ZIRCONIA-BASED COMPOSITIONS FOR USE AS THREE WAY CATALYSTS

Abstract

This invention relates to a cerium-zirconium based mixed oxide having: (a) a Ce:Zr molar ratio of 1 or less, and (b) a cerium oxide content of 10-50% by weight, wherein the composition has (i) a surface area of at least 18 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.11 cm.sup.3/g, after ageing at 1100? C. in an air atmosphere for 6 hours, and (ii) a surface area of at least 42 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.31 cm.sup.3/g, after ageing at 1000? C. in an air atmosphere for 4 hours. The invention also relates to a catalytic system comprising the cerium-zirconium based mixed oxide, as well as to a process 10 for treating an exhaust gas from a vehicle engine comprising contacting the exhaust gas with the cerium-zirconium based mixed oxide. In addition, the invention relates to a process for preparing a cerium-zirconium based mixed hydroxide or mixed oxide as claimed in any preceding claim, the process comprising the steps of: (a) dissolving a zirconium salt in an aqueous acid, (b) adding one or more complexing agents to the resulting solution, the one or more complexing agents being an organic compound comprising at least one of the following functional groups: an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group, (c) heating the solution or sol formed in step (b), (d) adding a cerium salt, and adding a sulphating agent either before or after the addition of the cerium salt, and (e) adding a base to form a cerium-zirconium based mixed hydroxide.

Claims

1. A cerium-zirconium based mixed oxide having: (a) a Ce:Zr molar ratio of 1 or less, and (b) a cerium oxide content of 10-50% by weight, wherein the composition has (i) a surface area of at least 18 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.11 cm.sup.3/g, after ageing at 1100? C. in an air atmosphere for 6 hours, and (ii) a surface area of at least 42 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.31 cm.sup.3/g, after ageing at 1000? C. in an air atmosphere for 4 hours.

2. A cerium-zirconium based mixed oxide as claimed in claim 1 having a surface area of at least 33 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.20 cm.sup.3/g, after ageing at 1050? C. in an air atmosphere for 2 hours.

3. A cerium-zirconium based mixed oxide as claimed in claim 1 having a surface area of at least 48 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.29 cm.sup.3/g, after ageing at 950? C. in an air atmosphere for 2 hours.

4. A cerium-zirconium based mixed oxide as claimed in claim 1 having a surface area of at least 18 m.sup.2/g, and a total pore volume as measured by N.sub.2 physisorption of at least 0.11 cm.sup.3/g, after hydrothermal ageing at 1100? C. for 12 hours in an air atmosphere comprising 10% by volume of water.

5. A cerium-zirconium based mixed oxide as claimed in claim 1, comprising one or more rare earth oxides other than cerium oxide in an amount of 1-15% by weight individually, and 1-20% by weight in total.

6. A cerium-zirconium based mixed oxide as claimed in claim 1, wherein the total amount of cerium oxide and zirconium oxide is at least 80% by weight.

7. A catalytic system comprising a cerium-zirconium based mixed oxide as claimed in claim 1.

8. A process for treating an exhaust gas from a vehicle engine comprising contacting the exhaust gas with a cerium-zirconium based mixed oxide as claimed in claim 1.

9. A process for preparing a cerium-zirconium based mixed hydroxide or the mixed oxide as claimed in claim 1, the process comprising the steps of: (a) dissolving a zirconium salt in an aqueous acid, (b) adding one or more complexing agents to the resulting solution, the one or more complexing agents being an organic compound comprising at least one of the following functional groups: an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group, (c) heating the solution or sol formed in step (b), (d) adding a cerium salt, and adding a sulphating agent either before or after the addition of the cerium salt, and (e) adding a base to form a cerium-zirconium based mixed hydroxide.

10. A process as claimed in claim 9, wherein the zirconium salt is zirconium basic carbonate or zirconium hydroxide.

11. A process as claimed in claim 9, wherein the aqueous acid is hydrochloric acid, sulphuric acid, nitric acid or acetic acid.

