Preparation method of metal-oxide interface catalyst for improving ammoxidation activity

Abstract

The invention discloses a preparation method of a catalyst for improving ammoxidation activity on a metal-oxide interface, and relates to the technical field of new energy materials, carbon black and ethylene glycol are mixed uniformly, potassium chloroplatinite and cobalt nitrate are added and mixed uniformly, ascorbic acid is added, the mixture is placed in an oil bath pan to be heated, cooled and centrifugally washed, and an obtained sample is obtained; a sample is placed in a vacuum drying box to be dried, the obtained catalyst is placed in the atmosphere of air and nitrogen to be subjected to annealing treatment, the catalyst PtCoOx / C prepared through the method is a material formed by compounding a PtCo-C structure and CoOx with * OH affinity, and efficient ammoxidation catalytic performance is achieved; coOx enhances the combination of * OH on the surface of the catalyst, Co is introduced to form an alloy with Pt so as to optimize the adsorption of a series of intermediates, and NH3 is dehydrogenated after a series of intermediates are combined with * OH, so that the adsorption energy of AOR dynamics is effectively reduced, and higher ammoxidation performance and excellent stability are broken through.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, and particularly relates to a preparation method of a metal-oxide interface promoted ammonia oxidation activity catalyst. BACKGROUND

[0002] In recent years, with the transformation of energy structure, ammonia (NH3) as a carbon-free hydrogen carrier and direct fuel has become increasingly prominent. Ammonia is a promising carbon-free fuel with high energy density (13 MJ / L), high hydrogen content (17.6 wt%) and mature existing infrastructure. Ammonia catalytic oxidation reaction (AOR) is a key process in the anode reaction of ammonia fuel cell. The reaction aims to oxidize NH3 to N2 with high efficiency and selectivity, and release electrons and protons. However, AOR is a complex six-electron transfer process, and the reaction kinetics is extremely slow, and there are competitive hydrogen evolution reaction (HER) and nitrogen oxide (NO x ) and other byproduct formation pathways, resulting in low energy conversion efficiency of fuel cells and poor catalyst stability, which seriously restricts its further development.

[0003] Currently, the catalysts for AOR mainly rely on platinum (Pt), iridium (Ir) and other noble metal-based materials. Although these catalysts show high initial activity, due to the scarcity of noble metal resources, the high price, and the easy poisoning of noble metal surface by AOR reaction intermediates (especially strong adsorption *N species), the active sites are occupied or the catalyst is deactivated, making it difficult to be applied on a large scale. In order to overcome these problems, researchers have explored alloying platinum with non-noble metal catalysts (such as Ni, Co, Cu) or forming composite materials through interface engineering to optimize the inherent properties of platinum. Although these studies have made some improvements, their AOR performance is still not as good as hydrogen oxidation, highlighting the urgent need to further optimize the catalyst.

[0004] In recent years, it has been found that interface engineering, especially the construction of metal-oxide interface, can significantly improve the catalytic activity and stability of the catalyst. The fundamental reason is that there is an electronic effect and a synergistic effect at the interface between the metal and the oxide. This interface effect can enhance the adsorption strength of the reaction intermediates, promote the formation of oxygen vacancies on the surface, and form unique active sites, thereby reducing the reaction energy barrier of AOR, so as to achieve high ammonia conversion rate at low temperature. However, how to reasonably integrate the metal-oxide interface so that both of them can play the greatest advantage is still a technical problem that has not been well solved in the current field. Therefore, it is urgent to develop a simple catalyst preparation method that can cleverly use this "oxidation interface" effect to provide a new solution for developing high-performance, low-cost ammonia oxidation catalysts. SUMMARY

[0005] Technical problems solved: This application addresses the shortcomings of existing technologies by solving the following technical problems: low energy conversion efficiency of fuel cells, poor catalyst stability, scarcity and high price of precious metal resources, easy poisoning of precious metal surfaces by AOR reaction intermediates, high cost of precious metal Pt in ammonia oxidation applications, Pt susceptibility to poisoning by reaction intermediate *N, and poor long-term stability, which lead to the occupation of active sites or catalyst deactivation, making it difficult to apply on a large scale. The application provides a method for preparing a metal-oxide interface catalyst to enhance ammonia oxidation activity.

[0006] Objective of the Invention: This application discloses a method for preparing a metal-oxide interface-enhanced ammonia oxidation catalyst. The method accelerates the electron transport rate of the catalyst through the synergistic effect between the interfaces, and optimizes the adsorption of hydroxyl intermediates and the desorption of nitrogen-containing intermediates in the AOR process, potentially accelerating the dehydrogenation process of NH3 and significantly improving the activity of PtCoO2. x The catalytic performance of / C is improved; at the same time, changes in the material microenvironment can influence the kinetics of electrochemical reactions, reveal the structure-activity relationship between the metal-oxide interface structure and AOR, and further guide the synthesis of novel and efficient catalysts with interface effects.

