COMPOSITION OF ALUMINIUM OXIDE AND CERIUM OXIDE WITH A PARTICULAR POROSITY PROFILE

Abstract

The present invention relates to a composition based on Al and Ce in the form of oxides (composition C1); or based on Al, Ce and La in the form of oxides (composition C2), with the following proportions: the proportion of CeO.sub.2 is between 3.0 wt % and 35.0 wt %; the proportion of La.sub.2O.sub.3 (for composition C.sub.2 only) is between 0.1 wt % and 6.0 wt %; the remainder as Al.sub.2O.sub.3; exhibiting the following porosity profile: a pore volume in the range of pores with a size of between 5 nm and 100 nm which is between 0.35 and 1.00 mL/g; anda pore volume in the range of pores with a size of between 100 nm and 1000 nm which is less than or equal to 0.15 mL/g, these pore volumes being determined by means of the mercury porosimetry technique; and the following properties: a mean size of the crystallites after calcination in air at 1100? C. for 5 hours (denoted D1100? C.-5 h) which is lower than 45.0 nm, preferably lower than 40.0 nm; a mean size of the crystallites after calcination in air at 900? C. for 2 hours (denoted D900? C.-2 h) which is lower than 25.0 nm, preferably lower than 20.0 nm, even more preferably lower than 15.0 nm; andan increase ?D of the mean size of the crystallites lower than 30.0 nm, preferably lower than 25.0 nm, ?D being calculated with the following formula: ?D=D.sub.1100?C-2h-D.sub.900C-5h; the mean size of the crystallites being obtained by XRD from the diffraction peak [111] of the cubic phase corresponding to cerium oxide, generally present at 2? between 28.0 and 30.0.

Claims

1. A composition: based on Al and Ce in a form of oxides (composition C1); or based on Al, Ce and La in a form of oxides (composition C2), with proportions as follows: a proportion of CeO.sub.2 is between 3.0 wt % and 35.0 wt %; a proportion of La.sub.2O.sub.3 (for composition C2 only) is between 0.1 wt % and 6.0 wt %; a remainder as Al.sub.2O.sub.3; wherein the composition exhibits a porosity profile as follows: a pore volume in a range of pores with a size of between 5 nm and 100 nm which is between 0.35 and 1.00 mL/g; and a pore volume in a range of pores with a size of between 100 nm and 1000 nm which is less than or equal to 0.15 mL/g, wherein these pore volumes are determined by a mercury porosimetry technique; wherein the composition is further characterized by: a mean size of crystallites after calcination in air at 1100? C. for 5 hours (denoted D1100? C.-5 h) which is lower than 45.0 nm; a mean size of crystallites after calcination in air at 900? C. for 2 hours (denoted D.sub.900? C.-2h) which is lower than 25.0 nm; and an increase ?D of the mean size of the crystallites lower than 30.0 nm, wherein ?D is calculated using formula: ?D=D.sub.1100? C.-5h?D.sub.900? C.-2h; wherein the mean size of the crystallites is obtained by X-ray diffraction (XRD) from a diffraction peak of a cubic phase corresponding to cerium oxide, present at 2? between 28.0? and 30.0?.

2. The composition according to claim 1 consisting of oxides of Ce and Al (composition C1) or consisting of oxides of Ce, Al and La (composition C2).

3. (canceled)

4. (canceled)

5. The composition according to claim 1, wherein the proportion of Al.sub.2O.sub.3 is: between 65.0 wt % and 97.0 wt % for composition C1; between 59.0 wt % and 96.9 wt % for composition C2.

6. The composition according to claim 1 comprising a crystalline phase based on alumina.

7. The composition according to claim 1 comprising a crystalline phase based on cerium oxide.

8. The composition according to claim 7 wherein the crystalline phase based on cerium oxide corresponds to pure CeO.sub.2 or to CeO.sub.2 containing lanthanum.

9. (canceled)

10. (canceled)

11. (canceled)

12. (canceled)

13. (canceled)

14. (canceled)

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. The composition according to claim 1 exhibiting a BET specific surface area of between 80 and 300 m.sup.2/g.

20. The composition according to claim 1 exhibiting a BET specific surface area after calcining in air at 1100? C. for 5 hours higher than 40 m.sup.2/g.

