Patent Description:
An ammoxidation process of propylene is based on a mechanism of reduction in which ammonia and propylene are reacted and reoxidation by oxygen, and in order to increase conversion of the reactant (namely, propylene) and selectivity and yield of the reaction product (namely acrylonitrile), catalysts of various compositions have been studied.

Specifically, since a Mo(molybdenum)-Bi(bismuth) oxide catalyst has been suggested, in order to increase the catalytic activity and stability, catalysts to which metals of various oxidation states are added have been studied. As the result, the yield of acrylonitrile was improved compared to the initial studies, according to the kind or amount of added metals.

However, despite diversification of catalyst compositions, due to insufficient studies on the structure and properties, remarkable increase in the conversion of the reactant (namely, propylene) and selectivity of the reaction product (namely, acrylonitrile) during the ammoxidation of propylene was limited.

Specifically, in general, metal precursors of aimed compositions and nano silica sol are coprecipitated, and then, spray dried and calcined, thus obtaining a catalyst of a secondary particle structure in which metal oxide particles and silica particles are agglomerated.

More specifically, in the catalyst of a secondary particle structure, metal oxide particles are uniformly distributed inside and outside, but internal pore are scarcely included, and thus, parts capable of participating in ammoxidation of propylene are limited to the external surface part. <CIT> discloses an ammoxidation catalyst composition comprising a metal oxide represented by e.g. Mo12Bi0.166Ce0.730Fe1.185Cr0.173Mg1.370Co6.515Mn0.426K0.077Cs0.040x/<NUM> wt % SiO2, having with a diameter of <NUM> to <NUM> and a volume of <NUM> to <NUM> cm3/g, and a BET S. that may be <NUM> to <NUM> m2/g and a D50 size of <NUM> to <NUM> microns.

It is an object of the invention to provide an ammoxidation catalyst for propylene in which not only the external surface part (namely, the surface of a catalyst) but also the internal surface(pores) can participate in reactions, and to prepare acrylonitrile with higher yield by using such a catalyst.

Specifically, according to one embodiment of the invention, there is provided an ammoxidation catalyst for propylene having a structure wherein metal oxide of a specific composition is supported in a silica carrier, and having large pore size and volume and wide BET specific surface area in the supported state.

The catalyst of one embodiment has wide effective surface area capable of participating in reactions, and thus, has high catalytic efficiency and reactivity.

Thus, using the catalyst of one embodiment, propylene can be converted with higher rate, and acrylonitrile can be prepared with higher selectivity and yield.

Although various modifications can be made to the invention and the invention may have various forms, specific examples will be illustrated and explained in detail below. However, it should be understood that these are not intended to limit the invention to specific disclosure, and that the invention includes all the modifications, equivalents or replacements thereof without departing from the spirit and technical scope of the invention. In explanation of the invention, in case it is judged that specific explanations regarding related known technologies may obscure the subject matter of the invention, the explanations will be omitted.

And, terms including ordinal numbers such as "a first" , "a second" and the like are used to explain various constructional elements, but the constructional elements are not limited by these terms. These terms are used only to distinguish one constructional element from other constructional elements. For example, the first constructional element may be named as the second constructional element, and similarly, the second constructional elements may be also named as the first constructional elements, without departing from the scope of the right of the invention.

A singular expression includes a plural expression thereof, unless it is expressly stated or obvious from the context that such is not intended. As used herein, the terms "comprise" or "have" , etc. are intended to designate the existence of practiced characteristic, number, step, constructional element or combinations thereof, and they are not intended to preclude the possibility of existence or addition of one or more other characteristics, numbers, steps, constructional elements or combinations thereof.

Hereinafter, "particle diameter Dv" means a particle diameter at v% point in cumulative volume distribution according to particle diameter. Namely, D50 is a particle diameter at <NUM>% point in cumulative volume distribution according to particle diameter, D90 is a particle diameter at <NUM>% point in the cumulative volume distribution according to particle diameter, and D10 is a particle diameter at <NUM>% point in cumulative volume distribution according to particle diameter.

