JP5084004B2 - Palladium-containing supported catalyst, method for producing the same, and method for producing α, β-unsaturated carboxylic acid - Google Patents

Description

  The present invention relates to a supported catalyst containing paradidymium for producing an α, β-unsaturated carboxylic acid from an olefin or an α, β-unsaturated aldehyde by liquid phase oxidation, a method for producing the same, and α, β using the catalyst. -It relates to a process for producing unsaturated carboxylic acids.

A palladium-containing catalyst is known as a catalyst for oxidizing an olefin or an α, β-unsaturated aldehyde with molecular oxygen in a liquid phase to obtain an α, β-unsaturated carboxylic acid. For example, an example of Patent Document 1 discloses a palladium-containing catalyst in which palladium having an average particle diameter in the range of 1 to 8 nm is supported on activated carbon and a method for producing the catalyst. In the specification of Patent Document 1, activated carbon, silica, alumina, titania, and zirconia are listed as carriers.
JP 2005-224657 A

  However, the amount of palladium in the catalyst disclosed in the example of Patent Document 1 is 0.10 parts by mass at the maximum with respect to 1 part by mass of the carrier (hereinafter, the ratio of the mass of palladium to the mass of the carrier is “palladium loading” or simply It is referred to as “loading rate”). Patent Document 1 does not disclose any average pore diameter of the carrier used. When the present inventor produces a catalyst having a loading ratio exceeding 0.10 using a carrier having an average pore diameter exceeding 8 nm by such a conventional method, the average particle diameter of palladium is the average pore diameter of the carrier. Since it is not restricted to 8 nm, the average particle diameter of palladium exceeded 8 nm, and the problem that the catalyst activity per mass of a supported catalyst tends to peak was found.

  Accordingly, an object of the present invention is to provide a palladium-containing supported for producing an α, β-unsaturated carboxylic acid from an olefin or α, β-unsaturated aldehyde with a high yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst. It is an object of the present invention to provide a catalyst, a method for producing the same, and a method for producing an α, β-unsaturated carboxylic acid having a high yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst.

The present invention is for producing an α, β-unsaturated carboxylic acid by oxidizing an olefin or α, β-unsaturated aldehyde formed of palladium supported on an inorganic oxide support in a liquid phase with molecular oxygen. A palladium-containing supported catalyst comprising:
The average pore diameter of the inorganic oxide carrier is 2 to 8 nm, the mass of the supported palladium is 0.12 to 1 part by mass with respect to 1 part by mass of the inorganic oxide carrier, and the average particle size of the supported palladium is It is a catalyst in the range of 1-8 nm.

Further, in the present invention, a palladium salt is supported on an inorganic oxide carrier having an average pore diameter of 2 to 8 nm by an impregnation method , followed by heat treatment to convert the palladium salt to palladium oxide, and in the presence of the inorganic oxide carrier. This is a method for producing the above-described catalyst for reducing palladium in an oxidized state.

Furthermore, the present invention is a method for producing an α, β-unsaturated carboxylic acid in which an olefin or an α, β-unsaturated aldehyde is oxidized in the liquid phase with molecular oxygen in the presence of the aforementioned catalyst.

  According to the present invention, when α, β-unsaturated carboxylic acid is produced from olefin or α, β-unsaturated aldehyde by liquid phase oxidation, the yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst is increased. A high palladium-containing supported catalyst and a method for producing the same can be provided.

  In addition, when the palladium-containing supported catalyst of the present invention is used, an α, β-unsaturated carboxylic acid can be produced with a high yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst.

