A catalytic microreactor and its preparation method and application

Abstract

The present invention provides a catalytic microreactor comprising a cordierite honeycomb ceramic substrate; Ce-Al-Si-O mixed oxide nanosheets are loaded on the pore walls of the cordierite honeycomb ceramic substrate; the Ce-Al-Si-O mixed oxide nanosheets contain interstitial solid solutions of Ce-Al-Si-O with oxygen vacancies; and the Ce-Al-Si-O mixed oxide nanosheets are loaded with CuO nanoparticles and ZnO nanoparticles. The present invention also provides a preparation method and application of the catalytic microreactor.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic micro-reactions, and in particular relates to a catalytic micro-reactor and a preparation method and application thereof. Background Art

[0002] With increasing environmental pollution and the scarcity of fossil fuels, the development of sustainable, clean energy has become increasingly important in future energy systems. Among emerging energy sources, hydrogen is considered the most important clean and green energy source due to its high energy density, abundant sources, and carbon-free nature. However, the promotion of hydrogen energy has been challenging due to safety concerns during transportation and high storage costs. Methanol is a promising natural liquid hydrogen carrier with a wide range of sources and low cost. It can be obtained not only from traditional fossil energy sources but also from renewable energy sources such as solar, wind, and biomass. Furthermore, methanol is easier to store and transport and has a high hydrogen storage density of 12.5 wt.%. Therefore, methanol (CH3OH) can be used for on-site hydrogen production. In particular, methanol steam reforming (MSR) has attracted increasing attention as an efficient hydrogen production method due to its high energy density, low reforming temperature (200-350°C), and high H / C ratio.

[0003] A key factor in the MSR reaction is the choice of catalyst. Non-precious metal catalysts, particularly copper-based catalysts, have been extensively studied due to their low cost, high activity, and hydrogen selectivity. However, copper-based catalysts are easily deactivated in the MSR reaction due to copper sintering and agglomeration at high temperatures, as well as carbon deposition. An effective strategy to overcome these shortcomings is to select an appropriate promoter. Zinc oxide has been reported as an ideal promoter, not only promoting the dispersion of Cu species by acting as a physical spacer between Cu species (CuO, Cu2O, or Cu), but also promoting the MSR reaction through a synergistic effect of Cu-ZnO, as zinc oxide can accept hydrogen protons generated by methanol dissociation and stabilize the intermediates. Similarly, cerium is also well-known as a promoter due to its unique redox properties, which not only improves the dispersion of Cu species but also inhibits carbon deposition, reducing the production of CO, a byproduct in the MSR reaction, thereby avoiding CO poisoning of the anode catalyst in hydrogen fuel cells.

[0004] However, how to make copper, zinc and cerium play a better catalytic role remains an important issue. Nowadays, the application prospects of structuring catalysts in large-scale catalytic processes are getting better and better, because compared with extruded particle catalysts, they have lower pressure drop, larger open area and higher utilization efficiency. It is worth noting that cordierite honeycomb ceramics have become one of the potential candidate materials for standard substrates of structured catalysts due to their good mechanical strength, low thermal expansion coefficient and high corrosion resistance. However, the main disadvantage of cordierite honeycomb ceramics is their low specific surface area, which makes it inconvenient to load catalysts. A good way to solve this problem is to increase the specific surface area by depositing secondary support materials (such as γ-Al2O3, TiO2 and ZnO, etc.) on the surface of the substrate. For example, O.Fasanya et al. disclosed in the article "Copper zinc oxide nanocatalysts grown on cordierite substrate for hydrogen production using methanol steam reforming" that ZnO nanorods were hydrothermally grown on the surface of cordierite, and then the support was impregnated with copper nitrate to form a method for structured catalysts for MSR. High H2 selectivity and low CO selectivity are observed at low temperatures, but this is accompanied by low methanol conversion, which is attributed to the relatively low copper content on the cordierite surface. In "Upgrading biomass fuel gas by reforming over Ni–MgO / γ-Al2O3 cordierite monolithic catalysts in the lab-scale reactor and pilot-scale multi-tube reformer," Qiu et al. coated the cordierite surface with ultrafine γ-Al2O3 powder under vacuum conditions to increase the specific surface area. NiO-MgO solid solution was then loaded onto the γ-Al2O3 / cordierite, demonstrating good resistance to sintering and carbon deposition in the reforming of biomass fuel gas. However, how to increase the specific surface area while improving the catalytic activity of the secondary support material in the structured catalyst and reducing the CO selectivity in the MSR reaction has become an urgent problem. Summary of the Invention

[0005] The first object of the present invention is to provide a catalytic microreactor with high specific surface area, high catalytic activity and low CO selectivity in the MSR reaction.

[0006] The second object of the present invention is to provide a method for preparing the catalytic microreactor.

[0007] The third object of the present invention is to provide an application of the catalytic microreactor in MSR reaction.

[0008] To achieve the above objectives, the present invention adopts the following technical means:

[0009] A catalytic microreactor comprises a cordierite honeycomb ceramic substrate; Ce-Al-Si-O mixed oxide nanosheets are loaded on pore walls of the cordierite honeycomb ceramic substrate; interstitial solid solutions of Ce-Al-Si-O with oxygen vacancies exist in the Ce-Al-Si-O mixed oxide nanosheets; and nano-CuO particles and nano-ZnO particles are loaded on the Ce-Al-Si-O mixed oxide nanosheets.

[0010] The channel width of the cordierite honeycomb ceramic matrix is 0.9-1.0 mm;

[0011] The total thickness of the Ce-Al-Si-O mixed oxide nanosheets is 6.6-6.7 microns.

