The oxidative coupling of benzyl amines to form N-benzylidenebenzyl amines and benzimidazoles is a highly significant reaction with extensive applications in both industrial and pharmaceutical chemistry (Dong et al., 2016; Zeng et al., 2021; He et al., 2022; Yamamoto et al., 2022). N-benzylidenebenzyl amines, along with their imine derivatives, serve as versatile intermediates in the synthesis of various essential compounds, including those used in inorganic, organic, pharmaceutical, polymer, and bio-fertilizer production (Oiye et al., 2019; Ay et al., 2020; Orr et al., 2021). In particular, imines are critical in the pharmaceutical industry for the creation of heterocyclic compounds, which are pivotal in drug discovery, as well as for synthesizing bioactive molecules, and dyes in various industrial chemical processes. Imines also play a key role as reactive intermediates in major reactions, including the Diels–Alder reaction, Umpolung reactions, Aza–Baylis–Hillman, and Amadori rearrangement, thereby expanding their utility in organic synthesis (Layer, 1963; Ravula et al., 2024) Benzimidazoles, which are formed in this process, are particularly important as a structural framework in numerous bioactive molecules. These nitrogen-containing hetero cycles exhibit diverse biological activities, making them valuable in pharmaceuticals, especially as anti-cancer, anti-viral, and anti-fungal agents (Brishty et al., 2021; Chung et al., 2023; Mahurkar et al., 2023; Ahmad G. et al., 2024; Kumari et al., 2024). In cancer treatment, benzimidazoles inhibit tumour growth, while their anti-viral properties help combat diseases like HIV and hepatitis by interfering with viral replication. Furthermore, they act as effective anti-fungal agents, protecting against fungal infections. In addition, benzimidazoles play key roles in agrochemicals, functioning as pesticides and fungicides to protect crops, and in material science, where they contribute to the development of polymers and dyes (Zubrod et al., 2019; Ahmad M. F. et al., 2024; Bai et al., 2024; Lewicka et al., 2024). Therefore, the sustainable synthesis of N-benzylidenebenzyl amines and benzimidazoles via oxidative coupling provides an eco-friendly pathway for producing these essential compounds, which are vital not only for pharmaceuticals but also for agriculture, materials science, and green chemistry initiatives.

In recent years, both homogeneous and heterogeneous catalysts have been extensively explored for the oxidation of benzyl amines and the synthesis of benzimidazoles (Chen et al., 2015; Lu et al., 2024) While homogeneous catalysts, such as KMnO⁴, K₂Cr₂O₇, two-iodoxybenzoic acid, and N-tert-butylphenylsulfinimidoyl chloride, have demonstrated high efficiency, their significant drawbacks include challenging catalyst separation, complex work-up procedures, and substantial waste produced (Matsuo et al., 2001; Nicolaou et al., 2003; 2004; Furukawa et al., 2011). For instance, Dong et al. reported a metal-free oxidative approach using salicylic acid derivatives under oxygen for the selective oxidation of benzyl amines to imines and the synthesis of nitrogen-containing hetero cycles, for example, benzimidazoles (Dong et al., 2016). Additionally, a sustainable alternative involves the dehydrogenative coupling of aromatic diamines with alcohols, yielding water and hydrogen gas as eco-friendly by-products. As a result, attention has shifted toward heterogeneous catalysts, which offer easy catalyst separation, reusability, and economic feasibility (Qian et al., 2018; Bera et al., 2019; Tian et al., 2024a; Wang et al., 2024b). Although noble metals like Pt, Pd, Ru, Ir, and Rh have shown effectiveness in oxidation reactions, their high cost and scarcity necessitate the development of more abundant non-noble metal alternatives (Tateyama et al., 2016; Slanina and Oberschmid, 2018). Recent advances highlight the potential of base metals viz., Fe, Cu, Co, and Mn in catalyzing the dehydrogenative coupling of alcohols with o-phenylenediamine for benzimidazole synthesis (Bauer and Knölker, 2015; Wang et al., 2015; Chakraborty et al., 2017; Sadhasivam et al., 2017; Huang et al., 2024; Tian et al., 2024b). Amongst, Cu-based catalysts stand out for their efficiency and environmental benefits, present a viable path toward scalable green methodologies for producing N-benzylidenebenzyl amines and benzimidazole derivatives. The attractiveness of copper as a catalyst stems from its excellent catalytic activity in facilitating oxidation reactions, which are essential for synthesizing various organic compounds. Copper’s redox flexibility, switching between Cu(I) and Cu(II) oxidation states, plays a critical role in promoting the oxidation reactions, making it highly effective for transformations like amine to imine conversion. This ability to facilitate electron transfer is crucial in reactions involving molecular oxygen as an oxidant, further enhancing copper’s catalytic efficiency in aerobic conditions. Recent efforts have focused on elucidating the strong metal–support interaction (SMSI) between CuO and support, as this interaction plays a crucial role in modulating catalytic behaviour. Therefore, the redox properties and catalytic performance of metal-oxide-supported catalysts are greatly influenced by several key factors, including SMSI, type of support, the method of catalyst preparation, dopants and the calcination temperature. These parameters collectively determine the dispersion of the active species, oxygen vacancy formation, acidic sites and the overall stability of the catalyst, all of which are crucial in enhancing catalytic efficiency.

