A METHOD OF PRODUCING A CERAMIC SUPPORT AND A CERAMIC SUPPORT

Abstract

Herein is disclosed a method of producing a ceramic support suitable for a catalyst, the method comprising providing a porous ceramic structure, comprising a body portion with a monomodal macropore structure, wherein the macropores comprises a first mean pore size; washcoating the porous ceramic structure using a suspension comprising oxide and/or hydroxide nanoparticles and drying and calcinating the washcoated porous ceramic structure at a temperature below the melting point of the nanoparticles. In addition, the ceramic support and its structure is disclosed.

Claims

1. A method of producing a ceramic support suitable for a catalyst, the method comprising providing a porous ceramic structure, comprising a body portion with a monomodal macropore structure, wherein the macropores comprises a first mean pore size; washcoating the porous ceramic structure using a suspension comprising oxide and/or hydroxide nanoparticles; drying and calcinating the washcoated porous ceramic structure at a temperature below the melting point of the nanoparticles.

2. The method of claim 1, wherein macropores with the first mean pore size has a narrow pore size distribution wherein at least 50% by volume of the macropores has a pore size diameter within±5% from the mean pore size, preferably at least about 75% by volume of the macropores has a pore size diameter within±5% from the mean pore size, preferably at least about 95% by volume of the macropores has a pore size diameter within±5% from the mean pore size.

3. The method of claim 1 or claim 2, wherein first mean pore size is between 2 and 100 μm, such as between 4 and 50 μm, such as between 6 and 25 μm.

4. The method of any one of the preceding claims, wherein the porous ceramic structure comprises a skin layer comprising a skin layer mean pore size, preferably the skin layer mean pore size is up to about 25% of the first mean pore size, such as up to about 15% of the first mean pore size.

5. The method of claim 4, wherein the pores of the skin layer has a narrow pore size distribution wherein at least 50% by volume of the skin layer pores has a pore size diameter within±5% from the skin layer mean pore size, preferably at least about 75% by volume of the skin layer has a pore size diameter within±5% from the skin layer mean pore size, preferably at least about 95% by volume of the skin layer pores has a pore size diameter within±5% from the skin layer mean pore size.

6. The method of claim 4 or claim 5, wherein skin layer mean pore size is between 100 nm and 3 μm, such as between 400 nm and 2 μm, such as between 600 nm and 1 μm.

7. The method of any one of claims 4-6, wherein the body portion comprises one or more ceramic components forming the macropores, and wherein said skin layer comprises at least one of said one or more ceramic components.

8. The method of any one of claims 4-7, wherein the body portion comprises one or more ceramic components forming the macropores, and wherein said skin layer comprises at least one other ceramic component than the body portion.

9. The method of any one of claims 4-8, wherein the skin layer forms an outer surface layer of the porous ceramic structure and is at least partly covering the body portion.

10. The method of any one of the preceding claims, wherein the porous ceramic structure comprises one or more crystalline ceramic components, such as alumina, zirconia, titania, boride, nitride, silicon carbide, mullite or any combinations comprising one or more of these.

11. The method of any one of the preceding claims, wherein the porous ceramic structure comprises one single ceramic component.

12. The method of any one of the preceding claims, wherein the porous ceramic structure comprises silicon carbide.

13. The method of any one of the preceding claims, wherein the nanoparticles are selected from metal oxides or metal hydroxides, such as but not limited to, scandium, yttrium, titanium, zirconium, aluminum, gallium, indium, silicon, germanium, antimony, lanthanum, cerium, samarium, hafnium oxide and/or hydroxide or any combinations comprising one or more thereof.

14. The method of any one of the preceding claims, wherein the nanoparticles have a D50 grain size of from about 0.1-200 nm, such as from about 1-150 nm.

15. The method of any one of the preceding claims, wherein the nanoparticles are selected to have grain size distribution wherein at least 50% by number of the nanoparticles have a particle size within±5% from the mean particle size, preferably at least about 75% by number of the nanoparticles have a particle size within±5% from the mean particle size, preferably at least about 95% by number of the nanoparticles have a particle size within±5% from the mean particle size.