[0012] The Ce-Al-Si-O mixed oxide nanosheets have a Ce content of 31.1 wt.%, an Al content of 15.0 wt.%, a Si content of 10.5 wt.%, and an O content of 43.4 wt.%;

[0013] The size of the nano CuO particles is 8-10 nm.

[0014] The size of the nano ZnO particles is 8-10 nm.

[0015] A method for preparing the catalytic microreactor comprises the following steps:

[0016] The cordierite honeycomb ceramic substrate is immersed in a strong acid salt solution of cerium for hydrothermal reaction, and then immersed in a solution of copper salt, zinc salt and citric acid, and the pH value is adjusted to neutral, followed by drying and calcining to obtain the product.

[0017] The strong acid salt of cerium includes cerium nitrate, cerium sulfate or cerium chloride;

[0018] The concentration of the cerium strong acid salt solution is 0.5M

[0019] The hydrothermal reaction time is 0-60h.

[0020] The temperature of the hydrothermal reaction is 180°C.

[0021] The drying temperature is 80°C.

[0022] The combustion temperature is 500°C.

[0023] The copper salt includes copper nitrate.

[0024] The zinc salt includes zinc nitrate.

[0025] The total concentration of the copper salt and zinc salt is 0.5M;

[0026] The concentration ratio of the copper salt to the zinc salt is 3-1:1-3;

[0027] The concentration of the citric acid is 0.6M.

[0028] An application of the catalytic microreactor is to reform organic fuels to produce hydrogen.

[0029] The organic fuel includes C1-C5 alcohol.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The catalytic microreactor provided by the present invention has a large specific surface area, and its pore surface has a high concentration of oxygen vacancies, and has strong catalytic activity.

[0032] 2. The preparation method of the catalytic microreactor provided by the present invention is simple and low in cost.

[0033] 3. When the catalytic microreactor provided by the present invention is applied to the reforming of alcohol to produce hydrogen, the conversion rate of alcohol can reach more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The preparation process of the catalytic microreactor is shown;

[0035] Figure 2 shows a schematic diagram of a catalytic activity testing device;

[0036] Figure 3 (a) Schematic diagram showing the structural evolution of Ce-based nanosheet arrays during hydrothermal growth;

[0037] Figure 3 (b) shows the FE-SEM image of HC without hydrothermal treatment;

[0038] Figure 3 (c) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 12 h;

[0039] Figure 3 (d) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 24 h;

[0040] Figure 3 (e) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 36 h;

[0041] Figure 3 (f) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 48 h;

[0042] Figure 3 (g) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 60 h;

[0043] Figure 4 (a) shows the FE-SEM image of HC without hydrothermal treatment;

[0044] Figure 4 (b) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 48 h;

[0045] Figure 4 (c) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 48 h;

[0046] Figure 4 (d) FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 48 h;

[0047] Figure 4 (e) shows the FE-SEM image of CeO2 nanostructures on the HC surface when the hydrothermal reaction time is 48h;

[0048] Figure 4 (f) shows the EDS spectrum of Al of CeO2 nanostructure on HC surface when the hydrothermal reaction time is 48h;

[0049] Figure 4 (g) shows the EDS spectrum of Ce of CeO2 nanostructure on the HC surface when the hydrothermal reaction time is 48h;

[0050] Figure 4 (h) shows the EDS spectrum of Si of CeO2 nanostructure on the HC surface when the hydrothermal reaction time is 48h;

[0051] Figure 4 (i) shows the EDS spectrum of O in CeO2 nanostructures grown on the HC surface after hydrothermal reaction for 48 h.

[0052] Figure 5 The XRD pattern of the catalytic microreactor prepared in Example 1 is shown;

[0053] Figure 6(a) shows a schematic diagram of the methanol conversion of Cu1Zn3, Cu1Zn2, Cu1Zn1, Cu2Zn1 and Cu3Zn1 as the reforming temperature changes;

[0054] Figure 6(b) shows a schematic diagram of the gas selectivity of Cu1Zn3;

[0055] Figure 6(c) shows a schematic diagram of the gas selectivity of Cu1Zn2;

[0056] Figure 6(d) shows a schematic diagram of the gas selectivity of Cu1Zn1;

[0057] Figure 6(e) shows a schematic diagram of the gas selectivity of Cu2Zn1;

[0058] Figure 6(f) shows a schematic diagram of the gas selectivity of Cu3Zn1;

[0059] FIG7( a ) shows a schematic diagram of methanol conversion and gas selectivity over the use time of Cu1Zn3;

[0060] FIG7( b ) shows a schematic diagram of methanol conversion and gas selectivity over the use time of Cu1Zn2;

[0061] FIG7( c ) shows a schematic diagram of methanol conversion and gas selectivity over the use time of Cu1Zn1;

[0062] Figure 7(d) shows a schematic diagram of the change in effective catalyst loading of CuO-ZnO / HC and Cu1Zn2 after ultrasonic oscillation;

[0063] Figure 8 (a) shows the FE-SEM image of Cu3Zn1;

[0064] Figure 8 (b) shows the FE-SEM image of Cu2Zn1;

[0065] Figure 8 (c) shows the FE-SEM image of Cu1Zn1;

[0066] Figure 8 (d) shows the FE-SEM image of Cu1Zn2;

[0067] Figure 8 (e) shows the FE-SEM image of Cu1Zn3;

[0068] Figure 8 (f) shows the HRTEM image of Cu1Zn2;

[0069] Figure 8 (g) shows the HRTEM image of Cu1Zn2;

[0070] Figure 8 (h) shows the HRTEM image of Cu1Zn2;

