Heteropolyacid-type catalyst composition containing whiskers

A catalyst composition having excellent mechanical strength comprising a compound containing a heteropolyacid as a base and whiskers.

This invention relates to a heteropolyacid-type catalyst. More 
specifically, it relates to a catalyst composition which comprises a 
heteropolyacid-type catalytically active ingredient based on 
molybdophosphoric or molybdovanadophosphoric acid as a base and whiskers, 
has excellent mechanical strengths (e.g., compressive strength, abrasion 
resistance and falling strength) in industrial use, and exhibits an 
excellent catalytic performance in the production of methacrylic acid by 
the oxidation or oxidative dehydrogenation of methacrolein, 
isobutyraldehyde or isobutyric acid in the vapor phase. 
It has been known to use inorganic fibers or whiskers as a catalyst 
carrier. In the prior art, glass fibers, asbestos or whiskers are used as 
means for highly dispersing catalytically active substances, namely as a 
carrier. In the present invention, however, whiskers are used not as a 
carrier but as a minor component to be added to a catalytically active 
substance containing a heteropolyacid as a base. 
Many compounds containing phosphorus-molybdenum or 
phosphorus-molybdenum-vanadium as a base have been reported heretofore as 
catalysts for the production of methacrylic acid by the catalytic 
vapor-phase oxidation of methacrolein, isobutyraldehyde or isobutyric 
acid. However, phosphorus-molybdenum or phosphorus-molybdenum-vanadium 
assumes a heteropolyacid structure as molybdophosphoric acid or 
molybdovanadophosphoric acid, and catalysts containing such a 
heteropolyacid as a base have the defect of very poor moldability. Various 
investigations have therefore been made about the form and mechanical 
strength of these catalysts in order to make them industrially feasible. 
Generally, catalysts are in the form of supported catalysts prepared by 
depositing catalyst ingredients on suitable carriers, compression-molded 
catalysts prepared by a tableting method or an extruding method, and 
granular catalysts prepared by a rolling granulating method. Which of such 
forms is to be selected is determined by an overall consideration of the 
nature of a given catalytically active substance and the required 
catalytic performance and mechanical strength. In any of these forms, 
however, catalysts having such high mechanical strength as to fully 
withstand industrial use are extremely difficult to prepare from compounds 
containing heteropolyacid-type compounds as a base, and various 
improvements have been suggested. 
For example, U.S. Pat. No. 4,364,844 discloses a catalyst having improved 
mechanical strength prepared by supporting a composition comprising 
phosphorus-molybdenum-vanadium and an alkali metal element on a 
heat-resistant inorganic material. Investigations of the present inventors 
have shown, however, that a compound containing a heteropolyacid compound 
as a base has poor adhesion to a carrier, and the ratio of adhesion is 
low. In order to impart some degree of mechanical strength, the amount of 
the heteropolyacid-type compound to be deposited is naturally limited, and 
consequently, the resulting catalyst tends to have insufficient activity. 
Generally, a supported catalyst has the advantage that when used in a 
catalytic vapor-phase reaction, it inhibits both heat generation in a 
catalyst bed and consecutive reactions of the desired product. The 
reaction temperature, however, should be elevated in order to maintain its 
sufficient catalytic activity, and consequently, the elevated temperature 
tends to adversely affect the life of the catalyst. 
When a catalytic substance is compression-molded by tableting or extrusion, 
the surface area, the pore volume, etc. of the catalyst change and may 
result in an undesirable phenomenon of reduction in catalytic performance. 
Furthermore, since the compound containing a heteropolyacid compound as a 
base is difficult to mold as stated hereinabove, molding it without using 
molding aids, a bonding agent, etc. does not produce a catalyst having 
sufficient mechanical strength. In addition, when prepared by a molding 
method which imparts strength (by elevating the molding pressure or adding 
molding aids, a bonding agent, etc.), molded catalysts generally decrease 
in catalytic performance. 
As a method of solving these problems of molded catalysts, U.S. Pat. No. 
4,238,359 discloses that a catalyst having strength without a reduction in 
performance can be obtained by adding a volatile substance or a finely 
divided carrier to a composition comprising phosphorus-molybdenum and 
another metallic element and molding the mixture while defining the 
surface area and pore volume of the catalyst within preferred ranges. 
Those skilled in the art may expect that if a catalyst composition is 
extrusion-molded in admixture with heat-resistant fibers such as glass 
fibers and ceramic fibers, a molded catalyst having high mechanical 
strength will be obtained. Investigations of the present inventors, 
however, have shown that the application of these methods to compounds 
containing heteropolyacids as a base cannot give catalysts which 
simultaneously have excellent catalytic performance and mechanical 
strength. 
U.S. Pat. No. 4,419,270 discloses that a catalyst having hiqh mechanical 
strength and properties suitable for industrial use is obtained by 
extrusion-molding a catalyst containing a heteropolyacid compound as a 
base in the presence of a nitrogen-containing heterocyclic organic 
compound such as pyridine, piperidine or piperazine. Since, however, this 
technique is limited to the production of extrusion-molded catalysts and 
it is difficult to form catalysts in other forms such as a ring-shaped 
catalyst or a supported catalyst, it is not entirely satisfactory in 
industrial practice. 
It is an object of this invention to improve the various prior techniques 
described above, and to provide a catalyst which can be produced 
industrially and can be actually used in industrial practice. 
According to this invention, there is provided a catalyst composition 
comprising a compound containing a heteropolyacid as a base, preferably 
molybdophosphoric acid or molybdovanadophosphoric acid, and whiskers, 
preferably whiskers having an average diameter of not more than 5 microns 
and an average length of not more than 1000 microns. 
