CATALYST MANUFACTURING METHOD

Abstract

A method for producing a catalyst or catalyst precursor is described including: applying a slurry of a particulate catalyst compound in a carrier fluid to an additive layer manufactured support structure to form a slurry-impregnated support, and drying and optionally calcining the slurry-impregnated support to form a catalyst or catalyst precursor. The mean particle size (D50) of the particulate catalyst compound in the slurry is in the range 1-50 μm and the support structure has a porosity ≧0.02 ml/g.

Claims

1. A method for producing a catalyst or catalyst precursor comprising: (i) applying a slurry of a particulate catalyst compound in a carrier fluid to an additive layer manufactured support structure to form a slurry-impregnated support, and (ii) drying and optionally calcining the slurry-impregnated support to form a catalyst or catalyst precursor, wherein the mean particle size (D50) of the particulate catalyst compound in the slurry is in the range 1-50 μm and the support structure has a porosity ≧0.02 ml/g.

2. A method according to claim 1 wherein the support structure is manufactured by steps comprising (i) combining a particulate support material with a binder to form a preform mixture, (ii) forming a layer of the preform mixture, (iii) applying a binding solvent from a print-head to the layer of preform mixture according to a predetermined pattern to bind the particulate support material, (iv) repeating (ii) and (iii) layer upon layer, (v) removing un-bound material and (vi) drying and optionally calcining to form the support structure.

3. A method according to claim 2 wherein the particulate support material is a powder with a particle size in the range 0.1 to 400 μm.

4. A method according to claim 2 wherein the particulate support material comprises an alumina, metal-aluminate, silica, alumino-silicate, cordierite, titanium (IV) oxide, zirconia, cerium (IV) oxide, zinc oxide, or a mixture thereof, a zeolite, a metal powder, silicon carbide, silicon nitride or carbon.

5. A method according to claim 2 wherein the particulate support material comprises one or more aluminous materials selected from hydrous aluminas, transition aluminas, alpha alumina, and metal-aluminates.

6. A method according to claim 2 wherein the binder is selected from dextrin, sucrose and mixtures thereof or PVA.

7. A method according to claim 2 wherein the preform mixture contains 1-10% by weight of polymer or ceramic fibres.

8. A method according to claim 2 wherein the preform mixture contains 0.5 to 5% by weight of one or more sintering aids selected from titanium oxide iron oxide copper oxide, magnesium oxide and calcium carbonate.

9. A method according to claim 8 wherein the sintering aid is a mixture of titanium oxide and iron or copper oxide, preferably at weight ratios of TiO.sub.2 to Fe.sub.2O.sub.3 or CuO in the range 40:60 to 60:40.

10. A method according to claim 2 wherein the layers of preform material are in the range 0.02 to 5.0 mm thick, preferably 0.02 to 2.5 mm thick.

11. A method according to claim 2 wherein the binding solvent is an organic solvent or water.

12. A method according to any claim 2 wherein the printing head is used at printing resolution in the x-direction in the range 40 μm to 70 μm and in the y-direction of 80 to 100 μm for layer thicknesses in the range 50 to 150 μm.

13. A method according to claim 2 wherein the dried support structure is subjected to a calcination stage at a temperature in the range 500-2000° C.

14. A method according to claim 1 wherein the slurry has a solids content in the range 5 to 80% by weight.

15. A method according to claim 1 wherein the particulate catalyst compound applied to the support structure comprises a metal powder, metal compound or a zeolite.

16. A method according to claim 1 wherein the particulate catalyst compound comprises a precious metal powder selected from one or more of Pt, Pd, Rh, Ir, Ru, Re.

17. A method according to claim 1 wherein the particulate catalyst compound is selected from one or more transition metal compounds, including lanthanide metal compounds and actinide metal compounds.

18. A method according to claim 17 wherein the transition metal compound comprises one or more metals selected from the group consisting of Na, K, Mg, Ca, Ba, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Hf, W, Re, Ir, Pt, Au, Pb, or Ce.