[0071] Figure 8 (i) shows the EDS image of Cu1Zn2;

[0072] Figure 8 (j) shows the EDS image of Cu1Zn2;

[0073] Figure 8 (k) shows the EDS image of Cu1Zn2;

[0074] Figure 8 (l) shows the EDS image of Cu1Zn2;

[0075] Figure 9 (a) shows the XRD spectra of Cu1Zn3, Cu1Zn2, Cu1Zn1, Cu2Zn1 and Cu3Zn1;

[0076] Figure 9 (b) shows the H2-TPR spectra of Cu1Zn3, Cu1Zn2, Cu1Zn1, Cu2Zn1 and Cu3Zn1;

[0077] Figure 9 (c) shows the BET spectra of Cu1Zn3, Cu1Zn2, Cu1Zn1, Cu2Zn1 and Cu3Zn1;

[0078] Figure 9 (d) shows the XPS (O 1s) spectra of the HC surface before hydrothermal treatment and after hydrothermal treatment for 48 h.

[0079] Figure 9 (e) shows the schematic diagram of the change of CuO-ZnO / HC and Cu1Zn2 methanol conversion with reforming temperature;

[0080] Figure 9 (f) Schematic diagram showing the gas selectivity of CuO-ZnO / HC and Cu1Zn2 at 260 °C;

[0081] Figure 10(a) shows the TG spectrum of Cu1Zn2;

[0082] FIG10( b ) shows the Raman spectrum of Cu1Zn2. DETAILED DESCRIPTION

[0083] The present invention provides a catalytic microreactor that can be used for reforming alcohol fuels to produce hydrogen. The alcohol fuels include methanol, ethanol, propanol, glycerol, etc. Taking methanol reforming to produce hydrogen as an example, the following chemical reactions mainly occur during the methanol reforming hydrogen production process:

[0084] CH3OH→HCHO+H2

[0085] HCHO+H2O→HCOOH+H2

[0086] HCOOH→CO2+H2

[0087] The above reaction mechanism was confirmed by Breen and Ross in Catal. Today 51 (1999) 521–533. In this literature, CH3OH was shown to first dehydrogenate to form HCHO, which is then nucleophilically attacked by HO to form HCOOH. HCOOH then decomposes into H2 and CO2 at high temperatures. During hydrogen production through reforming, CO formation may be due to the reverse water-gas shift reaction. The catalyst for this reaction can be a copper-zinc catalyst. The presence of oxygen vacancies facilitates the dissociation of HO, thereby promoting the nucleophilic reaction. Therefore, cerium oxide is often added to provide oxygen vacancies to further activate the copper-zinc catalyst. Compared to existing technical solutions that directly add cerium oxide, the present invention introduces cerium oxide by depositing Ce-Al-Si-O mixed oxide nanosheets as a secondary support material on the pore walls of the cordierite honeycomb ceramic substrate to provide a high concentration of oxygen vacancies. Furthermore, because cerium, aluminum, and silicon can form a solid solution to some extent, a certain amount of interstitial solid solution of Ce-Al-Si-O exists within the Ce-Al-Si-O mixed oxide nanosheets. This interstitial solid solution provides more oxygen vacancies than cerium oxide, thus enhancing catalyst activation. Furthermore, the Ce-Al-Si-O mixed oxide exists in the form of nanosheets, which significantly increases the specific surface area of the cordierite honeycomb ceramic substrate. Finally, nano-CuO and nano-ZnO particles are loaded onto the Ce-Al-Si-O mixed oxide nanosheets to create a Cu-Zn-Ce catalytic microreactor with high oxygen vacancies and a high specific surface area, enabling efficient catalytic reforming hydrogen production.

[0088] More specifically, when selecting a cordierite honeycomb ceramic matrix, a matrix with a channel width of 0.9-1.0 mm should be selected. The appropriate channel width can control the gas passage speed, and at the appropriate speed, the catalytic efficiency can be maximized. The total thickness of the Ce-Al-Si-O mixed oxide nanosheets is 6.6-6.7 microns. Nanosheets of this thickness can better improve the specific surface area of the ceramic matrix, and also provide a good basis for the loading of nano-CuO particles and nano-ZnO particles. More specifically, the Ce content in the Ce-Al-Si-O mixed oxide nanosheets is 31.1wt.%, the Al content is 15.0wt.%, the Si content is 10.5wt.%, and the O content is 43.4wt.%. The above mass percentages are instrument measurement results. In fact, due to the existence of instrument errors, the actual ratios should be close to the above ratios. Preferably, the size of the nano-CuO particles and the nano-ZnO particles is 8-10nm. The smaller the particle size, the better the catalytic effect.

[0089] The present invention also provides a method for preparing the catalytic microreactor. Specifically, the cordierite honeycomb ceramic substrate is first immersed in a solution of a strong acid salt of cerium for a hydrothermal reaction, and then immersed in a solution of copper salt, zinc salt, and citric acid. The pH is adjusted to neutral, followed by drying and calcination to obtain the product. During the hydrothermal reaction, the pore wall surface of the cordierite honeycomb ceramic substrate is corroded due to the high temperature and hydrolysis of the cerium salt, causing aluminum ions and silicate ions to enter the solution. After the hydrothermal reaction, these ions form Ce-Al-Si-O mixed oxide nanosheets. Surprisingly, magnesium ions do not enter the solution of the hydrothermal reaction. This may be because the solubility product of magnesium ions and hydroxide ions is too small, making it difficult for magnesium ions to enter the solution. Although the solubility product of aluminum ions and hydroxide ions is also very small, aluminum hydroxide can enter the solution because it is an amphoteric hydroxide. Citric acid acts as a chelating agent, dispersing the catalyst precursor. The method, described in this paper, uses a simple and feasible hydrothermal method to successfully grow CeO2-based nanosheet arrays on the surface of cordierite honeycomb ceramics. This method involves only a cerium precursor, without the addition of other material additives or seed layers. The resulting nanosheet arrays not only increase the specific surface area of the cordierite but also enhance the oxygen vacancy concentration on the support surface.

