A Pd catalyst for low-temperature H2 catalysis and its preparation method

Abstract

The present invention discloses a Pd catalyst for low-temperature H2 catalysis and its preparation method, which relates to the field of synthesis of novel hydrogen combustion catalysts. The chemical general formula of the Pd catalyst is Pd / ZnO / Ca 1‑1.5x Al 2+x O4, wherein, -0.1 ≤ x ≤ 0.15, the mass percentage of Pd is 1-1.5%, and the mass percentage of ZnO is 10-30%. The Pd catalyst prepared by the present invention has high catalytic activity for hydrogen catalytic reaction at low temperature (80°C), and its catalytic activity is even higher than that of the Pt catalyst prepared under the same reaction conditions and steps at the same reaction temperature. It has obvious advantages in terms of preparation cost. By setting a specific Ca:Al ratio, a catalyst with optimal catalytic activity is obtained.

Description

Technical Field

[0001] The present invention relates to the field of synthesis of novel hydrogen combustion catalysts, and specifically relates to a Pd catalyst for low-temperature catalysis of H2 and a preparation method thereof. Background Art

[0002] Hydrogen is a flammable gas and a clean energy source. Our research on hydrogen reactions, especially further research on its low-temperature catalytic reactions, is of great significance for the future energy field. For example, the realization of the conversion of chemical energy and electrical energy through low-temperature reactions contributes to the further development of new energy batteries; also, a certain amount of hydrogen will be generated or leaked in nuclear power plant reactors. If hydrogen is not removed as soon as possible, the accumulation of hydrogen concentration is likely to cause an explosion, resulting in a serious nuclear accident. And the low-temperature catalytic combustion of H2 is conducive to hydrogen removal in nuclear power plants under low-energy consumption conditions, ensuring the safety of nuclear power plants.

[0003] At present, the technology of low-temperature catalytic combustion of H2 is a relatively popular research direction, and is mentioned in many scientific research papers. For example, Kramer et al. studied the low-temperature catalytic combustion performance of hydrogen using Pd / γ-Al2O3 as a catalyst. The low temperature in this paper refers to a reaction temperature where the combustion condition is not higher than 250 °C, and the active reaction temperature is still not ideal. How to further reduce the low-temperature catalytic combustion temperature of hydrogen is crucial for dealing with hydrogen in nuclear power plants. Summary of the Invention

[0004] The present invention aims to provide a Pd catalyst for low-temperature catalysis of H2 and a preparation method thereof to solve the technical problem that the active reaction temperature of the existing Pd catalyst is too high.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A Pd catalyst for low-temperature catalysis of H2, characterized in that the chemical general formula of the Pd catalyst is Pd / ZnO / Ca 1-1.5x Al 2+x O4, where -0.1 ≤ x ≤ 0.15, the mass percentage of Pd is 1-1.5%, and the mass percentage of ZnO is 10-30%.

[0007] The preparation method of the above Pd catalyst includes the following steps:

[0008] (1) Prepare Ca 1-1.5x Al 2+x O4 material;

[0009] (2) Immerse the Ca 1-1.5x Al 2+x O4 material fully in an acidic ZnO slurry, and then take it out and dry it to obtain ZnO / Ca 1-1.5x Al 2+xO4;

[0010] (3) Immerse ZnO / Ca 1-1.5x Al 2+x O4 in a palladium nitrate solution, then take it out and dry it, calcine it at 450 - 550 °C for 10 - 16 h, and then reduce it in a H2 / N2 atmosphere for 5 h to obtain the Pd catalyst Pd / ZnO / Ca 1-1.5x Al 2+x O4.

[0011] Furthermore, the preparation process of the Ca 1-1.5x Al 2+x O4 material in step (1) includes the following steps:

[0012] A. Place Ca(OH)2 and Al(NO3)3 in deionized water, stir and sonicate thoroughly until an emulsion is formed;

[0013] B. Put the above emulsion into an oven and dry it at 100 °C for 24 h;

[0014] C. Calcinate the solid obtained after drying at 450 - 550 °C for 6 - 8 h to obtain the Ca 1-1.5x Al 2+x O4 material.

[0015] Furthermore, the solid-liquid ratio of the acidic ZnO slurry in step (2) is 0.2 g / ml, and the pH value is between 3.8 and 4.

