MANGANESE-DOPED NICKEL-METHANATION CATALYSTS

Abstract

The invention relates to a catalyst for the methanation of carbon monoxide and/or carbon dioxide, said catalyst comprising aluminium oxide, an Ni-active substance and Mn and being characterised in that the molar Ni/Mn ratio in the catalyst is 3.0 to 10.0, preferably 4.0 to 9.0 and especially preferably 5.5 to 6.5. The catalyst is characterised by an increased activity with high selectivity and stability. The invention also relates to a method for producing a catalyst according to the invention, comprising the steps: a) co-precipitation from a solution containing Al, Ni and Mn in dissolved form in order to obtain a precipitate; b) isolation of the precipitate from step a); c) drying the isolated precipitate from step b); and d) calcination of the dried precipitate from step c).

Claims

1. A catalyst for the methanation of carbon monoxide and/or carbon dioxide, comprising aluminum oxide, a Ni active mass, and Mn, wherein the Ni/Mn molar ratio in the catalyst is 3.0 to 10.0.

2. The catalyst as claimed in claim 1, wherein the Ni active mass contains crystallites with a diameter below 20 mm, preferably below 10 nm.

3. The catalyst as in claim 1, wherein by an CO.sub.2 uptake capacity at 35 C. of greater than 200 mol/g, preferably 200 to 300 mol/g.

4. The catalyst of claim 1, wherein the Ni/Mn molar ratio is preferably 4.0 to 9.0.

5. The catalyst of claim 1, wherein the Ni/Mn molar ratio is preferably 5.5 to 6.5

6. The use of a catalyst as claimed in claim 1 for the methanation of carbon monoxide and/or carbon dioxide with gaseous hydrogen.

7. A method for the preparation of a catalyst as claimed in claim 1, comprising the steps: a) co-precipitation from a solution containing Al, Ni, and Mn in dissolved form to obtain a precipitate, b) isolation of the precipitate from step a), c) drying of the isolated precipitate from step b), and d) calcining of the dried precipitate from step c).

8. The method as claimed in claim 7, wherein the solution from step a) is an aqueous solution.

9. The method as claimed in claim 7, wherein the precipitate in the solution is aged for at least 30 minutes.

10. The method as claimed in claim 7, wherein the isolated precipitate from step b) is washed.

11. The method as claimed in claim 7, wherein the Al, Ni, and Mn are present in the solution in dissolved form, as ionic compounds, and these ionic compounds have the same anion.

12. The method as claimed in claim 11, wherein the anion is nitrate, sulfate, a halide, chloride or acetate.

13. The method as claimed in claim 7, wherein Mn in the solution from step a) is in oxidation state II or Ill.

14. The method as claimed in claim 7, wherein the dried precipitate is calcined at a temperature of 300 to 600 C. in air.

15. The method for the methanation of carbon dioxide and/or carbon monoxide in which a gas containing carbon dioxide and/or carbon monoxide is brought into contact with a catalyst as claimed in claim 1.

16. The method as claimed in claim 15, in which the gas is brought into contact with the catalyst at a temperature above 200 C.

Description

[0043] FIGS. 1 to 4 show the catalytic profile of the manganese-doped catalysts Mn1, Mn4, Mn6, and Mn8 before and after ageing.

[0044] FIG. 1: Catalytie test results for Mn1 (comparative example)

[0045] FIG. 2: Catalytie test results for Mn4 (example)

[0046] FIG. 3: Catalytie test results for Mn6 (example)

[0047] FIG. 4: Catalytie test results for Mn8 (comparative example)

[0048] FIG. 5: Activity/stability diagram for the described samples.

METHODS

[0049] Elemental Analysis

[0050] The composition of the calcined catalysts was determined by inductively-coupled plasma optical emission spectroscopy (ICP-OES). 50 mg of catalyst was dissolved in 50 ml of 1 molar phosphoric acid (VWR, analytical grade) at 60 C. To dissolve the manganese dioxide that forms, 50 mg of Na.sub.2SO.sub.3 (Sigma-Aldrich, analytical grade) was added to the solution. The solutions were cooled and then diluted 1/10 and filtered through 0.1 m filters (Pall). The calibration solutions were made up at concentrations of 1, 10, and 50 mg l.sup.1 (Merck). The metal concentrations were determined using an Agilent 700 ICP-OES.

