Gold-based catalyst for oxidative esterification of aldehydes to carboxylic acid esters

Abstract

The present invention relates to novel catalysts for oxidative esterification, by means of which, for example, (meth)acrolein can be converted to methyl (meth)acrylate. The catalysts of the invention are especially notable for high mechanical and chemical stability even over very long periods. This especially relates to an improvement in the catalyst service life, activity and selectivity over prior art catalysts which lose activity and/or selectivity relatively quickly in continuous operation in media having even a small water content.

Claims

1. A catalyst particle; comprising: oxygen; silicon; aluminum; a basic element; gold; and iron, zinc, and/or cobalt, wherein a maximum gold concentration or a maximum iron, zinc and/or cobalt concentration of the catalyst particle in an outer region which makes up a maximum of 60% of a geometric equivalent diameter is at least 1.5 times as high as a gold concentration or iron, zinc or cobalt concentration in a middle region which makes up the remaining region of the geometric equivalent diameter.

2. The catalyst particle according to claim 1, wherein the particle comprises oxygen, silicon, aluminum, a basic element, gold and cobalt.

3. The catalyst particle according to claim 1, wherein the basic element is an alkali metal, an alkaline-earth metal, a rare-earth metal or a mixture of one or more of these metals.

4. The catalyst particle according to claim 1, wherein the catalyst particle comprises, based on the total molar amount of gold, silicon, aluminum and basic elements, and iron, zinc and/or cobalt, 0.03 to 3 mol % of gold, 40 to 90 mol % of silicon, 3 to 40 mol % of aluminum, 2 to 40 mol % of the basic element and 0.1 to 20 mol % of iron, zinc and/or cobalt, where the molar ratio of iron, zinc and/or cobalt to gold is between 0.1 and 20 and all these elements except for the gold are present in the form of oxides.

5. The catalyst particle according to claim 1, wherein the catalyst particle has a mean geometric equivalent diameter between 10 and 250 m, and the thickness of the outer region is between 2 and 100 sm.

6. The catalyst particle according to claim 1, wherein gold and/or gold- and iron-, zinc- and/or cobalt oxide-containing particles have a mean diameter between 2 and 10 nm and are present in the outer region of the catalyst particle.

7. The catalyst particle according to claim 1, wherein the particles are porous and have a specific surface area between 100 and 300 m.sup.2/g, and an average pore diameter thereof is 1 to 50 nm.

8. The catalyst particle according to claim 7, wherein the specific surface area of the catalyst particle is between 150 and 250 m.sup.2/g, and the average pore diameter is 2 to 20 nm.

9. The catalyst particle according to claim 1, wherein a thickness of the outer region is between 2 and 100 m.

10. A process for producing a catalyst particle according to claim 1, comprising: 1) applying at least one iron, zinc and/or cobalt compound to a particle comprising an oxide of silicon, of aluminum and optionally of one or more alkali metals, alkaline-earth metals or rare-earth metals, 2) optionally partly or fully oxidizing the material from 1) and optionally drying/calcining, 3) applying at least one gold compound to the material from 2) and 4) drying or calcining the material from 3).

11. The process according to claim 10, wherein a cobalt compound is applied in 1).

12. The process according to claim 10, wherein 2) comprises heating in the presence of oxygen or the addition of an oxidizing agent to an aqueous suspension of the particle from 1).

13. The process according to claim 12, wherein 2) comprises a calcination in the presence of oxygen.

14. The process according to claim 10, wherein the particle comprising the oxides of silicon, of aluminum and optionally of one or more alkali metals, alkaline-earth metals or rare-earth metals goes through at least one thermal treatment with water within 1) to 3), the water temperature being between 50 and 100 C.

15. The process according to claim 14, wherein the water temperature is between 70 and 95 C.

16. The process according to claim 10, wherein 1), 3), and optionally 2) are conducted in an aqueous medium, and 1) and 3) are effected using a water-soluble cobalt compound or a water-soluble gold compound.

17. The process according to claim 10, wherein in 3), first a basic solution and then a solution comprising auric acid, having a pH between 0.5 and 5, are added to an aqueous suspension of the particles from 2).

18. The process according to claim 10, wherein in 3), a solution which has been obtained by the partial or complete neutralization of an auric acid solution, having a pH between 0.5 and 5, with a base is added to an aqueous suspension of the particles from 2).

19. A process for producing a carboxylic ester, comprising oxidatively esterifying an aldehyde in the presence of oxygen, an alcohol, and the catalyst particle according to claim 1, to obtain a carboxylic ester.