Recent reports suggest that metal oxide catalysts were used in oxidation reactions because of their excellent acid and redox properties. There has been considerable interest in ceria-based material as catalysts for various oxidation reactions because of their significant properties such as oxygen storage/release capacity and redox properties and creates more reactive oxygen defects due to the redox nature of Ce³⁺/Ce⁴⁺. According to the literature, the crystalline structure of ceria (CeO₂) is fluorite. However, pure CeO₂ has less thermal resistance, and poor oxygen storage capacity. To account these limitations, suitable metal ions have been incorporated into the ceria lattice which creates high surface area, more oxygen defects there by enhances its unique structural and redox properties compared to parent Ceria (Rao et al., 2011). It is reported that the doping of suitable transition metal ions such as Si⁴⁺ and Zr⁴⁺ into the ceria lattice can introduce a strain in the ceria lattice attributed to the difference in the ionic radius of dopant and cerium. Furthermore, interaction of two metal cations in an oxide improves the properties such as formation of oxygen vacancies and improves the textural, redox, and acidic thus enhances the catalytic efficiency.

In this present study, we explored the rational design of CuO-supported doped-CeO₂ catalysts for the selective oxidative coupling of benzyl amines to produce N-benzylidenebenzyl amines and benzimidazoles under ambient conditions. The role of acidic, redox, and defect sites, particularly oxygen vacancies, is highlighted as a key factor in improving the catalytic performance. Characterization techniques such as XRD, Raman spectroscopy, SEM, TEM, and XPS have been employed to confirm the structural and surface properties of the synthesized catalysts. Our findings provide a comprehensive understanding of how acidic, redox, and defect sites contribute to enhanced catalytic activity, offering valuable insights for developing efficient nano structured non-noble metal catalysts.

The XRD profiles of CeO₂, 50 wt% SiO₂-doped CeO₂ (CeSi), 50 wt% ZrO₂-doped CeO₂ (CeZr), and 10 wt% CuO-supported Ce, Ce-Si, and CeZr catalysts are shown in Figure 1. The diffraction peaks at approximately 29.3° (111), 32.78° (200), 47.88° (220), 56.33° (311), 59.14° (222), 69.52° (400), 76.36° (331), and 79.81° (420) correspond to the fluorite-type structure of ceria, consistent with previous reports (Potdar et al., 2011; Yashima et al., 1993; Sun and Sermon, 1996). The XRD patterns for the CeSi and CeZr samples did not exhibit any additional crystalline peaks for SiO₂ or ZrO₂, likely due to the amorphous nature of SiO₂/ZrO₂ or the complete incorporation of Si⁴⁺ and Zr⁴⁺ ions into the ceria lattice. Interestingly, the diffraction peaks for doped ceria were broadened, and 2θ values were shifted compared to pure ceria, indicating the presence of smaller crystallite sizes and lattice distortions. The shifts in peak positions for CeSi and CeZr relative to CeO₂ can be explained by the difference in ionic radii between the dopant ions (Si⁴⁺ ∼0.040 nm, Zr⁴⁺ ∼0.084 nm) and Ce⁴⁺ (∼0.097 nm), resulting in lattice contraction due to the substitution of Ce⁴⁺ by smaller Si⁴⁺ and Zr⁴⁺ (Liang et al., 2008; Rao et al., 2011). The calculated lattice parameters corresponding to the highest-intensity XRD peak of CeO₂ were determined to be 0.541, 0.540, and 0.539 nm, respectively. A noticeable reduction in lattice parameters was observed for the CeSi and CeZr supports compared to pristine CeO₂. This reduction, coupled with peak broadening, lattice parameter variation, and peak position shifts, strongly suggests the incorporation of dopants such as SiO₂ and ZrO₂ into the CeO₂ lattice. These findings confirm the successful formation of ceria-based solid solutions. These results were well agreement with earlier reports (Sudarsanam et al., 2014; Ravula et al., 2024).

