GOLD-BASED CATALYST FOR THE OXIDATIVE ESTERIFICATION OF ALDEHYDES TO OBTAIN CARBOXYLIC ESTERS

Abstract

Catalysts for oxidative esterification can be used, for example, fro converting (meth)acrolein to methyl (meth)acrylate. The catalysts are especially notable for high mechanical and chemical stability even over very long time periods, including activity and/or selectivity relatively in continuous operation in media having even a small water content.

Claims

1. A hydrolysis-resistant catalyst, comprising: a) 0.01 to 10 mol % of gold, b) 40 to 94 mol % of silicon, c) 3 to 40 mol % of aluminium, and d) 2 to 40 mol % of at least one element selected from the group consisting of alkali metals, alkaline earth metals, lanthanoids having atomic numbers 57 to 71, Y, Sc, Ti, Zr, Cu, Mn, Pb and Bi, wherein components b) to d) are present as oxides and the stated amounts of components a) to d) relate to 100 mol % of the composition of the catalyst without oxygen, wherein the catalyst is in the form of particles and is suitable for the oxidative esterification of aldehydes to carboxylic esters, wherein the catalyst has a shell structure comprising a core and at least one shell, where at least 80% of the total amount of component a) is part of a shell, and wherein the catalyst has a PZC value between 7 and 11.

2. The catalyst according to claim 1, which, except for the oxygen, consists of components a) to d).

3. The catalyst according to claim 1, wherein the catalyst comprises between 0.05 and 2 mol % of component a).

4. The catalyst according to claim 1, wherein component a) is in the form of particles having a mean diameter between 2 and 10 nm.

5. The catalyst according to claim 1, wherein the catalyst particles have an average diameter between 10 and 200 μm and a spherical shape.

6. The catalyst according to claim 1, wherein the catalyst comprises between 2 and 30 mol % of Mg, Ce, La, Y, Zr, Mn, Pb and/or Bi as component d).

7. The catalyst according to claim 1, wherein the catalyst has a core and two shells, wherein at least 80% of the total amount of component a) is within an inner shell of the two shells.

8. A process for producing catalyst particles, wherein admixing a basic mixed oxide support with a gold-containing solution to form a component a) having a pH between 0.5 and 5.0, wherein the basic mixed oxide support has a PZC value between 8 and 12 and a mean diameter between 10 and 200 μm, consists of b) 40 to 94 mol % of silicon, c) 3 to 40 mol % of aluminium and d) 2 to 40 mol % of at least one element selected from alkali metals, alkaline earth metals, rare earth metals, Ti, Zr, Cu, Mn, Pb and Bi, wherein components b) to d) are present as oxides and the stated amounts of components a) to d) relate to 100 mol % of the composition of the catalyst without oxygen.

9. The process according to claim 8, wherein the gold-containing solution contains at least one additional compound including components b), c) and/or d) in ionic form.

10. A method of producing an alkyl (meth)acrylate, comprising reacting (meth)acrolein with oxygen and a monofunctional alcohol to give the alkyl (meth)acrylate; wherein the reacting is in the presence of a catalyst according to claim 1.

11. The method according to claim 10, wherein methacrolein is reacted with oxygen and methanol to give MMA.

12. A method of producing a hydroxyalkyl (meth)acrylate or a di-, tri- or tetra(meth)acrylate, comprising reacting (meth)acrolein with oxygen and a di-, tri- or tetrafunctional alcohol to give the hydroxyalkyl (meth)acrylate or to give the di-, tri- or tetra(meth)acrylate; wherein the reacting is in the presence of a catalyst according to claim 1.

13. The method according to claim 10, wherein the reacting is conducted continuously.

14. The method according to claim 13, wherein the catalyst is present in suspension form in a stirred reactor during the reacting.

15. The method according to claim 12, wherein the reacting is conducted continuously.

16. The method according to claim 15, wherein the catalyst is present in suspension form in a stirred reactor during the reacting.

Description

EXAMPLES

PZC Measurement

[0030] Powder material (3.0 g) is suspended in 7.5 ml of a 0.1% by weight solution of NaCl in demineralized water and stirred with a magnetic stirrer (100 rpm). After stirring at room temperature for 15 min, the pH of the suspension is measured with a pH probe. This value is referred to hereinafter as PZC.

