Catalysts and process for the ammoxidation of olefins

Catalysts containing a rare earth, tantalum or niobium plus iron, bismuth and molybdenum and at least one element of nickel, cobalt, magnesium, zinc, cadmium or calcium are especially effective for the ammoxidation of olefins.

BACKGROUND OF THE INVENTION 
The catalysts of this invention have a high activity for the production of 
unsaturated nitriles at a relatively low reaction temperature. This high 
activity at a low reaction temperature is surprising in view of U.S. Pat. 
No. 2,904,580 issued Sept. 15, 1959, which discloses a process for the 
production of acrylonitrile from propylene and ammonia in the presence of 
a catalyst selected from the group consisting of bismuth, tin and antimony 
salts of molybdic and phosphomolybdic acids and bismuth phosphotungstate, 
and U.S. Pat. No. 3,226,422 issued Dec. 28, 1965, which discloses a 
catalyst comprising the oxides of iron, bismuth, molybdenum and phosphorus 
for the production of unsaturated nitriles from olefin-ammonia mixtures. 
In addition to high activity for nitrile production, the catalyst employed 
in the process of this invention has a number of other important 
advantages that contribute greatly to the efficient and economic operation 
of the process. The catalyst has excellent redox stability under the 
reaction conditions of the process. This permits the use of low process 
air to olefin ratios and high weight hourly space velocities. The catalyst 
exhibits efficient ammonia utilization thus greatly reducing the amount of 
unreacted ammonia appearing in the reactor effluent and thus lowering the 
amount of sulfuric acid required to neutralize the ammonia in the 
effluent. Improvements are obtained in the recovery section operation and 
pollution control resulting from the lowering of polymer waste products 
that are formed. The catalyst performs optimally at a lower reactor 
temperature than is normally employed for this type of reaction with per 
pass conversions to the nitrile product as high as 80 percent and above. 
Use of lower operating temperatures favors longer catalyst life and 
minimizes effluent problems such as afterburning. Ease of catalyst 
preparation and lower cost of the essential catalytic components are 
additional benefits that can be realized with the use of the catalyst of 
this invention. 
SUMMARY OF THE INVENTION 
The present invention is catalysts described by the formula 
EQU A.sub.a D.sub.g E.sub.b G.sub.c Fe.sub.d Bi.sub.e Mo.sub.12 O.sub.x 
Wherein 
A is a rare earth metal, tantalum, niobium or mixture thereof; 
D is an alkali metal; 
E is nickel, cobalt, magnesium, zinc, cadmium, calcium or mixture thereof; 
G is phosphorus, boron, arsenic or mixture thereof; and 
wherein 
a is greater than zero to about 3; 
b is about 0.1 to about 20; 
c and g are 0 to about 3; 
d is about 0.1 to about 8; 
e is about 0.1 to about 6; 
f is about 8 to about 16; and 
x is a number determined by the valence requirements of the other elements 
present. 
Another facet of this invention is the use of these catalysts in the known 
ammoxidation of propylene or isobutylene. 
The catalyst is any catalyst described by the empirical formula above. 
Preferred catalysts are those that contain nickel, cobalt or magnesium, 
i.e. where B is nickel, cobalt or magnesium, with those catalysts 
containing nickel and cobalt being especially preferred. Also preferred 
are those catalysts wherein C represents phosphorus, arsenic or mixtures 
thereof. 
The catalyst of this invention may be prepared by any of the numerous 
methods of catalyst preparation which are known to those skilled in the 
art. For example, the catalyst may be manufactured by co-gelling the 
various ingredients. The co-gelled mass may then be dried and ground to an 
appropriate size. Alternately, the co-gelled material may be slurried and 
spray dried in accordance with convention techniques. The catalyst may be 
extruded as pellets or formed into spheres in oil as is well known in the 
art. Alternatively, the catalyst components may be mixed with the support 
in the form of the slurry followed by drying, or may be impregnated on 
silica or other supports. 
The alkali metal may be introduced into the catalyst as an oxide or as any 
salt which upon calcination will yield the oxide. Preferred salts are the 
nitrates which are readily available and easily soluble. 