For the CuO-added samples, CuO XRD peaks were observed at 35.5° (002) and 39.8° (200), in agreement with previously reported CuO particles (Rao et al., 2011; Sudarsanam et al., 2014). Peak broadening was also noted, attributed to changes in the crystallite size of ceria. To further investigate, the influence of dopants on the structural properties of ceria, the average crystallite size and specific surface area were determined (Table 1). The addition of dopants resulted in a reduction in crystallite size, indicating their role in inhibiting crystal growth, even under high thermal conditions. The average crystallite size was calculated using the Scherrer equation: d = 0.9 λ β ⁡ cos ⁡ θ where λ is the X-ray wavelength, β is the full width at half maximum (FWHM), and d is the average crystallite size.

Raman spectroscopy is highly effective for investigating the structural characteristics of ceria-based materials due to its sensitivity to variations in M–O bond arrangements and lattice defects. Figure 2 Represents the Raman spectra of CeO₂, SiO₂-doped CeO₂, ZrO₂-doped CeO₂, and CuO-supported on Ce, CeSi, and CeZr catalysts. The spectrum of pure CeO₂ exhibits a prominent peak near 460 cm⁻¹, attributed to the F_2g Raman-active mode characteristic of the fluorite structure, in agreement with XRD results (Figure 1) and addition of dopants (SiO₂, ZrO₂) to the pure ceria shifts the peak around 457 cm^-1 (F_2g) attributed to the changes in M-O vibration frequencies, which are influenced by differences in the ionic radii of Ce⁴⁺ and the dopants (Reddy et al., 2005). The broadening of the F_2g vibration mode observed may be due to the lattice defects, lattice strain, phonon confinement associated with the variation in the particle size. No Raman peaks associated with the SiO₂, ZrO₂ were observed confirming the formation of ceria solid solutions, which are correlating with the XRD results (Figure 1). An additional shoulder peak around 600 cm^-1 was observed in CeSi, CeZr, Cu/Ce, Cu/CeSi and Cu/CeZr catalysts due to the formation of oxygen vacancies. The incorporation of dopants enhances the concentration of oxygen vacancies (O_v) which is evident from Figure 2. Interestingly, a strong enhancement in this peak was observed in Cu/CeZr due to formation of more oxygen vacancies and there by enhances the acidic properties of CuO doped into the Ce, CeSi and CeZr, respectively.

The presence of defect sites, specifically oxygen vacancies (O_v), can be determined through the analysis of Raman spectra (Figure 2). As illustrated in Figure 2, all the synthesized samples exhibited a prominent band at ∼460 cm^-1corresponding to F_2g mode of vibration in the CeO₂, which confirms the fluorite structure of Ceria. The broadening of the F_2g vibration mode was observed when SiO₂, ZrO₂ and CuO were doped into the CeO₂ lattice. This significant finding could be attributed to several factors, including lattice defects, lattice strain, phonon confinement, and variations in phonon relaxation associated with particle size. These results are in co-relation with the XRD results (Figure 1). An additional shoulder band around 600 cm^-1 was observed in CeSi, CeZr, Cu/Ce, Cu/CeSi and Cu/CeZr catalysts due to the formation of oxygen vacancies (Sudarsanam et al., 2014; Ravula et al., 2024). The formation of oxygen vacancies is due to either the incorporation of Si⁴⁺ and Zr⁴⁺ into the CeO₂ lattice or the interaction between the oxides of copper and Ce, CeSi and CeZr support matrix. Interestingly, a strong enhancement in this peak was observed in Cu/CeZr due to formation of more oxygen vacancies and there by enhances the acidic properties of CuO doped into the Ce, CeSi and CeZr, respectively.