Production of a Preformed Support

Example 1

[0031] A 250 ml beaker is initially charged with 21.35 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 which are dissolved in 41.85 g of demineralized water while stirring on a magnetic stirrer. Thereafter, 1.57 g of 60% by weight HNO.sub.3 are added while stirring. 166.67 g of silica sol (Köstrosol 1530AS from Bad Köstritz) are weighed into a 500 ml three-neck flask and cooled to 15° C. while stirring. 2.57 g of 60% by weight HNO.sub.3 are added gradually to the sol while continuing to stir. 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 thin layer on a preheated dish at 130° C. in a drying cabinet and then crushed with a mortar and pestle to give a fine powder. 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. over the course of 2 h and kept at 600° C. for a further 3 h. The PZC of this material was 9.81.

Example 2

[0032] A 250 ml beaker is initially charged with 32.03 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% by weight HNO.sub.3 are added while stirring. 166.67 g of silica sol (Köstrosol 1530AS from Bad Köstritz) are weighed into a 500 ml three-neck flask and cooled to 15° C. while stirring. 2.57 g of 60% by weight HNO.sub.3 are added gradually to the sol with stirring. At 15° C., the nitrate solution is added to the sol over the course of 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 thin layer on a preheated dish at 130° C. in a drying cabinet, then crushed with a mortar and pestle to give a fine powder. The dried powder 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 a further 2 h and finally kept at 600° C. for a further 3 h. The PZC of this material was 9.36.

Example 3

[0033] A 250 ml beaker is initially charged with 10.68 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% by weight HNO.sub.3 are added while stirring. 166.67 g of silica sol (Köstrosol 1530AS from Bad Köstritz) are weighed into a 500 ml three-neck flask and cooled to 15° C. while stirring. 2.57 g of 60% by weight 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 dried in a thin layer on a preheated dish at 130° C. in a drying cabinet, then crushed with a mortar and pestle to give a fine powder. 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 PZC of this material was 7.91.

Production of a Doped Support

Examples 4 to 13 and Comparative Example 1

Comparative Example 1 (Sn)

[0034] SnCl.sub.2*2H.sub.2O (440 mg, 1.95 mmol) was dissolved in 5 g of distilled methanol and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 a further 3 h. The PZC of this material was 6.85.

Example 4 (Bi)

[0035] Bi(NO.sub.3).sub.3*5H.sub.2O (947 mg, 1.95 mmol) was dissolved in 5 g of demineralized water with addition of 2.9 g of 60% by weight HNO.sub.3 and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and kept at 600° C. for a further 3 h. The PZC of this material was 9.21.

Example 5 (Mn)

[0036] Mn(NO.sub.3).sub.2*4H.sub.2O (494 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and kept at 600° C. for a further 3 h. The PZC of this material was 8.95.

Example 6 (Ce)

[0037] Ce(NO.sub.3).sub.3*6H.sub.2O (848 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 9.56.

Example 7 (Zr)

[0038] ZrO(NO.sub.3).sub.2*6H.sub.2O (663 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 8.90.

Example 8 (Pb)

[0039] Pb(NO.sub.3).sub.2 (647 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 9.35.

Example 9 (Al)

[0040] Al(NO.sub.3).sub.3*9H.sub.2O (734 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in a mortar and pestle and heated in a thin layer in a Naber oven to 300° C. in 2 h, kept at 300° C. for 3 h, heated to 600° C. in 2 h and kept at 600° C. for 3 h. The PZC of this material was 9.12.

Example 10 (Y)

[0041] Y(NO.sub.3).sub.3*6H.sub.2O (750 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 9.34.

Example 11 (La)

[0042] La(NO.sub.3).sub.3*6H.sub.2O (845 mg, 1.95 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO support. 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 10.20.

Example 12 (Mg)

[0043] Mg(NO.sub.3).sub.2*6H.sub.2O (2.0 g, 7.8 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 12.14.

Example 13 (Li)

[0044] LiOH (470 mg, 19.5 mmol) was dissolved in 5 g of demineralized water and the solution was mixed and shaken vigorously with 10 g of the above-described preformed SiO.sub.2—Al.sub.2O.sub.3—MgO 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 in 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 2 h and finally kept at 600° C. for 3 h. The PZC of this material was 12.31.

Catalyst Production (Application of Au to a Doped Support)

Examples 14 to 27 and Comparative Examples 2 to 5

Comparative Example 2

[0045] A suspension of 10 g of doped support from Comparative Example 1 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.89.

Example 14

[0046] A suspension of 10 g of doped support from Example 4 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.09.

Example 15

[0047] A suspension of 10 g of doped support from Example 5 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.72.

Example 16

[0048] A suspension of 10 g of doped support from Example 6 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.92.

Example 17

[0049] A suspension of 10 g of doped support from Example 7 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.87.

Example 18

[0050] A suspension of 10 g of doped support from Example 8 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.59.

Example 19

[0051] A suspension of 10 g of doped support from Example 9 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.82.

