A rare earth modified oxide catalyst using copper-aluminum hydrotalcite as a precursor, and a preparation method and application thereof

Abstract

The application discloses a preparation method of a rare earth modified oxide taking copper-aluminum hydrotalcite as a precursor, and belongs to the technical field of catalytic material preparation. In the preparation method, rare earth elements are simply introduced to be anchored on the copper-aluminum hydrotalcite layer plate, and the obtained samarium modified copper-aluminum oxide catalyst in-situ forms a samarium oxide coated copper nanoparticle structure through metal-support strong interaction in a methanol steam reforming reaction. The rare earth modified catalyst has better methanol steam reforming reaction activity and better stability than the unmodified copper-aluminum catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalytic material preparation, and particularly relates to a rare earth modified oxide catalyst taking copper-aluminum hydrotalcite as a precursor and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen (H2) is known as "the fuel of the future" due to its high mass energy density and the fact that the combustion product is only water, which is harmless to the environment. In the past two decades, hydrogen has been intensively developed and researched. Hydrogen can be derived from clean energy such as solar energy, wind energy and geothermal energy. Therefore, clean "green hydrogen" is one of the effective solutions to the current energy problem. However, due to the wide explosive limit range of hydrogen, the transportation and storage of hydrogen are still the biggest obstacles to hydrogen economy. Methanol (CH3OH) is known as clean "coal", cheap "oil", simple "gas", mobile "electricity" and liquid "hydrogen" due to its high hydrogen-carbon ratio as a small hydrogen storage energy molecule. At the same time, methanol is also an easily obtained biofuel. The methanol steam reforming (MSR) reaction converts CH3OH and H2O into H2 and CO2. The methanol steam reforming process has been relatively mature, and the Sinopec Group has built China's first methanol-to-hydrogen hydrogenation integrated station in 2023. Using the MSR reaction for in-situ hydrogen production for hydrogen energy vehicles or coupling proton exchange membrane fuel cells for new energy vehicles is an important part of the current "hydrogen economy". In order to apply MSR to actual small mobile hydrogen production devices, researchers have devoted themselves to the development of low-temperature catalysts for MSR. The research is more in-depth in noble metal-based catalysts and copper-based catalysts. Due to the high cost and limited reserves of noble metal-based catalysts, their large-scale application is limited. Copper-based catalysts represented by commercial copper-zinc-aluminum still have two main problems of low low-temperature activity and poor stability and easy agglomeration. Therefore, constructing a more reactive reaction interface or site and improving the stability of copper-based catalysts in the MSR reaction are the main directions of copper-based catalyst research.

[0003] Layered double hydroxides, also known as hydrotalcite, have micro-adjustable chemical composition of the layer plate and meso-adjustable size and distribution of the crystal grain, and the metals in the hydrotalcite layer plate are uniformly dispersed, so that a uniformly dispersed metal catalyst can be obtained after calcination and reduction. However, the oxide catalyst taking hydrotalcite as a precursor still lacks excellent low-temperature activity and good stability in the MSR reaction. SUMMARY

[0004] The application aims to provide a preparation method of an oxide catalyst with a rare earth modified copper-aluminum hydrotalcite as a precursor and application thereof in a methanol reforming reaction.

[0005] The application aims to provide the technical scheme as follows.

[0006] The application provides a preparation method of a rare earth modified oxide with a copper-aluminum hydrotalcite as a precursor, comprising the following steps.

[0007] (1) a mixed solution of Al(NO3)3·9H2O and Cu(NO3)2·3H2O and a NaOH solution are simultaneously dropped into a Na2CO3 solution under a constant pH condition by using a double-drop method, and stirring is performed for a period of time to obtain a copper-aluminum hydrotalcite suspension;

[0008] (2) a rare earth nitrate solution is added into the copper-aluminum hydrotalcite suspension obtained in step (1), a NaOH solution is simultaneously added by using a double-drop method to maintain a constant pH, and water bath aging is performed to anchor the rare earth hydroxide on the layer plate of the copper-aluminum hydrotalcite, so that a rare earth modified copper-aluminum hydrotalcite is obtained;

[0009] (3) the rare earth modified copper-aluminum hydrotalcite prepared in step (2) is calcined in air, and finally a rare earth modified copper-aluminum oxide catalyst is obtained.

[0010] Further, in step (1), the concentration of the Al(NO3)3·9H2O solution in the mixed solution of Al(NO3)3·9H2O and Cu(NO3)2·3H2O is 0.1-0.5 mol / L, preferably 0.25 mol / L, the concentration of the Cu(NO3)2·3H2O solution is 0.3-1.5 mol / L, preferably 0.75 mol / L, the concentration of the NaOH solution is 0.5-3.0 mol / L, the pH is 9.0-10.0, the concentration of the Na2CO3 solution is 0.03-0.06 mol / L, and the stirring time is 5-60 min, preferably 10-30 min.

