Reforming catalyst, production thereof, use thereof for the generation of hydrogen, and device for

Abstract

The present invention relates to a catalyst, a catalyst body and a device for reforming hydrocarbons, in particular methane from natural gas. The catalyst contains noble metals, in particular platinum and rhodium, as well as special support oxides comprising magnesium spinel, cerium oxide and aluminum oxide. The invention also relates to a method for producing the catalyst and to the use of the catalyst for producing hydrogen.

Description

[0001] Specification

[0002] The present invention relates to a catalyst, a catalyst body and a device for reforming hydrocarbons, in particular methane from natural gas. The catalyst contains noble metals and a special support oxide. The present invention also relates to a method for preparing the catalyst and the use of the catalyst for producing hydrogen.

[0003] Low-emission mobility and power generation will play an increasingly important role in the future. One way to achieve low-emission mobility and power generation is to use hydrogen as an energy carrier. There are many methods for this. A problem in this context is the production and storage of hydrogen. Hydrogen is very volatile and can only be liquefied under extreme conditions as the lightest chemical element.

[0004] Therefore, there is an increasing search for solutions for generating hydrogen where it is needed. One method for generating hydrogen in situ is to convert hydrocarbons, such as natural gas, through a reforming catalyst at elevated temperatures. Hydrocarbons and natural gas are relatively easy to store and are available almost anywhere due to the existing infrastructure. The hydrogen can then be converted into an electric current, for example, in a fuel cell, and this electric current can be used for mobile or stationary applications.

[0005] The corresponding methods and catalysts for reforming are known to those skilled in the art (for example, WO201103338A2, WO2003104143A1, US2013079217AA, US2009283419AA, US2008219918AA, EP2251080A1). WO2005056179A1 describes a catalyst for reforming hydrocarbons to produce hydrogen, which contains noble metals and a support oxide. In particular, support oxides based on alumina, magnesia and ceria are proposed herein. Alumina is mixed into the support oxide in the form of a spinel containing magnesium. Further addition of alumina and addition of ceria complete the composition of the support oxide.

[0006] Despite many suggestions for the corresponding catalysts, the problem of providing further improved reforming catalysts still remains. These reforming catalysts should have sufficient stability and activity to be able to produce hydrogen under the most efficient possible conditions. In addition, the corresponding catalysts should be highly robust and durable and as cost-effective as possible. In particular, the significant increase in the price of rhodium requires further optimization of such catalysts, especially in terms of their activity. Against this background, replacing rhodium with platinum may be helpful. Platinum has lower activity in the steam reforming of methane, but is more advantageous to use due to its significantly lower price.

[0007] These and other problems that are clearly present in the prior art are solved by a reforming catalyst comprising the features of claim 1. Claims 2 to 8 relate to preferred embodiments of the catalyst according to the invention. Claim 1 relates to a substrate monolith comprising the catalyst, and claim 9 teaches a corresponding apparatus for power generation. Claims 10 to 11 relate to a method for preparing the corresponding catalyst, and claims 12 to 14 relate to suitable uses of the catalyst.

[0008] By specifying a reforming catalyst for the production of hydrogen from hydrocarbons, in particular methane, a very simple but equally surprising solution to the said problems can be found, which reforming catalyst comprises a noble metal and at least one support oxide on which the noble metal is deposited, wherein the noble metal is selected from the group consisting of Pt, Pd and Rh, and the support oxide comprises MgAl 2 O 4 spinel, CeO 2 and Al 2 O 3 . Compared with examples of the prior art, the reforming catalyst proposed herein shows extremely advantageous activity, especially with regard to the sectional structure and noble metal distribution. Furthermore, the catalyst is very robust under changing environmental conditions and shows extraordinary long-term stability (see Table 1). As of the priority date, this was unexpected.