[0007] To achieve the above objectives, this application provides the following technical solution: A method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity specifically includes the following steps: Step 1: Mix 1-3 mg of carbon black with 10 mL of ethylene glycol in a 50 mL round-bottom flask according to the mass-volume ratio to obtain solution A; Step 2: Add 0.8-1.2 parts of platinum source and 0.6-1 parts of cobalt source to 0.5-1 parts of solution A according to the mass ratio, and then sonicate at a frequency of 50 kHz for 30 min to obtain solution B; Step 3: Add 26-32 parts of ascorbic acid to solution B and sonicate at a frequency of 50 kHz for 1 h to obtain solution C; Step 4: Place solution C in an oil bath and heat it; Step 5: After the heating reaction is complete, clean the sample and place it in a vacuum drying oven at 60 °C for 8 hours. Step 6: The vacuum-dried product is annealed in air to finally generate a metal-oxide interface catalyst. Step 7: Anneal the catalyst at the metal-oxide interface under a nitrogen atmosphere to finally generate a metal-oxide interface catalyst that enhances the activity of ammonia oxidation.

[0008] Furthermore, in the first step, the carbon black is XC-72 carbon black, and the concentration of XC-72 carbon black in ethylene glycol is 0.2 mg / mL.

[0009] Furthermore, in the second step, the platinum source is potassium chloroplatinate.

[0010] Furthermore, in the second step, the cobalt source is cobalt nitrate.

[0011] Furthermore, the mass ratio of potassium chloroplatinate to cobalt nitrate is 1:0.8.

[0012] Furthermore, in the third step, the ascorbic acid is L-ascorbic acid, and the concentration of L-ascorbic acid is 18 mg / mL.

[0013] Furthermore, in the fourth step, the heating temperature is 80-100 ℃, and the heating time is 12 h.

[0014] Furthermore, in the fifth step, the solvent for sample cleaning is ethanol, and the ethanol washing is performed 3-4 times.

[0015] Furthermore, the metal-oxidation interface catalyst in the sixth step is PtCoO. x / C, annealing temperature is 200-400℃, annealing time is 1-2 h.

[0016] Furthermore, in the seventh step, the metal-oxide interface catalyst for enhancing ammonia oxidation activity is PtCo / C, the annealing temperature is 200-400 ℃, and the annealing time is 1-2 h.

[0017] Explanation of principle: Based on the synergistic effect of the metal-oxide interface, PtCo and CoO x The synergistic effect between the formed interfaces enhances the electron transfer rate. PtCo alloys can optimize the Pt-Pt spacing and d-band center, while CoO... x By enhancing the affinity of *OH, promoting the dehydrogenation of NH3, and weakening the *N adsorption structure, the problems of Pt-based catalysts being susceptible to *N poisoning and having low catalytic activity are solved, thus improving the catalytic performance of the material. Furthermore, based on the electronic interaction of this metal-oxide structure, charge transfer occurs at the interface, which is beneficial for surface electronic modulation.

[0018] This application provides a method for preparing a metal-oxide interface catalyst with enhanced ammonia oxidation activity, which has the following advantages compared with the prior art: 1. The catalyst prepared by the method described in this application is a PtCoO4 catalyst with interfacial effects. x / C, which exhibits a uniform distribution on XC-72 carbon black.

[0019] 2. The catalyst PtCoO prepared by the method disclosed in this inventionx / C is based on the PtCo-C structure and CoO with *OH affinity. x The composite material can leverage the synergistic effect of two superior structures to achieve highly efficient ammonia oxidation catalytic performance.

[0020] 3. CoO x It can enhance the binding of *OH on the catalyst surface. The introduction of Co and the formation of an alloy with Pt can optimize the adsorption of a series of intermediates such as NH3. After the NH3 and other intermediates combine with *OH, they are dehydrogenated, effectively reducing the adsorption energy of AOR kinetics, thereby achieving higher ammonia oxidation performance and better stability.

[0021] 4. During the experimental testing, the PtCoOx / C ratio measured by cyclic voltammetry (CV) in a 1 M KOH + 0.1 M NH3 electrolyte reached 15 mA cm⁻¹. -2 The current density is higher than that of PtCo / C (10 mA cm⁻¹). -2 After stability testing under constant voltage conditions of 0.65 V vs. RHE, it still maintains good stability after 1000 s compared with the current existing technology. Attached Figure Description