[0011] Further, in step (2), the concentration of the NaOH solution is 0.5-3.0 mol / L; the concentration of the rare earth nitrate solution is 0.05-0.80 mol / L, preferably 0.1-0.4 mol / L; the rare earth nitrate includes hydrates of Sm(NO3)3, Y(NO3)3, Gd(NO3)3, Pr(NO3)3; the pH is 9.0-10.0; the water bath temperature is 45-65℃, and the water bath time is 6-24 h, preferably 8-15 h.

[0012] Further, in step (3), the calcination temperature is 300-600℃, and the calcination time is 1-6 h, preferably 4 h.

[0013] Further, the molar ratio of the sum of Al(NO3)3·9H2O and Cu(NO3)2·3H2O to Na2CO3 is 1-3:1, preferably 2:1; and the molar ratio of the sum of Al(NO3)3·9H2O and Cu(NO3)2·3H2O to the rare earth nitrate is 1:0.025-0.4, preferably 1:0.05-0.3, more preferably 1:0.05-0.15.

[0014] The application also provides a rare earth modified copper-aluminum oxide catalyst prepared by the above preparation method.

[0015] The application also provides application of the above rare earth modified copper-aluminum oxide catalyst in a methanol steam reforming reaction.

[0016] The rare earth element has a unique 4f electron structure and a variable valence state. The surface of the rare earth oxide has abundant oxygen vacancies, so the method of using rare earth modification can effectively construct active sites (Cu + ) and interfaces (Cu + / Cu 0 ) in the copper-based catalyst and adjust its catalytic activity. In addition, the dynamic transformation of the valence state of the rare earth element in the reaction is conducive to the dispersion of copper elements and thus improves the stability of the copper-based catalyst in the MSR reaction.

[0017] Further, the conditions of the methanol steam reforming reaction are as follows: the reaction space velocity is 30000-200000 mL / g / h, preferably 30000-120000 mL / g / h; the reaction temperature is 200-300℃; and the reaction atmosphere is a mixed gas of 5-30 vol% CH3OH, 10-60 vol% H2O and balanced N2, preferably a mixed gas of 10 vol% CH3OH, 15 vol% H2O and balanced N2.

[0018] Further, the catalyst also includes an activation process, the atmosphere of the activation process is a mixed gas of 5-30 vol% H2 and Ar, preferably a mixed gas of 10 vol% H2 and Ar, the temperature of the activation process is 200-500°C, preferably 250-400°C, more preferably 300°C, the time is 0.5-4 hours, preferably 2 hours, and the pretreated catalyst is cooled to the target reaction temperature under a pure Ar atmosphere.

[0019] Further, the catalyst also includes an activation process, the atmosphere of the activation process is a mixed gas of 5-30 vol% H2 and Ar, preferably a mixed gas of 10 vol% H2 and Ar, the temperature of the activation process is 200-500°C, preferably 250-400°C, more preferably 300°C, the time is 0.5-4 hours, preferably 2 hours, and the pretreated catalyst is cooled to the target reaction temperature under a pure Ar atmosphere.

[0020] Further, the catalyst also includes an activation process, the atmosphere of the activation process is a mixed gas of 5-30 vol% H2 and Ar, preferably a mixed gas of 10 vol% H2 and Ar, the temperature of the activation process is 200-500°C, preferably 250-400°C, more preferably 300°C, the time is 0.5-4 hours, preferably 2 hours, and the pretreated catalyst is cooled to the target reaction temperature under a pure Ar atmosphere.

[0021] The present application has the following advantages:

[0022] 1) The present application develops a method for preparing a rare earth modified copper-aluminum oxide catalyst based on a rare earth modified copper-aluminum hydrotalcite as a precursor. In the process of preparing the hydrotalcite by using a double drop method, the rare earth nitrate is directly introduced into the copper-aluminum hydrotalcite to simply load the rare earth element on the copper-aluminum hydrotalcite, and the XRD diffraction peak of the rare earth oxide is not found in the finally obtained rare earth modified copper-aluminum oxide, which indicates that the rare earth element maintains good dispersion.