16. The method of any one of the preceding claims, wherein the nanoparticles have a grain size distribution comprising that at least 90% by weight of the grains is within 0.5 times to 2 times the D50 grain size.

17. The method of any one of the preceding claims, wherein the washcoating is repeated, preferably until saturation is reached.

18. The method of any one of the preceding claims, wherein the suspension of nanoparticles is an aqueous or organic suspension of from about 1% by weight to about 70% by weight of the nanoparticles.

19. The method of any one of the preceding claims, wherein the porous ceramic structure is of composite material, preferably comprising two or more different ceramic components.

20. The method of any one of the preceding claims, wherein an outer surface part of porous ceramic structure is coated, preferably with a selective membrane.

21. The method of claim 20, wherein the porous ceramic structure comprises said skin layer and wherein said selective membrane is coated onto at least a part of said skin layer.

22. The method of any one of the preceding claims, wherein the porous ceramic structure is a monolithic structure.

23. The method of any one of the preceding claims, wherein the porous ceramic structure is a pellet.

24. The method of any one of the preceding claims, wherein the porous ceramic structure comprises at least one channel, such as at least one, preferably a plurality of channels of polygonal, circular or elliptical shape.

25. The method of any one of the preceding claims, wherein the method comprises producing the body portion of the porous ceramic structure, the method comprising selecting a first ceramic powder with a first mean grain size, selecting a second ceramic powder with a second mean grain size that is substantially smaller than the first mean grain size, mixing of the first and second ceramic powders with one or more additive to form a paste, shaping the paste to a green ceramic structure, and sintering the green ceramic structure at a temperature sufficiently high to at least partly sintering the ceramic grains.

26. The method of claim 25, wherein the sintering of the green ceramic structure is performed in inert environment, such as in a vacuum atmosphere or in an inert gas atmosphere.

27. The method of any one of the preceding claims, wherein at least the body portion of the porous ceramic structure is subjected to heat treatment in an oxidizing gas environment.

28. The method of claim 27, wherein the heat treatment is performed at a temperature sufficiently high to oxidize at least a part of fee carbon located in the body portion.

29. The method of any one of claims 25-38, wherein the size ratio between the mean grain size of the first ceramic powder and the mean grain size of the second ceramic powder lies in the range of approximately 10:1 to 2:1, such as 6:1 to 3:1.

30. The method of any one of claims 25-29, wherein the mean grain size of the first ceramic powder and/or the mean grain size of the second ceramic powder has a narrow grain size distribution, preferably at least 90% by weight of the first ceramic powder and/or the second ceramic powder are within about 0.5 and about 2 times the mean grain size of the respective ceramic powder.

31. The method of any one of claims 25-30, wherein the mean grain size of the first ceramic powder is from about 5 μm to about 50 μm and the mean grain size of the second ceramic powder is from about 0.5 μm to about 10 μm, such as wherein the mean grain size of the first ceramic powder is from about 10 μm to about 30 μm and the mean grain size of the second ceramic powder is from about 1 μm to about 5 μm.

32. The method of any one of claims 25-31, wherein the additive comprises one or more of a binder, a plasticizer, a dispersant, a surfactant a lubricant or any combinations thereof.

33. The method of any one of claims 25-32, wherein the method comprises burning off the additive prior to sintering.

34. The method of any one of claims 25-33, wherein the shaping comprises casting, isostatic pressing, 3D-printing, injection molding, extruding, cutting or any combinations thereof.

35. The method of any one of claims 25-34, wherein the shaping comprises providing the green ceramic structure to have an elongate shape, such as a cylinder shape or an angular prism shape, with one or more elongate through going channels, preferably arranged in a honeycomb structure, such as channels of polygonal, circular or elliptical shape or any combinations thereof.

36. The method of any one of claims 25-35, wherein the sintering comprises treating the green ceramic structure at a sintering temperature for a sufficient time to bind the ceramic grains to form the ceramic body portion.

