may be added in the form of an acid, an ammonium salt, an amine salt, 
etc., or a portion of the alkali metal and/or alkaline earth metal may be 
added as an acid salt, e.g., potassium hydrogen sulfate. 
Catalyst Preparation 
A variety of procedures may be employed for preparing catalysts containing 
the aforementioned cesium salts, alone or with one or more other alkali 
metal salts (excluding francium salts), and/or alkaline earth metal salts 
or other salts in accordance with the present invention. The preferred 
procedure comprises: (1) impregnating a porous catalyst carrier with a 
solution comprising a solvent or solubilizing agent, silver complex in an 
amount sufficient to deposit the desired weight of silver upon the 
carrier, and the aforementioned alkali metal and alkaline earth metal 
salts sufficient to deposit respective amounts of them on the support such 
that the efficiency of ethylene oxide manufacture of the finished catalyst 
when tested at STANDARD ETHYLENE OXIDE PROCESS CONDITIONS under oxygen 
process conditions is at least 79 percent and (2) thereafter treating the 
impregnated support to convert the silver salt to silver metal and effect 
deposition of silver, and the alkali metal and alkaline earth metal salts 
on the exterior and interior surfaces of the support. Silver and alkali 
(and alkaline earth) metal salt deposition are generally accomplished by 
heating the carrier at elevated temperatures to evaporate the liquid 
within the support and effect deposition of the silver and metal salt onto 
the interior and exterior carrier surfaces. Impregnation of the carrier is 
the preferred technique for silver deposition because it utilizes silver 
more efficiently than coating procedures, the latter being generally 
unable to effect substantial silver deposition onto the interior surfaces 
of the carrier. In addition, coated catalysts are more susceptible to 
silver loss by mechanical abrasion. 
The sequence of impregnating or depositing the surfaces of the carrier with 
silver and alkali and alkaline earth metal salts is optional. Thus, 
impregnation and deposition of silver and alkali and/or alkaline earth 
metal salts may be effected coincidentally or sequentially, i.e., the 
alkali and/or alkaline earth metal salts may be deposited prior to, 
during, or subsequent to silver addition to the carrier. The alkali metal 
salts may be deposited together or sequentially. For example, cesium salts 
may be deposited first, followed by the coincidental or sequential 
deposition of silver and the other alkali or alkaline earth metal salts, 
or such other alkali or alkaline earth metal salts may be deposited first 
followed by coincidental or sequential deposition of silver and cesium 
salt. 
Impregnation of the catalyst carrier is effected using one or more 
solutions containing silver and alkali metal and/or alkaline earth metal 
salts in accordance with well known procedures for coincidental or 
sequential depositions. For coincidental deposition, following 
impregnation the impregnated carrier is heat or chemically treated to 
reduce the silver compound to silver metal and deposit the metal salts 
onto the catalyst surfaces. 
For sequential deposition, the carrier is initially impregnated with silver 
or alkali and/or alkaline earth metal salt (depending upon the sequence 
employed) and then heat or chemically treated as described above. This is 
followed by a second impregnation step and a corresponding heat or 
chemical treatment to produce the finished catalyst containing silver and 
salts. 
In making the catalysts of this invention, the alkali and alkaline earth 
metal salts have such high melting temperatures that when deposited on the 
support with silver compound, and subject to heating to convert the silver 
compound to silver metal, the salts preferably remain essentially 
unchanged. Of course, it is realized that alkali metal and alkaline earth 
metal salts having an unstable oxidation state will change to a stable 
oxidation state or states, e.g., sulfites to sulfates. Alkali metal and 
alkaline earth metal salts used in this invention having a stable 
oxidation state will remain essentially unchanged. This is contrary to 
what occurs when, e.g., alkali metal is deposited as the hydroxide or 
carbonate both of which may transform to different salt form (e.g. 
nitrate) during the heating (roasting) step depending on the roast 
conditions, see Nielsen and Schroer, supra, and/or during use. 
The silver solution used to impregnate the carrier is comprised of a silver 
compound in a solvent or complexing/solubilizing agent such as the silver 
solutions disclosed in the art. The particular silver compound employed 
may be chosen, for example, from among silver complexes, nitrate, silver 
oxide or silver carboxylates, such as, silver acetate, oxalate, citrate, 
phthalate, lactate, propionate, butyrate and higher fatty acid salts. 