21. The composition according to claim 1 exhibiting a BET specific surface area after calcining in air at 1100? C. for 5 hours which is strictly lower than 82.35? (Al.sub.2O.sub.3)+11.157 m.sup.2/g wherein (Al.sub.2O.sub.3) corresponds to the proportion of Al.sub.2O.sub.3 in wt % in the composition.

22. The composition according to claim 1 exhibiting a BET specific surface area after calcining in air at 1200? C. for 5 hours of between 25 and 60 m.sup.2/g.

23. The composition according to claim 1 exhibiting a total pore volume which is greater than 0.70 mL/g; the total pore volume being determined by the mercury porosimetry technique.

24. The composition according to claim 1 exhibiting a total pore volume which is no more than 2.50 mL/g, the total pore volume being determined by the mercury porosimetry technique.

25. The composition according to claim 1 exhibiting a bulk density of between 0.35 g/cm.sup.3 and 0.90 g/cm.sup.3.

26. (canceled)

27. The composition according to claim 1 exhibiting: a D50 between 2.0 and 15.0 ?m; a bulk density between 0.35 and 0.55 g/cm.sup.3.

28. The composition according to claim 27 with a D90 between 20.0 ?m and 60.0 ?m.

29. The composition according to claim 1 exhibiting: a D50 between 15.0 and 80.0 ?m; a bulk density between 0.40 and 0.90 g/cm.sup.3.

30. The composition according to claim 29 with a D90 between 40.0 ?m and 150.0 ?m.

31. The composition according to claim 1, having a sodium content of less than or equal to 0.50% by weight, this sodium content being expressed as weight of Na.sub.2O relative to a total weight of the composition.

32. The composition according to claim 1, having a sodium content of greater than or equal to 50 ppm, this sodium content being expressed as weight of Na.sub.2O relative to a total weight of the composition.

33. The composition according to claim 1, having a sulfate content of less than or equal to 1.00% by weight, this sulfate content being expressed as weight of SO.sub.4 relative to a total weight of the composition.

34. The composition according to claim 1, having a sulfate content of greater than or equal to 50 ppm, this sulfate content being expressed as weight of SO.sub.4 relative to a total weight of the composition.

35. A catalytic composition comprising: (i) the composition according to claim 1; and (ii) optionally at least one inorganic material other than the composition; and/or (iii) optionally at least one platinum group metal (PGM).

36. (canceled)

37. (canceled)

38. The catalytic composition according to claim 35 wherein the inorganic material (ii) is selected in the group consisting of zeolites; alumina-based materials; ceria-based materials; zirconia-based materials; mixed oxides comprising oxides of cerium and zirconium; mixed oxides comprising oxides of aluminium, cerium and zirconium; and combinations thereof.

39. The catalytic composition according to claim 35 wherein the PGM is selected in the group consisting of Pt, Pd, Rh and combinations thereof.

40. The catalytic composition according to claim 35 also comprising at least one element selected in the group consisting of alkali metals and the alkaline earth metals.

41. (canceled)

42. (canceled)

43. A process for preparing a composition according to claim 1, the process comprising: (a) introducing with stirring into a tank initially containing an acidic aqueous solution with a pH of between 0.5 and 4.0: (a1)either an aqueous solution of sodium aluminate until a pH of a reaction mixture of between 8.0 and 10.0, is obtained; (a2)or, simultaneously, (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate until a pH of the reaction mixture of between 6.5 and 10.0, is obtained; so that, on conclusion of step (a), the aluminum concentration of the reaction mixture is between 0.50% and 3.0% by weight; (b) simultaneous introducing an aqueous solution of aluminum sulfate and an aqueous solution of sodium aluminate, wherein rates of introduction of which are such that a mean pH of the reaction mixture is maintained within the pH range targeted in step (a); wherein a temperature of the reaction mixture for steps (a) and (b) is at least 60? C.; (c) optionally adjusting at the end of step (b), the pH of the reaction mixture to a value of between 7.5 and 10.5; (d) filtering the reaction mixture and washing a solid recovered; (e) reducing a particle size of a dispersion in water of the solid recovered on conclusion of step (d) by applying a mechanical or ultrasonication treatment; (f) adding at least one salt of cerium to a dispersion obtained on conclusion of step (e); (g) drying a dispersion obtained on conclusion of step (f); and (h) calcinating in air a solid obtained from step (g), wherein: for composition C1 and C2, at least one salt of cerium is added in step (f) and before step (d), a proportion ? of the salt of cerium added in step (f) being between 20% and 100% wherein ? is calculated by formula: ?=amount added in step (f)/total amount of cerium added?100; and for composition C2, at least one salt of lanthanum is added before step (d) or at step (f).

