A cobalt-doped cuprous oxide catalyst, a preparation method and application thereof

Abstract

The application discloses a high-performance cobalt-doped cuprous oxide (Co-CuOx) catalyst, a preparation method thereof and application of the catalyst in catalyzing reduction of nitroaromatic compounds. + / Cu 2+ and Co 2+ / Co 3+ bivalent states, and is rich in oxygen vacancies, thus significantly optimizing the electronic structure and specific surface area of the catalyst. The preparation method is as follows: after copper and cobalt salts are co-precipitated, the salts are reduced in an alkaline environment by using glucose, and then subjected to water bath reaction. The catalyst can efficiently catalyze reduction reactions such as reduction of 4-nitrophenol, and the apparent rate constant is as high as 38.4 min ‑1 g ‑1 , which is 24 times that of pure cuprous oxide, and the stability of the catalyst is excellent, and the activity of the catalyst can be maintained above 90% after being reused for 30 times, thus showing great practical application potential.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, and specifically relates to a cobalt-doped cuprous oxide catalyst, its preparation method, and its application. Background Technology

[0002] Nitro aromatic compounds are an important class of industrial intermediates, widely used in agriculture, pharmaceuticals, textiles, and dye manufacturing. However, these compounds are highly soluble, polar, and toxic, leading to their frequent detection in industrial wastewater and posing a significant threat to environmental health and ecological balance. For example, 4-nitrophenol (4-NP) is not only highly toxic and bioaccumulative but also carcinogenic. Long-term exposure to 4-NP can cause blood cell damage, central nervous system damage, and liver damage. Selectively converting nitro aromatic hydrocarbons into corresponding amine derivatives through catalytic hydrogenation not only promises detoxification but also yields high-value-added amine products. Compared to nitro aromatic compounds, nitramines have lower toxicity and have been identified as key raw materials for the synthesis of pharmaceuticals, surfactants, and agrochemicals. The strong N=O bond in the nitro structure results in high energy consumption during reduction and requires large amounts of hydrogenation reagents. Currently, catalysts composed of noble metals (such as palladium, platinum, and gold) exhibit excellent hydrogen activation and hydrogenation capabilities under mild conditions. However, the high cost and limited availability of these elements still restrict their widespread application in the industrial sector. Despite these significant challenges, developing non-precious metal catalysts that combine highly efficient hydrogen activation capabilities with strong stability remains key to driving the development of the hydrogenation industry.

[0003] The adsorption and activation capacity of metal sites for hydrogen species is closely related to their redox properties. Therefore, enhancing the redox capacity of metal catalysts is an effective strategy to improve their catalytic performance in hydrogenation reactions. To date, researchers have achieved some success in the design of transition metal (such as nickel, cobalt, and copper) catalysts through methods such as crystal phase engineering, defect engineering, and alloying. Among these transition metals, copper-based catalysts are considered the best candidate materials for selective hydrogenation reactions due to their excellent hydrogen activation capacity, low cost, environmental friendliness, and tunable electronic structure. The unique arrangement of 3d orbital electrons allows copper oxide to exhibit redox properties by adjusting its electronic structure. For example, Cheng et al. successfully constructed Cu-O-Si units by introducing silicon atoms into copper oxide, thereby enhancing the hybridization of O 2p and Cu 3d orbitals. This process further leads to the enhancement of Cu-O bonds and Cu... + / Cu 0Site stabilization. Despite significant progress, current copper-based catalytic systems still suffer from a major drawback: their dependence on excess reducing agent far exceeds that of the substrate by hundreds to thousands of times. This characteristic not only drives up processing costs but also disrupts redox cycles and can even lead to the deactivation of copper sites during hydrogenation. Therefore, developing highly active and stable catalysts that can operate efficiently under low reducing agent consumption conditions remains a critical technical challenge that urgently needs to be addressed. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a Co-CuOx microsphere, its preparation method, and its application.