[0009] The reforming catalyst according to the invention is surprisingly simple in structure. It advantageously consists of a noble metal, in particular Pt and Rh or only Rh, deposited on a support oxide. It has been shown that it is advantageous for the noble metals, in particular Pt and Rh, to be deposited together on the oxide. In this context, co-deposition means that there is no differentiation with respect to the oxide to the extent that, for example, Rh is only deposited on cerium oxide and Pt is only deposited on alumina. During co-deposition, alloying of the noble metals, in particular by alloying of Pt and Rh, has the potential to have a beneficial effect on the substantial production of hydrogen (CH 4 +2H 2 O -> 4H 2 +CO 2 ).

[0010] In this case, the components of the oxidic support are a physical mixture of alumina, cerium dioxide and spinel (MgAl 2 O 4 ; https: / / de.wikipedia.org / w / index.php?title=Spinell&oldid= 224329096 ). The composition of the support oxide can be variable. In this case, the currently best composition is 8.7MgAl 2 O 4 +CeO 2 +3Al 2 O 3. Although at least all three components must always be included, additional possible compositions can be obtained by mixing them as needed. Preferred mixtures are between 5MgAl 2 O 4 +CeO 2 +1.7Al 2 O 3 and 20MgAl 2 O 4 +CeO 2 +6.9Al 2 O 3 . In the context of the present invention, all materials familiar to those skilled in the art for this purpose can be considered as components of the support oxide.

[0011] Here, particularly suitable aluminas are selected from the series consisting of alumina and doped alumina. Doped alumina is, for example, alumina doped with lanthanum oxide, zirconium oxide, silicon oxide, cerium oxide, barium oxide, and / or titanium oxide. Advantageously, alumina, La-doped alumina, or Cer-doped alumina is used, in each case calculated as La 2 O 3 and based on the weight of the stabilized alumina, the amount of lanthanum is specifically 1 wt% to 10 wt%, preferably 3 wt% to 6 wt%. Additionally, in the case of doping alumina with barium oxide, in each case calculated as BaO and based on the weight of the stabilized alumina, the proportion of barium oxide is specifically 1 wt% to 10 wt%, preferably 3 wt% to 6 wt%. Particularly suitable alumina is lanthanum-stabilized alumina, which is optionally additionally doped with cerium oxide, barium oxide, and / or strontium. The support oxide preferably contains at least one alumina or doped alumina. Particularly preferred herein is specifically γ-alumina or La-stabilized γ-alumina, which has a BET surface area of 30 m 2 / g to 250 m 2 / g, preferably 100 m 2 / g to 200 m 2 / g (determined according to the latest version of DIN 66132 as of the filing date). Such activated alumina is widely described in the literature and, as mentioned above, is commercially available (e.g., from company). Most preferably, the alumina or doped alumina has a particle size distribution d50 value < 100 μm, preferably < 70 μm, most preferably < 50 μm (Q3 distribution, latest version of ISO 13320-1 as of the filing date).

[0012] The support oxide contains at least one high-surface-area and temperature-stable cerium oxide, which is also commercially available (e.g., from (obtained by the company). The amount of cerium oxide in the support oxide is from 1 wt% to 20 wt%, preferably from 8 wt% to 12 wt%.

[0013] The support oxide has at least one MgAl 2 O 4 type spinel as the third component. The spinel is used as the main component in the support oxide, and its amount is from 50 wt% to 90 wt%, preferably from 60 wt% to 80 wt%. This can be produced by oneself (for example, DE1571299B2 ; https: / / de.wikipedia.org / w / index.php?title=Spinelle&oldid= 225306698 ), or it can be obtained commercially. The remainder of the support oxide is preferably only the above-mentioned alumina.

[0014] Particularly advantageously, the reforming catalyst of the present invention does not require any additional transition metals or transition metal oxides. Specifically, the catalyst of the present invention does not contain elements selected from the group consisting of zirconium, chromium, and nickel.

[0015] The reforming catalyst contains noble metals deposited on the support oxide, especially Pt and Rh. Preferably Pt and Rh. Therefore, the molar ratio of Pt to Rh is preferably from 1:2 to 8:1, more preferably from 1:1 to 5:1, and most preferably from 2:1 to 3:1. It is also possible that only Rh is present on the entire catalyst or in a zone without Pt.

