Method for producing catalysts of formula my(Ce1-xLxO2-x/2)1-y for the use thereof in the reverse water-gas shift reaction and partial oxidation of methane into synthesis gas by means of the method of combustion in solution

Abstract

The invention relates to a method for producing catalysts by the method of combustion in solution, to the catalysts produced by said method, and to the particular use thereof in the reverse water-gas shift reaction and in the partial oxidation of the methane into synthesis gas. Therefore, it is understood that the present invention pertains to the area of the green industry aimed at the reduction of CO.sub.2 on the planet.

Claims

1. A process for the obtainment of a cerium oxide partially substituted with a lanthanide in the positions of the Ce, and nanoparticles of a precious or semi-precious metal selected from the groups 8, 9, 10 and 11 of the periodic table of the elements deposited in metallic form on the surface of the cerium oxide, which is a compound of formula:
M.sub.y(Ce.sub.1-xL.sub.xO.sub.2-x/2).sub.1-y wherein M is a metal selected from Ni, Ru, Rh, Pd, Ir, Pt, Ag, Au and Cu, which is in metallic state; wherein x is different to 0, and less than or equal to 0.4 and y=0.001-0.6, and wherein L is a lanthanide selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, characterised in that it comprises the following steps: a) adding in the minimum essential amount of water, stoichiometric amounts of Cerium nitrate, Water soluble salt of a metal selected from the group consisting of Ni, Ru, Rh, Pd, Ir, Pt, Ag, Au and Cu, and a nitrate of a lanthanide selected from the group consisting of La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and adding to the previous solution a fuel in a molar ratio of between 0.7 and 1.0 with respect to the total amount of nitrates, and stirring at room temperature till complete dissolution, and b) heating the solution obtained in step (a) at a temperature between 200° C. and 600° C. in a controlled atmosphere, thereby preventing water present in the solution from evaporating completely.

2. The process according to claim 1, wherein the water soluble salt used in step (a) is Ni(NO.sub.3).sub.2.6H.sub.2O and the metal is Ni.

3. The process according to claim 1, wherein the water soluble salt used in step (a) is Cu(NO.sub.3).sub.2.6H.sub.2O and the metal is Cu.

4. The process according to claim 1, wherein the Pt water soluble salt used in step (a) is a salt selected from Tetraammineplatinum (II) Hydroxide Hydrate ((NH.sub.3).sub.4Pt(OH).sub.2.xH.sub.2O) and Tetraammineplatinum(II) nitrate (Pt(NH.sub.3)4(NO.sub.3).sub.2).

5. The process according to claim 1, characterized in that the lanthanide is Gd.

6. The process according to claim 1, characterized in that x has a value between 0.05 and 0.2; and y has a value between 0.001 and 0.15.

7. The process according to claim 1, characterized in that the lanthanide is La.

8. The process according to claim 7, characterized in that x has a value between 0.05 and 0.2; and y has a value between 0.001 and 0.15.

9. The process according to claim 1, characterized in that the lanthanide is Sm.

10. The process according to claim 9, characterized in that x has a value between 0.05 and 0.2 and y has a value between 0.001 and 0.15.

11. The process according to claim 1, wherein the fuel use in step (a) is selected from glycine, urea, citric acid and a combination thereof.

12. The process according to claim 11, wherein the fuel use in step (a) is glycine.

13. The process according to claim 1, characterised in that step (c) is performed at a temperature between 200° C. and 500° C.

14. A compound of a cerium oxide partially substituted with a lanthanide in the positions of the Ce, and nanoparticles selected from Pt and Cu in metallic form deposited on the surface of the cerium oxide, which is a compound of formula:
M.sub.y(Ce.sub.1-xL.sub.xO.sub.2-x/2).sub.1-y wherein M is a metal selected from Pt and Cu, which is in metallic state, and wherein the formula is Cu.sub.y(Ce.sub.1-xL.sub.xO.sub.2-x/2).sub.1-y and Pt.sub.y(Ce.sub.1-xL.sub.xO.sub.2-x/2).sub.1-y respectively; wherein x is different to 0, and less than or equal to 0.4 and y=0.005-0.6, if M is Cu; and wherein x is different to 0, and less than or equal to 0.4 and y=0.001-0.6, if M is Pt; L is a lanthanide selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and wherein the compound presents a porosity percent between 70% and 95% and a pore mean diameter between 0.5 μm and 5 μm.