[0005] This invention is achieved through the following technical solution: The first objective of this invention is to provide a cobalt-doped cuprous oxide catalyst, wherein the catalyst is a cobalt-doped cuprous oxide composite material with a hierarchical microsphere structure and a surface array of nanosheets, wherein cobalt is incorporated into the cuprous oxide lattice in a doping form to form Cu. + / Cu 2+ and Co 2+ / Co 3+ Dual valence state.

[0006] The second objective of this invention is to provide a method for preparing the cobalt-doped cuprous oxide catalyst, comprising the following steps: first, dissolving copper sulfate pentahydrate and cobalt nitrate in deionized water and continuously stirring to form a homogeneous solution; then preparing a sodium hydroxide solution and adding it dropwise to the homogeneous solution to generate a suspension; next, dissolving glucose in deionized water and adding it to the suspension; stirring the resulting suspension in a water bath, separating the solid, washing it three times with deionized water, and finally vacuum drying to obtain the final product Co-CuOx microspheres.

[0007] Furthermore, the mass ratio of copper sulfate pentahydrate to cobalt nitrate is 1:(0.04-0.16).

[0008] Furthermore, the concentration of the sodium hydroxide solution should be 0.5-3 mol / L. The sodium hydroxide solution should be added dropwise, with a moderate concentration to avoid excessive alkalinity in certain areas and overly rapid reactions. A concentration of 2 mol / L is preferred.

[0009] Furthermore, the mass ratio of glucose to copper sulfate pentahydrate is (1.5-3):1, and the dosage of 1.5:1 ensures that even if side reactions occur, there is still sufficient reducing agent to reduce Cu. 2+ When reduced to Cu₂O, an upper limit of 3:1 can effectively suppress the formation of elemental Cu, maintaining Cu₂O as the main phase. Within the range of 1.5-3:1, nucleation and growth reach equilibrium, forming spherical particles with moderate size and regular morphology. The optimal ratio is 1.6:1.

[0010] Furthermore, the reaction conditions in the water bath were: 50°C with stirring for 2 hours.

[0011] A third objective of this invention is to provide the application of the aforementioned cobalt-doped cuprous oxide catalyst in the recatalytic reduction reaction of nitro aromatic compounds.

[0012] Beneficial technical effects of the present invention: (1) The morphology and electronic structure of cuprous oxide were successfully reconstructed through cobalt doping, and the resulting hierarchical microsphere structure exposed more active sites. The optimized Co-CuOx-20 catalyst exhibited an apparent rate constant of 38.4 min for the reduction of 4-nitrophenol (4-NP). -1 g -1 It is a pure cuprous oxide catalyst (1.6 min). -1 g -1 It is 24 times more potent than copper-based catalysts, and its activity is superior to most reported copper-based catalysts.

[0013] (2) The catalyst of the present invention can achieve efficient conversion under mild conditions (25°C, 1 atm) with only a molar ratio of reducing agent to substrate of 20:1.

[0014] (3) The apparent activation energy of Co-CuOx-20 catalyzing the reduction of 4-NP (53.32 kJ / mol) is significantly lower than that of pure cuprous oxide (59.29 kJ / mol), indicating that cobalt doping effectively enhances the catalyst’s activation ability for the reaction substrate, making the reaction easier to proceed.

[0015] (4) Cobalt doping not only induced a unique hierarchical microsphere structure, increasing the specific surface area to 11.3 times that of pure cuprous oxide, but also successfully introduced abundant oxygen vacancies (accounting for 45.4%) and Cu. + / Cu 2+ and Co 2+ / Co 3+ Dual valence states. These properties work synergistically to optimize charge transport and substrate adsorption / activation processes, and enhance redox cycling capabilities.

[0016] (5) The Co-CuOx-20 catalyst maintained a conversion rate of over 90% for 4-NP after 30 cycles, demonstrating excellent stability. At the same time, it also exhibited high catalytic activity (>95%) for various nitrophenols (such as 2-NP and 3-NP), indicating its broad substrate versatility.

