A trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, its preparation method and application

Abstract

This invention belongs to the field of energy catalysis, and relates to a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, its preparation method, and its application. The trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst comprises an Al2O3 support, Ni supported on the Al2O3 support, and a noble metal M supported on the Al2O3 support. Ni accounts for 5-15 wt% of the Al2O3 support, and the noble metal M accounts for 0.001-0.005 wt% of the Al2O3 support. M is selected from one or more of Pt, Rh, Ir, Pd, and Au. This invention significantly enhances the activity of methane steam reforming through the synergistic effect between trace noble metals and Ni, achieving a significant performance improvement even with a 2-3 order of magnitude reduction in the amount of noble metal used. This invention significantly reduces the consumption and cost of noble metals while ensuring efficient hydrogen production, and has good prospects for engineering applications.

Description

Technical Field

[0001] This invention relates to the field of energy catalysis technology, specifically to a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, its preparation method, and its application. Background Technology

[0002] In the hydrogen energy industry chain, stable, continuous, and cost-controllable hydrogen production technologies are crucial for ensuring the supply of chemical raw materials and supporting a clean and low-carbon transformation. Steam Methane Reforming (SMR) technology has long dominated industrial hydrogen production due to its readily available raw materials, mature processes, and large-scale single-unit operation. Currently, nickel-based supported catalysts, such as Ni / Al2O3, are widely used in industrial and engineering applications because nickel possesses good CH bond activation capabilities and is relatively inexpensive. However, under the typical high-temperature, steam-rich, and long-term continuous operation conditions of SMR, nickel species are prone to sintering and structural migration, leading to decreased metal dispersion and fewer active sites. Simultaneously, side reactions such as carbon deposition accelerate deactivation, resulting in decreased conversion rates and shortened operating cycles.

[0003] To address these issues, some existing technologies propose adjusting the crystal phase and pore structure of the support, introducing modifying components such as alkali metals or rare earth elements, constructing bimetallic nickel-based systems, or introducing noble metals into nickel-based systems to enhance activity and resistance to deactivation. Among these, the synergistic effect of noble metals and nickel is considered beneficial for improving nickel reduction behavior, increasing reactivity, and inhibiting carbon deposition.

[0004] However, in existing publicly available solutions, the amount of precious metals used is mostly in a relatively high loading range. Typically, to ensure satisfactory catalytic activity, the content of precious metals in the catalyst needs to reach about 1 wt% of the support or even higher, and in some solutions, the proportion of precious metals can reach 10 wt% of the support. Although high loading of precious metals can significantly improve catalytic performance, it also brings about a significant increase in material costs, which reduces the economic viability of the catalyst and makes it difficult to meet the economic requirements of large-scale hydrogen production.

[0005] Therefore, there is a need to provide a methane steam reforming catalyst system that combines high activity and economy. Summary of the Invention

[0006] (a) Technical problems to be solved To address the problem that the high amount of precious metals used in existing precious metal-enhanced nickel-based methane steam reforming catalysts leads to excessive catalyst costs and poor economic efficiency, this invention provides a trace precious metal synergistic Ni / Al2O3 methane steam reforming catalyst, its preparation method, and its application.

[0007] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by the present invention include: A trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst includes an Al2O3 support, Ni supported on the Al2O3 support, and a noble metal M supported on the Al2O3 support. Ni accounts for 5-15 wt% of the Al2O3 support, and the noble metal M accounts for 0.001-0.005 wt% of the Al2O3 support. M is selected from one or more of Pt, Rh, Ir, Pd, and Au.

[0008] In the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst described above, preferably, the Al2O3 support is one or more of α-Al2O3, γ-Al2O3, and θ-Al2O3.

[0009] This invention also provides a method for preparing the above-mentioned trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising the following steps: S1: The Al2O3 support is impregnated into a mixed solution containing Ni precursor and noble metal M precursor to obtain an impregnated sample; S2: The impregnated sample is calcined in air atmosphere to obtain the catalyst precursor; S3: The catalyst precursor is reduced under a hydrogen atmosphere to obtain the M-Ni / Al2O3 catalyst.

[0010] In the preparation method described above, preferably, in step S1, the Ni precursor is at least one of nickel nitrate, nickel chloride, and nickel acetate, and the noble metal M precursor is at least one of chloroplatinic acid and its salt, tetraammineplatinum salt, chloroauric acid and its salt, rhodium chloride, chloroiridic acid and its salt, palladium chloride, and palladium nitrate.

[0011] In the preparation method described above, preferably, in step S1, the Al2O3 support is impregnated into a mixed solution containing Ni precursor and noble metal M precursor, stirred for 5-30 min during the impregnation process, then allowed to stand for 2-4 h, and dried to obtain the impregnated sample.

[0012] In the preparation method described above, preferably, in step S1, the drying temperature is 80-120℃ and the drying time is 6-12h.

[0013] In the preparation method described above, preferably, in step S2, the temperature is increased to 400-600℃ in an air atmosphere at a heating rate of 1-5℃ / min and held for 1.5-4.5h to obtain the catalyst precursor.