A catalyst prepared by extrusion-molding a mixture of a compound containing 
a heteropolyacid as a base and whiskers in accordance with one embodiment 
of this invention has excellent compressive strength, abrasion resistance 
and falling strength which can hardly be imagined from a catalyst composed 
solely of a heteropolyacid-type compound. When this catalyst is used in 
the catalytic vapor-phase reaction of methacrolein, isobutyraldehyde or 
isobutyric acid, no decrease in activity and methacrylic acid selectivity 
is observed, and its activity rather increases. While it has been thought 
that a catalyst molded in a ring-like shape by the extrusion molding 
method generally has low mechanical strength, the ring-shaped catalyst in 
accordance with this invention has no problem in regard to its mechanical 
strength. In addition, it has the advantage that methacrylic acid 
selectivity increases. 
When a supported catalyst is prepared by spraying a slurry of a mixture of 
a compound containing a heteropolyacid as a base and whiskers onto a 
suitable carrier in accordance with another embodiment of this invention, 
the yield of the catalytically active substance deposited on the carrier 
is greatly increased, and the catalyst has unexpectedly high abrasion 
strength. In addition, it is surprising that when this catalyst is used in 
the same vapor-phase reaction as mentioned above with regard to the molded 
catalyst, both its activity and selectivity are increased. 
Thus, the present invention provides catalysts which are very advantageous 
industrially for the production of methacrylic acid by catalytic 
vapor-phase reaction. 
The form of the catalyst of this invention is not limited to the 
extrusion-molded catalyst and supported catalyst described above, and can 
be properly determined by an overall consideration of the ease, yield 
reproducibility of actual catalyst preparation, and the desired properties 
of the catalyst. Accordingly, the tableting method, rolling granulating 
method, marmerizer molding method, etc. which are generally known can also 
be employed in preparing the catalyst of this invention. 
Whiskers are generally defined as monocrystalline fibers having a diameter 
of not more than 200 microns and an aspect ratio (length-to-diameter 
ratio) of at least 10. In recent years, however, they have gained broad 
interpretation, and include polycrystalline fibers as well. In the present 
invention, whiskers having an average diameter of not more than 5 microns 
and an average length of not more than 1000 microns are preferably used. 
The material for the whiskers used in this invention is not limited to 
metals, and may be a refractory. Specific examples include tungsten, iron, 
nickel, silicon carbide, boron carbide, titanium carbide, silicon nitride, 
silica-alumina, alumina, titanium oxide, beryllium oxide, potassium 
titanate, and calcium phosphate. Whiskers made from the above materials 
can be suitably used in this invention so long as they remain as whiskers 
in the final catalyst composition of this invention. 
Investigations of the present inventors have shown that the shape of the 
whiskers (particularly their diameter and length) subtly affect the 
mechanical strength of the final catalyst, and a tremendous improvement in 
mechanical strength is achieved when the whiskers have an average particle 
diameter of not more than 5 microns, preferably not more than 1 micron, 
and a length of not more than 1000 microns, preferably not more than 500 
microns. The whiskers exhibit their effect when used in a small amount, 
but their suitable amount differs slightly depending upon their type or 
the shape of the catalyst. Usually, the whiskers can be included in an 
amount of 1 to 50% by weight based on the catalyst ingredients. Much is 
left unknown about the cause of the effect achieved by the use of the 
whiskers, but theoretically, the following may possibly be the cause. 
The size of the particles of the compound containing a heteropolyacid as a 
base differs somewhat depending upon the preparing conditions. But 
generally, they are observed as spherical or block-like particles having a 
size of less than about 1 micron. Accordingly, the whiskers are more 
effectively dispersed as they have a smaller diameter or to some exent a 
shorter length. Furthermore, even when the amount of the whiskers is 
small, they mechanically well match the particles of the 
heteropolyacid-type compound, and this will result in a striking increase 
in the physical strength of the catalyst. Furthermore, by the dispersing 
effect mentioned above, the volume of spaces in the catalytically active 
substance layer increases to provide good air-permeability. This will 
produce an effect of removing heat during the reaction and inhibiting the 
occurrence of consecutive reactions, and result in an increase in activity 
and selectivity. 
The compound containing a heteropolyacid as a base may be any compound 
composed mainly of a heteropolyacid compound such as molybdophosphoric 
acid, molybdovanadophosphoric acid and metal salts of these acids. To 
produce methacrylic acid in a high yield, however, it is preferably a 
compound having the composition of the following general formula 
EQU P.sub.a Mo.sub.b V.sub.c X.sub.d Y.sub.e O.sub.f 
wherein P represents phosphorus, Mo represents molybdenum, V represents 
vanadium, X represents at least one element selected from alkali metals 
and alkaline earth metals, Y represents at least one element selected from 
copper, silver, arsenic, antimony, tellurium, cobalt, bismuth, tungsten 
and zirconium, and O represents oxygen; the subscripts a, b, c, d, e and f 
represent the atomic ratios of the elements, and when b is 12, 
a is 0.1 to 3.0, preferably 0.5 to 1.5, 
c is 0 to 6.0, preferably 0.1 to 2.5, 
d is 0.05 to 5.0, preferably 0.1 to 2.0, 
e is 0.01 to 5.0, preferably 0.05 to 2.0, and 
f is a number determined by the atomic numbers and atomic ratios of the 
individual elements. 
Various materials for the catalyst can be used. For example, 
orthophosphoric acid, disodium hydrogen phosphate, monoammonium phosphate 
and diammonium phosphate are used as phosphorus compounds. Molybdenum 
compounds include, for example, molybdenum trioxide, molybdic acid, sodium 
molybdate, ammonium paramolybdate and phosphomolybdic acid. Examples of 
vanadium compounds include vanadium pentoxide, ammonium metavanadate, 
sodium metavanadate, vanadyl oxalate and vanadyl sulfate. As the X and Y 
components, the hydroxides, nitrates, sulfates, carbonates, halides, 
ammonium salts, oxy acids, etc. of the elements described above for these 
components may be used. 