[0017] (6) Pilot-scale and continuous flow experiments showed that after the catalyst was loaded onto the sponge support, the degradation efficiency was still higher than 95% in the treatment of 10-liter wastewater after 10 cycles, and the conversion rate was still close to 100% after 36 hours of continuous operation, which proved its strong practical application potential. Attached Figure Description

[0018] Figure 1 (a) Schematic diagram of the synthesis process of cuprous oxide and Co-CuOx catalyst. (b) SEM image of cuprous oxide, (c) SEM images of Co-CuOx-5, (d) Co-CuOx-10 and (e) Co-CuOx-20. (f) Conceptual schematic diagram of catalyst morphology changes. (g) Elemental distribution image of Co-CuOx-20. (h, i) TEM images of Co-CuOx-20, (j~k) HRTEM images of Co-CuOx-20. (l) Elemental distribution image of Co-CuOx-20 catalyst.

[0019] Figure 2 (a, b) Co-CuO x SEM image at -50°C.

[0020] Figure 3 (a, b) XPS spectra of all catalysts. (c) N2 adsorption-desorption isotherms and pore size distributions of all catalysts. (d) High-resolution XPS signals of Cu 2p, (e) Co 2p, and (f) O 1s in cuprous oxide and Co-CuOx-20. (g) Electronic localization functions of cuprous oxide and (h) Co-CuOx-20. (i) DOS spectra of cuprous oxide and (j) Co-CuOx-20.

[0021] Figure 4 .Cu2O and Co-CuO x -20 contact angle.

[0022] Figure 5 (a) UV-Vis spectral evolution of 4-NP solution after the addition of (a) copper oxide and (b) Co-CuOx-20. (c) Catalytic performance of all catalysts prepared in the 4-NP reduction process and (d) corresponding first-order kinetic rate constants. (e) Comparison of the activities of various copper-based and noble metal-based catalysts for 4-NP reduction in the reported literature. (f) Effect of catalyst dosage on 4-NP reduction. (g) Activation energy of copper oxide and Co-CuOx-20 for 4-NP reduction. (h) Catalytic performance of Co-CuOx-20 catalyst for the reduction of various nitrophenols. (i) Performance of Co-CuOx-20 in the stable catalytic reduction of 4-NP.

[0023] Figure 6 Catalytic performance of (a) Cu2O and (b) Co-CuOx-20 on 4-nitrophenol under different catalyst dosages.

[0024] Figure 7 Catalytic performance of (a) Cu2O and (b) Co-CuOx-20 on 4-nitrophenol under different NaBH4 dosages.

[0025] Figure 8 Catalytic performance of (a) Cu2O and (b) Co-CuOx-20 on 4-nitrophenol at different reaction temperatures.

[0026] Figure 9 Rate constants for the reduction of 4-nitrophenol catalyzed by Cu2O and Co-CuOx-20.

[0027] Figure 10 Comparative display: (a) Appearance differences between the original sponge and (b) the catalyst-supported sponge; (c, d) are scanning electron microscope images. (e) Schematic diagram of the pilot-scale experimental process for treating 10 liters of 4-NP wastewater. (f) Circulating degradation effect for treating 10 liters of 4-NP wastewater. (g) Schematic diagram of the continuous flow reactor. (h) Changes in 4-NP removal efficiency and flow rate during continuous degradation. High-resolution XPS spectroscopy display: (i, j) 2p values ​​of Cu in the Co-CuOx-20 material before and after the reaction. 3 / 2 The valence states of Cu and Co before and after the reaction (k) are compared with the 2p state of Co. Detailed Implementation

[0028] Example 1: Preparation of Co-CuOx-5 microspheres First, 1.5 g of copper sulfate·5H₂O and 0.06 g of cobalt nitrate were dissolved in 60 mL of deionized water and stirred continuously to form a homogeneous solution. Then, 20 mL of 2 mol / L sodium hydroxide solution was prepared and added dropwise to the copper salt solution, forming a blue suspension. Next, 2.378 g of glucose was dissolved in 20 mL of deionized water and added to the mixture. The resulting suspension was stirred in a water bath (50°C) for 2 hours, the solid was separated, washed three times with deionized water, and finally dried under vacuum to obtain the final product, Co-CuOx⁻⁵ microspheres.

