NL7909142A - CATALYST AND METHOD FOR PREPARING METHACRYLIC ACID. - Google Patents

Description

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Catalyst and Process for the Preparation of Methacrylic Acid.

The invention relates to a process and catalyst for the oxidation in the vapor phase with molecular oxygen of methacroleins to methacrylic acid.

It is known that unsaturated acids, such as acrylic acid and methacrylic acid, can be prepared by vapor phase oxidation of the corresponding unsaturated aldehydes using molecular oxygen in the presence of a suitable oxidation catalyst. A variety of catalyst products have been proposed for this purpose. Many such products include the oxides of molybdenum and phosphorus in combination with the oxides of various other elements, both metallic and non-metallic.

The known catalysts have generally been found to require elements which are not included in the catalysts of the invention, or some of the essential elements of the catalysts of the invention are not present in the previously known catalysts.

It has been found that catalysts for the oxidation of methacroleins to methacrylic acid have the characteristic property of remaining stable for a period of time and then suddenly showing a rapid decrease in activity. Accordingly, an extension of the useful activity of such catalysts is desirable.

Despite the many references in the literature, an improved catalyst of this type cannot be developed by merely randomly selecting a group of elements from the many elements reported in the literature. Small composition changes can be very important for obtaining improved catalyst performance and in particular for optimizing the catalyst product to make it suitable not only for a specific reaction but also for the desired operating conditions. The latter is evident from the 5 improved catalyst products, which will be described below.

It has now been found that using the catalysts described below to prepare methacrylic acid by gas-phase oxidation of methacroleins, it is possible to obtain both high activity and high selectivity over long periods of time. Generally, the catalyst product includes oxides of molybdenum, copper, phosphorus, antimony, and cesium and / or calcium, and the product may contain one or more of the elements Ni, Zn, Ru, Rh, Pd, Pt, As, K , Rb, Sr, Ba, Cr, V, Nb, W, Mn, 15 Re and rare earth metals, including La.

The catalyst product used in the process of the invention can also be represented by the general formula

Mo. "Cu P, Sb A, B 0, 12 a b c d e x" 20 where A represents cesium and / or calcium and B represents Ni, Zn, Ru,

Rh, Pd, Pt, As, K, Rb, Ca, Sr, Ba, Cr, V, Nb, W, Mn, Re and rare earths, including La, where ae and x represent the atomic ratio of each component and where a is 0.05-3, b is 0.1-5, c is 0.01-3, d is 0.1-3, e is 0-3 and x has a value determined by valence and amounts of the other elements in the catalyst. Preferably b is 0.5-3 and in particular 1-2, while c is preferably 0.01-1.

Preferred embodiments of the invention include catalysts containing cesium, either alone with either rhenium, or calcium, or alone with either rhenium or tungsten. When tungsten is used, arsenic may be added. Especially preferred are a catalyst in which A represents cesium, B is either absent or is present when rhenium and b is 1.2-1.8, or a catalyst in which A represents calcium, B or is absent is either present as rhenium or tungsten (arsenic optionally present) and b is 1-2.

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When such a catalyst, as described above, is in contact with a gas phase mixture of methacroleins, molecular oxygen, steam and nitrogen at typical temperatures in the range of 250-400 ° C and pressures in the range of 0-5 atmosphere, excellent activity and selectivity for the formation of methacrylic acid over long periods of time.

Preferred embodiments of the invention will be described below.

10 Catalyst Product and Preparation.

The catalyst of the invention includes oxides or oxygen-containing compounds of molybdenum, copper, phosphorus, antimony, and cesium and / or calcium and may optionally contain members of a group of elements, designated "B" below. The catalyst can be represented by the general formula

Mo, -Cu P, Sb A, B 0, 12 abcde x 'where A represents cesium and / or calcium and B represents Ni, Zn, Ru, Rh, Pd, Pt, As, K, Rb, Sr, Ba, Cr , V, Nb, W, Mn, Re and rare earth metals, including La, and where ae and x represent the atomic-20 ratio of each component with respect to Mo ^ and where a is 0.05-3, b is 0, 1-5, c is 0.01-3, d is 0.1-3, e is 0-3, and x is a value determined by the valency and amounts of the other elements in the catalyst. Preferably b is 0.5-3 and in particular 1-2, while c is preferably 0.01-1. Preferred catalysts include those in which component B is tungsten (with optional arsenium) or rhenium. Other elements, which can be incorporated into the catalyst product in small amounts to promote the catalyst activity or selectivity and without compromising the above advantages, are within the scope of the invention. The catalyst product can be considered as a mixture of oxides of the said elements or as oxygen-containing compounds of the elements or both. As prepared and / or under reaction conditions, the catalyst may contain either of the said forms or both, and both are embraced by the term "mixtures of oxides".