[0016] Even further, the acid in the acidic ZnO slurry is nitric acid.

[0017] Even further, the specific surface area of the ZnO is 80 - 100 m 2 / g, and the average diameter of the particles is not more than 1 μm.

[0018] Even further, the impregnation time of the Ca 1-1.5x Al 2+x O4 material in the acidic ZnO slurry is 48 h.

[0019] Furthermore, the concentration of the palladium nitrate solution in step (3) is 20 - 25 mg / ml.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The Pd catalyst prepared by the present invention has high catalytic activity for hydrogen catalytic reaction at low temperature (80 °C).

[0022] 2. The Pd catalyst prepared by the present invention has a catalytic activity even higher than that of the Pt catalyst prepared under the same reaction conditions and steps at the same reaction temperature, and has obvious advantages in terms of preparation cost.

[0023] 3. By setting a specific Ca:Al ratio, the present invention obtains a catalyst with optimal catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 TEM image of the Pd catalyst prepared in Example 1;

[0025] Figure 2 Line graph of hydrogen conversion rate - reaction temperature of Pd catalysts prepared using different carriers;

[0026] Figure 3 Line graph of hydrogen conversion rate - reaction temperature of Pd catalysts prepared using different active components;

[0027] Figure 4 Bar graph of hydrogen conversion rate of Pd catalysts with different Ca:Al ratios at 80 °C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with each embodiment and the drawings. The implementation manners of the present invention include but are not limited to the following embodiments.

[0029] Example 1

[0030] The preparation process of the Pd catalyst provided in this example is as follows:

[0031] (1) Preparation of Ca 1-1.5x Al 2+x O4 material

[0032] a) Dissolve 3.7 g of Ca(OH)2 and 21.3 g of Al(NO3)3 in 150 ml of deionized water.

[0033] b) Stir well for 30 min, and ultrasonically treat the above solution for 1 h until an emulsion is formed.

[0034] c) Put the above solution into an oven and dry it at 100 °C for 24 h.

[0035] d) Calcinate the dried solid at 500 °C for 6 h to obtain Ca 1-1.5x Al 2+x O4 material. At this time, x = 0, that is, CaAl2O4 material is obtained.

[0036] (2) Preparation of ZnO / CaAl2O4 material

[0037] a) Mix 20 g of ZnO powder (80 - 100 m2 / g) with 100 mL of deionized water, stir for 30 min, and sonicate for 1 h.

[0038] b) Add nitric acid to the above solution to make the pH of the slurry between 3.8 and 4. Ball mill the prepared slurry at a speed of 250 rpm for 5 days to reduce the average diameter of Zn particles to less than 1 μm.

[0039] c) Immerse the CaAl2O4 material in the ZnO slurry for 48 h.

[0040] d) Take out the fully immersed CaAl2O4, wash it twice with deionized water, and then dry it to obtain ZnO / CaAl2O4.

[0041] (3) Preparation of Pd / ZnO / CaAl2O4 catalyst

[0042] a) Dissolve 0.23 g of palladium nitrate in 10 ml of water.

[0043] b) Immerse ZnO / CaAl2O4 in the above solution and dry at 70 °C for 2 h.

[0044] c) Calcinate at 500 °C for 12 h to remove other organic substances.

[0045] d) At 500 °C, reduce Pd / ZnO / CaAl2O4 in a 4% H2 / N2 atmosphere at 50 mL / min for 5 h to obtain a 1 wt% Pd / ZnO / CaAl2O4 catalyst.

[0046] As Figure 1 shown, the TEM image of the Pd catalyst prepared in this example.

[0047] Example 2

[0048] On the basis of Example 1, by changing the concentration of the palladium nitrate solution and the impregnation time, with other treatment steps unchanged, 0.5 wt% and 1.5 wt% Pd / ZnO / Ca 1-1.5x Al 2+x O4 catalysts are obtained respectively.

[0049] Example 3

[0050] The preparation process of the Pd catalyst provided in this example is as follows:

[0051] a) Dissolve 0.23 g of palladium nitrate in 10 ml of water.

[0052] b) Immerse ZnO in the above solution and dry at 70 °C for 2 h.

[0053] c) Calcinate at 500 °C for 12 h to remove other organic substances.