[0016] The reforming catalyst is usually present as a conventional coating on a substrate monolith. In this regard, embodiments in which the reforming catalyst according to the present invention contains an additional binder are therefore advantageous. For example, active temperature-stable metal oxides with little or no catalytic activity such as SiO 2 、Al 2 O 3 and ZrO 2 are suitable as binders. Those skilled in the art know the materials that can be used here. The proportion of such a binder in the reforming catalyst can reach, for example, at most 10 wt% of the total mass of the reforming catalyst, preferably at most 5 wt%. The binder is suitable for ensuring a stronger adhesion of the coating to the support. For this purpose, a specific particle size of the metal oxide in the binder is advantageous. This can be adjusted accordingly by those skilled in the art according to individual requirements. For example, adding a sol of the above elements to the coating suspension has proven to be advantageous. In this context, aluminum sols such as or boehmite ( https: / / de.wikipedia.org / w / index.php?title= B%C3%B6hmit&oldid=226104395 ) are particularly advantageous.

[0017] The absolute length of the reforming catalyst according to the invention can also be adjusted by those skilled in the art and adapted to individual needs. It has been shown that lengths from 5.0 cm to 16.0 cm, preferably from 6.0 cm to 14.0 cm and most preferably from 7.0 cm to 13.0 cm are advantageous for the intended use of the invention.

[0018] The invention also relates to a substrate monolith comprising the reforming catalyst according to the invention. The reforming catalyst can be applied to the substrate monolith by coating steps familiar to those skilled in the art, preferably to a flow-through substrate (DE102019100099A1 and the documents cited therein). In this context, filter substrates such as wall-flow filters are also possible. Flow-through substrates are substrate monoliths commonly used in the prior art and can be composed of metals (e.g., WO17153239A1, WO16057285A1, WO15121910A1 and the documents cited therein) or ceramic materials. "Corrugated substrates" can also be considered flow-through substrates. These are known to those skilled in the art as carriers and are made of corrugated sheets composed of inert materials. Suitable inert materials are, for example, fibrous materials having an average fiber diameter of 50 μm to 250 μm and an average fiber length of 2 mm to 30 mm. Fiber heat-resistant materials made of silica, especially glass fiber, are preferred. However, refractory ceramics such as cordierite, silicon carbide or aluminum titanate, etc. are preferably used as honeycomb carriers. The number of channels of these carriers per surface area is characterized by the pore density, and the pore density generally ranges between 300 pores per square inch and 900 pores per square inch (cpsi). The wall thickness of the channel walls in the ceramic is between 0.5 mm and 0.05 mm.

[0019] The total amount of the coating in the substrate monolith is selected such that the catalyst according to the invention is utilized as effectively as possible overall. In the case of a flow-through substrate, the total amount of the reforming catalyst in the coating (solid ratio) / carrier volume (total volume of the carrier) can be, for example, between 100 g / L and 300 g / L, especially between 120 g / L and 250 g / L. The total noble metal content of the substrate monolith is preferably from 0.015 g / L to 5 g / L of carrier volume, more preferably from 1.0 g / L to 3.0 g / L of carrier volume, and particularly preferably from 1.6 g / L to 2.2 g / L of carrier volume. If platinum is used, it should be in the range of 0.5 g / L to 2.5 g / L of carrier volume, more preferably 1.3 g / L to 1.9 g / L of carrier volume. The amount of rhodium present in the reforming catalyst is from 0.1 g / L to 1.0 g / L, more preferably from 0.3 g / L to 0.4 g / L of carrier volume in the relevant components.