[0029] Example 2 Preparation of Co-CuOx-10 microspheres The difference between Example 2 and Example 1 is that 0.12g of cobalt nitrate was added, while the other conditions were exactly the same.

[0030] Example 3 Preparation of Co-CuOx-20 microspheres The difference between Example 3 and Example 1 is that 0.24g of cobalt nitrate was added, while the other conditions were exactly the same.

[0031] Example 4: Preparation of Co-CuOx-50 microspheres The difference between Example 4 and Example 1 is that 0.6g of cobalt nitrate was added, while the other conditions were exactly the same.

[0032] Comparative Example 1: Preparation of Cuprous Oxide The difference between Comparative Example 1 and Example 1 is that cobalt nitrate was not added; all other conditions were exactly the same.

[0033] A schematic diagram of the synthesis process of cuprous oxide and Co-CuOx catalyst is shown below. Figure 1 As shown in a, the materials obtained in Examples 1-4 and Comparative Example 1 were characterized: Scanning electron microscope (SEM) images of cuprous oxide, Co-CuOx-5, Co-CuOx-10, Co-CuOx-20, and Co-CuOx-50 are shown in [the image]. Figure 1 In b-1e, the exposed cuprous oxide catalyst exhibits a uniform spherical morphology, with particle sizes concentrated in the 800-1000 nm range. With increasing cobalt doping concentration, the microsphere structure of the cuprous oxide undergoes a texture reconstruction process, as shown in the figure. Figure 1 As shown in f, as the cobalt doping concentration increases from 0% to 20%, the Co-CuOx catalyst largely maintains its microsphere structure, but the surface gradually becomes rougher, and some nanosheet arrays can be observed. Compared with cuprous oxide nanospheres, the layered microsphere structure increases the effective surface area and exposes more active sites on Co-CuOx-20, thereby improving the efficiency of charge and mass transport in the catalytic reaction. Figure 2 a and 2b show that Co-CuOx-50 mainly exhibits an amorphous nanobulb morphology, indicating that the microsphere structure will disintegrate when the cobalt doping level reaches 50%.

[0034] The microstructure of Co-CuOx-20 was further characterized using transmission electron microscopy (TEM). Figure 1 As shown in g, the sample exhibits a hierarchical microsphere structure with an approximate diameter of 1.0 μm, and its surface is composed of nanosheets, consistent with the observation results of scanning electron microscopy (SEM). Figure 1 The high-resolution TEM (HRTEM) images in h and 1i did not observe the formation of CoOx nanoparticles, confirming that cobalt was successfully doped into the cuprous oxide lattice. Furthermore, Figure 1 In addition to showing cuprous oxide (111) crystal planes (0.246 nm spacing), the presence of an amorphous phase was also observed in j. Figure 1 k further reveals the evolution trend of cuprous oxide crystallinity with increasing cobalt content. These results indicate that the introduction of cobalt can induce morphological and crystal structure reconstruction in cuprous oxide, representing an effective strategy for controlling its charge structure. Figure 1The elemental distribution diagram and energy-dispersive X-ray (EDX) spectroscopy of l confirmed that copper (Cu), cobalt (Co), and oxygen (O) were uniformly distributed in Co-CuOx-20, verifying the uniform doping of cobalt in the crystal lattice. Uniform cobalt (Co) doping is crucial for achieving targeted structural control, as the resulting disordered atomic arrangement ultimately drives the improvement in catalytic performance.