A detailed description will now be made of methods for preparing the 
extrusion-molded catalyst and the supported catalysts in the preferred 
embodiments of the catalyst composition of this invention. 
(1) Extrusion-molded catalysts 
To prepare the extrusion-molded catalyst, all known methods of prepa ing 
catalysts based on phosphorus-molybdenum or phosphorus-molybdenum-vanadium 
can be used. For example, to an aqueous solution prepared in advance of 
molybdophosphoric acid or molybdovanadophosphoric acid, an aqueous 
solution of compounds of the other required elements is added to form a 
slurry. Whiskers in a suitable amount are added to the slurry, and the 
slurry is evaporated to dryness. The dried product is pulverized to make a 
powder of a heteropolyacid compound containing the whiskers. Or compounds 
of phosphorus, molybdenum, vandadium and other required additive metal 
elements are added to water to form a slurry, and whiskers are added in a 
suitable amount. The slurry is evaporated to dryness and pulverized to 
form a powder containing the whiskers. A small amount of water is added to 
the resulting powder and well mixed. It is then molded, for example, into 
a solid cylindrical form having a diameter of 5.5 mm and a length of 6 mm, 
or a ring having an outside diameter of 5.5 mm, an inside diameter of 2.0 
mm and a length of 6 mm by an extrusion-molding machine. The molded 
catalyst is dried, and calcined at 350.degree. to 400.degree. C. in the 
presence of air. 
When the extrusion-molded catalyst of this invention is prepared by 
utilizing the method for preparing a catalyst using a nitrogen-containing 
organic compound described above (U.S. Pat. No. 4,419,270), a step of 
removing this organic compound is provided before the calcination step. 
This step can be carried out by heat-treating the molded catalyst at a 
temperature of 200.degree. to 600.degree. C. in an atmosphere of an inert 
gas such as nitrogen, helium, argon or carbon dioxide gas, or a reducing 
gas such as a hydrocarbon gas. 
The whiskers may be mixed with the powder obtained by drying and 
pulverizing the aforesaid slurry instead of adding them to the slurry. 
All of the molded catalysts obtained by the aforesaid methods are in a good 
molded condition, and their excellency is also demonstrated by the results 
of measuring their mechanical strengths. 
(2) Supported catalysts 
All known catalyst preparing methods involving the use of 
phosphorus-molybdenum or phosphorus-molybdenum-vanadium as a base can be 
applied to the preparation of supported catalysts. For example, to an 
aqueous solution prepared in advance of molybdophosphoric acid or 
molybdovanadophosphoric acid, an aqueous solution of compounds of the 
other required elements is added, and whiskers are added in a suitable 
amount to form a slurry. The slurry is then heated and sprayed onto, an 
ordinary spherical carrier material having a diameter of 3 to 5 mm in a 
rotating drum. The supported product is then heat-treated in the same way 
as described above for preparation of the molded catalysts. The catalyst 
preparing method involving the use of a nitrogen-containing heterocyclic 
organic compound described above may be used by providing the same step of 
removing the organic compound as described above. 
The shape of the carrier is not limited to a sphere as described above, and 
it may be in the form of a solid cylinder, a hollow cylinder, broken 
fragments, a triangular pyramid, etc. Preferably, its size is 1 to 10 mm. 
The carrier may also be in the form of a honeycomb or pipe. The material 
for the carrier may be an ordinary carrier material for molding, such as 
silicon carbide, alumina, silica and silica-alumina. Supported catalysts 
so obtained are in a well supported condition and the yield of the 
catalytically active substance deposited on the carrier is very high. 
Their excellency is also demonstrated by the results of measuring their 
mechanical strengths. 
By using whiskers in accordance with this invention, a compound containing 
a heteropolyacid as a base, of which molding has been considered difficult 
heretofore, can be molded as desired to produce a catalyst that can be 
industrially used. Furthermore, the use of whiskers has favorable effects 
(increased activity and alleviation of the buildup of heat in the catalyst 
bed) on the properties of the catalyst, and inhibits undesirable 
consecutive reactions and increases the selectivity of reaction. 
The catalyst of this invention is useful for producing methacrylic acid by 
the catalytic vapor-phase reaction of methacrolein, isobutyraldehyde or 
isobutyric acid and molecular oxygen. Industrially, air is an advantageous 
source of oxygen. The reaction may be carried out in an inert gas such as 
nitrogen, carbon dioxide, helium, argon, carbon monoxide and steam as a 
diluent. Use of steam is particularly advantageous because it serves to 
inhibit formation of by-products. 
In the reaction, the concentration of the starting materials in the feed 
gas is suitably in the range of 0.5 to 10% by volume; the suitable ratio 
of the volume of oxygen to that of the starting materials is from 0.5 to 
10; and the suitable space velocity of the feed gas is in the range of 100 
to 5000 hr.sup.-1 (S. T. P.). 
Generally, the catalyst of this invention is used in a reaction apparatus 
of the fixed bed type. But because of its very high mechanical strength, 
it can also be used satisfactorily in reaction apparatuses of the 
fluidized or moving bed type. 
The following examples illustrate the preparation and testing of catalysts 
in accordance with this invention. The mechanical strengths of the molded 
catalysts and the supported catalysts were measured by the following 
methods. 