[0051] Determination of Specific Surface Area

[0052] The specific surface areas of the catalysts (S.sub.BET) were determined by N.sub.2-BET analysis on a Nova 4000e (Quantachrome). For this, 100 mg of catalyst was degassed for 3 hours at 120 C. and adsorption and desorption isotherms were then recorded in the 0.007 to 1 p/p.sub.0 range. The BET surface area was determined using the data points in the 0.007 to 0.28 p/p.sub.0 range.

[0053] Chemisorption

[0054] Chemisorption experiments were carried out on an Autosorb 1C (Quantachrome). Before measurement, 100 mg of catalyst was activated at 500 C. in 10% H.sub.2 in N.sub.2 for 6 hours. The heating ramp was 2 K min.sup.1.

[0055] The metal surface area (S.sub.MET) was determined in accordance with DIN 66136-2 (vers. 2007-01) by H.sub.2 chemisorption at 35 C. For this purpose, 20 adsorption points were recorded equidistantly from 40 mmHg to 800 mmHg. The equilibration time was 2 min for adsorption and 10 min for thermal equilibration. For the determination of the metal surface area, the metal atom/H stoichiometry was set at 1. For the CO.sub.2 chemisorption measurements to determine the CO.sub.2 uptake capacity (U(CO.sub.2)), the equilibration time for adsorption was set at 10 min with the parameters otherwise unchanged. Before recording the chemisorption data, any kinetic inhibition of CO.sub.2 chemisorption under these conditions was ruled out experimentally. Metal surface areas and CO.sub.2 uptake capacities were extrapolated to a pressure of 0 mmHg by the extrapolation method.

[0056] Synthesis

[0057] The catalysts were prepared by co-precipitation, with the nickel/aluminum atomic ratio set at 1. To investigate the effect of iron on the behavior of the catalyst, iron(III) nitrate was added to the nickel nitrate/aluminum nitrate salt solution during the synthesis of the catalyst. To investigate the concomitant effect of iron and manganese on the behavior of the catalyst, manganese(II) nitrate and iron(III) nitrate were added to the nickel nitrate/aluminum nitrate salt solution during the synthesis of the catalyst. All chemicals used were of analytical grade purity. Water was purified in a Millipore filter system and the purity verified by conductivity measurements. The synthesis was carried out in a double-jacketed stirred-tank reactor with a capacity of 3 I. The thermostat fitted to the water-filled double jacket allowed the temperature to be maintained at 30 C. during the synthesis run and two baffles were employed for better mixing. Stirring was carried out using a precision glass stirrer operating at 150 rpm. For the synthesis, the stirred-tank reactor was charged with 1 I of H.sub.2O, which was adjusted to pH 90.1. The addition of the mixture of dissolved nitrates was carried out at a rate of 2.5 ml min.sup.1. The controlled addition of the precipitation reagent at the same time served to maintain the pH. The starting materials used were one-molar solutions of the respective nitrates (Ni(NO.sub.3).sub.2.6H.sub.2O, Al(NO.sub.3).sub.2.9H.sub.2O, Fe(NO.sub.3).sub.3.9H.sub.2O, and Mn(NO.sub.3).sub.2.4H.sub.2O). These were mixed, as shown in Table 2, to a total volume of 120 ml min.sup.1 before undergoing dropwise addition to the reactor. The precipitation reagent used was a mixture of equal volumes of 0.5 M NaOH and 0.5 M Na.sub.2CO.sub.3 solutions, which was added using a titrator. The suspension was aged overnight in the mother liquor with constant stirring, after which the precipitate was filtered off and washed with H.sub.2O until the filtrate was of neutral pH. After drying overnight at 80 C. in a drying cabinet, the dried precipitate (precursor) was heated to 450 C. at a heating rate of 5 K min.sup.1 and calcined for 6 hours in synthetic air.

[0058] Activity and Stability Measurement

[0059] In order to be able to compare different catalysts in terms of their CO.sub.2 methanation activity, a test program was developed that information on their activity and stability. For this, 25 mg of catalyst from the 150-200 m sieve fraction was diluted with nine times the amount of SiC and placed in the reactor. The successive measurement steps performedreduction, equilibration, S-curve 1, ageing, S-curve 2are shown in detail in Table 1.