Desirably, silver oxide complexed with amines is the preferred form of 
silver in the practice of the invention. 
A wide variety of solvents or complexing/solubilizing agents may be 
employed to solubilize silver to the desired concentration in the 
impregnating medium. Among those disclosed in the art as being suitable 
for this purpose are lactic acid (U.S. Pat. Nos. 2,477,436 to Aries; and 
3,501,417 to DeMaio); ammonia (U.S. Pat. No. 2,463,228 to West, et al); 
alcohols, such as ethylene glycol (U.S. Pat. Nos. 2,825,701 to Endler, et 
al.,; and 3,563,914 to Wattimina); and amines and agueous mixtures of 
amines (U.S. Pat. Nos. 2,459,896 to Schwarz; 3,563,914 to Wattimina; 
3,215,750 to Benisi; 3,702,259 to Nielsen; and 4,097,414, 4,374,260 and 
4,321,206 to Cavitt). 
Following impregnation of the catalyst carrier with silver and alkali metal 
and/or alkaline earth metal salts, the impregnated carrier particles are 
separated from any remaining non absorbed solution. This is conveniently 
accomplished by draining the excess impregnating medium or, alternatively, 
by using separation techniques, such as filtration or centrifugation. The 
impregnated carrier is then generally heat treated (e.g., roasted) to 
effect decomposition and reduction of the silver metal compound (complexes 
in most cases) to metallic silver and the deposition of alkali metal and 
alkaline earth metal salt. Such roasting may be carried out at a 
temperature of from about 100.degree. C. to 900.degree. C., preferably 
from 200.degree. to 700.degree. C., for a period of time sufficient to 
convert substantially all of the silver salt to silver metal. In general, 
the higher the temperature, the shorter the required reduction period. For 
example, at a temperature of from about 400.degree. C. to 900.degree. C., 
reduction may be accomplished in about 1 to 5 minutes. Although a wide 
range of heating periods have been suggested in the art to thermally treat 
the impregnated support (e.g., U.S. Pat. No. 3,563,914 suggests heating 
for less than 300 seconds to dry, but not roast to reduce, the catalyst, 
U.S. Pat. No. 3,702,259 discloses heating from 2 to 8 hours at a 
temperature of from 100.degree. C. to 375.degree. C. to reduce the silver 
salt in the catalyst; and U.S. Pat. No. 3,962,136 suggests 1/2 to 8 hours 
for the same temperature range), it is only important that the reduction 
time be correlated with temperature such that substantially complete 
reduction of the silver salt to metal is accomplished. A continuous or 
step-wise heating program is desirably used for this purpose. Continuous 
roasting of the catalyst for a short period of time, such as for not 
longer than 1/2 hour is preferred and can be effectively done in making 
the catalysts of this invention. A special attribute of the catalysts of 
this invention is that they are more amenable to roasting at lower 
temperatures, such as lower than about 500.degree. C., than the catalysts 
of U.K. Patent 2,043,481, without the sacrifice of performance 
characteristics. 
Heat treatment is preferably carried out in air, but a nitrogen or carbon 
dioxide atmosphere may also be employed. The equipment used for such heat 
treatment may use a static or flowing atmosphere of such gases to effect 
reduction, but a flowing atmosphere is much preferred. 
An important consideration in making the catalyst of this invention is to 
avoid the use of strongly acidic or basic solutions which can attack the 
support and deposit impurities which can adversely affect the performance 
of the catalyst. Acidic or basic components which do not adversely affect 
the catalyst can be, and are often, used, e.g., amines and compounds to 
provide the desired anions such as sulfuric acid, ammonium sulfate, 
molybdic acid, and the like. These compounds may be present in greater 
than the amounts required for stoichiometric combination. The preferred 
impregnation procedure of U.K. Patent 2,043,481 coupled with the high 
roasting temperature, short residence time procedure which the patent also 
described is especially beneficial in minimizing such catalyst 
contamination. However, the use of the salts of this invention coupled 
with the high purity supports allows one to use lower temperatures though 
short residence times ar preferred. 