19. A method according to claim 17 wherein the metal compound is a metal oxide, metal hydroxide, metal carbonate, metal hydroxycarbonate or mixture thereof.

20. A method according to claim 17 wherein the particulate catalyst compound is a bulk catalyst particle in which the catalytic metal is distributed throughout the particle, or is a coated catalyst particle in which the catalytic metal is present as a surface layer on the surfaces of the particle.

21. A method according to claim 17 wherein the particulate catalyst compound comprises one or more of Pt, Pd, Rh and Ir coated onto a support material.

22. A method according to claim 17 wherein the particulate catalyst compound is a coated or bulk catalyst comprising one or more catalytic metals selected from Ni, Co, Mo, W, Cu and Fe.

23. A method according to claim 17 wherein the particulate catalyst compound is selected from LaCoO.sub.3, LaCoO.sub.3 in which partial substitution of the A-site has been made by Sr or Ce, La.sub.2CoO.sub.4, Co.sub.3O.sub.4 supported on alumina, ceria zirconia or mixtures thereof, Co.sub.3O.sub.4 promoted by rare earth elements.

24. A catalyst or catalyst precursor obtained by the method of claim 1.

25. A process using a catalyst according to claim 24 comprising contacting a reactant mixture with the catalyst or catalyst precursor under conditions to effect a catalysed reaction.

26. A process according to claim 25 comprising a catalysed reaction selected from hydroprocessing including hydrodesulphurisation, a hydrogenation, steam reforming including pre-reforming, catalytic steam reforming, autothermal reforming and secondary reforming and reforming processes used for the direct reduction of iron, catalytic partial oxidation, a water-gas shift including isothermal-shift, sour shift, low-temperature shift, intermediate temperature shift, medium temperature shift and high temperature shift reactions, a methanation, a hydrocarbon synthesis by the Fischer-Tropsch reaction, methanol synthesis, ammonia synthesis, VOC or methane oxidation, ammonia oxidation and nitrous oxide decomposition reactions, or oxidation, three-way catalysis or selective reduction reactions of internal combustion engine or power station exhaust gases.

27. A process according to claim 26 comprising ammonia oxidation and nitrous oxide decomposition reactions wherein the catalyst is used in combination with a precious metal gauze catalyst.

28. A process according to claim 26 comprising a sorption selected from the recovery of sulphur compounds or heavy metals such as mercury and arsenic from contaminated gaseous or liquid fluid streams, or particulate matter from the exhaust gases of internal combustion engines or power stations.

Description

EXAMPLE 1. PREPARATION OF SUPPORT STRUCTURES

[0047] A support mixture was prepared by mixing alpha alumina (MARTOXID PN-202, >70% alpha alumina; BET surface area 8-15 m.sup.2/g; D50 2-4 μm) with titanium (IV) oxide (Acros Organics, anatase 99%) and copper (II) oxide (Fisher Scientific >98%). The alumina, titanium (IV) oxide and copper (II) oxide were used as received. Different binders and in one case cellulose fibres were combined with the resulting support mixture to create preform mixtures as follows;

TABLE-US-00001 Preform mixture Wt % Ingredient 1A 88.2 Alumina 0.9 CuO 0.9 TiO2 10 PVA (Acros Organics 88% hydrolyzed; mean M.W 20,000-30,000) 1B 65.33 Alumina 0.67 CuO 0.67 TiO2 13.33 Sucrose (British Sugar, Silk Sugar) 13.33 Dextrin (Acros Organics) 6.67 Cellulose fibres (Sigma Aldrich type 50, 50 μm) 1C 70 Alumina 0.71 CuO 0.71 TiO2 14.29 Sucrose 14.29 Dextrin 1D 88.2 Alumina 1.8 Magnesium Oxide (Fisher Scientific) 10 PVA (Acros Organics 88% hydrolyzed; mean M.W 20,000-30,000) 1E 88.2 Alumina 1.8 Calcium Carbonate 10 PVA (Acros Organics 88% hydrolyzed; mean M.W 20,000-30,000) 1F 88.2 Alumina 1.8 CuO 10 PVA (Acros Organics 88% hydrolyzed; mean M.W 20,000-30,000)