TABLE-US-00001 TABLE 1 Parameters for the measurement steps for determination of the activity and stability profile Reaction gas, Dura- ratio Reaction gas Q p.sub.abs tion H.sub.2/CO.sub.2/Ar [l (STP) g.sub.cat.sup.1 h.sup.1] T [ C.] [bar] [h] Reduction 5/0/95 130 485 1 8 Equilibration 4/1/5 150 260 7 24 S-curve 1 4/1/5 150 170-500 8 Ageing 4/1/5 150 500 7 32 S-curve 2 4/1/5 150 170-500 8

[0060] To determine the temperature-CO.sub.2 conversion curves, the temperature was increased in 25 C. increments in the specified range and the activity in each case determined. A comparison of the two S-curves before and after ageing for 32 hours at 500 C. gives an insight into the stability of the systems to high temperatures.

[0061] As a measure of the activity, on a representative basis, the temperature T75.1 necessary to achieve a CO.sub.2 conversion of 75% during the S-curve 1 measurement step was determined. For this, the temperature was increased in 25 C. increments in the specified range. The lower T75.1 is, the higher therefore the activity of the catalyst.

[0062] As a measure of the activity after ageing, on a representative basis, the temperature T75.2 necessary to achieve a CO.sub.2 conversion of 75% during the S-curve 2 measurement step was determined. For this, the temperature was increased in 25 C. increments in the specified range. The lower T75.2 is, the higher therefore the activity of the catalyst after ageing.

[0063] Calculation of the difference between T75.1 and T75.2 from the two conversion temperature characteristics gives a measure of the stability of the catalyst. Here too, the smaller the difference, the more stable the catalyst. For better comparability, all calculated activities and stabilities were normalized with reference to the nickel-aluminum oxide catalyst without promoter (Ni). The normalized activity and stability are given by the following expressions:

[00001]$\mathrm{Normalized}.Math..Math.\mathrm{activity}=\frac{T_{75.1}\left(\mathrm{Ni}.Math.\text{/}.Math.{\mathrm{AlO}}_x\right)}{T_{75.1}\left(\mathrm{dop}.\mathrm{cat}.\right)}$$\mathrm{Normalized}.Math..Math.\mathrm{stability}=\frac{\frac{T_{75.2}\left(\mathrm{Ni}.Math.\text{/}.Math.{\mathrm{AlO}}_x\right)}{T_{75.1}\left(\mathrm{Ni}.Math.\text{/}.Math.{\mathrm{AlO}}_x\right)}}{\frac{T_{75.2}\left(\mathrm{dop}.\mathrm{cat}.\right)}{T_{75.1}\left(\mathrm{dop}.\mathrm{cat}.\right)}}$

[0064] The results in FIGS. 1 to 4 show that addition of a manganese promoter to a Ni/AlO.sub.x catalyst results in a significant increase in catalyst activity.

EXAMPLES

[0065]

TABLE-US-00002 TABLE 2 Molar metal salt solutions used in the co-precipitation Example V.sub.Ni(NO3)2 V.sub.Al(NO3)2 V.sub.Fe(NO3)3 V.sub.Mn(NO3)2 No. Catalyst [ml] [ml] [ml] [ml] Comparative examples 1 Ni 60.0 60.0 2 Fe2 59.0 59.0 2.0 3 Fe4 57.0 57.0 6.0 4 Fe7 55.0 55.0 10.0 5 Fe10 52.5 52.5 15.0 6 Mn1 59 59 2 7 Mn4 57 57 6 8 Mn11 51 51 18 9 Fe4Mn4 54.29 54.29 5.71 5.71 10 Fe4Mn1 56.10 56.10 5.90 1.90 11 Fe5Mn4 53.38 53.38 7.63 5.62 12 Fe5Mn1 55.13 55.13 7.88 1.87 13 Fe6Mn4 52.47 52.47 9.54 5.52 14 Fe7Mn1 54.16 54.16 9.85 1.84 Examples 1 Mn6 55 55 10 2 Mn8 52.5 52.5 15 3 Fe3Mn6 52.47 52.47 5.52 9.54 4 Fe5Mn6 51.62 51.62 7.37 9.39 5 Fe6Mn6 50.77 50.77 9.23 9.23