[0020] In another preferred embodiment, the substrate blank discussed herein has a design that is particularly advantageous for the intended use of the present invention. In this case, a partitioned and / or layered design is possible. In this case, a layered design such as Figure 2 as shown may be used. However, as shown by the examples in Figure 1 , a partitioned design is also preferred. It is particularly preferred to construct the substrate blank in such a way that it has a coated zone containing Pt on a support oxide on the upstream side and a coated zone containing a metal mixture of Pt and Rh on a support oxide on the downstream side. It may also be advantageous if both zones contain Pt and Rh, where the former zone contains a higher concentration of Pt and the latter zone contains a higher concentration of Rh. If Pt and Rh occur together in one zone or together in an entire section, it is surprisingly advantageous to mix them before introducing them into the washcoat so that methane reforming can be carried out as effectively as possible. A complete separation of Pt and Rh has not proven to be advantageous. It is also possible to locate these zones on different flow-through substrates that are directly connected one after the other. Upstream means that this zone first comes into contact with the medium to be converted and then the other zone does. Downstream should be understood accordingly.

[0021] The amount of the preferred upstream zone containing Pt on a support oxide is from 15 g / L to 200 g / L, in particular from 20 g / L to 200 g / L, and particularly preferably about 30 g / L to 100 g / L of the total support volume. The noble metal content in the coating can range from 0.01 g / L to 1.50 g / L, more preferably from 0.5 g / L to 1.3 g / L of the total support volume.

[0022] Downstream of the zone containing the Pt coating, a Pt / Rh zone is more preferably present. The Pt / Rh zone preferably contains Pt:Rh in a molar ratio of 1:1, but may also have other ratios from 3:1 to 1:2, depending on the gas composition and the temperature profile of the catalyst. It is also advantageous to use only rhodium as the noble metal in this zone. Therefore, the values for the total noble metal content given above apply.

[0023] Alternatively, depending on the gas composition and the temperature profile of the catalyst, the upstream zone may contain additional Rh or only Rh, in an amount preferably from 0.07 g / l to 0.3 g / l, in particular from 0.1 g / L to 0.2 g / L. Then the platinum content in the downstream zone can be from 0.07 g / l to 1.0 g / l, preferably from 0.5 g / l to 1.0 g / l. Therefore, the values for the total noble metal content given above apply.

[0024] As already mentioned, these zones can be present on a single substrate blank or on two substrate blanks, which are then arranged directly one after the other. The zone lengths can be chosen by a person skilled in the art. It has proven advantageous for the upstream zone in the reforming catalyst according to the invention to be shorter than the downstream zone due to a significant temperature drop in the catalyst. The ratio of the zone lengths is preferably between 50 / 50 and 30 / 70, and more preferably about 40 / 60.

[0025] The invention also relates to a device for power generation, which comprises the substrate blank just outlined and a fuel cell in fluid contact therewith. Such devices and their design principles are known in principle to a person skilled in the art (e.g. JP2008007359(A), CN111029628). Via a fluid connection, the hydrogen produced on the substrate blank by the reforming catalyst according to the invention is brought into contact with the anode of the fuel cell. The hydrogen is then converted into hydrogen ions, which are oxidized with oxygen from the atmosphere at the cathode to form H 2 O, which can be released into the ambient air.

[0026] The invention also relates to a method for producing the corresponding reforming catalyst substrate, in which a substrate blank is coated with a coating suspension comprising the reforming catalyst components according to the invention in water, subsequently dried and calcined, and finally tempered at a temperature of 400 °C to 600 °C for up to 6 hours.

[0027] In a first step, a coating suspension is preferably produced from a support oxide component and an optional binder in water. The suspension is then mixed with a solution of a water-soluble noble metal compound, in particular an Rh compound and an optional Pt compound. Thus, the noble metals are preferably deposited together on the entire support oxide by mixing and subsequent injection. It is also possible to produce oxides with noble metals separately and subsequently mix them. Producing the corresponding suspension for coating the substrate is known to a person skilled in the field of automotive exhaust catalysts (e.g. DE202016008848A1).

[0028] Subsequently, the suspension is applied to the substrate blank, in particular a flow-through substrate. These procedures are also familiar to a person skilled in the art, for example a person skilled in the field of automotive exhaust catalysts (e.g. WO2020141188A1 and the documents cited therein). The zones can be coated using methods familiar to a person skilled in the art (e.g. EP1273344A1, EP 2533901A1). The coated substrate blank is then optionally dried and calcined. It has proven advantageous for the coated substrate blank to be finally tempered at a slightly higher temperature to completely remove the organic components of the coating, such as CO 2 or NO x . This also makes it possible to establish an oxide-based mass balance.

