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Article

High-Performance CoxNiy@NC/SiO2 Catalysts Derived from ZIF-67 for Enhanced Hydrogenation of 1-Nitronaphthalene

by
Xuedong Lan
1,
Ming Zhong
2,
Weidi Dai
1 and
Pingle Liu
1,*
1
College of Chemical Engineering, National & Local United Engineering Research Centre for Chemical Process Simulation and Intensification, Xiangtan University, Xiangtan 411105, China
2
School of Energy Resources, China University of Geosciences, Beijing 100089, China
*
Author to whom correspondence should be addressed.
Catalysts 2026, 16(1), 93; https://doi.org/10.3390/catal16010093
Submission received: 22 December 2025 / Revised: 6 January 2026 / Accepted: 14 January 2026 / Published: 16 January 2026
(This article belongs to the Special Issue Catalysis and Sustainable Green Chemistry)
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Abstract

A series of silica-supported, nitrogen-doped carbon-encapsulated cobalt–nickel alloy catalysts (CoxNiy@NC/SiO2) was successfully synthesized and systematically evaluated for the liquid-phase hydrogenation of 1-nitronaphthalene to 1-naphthylamine. Physicochemical characterization confirmed that the incorporation of nickel promotes the formation of Co–Ni alloys and modulates the electronic structure of the catalysts. The catalytic performance was found to be highly sensitive to the Co/Ni ratio, with Co2Ni1@NC/SiO2 exhibiting the most outstanding activity. Under optimized reaction conditions (90 °C, 0.6 MPa H2, 5.5 h), both the conversion of 1-nitronaphthalene and the selectivity toward 1-naphthylamine reached approximately 99%. The catalyst also demonstrated excellent stability and recyclability, attributed to the protective nitrogen-doped carbon shell and the synergistic interaction between the Co–Ni alloy and M–Nx active sites. This work provides a new strategy for designing efficient and robust non-noble-metal catalysts for hydrogenation reactions.

Graphical Abstract

1. Introduction

Aromatic amines constitute a pivotal class of compounds in the chemical industry, serving as essential intermediates in the synthesis of organic raw materials [1,2] and fine chemicals [3], and occupying a substantial share of the global market. These compounds also find widespread applications in agrochemicals [4] and pharmaceuticals [5], underscoring their industrial significance.
Among them, 1-naphthylamine is a representative aromatic amine with irreplaceable utility in pesticide manufacturing, particularly as a key intermediate in the synthesis of carbaryl [6]. In the dye industry, 1-naphthylamine serves as a crucial precursor for the production of direct, acid, and ice dyes [7], offering a less toxic alternative to traditional dye intermediates such as benzidine and aniline [8]. This substitution not only enhances dye performance but also mitigates adverse effects on human health and the environment. Additionally, 1-naphthylamine is employed as a stationary phase in gas chromatography and as a standard solution in high-performance liquid chromatography, highlighting its analytical relevance in chemical and industrial applications [9].
The discovery of aromatic amines dates back approximately two centuries, when Russian chemist Nikolay N. Zinin first synthesized aniline via the chemical reduction of nitrobenzene [10]. Since then, extensive research has progressively refined the synthetic methodologies and mechanistic understanding of aromatic amine formation, culminating in a robust theoretical framework. This progress has catalyzed the development of diverse catalytic systems—including noble metal catalysts [11,12], non-noble metal catalysts [13,14], and metal-free catalysts [15]—which have significantly advanced the field.
Given the high cost and environmental concerns associated with noble metal catalysts (e.g., Pt, Pd, Ru) [16,17,18], the development of cost-effective and sustainable non-noble metal catalysts based on transition metals such as Co, Ni, Cu, and Fe [19,20] has emerged as a critical research frontier.
Fu et al. [21] studied a bimetallic PtNi/C nanocatalyst, which exhibited higher catalytic activity than the monometallic Pt/C nanocatalyst. Under the reaction conditions of 30 °C and 3.0 MPa H2, the conversion of 1-nitronaphthalene reached 100%, with selectivity toward 1-naphthylamine also reaching 100%. However, due to the scarcity and high cost of precious metal catalysts, their widespread application in industrial production remains challenging. Researchers have therefore turned their attention to non-precious metal catalysts.
Viswanathan et al. [22] investigated the hydrogenation of nitrobenzene to aniline using rutile-supported Ni as a catalyst. Leveraging the simplicity of catalyst preparation, they applied the catalyst to the hydrogenation of nitrobenzene, achieving a 1-nitrobenzene conversion of 99% under conditions of 140 °C and 1.96 MPa H2. Huang et al. [23] found that the introduction of a metal promoter inhibited the sintering of nickel and improved the reducibility of the catalyst. They prepared a Ni-Zn/AC catalyst for the hydrogenation of 1-nitronaphthalene, achieving a conversion of 96.2% and a selectivity of 96.82% toward 1-naphthylamine under mild conditions.
Pan et al. [24] prepared a Ni@CN nanocatalyst by pyrolyzing Ni-MOFs. The carbon-nitrogen coating enhanced hydrogen dissociation and promoted the adsorption of reactants, thereby improving catalytic activity. This catalyst achieved 99.1% conversion and 99% selectivity in the hydrogenation of nitrobenzene to aniline at 60 °C and 2.0 MPa H2. Metal–organic frameworks (MOFs) have emerged as an ideal platform for developing efficient catalysts, owing to their highly designable periodic structures, enormous specific surface area, and precisely tunable active sites.
Metal–organic frameworks (MOFs), particularly zeolitic imidazolate frameworks (ZIFs), have attracted considerable attention due to their tunable porosity and structural versatility [25,26]. ZIF-67 (Co-based) and ZIF-8 (Zn-based), synthesized via room-temperature stirring, microwave-assisted, or hydrothermal methods using 2-methylimidazole as the organic linker, are among the most extensively studied. ZIF-67 exhibits excellent thermal stability during pyrolysis, retaining cobalt species and yielding highly graphitized carbon matrices with uniformly dispersed nitrogen functionalities [27,28]. In contrast, pyrolysis of ZIF-8 at temperatures above 600 °C leads to zinc volatilization, generating abundant surface defects and significantly increasing the specific surface area of the resulting carbon material [29].To further enhance catalytic performance, Pan. et al. have engineered core–shell ZIF-67@ZIF-8 structures, which upon pyrolysis yield nitrogen-doped carbon materials encapsulating cobalt nanoparticles with improved catalytic activity [30].
In this study, a silica-supported bimetallic CoxNiy@NC/SiO2 catalyst was synthesized using ZIF-67 as the precursor via a room-temperature stirring method, followed by high-temperature pyrolysis and hydrogen reduction. This process resulted in the collapse of the ZIF framework and the formation of a carbon–nitrogen matrix encapsulating Co–Ni alloy nanoparticles. The catalyst was comprehensively characterized using a suite of analytical techniques and applied to the liquid-phase hydrogenation of 1-nitronaphthalene to 1-naphthylamine. A volcano-type relationship was observed between the Co/Ni molar ratio and the product yield, with optimal conditions (90 °C, 0.6 MPa H2, 5.5 h) affording >99% yield of 1-naphthylamine. The catalyst also demonstrated excellent recyclability and structural stability. Mechanistic investigations revealed that the enhanced catalytic performance originated from the increased specific surface area, improved dispersion of active metal sites, and the Metallic synergistic interaction between Co and Ni. These findings offer valuable guidance for the rational design of high-performance, non-noble metal hydrogenation catalysts leveraging bimetallic synergy.

