Reforming catalyst, preparation thereof, use thereof for producing hydrogen, and device for generating electricity

Abstract

The present invention relates to a catalyst, a catalyst body, and a device for reforming hydrocarbons, in particular methane, from natural gas. Said catalyst contains precious metals, in particular platinum and rhodium, and a special carrier oxide, which contains magnesium spinel as well as cerium oxide and aluminium oxide. The invention also relates to a method for preparing said catalyst, and to the use of said catalyst to produce hydrogen.

Description

[0001] Reforming catalyst, production thereof, use thereof for producing hydrogen and device for generating electricity

[0002] Description

[0003] The present invention is directed to a catalyst, catalyst body, and a device for reforming hydrocarbons, in particular methane from natural gas. This catalyst contains precious metals and a specific carrier oxide. A process for its production and its use in the production of hydrogen are also claimed.

[0004] Low-emission mobility and power generation will play an increasingly important role in the future. One way to achieve this is to use hydrogen as an energy carrier. There are many approaches to this. One problem in this context is the production and storage of hydrogen. Hydrogen is highly volatile and, as the lightest chemical element, can only be liquefied under extreme conditions.

[0005] Therefore, there is an increasing search for solutions to produce hydrogen where it is needed. One approach to producing hydrogen in situ is the conversion of hydrocarbons, such as natural gas, using a reforming catalyst at elevated temperatures. Hydrocarbons and natural gas are comparatively easy to store and, thanks to existing infrastructure, are available almost everywhere. This hydrogen can then be converted into electricity in a fuel cell, for example, which can be used for transportation or stationary applications.

[0006] Corresponding processes and catalysts for reforming are known to the person skilled in the art (e.g. WO201103338A2, WG2003104143A1 , US2013079217AA,

[0007] US2009283419AA, US2008219918AA, EP2251080A1). WG2005056179A1 specifies catalysts for the reforming of hydrocarbons to produce hydrogen, which contain precious metals and carrier oxides. Among other things, carrier oxides based on aluminum oxide, magnesium oxide, and cerium oxide are proposed. The aluminum oxide is mixed with magnesium in the form of a spinel into the carrier oxide. Further addition of aluminum oxide and cerium oxide completes the structure of the carrier oxide.

[0008] Despite the wealth of proposals for suitable catalysts, the challenge still remains to develop further, improved reforming catalysts. These should exhibit sufficient stability and activity to generate hydrogen under the most efficient conditions possible. Furthermore, such a catalyst should be highly robust and durable, as well as cost-effective. The sharp rise in the price of rhodium, in particular, requires further optimization of such catalysts, including with regard to their activity. In this context, substitution with platinum may be helpful. Although less active in the steam reforming of methane, it can be used more advantageously due to its significantly lower price.

[0009] These and other problems arising from the prior art are solved by a reforming catalyst having the features of the present claim 1. Claims 2-8 relate to preferred embodiments of the catalyst according to the invention. Claim 1 is directed to a substrate monolith comprising the catalyst, while claim 9 teaches a corresponding device for power generation. Claims 10-11 are directed to a process for producing the corresponding catalysts, and claims 12-14 are directed to suitable uses thereof.

[0010] By specifying a reforming catalyst for generating hydrogen from hydrocarbons, in particular methane, which comprises precious metals and at least one carrier oxide on which the precious metals are deposited, wherein the precious metals are selected from the group consisting of Pt, Pd, and Rh, and the carrier oxide comprises a MgAhCU spinel, CeCl2, and Al2O3, the stated problem is solved very simply, but no less surprisingly. The reforming catalyst presented here exhibits extremely advantageous activity compared to the prior art examples, particularly in terms of the zoned architecture and distribution of the precious metals. Furthermore, the catalyst is very robust against changing ambient conditions and exhibits exceptional long-term stability (see Table 1). This was not expected on the priority date.

[0011] The reforming catalyst according to the invention is surprisingly simple in its construction. It advantageously consists of precious metals deposited on a carrier oxide, in particular Pt and Rh or only Rh. It has proven advantageous for the precious metals, in particular Pt and Rh, to be deposited together on the oxides. In this case, "co-deposited" means that no differentiation is made with regard to the oxides, such that, for example, Rh is deposited only on cerium oxide and Pt only on aluminum oxide. It is possible that the co-deposition of the precious metals, in particular Pt and Rh, promotes strong hydrogen production (CH4 + 2 H2O -> 4 H2 + CO2).