44. The process according to claim 43 wherein ?=100%.

Description

EXAMPLES

Measurement of the Specific Surface Area:

[0184] For the continuation of the description, the term specific surface area means the BET specific surface area determined by nitrogen adsorption in accordance with the standard ASTM D 3663-03 established from the Brunauer-Emmett-Teller method described in the journal The Journal of the American Chemical Society, 60, 309 (1938). The specific surface area is determined automatically using, for example, a Tristar II 3020 machine from Micromeritics in accordance with the instructions recommended by the manufacturer. The samples are pretreated at 250? C. for 90 min under vacuum (for example to reach a pressure of 50 mmHg). This treatment makes it possible to remove the physisorbed volatile species at the surface (for instance H.sub.2O, etc.).

Measurement of the Porosity with Mercury (Hg Porosimetry)

[0185] The measurement is performed using a mercury porosimetry machine. In the present case, use was made of a Micromeritics Autopore IV 9520 machine equipped with a powder penetrometer, in accordance with the instructions recommended by the manufacturer. The following parameters were used: penetrometer used: 3.2 ml (Micromeritics reference: penetrometer type No. 8); capillary volume: 0.412 ml; max. pressure (head pressure): 4.68 psi; contact angle: 130?; surface tension of the mercury: 485 dynes/cm; density of the mercury: 13.5335 g/ml. At the start of the measurement, a vacuum of 50 mmHg is applied to the sample for 5 min. The equilibrium times are as follows: low pressure range (1.3-30 psi): 20 s-high pressure range (30-60 000 psi): 20 s. Prior to the measurement, the samples are treated at 200? C. for 120 min to remove the physisorbed volatile species at the surface (for instance H.sub.2O, etc). From this measurement, the pore volumes may be deduced.

[0186] X-ray diffraction: use was made of an x-ray diffractometer X'Pert Pro with a copper source (CuK?1, ?=1.5406 Angstrom).

Measurement of the Particle Size (D10, D50, D90)

[0187] To perform the particle size measurements, use is made of a Malvern Mastersizer 2000 or 3000 laser diffraction particle size analyzer (further details regarding this machine are given here: https://www.malvernpanalytical.com/fr/products/product-range/mastersizer-range/mastersizer-3000). The laser diffraction technique used consists in measuring the intensity of the light scattered during the passage of a laser beam through a sample of dispersed particles. The laser beam passes through the sample and the intensity of the scattered light is measured as a function of the angle. The diffracted intensities are then analyzed to calculate the particle size using the Mie scattering theory. The measurement makes it possible to obtain a volume-based size distribution, from which the parameters D10, D50 and D90 are deduced.

Example 1: Preparation of a Composition of Aluminum Oxide and Cerium Oxide According to the Invention (80 wt % Al.SUB.2.O.SUB.3.-20 wt % CeO.SUB.2.) According to Embodiment (a1) and with ?=100%

[0188] 157 kg of deionized water are introduced into a stirred reactor and heated to 85? C. This temperature is maintained throughout steps (a) to (c). 13.8 kg of an aluminum sulfate solution with a concentration of 8.3 wt % of alumina (Al.sub.2O.sub.3) are introduced at a flow rate of 920 g of solution/min via an introduction cannula close to the stirring rotor. At the end of the introduction, the pH in the reactor is close to 2.6 and the aluminum concentration is 0.7% by weight of alumina (Al.sub.2O.sub.3). The introduction of the aluminum sulfate solution is then stopped.

[0189] step (a): a sodium aluminate solution with a concentration of 24.9 wt % of alumina (Al.sub.2O.sub.3) and a Na.sub.2O/Al.sub.2O.sub.3 molar ratio of 1.27 is introduced at a flow rate of 690 g of solution/min via a second introduction cannula close to the stirring rotor, until a pH of 9.0 is reached. The introduction is then stopped. The aluminum concentration of the reaction mixture is then 2.10 wt % of alumina (Al.sub.2O.sub.3).

[0190] In step (b), the introduction of the aluminum sulfate solution is again started at a flow rate of 570 g of solution/min and the sodium aluminate solution is simultaneously introduced into the stirred reactor at a regulated flow rate so as to maintain the pH at a value of 9.0. This step lasts 45 minutes.

