NI-BASED CATALYST FOR NH3 REFORMING APPLICATIONS

Abstract

The present invention relates to a catalyst comprising Ni, Ru, and a promoter metal M1, wherein the catalyst displays an Ru:Ni weight ratio in the range of from 0.0001:1 to 0.5:1, wherein the promoter metal M1 is selected from the group consisting of Li, K, Na, Cs, Mg, Ca, Sr, and Ba, including mixtures of two or more thereof, and wherein the catalyst further comprises one or more support materials onto which Ni, Ru, and the promoter metal M1 are respectively supported. Furthermore, the present invention relates to a method for the preparation of a catalyst comprising Ni, Ru, and a promoter metal M1, as well as to a catalyst obtainable according to said method, and to a process for the reforming of ammonia employing the inventive catalyst.

Claims

1.-15. (canceled)

16. A catalyst comprising Ni, Ru, and a promoter metal M1, wherein the catalyst displays an Ru:Ni weight ratio in the range of from 0.0001:1 to 0.5:1, wherein the promoter metal M1 is selected from the group consisting of Li, K, Na, Cs, Mg, Ca, Sr, and Ba, including mixtures of two or more thereof, wherein the catalyst further comprises one or more support materials onto which Ni, Ru, and the promoter metal M1 are respectively supported, wherein the catalyst displays an Ni:M1 atomic ratio in the range of from 1.5:1 to 10:1, wherein the catalyst comprises Ni in an amount in the range of from 10 to 25 wt.-% calculated as the element and based on 100 wt.-% of the catalyst, wherein the catalyst comprises Ru in an amount in the range of from 0.3 to 0.8 wt.-% calculated as the element and based on 100 wt.-% of the catalyst, and wherein the catalyst comprises the promoter metal M1 in an amount in the range of from 0.5 to 10 wt.-% calculated as the element and based on 100 wt.-% of the catalyst.

17. The catalyst of claim 16, wherein the catalyst displays an Ni:M1 atomic ratio in the range of from 2:1 to 6:1.

18. The catalyst of claim 16, the catalyst comprises Ni in an amount in the range of from 12 to 18 wt.-% calculated as the element and based on 100 wt.-% of the catalyst.

19. The catalyst of claim 16, the catalyst comprises Ru in an amount in the range of from 0.4 to 0.6 wt.-% calculated as the element and based on 100 wt.-% of the catalyst.

20. The catalyst of claim 16, the catalyst comprises the promoter metal M1 in an amount in the range of from 1 to 8 wt.-% calculated as the element and based on 100 wt.-% of the catalyst.

21. The catalyst of claim 16, wherein the catalyst comprises the one or more promoter metal M1 as a hydroxide, as a hydrogencarbonate, and/or as a carbonate.

22. The catalyst of claim 16, wherein the catalyst is in the form of a molding, in the form of extrudates, and/or in powder form.

23. A method for the preparation of a catalyst according to claim 16, the method comprising: (1) preparing a mixture comprising one or more sources of Ni, one or more support materials and/or one or more precursors thereof, and water; (2) shaping of the mixture obtained in (1); (3) calcination of the shaped body obtained in (2); (4) impregnation of the calcined shaped body obtained in (3) with an aqueous solution of one or more Ru salts; (5) calcination of the impregnated shaped body obtained in (4); (6) impregnation of the calcined shaped body obtained in (5) with an aqueous solution of one or more salts of a promoter metal M1, wherein the promoter metal M1 is selected from the group consisting of Li, K, Na, Cs, Mg, Ca, Sr, and Ba, including mixtures of two or more thereof, and (7) calcination of the impregnated shaped body obtained in (6).

24. A process for the reforming of ammonia, wherein the process comprises: (i) providing a reactor containing a catalyst according to claim 16; (ii) preparing a feed gas stream comprising NH.sub.3; (iii) feeding the feed gas stream prepared in (ii) into the reactor provided in (i) and contacting the feed gas stream with the catalyst; and (iv) removing an effluent gas stream from the reactor, the effluent gas stream comprising H.sub.2 and N.sub.2.