[0014] In the preparation method described above, preferably, in step S3, the catalyst precursor is reduced in a mixed atmosphere of hydrogen and inert gas at a temperature of 450-700°C for 1-4 hours; the volume fraction of hydrogen in the mixed atmosphere is 2.5-10 vol.

[0015] The present invention also provides the application of the above-described catalyst or the catalyst prepared by the above-described preparation method in the methane steam reforming hydrogen production reaction.

[0016] As described above, preferably, the methane steam reforming reaction for hydrogen production is carried out in a fixed-bed reactor at a reaction temperature of 450-700℃ and a reaction pressure of atmospheric pressure. The reaction atmosphere for methane steam reforming is a mixture of CH4, H2O, and Ar, wherein the volume fraction of CH4 is 10-30 vol%, the molar ratio of H2O to CH4 is (2.5-5):1, and the total inlet gas flow rate is 10-40 mL·min. -1 .

[0017] (III) Beneficial Effects First, the catalyst provided by this invention has a noble metal loading of only 0.001-0.005 wt%, which is two to three orders of magnitude lower than the 1 wt% or even 10 wt% noble metal loading typically required in existing technologies. At this trace level, a significant synergistic catalytic effect can still be formed between the noble metal and Ni, resulting in a significant improvement in the methane steam reforming activity of the Ni / Al2O3 catalyst, even surpassing that of conventional high-loaded noble metal catalysts. This indicates that the trace noble metal and Ni produce a synergistic enhancement effect that exceeds the sum of the individual components, demonstrating a nonlinear performance gain.

[0018] Secondly, the amount of precious metals in the catalyst of this invention is controlled in an extremely low trace range. While ensuring the improvement of methane steam reforming performance, the consumption of precious metals is greatly reduced, thereby significantly reducing the raw material cost of the catalyst and weakening the impact of precious metal market price fluctuations on the catalyst preparation cost. It has good economic benefits and engineering application prospects.

[0019] Third, the noble metals in the catalyst of the present invention can be selected from one or more combinations of Pt, Rh, Ir, Pd and Au. Under the premise of maintaining trace amounts, the types and combinations of noble metals can be flexibly adjusted according to actual needs to adapt to different reaction conditions and equipment conditions, showing good applicability and configurability. Attached Figure Description

[0020] Figure 1X-ray diffraction patterns of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1, and the Ni / θ-Al2O3 catalyst prepared in Comparative Example 1, after 8 h of reforming catalytic hydrogen production reaction; Figure 2 TEM images and particle size distribution of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1 and the Ni / θ-Al2O3 catalyst prepared in Comparative Example 1 after 8 h of reforming catalytic hydrogen production reaction; Figure 3 The graph shows the effect of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1 on hydrogen production from methane steam reforming at different temperature ranges. Figure 4 The graph shows a comparison of the methane conversion performance of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1, the 10 wt% Ni / θ-Al2O3 prepared in Comparative Example 1, and the 0.005 wt% Pt / θ-Al2O3 prepared in Comparative Example 3. Figure 5 This is a comparison chart of the methane conversion performance of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1 and the 1wt% Pt / θ-Al2O3 catalyst prepared in Comparative Example 4. Detailed Implementation

[0021] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] This invention provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising an Al2O3 support, Ni supported on the Al2O3 support, and a noble metal M supported on the Al2O3 support. Ni comprises 5-15 wt% of the Al2O3 support, and the noble metal M comprises 0.001-0.005 wt% of the Al2O3 support. M is selected from one or more of Pt, Rh, Ir, Pd, and Au.

[0023] The catalyst provided by this invention has a noble metal loading of only 0.001-0.005 wt%, which is two to three orders of magnitude lower than the 1 wt% or even 10 wt% noble metal loading typically required in existing technologies. At this trace level, a significant synergistic catalytic effect can still be formed between the noble metal and Ni, resulting in a significant improvement in the methane steam reforming activity of the Ni / Al₂O₃ catalyst, even surpassing that of conventional high-loaded noble metal catalysts. This indicates that the trace noble metal and Ni produce a synergistic enhancement effect that exceeds the sum of the individual components, demonstrating a nonlinear performance gain.

[0024] The amount of precious metals in the catalyst of this invention is controlled in an extremely low trace range. While ensuring the improvement of methane steam reforming performance, the consumption of precious metals is greatly reduced, thereby significantly reducing the raw material cost of the catalyst and weakening the impact of precious metal market price fluctuations on the catalyst preparation cost. It has good economic benefits and engineering application prospects.

[0025] In the catalyst of this invention, one or more of the noble metals can be selected from Pt, Rh, Ir, Pd, and Au. While maintaining trace amounts, the types and combinations of noble metals can be flexibly adjusted according to actual needs to adapt to different reaction conditions and equipment conditions, demonstrating good applicability and configurability.