[0054] d) At 500 °C, reduce Pd / ZnO in a 4% H2 / N2 atmosphere at 50 mL / min for 5 h to obtain a 1 wt% Pd / ZnO catalyst.

[0055] Example 4

[0056] The preparation process of the Pd catalyst provided in this example is as follows:

[0057] (1) Preparation of Ca 1-1.5x Al 2+x O4 material

[0058] a) Dissolve 3.7 g of Ca(OH)2 and 21.3 g of Al(NO3)3 in 150 ml of deionized water.

[0059] b) Stir well for 30 min and sonicate the above solution for 1 h until an emulsion is formed.

[0060] c) Put the above solution into an oven and dry at 100 °C for 24 h.

[0061] d) Calcinate the dried solid at 500 °C for 6 h to obtain the Ca 1-1.5x Al 2+x O4 material, where x = 0, i.e., the CaAl2O4 material is obtained.

[0062] (2) Preparation of Pd / CaAl2O4 catalyst

[0063] a) Dissolve 0.23 g of palladium nitrate in 10 ml of water.

[0064] b) Immerse CaAl2O4 in the above solution and dry at 70 °C for 2 h.

[0065] c) Calcinate at 500 °C for 12 h to remove other organic substances.

[0066] d) At 500 °C, reduce Pd / CaAl2O4 in a 4% H2 / N2 atmosphere at 50 mL / min for 5 h to obtain a 1 wt% Pd / CaAl2O4 catalyst.

[0067] Example 5

[0068] On the basis of Example 1, other steps remain unchanged, and only replace palladium nitrate in step (3) with 0.22 g of Pt(NO3)2, 0.28 g of Rh(NO3)3, 0.43 g of Fe(NO3)3, 0.031 g of Co(NO3)2, and 0.031 g of Ni(NO3)2.

[0069] Example 6

[0070] This example explores the influence of different Ca:Al ratios on the catalytic activity. Based on Example 1, only the dosages of Ca(OH)2 and Al(NO3)3·6H2O are changed, and their dosages are shown in Table 1 as follows:

[0071] Table 1 Dosages of Ca(OH)2 and Al(NO3)3·6H2O

[0072] <![CDATA[Ca 1-1.5x Al 2+x O4]]> <![CDATA[Dosage of Ca(OH)2 (g)]]> <![CDATA[Dosage of Al(NO3)3·6H2O (g)]]> X＝0.4 3.7 63.90 X＝0.3 3.7 44.54 X＝0.2 3.7 33.47 X＝0.1 3.7 26.31 X＝0 3.7 21.30 X＝-0.1 3.7 17.60 X＝-0.2 3.7 14.75 X＝-0.3 3.7 12.49 X＝-0.4 3.7 10.65

[0073] Experimental example:

[0074] 1. The Pd catalysts obtained in Examples 1 - 4 and commercially available Pd / C were put into the catalytic reaction. The reaction process was as follows: 0.5 g of the catalyst was loaded into a straight - tube quartz reactor with a diameter of 1 cm, heated to the target temperature for reaction. The gas flow rate at the reactor inlet was 200 mL / min, and the gas composition was 3% H2 and 97% air. A mass spectrometer was used to analyze the gas composition after reaction at the reactor outlet.

[0075] As Figure 2 shown, it is a broken - line graph of hydrogen conversion rate - reaction temperature of Pd catalysts prepared with different carriers. The ZnO / CaAl2O4 matrix has more oxygen defect sites, enabling O2 to be better adsorbed on the carrier and react with H2, so that the Pd / ZnO / CaAl2O4 catalyst with a low loading amount has higher activity. As Figure 2 can be seen, both 1wt% Pd / ZnO / CaAl2O4 and 1.5wt Pd / ZnO / CaAl2O4 can completely catalytically combust hydrogen at low temperature at 80°C. The activity of 0.5wt% Pd / ZnO / CaAl2O4 is slightly worse, and the hydrogen conversion rate at 80°C is 88%. While the activities of catalysts such as Pd / C, Pd / ZnO, and Pd / CaAl2O4 are lower, and they need to catalytically combust hydrogen at low temperature at 100°C.