25. The process of claim 24, wherein contacting in (iii) is performed at a temperature in the range of from 300 to 1,100 C.

26. The process of claim 24, wherein the feed gas stream prepared in (ii) comprises from 100 to 50,000 ppm of H.sub.2O.

27. The process of claim 24, wherein the total amount of NH.sub.3, N.sub.2, and H.sub.2 comprised in the feed gas stream prepared in (ii) is in the range from 90 to 100 wt.-%.

28. The process of claim 24, wherein the feed stream is fed into the reactor at a gas hourly space velocity in the range of from 500 to 40,000 h.sup.1.

29. The process of claim 24, wherein after (i) and prior to (iii) the catalyst contained in the reactor provided in (i) is reduced in an atmosphere comprising hydrogen and/or NH.sub.3.

30. Use of a catalyst according to claim 16 in the reforming of NH.sub.3 to N.sub.2 and H.sub.2.

Description

DESCRIPTION OF THE FIGURES

[0194] FIG. 1 displays the results of NH.sub.3 reforming on the extruded catalysts at a GHSV of 4,000 h.sup.1, p(NH.sub.3)=20 bara and co-feeding of 5,000 ppm-vol of H.sub.2O. The extruded catalysts were tested between 30 and 650 C. The results obtained for 15 wt.-% of Ni supported on MgO/Al.sub.2O.sub.3 mixed oxide, without (catalyst of reference example 2) and with (catalysts from reference example 3) 0.1 and 0.5 wt.-% Ru promotion is shown, as well as the results obtained with the latter Ru-promoted catalyst which were additionally promoted with 3.5 wt.-% K according to inventive example 4.

[0195] FIG. 2 displays the results of NH.sub.3 reforming on the tableted catalysts at a GHSV of 4,000 h.sup.1, p(NH.sub.3)=30 bara and co-feeding of 5,000 ppm-vol of H.sub.2O. The tableted catalysts were tested between 30 and 650 C. The results obtained for 15 wt.-% of Ni supported on MgO/Al.sub.2O.sub.3 mixed oxide, without (catalyst of reference example 2) and with (catalyst from reference example 3) 0.5 wt.-% Ru promotion is shown, as well as the results obtained with the latter Ru-promoted catalyst which were additionally promoted with 3.5 wt.-% K according to inventive example 4. Furthermore, for comparison, a catalyst with 15 wt. % Ni and 3.5 wt. % KOH without Ru is included (catalyst from comparative example 5).

[0196] FIG. 3 displays the XRD pattern of the catalyst of reference example 2, wherein the Mg,Al-spinel structure is clearly identified as constituting part of the support material. In the diffractogram, the line pattern (without an asterix) of MgAl.sub.2O.sub.4 as well as the line pattern of cubic MgNiO.sub.2 (lines with an asterix) have been included.

EXPERIMENTAL SECTION

[0197] The present invention is further illustrated by the following examples.

Reference Example 1: Preparation of a Tableted Ni (15.5 wt.-%) Catalyst Supported on MgO/Al.SUB.2.O.SUB.3 .Mixed Oxide

[0198] A catalyst comprising Ni was prepared based on the process described as example E1 of WO 2013/068905 A1. As opposed to example E1 of WO 2013/068905 A1, an aqueous solution of nickel nitrate (14 wt.-% Ni concentration) was used instead of the pulverulent nickel nitrate hexahydrate. The various ingredients were mixed to a paste which was extruded. The extrudates were crushed and sieved to a target fraction having a particle size of from 200 to 900 m after drying and low temperature calcination.

[0199] The sieved powder was then mixed with graphite 2.8 weight.-% (Asbury Graphite 3160) and 5.5 weight-% cellulose (Arbocel BWW 40). The resulting mixture was tableted to moldings having a four-hole cross-section as shown in FIG. 1 of WO 2020/157202 A. For calcination, the moldings were heated in an annealing furnace to a temperature of 1,030 to 1,050 C. which was held for 4 hours.