  The present invention relates to a palladium-containing supported catalyst (hereinafter referred to as “palladium-containing catalyst”) for producing an α, β-unsaturated carboxylic acid by oxidizing an olefin or α, β-unsaturated aldehyde with molecular oxygen in a liquid phase. Or may be simply referred to as “catalyst”), the average pore diameter of the inorganic oxide support is 2 to 8 nm, and the mass of the supported palladium is 0.12 to 1 part by mass of the inorganic oxide support. 1 part by mass (supporting rate 0.12-1), the average particle diameter of the supported palladium is a catalyst in the range of 1-8 nm. A catalyst in which the average pore size of the inorganic oxide support, the palladium loading rate, and the palladium average particle size are in the above ranges is characterized by a high yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst.

  The palladium loading in the present invention can be calculated from the mass of the carrier and the mass of palladium contained in the supported catalyst. Further, when the mass of palladium lost in the reduction treatment or the washing treatment is negligible, it can also be calculated from the mass of the carrier used in producing the catalyst and the mass of palladium contained in the used palladium compound.

  When the support is silica, analysis is performed as follows. A palladium-containing catalyst, concentrated nitric acid, and 48% by mass hydrofluoric acid are placed in a decomposition tube made of Teflon (registered trademark) and dissolved by a microwave thermal decomposition apparatus. The sample is filtered, and the filtrate and the washing water are combined and made up into a measuring flask, and the mass of palladium contained in the processing solution is quantified with an ICP emission spectroscopic analyzer. Separately, a palladium-containing catalyst is placed in a platinum crucible, and sodium carbonate is added to perform alkali melting, followed by addition of distilled water. The sample is filtered, and the filtrate and washing water are combined to make up a measuring flask. The mass of Si atoms contained in the treatment liquid is quantified with an ICP emission spectroscopic analyzer and converted to the mass of silica.

  In the catalyst of the present invention, the palladium loading calculated as described above is 0.12 or more, preferably 0.20 or more, and particularly preferably 0.41 or more. The supported rate of palladium is preferably 1.0 or less, more preferably 0.85 or less, and particularly preferably 0.65 or less.

  In the catalyst of the present invention, at least palladium is supported on an inorganic oxide as a carrier. Examples of the inorganic oxide used as the carrier (hereinafter also simply referred to as “carrier”) include silica, alumina, magnesia, calcia, titania and zirconia. Among them, silica, titania and zirconia are preferable, and silica is preferable. Particularly preferred.

  In the present invention, the average pore diameter of the carrier is measured by a nitrogen gas adsorption method. The isotherm on the adsorption side obtained by the measurement of the nitrogen gas adsorption method is represented by BJH (Barrett-Joyner- described in J. Am. Chem. Soc., 73, 373-380 (1951)). By analyzing by the Halenda method, the average pore diameter is determined. Although it is usually difficult to measure the average pore diameter of the support in the state of the catalyst, the average pore diameter of the support does not substantially change before and after the preparation of the catalyst. The average pore diameter may be measured by Also, if it is possible to remove supported components such as palladium from the catalyst without substantially changing the average pore size of the support, the supported components are removed from the catalyst and the average pore size of the support is measured by the above method. May be.

  The average pore diameter of the carrier is 2 nm or more, preferably 3 nm or more, and particularly preferably 4 nm or more. The average pore diameter of the carrier is 8 nm or less, preferably 7 nm or less, and particularly preferably 6 nm or less.

  When the average pore diameter exceeds 8 nm, the average particle diameter of palladium increases and exceeds 8 nm, so that the activity of the catalyst decreases, and the yield of α, β-unsaturated carboxylic acid tends to decrease. When the average pore diameter is less than 2 nm, diffusion of olefin or α, β-unsaturated aldehyde into the pores and diffusion of α, β-unsaturated carboxylic acid outside the pores are suppressed in the liquid phase reaction. Therefore, the activity of the catalyst is lowered, and the yield of the α, β-unsaturated carboxylic acid tends to be lowered.