The Dv may be measured using a laser diffraction method. Specifically, particle size distribution is calculated by dispersing powders to be measured in a dispersion medium, and then, introducing them in a commercially available laser diffraction particle size measuring device (for example, Micritrac S3500), and measuring diffraction pattern difference according to particle size when particles pass through laser beam. By calculating particle diameter at <NUM>%, <NUM>% and <NUM>% points in cumulative volume distribution according to particle diameter, D10, D50 an D90 can be measured.

Hereinafter, an ammoxidation catalyst for propylene according to one embodiment will be explained in detail with reference to drawings.

According to one embodiment of the invention, there is provided an ammoxidation catalyst for propylene in which metal oxide represented by the following Chemical Formula <NUM> is supported in a silica carrier,.

Commonly known propylene ammoxidation catalysts are prepared by coprecipitation and spray drying, and provided as a secondary particle structure in which metal oxide nanoparticles and silica nanoparticles are agglomerated (<FIG>).

Since metal oxide particles are uniformly distributed inside and outside, but parts capable of participating in propylene ammoxidation reactions are limited to the external surface part (namely, the surfaces of secondary particles), and a small surface area is provided, the amount of ammonia detached from the catalyst surface during the propylene ammoxidation reaction is large.

On the contrary, since the catalyst of one embodiment is prepared by impregnation, it may be provided as a structure wherein metal oxide is supported in a silica carrier (<FIG>).

For example, a silica carrier may be impregnated in a metal precursor solution by immersing the silica carrier in the metal precursor solution prepared such that stoichiometric mole ratio of metal oxide aimed is satisfied.

Thereafter, if a solvent (namely, water) is removed by drying, the metal precursor may remain on the pore walls of the silica carrier, and the metal precursor may be oxidized during a calcinations process to form a film continuously coating the pore walls of the silica carrier.

The catalyst of one embodiment thus prepared, even if a classification process is not progressed as post treatment after preparation, may have smaller fine powder content and more excellent durability than the catalyst prepared with the same composition by coprecipitation and spray drying.

And, by controlling the composition of the metal oxide so as to further include metals forming active sites for a propylene ammoxidation reaction, as well as Mo and Bi known to increase the activity of an ammoxidation reaction, the catalytic activity may be further increased.

Particularly, in the catalyst of one embodiment, by uniformly supporting the metal oxide in the internal pores of the silica carrier, parts capable of participating in a propylene ammoxidation reaction may be extended to the internal surface (pores) as well as to the external surface part (namely, the surface of the catalyst).

Specifically, the catalyst of one embodiment may comprise pores having a diameter of <NUM> to <NUM> and a volume of <NUM> to <NUM><NUM>/g, and have BET specific surface area of <NUM><NUM>/g to <NUM><NUM>/g, when the metal oxide is supported in a silica carrier.

This means that compared to catalysts prepared through coprecipitation and spray drying and having a secondary particle structure, pore size and volume are remarkably large, and BET specific surface area directly connected to the effective surface area capable of adsorbing ammonia gas and propylene gas is much broader.

Hereinafter, the catalyst of one embodiment will be explained in detail.

The catalyst of one embodiment may have a structure comprising a silica carrier comprising second pores; an internal coating layer that continuously coats the wall surfaces of the second pores, and comprises metal oxide represented by the Chemical Formula <NUM>; and first pores positioned inside of the second pores, and occupying empty spaces except the internal coating layer.

Specifically, the catalyst of one embodiment may have an egg-shell structure.

For this purpose, a silica carrier comprising a non-porous core part; and a porous shell part positioned on the surface of the non-porous core, and comprising second pores; may be used.

More specifically, the porous shell comprises depressed parts and protruded parts of the surface, wherein the depressed parts may be formed by opening of the second pores toward the surface of the porous shell.

Thus, the catalyst of one embodiment may have a structure comprising a coating layer that continuously coats the depressed and protruded parts of the porous shell, and comprises metal oxide represented by the Chemical Formula <NUM>; and first pores occupying empty spaces except the coating layer, in the depressed parts of the silica carrier.

In the above structure, by controlling the properties of the second pores of the silica carrier, the properties of the first pores of the final catalyst may be controlled.