[0200] The nickel content of the calcined moldings was 15.5 weight-%, the magnesium content 14.0 weight-%, and the aluminium content was 29.5 weight-%.

Reference Example 2: Preparation of an Extruded Ni (15.0 wt.-%) Catalyst Supported on MgO/Al.SUB.2.O.SUB.3 .Mixed Oxide

[0201] As for reference example 1, a catalyst comprising Ni was prepared based on the process described as example E1 of WO 2013/068905 A1. The Ni-salt solution employed in reference example 1 was mixed with the hydrotalcite and suitable amounts of water to prepare an extrudable paste. This paste was extruded in the next step. The subsequent heat treatment of the resulting extrudate was kept between 85 and 1050 C.

[0202] The nickel content of the calcined extrudates was 15.0 weight-%, the magnesium content 14.0 weight-%, the aluminium content was 29.5 weight-%.

Reference Example 3: Promotion of the Ni Catalysts of Examples 1 and 2 with Ru (0.1 and 0.5 wt.-%)

[0203] The catalysts prepared in examples 1 and 2 were respectively impregnated based on the water-uptake of the materials with a solution of Ru(NO(NO.sub.3).sub.3). The Ru loadings were fixed to 0.1 and 0.5 weight-%. Further, the impregnated samples were respectively heat treated up to 500 C.

Example 4: Promotion of the Ni/Ru Catalysts of Example 3 with K (3.5 wt.-%)

[0204] The catalysts prepared in example 3 were respectively impregnated based on the water-uptake of the materials with a KOH-solution. The KOH loading was fixed to 3.5 weight-% of K (5 wt.-% of KOH). Further, the impregnated samples were heat treated up to 500 C.

Comparative Example 5: Promotion of the Ni Catalyst of Example 1 with K (3.5 wt.-%)

[0205] The catalyst prepared in example 1 was impregnated based on the water-uptake of the material with a KOH-solution. The KOH loading was fixed to 3.5 wt. % of K (5 wt.-% of KOH) and the impregnated sample was heated to 500 C.

Example 6: Catalytic Tests in NH3-Reforming Under High Pressure

[0206] The catalysts of examples 1 to 5 were activated in a reducing atmosphere of 5-50 vol.-% H.sub.2 in an inert gas (Ar or N.sub.2) at temperatures of 450-850 C. The catalytic NH.sub.3-reforming tests were conducted under a partial pressure of ammonia (p(NH.sub.3)) of 20 bar (see results in Table 1), and 30 bar (see results in Table 2). To the NH.sub.3 feed, a fraction of 5,000 vol.-ppm of H.sub.2O was added. Further, the catalysts were tested at GHSV of 4,000 h.sup.1 and the temperature was varied from 300 to 650 C. The conversion of NH.sub.3 as function of the temperature are shown in FIGS. 1 and 2 and Tables 1 and 2.

TABLE-US-00001 TABLE 1 Results for the conversion of ammonia over the Ni-based catalysts (extrudates) of reference examples 2 and 3 and of example 4. Sample (Ex.) 15-Ni + 15-Ni + 15-Ni + 0.5 Ru / 15-Ni 0.1 Ru 0.5 Ru 5 KOH Temp. (Ref. Ex. 2) (Ref. Ex. 3) (Ref. Ex. 3) (Ex. 4) [ C.] X(NH3) [%] X(NH3) [%] X(NH3) [%] X(NH3) [%] 300 0.10 0.06 0.10 0.40 350 0.32 0.43 0.46 1.96 400 1.93 1.77 2.89 8.89 450 7.12 6.18 10.67 24.44 500 14.98 16.93 21.20 55.67 550 34.34 40.97 46.53 86.65 600 62.45 73.81 76.51 97.51 650 93.05 95.58 96.37 98.69