[0026] Al₂O₃, as a support, possesses a large specific surface area and good thermal stability, providing a dispersed framework structure for active metals. In a preferred embodiment of the present invention, the Al₂O₃ support can be one or more of α-Al₂O₃, γ-Al₂O₃, and θ-Al₂O₃. Different crystalline phases of Al₂O₃ have different pore structures, specific surface areas, and surface acidity / alkalinity, which can be selected according to specific reaction conditions. For example, γ-Al₂O₃ has a higher specific surface area, which is beneficial for the dispersion of active metals, while θ-Al₂O₃ and α-Al₂O₃ have better hydrothermal stability and are suitable for harsh conditions of high temperature and high vapor pressure.

[0027] Ni is the main active component in methane steam reforming, and its content needs to be controlled within an appropriate range. If the Ni loading is too low, for example, below 5 wt%, the number of active sites is insufficient, limiting the methane conversion rate. If the Ni loading is too high, for example, above 15 wt%, Ni particles tend to agglomerate and grow, leading to a decrease in metal dispersion, which is detrimental to catalytic activity and increases costs. Within this optimized range, Ni can exist in the form of highly dispersed nanoparticles, providing sufficient CH bond activation sites.

[0028] Unlike existing technologies that typically control the noble metal content at 1 wt% or even 10 wt% or more of the carrier, this invention controls the loading of noble metal M in an extremely low trace range, namely 0.001-0.005 wt% of the Al2O3 carrier. At this trace level, the noble metal can exert a strong synergistic effect through electronic and / or geometric effects with Ni.

[0029] In this invention, the amount of precious metal used is only a fraction of that in the prior art, yet it still achieves a significant improvement in catalytic performance. This indicates that the synergistic effect between Ni and trace amounts of precious metal is a non-linear, synergistic enhancement effect that exceeds the summation effect of a single component, rather than a simple performance superposition.

[0030] This invention also provides a method for preparing the above-mentioned trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising the following steps: S1: The Al2O3 support is impregnated in a mixed solution containing Ni precursor and noble metal M precursor. The impregnation process involves stirring for 5-30 minutes, followed by standing for 2-4 hours, and then drying at 80-120℃ for 6-12 hours to obtain the impregnated sample. Unlike the stepwise impregnation method, which involves loading one metal first, calcining, and then loading another metal, this invention employs a one-step co-impregnation method, simultaneously loading Ni and noble metal M precursors in the same solution. The advantage of co-impregnation is that the two metal precursors are uniformly mixed and simultaneously adsorbed into the pores of the support during the impregnation process. After subsequent calcination and reduction, Ni and noble metal M become spatially closer, facilitating the formation of a tightly contacted Ni-M interface, which is the structural basis for achieving electronic and geometric synergy.

[0031] S2: The impregnated sample is calcined in air to obtain the catalyst precursor. During the calcination process, the Ni precursor and the noble metal M precursor undergo thermal decomposition under high-temperature oxygen conditions, transforming into NiO and oxides or corresponding oxidized species of the noble metal, respectively.

[0032] S3: The catalyst precursor was reduced under a hydrogen atmosphere to obtain the M-Ni / Al2O3 catalyst. After air calcination, both Ni and the noble metal M exist in their oxidized forms, while the active species in the methane steam reforming reaction are elemental metals. Therefore, NiO can be reduced to metallic Ni by hydrogen reduction, while the noble metal oxide can be reduced to the elemental noble metal.

[0033] Preferably, in step S1, the Ni precursor can be at least one of nickel nitrate, nickel chloride, and nickel acetate, and the noble metal M precursor can be at least one of chloroplatinic acid and its salts, tetraammineplatinum salt, chloroauric acid and its salts, rhodium chloride, chloroiridium acid and its salts, palladium chloride, and palladium nitrate. The above precursors have good solubility in solvents and moderate thermal decomposition temperatures, facilitating subsequent calcination into metal oxides.

[0034] In a preferred embodiment, the present invention employs an equal-volume impregnation method in step S1. Specifically, the pore volume of the Al2O3 support is predetermined, and then a mixed impregnation solution with a volume exactly equal to the total pore volume of the support is prepared. The advantage of equal-volume impregnation is that the impregnation solution is completely absorbed into the pores of the support, with no excess liquid remaining on the outer surface of the support. Therefore, the loading of the metal precursor can be precisely controlled, eliminating the need for filtration or evaporation to remove liquid. Furthermore, the metal components are uniformly distributed within the pores of the support, avoiding agglomeration caused by excessive metal enrichment on the outer surface.

[0035] The calcination temperature and time directly affect the grain size and dispersion state of the metal oxides. Therefore, in step S2 of this invention, it is preferable to heat the catalyst precursor to 400-600℃ in an air atmosphere at a heating rate of 1-5℃ / min and hold for 1.5-4.5h. A heating rate that is too slow results in low preparation efficiency, while a rate that is too fast may lead to localized overheating and metal species agglomeration. A calcination temperature that is too low will result in incomplete decomposition of the precursor, while a temperature that is too high will cause NiO grains to grow excessively, leading to larger Ni particles obtained from subsequent reduction and a decrease in the active specific surface area. Under the above preferred conditions, this invention can obtain fine-grained and uniformly dispersed NiO and noble metal oxide species, laying a good foundation for subsequent reduction steps.