2. Results and Discussion

2.1. Characterization of Catalysts

Figure 1 presents the XRD patterns of catalyst samples with varying Ni/Co molar ratios. Upon the incorporation of SiO2, a broad arch-shaped diffraction feature appears at 2θ ≈ 26°, which can be attributed to the combined contributions of graphitic carbon and amorphous silica within the catalyst matrix [31].
In the XRD pattern of sample (a), corresponding to Co@NC, a distinct diffraction peak assigned to the (002) plane of graphitic carbon is clearly observed. However, in samples (b) through (e), this carbon-related peak is largely obscured by the broad background signal from amorphous SiO2 [32].
Characteristic diffraction peaks located at 2θ = 44.2°, 51.7°, and 76.2° are indexed to the (111), (200), and (220) planes of metallic cobalt, respectively [33], confirming the successful reduction of Co2+ to metallic Co0 under a hydrogen atmosphere at 500 °C. Notably, the diffraction peak at 2θ = 51.7° overlaps with that of metallic nickel, and a slight shift in peak position is observed, suggesting that Ni2+ was also effectively reduced to Ni0. This shift may be indicative of the formation of a Co–Ni alloy [34,35] phase at elevated temperatures above 500 °C.
For all CoxNiy@NC/SiO2 catalysts subjected to calcination and hydrogen reduction at 500 °C, the sharp and well-defined diffraction peaks of Co and Ni reflect high crystallinity of the metallic phases, further confirming the efficient reduction and potential alloying of the active metal components.
To investigate the effect of Ni addition on the reducibility and bimetallic synergistic effect of the catalyst, H2-TPR measurements were performed on the precursors of the CoxNiy@NC/SiO2 catalyst.
For nickel-based catalysts, reduction peaks are usually of two types: [36] ① Peaks in the range of 240–450 °C correspond to the reduction of free NiO with weak interaction with the support. ② Peaks above 500 °C are attributed to the reduction of NiO strongly interacting with the support or Ni2+ dissolved in the support lattice.
For cobalt-based catalysts, reduction peaks are usually of two types: [37] ① Peaks in the range of 300–480 °C correspond to the two-step reduction of Co3O4 (Co3O4 → CoO → Co0). ② Peaks in the range of 500–800 °C are associated with the reduction of cobalt oxides (Co2+ and Co3+).
Figure 2: H2-TPR profile of the Co2Ni1@NC/SiO2 catalyst, a weak shoulder peak appears at about 255 °C, a broad peak around 410 °C, and a small peak at 560 °C. Due to the interaction between nickel and cobalt, the characteristic peaks in the H2-TPR profiles are all shifted.
With increasing cobalt content, the peaks in Region I shift toward lower temperatures, and similarly, the peaks in Region II also move to lower temperatures. As the cobalt content gradually increases, the bimetallic interaction between Co and Ni becomes stronger, indicating that the bimetallic catalyst facilitates the reduction of NiO/Co3O4. The synergistic effect between the metals reduces the activation energy for the reduction of NiO/Co3O4 [23]. When the Co:Ni ratio is 3:1, the peaks in Region II shift toward higher temperatures, and the peaks in the 350–500 °C range become narrower and higher, suggesting a weakened bimetallic interaction between Co and Ni. This demonstrates that the most favorable interaction can be achieved by adjusting the Co–Ni metal ratio.
Irregular ZIF-67 polyhedral structures and spherical SiO2 particles are clearly visible in the catalyst precursors (Figure 3). The introduction of nickel nitrate hexahydrate during precursor synthesis, coupled with the in situ formation of SiO2, led to the distortion of the ZIF-67 polyhedral morphology [38]. Following high-temperature calcination, the ZIF-67 framework collapsed, and volatile components were removed. The resulting Co–Ni metallic species were uniformly dispersed and anchored onto the SiO2 support. Simultaneously, a carbon/nitrogen (C/N) [27] shell formed around the metal particles, providing protection against metal leaching during hydrogenation and enhancing both thermal stability and catalyst recyclability.
Across the entire series of catalysts, particle aggregation was consistently observed. The extent of aggregation and morphological variation was closely related to the Co/Ni ratio [39]. As the cobalt content increased and the nickel content decreased, the degree of aggregation was reduced, resulting in more interconnected pore networks. These structural features are beneficial for improving the selectivity and yield of 1-naphthylamine in liquid-phase hydrogenation [40]. The influence of the Co/Ni ratio on catalytic performance will be discussed in detail in the following sections.
The X-ray photoelectron spectroscopy (XPS) survey spectra reveal the presence of Co, Ni, O, N, Si, and C elements in all CoxNiy@NC/SiO2 catalyst samples (Figure 4). Distinct characteristic peaks corresponding to the Co 2p and Ni 2p orbitals confirm the successful incorporation of cobalt and nickel into the catalyst framework. The presence of O 1s and Si 2p signals originates from the SiO2 support, while the N 1s and C 1s peaks are attributed to the nitrogen-doped carbon matrix derived from the ZIF precursor. To further investigate the electronic structure and oxidation states of the active metals, high-resolution Co 2p and Ni 2p spectra were deconvoluted using peak-fitting analysis. This enabled detailed evaluation of the valence state distribution and potential electronic interactions between Co and Ni within the bimetallic system.
XPS of the Co 2p region revealed a peak at 780.6 eV, assignable to Co0, and a peak at 783.6 eV, attributable to (Co2+/Co3+) [41] (Figure 5a). The presence of satellite features indicates that metallic cobalt and cobalt oxides coexist on the catalyst surface [42,43]. Incorporation of metallic nickel increases the surface fraction of reduced Co0, as evidenced by the relative peak intensities.
A third deconvoluted component is consistent with Co–Nx species arising from bonding between graphitic carbon and nitrogen. Nitrogen incorporation facilitates electron transfer; the resulting Co–Nx active sites can promote electron enrichment of the catalyst via H2 dissociation [44]. Such electron-rich sites are expected to interact more effectively with strongly electron-withdrawing substrates (for example, 1-nitronaphthalene), which likely contributes to the observed high hydrogenation activity. Experimental data presented below indicate that the catalyst prepared with a Co:Ni = 2:1 ratio exhibits superior hydrogenation performance.
XPS of the Ni 2p region was deconvoluted into two principal components, which are assigned to metallic Ni (Ni0) and nickel oxide (Ni2+) [41] (Figure 5b). The features at 855.8 eV and 854.6 eV are attributed to Ni0 and Ni2+, respectively, and the presence of characteristic satellite peaks corroborates the simultaneous existence of reduced and oxidized nickel at the catalyst surface [45].