Specifically, a silica carrier in which the metal oxide is not supported may have D50 size of <NUM> to <NUM>; comprise second pores having diameter of <NUM> to <NUM>, and volume of <NUM> to <NUM><NUM>/g; and have BET specific surface area of <NUM> to <NUM><NUM>/g.

More specifically, a silica carrier on which the metal oxide is not supported may have D50 of <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or more, and <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

And, the second pores included in a silica carrier in the which metal oxide is not supported may have diameter of <NUM> or more, <NUM> or more, or <NUM> or more, and <NUM> nmor less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less; volume of <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, or <NUM><NUM>/g or more, and <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, or <NUM><NUM>/g or less.

And, a silica carrier in which the metal oxide is not supported may have BET specific surface area of <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, or <NUM><NUM>/g or more, and <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, or <NUM><NUM>/g or less.

In this case, when the metal oxide is supported in a silica carrier, the catalyst of one embodiment may have D50 size of <NUM> to <NUM>; comprise first pores having diameter of <NUM> to <NUM>, and volume of <NUM> to <NUM><NUM>/g; and have BET specific surface area of <NUM> to <NUM><NUM>/g.

More specifically, when the metal oxide is supported in a silica carrier, D50 particle diameter may be <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or <NUM>, and <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

And, when the metal oxide is supported in a silica carrier, the first pores included in the catalyst of one embodiment may have diameter of <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or more, and <NUM> or less, <NUM> or less <NUM> or less, <NUM> or less or <NUM> or less; volume of <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more or <NUM><NUM>/g or more, and <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less or <NUM><NUM>/g or less.

And, when the metal oxide is supported in a silica carrier, the catalyst of one embodiment may have BET specific surface area of <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, <NUM><NUM>/g or more, or <NUM><NUM>/g or more, and <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, <NUM><NUM>/g or less, or <NUM><NUM>/g or less.

For reference, the pore diameter and volume before and after supporting the metal oxide respectively mean average pore size and volume derived from BJH Formula through commonly known nitrogen adsorption/desorption test. The BET specific surface area before and after supporting the metal oxide may be calculated using commonly know BET measuring device.

The BET specific surface area of the catalyst of one embodiment, and diameter and volume of the first pores are improved compared to a catalyst having a secondary particle structure, thereby converting propylene with higher rate, and obtaining acrylonitrile with higher selectivity and yield.

In the above suggested ranges, as the diameter of the first pore is larger, the volume may increase and BET specific surface area may broaden. However, when the diameter and volume of the total catalyst are identical, as the diameter occupied by the first pores is larger, inflow of reactant propylene and discharge of product acrylonitrile may become easy and reaction properties may be improved, but volume occupied by the first pores may decrease and thus volume occupied by the metal oxide may relatively decrease, and thus, active sites may decrease and reactivity may be deteriorated.

Thus, considering overall properties of the catalyst aimed, the diameter and volume of the first pores, the diameter and BET specific surface area of the catalyst comprising the same, and the like may be controlled.

The properties of the first pores of the final catalyst may be also influenced by the amount of the metal precursor solution impregnated in the silica carrier, as well as by the properties of the second pores of the silica carrier. The detailed explanations thereof will be described later.

Meanwhile, even if a catalyst has the same structure as the catalyst of one embodiment, if the kind and content of the components constituting the metal oxide do not satisfy the Chemical Formula <NUM>, active sites formed may be insufficient for propylene ammoxidation or have excessively high density.

Thus, the kind and content of the components constituting the metal oxide should satisfy the Chemical Formula <NUM>.

Particularly, when the metal oxide is represented by the Chemical Formula <NUM>-<NUM>, due to synergistic effects of increasing movement speed of Fe, molybdenum, and lattice oxygen to increase conversion, increasing partial oxidation reaction property of propylene due to the formation of complex oxide of Co and molybdenum, and dispersing the active sites of complex oxide including K and molybdenum to increase selectivity of acrylonitrile, the activity in a propylene ammoxidation reaction may be further increased:.

[Chemical Formula <NUM>-<NUM>]     Mo<NUM>BiaFebCocKdOx.