The catalyst product is preferably 7909142 - Λ

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4 used in unsupported form, for example, in the form of pellets or other analog compressed forms of varying sizes, although conventional carriers may be used instead. The product can be formed in a conventional manner using techniques known per se. For example, compounds of molybdenum, copper, phosphorus, antimony, cesium, and rhenium are dissolved in a small amount of water or other solvent and the solutions are then combined and evaporated to dryness, for example, in a rotary dryer. The various components can be added to the solution in the form of varying salts or other compounds of suitable types and no specific form for the catalyst precursors is necessary. However, the use of ammonium salts, halides, for example chlorides, nitrates or acid forms of the elements, for example phosphoric acid, are particularly suitable. Preferably, however, aqueous solutions are used and water-soluble forms of the elements are used. In some cases, acids and / or bases can be added to the solutions to facilitate the dissolution of the catalyst precursors. For example, acids such as hydrochloric or nitric acid, or bases such as ammonium hydroxide can be used if desired. The resulting evaporation powder is then thoroughly dried and preferably sieved to remove large particles which complicate the preparation of uniformly compressed forms such as pellets. For example, the powder is passed through a 20 mesh screen. The powder is then mixed with an organic binder, which can be of any conventional type, such as polyvinyl alcohol, and the mixture is thoroughly dried and sieved, for example, to provide sizes of 20-60 mesh. The dried mixture is then preferably combined with a lubricant, again of any conventional type, such as stearic acid or graphite, and compressed to the desired shape, e.g. pelleted, with the compressed moldings, for example, heights and diameters of 0.16-0 , 95 cm be-35. Finally, the catalyst product thus obtained is activated at a high temperature for a long period of time according to the procedure customary in this technique. For example, the pellets are placed in an oven or in a tube, through which air is passed, at an elevated temperature (e.g., 300-500 ° C and preferably 325-450 ° C) for at least 10 hours.

In a particularly preferred activation step, the temperature is increased at a rate of 20 ° C per hour to a maximum of 420 ° C, preferably 320-400 ° C, and this temperature is maintained for 8 hours .

It will be understood that the above described preparation of the catalyst in a form suitable for use in a vapor phase oxidation reaction is merely illustrative of the many possible preparation methods, although the method described is particularly suitable and preferred enjoy.

Application methods.

The catalysts described are generally useful for the preparation of unsaturated acids by oxidation of unsaturated aldehydes with molecular oxygen, although the reaction of methacrolein to form methacrylic acid is particularly important. Other possible starting materials are the monoethylenically unsaturated aliphatic monoaldehydes of 3-6 carbon atoms, such as acroleins, crotonaldehyde, 2-methyl-2-butenal and the like or mixtures thereof.

The reaction, the catalyst products of the invention being particularly useful and providing high conversions and selectivities, involves contacting the catalyst with vapor phase methacroleins and oxygen, preferably also in the presence of steam and diluents . When the catalyst of the invention is used in the vapor phase oxidation of methacroleins to form methacrylic acid, the oxidation conditions employed are those generally used in this reaction, although it is preferred that the oxygen molar ratio until methacroleins are held at a high value near the ignition range. Once started, the reaction is self-supporting because of its exothermic nature. A variety of reactor types can be used, such as GE 7909142

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6 fluidized or fixed bed types, but reactors in which the catalyst is disposed within a plurality of heat exchange tubes are particularly useful and convenient.