When considered together with the high-resolution Co spectra, systematic shifts in the diffraction and XPS binding energies assigned to cobalt and nickel indicate partial Co–Ni alloy [35] formation. Alloying induces progressive modifications of the catalyst lattice, altering local ordering and electronic structure and thereby shifting the core-level binding energies of both metals. In addition, the possible formation of trace M–Nx nitride at the metal–nitrogen interface can generate locally perturbed heterojunctions that facilitate electron transfer between the metal phase and the carbon-nitrogen matrix [46,47]. These electronic and structural effects—Co–Ni [48] alloying and Ni–Nx [49] formation—are therefore implicated in promoting electron enrichment at active sites and are likely contributors to the observed enhancement in hydrogenation activity [50].
Figure 6a,b presents the TEM image of the Co2Ni1@NC/SiO2 catalyst. Figure 6d reveals that the metal nanoparticles exhibit relatively uniform particle sizes with an average diameter of 7.92 nm and are well dispersed.
High-resolution TEM of the Co2Ni1@NC/SiO2 catalyst (Figure 6c) shows lattice fringes of 0.205 nm and 0.203 nm, which are assigned to the Co (111) and Ni (011) planes, respectively, providing direct evidence for the coexistence of cobalt and nickel lattice domains and consistent with partial Co–Ni alloy formation. The measured interlayer spacing of carbon is 0.340 nm, in agreement with the graphite (002) plane [51], indicating the presence of a graphitic carbon shell. This carbon-coating encapsulation serves as an effective physical barrier that suppresses metal leaching and particle agglomeration and can also modulate metal–support electronic interactions [52], thereby contributing to the observed enhancement in catalyst stability under reaction conditions.
Figure 7 shows corresponding EDX-mapping images of the Co2Ni1@NC/SiO2 catalyst. The elemental mappings demonstrate that the signals of Ni, Co, N, and C overlap with each other and are homogeneously distributed at the nanoscale. The uniform distribution of Ni and Co within the nanoparticles, together with previous characterization results in this study, confirms the synergistic effect between Ni-Co bimetals, which is consistent with the shifted diffraction peaks observed in the XRD pattern due to alloy formation. Introducing a second metal into nickel-based catalysts can reduce particle size and ensure a uniform distribution [53], which effectively increases the exposure area of active sites. This is a key reason for the enhanced catalytic performance of the catalyst.
Figure 8 presents N2 physisorption–desorption isotherms and corresponding pore size distributions for the CoxNiy@NC/SiO2 catalysts with varying Co/Ni ratios. Curves a, c, and d display a pronounced uptake at high relative pressures (P/P0) with no low-P/P0 plateau, and a well-defined hysteresis loop indicative of capillary condensation, consistent with a Type IV isotherm. In contrast, curve b exhibits a mixed Type I/IV behavior [54]. The pore size distributions corroborate these observations and confirm that the materials are predominantly mesoporous. Such a mesoporous architecture enhances catalytic performance by increasing the exposure of active sites, improving mass transport and reactant accessibility through interconnected pore channels, and reducing diffusion limitations [55]—factors that together accelerate reaction kinetics and contribute to the catalysts’ superior hydrogenation activity.
As summarized in Table 1, the specific surface area, pore volume, and average pore size of the CoxNiy@NC/SiO2 catalysts vary markedly with the Co/Ni ratio. The Co3Ni1@NC/SiO2 (H2-500) sample exhibits the highest values, with a specific surface area of 355.9 m2·g−1, a pore volume of 0.26 cm3·g−1, and an average pore diameter of 3.25 nm. These features are attributed to collapse of the ZIF-67 polyhedral precursor during calcination, when deposited on the silica support, which generates large surface area. With increasing Ni content, the catalysts show a systematic decline in specific surface area, pore volume, and pore size, consistent with progressive modification of the precursor decomposition pathway and pore formation dynamics.
The design of high-performance catalysts stems from understanding of the hydrogenation mechanism. The hydrogenation of aromatic nitro compounds predominantly follows the classical Haber mechanism [56], which involves two main pathways: first, the direct hydrogenation via nitroso compounds and hydroxylamine intermediates to form amines; and second, the condensation of these intermediates to produce azoxy/azo compounds [57], which are then further hydrogenated. Side reactions such as condensation and disproportionation lead to various by-products, the extent of which is strongly influenced by catalyst properties, substrate concentration, and hydrogen activity. Noble metals (e.g., Pd, Pt) exhibit significant advantages in hydrogenation due to their high affinity for hydrogen, excellent selectivity for functional groups on the side chains of aromatic compounds [58], and their ability to preserve the aromatic ring structure. However, challenges such as high cost, susceptibility to over-reduction, and poisoning limit their widespread application. In recent years, research focus has gradually shifted toward non-noble metal catalysts. Strategies including multi-metal synergy and the construction of M–Nx active sites have shown progress in enhancing hydrogenation activity and stability, providing valuable directions for the development of efficient, low-cost catalysts.
The Mg–Al oxide-supported Co–Ni bimetallic catalyst reported by Gong et al. [59]. has been employed for the liquid-phase hydrogenation of furfural to 2-methylfuran, achieving a yield of 92.1%. Their study revealed that the distribution of metal sites and acid sites is strongly influenced by the reduction conditions, and the high selectivity in the hydrogenation reaction was attributed to the cooperative interaction between metal sites and acid sites on the catalyst surface.
Meanwhile, an N-doped carbon-coated Co-based catalyst developed by Silvia et al. [60]. has been applied to the reduction of nitro compounds. Their work proposed that Co–Nx active sites play a key role in delivering high activity, chemoselectivity, and stability.
In the catalyst studied in this work, CoxNiy@NC/SiO2, the formation of a Co–Ni alloy during synthesis modulates the electronic structure of the active sites, facilitating H2 dissociation and weakening the N–O bond in the nitro group. The nitrogen-doped carbon shell derived from ZIF-67 not only protects the metal nanoparticles from leaching and aggregation but also generates M–Nx active sites. These species promote electron transfer to the metal centers, creating an electron-rich surface that favors the adsorption and activation of electron-deficient nitroarenes.