[0036] Preferably, in step S3, the catalyst precursor can be reduced in a mixed atmosphere of hydrogen and inert gas at a temperature of 450-700℃ for 1-4 hours. The volume fraction of hydrogen in the mixed atmosphere is 2.5-10 vol%. Using diluted hydrogen instead of pure hydrogen aims to control the intensity of the reduction reaction and prevent sintering of metal particles due to excessively rapid exothermic reduction. In this step, Ni and the noble metal M are fully reduced to elemental metals, and due to the spatial proximity resulting from co-impregnation, an alloy structure or a closely contacting bimetallic interface may form between Ni and the noble metal M. This forms the microstructural basis for achieving the synergistic enhancement effect of trace noble metals.

[0037] It is important to emphasize that the catalyst after the reduction treatment in step S3 can directly participate in the reaction without additional activation treatment when used in the methane steam reforming hydrogen production reaction. This is because the hydrogen reduction treatment used in step S3 has fully reduced the NiO and noble metal oxides in the catalyst precursor to catalytically active elemental Ni and M. In contrast, nickel-based catalysts prepared in the prior art usually require pre-reduction activation at high temperature after being loaded into the reactor with hydrogen to obtain sufficient catalytic activity. This additional step not only increases the complexity and time cost of operation, but may also lead to sintering of metal particles due to improper control of reduction conditions. Therefore, the one-step reduction to obtain an active catalyst characteristic of the present invention further simplifies the catalyst usage process and improves the convenience of operation and process compatibility.

[0038] This invention also provides the application of the above-mentioned catalyst in the methane steam reforming reaction for hydrogen production. The main reaction of methane steam reforming is a strongly endothermic reaction, therefore a high reaction temperature is required to obtain the ideal equilibrium conversion rate.

[0039] In a preferred embodiment of the present invention, the reaction can be carried out in a fixed-bed reactor, where the catalyst can be directly heated to the reaction temperature after loading. The preferred reaction temperature is 450-700°C. Too low a temperature results in a slow reaction rate and low equilibrium conversion, while too high a temperature increases energy consumption and places higher demands on the reactor material. With the synergistic effect of trace precious metals in this invention, a high methane conversion rate can be achieved even in the intermediate temperature range, such as 550-650°C.

[0040] The preferred reaction pressure is atmospheric pressure. Although pressurization is beneficial for increasing processing capacity, methane steam reforming is a reaction involving an increase in the molar number, and pressurization is detrimental to the equilibrium conversion rate. Therefore, industrially, it is mostly carried out at atmospheric or low pressure. The reaction atmosphere is a mixture of H2O, CH4, and an inert gas such as Ar. The volume fraction of CH4 is preferably 10-30 vol%, and the molar ratio of H2O to CH4 is preferably (2.5-5):1. The total inlet gas flow rate is 10-40 mL / min. -1 This flow rate range ensures that the reaction is in the kinetically controlled region or a region where internal diffusion has a small impact.

[0041] The core of this invention lies in simultaneously loading Ni and trace amounts of noble metal M onto an Al2O3 support, and through a specific preparation process, including co-impregnation, air calcination, and hydrogen reduction, a significant synergistic catalytic effect is formed between the trace noble metal and Ni. Thus, even with the amount of noble metal reduced by two to three orders of magnitude compared to existing technologies, excellent methane steam reforming activity can still be obtained, even surpassing conventional high-loaded noble metal catalysts, while significantly reducing catalyst costs.

[0042] To further clarify the present invention and its technological advancements, the following description is provided in conjunction with specific embodiments and technical effects.

[0043] Example 1 This embodiment provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising an θ-Al2O3 support, Ni supported on the θ-Al2O3 support, and a noble metal Pt supported on the θ-Al2O3 support. Ni accounts for 10 wt% of the Al2O3 support, and Pt accounts for 0.005 wt% of the Al2O3 support.

[0044] The preparation method of the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst in this embodiment is as follows: S1: The Al2O3 support was impregnated into the mixed impregnation solution using an equal-volume co-impregnation method. The mixture was stirred for 25 minutes during impregnation, then allowed to stand for 3 hours, and finally dried at 100°C for 8 hours to obtain the impregnated sample. The mixed impregnation solution was prepared from an aqueous solution of nickel chloride, chloroplatinic acid, and sodium chloroplatinate.

[0045] S2: In an air atmosphere, the temperature is increased to 600℃ at a heating rate of 3℃ / min and held for 4h to obtain the catalyst precursor Pt-Ni / θ-Al2O3.

[0046] S3: In a reactor, the catalyst precursor was reduced under a mixed atmosphere of hydrogen and Ar at 700℃ for 2 hours to obtain the Pt-Ni / θ-Al₂O₃ catalyst. The hydrogen volume fraction in the mixed atmosphere was 10%, and the total gas flow rate was 15 mL / min. -1 .