The gaseous feed to the reactor contains suitable concentrations of methacroleins, oxygen and steam and usually an inert gas such as nitrogen and the like is also present. The oxygen is usually supplied as such or as air, which may be oxygen enriched. As mentioned above, conventional oxidation processes can be used, but a feature of the catalyst of the invention is that methacroleins can be present in concentrations of more than 5 to about 20% by volume of the total feed with a preferred range of greater than 5 to about 15% by volume. Generally, at least 6% by volume of the aldehyde is used in the diet. The corresponding ranges for oxygen are 3-15% by volume, preferably 5-12% by volume, and for steam up to 50% by volume, preferably 5-35% by volume, the balance being inert gas or inert gases.

The reaction temperature, for best results, should be in the range of about 270-20 450 ° C, preferably 280-400 ° C, and the optimum temperature range is 290-325 ° C. Because the reaction is exothermic, use is usually made of means for diverting the reaction heat from the reactor to prevent a temperature increase, which temperature increase promotes the decomposition of methacroleins by complete oxidation to carbon oxides and water. The reactor temperature can be controlled by conventional methods, such as by encapsulating the catalyst-containing tubes with a molten salt bath.

The reaction can be carried out under atmospheric, superatmospheric or subatmospheric pressure. Preferably, however, pressures are used ranging from atmospheric pressure to about 8 kg / cm absolute, preferably to about 6.3 kg / cm absolute and in particular to about 4.5 kg / cm absolute. cm absolutely.

The unsaturated acid product can be recovered using a number of art per se 7909142

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7 known methods. For example, the acid can be condensed or rinsed with water or other suitable solvents, followed by separation of the unsaturated acid product from the rinsing liquid.

The residual gases after the acid removal step can be recycled to the reaction, preferably after the removal of CO 2 using conventional means, for example, absorption in aqueous carbonate solution.

The invention is further illustrated but not limited by the following examples of typical catalyst preparations and their use in the oxidation of methacrolees.

Example I Catalyst preparation.

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Dissolved in 750 cm water 636 g 15 (NH ^) gMo ^ 024 Then 21.7 g CuCNO ^^^ HgO -dissolved in 100 cm ^ water, 58.4 g CsNO dissolved in 150 cm water, 20.5 g J o 3

SbCl, dissolved in a mixture of 30 cm-5 water and 10 cm concentrated HCl and 34.5 g H_P0, dissolved in a mixture of 100 cm 3 -5 ** water and 50 cm of a 58% s NH, 0H solution. These solutions 3 ^ 20 are mixed with 400 cm 58% ΝΗ, ΟΗ and the mixture is fed 4 · 3 to a rotary dryer with a capacity of 4000 cm and the mixture is evaporated to dryness at a temperature which reaches a maximum of 140-200 ° C. The resulting powder is removed from the dryer and dried in an oven at 200 ° C for 4 hours. The dried powder is sieved through a 20 mesh sieve, a 4% aqueous solution of polyvinyl alcohol is added in an amount sufficient to obtain a moist mixture and this mixture is dried at 75-80 ° C until the moisture content has decreased up to 2-4% by weight. The dried mixture is then screened to particles of 20-60 mesh size and about 2-6% stearic acid powder is mixed thoroughly therein. The resulting mixture is then pelleted to form pellets with a height and diameter of 0.95 cm, the catalyst components of molybdenum, copper, phosphorus, antimony and cesium being present (by calculation) in the atomic ratios of 12.0, respectively. , 3, 1, 0.3 and 1. The pellets are then activated in an oven by heating them to 100 ° C in 1 hour and then gradually increasing the temperature at a rate of about 20 ° C per hour to 370 ° C and maintain this temperature for 8 hours. The catalyst is tested according to the procedure of Example II.

Example II Catalyst Testing.

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150 cm. Of the catalyst product of Example 1 is introduced into a reactor bounded by a 1.27 x 228.6 cm stainless steel pipe, the 3 reactor pipe being filled with 50 cm of an inert filler ( silicon carbide) below the catalyst bed and 100 cm of the inert filler above the catalyst bed in a conventional manner to ensure uniform temperature contact with the catalyst. The 15 'nitrogen-diluted mixtures containing methacroleins, oxygen and 3. steam are fed to the reactor at a pressure of 1.74 kg / cm (absolute) and at a space velocity of about 1200 hours *.