20. The process of claim 19, wherein the aldehyde is methacrolein and the obtained carboxylic ester is an alkyl methacrylate.

Description

EXAMPLES

(1) The analysis of the concentration profiles for Co and Au within the catalyst particles is effected by means of the SEM-EDX line scan method. This was done using the following setup:

(2) Microscope: Jeol JSM 7600F; analysisOxford AZtec with X-Max 150 detector.

(3) The samples were embedded in a resin and a section was cut with a Leica ultramicrotome with a diamond blade.

(4) The analysis method is based on EDX at acceleration voltage 20 kV. The Co K-alpha peak at 6.924 keV and Au M-alpha peak at 2.120 keV were evaluated.

(5) The examples which follow document the effect mainly for cobalt-containing catalysts. The effect was also shown for Zn-containing catalysts. The results are applicable in a simple manner to catalysts containing iron or mixtures of two or three elements selected from iron, zinc and cobalt.

Example 1 (SiO.SUB.2.Al.SUB.2.O.SUB.3.MgO)

(6) A 250 ml beaker is initially charged with 21.36 g of Mg(NO.sub.3).sub.2*6H.sub.2O and 31.21 g of Al(NO.sub.3).sub.3*9H.sub.2O together, which are dissolved in 41.85 g of demineralized water while stirring with a magnetic stirrer. Thereafter, 1.57 g of 60% HNO.sub.3 are added while stirring. 166.67 g of silica sol (Kstrosol 1530AS from Bad Kstritz, 30% by weight of SiO.sub.2, median size of the particles: 15 nm) are weighed into a 500 ml three-neck flask and cooled to 15 C. while stirring. 2.57 g of 60% HNO.sub.3 are added gradually to the sol while stirring. At 15 C., the nitrate solution is added to the sol within 45 min while stirring. After the addition, the mixture is heated to 50 C. within 30 min and stirred at this temperature for a further 24 h. After this time, the mixture is spray-dried at exit temperature 130 C. The dried powder (spherical, median particle size 60 m) is heated in a thin layer in a Naber oven to 300 C. within 2 h, kept at 300 C. for 3 h, heated to 600 C. within 2 h and finally kept at 600 C. for 3 h.

Example 2

(7) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) in 8.3 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and finally washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and then calcined at 450 C. for 5 h.

Example 3

(8) A suspension of 15 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 50 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of CoCl.sub.2 (697 mg, 2.93 mmol) and LiCl (1.24 g) in 12.5 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and finally washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and then calcined at 450 C. for 5 h.

Example 4

(9) A suspension of 10 g of a cobalt-doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 2 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and finally washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and then calcined at 450 C. for 5 h.

(10) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for cobalt and for gold in the particle.

Example 5

(11) A suspension of 10 g of a cobalt-doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 2 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) and 0.52 ml of a one molar NaOH solution (Au/Na=1:1 mol/mol) in 8.3 g of water. After the addition, the mixture is stirred for a further 60 min, then cooled down, filtered at room temperature and finally washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and then calcined at 450 C. for 5 h.

(12) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for cobalt and for gold in the particle.

Example 6

(13) A suspension of 10 g of a cobalt-doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 2 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. This suspension is admixed while stirring with a solution, heated to 90 C. beforehand, of 0.52 ml of a one molar NaOH solution. After stirring at 90 C. for 30 minutes, HAuCl.sub.4*3H.sub.2O (205 mg) in 4.3 g of water is added. After the addition, the mixture was stirred for a further 60 min, then cooled down, filtered at room temperature and finally washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and then calcined at 450 C. for 5 h.

(14) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for cobalt and for gold in the particle.

Example 7

(15) A suspension of 10 g of a cobalt-doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 3 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) and 0.52 ml of a one molar NaOH solution (Au/Na=1:1 mol/mol) in 8.3 g of water. After the addition, the mixture is stirred for a further 60 min, then cooled down, filtered at room temperature and finally washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and then calcined at 450 C. for 5 h.

(16) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for cobalt and for gold in the particle.

Example 8

(17) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 60 min, in the course of which an air stream is bubbled into the solution. After stirring for 60 minutes, added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

(18) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for Co and for gold.

Example 9

(19) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min. H.sub.2O.sub.2 (30 wt %, 0.45 g) was added dropwise to the mixture. After stirring for a further 60 minutes, added to the suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

(20) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for Co and for gold.