[0023] 2) The strategy of developing a rare earth modified copper-aluminum hydrotalcite effectively avoids the generation of copper oxide in the traditional copper-aluminum hydrotalcite aging process, and the addition of the rare earth element promotes the formation of a pure phase copper-aluminum hydrotalcite. The metal-support strong interaction phenomenon occurs in the methanol steam reforming reaction of the rare earth modified copper-aluminum oxide catalyst prepared by the present application to form an active structure of rare earth oxide coated copper nanoparticles, the formation of the coating structure significantly improves the reaction activity of the copper-aluminum oxide catalyst and significantly inhibits the agglomeration and sintering of the copper nanoparticles, so that the rare earth modified copper-aluminum oxide catalyst has good catalytic activity and stability in the methanol steam reforming reaction.

[0024] 3) The rare earth modified copper-aluminum oxide catalyst prepared by the present application exhibits good low-temperature activity in the methanol steam reforming reaction compared with the unmodified copper-aluminum oxide catalyst, the CH3OH conversion rate can reach 84.8% under the reaction condition of 250°C, and the catalytic activity of the unmodified copper-aluminum catalyst is improved by 30.6%. At the same time, the hydrogen production rate can reach 594.9 mmol / g / h under the reaction condition of 60000 mL / g / h mass air speed and 250°C. cat

[0025] ​In addition, the rare earth modified copper-aluminum oxide catalysts exhibit better stability than the unmodified copper-aluminum oxide catalysts and the commercial copper-zinc-aluminum catalysts. The present application establishes a regeneration method for the rare earth modified copper-aluminum oxide catalysts. After the stability test, the catalysts are calcined in air at 300°C for 2h and then activated using 10% H2 / Ar, which can restore the methanol steam reforming reaction activity of the rare earth modified copper-aluminum oxide catalysts to the initial activity and keep the repeatable regeneration in multiple cycle tests. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Activity comparison chart of the rare earth modified copper-aluminum oxide catalysts prepared in Examples 1-4 and the copper-aluminum oxide catalysts obtained in Comparative Examples 1-2 in the methanol steam reforming reaction;

[0027] Figure 2 XRD spectra of the samarium modified copper-aluminum hydrotalcite precursors prepared in Example 1 and Examples 5-6 and the copper-aluminum hydrotalcite obtained in Comparative Example 1;

[0028] Figure 3 a is the nitrogen adsorption-desorption curve of the samarium modified copper-aluminum oxide catalyst prepared in Example 1 and the copper-aluminum oxide catalyst obtained in Comparative Example 1, and b is the pore size distribution chart of the samarium modified copper-aluminum oxide catalyst prepared in Example 1 and the copper-aluminum oxide catalyst obtained in Comparative Example 1;

[0029] Figure 4 Activity comparison chart of the samarium modified copper-aluminum oxide catalysts prepared in Example 1 and Examples 5-6 and the copper-aluminum oxide catalyst obtained in Comparative Example 1 in the methanol steam reforming reaction;

[0030] Figure 5 a is the TEM image of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 after activation in a 10% H2 / Ar atmosphere, and b is the TEM image of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 after the methanol steam reforming reaction stability test, and the stability test conditions are a reaction temperature of 250°C and a reaction space velocity of 60000 mL / g / h;

[0031] Figure 6 Stability test chart of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 and the copper-aluminum oxide catalyst obtained in Comparative Example 1 and the commercial copper-zinc-aluminum catalyst in Comparative Example 3 in the methanol steam reforming reaction, and the reaction temperature is 250°C and the reaction space velocity is 60000 mL / g / h;

[0032] Figure 7 Stability test chart of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 and the copper-aluminum oxide catalyst obtained in Comparative Example 1 in the methanol steam reforming reaction, and the reaction temperature is 300°C and the reaction space velocity is 200000 mL / g / h;

[0033] Figure 8 TEM images of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 after activation in 10% H2 / Ar atmosphere, b is the TEM images of the copper-aluminum oxide catalyst obtained in Comparative Example 1 after activation in 10% H2 / Ar atmosphere, c is the TEM images of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 after stability test in methanol steam reforming reaction, d is the TEM images of the copper-aluminum oxide catalyst obtained in Comparative Example 1 after stability test in methanol steam reforming reaction, the stability test conditions are reaction temperature 300°C and reaction space velocity 200000 mL / g / h;

[0034] Figure 9 Regeneration-stability test results of the samarium modified copper-aluminum oxide catalyst prepared in Example 6 in methanol steam reforming reaction. DETAILED DESCRIPTION

[0035] The following non-limiting examples can make those skilled in the art more fully understand the present application, but in no way limit the present application.

[0036] The catalyst provided by the present application is prepared in detail as follows:

[0037] 1) Preparation of copper-aluminum hydrotalcite suspension: a mixed solution of 0.1-0.5 mol / L Al(NO3)3·9H2O and 0.3-1.5 mol / L Cu(NO3)2·3H2O and a 0.5-3.0 mol / L NaOH solution are simultaneously added dropwise into a 0.03-0.06 mol / L Na2CO3 solution under constant pH 9.0-10.0 conditions and stirred for 5-60 min to obtain a copper-aluminum hydrotalcite suspension. The molar ratio of the sum of Al(NO3)3·9H2O and Cu(NO3)2·3H2O to Na2CO3 is 1-3:1.