2.2. Activity of CoxNiy@NC/SiO2 Catalysts for the Hydrogenation of 1-Nitronaphthalene

Under the reaction conditions specified in Section 2.3, Co@NC/SiO2 afforded 72% conversion with 90% selectivity to 1-naphthylamine, whereas incorporation of Ni markedly improved catalytic performance: the Co:Ni = 2:1 catalyst achieved > 99% conversion and ≈95% selectivity to 1-naphthylamine. By contrast, Ni@NC/SiO2 delivered only ~30% conversion and ~68% selectivity (Figure 9), which is attributed to the absence of a well-defined polyhedral MOF precursor between Ni and 2-methylimidazole; during pyrolysis under H2 this precursor yields predominantly metallic Ni0 and decomposed organic fragments rather than a structured metal–nitrogen–carbon architecture [61]. The superior performance of the bimetallic catalysts is ascribed to synergistic structural and electronic effects induced by Ni addition—partial Co–Ni alloying [48], enhanced formation of M–Nx [49] sites, and improved metal dispersion—which collectively increase the density of electron-rich active sites for H2 activation and nitro-group hydrogenation, thereby accounting for the pronounced enhancement in conversion and selectivity observed at the Co:Ni = 2:1 composition.
Table 2 summarizes the performance of Co2Ni1@NC/SiO2 catalysts prepared at different calcination temperatures for the liquid-phase hydrogenation of 1-nitronaphthalene. The precursor was heated under N2 to the target temperature (400–600 °C, in 50 °C increments), after which the atmosphere was switched to H2 and the sample was held for 2 h to affect calcination reduction. As the calcination temperature was raised from 400 °C, the conversion of 1-nitronaphthalene increased progressively, reaching a maximum at 500 °C, and then declined at higher temperatures. The reduced activity and selectivity observed below 500 °C are attributed to incomplete reduction of the metal [62,63], whereas the loss of activity above 500 °C is ascribed to extensive carbon and nitrogen depletion from the Co2Ni1@NC/SiO2 matrix, which promotes particle agglomeration and disrupts the cobalt–nitrogen coordination environment [64]. The catalyst prepared at 500 °C exhibited the best performance, with conversion exceeding 99% and selectivity of 95.3%, indicating that 500 °C is the optimal calcination–reduction temperature for this system.
Figure 10 presents the hydrogenation performance of Co2Ni1@NC/SiO2 as a function of reaction temperature, evaluated in 10 °C increments from 110 °C to 70 °C while all other parameters were held constant. At 110 °C and 100 °C, both conversion of 1-nitronaphthalene and selectivity to 1-naphthylamine exceeded 99%. Lowering the temperature to 90 °C maintained a conversion of 99% but reduced selectivity to approximately 95%; further decreases in temperature produced progressively lower conversions and selectivities. Notably, prolonging the reaction time at 90 °C, 80 °C and even 70 °C restored both conversion and selectivity to >99% (Table 3), demonstrating that the Co2Ni1@NC/SiO2 catalyst exhibits robust hydrogenation performance and that its activity can be compensated for by extended residence time, achieving exceed 99% conversion and selectivity even at relatively low temperatures.

2.3. Stability and Recyclability of Co2Ni1@NC/SiO2

Figure 11a presents the oxidation-resistance stability of Co2Ni1@NC/SiO2. The as-prepared catalyst was exposed to air for 12–96 h prior to evaluation in the liquid-phase hydrogenation of 1-nitronaphthalene to 1-naphthylamine. After 12 h of air exposure the catalyst retained activity comparable to the fresh material, achieving >99% conversion with ≈95% selectivity to 1-naphthylamine. Prolonged air exposure led to progressively lower conversion and selectivity, although the rate of performance decline markedly slowed after 72–96 h. This attenuation in deactivation is consistent with formation of an oxidized outer metal layer that passivates and thereby protects the subsurface metal phase from further oxidation [65,66]. Overall, these results indicate that Co2Ni1@NC/SiO2 exhibits good resistance to air-induced deactivation and maintains substantial catalytic activity after moderate exposure to ambient conditions.
As shown in Figure 11b, the catalyst retained activity comparable to the fresh material in the first reuse, but both conversion and selectivity progressively declined from the second cycle onward, reaching 71% conversion and 83% selectivity to 1-naphthylamine after the fourth cycle. Following the fourth cycle, the spent catalyst was regenerated by calcination at 500 °C under H2 for 2 h. The regenerated material was then evaluated under the same conditions, yielding the fifth-cycle data in Figure 11b, which shows that regeneration restored much of the lost performance, increasing conversion to 92% and selectivity to 91%.
The observed deactivation is attributed primarily to the partial oxidation of the active Co and Ni species during the reaction and to metal leaching from the catalyst under the hydrogenation conditions. Overall, the data in Figure 11 indicate that Co2Ni1@NC/SiO2 combines appreciable resistance to oxidative deactivation with good Recyclability and regenerability via hydrogen-assisted thermal treatment.