[0191] In step (c), the introduction of the aluminum sulfate solution is stopped and the addition of the sodium aluminate solution is continued at a flow rate of 320 g of solution/min until a pH of 9.5 is reached. The addition of the sodium aluminate solution is stopped.

[0192] In step (d), the reaction slurry is poured onto a vacuum filter. At the end of the filtration step, the cake is washed with deionized water at 65? C.

[0193] In step (e), the cake is redispersed in deionized water to obtain a suspension having a concentration close to 9 wt % of oxide (Al.sub.2O.sub.3). A nitric acid solution at a concentration of 69% by weight is added to the suspension so as to obtain a pH close to 6. The suspension is passed through an LME20 brand ball mill from the manufacturer Netzsch. The operating conditions of the mill are adjusted so as to obtain a D50 of 5 microns.

[0194] In step (f), a cerium nitrate solution is prepared at a concentration in the region of 29% by weight of oxide (CeO.sub.2). This solution is added with stirring to the suspension obtained from step (e) so as to obtain a CeO.sub.2/(CeO.sub.2+Al.sub.2O.sub.3) mass ratio of 20 wt %.

[0195] In step (g), the suspension obtained from step (f) is spray-dried to obtain a dried powder.

[0196] In step (h), the spray-dried powder is calcined in air at 940? C. for 2 hours (temperature increase rate of 3? C./min). The loss of mass observed during this calcination is 47% wt %.

Example 2: Preparation of a Composition of Aluminum Oxide and Cerium Oxide According to the Invention (80 wt % Al.SUB.2.O.SUB.3.-20 wt % CeO.SUB.2.) According to Embodiment (a1) and with ?=60%

[0197] 157 kg of deionized water are introduced into a stirred reactor and heated to 85? C. This temperature is maintained throughout steps (a) to (c). An acid mixture consisting of 36.3 kg of aluminum sulfate solution with a concentration of 8.3 wt % of alumina (Al.sub.2O.sub.3) and 3.2 kg of cerium nitrate solution with a concentration of 29.0 wt % of ceria (CeO.sub.2) is made up.

[0198] 13.8 kg of the acid mixture are introduced at a flow rate of 920 g of solution/min via an introduction cannula close to the stirring rotor. At the end of the introduction, the pH in the reactor is close to 2.6 and the aluminum concentration is 0.62% by weight of alumina (Al.sub.2O.sub.3). The introduction of the acid mixture is then stopped.

[0199] step (a): a sodium aluminate solution with a concentration of 24.9 wt % of alumina (Al.sub.2O.sub.3) and a Na.sub.2O/Al.sub.2O.sub.3, molar ratio of 1.27 is introduced at a flow rate of 690 g of solution/min via a second introduction cannula close to the stirring rotor, until a pH of 9.0 is reached. The introduction is then stopped.

[0200] In step (b), the introduction of the acid mixture is again started at a flow rate of 570 g of solution/min and the sodium aluminate solution is simultaneously introduced into the stirred reactor at a regulated flow rate so as to maintain the pH at a value of 9.0. This step lasts 45 minutes.

[0201] In step (c), the introduction of the acid mixture is stopped and the addition of the sodium aluminate solution is continued at a flow rate of 320 g of solution/min until a pH of 9.5 is reached. The addition of the sodium aluminate solution is stopped.

[0202] In step (d), the reaction slurry is poured onto a vacuum filter. At the end of the filtration step, the cake is washed with deionized water at 65? C.

[0203] In step (e), the cake is redispersed in deionized water to obtain a suspension having a concentration close to 9 wt % of oxide (Al.sub.2O.sub.3). A nitric acid solution at a concentration of 69% by weight is added to the suspension so as to obtain a pH close to 6. The suspension is passed through an LME20 brand ball mill from the manufacturer Netzsch. The operating conditions of the mill are adjusted so as to obtain a D50 of 5.1 microns.

[0204] In step (f), a cerium nitrate solution is prepared at a concentration of 29% by weight of oxide (CeO.sub.2). This solution is added with stirring to the suspension obtained from step (e) so as to obtain a CeO.sub.2/(CeO.sub.2+Al.sub.2O.sub.3) mass ratio of 20 wt %.

[0205] In step (g), the suspension obtained from step (f) is spray-dried to obtain a dried powder.

[0206] In step (h), the spray-dried powder is calcined in air at 940? C. for 2 hours (temperature increase rate of 3? C./min).