[0035] The crystal phase and composition of the synthesized sample were determined by X-ray diffraction (XRD), and the results are as follows: Figure 3 As shown in Figure a, all Co-CuOx samples exhibited characteristic peaks corresponding to those of cuprous oxide crystals (JCPDS card number 05-0667) at (110), (111), (220), (220), and (311), indicating that cobalt ion doping did not alter the crystal composition of cuprous oxide. As the cobalt doping concentration increased from 0% to 50%, the intensity of all characteristic peaks gradually decreased, indicating a gradual decrease in the crystallinity of the catalyst. Furthermore, as shown in Figure a... Figure 3 As shown in b, increasing cobalt doping caused the cuprous oxide (111) peak to shift from 36.59° to 36.67°. This phenomenon is attributed to the shrinkage of the cuprous oxide lattice, induced by the insertion of cobalt ions. The pore structure and specific surface area of ​​the catalyst were analyzed by nitrogen adsorption-desorption studies. Figure 3 As shown in Figure c, cuprous oxide, Co-CuOx-5, and Co-CuOx-10 catalysts exhibit relatively low adsorption characteristics, consistent with their bulk structures. In contrast, Co-CuOx-20 and Co-CuOx-50 catalysts display typical type IV adsorption isotherm characteristics and show significant hysteresis loops in the P / P0 = 0.7–1.0 range, confirming their mesoporous structures. Figure 3 The pore size distribution data in illustration c also confirms the mesoporous characteristics of these two catalysts. The mesoporous structure of a catalyst is crucial for the diffusion of reactants and products within it, directly affecting the overall activity and selectivity of the catalyst. Table 1 summarizes the structural parameters of different catalysts. The specific surface area of ​​Co-CuOx-20 is 10.2 m². 2 ·g -1 It is approximately cuprous oxide (0.9m). 2 ·g -1 It is 11.3 times more hydrophilic than cuprous oxide. Contact angle experiments further demonstrate that Co-CuOx-20 has stronger hydrophilicity than cuprous oxide (see...). Figure 4 This will promote the interaction between the catalyst and the nitro compound in the catalytic reaction.

[0036] Table 1. Structural parameters of different catalysts

[0037] aThe average pore size was calculated using the BJH model based on the desorption support data.

[0038] XPS technology was used to investigate the chemical state of the metal sites. Cu, Co, and O elements were successfully identified in the scanning spectrum of Co-CuOx-20, and the results are in good agreement with EDS mapping data. Figure 3 d shows a high-resolution Cu2p XPS spectrum. For cuprous oxide, the copper species is attributed to 932.39 eV (2p) by peak fitting. 3 / 2 ) and 952.22eV (2p 1 / 2 Cu at ) + The species were verified to be a pure-phase structure of cuprous oxide. As for Co-CuOx-20, except for 934.38 eV (2p3 / 2) and 954.25 eV (2p3 / 2), the structure was confirmed. 1 / 2 Cu at ) + In addition to the signal, the XPS spectrum also showed 934.38 eV (2p). 3 / 2 ) and 954.25 eV (2p 1 / 2 Cu at ) 2+ Characteristic peaks, and broad satellite peaks at 942.65 eV and 962.40 eV. The results confirm the presence of Cu in Co-CuOx-20. + The sites exhibit higher redox properties. Co2p sites were detected in the Co2p XPS spectrum of Co-CuOx-20. 3 / 2 and Co2p 1 / 2 Characteristic peaks. For example... Figure 3 As shown in e, 782.04 eV and 797.94 eV correspond to Co 2+ 2p 3 / 2 and 2p 1 / 2 The main peaks, 780.65 eV and 796.55 eV, correspond to Co. 3+ The main peak of Co appears, with satellite peaks at 786.37 eV and 802.60 eV, indicating that Co is mainly composed of Co. 2+ and Co 3+ Two valence states coexist. Cu (Cu + / Cu 2+ ) and Co (Co 2+ / Co 3+ The dual valence state of ) helps ensure the sustainability and durability of catalytic reactions.