2.4. Applicability of CoxNiy@NC/SiO2 Catalysts

In the aforementioned study, the Co2Ni1@NC/SiO2 catalyst demonstrated excellent hydrogenation activity and product selectivity in the reduction of 1-nitronaphthalene to 1-naphthylamine. To evaluate the applicability of the CoxNiy@NC/SiO2 catalyst toward the hydrogenation of other aromatic nitro compounds, it was applied to the reduction of several different nitro-substituted aromatics, aiming to explore its hydrogenation capability for this broader class of substrates.
The applicability of the CoxNiy@NC/SiO2 catalyst was evaluated using several different aromatic nitro compounds as reactants. In the hydrogenation reduction of 1,5-dinitronaphthalene and 1,8-dinitronaphthalene, which are more challenging for catalytic hydrogenation, simply increasing the reaction temperature and time resulted in selectivity exceeding 99% for 1,5-diaminonaphthalene and 1,8-diaminonaphthalene, demonstrating excellent catalytic activity and product selectivity. In a series of hydrogenation reduction reactions of halogenated nitrobenzenes, selectivities of 98.5% for nitrobenzene, 96.8% for o-chloroaniline, 98.1% for m-chloroaniline, and 97.8% for p-chloroaniline were achieved, indicating the broad applicability of the CoxNiy@NC/SiO2 catalyst (Table 4). The high selectivity of the CoxNiy@NC/SiO2 catalyst toward halogenated nitroarenes may be attributed to the fact that hydrogenolysis of the C–Cl bond in halogenated aromatics involves electrophilic attack by active hydrogen atoms, while hydrogenation of the nitro group proceeds via nucleophilic attack, the H− adsorbed and dissociated on the Co–Ni metal active sites act as nucleophiles, thus preferentially activating the nitro group [67]. Moreover, the preferential adsorption of the nitro group on the metal active sites of the catalyst surface minimizes the likelihood of by-product formation.
The Ni-Zn/AC catalyst reported by Huang et al. [23] also achieved an excellent conversion of 99% under highly similar reaction conditions (90 °C, 0.6 MPa H2, 5 h), with a selectivity of 96.82% toward 1-naphthylamine. In this work, by only slightly extending the reaction time to 5.5 h, the product selectivity was significantly improved to 99%. This enhancement is crucial, as it demonstrates that the catalyst designed in this study effectively directs the reaction exclusively toward the target product, 1-naphthylamine, while effectively suppressing possible over-hydrogenation and avoiding the formation of other by-products. The direct improvement in selectivity implies a simpler product purification process, higher product yield, and better atom economy, which positively contributes to reducing downstream separation costs and enhancing overall process efficiency.
Compared with the PtNi/C catalyst reported by Fu et al. [21] (30 °C, 3.0 MPa H2, with both conversion and selectivity reaching 100%), although the reaction temperature of the catalyst studied in this work is slightly higher, the required hydrogen pressure is significantly reduced by 80% (from 3.0 MPa to 0.6 MPa). This change reduces the reliance on high-pressure reaction equipment. More importantly, the present catalyst completely avoids the use of expensive precious metal active components, instead employing abundant and low-cost cobalt and nickel, fundamentally overcoming the industrialization bottleneck of precious metal catalysts caused by their scarcity and high cost. At the minor cost of a slight reduction in reaction rate (compensated by moderately extending the reaction time or increasing the temperature), it achieves conversion and selectivity comparable to precious metal catalysts, making the process safer and more economical, demonstrating extremely high value for industrial scale-up.
The CoxNiy@NC/SiO2 catalyst developed in this work successfully achieves a breakthrough balance among three key performance indicators: mild reaction conditions, excellent catalytic performance (high conversion and high selectivity), and low manufacturing cost. This provides a new and promising design strategy for developing industrial catalysts that can replace precious metals and are suitable for the selective hydrogenation of aromatic nitro compounds.

3. Experimental

3.1. Synthesis Method of Catalysts

A series of bimetallic CoxNiy@NC/SiO2 catalysts were synthesized via a room-temperature coordination–precipitation method followed by pyrolysis and reduction. Initially, weigh out a certain mass of cobalt(II) (Shanghai Aibi Chemistry Reagent Co., Ltd., Shanghai, China) nitrate hexahydrate and nickel(II) (Shanghai Aibi Chemistry Reagent Co., Ltd., Shanghai, China) nitrate hexahydrate(with a molar ratio of Co:Ni = x:y, Based on the subsequent use of 48 g of 2-methylimidazole and a metal-to-ligand molar ratio of 1:8, the specific masses of the salts were calculated based on the aforementioned proportional relationships) were dissolved in 150 mL of anhydrous methanol (KMO Chemicals, Tianjin, China). Subsequently, 8 mL of tetraethyl orthosilicate (TEOS) (KMO Chemicals, Tianjin, China) was added to the solution under stirring. The resulting mixture was sealed with plastic film and set aside for preparation.
In a separate vessel, 48 g of 2-methylimidazole (KMO Chemicals, Tianjin, China) and 16 mL of aqueous ammonia (KMO Chemicals, Tianjin, China) were dissolved in 150 mL of anhydrous methanol. This solution was also sealed and allowed to equilibrate. The molar ratio of total metal ions (Co + Ni) to 2-methylimidazole was maintained at 1:8 to ensure sufficient ligand coordination.
After ultrasonication of both solutions for 5 min to ensure homogeneity, the metal salt/TEOS solution was slowly added to the 2-methylimidazole/ammonia solution under magnetic stirring. The resulting suspension was stirred continuously at room temperature for 24 h, followed by static aging in the dark for an additional 6 h to promote framework formation. Zif-67 is not pre-synthesized separately before catalyst preparation, but is synthesized synchronously with silicon dioxide in a single reaction system.
The resulting precipitate was collected by centrifugation and washed five times with anhydrous methanol to remove unreacted species and byproducts. The obtained purple solid—designated as the catalyst precursor—was vacuum-dried at 80 °C for 24 h.
The dried precursor was ground and sieved to 60–80 mesh, then subjected to pyrolysis in a tubular furnace. Under a nitrogen atmosphere (Zhuzhou Diamond Gas Company, Zhuzhou, China), the temperature was ramped to 500 °C at a rate of 4 °C/min. Once the target temperature was reached, the gas flow was switched to hydrogen (Zhuzhou Diamond Gas Company, Zhuzhou, China), and the sample was reduced for 2 h. After reduction, the system was purged with nitrogen and allowed to cool naturally to room temperature. During the catalyst preparation process, no additional cobalt was introduced; all cobalt in the catalyst is exclusively derived from ZIF-67.
The final catalyst, denoted as CoxNiy@NC/SiO2 (where x and y represent the molar ratio of cobalt to nickel), consisted of cobalt–nickel alloy nanoparticles embedded in a nitrogen-doped carbon matrix supported on silica.