Comparative Example 3: Preparation of a Composition of Aluminum Oxide and Cerium Oxide Containing 20% of Cerium Oxide (80% Al.SUB.2.O.SUB.3.-20% CeO.SUB.2.) and with ?=0%

[0207] 157 kg of deionized water are introduced into a stirred reactor and heated to 85? C. This temperature is maintained throughout steps (a) to (c). An acid mixture consisting of 31.6 kg of aluminum sulfate solution with a concentration of 8.3 wt % of alumina (Al.sub.2O.sub.3) and 7.9 kg of cerium nitrate solution with a concentration of 29.0 wt % of ceria (CeO.sub.2) is made up.

[0208] 13.8 kg of the acid mixture are introduced at a flow rate of 920 g of solution/min via an introduction cannula close to the stirring rotor. At the end of the introduction, the pH in the reactor is close to 2.7 and the aluminum concentration is 0.54% by weight of alumina (Al.sub.2O.sub.3). The introduction of the acid mixture is then stopped.

[0209] step (a): a sodium aluminate solution with a concentration of 24.9 wt % of alumina (Al.sub.2O.sub.3) and a Na.sub.2O/Al.sub.2O.sub.3 molar ratio of 1.27 is introduced at a flow rate of 690 g of solution/min via a second introduction cannula close to the stirring rotor, until a pH of 9.0 is reached. The introduction is then stopped. The aluminum concentration of the reaction mixture is then 1.60 wt % of alumina (Al.sub.2O.sub.3).

[0210] In step (b), the introduction of the acid mixture is again started at a flow rate of 570 g of solution/min and the sodium aluminate solution is simultaneously introduced into the stirred reactor at a regulated flow rate so as to maintain the pH at a value of 9.0. This step lasts 45 minutes.

[0211] In step (c), the introduction of the acid mixture is stopped and the addition of the sodium aluminate solution is continued at a flow rate of 320 g of solution/min until a pH of 9.5 is reached. The addition of the sodium aluminate solution is stopped.

[0212] In step (d), the reaction slurry is poured onto a vacuum filter. At the end of the filtration step, the cake is washed with deionized water at 65? C.

[0213] In step (e), the cake is redispersed in deionized water to obtain a suspension having a concentration close to 9 wt % of oxide (Al.sub.2O.sub.3). A nitric acid solution at a concentration of 69% by weight is added to the suspension so as to obtain a pH close to 6. The suspension is passed through an LME20 brand ball mill from the manufacturer Netzsch. The operating conditions of the mill are adjusted so as to obtain a D50 of 5.4 microns.

[0214] In next step, the suspension obtained from step (e) is spray-dried to obtain a dried powder.

[0215] In next step, the spray-dried powder is calcined in air at 940? C. for 2 hours (temperature increase rate of 3? C./min). The loss of mass observed during this calcination is 46.3 wt %.

TABLE-US-00001 TABLE I porous volumes D.sub.900? C.-2 h (nm) ?D bulk BET (Hg porosimetry) D.sub.1100? C.-5 h (nm) (nm) density Ex. (m.sup.2/g) (mL/g) by XRD by XRD (g/cm.sup.3) 1 80% fresh: PV.sub.5-100 = 0.46 11 23 0.62 Al.sub.2O.sub.3 ? 20% 129 PV.sub.100-1000 = 0.03 34 CeO.sub.2 1100? C./ TPV = 1.05 ? = 100% 5 h: 50 2 80% fresh: PV.sub.5-100 = 0.49 14 24 0.54 Al.sub.2O.sub.3 ? 20% 141 PV.sub.100-1000 = 0.03 38 CeO.sub.2 1100? C./ TPV = 1.06 ? = 60% 5 h: 53 Cex 80% fresh: PV.sub.5-100 = 0.56 28 21 0.48 3 Al.sub.2O.sub.3 ? 20% 158 PV.sub.100-1000 = 0.02 49 CeO.sub.2 1100? C./ TPV = 1.11 ? = 0% 5 h: 59

TABLE-US-00002 TABLE II D10 D50 D90 Na.sub.2O SO.sub.4 Ex. (?m) (?m) (?m) (ppm) (ppm) 1 0.9 10.2 24.6 410 690 2 1.3 14.1 30.1 360 940 Cex3 1.5 14.6 32.3 160 7550

[0216] As is visible, the process of the invention makes it possible to obtain a composition with a low crystallite size at 900? C. and 1100? C.