15. The compound according to claim 14, wherein the lanthanide is Gd.

16. The compound according to claim 15, characterized in that x has a value of between 0.05 and 0.2; and y has a value of between 0.001 and 0.15.

17. The compound according to claim 14, wherein the lanthanide is La.

18. The compound according to claim 17, characterized in that x has a value of between 0.05 and 0.2; and y has a value of between 0.001 and 0.15.

19. The compound according to claim 14, wherein the lanthanide is Sm.

20. The compound according to claim 19, characterized in that x has a value of between 0.05 and 0.2; and y has a value of between 0.001 and 0.15.

21. The compound according to claim 14, characterized in that the compound is selected from Ni.sub.0.1(Ce.sub.0.96Gd.sub.0.04O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9, and Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. SEM micrograph of the catalyst Ni.sub.0.04(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.96 after synthesis by the method of combustion in solution

(2) FIG. 2. Represents the conversion percentage of CO.sub.2 throughout the reaction time (reaction RWGS) for the catalyst Ni.sub.0.04(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.96.

(3) FIG. 3. Pore size distribution of the compounds of formula Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9Nd.sub.0.1O.sub.1.95).sub.0.9 and Ni.sub.0.1(Ce.sub.0.9Sm.sub.0.1O.sub.1.96).sub.0.9.

EXAMPLES

(4) The invention will be illustrated below by assays carried out by the inventors, which show the improvement in the synthesis conditions and catalytic activity.

Example 1

(5) In a beaker, 1.051 grams glycine, 2.606 grams nitrate cerium ((Ce(NO.sub.3).sub.3.6H.sub.2O), 0.229 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 25 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cerium and gadolinium mixed oxide is formed. This material is designated Ce.sub.0.9Gd.sub.0.1O.sub.1.95.

Example 2

(6) In a beaker, 1.044 grams glycine, 0.039 grams nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O), 2.553 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.224 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 25 mL of distilled water is added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed with a microporous morphology and constituted by metallic nickel nanoparticles supported on a cerium and gadolinium mixed oxide. This material is designated (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98.

Example 3

(7) In a beaker, 1.037 grams glycine, 0.078 grams nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O), 2.501 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.220 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 25 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed with a microporous morphology and constituted by metallic nickel nanoparticles supported on a cerium and gadolinium mixed oxide. This material is designated (Ni).sub.0.04(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.96. Its SEM micrograph (obtained by Scanning Electron Microscopy) is shown, by way of example in FIG. 1.

Example 4

(8) In a beaker, 1.016 grams glycine, 0.194 grams nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O), 2.345 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.206 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 25 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed, constituted by metallic nickel nanoparticles supported on a cerium and gadolinium mixed oxide. This material is designated (Ni).sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.98).sub.0.9.

Example 5

(9) In a beaker, 1.016 grams glycine, 0.194 grams nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O), 2.345 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.260 grams lanthanum nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 25 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed with a microporous morphology and constituted by metallic nickel nanoparticles supported on a cerium and lanthanum mixed oxide. This material is designated (Ni).sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9.

Example 6

(10) In a beaker, 1.0473 grams glycine, 0.0194 grams nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O), 2.5793 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.2979 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 25 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed with a microporous morphology and constituted by metallic nickel nanoparticles supported on a cerium and gadolinium mixed oxide. This material is designated (Ni).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.99.

Example 7

(11) In a beaker, 1.5620 grams glycine, 0.0189 grams copper nitrate (Cu(NO.sub.3).sub.2.6H.sub.2O), 3.869 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.4470 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed. Then 37 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed with a microporous morphology and constituted by metallic nickel nanoparticles supported on a cerium and gadolinium mixed oxide. This material is designated (Cu).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.99.