[0029] Particularly advantageously, the coated substrate blank is dried at 100 °C to 150 °C, preferably 110 °C to 130 °C. The calcination temperature should not be too high. It should preferably be between 300 °C and a maximum of 500 °C, preferably between 320 °C and 400 °C. Subsequently, the catalyst is tempered at a temperature of 400 °C to 600 °C, preferably 520 °C to 580 °C, preferably for a maximum of 6 hours, more preferably for a maximum of 4.3 hours, particularly preferably for a maximum of 3 hours or 2 hours. Subsequently, the reforming catalyst on the substrate blank is ready to be inserted into the device according to the invention.

[0030] The invention also relates to the use of the reforming catalyst according to the invention for the production of hydrogen from hydrocarbons, in particular methane. For example, methane is the most stable hydrocarbon. It is relatively difficult to carry out the conversion using a catalyst. However, it is the main component of natural gas. The reforming catalyst according to the invention is capable of converting methane in a satisfactory manner. Therefore, the conversion is preferably carried out adiabatically at a temperature of 300 °C to 900 °C, preferably 650 °C to 800 °C, in an atmosphere preferably consisting of methane, steam and additionally CO, CO 2 and H 2 (by possible exhaust gas recirculation). A preferred use is the production of hydrogen from natural gas (CNG, LNG). In another preferred use, the hydrogen thus produced is used for power generation in a fuel cell. Further preferred uses according to the invention can be found in the mobile field (vehicles) and the stationary field (industrial equipment).

[0031] By coating a flow-through substrate, for example composed of cordierite, with a coating medium containing Rh and optionally Pt on the corresponding support oxide and subsequently carrying out a heat treatment, a reforming catalyst substrate is produced which produces hydrogen from hydrocarbons, in particular methane, in an oxygen-free reaction atmosphere containing a high water content and at an elevated temperature. The reforming catalyst is long-term stable and still has sufficient activity to produce hydrogen even when continuous use for more than 50,000 hours is expected and under very harsh conditions, even towards the end of its service life. Due to the endothermic reaction, there is a very significant temperature gradient within the reforming catalyst, which can be up to 200 °C under the expected application parameters. The reforming catalyst according to the invention manages to meet these requirements.

[0032] The drawings show:

[0033] Figure 1 : Preferred layout of the reforming catalyst according to the invention: Zoning.

[0034] Figure 2 : Further conceivable embodiments of the reforming catalyst according to the invention: Layers.

[0035] Figure 3 : Further conceivable embodiments of the reforming catalyst according to the invention: mixtures. Example:

[0036] To produce the catalyst, a cordierite substrate from NGK (4.66" x 4.66" x 5.00", 4.3 / 300) was coated with a washcoat. Other flow-through substrates are also possible, in particular other flow-through substrates having different pore densities and wall thicknesses and also made of cordierite (e.g. 5.66" x 5.66" x 5.00", 4 / 400). Metal substrates can also be used. The catalytic activity is not substrate-dependent.

[0037] To produce the washcoat, the carrier oxide (from Sasol) was first SCFa 110) and AlO(OH) binder (from Nyacol AL20) were dispersed in water one by one. The precious metal solutions were subsequently injected. For the catalyst zone containing two precious metals, the platinum nitrate and rhodium nitrate solutions were mixed and diluted with water before injection. After stirring for 30 minutes, the pH was adjusted to >7 and the repair substrate was ground once. The target particle size distribution had a d 50 values ​​and d of 10.6 μm to 14.8 μm 90 value.

[0038] Depending on the solids content based on the oxide (which is ideally 33% to 36%), and depending on the rheological properties of the washcoat, nitric acid (HNO 3 ), tetraethylammonium hydroxide (TEAH) or acetic acid (HCOOH) to make it easier to coat.

[0039] 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 sucked out again. Any remaining mass is determined by weighing after the drying and calcination steps and optionally reapplied.