[0012] In this case, physical mixtures of aluminum oxide, cerium oxide, and spinel (MgAhC; https: / / de.wikipedia.org / w / index.php?title=Spi- nell&oldid=224329096) are constituents of the carrier oxide. The composition of the carrier oxide can vary. In the present case, the currently best composition is 8.7 MgAhC + CeC>2 + 3 Al2O3. Possible further compositions can be obtained as desired through mixtures, whereby at least all three components must always be included. Preferred mixtures are between 5 MgAhC + CeC>2 + 1.7 Al2O3 and 20 MgAhC + CeC>2 + 6.9 Al2O3. All materials familiar to the person skilled in the art for this purpose are suitable as constituents of the carrier oxide within the scope of the invention.

[0013] Particularly suitable aluminum oxides in this context are selected from the series consisting of aluminum oxide and doped aluminum oxide. Doped aluminum oxides are, for example, aluminum oxides doped with lanthanum oxide, zirconium oxide, silicon oxide, cerium oxide, barium oxide, and / or titanium oxide. Aluminum oxide, La- or cerium-doped aluminum oxide is advantageously used, with lanthanum being used in amounts of, in particular, 1 to 10 wt. %, preferably 3 to 6 wt. %, each calculated as La2O3 and based on the weight of the stabilized aluminum oxide. Even in the case of barium oxide-doped aluminum oxide, the proportion of barium oxide is, in particular, 1 to 10 wt. %, preferably 3 to 6 wt. %, each calculated as BaO and based on the weight of the stabilized aluminum oxide. A particularly suitable aluminum oxide is lanthanum-stabilized aluminum oxide, which may optionally be further doped with cerium oxide, barium oxide, and / or strontium oxide.The carrier oxide preferably comprises at least one aluminum oxide or doped aluminum oxide. In this context, γ-aluminum oxide or La-stabilized γ-aluminum oxide with a BET surface area of ​​30 to 250 m² is particularly preferred. 2 / g, preferably from 100 to 200 m 2 / g (determined according to DIN 66132 - latest version on the date of filing). Such active aluminum oxide is widely described in the literature and - as already mentioned - is available on the market (e.g. from Sasol®). Very preferred is an aluminum oxide or doped aluminum oxide with a particle size distribution of d50 - value of < 100 pm, preferably < 70 pm and very preferably < 50 pm (Q3 distribution, ISO 13320-1 - latest version on the date of filing). The carrier oxide comprises at least one high-surface-area and temperature-stable cerium oxide, which can also be purchased commercially (e.g. from Solvay®). Cerium oxide is used in amounts of 1 to 20 wt.%, preferably 8 to 12 wt.% in the carrier oxide.

[0014] As a third component, the carrier oxide contains at least one MgAhO4-type spinel. This is used as the main component in amounts of 50 to 90 wt.%, preferably 60 to 80 wt.%, in the carrier oxide. This can be produced in-house (e.g., DE1571299B2; https: / / de.wikipedia.orq / w / index.php?title=Spinelle&oldid=225306698) or obtained commercially. The remainder of the carrier oxide is then preferably only the above-mentioned aluminum oxide.

[0015] It is particularly advantageous that the present reforming catalyst does not contain any additional transition metals or transition metal oxides. In particular, the present catalyst does not contain elements selected from the group consisting of zirconium, chromium, and nickel.

[0016] The reforming catalyst comprises precious metals, particularly Pt and Rh, deposited on the support oxide. Pt and Rh are preferably used. The molar ratio of Pt to Rh is preferably 1:2 to 8:1, more preferably 1:1 to 5:1, and most preferably 2:1 to 3:1. It is also possible for no Pt and only Rh to be present on the entire catalyst or in zones.