12. A process as claimed in claim 11, wherein the aqueous acid is nitric acid.

13. A process as claimed in claim 12, wherein in step (a) the molar ratio of zirconium ions to nitrate ions in the solution or sol is 1:0.8 to 1:1.5.

14. A process as claimed in claim 9, wherein the complexing agent is an alpha hydroxy carboxylic acid.

15. A process as claimed in claim 14, wherein the alpha hydroxy carboxylic acid is mandelic acid.

16. A process as claimed in claim 9, wherein in step (a) the solution is heated to at least 40? C.

17. A process as claimed in claim 9, wherein in step (c) the solution or sol is heated to a temperature of 80-100? C.

18. A process as claimed claim 9, wherein the sulphating agent is sulphuric acid.

19. A process as claimed in claim 18, wherein in step (d) the solution is allowed to cool, or cooled, to a temperature less than 40? C. before adding the sulphuric acid.

20. A process as claimed in claim 9, wherein step (d) additionally comprises adding an aqueous electrolyte.

21. A process as claimed in claim 20, wherein the aqueous electrolyte is fully or partially neutralised hydrochloric acid, nitric acid or acetic acid.

22. A process as claimed in claim 9, wherein step (d) additionally comprises adding one or more salts of: silica, aluminium, strontium, a transition metal or a rare earth element including yttrium.

23. A process as claimed in claim 9, wherein step (e) is carried out at a temperature of from ?5? C. to 95? C.

24. A process as claimed in claim 9, wherein the cerium-zirconium based mixed hydroxide or mixed oxide comprises 10-50% by weight of cerium oxide and at least 20% by weight of zirconium oxide.

Description

[0142] FIG. 1 shows air aged (1100? C./6 hr) porosity data for the compositions of Preparative Examples 6, 9 and 11-14,

[0143] FIG. 2 shows air aged (1100? C./6 hr) incremental pore volume data for the compositions of Preparative Examples 6, 9 and 11-14,

[0144] FIG. 3 shows air aged (1100? C./6 hr) incremental pore volume data for the compositions of Preparative Examples 6, 9 and 11-14,

[0145] FIG. 4 shows H.sub.2 pulse data for Preparative Examples 3, 5 and 8 and Comparative Example 1,

[0146] FIG. 5 shows O.sub.2 pulse data for Preparative Examples 3, 5 and 8 and Comparative Example 1.

[0147] The invention will now be described by way of example with reference to the following Examples.

COMPARATIVE EXAMPLE 140CE/5LA/5PR

[0148] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide.

[0149] 118.8 g of zirconium basic carbonate (ZBC, 42.1% ZrO.sub.2) was dissolved in 126.9 g of nitric acid. This solution was then heated to 60? C. 119.5 g of water was then added. In this example, a complexing agent was not added to the solution. This solution was then heated to boiling and boiled for 2 hours.

[0150] After cooling to room temperature 156.3 g cerium (Ill) nitrate (25.6% CeO.sub.2), 23.3 g lanthanum nitrate (21.5% La.sub.2O.sub.3), 25.6 g praseodymium nitrate (19.5% Pr.sub.6O.sub.11) solutions and 355.6 g of de-ionised water were added. 98.7 g of sulphuric acid was then added.

[0151] A 10 wt % aqueous solution of NaOH was then added dropwise to the mixture with stirring. Stirring and addition of the 10 wt % aqueous solution of NaOH was continued until the pH became approximately 8. At this point, a 28 wt % aqueous solution of NaOH was substituted for the 10 wt % solution and the dropwise addition was continued with stirring until the pH became approximately 13.

[0152] The resulting slurry was then filtered. The filter cake was washed with deionised water at 60? C. The cake was then re-dispersed and then adjusted to pH 8.0 with a 30 wt % solution of nitric acid. The resulting slurry was then filtered. The filter cake was washed with deionised water at 60? C.

[0153] The final filter cake was heated in an autoclave to 127? C. for 1 hour. The resulting suspension was then filtered and the resulting filter cake was calcined in air for 3 hours at 930? C., and milled, to give a cerium-zirconium based mixed oxide.

PREPARATIVE EXAMPLE 240CE/5LA/5PR

[0154] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide.