β

The term "space velocity" is used in its ordinary meaning and means the number of liters of gas (at standard temperature and pressure) per liter of catalyst per hour. The feed composition is about 6-7% by volume of methacroleins, 11-12% by volume of oxygen and 20% by volume of steam, the remainder being nitrogen, the determination of which is on a wet basis. The reaction is run continuously and the effluent gas is analyzed at several hourly intervals. The analyzes are performed by gas chromatography and infrared spectrography using conventional techniques. The average amount of methacrylic acid formed is determined periodically and the reactor temperature is adjusted, if necessary, to obtain the desired yield, that is, the product of the conversion and the selectivity, which for the purposes of the equations to be performed is about 0. 15 g of methacrylic acid per hour per gram of catalyst. Example III

A catalyst is prepared according to the method of Example I with the exception that the phosphorus content is increased to provide a catalyst with 7909142 * 9 of the following nominal composition (by calculation) Mo12Cu0.3P1.5Sb0.3Gsl ° x

The catalyst is tested according to the method of Example II. Example IV

A catalyst is prepared according to the method of Example I but with a higher phosphorus content than the catalyst of Example III, thereby providing a catalyst of the following nominal composition (by calculation)

Mo, _Cun „P„ Sbn oCs, 0.

12 0.3 2 0.3 1 x 10 The catalyst is tested according to the method of Example II.

The results of the tests carried out on the catalysts of Examples I, III and IV are shown in Table A below.

Table A

15 Cat. Phosphorus Hours Temp. Selectivity over Activity

content (° C) methacrylic acid coeff. K

_ (a) _ _ (b) _ (c) I 1 35 293 77 23 80 323 74.5 6 20 III 1.5 150 298 77.6 26 200 296 79.7 26 IV 2 26 320 70 10 122 324 65 7 25 (a) with respect to Mo ^ (b)% reacted methacrolein, which is converted into methacrylic acid (c) a value calculated from experimental data to provide a measure of the catalyst activity and derived from the equation: K = F. X. S. cE / RT, where F = methacrolein concentration in feed S = feed gas space velocity X = conversion of methacrolein 35 E = activation energy, 25,000 kcal / mol.

R = gas constant T = absolute temperature.

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As explained in Example II, the catalysts are operated to provide a constant predetermined yield of methacrylic acid. In order to provide a suitable comparison, the behavior of a catalyst 5 is reported during the time period in which the catalyst activity has stabilized after an initial induction period. This may mean, as in Table A, that the time chosen for the comparisons is not the same if the catalyst behavior differs significantly. A stable period of 150-200 hours could easily be established for the catalyst of Example III, while the catalysts of Examples I and IV showed relatively poorer behavior and reduced their activities rather, as shown by the values reported. It is clear that the catalyst of Example III is superior to that of Examples I and IV because it operated continuously at a lower temperature and with higher activity and selectivity after the activity of the other catalysts was significantly reduced. It therefore follows that catalysts containing molybdenum, copper, antimony and cesium are sensitive to the phosphorus content. An optimal value must be found between a phosphorus value of 1 and 2 (with respect to Mo ^). It is assumed that the optimum value is between P., and P, 0 and in particular between P. 0 and P.,.

i 3 6 1 3 O 1 3 J 1 3 /

Example V

A catalyst, similar to that of Example I, is prepared according to the same general technique, with. 3 this exception, that 5 g of perrhenic acid, dissolved in 100 cm of water, are included in the starting solution to provide rhenium in a catalyst of the following nominal composition (by calculation) 30 M ° 12Cu0.3PlSb0.3CslRe0.07 ° x ·

Example VI

A catalyst is prepared according to the general method of Example V with the exception that the amount of phosphorus is increased to obtain a catalyst of the following nominal composition (by calculation)

Mo12Cu0,3PI, 5SÏ0,3CslEe0,07 ° x7909142 11

The catalyst is tested according to the method of Example II. Example VII

A catalyst is prepared according to the method of Example V, but the amount of phosphorus is doubled to provide a catalyst of the following nominal composition (by calculation)

Mo12Cu0,3P2Sb0,3CslRe0507 ° x

The catalyst is tested according to the procedures of Example II.

The results of the investigation of the catalysts of Examples V, VI and VII are shown in Table B below, also including the footnotes of Table Δ.