[0047] The Pt-Ni / θ-Al2O3 prepared in this embodiment was used in a methane steam reforming reaction to produce hydrogen. Specifically, the methane steam reforming reaction was carried out under the conditions of 20 vol% CH4, H2O:CH4 molar ratio of 3:1, balance Ar, and atmospheric pressure. The conversion rate was recorded in the range of 450-700℃. The reaction tail gas was analyzed by gas chromatography to obtain... Figure 3 ,according to Figure 3 It can be seen that the methane conversion rate reaches 91% when the reaction temperature is 650℃.

[0048] Example 2 This embodiment provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising a γ-Al2O3 support, Ni supported on the γ-Al2O3 support, and Au, a noble metal supported on the γ-Al2O3 support. Ni accounts for 10 wt% of the γ-Al2O3 support, and Au accounts for 0.001 wt% of the γ-Al2O3 support.

[0049] The preparation method of the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst in this embodiment is as follows: S1: The Al2O3 support was impregnated into the mixed impregnation solution using an equal-volume co-impregnation method. The mixture was stirred for 5 minutes during impregnation, then allowed to stand for 2 hours, and finally dried at 80°C for 6 hours to obtain the impregnated sample. The mixed impregnation solution was prepared from an aqueous solution of nickel nitrate, chloroauric acid, and sodium chloroaurate.

[0050] S2: In an air atmosphere, the temperature is increased to 500℃ at a heating rate of 2℃ / min and held for 4h to obtain the catalyst precursor Au-Ni / γ-Al2O3.

[0051] S3: In a reactor, the catalyst precursor was reduced under a mixed atmosphere of hydrogen and Ar at 600℃ for 3 hours to obtain the Au-Ni / γ-Al₂O₃ catalyst. The hydrogen volume fraction in the mixed atmosphere was 5%, and the total gas flow rate was 15 mL / min. -1 .

[0052] The Au-Ni / γ-Al₂O₃ prepared in this embodiment was used in the steam reforming of methane for hydrogen production. Specifically, the steam reforming of methane was carried out under the conditions of 20 vol% CH₄, a molar ratio of H₂O:CH₄ of 2.5:1, the balance being Ar, and atmospheric pressure. The conversion rate was recorded in the range of 450-700℃, and the reaction tail gas was analyzed by gas chromatography. The results showed that the methane conversion rate continuously increased with increasing temperature, reaching 82% at 600℃ and further increasing to 92% at 700℃. It can be seen that even with a noble metal Au loading as low as 0.001 wt%, it can still effectively synergistically enhance the reforming activity with Ni.

[0053] Example 3 This embodiment provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising a γ-Al2O3 support, Ni supported on the γ-Al2O3 support, and a noble metal Rh supported on the γ-Al2O3 support. Ni accounts for 15 wt% of the Al2O3 support, and Rh accounts for 0.002 wt% of the Al2O3 support.

[0054] The preparation method of the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst in this embodiment is as follows: S1: The Al2O3 support was impregnated into the mixed impregnation solution using an equal-volume co-impregnation method. The mixture was stirred for 30 minutes during impregnation, then allowed to stand for 4 hours, and finally dried at 120°C for 12 hours to obtain the impregnated sample. The mixed impregnation solution was prepared from an aqueous solution of nickel nitrate and rhodium chloride.

[0055] S2: In an air atmosphere, the temperature is increased to 400℃ at a heating rate of 5℃ / min and held for 4h to obtain the catalyst precursor Rh-Ni / γ-Al2O3.

[0056] S3: In a reactor, the catalyst precursor was reduced under a mixed atmosphere of hydrogen and Ar at 650℃ for 1.5 h to obtain the Rh-Ni / γ-Al2O3 catalyst. The hydrogen volume fraction in the mixed atmosphere was 5%, and the total gas flow rate was 15 mL / min. -1 .

[0057] The Rh-Ni / γ-Al2O3 prepared in this embodiment was used in the steam reforming of methane for hydrogen production. Specifically, the steam reforming of methane was carried out under atmospheric pressure conditions with 20 vol% CH4, a molar ratio of H2O:CH4 of 2.5:1, and the balance being Ar. The conversion rate was recorded in the range of 450-700℃, and the reaction tail gas was analyzed by gas chromatography. The experimental results showed that the methane conversion rate continuously increased with increasing temperature, exceeding 70% at 550℃, reaching 85% at 600℃, and as high as 97% at 700℃. This catalyst exhibited excellent low-temperature activity with the synergistic effect of trace amounts of Rh.

[0058] Example 4 This embodiment provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising α-Al2O3, a support, Ni supported on the α-Al2O3 support, and a noble metal Pt supported on the α-Al2O3 support. Ni accounts for 5 wt% of the Al2O3 support, and Pt accounts for 0.003 wt% of the Al2O3 support.

[0059] The preparation method of the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst in this embodiment is as follows: S1: The Al2O3 support was impregnated into the mixed impregnation solution using an equal-volume co-impregnation method. The mixture was stirred for 15 minutes during impregnation, then allowed to stand for 3.5 hours, and finally dried at 90°C for 8 hours to obtain the impregnated sample. The mixed impregnation solution was prepared from an aqueous solution of nickel acetate and tetraammineplatinum salt.