Bismuth may be introduced into the catalyst as an oxide or as any salt 
which upon calcination will yield the oxide. Most preferred are the 
water-soluble salts which are easily dispersible within the catalyst and 
which form stable oxides upon heat-treating. The most preferred salt for 
introducing bismuth is bismuth nitrate. 
To introduce the iron component into the catalyst one may use any compound 
of iron which, upon calcination, will result in the oxides. As with the 
other elements, water-soluble salts are preferred for the ease with which 
they may be uniformly dispersed within the catalyst. Most preferred is 
ferric nitrate. Cobalt, nickel, magnesium, zinc, cadmium, calcium and the 
rare earth metals are similarly introduced. 
To introduce the molybdenum component, any molybdenum oxide such as the 
dioxide, trioxide, pentoxide, or sesquioxide may be used; more preferred 
is a hydrolyzable or decomposable molybdenum salt such as a molybdenum 
halide. A preferred starting material is ammonium heptamolybdate. 
Arsenic may be introduced as orthoarsenic acid. Other elements may be 
introduced, starting with the metal, oxidizing the metal with an oxidizing 
acid such as nitric acid, and then incorporating the nitrate into the 
catalyst. Generally, the nitrates are readily available and form a very 
convenient starting material. 
Other variations in starting materials will suggest themselves to one 
skilled in the art, particularly when the preferred starting materials 
mentioned hereinabove are unsuited to the economics of large-scale 
manufacture. In general, any compounds containing the desired catalyst 
components may be used provided that they result, upon heating to a 
temperature within the range disclosed hereinafter, in the oxides of the 
instant catalyst. 
The catalyst can be employed without a support and will display excellent 
activity. It also can be combined with a support, and preferably at least 
10 percent up to about 90 percent of the supporting compound by weight of 
the entire composition is employed in this event. Any known support 
materials can be used, such as, for example, silica, alumina, zirconia, 
titania, alundum, silicon carbide, alumina-silica, and the inorganic 
phosphates, silicates, aluminates, borates and carbonates which are stable 
under the reaction conditions to be encountered in the use of the 
catalyst. 
The catalytic activity of the system is enhanced by heating at an elevated 
temperature. Generally, the catalyst mixture is dried and heated at a 
temperature of from about 750.degree. to about 1850.degree. F., preferably 
at about 900.degree. to 1300.degree. F., for from one to twenty-four hours 
or more. If activity then is not sufficient, the catalyst can be further 
heated at a temperature above about 1000.degree. F. but below a 
temperature deleterious to the catalyst at which it is melted or 
decomposed. Usually this limit is not reached before 2000.degree. F., and 
in some cases this temperature can be exceeded. 
In general, the higher the activation temperature, the less time required 
to effect activation. The sufficiency of activation at any given set of 
conditions is ascertained by a spot test of a sample of the material for 
catalytic activity. Activation is best carried out in an open chamber, 
permitting circulation of air or oxygen, so that any oxygen consumed can 
be replaced. 
Further, pre-treatment or activation of the catalyst before use with a 
reducing agent such as ammonia in the presence of a limited amount of air 
at a temperature in the range of 550.degree. to 900.degree. F. is also 
beneficial. 
A preferred method of preparing the catalyst of this invention will be 
described hereinafter in connection with the Specific Embodiments of the 
invention. 
In the ammoxidation, the reactants employed in producing the unsaturated 
nitriles of this invention are oxygen, ammonia and an olefin having only 
three carbon atoms in a straight chain such as propylene or isobutylene or 
mixtures thereof. 
The olefins may be in admixture with paraffinic hydrocarbons, such as 
ethane, propane, butane and pentane; for example, a propylene-propane 
mixture may constitute the feed. This makes it possible to use ordinary 
refinery streams without special preparation. Likewise, diluents such as 
nitrogen and the oxides of carbon may be present in the reaction mixture 
without deleterious effect. 
In its preferred aspect, the process comprises contacting a mixture 
comprising propylene or isobutylene, ammonia and oxygen with the catalyst 
at an elevated temperature and at atmospheric or near atmospheric 
pressure. 
Any source of oxygen may be employed in this process. For economic reasons, 
however, it is preferred that air be employed as the source of oxygen. 