37. The method of any one of claims 25-36, wherein the method comprising applying the skin layer onto the body portion, the method comprises applying a suspension of ceramic nanoparticles onto a preselected outer surface area of the body portion, drying the coated body portion and sintering the ceramic nanoparticles to form the skin layer.

38. The method of claim 37, wherein the ceramic nanoparticles have a mean grain size of less than about 1 μm, such as from about 5 nm to about 800 nm, such as from about 10 nm to about 500 nm.

39. The method of claim 37 or claim 38, wherein the ceramic nanoparticles have a mean grain size of less than about 25% of the mean grain size of the second ceramic powder, preferably less than about 10% of the mean grain size of the second ceramic powder.

40. A ceramic support suitable for a catalyst, the ceramic support comprises a body portion with a multi modal pore structure, having a modality selected from trimodal, quadrimodal and pentamodal, and wherein the body portion of the ceramic body comprises a first mode of pores, a second mode of pores and a third mode of pores, wherein the first mode of pores having a first mean pore size MP50, which is between 2 and 100 μm, the third mode of pores having a third mean pore size up to 100 nm and the second mode of pores having a second mean pore size between the first mean pore size and the third mean pore size, preferably the first mean pore size is between 4 and 50 μm, such as between 6 and 25 μm.

41. The ceramic support of claim 40, wherein the body portion of the ceramic body comprises pores of a second mean pore size smaller than the first mean pore size, pores of a third mean pore size smaller than the second mean pore size and optionally pores of a fourth mode of pores having pores of a fourth mean pore size smaller than the third mean pore size and optionally a fifth mode of pores having pores of a fifth mean pore size smaller than the fourth mean pore size.

42. The ceramic support of claim 40 or claim 41, wherein at least about 90% of the pore volume of the body portion are formed by pores of the first, the second and the third mean pore size and optionally of the fourth and the fifth mean pore size, preferably at least about 95%, such as 98% of the pore volume of the body portion are formed by pores of the first, the second and the third mean pore size and optionally of the fourth and the fifth mean pore size.

43. The ceramic support of any one of claims 40-42, wherein one or more, preferably each, of the modes of pores has a narrow pore size distribution wherein at least 50% by volume of the pores has a pore size diameter within±5% from the mean pore size, preferably at least about 75 by volume of the pores has a pore size diameter within±5% from the mean pore size, preferably at least about 95% by volume of the pores has a pore size diameter within±5% from the mean pore size.

44. The ceramic support of any one of claims 40-43, wherein the body portion has a trimodal pore structure.

45. The ceramic support of any one of claims 40-44, wherein the second mean pore size, is between 100 nm and 1 μm, such as between 200 nm and 500 nm.

46. The ceramic support of any one of claims 40-45, wherein the third mean pore size, is between 10 nm and 100 μm, such as between 20 nm and 50 nm.

47. The ceramic support of any one of claims 40-46, wherein the ceramic support comprises one or more crystalline ceramic components, such as alumina, zirconia, titania, boride, nitride, silicon carbide, mullite or any combinations comprising one or more of these.

48. The ceramic support of any one of claims 40-47, wherein the ceramic support comprises one single ceramic component, preferable the porous ceramic structure comprises silicon carbide.

49. The ceramic support of any one of claims 40-48, wherein the ceramic support comprises a chemically selective membrane, the chemically selective membrane is preferably formed as a polymeric coating of at least a part the outer surface area of the body portion.

50. The ceramic support of any one of claims 40-49, wherein the ceramic support is a monolithic ceramic support.

51. The ceramic support of any one of claims 40-49, wherein the ceramic support is a pellet.

52. The ceramic support of any one of claims 40-51, wherein the ceramic support comprises at least one channel, such as at least one, preferably a plurality of channels of polygonal, circular or elliptical shape.

53. The ceramic support of claim 52, wherein the ceramic support has an elongate shape comprising a first and a second end faces and wherein the at least one channel is a through going channel, preferably passing through said first and said second end faces.