Comparative Example 3

[0052] A suspension of 10 g of doped support from Example 1 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=12.0, adjusted by addition of 20% by weight NaOH). After the addition, the mixture was stirred for a further 30 min, then cooled down and cooled down to room temperature. 1.0 g of NaBH.sub.4 was added at RT, and the reaction mixture was stirred for a further 30 min and then filtered. Subsequently, the mixture was washed six times with 50 ml each time of water. The material was dried at 105° C. for 10 h. The PZC of this material was 11.15.

Example 20

[0053] A suspension of 10 g of doped support from Example 1 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.49.

Example 21

[0054] A suspension of 10 g of doped support from Example 2 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.57.

Comparative Example 4

[0055] A suspension of 10 g of doped support from Example 3 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 6.99.

Example 22

[0056] A suspension of 10 g of doped support from Example 1 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=0.4, adjusted by addition of concentrated hydrochloric acid). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.29.

Example 23

[0057] A suspension of 10 g of doped support from Example 1 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=5.2, adjusted by addition of 20% by weight NaOH solution). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.63.

Example 24

[0058] A suspension of 10 g of doped support from Example 10 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.80.

Comparative Example 5

[0059] A suspension of 10 g of doped support from Example 1 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., 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 (pH=2.3). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 8.64.

Example 25

[0060] A suspension of 10 g of doped support from Example 11 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.69.

Example 26

[0061] A suspension of 10 g of doped support from Example 12 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.29.

Example 27

[0062] A suspension of 10 g of doped support from Example 13 in 33.3 g of demineralized water was heated to 90° C. and stirred at this temperature for 15 min. Added to the suspension while stirring was a solution, previously preheated to 90° C., of HAuCl.sub.4*3H.sub.2O (205 mg) in 8.3 g of water (pH=1.6). After the addition, the mixture was stirred for a further 30 min, then cooled and 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 finally calcined at 450° C. for 5 h. The PZC of this material was 9.14.

Examples in a Batch Process for MMA Preparation

[0063] A gold-containing catalyst (384 mg), methacrolein (1.20 g) and methanol (9.48 g) were stirred for 2 h in an atmosphere of 7% by volume of O.sub.2 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 gas chromatography (GC). Each catalyst was tested at least twice under identical conditions and the results of the respective experiments were averaged. The resulting conversion of methacrolein (C(MAL) in %), the space-time yield (STY, reported in mol MMA/kg cat.*h) and the selectivity of the conversion of the methacrolein to MMA (S(MMA), in %) for every catalyst tested are collated in Table 1 below.

TABLE-US-00001 TABLE 1 (catalyst performance in batch tests after production): pH STY, PZC (Au mol Do- PZC (sup- solu- C(MAL), MMA/kg S(MMA), Ex. pant (cat.) port) tion) % cat.*h % CE2 Sn 8.89 6.85 1.6 20.7 3.8 85.3 14 Bi 9.09 9.21 1.6 42.5 8.2 91.4 15 Mn 8.72 8.95 1.6 49.4 9.4 89.7 16 Ce 8.92 9.56 1.6 65.0 13.2 95.5 17 Zr 8.87 8.90 1.6 37.6 7.3 90.3 18 Pb 8.59 9.35 1.6 62.4 12.5 94.2 19 Al 8.82 9.12 1.6 30.7 6.3 93.1 CE3 Mg 11.15 9.81 12.0 20.1 3.6 92.3 20 Mg 9.49 9.81 1.6 41.7 8.5 98.6 21 Mg 8.57 9.36 1.6 29.5 6.3 91.9 CE4 Mg 6.99 7.91 1.6 21.2 3.9 82.3 22 Mg 9.29 9.81 0.4 31.9 6.5 85.3 23 Mg 9.63 9.81 5.2 34.8 7.1 92.5 24 Y 8.80 9.34 1.6 43.7 8.7 92.8 CE5 Ni 8.64 9.81 2.3 74.9 15.4 99.0 25 La 9.69 10.20 1.6 48.8 10.1 95.7 26 Mg 9.29 12.14 1.6 31.6 5.5 81.4 27 Li 9.14 12.31 1.6 29.2 5.2 81.9

[0064] These examples and comparative example showed that catalysts having too high a PZC value (CE3) or too low a PZC value (CE4) have a lower activity compared to comparable catalysts having a PZC value of the invention (Examples 20 and 21), in the form of a reduced space-time yield (STY). It was also possible to show that a number of metals—as claimed—exhibit good activities and selectivities, whereas, for example, contrary to expectation, tin (CE2) is less suitable and therefore cannot be used in accordance with the invention as component d).