The particle size of silver metal deposited upon the carrier is asserted by 
a portion of the prior art to be a function of the catalyst preparation 
procedure employed. This may seem to be the case because of the limited 
ability of the art to effectively view the surface of the catalyst. Thus 
the space between the silver particles seen on the carrier has not been 
characterized sufficiently to say whether only such particles of silver 
represent the silver on the carrier. However, the particular choice of 
solvent and/or complexing agent, silver compound, heat treatment 
conditions and catalyst carrier may affect, to varying degrees, the range 
of the size of the resulting silver particles seen on the carrier. For 
carriers of general interest for the production of ethylene oxide, a 
distribution of silver particles sizes in the range of 0.005 to 2.0 
microns is typically obtained. However, the role of particle size of the 
silver catalyst upon the effectiveness of the catalyst in making ethylene 
oxide is not clearly understood. In view of the fact that the silver 
particles are known to migrate on the surface of the catalyst when used in 
the catalytic reaction resulting in a marked change in their size and 
shape while the catalyst is still highly effective suggests that the 
silver particle size viewed on the support surfaces of the catalyst may 
not be a significant factor in catalytic performance 
Ethylene Oxide Production 
The silver catalysts of the invention are particularly suitable for use in 
the production of ethylene oxide by the vapor phase oxidation of ethylene 
with molecular oxygen. The reaction conditions for carrying out the 
oxidation reaction are well-known and extensively described in the prior 
art. This applies to reaction conditions, such as temperature, pressure, 
residence time, concentration of reactants, gas phase diluents (e.g., 
nitrogen, methane and CO.sub.2), gas phase inhibitors (e.g., ethylene 
dichloride), and the like. The gases passed to the reactor may contain 
modifiers or inhibitors or additives such as disclosed by Law, et al., in 
U.S. Pat. Nos. 2,279,469 and 2,279,470, such as nitrogen oxides and 
nitrogen oxides generating compounds. See also, European Patent No. 3642. 
In addition, the desirability of recycling unreacted feed, or employing a 
single-pass system, or using successive reactions to increase ethylene 
conversion by employing reactors in series arrangement can be readily 
determined by those skilled in the art. The particular mode of operation 
selected will usually be dictated by process economics. 
Generally, the commercially practiced processes are carried out by 
continuously introducing a feed stream containing ethylene and oxygen to a 
catalyst-containing reactor at a temperature of from about 200.degree. C. 
to 300.degree. C., and a pressure which may vary from about five 
atmospheres to about 30 atmospheres depending upon the mass velocity and 
productivity desired. Residence times in large scale reactors are 
generally on the order of about 0.1 5 seconds. Oxygen may be supplied to 
the reaction in an oxygen-containing stream, such as air or as commercial 
oxygen. The resulting ethylene oxide is separated and recovered from the 
reaction products using conventional methods. However, for this invention, 
the ethylene oxide process envisions the normal gas recycle encompassing 
carbon dioxide recycle in the normal concentrations. 