54. The ceramic support of claim 52 or claim 53, wherein, wherein the ceramic support has a cylinder shape or an angular prism shape, with one or more elongate through going channels, preferably arranged in a honeycomb structure, such as channels of polygonal, circular or elliptical shape or any combinations thereof.

55. The ceramic support of any one of claims 40-54, wherein the ceramic support is obtainable by the method as claimed in any one of claims 1-36.

Description

BRIEF DESCRIPTION OF THE EXAMPLES AND DRAWING

[0123] The invention is illustrated further below in connection with selected examples and embodiments and with reference to the figures. The figures are schematic and may not be drawn to scale.

[0124] FIG. 1 (left) shows the morphology of an embodiment of the body portion of the support structure of the invention.

[0125] FIG. 1 (right) shows a skin layer of an embodiment of the support structure of the invention.

[0126] FIG. 2 shows meso-pore size distribution as a function of oxide/hydroxide nanoparticles of the washcoating,

[0127] FIG. 3 shows pore size distributions of embodiments of the ceramic support of the invention.

[0128] FIG. 4 shows pore size distribution of the SiCf and SiCc of example 1 and 2.

[0129] FIGS. 5a and 5b show pore size distributions of embodiments of the ceramic support of the invention according to example 5.

[0130] FIG. 6 shows is a cross sectional and magnified view of an embodiment of the ceramic support of the invention.

[0131] FIG. 7 shows a number of embodiments of support structures of the invention.

Example 1

[0132] A number of monolithic porous ceramic structures were produced using the method described in U.S. Pat. No. 7,699,903. For each porous ceramic structure, a paste of a-SIC powder with well-defined particle size distribution was produced and shaped into a multi-channel monolith, dried, and sintered at an appropriate temperature. The monolith structures were shaped to have a cylindrical form with a length of 200 and a diameter of 25.4 mm. Each monolithic structure contained 30 elongate through going channels extending in the length of the monolithic structure. Each channel was 3 mm in diameter.

[0133] To obtain monoliths with a finer or coarser core, namely SiCf and SiCc, two different first ceramic powders with respective first mean particle sizes were used: 17.3 μm (fine) and 36.5 μm (coarse). Each of these first ceramic powders were mixed with a second ceramic powder with a second mean particle size about 0.1 times the respective first mean particle size.

[0134] The monolithic porous ceramic structures had a monomodal macropore structure, half of the monolithic porous ceramic structures had a coarser mean pore size of 14.9 μm (referred to as SICc) and the other half had a finer mean pore size of 7.5 μm (referred to as SICf). The pore size distribution of the SiCf and SiCc are shown in FIG. 4.

Example 2

[0135] A skin layer was applied to the monolithic porous ceramic structures. A suspension of sub-μ sized α-SiC particles was prepared and applied onto the outer surface, leaving the channels free of the suspension. The suspension was dried and sintered, to form a SiC skin. The skin had a mean pore size of 848 nm and a thickness of 45-60 μm.

[0136] The skin layer resulted in that the external surface roughness was reduced without altering the composition of the body portion of the support. FIG. 1 (left) shows the morphology of the body portion of the SiC monolithic structure, with large macrovoids (pores) between SiC particles of smooth surface. FIG. 1 (right) focuses on the defect-free SiC skin.

Example 3

[0137] The monolithic porous ceramic structures of example 2 were infiltrated with metal oxide particles by submerging the structures into a colloidal silica suspension with particle sizes of 7 nm. The infiltration was performed by immersing (washcoating) the monolithic porous ceramic structures into the respective colloidal suspensions. After immersing, excess suspension was removed.

[0138] For some of the monolithic porous ceramic structures the washcoating was repeated. After four layers of washcoat, followed by calcination, 17% of the monolith mass consisted of silica and the prevalent pore size was below 1.5 μm as shown in FIGS. 2 and 3. FIG. 3 also demonstrates how calcination temperature can is used to tune pore size distribution.

TABLE-US-00001 # calcination temperature A (red) 900° C. B (blue) 700° C. D (Black) 500° C.

Example 4

[0139] The monolithic porous ceramic structures of example 2 were infiltrated following the method of example 3 by submerging the structures into a colloidal silica suspension with particle sizes of 70 nm.