XPS analysis was conducted to determine the elemental valence states and investigate changes in surface composition. The Ce 3d XP spectra of ceria-based mixed oxide-supported copper catalysts are depicted in Figure 3. The spectra, ranging from 870 to 920 eV, are notably complex due to the hybridization of the O 2p valence band with the Ce 4f level during the final state of photo ionization. The spin-orbit components 3d_3/2 and 3d_5/2 are labelled as u and v, respectively and these notations are same as that of literature. Peaks identified as u₀, v₀, u', and v' are characteristic of Ce³⁺ ions, featuring one main line and one satellite. In contrast, peaks marked as v, u, v'', u'', v''', and u''' correspond to Ce⁴⁺ ions, each displaying one main line and two satellites (the peaks v'' and v''' are the satellites arising from the ionization of Ce 3d_5/2, whereas the signals u'' and u''' account for the ionization of Ce 3d_3/2). Specifically, the u'''/v''' doublet is due to primary photoemission from Ce⁴⁺. In contrast, the u/v and u''/v'' doublets are shakedown features. These shakedown features result from the transfer of one or two electrons from a filled O 2p orbital to an empty Ce 4f orbital. Furthermore, the u₀, v₀, and u'/v' signals are attributed to photoemission from Ce³⁺ cations. As shown in Figure, the Ce 3d spectrum is integrated into subsequent peaks at about 881.38 eV (v₀), 882.68 eV (v), 885.60 eV (v'), 888.81 eV (v''), 897.45 eV (v'''), 899.69 eV (u₀), 901.76 eV (u), 904.08 eV (u'), 907.68 eV (u''), and 916.72 eV (u'''). The principal peaks of 3d_5/2 and 3d_3/2 are located at 882.68eV and 901.76 eV, respectively which are inconsistent with the previously reported results (Bêche et al., 2008; Rao et al., 2011; Isaacs et al., 2023). This indicates that all samples contain both Ce⁴⁺ and Ce³⁺ ions. The Ce 3d XP Spectra of Cu/CeZr sample shows signal splitting around 915–920 eV, which results in less concentration of Ce⁴⁺ ions in the sample. From Figure 3, the ratio of Ce³⁺ intensity I_u ^////I_Total to the total intensity provides insight into the proportion of Ce³⁺ ions in the sample (Reddy et al., 2005; Sudarsanam et al., 2014; Ravula et al., 2024). This ratio is significant because Ce³⁺ ions are closely associated with oxygen vacancies, which are critical defect sites in the material. The reduction of Ce⁴⁺ to Ce³⁺ often compensates for the creation of these oxygen vacancies, making the I_u ^////I_Total ​ratio a reliable indicator of defect density. The Cu/CeZr sample exhibits the lowest I_u ^////I_Total ratio (0.0567) compared to the Cu/Ce (0.0843) and Cu/CeSi (0.0672) samples, indicating a higher number of Ce³⁺ species or a greater number of oxygen defect sites in the sample. By analysing this ratio, XPS enables a deeper understanding of the material’s structural and electronic properties. This indicates a greater number of oxygen vacancies in the ceria lattice, which are in line with the Raman spectra results.

Figure 4A–D presents the XPS of Cu 2p, O 1s, Si 2p, and Zr 3d spectra for all three samples. Figure 4A presents the XPS of Cu 2p spectra for all three samples, highlighting the characteristic spin-orbit splitting into the Cu 2p_3/2 and Cu 2p_1/2 peaks. The Cu 2p_3/2 peak, a key feature for identifying the oxidation state of copper, appears prominently at approximately 932.8 eV across the samples. This binding energy is typically associated with Cu²⁺ species, confirming the presence of divalent copper ions (Rao et al., 2011; Mallesham et al., 2016). Additionally, a satellite peak observed around 941.9 eV further supports this assignment to Cu²⁺, as such satellite structures are known to arise from shake-up processes unique to high-spin Cu²⁺ species. However, the range of Cu 2p_3/2 binding energies across the samples, spanning from 930.6 to 936.9 eV, suggests the co-existence of multiple copper species (Mallesham et al., 2016). This range indicates the possible presence of both Cu²⁺ and Cu⁺ species in the catalysts, as Cu⁺ typically exhibits binding energies lower than that of Cu²⁺. The calculated full width at half maximum (FWHM) of around 3 eV provides further evidence for this dual copper state, implying a mixture of oxidation states, which could influence catalytic performance through redox cycling between Cu⁺ and Cu²⁺ (Velu et al., 2005; Mallesham et al., 2016; Scherzer et al., 2019).