[0060] S2: In an air atmosphere, the temperature is increased to 450℃ at a heating rate of 1℃ / min and held for 1.5h to obtain the catalyst precursor Pt-Ni / α-Al2O3.

[0061] S3: In a reactor, the catalyst precursor was reduced under a mixed atmosphere of hydrogen and Ar at 700℃ for 1 h to obtain a Pt-Ni / α-Al₂O₃ catalyst. The hydrogen volume fraction in the mixed atmosphere was 2.5%, and the total gas flow rate was 15 mL / min. -1 .

[0062] The Pt-Ni / α-Al2O3 prepared in this embodiment was used in the steam reforming of methane for hydrogen production. Specifically, the steam reforming of methane was carried out under the conditions of 10 vol% CH4, a molar ratio of H2O:CH4 of 5:1, the balance being Ar, and atmospheric pressure. The conversion rate was recorded in the range of 450-700℃, and the reaction tail gas was analyzed by gas chromatography. The results showed that the methane conversion rate continuously increased with increasing temperature. Under conditions of higher water-to-carbon ratio and lower methane concentration, the catalyst still showed good temperature rise response: the conversion rate was 86% at 600℃ and increased to 93% at 700℃.

[0063] Example 5 This embodiment provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising a θ-Al2O3 support, Ni supported on the θ-Al2O3 support, and a noble metal Ir supported on the θ-Al2O3 support. Ni accounts for 8 wt% of the Al2O3 support, and Ir accounts for 0.004 wt% of the Al2O3 support.

[0064] The preparation method of the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst in this embodiment is as follows: S1: The Al2O3 support was impregnated into the mixed impregnation solution using an equal-volume co-impregnation method. The mixture was stirred for 10 min during impregnation, then allowed to stand for 4 h, and dried at 110 °C for 7 h to obtain the impregnated sample. The mixed impregnation solution was prepared by reacting nickel chloride with aqueous solutions of chloroiridic acid and ammonium chloroiridate.

[0065] S2: In an air atmosphere, the temperature is increased to 550℃ at a heating rate of 4℃ / min and held for 4.5h to obtain the catalyst precursor Ir-Ni / θ-Al2O3.

[0066] S3: In a reactor, the catalyst precursor was reduced under a mixed atmosphere of hydrogen and Ar at 450℃ for 4 h to obtain the Ir-Ni / θ-Al2O3 catalyst. The hydrogen volume fraction in the mixed atmosphere was 5.5%, and the total gas flow rate was 15 mL / min. -1 .

[0067] The Ir-Ni / θ-Al2O3 prepared in this embodiment was used in the steam reforming of methane for hydrogen production. Specifically, the steam reforming of methane was carried out under the conditions of 25 vol% CH4, a molar ratio of H2O:CH4 of 2.5:1, the balance being Ar, and atmospheric pressure. The conversion rate was recorded in the range of 450-700℃. Gas chromatography analysis of the reaction tail gas showed that the methane conversion rate reached 93% at a reaction temperature of 700℃. The results indicate that the methane conversion rate continuously increases with increasing temperature, reaching 85% at 600℃ and 93% at 700℃.

[0068] Example 6 This embodiment provides a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising an α-Al2O3 support, Ni supported on the α-Al2O3 support, and a noble metal Pd supported on the α-Al2O3 support. Ni accounts for 9 wt% of the Al2O3 support, and Pd accounts for 0.002 wt% of the Al2O3 support.

[0069] The preparation method of the trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst in this embodiment is as follows: S1: The Al2O3 support was impregnated into the mixed impregnation solution using an equal-volume co-impregnation method. The mixture was stirred for 18 min during impregnation, then allowed to stand for 3.2 h, and dried at 95 °C for 8 h to obtain the impregnated sample. The mixed impregnation solution was prepared by aqueous solutions of nickel chloride, palladium chloride, and palladium nitrate.

[0070] S2: In an air atmosphere, the temperature is increased to 450℃ at a heating rate of 3℃ / min and held for 2h to obtain the catalyst precursor Pd-Ni / α-Al2O3.

[0071] S3: In a reactor, the catalyst precursor was reduced under a mixed atmosphere of hydrogen and Ar at 600℃ for 2.5 h to obtain the Pd-Ni / α-Al₂O₃ catalyst. The hydrogen volume fraction in the mixed atmosphere was 7.5%, and the total gas flow rate was 15 mL / min. -1 .

[0072] The Pd-Ni / α-Al2O3 prepared in this embodiment was used in the steam reforming of methane for hydrogen production. Specifically, the steam reforming of methane was carried out under atmospheric pressure conditions with 15 vol% CH4, a molar ratio of H2O:CH4 of 3:1, and the balance being Ar. The conversion rate was recorded in the range of 450-700℃. Gas chromatography analysis of the reaction tail gas showed that the methane conversion rate reached 91% at a reaction temperature of 670℃. The results indicate that the methane conversion rate continuously increases with increasing temperature, reaching 79% at 600℃ and 91% at 700℃.