3.2. Catalyst Characterization

X-ray diffraction (XRD) patterns were recorded on a Rigaku D/MAX-2500/PC diffractometer (Akishima, Japan) using Cu Kα radiation (λ = 1.5406 Å). Data were collected over a 2θ range of 10–90° at a scanning rate of 4°/min to identify the crystalline phases and assess the structural evolution of the catalysts.
Nitrogen adsorption–desorption isotherms were measured using a Micromeritics ASAP 2020 PLUS HD88 surface area and porosity analyzer (Norcross, GA, USA). Prior to analysis, the samples were degassed under vacuum at 150 °C to remove physisorbed species. The specific surface area was calculated using the Brunauer–Emmett–Teller (BET) method, while the pore size distribution was derived from the desorption branch using the Barrett–Joyner–Halenda (BJH) model.
Hydrogen temperature-programmed reduction (H2-TPR) experiments were carried out on a Micromeritics AutoChem II 2920 chemisorption analyzer. Approximately 100 mg of catalyst was loaded into a U-shaped quartz reactor and pretreated under flowing argon. The sample was then heated from 25 °C to 900 °C at a rate of 10 °C/min under a 5% H2/He mixture, and the hydrogen consumption was monitored using a thermal conductivity detector (TCD). H2 pulse chemisorption measurements were also performed on the same instrument to evaluate the metal dispersion and active site accessibility.
X-ray photoelectron spectroscopy (XPS) was conducted using a Thermo Fisher ESCALAB 250Xi spectrometer (Waltham, MA, USA) equipped with a monochromatic Al Kα X-ray source (1486.7 eV). A 180° double-focusing hemispherical analyzer with a six-channel detector was employed to analyze the surface elemental composition and chemical states of the catalyst components.
Scanning electron microscopy (SEM) images were obtained using a JEOL JSM-6610LV microscope (Akishima, Japan) to examine the surface morphology and particle aggregation behavior.
Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analyses were performed on a Thermo Scientific Talos L120C (120 kV) and a Talos F200X (300 kV) transmission electron microscope, respectively. Elemental distribution was further investigated using super-energy dispersive X-ray spectroscopy (super-EDX) mapping. For TEM observation, the catalyst powder was ultrasonically dispersed in ethanol for 5 min, drop-cast onto a carbon-coated copper grid, and dried under ambient conditions.

3.3. Hydrogenation of Nitronaphthalene

The liquid-phase hydrogenation of 1-nitronaphthalene was carried out in a 300 mL stainless-steel Micro liquid phase batch reactor (Shanghai Yanzheng Experimental Instrument Co., Ltd., Shanghai, China) equipped with Magnetic stirring (600 rpm). The reaction mixture comprised 0.1 g of pre-calcined and reduced catalyst and 1 g of 1-nitronaphthalene dissolved in 20 mL of anhydrous ethanol. Prior to the reaction, the reactor was sealed and purged with nitrogen to ensure leak-tightness. After confirming reactionsystem leakproofness, the nitrogen atmosphere was replaced with hydrogen through five successive purge–pressurization cycles.
The reactor was then rapidly heated to the target temperature under an initial hydrogen pressure of 0.6 MPa to initiate the hydrogenation reaction. Hydrogenation of 1-nitronaphthalene was carried out in a miniature autoclave using 1.0 g substrate, 0.1 g catalyst, and 20 mL anhydrous ethanol at 90 °C under 0.6 MPa H2 in the Micro liquid phase batch reactor with stirring at 600 rpm for 5 h
For catalyst recyclability evaluation, the spent catalyst was recovered after each run by filtration, thoroughly washed with anhydrous ethanol, centrifuged, and dried before reuse in the next cycle.

3.4. Stability Testing of Catalysts

Post-reaction, the catalyst was separated from the reaction mixture via centrifugation, washed repeatedly with anhydrous ethanol, and vacuum-dried at room temperature. A slight decrease in catalyst mass was observed after each cycle. To ensure consistency and comparability across recycling experiments, the quantities of 1-nitronaphthalene and ethanol were proportionally adjusted based on the actual recovered catalyst mass, thereby maintaining a constant substrate-to-catalyst ratio and substrate concentration.
All recycling experiments were conducted under strict control of experimental variables reaction conditions. After the fourth cycle, the spent catalyst was subjected to regeneration by thermal treatment in a tubular furnace under a hydrogen atmosphere at 500 °C for 2 h. The regenerated catalyst was then reused under the same hydrogenation conditions, and the resulting data were recorded as the fifth cycle.