The preferred specific surface area of the inorganic oxide used as the carrier varies depending on the type of carrier and the like, and thus cannot be generally stated. In the case of silica, it is preferably 50 m ² / g or more, more preferably 100 m ² / g or more. Moreover, 1500 m < ² > / g or less is preferable and 1000 m < ² > / g or less is more preferable. In addition, the smaller the specific surface area of the carrier, the more capable of producing a catalyst having a supported component such as palladium supported on the surface, and the larger the specific surface area of the carrier, the more capable of producing a catalyst having more supported component.

  The pore volume of the carrier is not particularly limited, but is preferably 0.1 cc / g or more, and more preferably 0.2 cc / g or more. Moreover, 2.0 cc / g or less is preferable and 1.5 cc / g or less is more preferable.

  The preferred volume average particle size of the carrier varies depending on the shape and size of the apparatus and is not particularly limited, but is preferably 0.5 μm or more, more preferably 1.0 μm or more. Moreover, 200 micrometers or less are preferable and 100 micrometers or less are more preferable. The larger the volume average particle size of the carrier, the easier the separation of the catalyst and the reaction solution, and the smaller the support, the better the dispersibility of the reaction solution and the catalyst.

  The average particle diameter of palladium in the present invention is measured with a transmission electron microscope for palladium in the catalyst, and is specifically a value calculated as follows. Particle size of 100 palladium particles selected at random using image processing software such as IMAGE PRO plus for each field of view of a transmission electron microscope with an observation magnification capable of measuring the particle size of palladium. Measure. This operation is carried out for a plurality of visual fields, and the average of the measured values is taken as the average particle diameter.

  When the palladium-containing catalyst does not contain a component that inhibits carbon monoxide adsorption on palladium in the metal state, the degree of palladium dispersion and the surface area of the palladium metal are obtained from the amount of carbon monoxide adsorbed by the carbon monoxide pulse method, and then a spherical shape is assumed. In this case, the average particle diameter of palladium may be calculated. In the measurement of the carbon monoxide adsorption amount, a reduction treatment is performed in advance in a hydrogen atmosphere on a catalyst having a known palladium content.

  The lower limit value of the average particle diameter of palladium calculated as described above is 1 nm or more, preferably 1.2 nm or more, more preferably 1.4 nm or more, and the upper limit value of the average particle diameter of palladium is 8 nm or less. Yes, 7 nm or less is preferable, and 6 nm or less is more preferable. When the average particle diameter of palladium is outside the predetermined range, the activity of the palladium-containing supported catalyst containing the palladium tends to decrease, and the yield of the α, β-unsaturated carboxylic acid tends to decrease.

  The method for supporting palladium on an inorganic oxide as a carrier is not particularly limited, but since the proportion of palladium that is supported in the pores of the carrier and has a particle size equal to or smaller than the pore size of the carrier increases, palladium is impregnated by the impregnation method. It is preferable to carry it on a carrier. In this case, a method of evaporating the solvent after immersing the carrier in a solution of palladium salt, or a so-called pore filling method of evaporating the solvent after absorbing the palladium salt solution for the pore volume of the carrier into the carrier. Is particularly preferred.

  The palladium salt to be used is not particularly limited, and examples thereof include palladium chloride, palladium acetate, palladium nitrate, palladium sulfate, tetraammine palladium chloride, and bis (acetylacetonato) palladium, among which palladium chloride and palladium acetate. Palladium nitrate and tetraamminepalladium chloride are preferable, and palladium nitrate is particularly preferable. The solvent for dissolving the palladium salt is not particularly limited as long as it dissolves the palladium salt.

  Also preferred is a method in which a palladium salt is supported on a carrier and then subjected to a heat treatment to once convert the palladium salt on the carrier to palladium oxide, followed by reduction.

  The temperature of the heat treatment is preferably a temperature equal to or higher than the decomposition temperature of the palladium salt used. The time for the heat treatment is not particularly limited as long as the palladium salt becomes palladium oxide, but is preferably 1 hour or longer, and preferably 12 hours or shorter.