The O 1s spectra of the catalysts reveal broad signals that represent overlapping contributions from oxygen species in both copper oxide and the ceria-based supports (Figure 4B). The binding energies associated with oxygen in the Cu/CeZr catalyst are observed at 529.7 eV and 530.8 eV. These peaks can be attributed to lattice oxygen in the CuO and CeO₂ phases, as well as oxygen vacancies within the ceria-Zirconia matrix (Zhang et al., 2014; Mallesham et al., 2016; Yang et al., 2021). The formation of oxygen vacancies is a well-known characteristic of ceria-based materials, enhancing their redox properties and catalytic activity, particularly in oxidation reactions. For the Cu/CeSi catalyst, the O 1s binding energies at 529.7 eV and 532.4 eV suggest an interaction between silica and hydroxyl groups (Sudarsanam et al., 2014; Dong et al., 2016; Mallesham et al., 2016). The higher binding energy peak at 532.4 eV likely corresponds to surface hydroxyls, which may play a role in modulating the catalytic environment by influencing the dispersion and reducibility of the copper species. The accessibility of these hydroxyl groups, as suggested by the XPS data, indicates that silica enhances the interaction with copper species, potentially improving catalytic performance.

The Si 2p spectrum, with a prominent peak at 103.02 eV, indicates the presence of Si⁴⁺ in the Cu/CeSi catalyst. This result is consistent with the incorporation of silica into the catalyst framework, potentially affecting the distribution and electronic properties of the active copper sites. The presence of Si⁴⁺ may also contribute to the formation of stronger Cu-O-Si interactions, further stabilizing the catalyst. Similarly, the Zr 3d XPS spectra for the Cu/CeZr catalyst exhibit two distinct spin-orbit-split peaks, with Zr 3d_5/2 at 181.7 eV and Zr 3d_3/2 at 184.1 eV, indicative of Zr⁴⁺ (Zhang et al., 2005; Sudarsanam et al., 2014). The incorporation of Zirconia into the ceria support is expected to enhance the oxygen mobility and defect formation, which can facilitate redox reactions and improve the overall catalytic performance in oxidation processes.

Figure 5 represents the H₂-TPR profiles of the Cu/Ce, Cu/CeSi, and Cu/CeZr samples reveal distinct reduction behaviour due to variations in copper oxide dispersion and interaction with the supports (Dou et al., 2021). The Cu/Ce sample shows multiple reduction peaks, indicating the presence of highly dispersed copper species (∼396.96K), weakly interacting copper (∼433.56K), small CuO/Cu₂O clusters (∼470.15K), and crystalline CuO (∼508.21K), reflecting strong interactions with CeO₂ (Rao et al., 2011; Sudarsanam et al., 2014). In contrast, the Cu/CeSi profile shifts towards higher temperatures, suggesting weaker interactions with the inert SiO₂, leading to the presence of more crystalline copper oxide species and subsurface formations. These differences highlight the significant role of the support material in influencing the reduction behaviour and thermal stability of copper oxide species.

The H₂-TPR profiles and XPS results together provide a comprehensive understanding of the metal-support interaction (MSI) in Cu/Ce, Cu/CeSi, and Cu/CeZr systems. In the Cu/Ce sample, the strong interaction between CuO and CeO₂ is evident from multiple reduction peaks, indicating the presence of various copper species—ranging from highly dispersed (∼396.96K) to weakly interacting copper (∼433.56K), small clusters of CuO/Cu₂O (∼470.15K), and crystalline CuO (∼508.21K). This broad range reflects a high degree of MSI, where CeO₂, known for its oxygen storage capacity, creates oxygen vacancies that facilitate the reduction of dispersed copper at lower temperatures (Layer, 1963; Rao et al., 2011; Mallesham et al., 2016) The strong MSI in Cu/Ce stabilizes smaller copper species, promoting a higher degree of reduction. In contrast, Cu/CeSi displays a shift to higher reduction temperatures, which suggests weaker MSI due to the inert nature of SiO₂. This weak interaction leads to the presence of more crystalline copper oxide species and subsurface formations, requiring more energy for reduction and resulting in less dispersed copper. XPS data corroborate these observations, as Cu/Ce likely shows a higher proportion of Cu⁺/Cu²⁺ species due to the stabilization of copper by CeO₂. In contrast, Cu/CeSi would exhibit a larger proportion of Cu²⁺, indicative of less reduction and the presence of more bulk-like CuO. The TPR profiles, combined with the oxidation states revealed by XPS, underline how the support material significantly influences the dispersion, reduction behavior, and electronic properties of copper oxide species, with stronger MSI facilitating more efficient reduction and stabilization of reduced copper species in the Cu/CeZr.