[0038] 2) Preparation of rare earth modified copper-aluminum hydrotalcite: a 0.05-0.80 mol / L rare earth nitrate solution and a 0.5-3.0 mol / L NaOH solution are added dropwise into the above suspension under constant pH 9.0-10.0 conditions, and the mixture is aged at 45-65°C for 6-24 h to obtain a rare earth modified copper-aluminum hydrotalcite. The molar ratio of the sum of Al(NO3)3·9H2O and Cu(NO3)2·3H2O to the rare earth nitrate is 1:0.025-0.4.

[0039] 3) Preparation of rare earth modified copper-aluminum oxide: the above rare earth modified copper-aluminum hydrotalcite is calcined at 300-600°C in air for 4 h to obtain a rare earth modified copper-aluminum oxide catalyst.

[0040] The rare earth modified copper-aluminum oxide catalyst is pretreated before the methanol steam reforming reaction, and the process is as follows: 10% H2 / Ar mixed gas is introduced into the reaction tube containing the catalyst, and the temperature is raised to 200-500°C at a rate of 5°C / min, and maintained for 2 hours, then the temperature is lowered to the target reaction temperature under pure Ar atmosphere, and then switched to the reaction gas for methanol steam reforming performance evaluation. Preferably, the conditions of the methanol steam reforming reaction are as follows: the reaction space velocity is 30000-200000 mL / g / h; the reaction temperature is 200-300°C; and the reaction atmosphere is 10% CH3OH, 15% H2O and balanced N2.

[0041] The following examples and comparative examples are used to further illustrate the present application, but are not limited to the present application.

[0042] Example 1

[0043] Catalyst preparation

[0044] 1) Preparation of copper-aluminum hydrotalcite suspension: 20 mL of mixed solution of 0.25 mol / L Al(NO3)3·9H2O and 0.75 mol / L Cu(NO3)2·3H2O and 1.5 mol / L NaOH solution were simultaneously added dropwise into 180 mL of 0.056 mol / L Na2CO3 solution under constant pH of 9.5, and stirred for 20 min to obtain a copper-aluminum hydrotalcite suspension.

[0045] 2) Preparation of samarium modified copper-aluminum hydrotalcite: 10 mL of 0.1 mol / L Sm(NO3)3·6H2O solution and 1.5 mol / L NaOH solution were added dropwise into the above suspension under constant pH of 9.5, and aged at 65°C for 12 h to obtain samarium modified copper-aluminum hydrotalcite (denoted as 10Sm-CuAl-LDH).

[0046] 3) Preparation of samarium modified copper-aluminum oxide: the above samarium modified copper-aluminum hydrotalcite was calcined at 500°C for 4 h in air to obtain a samarium oxide modified copper-aluminum oxide catalyst (denoted as 10Sm-CuAl).

[0047] Catalyst activity evaluation

[0048] The methanol steam reforming reaction was carried out in a quartz tube fixed bed reactor with an inner diameter of 6 mm. The flow rates of each gas required for the experiment were adjusted and controlled by mass flow meters, and the mixed gas was then introduced into the reactor. 100 mg of 10Sm-CuAl was weighed into the quartz tube, and then treated at 300°C for 2 hours under 10% H2 / Ar mixed gas. The target reaction temperature was then lowered, and the activity test was carried out under the following reaction conditions: the reaction atmosphere was 10% CH3OH / 15% H2O / N2; the reaction temperature was 200°C, 220°C, 250°C, 270°C, and 300°C, respectively; the reaction space velocity was 30000 mL / g / h; and the CH3OH conversion rate of 10Sm-CuAl catalyst at 250°C was 84.8%, as shown in Figure 1 .

[0049] Example 2

[0050] The steps and process conditions for preparing the catalyst of this example were the same as those of Example 1, except for the following point: 10 mL of Y(NO3)3·6H2O solution with a concentration of 0.1 mol / L was added dropwise into the copper-aluminum hydrotalcite suspension under the condition of constant pH of 9.5, and 1.5 mol / L NaOH solution was finally obtained. The resulting catalyst was a yttrium oxide modified copper-aluminum oxide catalyst (denoted as 10Y-CuAl).

