Novel synthesis of vanadium phosphorus/ cerium promoted manganese oxide (VPO/Ce-OMS-2) nanocomposite as an efficient and selective catalyst for the aerobic oxidative coupling of benzyl alcohol and aniline to imine in the liquid phase

• Published in: Journal of organometallic chemistry 2024-12, Vol.1022, p.123381, Article 123381
• Main Authors: Shahbazi, Elham, Mahdavi, Vahid
• Format: Article
• Language: English
• Subjects: Cerium metal-doped MnO2; Imines; Oxidative coupling; Vanadium phosphorus oxide; VPO/Ce-OMS-2 composite
• ISSN: 0022-328X
• DOI: 10.1016/j.jorganchem.2024.123381

•VPO/Ce-OMS-2 nanocomposite synthesized by mechanochemical method.•VPO/Ce-OMS-2 is solid acid environmentally friendly and reusable catalyst.•VPO/Ce-OMS-2 (2:1) is a highly active catalyst for imine synthesis reaction.•Micro-meso hybrid structures and Red-Ox systems has facilitated the synergistic relationship between VPO and OMS-2.•Conversion (%) of benzyl alcohol reaches 93% and selectivity of imine 100% on 0.5 g of VPO/Ce-OMS-2 (2:1) catalyst. In this investigation, the VPO/Ce-OMS-2 composite was synthesized via the mechanochemical method and it was employed for the synthesis of imine in the liquid phase through a two-step process of oxidation of benzyl alcohol and subsequent condensation with aniline using air as an oxidant. The composite was synthesized with different mass ratios of (1:1), (1.5:1), (2:1) and (2.5:1). The effect of the VPO/Ce-OMS-2 mass ratio on catalyst activity has been investigated. As the mass ratio increases from (1:1) to (2:1), the benzyl alcohol conversion gradually increases, reaching 93% at a (2:1) mass ratio. Among the synthesized samples, the VPO/Ce-OMS-2(2:1) composite exhibited the highest selectivity towards imine formation and conversion of benzyl alcohol. Various techniques, such as XRD, FT-IR, BET, FESEM, EDX, DRS, NH3-TPD, and HRTEM, were utilized to characterize the catalysts. Results indicated that the composite synthesized with a (2:1) mass ratio has a favorable surface area, a mixture of micro-meso structures, and a high number of acidic sites, as confirmed by BET-BJH and NH3-TPD techniques. The DRS analysis demonstrated that the interaction between the two catalysts, VPO and Ce-OMS-2, enhances the selectivity for the desired product. The results clearly show the synergism effect in the combination of components VPO and Ce-OMS-2 and improving the activity and selectivity of the synthesized nanocomposite. The effects of reaction temperature, reaction time, solvents, VPO/Ce-OMS-2 mass ratio, catalyst amount, and reusability were studied. Recycling results for the VPO/Ce-OMS-2(2:1) composite show that the benzyl alcohol conversion decreases slightly after five cycles of use, and its stability is almost maintained. Optimizing the reaction conditions (0.2 g catalyst, VPO/Ce-OMS-2 mass ratio (2:1), solvent toluene, reaction temperature 90°C, and t = 8 h) resulted in a 93% conversion of benzyl alcohol with complete selectivity for the imine. [Display omitted]