[0140] After two layers of washcoat, followed by calcination, 20% of the monolith mass consisted of silica and the prevalent pore size was below 0.1 μm as shown in FIGS. 2 and 3. FIG. 3 also demonstrates how calcination temperature can is used to tune pore size distribution.

TABLE-US-00002 # calcination temperature A (red) 900° C. B (blue) 700° C. D (Black) 500° C.

Example 5

[0141] The monolithic porous ceramic structures of example 2 were infiltrated with metal oxide particles following example 3 using a colloidal alumina suspension with particle sizes of 60-90 nm. After four layers of washcoat, followed by calcination, 14% of the monolith mass consisted of silica and new population of 10 nm pores was formed while the main prevalent pore size was between 1 and 10 μm as shown in FIGS. 2, 5a and 5b. FIGS. 5a and 5b also demonstrates how calcination temperature can is used to tune pore size distribution. The calcination temperatures were as follows:

TABLE-US-00003 # calcination temperature A (red) 900° C. B (blue) 700° C. C (green) 600° C. D (Black) 500° C.

[0142] The dotted line indicates the macropore structure prior to washcoating with oxide/hydroxide nanoparticles.

[0143] The ceramic supports obtained in examples 3-5 were further analyzed.

[0144] It was found that the washcoating and calcinating with metal oxides or metal hydroxides resulted in that a plurality of the macropores of the body portion was partially filled and the porous distribution, which is obtained, is different from the original. The inter-particle voids of the SiC body were filled with metal oxide nanoparticles, which lead to the formation of two populations of smaller pores. Thus, the monoliths infiltrated by this procedure present a trimodal pore size distribution, with a portion of big macropores, a portion of small macropores, and a portion of mesopores. The formation process of the smaller macropores may be explained by the adhesion of the metal oxide on the walls of macropores. At higher calcination temperatures these pores increase in volume and diameter as the nanoparticles melts to a larger extend.

[0145] The accumulated pore volumes and pore size distributions obtained at maximum silica loads are depicted in FIG. 3 and contain the pore volume fraction for each kind of pore. The voids generated with the small (7 nm) and the big (70 nm) nanoparticles are around 5 and 24 nm in diameter, respectively.

[0146] The specific surface area was determined by MIP. The non-infiltrated monolith (SiCf) has a specific surface area of 0.1 m.sup.2 g.sup.−1. The infiltrated samples calcined at moderate temperatures present significantly higher values, as the specific surface area essentially is closely linked to the size and volume of the micro- and mesopores.

[0147] The specific surface area obtained may depend on the colloidal solution employed for the washcoat as well as the calcination temperature. The highest specific surface area was obtained for the samples infiltrated with alumina four times and smallest particles (7 nm). It is believed that this is caused by the higher volume of relatively smaller mesopores.

[0148] The washcoating and calcinating with metal oxides or metal hydroxides showed that a plurality of the macropores of the body portion, are filled and a new porous distribution is obtained. The inter-particle voids among the SiC macroporous are filled with metal oxide nanoparticles, which lead to the formation of two populations of smaller pores. Thus, the monoliths infiltrated by this procedure present a trimodal pore size distribution, with some remaining large macropores, some newly formed smaller macropores, and some mesopores not previously present. The origin of the smaller macropores can be assigned to the agglomeration of the metal oxide on. The size and volume of these small pores grow with the calcination temperature due to the increased viscosity of the oxides at higher temperature.

[0149] FIG. 6 shows an outer wall section of an embodiment of a support structure of the invention. It can be seen that the body portion 1, is coated with a skin layer 2, which again is coated with a selective membrane 3.

[0150] FIG. 7 shows a number of embodiments of support structures of the invention. As illustrated the support structure may have channels 6 e.g. of polygonal, circular or elliptical shape. The ceramic support preferably has a cylinder shape or an angular prism shape, e.g. square or hexagonal as illustrated. A number of elongate through going channels passing through the first and said second end faces 5. An outer surface 4 may be covered by a selective membrane.