(1) Extrusion-molded catalysts 
Compressive strength 
By using a "Kiya-type" hardness tester, a load is exerted on one particle 
of the catalyst in the direction of its longitudinal axis or in a 
direction at right angles to the longitudinal axis until cracking took 
place. The load upon cracking was measured (with a pelletized sample, the 
compressive strength was measured only in the direction of its 
longitudinal axis). 
Degree of abrasion 
Fifty grams of the catalyst was put in a cylinder made of a 12-mesh 
stainless steel wire gauze and having an inside diameter of 100 mm and a 
width of 100 mm. The cylinder was continuously rotated at a speed of 100 
rpm for 30 minutes, and then the weight of the catalyst was measured. The 
ratio of abrasion was calculated in accordance with the following 
equation. 
##EQU1## 
Falling strength 
Thirty grams of the catalyst was let fall from the upper portion of an 
upstanding iron pipe having an inside diameter of 25 mm and a length of 
5000 mm, and received by a 4-mesh sieve. The weight of the catalyst 
remaining on the sieve was measured, and the falling strength ratio (%) 
was measured in accordance with the following equation. 
##EQU2## 
(2) Supported catalysts 
Ratio of abrasion 
The same measuring device as in the case of the molded catalysts above was 
used and rotated under the same conditions. The weight of the catalyst 
remaining in the cylinder was measured, and the ratio of abrasion was 
calculated in accordance with the following equation. 
##EQU3## 
Falling strength 
The same measuring device as in the case of the molded catalysts above was 
used, and the catalyst was let fall under the same conditions. The weight 
of the catalyst remaining on the sieve was measured, and the falling 
strength ratio was calculated in accordance with the following equation. 
##EQU4## 
In the following Examples and Comparative Examples, the conversion, 
selectivity and one-pass yield are defined as follows: 
##EQU5##

In the following Examples and Comparative Examples, all pellets had a 
diameter of 5.5 mm and a length of 6 mm, and all rings had an outside 
diameter of 5.5 mm, an inside diameter of 2 mm and a length of 6 mm. 
EXAMPLE 1 
Ammonium paramolybdate (441.4 g) and 24.4 g of ammonium metavanadate were 
dissolved in 1000 ml of heated water, and the solution was stirred. A 
solution of 31.2 g of phosphoric acid (85% by weight) in 100 ml of water 
was added to the solution to form a slurry containing a 
phosphorus-molybdenum-vanadium compound. A solution of 40.6 g of cesium 
nitrate in 200 ml of water, and 9.5 g of silicon carbide whiskers 
(diameter 0.1 to 0.5 microns, length 10 to 100 microns) were added. The 
slurry was evaporated to dryness, and the resulting solid was pulverized 
to form a powder of a molding material. A small amount of water was added 
to the powder and well mixed. The mixture was pelletized by an extrusion 
molding machine, dried at 250.degree. C., and calcined at 400.degree. C. 
for 4 hours in an air current to obtain a catalytic oxide having the 
composition P.sub.1.3 Mo.sub.12 V.sub.1 Cs.sub.1 in atomic ratio excepting 
oxygen (containing 2% by weight of the whiskers). The mechanical strengths 
of this catalyst were measured, and are shown in Table 1. 
The catalyst (50 ml) was filled in a stainless steel U-shaped tube having 
an inside diameter of 25 mm, and immersed in a molten salt bath at 
280.degree. C. A starting gaseous mixture consisting of methacrolein, 
oxygen, nitrogen and water in a volume ratio of 1:5:34:10 was passed 
through the tube at a space velocity of 1000 hr.sup.-1. The results of the 
reaction are shown in Table 1. 
COMATIVE EXAMPLE 1 
A catalyst was prepared in the same way as in Example 1 except that the 
silicon carbide whiskers was not used. The strengths of this catalyst were 
measured, and are shown in Table 2. This catalyst had a much worse molded 
condition than the catalyst of Example 1, and was far from satisfactory in 
practical applications. 
The same reaction as in Example 1 was carried out using the resulting 
catalyst. The results are shown in Table 2. 
EXAMPLE 2 
A catalyst was prepared in the same way as in Example 1 except that the 
amount of the whiskers was changed to 23.8 g. The strengths of the 
catalyst were measured, and by using this catalyst, the same reaction as 
in Example 1 was carried out. The results are shown in Table 1. 
EXAMPLE 3 
A catalyst was prepared in the same way as in Example 2 except that the 
shape of the extrusion-molded catalyst was changed to a ring-like shape. 
The strengths of the catalyst were measured, and the same reaction as in 
Example 1 was carried out by using this catalyst. The results are shown in 
Table 1. 
COMATIVE EXAMPLES 2 TO 4 
In each run, a catalyst was prepared in the same way as in Example 1 except 
that the whiskers used in Example 1 were changed to the other fibers or 
fine powders shown in Table 2, and their amount was changed as shown in 
Table 2. The strengths of the catalysts were measured, and the same 
reaction as in Example 1 was carried out by using the resulting catalysts. 
The results are shown in Table 2. 
These catalysts did not have satisfactory mechanical strength for use in 
industrial practice, and could not be molded into a ring-like shape. 