  The reducing agent used for reducing palladium oxide is not particularly limited. For example, hydrazine, formaldehyde, sodium borohydride, hydrogen, formic acid, formic acid salt, ethylene, propylene, 1-butene, 2-butene, isobutylene, 1, 3 -Butadiene, 1-heptene, 2-heptene, 1-hexene, 2-hexene, cyclohexene, allyl alcohol, methallyl alcohol, acrolein, methacrolein and the like. Hydrogen, hydrazine, formaldehyde, formic acid and formic acid salts are preferred. Two or more of these may be used in combination.

  The solvent used in the reduction in the liquid phase is preferably water, but depending on the dispersibility of the carrier, alcohols such as ethanol, 1-propanol, 2-propanol, n-butanol and t-butanol; acetone Ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; organic acids such as acetic acid, n-valeric acid and isovaleric acid; and organic solvents such as hydrocarbons such as heptane, hexane and cyclohexane, or a combination thereof Can do. A mixed solvent of these and water can also be used.

  When the reducing agent is a gas, it is preferably carried out in a pressurizing apparatus such as an autoclave in order to increase the solubility in the solution. At that time, the inside of the pressurizer is pressurized with a reducing agent. The pressure is preferably 0.1 MPa (gauge pressure; hereinafter referred to as gauge pressure) or more, and preferably 1.0 MPa or less.

  When the reducing agent is a liquid, there is no limitation on the apparatus for reducing palladium oxide or palladium salt, and the reduction can be performed by adding the reducing agent to the solution. The amount of the reducing agent used at this time is not particularly limited, but it is preferably 1 mol or more, and preferably 100 mol or less with respect to 1 mol of palladium oxide or palladium salt.

  The reduction temperature and reduction time vary depending on the palladium oxide or palladium salt used, the reducing agent, etc., but the reduction temperature is preferably −5 ° C. or higher, more preferably 15 ° C. or higher. Moreover, 150 degrees C or less is preferable and 80 degrees C or less is more preferable. The reduction time is preferably 0.1 hour or longer, more preferably 0.25 hour or longer, and further preferably 0.5 hour or longer. Moreover, 4 hours or less are preferable, 3 hours or less are more preferable, and 2 hours or less are more preferable.

  The obtained palladium-containing catalyst is preferably washed with water, an organic solvent or the like. By washing with water, an organic solvent or the like, impurities derived from palladium salts such as chloride, acetate radical, nitrate radical and sulfate radical are removed. The washing method and number of times are not particularly limited, but depending on the impurities, the liquid phase oxidation reaction of olefins or α, β-unsaturated aldehydes may be hindered. Therefore, washing is preferably performed to such an extent that impurities can be sufficiently removed. The washed catalyst may be recovered by filtration or centrifugation and used for the reaction as it is.

  Further, the recovered catalyst may be dried. The drying method is not particularly limited, but it is preferable to dry in air or an inert gas using a dryer. The dried catalyst can also be activated before use in the reaction if desired. The activation method is not particularly limited, and examples thereof include a heat treatment method in a reducing atmosphere in a hydrogen stream. According to this method, the oxide film on the palladium surface and impurities that could not be removed by washing can be removed.

  In addition, in the palladium containing catalyst of this invention, metal components other than palladium can be included. Examples of metal components other than palladium include antimony, tellurium, thallium, lead, bismuth and the like. Two or more metal components other than palladium can be contained. From the viewpoint of expressing high catalytic activity, it is preferable that 50% by mass or more of the metal contained in the palladium-containing catalyst is palladium.

  A palladium-containing catalyst containing a metal component other than palladium can be obtained by performing the above-described reduction while a metal compound such as a corresponding metal salt or oxide is supported on a carrier. The method for supporting the metal compound at that time is not particularly limited, but can be carried out in the same manner as the method for supporting the palladium salt. Further, the metal compound of a metal other than palladium can be supported before the palladium salt is supported, can be supported after the palladium salt is supported, or can be supported simultaneously with the palladium salt.