[0022] Figure 1 The PtCoO obtained in Example 1 of this application x Transmission electron microscopy images of PtCo / C and PtCo / C catalysts, where a is PtCoO x The structural morphology of / C, and b is the structural morphology of PtCo / C; Figure 2 The PtCoO obtained in Example 1 of this application x The CV curves of the catalytic activity of PtCoO₂ and PtCo / C catalysts in the ammonia oxidation reaction in an alkaline 1 M KOH + 0.1 M NH₃ solution are shown in the figure. The blue line represents PtCoO₂. x / C catalyst, the red line represents the PtCo / C catalyst; Figure 3 The PtCoO obtained in Example 1 of this application x Stability test of / C in alkaline 1 M KOH + 0.1 M NH3 using potentiostatic polarization (it) curves. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: A method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity, comprising the following steps: Step 1: Mix 2 mg of carbon black and 10 mL of ethylene glycol in a 50 mL round-bottom flask according to the mass-volume ratio to obtain solution A; Step 2: Add 1 part potassium chloroplatinate and 0.8 parts cobalt nitrate to 0.5 parts of solution A according to the mass ratio, and then sonicate at a frequency of 50 kHz for 30 min to obtain solution B; Step 3: Add 32 portions of L-ascorbic acid at a concentration of 18 mg / mL to solution B and sonicate at a frequency of 50 kHz for 1 h to obtain solution C; Step 4: Place solution C in an oil bath and heat it at 100 ℃ for 12 h. Step 5: After the heating reaction is complete, wash the sample with ethanol 3-4 times, and put the washed sample into a vacuum drying oven and vacuum dry at 60 ℃ for 8 hours; Step 6: After vacuum drying, the product is annealed in air at 200 ℃ for 1-2 h to finally generate the metal-oxide interface catalyst PtCoO. x / C; Step 7: Apply PtCoO, a catalyst at the metal-oxide interface. x / C was annealed under a nitrogen atmosphere at a temperature of 200 °C for 1-2 h to finally generate a metal-oxide interface catalyst for enhanced ammonia oxidation activity, PtCo / C.

[0025] The PtCoO obtained above x / C and PtCo / C catalysts were observed using transmission electron microscopy (TEM), such as Figure 1 As shown, the obtained PtCoO x / C and PtCo / C have a good degree of alloying, PtCoO x / C and PtCo / C catalysts are uniformly deposited on carbon.

[0026] Electrochemical testing: (1) Preparation of catalytic electrode Electrochemical tests were performed on a rotating disk apparatus. For AOR testing, a standard three-electrode system was used, with the prepared sample as the working electrode, a platinum mesh as the counter electrode, and a standard Hg / HgO electrode as the reference electrode. The electrolyte used was 1 M KOH + 0.1 M NH3, with the pH set at 14.

[0027] (2) AOR activity test At 5 mV s -1CV curves were obtained at a scan rate of 0.65 V vs. RHE constant voltage conditions, and stability tests were performed.

[0028] Figure 2 It is the PtCoO obtained in Example 1 of this invention. x / C and PtCo / C catalysis in 1 M KOH + 0.1 M NH3, with a potential range of -0.8 V to 0.1 V (relative to the mercury oxide electrode), and a scan rate of 5 mV s. -1 The CV curves, where the blue line represents PtCoO x The CV curves of the PtCo / C catalyst are shown in the figure, with the red line representing the CV curve of the PtCo / C catalyst. The figure also shows that PtCoO... x The current density of the / C catalyst is significantly higher than that of PtCo / C.

[0029] Figure 3 It is the PtCoO obtained in Example 1 of this invention. x The stability of / C in 1 M KOH + 0.1 M NH3 was tested under constant voltage conditions of 0.65 V vs. RHE. Figure 3 It can be seen that the curve still maintains activity after 1000 s of continuous testing, indicating that PtCoO x / C has good stability.

[0030] Example 2, a method for preparing a metal-oxide interface-enhanced ammonia oxidation activity catalyst, comprising the following steps: Step 1: Mix 1 mg of carbon black and 10 mL of ethylene glycol in a 50 mL round-bottom flask according to the mass-volume ratio to obtain solution A; Step 2: Add 0.8 parts potassium chloroplatinate and 0.6 parts cobalt nitrate to 0.8 parts of solution A according to the mass ratio, and then sonicate at a frequency of 50 kHz for 30 min to obtain solution B; Step 3: Add 26 portions of L-ascorbic acid at a concentration of 18 mg / mL to solution B and sonicate at a frequency of 50 kHz for 1 h to obtain solution C; Step 4: Place solution C in an oil bath and heat it at 80 ℃ for 12 h. Step 5: After the heating reaction is complete, wash the sample three times with ethanol, and then put the washed sample into a vacuum drying oven and vacuum dry at 60 °C for 8 hours. Step 6: The vacuum-dried product is annealed in air at 300 °C for 1 h, ultimately producing the metal-oxide interface catalyst PtCoO. x / C; Step 7: Apply PtCoO, a catalyst at the metal-oxide interface.x / C was annealed under a nitrogen atmosphere at a temperature of 300℃ for 1 h, ultimately producing a metal-oxide interface catalyst, PtCo / C, which enhances the activity of ammonia oxidation.