Table B

15 Cat. Phosphorus Hours Temp. Selectivity to Activity content (° C) methacrylic acid coefficient. K

_ (a) _ _ (b) __ (O

V 1 150 292 75 26 200 293 75.5 26 20 VI 1.5 150 279 77 46.6 250 279 77 40 VII 2 150 311 73.6 * 11.6 250 311 76 12

As in Table A, the catalysts are run to provide the same yield of methacrylic acid and the performance is shown over a stable operating period after an initial catalyst induction period. It will be appreciated that the catalysts to which rhenium has been added exhibit better performance than those of Table A, which do not contain rhenium, because they have higher activity and suggest improved aging properties, especially with regard to the comparison of catalysts V and VII with catalysts I and IV. The rhenium-containing catalysts are also sensitive to the phosphorus content and an optimum value again appears to be between P {and p £ (with respect to Mo ^). The optimum value is assumed to be between P 1 and P. 0 f 1 l yö and in particular between P ^ ^ and Pj

When the results of Tables A and B

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considered in combination, it follows that the molybdenum to phosphorus ratio for catalysts of this type will exhibit optimal performance at ratios between 12/1 and 12/2. Example VIII

A catalyst is prepared according to the general method of Example I with the exception that 79.2 g of Ca 2 HgC 2 X 1 X 1 are used instead of cesium nitrate and no aqueous ammonia is added, a catalyst having the nominal composition (by calculation) 10 Mo12Cu0.3P1Sb0.3Ca1.50x is obtained. This catalyst is tested according to the methods of Example II, showing the significance of the ratio of phosphorus to molybdenum for the catalyst behavior. The catalyst operates at about 304 ° C for a period of about 20-80 hours with a selectivity of 76.3 and an activity coefficient of 18.6.

Example IX

A catalyst is prepared according to Example VIII with the exception that 5 g of dissolved m 100 cm 2 of water is included in the solution to provide rhenium in a catalyst of the following nominal composition (by calculation)

Mo, "Cun 0P.Sbn -Ca, cRe_. .

12 0.3 1 0.3 1.5 0.07 x

The catalyst is tested according to the method of Example II.

The significance of the ratio of phosphorus to molybdenum for the catalyst behavior appears. The catalyst operates at about 286 ° C over a period of about 30-200 hours with a selectivity of 75.2 and an activity coefficient of 42.

Example X.

A catalyst is prepared according to the general method of Example IX with the exception that instead of rhenium tungsten is included and no aqueous ammonia is used to provide a catalyst of the nominal composition (by calculation) 35 Mo12Cu0.3PlSb0.3CalW0 , 50x '

The catalyst is tested according to the method of Example II

7909142 13 and the significance of the ratio of phosphorus to molybdenum for the catalyst behavior appears. For a period of about 20-170 hours, the catalyst operates at about 302 ° C with a selectivity of about 76.5 and an activity coefficient of about 22.4.

Example XI

A catalyst is prepared by the general method of Example Imet with this exception, that the phosphorus content is increased and palladium is taken up to form a catalyst of the nominal composition M ° 12Cu0.3P2Sb0.3CslPd0.03 ° x *.

The catalyst is tested under the conditions of Example II and the significance of the ratio of phosphorus to molybdenum for the catalyst behavior appears.

Example XII

A catalyst is prepared according to the general method of Example I with the exception that the phosphorus content is increased and rubidium is added to provide a catalyst of nominal composition 20 (Mo12Cu0.3P1, 75Sb0.3Cs0.5Rb0.5 ° x) '

The catalyst is tested under the conditions of Example II and the significance of the ratio of phosphorus to molybdenum for the catalyst behavior is apparent.

Example XIII

A catalyst is prepared according to Example IX with the exception that the phosphorus content is doubled, whereby a catalyst of the nominal composition (by calculation)

Mo10Cun, P4 Sbn -Cat, -Re n70 12 0.3 2 0.3 1.5 0.07 x 30 is obtained. In an examination under the conditions of Example II and at an operating temperature of 276 ° C, the conversion of methacroleins was about 26% and the selectivity to methacrylic acid about 54%.