[0073] As demonstrated in Examples 1-6, the trace noble metal synergistic Ni / Al2O3 catalyst provided by this invention exhibits a continuously increasing methane conversion rate with increasing temperature within a temperature range of 450-700℃, even at an extremely low noble metal loading level of only 0.001-0.005 wt%. In all examples, the conversion rate generally exceeds 80% above 600℃, reaches over 90% at 700℃, and some systems approach 97% at 700℃. The effective synergistic enhancement effect can be achieved with different noble metal types and different Al2O3 crystal phases, proving the universality and reliability of the technical solution of this invention.

[0074] Comparative Example 1 This comparative example provides a Ni / Al2O3 methane steam reforming catalyst. The difference from Example 1 is that only Ni is loaded on the θ-Al2O3 support, and the noble metal content is 0. The rest of the preparation method is the same as that in Example 1, and the Ni / θ-Al2O3 catalyst is obtained.

[0075] The Ni / θ-Al2O3 prepared in this comparative example was used in the methane steam reforming reaction to produce hydrogen. The reaction conditions were the same as in Example 1, and the conversion rate was recorded in the range of 450-700℃. The reaction tail gas was analyzed by gas chromatography to obtain... Figure 4 ,according to Figure 4 It can be seen that the methane conversion rate is only 43% when the reaction temperature is 650℃.

[0076] Figure 1 The X-ray diffraction patterns of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1, as well as the Ni / θ-Al2O3 catalyst prepared in Comparative Example 1, after 8 h of reforming catalytic hydrogen production reaction. Figure 2 TEM images and particle size distribution of the Pt-Ni / θ-Al2O3 catalyst prepared in Example 1 and the Ni / θ-Al2O3 catalyst prepared in Comparative Example 1 after 8 hours of reforming catalytic hydrogen production reaction. Figure 2It can be seen that after 8 hours of high-temperature reaction, the Ni particles in the Pt-Ni / θ-Al2O3 catalyst of Example 1 were relatively uniformly distributed with little agglomeration, and the average particle size was 24.4 nm. In contrast, in the Ni / θ-Al2O3 catalyst of Comparative Example 1, the Ni particles were significantly larger, with some particles undergoing severe agglomeration, and the average particle size reached 33.7 nm, much larger than that of Example 1. This indicates that the introduction of trace noble metal Pt effectively inhibited the sintering and migration of Ni particles during the reaction process, thereby maintaining a small metal particle size and high metal dispersion. The difference in metal particle size directly affects the catalytic activity. Furthermore, the average particle size of the catalysts in Examples 2-6 after 8 hours of reaction did not exceed 30 nm, further verifying that trace noble metals have a significant anti-sintering effect on Ni on Al2O3 supports of different crystal phases.

[0077] Comparative Example 2 This comparative example provides a Pt / Al2O3 methane steam reforming catalyst. The difference from Example 1 is that only Pt is loaded on the θ-Al2O3 support, with Pt accounting for 0.002 wt% of the Al2O3 support and Ni content being 0. The rest of the preparation method is the same as in Example 1, resulting in a Pt / θ-Al2O3 catalyst.

[0078] The Pt / θ-Al2O3 prepared in this comparative example was used in the methane steam reforming reaction to produce hydrogen. The reaction conditions were the same as in Example 1. The conversion rate was recorded in the range of 450-700℃. The reaction tail gas was analyzed by gas chromatography. The results showed that the methane conversion rate continued to increase with increasing temperature. When the reaction temperature was 650℃, the methane conversion rate was only 8%.

[0079] Comparative Example 3 This comparative example provides a Pt / Al2O3 methane steam reforming catalyst. The difference from Example 1 is that only Pt is loaded on the θ-Al2O3 support, with Pt accounting for 0.005 wt% of the Al2O3 support and Ni content being 0. The rest of the preparation method is the same as in Example 1, resulting in a Pt / θ-Al2O3 catalyst.

[0080] The Pt / θ-Al2O3 prepared in this comparative example was used in the methane steam reforming reaction to produce hydrogen. The reaction conditions were the same as in Example 1, and the conversion rate was recorded in the range of 450-700℃. The reaction tail gas was analyzed by gas chromatography to obtain... Figure 4 ,according to Figure 4 It can be seen that the methane conversion rate is only 23% when the reaction temperature is 650℃.

[0081] Comparative Example 4 This comparative example provides a Pt / Al2O3 methane steam reforming catalyst. The difference from Example 1 is that only Pt is loaded on the θ-Al2O3 support, with Pt accounting for 1 wt% of the Al2O3 support and Ni content being 0. The rest of the preparation method is the same as in Example 1, resulting in a Pt / θ-Al2O3 catalyst.

[0082] The Pt / θ-Al2O3 prepared in this comparative example was used in the methane steam reforming reaction to produce hydrogen. The reaction conditions were the same as in Example 1, and the conversion rate was recorded in the range of 450-700℃. The reaction tail gas was analyzed by gas chromatography to obtain... Figure 5 ,according to Figure 5 It can be seen that the methane conversion rate is only 76% when the reaction temperature is 650℃.