STANDARD ETHYLENE OXIDE PROCESS CONDITIONS 
The STANDARD ETHYLENE OXIDE PROCESS CONDITIONS (ABBR. "CONDITIONS") for 
characterizing the catalysts of this invention involves the use of a 
standard backmixed autoclave with full gas recycle including carbon 
dioxide. The CONDITIONS may be operated with some variation in ethylene, 
oxygen and gas phase inhibitor feed. Two cases are illustrated: air 
process conditions, which simulates in the backmixed reactor the typical 
conditions employed in commercial air type ethylene oxide processes where 
air is used to supply the molecular oxygen and the oxygen process 
conditions, which simulates in the backmixed reactor the typical 
conditions in commercial oxygen type ethylene oxide processes where 
molecular oxygen, as such, is employed. Each case provides a different 
efficiency but it is the rule for practically all cases that air as the 
oxygen feed, using lower amounts of oxygen and ethylene, will yield an 
efficiency to ethylene oxide which is about 2 to 4 percentage points lower 
than that when molecular oxygen is employed as oxygen feed. The CONDITIONS 
employ the well known backmixed bottom agitated "Magnedrive" autoclaves 
described in FIG. 2 of the paper by J. M. Berty entitled "Reactor for 
Vapor Phase Catalytic Studies", in Chemical Engineering Progress, Vol. 70 
No. 5, pages 78-84. 1974. The CONDITIONS employ 1.0 mole % ethylene oxide 
in the outlet gas of the reactor under the following standard inlet 
conditions: 
______________________________________ 
Air process Oxyen process 
Conditions, Conditions, 
Component Mole % Mole % 
______________________________________ 
Oxygen 6.0 8.0 
Ethylene 8.0 30 
Ethane 0.5 0.5 
Carbon Dioxide 
6.5 6.5 
Nitrogen Balance of Gas 
Balance of Gas 
Parts per million 
7.5 10 
ethyl chloride 
(or one-half such 
amount when ethylene 
dichloride is used) 
______________________________________ 
The pressure is maintained constant at 275 psig and the total outlet flow 
is maintained at 22.6 SCFH. SCFH refers to cubic feet per hour at standard 
temperature and pressure, namely, 0.degree. C. and one atmosphere. The 
outlet ethylene oxide concentration is maintained at 1.0% by adjusting the 
reaction temperature. Thus, temperature (.degree. C.) and catalyst 
efficiency are obtained as the responses describing the catalyst 
performance. 
The catalyst test procedure used in the CONDITIONS involves the following 
steps: 
1. 80 cc of catalyst is charged to the backmixed autoclave. The volume of 
catalyst is measured in 1" I.D. graduated cylinder after tapping the 
cylinder several times to thoroughly pack the catalyst. The volume of 
catalyst is alternatively calculated from the packing density of the 
carrier and the amount of silver and additives. The weight of the catalyst 
is noted. 
2. The backmixed autoclave is heated to about reaction temperature in a 
nitrogen flow of 20 SCFH with the fan operating at 1500 rpm. The nitrogen 
flow is then discontinued and the above described feed stream is 
introduced into the reactor. The total gas outlet flow is adjusted to 22.6 
SCFH. The temperature is adjusted over the next few hours so that the 
ethylene oxide concentration in the outlet gas is approximately 1.0%. 
3. The outlet oxide concentration is monitored over the next 4-6 days to 
make certain that the catalyst has reached its peak steady state 
performance. The temperature is periodically adjusted to achieve 1% outlet 
oxide. The selectivity of the catalyst to ethylene oxide and the 
temperature are thus obtained. 
The standard deviation of a single test result reporting catalyst 
efficiency in accordance with the procedure described above is 0.7% 
efficiency units. The running of a multiplicity of tests will reduce the 
standard deviation by the square root of the number of tests. 
The specific STANDARD ETHYLENE OXIDE PROCESS CONDITIONS are used in the 
examples below unless indicated otherwise. In commercial processes, 
typical operating conditions can vary and the amounts of the ingredients 
employed can be adjusted to achieve the best efficiencies. In particular 
the amounts of ethane, carbon dioxide and organic chloride can be varied 
to optimize efficiency for the manufacture of ethylene oxide. Ethane is an 
impurity contained in varying amounts in ethylene raw material. Ethane can 
also be added to a commercial reactor to provide better control of the 
chloride's inhibitor action. Typically, the amount of ethane used in 
commercial processes can vary from about 0.001 to about 5 mole percent for 
achieving optimization under both air process conditions and oxygen 
process conditions. As the concentration of ethane increases in the 
reactor, the effective surface chloride concentration on the catalyst is 
believed to be decreased, thereby decreasing the ability of chloride to 
promote/inhibit reactions that increase efficiency for the manufacture of 
ethylene oxide. The amount of chloride, e.g., ethyl chloride or ethylene 
dichloride, can be varied to provide the needed promoter/inhibitor action 
commensurate with the ethane levels encountered in a particular process 
and the type of alkali and alkaline earth metal salt used in the catalyst. 
The amount of organic chloride used in commercial processes can typically 
vary from about 1.0 ppm to about 100 ppm for achieving optimization under 
both air process conditions and oxygen process conditions. Carbon dioxide 
is generally considered an inhibitor, and the inhibitor effect of carbon 
dioxide on process efficiency may be variable with its concentration. With 
different types of alkali metal and alkaline earth metal salts used in 
preparation of the catalysts of this invention, different concentrations 
of carbon dioxide may be more desirable in certain commercial processes. 