[0207] Thus, as may be taken from the results obtained from the testing of the respective catalysts displayed in Table 1 and FIG. 1, the promotion of the Ni-based catalyst of reference example 2 with relatively small amounts of Ru already leads to noticeable improvements in the ammonia conversion rates, wherein higher conversion may already be obtained at lower temperatures for the catalysts of reference example 3. Quite surprisingly, however, the further addition of K as a promoter in the Ru-promoted Ni-catalyst in example 4 leads to a considerable leap in ammonia conversion at lower temperatures, such that a 50% ammonia conversion rate is already achieved at 490 C. Furthermore, the inventive catalyst according to example 4 displays an ammonia conversion rate corresponding to the equilibrium conversion at around 600 C., whereas the Ni catalyst of reference example 2 only displays a conversion rate of slightly greater that 60% at that temperature, whereas the conversion rate of the Ru-promoted Ni catalysts of reference example 3 do not exceed 77%. Accordingly, it has quite unexpectedly been found that the use of comparatively low amounts of Ru in a Ni-based catalyst promoted with K affords unexpectedly high conversion rates at low temperatures when employed for the decomposition of ammonia, wherein only small amounts of Ru are required for obtaining a highly efficient catalyst.

TABLE-US-00002 TABLE 2 Results for the conversion of ammonia over the Ni-based catalysts (tablets) of reference examples 1 and 3 and of examples 4 and 5. Sample (Ex.) 15-Ni + 15-Ni + 0.5 Ru / 15-Ni + 15-Ni 0.5 Ru 5 KOH 5 KOH Temp. (Ref. Ex. 1) (Ref. Ex. 3) (Ex. 4) (Comp. Ex. 5) [ C.] X(NH3) [%] X(NH3) [%] X(NH3) [%] X(NH3) [%] 350 0.37 0.78 1.89 0.19 400 1.43 2.95 8.14 0.81 450 4.85 8.27 25.06 2.97 500 14.18 19.67 53.90 9.93 550 33.27 41.68 81.10 22.85 600 64.57 73.96 95.47 45.64 650 90.88 94.37 98.16 74.08

[0208] As may be taken from the results obtained from the testing of the respective catalysts displayed in Table 2 and FIG. 2, on the other hand, corresponding results are obtained for the tableted Ni-catalyst from reference example 1 compared to the extruded Ni-catalyst from reference example 2 as shown in Table 1 and FIG. 1. Same applies accordingly for the tableted catalyst of reference example 3 loaded with 0.5 wt.-% Ru and for the inventive tableted catalyst of example 4 loaded with 0.5 wt.-% Ru and 3.5 wt. % K. In Table 2 and FIG. 2, the results obtained using a tableted Ni-catalyst which has only been loaded with 3.5 wt.-% of K according to comparative example 5 is shown for comparison. As may be taken from the results, the Ni-catalyst of the comparative example which only contains K and does not additionally contain any Ru shows a performance which is considerably inferior to the Ni-catalyst of reference example 1. Accordingly, it has quite unexpectedly been found that there is a very strong synergetic effect may be achieved by adding small amounts of Ru to a catalyst containing Ni and K, wherein said effect is magnitudes greater than the improvement observed when adding the same small amount of Ru to a catalyst only containing Ni.

[0209] Therefore, it has quite surprisingly been found that the catalyst of the present invention shows a very strong synergetic effect between the Ni, Ru, and K components which would by no means have been expected when considering the results obtained for the catalyst containing only Ni, the catalyst containing only Ni and Ru, and the catalyst containing only Ni and K. This result is all the more surprising in view of the fact that the performance of the catalyst containing only Ni and K is significantly worse than the performance of the catalyst containing only Ni.

CITED PRIOR ART

[0210] I. Lucentini et al., Ind. Eng. Chem. Res. 2021, 60, 18560-18611 [0211] T. Le et al., Korean J. Chem. Eng., 2021, 38(6), 1087-1103 [0212] Bell et al., Top Catal., 2016, 59,1438-1457 [0213] X.-K. Li et al., Journal of Catalysis, 2005, 236, 181-189