[0051] The methanol steam reforming reaction was carried out in a quartz tube fixed bed reactor with an inner diameter of 6 mm. The flow rates of each gas required for the experiment were adjusted and controlled by mass flow meters, and the mixed gas was then introduced into the reactor. 100 mg of 10Y-CuAl was weighed into the quartz tube, and then treated at 300°C for 2 hours under 10% H2 / Ar mixed gas. The target reaction temperature was then lowered, and the activity test was carried out under the following reaction conditions: the reaction atmosphere was 10% CH3OH / 15% H2O / N2; the reaction temperature was 200°C, 250°C, and 300°C, respectively; the reaction space velocity was 30000 mL / g / h, and the results are shown in Figure 1 .

[0052] Example 3

[0053] The steps and process conditions for preparing the catalyst of this example were the same as those of Example 1, except for the following point: 10 mL of Gd(NO3)3·6H2O solution with a concentration of 0.1 mol / L was added dropwise into the copper-aluminum hydrotalcite suspension under the condition of constant pH of 9.5, and 1.5 mol / L NaOH solution was finally obtained. The resulting catalyst was a gadolinium oxide modified copper-aluminum oxide catalyst (denoted as 10Gd-CuAl).

[0054] The steps and process parameters for catalyst activity testing were consistent with those described in Example 2, and the results are shown in Figure 1 .

[0055] Example 4

[0056] The steps and process conditions for preparing the catalyst of this example are the same as those of Example 1, except that 10 mL of a Pr(NO3)3.6H2O solution with a concentration of 0.1 mol / L and a 1.5 mol / L NaOH solution are added dropwise into the copper-aluminum hydrotalcite suspension at a constant pH of 9.5, and finally a praseodymium oxide-modified copper-aluminum oxide catalyst (denoted as 10Pr-CuAl) is obtained.

[0057] The steps and process parameters for testing the activity of the catalyst are the same as those described in Example 2, and the results are shown in Table 2. Figure 1

[0058] Example 5

[0059] The steps and process conditions for preparing the catalyst of this example are the same as those of Example 1, except that 10 mL of a Sm(NO3)3.6H2O solution with a concentration of 0.15 mol / L and a 1.5 mol / L NaOH solution are added dropwise into the copper-aluminum hydrotalcite suspension at a constant pH of 9.5, and finally a samarium oxide-modified copper-aluminum oxide catalyst (denoted as 15Sm-CuAl) is obtained. By changing the concentration of the Sm(NO3)3.6H2O solution to 0.05 mol / L, 0.2 mol / L and 0.7 mol / L, respectively, 5Sm-CuAl, 20Sm-CuAl and 70Sm-CuAl catalysts are obtained using the same preparation method.

[0060] The steps and process parameters for testing the activity of the catalyst are the same as those described in Example 2, and the results are shown in Table 2. Figure 4

[0061] Example 6

[0062] The steps and process conditions for preparing the catalyst of this example are the same as those of Example 1, except that 10 mL of a Sm(NO3)3.6H2O solution with a concentration of 0.3 mol / L and a 1.5 mol / L NaOH solution are added dropwise into the copper-aluminum hydrotalcite suspension at a constant pH of 9.5, and finally a samarium oxide-modified copper-aluminum oxide catalyst (denoted as 30Sm-CuAl) is obtained.

[0063] Nitrogen physical adsorption-desorption test results show that the catalyst has a specific surface area of 114 m 2 / g.

[0064] The steps and process parameters for testing the activity of the catalyst are the same as those described in Example 2, and the results are shown in Table 2. Figure 4

[0065] Catalyst stability test method

[0066] ​​​The methanol steam reforming reaction stability test was carried out in a 6 mm inner diameter quartz tube fixed bed reactor. The flow rates of each gas required for the experiment were adjusted and controlled by mass flow meters, and the mixed gas was introduced into the reactor. 50 mg of 30Sm-CuAl was weighed into a quartz tube, and then treated at 300°C for 2 hours under 10% H2 / Ar mixed gas, and then reduced to the target reaction temperature. The stability test was carried out under the following reaction conditions: the reaction atmosphere was 10% CH3OH / 15% H2O / N2, the reaction temperature was 250°C, the reaction space velocity was 60000 mL / g / h, and the results are shown in Figure 6 、 Figure 7 .

[0067] Catalyst regeneration method

[0068] After the methanol steam reforming reaction stability test, anhydrous air was introduced into the 6 mm quartz tube fixed bed reactor and treated at 300°C for 1 h at a temperature rising rate of 5°C / min, and then reduced to room temperature and treated at 300°C for 2 h using 10% H2 / Ar atmosphere, and then reduced to the target reaction temperature. The methanol steam reforming reaction stability test was carried out again under the following reaction conditions: the reaction atmosphere was 10% CH3OH / 15% H2O / N2, the reaction temperature was 250°C, and the reaction space velocity was 60000 mL / g / h, and the results are shown in Figure 9 .