[0039] Figure 3The O 1s spectra of copper oxide and Co-CuOx-20 can be divided into three oxygen species: lattice oxygen (OL, 530.8 eV), oxygen vacancies (OV, 531.7 eV), and adsorbed oxygen (OA, 533.0 eV). Oxygen vacancies (OV) account for 45.4% in Co-CuOx-20, significantly higher than in copper oxide (22.8%). This finding indicates that more oxygen vacancies are generated in Co-CuOx-20. The presence of oxygen vacancies on the Co-CuOx-20 surface has been shown to be related to the Co doping process and the relatively low crystallinity of the catalyst. Oxygen vacancies have been shown to enhance the charge properties of the metal center and the substrate adsorption capacity, thereby improving the catalytic activity of the catalyst.

[0040] The effect of cobalt doping on the electronic structure of copper sites in Co-CuxO catalysts was investigated using density functional theory (DFT) simulations. Figure 3 As shown in g and 3h, the electron localization functions (ELFs) indicate that electrons in both cuprous oxide and Co-CuOx are in a state between complete localization and complete delocalization. However, Co-CuOx exhibits a higher degree of structural disorder, a characteristic that generally favors electron transfer in catalytic reactions. Figure 3 i and 3j show the density of states of cuprous oxide and Co-CuOx-20. The band gap of cuprous oxide is measured to be 0.59 eV, while the band gap of Co-CuOx narrows to 0.16 eV. This reduced band gap facilitates electron transfer from the valence band to the conduction band during the reaction. Furthermore, compared to cuprous oxide (-2.47 eV), the d-band center of Co-CuOx shifts to a lower energy level (-2.69 eV). This shift favors weakening the binding strength of the reaction intermediate, thereby promoting its desorption during the reaction.

[0041] Catalytic activity assessment To evaluate the catalytic activity of the synthesized catalyst, the reduction of 4-NP (4-nitrophenol) to 4-AP (4-aminophenol) was first used as a model reaction. 100 mL of 0.16 mM 4-NP solution was mixed with 3.2 mM sodium borohydride under magnetic stirring. Subsequently, 5 mg of catalyst was added to the mixture to initiate the reduction reaction. During the reaction, 3 mL samples of the reaction mixture were taken at specified time intervals and analyzed by UV-Vis spectroscopy. The conversion rate of 4-NP was calculated from the absorbance change using the formula A. t / A0, where A0 and A t These represent the absorbance values ​​at the initial time and at a specific time (wavelength 400 nm), respectively.

[0042] The hydrogenation of aromatic nitro compounds was used as a model reaction to evaluate the catalytic performance of the prepared catalyst, with sodium borohydride acting as a reducing agent. For conventional catalysts, an excess of sodium borohydride (100-1000 times) is required to achieve efficient conversion. In this invention, the catalytic reaction is carried out under mild conditions (25°C, 1 atm) with a reducing agent to substrate molar ratio of 20:1.

[0043] like Figure 5 As shown in a and 5b, the characteristic peak of 4-NP at 400 nm gradually weakened after the addition of copper oxide and Co-CuOx-20 catalysts, while a novel absorption peak corresponding to 4-aminophenol (4-AP) appeared at 304 nm, verifying the activity of both catalysts. For copper oxide, the conversion rate of 4-NP reached 15.3% within 20 minutes. Co-CuOx-20, under the same conditions, efficiently activated hydrogen species and achieved near-complete 4-NP conversion, demonstrating excellent activity.

[0044] Figure 5 This paper briefly summarizes the catalytic activities of copper oxide and various Co-CuOx catalysts. The results show a positive correlation between cobalt doping concentration and the hydrogenation activity of the Co-CuOx catalyst. When the cobalt doping concentration of the Co-CuOx catalyst increases from 5% to 20%, the 4-NP conversion increases from 48.6% to 99.4%. However, on the Co-CuOx-50 catalyst, the 4-NP conversion is only 83%, which can be attributed to structural collapse. The catalytic performance of the Co3O4 catalyst was also tested. Under the same conditions, the 4-NP conversion on the Co3O4 catalyst was only 0.3%, confirming that copper species constitute the main active sites.