[0083] Comparative Example 5 This comparative example provides a noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, comprising an θ-Al2O3 support, Ni supported on the θ-Al2O3 support, and a noble metal Pt supported on the θ-Al2O3 support. Ni accounts for 10 wt% of the Al2O3 support, and Pt accounts for 1 wt% of the Al2O3 support. The preparation method of this comparative example product is the same as in Example 1, yielding a Pt-Ni / θ-Al2O3 catalyst.

[0084] The Pt / θ-Al2O3 prepared in this comparative example was used in the methane steam reforming reaction to produce hydrogen, under the same reaction conditions as in Example 1. The conversion rate was recorded within the range of 450-700℃, and the reaction tail gas was analyzed by gas chromatography. The results showed that the methane conversion rate continuously increased with increasing temperature, reaching 84% at 600℃ and 88% at 700℃.

[0085] In Comparative Example 1, the methane conversion rate of Ni / Al2O3 at 650℃ was only 43%, indicating that the activity of a single Ni catalyst is limited. Comparative Examples 2 and 3 show that when only trace Pt is loaded without Ni, the conversion rates at 650℃ are only 8% and 23%, respectively, proving that trace noble metals alone have almost no catalytic activity. Comparative Example 4 increased the Pt loading to a conventional high loading level, but the conversion rate at 650℃ was only 76%, which is higher than that of trace pure Pt but still lower than that of Example 1, and the amount of noble metal used was 200 times higher. Comparative Example 5 increased Pt to 1 wt% and co-loaded it with Ni, with conversion rates of 84% and 88% at 600℃ and 700℃, respectively, which are still slightly lower than those of the examples, while the amount of noble metal used is still more than 100 times that of the examples. In summary, under the condition of reducing the amount of precious metals by two to three orders of magnitude, the methane conversion rate of all embodiments of this invention is significantly better than that of pure Ni or pure precious metal catalysts, and most of them are better than those of high-loaded precious metal and high-loaded precious metal-nickel composite catalysts. This fully demonstrates the nonlinear synergistic enhancement effect between trace precious metals and Ni, while significantly reducing the cost of catalysts.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst, characterized in that, It includes an Al2O3 support, Ni supported on the Al2O3 support, and a noble metal M supported on the Al2O3 support; Ni accounts for 5-15 wt% of the Al2O3 support, and the noble metal M accounts for 0.001-0.005 wt% of the Al2O3 support. M is selected from one or more of Pt, Rh, Ir, Pd, and Au.

2. The trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst according to claim 1, characterized in that, The Al2O3 support is one or more of α-Al2O3, γ-Al2O3, and θ-Al2O3.

3. A method for preparing a trace noble metal synergistic Ni / Al2O3 methane steam reforming catalyst according to any one of claims 1-2, characterized in that, Includes the following steps: S1: The Al2O3 support is impregnated into a mixed solution containing Ni precursor and noble metal M precursor to obtain an impregnated sample; S2: The impregnated sample is calcined in air atmosphere to obtain the catalyst precursor; S3: The catalyst precursor is reduced under a hydrogen atmosphere to obtain the M-Ni / Al2O3 catalyst.

4. The preparation method according to claim 3, characterized in that, In step S1, the Ni precursor is at least one of nickel nitrate, nickel chloride, and nickel acetate, and the noble metal M precursor is at least one of chloroplatinic acid and its salt, tetraammineplatinum salt, chloroauric acid and its salt, rhodium chloride, chloroiridic acid and its salt, palladium chloride, and palladium nitrate.

5. The preparation method according to claim 3, characterized in that, In step S1, the Al2O3 support is impregnated in a mixed solution containing Ni precursor and noble metal M precursor. The impregnation process is stirred for 5-30 min, then allowed to stand for 2-4 h, and dried to obtain the impregnated sample.

6. The preparation method according to claim 5, characterized in that, In step S1, the drying temperature is 80-120℃ and the drying time is 6-12h.

7. The preparation method according to claim 3, characterized in that, In step S2, the temperature is increased to 400-600℃ in an air atmosphere at a heating rate of 1-5℃ / min and held for 1.5-4.5h to obtain the catalyst precursor.

8. The preparation method according to claim 3, characterized in that, In step S3, the catalyst precursor is reduced in a mixed atmosphere of hydrogen and inert gas at a temperature of 450-700℃ for 1-4 hours; the volume fraction of hydrogen in the mixed atmosphere is 2.5-10 vol.

9. The application of the catalyst according to any one of claims 1-2 or the catalyst prepared by the preparation method according to any one of claims 3-8 in the methane steam reforming hydrogen production reaction.

10. The application according to claim 9, characterized in that, The methane steam reforming reaction for hydrogen production is carried out in a fixed-bed reactor at a temperature of 450-700℃ and a pressure of atmospheric pressure. The reaction atmosphere is a mixture of CH4, H2O, and Ar, with CH4 having a volume fraction of 10-30 vol% and an H2O to CH4 molar ratio of (2.5-5):

1. The total inlet gas flow rate is 10-40 mL / min. -1 .

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