Example 8

(12) In a beaker, 1.5620 grams glycine, 0.0297 grams Tetraammineplatinum (II) Hydroxide Hydrate ((NH.sub.3).sub.4Pt(OH).sub.2.xH.sub.2O), 3.8690 grams cerium nitrate (Ce(NO.sub.3).sub.3.6H.sub.2O), 0.4470 grams gadolinium nitrate (Gd(NO.sub.3).sub.3.6H.sub.2O) are mixed.

(13) Then 37 mL of distilled water are added to dissolve the above-mentioned compounds. The beaker with the mixture of the above reagents is placed on a heating plate with another inverted larger beaker covering the former and with aluminium foil on its base. The temperature of the plate is then increased to 300 degrees Celsius and, after waiting a few minutes until the synthesis by combustion in solution occurs, a cermet type material is formed with a microporous morphology and constituted by metallic nickel nanoparticles supported on a cerium and gadolinium mixed oxide. This material is designated (Cu).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.99.

Example 9

(14) The materials prepared according to the methodology described in Examples 1 to 5 have been tested as catalysts in the reverse water-gas shift reaction. These catalysts have been selected to find the limits of use with regard to the different compositions. The process has been conducted under the following reaction conditions: 300,000 mLN/h.Math.g, 700° C., H.sub.2/CO.sub.2=2, 10% volume of N.sub.2. The reaction temperature is increased from room temperature to that of the reaction in the reaction gas mixture itself.

(15) According to the results obtained (Table 1), the conversion of CO.sub.2 and catalytic stability vary according to the proportion of nickel. The catalyst without nickel is that which, after requiring a period of induction of about 3 hours, shows its activity towards a stable conversion increased by close to 26%. The other catalysts had, at the beginning of the reaction, a similar conversion between 55 and 59%, but experience a different behaviour throughout the reaction. Thus, the one with lower proportion of nickel (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98) is slightly deactivated after 6 hours reaction, reaching a conversion of about 53%, respectively. The other catalysts result in fairly stable conversions throughout the 6 hours reaction. According to the results obtained, a slightly higher conversion for a mole fraction between the nickel and the mixed oxide equal to 4:96 is observed. This catalyst experiences a slight increase in conversion after 6 hours reaction, and the obtained conversion is, for this reaction time, practically on the thermodynamic equilibrium (which is of 59.3% for these reaction conditions). Regarding the CO selectivity (Table 2) it is observed that its values are over 96% for all the catalysts tested, with CH.sub.4 being the minority compound that is formed and which adjusts the carbon equilibrium.

(16) The catalyst comprising metallic nickel supported on lanthanum-doped ceria ((Ni).sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9) shows high activity and stability, compared to its analogue doped with gadolinium ((Ni).sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9).

(17) TABLE-US-00001 TABLE 1 It shows the conversion percentage of the CO.sub.2 throughout the reaction time (RWGS reaction) for various catalysts. Ce.sub.0.9Gd.sub.0.1O.sub.1.95 (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.96 (Ni).sub.0.04(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98 (Ni).sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9 (Ni).sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9 CO2 Conv CO2 Conv CO2 Conv CO2 Conv CO2 Conv t (h) (%) t (h) (%) t (h) (%) t (h) (%) t (h) (%) 0 19.6 0 56.7 0 54.82 0 55.2 0 55.5 0.5 22.2 0.82 57.2 0.55 56.96 0.50 55.9 0.50 56.3 1.07 23.9 1.62 56.0 1.13 57.15 1.02 56.2 1.01 56.5 1.62 24.8 2.40 55.7 1.73 57.33 1.54 56.1 1.52 56.7 2.19 25.6 3.14 54.0 2.36 57.45 2.06 56.2 2.05 56.7 2.79 26.1 3.86 53.4 3.02 57.48 2.61 56.4 2.59 56.8 3.39 26.3 4.57 53.2 3.69 57.54 3.17 56.3 3.14 56.8 4.03 26.4 5.25 53.1 4.40 57.58 4.33 56.4 4.25 56.9 4.72 26.4 5.90 52.9 5.15 57.75 4.92 56.5 4.83 56.9 5.47 26.5 5.94 58.62 6.14 56.6 6.00 57.0