[0155] 119.9 g of zirconium basic carbonate (ZBC, 41.7% ZrO.sub.2) was dissolved in 126.9 g of nitric acid. This solution was then heated to 60? C. 3.0 g of soluble starch was added to the solution, along with 108.0 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0156] After cooling to room temperature 156.3 g cerium (III) nitrate (25.6% CeO.sub.2), 23.3 g lanthanum nitrate (21.5% La.sub.2O.sub.3), 25.6 g praseodymium nitrate (19.5% Pr.sub.6O.sub.11) solutions and 355.6 g of de-ionised water were added. 98.7 g of sulphuric acid was then added.

[0157] The same procedure as Preparative Example 3 below was then followed, up to the formation of the final filter cake.

[0158] The final filter cake was calcined in air for 2 hours at 850? C. and then milled.

PREPARATIVE EXAMPLE 340CE/5LA/5PR

[0159] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide.

[0160] 118.8 g of zirconium basic carbonate (ZBC, 42.1% ZrO.sub.2) was dissolved in 126.9 g of nitric acid. This solution was then heated to 60? C. 0.92 g of mandelic acid was added to the solution, along with 110.2 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0161] After cooling to room temperature 161.9 g cerium (III) nitrate (24.7% CeO.sub.2), 24.2 g lanthanum nitrate (20.7% La.sub.2O.sub.3), 23.4 g praseodymium nitrate (21.4% Pr.sub.6O.sub.11) solutions and 362.9 g of de-ionised water were added. 98.7 g of sulphuric acid was then added.

[0162] The pH of the solution was then adjusted to pH 13.0 with a dilute sodium hydroxide solution. 45.2 g of a 35 wt % hydrogen peroxide solution was then added.

[0163] The resulting slurry was then filtered. The filter cake was washed with deionised water at 60? C. The cake was then re-dispersed and then adjusted to pH 8.0 with a 30 wt % solution of nitric acid. The resulting slurry was then filtered. The filter cake was washed with deionised water at 60? C.

[0164] The precipitate was calcined in air for 3 hours at 920? C. and milled.

PREPARATIVE EXAMPLES 4A AND 4B40CE/5LA/5PR

[0165] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide.

[0166] The same procedure as Preparative Example 3 was followed, except that 124.4 g of nitric acid was used to dissolve the ZBC, and 96.7 g of sulphuric acid was subsequently added. Preparative example 4a was thus prepared.

[0167] Preparative example 4b was prepared by subjecting 4a to an additional milling step.

PREPARATIVE EXAMPLE 540CE/5LA/5PR

[0168] The same procedure as Preparative Example 3 was followed, up to the formation of the final filter cake.

[0169] The final filter cake was heated in an autoclave to 127? C. for 1 hour. The resulting suspension was then dried at 110? C. in a static air oven. The solid was calcined in air for 3 hours at 930? C. and milled.

PREPARATIVE EXAMPLE 640CE/5LA/5PR

[0170] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide.

[0171] 117.1 g of zirconium basic carbonate (ZBC, 42.7% ZrO.sub.2) was dissolved in 120.6 g of nitric acid. This solution was then heated to 60? C. 0.92 g of mandelic acid was added to the solution, along with 118.5 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0172] After cooling to room temperature, 296.5 g of sodium nitrate solution, 233.1 g of de-ionised water and 98.7 g of sulphuric acid was then added. This was followed by 161.9 g cerium (III) nitrate (24.7% CeO.sub.2), 22.8 g lanthanum nitrate (21.9% La.sub.2O.sub.3) and 25.6 g praseodymium nitrate (19.5% Pr.sub.6O.sub.11) solutions.

[0173] The same procedure as Preparative Example 3 was then followed, up to the formation of the final filter cake.

[0174] The final filter cake was calcined in air for 3 hours at 910? C. and then milled.

COMPARATIVE EXAMPLE 740CE/5LA/5PR

[0175] Mixed solution A was prepared by combining 241.5 g of ZOC (20.7% ZrO.sub.2), 156.3 g cerium (III) nitrate (25.6% CeO.sub.2), 23.3 g lanthanum nitrate (21.5% La.sub.2O.sub.3), 26.7 g praseodymium nitrate (18.8% Pr.sub.6O.sub.11), 121.0 g of sulphuric acid and 98.0 g of de-ionised water.

