Rhenium-doped catalyst and a method for the selective methanation of carbon monoxide

Abstract

The present invention relates to a catalytically active composition for the selective methanation of carbon monoxide in reformate streams comprising hydrogen and carbon dioxide, comprising at least one element selected from the group consisting of ruthenium, rhodium, nickel and cobalt as active component and rhenium as dopant on a support material. The catalyst according to the invention is preferably used for carrying out methanation reactions in a temperature range from 100 to 300 C. for use in the production of hydrogen for fuel cell applications.

Claims

1. A catalytically active composition for the selective methanation of carbon monoxide in reformate streams comprising hydrogen and carbon dioxide, comprising at least one element selected from the group consisting of ruthenium, rhodium, nickel and cobalt as active component and rhenium as dopant on a lanthanum-cerium-zirconium oxide support material; wherein the active component is present in an amount of from 0.1 to 20% by weight and rhenium is present in an amount of from 0.01 to 20% by weight, in each case based on the total amount of the catalytically active composition; wherein the support material is in the form of a shaped body with a compressive strength of at least 0.2 kgf; wherein the support material has a pore volume of from 0.05 to 1.5 cm.sup.3/g.

2. The catalytically active composition according to claim 1, wherein the composition comprises ruthenium as active component.

3. The catalytically active composition according to claim 1, wherein the support material comprises lanthanum oxide in an amount of from 0.1 to 15% by weight, cerium oxide in an amount of from 0.1 to 20% by weight and zirconium oxide in an amount of from 30 to 99.8% by weight, in each case based on the total amount of the support material.

4. The catalytically active composition according to claim 1, wherein the rhenium is present in an amount of from 0.1 to 2% by weight, based on the total amount of the catalytically active composition.

5. The catalytically active composition according to claim 4, wherein the active component is present in an amount of 2% by weight, based on the total amount of the catalytically active composition.

6. The catalytically active composition according to claim 1, wherein the active component is Ru.

7. The catalytically active composition according to claim 1, wherein the catalytically active composition has a BET surface area of at least 20 m.sup.2/g.

8. The catalytically active composition according to claim 6, wherein the catalytically active composition comprises 0.07 to 5% by weight of rhenium and 0.7 to 4% by weight of ruthenium, based on the total weight of the catalytically active composition.

9. The catalytically active composition according to claim 6, wherein the catalytically active composition comprises 0.08-4% by weight of rhenium and from 1 to 3% by weight of ruthenium, based on the total weight of the catalytically active composition.

10. The catalytically active composition according to claim 6, wherein the catalytically active composition comprises 2% by weight of ruthenium and 0.1-2% by weight of rhenium, based on the total weight of the catalytically active composition.

11. A process for producing a catalytically active composition according to claim 1, which comprises the steps of bringing the active component and the dopant into solution and applying the solution to the support material by impregnation.

12. The process for producing a catalytically active composition according to claim 1, which comprises the steps of kneading the support material with the salts and/or hydrates of the active component and of the dopant and subsequently extruding and drying the mixture.

13. A process comprising selectively methanating carbon monoxide in the presence of catalytically active composition according to claim 1.

14. The process according to claim 13, wherein the me thanation is carried out in a temperature range from 100 to 300 C.

15. The process according to claim 13, wherein it directly follows a low-temperature conversion stage.

Description

EXAMPLES

Example 1

(1) 148.1 g of a lanthanum-cerium-zirconium oxide support (comprising 65% by weight of ZrO.sub.2, 15% by weight of CeO.sub.2, 5% by weight of La.sub.2O.sub.3 and 15% by weight of Al.sub.2O.sub.3) were impregnated with an about 30% strength by weight RuCl.sub.3 solution, the amount of which was set so that the finished catalyst bore 2% by weight of Ru as active composition. The impregnated support was subsequently dried in a rotary tube furnace at 120 C. for 16 hours and then calcined at 475 C. for 2 hours (at a heating rate of 4 C./min). The ruthenium catalyst obtained in this way was subsequently impregnated with a perrhenic acid solution (HReO.sub.4) and dried again at 120 C. for 16 hours. The concentration of perrhenic acid was set so that the finished catalyst after drying comprised 2% by weight of Re as dopant. The BET surface area of the finished catalyst was 83 m.sup.2/g*).

Example 2

(2) 148.1 g of a lanthanum-cerium-zirconium oxide support (comprising 65% by weight of ZrO.sub.2, 15% by weight of CeO.sub.2, 5% by weight of La.sub.2O.sub.3 and 15% by weight of Al.sub.2O.sub.3) were impregnated with an about 30% strength by weight RuCl.sub.3 solution, the amount of which was set so that the finished catalyst bore 1% by weight of Ru as active composition. The impregnated support was subsequently dried in a rotary tube furnace at 120 C. for 16 hours and then calcined at 475 C. for 2 hours (at a heating rate of 4 C./min). The ruthenium catalyst obtained in this way was subsequently impregnated with a perrhenic acid solution (HReO.sub.4) and dried again at 120 C. for 16 hours. The concentration of perrhenic acid was set so that the finished catalyst after drying comprised 1% by weight of Re as dopant. The BET surface area of the finished catalyst was 86 m.sup.2/g*).