[0090] Preferably, the strong acid salt of cerium includes cerium nitrate, cerium sulfate or cerium chloride. Other strong acid salts of cerium can also realize the present invention. Preferably, the concentration of the strong acid salt solution of cerium is 0.4-0.6M; the time of the hydrothermal reaction is 0-60h; the temperature of the hydrothermal reaction is 160-200°C. The temperature of the drying is 70-90°C. The temperature of the combustion is 480-520°C. The copper salt includes copper nitrate. The zinc salt includes zinc nitrate. The total concentration of the copper salt and the zinc salt is 0.5mM. The concentration ratio of the copper salt to the zinc salt is 3-1:1-3; the concentration of the citric acid is 0.6M. Excess citric acid is conducive to the formation of the catalyst.

[0091] An application of the catalytic microreactor is to reform organic fuels to produce hydrogen.

[0092] The organic fuel includes C1-C5 alcohol.

[0093] The present invention will be further described below with reference to specific embodiments.

[0094] The cordierite honeycomb ceramics (Φ20×50 mm) used in the specific embodiment of the present invention were obtained from Jiangxi Tianma Industrial Ceramics Co., Ltd., with approximately 400 cells per square inch (cpsi) and a wall thickness of 0.17 mm.

[0095] Cu(NO3)2-3H2O (purity ≥99%), Zn(NO3)2-6H2O (purity ≥99%), ethanol and ammonia water used in the specific embodiments of the present invention were purchased from Shanghai Chemical Reagent Co., Ltd.

[0096] The Ce(NO3)3-6H2O (purity ≥99.5%) and citric acid monohydrate (CA, purity ≥99.5%) used in the specific embodiments of the present invention are from Macklin.

[0097] All reagents were used without further purification.

[0098] Example 1

[0099] (1) Pretreatment of cordierite honeycomb ceramics

[0100] Prior to the hydrothermal reaction, the cordierite honeycomb ceramics were immersed in 8 wt.% nitric acid for 12 hours. The nitric acid-treated honeycomb ceramics were repeatedly rinsed with deionized water, dried overnight at 90°C, and finally calcined at 550°C (at a rate of 5°C / min) for 4 hours to remove residual contaminants. The pretreated honeycomb ceramics are labeled HC.

[0101] (2) Hydrothermal synthesis of CeO2 / HC

[0102] The preparation process of catalytic microreactor is as follows Figure 1As shown. Under normal circumstances, 20mmol Ce(NO3)3-6H2O is dissolved in 40mL deionized water, and then HC is immersed in the above solution. Afterwards, it is transferred into a Teflon stainless steel autoclave with a volume of 100mL and subjected to a hydrothermal reaction in a forced air drying furnace at 180°C for 12h. After cooling to room temperature, the hydrothermally treated HC is carefully washed with water and ethanol, and then dried at 80°C for 12h. Finally, the synthesized sample is calcined in ambient air at 500°C for 2 hours (heating rate: 5°C / min). The obtained sample is named HC-12h.

[0103] Example 2

[0104] The difference from Example 1 is that the hydrothermal time is 24 hours. The obtained sample is named HC-24h.

[0105] Example 3

[0106] The difference from Example 1 is that the hydrothermal time is 36 hours. The obtained sample is named HC-36h.

[0107] Example 4

[0108] The difference from Example 1 is that the hydrothermal time is 48 hours. The obtained sample is named HC-48h.

[0109] Example 5

[0110] The difference from Example 1 is that the hydrothermal time is 60 hours. The obtained sample is named HC-60h.

[0111] Example 6

[0112] Synthesis of CuO-ZnO / CeO2 / HC Structured Catalyst

[0113] Cu(NO₃)₂-3H₂O, Zn(NO₃)₂-6H₂O, and CA (18 mmol) were dissolved in 30 mL of deionized water with a Cu / Zn molar ratio of 3:1. The solution was then stirred for 2 hours. During this stirring, aqueous ammonia was introduced to maintain a neutral pH. HC-48h was then transferred to the solution and dried in an oven at 120°C for 12 hours. During this process, the evaporation of excess water resulted in the formation of a viscous gel on the HC-48h. Finally, the HC-48h containing the gel was calcined at 400°C for 2 hours in ambient air (heating rate: 5°C / min). The synthesized CuO-ZnO / CeO₂ / HC catalytic microreactor was designated Cu₃Zn₁. The CuO-ZnO catalyst loading was controlled to approximately 6 wt.% of the structural catalyst.

[0114] Example 7

[0115] The difference from Example 6 is that the molar ratio of Cu / Zn is 2: 1. The synthesized CuO-ZnO / CeO2 / HC catalytic microreactor is named Cu2Zn1.

[0116] Example 8

[0117] The difference from Example 6 is that the molar ratio of Cu / Zn is 1: 1. The synthesized CuO-ZnO / CeO2 / HC catalytic microreactor is named Cu1Zn1.

[0118] Example 9

[0119] The difference from Example 6 is that the molar ratio of Cu / Zn is 1:2. The synthesized CuO-ZnO / CeO2 / HC catalytic microreactor is named Cu1Zn2.