[0176] A reaction vessel was charged with 765 g of de-ionised water, at room temperature. To this was added 45.2 g of 35% hydrogen peroxide solution, and the pH adjusted to ?9.75 with sodium hydroxide solution.

[0177] Mixed solution A was titrated against 27% sodium hydroxide solution, into the reaction vessel, at such a rate as to complete the addition over ?80 mins whilst maintaining a system pH of 9.5-10. Following this, the pH was increased to 13 with further addition of 27% sodium hydroxide. In this example, a complexing agent was not added to the solution.

[0178] The resulting slurry was then filtered. The filter cake was washed with deionised water at 60? C. The cake was then re-dispersed and then adjusted to pH 8.0 with a 30 wt % solution of nitric acid. The resulting slurry was then filtered. The filter cake was washed with deionised water at 60? C.

[0179] The precipitate was hydrothermally treated at 127? C. for 1 hour. The resulting suspension was then dried at 110? C. in a static air oven and calcined in air for 2 hours at 800? C. and milled.

COMPARATIVE EXAMPLE 840CE/5LA/5PR

[0180] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide. The sample was prepared according to patent EP1444036B1 (ie no complexing agent).

PREPARATIVE EXAMPLE 940CE/5LA/5PR

[0181] This was prepared in the same way as Preparative Example 6, except that 126.9 g of nitric acid was used to dissolve the ZBC. The precipitate was heated in an autoclave to 127? C. for 1 hour. The resulting suspension was then filtered and the resulting filter cake was calcined in air for 3 hours at 930? C. and milled.

COMPARATIVE EXAMPLE 1040CE/5LA/5PR

[0182] A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. ?50% by weight) zirconium dioxide. A zirconium basic sulphate precursor was prepared according to the following reference [S. M. Flask, I. A. Sheka, Interaction of zirconium oxychloride and sulfuric acid in aqueous solution, Russ. J. Inorg. Chem. 1969, 17 (1), 60-65]. A sample of this precursor containing 50 g ZrO.sub.2 equivalent was mixed with 161.9 g cerium (III) nitrate (24.7% CeO.sub.2), 22.8 g lanthanum nitrate (21.9% La.sub.2O.sub.3) and 25.6 g praseodymium nitrate (19.5% Pr.sub.6O.sub.11) solutions. In this example, a complexing agent was not added to the solution. The pH of the solution was then adjusted to pH 13.0 with 27% sodium hydroxide solution. 45.2 g of a 35 wt % hydrogen peroxide solution was then added. The sample was calcined in air for 2 hours at 600? C.

PREPARATIVE EXAMPLE 1145CE/5LA/5Y

[0183] A sample was prepared according to the composition defined above, i.e. 45% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight yttrium oxide and the remainder (i.e. ?45% by weight) zirconium dioxide.

[0184] 109.0 g of zirconium basic carbonate (ZBC, 41.3% ZrO.sub.2) was dissolved in 107.4 g of nitric acid. This solution was then heated to 60? C. 0.83 g of mandelic acid was added to the solution, along with 104.2 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0185] After cooling to room temperature, 266.8 g of sodium nitrate solution, 248.3 g of de-ionised water and 88.8 g of sulphuric acid was then added. This was followed by 182.2 g cerium (III) nitrate (24.7% CeO.sub.2), 22.8 g lanthanum nitrate (21.9% La.sub.2O.sub.3) and 26.6 g yttrium nitrate (18.8% Y.sub.2O.sub.3) solutions.

[0186] The same procedure as Preparative Example 3 was then followed, up to the formation of the final filter cake.

[0187] The final filter cake was hydrothermally treated at 127? C. for 1 hour. The resulting suspension was then dried at 110? C. in a static air oven and calcined in air for 3 hours at 900? C. and then milled.