In the Chemical Formula <NUM>-<NUM>,
a to d, and x are respectively fractions of each atom or atomic group, and a may be <NUM> to <NUM>,specifically <NUM> to <NUM>, b may be <NUM> to <NUM>, specifically <NUM> to <NUM>, c may be <NUM> to <NUM>, specifically <NUM> to <NUM>, d may be <NUM> to <NUM>, specifically <NUM> to <NUM>, and x may be <NUM> to <NUM>, specifically <NUM> to <NUM>.

The catalyst of one embodiment may comprise the metal oxide and the silica carrier at a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>, specifically <NUM>:<NUM> to <NUM>:<NUM>, for example <NUM>:<NUM> to <NUM>:<NUM> (metal oxide:silica carrier).

Within this range, the catalyst of one embodiment may have high activity and high selectivity of acrylonitrile.

According to another embodiment of the invention, there is provided a method for preparing the catalyst of one embodiment as explained above using impregnation.

As briefly explained above, the catalyst of one embodiment may be prepared by the processes of supporting a metal precursor solution in the silica carrier using impregnation, drying, and then, calcining.

More specifically, the method for preparing the catalyst of one embodiment comprises the steps of:.

The step of preparing a first precursor solution may comprise dissolving a Mo precursor in water of <NUM> to <NUM> to prepare a solution comprising water and Mo precursor.

In the step of preparing the first precursor solution, additives including citric acid, oxalic acid, or a mixture thereof may be used.

In the catalyst preparation process using coprecipitation and spray drying, these additives function as a strength control agent. However, in the above one embodiment, these additives make the first precursor solution transparent, enabling the preparation of a completely dissolved precursor mixture.

When adding the additives, the weight ratio of the molybdenum precursor and the additives may be controlled to satisfy <NUM>:<NUM> to <NUM>:<NUM>, specifically <NUM>:<NUM> to <NUM>:<NUM>, and within this range, solubility of the molybdenum precursor may be increased, but it is not limited thereto.

Meanwhile, the second solution may comprise metal precursors, other than the Mo precursor included in the first precursor solution.

Specifically, the step of preparing the second precursor solution may prepare a second precursor solution essentially comprising a Bi precursor, a Fe precursor, an A precursor, and a B precursor, and optionally, further comprising a C precursor(one or more elements of Cr, W, B, Al, Ca, and V), in water of <NUM> to <NUM>.

More specifically, in the step of preparing the second precursor solution, considering the composition of metal oxide in the catalyst finally aimed, the kinds of metal precursors other than Mo precursor may be selected.

For example, considering the composition of metal oxide satisfying the Chemical Formula <NUM>-<NUM>, a second precursor solution comprising water, a Bi precursor, a Fe precursor, a Co precursor, and a K precursor may be prepared.

The processes of preparing the first and second precursor solutions are independent from each other, and the preparation sequence is not limited.

After mixing the first and second precursor solutions, the mixture may be supported in a silica carrier.

Wherein, the mixture of the first and second precursor solutions may be supported in the first pores in the silica carrier, by introducing the silica carrier comprising second pores as explained above in the mixture of the first and second precursor solutions.

Specifically, a silica carrier in which metal oxide is not supported may have D50 of <NUM> to <NUM>; and comprise second pores having a diameter of <NUM> to <NUM>, and a volume of <NUM> to <NUM><NUM>/g.

And, a silica carrier in which metal oxide is not supported may have BET specific surface area of <NUM> to <NUM><NUM>/g, specifically <NUM> to <NUM><NUM>/g.

When using such a silica carrier, catalyst comprising first pores having a diameter of <NUM> to <NUM>, specifically <NUM> to <NUM>, and a volume of <NUM> to <NUM><NUM>/g, specifically <NUM> to <NUM><NUM>/g may be obtained.

And, as explained above, the BET specific surface area of the final catalyst may be <NUM> to <NUM><NUM>/g, specifically <NUM> to <NUM><NUM>/g.