[0120] Example 10

[0121] The difference from Example 6 is that the Cu / Zn molar ratio is 1:3. The synthesized CuO-ZnO / CeO2 / HC catalytic microreactor is named Cu1Zn3.

[0122] Comparative Example 1

[0123] Synthesis of CuO-ZnO / HC Structured Catalyst

[0124] Using the above catalyst synthesis method, a catalyst with a Cu / Zn molar ratio of 1:2 was directly loaded on HC, which was labeled as CuO-ZnO / HC.

[0125] The catalytic microreactors prepared in the above examples and comparative examples are characterized as follows.

[0126] Specifically, the instruments involved in the characterization are as follows:

[0127] The morphology and elemental distribution of the catalytic microreactors were observed using field-emission scanning electron microscopy (FE-SEM, Igmahd, Zeiss, UK) coupled with EDAX energy-dispersive X-ray spectroscopy (EDS). N2 adsorption-desorption experiments were performed using a surface analyzer (JW-BK200C, JWGB, Beijing, China), and the specific surface area and pore size distribution of the hydrothermally treated HC and catalytic microreactors were measured using Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analysis. All samples were degassed at 200°C overnight before testing. A Tecnai G2 F20 transmission electron microscope (TEM) was used to measure the particle size and lattice spacing of the catalysts. Ultrasonic vibration (F-031S, China) was used to characterize the mechanical stability of the structured catalysts.

[0128] Specifically, the characterization method is as follows:

[0129] First, the structured catalyst was placed in deionized water and sonicated for 30 minutes. Afterwards, the sample was dried at 120°C and the mass was recorded. The mechanical stability of the catalytic microreactor was evaluated based on the mass loss. The crystalline phase of the catalyst was analyzed using an X-ray diffractometer (SmartLab SE, Rigaku, Japan) with a scan range of 10° to 80° (2θ) and a scan rate of 5° / min. The reducibility of the catalyst was examined using H2-temperature programmed reduction (H2-TPR, AutoChemII2920, Micromeritics, USA). X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, USA) was used to examine the chemical state of HC before and after the hydrothermal process. The obtained binding energies were calibrated using the C1s peak at 284.8 eV as a reference. Thermogravimetric analysis (TG, STA449C, Netzsch, Germany) and Raman spectroscopy (Alpha300R, WITec GmbH, Germany) were used to detect the presence of carbon species in the catalytic microreactor used.

[0130] Catalytic activity test

[0131] Figure 2 A schematic diagram of the catalytic activity test apparatus is shown. The catalytic microreactor was placed in a tube furnace controlled by a thermocouple for MSR reaction, and the reforming temperature varied between 220-300°C. A methanol aqueous solution (H2O / CH3OH = 1.05 molar ratio) was introduced into the quartz tube of the tube furnace via a syringe pump. The liquid phase product was captured by a condenser, and the final gaseous products, including H2, CO, and CO2, were detected using an online gas chromatograph (GC, SP-7890, China) equipped with a thermal conductivity detector (TCD). In the gas chromatograph, argon was used as a carrier gas. In addition, the gas flow rate was measured by a soap bubble flowmeter (SCalPlus, China). In order to calculate the methanol conversion and the selectivity of the gas products, the following formula was used.

[0132]

[0133]

[0134]

[0135]

[0136] In the above equation, X MeOH 、S H2 、S CO and SCO2 Represents methanol conversion and selectivity of H2, CO and CO2 respectively. i = represents the molar flow rate of component i in the gas stream. Before the reforming reaction, the catalytic microreactor was pre-reduced with 10% H2 / N2 at 300°C for 2 hours.

[0137] The results of the above tests are analyzed as follows:

[0138] Growth of CeO2 Nanostructures

[0139] The growth of cerium nanostructures on the HC surface only involved Ce(NO3)3-6H2O as a cerium source, without the addition of other additives. During the growth period, the hydrolysis of cerium ions proceeded slowly at 180°C. In order to illustrate the relationship between the formation of cerium nanostructures on the HC surface and the hydrothermal time, products at different reaction times were collected and observed by FE-SEM. Figure 3 As shown in bg, due to the formation of a large number of CeO2 nanoparticles, the channel surface of HC became rough after 12 hours of reaction. Subsequently, after 24 hours of hydrothermal treatment, some nanosheet clusters began to grow on top of the nanoparticle layer. When the reaction time was extended to 36 hours, the growth of the nanosheets was more obvious, and after 48 hours, the surface coverage of the nanosheets was more uniform, forming an array morphology. As the reaction time was further extended to more than 48 hours, the nanosheets will continue to grow. Table 1 lists the BET results of cerium nanostructures grown on the surface of HC at different hydrothermal reaction times. It can be seen that with the increase of reaction time, the specific surface area of HC increased significantly from 4.4 to 252.6 m 2 / g, which indicates that the textural properties of HC are significantly modified by the hydrothermal method. However, as the hydrothermal reaction time is extended to 60 h, the specific surface area of HC-60h is lower than that of HC-48h, which is due to the excessive growth and aggregation of nanosheets.

[0140] Table 1

[0141]

[0142] Among these samples, HC-48h with the highest specific surface area is preferred as the support for catalyst loading because a higher specific surface area is beneficial for the loading of active materials. Figure 4 As shown in ad, the channel width of HC is 0.95 mm, the total thickness of the sheet-like nanoarray layer of HC-48h is about 6.68 μm, and the thickness of each unit nanosheet is about a few nanometers. Energy dispersive spectroscopy was used to further describe the elemental composition of HC-48h. It was detected that the nanosheet structure is mainly composed of Ce (31.1 wt.%), Al (15.0 wt.%), Si (10.5 wt.%) and O (43.4 wt.%), with no Mg present ( Figure 4ei), indicating that the nanosheet array is composed of Ce-Al-Si-O mixed oxide. Figure 5 As shown in the figure, since Ce-Al-Si has a certain solid solubility, there is a certain interstitial solid solution in the Ce-Al-Si-O mixed oxide.