TABLE-US-00003 TABLE 3 Composition of the calcined catalysts Element contents [%] [% by wt.] Atomic ratios Example Catalyst Ni Mn Fe Al Ni/Al Ni/Mn Ni/Fe Comparative examples 1 Ni 44.3 19.8 1.03 2 Fe2 40.0 1.7 19.4 0.95 22.0 3 Fe4 39.7 4.3 19.4 0.94 8.8 4 Fe7 39.6 6.9 17.3 1.05 5.4 5 Fe10 36.1 10.1 17.9 0.93 3.4 6 Mn1 38.7 1.3 18.0 0.99 27.3 7 Mn4 38.9 3.7 18.2 0.98 9.8 8 Mn11 34.0 10.8 16.2 0.97 3.0 9 Fe4Mn4 39.9 17.8 4.2 4.0 1.03 9.0 9.5 10 Fe4Mn1 39.5 17.7 1.3 3.9 1.03 28.9 9.7 11 Fe5Mn4 38.1 17.3 3.8 5.3 1.01 9.4 6.8 12 Fe5Mn1 38.7 17.4 1.2 5.3 1.02 29.4 6.9 13 Fe6Mn4 36.9 18.2 3.5 6.2 0.93 9.8 5.6 14 Fe7Mn1 37.2 16.0 1.3 6.5 1.07 26.5 5.4 Examples 1 Mn6 36.3 6.1 15.5 1.08 5.6 2 Mn8 31.9 8.3 15.2 0.97 3.6 3 Fe3Mn6 35.6 16.0 6.0 3.4 1.02 6.0 10.0 4 Fe5Mn6 36.3 16.6 6.1 4.8 1.01 5.5 7.2 5 Fe6Mn6 34.1 16.8 5.8 5.9 0.93 5.5 5.5

TABLE-US-00004 TABLE 4 Characterization data for the catalysts S.sub.BET.sup.a S.sub.met.sup.a U(CO.sub.2).sup.a Example Catalyst [m.sup.2 g.sub.cat.sup.1] [m.sup.2 g.sub.cat.sup.1] [mol g.sub.cat.sup.1] Comparative examples 1 Ni 209 21.1 172 2 Fe2 227 19.8 199 3 Fe4 244 18.3 198 4 Fe7 216 11.4 196 5 Fe10 250 9.3 188 6 Mn1 211 19.2 197 7 Mn4 223 20.1 215 8 Mn11 213 10.8 242 9 Fe4Mn4 275 12.9 345 10 Fe4Mn1 241 16.1 204 11 Fe5Mn4 238 17.8 298 12 Fe5Mn1 251 17.6 269 13 Fe6Mn4 262 7.6 276 14 Fe7Mn1 237 11.2 223 Examples 1 Mn6 231 20.0 244 2 Mn8 214 17.6 240 3 Fe3Mn6 249 11.9 277 4 Fe5Mn6 268 15.8 327 5 Fe6Mn6 239 5.5 322 *normalized to mass of the calcined catalyst

TABLE-US-00005 TABLE 5 Results for the catalytic test reaction T.sub.75.1 T.sub.75.2 Normalized Normalized Example Catalyst [ C.] [ C.] T.sub.75.2/T.sub.75.1 activity stability Comparative examples 1 Ni 289.41 314.11 1.085 1.000 1.000 2 Fe2 279.29 296.86 1.063 1.036 1.021 3 Fe4 275.05 293.37 1.067 1.052 1.018 4 Fe7 276.35 286.84 1.038 1.047 1.046 5 Fe10 290.54 319.21 1.099 0.996 0.998 6 Mn1 282.04 300.91 1.067 1.026 1.017 7 Mn4 274.57 293.36 1.068 1.054 1.016 8 Mn11 269.95 289.67 1.073 1.072 1.011 9 Fe4Mn4 266.34 280.27 1.052 1.087 1.031 10 Fe4Mn1 274.18 286.01 1.043 1.056 1.040 11 Fe5Mn4 264.02 275.09 1.042 1.096 1.042 12 Fe5Mn1 262.62 271.83 1.035 1.102 1.049 13 Fe6Mn4 270.01 278.48 1.031 1.072 1.052 14 Fe7Mn1 269.11 280.15 1.041 1.075 1.043 Examples 1 Mn6 256.71 275.50 1.073 1.127 1.011 2 Mn8 259.31 272.67 1.052 1.116 1.032 3 Fe3Mn6 253.42 278.06 1.097 1.142 0.989 4 Fe5Mn6 258.16 281.24 1.089 1.121 0.996 5 Fe6Mn6 266.56 290.13 1.088 1.086 0.997