[0048] The preform mixtures were placed in the hopper of a 3-D printing apparatus (ink-jet powder bed apparatus available from Voxeljet Technology AG) and used to 3-D print 10 mm cubic support structures. The layer thickness was set at 0.1 mm, the x-direction resolution from the print-head was 50 μm and the y-direction resolution was 88 μm.

[0049] The printed support structures were dried at 105° C. overnight and then calcined at 1200° C. for 2 hours.

[0050] The cubes were immersed in a bath of water at 22° C. The dry mass, buoyant mass and wet mass were recorded and from these the density and cold water pick-up (CWP) were determined. Five cubes were tested and a mean taken.

[0051] The compressive strength of the cubes was also measured. Measurements were made from the ‘side’ of the cube along the plane of the layers formed during the 3-D printing process (the x-direction) and from the ‘top’ of the cube through the layers (the z-direction). Two cubes were tested and a mean taken. The results were as follows;

TABLE-US-00002 Preform Compressive mixture Density CWP strength (MPa) reference (g/cm.sup.3) (ml/g) z x 1A 1.47 0.41 5.5 8.8 1B 1.69 0.28 29.3 36.1 1C 1.38 0.45 9.1 17.2

[0052] The PVA-bound structure has a higher CWP indicating a more porous structure. The cellulose fibres appear to have markedly increased the strength of the structure which also has a higher CWP.

[0053] The printing resolution was varied to determine its effect on porosity of the resulting structures. Lower densities and higher CWP figures were obtained for x-direction resolutions of 60 μm and 70 μm.

[0054] The support preparation was repeated for x-direction resolutions of 60 μm and either 40 μm or 70 μm. The D10, D50 and D90 of the main peaks of the porosimetry analysis for the supports 1A and 1B were as follows.

Support 1A

[0055]

TABLE-US-00003 Resolution 40 μm 50 μm 60 μm D50 D10-D90 D50 D10-D90 D50 D10-D90 (μm) (μm) (μm) (μm) (μm) (μm) 53.98 51.20 49.24 30.72 48.24 30.72

Support 1B

[0056]

TABLE-US-00004 Resolution 50 μm 60 μm 70 μm D50 D10-D90 D50 D10-D90 D50 D10-D90 (μm) (μm) (μm) (μm) (μm) (μm) 83.23 46.08 75.05 35.84 74.05 30.72

Support 1C:

[0057]

TABLE-US-00005 Resolution 65 μm D50 D10-D90 (μm) (μm) 60.3 34.84

EXAMPLE 2. PREPARATION OF CATALYSTS

[0058] Two cubes prepared from preform mixtures A, B, C, D, E & F according to the method of Example 1 using x-direction printing resolutions in the range 40-70 μm were dried at 105° C. overnight, fired at 1200° C. for 2 hours then allowed to cool, then coated with catalyst by dipping the cubes in a slurry of La.sub.0.8Ce.sub.0.2CoO.sub.3.

[0059] The La.sub.0.8Ce.sub.0.2CoO.sub.3 slurry was prepared by dispersing 400 g of La.sub.0.8Ce.sub.0.2CoO.sub.3 prepared according to WO 98/28073 and milled in a bead mill to a D.sub.50 particle size of 2.5 to 3.0 μm, in 600 ml of demineralized water (40% solids). This produced a slurry with a D10, D50 and D90 particle size of 0.956, 2.942 and 7.525 μm respectively. Two cubes were soaked in 60 ml of the slurry. The cubes were allowed to soak for 5 minutes, then removed and dried at 105° C. overnight. The catalyst pickup for the different cubes is given below;