[0069] Comparative Example 1

[0070] Catalyst preparation

[0071] 1) Preparation of copper aluminum hydrotalcite: A mixed solution of 0.25 mol / L Al(NO3)3·9H2O and 0.75 mol / L Cu(NO3)2·3H2O was simultaneously dropped into a 180 mL solution of 0.056 mol / L Na2CO3 under the condition of constant pH of 9.5, and stirred for 20 min, and then aged in a 65°C water bath for 12 h to obtain copper aluminum hydrotalcite (denoted as CuAl-LDH).

[0072] 2) Preparation of copper aluminum oxide: The copper aluminum hydrotalcite prepared above was calcined at 500°C for 4 h in air to obtain a copper aluminum oxide catalyst (denoted as CuAl).

[0073] Catalyst activity evaluation

[0074] The methanol steam reforming reaction activity evaluation was carried out under the reaction conditions described in Reference Example 2 at a space velocity of 30000 mL / g / h. The CH3OH conversion rate of CuAl catalyst was 54.2% at 250°C, as shown in Figure 1 .

[0075] The catalyst stability test procedure and process parameters were consistent with those described in Example 6, and the results are shown in Table 6. Figure 6 , Figure 7

[0076] Comparative Example 2

[0077] 1) Preparation of samarium copper aluminum hydroxide by coprecipitation: 40 mL of 1.2 mol / L NaOH solution was added dropwise into a mixed solution of 0.25 mol / L Al(NO3)3·9H2O, 0.75 mol / L Cu(NO3)2·3H2O and 0.05 mol / L Sm(NO3)3, 20 mL, to obtain samarium copper aluminum hydroxide.

[0078] 2) Preparation of samarium copper aluminum oxide by coprecipitation: the samarium copper aluminum hydroxide prepared above was calcined at 500°C for 4 h in air to obtain a coprecipitation-prepared samarium copper aluminum oxide catalyst (denoted as 10SmCuAl-copre).

[0079] The catalyst activity test procedure and process parameters were consistent with those described in Example 2, and the results are shown in Table 2. Figure 1

[0080] Comparative Example 3

[0081] The commercial Cu / ZnO / Al2O3 catalyst was purchased from Alfa Aesar Company.

[0082] The catalyst stability test procedure and process parameters were consistent with those described in Example 6, and the results are shown in Table 6. Figure 5