[0017] The reforming catalyst is generally present as a normal coating on a substrate monolith. Therefore, the embodiment in which the reforming catalyst according to the invention comprises additional binders is advantageous in this regard. Suitable binders include, for example, non-catalytically active or only slightly active, temperature-stable metal oxides, such as SiO2, Al2O3, and ZrO2. The person skilled in the art knows which materials are suitable here. The proportion of such binders in the reforming catalyst can, for example, amount to up to 10 wt.%, preferably up to 5 wt.%, of the total mass of the reforming catalyst. Binders are suitable for ensuring stronger adhesion of the coating to a support. For this purpose, a certain particle size of the metal oxides in the binder is advantageous. This can be adjusted by the person skilled in the art according to their requirements. For example,The addition of sols of the above-mentioned elements to the coating suspension has proven particularly advantageous. An aluminum sol, such as Nyacol® or boehmite (https: / / de.wikipedia.orq / w / index.php?title=B%C3%B6hmit&oldid=226104395), is particularly advantageous in this context.

[0018] The absolute length of the reforming catalysts according to the invention can also be adjusted by the person skilled in the art and adapted to their needs. A length of 5.0-16.0 cm, preferably 6.0-14.0 cm, and most preferably 7.0-13.0 cm has proven advantageous for the present application.

[0019] In a further aspect, the present invention relates to a substrate monolith comprising a reforming catalyst according to the invention. The latter can be applied to a substrate monolith, preferably to a flow-through substrate, by a coating step familiar to those skilled in the art (DE102019100099A1 and literature cited therein). A filter substrate such as a wall-flow filter is also possible in this context. Flow-through substrates are substrate monoliths commonly used in the art and can consist of metal (e.g., WO17153239A1, WO16057285A1, WO15121910A1 and literature cited therein) or ceramic materials. Corrugated substrates can also be regarded as flow-through substrates. These are known to those skilled in the art as supports made of corrugated sheets made of inert materials.Suitable inert materials include fibrous materials with an average fiber diameter of 50 to 250 μm and an average fiber length of 2 to 30 mm. Fiber-shaped, heat-resistant materials made of silicon dioxide, especially glass fibers, are preferred. However, refractory ceramics such as cordierite, silicon carbide, or aluminum titanate, etc., are preferably used as honeycomb supports. The number of channels in these supports per unit area is characterized by the cell density, which is typically between 300 and 900 cells per square inch (cpsi). The wall thickness of the channel walls for ceramics is between 0.5 and 0.05 mm.

[0020] The total amount of coatings in the substrate monolith is selected so that the catalyst according to the invention is used as efficiently as possible. In the case of a flow-through substrate, for example, the total amount of reforming catalyst in the coating (solids content) per support volume (total volume of the support) can be between 100 and 300 g / L, in particular between 120 and 250 g / L. The total precious metal content of the substrate monolith is preferably from 0.015 to 5 g / L, more preferably from 1.0 to 3.0 g / L, and particularly preferably from 1.6 to 2.2 g / L of support volume. If platinum is used, it should be in the range of 0.5 to 2.5 g / L, more preferably 1.3 to 1.9 g / L of support volume in the coating. Rhodium is present in the reforming catalyst in an amount of 0.1 - 1.0 g / L, more preferably 0.3 - 0.4 g / L carrier volume in the respective component.

[0021] In a further preferred embodiment, the substrate monolith discussed here has a design that is particularly advantageous for the present application. In this case, a zoned and / or layered design is possible. A layered design - as shown in Fig. 2 - can be used. However, a zoned design as shown by way of example in Fig. 1 is also preferred. The substrate monolith is particularly preferably constructed in such a way that it has a coating zone comprising Pt on the carrier oxide on the upstream side and a coating zone with a metal mixture comprising Pt and Rh on the carrier oxide on the downstream side. It can also be advantageous if both zones contain Pt and Rh and the front zone contains a higher concentration of Pt and the rear zone a higher concentration of Rh.For the most efficient methane reforming, it is surprisingly advantageous to mix Pt and Rh before introducing them into the washcoat, whether they occur together in one zone or together throughout the entire section. Complete separation of Pt and Rh has not proven advantageous. It is also possible to locate the zones on different flow-through substrates connected directly one after the other. Upstream means that this zone comes into contact with the medium to be converted first, before the other. Downstream is understood accordingly.