[0045] The reaction kinetics of the prepared catalyst in the reduction of 4-NP were evaluated using a pseudo-first-order kinetic model. Figure 5 As shown in d, the apparent rate constants for each reaction are as follows: Co-CuOx-20 is 38.4 min. -1 g -1 Co-CuOx-50 takes 18 min. -1 g -1 The Co-CuOx-10 concentration was 12.8 min. -1 g -1 Co-CuOx-5 takes 7 min -1 g -1 Copper oxide content was 1.6 min. -1 g -1 The reduction kinetics of Co-CuOx-20 are approximately 24 times that of copper oxide catalysts. Furthermore, as... Figure 5The Co-CuOx-20 catalyst shown in Figure e exhibits a rate constant exceeding that of most reported copper-based catalysts and approaching that of certain noble metal systems in the 4-NP reduction reaction.

[0046] Given the excellent performance of Co-CuOx-20 in the reduction of 4-NP, the influence of reaction conditions on its catalytic behavior was investigated. For example... Figure 5 As shown in f and 6a, the conversion of 4-NP was only 62.7% when using 3 mg of catalyst. When the catalyst dosage was increased from 5 mg to 20 mg, the reaction time decreased from 20 minutes to 7 minutes. The apparent rate constant (k) was ranked as follows: 20 mg (0.585 min). -1 >10 mg (0.273 min) -1 >5 mg (0.192 min) -1 >3 mg (0.05 min) -1 This is consistent with theoretical predictions that increased availability of active sites occurs with higher catalyst concentrations. Furthermore, the study identified the concentration of the reducing agent as a key factor influencing the reaction rate (see [link to study].) Figure 7 a) When the amount of sodium borohydride was ten times the molar amount of 4-NP, the reduction reaction was severely limited (54.7%). Complete conversion of 4-NP was achieved as the sodium borohydride concentration increased from 20 to 40 times. k The value increased from 0.04 to 0.248 min. -1 This indicates that a higher amount of reducing agent contributes to the reduction of 4-NP. Although copper oxide exhibits a similar dependence on both catalyst and reducing agent amounts (see...). Figure 6 (b and 7b), but it failed to achieve complete conversion even with an excess of 20-fold (82.1%) or 40-fold (48.1%) of reducing agent, which indirectly reflects the higher energy barrier in the catalytic process.

[0047] Figure 8 a, 8b and Figure 9 The thermodynamic properties of Co-CuOx-20 and copper oxide in the 4-NP reduction reaction are presented. Both catalysts exhibit increased catalytic activity with increasing temperature, indicating that the reaction is a thermodynamically favorable process. The apparent activation energy of 4-NP reduction on Co-CuOx-20 is calculated using the Arrhenius equation. Ea () Figure 5 The effective concentration (f / mol) for Co-CuOx-20 was 53.32 kJ / mol. This value is significantly lower than that of the copper oxide catalyst (59.29 kJ / mol), indicating that Co-CuOx-20 has a stronger substrate activation ability. In addition to 4-NP reduction, other nitroaromatic substrates (such as 2-NP and 3-NP) were used to further evaluate the catalytic multifunctionality of Co-CuOx-20. Figure 5As shown in h, the Co-CuOx-20 / sodium borohydride system achieved a conversion rate exceeding 95% for all tested compounds within 20 minutes, demonstrating its broad substrate tolerance in nitro reduction reactions. Figure 5 As shown in i, the Co-CuOx-20 catalyst achieved a conversion of over 90% for 4-NP in 30 reaction cycles, demonstrating its excellent reusability.