From a purely technical viewpoint, relatively pure molecular oxygen will 
give equivalent results. The molar ratio of oxygen to the olefin in the 
feed to the reaction vessel should be in the range of 0.5:1 to 4:1 and a 
ratio of about 1:1 to 3:1 is preferred. 
The molar ratio of ammonia to olefin in the feed to the reaction may vary 
between about 0.5:1 to 5:1. There is no real upper limit for the 
ammonia-olefin ratio, but there is generally no reason to exceed the 5:1 
ratio. At ammonia-olefin ratios appreciably less than the stoichiometric 
ratio of 1:1, various amounts of oxygenated derivatives of the olefin will 
be formed. Outside the upper limit of this range only insignificant 
amounts of aldehydes and acids will be produced, and only very small 
amounts of nitriles will be produced at ammonia-olefin ratios below the 
lower limit of this range. It is unexpected that within the ammonia-olefin 
range stated, maximum utilization of ammonia is obtained, and this is 
highly desirable. It is generally possible to recycle any unreacted olefin 
and unconverted ammonia. 
We have found that in many cases water in the mixture fed to the reaction 
vessel improves the selectivity of the reaction and yield of nitrile. 
However, reactions not including water in the feed are not to be excluded 
from this invention, inasmuch as water is formed in the course of the 
reaction. 
In general, the molar ratio of added water to olefin, when water is added, 
is at least about 0.25:1. Ratios on the order of 1:1 to 4:1 are 
particularly desirable, but higher ratios may be employed, i.e., up to 
about 10:1. 
The reaction is carried out at a temperature within the range of from about 
500.degree. to about 1100.degree. F. The preferred temperature range is 
from about 600.degree. to 900.degree. F. 
The pressure at which reaction is conducted is also an important variable, 
and the reaction should be carried out at about atmospheric or slightly 
above atmospheric (2 to 3 atmospheres) pressure. In general, high 
pressures, i.e., about 250 p.s.i.g., are not suitable since higher 
pressures tend to favor the formation of undesirable by-products. 
The apparent contact time is not critical, and contact times in the range 
of from 0.1 to about 50 seconds may be employed. The optimum contact time 
will, of course, vary depending upon the olefin being treated, but in 
general, a contact time of from 1 to 15 seconds is preferred. 
In general, any apparatus of the type suitable for carrying out oxidation 
reactions in the vapor phase may be employed in the execution of this 
process. The process may be conducted either continuously or 
intermittently. The catalyst bed may be a fixed-bed employing a large 
particulate or pelleted catalyst or, in the alternative, a so-called 
"fluidized" bed of catalyst may be employed. The fluid reactor may 
comprise an open column or the reactor may contain a plurality of 
perforated trays stacked horizontally throughout the length of the column, 
as described in U.S. Pat. No. 3,230,246 issued Jan. 18, 1966. 
The reactor may be brought to the reaction temperature before or after the 
introduction of the reaction feed mixture. However, in a large scale 
operation, it is preferred to carry out the process in a continuous 
manner, and in such a system the circulation of the unreacted olefin is 
contemplated. Periodic regeneration or reactivation of the catalyst is 
also contemplated, and this may be accomplished, for example, by 
contacting the catalyst with air at an elevated temperature. 
The products of the reaction may be recovered by any of the methods known 
to those skilled in the art. One such method involves scrubbing the 
effluent gases from the reactor with cold water or an appropriate solvent 
to remove the products of the reaction. If desired, acidified water can be 
used to absorb the products of reaction and neutralize unconverted 
ammonia. The ultimate recovery of the products may be accomplished by 
conventional means. The efficiency of the scrubbing operation may be 
improved when water is employed as the scrubbing agent by adding a 
suitable wetting agent in the water. Where molecular oxygen is employed as 
the oxidizing agent in this process, the resulting product mixture 
remaining after the removal of the nitriles may be treated to remove 
carbon dioxide with the remainder of the mixture containing the unreacted 
olefin and oxygen being recycled through the reactor. In the case where 
air is employed as the oxidizing agent in lieu of molecular oxygen, the 
residual product after separation of the nitriles and other carbonyl 
products may be scrubbed with non-polar solvent, e.g., a hydrocarbon 
fraction in order to recover unreacted olefin, and in this case the 
remaining gases may be discarded. The addition of a suitable inhibitor to 
prevent polymerization of the unsaturated products during the recovery 
steps is also contemplated.