The temperature-programmed desorption of ammonia (NH₃-TPD) is a widely used technique for examining the quantitative and qualitative analysis of amount of acidic sites. NH₃-TPD is the important method to understand the acidic sites of the Cu/Ce, Cu/CeSi and Cu/CeZr. In general, the distribution of acidic sites follows: weak acidic sites (<423K), medium acidic sites (423–623K) and strong acidic sites (>623K) (Boréave et al., 1997; Mohan et al., 2014). NH₃-TPD profiles for the synthesized catalysts of Cu/Ce, Cu/CeSi and Cu/CeZr were shown in Figure 6. It is observed that the CuO promoted CeO₂ doped catalysts show all the three types of acidic sites. The quantification of the acidic sites was also performed and the number of weak sites for Cu/Ce, Cu/CeSi and Cu/CeZr are ∼24, 35, 51 μmol/g, respectively. The number of medium sites follows ∼10, 17, and 18 μmol/g, respectively. Similarly, the number of strong acidic sites is ∼9, 10, and 14 μmol/g, respectively. When Zr⁴⁺ ions are incorporated into the CeO₂ lattice in the CuO/CeO₂-ZrO₂ system, they induce structural distortions due to the smaller ionic radius of Zr⁴⁺ compared to Ce⁴⁺. These distortions generate oxygen vacancies, which play a critical role in enhancing the material’s catalytic properties (Oh et al., 2024). The creation of oxygen vacancies modifies the local electronic environment, leading to an increase in Lewis acidic sites. In the CuO/CeO₂-ZrO₂ catalyst, these oxygen vacancies and the enhanced Lewis acidity improve the dispersion and redox activity of CuO species (Zhang et al., 2019). This synergistic interaction between CuO and the modified CeO₂-ZrO₂ support contributes to superior catalytic performance, particularly in reactions requiring efficient oxygen transfer and strong metal-support interactions.

The FTIR spectra of pyridine-adsorbed samples, as depicted in Figure 7, reveal significant insights into the nature of acid sites present in the catalyst. The observed peaks around 1,545 cm⁻¹, 1,490 cm⁻¹, and 1,445 cm⁻¹ can be ascribed to specific types of acid sites: the peak at 1,545 cm⁻¹ corresponds to Brønsted acid sites, the one at 1,490 cm⁻¹ indicates the presence of both Brønsted and Lewis acid sites, and the peak at 1,445 cm⁻¹ is characteristic of Lewis acid sites [(Baithy et al., 2022; Mohan et al., 2014; Mallesham et al., 2020; Nagu et al., 2023)]. Additionally, distinct peaks around 1,590 cm⁻¹ and 1,635 cm⁻¹ further confirm the presence of Brønsted acid sites. These observations suggest that the catalyst samples exhibit a combination of Brønsted and Lewis acid sites. This duality is likely a key factor contributing to the samples’ exceptional catalytic activity, as both types of acid sites play critical roles in facilitating catalytic processes. The interplay between these sites enhances the catalyst’s overall performance, making it highly effective for the intended reactions.

The SEM and TEM analyses of the CuO/CeO₂-ZrO₂ catalyst provide critical insights into its morphology and structure (Figures 8A–D). The SEM images at resolutions of 100 nm and 200 nm reveal spherical CuO particles dispersed on the irregular surface of the CeO₂ support, indicating a relatively homogeneous surface that enhances the catalyst’s surface area. TEM images at higher resolutions (20 nm and 2 nm) show that the CuO nanoparticles are uniformly distributed across the zirconia-doped CeO₂ support, with lattice fringes confirming a well-defined cubic crystal structure aligned with the (111) plane. The measured particle size of ∼6.2 nm highlights the nanoscale precision, while the intimate contact between CuO and CeO₂ observed in TEM suggests strong interfacial interactions, which are crucial for boosting catalytic performance. Together, the SEM and TEM results demonstrate a catalyst with well-dispersed, crystalline CuO nanoparticles that can significantly enhance catalytic activity.

In summary, the CuO/CeO₂-ZrO₂ catalyst developed in this study offers a highly efficient, robust, and recyclable system for the selective oxidative coupling of benzylamines to imine (99.5%), benzimidazole (99.2%) and its derivatives under solvent-free conditions. The catalytic activity is obtained by the presence of oxygen vacancy sites, enhanced redox behavior, strong metal support interaction, and a high density of acidic sites, which collectively contribute to its superior performance. The catalyst also demonstrates excellent functional group tolerance, short reaction times, and durability over multiple cycles (upto fifth cycle). These features make the catalyst an attractive option for industrial applications in green and sustainable chemistry, particularly in the fields of pharmaceuticals and organic synthesis. The achievement of the CuO/CeO₂-ZrO₂ catalytic system covers the way for further exploration of doped ceria-based catalysts in oxidative processes.