[0022] The preferred upstream zone with the Pt on a carrier oxide is used in an amount of 15 to 200 g / L, in particular between 20 and 200 g / L, particularly preferably about 30-100 g / L total carrier volume. The precious metal content here can be in the range of 0.01-1.50 g / L, more preferably 0.5-1.3 g / L total carrier volume in the coating.

[0023] Downstream of the zone with the Pt coating, a Pt / Rh zone is also preferably located. This preferably contains Pt:Rh in a molar ratio of 1:1, but can have other ratios of 3:1 to 1:2 depending on the gas composition and temperature profile of the catalyst. It may also be advantageous to use only rhodium as the precious metal in this zone. Therefore, the values ​​specified above for the total precious metal content apply.

[0024] Alternatively, depending on the gas composition and temperature profile of the catalyst, Rh may be present in the upstream zone in addition to or only in concentrations of preferably 0.07–0.3 g / l, especially 0.1–0.2 g / l. The platinum content in the downstream zone can then be 0.07–1.0 g / l, preferably 0.5–1.0 g / l. Therefore, the values ​​given above for the total precious metal content apply.

[0025] As already indicated, the zones can be present on a single substrate monolith or on two, which are then arranged directly one behind the other. The zone lengths can be selected by the person skilled in the art. It has proven advantageous if, in the reforming catalyst according to the invention, the upstream zone is shorter than the downstream zone due to the sharp temperature drop in the catalyst. The ratio of the zone lengths is preferably between 50 / 50 and 30 / 70, and more preferably around 40 / 60.

[0026] The present invention also relates to a device for generating electricity, comprising a substrate monolith as just outlined and a fuel cell in fluid contact with the substrate monolith. Such devices and their design are known in principle to those skilled in the art (e.g., JP2008007359 (A), CN111029628). The hydrogen produced on the substrate monolith over the reforming catalyst according to the invention is brought into contact with the anode of the fuel cell via a fluid connection. It is then converted into hydrogen ions, which oxidize with atmospheric oxygen at the cathode to form H2O, which can be released into the ambient air.

[0027] The present invention further provides a process for producing a corresponding reforming catalyst substrate, in which the substrate monolith is coated with a coating suspension comprising the components of the reforming catalyst according to the invention in water, then dried and calcined and finally tempered at a temperature of 400 - 600°C for a maximum of 6 hours.

[0028] In a first step, a coating suspension is preferably prepared from the carrier oxide components and, if appropriate, binders in water. This suspension is then mixed with solutions of water-soluble precious metal compounds, in particular Rh compounds and, if appropriate, Pt compounds. The precious metals are thus preferably deposited together by mixing and subsequent injection onto the entire carrier oxide. Separate preparation of the oxides containing precious metals and their subsequent blending is also possible. The preparation of corresponding suspensions for coating substrates is well known to the person skilled in the art from the field of manufacturing automotive exhaust catalysts (e.g.,

[0029] DE202016008848A1).

[0030] This suspension is then applied to a substrate monolith, in particular a flow-through substrate. These procedures are also familiar to those skilled in the art, for example from the field of automotive exhaust gas catalysts (e.g. W02020141188A1 and the literature cited therein). The zones can be coated using methods familiar to those skilled in the art (e.g. EP1273344A1, EP 2533901 A1). The coated substrate monolith is then dried and calcined, if necessary. It has proven advantageous if the coated substrate monolith is subsequently tempered at a somewhat higher temperature in order to completely expel organic constituents from the coating, for example in the form of CO2 or NOx. This also makes it possible to establish a mass balance based on oxides.

[0031] It is particularly advantageous if the coated substrate monolith is dried at 100–150°C, preferably 110–130°C. The calcination temperature should not be too high. It is preferably between 300°C and a maximum of 500°C, preferably between 320°C and 400°C. The catalyst is then tempered for a maximum of 6 hours, more preferably a maximum of 43 hours, and particularly preferably for up to 3 or 2 hours at a temperature of 400–600°C, preferably 520–580°C. The reforming catalyst on the substrate monolith is then ready for installation in the device according to the invention.