EXAMPLE 4 
Molybdenum trioxide (72.0 g), 3.79 g of vanadium pentoxide and 6.25 g of 
phosphoric acid (85% by weight) were added to 1000 ml of heated water, and 
the mixture was heated under reflux for 24 hours. The resulting reddish 
brown solution was filtered to remove a trace of an insoluble solid. While 
the solution was being stirred, a solution of 8.12 g of cesium nitrate in 
50 ml of water was added to it at room temperature to obtain a yellow 
slurry of a heteropolyacid salt. Then, 7.2 g of potassium titanate 
whiskers (fiber diameter 0.2 to 0.5 micron, length 10 to 20 microns) were 
added, and mixed fully by a homomixer with stirring to obtain a slurry 
having a very high degree of emulsification. The slurry was then sprayed 
onto a silicon carbide carrier, 3 mm in diameter, fluidized at a 
temperature of 100.degree. to 200.degree. C. The carrier was then calcined 
at 400.degree. C. in an air current to give a catalytic oxide of the 
composition P.sub.1.3 Mo.sub.12 V.sub.1 Cs.sub.1 in atomic ratio excepting 
oxygen (containing 8% by weight of the whiskers based on the catalytic 
ingredient excepting the carrier). The amount of the catalytically active 
substance deposited on the carrier was 50 g/100 cc of carrier, and the 
yield of deposition was 77% by weight. The strengths of the resulting 
catalyst were measured, and by using this catalyst, the same reaction as 
in Example 1 was carried out. The results are shown in Table 1. 
COMATIVE EXAMPLE 5 
A catalyst was prepared in the same way as in Example 4 except that the 
whiskers were not added. The strengths of the catalyst measured are shown 
in Table 2. This catalyst underwent more abrasion and exfoliation than the 
catalyst of Example 4, and the yield of deposition was as low as 15% by 
weight. The catalytically active substance could be deposited only in an 
amount of 20 g/100 cc of carrier. The same reaction as in Example 1 was 
carried out using the resulting catalyst. The results are shown in Table 
2. 
COMATIVE EXAMPLE 6 
A catalyst was prepared in the same way as in Example 4 except that silicon 
carbide whiskers (fiber diameter 4 to 10 microns, length 200 to 900 
microns) were used instead of the potassium titanate whiskers. The 
strengths of the catalyst are shown in Table 2. During the catalyst 
preparation, the whiskers blocked up the spray nozzle (diameter 1 mm), and 
the spray could not be used continuously. The depositing operation, 
however, was continued by occasionally exchanging the nozzle. The yield of 
deposition was 33% by weight, and the amount of the catalytically active 
substance deposited was 25 g/100 cc of carrier. The same reaction as in 
Example 1 was carried out using this catalyst, and the results shown in 
Table 2 were obtained. 
EXAMPLE 5 
492.8 g of 12-molybdophosphoric acid was dissolved in 500 ml of water, and 
the solution was stirred at room temperature. A solution of 48.7 g of 
cesium nitrate and 5.0 g of copper nitrate in 200 ml of water, and 23.8 g 
of silicon nitride whiskers (0.2 to 0.5 microns in diameter and 50 to 300 
microns in length) were added to the solution. The mixture was evaporated 
to dryness and pulverized to obtain a powder of a molding material. The 
powder was well mixed with a small amount of water, and the mixture was 
molded into rings by an extrusion molding machine. The rings were dried 
and then calcined in an air current at 370.degree. C. for 4 hours to give 
a catalyst of the composition P.sub.1 Mo.sub.12 Cs.sub.1.2 Cu.sub.0.1 in 
atomic ratio (containing 5% by weight of the whiskers). The mechanical 
strengths of the catalyst were measured, and the results are shown in 
Table 3. Using the resulting catalyst, the same reaction as in Example 1 
was carried out except that the reaction temperature was changed to 
320.degree. C. The results shown in Table 3 were obtained. 
COMATIVE EXAMPLE 7 
A catalyst was prepared in the same way as in Example 5 except that the 
silicon nitride whiskers were not added. Using this catalyst, the same 
reaction as in Example 5 was carried out. The results are shown in Table 
4. 
EXAMPLE 6 
Ammonium paramolybdate (441.4 g) and 18.3 g of ammonium metavanadate were 
dissolved in 1000 ml of heated water, and the solution was stirred. To the 
solution were added 100 g of pyridine and 31.2 g of phosphoric acid (85% 
by weight). Subsequently, 200 ml of nitric acid (specific gravity 1.38) 
and a solution of 21.4 g of rubidium hydroxide and 3.5 g of silver nitrate 
in 200 ml of water were added, and with stirring, 47.5 g of potassium 
titanate whiskers (0.2 to 0.5 microns in diameter and 10 to 100 microns in 
length) were added. The mixture was concentrated by heating. The clay-like 
material obtained was dried, pulverized, mixed well with a small amount of 
water, and molded into rings by an extrusion-molding machine. The rings 
were dried at 250.degree. C., and then calcined in a nitrogen atmosphere 
at 450.degree. C. for 4 hours and subsequently in an air current at 
400.degree. C. for 2 hours to give a catalytic oxide of the composition 
P.sub.1.3 Mo.sub.12 V.sub.0.75 Rb.sub.1.0 Ag.sub.0.1 in atomic ratio 
excepting oxygen (containing 10% by weight of the whiskers). The 
mechanical strengths of the catalyst were measured, and by using this 
catalyst, the same reaction as in Example 1 was carried out except that 
the reaction temperature was changed to 290.degree. C. The results are 
shown in Table 3. 
EXAMPLE 7 
A catalyst having the composition P.sub.1.3 MO.sub.12 V.sub.1 Cs.sub.1.2 
Ag.sub.0.1 in atomic ratio excepting oxygen was prepared in the same way 
as in Example 6 except that the amount of the ammonium metavanadate was 
changed to 24.4 g, 48.7 g of cesium nitrate was used instead of 21.4 g of 
rubidium hydroxide, 33.3 g of the same silicon carbide whiskers as used in 
Example 1 were used instead of 47.5 g of the potassium titanate whiskers, 
and the form of the catalyst was changed to pellets. The catalyst 
contained 7% by weight of the whiskers. The mechanical strengths of the 
catalyst were measured, and by using the catalyst, the same reaction as in 
Example 1 was carried out. The results are shown in Table 3. 