  The physical properties of the obtained palladium-containing catalyst can be confirmed by BET specific surface area measurement, XRD measurement, CO pulse adsorption method, TEM observation and the like.

  Next, a method for producing an α, β-unsaturated carboxylic acid by oxidizing an olefin or an α, β-unsaturated aldehyde with molecular oxygen in a liquid phase using the palladium-containing catalyst of the present invention will be described.

  Examples of the raw material olefin include propylene, isobutylene, and 2-butene. Among these, propylene and isobutylene are preferable. The raw material olefin may contain a small amount of saturated hydrocarbon and / or lower saturated aldehyde as impurities. The α, β-unsaturated carboxylic acid produced is an α, β-unsaturated carboxylic acid having the same carbon skeleton as the olefin. Specifically, acrylic acid is obtained when the raw material is propylene, and methacrylic acid is obtained when the raw material is isobutylene.

  Examples of the raw α, β-unsaturated aldehyde include acrolein, methacrolein, crotonaldehyde (β-methylacrolein), and cinnamaldehyde (β-phenylacrolein). Of these, acrolein and methacrolein are preferable. The raw α, β-unsaturated aldehyde may contain a small amount of saturated hydrocarbon and / or lower saturated aldehyde as impurities. The α, β-unsaturated carboxylic acid produced is an α, β-unsaturated carboxylic acid in which the aldehyde group of the α, β-unsaturated aldehyde is changed to a carboxyl group. Specifically, acrylic acid is obtained when the raw material is acrolein, and methacrylic acid is obtained when the raw material is methacrolein.

  The liquid phase oxidation reaction may be carried out in either a continuous type or a batch type, but in view of productivity, the continuous type is preferred industrially.

  As the source of molecular oxygen used in the liquid phase oxidation reaction, air is economical and preferable. However, pure oxygen or a mixed gas of pure oxygen and air can also be used. If necessary, air or pure oxygen is converted into nitrogen, A mixed gas diluted with carbon dioxide, water vapor or the like can also be used. This gas such as air is usually supplied in a pressurized state into a reaction vessel such as an autoclave.

  Examples of the solvent used in the liquid phase oxidation reaction include t-butanol, cyclohexanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetic acid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid, iso-valeric acid, It is preferable to use at least one organic solvent selected from the group consisting of ethyl acetate and methyl propionate. Among these, at least one organic solvent selected from the group consisting of t-butanol, methyl isobutyl ketone, acetic acid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid and iso-valeric acid is more preferable. Further, in order to produce an α, β-unsaturated carboxylic acid with higher selectivity, it is preferable to coexist water in these organic solvents. The amount of water to be coexisted is not particularly limited, but is preferably 2% by mass or more, more preferably 5% by mass or more, and preferably 70% by mass or less, more preferably 50% by mass with respect to the total mass of the organic solvent and water. % Or less. The mixture of the organic solvent and water is desirably in a uniform state, but may be in a non-uniform state.

  The concentration of the olefin or α, β-unsaturated aldehyde that is a raw material for the liquid phase oxidation reaction is preferably 0.1% by mass or more, more preferably 0.5% by mass or more with respect to the solvent present in the reactor. Yes, 30 mass% or less is preferable, More preferably, it is 20 mass% or less.

  The amount of molecular oxygen used is preferably at least 0.1 mol, more preferably at least 0.2 mol, even more preferably at least 0.3 mol, based on 1 mol of the raw material olefin or α, β-unsaturated aldehyde. It is preferably 20 mol or less, more preferably 15 mol or less, still more preferably 10 mol or less.

  Usually, the catalyst is used in a state suspended in a reaction solution for liquid phase oxidation, but may be used in a fixed bed. The amount of the catalyst used is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and 30% by mass or less with respect to the solution present in the reactor. More preferably, it is 20 mass% or less, More preferably, it is 15 mass% or less. The catalyst of the present invention has a high yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst, so that the yield of α, β-unsaturated carboxylic acid per reactor is increased particularly in a reaction in a suspended bed. Is suitable.