[0048] Pilot-scale experiment of Co-CuOx-20 nitro reduction Maintaining a balance between high catalytic activity and stability during the reaction remains a significant challenge for heterogeneous catalysts. For hydrogenation reactions, active sites are prone to demetallization or excessive oxidation / reduction under harsh conditions, leading to a gradual deterioration in catalytic performance. To evaluate the practical application potential of the Co-CuOx-20 catalyst, researchers immobilized it on a polyurethane sponge support and conducted large-scale experiments on the reduction of nitro compounds. Figure 10 As shown in a and 10b, Co-CuOx-20 is uniformly distributed on the surface of the sponge. Figure 10 Scanning electron microscopy (SEM) images at c and 10d show that the sponge substrate possesses a dense porous structure and excellent buoyancy properties, ensuring sufficient contact between the catalyst, reducing agent, and nitro compound. For example... Figure 10 As shown in e and 10f, under low reducing agent concentration conditions, the Co-CuOx-20 catalyst maintained a conversion efficiency of over 95% after ten hydrogenation cycles (10 L reaction system). Furthermore, the researchers evaluated the activity of Co-CuOx-20 in continuous flow hydrogenation using a fixed-bed reactor. Figure 10 g). Figure 10 Data shows that after 36 hours of continuous operation, the catalyst achieved a conversion rate of nearly 100% for 4-nitrophenol. These results fully demonstrate the catalyst's excellent stability and outstanding practical value.

[0049] Cu sites serve as the primary active centers, promoting the adsorption and activation of hydrogen donors and the nitro reduction process throughout the reaction. High-resolution Cu 2p 3 / 2 Spectrum ( Figure 10 i) shows that Cu on the surface of the Co-CuOx-20 catalyst + The proportion remained at approximately 50%, confirming the excellent stability of the copper sites. Furthermore, the recovered Co-CuOx-20 catalyst contained Co... 3+ The proportion increased only slightly from 55.4% to 56.1%, while the proportion of Co²⁺ decreased by only 0.7% compared to the fresh sample (see [link to sample description]). Figure 10 These results indicate that Co species act as electronic regulators by promoting Cu... (j and 10k). + With Cu 2+The efficient redox cycle between the catalysts maintains the long-term stability of the catalyst.

[0050] In summary, this invention successfully synthesized a series of cobalt-doped copper oxide hierarchical microspheres (Co-CuOx) capable of efficiently and sustainably reducing nitroaromatic compounds with low reducing agent consumption. The optimized Co-CuOx-20 catalyst exhibited superior catalytic performance, with a 24-fold improvement in reaction kinetics compared to pure copper oxide, and a significantly reduced activation energy for the 4-NP hydrogenation reaction. Furthermore, Co-CuOx-20 demonstrated excellent stability, maintaining high conversion rates over multiple cycles and exhibiting robust performance during long-term operation in a continuous flow reactor. Structural and electronic characterization revealed that cobalt doping induced morphological reconstruction, increased surface area, enriched oxygen vacancies, and modulated the electronic environment of the copper active sites, collectively promoting enhanced hydrogen activation and improved mass / charge transfer.

Claims

1. A cobalt-doped cuprous oxide catalyst, characterized in that, The catalyst is a cobalt-doped cuprous oxide composite material with a hierarchical microsphere structure and a surface array of nanosheets. Cobalt is incorporated into the cuprous oxide lattice in a doping form to form Cu. + / Cu 2+ and Co 2+ / Co 3+ Dual valence; The preparation method of the cobalt-doped cuprous oxide catalyst includes the following steps: First, copper sulfate pentahydrate and cobalt nitrate are dissolved in deionized water and stirred continuously to form a homogeneous solution; then, a sodium hydroxide solution is prepared and added dropwise to the homogeneous solution to generate a suspension; next, glucose is dissolved in deionized water and added to the suspension; after stirring the resulting suspension in a water bath, the solid is separated, washed three times with deionized water, and finally vacuum dried to obtain the final product Co-CuOx microspheres; The mass ratio of copper sulfate pentahydrate to cobalt nitrate is 1:(0.04-0.16). The concentration of sodium hydroxide solution is 0.5-3 mol / L; The mass ratio of glucose to copper sulfate pentahydrate is (1.5-3):1; The reaction conditions in the water bath were: stirring at 50°C for 2 hours.

2. The application of the cobalt-doped cuprous oxide catalyst as described in claim 1 in the catalytic reduction reaction of nitroaromatic compounds.

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