EXAMPLE 8 
A catalyst was prepared in the same way as in Example 7 except that the 
shape of the catalyst was changed to a ring-like shape. The strengths of 
the catalyst were measured, and by using this catalyst, the same reaction 
as in Example 1 was carried out. The results are shown in Table 3. 
COMATIVE EXAMPLE 8 
A catalyst was prepared in the same way as in Example 8 except that the 
silicon carbide whiskers were not used. Various data of this catalyst are 
shown in Table 4. 
COMATIVE EXAMPLE 9 
A catalyst was prepared in the same way as in Example 8 except that fumed 
silica (Aerosil, 10 to 40 microns) was used instead of the silicon carbide 
whiskers. Various data of this catalyst are shown in Table 4. 
EXAMPLE 9 
Ammonium paramolybdate (88.3 g) and 4.88 g of ammonium metavanadate were 
dissolved in 400 ml of heated water, and the solution was stirred. 
Pyridine (20 g) and 6.25 g of phosphoric acid (85% by weight) were added 
to the solution, and subsequently 40 ml of nitric acid (specific gravity 
1.38) and a solution of 14.62 g of cesium nitrate and 2.01 g of copper 
nitrate in 50 ml of water were added to form a yellow slurry. Then, 4.55 g 
of silicon carbide whiskers (fiber diameter 0.1 to 0.5 microns, length 10 
to 100 microns) were added to the slurry and mixed well by a homomixer 
with stirring. The slurry was then sprayed onto a silicon carbide carrier, 
3 mm in diameter, fluidized at a temperature of 100.degree. to 200.degree. 
C., and dried at 250.degree. C. The dried product was then calcined in a 
stream of nitrogen at 450.degree. C. for 4 hours and then in an air stream 
at 400.degree. C. for 2 hours to give a catalyst of the composition 
P.sub.1.3 Mo.sub.12 V.sub.1 Cs.sub.1.8 Cu.sub.0.2 in atomic ratio 
excepting oxygen (containing 5% of the whiskers based on the catalyst 
ingredients excepting the carrier). The amount of the catalytically active 
substance deposited on the carrier was 56 g/100 cc of carrier, and the 
yield of deposition was 82% by weight. The strengths of the catalyst were 
measured, and by using this catalyst, the same reaction as in Example 1 
was carried out except that the reaction temperature was changed to 
300.degree. C. The results are shown in Table 3. 
COMATIVE EXAMPLE 10 
A catalyst was prepared in the same way as in Example 9 except that the 
whiskers were not used. The strengths of this catalyst were measured, and 
the results are shown in Table 4. This catalyst underwent more abrasion 
and exfoliation than the catalyst of Example 9, and the yield of 
deposition was as low as 34% by weight. The amount of the catalytically 
active material deposited was as small as 28 g/100 cc of carrier. Using 
the resulting catalyst, the same reaction as in Example 1 was carried out 
except that the reaction temperature was changed to 300.degree. C. The 
results are shown in Table 4. 
EXAMPLE 10 
A ring-shaped catalyst of the composition P.sub.1.3 Mo.sub.12 V.sub.1.5 
Cs.sub.1.2 Ag.sub.0.2 in atomic ratio excepting oxygen was prepared in the 
same way as in Example 7 except that the amount of the ammonium 
metavanadate was changed to 36.6 g, the amount of silver nitrate was 
changed to 7.1 g, and the amount of the silicon carbide whiskers was 
changed to 71.4 g. The mechanical strengths of the catalyst were measured, 
and the results are shown in Table 5. Using this catalyst, the same 
reaction as in Example 1 was carried out except that methacrolein was 
changed to isobutyraldehyde. The results are shown in Table 5. 
COMATIVE EXAMPLE 11 
A catalyst was prepared in the same way as in Example 10 except that the 
silicon carbide whiskers were not used. The mechnanical strengths of the 
catalyst were measured, and by using this catalyst, the same reaction as 
in Example 10 was carried out. The results are shown in Table 5. 
EXAMPLE 11 
Ammonium paramolybdate (441.4 g) and 30.5 g of ammonium metavanadate were 
dissolved in 1000 ml of heated water, and the solution was stirred. 
Pyridine (100 g) and 36.0 g of phosphoric acid (85% by weight) were added 
to the solution. Subsequently, 200 ml of nitric acid (specific gravity 
1.38), a solution of 40.6 g of cesium nitrate, 8.8 g of strontium nitrate 
and 10.1 g of copper nitrate in 200 ml of water, and 15.2 g of antimony 
trioxide were added to the solution, and with stirring, the mixture was 
concentrated by heating. The resulting clay-like material was dried and 
pulverized, and the powder was fully mixed with 71.4 g of the same silicon 
nitride whiskers as used in Example 5 and a small amount of water. The 
mixture was molded into rings by an extrusion molding machine. The rings 
were dried at 250.degree. C., and calcined in a nitrogen stream at 
450.degree. C. for 4 hours and subsequently in an air stream at 
400.degree. C. for 2 hours to give a catalyst of the composition P.sub.1.5 
Mo.sub.12 V.sub.1.25 Cs.sub.1.0 Sr.sub.0.2 Cu.sub.0.2 Sb.sub.0.5 in atomic 
ratio excepting oxygen (containing 15% by weight of the whiskers). 
The mechanical strengths of the catalyst were measured, and the results are 
shown in Table 5. 
The catalyst (50 ml) was filled in a stainless steel U-shaped tube having 
an inside diameter of 25 mm. The tube was immersed in a molten salt bath 
at 270.degree. C., and a starting gaseous mixture composed of isobutyric 
acid, oxygen, nitrogen and water in a volume ratio of 2:3:90:5 was passed 
through the tube at a space velocity of 2000 hr.sup.-1. The results of the 
reaction are shown in Table 5. 