  The reaction temperature and reaction pressure are appropriately selected depending on the solvent and raw materials used. The reaction temperature is preferably 30 ° C. or higher, more preferably 50 ° C. or higher. The reaction temperature is preferably 200 ° C. or lower, more preferably 150 ° C. or lower. The reaction pressure is preferably 0 MPa or more, more preferably 0.5 MPa or more. The reaction pressure is preferably 10 MPa or less, more preferably 5 MPa or less.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to an Example. The “parts” in the following examples and comparative examples are parts by mass.

(Measurement of average pore diameter of support)
The average pore diameter of the carrier was measured by a nitrogen gas adsorption method using an automatic specific surface area / pore distribution measuring device TriStar 3000 (trade name) manufactured by Micromeritics. The average pore diameter was determined by analyzing the isotherm on the adsorption side by the BJH method. The specific surface area of the carrier was also measured with the above apparatus and calculated by the BET method.

(Measurement of palladium loading on carrier)
Take 1 part of the dried catalyst, 50 parts of 62% by mass nitric acid and 50 parts of 48% by mass hydrofluoric acid in a Teflon (registered trademark) decomposition tube, and use a microwave thermal decomposition apparatus (CEM, MARS5 (trade name)). Dissolution treatment was performed. Palladium contained in the obtained homogeneous solution was quantified with an ICP emission spectrometer (manufactured by Thermo Elemental, IRIS-Advantage (trade name)).

  Separately, 1 part of the dried catalyst was placed in a platinum crucible, 5 parts of sodium carbonate was added and alkali fusion was performed, and then distilled water was added. The sample was filtered, and the filtrate and washing water were combined to make up a measuring flask. The mass of Si atoms contained in the treatment liquid was quantified with an ICP emission spectroscopic analyzer and converted to the mass of silica. From the mass of silica and the mass of palladium contained in the supported catalyst measured by the method described above, the palladium loading on the carrier was calculated.

(Measurement of average particle diameter of palladium)
The catalyst whose palladium content was measured in advance was subjected to reduction treatment at 200 ° C. in a hydrogen atmosphere, and then the amount of carbon monoxide adsorbed was measured by a carbon monoxide pulse method (thermal conductivity detector). From this, assuming that one molecule of carbon monoxide is adsorbed to 2 atoms of surface palladium, the degree of palladium dispersion and the surface area of palladium metal were determined, and the average particle diameter of palladium when a spherical shape was assumed was calculated.

(Analysis of raw materials, products and by-products in the production of α, β-unsaturated carboxylic acids)
Analysis of raw materials, products and by-products in the production of α, β-unsaturated carboxylic acid was performed using gas chromatography. The reaction rate of the olefin, the α, β-unsaturated aldehyde to be produced, and the selectivity of the α, β-unsaturated carboxylic acid are defined as follows.

Olefin reaction rate (%) = (B / A) × 100
Selectivity of α, β-unsaturated aldehyde (%) = (C / B) × 100
Selectivity of α, β-unsaturated carboxylic acid (%) = (D / B) × 100
Here, A is the number of moles of olefin supplied, B is the number of moles of reacted olefin, C is the number of moles of α, β-unsaturated aldehyde produced, and D is the mole of α, β-unsaturated carboxylic acid produced. Is a number.

[Example 1]
(Catalyst preparation)
1 part of distilled water was added to 1.025 part (0.25 parts as palladium) of an aqueous palladium nitrate solution (manufactured by NE Chemcat: 24.4% by mass palladium nitrate).