TABLE-US-00006 Preform mixture Printing Resolution Total Porosity La.sub.0.8Ce.sub.0.2CoO.sub.3 reference (μm) (ml/g) Loading (wt %) 1A 40 0.354 14.7 1A 50 0.457 16.8 1A 60 0.547 19.3 1B 50 0.327 11.2 1B 60 0.548 23.3 1B 70 0.460 19.6 1C 65 0.470 19.1 1D 65 1.016 41.1 1E 65 0.904 36.4 1F 65 0.854 39.6

[0060] If the catalyst loading is plotted against the total porosity for the supports 1A-1F it can be seen that there is a strong correlation. The plot is depicted in FIG. 1. FIG. 1 shows that in each case as the total porosity increases, the catalyst pickup also increases. Additionally, the results suggest that there are pore size distributions which are better than others at picking up the catalyst.

EXAMPLE 3. CATALYST TESTING

[0061] La.sub.0.8Ce.sub.0.2CoO.sub.3 catalysts were prepared on aluminosilicate and alumina tetrahedra-shaped support structures (with rectilinear basal dimensions of 7.95+/−0.5 mm and 7.3+/−0.5 mm and a height of 5.75+/−0.5 mm) according to the above method and tested for ammonia oxidation and nitrous oxide abatement in a laboratory test reactor.

[0062] The aluminosilicate support structure exhibited single major peak with a d.sub.50 of 25.7 μm and a total intrusion volume of 0.484 ml/g.

TABLE-US-00007 D50 D10-D90 (μm) (μm) aluminosilicate 25.7 18.4 alumina 50.17 46.08

[0063] Two catalysts were prepared according to the methods described in Examples 1 and 2. Example 3a in which tetrahedra-shaped aluminosilicate structures were dip coated with a 40 wt % slurry of La.sub.0.8Ce.sub.0.2CoO.sub.3 (as described in Example 2) and dried at 105° C. to provide a catalyst with 25 wt % La.sub.0.8Ce.sub.0.2CoO.sub.3; and Example 3b, which was prepared in an identical manner to Example 3a but further subjected to calcination in air at 900° C. for 6 hours after drying.

[0064] For comparison, La.sub.0.8Ce.sub.0.2CoO.sub.3 cylindrical catalyst pellets prepared by conventional pelleting methods were also tested.

[0065] The test method was as follows. A known mass of catalyst was loaded into a quartz reactor tube of internal diameter 24.6 mm to give a 20 mm deep catalyst bed. A thermocouple was placed 1 mm into the bottom of the bed to measure the catalyst temperature during the tests. A second thermocouple placed 25 mm above the top of the bed measured the inlet gas temperature. Catalyst performance and activity was determined using one of two different test procedures. A quadrupole mass spectrometer was used to measure the concentrations of various background gases and nitrogen-containing species during the course of each method and the data collected was used to assess the catalyst performance.

[0066] Procedure (I). Nitrous Oxide Abatement. A synthetic air mixture comprising 10.5% O.sub.2, 1% Ar and balance He was flowed over the catalyst bed at a rate of 35 L min.sup.−1 and pre heated to 100° C. A 0.3 L min.sup.−1 flow of 25% N.sub.2O in N.sub.2 was then added to the air mixture and the reactor was heated to 850° C. at a rate of 10° C. min.sup.−1. The reaction was allowed to dwell at 850° C. for 30 minutes before being cooled back down to 100° C. at 10° C. min.sup.−1. The concentration of nitrous oxide which has been abated, [N.sub.2O].sub.A, was calculated by measuring the concentration of the evolved gas at time=t, [N.sub.2O].sub.t, and subtracting from the initial concentration at time=0, [N.sub.2O].sub.0. Percentage abatement was then calculated by division of [N.sub.2O].sub.A with [N.sub.2O].sub.0.