[0143] Considering that the reactants are cerium nitrate, cordierite honeycomb ceramics (Mg2Al4Si5O 18 ) and deionized water, the presence of Al and Si elements on the nanosheets is due to the partial dissolution of the cordierite surface and the subsequent recrystallization of the dissolved elements in the hydrothermal reaction. According to the observed changes in the growth structure over time ( Figure 3 a), the corresponding formation mechanism can be proposed, involving the in situ dissolution, self-seeding nucleation and in situ recrystallization growth of CeO2-based nanoarrays. In the early hydrothermal stage, the surface of HC is first slowly corroded by an appropriate amount of cerium nitrate solution at 180℃. At the same time, the formation of CeO2 nanoparticles on HC is due to the Ce 3+ The hydrolysis reaction under O₂ conditions and subsequent dehydration condensation. As the reaction proceeds, cerium-based nanosheets form on top of the nanoparticle layer through the recrystallization / recombination of cerium ions with dissolved Al and Si species, which is attributed to the change in solution acidity driven by the crystallization of CeO₂ nanoparticles. Ultimately, with further extension of the hydrothermal reaction time, the density of the growing nanosheets increases, leading to the formation of a nanosheet array structure.

[0144] The catalytic performance of the structured catalyst was measured in a quartz tube reactor in the range of 220-280 °C. The relationship between methanol conversion and temperature is shown in Figure 2. Figure 6a As shown. It can be seen that the methanol conversion rate increases with the increase of temperature, which is attributed to the fact that the MSR reaction is an endothermic reaction (Formula (5)). The selectivity of the product is also a key parameter of the MSR reaction. Figure 6b-f, the hydrogen selectivity of all samples is close to its stoichiometric value (75%), which indicates that the structured catalyst is capable of producing a moderate amount of hydrogen. However, the increase in temperature during the reaction leads to a higher CO content, which is related to the reverse water gas shift reaction (Equation (6)). Considering that supplying hydrogen to fuel cell systems is one of the most important applications of the MSR reaction, the presence of carbon monoxide is highly toxic to fuel cell anode catalysts. Therefore, it is necessary to lower the reforming temperature to minimize the carbon monoxide produced by side reactions while maintaining a high methanol conversion rate. Among these samples, Cu1Zn2, as the catalyst with the best structure, showed the best catalytic performance, with a methanol conversion rate of 100% at 260℃ and no byproduct CO. In addition, the catalytic performance of various copper-based catalysts in the MSR reaction in recent years is summarized in Table 2. It was found that compared with existing catalysts, the structured catalyst (Cu1Zn2) prepared in this work showed excellent catalytic activity at a lower conversion temperature and did not produce CO.

[0145] CH3OH+H2O→3H2+CO2 ΔH=+49kJ·mol -1 (6)

[0146]

[0147] Table 2

[0148]

[0149]

[0150] The literature mentioned in Table 2 is as follows:

[0151] [1]M.Cui,F.Wang,W.Zhao,D.Zhang,R.Liang,Q.Ou,et al.Plasma-synthesizedplatinum single atom and nanoparticle catalysts for high-current–densityhydrogen evolution.Chemical Engineering Journal.460(2023)141676.

[0152] [2]J.Tian,Y.Hu,W.Lu,J.Zhu,X.Liu,J.Shen,et al.Dealloying of anamorphous TiCuRu alloy results in a nanostructured electrocatalyst forhydrogen evolution reaction.Carbon Energy.n / a(2023)e322.

[0153] [3]N.Garg,A.Sarkar,B.Sundararaju.Recent developments on methanol asliquid organic hydrogen carrier in transfer hydrogenationreactions.Coordination Chemistry Reviews.433(2021)213728.

[0154] [4]F.Cannizzaro,E.J.M.Hensen,I.A.W.Filot.The Promoting Role of Ni onIn2O3 for CO2 Hydrogenation to Methanol.ACS Catalysis.13(2023)1875-92.

[0155] [5]Z.Sun,J.Liu,R.Zhang,Y.Wu,H.Li,S.Toan,et al.Fabricating Ga dopedand MgO embedded nanomaterials for sorption-enhanced steam reforming ofmethanol.Journal of Materials Chemistry A.10(2022)7300-13.

[0156] [6]L.Liu,Y.Lin,Y.Hu,Z.Lin,S.Lin,M.Du,et al.ZnAl2O4 Spinel-SupportedPdZnβCatalyst with Parts per Million Pd for Methanol Steam Reforming.ACSCatalysis.12(2022)2714-21.

[0157] [7]S.Sá,H.Silva,L. JMSousa,A.Mendes.Catalysts for methanolsteam reforming—A review.Applied Catalysis B:Environmental.99(2010)43-57.

[0158] [8] K.Nomoto, H.Miura, T.Shishido. Inhibitory effect of trace impurities on methanol reforming by Cu / ZnO / Al2O3 catalyst:Steam reforming andautothermal reforming of model bio-methanol.Applied Catalysis B:Environmental.325(2023)122374.

[0159] [9] Y. Shao, HC Zeng. Self-assembly of metal–organosilicate on poroussilica substrates for efficient CO2 hydrogenation to methanol. Journal of Materials Chemistry A. 11 (2023) 2698-710.