3.5. Product Analysis Methods and Calculation Methods

Using an Agilent 1260 (Santa Clara, CA, USA) high performance liquid chromatograph, qualitative and quantitative analyses of the 1-nitronaphthalene feedstock and its hydrogenation products were conducted using reversed-phase high-performance liquid chromatography (RP-HPLC) with an external standard method. The chromatographic conditions were as follows: HPLC system—Agilent LC 1260 (Santa Clara, CA, USA); analytical column—Elite ODS (5 μm, 4.6 mm × 250 mm); detector—SPD-20A UV detector; mobile phase—methanol: acetonitrile: water = 20: 40: 40 (v/v/v); column temperature—25 °C; detection wavelength—254 nm; and flow rate—1.0 mL/min.
The mass fraction of 1-naphthylamine in the sample was calculated using the following equation:
c 1 = A 2 × m 1 × B 1 A 1 × m 2 × 100 %
where
A1: Average peak area of 1-naphthylamine in the standard sample
A2: Average peak area of 1-naphthylamine in the test sample
m1: Mass of the standard sample (g)
m2: Mass of the test sample (g)
B1: Mass fraction of 1-naphthylamine in the standard sample (%)
The yield of 1-naphthylamine was calculated as:
Y = m × c 1 m 3 × 100 %
where:
m: Total mass of the reaction products (g)
c1: Mass fraction of 1-naphthylamine in the product (%)
m3: Theoretical yield of 1-naphthylamine (g)
Y: Yield of 1-naphthylamine in the reaction (%)
The mass fraction of 1-nitronaphthalene in the sample was determined using:
c 2 = A 4 × m 4 × B 2 A 3 × m 2 × 100 %
where:
A3: Average peak area of 1-nitronaphthalene in the standard sample
A4: Average peak area of 1-nitronaphthalene in the test sample
m2: Mass of the test sample (g)
m4: Mass of the standard sample of 1-nitronaphthalene (g)
B2: Mass fraction of 1-nitronaphthalene in the standard sample (%)
c2: Mass fraction of 1-nitronaphthalene in the test sample (%)
The conversion of 1-nitronaphthalene was calculated as:
X = m × c 2 m 1 × 100 %
where:
m1: Initial feed amount of 1-nitronaphthalene (g)
m: Total mass of the reaction products (g)
c2: Mass fraction of 1-nitronaphthalene in the product (%)
X: Conversion of 1-nitronaphthalene (%)
The selectivity toward 1-naphthylamine was calculated using:
S = Y X × 100 %

4. Conclusions

A series of silica-supported, nitrogen-carbon-coated cobalt–nickel catalysts (CoxNiy@NC/SiO2) was successfully synthesized via a room-temperature stirring protocol followed by calcination–reduction. Performance evaluation revealed a strong dependence on the Co/Ni molar ratio; the Co2Ni1@NC/SiO2 (Co:Ni = 2:1) composition exhibited the best overall performance, delivering near-quantitative conversion of 1-nitronaphthalene and a 1-naphthylamine yield ≥ 99%, together with high activity, excellent stability, and good recyclability.
  • Characterization and correlation analyses indicate that the pronounced enhancement in catalytic activity is primarily attributable to a synergistic interaction between Ni and Co. This bimetallic synergy optimizes the electronic structure of the active centers, thereby facilitating H2 activation and accelerating the hydrogenation pathway.
  • Spectroscopic and structural data suggest that nitrogen derived from the 2-methylimidazole ligand coordinates with cobalt to form Co–Nx active sites and Ni-Nx sites formed during high-temperature calcination reduction process. These M–Nx sites promote electron transfer to the catalyst surface, generating electron-rich active sites. Given the strongly electron-withdrawing nature of the nitro group, such electron-rich surfaces enhance substrate–catalyst interactions and thereby improve nitro-group hydrogenation efficiency.
  • The in situ formed carbon-nitrogen matrix produced during thermal treatment stabilizes and disperses the metal active sites, to improve the hydrogenation activity of the catalyst, while also significantly improving the catalyst’s thermal stability and oxidation resistance, contributing to the observed durability and regenerability of the CoxNiy@NC/SiO2 catalysts.
  • The superior performance of CoxNiy@NC/SiO2 catalysts is underpinned by dynamic evolution mechanisms that generally require independent and systematic investigation to elucidate, such as the structural evolution of the carbon-nitrogen layers during cycling, the dynamic changes in metal valence states, and the continuous evolution of metal particle size within the catalyst, highlighting future directions for in-depth exploration.