Typically, the amount of carbon dioxide used in commercial processes can 
vary from about 2 to about 15 mole percent for achieving optimization 
under both air process conditions and oxygen process conditions. The 
amount of carbon dioxide is dependent on the size and type of carbon 
dioxide scrubbing system employed. The optimization of the amounts of 
ethane, carbon dioxide and organic chloride provides catalysts which are 
especially suitable for obtaining desired efficiencies in commercial 
ethylene oxide manufacture. Catalysts which have been subjected to process 
conditions for ethylene oxide manufacture such as STANDARD ETHYLENE OXIDE 
PROCESS CONDITIONS are considered an important aspect of this invention. 
The following detailed procedures are provided as illustrative of methods 
and carriers which are useful for preparing catalysts according to the 
invention. These examples are by way of illustration only and are not to 
be construed as limiting the scope of the invention described herein. 
Typical alpha alumina carriers useful in practicing this invention are the 
following: 
______________________________________ 
CARRIER "A" 
Chemical Composition of Carrier "A" 
alpha-Alumina 98.57 wt. % 
Impurities (in bulk): 
SiO.sub.2 .99 wt. % 
CaO .008 wt. % 
Na.sub.2 O .226 wt. % 
Fe.sub.2 O.sub.3 .034 wt. % 
K.sub.2 O 
Physical Properties of Carrier "A" 
Surface Area (1) 0.36-0.55 m.sup.2 /g 
typically between 
0.40 and 0.50 m.sup.2 /g 
Pore Volume (2) 0.52 cc/g 
(or water absorption) 
Packing Density (3) 0.71 g/ml 
Median Pore diameter (4) 
20-30 microns 
Pore size Distribution, % Total Pore Volume (4) 
% Total 
Pore Size Microns Pore Volume 
______________________________________ 
&lt;0.1 0.0 
0.1-1.0 About 6.0 
1.0-10.0 37.0 
10.0-30.0 16.0 
30.0-100 32.0 
&gt;100 9.0 
______________________________________ 
CARRIER "B" 
Chemical Composition of Carrier "B" 
alpha-Alumina about 99.5 + wt. % 
Acid Leachable Impurities: 
Leachate contained 5 ppm SO.sub.4.sup.-2, 18 ppm 
Na.sup.+, 1.4 ppm Li+, 1 ppm Cl.sup.-, 2 ppm NO.sub.3.sup.- 
Physical Properties of Carrier "B" 
Surface Area (1) 0.43 m.sup.2 /g 
Pore Volume (2) 0.44 cc/g 
Packing Density (3) 0.705 g/cc 
Median Pore Diameter (4) 
10.2 microns 
Pore size Distribution, % Total Pore Volume (4) 
% Total 
Pore Size, Microns Pore Volume 
______________________________________ 
&lt;0.1 0 
0.1-1.0 0 
1-10 51.4 
10-30 4.6 
30-100 21.0 
&gt;100 23.0 
______________________________________ 
CARRIER "C" 
Chemical Composition of Carrier "C" 
alpha-Alumina about 99.84 wt. % 
Impurities (in bulk) 
Na.sub.2 O 0.02 wt. % 
K.sub.2 O 0.01 wt. % 
SiO.sub.2 0.01 wt. % 
Oxides of Ca and Mg 0.03 wt. % 
Acid Leachable Impurities: 
Leachate contained 80 ppm Na.sup.+, 17 ppm 
K.sup.+. 
Physical Properties of Carrier "C" 
Surface Area (1) 0.436 m.sup.2 /g 
Pore Volume (2) 0.502 cc/g 
Packing Density (3) 0.696 g/cc 
Median Pore Diameter (4) 
20.0 microns 
Apparent Porosity (%) 
66.3 
% Water Absorption 50.0 
Attrition Loss/Hr. (%) 
23.2 
25 Ft. Drop Test (% Passing) 
97 
Crush Strength Averae, lbs. 