The process of drying the silica carrier in which the mixture of the first and second precursor solutions is supported may comprise the steps of: first vacuum drying the silica support in which a mixture of the first and second precursor solutions is supported at <NUM> to <NUM> mbar, and second vacuum drying the first vacuum dried material at <NUM> to <NUM> mbar, to obtain a silica carrier in which a mixture of the first and second precursor solutions is supported.

Specifically, by conducting the first vacuum drying at <NUM> to <NUM> for <NUM> to <NUM> hours, and conducting the second vacuum drying at <NUM> to <NUM> for <NUM> to <NUM> minutes, the solvent(namely, water) may be removed, and only the first and second precursors may remain on the wall surfaces of the first pores.

Although the second vacuum dried material may be immediately calcined, by third drying at atmospheric pressure, even the solvent (namely, water) remaining after the second vacuum drying may be effectively removed.

Specifically, the third drying may be conducted at <NUM> to <NUM> for <NUM> to <NUM> hours.

However, these are no more than examples, and drying conditions are not specifically limited as long as a carrier in which the first and second precursors are supported may be obtained.

Finally, the dried material, namely, a carrier in which the first and second precursors are supported may be calcined at <NUM> to <NUM> for <NUM> to <NUM> hours to finally obtain a catalyst.

However, the drying and calcinations conditions are no more than examples, and any conditions may be sufficient as long as the solvents may be sufficiently removed from the internal pores of the carrier, and metal precursor may be oxidized.

According to yet another embodiment of the invention, there is provided a method for ammoxidation of propylene, comprising a step of reacting propylene and ammonia in the presence of the catalyst of the one embodiment as above explained, in a reactor.

The catalyst of one embodiment has high activity and high temperature stability, and may be used for propylene ammoxidation reaction to increase converson of propylene and selectivity and yield of acrylonitrile.

For the details other than the catalyst of one embodiment, matters commonly known in the art may be referred to, and the detailed explanations thereof are omitted.

Hereinafter, embodiments of the invention will be explained in more detail in the following examples. However, these examples are presented only as the illustrations of the invention, and the scope of the invention is not limited thereby.

In distilled water of <NUM>, <NUM> of a Mo precursor ((NH<NUM>)<NUM>Mo<NUM>O<NUM>) and <NUM> of citric acid were introduced, and mixed to prepared a Mo precursor solution.

Separately, in distilled water of room temperature, <NUM> of a Bi precursor(Fe(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Co precursor(Co(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Fe precursor (Fe(NOs)<NUM>·<NUM><NUM>O), and <NUM> of a K precursor(KNO<NUM>) were introduced, and <NUM> of nitric acid(HNO<NUM>) was added, and then, they were mixed to prepare a mixed solution of Bi, Fe, Co, and K precursors.

The Mo precursor solution; and the mixed solution of Bi, Fe, Co, and K precursors were mixed to complete a mixed solution of Mo, Bi, Fe, Co, and K precursors.

In the mixed solution of precursors, the total amount of distilled water was <NUM>.

Silica (SiO<NUM>, SP948, Grace) particles having D50 particle diameter of <NUM>, internal pore size of <NUM>, BJH pore volume according to nitrogen adsorption of <NUM><NUM>/g, and BET specific surface area of <NUM><NUM>/g were used as a carrier.

In the mixed solution of Mo, Bi, Fe, Co, and K precursors, the silica carrier was introduced, and the solution was stirred sequentially at room temperature and <NUM>, respectively for <NUM> hours, such that the mixed solution of Mo, Bi, Fe, Ni, Co, and K precursors was sufficiently supported in the internal pores of the silica carrier.

Thereafter, the silica carrier in which the mixed solution of Bi, Fe, Co, and K precursors was supported was recovered and introduced in a rotary vacuum dryer, and then, first vacuum dried under pressure of <NUM> mbar and temperature of <NUM> for <NUM> hour and <NUM> minutes, and second vacuum dried under pressure of <NUM> mbar and temperature of <NUM> for <NUM> minutes.

The second vacuum dried material was recovered and introduced into an oven, and third dried under atmospheric pressure and temperature of <NUM> for <NUM> hours, and then, while maintaining a temperature of <NUM> in a box calcination furnace of air atmosphere, heat treated for <NUM> hours to finally obtain a catalyst of Example <NUM>.