(3) The XRD pattern of this catalyst is shown in the figure.

Example 3

(4) 148.1 g of a lanthanum-cerium-zirconium oxide support (comprising 65% by weight of ZrO.sub.2, 15% by weight of CeO.sub.2, 5% by weight of La.sub.2O.sub.3 and 15% by weight of Al.sub.2O.sub.3) were impregnated with an about 30% strength by weight RuCl.sub.3 solution, the amount of which was set so that the finished catalyst bore 2% by weight of Ru as active composition. The impregnated support was subsequently dried in a rotary tube furnace at 120 C. for 16 hours and then calcined at 475 C. for 2 hours (at a heating rate of 4 C./min). The ruthenium catalyst obtained in this way was subsequently impregnated with a perrhenic acid solution (HReO.sub.4) and dried again at 120 C. for 16 hours. The concentration of perrhenic acid was set so that the finished catalyst after drying comprised 0.5% by weight of Re as dopant. The BET surface area of the finished catalyst was 85 m.sup.2/g*).

Example 4

(5) 148.1 g of a lanthanum-cerium-zirconium oxide support (comprising 65% by weight of ZrO.sub.2, 15% by weight of CeO.sub.2, 5% by weight of La.sub.2O.sub.3 and 15% by weight of Al.sub.2O.sub.3) were impregnated with an about 30% strength by weight RuCl.sub.3 solution, the amount of which was set so that the finished catalyst bore 2% by weight of Ru as active composition. The impregnated support was subsequently dried in a rotary tube furnace at 120 C. for 16 hours and then calcined at 475 C. for 2 hours (at a heating rate of 4 C./min). The ruthenium catalyst obtained in this way was subsequently impregnated with a perrhenic acid solution (HReO.sub.4) and dried again at 120 C. for 16 hours. The concentration of perrhenic acid was set so that the finished catalyst after drying comprised 0.25% by weight of Re as dopant. The BET surface area of the finished catalyst was 88 m.sup.2/g*).

Example 5

(6) 148.1 g of a lanthanum-cerium-zirconium oxide support (comprising 65% by weight of ZrO.sub.2, 15% by weight of CeO.sub.2, 5% by weight of La.sub.2O.sub.3 and 15% by weight of Al.sub.2O.sub.3) were impregnated with an about 30% strength by weight RuCl.sub.3 solution, the amount of which was set so that the finished catalyst bore 2% by weight of Ru as active composition. The impregnated support was subsequently dried in a rotary tube furnace at 120 C. for 16 hours and then calcined at 475 C. for 2 hours (at a heating rate of 4 C./min). The ruthenium catalyst obtained in this way was subsequently impregnated with a perrhenic acid solution (HReO.sub.4) and dried again at 120 C. for 16 hours. The concentration of perrhenic acid was set so that the finished catalyst after drying comprised 0.1% by weight of Re as dopant. The BET surface area of the finished catalyst was 86 m.sup.2/g*).

(7) The BET surface area of the respective catalysts according to the invention was determined in accordance with DIN 66131.

Example 6 (Comparative Example)

Reproduction of the Patent EP 2 125 201 B1, Example 7d

(8) A support composed of 70% by weight of ZrO.sub.2, 15% by weight of CeO.sub.2, 5% by weight of La.sub.2O.sub.3 and 10% by weight of Al.sub.2O.sub.3 was admixed with an RuCl.sub.3 solution, the concentration of which was set so that the calcined end product bore 2% by weight of Ru as active composition.

Example 7 (Comparative Example)

(9) 147 g of a -Al.sub.2O.sub.3 support (0.8 mm spheres, Sasol GmbH) were impregnated with an about 30% strength by weight RuCl.sub.3 solution, the amount of which was set so that the finished catalyst bore 2% by weight of Ru as active composition. The impregnated support was subsequently dried in a rotary tube furnace at 120 C. for 16 hours and then calcined at 475 C. for 2 hours (at a heating rate of 4 C./min).

(10) TABLE-US-00001 TABLE 1 Composition of the catalysts of examples 1 to 7 Ru [% by Re [% by Catalyst weight] weight] Support Example 1 2 2 LaCeZr oxide Example 2 2 1 LaCeZr oxide Example 3 2 0.5 LaCeZr oxide Example 4 2 0.25 LaCeZr oxide Example 5 2 0.10 LaCeZr oxide Example 6* 2 0 LaCeZr oxide Example 7* 2 0 Al.sub.2O.sub.3 *Comparative examples

Example 8Selective Methanation Using the Catalysts from Examples 1 to 7

(11) Test Conditions:

(12) An electrically heated fixed-bed tube reactor having a length of 530 mm and an internal diameter of 10 mm was used for the experiment.