(18) TABLE-US-00002 TABLE 2 It shows the selectivity percentage of the CO throughout the reaction time (RWGS reaction) for various catalysts. Ce.sub.0.9Gd.sub.0.1O.sub.1.95 (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98 (Ni).sub.0.04(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.95 (Ni).sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9 (Ni).sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9 Select Select Select Select Select t (h) CO (%) t (h) CO(%) t (h) CO(%) t (h) CO(%) t (h) CO(%) 0 100 0 98.2 0 96.6 0 96 6 0 96.1 0.53 100 0.82 99.0 0.55 98.1 0.50 96.3 0.50 97.3 1.07 100 1.62 99.6 1.13 98.4 1.02 96.6 1.01 97.6 1.62 100 2.40 99.7 1.73 98.7 1.54 96.5 1.52 98.5 2.19 100 3.14 99.9 2.36 98.9 2.06 97.0 2.05 98.2 2.79 100 3.86 100 3.02 98.9 2.61 97.1 2.59 98.3 3.39 100 4.57 100 3.69 99.3 3.17 97.1 3.14 98.2 4.03 100 5.25 100 4.40 99.3 4.33 97.0 4.25 98.4 4.72 100 5.90 100 5.15 99.2 4.92 97.2 4.83 98.3 5.47 100 98.2 5.94 99.3 6.14 97.2 6.00 98.7

Example 10

(19) The materials prepared according to the methodology described in Examples 6 to 8 have been tested as catalysts in the reverse water-gas shift reaction. These catalysts have been chosen to analyse the influence of the type of active phase supported on the cerium-lanthanide mixed oxide. The process has been conducted under the following reaction conditions: 300,000 mLN/h.Math.g, 700° C., H.sub.2/CO.sub.2=2, 10% volume of N.sub.2. The reaction temperature is increased from room temperature to that of the reaction in the reaction gas mixture itself.

(20) According to the results obtained (Table 3), the conversion of CO.sub.2 and CO selectivity vary according to the type of active phase. Thus, those based on nickel ((Ni).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.99)) and Pt ((Pt).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.99)) produced higher CO.sub.2 conversion than that based on copper ((Cu).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.99)). However, that which is based on platinum is somewhat less carbon monoxide-selective, with a small proportion of methane being formed under these reaction conditions.

(21) TABLE-US-00003 TABLE 3 It shows the conversion percentage of the CO.sub.2 and CO selectivity throughout the reaction time (RWGS reaction) for various catalysts. (Ni).sub.0.01(Ce.sub.0.9Gd.sub.0.1).sub.0.99 (Pt).sub.0.01(Ce.sub.0.9Gd.sub.0.1).sub.0.99 (Cu).sub.0.01(Ce.sub.0.9Gd.sub.0.1).sub.0.99 Time CO.sub.2 Conv Select to Time CO.sub.2 Conv Select to Time CO.sub.2 Conv Select to (h) (%) CO (%) (h) (%) CO (%) (h) (%) CO (%) 0.00 60.9 97.6 0.00 52.9 96.2 0.00 38.3 100.0 0.87 59.0 100.0 0.54 56.0 97.4 0.47 45.7 100.0 1.74 54.0 100.0 1.09 55.9 97.0 0.94 46.2 100.0 2.61 53.7 100.0 1.64 55.6 96.9 1.41 46.5 100.0 3.41 55.7 100.0 2.23 56.0 96.9 1.88 46.4 100.0 4.15 55.3 100.0 2.79 56.0 96.9 2.35 46.2 100.0 4.87 55.4 100.0 3.41 55.9 97.0 2.82 46.3 100.0

Example 11

(22) The activity and stability of the catalyst (Ni).sub.0.04(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.96 has been determined by performing a test of durability, during 100 hours of continuous reaction for the of RWGS reaction. The reaction conditions are identical to those used in Example 6. According to the results obtained, the catalyst increases its activity up to a CO.sub.2 conversion value very close to thermodynamic equilibrium in the first 4 hours of reaction, and then it experiences a deactivation of less than 6% of conversion in the following 4 hours. From then on, its activity remains virtually stable for 92 hours. See FIG. 2.