14.9 
Pore Size Distribution, % Total Pore Volume (4) 
Total 
Pore Size, Microns Pore Volume 
______________________________________ 
P.sub.1 (&lt;0.1) 0 
P.sub.2 (0.1-0.5) 2.0 
P.sub.3 (0.5-1.0) 5.5 
P.sub.4 (1.0-10.0) 35.0 
P.sub.5 (10.0-100) 53.0 
P.sub.6 (&gt;100) 4.5 
______________________________________ 
CARRIER "D" 
Chemical Composition of Carrier "D" 
alpha-Alumina about 99.5 + wt. % 
Acid Leachable Impurities: 
Leachate contained 4 pm Na.sup.+, less than 
0.01 ppm K.sup.+, less than 0.01 ppm Ca.sup.++, less than 
0.01 ppm Mg.sup.++. 
Physical Properties of Carrier "D" 
Surface Area (1) 0.487 m.sup.2 /g 
Pore Volume (2) 0.429 cc/g 
Packing Density (3) 41.64 lbs/ft.sup.3 
Median Pore Diameter (4) 
47 microns 
Apparent Porosity (%) 
65 
% Water Absorption 48.9 
Crush Strength Average, lbs. 
9.0 
Pore Size Distribution, % Total Pore Volume (4) 
% Total 
Pore Size, Microns Pore Volume 
______________________________________ 
P.sub.1 (&lt;0.1) 0 
P.sub.2 (0.1-0.5) 2.0 
P.sub.3 (0.5-1.0) 7.0 
P.sub.4 (1.0-10.0) 30.0 
P.sub.5 (10.0-100) 26.0 
P.sub.6 (&gt;100) 35.0 
______________________________________ 
CARRIER "E" 
Carrier E is an alpha-alumina carrier prepared by calcining to a maximum 
temperature of about 1025.degree. C., gamma-alumina (available as N-6573 
from the Norton Company, Akron, Oh.) in the presence of about 3.55 weight 
percent aluminum fluoride as fluxing agent. The carrier contains at least 
99.0 weight percent alpha alumina, about 0.2 weight percent fluoride and 
as water leachable components: 
______________________________________ 
aluminum 132 ppmw 
calcium 50 ppmw 
magnesium 5 ppmw 
sodium 66 ppmw 
potassium 14 ppmw 
fluoride 425 ppmw 
nitrate 1 ppmw 
phosphate 11 ppmw 
fluorophosphate 2 ppmw 
sulfate 6 ppmw 
silicon 10 ppmw 
Physical Properties of Carrier "E" 
Surface Area (1) 1.17 m.sup.2 /g 
Pore Volume (2) 0.68 cc/g 
Median Pore Diameter (3) 
1.8 microns 
Packing Density (4) 
0.53 g/ml. 
Pore Size Distribution, % Total Pore Volume (4) 
% Total 
______________________________________ 
Pore Size, Microns 
Pore Volume 
P.sub.1 (&lt;0.1) 0 
P.sub.2 (0.1-0.5) 2.0 
P.sub.3 (0.5-1.0) 9.5 
P.sub.4 (1.0-10.0) 
84.5 
P.sub.5 (10.0-100) 
1.0 
P.sub.6 (&gt;100) 3.0 
______________________________________ 
CARRIER "F" 
Carrier F is an alpha-alumina carrier prepared by calcining to a maximum 
temperature of about 1100.degree. C., gamma alumina (N-6573) which had 
been impregnated with an aqueous 1M ammonia fluoride solution. The carrier 
contains at least 99.0 weight percent alpha-alumina and about 0.2 weight 
percent fluoride and has a surface area of 1.1 square meters per gram, a 
pore volume of 0.76 cubic centimeters per gram and a packing density of 
about 0.52 grams per milliliter. 
CARRIER "G" 
Carrier G is an alpha-alumina carrier prepared by calcining to a maximum 
temperature of about 1100.degree. C., gamma alumina (N 6573) which had 
been impregnated with aqueous 1M ammonium fluoride solution. The carrier 
contains at least 99.0 weight percent alpha alumina and about 0.25 weight 
percent fluoride and has a surface area of 1.0 square meter per gram, a 
pore volume of 0.76 cubic centimeters per gram and a packing density of 
0.52 grams per milliliter. 