[0065] It was also possible to show that catalysts that are in accordance with the invention but have not been prepared by the particularly preferred process likewise according to the invention have poorer properties compared to catalysts produced with preference in accordance with the invention. For instance, in Examples 26 and 27, the PZC value of the support material was too high according to the invention. In both cases, this results in acceptable but non-ideal selectivities and activities of the catalysts. This relationship is especially apparent from a comparison of Example 26 with Example 20. The same applies to the pH of the gold-containing solution. Thus, compared to Example 20 with an ideal value, the catalysts which have been produced with too low (Example 22) or too high (Example 23) a pH give likewise selectivities (Example 22) and activities (Examples 22 and 23) that are acceptable but also in need of improvement.

[0066] The initially very good performance of the Ni-containing catalyst known from the literature according to CE5 becomes the opposite when the long-term action of this catalyst is considered (see CE5, Table 2).

Hydrolysis Tests with Gold Catalysts

Examples 28 to 32, Comparative Examples 6 and 7

[0067] 4 g of a catalyst powder were suspended in 200 g of a 10% by weight sodium acetate solution (pH=7, adjusted by addition of acetic acid) at 80° C. while stirring (500 rpm). Acetic acid was added as required to keep the pH constant at 7. After stirring at 80° C. for 16 h, the catalyst was filtered off, washed with demineralized water and dried in a drying cabinet at 105° C. within 10 h. The (dry) catalyst thus treated was tested in a batch test for MMA preparation as described above. The results of these tests (mean values from two batch tests in each case) are compiled in the table which follows and compared with the batch tests with the fresh catalysts.

TABLE-US-00002 TABLE 2 (catalyst performance in batch tests after a hydrolysis test) Treated catalyst Fresh catalyst STY, STY, mol mol Cat. C(MAL), MMA/kg S(MMA), C(MAL), MMA/kg S(MMA), Ex. Ex. % cat.*h % % cat.*h % CE6 CE5(Ni) 74.9 15.4 99.0 8.5 1.1 59.9 28 16(Ce) 65.0 13.2 95.5 46.3 8.9 91.6 29 25(La) 48.8 10.1 95.7 56.2 10.8 92.8 30 18(Pb) 62.4 12.5 94.2 55.9 11.2 93.5 31 20(Mg) 41.7 8.5 98.6 40.1 8.3 93.8 CE7 22(Mg) 31.9 6.5 85.3 23.6 4.8 85.6 32 23(Mg) 34.8 7.1 92.5 35.1 6.9 87.6

[0068] These experiments showed that the long-term activity of the catalysts of the invention is very good, whereas catalysts according to the prior art containing non-inventive components d), for example Ni (CE5), show a very significant drop in activity and would have to be exchanged again quickly under continuous production conditions.

[0069] According to Comparative Example 7, the same applies to catalysts having a non-optimal pH of the gold-containing solution in the catalyst production. These too suffer a high loss of activity in an aqueous medium.

Continuous Test for Preparation of MMA (General Description)

[0070] A stirred tank reactor having a total volume of 400 ml was initially charged with 20 g of powder catalyst. The pH of a 42.5% by weight solution of MAL in methanol was adjusted to pH=7 while stirring by the addition of a 1% by weight solution of NaOH in methanol. This solution was fed continuously at a constant rate of addition to the 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, a sufficient amount of 1% by weight NaOH solution (in methanol) was fed into this reactor that the value in the reactor remained constant at pH=7. 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 gas chromatography.

Comparative Example 8: Continuous Test for Preparation of MMA with Au/NiO Catalyst

[0071] In this example, 20 g of the NiO—Au catalyst from Comparative Example 5 (prepared analogously to EP2177267A1 and EP2210664A1) were used in the continuous MMA preparation as described above. The results are compiled in Table 3.

Example 33

[0072] In this example, 20 g of a CeO.sub.2—Au catalyst of the invention from Example 15 were used in the MMA preparation as described above. The results are compiled in Table 3.

TABLE-US-00003 TABLE 3 Continuous MMA preparation with selected catalysts STY, TOS Feed C(MAL), mol MMA/kg S(MMA), Ex. [h] [g/h] % cat. *h % CE5 100 47.0 77.6 10.4 96.1 CE5 1000 47.0 69.7 9.3 91.5 33 100 55.6 68.2 10.1 96.0 33 1000 55.0 62.5 9.9 96.0

[0073] Finally, comparison in a continuous oxidative esterification can show that, compared to the Ni-containing catalyst as described in the prior art, the selectivity of a catalyst of the invention remains at a constantly high level after 1000 h of operating time, whereas the prior art catalyst loses 4.6% selectivity. The activity of the catalyst of the invention also declines to a much lesser degree within this period.