SPECIFIC EMBODIMENTS 
Comparative Examples A and B and Examples 1-3--Ammoxidation of propylene 
Catalysts of the invention containing tantalum or samarium were prepared in 
the same manner as the two catalysts described below. 
A catalyst having the composition 82.5 wt. % -Ni.sub.10.5 FeBiPMo.sub.12 
O.sub.57 -17.5 wt. %-SiO.sub.2 was prepared as follows: 
229.3 grams of (NH.sub.4)6Mo.sub.7 O.sub.27.4H.sub.2 O were dissolved in 
water with a minimum amount of heating. 12.5 grams of H.sub.3 PO.sub.4 (85 
wt. %) and 228 grams of DuPont Ludox AS (30 wt. %) colloidal silica sol 
were added in succession with stirring. 330.4 grams of 
Ni(NO.sub.3).sub.2.6H.sub.2 O dissolved in water were added to the slurry 
and stirred for 15 minutes. 43.8 grams of Fe(NO.sub.3).sub.3.9H.sub.2 O 
dissolved in water were added to this slurry followed by the addition of 
52.5 grams of Bi(NO.sub.3).sub.3.5H.sub.2 O dissolved in water containing 
5.3 cc. of concentrated HNO.sub.3 (60 wt. %). The slurry was stirred 
constantly for about 15 minutes. 
The slurry was then spray dried and the powder obtained from the spray 
drier was further dried in an oven at 230.degree. F. for 16 hours. The 
resulting dry powder was well mixed with 1 wt. % graphite and compacted 
into 1/16".times.3/16" pellets with a convention pelleting machine. The 
pellets were heated for five hours at 446.degree. F. to decompose the 
nitrates and were then calcined for twenty hours at 1022.degree. F. The 
pelleted catalyst was crushed and sized to 20-35 Tyler mesh size. 
In an alternate method a catalyst having the composition 80 wt. % 
Ni.sub.4.5 Co.sub.4 FeBiAs.sub.0.5 P.sub.0.5 Mo.sub.12 O.sub.54 -20 wt. 
%-SiO.sub.2 was prepared by co-gelling the ingredients according to the 
following procedure: 
A mixture of 76.4 grams (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 O, 
2.1 grams H.sub.3 PO.sub.4 (85%), 
2.7 grams H.sub.3 As.sub.3 O.sub.4.1/2H.sub.2 O, 
85.0 grams SiO.sub.2, (Ludox AS, 30% silica sol), 
47.2 grams Ni(NO.sub.3).sub.2.6H.sub.2 O and 
41.9 grams Co(NO.sub.3).sub.2.6H.sub.2 O 
was dissolved in water and stirred for 15 minutes. To this slurry was added 
an aqueous solution containing 14.6 grams of Fe(NO.sub.3).sub.3.9H.sub.2 O 
and 17.5 grams of Bi(NO.sub.3).sub.3.5H.sub.2 O previously dissolved in 20 
cc. of a 10% HNO.sub.3 solution. The combined mixtures were heated with 
constant stirring until gel formation occurred. The gel was then dried at 
approximately 266.degree. F. The resulting catalyst was heat treated at 
800.degree. F. for four hours, and at 1022.degree. F. for 16 hours, and 
then was sized to 20-35 Tyler screen mesh. 
The reactor was a standard reactor with a fixed catalyst bed. The catalyst 
volume was about 5 cc. and the catalyst mesh size was 20 to 35 Tyler 
screen mesh. The gases were metered to the reactor with rotameters. The 
products of the reaction were recovered by scrubbing the effluent gases 
from the reactor with water and were then analyzed by means of a gas 
chromatograph. 
The results are stated using the following definition: 
##EQU1## 
Comparative Examples A and B show catalysts of the art. 
The reaction was run using a reaction temperature of 752.degree. F., a 
contact time of 2.9 seconds and a feed of propylene/ammonia/air of 
1/1.5/11. The reaction was run for 15 minutes and product was collected 
for analysis over 30 minutes. 