CARRIER "H" 
Carrier H is an alpha-alumina carrier prepared by calcining to a maximum 
temperature of about 1100.degree. C., gamma-alumina (available as N 7759 
from The Norton Company) which has been impregnated with aqueous 1M 
ammonia fluoride solution. The carrier contains at least 99.0 weight 
percent alpha-alumina and about 0.62 weight percent fluoride and has a 
surface area of 1.0 square meter per gram, a pore volume of 0.74 cubic 
centimeters per gram and a packing density of 0.49 grams per milliliter. 
______________________________________ 
CARRIER "I" 
Carrier I is a high purity (99.3), alpha- 
alumina support containing as acid leachable 
components (Inductively Coupled Plasma Spectroscopy): 
Element PPM (Weight) 
______________________________________ 
Ag 0.2 
Al 164 
B 0.2 
Ba 0.3 
Ca 83 
Cd less than 0.1 
Co less than 0.1 
Cr less than 0.1 
Cu less than 0.1 
Fe 2 
Mg 6 
Na 130 
Pb 0.5 
Sb 0.7 
Si 104 
Sn 0.7 
Ti 7 
V 7 
Zn 0.2 
The carrier has an average pore diameter of 
0.54 micron, a pore volume of about 0.31 cc/g, and a 
surface area of about 0.8 square meter per gram. 
______________________________________ 
(1)Method of Measurement described in "Adsorption Surface Area and 
Porosity", S. J. Gregg and K. S. W. Sing, Academic Press (1967), pages 
316-321. 
(2)Method of Measurement as described in ASTM C20-46. 
(3)Calculated value based on conventional measurement of the weight of th 
carrier in a known volume container. 
(4)Method of Measurement described in "Application of Mercury Penetration 
to Materials Analysis", C. Orr, Jr., Powder Technology, Vol. 3, pp. 
117-123 (1970). 
Attrition Loss and Crush Strength Average and Range were determined 
according to Test No. 45 and Test No. 6, respectively, as referred to in 
Catalyst Carriers Norton Company, Akron, Ohio Bulletin CC-11, 1974. 25 Ft. 
Drop Test was determined by dropping carrier pills through a tube for a 
vertical distance of 25 feet onto a steel plate and observing for 
breakage. Non-breakage of carrier pills indicated percent passing. Acid 
Leachable Impurities were determined by contacting carrier pills with 10% 
nitric acid for one hour and determining extracted cations by standard 
Atomic Absorption spectroscopy techniques. Inductively Coupled Plasma 
Spectroscopy techniques may also be used for such determinations. 
Catalyst Preparation Techniques 
The carrier, as indicated, was impregnated under vacuum as hereinafter 
described with a solution of silver complex and alkali metal and alkaline 
earth metal salts. The alkali metal and/or alkaline earth metal containing 
components need not be introduced as the salts. For instance, cesium 
hydroxide may be used in conjunction with an ammonium salt (e.g., ammonium 
sulfate) or acid (e.g., sulfuric acid) or organic compound (e.g., 
ethylsulfonate) and under conditions of catalyst preparation or use, 
conversion is made to the desired species. The impregnating solution was 
prepared at a concentration such that the finished catalyst contained the 
desired amounts of silver cesium salt and/or the other alkali metal and/or 
alkaline earth metal salts. The required concentration of silver and 
alkali metal and alkaline earth metal salts in solution for the given 
carrier is calculated from the packing density (grams/cc) and pore volume 
of the carrier which are either known or readily determined. Assuming that 
all of the silver in the impregnating solution contained in the pores of 
the carrier is deposited upon the carrier, approximately 21 wt. % silver 
in solution is necessary to prepare a catalyst containing about 11 wt. % 
silver on the catalyst. This relationship can vary depending upon the 
nature of the carrier, e.g., pore volume of the carrier may influence the 
amount of silver deposited from a given solution. The required 
concentration of alkali metal or alkaline earth metal salts in solution is 
obtained by dividing the solution silver concentration by the ratio of 
silver to alkali metal or alkaline earth metal salts desired in the 
finished catalyst. Thus, to obtain 11.0 wt. % Ag and 0.0047 wt. % Cs, the 
ratio is approximately 2330 and the required cesium concentration in 
solution is 0.009 wt. %. The solution containing the desired 
concentrations of silver and alkali metal and alkaline earth metal salts 
was prepared as described below. 