In a tubular reactor having an inner diameter of <NUM>/<NUM> inches, <NUM> of quartz wool was charged and <NUM> of the catalyst of Example <NUM> was charged in the reactor.

The internal pressure of the reactor charged with quartz wool and catalyst was maintained at atmospheric pressure (<NUM> atm), and while raising the internal temperature of the reactor at <NUM>/min, nitrogen and ammonia gas were flowed as pretreatment. After the internal temperature of the reactor reached <NUM> at which an ammoxidation reaction can be progressed, it was maintained under reducing gas atmosphere for <NUM> minutes so as to achieve sufficient pretreatment.

While supplying air together with reactants of propylene and ammonia in the pretreated reactor, an ammoxidation process of propylene was conducted. Wherein, the amounts of the reactants supplied were such that a volume ratio became propylene:ammonia:air=<NUM>:<NUM>:<NUM> , and the total weight hourly space velocity(WHSV) of propylene, ammonia and air became <NUM>-<NUM>.

After the ammoxidation reaction was completed, the product was recovered, and in order to confirm whether acrylonitrile was sufficiently produced, it was analyzed using various apparatuses.

The analysis method, analysis results, and the like will be explained in detail in Experimental Examples below.

Each catalyst of Examples <NUM> to <NUM> was prepared by the same method as Example <NUM>, except that a precursor solution was prepared according to the composition described in the following Table <NUM>, and a silica carrier described in the following Table <NUM> was used.

An ammoxidation process of propylene was conducted using each catalyst of Examples <NUM> to <NUM> instead of Example <NUM>, and then, the product was recovered, and analyzed by the same method as Example <NUM>.

First, in distilled water of <NUM>, <NUM> of a Mo precursor((NH<NUM>)<NUM>Mo<NUM>O<NUM>) and <NUM> of citric acid were introduced and mixed to prepare a Mo precursor solution.

Separately, in distilled water of room temperature, <NUM> of a Bi precursor(Fe(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Co precursor(Co(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Fe precursor(Fe(NO<NUM>)<NUM>·<NUM><NUM>O), and <NUM> of a K precursor(KNO<NUM>) were introduced, and <NUM> of nitric acid(HNO<NUM>) was added, and then, they were mixed to prepare a mixed solution of Bi, Fe, Co, and K precursors.

The Mo precursor solution; and the mixed solution of Bi, Fe, Co, and K precursors were mixed, and <NUM> of silica sol(LUDOX AS <NUM>, solid content: <NUM> %) was added thereto, and the mixture was stirred, and then, spray dried under conditions of <NUM>(inlet) and <NUM>(outlet) using a disk-type spray dryer.

The obtained powders were calcined at <NUM> for <NUM> hours to finally obtain a catalyst of Comparative Example <NUM>.

An ammoxidation process of propylene was conducted by the same method as Example <NUM>, except that the catalyst of Comparative Example <NUM> was used instead of the catalyst of Example <NUM>.

After the ammoxidation reaction of Comparative Example <NUM> was finished, the product was recovered, and analyzed by the same method as Example <NUM>.

A catalyst of Comparative Example <NUM> was prepared by the same method as Comparative Example <NUM>, except that a precursor solution was prepared according to the composition described in the following Table <NUM>, and a silica carrier described in the following Table <NUM> was used.

An ammoxidation process of propylene was conducted using the catalyst of Comparative Example <NUM> instead of the catalyst of Comparative Example <NUM>, and then, the product was recovered and analyzed by the same method as Comparative Example <NUM>.

A catalyst of Comparative Example <NUM> was prepared by the same method as Example <NUM>, except that a precursor solution was prepared according to the composition described in the following Table <NUM>, and a silica carrier described in the following Table <NUM> was used.

An ammoxidation process of propylene was conducted using the catalyst of Comparative Example <NUM> instead of the catalyst of Example <NUM>, and then, the product was recovered and analyzed by the same method as Example <NUM>.