[0040] In an alternative coating method, the washcoat is applied to a vertically aligned substrate. By applying negative pressure, the washcoat is subsequently sucked through the substrate. Any remaining mass is determined by weighing after the drying and calcining steps and reapplied from the other side. As an alternative to this coating method, the required washcoat can also be determined before coating, divided into two halves corresponding to any existing divisions and sucked into the substrate from both sides in two steps.

[0041] The last step is the heat treatment of the catalyst. After each coating step, after drying at 100 to 120°C and calcination at 350°C for about 15 minutes, tempering is performed at 550°C for 2 hours.

[0042] For testing, 1"×3" drill cores were taken from the coated catalysts and their methane conversion was tested in an adiabatic quartz glass reactor.

[0043] The main reaction gas mixture for the test consisted of 5.9% CH 4 , 21.9% H 2 O, 1.8% CO, 12.9% CO 2 , 7.5% H 2 and N 2 and was balanced at a space velocity of 25,000 l / h. Measurements were started at a gas temperature of 150 °C. It was heated to a maximum of 700 °C at 10 K / min. When this maximum temperature was reached, the temperature was kept constant for another 30 minutes, after which the measurement ended. Finally, the mixture was cooled to 450 °C in the reaction gas atmosphere and then to room temperature in air.

[0044] The methane conversion is a measure of the catalyst activity and is calculated from the methane input concentration before conversion and the concentration at the highest reactor temperature.

[0045] In addition to testing the fresh catalyst, it was necessary to simulate catalyst aging in order to be able to evaluate the long-term stability and long-term activity. For this purpose, the produced catalyst drill cores were aged for about 50 hours at 850 °C in a permeation atmosphere of synthesis gas (3.3% H 2 , N 2 ) and 44% H 2 O. The decrease in catalytic activity after aging is a measure of the long-term stability and long-term activity of the catalyst.

[0046] Measurement results (Table 1: Test catalyst with Pt:Rh = 2:1)

[0047]

[0048] As can be seen from the above table, the structure with a Pt:Rh ratio of 2:1 according to Figure 1 a) produced the highest methane conversion before and after aging (Example 1). In contrast, in Example 4 with the structure according to Figure 3 , the conversion decrease after aging was the lowest.

[0049] The methane conversion seems low at first glance because only small drill cores were tested and not the complete catalyst.

Claims

1. A reforming catalyst for generating hydrogen from hydrocarbons, especially methane, said reforming catalyst comprising a noble metal and at least one support oxide on which the noble metal is deposited, characterized in that The noble metal is selected from the group consisting of Pt, Pd, and Rh, and the support oxide contains MgAl 2 O 4 spinel and CeO 2 and Al 2 O 3 .

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

3. The reforming catalyst according to claim 1 or 2, characterized in that the reforming catalyst contains a binder.

4. The reforming catalyst according to any one of claims 1 to 3, characterized in that the molar ratio of Pt to Rh is from 1:2 to 8:

1.

5. A substrate monolith, said substrate monolith comprising the reforming catalyst according to any one of claims 1 to 4.

6. The substrate monolith according to claim 5, characterized in that the substrate monolith has a coating zone containing Pt on the support oxide on the upstream side and a coating zone containing a metal mixture of Pt and Rh on the support oxide on the downstream side.

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

9. A device for power generation, said device comprising the substrate monolith according to claims 5 to 8 and a fuel cell in fluid contact therewith.

10. A method for producing the substrate monolith according to any one of claims 5 to 7, characterized in that the substrate monolith is coated with a coating suspension containing the components of the reforming catalyst according to claims 1 to 4 in water, followed by drying and / or calcination, and finally tempered at a temperature of 400 °C to 600 °C for at most 6 hours.

11. The method according to claim 9, characterized in that the noble metals are deposited together on the entire support oxide.

12. Use of the catalyst according to any one of claims 1 to 4 for generating hydrogen from hydrocarbons.

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

14. Use according to claim 12 or 13, characterized in that the generated hydrogen is used for power generation in a fuel cell.

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