Author Contributions

Conceptualization, P.L. and X.L.; methodology, X.L.; formal analysis, M.Z.; investigation, W.D.; writing—original draft preparation, X.L.; writing—review and editing, M.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data generated or analysed during this study are included in this published article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 16 00093 g001
Figure 1. XRD patterns of CoxNiy@NC/SiO2 catalysts with varying cobalt-to-nickel ratios.
Figure 1. XRD patterns of CoxNiy@NC/SiO2 catalysts with varying cobalt-to-nickel ratios.
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Figure 2. H2-TPR profiles of CoxNiy@NC/SiO2 catalyst precursors.
Figure 2. H2-TPR profiles of CoxNiy@NC/SiO2 catalyst precursors.
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Figure 3. SEM images of (a) Catalyst precursor of Co2Ni1@NC/SiO2, (b) The calcined and reduced catalyst of Co2Ni1@NC/SiO2.
Figure 3. SEM images of (a) Catalyst precursor of Co2Ni1@NC/SiO2, (b) The calcined and reduced catalyst of Co2Ni1@NC/SiO2.
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Figure 4. XPS survey spectra of CoxNiy@NC/SiO2 catalysts.
Figure 4. XPS survey spectra of CoxNiy@NC/SiO2 catalysts.
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Figure 5. XPS spectra of (a) Co 2p regions in reduced samples; (b) Ni 2p regions in reduced samples.
Figure 5. XPS spectra of (a) Co 2p regions in reduced samples; (b) Ni 2p regions in reduced samples.
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Catalysts 16 00093 g006
Figure 6. (a,b) TEM images of Co2Ni1@NC/SiO2 (c) HRTEM images of Co2Ni1@NC/SiO2 (d) Particle size distribution of Co2Ni1@NC/SiO2.
Figure 6. (a,b) TEM images of Co2Ni1@NC/SiO2 (c) HRTEM images of Co2Ni1@NC/SiO2 (d) Particle size distribution of Co2Ni1@NC/SiO2.
Catalysts 16 00093 g006
Catalysts 16 00093 g007
Figure 7. The corresponding EDX-mapping of Co2Ni1@NC/SiO2.
Figure 7. The corresponding EDX-mapping of Co2Ni1@NC/SiO2.
Catalysts 16 00093 g007
Catalysts 16 00093 g008
Figure 8. N2 adsorption–desorption isotherms and pore size distributions of CoxNiy@NC/SiO2 catalysts with different Co/Ni ratios.
Figure 8. N2 adsorption–desorption isotherms and pore size distributions of CoxNiy@NC/SiO2 catalysts with different Co/Ni ratios.
Catalysts 16 00093 g008
Catalysts 16 00093 g009
Figure 9. Hydrogenation performance as a function of catalyst composition (Co/Ni ratio).
Figure 9. Hydrogenation performance as a function of catalyst composition (Co/Ni ratio).
Catalysts 16 00093 g009
Catalysts 16 00093 g010
Figure 10. Catalytic performance of Co2Ni1@NC/SiO2 in the hydrogenation of 1-nitronaphthalene as a function of reaction temperature.
Figure 10. Catalytic performance of Co2Ni1@NC/SiO2 in the hydrogenation of 1-nitronaphthalene as a function of reaction temperature.
Catalysts 16 00093 g010
Catalysts 16 00093 g011
Figure 11. The performance of Co2Ni1@NC/SiO2 (a) Air-exposure stability test; (b) Recycling test and regeneration performance.
Figure 11. The performance of Co2Ni1@NC/SiO2 (a) Air-exposure stability test; (b) Recycling test and regeneration performance.
Catalysts 16 00093 g011
Table 1. Comparison of the textural properties for the CoxNiy@NC/SiO2 catalysts.
Table 1. Comparison of the textural properties for the CoxNiy@NC/SiO2 catalysts.
CatalystsBET Surface Area (m2/g)Total Pore Volume (cm3/g)Pore Size (nm)
Co3Ni1@NC/SiO2355.90.263.25
Co2Ni1@NC/SiO2324.60.243.12
Co1Ni1@NC/SiO2298.30.213.02
Co1Ni2@NC/SiO2276.40.202.98
Table 2. Effects of Co2Ni1@NC/SiO2 at different calcination temperatures on hydrogenation properties of 1-nitronaphthalene.
Table 2. Effects of Co2Ni1@NC/SiO2 at different calcination temperatures on hydrogenation properties of 1-nitronaphthalene.
CatalystsReducing ConditionConversionSelectivityYield
1-NaphthylamineOthers
Co2Ni1@NC/SiO2H2-400 °C for 2 h82.5%87.3%12.7%72.1%
Co2Ni1@NC/SiO2H2-450 °C for 2 h94.6%94.4%5.6%89.2%
Co2Ni1@NC/SiO2H2-500 °C for 2 h99.9%95.3%4.7%95.3%
Co2Ni1@NC/SiO2H2-550 °C for 2 h91.5%96.6%3.4%88.4%
Co2Ni1@NC/SiO2H2-600 °C for 2 h79.2%81.4%18.6%64.5%
Table 3. Effect of Co2Ni1@NC/SiO2 on hydrogenation of 1-nitronaphthalene by prolonging reaction time.
Table 3. Effect of Co2Ni1@NC/SiO2 on hydrogenation of 1-nitronaphthalene by prolonging reaction time.
CatalystsReaction TemperatureReaction TimeConversionSelectivity
1-NaphthylamineOthers
Co2Ni1@NC/SiO2H250090 °C5.5 h>99.9%>99.9%/
Co2Ni1@NC/SiO2H250080 °C6.5 h>99.9%>99.9%/
Co2Ni1@NC/SiO2H250070 °C9 h>99.9%>99.9%/
Table 4. The hydrogenation of other aromatic nitro compounds over CoxNiy@NC/SiO2.
Table 4. The hydrogenation of other aromatic nitro compounds over CoxNiy@NC/SiO2.
EntrySubstratesProductsReaction
Temperature
(°C)		Reaction Time
(h)		Con. (%)/Sel. (%)
1Catalysts 16 00093 i001Catalysts 16 00093 i002957>99%/>99%
2Catalysts 16 00093 i003Catalysts 16 00093 i004958.5>99%/>99%
3Catalysts 16 00093 i005Catalysts 16 00093 i006705>99%/>98.5%
4Catalysts 16 00093 i007Catalysts 16 00093 i008707.5>99%/>96.8%
5Catalysts 16 00093 i009Catalysts 16 00093 i010705>99%/>98.1%
6Catalysts 16 00093 i011Catalysts 16 00093 i012705.5>99%/>97.8%
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MDPI and ACS Style

Lan, X.; Zhong, M.; Dai, W.; Liu, P. High-Performance CoxNiy@NC/SiO2 Catalysts Derived from ZIF-67 for Enhanced Hydrogenation of 1-Nitronaphthalene. Catalysts 2026, 16, 93. https://doi.org/10.3390/catal16010093

AMA Style

Lan X, Zhong M, Dai W, Liu P. High-Performance CoxNiy@NC/SiO2 Catalysts Derived from ZIF-67 for Enhanced Hydrogenation of 1-Nitronaphthalene. Catalysts. 2026; 16(1):93. https://doi.org/10.3390/catal16010093

Chicago/Turabian Style

Lan, Xuedong, Ming Zhong, Weidi Dai, and Pingle Liu. 2026. "High-Performance CoxNiy@NC/SiO2 Catalysts Derived from ZIF-67 for Enhanced Hydrogenation of 1-Nitronaphthalene" Catalysts 16, no. 1: 93. https://doi.org/10.3390/catal16010093

APA Style

Lan, X., Zhong, M., Dai, W., & Liu, P. (2026). High-Performance CoxNiy@NC/SiO2 Catalysts Derived from ZIF-67 for Enhanced Hydrogenation of 1-Nitronaphthalene. Catalysts, 16(1), 93. https://doi.org/10.3390/catal16010093

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