Separately, in distilled water of room temperature, <NUM> of a Bi precursor(Fe(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Co precursor(Co(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Fe precursor(Fe(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a Ni precursor(Ni(NO<NUM>)<NUM>·<NUM><NUM>O), <NUM> of a K precursor (KNO<NUM>), <NUM> of a Ce precursor(Ce(NO<NUM>)<NUM> ·<NUM><NUM>O), <NUM> of a Mg precursor(Mg(NO<NUM>)<NUM>·<NUM><NUM>O), and <NUM> of a Rb precursor(RbNO<NUM>) were introduced, and <NUM> of nitric acid(HNO<NUM>) was added, and they were mixed to prepare a mixed solution of Bi, Co, Fe, Ni, K, Ce, Mg, and Rb precursors.

The Mo precursor solution; and the mixed solution of Bi, Co, Fe, Ni, K, Ce, Mg, and Rb precursors were mixed to complete a mixed solution of Mo, Bi, Fe, Co, and K precursors.

In the Table <NUM>, Mo is (NH<NUM>)<NUM>Mo<NUM>O<NUM>, Bi is Bi(NO<NUM>)<NUM>·<NUM><NUM>O, Co is Co(NO<NUM>)<NUM>·<NUM><NUM>O, Fe is Fe(NO<NUM>)<NUM>·<NUM><NUM>O, and K is KNO<NUM>. And, the omitted unit is g.

Meanwhile, Comparative Example <NUM> wherein many materials were added to a heterogeneous metal precursor solution was omitted in the Table <NUM> for convenience.

According to the following analysis method, each catalyst of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was analyzed:.

According to Table <NUM>, it can be seen that compared to coprecipitation and spray drying used for preparing the catalysts of Comparative Examples <NUM> and <NUM>, impregnation used for preparing the catalysts of Examples <NUM> to <NUM> is favorable for the preparation of a catalyst having large pore size and volume, and thus wide BET specific surface area.

Wherein, since the catalysts of Comparative Example <NUM> and <NUM> were prepared through coprecipitation and spray drying, they scarcely include pores, and have relatively narrow BET specific surface area. On the contrary, since the catalysts of Examples <NUM> to <NUM> were prepared using impregnation, they include a plurality of large pores, and have relatively wide BET specific surface area.

As representative examples, for each catalyst of Example <NUM> and Comparative Example <NUM>, using SEM: Hitachi S-<NUM> Scanning Electron Microscope, the SEM(Scanning Electron Microscope) image of <NUM> magnification was obtained, and each SEM image was shown in <FIG>(Example <NUM>) and <FIG>(Comparative Example <NUM>).

Specifically, it can be seen that the catalyst of Comparative Example <NUM> generally has a particle diameter of <NUM> to <NUM>, and has a secondary particle structure wherein metal oxide particles are uniformly distributed inside and outside, but scarcely includes internal pores.

On the contrary, it can be seen that the catalyst of Example <NUM> generally has a particle diameter of <NUM> to <NUM>, a metal oxide coating layer that continuously coats the porous shell part of the silica carrier is formed, and a plurality of large empty spaces(pores) except the coating layer exist in the porous shell part of the silica carrier.

Meanwhile, the catalyst of Comparative Example <NUM>, although prepared using impregnation, the pore size and volume, and BET specific surface area are equivalent to those of Comparative Examples <NUM> and <NUM>.

It means that by the influence of metal oxide comprising only Mo and Bi as active metals, a catalyst having relatively small pore size and volume, and narrow BET specific surface area was prepared.

Since the catalyst of Comparative Example <NUM> was prepared by impregnation and comprises a plurality of heterogeneous metals as well as Mo and Bi as active metals, it has BET specific surface area equivalent to those of Examples <NUM> to <NUM>. However, in order to evaluate the influence by the active metals, there is a need to additionally analyze the ammoxidation product.

Using Gas chromatography(Manufacturing company: Agilent Device name: HP <NUM> N) equipped with FID(Flame Ionization Detector and TCD(Thermal conductivity detector), each ammoxidation product of Examples and Comparative Examples was analyzed.