[0067] Procedure (II) Ammonia Oxidation. A synthetic air mixture comprising 10.5% O.sub.2, 1% Ar and balance He was flowed over the catalyst bed at a rate of 35 L min.sup.−1 and pre heated to 100° C. A 1.85 L min.sup.−1 ammonia flow was then added to the air mixture and the reactor was then heated to 415° C. at a rate of 10° C. min.sup.−1. The reaction was allowed to dwell at a 415° C. preheat for 30 minutes before being cooled back down to 100° C. at 10° C. min.sup.−1. The exotherm from the ammonia oxidation reaction combines with the preheat temperature to give a maximum catalyst temperature between 750° C. and 900° C. The ammonia oxidation was reported as the percentages of NO, N.sub.2 and N.sub.2O selectivity.

[0068] The nitrous oxide abatement results were as follows;

TABLE-US-00008 Nitrous oxide Catalyst La.sub.0.8Ce.sub.0.2CoO.sub.3 abatement (%) Example shape content (wt %) 700° C. 800° C. Example 3a tetrahedra 25 45 71 Example 3b tetrahedra 25 45 70 Comparative cylinders >95 52 71 pellets

[0069] These results suggest that, despite a lower active catalyst content, at temperatures close to plant operation temperatures (800-900° C.) the coated catalysts appear to perform equally as well as the solid La.sub.0.8Ce.sub.0.2CoO.sub.3 pellets.

[0070] The ammonia oxidation results were as follows;

TABLE-US-00009 NO Selectivity N.sub.2 Selectivity N.sub.2O Selectivity Example (%) (%) (%) Example 3a 80.56 17.42 2.02 Example 3b 86.92 10.25 2.83

[0071] These results suggest that there was a small increase in NO selectivity after the coated material was fired at 900° C.

[0072] The effect of the particle size of the particulate catalyst compound in the slurry was investigated using three further catalysts

EXAMPLE 3C

[0073] Milled La.sub.0.8Ce.sub.0.2CoO.sub.3 slurry dip coated on to aluminosilicate tetrahedra supports.

EXAMPLE 3D

[0074] Unmilled La.sub.0.8Ce.sub.0.2CoO.sub.3 slurry dip coated on to aluminosilicate tetrahedra supports.

EXAMPLE 3E

[0075] Milled La.sub.0.8Ce.sub.0.2CoO.sub.3 slurry dip coated on to alumina tetrahedra supports.

[0076] The milled slurries were prepared as per Example 2, the unmilled slurry had a particle size distribution of D10 1.48, D50 7.68 and D90 36.09 μm.

[0077] The nitrous oxide abatement results were as follows;

TABLE-US-00010 La.sub.0.8Ce.sub.0.2CoO.sub.3 Nitrous oxide Shaped content abatement (%) Example support (wt %) 750° C. 850° C. Example 3c aluminosilicate 8.1 26 40 tetrahedra Example 3d aluminosilicate 3.7 10 25 tetrahedra Example 3e alumina 13.0 57 80 tetrahedra

[0078] These results suggest that that the material prepared using alumina supports has higher activity than material prepared on aluminosilicate supports. The results also suggest that samples prepared with milled La.sub.0.8Ce.sub.0.2CoO.sub.3 slurries have higher activity towards N.sub.2O abatement than the sample prepared with unmilled La.sub.0.8Ce.sub.0.2CoO.sub.3 slurry.

EXAMPLE 4. CATALYST TESTING WITH PRECIOUS METAL GAUZES

[0079] The Example 3a and Example 3e catalysts were also tested in combination with precious metal ammonia oxidation catalysts. In these tests a reactor basket of 40 mm internal diameter was charged with a 5 ply gauze pack containing 5% Rhodium and 95% Platinum (5RhPt) on top of a low density stainless steel woven gauze. The La.sub.0.8Ce.sub.0.2CoO.sub.3 catalysts were then charged, pre-weighed, underneath the 5RhPt gauze pack. Another stainless steel woven gauze was clamped into the lower basket flange to support the La.sub.0.8Ce.sub.0.2CoO.sub.3 catalyst. Unless otherwise stated, the La.sub.0.8Ce.sub.0.2CoO.sub.3 catalyst bed is 54 mm deep and 40 mm in diameter. Unless otherwise stated, the catalysts were tested over 10 days under the following process conditions: 10 Nm.sup.3h.sup.−1 air, 10% vol NH.sub.3, 200° C. preheat and 4 bara. The evolved gases were analysed and the conversion efficiency (for NH.sub.3 to NO, expressed as a percentage) and amount of N.sub.2O by-product in the product gas stream recorded.