Example XIV

A catalyst is prepared according to Example X with the exception that arsenic is included, whereby a catalyst of the nominal composition (by calculation) 79 0 9 1 4 2 14

Mo12Cu0.3PlSb0.3CalW0.5As0.5 ° X

is acquired. This catalyst is tested with a feed gas containing 7 vol.% Methacroleins, 12 vol.% Oxygen, 20 vol.% Steam and the balance nitrogen, and at a pressure of 1.74 kg / cm 2 (absolute). At 288 ° C, 75% of the methacrolein was converted by the catalyst at a selectivity of 76% over methacrylic acid. An analogous catalyst without arsenic, tested under analogous conditions, gave a 62% conversion of methacroleins at a selectivity of 70% to methacrylic acid at a temperature of 285 ° C. Thus, arsenic is advantageous because it improves the performance of catalysts containing tungsten.

Example XV

Other suitable catalysts of the invention are prepared according to the general method of Example I and have the following nominal compositions, namely

Mo12CU0,3P 2Sb0,3CS0,3Ca0,7Cr0,3 ° x M ° 12Cu0,3P2Sb0,3Cs0,3K0,7V0,3 ° x Mo 12Cu0,3P2Sb0,3Cs0,3Sr0,7 *%, 3 ° x 20 12Cu0,3P1, 7 ^ b0.3Cs0.3Ba0.7 ^ 0.3 ° x

Mo.-Cu- -P. -Sb- -Cs.La- -.Ni- -0 12 0.3 l, 2 0.3 l 0.7 0.3 x

Mo „Cu- -P.Sb. -Cs- -Ce- -.Zn- -0 12 0.3 l 0.3 0.3 0.7 0.3 x

Mo10Cu_ -P.Sb „-Cs.Ru_ .0 12 0.3 l 0.3 l 0.1 x

Mo, -Cu_ -P- -Sb- -Cs.Rh- --0 12 0.3 0.5 0.3 l 0.03 x 25 Mol2Cu0.3PlSb0.3Cs0.3Pt0.03 ° x

Mol2Ca0.3P1.5Sb0.3CslW0.5

The catalysts were tested under the conditions of Example II, demonstrating the significance of the phosphorus to molybdenum ratio with respect to the catalyst behavior.

7909142

Claims (13)

1. A catalyst product suitable for the oxidation in the vapor phase of methacroleins to form methacrylic acid, which catalyst product mainly consists of the oxides of Mo, Cu, P, Sb, and Cs and / or Ca and optionally one or more of the elements Ni, Zn, Ru, Rh, Pd, Pt, As, K, Rb, Sr, Ba, Cr, V. Nb, W, Mn, Re and the rare earths, including La. Catalyst according to claim 1, characterized in that it has the formula Mo, "Cu P, Sb A, B 0 12 abcdex, wherein a = 0.05-3, b = 0.1-5, c = 0.01-1, d = 0.1-3, e = 0-3 and x has a value determined by the valency and amounts of the other elements of the formula, where A represents -15 Cs and / or Ca and B represents one or more of the elements Ni, Zn, Ru, Rh, Pd, Pt, As, K, Rb, Sr, Ba, Cr, V, Nb, W, Mn, Re and rare earths, including La . Method according to claim 2, characterized in that b = 1-2. Catalyst according to claims 2 or 3, characterized in that c = »0.01-1. Catalyst according to claims 1-4, characterized in that A represents Cs. Catalyst according to claims 1-4, 25, characterized in that A represents Ca. Catalyst according to claims 1-6, characterized in that B represents Re. Catalyst according to claim 6, characterized in that B represents W and that the catalyst optionally contains As. Catalyst according to claims 2-5, characterized in that A represents Cs, e 0 and b is 1.2-1.8. Catalyst according to claims 2-4cf 6, characterized in that A represents Ca and e is 0. Catalyst according to claims 2-5 or 35, characterized in that A represents Cs, B represents Re and b is 1.2-1.8. 7909142 * f Process for the preparation of methacrylic acid, characterized in that oxidation of methacroleins in the vapor phase is carried out with molecular oxygen in the presence of a catalyst according to claims 1-11. 13. Catalyst products and methods as described in the description and / or examples. '7 © 0 9 1 4 2 L-