Specifically, with FID, products including ethylene, hydrogen cyanide, acetaldehyde, acetonitrile, acrylonitrile, and the like were analyzed, and with TCD, gas products including NH<NUM>, O<NUM>, CO, CO<NUM>, and the like and unreacted propylene were analyzed, thus calculating the mole number of reacted propylene and the mole number of ammoxidation product in Examples and Comparative Examples.

The analysis results and the mole number of supplied propylene were substituted in the following Formulas <NUM>, <NUM> and <NUM>, thus calculating conversion of propylene, selectivity and yield of acrylonitrile, which is the ammoxidation reaction product of propylene, and the calculation values were described in the following Table <NUM>: <MAT> <MAT> <MAT>.

Since the catalysts of Comparative Examples <NUM> and <NUM> were prepared through coprecipitation and spray drying, internal pores are scarcely included, and thus, parts capable of participating in reactions are limited to the external surface part.

Practically, it is confirmed that during the reaction using when the catalyst of Comparative Examples <NUM> and <NUM>, conversion of propylene is less than <NUM>%, and yield of acrylonitrile is less than <NUM>%.

Meanwhile, the catalyst of Comparative Example <NUM>, although prepared by impregnation, due to the influence of metal oxide comprising only Mo and Bi as active metals, the effective surface area capable of participating in the reaction is small.

Practically, it is confirmed that during the reaction using the catalyst of Comparative Example <NUM>, conversion of propylene is <NUM>%, and yield of acrylonitrile is less than <NUM>%.

Since the catalyst of Comparative Example <NUM> is prepared by impregnation, and includes plural heterogeneous metals as well as Mo and Bi as active metals, the effective surface area capable of participating reactions is large.

Nevertheless, during the reaction using the catalyst of Comparative Example <NUM>, conversion of propylene is less than <NUM>%, selectivity to acrylonitrile is less than <NUM>%, and the yield is less than <NUM>%. It is assumed that since Ce, Fe, Ni, Co, Mg, K, and Rb as well as Mo and Bi were included as active metals, and particularly Ce is included, active sites of excessively high density was formed.

On the contrary, the catalysts of Examples <NUM> to <NUM> include pores of large size and volume, and have large effective surface area capable of participating in reactions.

Practically, it is confirmed that during the reactions using the catalysts of Examples <NUM> to <NUM>, conversion of propylene is remarkably increased to <NUM>% or more, and yield of acrylonitrile is remarkably increased to <NUM>% or more.

Thus, it can be seen that catalysts capable of improving converson of propylene and yield of acrylonitrile during the ammoxidation reaction of propylene are those wherein the composition of metal oxide satisfies the above explained Chemical Formula <NUM>, and when the metal oxide is supported in a silica carrier, pores having particle diameter of <NUM> to <NUM> and volume of <NUM> to <NUM><NUM>/g are included, and BET specific surface area is <NUM><NUM>/g to <NUM><NUM>/g.

Claim 1:
An ammoxidation catalyst for propylene in which metal oxide represented by Chemical Formula <NUM> is supported on a silica carrier,
wherein the catalyst comprises pores having a diameter of <NUM> to <NUM> and a volume of <NUM> to <NUM><NUM>/g, and
has BET specific surface area of <NUM><NUM>/g to <NUM><NUM>/g:

        [Chemical Formula <NUM>]     Mo<NUM>BiaFebAcBdCeOx

in Chemical Formula <NUM>,
A is one or more elements of Ni, Mn, Co, Zn, Mg, Ca, and Ba,
B is one or more elements of Li, Na, K, Rb, and Cs,
C is one or more elements of Cr, W, B, Al, Ca, and V, and
a to e, and x are respectively fractions of each atom or atomic group, wherein a is <NUM> to <NUM>, b is <NUM> to <NUM>, c is <NUM> to <NUM>, d is <NUM> to <NUM>, e is <NUM> to <NUM>, and x is <NUM> to <NUM>,
wherein the BET specific surface area, the pore size and pore volume have been measured using a BET specific surface area measuring device (Manufacturing company: BEL Japan, Device name: BELSORP_Mini), pore size and volume were measured from BJH Formula using adsorption amount measured until relative pressure(P/PO) of <NUM> under liquid nitrogen temperature(<NUM>), and desorption amount measured until <NUM>.