COMATIVE EXAMPLE 12 
A catalyst was prepared in the same way as in Example 11 except that the 
silicon nitride whiskers were not used. The mechanical strengths of this 
catalyst were measured, and by using this catalyst, the same oxidation 
reaction as in Example 11 was carried out. The results are shown in Table 
5. 
EXAMPLE 12 
The same oxidation reaction of isobutyric acid as in Example 11 was carried 
out except that the catalyst obtained in Example 9 was used and the 
reaction temperature was changed to 290.degree. C. The results are shown 
in Table 5. 
COMATIVE EXAMPLE 13 
The same reaction as in Example 11 was carried out except that the catalyst 
obtained in Comparative Example 10 was used and the reaction temperature 
was changed to 290.degree. C. The results are shown in Table 5. 
TABLE 1 
______________________________________ 
Example 1 2 3 4 
______________________________________ 
Catalyst 
P 1.3 1.3 1.3 1.3 
composition 
Mo 12 12 12 12 
(atomic V 1 1 1 1 
ratio) X Cs = 1 Cs = 1 Cs = 1 Cs = 1 
Type of Silicon carbide Potassium 
whiskers (0.1-0.5 .mu.m.phi. .times. 10-100 .mu.mL) 
titanate 
(0.2-0.5 
.mu.m.phi. .times. 
10-20 .mu.mL) 
Content of 2 5 5 8 
the whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Pellet Pellet Ring Spherical, 
catalyst supported 
Mechanical 
strength 
Compressive 
3.7 4.6 4.1/2.3* 
-- 
strength 
(kg/pellet) 
Ratio of 5.1 2.4 3.5 3.2 
abrasion 
(%) 
Falling 96.5 99.0 97.7 96.9 
strength 
(%) 
Reaction 280 280 280 310 
temperature 
(.degree.C.) 
Conversion 88.3 87.7 88.5 84.7 
(mole %) 
Selectivity 
74.5 74.6 76.8 75.3 
for meth- 
acrylic acid 
(mole %) 
One-pass yield 
65.8 65.4 68.0 63.8 
of methacrylic 
acid (mole %) 
______________________________________ 
*long axis direction/direction at right angles to the long axis 
: Content based on the catalytic substance deposited 
.phi.: diameter 
L: Length 
TABLE 2 
______________________________________ 
Comparative 
Example 1 2 3 
______________________________________ 
Catalyst 
P 1.3 1.3 1.3 
composition 
Mo 12 12 12 
(atomic V 1 1 1 
ratio) X Cs = 1 Cs = 1 Cs = 1 
Type of fibers 
None Glass Fine Sic 
and fine powder fibers powder 
8-12 .mu.m.phi. .times. 
(0.3 .mu.m.phi.) 
2000 .mu.mL) 
Content of 0 3 5 
whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Pellet Pellet Pellet 
catalyst 
Mechanical 
strength 
Compressive 
0.4 1.3 1.0 
strength 
(kg/pellet) 
Ratio of 50.8 37.2 40.6 
abrasion 
(%) 
Falling 54.4 76.8 66.1 
strength 
(%) 
Reaction 280 280 280 
temperature 
(.degree.C.) 
Conversion 86.4 86.0 85.7 
(mole %) 
Selectivity 
73.9 73.7 74.1 
for meth- 
acrylic acid 
(mole %) 
One-pass yield 
63.8 63.4 63.5 
of methacrylic 
acid (mole %) 
______________________________________ 
Comparative 
Example 4 5 6 
______________________________________ 
Catalyst 
P 1.3 1.3 1.3 
composition 
Mo 12 12 12 
(atomic V 1 1 1 
ratio) X Cs = 1 Cs = 1 Cs = 1 
Type of fibers 
Silicon None Silicone 
and fine powder 
carbide fiber carbide 
(10-15 .mu.m.phi. .times. 
(4-10 .mu.m.phi.) .times. 
3000 .mu.mL) 200-900 .mu.mL) 
Content of 3 0 8 
whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Pellet Spherical, 
Spherical, 
catalyst supported supported 
Mechanical 
strength 
Compressive 
1.1 -- -- 
strength 
(kg/pellet) 
Ratio of 46.9 58.5 38.4 
abrasion 
(%) 
Falling 78.1 40.3 55.7 
strength 
(%) 
Reaction 280 310 310 
temperature 
(.degree.C.) 
Conversion 85.9 71.0 79.5 
(mole %) 
Selectivity 
73.3 73.2 73.7 
for meth- 
acrylic acid 
(mole %) 
One-pass yield 
63.0 52.0 58.6 
of methacrylic 
acid (mole %) 
______________________________________ 
, .phi. and L: 
Same as the footnote to Table 1. 
TABLE 3 
______________________________________ 
Example 5 6 7 
______________________________________ 
Catalyst 
P 1 1.3 1.3 
Composition 
Mo 12 12 12 
(atomic V 0 0.75 1 
ratio) X Cs = 1.2 Rb = 1 Cs = 1.2 
Y Cu = 0.1 Ag = 0.1 Ag = 0.1 
Type of Silicon Potassium Silicone 
whiskers nitride titanate carbide 
(0.2-0.5 .mu.m.phi. .times. 
(0.2-0.5 .mu.m.phi. .times. 
50-300 .mu.mL) 
10-100 .mu.mL) 
Content of 5 10 7 
whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Ring Ring Pellet 
catalyst 
Mechanical strength 
Compressive 4.3/1.8* 5.2/2.6* 5.4 
strength 
(kg/pellet) 
Ratio of 4.0 0.6 0.8 
abrasion 
(%) 
Falling 97.1 99.4 99.6 
strength 
(%) 
Reaction 320 290 280 
temperature 
(.degree.C.) 