Table I 
______________________________________ 
Ammoxidation of Propylene 
% Per 
Pass Conver- 
sion to 
Example 
Catalyst Composition Acrylonitrile 
______________________________________ 
Comp. A 
50% Bi.sub.9 PMo.sub.12 O.sub.52 
39.9 
50% SiO.sub.2 
Comp. B 
50% Fe.sub.4.5 Bi.sub.4.5 PMo.sub.12 O.sub.56.5 
41.9 
50% SiO.sub.2 
1 80% Ta.sub.0.2 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 BiMo.sub.12 O.sub.55. 
5 65.4 
20% SiO.sub.2 
2 80% Sm.sub.0.1 Ni.sub.10 Co.sub.0.3 FeBiPMo.sub.12 O.sub.57 
68.3 
20% SiO.sub.2 
3 80% Sm.sub.0.1 Ni.sub.5.25 Co.sub.5.25 FeBiPMo.sub.12 O.sub.57 
64.9 
20% SiO.sub.2 
______________________________________ 
Examples 4-10--Ammoxidation of propylene using different catalysts 
In the same manner as shown above, various catalysts of the invention were 
prepared and used in the ammoxidation of propylene. The reactant ratios 
were propylene/ammonia/air/steam of 1/1.1/10/4, the contact time was six 
seconds, the temperature was 400.degree. F. All catalysts contained 20 
weight percent silica. The results are given in Table II. The following 
definitions are used: 
##EQU2## 
Table II 
__________________________________________________________________________ 
Ammoxidation of Propylene 
Results, % 
Example 
Catalyst Per Pass Yield 
Conversion 
Selectivity 
__________________________________________________________________________ 
4 Ce.sub.1.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.1.5 BiP.sub.0.5 
Mo.sub.12 O.sub.x ] 
74.0 96.6 77 
5 La.sub.1.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.1.5 BiP.sub.0.5 
Mo.sub.12 O.sub.x ] 
64.9 90.5 70 
6 Eu.sub.1.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.1.5 BiP.sub.0.5 
Mo.sub.12 O.sub.x ] 
78.0 96.7 81 
7 Di.sub.1.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.1.5 BiP.sub.0.5 
Mo.sub.12 O.sub.x ] 
55.2 85.7 64 
8 Ce.sub.0.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 Bi.sub.0.5 
P.sub.0.5 Mo.sub.12 O.sub.x ] 
71.2 88.7 80 
9 La.sub.0.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 Bi.sub.0.5 
P.sub.0.5 Mo.sub.12 O.sub.x ] 
79.1 98.9 80 
10 Sm.sub.0.5 [K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 Bi.sub.0.5 
P.sub.0.5 Mo.sub.12 O.sub.x ] 
76.4 98.3 78 
__________________________________________________________________________ 
Examples 11-18--Ammoxidation at high olefin throughput 
A catalyst of 80% Nb.sub.0.5 K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 
BiMo.sub.12 O.sub.x and 20% silica was prepared by dissolving 31.8 g. of 
(NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 O in water, adding to this 
solution 2.0 g. of NbCl.sub.2 slurried with water and 26.5 g. of 40% Nalco 
silica sol was added. A mixture of 10.9 g. of Ni(NO.sub.3l 
).sub.2.6H.sub.2 O and 19.7 g. Co(NO.sub.3).sub.2.6H.sub.2 O dissolved in 
water was added to the resulting slurry. 
Separately, an aqueous solution of 18.2 g. Fe(NO.sub.3).sub.3.9H.sub.2 O, 
7.2 g. Bi(NO.sub.3).sub.3.5H.sub.2 O and 0.19 g. of a 45% aqueous solution 
of KOH was added. This solution was added to above slurry with stirring 
and heating. The mixture was evaporated to dryness, dried over night at 
250.degree. C., and heat treated at 550.degree. F. for five hours, 
800.degree. F. for four hours, and 1020.degree. F. for 16 hours. 