[0083] Based on the exploration of Examples 1-6 and Comparative Examples 1-3, the activity comparison chart of the rare earth modified copper aluminum oxide catalysts prepared in Examples 1-4 and the copper aluminum oxide catalysts obtained in Comparative Examples 1-2 in the methanol steam reforming reaction is shown in Table 1; the XRD spectra of the samarium modified copper aluminum hydrotalcite prepared in Examples 1 and 5-6 and the copper aluminum hydrotalcite obtained in Comparative Example 1 are shown in Table 2; the nitrogen adsorption / desorption test chart and pore size distribution chart of Examples 1 and Comparative Example 1 are shown in Table 3; the activity comparison chart of the samarium modified copper aluminum oxide catalysts prepared in Examples 1 and 5-6 and the copper aluminum oxide catalyst obtained in Comparative Example 1 in the methanol steam reforming reaction is shown in Table 4; the TEM image of the samarium modified copper aluminum oxide catalyst prepared in Example 6 after activation and the TEM image after the 250°C methanol steam reforming reaction stability test are shown in Table 5. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 ​​​​​​​As shown in the figure; the stability test graphs of the samarium-modified copper-aluminum oxide catalyst prepared in Example 6, the copper-aluminum oxide catalyst obtained in Comparative Example 1, and the commercial copper-zinc-aluminum catalyst in Comparative Example 3 in methanol steam reforming reaction at a reaction temperature of 250°C and a reaction space velocity of 60000 mL / g / h are shown in the figure. Figure 6 As shown in the figure; the stability test graphs of the samarium-modified copper-aluminum oxide catalyst prepared in Example 6 and the copper-aluminum oxide catalyst obtained in Comparative Example 1 in the methanol steam reforming reaction at a reaction temperature of 300℃ and a reaction space velocity of 200,000 mL / g / h are shown in the figure. Figure 7 As shown; TEM images of the samarium-modified copper-aluminum oxide catalyst prepared in Example 6 and the copper-aluminum oxide catalyst obtained in Comparative Example 1 after activation with 10% H2 / Ar, and TEM images of the catalyst after stability testing under reaction conditions of 300℃ and 200,000 mL / g / h are shown. Figure 8 As shown; the results of the methanol steam reforming reaction regeneration-stability test in Example 6 are as follows. Figure 9 As shown in the figure. In summary, the results indicate that... Figure 1 The results show that the rare earth modified copper-aluminum oxide catalyst prepared with hydrotalcite as a precursor has significantly improved catalytic activity in the low-temperature methanol steam reforming reaction compared with the unmodified copper-aluminum oxide catalyst. At the same time, the activity of the samarium copper-aluminum oxide catalyst 10Sm-CuAl prepared with hydrotalcite as a precursor is significantly better than that of the samarium copper-aluminum oxide catalyst 10SmCuAl-copre prepared by coprecipitation method. This proves that using copper-aluminum hydrotalcite as a precursor can promote good dispersion of copper. The CH3OH conversion rate of 10Sm-CuAl can reach 84.8% at 250℃, which is 30.6% higher than that of the unmodified copper-aluminum catalyst. Figure 2 This indicates that the rare earth-modified copper-aluminum hydrotalcite prepared using the method of the present invention can effectively avoid the copper oxide that occurs in the traditional copper-aluminum hydrotalcite preparation process, and the added rare earth is uniformly dispersed on the copper-aluminum hydrotalcite layer without obvious diffraction peaks. Figure 3 The value of a in the figure indicates that the specific surface area of ​​samarium-modified copper aluminum oxide is 114 m². 2 / g, compared to 57m of unmodified copper aluminum oxide 2 / g shows a significant improvement Figure 3 Figure b indicates that the pore size distribution of the samarium-modified copper-aluminum oxide catalyst is more concentrated than that of the unmodified copper-aluminum oxide catalyst. Figure 4 This indicates that the activity of the samarium-modified copper-aluminum oxide catalyst prepared in this invention, with copper-aluminum hydrotalcite as a precursor, in methanol steam reforming exhibits a volcano curve relationship with the amount of samarium added. Figure 5 Figure a shows that after 30Sm-CuAl is activated by 10% H2 / Ar, there are Sm2O3 lattice fringes and Cu lattice fringes, but the characteristic Sm2O3-coated Cu structure does not appear in the TEM image. Figure 5The TEM image of the Sm2O3-coated Cu nanoparticle structure in the 30Sm-CuAl catalyst after a 30S 60,000 mL / g / h reaction space velocity stability test at 250°C indicates that the metal-support strong interaction in situ generates a coated structure in the methanol steam reforming reaction, and the formation of the coated structure significantly improves the catalytic activity of the samarium-modified copper-alumina oxide catalyst in the methanol steam reforming reaction. Compared with the unmodified copper-alumina oxide catalyst and other rare earth element-modified copper-alumina oxide catalysts, the samarium-modified copper-alumina oxide catalyst has a significant improvement in the reaction activity at 250°C. Figure 6 The 30Sm-CuAl samarium-modified copper-alumina oxide catalyst has a hydrogen production rate of 594.9 mmol / g / h at 250°C under a space velocity of 60,000 mL / g / h. cat In the stability test at a space velocity of 60,000 mL / g / h, the absolute activity of the samarium-modified copper-alumina catalyst decreases by 18.6% within 500 min, which is significantly improved compared with the absolute activity decrease of 28.5% of the unmodified copper-alumina oxide catalyst. Compared with the commercial copper-zinc-aluminum catalyst, the absolute activity of which decreases by 24.4% in the stability test, the samarium-modified copper-alumina oxide catalyst is superior to the commercial copper-zinc-aluminum catalyst in terms of reaction activity and stability. Figure 7 The unmodified copper-alumina oxide catalyst CuAl rapidly deactivates under the reaction conditions of 300°C and 200,000 mL / g / h, indicating that the Cu nanoparticles aggregate under high-temperature and high-space velocity conditions, changing the catalyst structure and causing the methanol steam reforming reaction activity to rapidly decrease. The samarium-modified copper-alumina oxide catalyst 30Sm-CuAl slowly deactivates under high-temperature and high-space velocity conditions compared with CuAl, and the deactivation rate is constant, indicating that the deactivation is caused by the accumulation of intermediates in the methanol steam reforming reaction, which slowly occupies the active sites and causes the catalyst activity to decrease. Figure 8 The TEM images of the Cu nanoparticles in the 30Sm-CuAl and CuAl catalysts after reduction in 10% H2 / Ar show that the particle size distribution of the Cu nanoparticles is uniform and similar, Figure 8 The TEM images of the Cu nanoparticles in the 30Sm-CuAl and CuAl catalysts after reduction in 10% H2 / Ar show that the particle size distribution of the Cu nanoparticles is uniform and similar, Figure 9The regeneration performance test shows that the samarium modified copper-aluminum oxide catalyst prepared by the application has the repeatable regeneration ability and the samarium modified copper-aluminum oxide catalyst is stably recovered to the initial activity in multiple regeneration cycles, and the intermediate adsorbed on the surface of the 30Sm-CuAl catalyst can be removed by the air calcination treatment, so that the catalyst is reactivated to recover the methanol steam reforming activity. In the methanol steam reforming reaction, the in-situ formed Sm2O3 coated Cu nanoparticle structure hinders the agglomeration of Cu, so that the 30Sm-CuAl can recover to the initial activity after the air calcination to remove the accumulated intermediate. In summary, the rare earth modified copper-aluminum oxide catalyst prepared by the application and taking the copper-aluminum hydrotalcite as the precursor has the metal-support strong interaction phenomenon in the methanol steam reforming reaction, the in-situ generated Sm2O3 coated Cu nanoparticle structure, and the generation of the coated structure on one hand significantly improves the methanol steam reforming reaction activity of the samarium modified copper-aluminum oxide catalyst, and on the other hand, the coated structure hinders the agglomeration and sintering of the copper nanoparticles in the reaction process, improves the stability of the catalyst and makes the catalyst have the repeatable regeneration characteristics.