PREPARATIVE EXAMPLE 1245CE/5LA/5Y

[0188] This was prepared in the same way as Preparative Example 10, except that 116.8 g of nitric acid was used to dissolve the ZBC, and 1.07 g of mandelic was added. The final filter cake was not hydrothermally treated. It was calcined in air for 3 hours at 900? C. and then milled.

PREPARATIVE EXAMPLE 1335.5CE/5.5LA

[0189] A sample was prepared according to the composition defined above, i.e. 35.5% by weight cerium (IV) oxide, 5.5% by weight lanthanum oxide and the remainder (i.e. ?59% by weight) zirconium dioxide.

[0190] 142.9 g of zirconium basic carbonate (ZBC, 41.3% ZrO.sub.2) was dissolved in 149.8 g of nitric acid. This solution was then heated to 60? C. 1.09 g of mandelic acid was added to the solution, along with 127.6 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0191] After cooling to room temperature 138.7 g cerium (Ill) nitrate (25.6% CeO.sub.2), 25.6 g lanthanum nitrate (21.5% La.sub.2O.sub.3) solutions and 306.7 g of de-ionised water were added. 98.7 g of sulphuric acid was then added.

[0192] The same procedure as Preparative Example 3 was then followed, up to the formation of the final filter cake.

[0193] The final filter cake was calcined in air for 3 hours at 900? C. and then milled.

PREPARATIVE EXAMPLE 1425CE/3.5LA/4Y

[0194] A sample was prepared according to the composition defined above, i.e. 25% by weight cerium (IV) oxide, 3.5% by weight lanthanum oxide, 4% by weight yttrium oxide and the remainder (i.e. ?67.5% by weight) zirconium dioxide.

[0195] 163.4 g of zirconium basic carbonate (ZBC, 41.3% ZrO.sub.2) was dissolved in 188.5 g of nitric acid. This solution was then heated to 60? C. 0.54 g of mandelic acid was added to the solution, along with 129.7 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0196] After cooling to room temperature, 400.3 g of sodium nitrate solution, 444.4 g of de-ionised water and 133.3 g of sulphuric acid was then added. This was followed by 101.2 g cerium (Ill) nitrate (24.7% CeO.sub.2), 16.0 g lanthanum nitrate (21.9% La.sub.2O.sub.3) and 21.3 g yttrium nitrate (18.8% Y.sub.2O.sub.3) solutions.

[0197] The same procedure as Preparative Example 3 was then followed, up to the formation of the final filter cake.

[0198] The final filter cake was calcined in air for 3 hours at 900? C. and then milled.

PREPARATIVE EXAMPLE 1520CE/1.5LA/5ND

[0199] A sample was prepared according to the composition defined above, i.e. 20% by weight cerium (IV) oxide, 1.5% by weight lanthanum oxide, 5% by weight neodymium oxide and the remainder (i.e. ?73.5% by weight) zirconium dioxide.

[0200] 178.0 g of zirconium basic carbonate (ZBC, 41.3% ZrO.sub.2) was dissolved in 205.3 g of nitric acid. This solution was then heated to 60? C. 0.59 g of mandelic acid was added to the solution, along with 141.1 g of water. This solution was then heated to boiling and boiled for 2 hours.

[0201] After cooling to room temperature, 491.1 g of sodium nitrate solution, 302.3 g of de-ionised water and 145.1 g of sulphuric acid was then added. This was followed by 81.0 g cerium (Ill) nitrate (24.7% CeO.sub.2), 6.9 g lanthanum nitrate (21.9% La.sub.2O.sub.3) and 23.5 g neodymium nitrate (21.3% Nd.sub.2O.sub.3) solutions.

[0202] The same procedure as Preparative Example 3 was then followed, up to the formation of the final filter cake.

[0203] The final filter cake was calcined in air for 3 hours at 900? C. and then milled.

EXAMPLE A

[0204] The samples prepared above were analysed as prepared (ie Fresh) for their surface area (SA), total pore volume (TPV, by N.sub.2 physisorption), crystallite size (CS, by applying the Scherrer equation to the relevant peak in its XRD scan) and average pore diameter (APD, by N.sub.2 physisorption). This data is shown in Table 1 below.