Conversion 79.3 90.4 92.3 
(mole %) 
Selectivity 70.8 86.4 87.7 
for meth- 
acrylic acid 
(mole %) 
One-pass yield 
56.1 78.1 80.9 
of methacrylic 
acid (mole %) 
______________________________________ 
Example 8 9 
______________________________________ 
Catalyst 
P 1.3 1.3 
composition 
Mo 12 12 
(atomic V 1 1 
ratio) X Cs = 1.2 Cs = 1.8 
Y Ag = 0.1 Cu = 0.2 
Type of Silicon Silicone 
whiskers carbide carbide 
Content of 7 5 
whiskers 
(wt. % based on 
the catalyst) 
Shape of the Ring Spherical, 
catalyst supported 
Mechanical strength 
Compressive 4.9/2.7* -- 
strength 
(kg/pellet) 
Ratio of 1.1 2.0 
abrasion 
(%) 
Falling 99.0 98.2 
strength 
(%) 
Reaction 280 300 
temperature 
(.degree.C.) 
Conversion 92.6 90.6 
(mole %) 
Selectivity 88.8 88.4 
for meth- 
acrylic acid 
(mole %) 
One-pass yield 82.2 80.1 
of methacrylic 
acid (mole %) 
______________________________________ 
*, , .phi. and L are the same as the footnote to Table 1. 
TABLE 4 
______________________________________ 
Comparative 
Example 7 8 9 10 
______________________________________ 
Catalyst 
P 1 1.3 1.3 1.3 
composition 
Mo 12 12 12 12 
(atomic V 0 1 1 1 
ratio) X Cs = 1.2 Cs = 1.2 
Cs = 1.2 
Cs = 1.8 
Y Cu = 0.1 Ag = 0.1 
Ag = 0.1 
Cu = 0.2 
Type of whiskers 
None None Fumed None 
and fine powder silica 
(10-40 .mu.m) 
Content of 0 0 7 0 
the whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Pellet Ring Ring Spherical, 
catalyst supported 
Mechanical 
strength 
Compressive 
0.5 2.9/1.0* 3.1/1.2* 
-- 
strength 
(kg/pellet) 
Ratio of 59.1 18.5 14.2 28.2 
abrasion 
(%) 
Falling 48.2 86.7 88.9 70.1 
strength 
(%) 
Reaction 320 280 280 300 
temperature 
(.degree.C.) 
Conversion 76.4 91.5 88.7 86.4 
(mole %) 
Selectivity 
68.2 87.0 76.5 86.8 
for meth- 
acrylic acid 
(mole %) 
One-pass yield 
52.1 79.6 67.9 75.0 
of methacrylic 
acid (mole %) 
______________________________________ 
*, .phi. and L are the same as the footnote to Table 1. 
TABLE 5 
______________________________________ 
Example (Ex.) 
or Comparative 
Example (CEx.) 
Ex. 10 CEx. 11 Ex. 11 
______________________________________ 
Catalyst 
P 1.3 1.3 1.5 
Composition 
Mo 12 12 12 
(atomic V 1.5 1.5 1.25 
ratio) X Cs = 1.2 Cs = 1.2 
Cs = 1.0 
Sr = 0.2 
Y Ag = 0.2 Ag = 0.2 
Cu = 0.2 
Sb = 0.5 
Type of Silicon None Silicone 
whiskers nitride nitride 
Content of 15 0 15 
the whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Ring Ring Ring 
catalyst 
Mechanical strength 
Compressive 6.3/2.8* 2.8/0.8* 5.9/2.9* 
strength 
(kg/pellet) 
Ratio of 0.4 16.7 0.5 
abrasion 
(%) 
Falling 99.8 84.5 99.7 
strength 
(%) 
Reaction 280 280 270 
temperature 
(.degree.C.) 
Conversion Isobutyr- Isobutyr- 
Isobutyric 
(mole %) aldehyde aldehyde acid 
100 100 100 
Selectivity 73.6 69.8 76.8 
for meth- 
acrylic acid 
(mole %) 
Selectivity for 
9.5 9.0 -- 
methacrolein 
(mole %) 
______________________________________ 
Example (Ex.) 
or Comparative 
Example (CEx.) 
CEx. 12 Ex. 12 CEx. 13 
______________________________________ 
Catalyst 
P 1.5 1.3 1.3 
composition 
Mo 12 12 12 
(atomic V 1.25 1 1 
ratio) X Cs = 1.0 Cs = 1.8 
Cs = 1.8 
Sr = 0.2 
Y Cu = 0.2 Cu = 0.2 
Cu = 0.2 
Sb = 0.5 
Type of None Silicon None 
whiskers carbide 
Content of 0 5 0 
the whiskers 
(wt. % based on 
the catalyst) 
Shape of the 
Ring Spherical, 
Spherical, 
catalyst supported supported 
Mechanical strength 
Compressive 2.6/1.1* -- -- 
strength 
(kg/pellet) 
Ratio of 18.6 -- -- 
abrasion 
(%) 
Falling 86.0 -- -- 
strength 
(%) 
Reaction 270 290 290 
temperature 
(.degree.C.) 
Conversion Isobutyric Isobutyric 
Isobutyric 
(mole %) acid acid acid 
100 100 100 
Selectivity 73.5 72.7 68.0 
for meth- 
acrylic acid 
(mole %) 
Selectivity for 
-- -- -- 
methacrolein 
(mole %) 
______________________________________ 
* and are the same as the footnote to Table 1.