Example 12

(23) The materials (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98 and (Ni).sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9 have been tested as catalysts in the partial oxidation reaction of methane into synthesis gas under the following reaction conditions: 36600 mL.sub.N/h.Math.g; 700° C., using a reaction mixture consisting of N.sub.2: 40%; CH.sub.4: 40% and O.sub.2: 20% (molar). Before passing the mixture of reaction gases, the temperature is increased from room temperature up to 700° C., under a nitrogen flow rate of 40 mL.sub.N/min and is maintained for 1 hour.

(24) The results of methane conversion and yield to hydrogen based on the reaction time (6 hours) obtained for the catalysts (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98 and (Ni).sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9 are shown in Table 4. For the catalyst with a Ni:mixed oxide mole fraction equal to 2:98, a deactivation is observed with the reaction time. By contrast, for the catalyst with a Ni:mixed oxide fraction equal to 10:90, greater stability as well as higher CH.sub.4 conversion values and hydrogen yield are observed. The values found are very close to the thermodynamic equilibrium for these reaction conditions.

(25) TABLE-US-00004 TABLE 4 It shows the CH.sub.4 conversion percentage and H.sub.2 yield throughout the reaction time (the partial oxidation reaction of methane to synthesis gas) for various catalysts. (Ni).sub.0.02(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.98 (Ni).sub.0.01(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.8 t(h) CH.sub.4 Conv (%) H.sub.2 moles yield/CH.sub.4mol fed t(h) CH.sub.4 Conv (%) H.sub.2 moles yield/CH.sub.4 mol fed 1 72.7 1.093 1 83.2 1.304 2 65.0 0.977 2 82.3 1.318 3 62.2 0.880 3 81.7 1.303 4 59.6 0.897 4 81.4 1.295 5 57.9 0.840 5 81.1 1.287 6 56.6 0.829 6 81.0 1.295

Example 13

(26) The textural properties of the catalysts Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9Nd.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9Sm.sub.0.1O.sub.1.95).sub.0.9 have been determined by Hg porosimetry.

(27) The protocol for determining the porosity, surface area, and average pore size by mercury porosimetry was as follows: The sample was degassed at 80 degrees Celsius for 3 hours. A sample amount of between 20 to 40 mg was introduced into a sample holder of a mercury porosimeter (Autopore IV mercury Porosimeter, Micromeritics). Then the mercury intrusion porosimetry, which is a technique of adsorption using mercury as the adsorbate, was performed.

(28) Through the application of pressure, mercury is forced to enter the pores of the solid. The value of the volume of mercury intruded allows calculating the area, distribution by pore size and porosity percentage of the material. This technique is used when the material under study has (2-50 nm) mesopores and (>50 nm) macropores. Analysis conditions used were: surface tension: 484 din/cm); contact angle: 141 degrees; Maximum pressure: 60000 psi.

(29) FIG. 3 shows the pore size distribution of the compounds of formula Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9Nd.sub.0.1O.sub.1.95).sub.0.9 and Ni.sub.0.1(Ce.sub.0.9Sm.sub.0.1O.sub.1.95).sub.0.9. The results are summarised in Table 5 below.

(30) TABLE-US-00005 TABLE 5 It shows the total pore area in m.sup.2/g, the porosity percentage and average pore diameter in μm for each of the following catalysts Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9Nd.sub.0.1 O.sub.1.95).sub.0.9, Ni.sub.0.1(Ce.sub.0.9SM.sub.0.1OR.sub.1.95).sub.0.9. Average pore Total pore area Porosity diameter Catalyst (m.sup.2g) (%) (μm) Ni.sub.0.1(Ce.sub.0.9Gd.sub.0.1O.sub.1.95).sub.0.9 8.6 92.4 2.03 Ni.sub.0.1(Ce.sub.0.9La.sub.0.1O.sub.1.95).sub.0.9 8.9 84.1 0.91 Ni.sub.0.1(Ce.sub.0.9Nd.sub.0.1O.sub.1.95).sub.0.9 10.4 95.3 2.96 Ni.sub.0.1(Ce.sub.0.9Sm.sub.0.1O.sub.1.95).sub.0.9 9.4 94.3 2.87