[0080] The results are given below;

TABLE-US-00011 2 days 4 days 6 days 8 days 10 days Nitrous oxide produced (ppmv) Example 3e 880 880 890 900 910 Example 3a 800 900 960 1000 1000 Ammonia oxidation conversion efficiency (%) Example 3e 92.0 92.0 92.1 92.2 92.1 Example 3a 95.0 94.3 93.6 93.6 93.6

[0081] Under the same conditions, the 5RhPt catalyst on its own provides a conversion efficiency of 94-95% and a N.sub.2O level of 1300-1400 ppmv.

[0082] These results indicate that both catalysts demonstrated an increase in the N.sub.2O produced over the course of the first two of days. Conversion efficiency remained reasonably steady at 92-94%.

EXAMPLE 5. CATALYST PREPARATION AND TESTING

[0083] ALM alumina and zirconia catalyst supports structures in the form of solid cylinders (diameter 3.7 mm, length 3.6 mm) were prepared using the apparatus and conditions set out in Example 1 but which were fired at 1700° C. for 2 hours.

TABLE-US-00012 Alumina Zirconia D50 D10-D90 D50 D10-D90 (μm) (μm) (μm) (μm) 50.17 46.08 23.10 23.04

[0084] The support structures were impregnated with milled slurries of La.sub.0.8Ce.sub.0.2CoO.sub.3 as set out in Example 2.

[0085] The resulting catalysts were tested according to the method set out in Example 4 above (Examples 5(d)-(f)) or in combination with a precious metal catalyst (Examples 5(a)-(c)) for conversion efficiency and N.sub.2O production. Unless otherwise stated, the La.sub.0.8Ce.sub.0.2CoO.sub.3 catalyst bed is 54 mm deep and 40 mm in diameter. Unless otherwise stated, the catalysts were tested for approximately 2 days under the following process conditions: 10 Nm.sup.3h.sup.−1 air, 10% vol NH.sub.3, 200° C. preheat and 4 bara. The evolved gases were analysed and the conversion efficiency (for NH.sub.3 to NO, expressed as a percentage) and amount of N.sub.2O by-product in the product gas stream recorded. The results are given below;

TABLE-US-00013 Catalyst Support La.sub.0.8Ce.sub.0.2CoO.sub.3 Conversion PGM structure loading efficiency N.sub.2O catalyst composition (wt %) (%) (ppmv) Example 5(a) 5 ply 100% Al.sub.2O.sub.3 12 95.4 400 5RhPt Example 5(b) 5 ply 98% Al.sub.2O.sub.3 13 95.2 300 5RhPt 1% CuO 1% TiO.sub.2 Example 5(c) 1 ply 100% Al.sub.2O.sub.3 32 93.1 141 5RhPt (16 days) (16 days) Example 5(d) None 100% alumina 23 93.3 90 (Bed depth 32 mm) Example 5(e) None 100% alumina 35 95.0 12 (17 days) (17 days) Example 5(f) None Zirconium (IV) 7.8 92.5 80 Oxide (98.5%) Acros Organics Comparative None None >95 pellet 92.0 80 Comparative 1ply None >95 pellet 93.9 116 5RhPt Comparative 5ply None >95 pellet 93.0 110 5RhPt Comparative 5ply None none 94-95 1300-1400 5RhPt

[0086] These results indicate that the coated support structures are able to effectively convert ammonia to nitric oxide with remarkably low N2O levels compared to conventional PGM or pelleted catalysts.