[0160] Catalytic stability is also crucial for the MSR reaction, not only for basic research but also for practical applications. In the stability experiment, Cu1Zn3, Cu1Zn2 and Cu1Zn1 were selected and tested at a temperature where the methanol conversion rate just reached 100%. After 100 hours of reaction, the methanol conversion rates of Cu1Zn3, Cu1Zn2 and Cu1Zn1 remained at 84.2%, 94.7% and 72.2% respectively. Figure 7a -c). Therefore, Cu1Zn2 exhibits excellent durability over long-term operation, likely due to the lower reforming temperature, which minimizes the sintering effect on the catalyst. Furthermore, Cu1Zn2 produces virtually no CO during the reaction, thus avoiding poisoning of the anode catalyst in fuel cells.

[0161] In practical applications, especially in-situ hydrogen production in automobiles, structured catalysts are inevitably subject to various physical damages caused by thermal, chemical and mechanical stresses generated during the operation of unstable engines, resulting in catalyst loss. Therefore, CuO-ZnO / HC and Cu1Zn2 were treated with ultrasound to evaluate their mechanical stability. With 30 minutes of ultrasonic vibration, the deionized water in CuO-ZnO / HC became turbid and the effective loading of the catalyst decreased by 36.4%, while the effective loading of the catalyst of Cu1Zn2 decreased by 19.4% ( Figure 7d ), indicating that Cu1Zn2 has better mechanical stability than CuO-ZnO / HC.

[0162] Catalyst characterization

[0163] The elemental composition of the catalysts on the surface of HC-48h was determined by EDS surface scanning. The loading of Cu species increased with increasing Cu / Zn molar ratios (Table 3). The morphologies of the catalysts with different Cu / Zn molar ratios on HC-48h were further examined by FE-SEM. The catalyst particle size on the surface of HC-48h decreased significantly with the addition of more Zn species ( Figure 6a Furthermore, it was found that the catalyst-loaded HC-48h retained a porous structure, which provided ideal space for the entry of reactants and the diffusion of mass transport, thus facilitating the triggering of the reaction and the discharge of products.

[0164] Table 3

[0165]

[0166] Considering the best catalytic performance of Cu1Zn2 among all samples, the catalysts were further characterized by particle size statistics and HRTEM. Figure 8 As shown in Figures fg, the average particle size of the catalyst is about 9.6 nm. The measured lattice spacing is 0.272 nm and 0.282 nm, corresponding to CuO(110) and ZnO(100), respectively, indicating that the crystallinity of these two metal oxides is good. In addition, the Cu, Zn, and Ce elements were confirmed by EDS analysis ( Figure 8 hl), indicating that CuO and ZnO were successfully dispersed on the Ce-based nanosheets.

[0167] The crystalline phase of the catalysts was determined by XRD analysis. CuO (PDF#89-5899) and ZnO (PDF#99-0111) phases were found in all samples. With the addition of more Zn species, the peak of CuO gradually became shorter and broader ( Figure 9 a), indicating that the CuO particle size is smaller and the dispersion is better. In order to further understand the reducibility of the catalyst, the H2-TPR curve of the catalyst is shown in Figure 9 b. Since zinc oxide cannot be reduced below 300°C, the H2 reduction peaks of all catalysts are decomposed into three reduction peaks (α, β, and γ) associated with CuO species. The low-temperature α peak is attributed to the reduction of highly dispersed CuO species, implying a strong interaction with ZnO. The formation of the β peak represents the reduction of small-crystal CuO species, while the γ peak corresponds to the reduction of bulk CuO phase. Among these samples, the α peak of Cu1Zn3 shows the highest peak area ratio (26.7%, Table 3) and the lowest reduction temperature (172.6°C), indicating the presence of more dispersed CuO species with smaller particle size and stronger interaction with ZnO. This result is consistent with the XRD results. The activity and selectivity of catalysts in many reactions are closely related to their particle size. Generally, smaller particles can provide more active sites for MSR, resulting in better catalytic activity. However, the catalytic activity of Cu1Zn3 is lower than that of Cu1Zn2 because when the ZnO content is too high, the active sites of the Cu species are blocked by ZnO, thereby reducing the contact area between the Cu species and the reactants, although ZnO can effectively promote the dispersion of Cu species. Therefore, among all the samples, Cu1Zn2 has the best catalytic performance.

[0168] The specific surface area, pore volume and average pore size of the structured catalysts were measured by N2 adsorption-desorption method. The specific surface area was calculated as Cu1Zn2(11.2m 2 / g)>Cu1Zn3(8.5m 2 / g)>Cu1Zn1(7.0m 2 / g)>Cu2Zn1(5.6m 2 / g)>Cu3Zn1(4.2m 2 / g) Figure 9 c), where the lower specific surface area of the sample is likely due to larger particles. Since the number of active sites on the catalyst surface is closely related to the specific surface area, Cu1Zn2 with a higher specific surface area exhibits better catalytic activity in the MSR reaction. Furthermore, the average pore size of the catalyst-supported HC-48h (8.9-17.5 nm, Table 3) is significantly larger than that of HC-48h (0.7 nm, Table 1), which is due to the pores of HC-48h being clogged by catalyst particles produced by the combustion reaction.