In the same manner, other catalysts of the invention shown in Table III 
were prepared. These catalysts were used in the preparation of 
acrylonitrile using the reactor described above. The feed was 
propylene/ammonia/oxygen/nitrogen/steam of 1.8/2.2/3.6/2.4/6, the contact 
time was three seconds and the temperature was 420.degree. F. Each of the 
catalysts have the basic structure X.sub.a K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 
Fe.sub.3 BiMo.sub.12 O.sub.x and contain 20% by weight silica. The results 
of these experiments are shown in Table III. 
Table III 
______________________________________ 
Ammoxidation of Propylene 
Results, % 
Example Xa = Per Pass Yield 
Conversion 
Selectivity 
______________________________________ 
11 Nb.sub.0.5 
79.3 99.9 79 
12 Nb.sub.1.0 
79.9 97.2 82 
13 Pr.sub.0.5 
75.4 100.0 75 
14 La.sub.0.5 
74.0 100.0 74 
15 Dy.sub.0.5 
79.2 98.7 80 
16 Ta.sub.0.5 
78.8 97.4 81 
17 Gd.sub.0.5 
75.0 87.7 86 
18 Yb.sub.0.5 
75.0 99.7 75 
______________________________________ 
In the same manner as shown by the examples above, isobutylene is reacted 
to give methacrylonitrile using catalysts of the invention. 
Examples 19-28--Higher catalyst vent treatment 
In the same manner as shown above, various catalysts of the invention were 
prepared and heat treated, except that an additional heat treatment for 
three hours at 650.degree. C. was given. The reactions were run in a 5 cc. 
reactor, at 420.degree. C. and a contact time of six seconds using a feed 
of propylene/ammonia/air/steam of 1/1.1/10/4. All catalysts contained 20% 
silica. The catalyst compositions and results are shown in Table IV. 
Table IV 
__________________________________________________________________________ 
Ammoxidation of Propylene 
Results, % 
Example 
Catalyst Per Pass Yield 
Conversion 
Selectivity 
__________________________________________________________________________ 
19 Nd.sub.0.67 (K.sub.0.1 Ni.sub.2.5 Co.sub.3.5 Fe.sub.3 BiP.sub.0.5 
Mo.sub.12 O.sub.x) 79.3 91.4 87 
20 Di.sub.0.67 (K.sub.0.1 Ni.sub.2.5 Co.sub.3.5 Fe.sub.3 BiP.sub.0.5 
Mo.sub.12 O.sub.x) 76.4 94.0 81 
21 Yb.sub.0.67 (K.sub.0.1 Ni.sub.2.5 Co.sub.3.5 Fe.sub.3 BiP.sub.0.5 
Mo.sub.12 O.sub.x) 74.9 90.2 83 
22 Di.sub.1.5 K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.1.5 BiP.sub.0.5 
Mo.sub.12 O.sub.x 75.3 95.5 79 
23 Di.sub.0.5 (K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 Bi.sub.0.5 
P.sub.0.5 Mo.sub.12 O.sub.x) 
81.6 96.1 85 
24 Ce.sub.0.5 (K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 Bi.sub.0.5 
P.sub.0.5 Mo.sub.12 O.sub.x) 
75.7 86.9 87 
25 Nd.sub.0.5 (K.sub.0.1 Ni.sub.3 Co.sub.5 Fe.sub.3 Bi.sub.0.5 P.sub.0.5 
Mo.sub.12 O.sub.x) 
77.1 96.0 80 
26 Yb.sub.0.5 (K.sub.0.1 Ni.sub.3 Co.sub.5 Fe.sub.3 Bi.sub.0.5 P.sub.0.5 
Mo.sub.12 O.sub.x) 
80.4 97.1 83 
27 Nb.sub.0.5 K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 BiMo.sub.12 
O.sub.x 82.9 95.6 87 
28 Nd.sub.0.5 K.sub.0.1 Ni.sub.2.5 Co.sub.4.5 Fe.sub.3 BiP.sub.0.5 
Mo.sub.12 O.sub.x 71.5 90.2 79 
__________________________________________________________________________ 
It will therefore be appreciated from the foregoing examples that samarium, 
cerium, lanthanum, europium, dysprosium, praseodymium, gadolinium, 
ytterbium, neodymium and didynium are especially useful as component A in 
the above noted formula, while the other rare earth, namely terbium, 
holmium, erbium, thulium and lutetium as well as promethium, if available, 
are also useful.