Impregnating Solution Preparation 
The indicated amounts of ethylenediamine (high purity grade) were mixed 
with indicated amounts of distilled water. Then oxalic acid dihydrate 
(reagent grade) was then added slowly to the solution at ambient 
temperature (23.degree. C) while continuously stirring. During this 
addition of oxalic acid, the solution temperature rose to about 40.degree. 
C. due to the reaction exotherm. Silver oxide powder (Metz Corporation) 
was then added to the diamine oxalic acid salt-water solution while 
maintaining the solution temperature below about 40.degree. C. Finally, 
monoethanolamine, aqueous alkali metal salt solution(s) and distilled 
water were added to complete the solution. The specific gravity of the 
resulting solution was about 1.3-1.4 g/ml. 
Catalyst Preparation 
Carrier was impregnated in a 12 inches long .times.2 inches I.D. glass 
cylindrical vessel equipped with a suitable stopcock for draining the 
carrier after impregnation. A suitable size separatory funnel for 
containing the impregnatinq solution was inserted through a rubber stopper 
equipped with a metal tube for attaching a vacuum line into the top of the 
impregnating vessel. The impregnating vessel containing the carrier was 
evacuated to approximately 2 inches of mercury pressure for about 20 
minutes after which the impregnatinq solution was slowly added to the 
carrier by opening the stopcock between the separatory funnel and the 
impregnating vessel until the carrier was completely immersed in solution, 
the pressure within the vessel being maintained at approximately 2 inches 
of mercury. Following addition of the solution, the vessel was opened to 
the atmosphere to attain atmospheric pressure, the carrier then remained 
immersed in the impregnatinq solution at ambient conditions for about 1 
hour, and thereafter drained of excess solution for about 30 minutes. The 
impregnated carrier was then heat treated as follows (unless stated 
otherwise) to effect reduction of silver salt and deposition of alkali 
metal salts on the surface. The impregnated carrier was spread out in a 
single layer on a 25/8 inches wide endless stainless steel belt (spiral 
weave) and transported through a 2 inches .times.2 inches square heating 
zone for 2.5 minutes, the heating zone being maintained at 500.degree. C 
by passing hot air upward through the belt and about the catalyst 
particles at the rate of 266 SCFH. The hot air was generated by passing it 
through a 5 ft. long .times.2 inches I.D. stainless steel pipe which was 
externally heated by an electric furnace (Lindberg.TM. tubular furnace: 
21/2 inches I.D., 3 feet long heating zone) capable of delivering 5400 
watts. The heated air in the pipe was discharged from a square 2 inches 
.times.2 inches discharge port located immediately beneath the moving belt 
carrying the catalyst carrier. After being roasted in the heating zone, 
the finished catalyst was weighed, and, based upon the weight gain of the 
carrier and the known ratios of silver to alkali metal salt in the 
impregnatinq solution, it was calculated to contain the wt. % of silver, 
and wt. % alkali metal salts indicated. 
The analysis for silver was carried out by the following method: An 
approximately 50 g sample of catalyst was powdered in a mill and 10 g of 
the powdered sample weighed to the nearest 0.1 mg. The silver in the 
catalyst sample was dissolved in hot (80.degree. C.) 50%, by volume, 
nitric acid solution. The insoluble alumina particles were filtered and 
washed with distilled water to remove all adhering nitrate salts of Ag, 
Cs, etc. This solution was made up to 250 ml in a volumetric flask using 
distilled water. A 25 ml aliquot of this solution was titrated according 
to standard procedures using a 0.1 Normal solution of ammonium thiocyanate 
and ferric nitrate as indicator. The amount of Ag so determined in 250 ml 
solution was then used to calculate the weight percent silver in the 
catalyst sample. 
Silver and alkali metal concentrations for all catalysts described in the 
specification are calculated values as described above. 
Carriers are nominally ring shape having dimensions of about 1/8.times.5/16 
x 5/16 inch or about 1/8.times.1/4.times.1/4 inch.