[0205] The results for Preparative Examples 6, 9 and 12-15 aged in air at 1100? C. for 6 hours are shown graphically in FIG. 1. The dV/dDiameter measurement on the y-axis of this graph is effectively a measurement of the number of pores of a particular size, with the average pore diameter shown along the x-axis. This data shows the improved porosity of the compositions of the invention after ageing in air at 1100? C. for 6 hours. FIG. 2 shows the incremental pore volume for these samples, and FIG. 3 shows the cumulative pore volume. FIGS. 4 and 5 show H.sub.2 and O.sub.2 pulse data respectively for Preparative Examples 3 and 5, as well as Comparative Examples 8 and 10. In FIG. 5, the O.sub.2 pulse data for Comparative Example 10 is zero at both ageing conditions.

TABLE-US-00001 TABLE 1 Fresh 950/2 (air) 1000/4 (air) SA TPV APD CS SA TPV CS SA TPV APD CS Sample (m.sup.2/g) (cm.sup.3/g) (nm) (nm) (m.sup.2/g) (cm.sup.3/g) (nm) (m.sup.2/g) (cm.sup.3/g) (nm) (nm) Comparative Example 1 74 0.35 18.9 7.7 51 0.29 22.6 10 Comparative Example 8 88 0.38 17.3 5 64 0.33 7 48 0.29 24.5 9 Comparative Example 10 71 0.08 4.6 5.5 15 0.04 10.2 11 Comparative Example 7 70 0.35 20.1 5.6 49 0.30 8 43 0.30 27.5 9.6 Preparative Example 3 77 0.34 17.9 7.9 65 0.32 8.5 57 0.33 22.8 10 Preparative Example 4b 83 0.46 22.0 8.1 73 0.42 8.9 57 0.40 28.2 10 Preparative Example 4a 83 0.52 24.9 8.1 62 0.41 26.2 11 Preparative Example 5 82 0.39 19.1 8.1 64 0.37 9.2 55 0.33 24.3 11 Preparative Example 6 85 0.50 23.5 7.9 61 0.40 26.5 10 Preparative Example 9 79 0.40 20.5 7.6 Preparative Example 2 87 0.42 23.4 6.3 Preparative Example 14 70 0.40 22.8 10 Preparative Example 15 76 0.45 23.8 12 Preparative Example 13 82 0.41 19.9 7.3 Preparative Example 11 90 0.54 24.0 7.6 57 0.38 26.3 10 Preparative Example 12 82 0.44 21.4 7.2 1050/2 (air) 1100/6 (air) 1100/12 (HT) SA TPV CS SA TPV APD CS SA TPV APD CS Sample (m.sup.2/g) (cm.sup.3/g) (nm) (m.sup.2/g) (cm.sup.3/g) (nm) (nm) (m.sup.2/g) (cm.sup.3/g) (nm) (nm) Comparative Example 1 24 0.14 23.9 19 Comparative Example 8 39 0.24 11 17 0.13 31.3 17 19 0.15 31.9 17 Comparative Example 10 3.5 0.01 9.7 19 3.6 0.01 11.8 19 Comparative Example 7 34 0.23 12 21 0.15 28.7 18 21 0.15 28.6 17 Preparative Example 3 41 0.22 13 24 0.13 21.8 19 23 0.13 23.1 18 Preparative Example 4b 41 0.25 13 23 0.15 25.9 20 20 0.14 27.6 19 Preparative Example 4a 22 0.15 28.3 20 20 0.14 26.9 19 Preparative Example 5 42 0.29 13 21 0.14 27.0 21 21 0.16 29.1 19 Preparative Example 6 23 0.20 35.3 20 21 0.17 31.2 20 Preparative Example 9 28 0.21 30.1 18 Preparative Example 2 20 0.12 23.4 24 Preparative Example 14 21 0.17 33.2 22 20 0.15 29.9 22 Preparative Example 15 22 0.17 31.7 22 Preparative Example 13 23 0.17 29.9 12* Preparative Example 11 23 0.18 30.6 21 25 0.16 26.4 19 Preparative Example 12 28 0.22 32.2 19 22 0.20 36.6 20