[0169] XPS spectra were acquired to examine the chemical states of HC and HC-48h. The O 1s spectra of these samples were decomposed into three contribution peaks: lattice oxygen (OL), oxygen vacancies (OV), and surface chemisorbed oxygen (OC). Figure 9d). After 48 hours of hydrothermal treatment, the OV peak area ratio of HC (OV / (OL+OV+OC)) increased from 28.8% to 42.1%, indicating an increase in the OV concentration on the support surface. The increase in oxygen vacancies can promote the dissociation of H2O, thereby accelerating the MSR reaction rate and reducing the selectivity of the byproduct CO. Therefore, the catalytic performance of CuO-ZnO / HC and Cu1Zn2 was further compared, and the results are shown in Figure 2. Figure 9 The methanol conversion of CuO-ZnO / HC reached 97.8% at 260°C with a CO selectivity of 0.75%, while the methanol conversion of Cu1Zn2 reached 100% at 260°C with no CO byproduct. These results collectively indicate that the synergistic effect of Cu species, ZnO, and CeO2 is beneficial for improving catalytic activity and reducing CO selectivity in the MSR reaction.

[0170] Mechanism of catalyst deactivation

[0171] The most important deactivation parameters of copper-based catalysts in MSR reactions are sintering and carbon deposition. To gain deeper insights into the deactivation mechanism, the structured catalyst, labeled as Used-Cu1Zn2, was characterized by thermogravimetric analysis and Raman spectroscopy after 100 hours of MSR reaction. The mass loss of Used-Cu1Zn2 (0.74%) did not change significantly compared to fresh Cu1Zn2 (0.77%). Figure 10a ). In addition, no 1360 cm -1 (D band) and 1580cm -1 (G band) near the carbon signal peak ( Figure 10b ), indicating that no carbon species are deposited on the surface of the structured catalyst. The D band corresponds to disorder and defects in the carbon material, while the G band originates from well-structured coke or graphite structures. Therefore, sintering growth of copper particles is the cause of deactivation of the structured catalyst, which is due to the mobility, aggregation, and Ostwald ripening of the nanoparticles during the MSR reaction.

[0172] In summary, the present invention successfully prepared a structured catalyst composed of CuO-ZnO catalyst supported on CeO2-based nanosheet arrays grown in situ on the surface of HC by combining a simple hydrothermal process and a sol-gel combustion method. The generated nanosheet structure not only increased the specific surface area of HC from 4.4 to 252.6 m 2 / g, and also increased the oxygen vacancy concentration on the support surface. The porous surface structure of the synthesized structured catalyst ensures the access of reactants and efficient mass transfer and diffusion, while also increasing the exposure of active sites, resulting in excellent catalytic performance. In the MSR reaction, the optimal structured catalyst (Cu1Zn2) achieved 100% methanol conversion at 260°C without CO, and the methanol conversion remained at 94.7% after 100 hours of reaction, demonstrating excellent catalytic activity and stability. Compared with the structured catalysts with and without CeO2-based nanosheet arrays, the effective catalyst loading of CuO-ZnO / HC decreased by 36.4% after 30 minutes of ultrasonic vibration, while that of Cu1Zn2 decreased by 19.4%. Furthermore, at 260°C, the methanol conversion of CuO-ZnO / HC reached 97.8% with a CO selectivity of 0.75%. These results demonstrate that Cu1Zn2 exhibits excellent mechanical stability, good catalytic activity, and lower CO selectivity than CuO-ZnO / HC.

Claims

1. A catalytic microreactor, characterized in that: including a cordierite honeycomb ceramic matrix; Ce-Al-Si-O mixed oxide nanosheets are loaded on the pore walls of the cordierite honeycomb ceramic matrix; There is an interstitial solid solution of Ce-Al-Si-O with oxygen vacancies in the Ce-Al-Si-O mixed oxide nanosheets; The Ce-Al-Si-O mixed oxide nanosheets are loaded with nano-CuO particles and nano-ZnO particles.

2. The catalytic microreactor according to claim 1, wherein: The channel width of the cordierite honeycomb ceramic matrix is 0.9-1.0 mm; The total thickness of the Ce-Al-Si-O mixed oxide nanosheets is 6.6-6.7 microns.

3. The catalytic microreactor according to claim 1, wherein: The Ce-Al-Si-O mixed oxide nanosheets have a Ce content of 31.1 wt.%, an Al content of 15.0 wt.%, a Si content of 10.5 wt.%, and an O content of 43.4 wt.%.

4. The catalytic microreactor according to claim 1, wherein: The size of the nano CuO particles is 8-10 nm. The size of the nano ZnO particles is 8-10 nm.

5. The method for preparing a catalytic microreactor according to claim 1, wherein The steps include: The cordierite honeycomb ceramic substrate is immersed in a strong acid salt solution of cerium for hydrothermal reaction, and then immersed in a solution of copper salt, zinc salt and citric acid, and the pH value is adjusted to neutral, followed by drying and calcining to obtain the product.

6. The method for preparing a catalytic microreactor according to claim 5, wherein: The strong acid salt of cerium includes cerium nitrate, cerium sulfate or cerium chloride; The concentration of the cerium strong acid salt solution is 0.5M.

7. The method for preparing a catalytic microreactor according to claim 5, wherein: The hydrothermal reaction time is 0-60h; The temperature of the hydrothermal reaction is 180°C; The drying temperature is 80°C; The calcination temperature is 500°C.

8. The method for preparing a catalytic microreactor according to claim 5, wherein: The copper salt includes copper nitrate; The zinc salt includes zinc nitrate; The total concentration of the copper salt and zinc salt is 0.5M; The concentration ratio of the copper salt to the zinc salt is 3-1:1-3; The concentration of the citric acid is 0.6M.

9. The use of the catalytic microreactor according to claim 1, characterized in that: Applied to hydrogen production from reforming of organic fuels.

10. Use of the catalytic microreactor according to claim 9, characterized in that: The organic fuel includes C1-C5 alcohol.

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