1.25 parts of silica (average pore diameter: 5.0 nm, specific surface area: 528 m ^{2 /} g) used as a carrier was immersed in the above solution and evaporated. Then, it baked at 200 degreeC in the air for 3 hours. To the obtained catalyst precursor, 5 parts of a 37 mass% aqueous formaldehyde solution was added. The mixture was heated to 70 ° C., stirred and held for 2 hours, suction filtered, and then filtered and washed with 100 parts of distilled water to obtain 1.50 parts of a palladium-containing catalyst. Table 1 shows the loading ratio of palladium on the carrier and the average particle diameter of palladium.

(Reaction evaluation)
Into the autoclave, the total amount of the catalyst obtained by the above method (0.25 parts as palladium) and 75 parts by weight of 75% by weight aqueous t-butanol solution as a reaction solvent were put, and the autoclave was sealed. Next, 1.96 parts of isobutylene was introduced, stirring (rotation speed: 1000 rpm) was started, and the temperature was raised to 90 ° C. After completion of the temperature increase, nitrogen was introduced into the autoclave to an internal pressure of 2.4 MPa, and then compressed air was introduced to an internal pressure of 4.8 MPa. When the internal pressure decreased by 0.1 MPa during the reaction (internal pressure 4.7 MPa), the operation of introducing 0.1 MPa of oxygen was repeated. The reaction was completed after a reaction time of 30 minutes.

  After completion of the reaction, the inside of the autoclave was ice-cooled in an ice bath. A gas collection bag was attached to the gas outlet of the autoclave, and the pressure in the reactor was released while collecting the gas that was opened by opening the gas outlet. The reaction solution containing the catalyst was taken out from the autoclave, the catalyst was separated with a membrane filter, and the reaction solution was recovered. The collected reaction liquid and the collected gas were analyzed by gas chromatography, and the reaction rate and selectivity were calculated. Moreover, the amount of methacrylic acid produced per part by mass of the supported catalyst (parts by mass) was also calculated. The results are shown in Table 2.

[Examples 2 to 8]
(Catalyst preparation)
A catalyst was prepared in the same manner as in Example 1 except that silica having the average pore diameter, specific surface area, and mass shown in Table 1 was used. Table 1 shows the loading ratio of palladium on the carrier and the average particle diameter of palladium.

(Reaction evaluation)
The catalysts prepared in Examples 2 to 6 were carried out in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 1]
(Catalyst preparation)
A palladium-containing catalyst was obtained in the same manner as in Example 1 except that 0.625 parts of silica (average pore diameter: 19 nm, specific surface area: 248 m ^{2 /} g) different from Example 1 was used as the carrier. Table 1 shows the loading ratio of palladium on the carrier and the average particle diameter of palladium.

(Reaction evaluation)
The same procedure as in Example 1 was performed using the catalyst obtained above. The results are shown in Table 2.

  As described above, it was found that according to the method of the present invention, α, β-unsaturated carboxylic acid can be produced in a state where the yield of α, β-unsaturated carboxylic acid per mass of the supported catalyst is high.

Claims (3)

A palladium-containing supported catalyst for producing an α, β-unsaturated carboxylic acid by oxidizing an olefin or α, β-unsaturated aldehyde in the liquid phase with molecular oxygen in a palladium supported on an inorganic oxide support Because
The average pore diameter of the inorganic oxide carrier is 2 to 8 nm, the mass of the supported palladium is 0.12 to 1 part by mass with respect to 1 part by mass of the inorganic oxide carrier, and the average particle size of the supported palladium is Catalyst in the range of 1-8 nm. After the palladium salt is supported on the inorganic oxide carrier having an average pore diameter of 2 to 8 nm by the impregnation method , the heat treatment is performed to convert the palladium salt to palladium oxide, and the palladium in the oxidized state in the presence of the inorganic oxide carrier. The method for producing a catalyst according to claim 1, wherein the catalyst is reduced.   A process for producing an α, β-unsaturated carboxylic acid, wherein an olefin or an α, β-unsaturated aldehyde is oxidized in the liquid phase with molecular oxygen in the presence of the catalyst according to claim 1.