[0032] The present invention also relates to the use of a reforming catalyst according to the invention for producing hydrogen from hydrocarbons, in particular methane. Methane, for example, is the most stable hydrocarbon and is comparatively difficult to convert catalytically. However, it forms the main constituent of natural gas. The reforming catalyst according to the invention is capable of sufficiently converting methane. The conversion preferably takes place adiabatically at temperatures of 300-900°C, preferably 650-800°C, in an atmosphere consisting preferably of methane, water vapor, and, through possible exhaust gas recirculation, additionally CO, CO2, and H2. Preference is given to using the hydrogen produced from natural gas (CNG, LNG). In a further preferred use, the hydrogen produced in this way is used to generate electricity in a fuel cell.Further preferred uses according to the invention can be found in both mobile (vehicles) and stationary applications (industrial plants). By coating, for example, a cordierite flow-through substrate with a Rh-containing and optionally Pt-containing coating medium on the corresponding carrier oxides, followed by thermal treatment, a reforming catalyst substrate is produced that generates hydrogen from hydrocarbons, in particular methane, in a highly water-containing and oxygen-free reaction atmosphere and at elevated temperatures. The reforming catalyst is long-term stable and, with a desired continuous use of over 50,000 hours and under very harsh conditions, is still sufficiently active to generate hydrogen accordingly, even towards the end of its service life.Due to the endothermic reaction, a very strong temperature gradient exists within the reforming catalyst, which can reach up to 200 °C under the desired application parameters. The reforming catalyst according to the invention meets these requirements.

[0033] Figures:

[0034] Fig. 1: Preferred layout of the reforming catalyst according to the invention: zoning.

[0035] Fig. 2: Further conceivable embodiments of the reforming catalyst according to the invention: layers.

[0036] Fig. 3: Further conceivable embodiments of the reforming catalyst according to the invention: mixtures.

[0037] Examples:

[0038] To manufacture the catalysts, cordierite substrates from NGK (4.66" x 4.66" x 5.00", 4.3 / 300) are coated with a washcoat. Other flow-through substrates, particularly those with different cell densities and wall thicknesses and also made of cordierite (e.g., 5.66" x 5.66" x 5.00", 4 / 400), are also possible. Metallic substrates can also be used. The catalytic activity is not substrate-dependent.

[0039] To prepare the washcoat, the carrier oxide (Puralox® SCFa 110 from Sasol) and the AlO(OH) binder (Nyacol® AL20 from Nyacol) are first dispersed in water one after the other. The precious metal solutions are then injected. For the catalyst zones containing both precious metals, the platinum nitrate and rhodium nitrate solutions are mixed and diluted with water prior to injection. After 30 minutes of stirring, the pH is adjusted to > 7, and the washcoat is circularly ground. The target particle size distribution is a d50 value of 4.5–5.5 pm and a d50 value of 10.6–14.8 pm.

[0040] Depending on the oxide-based solids content, which is ideally 33 - 36%, and the rheology of the washcoat, it can be adjusted using nitric acid (HNO3), tetraethylammonium hydroxide (TEAH) or acetic acid (HCOOH) to facilitate coatability.

[0041] Finally, the substrate is clamped vertically in a holding device, and the washcoat is pumped into the substrate from below to the desired height and then vacuumed out again. By weighing after a drying and calcining step, any remaining mass is determined and recoated if necessary.

[0042] In an alternative coating process, the washcoat is applied to the vertically aligned substrate. By applying negative pressure, it is then sucked through the substrate. By weighing after a drying and calcination step, any remaining mass is determined and then recoated from the other side. In addition to this coating process, the required washcoat can also be determined before coating and sucked into the substrate from each side in two steps, half according to the zones that may be present. The final step is the thermal treatment of the catalyst. After drying at 100 - 120 °C and calcination at 350 °C for approximately 15 minutes after each coating step, it is then annealed at 550 °C for 2 hours.

[0043] For testing, 1" x 3" cores are taken from the coated catalyst and tested for their methane conversion in an adiabatic quartz glass reactor.

[0044] The reaction gas mixture primarily tested consists of 5.9% CH4, 21.9% H2O, 1.8% CO, 12.9% CO2, 7.5% H2, and N2 for balance at a space velocity of 25,000 l / h. The measurement begins at a gas temperature of 150 °C. Heating is carried out at a rate of 10 K / min up to 700 °C. Once this maximum temperature is reached, it is held constant for 30 minutes, after which the measurement ends. Finally, the gas is cooled in the reaction gas atmosphere to 450 °C and then to room temperature in air.