[0084] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the application but not limit the application, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions of the application, and all should be covered in the scope of the claims of the application.

Claims

1. Use of a rare earth modified copper-alumina oxide catalyst in a methanol steam reforming reaction, characterized in that, The application relates to a preparation method of a rare earth modified copper-aluminum oxide catalyst using copper-aluminum hydrotalcite as a precursor, which comprises the following steps: (1) mixing an Al(NO3)3.9H2O and Cu(NO3)2.3H2O mixed solution with a NaOH solution under constant pH conditions, and simultaneously dropping into a Na2CO3 solution to stir for a period of time, so as to obtain a copper-aluminum hydrotalcite suspension; (2) adding a rare earth nitrate solution into the copper-aluminum hydrotalcite suspension obtained in the step (1), simultaneously dropping a NaOH solution to maintain constant pH, and performing water bath aging, so as to obtain a rare earth modified copper-aluminum hydrotalcite; (3) calcining the rare earth modified copper-aluminum hydrotalcite prepared in the step (2) in air, so as to obtain a rare earth modified copper-aluminum oxide catalyst. The rare earth nitrate includes Sm(NO3)3, Y(NO3)3, Gd(NO3)3 and Pr(NO3)3 hydrates.

2. Use according to claim 1, characterized in that, In the step (1), the concentration of the Al(NO3)3.9H2O solution in the Al(NO3)3.9H2O and Cu(NO3)2.3H2O mixed solution is 0.1-0.5 mol / L, the concentration of the Cu(NO3)2.3H2O solution is 0.3-1.5 mol / L, the concentration of the NaOH solution is 0.5-3.0 mol / L, the pH is 9.0-10.0, the concentration of the Na2CO3 solution is 0.03-0.06 mol / L, and the stirring time is 5-60 min.

3. Use according to claim 1, characterized in that, In the step (2), the concentration of the NaOH solution is 0.5-3.0 mol / L, the concentration of the rare earth nitrate solution is 0.05-0.80 mol / L, the pH is 9.0-10.0, the water bath temperature is 45-65 DEG C, and the water bath time is 6-24 h; in the step (3), the calcination temperature is 300-600 DEG C, and the calcination time is 1-6 h.

4. Use according to claim 1, characterized in that, The molar ratio of the sum of the Al(NO3)3.9H2O and Cu(NO3)2.3H2O to the Na2CO3 is 1-3:1, and the molar ratio of the sum of the Al(NO3)3.9H2O and Cu(NO3)2.3H2O to the rare earth nitrate is 1:0.025-0.

4.

5. The use according to claim 1, characterized in that, The methanol steam reforming reaction conditions are as follows: the reaction space velocity is 30000-200000 mL / g / h, the reaction temperature is 200-300 DEG C, and the reaction atmosphere is a mixed gas of 5-30 vol% CH3OH, 10-60 vol% H2O and N2.

6. Use according to claim 1, characterized in that, The catalyst further comprises an activation process, the activation atmosphere is a mixed gas of 5-30 vol% H2 and Ar, the activation temperature is 200-500 DEG C, and the activation time is 0.5-4 hours.

7. Use according to claim 1, characterized in that, The catalyst after the reaction is regenerated, the regeneration conditions are as follows: treating under an air atmosphere at 200-400 DEG C for 0.5-4 hours; and the regenerated catalyst needs to be activated.

8. The use according to claim 1, characterized in that, The catalyst after the reaction forms a coating structure in situ through metal-support strong interaction, and the coating structure is a rare earth oxide coating copper nanoparticle.

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