Example 10

(21) Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) is dissolved in 5 g of demineralized water and the solution is mixed by vigorous agitation with 10 g of an SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1. The support thus obtained, having a dry appearance, was dried in a thin layer in a drying cabinet at 105 C. for 10 h, then finely crushed with a mortar and pestle and heated in a thin layer in a Naber oven to 300 C. within 2 h, kept at 300 C. for 3 h, heated to 600 C. within a further 2 h and finally kept at 600 C. for 3 h.

Example 11

(22) A suspension of 10 g of the cobalt-doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 8 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water. After the addition, the mixture was stirred for a further 30 min, then cooled, filtered at room temperature, and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

(23) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for Co and for gold.

Example 12

(24) Zn(NO.sub.3).sub.2*6H.sub.2O (580 mg, 1.95 mmol) is dissolved in 5 g of demineralized water and the solution is mixed by vigorous agitation with 10 g of an SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1. The support thus obtained, having a dry appearance, was dried in a thin layer in a drying cabinet at 105 C. for 10 h, then finely crushed with a mortar and pestle and heated in a thin layer in a Naber oven to 300 C. within 2 h, kept at 300 C. for 3 h, heated to 600 C. within a further 2 h and finally kept at 600 C. for 3 h.

Example 13

(25) A suspension of 10 g of the zinc-doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 12 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water. After the addition, the mixture was stirred for a further 30 min, then cooled, filtered at room temperature, and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

(26) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for Zn and for gold.

Examples 14 to 21 (Batch Tests for MMA Preparation)

(27) A gold-containing catalyst according to Table 1 (384 mg), methacrolein (1.20 g) and methanol (9.48 g) were stirred for 2 h in an atmosphere of 7% by volume of 02 in N.sub.2 at 60 C. and a pressure of 30 bar in a 140 ml steel autoclave with a magnetic stirrer. After 2 h, the mixture was cooled down, degassed, filtered and analysed by means of GC. Each catalyst was tested at least twice under identical conditions; the results of the respective experiments were averaged. The resulting conversion of methacrolein (C(MAL), %), the space-time yield (STY, mol MMA/kg cat h) and the selectivity for MMA (S(MMA), %) for every catalyst tested are collated in Table 1 below.

(28) TABLE-US-00001 TABLE 1 STY, Cat. Co (or Zn) C(MAL) mol MMA/ S(MMA) Example Ex. Distribution % kg(cat) h % 14 4 eggshell 67.7 13.4 94.8 15 5 eggshell 64.6 12.5 94.3 16 6 eggshell 64.6 12.8 96.6 17 7 eggshell 59.6 11.6 95.5 18 8 eggshell 56.6 10.4 91.4 19 9 eggshell 56 10.6 94.3 20 11 eggshell 58.7 11.9 92.3 21 13 eggshell 47.1 9.9 93.5

Comparative Example 1

(29) A suspension of 10 g of the doped SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water. After the addition, the mixture was stirred for a further 30 min, then cooled, filtered at room temperature, and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

Comparative Example 2

(30) A 250 ml beaker is initially charged with 21.35 g of Mg(NO.sub.3).sub.2*6H.sub.2O, 31.21 g of Al(NO.sub.3).sub.3*9H.sub.2O and 4.72 g of Co(NO.sub.3).sub.2*6H.sub.2O together, which are dissolved in 41.85 g of demineralized water while stirring on a magnetic stirrer. Thereafter, 1.57 g of 60% HNO.sub.3 are added while stirring. 166.67 g of silica sol (Kstrosol 1530AS from Bad Kstritz) are weighed into a 500 ml three-neck flask and cooled to 15 C. while stirring. 2.57 g of 60% HNO.sub.3 are additionally added gradually to the sol while stirring. At 15 C., the nitrate solution is added to the sol within 45 min while stirring. After the addition, the mixture is heated to 50 C. within 30 min and stirred at this temperature for a further 24 h. After this time, the mixture is dried in a spray drier with an exit temperature of 120 C. The dried powder is heated in a thin layer in a Naber oven to 300 C. over the course of 2 h, kept at 300 C. for 3 h, heated to 600 C. within a further 2 h and finally kept at 600 C. for a further 3 h. The resulting material consisted of round particles having an average particle size of about 60 m.

Comparative Example 3

(31) A suspension of 10 g of cobalt-doped SiO.sub.2Al.sub.2O.sub.3MgO support from CE2 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water. After the addition, the mixture was stirred for a further 30 min, then cooled, filtered at room temperature, and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

(32) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded in the polymer matrix showed a homogeneous distribution of Co and a poorly defined inhomogeneous distribution for gold.