[0045] The methane conversion, which is a measure of the activity of the catalyst, is calculated from the methane input concentration before methane conversion and the concentration at maximum reactor temperature.

[0046] In addition to testing fresh catalysts, simulation of catalyst aging is necessary to evaluate long-term stability and activity. For this purpose, the prepared catalyst cores were aged for approximately 50 hours at 850 °C in a flowing atmosphere of forming gas (3.3% H2, N2) and 44% H2O. The decrease in catalytic activity after aging is a measure of the long-term stability and activity of the catalysts.

[0047] Measurement results (Table 1 : Tested catalysts with Pt:Rh = 2:1)

[0048] Catalyst name / Methane conversion Sales decline / % Molar Pt:Rh-

[0049] Parameters at Tm = 700 °C / % (fresh --> aged) Ratio Architecture

[0050] Example 1 fresh 27.12 _ _ . According to Example 1 aged 24.28 l-| 9-

[0051] Example 2 fresh 25.3523g 2 1 According to

[0052] Example 2 aged 22.96 Fig. 1. b)

[0053] Example 3 fresh 24.67 . _ . _ . According to i ,oi :1 c . . x

[0054] Example 3 aged 22.86 h| 9- 1 ■

[0055] Example 4 fresh 23.77 According to

[0056] Example 4 aged 23.08 Fig. 3

[0057] REPLACEMENT SHEET (RULE 26) As can be seen in the table above, the architecture shown in Fig. 1 a) with a Pt:Rh ratio of 2:1 results in the highest methane conversion before and after aging (Example 1). In contrast, the lowest conversion decline after aging is obtained in Example 4, based on the architecture shown in Fig. 3. The seemingly low methane conversion at first glance is due to the fact that only small cores and no full catalysts were tested.

Claims

Patent claims 1. Reforming catalyst for producing hydrogen from hydrocarbons, in particular methane, comprising noble metals and at least one carrier oxide on which the noble metals are deposited, characterized in that the noble metals are selected from the group consisting of Pt, Pd and Rh and the carrier oxide comprises a MgAhC spinel as well as CeC>2 and Al2O3.

2. Reforming catalyst according to claim 1, characterized in that it does not contain any elements selected from the group consisting of zirconium, chromium and nickel.

3. Reforming catalyst according to claim 1 or 2, characterized in that it comprises a binder.

4. Reforming catalyst according to one of claims 1 - 3, characterized in that the molar ratio of Pt to Rh is 1:2 to 8:

1.

5. Substrate monolith comprising a reforming catalyst according to any one of claims 1-4.

6. Substrate monolith according to claim 5, characterized in that it has on the upstream side a coating zone comprising Pt on the carrier oxide and on the downstream side a coating zone with a metal mixture comprising Pt and Rh on the carrier oxide.

7. Substrate monolith according to claim 6, characterized in that both zones contain Pt and Rh and the front zone contains a higher concentration of Pt and the rear zone contains a higher concentration of Rh.

8. Substrate monolith according to claim 6, characterized in that both zones contain Pt and Rh and the front zone contains a higher concentration of Rh and the rear zone contains a higher concentration of Pt.

9. Device for power generation comprising a substrate monolith according to claim 5 - 8 and a fuel cell in fluid contact therewith.

10. A process for producing a substrate monolith according to claims 5-7, characterized in that the substrate monolith is coated with a coating suspension comprising the components of the reforming catalyst according to claims 1-4 in water, then dried and / or calcined and finally tempered at a temperature of 400-600°C for a maximum of 6 hours.

11. A method according to claim 9, characterized in that the precious metals are deposited together on the entire carrier oxide.

12. Use of a catalyst according to any one of claims 1-4 for producing hydrogen from hydrocarbons.

13. Use of a catalyst according to claim 12, characterized in that the hydrogen is produced from natural gas (CNG, LNG).

14. Use according to one of claims 12 or 13, characterized in that the hydrogen produced is used to generate electricity in a fuel cell.

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