(13) 5 ml of steatite spheres having a diameter of from 1.8 to 2.2 mm were firstly installed, and the catalyst mixture was subsequently placed on these. The catalyst mixture consisted of about 20 ml of catalyst pellets (1.51.5 mm). 5 ml of steatite spheres having a diameter of from 1.8 to 2.2 mm, which filled the remaining volume of the reactor, served as guard bed.

(14) The catalyst was firstly reduced using 90 l/h of nitrogen and 10 l/h of hydrogen at 230 C. for one hour. The gas composition selected for the experiment is typical of the output of the low-temperature shift stage after the reforming of methane and was 22% by volume of Hz, 28% by volume of N.sub.2, 25% by volume of H.sub.2O, 13% by volume of CO.sub.2, 5% of volume of CO and 0.5% by volume of CH.sub.4. All experiments were carried out at a pressure of 2 bara and a space velocity of 5000 l.Math.h.sup.1.Math.l.sup.1.sub.cat.

(15) After all gases had been set and the reactor had (after the reduction at 230 C.) been heated to a temperature of 260 C., the experiment was started and the selectivity of the catalysts used in each case was monitored over a period of 90 hours.

(16) The concentration of the gases was determined by means of on-line GC downstream of the reactor.

(17) The parameters selectivity at conversion were employed for evaluating the results of the experiments. The selectivity is the ratio of the amount of CO reacted and the amount of methane formed (in % by volume). The conversion is based on CO.

(18) Results:

(19) The catalysts were measured under the abovementioned conditions. Complete conversion of CO (CO content=0 ppm, or below the detection limit of the GC instrument) could be achieved under these experimental conditions for all catalysts from examples 1 to 7.

(20) The CO selectivities at the beginning of the respective experiment [start of run (SOR)] and after a time on stream (TOS) of 90 hours are reported in table 2.

(21) As can be seen from table 2, the CO selectivity dropped significantly to values of 18 and 24% after a time of operation of 90 hours when using the comparative catalysts from examples 6 and 7, while in the case of the inventive catalysts from examples 1 to 5 a CO selectivity in the range from 46% to 53% was still observed.

(22) TABLE-US-00002 TABLE 2 Results of the selective methanation of CO Active composition/doping Selectivity at 260 C. element After 90 Catalyst Support Start of Run hours TOS Example 1: 2% by weight of Ru/2% by 83% 51% weight of Re LaCeZr oxide Example 2: 2% by weight of Ru/1% by 84% 53% weight of Re LaCeZr oxide Example 3: 2% by weight of Ru/0.5% by 82% 49% weight of Re LaCeZr oxide Example 4: 2% by weight of Ru/0.25% by 80% 45% weight of Re LaCeZr oxide Example 5: 2% by weight of Ru/0.1% by 82% 46% weight of Re LaCeZr oxide Example 6: 2% of Ru/ 81% 24% LaCeZr oxide Example 7: 2% of Ru/ 80% 18% -Al.sub.2O.sub.3

(23) TABLE-US-00003 TABLE 3 Selectivity profile after a time of operation of 90 hours at 260 C. and subsequent stepwise lowering of the temperature by in each case 20 C. over a period of 4 hours. The selectivity values indicated were determined at complete conversion of CO (0 ppm of CO). In the case of an incomplete conversion, the selectivity was reported as: =not applicable (n/a). (Test conditions: T = 200-260 C., p = 2 bar, GHSV = 5000 h.sup.1, inlet gas composition: 5% of CO, 13% of CO.sub.2, 0.5% of CH.sub.4, 22% of H.sub.2, 25% of H.sub.2O, 28% of N.sub.2) Active composition/doping element Selectivity profile after 90 h at various temperatures Catalyst Support 260 C. 240 C. 220 C. 200 C. Example 1 2% by weight of Ru/2% by 49% 67% 87% n/a weight of Re LaCeZr oxide Example 2 2% by weight of Ru/1% by 50% 62% 81% 100% weight of Re LaCeZr oxide Example 3 2% by weight of Ru/0.5% by 49% 66% 83% 97% weight of Re LaCeZr oxide Example 4 2% by weight of Ru/0.25% by 45% 61% 79% 95% weight of Re LaCeZr oxide Example 5 2% by weight of Ru/0.1% by 46% 58% 77% 95% weight of Re LaCeZr oxide Example 6 2% of Ru LaCeZr oxide 24% 36% 57% 88% Example 7 2% of Ru 18% 32% 54% 95% -Al.sub.2O.sub.3

(24) As can be seen from table 3, the rhenium-doped ruthenium catalysts according to the invention from examples 1 to 5 display significantly higher CO selectivities over the temperature range from 200 to 260 C. than the two rhenium-free catalysts from comparative examples 6 and 7.