[0031] PtCoO x / C Due to the formation of an oxide layer during air annealing, this oxide interface promotes electron transfer and enhances the activity of ammonia oxidation reaction.

[0032] Example 3: A method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity, comprising the following steps: Step 1: Mix 3 mg of carbon black and 10 mL of ethylene glycol in a 50 mL round-bottom flask according to the mass-volume ratio to obtain solution A; Step 2: Add 1.0 part potassium chloroplatinate and 1 part cobalt nitrate to 1 part of solution A according to the mass ratio, and then sonicate at a frequency of 50 kHz for 30 min to obtain solution B; Step 3: Add 30 portions of L-ascorbic acid at a concentration of 18 mg / mL to solution B and sonicate at a frequency of 50 kHz for 1 h to obtain solution C; Step 4: Place solution C in an oil bath and heat it at 90 ℃ for 12 h. Step 5: After the heating reaction is complete, wash the sample 4 times with ethanol, and then put the washed sample into a vacuum drying oven and vacuum dry at 60 °C for 8 hours. Step 6: The vacuum-dried product is annealed in air at 400 ℃ for 2 h to finally produce the metal-oxide interface catalyst PtCoO. x / C; Step 7: Apply PtCoO, a catalyst at the metal-oxide interface. x / C was annealed under a nitrogen atmosphere at a temperature of 400℃ for 2 hours, ultimately producing a metal-oxide interface catalyst, PtCo / C, which enhances the activity of ammonia oxidation.

[0033] In summary, the PtCoO prepared by the method of the present invention has a metal-oxide interface. x / C catalysts exhibit excellent catalytic activity for ammonia oxidation, meaning they possess superior ammonia oxidation activity and good stability. Furthermore, their preparation process is simple, low-cost, and suitable for large-scale industrial production.

[0034] The foregoing description has fully disclosed the specific embodiments of the present invention. It should be noted that any modifications made to the specific embodiments of the present invention by those skilled in the art do not depart from the scope of the claims. Accordingly, the scope of the claims is not limited to the foregoing specific embodiments.

Claims

1. A method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity, characterized in that, Includes the following steps: Step 1: Mix 1-3 mg of carbon black with 10 mL of ethylene glycol in a 50 mL round-bottom flask according to the mass-volume ratio to obtain solution A; Step 2: Add 0.8-1.2 parts of platinum source and 0.6-1 parts of cobalt source to 0.5-1 parts of solution A according to the mass ratio, and then sonicate at a frequency of 50 kHz for 30 min to obtain solution B; Step 3: Add 26-32 parts of ascorbic acid to solution B and sonicate at a frequency of 50 kHz for 1 h to obtain solution C; Step 4: Place solution C in an oil bath and heat it; Step 5: After the heating reaction is complete, clean the sample and place it in a vacuum drying oven at 60 °C for 8 hours. Step 6: The vacuum-dried product is annealed in air to finally generate a metal-oxide interface catalyst. Step 7: Anneal the catalyst at the metal-oxide interface under a nitrogen atmosphere to finally generate a metal-oxide interface catalyst that enhances the activity of ammonia oxidation.

2. The preparation method of the metal-oxide interface-enhanced ammonia oxidation activity catalyst according to claim 1, characterized in that: The carbon black used in the first step is XC-72 carbon black, and the concentration of XC-72 carbon black in ethylene glycol is 0.2 mg / mL.

3. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 1, characterized in that: In the second step, the platinum source is potassium chloroplatinate.

4. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 1, characterized in that: In the second step, the cobalt source is cobalt nitrate.

5. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 3 or 4, characterized in that: In the second step, the mass ratio of potassium chloroplatinate to cobalt nitrate is 1:0.

8.

6. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 1, characterized in that: In the third step, the ascorbic acid is L-ascorbic acid with a concentration of 18 mg / mL.

7. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 1, characterized in that: In the fourth step, the heating temperature is 80-100 ℃ and the heating time is 12 h.

8. The preparation method of a metal-oxide interface catalyst for enhancing ammonia oxidation activity as described in claim 1, characterized in that: In the fifth step, the sample is cleaned using ethanol as the solvent, and the sample is washed 3-4 times.

9. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 1, characterized in that: In the sixth step, the metal-oxidation interface catalyst is PtCoO. x / C, annealing temperature is 200-400 ℃, annealing time is 1-2 h.

10. The method for preparing a metal-oxide interface catalyst for enhancing ammonia oxidation activity according to claim 1, characterized in that: In the seventh step, the metal-oxide interface catalyst for enhancing ammonia oxidation activity is PtCo / C, with an annealing temperature of 200-400 ℃ and an annealing time of 1-2 h.

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