[0076] 2. The catalysts obtained in Examples 1 and 5 were put into the catalytic reaction. As Figure 3 shown, it is a broken - line graph of hydrogen conversion rate - reaction temperature of Pd catalysts prepared with different active components. It is not difficult to see that the preparation method provided by the present invention has different catalytic effects on different active components. The catalytic activity of noble metals is higher, while that of non - noble metals is lower. However, different from the traditional theory, the catalytic activity of Pd is higher than that of Pt.

[0077] 3. The catalyst obtained in Example 6 was put into the catalytic reaction. As Figure 4As shown, it is a bar chart of the hydrogen conversion rate of Pd catalysts with different Ca:Al ratios at 80°C. It is not difficult to see that when the x ratio is 0.1, Pd / ZnO / Ca 1-1.5x Al 2+x O4 has the highest catalytic activity.

[0078] The above embodiments are only one of the preferred embodiments of the present invention and should not be used to limit the protection scope of the present invention. Any meaningless changes or polish made on the main design concept and spirit of the present invention, as long as the technical problems solved are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A Pd catalyst for low-temperature H2 catalysis, characterized in that, The chemical general formula of the Pd catalyst is Pd / ZnO / Ca 1-1.5x Al 2+x O4, where -0.1 ≤ x ≤ 0.15, the mass percentage of Pd is 1-1.5%, and the mass percentage of ZnO is 10-30%; the preparation process of the Pd catalyst includes the following steps: (1) Prepare Ca 1-1.5x Al 2+x O4 material; A. Place Ca(OH)2 and Al(NO3)3 in deionized water, stir well and sonicate until an emulsion is formed; B. Put the above emulsion into an oven and dry it at 100 °C for 24 h; C. The solid obtained after drying is calcined at 450 - 550 °C for 6 - 8 h to obtain the Ca 1-1.5x Al 2+x O4 material; (2) Immerse the Ca 1-1.5x Al 2+x O4 material fully in the acidic ZnO slurry, and then take it out and dry it to obtain ZnO / Ca 1- 1.5x Al 2+x O4; (3) Immerse ZnO / Ca 1-1.5x Al 2+x O4 in a palladium nitrate solution, then take it out and dry it, calcine it at 450 - 550 °C for 10 - 16 h, and then reduce it in an H2 / N2 atmosphere for 5 h to obtain the Pd catalyst Pd / ZnO / Ca 1-1.5x Al 2+x O4.

2. The preparation method of the Pd catalyst according to claim 1, characterized in that, It includes the following steps: (1) Prepare Ca 1-1.5x Al 2+x O4 material; (2) Immerse the Ca 1-1.5x Al 2+x O4 material fully in the acidic ZnO slurry, and then take it out and dry it to obtain ZnO / Ca 1- 1.5x Al 2+x O4; (3) Immerse ZnO / Ca 1-1.5x Al 2+x O4 in a palladium nitrate solution, then take it out and dry it, calcine it at 450 - 550 °C for 10 - 16 h, and then reduce it in an H2 / N2 atmosphere for 5 h to obtain the Pd catalyst Pd / ZnO / Ca 1-1.5x Al 2+x O4.

3. The preparation method according to claim 2, characterized in that, The Ca 1-1.5x Al 2+x preparation process of the O4 material includes the following steps: A. Place Ca(OH)2 and Al(NO3)3 in deionized water, stir well and sonicate until an emulsion is formed; B. Put the above emulsion into an oven and dry it at 100 °C for 24 h; C. Calcinate the obtained solid after drying at 450 - 550 °C for 6 - 8 h to obtain Ca 1-1.5x Al 2+x O4 material.

4. The preparation method according to claim 2, characterized in that, In step (2), the solid-liquid ratio of the acidic ZnO slurry is 0.2 g / mL, and the pH value is between 3.8 and 4.

5. The preparation method according to claim 4, characterized in that, The acid in the acidic ZnO slurry is nitric acid.

6. The preparation method according to claim 4, characterized in that, The specific surface area of the ZnO is 80-100 m 2 / g, and the average diameter of the particles is not greater than 1 μm.

7. The preparation method according to claim 4, characterized in that The Ca 1-1.5x Al 2+x O4 material is impregnated in the acidic ZnO slurry for 48 h.

8. The preparation method according to claim 2, characterized in that, In step (3), the concentration of the palladium nitrate solution is 20 - 25 mg / mL.

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