Comparative Example 4

(33) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) and Ni(NO.sub.3).sub.2*6H.sub.2O (567 mg, 1.95 mmol) in 8.3 g of water. After the addition, the mixture was stirred for a further 30 min, then cooled, filtered at room temperature, and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, then heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

(34) A line scan SEM-EDX analysis of a cut section of catalyst particles embedded into polymer matrix showed an eggshell distribution for Ni and for gold.

Comparative Example 5

(35) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) and Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) in 8.3 g of water. After the addition, the mixture was stirred for a further 30 min, then cooled, filtered at room temperature, and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

Comparative Example 6

(36) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, brought to 90 C. beforehand, of Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) in 4.2 g of water. After the addition, the mixture is stirred at 90 C. for a further 30 min. Added to this suspension with stirring is a solution, brought to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, heated from 18 C. up to 450 C. within 1 h and calcined at 450 C. for 5 h.

Comparative Example 7

(37) A suspension of 10 g of the SiO.sub.2Al.sub.2O.sub.3MgO support from Example 1 in 33.3 g of demineralized water is heated to 90 C. and stirred at this temperature for 15 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of HAuCl.sub.4*3H.sub.2O (205 mg) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min. Added to this suspension while stirring is a solution, heated to 90 C. beforehand, of Co(NO.sub.3).sub.2*6H.sub.2O (569 mg, 1.95 mmol) in 4.2 g of water. After the addition, the mixture was stirred at 90 C. for a further 30 min, then cooled down, filtered at room temperature and subsequently washed six times with 50 ml each time of water. The material was dried at 105 C. for 10 h, finely crushed with a mortar and pestle, heated from 18 C. up to 450 C. in 1 h and calcined at 450 C. for 5 h.

Comparative Experiments CE8 to CE13

(38) TABLE-US-00002 TABLE 2 Batch tests with catalysts CE1, CE3 to CE7 STY, Cat. Co (or Ni) C(MAL), mol MMA/ S(MMA), Example Ex. Distribution % kg(cat) h % CE8 CE1 39 7.9 91.8 CE9 CE3 homogeneous 42 8.5 91.6 CE10 CE4 eggshell 75.6 15.5 94.2 CE11 CE5 6.5 1.2 86.2 CE12 CE6 55.9 10.9 89.1 CE13 CE7 13.8 2.3 76.1

(39) Continuous Test for Preparation of MMA (General Description)

(40) The pH of a 42.5% by weight solution of MAL in methanol is adjusted to pH=7 while stirring by the addition of a one percent by weight solution of NaOH in methanol. This solution is fed continuously at a constant rate of addition to a stirred and sparged stirred tank reactor (sparging with air) under pressure of 10 bar and at internal temperature of 80 C. At the same time, this reactor containing 20 g of powder catalyst is fed with a sufficient amount of one percent by weight NaOH solution (in methanol) that the value pH=7 in the reactor remains constant. The reaction mixture was withdrawn continuously from the reactor via a filter. After the time specified below, the product samples were taken and analysed by means of GC.

(41) TABLE-US-00003 TABLE 3 Continuous tests for MMA preparation with selected catalysts STY, D50, m Example mol MMA/ Fresh D50, m Cat. TOS [h] C (MAL), % kg (cat) h S (MMA), % cat. Used cat. 4 100 75.2 12.4 95.8 4 2000 73.8 12.2 95.5 55.6 55.2 CE4 100 77.6 10.4 96.1 CE4 2000 69.7 9.3 91.5 55.2 4.6

(42) The examples, especially according to the results in Table 3, show that the catalysts of the invention, compared to the prior art, given identical initial activity and selectivity, have much longer service lives than the prior art catalysts.

THE FIGURES

(43) FIG. 1 shows the distribution of gold (dotted line) and of cobalt (solid line) of a ground catalyst particle from Example 4. The higher concentration of both metals in the respective outer regions of the particles is apparent. The steep rise in the curve at the outermost edges can be explained by a non-smooth surface of the particle.

(44) FIG. 2 shows the distribution of gold (dotted line) and of cobalt (solid line) of a ground catalyst particle from Comparative Example 3. The uniform concentration of both metals over the entire particle is apparent. The steep rise in the curve at the outermost edges can be explained by a non-smooth surface of the particle.

(45) FIG. 3 shows the distribution of gold (dotted line) and of nickel (solid line) of a ground catalyst particle from Comparative Example 4. The higher concentration of both metals in the respective outer regions of the particles is apparent. The steep rise in the curve at the outermost edges can be explained by a non-smooth surface of the particle.