Highly Efficient CeO2–MoO3/SiO2 Catalyst for Solvent-Free Oxidative Coupling of Benzylamines into N-Benzylbenzaldimines with O2 as the Oxidant

• Published in: Catalysis letters 2015-07, Vol.145 (7), p.1436-1445
• Main Authors: Govinda Rao, Bolla, Sudarsanam, Putla, Rangaswamy, A., Reddy, Benjaram M.
• Format: Article
• Language: English
• Subjects: Acidic oxides; Ammonia; Catalysis; Catalysts; Cerium oxides; Chemical industry; Chemical synthesis; Chemistry; Chemistry and Materials Science; Crystal defects; Crystallites; Fourier transforms; Industrial Chemistry/Chemical Engineering; Infrared spectroscopy; Mixed oxides; Molybdenum trioxide; Noble metals; Organometallic Chemistry; Oxidation; Oxidizing agents; Oxygen; Photoelectrons; Physical Chemistry; Pore size distribution; Raman spectroscopy; Selectivity; Silicon dioxide; Solvents; Spectrum analysis; Strong interactions (field theory); Surface area; X ray photoelectron spectroscopy
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-015-1545-0

The development of noble-metal-free catalysts is currently a topic of paramount research investigation in the chemical industry. In this work, a promising CeO 2 –MoO 3 /SiO 2 catalyst was synthesized for the oxidation of a wide variety of benzylamines with O 2 as the oxidant under solvent-free conditions. For comparison, the efficiency of CeO 2 and CeO 2 –MoO 3 catalysts were also studied for the oxidation of benzylamine under identical conditions. The physicochemical properties of the catalysts were thoroughly analysed using X-ray diffraction, Raman spectroscopy, Barrett–Joyner–Halenda pore size distribution, Brunauer–Emmet–Teller (BET) surface area, Fourier-transform infrared spectroscopy, ammonia-temperature programmed desorption (NH 3 -TPD), and X-ray photoelectron spectroscopy techniques. Characterization studies revealed that the CeO 2 –MoO 3 /SiO 2 catalyst shows favourable structural, textural and acidic properties, which are due to strong interaction between the Ce–Mo mixed oxide and the SiO 2 . In particular, the CeO 2 –MoO 3 /SiO 2 sample exhibits smaller crystallite size and highest BET surface area compared with the CeO 2 –MoO 3 and bare CeO 2 . Raman analysis revealed that the CeO 2 –MoO 3 /SiO 2 sample exhibits greater number of oxygen vacancy defects. The NH 3 -TPD studies indicated that the CeO 2 –MoO 3 /SiO 2 sample has large amount of acidic sites. Owing to the beneficial properties, the CeO 2 –MoO 3 /SiO 2 sample exhibited an outstanding catalytic performance for the aerobic oxidation of various benzylamines. The achieved benzylamine conversions are ~16, 65 and 98 %, respectively, for CeO 2 , CeO 2 –MoO 3 and CeO 2 –MoO 3 /SiO 2 samples. Despite the nature of the catalyst used and the reaction conditions employed, almost ~100 % selectivity for the dibenzylimine product was found in the present study. Remarkably, the CeO 2 –MoO 3 /SiO 2 catalyst can be repeatedly used up to 5 cycles without any considerable variation in the benzylamine conversion and imine product selectivity. Graphical Abstract The CeO 2 –MoO 3 /SiO 2 catalyst showed an outstanding efficiency in the oxidation of benzylamine, which is attributed to abundant acidic sites, large number of oxygen vacancies, and superior BET surface area.